PIOLOGY

LIBRARY

:

m.

A TEXT BOOK

OP

PHYSIOLOGY

BIOLOGY

LIBRARY

G

PRINTED BY C. J. CLAY, M.A. & SON,
AT THE UNIVERSITY PRESS.

PREFACE TO THE FOURTH EDITION.

IN previous Editions of this work I endeavoured, by the
use of small and large print, to distinguish between the
more important and stable portions of Physiology, which
ought to be made known to every one engaged in a
serious study of the science, and the less settled, often
controverted views which should be attacked by the more
advanced students only. Experience however has taught
me that the advantages of such a plan are more than
counterbalanced by its disadvantages. I especially felt
that the amount of space which I could fairly allow to
the small print paragraphs was wholly insufficient to
permit me to do justice to the conflicting views which
I strove, in them, to expound.

In this Edition accordingly I have made no attempt
at any such distinction, and have used small print almost
exclusively for the description of methods and apparatus.
This step involving, as it necessarily did, the transference,
into the body of the work, of some of the statements
which previously had found their place in the small print

606165

vi PREFACE.

portions, has given the volume, at first sight, the appear-
ance of having been largely altered. This however is
not the case. For good or for bad, the book remains
very much as it was ; and though I have done my best
to remove some of the many defects present in previous
editions, I have been encouraged, by the favour with
which those editions have been successively received, to
persevere in the views which I have always held as to
which are the parts of physiology most to be insisted on,
and which may be lightly touched or wholly omitted ;
and though I would still most strenuously repudiate
the idea, put forward by some, that there is such a
thing as a physiology for medical men, different from
that physiology which is a part of science, I have
tried to make this volume especially useful to medical
students.

My decision to do away with the small print portions
of former editions has been largely determined by the
fact that my former pupils, now my colleagues at Cam-
bridge, have undertaken to join with me in treating
these higher or advanced parts of physiology in a more
extended and satisfactory form. And the hope that' the
result of their labours will soon appear has led me, in
this volume, to omit all references, and to use as little as
possible the personal authority of the names of investi-
gators. The fondness of students for the use of names
of persons is as marked as the pertinacity with which
they use them wrongly; and if any observer may feel
aggrieved at his name being absent from an ordinary text-
book, he may at least have the satisfaction of reflecting
that the omission of all names does something to prevent
others receiving the credit of his labours.

PREFACE. vii

I cannot say how much I am indebted to the con-
tinued help of those friends who assisted me in former
editions ; and I have also to acknowledge with gratitude
the aid afforded me by Prof. C. S. Boy, to whose kindness
I owe several of the new illustrations.

The appendix on chemical matters, as in former
editions, has been under the care of Mr Sheridan Lea;
in this, which stands on a somewhat different footing
from the rest of the work, references and names of authors
have been retained.

TRINITY COLLEGE, CAMBRIDGE,
February, 1883.

CONTENTS.

PAGE

INTEODUCTOEY 1

BOOK I.

BLOOD. THE TISSUES OF MOVEMENT.
THE VASCULAR MECHANISM.

CHAPTER I.
BLOOD, pp. 11—34.

Sec. 1. The Coagulation of Blood . . . . -. . . . 13

Sec. 2. The Chemical Composition of Blood . . . * . . . 24

Sec. 3. The History of the Corpuscles . .V . ~ „ . . . 28

Sec. 4. The Quantity of Blood, and its distribution in the body ... 33

CHAPTER II.

THE CONTRACTILE TISSUES, pp. 35 — 103.

Sec. 1. The Phenomena of Muscle and Nerve 37

Muscular and Nervous Irritability, p. 37. The Phenomena of a
simple muscular contraction, p. 39. Tetanic contractions, p. 48.

Sec. 2. The Changes in a Muscle during Muscular Contraction ... 54
The change in form, p. 54. Electrical changes, p. 58. Chemical
changes, p. 64. Thermal changes, p. 70. The changes in a Nerve
during the passage of a Nervous Impulse, p. 72.

Sec. 3. The Nature of the Changes through which an Electric Current is able

to generate a Nervous Impulse 75

The action of the Constant Current, p. 75. Electrotonus, p. 77.
Electrotonic Currents, p. 80.

x CONTENTS.

PAGE

Sec. 4. The Muscle-Nerve Preparation as a Machine . . . . 83

The nature and mode of application of the Stimulus as affecting
the amount and character of the Contraction, p. 83. The influence
of the Load, p. 87. The influence of the Size and Form of the
Muscle, p. 88. The work done, p. 89.

Sec. 5. The Circumstances which determine the Degree of Irritability of

Muscles and Nerves 90

The effects of severance from the Central Nervous System, p. 91.
The Influence of Temperature, p. 93. The Influence of Blood
Supply, p. 94. The Influence of Functional Activity, p. 95.

Sec. 6. The energy of Muscle and Nerve, and the nature of Muscular and

Nervous Action 98

Sec. 7. Other forms of Contractile Tissue 101

Unstriated Muscular Tissue, p. 101. Cardiac Muscles, p. 102.
Cilia, p. 102. Migrating Cells, p. 103.

CHAPTER III.

THE FUNDAMENTAL PROPEETIES OF NERVOUS TISSUES, pp. 104 — 114.

Automatic actions, p. 107. Eeflex actions, p. 109. Actions of
sporadic ganglia, p. 112. Inhibition, p. 113.

CHAPTER IV.

THE VASCULAR MECHANISM, pp. 115 — 230.

I. THE PHYSICAL PHENOMENA OF THE CIRCULATION .... 116
Sec. 1. Main general facts of the Circulation 117

The Capillary Circulation, p. 117. The flow in the Arteries, p. 120.
The flow in the Veins, p. 127. Hydraulic principles of the Circu-
lation, p. 128.

Sec. 2. The Heart 135

The Phenomena of the Normal Beat, p. 135. The Mechanism of
the Valves, p. 142. The Sounds of the Heart, p. 143. On the
relative duration and special characters of the cardiac events,
p. 146. The work done, p. 157. Variations in the Heart's Beat,
p. 159.
Sec. 3. The Pulse 161

n. THE VITAL PHENOMENA OF THE CIRCULATION .... 176

Sec. 4. Changes in the Beat of the Heart 178

The Mechanism of the normal beat, p. 180. Inhibition of the
beat, p. 184. The effects on the circulation of changes in the
heart's beat, p. 194.

CONTENTS. xi

PAGE

Sec. 5. Changes in the calibre of the minute arteries. Vaso-motor actions . 197
Vaso-motor Nerves, p. 139. Vase-motor Centres, p. 212. The
effects of local vascular constriction or dilation, p. 216.

Sec. 6. Changes in tJie Capillary Districts 219

Sec. 7. Changes in the Quantity of Blood 224

Sec. 8. The Mutual Relations and the Co-ordination of the Vascular Factors 227

BOOK II.

THE TISSUES OF CHEMICAL ACTION WITH THEIR RESPECTIVE
MECHANISMS. NUTRITION.

CHAPTER I.
THE TISSUES AND MECHANISMS OF DIGESTION, pp. 233 — 311.

Sec. 1. The Properties of the Digestive Juices 234

Saliva, p. 234. Gastric juice, p. 239. Bile, p. 247. Pancreatic
juice, p. 250. Succus entericns, p. 255.

Sec. 2. The act of secretion in the case of the Digestive Juices and the Nervous

Mechanisms which regulate it 256

Sec. 3. The Muscular MecJianisms of Digestion 281

Mastication, p. 281. Deglutition, p. 282. Movements of the
O3sophagus, p. 284. Movements of the stomach, p. 285. Move-
ments of the small intestine, p. 286. Movements of the large
intestine, p. 288. Defaecation, p. 288. Vomiting, p. 290.

Sec. 4, The Changes which the Food undergoes in the Alimentary Canal . 292

Sec. 5. Absorption of tJie Products of Digestion 301

The Lymphatics, p. 301. Entrance of the chyle into the lacteals,
p. 303. Movements of the chyle, p. 304. Lymph-hearts, p. 306.
The course taken by the several products of digestion, p. 306.

CHAPTER II.
THE TISSUES AND MECHANISMS OP RESPIRATION, pp. 312 — 383.

Sec. 1. The Mechanics of Pulmonary Respiration 314

The Rhythm of Respiration, p. 316. The Respiratory Move-
ments, p. 319. Facial and Laryngeal Respiration, p. 324.

Sec. 2. Clianges of the Air in Respiration 326

Sec. 3. The Respiratory Changes in the Blood 329

The relations of oxygen in the blood, p. 332. Hemoglobin ; its
properties and derivatives, p. 333. Colour of venous and arterial
blood, p. 338. The relations of the carbonic acid in the blood,
p. 342. The relations of the nitrogen in the blood, p. 343.

Sec. 4. The Respiratory Changes in the Lungs 344

The entrance of oxygen, p. 344. The exit of carbonic acid, p.
346.

xii CONTENTS.

PAGE

Sec. 5. The Respiratory Changes in the Tissues . . . . . . 348

Sec. 6. The Nervous Mechanism of Respiration 358

Sec. 7. The Effects of Respiration on the Circulation 304

Sec. 8. The Effects of Changes in the Air breathed 375

The effects of deficient air. Anphyxia. Phenomena of asphyxia,
p. 375. The circulation in asphyxia, p. 378. The effects of an
increased supply of air. Apnoea, p. 380. The effects of changes
in the composition of the air breathed, p. 380. The effects of
changes in the pressure of the air breathed, p. 381.

Sec. 9. Modified Respiratory Movements 382

Sighing, Yawning, Hiccough, Sobbing, Coughing, Sneezing,
Laughter and Crying, p. 382.

CHAPTER III.

SECRETION BY THE SKIN, pp. 384 — 391.
The nature and amount of Perspiration, p. 385. Cutaneous
Eespiration, p. 386. The Secretion of Perspiration, p. 387. The
Nervous Mechanism of Perspiration, p. 388. Absorption by the
Skin, p. 390.

CHAPTER IY.

SECRETION BY THE KIDNEYS, pp. 392 — 414.

Sec. 1. The Composition of Urine 393

Sec. 2. The Secretion of Urine 397

The relation of the secretion of urine to arterial pressure, p. 398.
Secretion by the renal epithelium, p. 404.

Sec. 3. Micturition 410

CHAPTER Y.

THE METABOLIC PHENOMENA OF THE BODY, pp. 415 — 478.

Sec. 1. Metabolic Tissues 416

The History of Glycogen, p. 416. Diabetes, p. 424. The History
of Pat. Adipose Tissue, p. 426. The Mammary Gland, p. 429.
The Spleen, p. 432.

Sec. 2. The History of Urea and its allies 436

Sec. 3. The Statistics of Nutrition 443

Comparison of Income and Output, p. 446. Nitrogenous Meta-
bolism, p. 449. The effects of Fatty and of Carbohydrate Food,
p. 453.

Sec. 4. The Energy of the Body 457

The income of energy, p. 457. The expenditure, p. 458. Tho
(sources of Muscular Energy, p. 459. The sources and distribution
of Heat, p. 461. Eegulation by variations in loss, p. 464. Regu-
lation by variations in production, p. 465.

Sec. 5. The Influence of the Nervous System on Nutrition . . . - 470

Sec. 6. Dietetics . 474

CONTENTS. xiii

BOOK III.

THE CENTRAL NERVOUS SYSTEM AND ITS INSTRUMENTS.

CHAPTER I.

SENSORY NERVES, pp. 481 — 489.

CHAPTER II.
SIGHT, pp. 490 — 555.

PAGE

Sec. 1. Dioptric Mechanisms 491

The Formation of the Image, p. 491. Accommodation, p. 493.
Movements of the Pupil, p. 500. Imperfections in the Dioptric
apparatus, p. 506.

Sec. 2. Visual Sensations , 511

The origin of Visual Impulses, p. 511. Simple Sensations, p. 519.
Colour Sensations, p. 524.

Sec. 3. Visual Perceptions 535

Modified Perceptions, p. 536.

Sec. 4. Binocular Vision 541

Corresponding or identical points, p. 541. Movements of the eye-
balls, p. 542. The Horopter, p. 547.

Sec. 5. Visual Judgments . 549

Sec. 6. The Protective Mechanisms of the Eye 554

CHAPTER III.
HEARING, SMELL, AND TASTE, pp. 556—571.

Sec. 1. Hearing 556

The acoustic apparatus, p. 557. Auditory Sensations, p. 559.
Auditory Judgments, p. 565.

Sec. 2. Smell .567

Sec. 3. Taste 570

xiv CONTENTS.

"

CHAPTER IV.

FEELING AND TOUCH, pp. 572 — 584.

PAGE

Sec. 1. General Sensibility and Tactile Perceptions . . . . . 572

Sec. 2. Tactile Sensations 575

Sensations of Pressure, p. 575. Sensations of Temperature,

p. 576.

Sec. 3. Tactile Perceptions and Judgments 579

Sec. 4. The Muscular Sense 582

CHAPTER Y.

THE SPINAL CORD, pp. 585—607.

Sec. 1. As a Centre or Group of Centres of Reflex Action .... 585
Inhibition of Reflex Action, p. 590. The Time required for Reflex
Actions, p. 5L3.

Sec. 2. As a Centre or Group of Centres of Automatic Action . . . 595
Sec. 3. As a Conductor of Afferent or Efferent Impulses .... 598

CHAPTER VI.

THE BRAIN, pp. 608—650.

Sec. 1. On the Phenomena exhibited by an animal deprived of its Cerebral

Hemispheres 608

Sec. 2. The Mechanisms of Co-ordinated Movements 614

Forced Movements, p. 620.

Sec. 3. The Functions of the Cerebral Convolutions 623

Sec. 4. The Functions of other parts of the Brain 636

Corpora striata and optic thalami, p. 636. Corpora quadrigernina,
p. 638. Cerebellum, p. 640. Crura cerebri and pons Varolii,
p. 641. Medulla oblongata, p. 642.

Sec. 5. The Rapidity of Cerebral Operations . . . . . . 643

Sec. 6. The Circulation in the Brain 645

Sec. 7. The Cranial Nerves 648

CHAPTER VII.

SPECIAL MUSCULAR MECHANISMS, pp. 651 — 664.

Sec. 1. The Voice 651

Sec. 2. Speech 657

Vowels, p. 657. Consonants, p. 658.

Sec. 3. Locomotor Mechanisms 662

CONTENTS. xv

BOOK IV.

THE TISSUES AND MECHANISMS OF REPRODUCTION.

CHAPTER I.
MENSTRUATION, pp. 669 — 671.

CHAPTER II.

IMPREGNATION, pp. 672 — 673.

CHAPTER III.
THE NUTRITION OF THE EMBRYO, pp. 674 — 680.

CHAPTER IV.

PARTURITION, pp. 681 — 683.

CHAPTER V.

THE PHASES OF LIFE, pp. 684—694.

CHAPTER VI.

DEATH, pp. 695—696.

APPENDIX.
ON THE CHEMICAL BASIS OP THE ANIMAL BODY, pp. 697 — 770.

INDEX, pp. 771—785.

INTRODUCTORY.

AMONG the simpler organisms known to Biologists, perhaps the
most simple as well as the most common is that which has received
the name of Amoeba. There are many varieties of Amoeba, and
probably many of the forms which have been described are, in
reality, merely amoebiform phases in the lives of certain animals or
plants ; but they all possess the same general characters. Closely
resembling the white corpuscles of vertebrate blood, they .are
wholly or almost wholly composed of undifferentiated protoplasm,
in the. midst of which lies a nucleus, though this is sometimes absent.
In many a distinction may be observed between a more solid external
layer or ectosarc, and a more fluid granular interior or endosarc;
but in others even this primary differentiation is wanting. By
means of a continually occurring flux of its protoplasmic substance,
the amoeba is enabled from moment to moment not only to change
its form but also to shift its position. By flowing round the sub-
stances which it meets, it, in a way, swallows them ; and having
digested and absorbed such parts as are suitable for food, ejects or
rather flows away from the useless remnants. It thus lives, moves,
eats, grows, and after a time dies, having been during its whole
life hardly anything more than a minute lump of protoplasm.
Hence to the Physiologist it is of the greatest interest, since
in its life the problems of physiology are reduced to their simplest
forms.

Now the study of an amoeba, with the help of knowledge
gained by the examination of more complex bodies, enables us to
state that the undifferentiated protoplasm of which its body is so
largely composed exhibits certain fundamental phenomena which
we may speak of as ' vital.'

F. 1

OF PROTOPLASM.

1. It is contractile. There can be little doubt that the
changes in the protoplasm of an amoeba which bring about its
peculiar ' amoeboid ' movements, are identical in their fundamental
nature with those which occurring in a muscle cause a contraction :
a muscular contraction is essentially a regular, an amoeboid move-
ment an irregular flow of protoplasm. The substance of the
amoeba may therefore be said to be contractile.

2. It is irritable and automatic. When any disturbance,
such as contact with a foreign body, is brought to bear on the
amoeba at rest, movements result. These are not passive move-
ments, the effects of the push or pull of the disturbing body,
proportionate to the force employed to cause them, but active
manifestations of the contractility of the protoplasm ; that is to
say, the disturbing cause, or ' stimulus/ sets free a certain amount
of energy previously latent in the protoplasm, and the energy set
free takes on the form of movement. Any living matter which,
when acted on by a stimulus, thus suffers an explosion of energy,
is said to be ' irritable.' The irritability may, as in the amoeba,
lead to movement ; but in some cases no movement follows the
application of the stimulus to irritable matter, the energy set free
by the explosion taking on some other form than movement,
ex. gr. heat. Thus a substance may be irritable and yet not
contractile, though contractility is a very common manifestation
of irritability.

The amoeba (except in its prolonged quiescent stage) is rarely
at rest. It is almost continually in motion. The movements
cannot always be referred to changes in surrounding circumstances
acting as stimuli ; in many cases the energy is set free in conse-
quence of internal changes, and the movements which result are
called spontaneous or automatic movements. We may therefore
speak of the protoplasm of the amoeba as being irritable and
automatic.

3. It is receptive and assimilative. Certain substances
serving as food are received into the body of the amoeba, and there
in large measure dissolved. The dissolved portions are subse-
quently converted from dead food into new living protoplasm, and
become part and parcel of the substance of the amoeba.

4. It is metabolic and secretory. Pari passu with the re-
ception of new material, there is going on an ejection of old
material, for the increase of the amoeba by the addition of food is
not indefinite. In other words, the protoplasm is continually
undergoing chemical change (metabolism), room being made for
the new protoplasm by the breaking up of the old protoplasm into
products which are cast out of the body and got rid of. These
products of metabolic action have, in many cases at all events,
subsidiary uses. Some of them, for instance, we have reason to
think, are of value for the purpose of dissolving and effecting other

INTRODUCTORY. 3

prelimiDary changes in the raw food introduced into the body of
the amoeba ; and hence are retained within the body for some little
time. Such products are generally spoken of as ' secretions.'
Others which pass more rapidly away are generally called 'ex-
cretions.' The distinction between the two is an unimportant and
frequently accidental one.

The energy expended in the movements of the amoeba is
supplied by the chemical changes going on in the protoplasm, by
the breaking up of bodies possessing much latent energy into
bodies possessing less. Thus the metabolic changes which the
food (as distinguished from the undigested stuff mechanically
lodged for a while in the body) undergoes in passing through the
protoplasm of the amoeba are of three classes : those preparatory
to and culminating in the conversion of the food into protoplasm,
those concerned in the discharge of energy, and those tending to
economise the immediate products of the second class of changes
by rendering them more or less useful in carrying out the first.

5. It is respiratory. Taken as a whole, the metabolic changes
are pre-eminently processes of oxidation. One article of food, i.e.
one substance taken into the body, viz. oxygen, stands apart from
all the rest, and one product of metabolism peculiarly associated
with oxidation, viz. carbonic acid, stands also somewhat apart from
all the rest. Hence the assumption of oxygen and the excretion
of carbonic acid, together with such of the metabolic processes as
are more especially oxidative, are frequently spoken of together as
constituting the respiratory processes.

6. It is reproductive. The individual amoeba represents a
unit. This unit, after a longer or shorter life, having increased in
size by the addition of new protoplasm in excess of that which it
is continually using up, may, by fission t(or by other means) resolve
itself into two (or more) parts, each of " which is capable of living
as a fresh unit or individual.

Such are the fundamental vital qualities of the protoplasm of
an amoeba; all the facts of the life of an amoeba are manifesta-
tions of these protoplasmic qualities in varied seouence and sub-
ordination.

The higher animals, we learn from morphological studies, may
be regarded as groups of amoebae peculiarly associated together.
All the physiological phenomena of the higher animals are simi-
larly the results of these fundamental qualities of protoplasm
peculiarly associated together. The dominant principle of this
association is the physiological division of labour corresponding to
the morphological differentiation of structure. Were a larger or
' higher' animal to consist simply of a colony of undifferentiated
amoebae, one animal differing from another merely in the number
of units making up the mass of its body, without any differences
between the individual units, progress of function would be an

1—2

4 THE FUNDAMENTAL TISSUES.

impossibility. The accumulation of units would be a hindrance to
welfare rather than a help. Hence, in the evolution of living
beings through past times, it has come about that in the higher
animals (and plants) certain groups of the constituent amcebiform
units or cells have, in company with a change in structure, been
set apart for the manifestation of certain only of the fundamental
properties of protoplasm, to the exclusion or at least to the
complete subordination of the other properties.

These groups of cells, thus distinguished from each other at
once by the differentiation of structure and by the more or less
marked exclusiveness of function, receive the name of 'tissues.'
Thus the units of one class are characterized by the exaltation of
the contractility of their protoplasm, their automatism, metabolism
and reproduction being kept in marked abeyance. These units
constitute the so-called muscular tissue. Of another tissue, viz.
the nervous, the marked features are irritability and automatism,
with an almost complete absence of contractility and a great
restriction of the other qualities. In a third group of units, the
activity of the protoplasm is largely confined to the chemical
changes of secretion, contractility and automatism (as manifested
by movement) being either absent or existing to a very slight
degree. Such a secreting tissue, consisting of epithelium-cells,
forms the basis of the mucous membrane of the alimentary canal.
In the kidney, the substances secreted by the cells, being of no
further use, are at once ejected from the body. Hence the renal
tissue may be spoken of as excretory. In the epithelium-cells of
the lungs, the protoplasm plays an altogether subordinate part in
the assumption of oxygen and the excretion of carbonic acid.
Still we may perhaps be permitted to speak of the pulmonary
epithelium as a respiratory tissue.

In addition to these distinctly secretory or excretory tissues,
there exist groups of cells specially reserved for the carrying on of
chemical changes, the products of which are neither cast out of the
body, nor collected in cavities for digestive or other uses. The
work of these cells seems to be of an intermediate character ; they
are engaged either in elaborating the material of food that it may
be the more easily assimilated, or in preparing used-up material
for final excretion. They receive their materials from the blood
and return their products back to the blood. They may be called
the metabolic tissues par excellence. Such are the fat-cells of
adipose tissue, the hepatic cells (as far as the work of the liver
other than the secretion of bile is concerned), and probably many
other cellular elements in various regions of the body.

Each of the various units retains to a greater or less degree
the power of reproducing itself, and the tissues generally are
capable of regeneration in kind. But neither units nor tissues
can reproduce other parts of the organism than themselves, much
less the entire organism. For the reproduction of the complex

INTRODUCTORY. 5

individual, certain units are set apart in the form of ovary and
testis. In these all the properties of protoplasm are distinctly
subordinated to the work of growth.

Lastly, there are certain groups of units, certain tissues,. which
are of use to the body of which they form a part, not by reason of
their manifesting any of the fundamental qualities of protoplasm,
but on account of the physical and mechanical properties of certain
substances which their protoplasm has been able by virtue of its
metabolism to manufacture and to deposit. Such tissues are bone,
cartilage, connective tissue in large part, and the greater portion
of the skin.

We may therefore consider the complex body of a higher
animal as a compound of so many tissues, each tissue correspond-
ing to one of the fundamental qualities of protoplasm, to the
development of which it is specially devoted by the division of
labour. It must however be remembered that there is probably
a distinct limit to the division of labour. In each and every
tissue, in addition to its leading quality, there are more or less
pronounced remnants or at least some traces of all the other
protoplasmic qualities. Thus, though we may call one tissue par
excellence metabolic, all the tissues are to a greater or less extent
metabolic. The energy of each, whatever be its particular mode,
has its source in the breaking-up of the protoplasm. Chemical
changes, including the assumption of oxygen and the production
complete or partial of carbonic acid, and therefore also entailing
a certain amount of secretion and excretion, must take place in
each and every tissue. And so with all the other fundamental
properties of protoplasm ; even contractility, which for obvious
mechanical reasons is soonest reduced where not wanted, is present
in many other tissues besides muscle. And it need hardly be said
that each tissue retains the power of assimilation. However
thoroughly the material of food be prepared by digestion and
subsequent metabolic action, the last stages of its conversion into
living protoplasm are effected directly and alone by the tissue of
which it is about to form a part.

Bearing this qualification in mind, we may draw up a physio-
logical classification of the body into the following fundamental
tissues : —

1. The eminently contractile : the muscles.

2. „ „ irritable and automatic : the nervous system.

3. „ „ secretory, or excretory : digestive, urinary,

and pulmonary, &c., epithelium.

4. „ „ metabolic : fat-cells, hepatic cells, lymphatic

and ductless glands, &c.

5. „ „ reproductive : ovary, testis.

6. The indifferent or mechanical : cartilage, bone, &c.

All these separate tissues, with their individual characters, are

6 INTEGRATION.

however but parts of one body ; and in order that they may be
true members working harmoniously for the good of the whole,
and not isolated masses, each serving its own ends only, they need
to be bound together by coordinating bonds. Some means of
communication must necessarily exist between them. In the
mobile homogeneous body of the amoeba, no special means of com-
munication are required. Simple diffusion is sufficient to make
the material gained by one part common to the whole mass, and
the native protoplasm is physiologically continuous, so that an
explosion set up at any one point may be immediately propagated
throughout the whole irritable substance. In the higher animals,
the several tissues are separated by distances far too great for the
slow process of diffusion to serve as a sufficient means of commu-
nication, and their primary physiological continuity is broken by
their being imbedded in masses of formed material, the product of
the indifferent tissues, which being devoid of irritability, present
an effectual barrier to the propagation of molecular explosions. It
thus becomes necessary that in the increasing complexity of animal
forms, the process of differentiation should be accompanied by a
corresponding integration, that the isolated tissues should be made
a whole by bonds uniting them together. These bonds moreover
must be of two kinds.

In the first place there must be a ready and rapid distribution
and interchange of material. The contractile tissues must be
abundantly supplied with material best adapted by previous elabo-
ration for direct assimilation, and the waste products arising from
their activity must be at once carried away to the metabolic or
excretory tissues. And so with all the other tissues. There must
be a free and speedy intercourse of material between each and all.
This is at once and most easily effected by the regular circulation
of a common fluid, the blood, into which all the elaborated food is
discharged, from which each tissue seeks what it needs, and to
which each returns that for which it has no longer any use. The
carrying on such a circulation of fluid, being in large measure a
mechanical matter, needs a machinery, and calls forth an expendi-
ture of energy. The machinery is supplied by a special con-
struction of the primary tissues, and the energy is arranged for
by the presence among these of contractile and irritable matter.
Thus to the fundamental tissues there is added, in the higher
animals, a vascular bond in the shape of a mechanism of
circulation.

In the second place, no less important than the interchange of
material is the interchange of energy. In the amoeba the irritable
surface is physiologically continuous with the more internal proto-
plasm, while each and every part of the body has automatic
powers. In the higher animal, portions only of the skin remain
as eminently irritable or sensitive structures, while automatic
actions are chiefly confined to a central mass of irritable nervous

INTRODUCTORY. 7

matter. Both forms of irritable matter are separated, by long
tracts of indifferent material, from those contractile tissues through
which they chiefly manifest the changes going on in themselves.
Hence the necessity for long strands of eminently irritable tissue
to connect the skin and contractile tissues as well with each other
as with the automatic centres. Similar strands are also needed,
though perhaps less urgently, to connect the other tissues with
these and with each other. To the vascular bond there must be
added an irritable bond, along the strands of which, impulses set
up by changes in one or another part, may travel in determinate
courses for the regulation of the energy of distant spots. In other
words, part of the irritable tissues must be specially arranged to
form a coordinating nervous system.

Still further complications have yet to be considered. In the
life of a minute homogeneous amoeba, possessing no special form
or structure, there is little scope for purely mechanical operations.
As however we trace out the gradual development of the more
complex animal forms, we see coming forward into greater and
greater prominence the arrangement of the tissues in definite
ways to secure mechanical ends. Thus the entire body acquires
particular shapes, and parts of the body are built up into mechan-
isms, the actions of which are to the advantage of the individual.
Into the composition of these mechanisms or ' organs ' the active
fundamental tissues, as well as the passive or indifferent tissues,
enter ; and the working of each mechanism, the function of each
organ, is dependent partly on the mechanical conditions offered by
the passive elements, partly on the activity of the active elements.
The vascular mechanism, of which we have just spoken, is such
a mechanism. Similarly the urgent necessity for the access of
oxygen to all parts of the body, has given rise to a complicated
respiratory mechanism ; and the needs of copious alimentation, to
an alimentary or digestive mechanism.

Further, inasmuch as muscular movement is one of the chief
ends, or the most important means to the chief ends, of animal
life, we find the animal body abounding in motor mechanisms,
in which the prime mover is muscular contraction, while the
machinery is supplied by complicated arrangements of muscles
with such indifferent tissues as bone, cartilage, and tendon. In
fact, the greater part of the animal body is a collection of mus-
cular machines, some serving for locomotion, others for special
manoeuvres of particular members and parts, others as an assist-
ance to the senses, and yet others for the production of voice, and
in man, of speech.

Lastly, the simple automatism of the amoeba, with its simple
responses to external stimuli, is replaced in the higher animals by
an exceedingly complex volition affected in multitudinous ways
by influences from the world without ; and there is a correspond-
ingly complex central nervous system. And here we meet with

.:

8 CENTRAL NERVOUS MECHANISM.

a new form of differentiation unknown elsewhere. While the
contractility of the amoeba! protoplasm differs but slightly from
the contractility of the vertebrate striated muscle, there is an
enormous difference between the simple irritability of the amoeba
and the complex action of the vertebrate nervous system. Except-
ing the nervous or irritable tissues, the fundamental tissues have
in ail animals the same properties, being, it is true, more acute
and perfect in one than in another, but remaining fundamentally
the same. The elementary muscular fibre of a mammal is a
mass of differentiated protoplasm, forming a whole physiologically
continuous, and in no way constituting a mechanism. Each fibre
is a counterpart of all others ; and the muscle of one animal
differs from that of another in such particulars only as are
wholly subordinate. In the nervous tissues of the higher animals,
on the contrary, we find properties unknown to those of the lower
ones ; and in proportion as we ascend the scale, we observe an
increasing differentiation of the nervous system into unlike parts.
Thus we have, what does not exist in any other tissue, a mechanism
of nervous tissue itself, a central nervous mechanism of complex
structure and complex function, the complexity of which is due
not primarily to any mechanical arrangements of its parts, but to
the further differentiation of that fundamental quality of irrita-
bility and automatism which belongs to all irritable tissues, and to
all native protoplasm.

In the following pages I propose to consider the facts of phy-
siology very much according to the views which have been just
sketched out. The fundamental properties of most of the ele-
mentary tissues will first be reviewed, and then the various special
mechanisms. It will be found convenient to introduce early the
account of the vascular mechanism, and of its nervous coordinating
mechanism, while the mechanisms of respiration and alimentation
will be best considered in connection with the respiratory and
secretory tissues. The description of the purely motor mechanisms
will be brief; and, save in a few instances, confined to a statement
of general principles. The special functions of the central nervous
system, including the senses, must of necessity be considered by
themselves. The tissues and mechanism of reproduction and the
phenomena of the decay and death of the organism will naturally
form the subject of the closing chapters.

BOOK I.

BLOOD. THE TISSUES OF MOVEMENT. THE
VASCULAR MECHANISM.

CHAPTEE I.
BLOOD.

BLOOD, when flowing in a normal condition through the blood-
vessels, consists of an almost colourless fluid, the plasma, in which
are suspended a number of more solid bodies, the red and white o '
corpuscles. Were we anxious to give a formal completeness to the
classification of the various parts of the body into tissues, we might £0
speak of the blood as a tissue of which the corpuscles are the
essential cellular elements, while the plasma is a liquid matrix.
We might compare it to a cartilage, the firm matrix of which had
become completely liquefied so that the cartilage-corpuscles were
perfectly free to move about.

In regarding blood as tissue, however, we come upon the
difficulty that it, unlike all the other tissues, possesses no one
characteristic property. The protoplasm of the white corpuscles
is native un differentiated protoplasm, in no respect fitted for any
special duty ; and though, as we shall see, the red corpuscles have
a definite respiratory function, inasmuch as they are carriers of
oxygen from the lungs to the several tissues, still this respiratory
work is only one of the very many labours of the blood. It will
be therefore far more profitable, indeed necessary, to treat of the
blood, not as a tissue by itself, but_as the great means of com-
munication of material between the tissues properly so called. Its
real usefulness lies not so much in any one property of either its
corpuscles or its plasma, as in its nature fitting it to serve as the
great medium of exchange between all parts of the body. The
receptive tissues pour into it the material which they have received
from without, the excreting tissues withdraw from it the things
which are no longer of any use, and the irritable, the contractile,
and indeed all the tissues, seek in it the substances (including

12 BLOOD AN INTERNAL MEDIUM. [BOOK i.

oxygen) which they need for the manifestation of energy or for
the storing up of differentiated material, and return to it the waste
products resulting from their activity. All over the body every-
where there is so long as life lasts a double current, here rapid,
there slow, of material from the blood to the tissues, and from the
tissues to the blood.

It, together with lymph (whether in the lymph-canals or in the
interstices of the tissues), may, as Bernard has suggested, be
regarded as an internal medium bearing the same relations to the
constituent tissues that the external medium, the world, does to
the whole individual. Just as the whole organism lives on the
things around it, its air and its food, so the several tissues live on
the complex fluid by which they are all bathed and which is to
them their immediate air and food.

From this it follows, on the one hand, that the composition and
characters of the blood must be for ever varying in different parts
of the body and at different times ; and on the other hand, that
the united action of all the tissues must tend to establish and
maintain an average uniform composition of the whole mass of
blood. The special changes which blood is known to undergo
while it passes through the several tissues will best be dealt with
when the individual tissues and organs come under our considera-
tion. At present it will be sufficient to study the main features,
which are presented by blood, brought so to speak into a state of
equilibrium by the common action of all the tissues.

Of all these main features of blood, the most striking if not
the most important is the property it possesses of clotting or
coagulating when shed.

SECT. 1. THE COAGULATION OF BLOOD.

Blood, when shed from the blood-vessels of a living body, is
perfectly fluid. In a short time it becomes viscid; it flows less
readily from vessel to vessel. The viscidity increases rapidly until
the whole mass of blood under observation becomes a complete
jelly. The vessel into which it has been shed, can at this stage be
inverted without a drop of the blood being spilt. The jelly is of :
the same bulk as the previously fluid blood, and if forcibly removed, -—
presents a complete mould of the interior of the vessel. If the
blood in this jelly stage be left untouched in a glass vessel, a few
drops of an almost colourless fluid soon make their appearance on
the surface of the jelly. Increasing in number, and running
together, the drops after a while form a superficial layer of pale
straw-coloured fluid. Later on, similar layers of the same fluid are
seen at the sides and finally at the bottom of the jelly, which, ^
shrunk to a smaller size and of firmer consistency, now forms a
clot or crassamentum, floating in a perfectly fluid serum. The
shrinking and condensation of the clot, and the corresponding
increase of the serum, continue for some time. The upper surface
of the clot is generally cupped. A portion of the clot examined
under the microscope is seen to consist of a feltwork of fine granular
fibrils, in the meshes of which are entangled the red and white
corpuscles of the blood. In the serum nothing can be seen but a
few stray corpuscles. The fibrils are composed of a substance
called fibrin. Hence we may speak of the clot as consisting
of fibrin and corpuscles ; and the act of clotting or coagulation is
obviously a conversion of the naturally fluid portion of the blood
or plasma into fibrin and serum, followed by separation of the
fibrin and corpuscles from the serum.

14 COAGULATION OF BLOOD. [BOOK i.

In man, blood when shed becomes viscid in about two or
three minutes, and enters the jelly stage in about five or ten
minutes. After the lapse of another few minutes the first drops

Jof serum are seen, and coagulation is generally complete in from
one to several hours. The times however will be found to vary
according to the condition of the individual, the temperature of
the air, and the size and form of the vessel into which the blood
is shed. Among animals the rapidity of coagulation varies ex-
ceedingly in different species. The blood of the horse coagulates
with remarkable slowness ; so slowly indeed that many of the red
corpuscles (these being specifically heavier than the plasma) have
time to sink before viscidity sets in. In consequence there ap-
pears on the surface of the blood an upper layer of colourless
plasma, containing in its deeper portions many colourless cor-
puscles (which are lighter than the red). This layer clots like
the other parts of the blood, forming the so-called 'buffy coat.'
A similar buffy coat is sometimes seen in the blood of man, in
inflammatory conditions of the body.

This buffy coat makes its appearance in horse's blood even at
the ordinary temperature of the air. If a portion of horse's blood
be surrounded by a cooling mixture of ice and salt, and thus kept
at about 0° C., coagulation may be almost indefinitely postponed.
Under these circumstances a more complete descent of the cor-
puscles takes place, and a considerable quantity of colourless
transparent plasma free from blood-corpuscles may be obtained.

portion of this plasma removed from the freezing mixture
clots exactly as does the entire blood. It first becomes viscid and
then forms a jelly, which subsequently separates into a colourless
shrunken clot and serum. This shews that the corpuscles are not
an essential part of the clot.

If a few cubic centimetres of the same plasma be diluted with
50 times its bulk of a 0'6 p.c. solution of sodium chloride1 coagu-
lation is much retarded, and the various stages may be more
easily watched. As the fluid is becoming viscid, fine fibrils of
fibrin will be seen to be developed in it, especially at the sides
of the containing vessel. As these fibrils multiply in number, the
fluid becomes more and more of the consistence of a jelly ., and at
the same time somewhat opaque. Stirred or pulled about with
a needle, the fibrils shrink up into a small opaque stringy mass ;
and a very considerable bulk of the jelly may by agitation be
resolved into a minute fragment of shrunken fibrin floating in a
quantity of what is really diluted serum. If a specimen of such
diluted plasma be stirred from time to time, as soon as coagulation
begins, with a needle or glass rod, the fibrin may be removed
piecemeal as it forms, and the jelly stage may be altogether done
away with. When fresh blood which has not yet had time to

1 A solution of sodium chloride of this strength will hereafter be spoken of as
' normal saline solution.'

CHAP. 1.1 BLOOD. 15

coagulate is stirred or whipped with a bundle of rods (or anything
presenting a large amount of rough surface), no jelly-like coagu-
lation takes place, but the rods become covered with a mass of
shrunken fibrin. Blood thus whipped until fibrin ceases to bef
deposited, is found to have entirely lost its power of coagulation.

Putting all these facts together, it is very clear that the
phenomena of the coagulation of blood are caused by the appear-
ance in the plasma of fine fibrils of fibrin. As long as these are
scanty, the blood is simply viscid. When they become sufficiently
numerous, they give the blood the firmness of a jelly. Soon after
their formation they begin to shrink ; and in their shrinking en-
close in their meshes the corpuscles, but squeeze out the fluid
parts of the blood. Hence the appearance of the shrunken
coloured clot and the colourless serum.

Fibrin, whether obtained by whipping freshly-shed blood, or
by washing either a normal clot, or a clot obtained from colourless
plasma, exhibits the same general characters. It belongs to that
class of complex unstable nitrogenous bodies called proteids which
form a large portion of all living bodies and an essential part of
all protoplasm1. It gives the ordinary proteid reactions. It is
insoluble in water and in dilute saline solutions; and though it
swells up in dilute hydrochloric acid, it is not thereby appreciably
dissolved2.

Coagulation then is brought about by the appearance in the;
blood-plasma of a substance, fibrin, which previously did not exist •
there as such. Such a substance must have antecedents, or anj
antecedent — what are they, or what is it ?

If blood be received direct from the blood-vessels into one-
third its bulk of a saturated solution of some neutral salt such as
magnesium sulphate, and the two gently but thoroughly mixed,
coagulation, especially at a moderately low temperature, will be
deferred for a very long time. If the mixture be allowed to stand,
the corpuscles will sink, and a colourless plasma will be obtained
similar to the plasma gained from horse's blood by cold, except
that it contains an excess of the neutral salt. The presence of
the neutral salt has acted in the same direction as cold : it has
prevented the occurrence of coagulation. It has not destroyed the
fibrin; for if some of the plasma be diluted with from five to
ten times its bulk of water, it will coagulate speedily in quite a
normal fashion, with the production of quite normal fibrin.

If some of the colourless transparent plasma, obtained either
by the action of neutral salts from any blood, or by the help of cold
from horse's blood, be treated with some solid neutral salt, such as
sodium chloride, to saturation, a white flaky somewhat sticky
precipitate will make its appearance. If this precipitate be re-
moved, the fluid is no longer coagulable. (or very slightly so),
even though the neutral salt present be removed by dialysis, or

1 See Appendix. 2 For further details see Appendix.

.

16 COAGULATION OF BLOOD. [BOOK i.

Uts influence lessened by dilution. With the removal of the
(substance precipitated, the plasma has lost its power of coagu-
lating.

If the precipitate itself, after being washed with a saturated
solution of the neutral salt (in which it is insoluble) so as to get
rid of all serum and other constituents of the plasma, be treated
with a small quantity of water, it readily dissolves1, and the solution
rapidly filtered gives a clear colourless filtrate, which is at first
rfectly fluid. Soon however the fluidity gives way to viscidity,
and this in turn to a jelly condition, and finally the jelly shrinks
into a clot floating in a clear fluid; in other words, the filtrate
clots like plasma. Thus there is present in cooled plasma, and
in plasma kept from clotting by the presence of neutral salts,
a something, precipitable by saturation with neutral salts, a some-
thing which, since it is soluble in very dilute saline solutions,
cannot be fibrin itself, but which in solution speedily gives rise to
the appearance of fibrin. To this substance its discoverer, Denis,
gave the name of plasmine. We are justified in saying that the
coagulation of blood is the result of the conversion of plasmine
I or some part of plasmine into fibrin.

But there are reasons for thinking that plasmine is a mixture
of at least two bodies. If sodium chloride be carefully added to
plasma to an extent of about 13 per cent, a white flaky viscid
precipitate is thrown down very much like plasmine. If after
the removal of the first precipitate more sodium chloride, and
especially if magnesium sulphate, be added a second precipitate
is thrown down, less viscid and more granular than the first.
The name fibrinogen is given to the former, paraglobulin to the
latter. Both are proteids belonging to the globulin family2, the
members of which while insoluble in distilled water are readily
soluble in dilute solutions of neutral salts. According to some
authors solutions of fibrinogen are characterized by their being
precipitated, and coagulated 3 at a temperature of about 55° — 60°
while solutions of paraglobulin are not so changed till the tempe-
rature rises to 68° — 70°. There are also other differences (see
Appendix).

Both these substances are thrown down when plasma is
saturated with sodium chloride so that the plasmine of Denis
appears to be a mixture of fibrinogen and paraglobulin, and the
question arises, Are both these concerned in the formation of fibrin ?

Paraglobulin Jhoi only occurs as a constituent of plasma, but
is found in considerable quantity in the serum left after clotting ;
it forms as we shall see a large portion of the proteids present in

1 The substance itself is not soluble in distilled water, but a quantity of the
neutral salts always clings to the precipitate, and thus the addition of water virtually
gives rise to a dilute saline solution, in which the substance is readily soluble.

2 See Appendix.

3 See Appendix for the distinction between the coagulation of proteids by heat,
and the coagulation due to the appearance of fibrin.

CHAP, i.]

BLOOD.

17

serum. Now the addition of serum will often bring about coagu-
lation in fluids which, left to themselves, will not coagulate, the
clot so formed being composed of fibrin with normal characters, and
the artificial coagulation thus induced being in all other respects
exactly like a natural clotting. Thus for instance bydrocele fluid,
carefully removed without admixture of blood from a hydrocele,
will in most cases remain fluid without any disposition to clot1.
So also the serous fluid removed from the pericardial, pleural, or
peritoneal cavities some hours after death in most cases shews no
disposition to clot2. But these fluids, hydrocele or pericardial,
though they do not clot spontaneously, will generally, upon the
addition of serum or a little whipped blood, clot in a most unmis-
takeable manner3. Now fibrinogen is certainly present in these
fluids, and may be thrown down from them by the addition of
sodium chloride or by other means ; and, since serum contains
paraglobulin, it was at first thought that the absence of spontaneous
coagulation in the untouched hydrocele or pericardial fluid was
due to the absence of paraglobulin, which as we have seen is
present with fibrinogen in the spontaneously coagulable plasma of
blood, and that the coagulating effect of the addition of the serum
was due to the paraglobulin it contained, the paraglobulin and
fibrinogen acting in some way or other upon each other to produce
fibrin. And this view was supported by the fact that paraglobulin
precipitated from serum was, like the entire serum, efficacious in
giving rise to a coagulation in fibrinogenous pericardial, or hydrocele
fluids.

It was soon found however that certain specimens of pericardial
and even hydrocele fluid did not need the addition of the para-
globulin to make them coagulate; that though they would not
coagulate spontaneously they might be made to coagulate by
adding to them a constituent of serum which was not paraglobulin
but something else. Thus if serum, or indeed whipped blood, be
mixed with a large quantity of alcohol and allowed to stand some
days, the proteids present are in time so changed by. the alcohol
as to become insoluble in water. Hence if the copious precipitate,
after long standing, be separated by filtration from the alcohol^
dried at a low temperature not exceeding 40°, and extracted with'
distilled water, the aqueous extract contains very little proteid
matter, indeed very little organic matter at all. Nevertheless
even a small quantity of this aqueous extract added alone to certain
specimens of hydrocele fluid will bring about a speedy coagulation.
The same aqueous extract has also a remarkable effect in hastening
the coagulation of fluids which though they will eventually clot,
do so very slowly. Thus plasma may, by the careful addition of a

1 In some specimens, however, a spontaneous coagulation, generally slight, but
in exceptional cases massive, may be observed.

2 If it be removed immediately after death it generally clots readily and firmly,
giving a colourless clot consisting of fibrin and white corpuscles only.

3 In a few cases no coagulation can thus be induced.

F. 2

/T

18 FIBRIN-FERMENT. [BOOK i.

certain quantity of neutral salt and water, be reduced to such a
condition that it coagulates very slowly indeed, taking perhaps
days to complete the process. The addition of a small quantity of
the aqueous extract we are describing will however bring about a
coagulation which is at once rapid and complete.

The active substance, whatever it be, in this aqueous extract
J exists in small quantity only, and its coagulating virtues are at
' Npnce and for ever lost when the solution is boiled. Further, there
.'is no reason to think that the active substance actually enters
$ into the formation of the fibrin to which it gives rise ; it seems,
\ $J ^ tnout undergoing changes in itself, to act in some way or other
N ^/ on the actual fibrin factors (fibrinogen and paraglobulin or one of
/vjy\f them) and to convert them or part of them into fibrin. It appears
to belong to a class of bodies playing an important part in
physiological processes and called ferments, of which we shall have
more to say hereafter. We may therefore speak of it as the fibrin-
ferment, the name given to it by its discoverer Alex. Schmidt.

Fibrin-ferment appears to make its appearance in blood soon
after it has been shed, and like other ferments is apt to be
entangled in and carried down by any precipitates which occur
in blood. It is carried down by the plasmine, and hence solutions
of plasmine coagulate spontaneously.

It exists in serum, and is carried down with paraglobulin when
that substance is precipitated. And hence arises the serious
question whether the coagulating effects of serum or prepared
paraglobulin on hydrocele or pericardial fluid are not, after all, due
to the ferment present rather than to the paraglobulin. So that
two views may be taken of the nature of coagulation. One1 teaches
that fibrin arises from some mutual action of fibrinogen and para-
globulin induced by the fibrin ferment ; the other2 that fibrin is
formed through the conversion of fibrinogen alone by the agency
of the ferment, paraglobulin either having nothing to do with the
matter, or merely assisting by its presence in some indirect way.

There can be no doubt that fibrinogen is an essential factor,
that coagulation cannot take place without it and that it or some
part of it actually becomes fibrin. There is equally no doubt that
the presence of the fibrin-ferment is absolutely necessary. It is
also more than probable that fibrin does not result from the union
of fibrinogen arid paraglobulin, since the quantity of fibrin formed
is not greater than that of either of these two substances used to
produce it. But we still need further light as to the exact nature
of the change produced by the ferment, the true characters of the
ferment itself, and the part played by paraglobulin.

In favour of the view that paraglobulin is not concerned in
the matter, it is asserted, that fibrinogen cautiously precipitated
from plasma by small quantities of sodium chloride so as to obtain

1 That of Alexander Schmidt, and his pupils and others.
" That of Hammarsten, Fredericq and others.

CHAP, i.] BLOOD. 19

it apart from paraglobulin, and then freed from ferment by repeated
washing, will yield a solution not spontaneously coagulable, but
clotting freely on the addition of ferment only. In favour of
the view that the presence of paraglobulin is essential may be
quoted the striking fact that certain specimens of hydrocele fluid
may be met with which will not coagulate either spontaneously or
upon the addition of ferment alone, but will coagulate upon the
addition of paraglobulin and ferment. Such fluids may be supposed
to contain fibrinogen only. And it has been argued that two
substances have been confused under the name of fibrinogen : one
coagulating at the same temperature as paraglobulin, and needing
the cooperation of paraglobulin to form fibrin ; and another body,
which may be thrown down from solutions of plasm ine or from
blood at the temperature of 55°— 60° (the fluids thereby losing the
power of coagulating), and which is fibrinogen already on its way
to become fibrin, in fact a sort of nascent fibrin, capable of becoming
actual fibrin in the total absence of paraglobulin. Lastly tbell
presence_of a neutral salt, such as sodium chloride, appears to be
essential to the process, coagulation not occurring even where all ,
three factors are present, if no neutral salt accompanies them.

Awaiting further investigation we may for the present conclude
that fibrin is formed by the conversion, through the agency of
a ferment, of a substance fibrinogen, which forms part° of the
plasm ine spoken of above, but the exact nature of that conversion
and whether paraglobulin has any share in the matter, and if so
what, must remain as yet undecided.

This conception of coagulation as a chemical process between
certain factors renders easy of comprehension the influence of
various conditions on the coagulation of blood. The quickening
influence of heat, the retarding effect of cold, the favourable action
of motion and of contact with surfaces, and hence the results
of whipping and the influence exerted by the form and surface of
vessels, become intelligible. The greater the number of points,
that is the larger and rougher the surface presented by the vessel
into which blood is shed, the more quickly coagulation comes on,
for contact with surfaces favours chemical union. So also the
presence of spongy platinum, or of an inert powder like charcoal,
quickens the coagulation of tardily clotting fluids, such as many
specimens of pericardia! fluid.

Having thus arrived at an approximative knowledge of the
nature of coagulation, we are in a better position for discussing the
question, Why does blood remain fluid in the vessels of the living
body and yet clot when shed ?

The older views may be at once summarily dismissed. The
clotting is not due to loss of temperature, for cold retards coagu-
lation, and the blood of cold-blooded animals behaves just like that
of warm-blooded animals in clotting when shed. It is not due to
loss of motion, for motion favours coagulation. It is not due to

2—2

20 INFLUENCE OF THE LIVING BLOOD-VESSELS. [BOOK i.

exposure to air, whereby either an increased access of oxygen or an
escape of volatile matters is facilitated, for on the one hand the
blood is fully exposed to the air in the lungs, and on the other
shed blood clots when received, without any exposure to the
atmosphere, in a closed tube over mercury.

All the facts known to us point to the conclusion, that when
blood is contained in healthy living blood-vessels, a certain relation
or equilibrium exists between the blood and the containing vessels
of such a nature that as long as this equilibrium is maintained the
blood remains fluid, but that when this equilibrium is disturbed by
events in the blood or in the blood-vessels or by the removal of the
blood, the blood undergoes changes which result in coagulation.
The most salient facts in support of this conclusion are as follows.

1. After death, when all motion of the blood has ceased, the
blood remains for a long time fluid. It is not till some time

, afterwards, at an epoch when post-mortem changes in the blood
and in the blood-vessels have had time to develope themselves,
that coagulation begins. Thus some hours after death the blood in
the great veins may be found perfectly fluid. Yet such blood has
not lost its power of coagulating ; it still clots when removed from
the body, and clots too when received over mercury without
r^ i exposure to air, shewing that the fluidity of the highly venous
blood is not due to any excess of carbonic acid or absence of oxygen.
Eventually it does clot even within the vessels, but perhaps
never so firmly and completely as when shed. It clots first in the
larger vessels, but remains fluid in the smaller veins, for a very long
time, for many hours in fact, since in these the same bulk of blood
is exposed to the influence of, and reciprocally exerts an influence
on, a larger surface of the vascular walls than in the larger veins.

2. If the vessels of the heart of a turtle (or any other cold-
W blooded animal) be ligatured, and the heart be cut out and

AT \ vJI$iace(^ in favourable circumstances so that it may continue to beat
P> V^V as ^on£ a Per*°d as possible, the blood will remain fluid within
•* *$^ ^he heart as long as the pulsations go on, i. e. for one or two days
(and indeed for some time afterwards), though a portion taken away
at any period of the experiment will clot very speedily.

3. If the jugular vein of a large animal, such as an ox or
horse, be ligatured when full of blood, and the ligatured portion
excised, the blood in many cases remains perfectly fluid, along the
greater part of the length of the piece, for twenty-four or even
forty-eight hours. The piece so ligatured may be suspended in
a framework and opened at the top so as to imitate a living
test-tube, and yet the blood will often remain long fluid, though
a portion removed at any time into another vessel will clot in
a few minutes. If two such living test-tubes be prepared, the
blood may be poured from one to the other without coagulation
taking place.

The above facts illustrate the absence of coagulation in intact

CHAP, i.] BLOOD. 21

or slightly altered living blood-vessels; the following shew that
coagulation may take place even in the living vessels.

4. If a needle or piece of wire or thread be introduced into f VA> 'w
the living blood-vessel of an animal, either during life or imme-; , !,"7',
diately after death, the piece will be found encrusted with fibrin.

5. If in a living animal a blood-vessel be ligatured, the
ligature being of such a kind as to injure the inner coat, coagu-
lation takes place at the ligature and extends for some distance
from it. Thus if the jugular vein of a rabbit be ligatured roughly
in two places, clots will in a few hours be found in the ligatured
portion, reaching upwards and downwards from the ligatures, the
middle portion being the least coagulated. Clots will also be
found on the far side of each ligature. The clots will still appear
if the ligature be removed immediately after being applied,
provided that in the process the inner coat has been wounded.
If the ligatures be applied in such a way as not to injure the
inner coat, coagulation will not take place, though the blood may
remain for many hours perfectly at rest between the ligatures.

So also when an artery is ligatured a conspicuous clot is formed
on the cardiac side of the ligature. The clot is largest and firmest
in the immediate neighbourhood of the ligature, gradually thinning
away from thence and reaching usually as far as where a branch J"
is given off. Between this branch and the ligature there is stasis ;
the walls of the artery suffer from the want of renewal of blood,
and thus favour the propagation of the coagulation. On the distal
side of the ligature where the artery is much shrunken, the clot
which is formed, though naturally small and inconspicuous, is
similar.

6. Any injury of the inner coat of a blood-vessel causes a
coagulation at the spot of injury. Any treatment of a blood-vessel
tending to injure its normal condition causes local coagulation.

7. Disease involving the inner coat of a blood-vessel causes a
coagulation at the part diseased. Thus inflammation of the lining
membrane of the valves of the heart in endocarditis is frequently
accompanied by the deposit of fibrin. In aneurism the inner coat
is diseased, and layers of fibrin are commonly deposited. So also
in fatty and calcareous degeneration without any aneurismal
dilation there is a tendency to the formation of clots.

Similar phenomena are seen in the case of serous fluids which
coagulate spontaneously. If, as soon after death as the body is
cold and the fat is solidified, the pericardium be carefully removed
from a sheep by an incision round the base of the heart,
the pericardial fluid may be kept in the pericardial bag as in
a living cup for many hours without clotting, and yet a small
portion removed with a pipette clots at once, and a thread left
hanging into the fluid soon becomes covered with fibrin.

The only interpretation which embraces these facts is that1
so long as a certain normal relation between the lining surfaces ofjj

22 SOURCES OF THE FIBRIN FACTORS. [BOOK i.

the blood-vessels and the blood is maintained, coagulation does not
take place ; but when this relation is disturbed by the more or
less gradual death of blood-vessels, or by their more sudden disease
or injury, or by the presence of a foreign body, coagulation sets in.
Two additional points may here be noticed. 1. Stagnation of
blood favours coagulation within the blood-vessels, apparently
because the blood-vessels, like other tissues, demand a renewal
of the blood on which they depend for the maintenance of their
vital powers. 2. The influence of surface is seen even in the
coagulation within the vessels. In cases of coagulation from
gradual death of the blood-vessels, as in the case of an excised
jugular vein, the fibrin, when its deposition is sufficiently slow, is
seen to appear first at the sides, and from thence gradually,
frequently in layers, to make its way to the centre. So in
aneurism, the deposit of fibrin is frequently laminated. In cases
where coagulation results from disease of the lining membrane, the
rougher the interior, the more speedy and complete the clotting.
So also a rough foreign body, presenting a large number of surfaces
and points of attachment, more readily produces a clot when intro-
duced into the living blood-vessels than a perfectly smooth one.

We may perhaps go a step further, for there are certain weighty
reasons for believing that in normal circulating blood all the fibrin-
factors are not present in the plasma, and that a disturbance of the
equilibrium between the blooid and the blood-vessels gives rise to
coagulation by inducing changes in certain corpuscles, either the
ordinary white corpuscles or corpuscles of a special kind, whereby
one or more of the fibrin-factors are discharged into the plasma.

1. When blood is received direct from the blood-vessels into
alcohol, the aqueous extract of the precipitate contains little or no
fibrin-ferment. If the blood be allowed to stand a little while before
being thrown into alcohol some ferment makes its appearance ; and
the longer, up to clotting, that the blood stands before being treated
with alcohol, the more efficacious is the aqueous extract of the
precipitate. Fibrin-ferment therefore seems to make its appearance
in blood after being shed.

2. When blood, kept from clotting by exposure to cold
or through being retained by ligatures in a living blood-vessel, is
allowed to stand till the corpuscles have sunk, the upper layers of
the plasma, free from both red and white corpuscles, exhibit when
removed very little power of coagulation and, upon examination, are
found to contain a very small quantity only of fibrin-ferment.

3. We have reasons for thinking that when blood is shed,
certain number of corpuscles, which we may speak of as

w -f j^hite corpuscles, leaving it for the present uncertain whether
J.<sthey are to be regarded as a special kind of corpuscles or not,
are broken- up and disappear.

Putting these facts together we are led to think that normal
plasma circulating in the normal blood-vessels contains

f

o

V

CHAP, i.] BLOOD. 23

no fibrin-ferment, but that when the equilibrium of blood is
disturbed, either by the shedding of the blood or by injury to the
blood-vessels or by the introduction of foreign bodies, fibrin-ferment
is discharged into the plasma, as the result of changes taking
place in certain corpuscles.

With regard to the other fibrin-factors our knowledge is at
present deficient. As we shall have to state presently, paraglo-
bulin apparently exists in serum and therefore in plasma, in very
considerable quantity; and to say nothing of the doubt as to
whether paraglobulin has any share in forming fibrin, it seems
extremely unlikely that the whole of this large quantity could
have come from disintegrating corpuscles. Fibrin ogen is generally
supposed to be pre-existent in the plasma; but there do not
appear to be adequate reasons for this view; and it is quite
possible that it too, like the ferment, comes from the corpuscles.
But this is almost tantamount to saying that the whole fibrin
comes from the corpuscles, and indeed it has been argued that the
white corpuscles are in part bodily converted into fibrin.

The whole matter needs further investigation, and when
we remember that fibrin-ferment and even masses of white
corpuscles injected into the living blood-vessels do not necessarily
bring about coagulation, it is clear that we have much yet to
learn. Moreover we have reason, as we shall see, to think that
corpuscles are continually dying in the body, and therefore continu-
ally setting free fibrin-factors ; and these, unless we suppose that
a certain quantity of fibrin can exist scattered so to speak in the
blood, must be made away with or at least prevented from giving

risetoclots-

/

SEC. 2. THE CHEMICAL COMPOSITION OF BLOOD.

As we have already urged, the chief chemical interests of blood
are attached to the changes which it undergoes in the several
tissues, and which will be considered in connection with each tissue
at the appropriate place. Nevertheless a brief summary of the
main characters of blood as a whole may be introduced here.
( The average specific gravity of human blood is 1055, varying
from 1045 to 1075 within the limits of health. The reaction of
•blood as it flows from the blood-vessels is found to be distinctly
though feebly alkaline.

If the corpusclelTbe supposed to retain the amount of water
proper to them, blood may, in general terms, be considered as
consisting by weight of from about one-third to somewhat less than
one-half of corpuscles, ;bhe rest being plasma. As will be insisted
on presently, the number of corpuscles in a specimen of blood
is found to vary considerably, not only in different animals and in
different individuals, but in the same individual at different times.

Conspicuous and striking as are the results of coagulation,
massive as appears to be the clot which is formed, it must be remem-
bered that by far the greater part of the clot consists of corpuscles.
The amount by weight of fibrin required to bind together a number
of corpuscles in order to form even a large firm clot is exceedingly
small. Thus the average quantity by weight of fibrin in human
blood is said to be '2 p. c., but the amount which can be obtained
from a given quantity of plasma varies extremely; the variation
being due not only to circumstances affecting the blood, but also to
the method employed.

The difficulties indeed of acquiring an exact knowledge of the
chemical constitution of the plasma, which as we have seen from the

CHAP, i.] BLOOD. 25

foregoing section is probably undergoing changes from the moment
of being shed, are very great; our information concerning the
composition of the serum and of the corpuscles is much more trust-
worthy.

Composition of serum. In 100 parts of serum there are in
round numbers

Water 90 parts

Proteid Substances 8 to 9 „

Fats, Extractives1, and Saline Matters 2 to 1 „
The proteid substances present in serum are2: — (1) The so-called
$erum albumin, (2) parafflobulin. The paraglobulin, as has been
stated in the preceding section, may be removed from the serum in
several ways: viz. by passing carbonic acid through, or by cautiously
adding dilute acetic acid to, the diluted serum, or more completely
by saturating the undiluted serum with magnesium sulphate.
When the whole of the paraglobulin has been removed a con-
siderable quantity of proteid material is still left in the serum
in the form known as serum albumin, distinguished from,
paraglobulin among other characters by its being soluble in
distilled water, and therefore not requiring for its solution the
presence of a neutral salt3. From the researches of Hammar-
sten it would appear that, owing to imperfect methods the
amount of paraglobulin in serum has been much underrated.
According to him, the quantity though varying in different animals,
is at times equal to and sometimes even greater than that of the
serum albumin. Even if we were to accept as definitely proved
the view that paraglobulin in some form or other is in some
way associated with the formation of fibrin, it seems hardly
probable that the whole of this large quantity of paraglobulin
present in serum is fibrinoplastic, i.e. capable of taking part in
the formation of fibrin. We cannot at present however attach
any definite functions to the paraglobulin and serum albumin
respectively, nor do we know much as to what extent they vary
in quantity, though the interesting observation has been made
that in snakes the serum albumin disappears during starvation,
while the paraglobulin is fairly constant. When serum, after the
cautious addition of acetic acid in order to neutralize its alkalinity,
is heated to about 75° C. both the serum albumin and paraglobulin
are thrown down in the form known as coagulated proteids, sub-
stauces characterized by their great insolubility. This 'coagulation'
by heat of these and other proteids is, it perhaps need hardly be
repeated, not to be confounded with the coagulation of plasma due
to the appearance of fibrin.

1 This word is used to denote substances of varied origin and nature, occurring
in small quantities, and therefore requiring to be ' extracted ' by special means.

a There seems no longer any reason to distinguish a serum-casein from paraglo-
bulin, see Appendix.

3 For further details see Appendix.

26 COMPOSITION OF THE RED CORPUSCLES. [BOOK i.

The fats, which are scanty, except after a meal or in certain
pathological conditions, consist of the neutral fats, stearin, pal-
mitin, and olein, with a certain quantity of their respective alkaline
soaps. Lecithin1 and cholesterin occur in very small quantities only.
Among the extractives present in serum may be put down all the
nitrogenous and other substances which form the extractives of the
body and of food, such as urea, kreatin, sugar, lactic acid, &c. A
very large number of these have been discovered in the blood
under various circumstances, the consideration of which must be
left for the present. The peculiar odour of blood-serum is pro-
bably due to the presence of volatile bodies of the fatty acid series.
The faint yellow colour of serum is due to a special yellow pigment.

e most characteristic and important chemical feature of the

ine constitution of the serum is the preponderance of sodium

In this respect the serum offers a
Less marked, but

salts over those or potassium.

marked contrast to the corpuscles (see below).

still striking, is the abundance of chlorides and the poverty of
phosphates in the serum as compared with the corpuscles. The
salts may ia fact briefly be described as consisting chiefly of
sodium chloride, with some amount of sodium carbonate, or more
correctly sodium bicarbonate, and potassium chloride, with small
quantities of sodium sulphate, sodium phosphate, calcium phos-
phate, and magnesium phosphate. And of even the small quantity
of phosphates found in the ash, part of the phosphorus exists in
the serum itself not as a phosphate but as phosphorus in some
organic body.

Composition of the red corpuscles. The corpuscles contain less
water than the serum, the amount of solid matter being variously
estimated at from 30 to 40 or more p. c. The solids are almost
entirely organic matter, the inorganic salts in the corpuscles
amounting to less than 1 p. c. Of the organic matter again by far
the larger part consists of haemoglobin. In 100 parts of the dried
organic matter of the corpuscles of human blood, Hoppe-Seyler
and Jiidell found, as the mean of two observations,

Haemoglobin 90*54 Lecithin '54

Proteid Substances 8'67 Cholesterin '25

There are reasons for believing that not only may the number

of red corpuscles vary, but also the quantity of haemoglobin present

in the corpuscles differ under different circumstances. Malassez,

by comparing the tint of a quantity of blood the numbers of whose

corpuscles had been estimated, with that of a graduated solution

of picrocarminate of ammonia, has been able to estimate the

amount of haemoglobin present in the corpuscles under different

circumstances. He finds that in anaemia the poverty of the

1 For detailed accounts of the characters of the several chemical substances
mentioned in this and succeeding chapters consult the Appendix under the appro-
priate headings.

CHAP, i.] BLOOD. 27

corpuscles in haemoglobin is even more striking than the scanti-
ness of the corpuscles, and is sooner affected by the administration

vroiL

e composition and properties of haemoglobin will be con-
sidered in connection with respiration.

Of the proteid substances which form the stroma of the red
corpuscles this much may be said, that they appear to belong to
the globulin family; their exact nature need not be considered
here. As regards the inorganic constituents, the corpuscles are
distinguished by the relative abundance of the salts of potassium
and of phosphates. This at least is the case in man ; the relative
quantities of sodium and potassium in the corpuscles and serum
respectively appear however to vary in different animals; in some
the sodium salts are in excess even in the corpuscles.

Composition of the white corpuscles. Our knowledge of the
exact nature of the proteid matrix of the white corpuscles is at
present too uncertain to enable any definite or useful statements
to be made, and the probable relation of the corpuscles to coagula-
tion has already been spoken of. The corpuscles are found to
contain in addition to proteid material, lecithin or protagon, gly-
cogen, extractives and inorganic salts, there being in the ash a
preponderance of potassium salts and of phosphates. The nuclei
contain nuclein. Upon the death of the corpuscle the glycogen
appears to be converted into sugar.

Both the corpuscles and the plasma (or serum) contain gases.
These will be considered in connection with respiration.

The main facts of interest then in the chemical composition of
the blood are as follows. The red corpuscles consist chiefly of
haemoglobin. The organic solids of serum consist partly of serum-
albumin, and partly of paroglobulin. The serum or plasma
contrasts in man at least, with the corpuscles, inasmuch as the
former contains chiefly chlorides and sodium salts while the latter
are richer in phosphates and potassium salts. The extractives of
the blood are remarkable rather for their number and variability
than for their abundance, the most constant and important being
perhaps urea, kreatin, sugar, and lactic acid.

SEC. 3. THE HISTORY OF THE CORPUSCLES.

In the living body red blood-corpuscles are continually being
destroyed, and new ones as continually being produced. The proofs
of this are,

/ 1. The number of the red corpuscles in the blood at any given
(time varies much.

The number of corpuscles in a specimen of blood is determined by
mixing a small but carefully measured quantity of the blood with a large
quantity of some indifferent fluid, and then actually counting the
corpuscles in a known minimal bulk of the mixture.

This may be done either by Yierordt's plan (somewhat modified by
Gowers), in which a minimal quantity of the diluted blood, measured
in a fine capillary tube, is spread on a surface marked out in square
areas, and the number of corpuscles in each square area counted under
the microscope; or by that of Malassez, in which the diluted blood
is drawn into a capillary tube with flattened sides, and the number
of corpuscles counted in situ in the tube by means of an ocular
marked out in squares, the microscope being so adjusted that each
area of the ocular corresponds to a certain capacity of the capillary tube.

The average number of red corpuscles in mammals generally
ranges from 3 to 18 millions; in human blood it is about 5 millions
in a cubic millimetre. The number is increased by meals, and dimi-
nished by fasting ; of course, the number of corpuscles present in any
given bulk of blood being merely the expression of the proportion
of corpuscles to the amount of plasma, variations in the number
counted might and in certain cases are probably caused by an
increase or decrease in the quantity of plasma, occurring while the
actual number of corpuscles is stationary. But many of the
variations cannot be so accounted for ; they must be due to an in-

CHAP, i.] BLOOD. 29

crease or decrease of the total number of corpuscles in the body.
After a very large reduction of the^ total number of red corpuscles.
as by haemorrhage or disease (anaemia), the normal proportion may
be regained even within a very short time.

2] There are reasons for thinking that the urinary and bile-
pigments are derivatives of haemoglobin. If this be so, an immense
number of corpuscles must be destroyed daily (and replaced by
new ones) in order to give rise to the amount of urinary and bile-
pigment discharged daily from the body.

3. When the blood of one animal is injected into the vessels
of another (ex. gr. that of a bird into a mammal), the corpuscles of
the first may for some time be recognised in blood taken from the
second; but eventually they wholly disappear. This of course is
no strong evidence, since the destruction of foreign corpuscles
might take place even though the proper ones had a permanent
existence.

That the white corpuscles or leucocytes also are continually being
destroyed and replaced is similarly probable from the fact that they
vary extremely in number at different times and under various
circumstances. Most observers agree that they are very largely
increased by taking food. Thus during fasting they may be seen
in a drop of blood to bear to the red the proportion of 1 in 800
or 1000. After a meal this proportion may rise to 1 in 300 or 400.-
The mode of origin of the red corpuscles is so fully dealt with
in histological treatises and at the same time the subject of so
many conflicting opinions, that it will be sufficient to remind the
reader that the facts at present in our possession seem to shew
that in the adult the generation of new corpuscles takes place
chiefly in the red medulla of bones, but also, at all events in young
animals, and especially after great loss or destruction of red
corpuscles, in the spleen and possibly in other places. In the
peculiar capillary mesh-work of the red medulla are found certain
corpuscles which differ, among other characters, from the normal
red corpuscles (in mammals) by possessing a nucleus, and from the
ordinary leucocytes by having their protoplasm impregnated with
a certain quantity of haemoglobin. These peculiar intermediate
corpuscles appear to be transformed into normal red corpuscles,
but the exact mode of transformation, whether for instance the
nucleus is bodily extruded from the cell, or broken up within the
cell, or whether indeed, as some think, the nucleus and not the
whole cell becomes the red corpuscle, is not yet wholly cleared up.
Nor are we at present sure whether these peculiar corpuscles
themselves arise by a metamorphosis of ordinary leucocytes, or
as Bizzozero urges, represent a special class of cells, whose
continual existence is ensured by their continually undergoing
division. Intermediate cells of this description (which must
not be confounded with smaller cells described by Hayem, and
called by him haematoblasts, but whose nature is doubtful) have

30 HISTORY OF THE CORPUSCLES. [BOOK i.

been seen in circulating and even shed blood by various observers,
and it is this kind of corpuscle which Alex. Schmidt believes to
break up so largely and disappear, with the production of fibrin-
factors, when blood is shed. Making every allowance for contro-
verted points, we may conclude, that the red-medulla of bones has
an important function in giving rise to new red corpuscles, and
that after unusual loss or destruction of these bodies, the normal
activity of this tissue at least is greatly increased.

When we come to treat of respiration, we shall bring forward
evidence that the red corpuscles, by virtue of haemoglobin, have a
most important use in carrying oxygen from the lungs to the
several tissues. It is through the red corpuscles that the tissues
themselves breathe, at least as far as breathing is the taking in of
oxygen. We do not know what wear and tear the red corpuscles
undergo in this respiratory function ; nor have we any evidence as
to any other work which they perform in the economy, and which
would tend to their being used up. But, as we have already urged,
we have reason to think that they afe~being constantly destroyed,
and apparently one place at least where this destruction goes on is

rthe spleen.

In this organ may be seen, as Kolliker long since pointed out,
large protoplasmic cells in which are included a number of red
corpuscles : and these red corpuscles may be observed in various
stages of apparent disintegration. Moreover the serum of the
blood of the splenic vein, unlike that of blood in general, is said to

<be tinged with haemoglobin. It would seem therefore probable that
a certain amount ot haemoglobin is set free in the spleen from
disintegrating red corpuscles, and carried, in part at least, from
thence through the portal circulation to the liver. Whether any
large amount of destruction of red corpuscles goes on elsewhere we
do not know.

Since the serum of blood, with the exception of that from the
splenic vein, contains no dissolved haemoglobin, it is clear that the
hemoglobin of the broken-up corpuscles must speedily be trans-
formed into some other body. Into what other body? In old
blood-clots (as in those of cerebral haemorrhage) there are fre-
quently found minute crystals of a body free from iron, which has
received the name hcematoidin. There can be no doubt that the
haematoidin of these clots is a derivative from the haemoglobin of
the escaped blood. We know1 that haemoglobin contains, besides
a proteid residue, a residue not proteid in nature, called haematin.
We know further that haematin may lose the iron which it contains
(and which appears to be loosely attached), and yet remain a
coloured body. So that there is no difficulty in the passage from
the proteid-and-iron-containing haemoglobin to the proteid-and-
iron-free haematoidin. But haematoidin, not only in the form and
appearance of its crystals, but also, as far as can be ascertained by
1 See Chapter on Changes of Blood in Respiration.

CHAP. i.J BLOOD. 31

the analysis of the small quantities at disposal, in its chemical
composition, is identical with bilirubin, the primary pigment of
bile. Moreover, according to some observers the injection of
haemoglobin, or of dissolved red corpuscles, into the vessels of a
living animal, gives rise to a large amount of bile-pigment in the
urine, and at the same time increases enormously the relative
quantity of bilirubin in the bile. Thus though no one has yet
succeeded in producing bilirubin artificially from haemoglobin, andj
the actual identity of the two cannot as yet perhaps be regarded'
as settled, facts, and especially perhaps the presence of haem
globin, in the serum of the splenic vein, and its disappearance aft
the blood has passed through the liver, point very strongly to th
view that the red corpuscles are used up to supply bile-pigment.

Our knowledge of urinary pigments is so imperfect that little
can be said as to their relation to haemoglobin. We cannot at
present definitely trace the normal urinary pigment back to
haemoglobin, however probable such a source may seem.

As regards the white corpuscles of the blood, using this
term without prejudice or as to the question whether or no
there be more than one distinct kind, these as we have seen
also come and go.

The fact that in the lymphatic glands, and other adenoid
structures, corpuscles, similar to if not identical with white blood-
corpuscles, are to be seen of very various sizes, many with double
nuclei and some indeed actually dividing into two corpuscles,
suggests that these organs are the birth-places of the white
corpuscles. The lymph is continually pouring into the blood a
crowd of white corpuscles, which, since they for the most part
make their appearance in the lymph-vessels after the latter have
traversed the lymphatic glands, probably take origin from those
bodies.

At the same time it is open for us to suppose that any
proliferating tissue may give rise to new corpuscles; and Klein
states that he has seen them budded off from the reticulum of the
spleen. The white corpuscles have also been observed to divide1.

We may conclude therefore that the white corpuscles probably!
arise, by division chiefly, from the corpuscles of adenoid tissue, but
that other sources may exist.

While we are able to attribute to the numerous red corpuscles
an important respiratory function, we are at present at all
events unaware of any special work carried on by the scantier
white corpuscles while they are being hurried along in the blood
current. As far as our present knowledge goes they seem to tarry
in the blood only on their way either to be broken up or to pass
into the tissues.

We have already referred to the probable view that it is not the
ordinary white corpuscle but a special kind of corpuscle which is
1 Klein, Hdb. Phys. Lab., p. 8.

32 HISTORY OF THE CORPUSCLES. [BOOK i.

transformed into the red corpuscle ; if this is the case the keeping
up a supply of red corpuscles cannot, as was once thought, be an
important end of the existence of white corpuscles in general. We
have already (p. 22) dwelt on the probability that the coagulation
of shed-blood is due to white corpuscles breaking up and discharg-
ing certain fibrin-factors into the plasma ; but it is uncertain in
the first place whether this function is to be attributed to all white
corpuscles or to a special kind only, and in the second place
whether in normal conditions of the economy any appreciable
amount of fibrin-factors are in this way habitually discharged into
the blood, and as constantly got rid of without fibrin being formed.
It is quite possible that normal circulating plasma may always
contain a certain stock for instance of fibrinogen, which is
continually being drawn upon for the nourishment of the tissues,
and as continually replaced by the destruction of corpuscles. But
there are no facts at present which absolutely contradict the view
that fibrinogen is normally absent from intact circulating plasma,
and that the arrangements for the manufacture of fibrin exist only
for the purpose of meeting the contingency of fibrin being required
under circumstances which may be considered abnormal.

On the other hand we know that in an inflamed area the white
corpuscles migrate in large numbers into the extravascular portions
of the tissues, and it has been maintained that not only the pus
corpuscles and ' exudation' corpuscles which are the common pro-
ducts of inflammation, but even the new tissue elements (connec-
tive-tissue cells and fibres), which make their appearance as the
result of the so-called 'productive' inflammations, are the descen-
dants, immediate, or remote, of such migratory corpuscles. But
a discussion of this question would lead us too far away from the
purpose of this work.

It would appear therefore that with the exception of the respira-
tory function of the red corpuscles, the physiological interest of the
blood is attached rather to the plasma than to the corpuscles.
\ II The work, done by the corpuscles, even when it is fully under-
, \ stood, will, with the exception of the carrying of oxygen by the
red corpuscles, always appear insignificant compared with the
incessant labours of the plasma, which is for ever busy as the
middle-man between the several tissues, bringing to each tissue
what it needs and taking from it that which is useless or even
injurious to itself but necessary to the well-being of some other
part.

SEC. 4. THE QUANTITY OF BLOOD, AND ITS
DISTRIBUTION IN THE BODY.

The total quantity of blood present in an animal body is
estimated in the following way. As much blood as possible is
allowed to escape from the vessels; this is measured directly.
The vessels are then washed out with water or normal saline
solution, and the washings carefully collected, mixed and measured.
A known quantity of blood is diluted with water or normal saline
solution until it possesses the same tint as a measured specimen of
the washings. This gives the amount of blood (or rather of
haemoglobin) in the measured specimen, from which the total
quantity in the whole washings is calculated. Lastly, the whole
body is carefully minced and washed free from blood. The
washings are collected and filtered, and the amount of blood in
them estimated as before by comparison with a specimen of diluted
blood. The quantity of blood in the two washings, together with
the escaped blood, gives the total quantity of blood in the body.

The method is not free from objections, the most serious
of which perhaps are attached to the difficulty of obtaining
infusions of the minced tissues clear enough to have their tint
accurately estimated, and to the fact that the animal must be
killed for the purpose; but other methods, for instance those in which
the quantity is calculated from the proportion of red corpuscles to
plasma before and after either diminution of the plasma by sweat-
ing or increase by the injection of serum or other fluids free from
corpuscles, are open to still graver objections.

F. 3

34 DISTRIBUTION OF BLOOD. [BOOK i.

From the result of a few observations on executed criminals it
has been concluded that the total quantity of blood in the human
body is about -^th of the body weight. But in various animals,
the proportion of the weight of the blood to that of the body has
been found to vary very considerably ; and probably this holds good
for man also, at all events within certain limits.

The blood is in round numbers distributed as follows :

About one-fourth in the heart, lungs, large arteries and veins,

» » liver,

„ „ „ „ skeletal muscles,

„ „ „ „ other organs.

Since in the heart and great blood-vessels the blood is simply
in transit, without undergoing any great changes (and in the lungs,
as far as we know, the changes are limited to respiratory changes),
it follows that the changes which take place in the blood passing
through the liver and skeletal muscles far exceed those which take
place in the rest of the body.

CHAPTER II.
THE CONTRACTILE TISSUES.

THE greater number of the movements of the complex animal
body are carried on by means of the skeletal striated muscles. A
skeletal muscle when subjected to certain influences contracts, i. e.
shortens, bringing its two ends nearer together ; and the shortening,
acting through various bony levers or by help of other mechanical
arrangements, produces a movement of some part of the body. The
striated tissue of which the skeletal muscles are composed is the
chief contractile tissue. The peculiar muscular tissue of the heart
is another contractile tissue; under certain influences the fibres
into which it is arranged, shorten and thus give rise to the beat of
the heart. A similar shortening or contraction of the fusiform
fibre cells of plain muscular tissue, gives rise to movements such as
changes of calibre &c. of the alimentary canal, the urinary bladder,
the uterus, the arteries and the like.

At first sight 'contraction' of any one of these forms of differen-
tiated muscular tissue seems wholly unlike an amoeboid movement
of an amoeba or of a white blood corpuscle. And yet the transition
from the one to the other is very slight. A typical amoeba may be
regarded as spherical in form, and when it is executing its move-
ments the pseudopodic bulging of its protoplasm may be seen
to occur now on this now on that part of its circumference and to
take now this and now that direction. The fibre cell of plain
muscular tissue is a nucleated protoplasmic mass of a distinctly
fusiform shape, and when it executes its movements, i. e. contracts,
the bulging of its protoplasm is always a lateral bulging in a
direction at right angles to the long axis of the fibre cell. Since as

3—2

36 MUSCULAR CONTRACTION. [BOOK i.

we shall see there is no change of total bulk, this thickening of the
fibre by means of the lateral bulging is necessarily accompanied
by a shortening of its length. The contraction of muscular tissue
iis in fact a limited and definite amoeboid movement in which
intensity and rapidity are gained at the expense of variety.

Besides these movements which are carried out in the body by
means of differentiated muscular tissue, there are others brought
about by the peculiar structures known as cilia, among which we
may include the motile tails of spermatozoa ; and ordinary amoeboid
movements are not wanting, being conspicuously shewn by the
so-called migrating cells. We may include both these under the
heading of contractile tissues.

Of all these various forms of contractile tissue the skeletal
striated muscles, on account of the more complete development of
their functions, will be better studied first ; the others, on account
of their very simplicity, are in many respects less satisfactorily
understood.

All the ordinary striated skeletal muscles are connected with
nerves. We have no reason for thinking that their contractility is
called into play, under normal conditions, otherwise than by the
agency of nerves.

Muscles and nerves being thus so closely allied, and having
besides so many properties in common, it will conduce to clearness
and brevity if we treat them together.

SEC. 1. THE PHENOMENA OF MUSCLE AND NERVE.
Muscular and Nervous Irritability.

The skeletal muscles of a frog, the brain and spinal cord of
which have been destroyed, do not exhibit any spontaneous move-
ments or contractions, even though the nerves be otherwise quite
intact. Left untouched the whole body may decompose without
any contraction of any of the muscles having been witnessed.
Neither the skeletal muscles nor the nerves distributed to them
possess any power of automatic action.

If however a muscle be laid bare and be more or less violently
disturbed, if for instance it be pinched, or touched with a hot wire,
or brought in contact with certain chemical substances, or subjected"
to the action of galvanic currents, it will contract whenever it is
thus disturbed. Though not possessing any automatism, the
muscle is (and continues for some time after the general death ot
the animal to be) irritable. Though it remains quite quiescent
when left untouched, its powers are then dormant only, not absent.
These require to be roused or 'stimulated' by some change or
disturbance in order that they may manifest themselves. The
substances or agents which are thus able to evoke the activity of
an irritable muscle are spoken of as stimuli.

But to produce a contraction in a muscle the stimulus need
not be applied directly to the muscle ; it may be applied indirectly
by means of the nerve. Thus, if the trunk of a nerve be pinched, \
or subjected to sudden heat, or dipped in certain chemical *>
substances, or acted upon by various galvanic currents^ contrac-
tions are seen in the muscles to which branches of the nerve are
distributed.

ne
> sti

38 MUSCULAR CONTRACTION. [BOOK i.

The nerve like the muscle is irritable, it is thrown into a state
of activity by a stimulus ; but unlike the muscle it does not itself
contract. The changes set up in the nerve by the stimulus are not
visible changes of form; but that changes of some kind or other
are set up and propagated along the nerve down to the muscle is
shewn by the fact that the muscle contracts when a part of the
nerve at some distance from itself is stimulated. Both nerve
'and muscle are irritable, but only the muscle is contractile, i. e.
manifests its irritability by a contraction. The nerve manifests its
irritability by transmitting along itself, without any visible alteration
:of form, certain molecular changes set up by the stimulus. We shall
icall these changes thus propagated along a nerve, 'nervous impulses.'

We have stated above that the muscle is irritable in the sense
that it may be thrown into contractions by stimuli applied directly
to itself. But it might fairly be urged that the contractions so pro-
duced are in reality due to the fact that, although the stimulus is
apparently applied directly to the muscle, it is, after all, the fine
nerve-branches, so abundant in the muscle, which are actually
stimulated. The following facts however go far to prove that
the muscular fibres themselves are capable of being directly stimu-
lated without the intervention of any nerves. When a frog (or other
animal) is poisoned with urari, the nerves may be subjected to
the strongest stimuli without causing any contractions in the
muscles to which they are distributed ; yet even ordinary stimuli
applied directly to the muscle readily cause contractions. If before
introducing the urari into the system, a ligature be passed under-
neath the sciatic nerve in one leg, for instance the right, and drawn
tightly round the whole leg to the exclusion of the nerve, it is
evident that the urari when injected into the back of the animal,
will gain access to the right sciatic nerve above the ligature, but
not below, while it will have free access to the whole left sciatic. If,
as soon as the urari has taken effect, the two sciatic nerves be
stimulated, no movement of the left leg will be produced by stimu-
lating the left sciatic, whereas strong contractions of the muscles of
the right leg below the ligature will follow stimulation of the right
sciatic, whether the nerve be stimulated above or below the ligature.
Now since the upper parts of both sciatics are equally exposed to
the action of the poison, it is clear that the failure of the left nerve
to cause contraction is not attributable to any change having taken
place in the upper portion of the nerve, else why should not the
right, which has in its upper portion been equally exposed to the
action of the poison, also fail ? Evidently the poison acts on some
parts of the nerve lower down. If a single muscle be removed from
the circulation (by ligaturing its blood-vessels), previous to the
poisoning with urari, that muscle will contract when any part of the
nerve going to it is stimulated, though no other muscle in the body
will contract when its nerve is stimulated. Here the whole nerve
right down to the muscle has been exposed to the action of the

CHAP, ii.] THE CONTRACTILE TISSUES. 39

poison ; and yet it has lost none of its power over the muscle. On
the other hand, if the muscle be allowed to remain in the body, and
so be exposed to the action of the poison, but the nerve be divided
high up and the part connected with the muscle gently lifted up
before the urari is introduced into the system, so that no blood
flows to it and so that it is protected from the influence of the
poison, stimulation of the nerve will be found to produce no con-
tractions in the muscle, though stimuli applied directly to the
muscle at once cause it to contract. From these facts it is clear
that urari poisons the ends of the nerve within the muscle long
before it affects the trunk, and it is exceedingly probable that it
is the very extreme ends of the nerves (possibly the end-plates, for
urari poisoning, at least when profound, causes a slight but yet
distinctly recognisable effect in the microscopic appearance of these
structures) which are affected. The phenomena of urari poisoning
therefore go far to prove that muscles are capable of being made
to contract by stimuli applied directly to the muscular fibres them-
selves ; and there are other facts which support this view.

This question of 'independent muscular irritability' was once thought
to be of importance. In old times, the swelling of a muscle during con-
traction was held to be caused by the animal spirits descending into it
along the nerves; and when the doctrine of 'spirits' was given up, it
was still taught that the vital activity of the muscle was something
bestowed upon it by the action of the nerve, and not properly belonging
to itself. We owe to Haller the establishment of the truth, that the
contraction of a muscle is a manifestation of the muscle's own energy,
excited it may be by nervous action, but not caused by it. Haller spoke
of the muscle as possessing a vis insita, while he called the nervous
action, which excites contraction, the vis nervosa. He used the word
irritability as almost synonymous with contractility, a meaning which is
still adopted by many authors. In this work we have used it in the
wider sense, first employed by Glisson, which includes other manifesta-
tions of energy than the change of form which constitutes a contraction.

The Phenomena of a simple Muscular Contraction.

If the far end of the nerve of a muscle-nerve preparation1,
Figs. 1 and 2, be laid on the electrodes of an induction-machine 2,

1 By this is meant a muscle dissected out with some length of nerve attached to it,
both being in a living condition, i.e. still irritable. The muscle generally used is the
gastrocnemius of the frog, the attachment to the femur and a portion of the tendo
Achillis, together with a considerable length of the sciatic nerve, being carefully
preserved.

2 It may perhaps be worth while to remind the reader of the following facts.

In a galvanic battery, the substance (plate of zinc for instance) which is acted
upon and used up by the liquid is called the positive element, and the sub-
stance which is not so acted upon and used up (plate &c. of copper, platinum, or
carbon, &c.) is called the negative element. A galvanic action is set up when the
positive (zinc) and the negative (copper) elements are connected outside the battery

40 MUSCULAR CONTRACTION. [BOOK i.

the passage of a single induction-shock, which may be taken as a
convenient form of an almost momentary stimulus, will produce no
visible change in the nerve, but the muscle will give a short sharp
contraction, i.e. will for an instant shorten itself, becoming thicker
the while, and then return to its previous condition. If one end of
the muscle be attached to a lever, while the other is fixed, the

by some conducting material, such as a wire, and the current is said to flow in a
circuit or circle, from the zinc or positive element to the copper or negative element
inside the battery and then from the copper or negative element back to the zinc or
positive element through the wire outside the battery. If the conducting wire be cut
through, the current ceases to flow, but if the cut ends be brought into contact,
the current is re-established and continues to flow so long as the contact is good.
The wires or the ends of the wires, which may be fashioned in various ways, are
called electrodes. When the electrodes are brought into contact or are connected
by some conducting material, galvanic action is set up, and the current flows
through the battery and wires; this is spoken of as "making the current" or
"completing or closing the circuit." When the electrodes are drawn apart from each
other, or when some non-conducting material is interposed between them, the
galvanic action is arrested; this is spoken of as "breaking the current" or "opening
the circuit." The current passes from the electrode connected with the negative
(copper) element in the battery to the electrode connected with the positive (zinc)
element in the battery ; hence the electrode connected with the copper (negative)
element is called the positive electrode, and that connected with the zinc (positive)
element is called the negative electrode.

In an "induction machine" the wire connecting the two elements of a battery
is twisted at some part of its course into a close spiral, called the primary coil.
Thus in Fig. 1 -the wire x"' connected with the copper or negative plate c.p. of
the battery, E, joins the primary coil pr. c., and then passes on as y'", through
the "key" F, to the positive (zinc) plate z.p. of the battery. (In Fig. 9. p. 51)
the direction of the current from x to y through the primary coil P is shewn by
arrows; but in this figure complications are introduced which will be explained
hereafter.) Over this primary coil, but quite unconnected with it, slides another
coil, the secondary coil, s.c. ; the ends of the wire forming this coil, y" and x", are
continued on in the arrangement illustrated in the figure as y' and y, and as x'
and x and terminate in electrodes. If these electrodes are in contact or connected
with conducting material, the circuit of the secondary coil is said to be closed ;
otherwise it is open.

In such an arrangement it is found that at the moment when the primary
circuit is closed, i.e. when the primary current is "made" a secondary "induced"
current is, for an exceedingly brief period of time, set up in the secondary coil.
Thus in Fig. 1 when by moving the "key" F, y'" and x'" previously not in con-
nection with each other, are put into connection and the primary current thus
made, at that instant a current appears in the wires y" x" &c., but almost
immediately disappears. A similar almost instantaneous current is also developed
when the primary current is "broken," but not till then. So long as the primary
current flows with uniform intensity, no current is induced in the secondary coil.
It is only when the primary current is either made or broken, or suddenly varies in
intensity that a current appears in the secondary coil. In each case the current
is of very brief duration, gone in an instant almost, and may therefore be spoken of
as " a shock," an induction shock ; being called a "making shock" when it is caused
by the making, and a "breaking shock" when it is caused by the breaking, of the
primary circuit. The direction of the current in the making shock is opposed
to that of the primary current; thus in the figure while the primary current flows
from of" to i/'", the induced making shock flows from y to x. The current of the
breaking shock on the other hand flows in the same direction as the primary current
from x to y, and is therefore in direction the reverse of the making shock.

When the primary current is repeatedly and rapidly made and broken, the
secondary current being developed with each make and with each break, a rapidly
recurring series of alternating currents is developed in the secondary coil and passes
through its electrodes. We shall frequently speak of this as the interrupted induction
current, or more briefly the interrupted current.

CHAP. TI.] THE CONTRACTILE TISSUES.

41

42 THE MUSCLE CURVE. [BOOK i.

FlG. 1. DlAGBAM ILLUSTRATING APPABATUS ABBANGED FOB ExPEBIMENTS WITH

MUSCLE AND NEBVE.

A. The moist chamber containing the muscle-nerve preparation. (The muscle-
nerve and electrode-holder are shewn on a larger scale in Fig. 2.) The muscle
m, supported by the clamp cl, which firmly grasps the end of the femur/, is
connected by means of the S hook s and a thread with the lever I, placed below
the moist chamber. The nerve n, with the portion of the spinal column n' still
attached to it, is placed on the electrode-holder el, in contact with the wires
x, y. The whole of the interior of the glass case gl. is kept saturated with
moisture, and the electrode-holder is so constructed that a piece of moistened
blotting-paper may be placed on it without coming into contact with the nerve.

B. The revolving cylinder bearing the smoked paper on which the lever writes.

(7. Du-Bois Eeymond's key arranged for short-circuiting. The wires x and y of
the electrode-holder are connected through binding screws in the floor of the
moist chamber with the wires x', y', and these are secured in the key, one on
either side. To the same key are attached the wires x" y" coming from the
secondary coils s. c. of the induction-machine D. This secondary coil can be
made to slide up and down over the primary coil pr. c. , with which are con-
nected the two wires x'" and y'". x'" is connected directly with one pole, for
instance the copper pole c. p. of the battery E. y'" is carried to a binding
screw a of the Morse key F, and is continued as T/IV from another binding
screw 6 of the key to the zinc pole z. p. of the battery.

Supposing everything to be arranged, and the battery charged, on depressing the
handle ha, of the Morse key F, a current will be made in the primary coil pr. c.,
passing from c. p. through x1" to pr. c., and thence through y'" to a, thence to 6,
and so through yiv to z. p. On removing the finger from the handle of F, a spring
thrusts up the handle, and the primary circuit is in consequence immediately
broken.

At the instant that the primary current is either made or broken, an induced
current is for the instant developed in the secondary coil s. c. If the cross bar h in
the du-Bois Eeymond's key be raised (as shewn in the thick line in the figure), the
wires x", x', x, the nerve between the electrodes and the wires y, y', y" form the
complete secondary circuit, and the nerve consequently experiences a making or
breaking induction-shock whenever the primary current is made or broken. If the
cross bar of the du-Bois Eeymond key be shut down, as in the dotted line h' in the
figure, the resistance of the cross bar is so slight compared with that of the nerve
and of the wires going from the key to the nerve, that the whole secondary (induced)
current passes from x" to y" (or from y" to x"), along the cross bar, and practically
none passes into the nerve. The nerve being thus "short-circuited," is not affected
by any changes in the current.

CHAP, ii.]

THE CONTRACTILE TISSUES.

43

FIG. 2. The muscle-nerve preparation of Fig. 1, with the clamp, electrodes, and
electrode-holder, are here shewn on a larger scale. The letters as in Fig. 1.

The apparatus figured in Figs. 1 and 2 is intended merely to illustrate the general
method of studying muscular contraction; it is not to be supposed that the
details here given are universally adopted or indeed the best for all purposes.

lever will by its movement indicate the extent and duration of the
shortening. If the point of the lever be brought to bear on some
rapidly travelling surface, on which it leaves a mark (being for this
purpose armed with a pen and ink if the surface be plain paper, or
with a bristle or needle if the surface be smoked glass or paper), so
long as the muscle remains at rest the lever will describe an even
line. When, however, a contraction takes place, as when a single
induction-shock is sent through the nerve, some such curve as that
shewn in Fig. 3 will be described, the lever rising with the shorten-

Fio. 3.

A MUSCLE- CURVE OBTAINED BY MEANS OF THE PENDULUM MTOQRAPH.
To be read from left to right.

6 the

a indicates the moment at which the induction- shock is sent into the nerve.

commencement, c the maximum, and d the close of the contraction.
Below the muscle-curve is the curve drawn by a tuning-fork making 180 double
vibrations a second, each complete curve representing therefore ^rv °f a second.
It will be observed that the plate of the myograph was travelling more rapidly
towards the close than at the beginning of the contraction, as shewn by the greater
length of the vibration- curves.

ing of the muscle, and descending as the muscle returns to its natural
length. This is known as the ' muscle-curve.' In order to make
the ' muscle-curve ' complete, it is necessary to mark on the record-
ing surface the exact time at which the induction-shock is sent
into the nerve, and also to note the speed at which the recording
surface is travelling. These points are best effected by means of
the pendulum myograph, Fig. 4.

In this instrument a smoked glass plate, on which a lever writes, forms
the bob of a pendulum and consequently swings with it. The pendulum
with the glass plate attached being raised up, is suddenly let go. It swings
of course to the opposite side, the glass plate travels through an arc of a
circle, and, the lever being stationary, the point of the lever describes an
arc on the glass plate. The rate at which the glass plate travels, i.e. the
time it takes for the lever-point to describe a line of a given length on

THE MUSCLE CURVE.

[BOOK i.

FIG. 4. THE PENDULUM MYOGRAPH.

The figure is diagrammatic, the essentials only of the instrument being shewn.
The smoked glass plate A swings with the pendulum B on carefully adjusted

CHAP, ii.] THE CONTRACTILE TISSUES. 45

bearings at C. The contrivances by which the glass plate can be removed and
replaced at pleasure are not shewn. A second glass plate so arranged that the
first glass plate may be moved up and down without altering the swing of the
pendulum is also omitted. Before commencing an experiment the pendulum is
raised up (in the figure to the right), and is kept in that position by the tooth a
catching on the spring-catch b. On depressing the catch 6 the glass plate is set
free, swings into the new position indicated by the dotted lines, and is held in that
position by the tooth a' catching on the catch b'. In the course of its swing the
tooth a' coming into contact with the projecting steel rod c, knocks it on one side
into the position indicated by the dotted line c'. The rod c is in electric continuity
with the wire x of the primary coil of an induction-machine. The screw d is
similarly in electric continuity with the wire y of the same primary coil. The
screw d and the rod c are armed with platinum at the points in which they are in
contact, and both are insulated by means of the ebonite block e. As long as c and d
are in contact the circuit of the primary coil to which x and y belong is closed.
When in its swing the tooth a' knocks c away from d, at that instant the circuit is
broken, and a 'breaking' shock is sent through the electrodes connected with the
secondary coil of the machine, and so through the nerve. The lever I, the end only
of which is shewn in the figure, is brought to bear on the glass plate, and when at
rest describes a straight line, or more exactly an arc of a circle of large radius. The
tuning-fork /, the ends only of the two limbs of which are shewn hi the figure
placed immediately below the lever, serves to mark the time.

the glass plate, may be calculated from the length of the pendulum, but it
is simpler and easier to place a vibrating tuning-fork immediately under
the point of the lever. If the vibrations of the tuning-fork are known,
then the number of vibrations which are marked on the plate between any
two points on the line described by the lever gives the time taken by the
lever in passing from one point to the other. An easy arrangement
permits the exact time at which the shock is sent through the nerve to
be marked on the line of the lever. To avoid the confusion of too
many markings on the plate the pendulum after describing an arc is
caught by a spring catch on the opposite side.

A complete muscle-curve, such as that shewn in Fig. 3, taken
from the gastrocnemius of a frog, teaches us the following facts :

1. That although the passage of the induced current from
electrode to electrode is practically instantaneous, its effect, measured
from the entrance of the shock into the nerve to the return of the
muscle to its natural length after the shortening, takes an appreci-
able time. In the figure, the whole curve from a to d takes up
about the same time as eighteen double vibrations of the tuning-
fork. Since each double vibration here represents -^ of a second,
the duration of the whole curve is ^ sec.

2. In the first portion of this period, from a to b, there is no
visible change, no shortening of the muscle, no raising of the lever.

3. It is not until 6, that is to say after the lapse of

IoU

i.e. about -^sec., that the shortening begins. The shortening as
shewn by the curve is at first slow, but soon becomes more rapid,
and then slackens again until it reaches a maximum at c; the
whole shortening occupying about -^ sec.

4. Arrived at the maximum of shortening, the muscle at once
begins to relax, the lever descending at first slowly, then very

.

46 THE MUSCLE CURVE. [BOOK i.

rapidly, and at last more slowly again, until at d the muscle has
regained its natural length ; the whole return from the maximum
of contraction to the natural length occupying yj^, i.e. about -fa sec.
Thus a simple muscular contraction, a simple spasm or twitch as
it is sometimes called, produced by a momentary stimulus, such as
a single induction-shock, consists of three main phases :

1. A phase antecedent to any visible alteration in the muscle.
This phase, during which invisible preparatory changes are taking
place in the nerve and muscle, is called the ' latent period '.

2. A phase of shortening or, in the more strict meaning of the
word, contraction.

3. A phase of relaxation or return to the original length.

In the case we are considering, the electrodes are supposed to be
applied to the nerve at some distance from the muscle. Consequently
the latent period of the curve comprises not only the preparatory
actions going on in the muscle itself, but also the changes necessary
to conduct the immediate effect of the induction-shock from the
part of the nerve between the electrodes, along a considerable
length of nerve down to the muscle. It is obvious that these latter
changes might be eliminated by placing the electrodes on the
muscle itself or on the nerve close to the muscle. If this were
done, the muscle and lever being exactly as before, and care were
taken that the induction-shock entered into the nerve at the new
spot, at the moment when the point of the lever had reached

a T>1>

FIG. 5. CURVES ILLUSTRATING THE MEASUREMENT OP THE VELOCITY or A NERVOUS
IMPULSE. (Diagrammatic.) To be read from left to right.

The same muscle-nerve preparation is stimulated (1) as far as possible from the
muscle, (2) as near as possible to the muscle ; both contractions are registered by
the pendulum myograph exactly in the same way.

In (1) the stimulus enters the nerve at the time indicated by the line a, the con-
traction, shewn by the dotted line, begins at V ; the whole latent period therefore is
indicated by the distance from a to &'.

In (2) the stimulus enters the nerve at exactly the same time a; the contraction,
shewn by the unbroken line, begins at b ; the latent period therefore is indicated by
the distance between a and 6.

The time taken up by the nervous impulse in passing along the length of nerve
between 1 and 2 is therefore indicated by the distance between & and &', which may
be measured by the tuning-fork curve below. N.B. No value is given in the figure
for the vibrations of the tuning-fork, since the figure is diagrammatic, the distance
between the two curves, as compared with the length of either, having been purposely
exaggerated for the sake of simplicity.

CHAP, ii.] THE CONTRACTILE TISSUES. 47

exactly the same point of the travelling surface as before, a curve
like that shewn by the plain line in Fig. 5 would be gained. It
resembles the first curve (indicated in the figure by a dotted line)
in all points, except that the latent period is shortened : the con-
traction begins rather earlier. From this we learn two facts :

The greater part of the latent period is taken up by changes
in tlie Nmuscle itself, preparatory to the actual visible shortening,
for the two latent periods do not differ much. Of course, even in
the second case, the latent period includes the changes going on in
the short piece of nerve still lying between the electrodes and the
muscular fibres. To eliminate this with a view of determining the
latent period in the muscle itself, the electrodes might be placed
directly on the muscle poisoned with urari. If this were done, it
would still be found that the latent period was chiefly taken up
by changes in the muscular as distinguished from the nervous
elements.

2. Such difference as does exist indicates the time taken up by
the propagation, along the piece of nerve, of the changes set up at
the far end of the nerve by the induction-shock. These changes
we shall hereafter speak of as constituting a nervous impulse ; and
the above experiment shews that it takes some appreciable time
for a nervous impulse to travel along a nerve. In the figure the
difference between the two latent periods, the distance between b
and 6', seems almost too small to measure accurately ; but if a long
piece of nerve be used for the experiment, and the recording
surface -be made to travel very fast, the difference between the
duration of the latent period when the induction-shock is sent in
at a point close to the muscle, and that when it is sent in at a
point as far away as possible from the muscle, may be satisfactorily
measured in fractions of a second. If the length of nerve between
the two points be accurately measured, the rate at which a nervous
impulse travels along the nerve to a muscle can thus be easily
calculated. This has been found to be in the frog about 28, and in
man about 33 metres per second.

Thus when a momentary stimulus, such as a single induction-
shock, is sent into a nerve connected with a muscle, the following
events take place :

1. The generation at the spot stimulated of a nervous impulse,
and the propagation of the impulse along the nerve to the muscle.
The time taken up by this varies according to the length of the
nerve but is always very short.

2. The setting up of certain molecular changes in the muscle,
unaccompanied by any visible alteration in its form, constituting
the latent period, and occupying on an average about y^th sec.

3. The shortening of the muscle up to a maximum, occupying
about sec.

48 TETANIC CONTRACTIONS. [BOOK i.

4. The return of a muscle to its former length, occupying about
ylfosec.

We have given what may be considered the average duration l
of each phase chiefly for the sake of shewing their relative propor-
tions. But it must be borne in mind that the duration of a
contraction differs in different animals and in different muscles of
the same animal ; in the rabbit the more deeply coloured SQ^called
"red" muscles have in their contraction a longer period than
have the pale muscles. The duration may also differ in the same
muscle under different conditions; moreover the duration of the
several phases may vary independently. Temperature has a marked
effect in varying the length of the muscle-curve, a higlTtemperature
shortening, and a low temperature prolonging, the contraction, and
especially the third phase or relaxation. Fatigue also lengthens
the contraction as do also to a remarkable extent certain poisons
such as veratrin. An increase in the load which the muscle is
lifting, shortens the descending or return part of the curve and
increases the length of the latent period. All such influences will
be better studied when we come to speak more in detail of the
changes which take place in a muscle during contraction. Their
effects are only mentioned now in order that the reader may
thus early learn to conceive of even a simple muscular contraction
as a complex act, the several parts of which are variable, so that
many differing forms of a muscle-curve may be obtained under
different circumstances.

Tetanic Contractions.

If a single induction-shock be followed at a sufficiently short
interval by a second shock of the same strength, the first simple

FIG. 6. TRACING or A DOUBLE MUSCLE-CURVE. To be read from left to right.

While the muscle2 was engaged in the first contraction (whose complete course,
had nothing intervened, is indicated by the dotted line), a second induction-shock
was thrown in, at such a time that the second contraction began just as the first
was beginning to decline. The second curve is seen to start from the first, as does
the first from the base-line.

1 The curve described in the previous text happened to have a rather long latent
period, and the lengthening to be of shorter instead of longer duration than the
shortening.

2 In this and the other curves of this section the tracings figured were taken
from frog's muscle.

CHAP, ii.]

THE CONTRACTILE TISSUES.

49

contraction or spasm will be followed by a second spasm, the two
bearing some such relation to each other as that shewn by the
curve in Fig. 6, where the interval between the two shocks was
just long enough to allow the first spasm to have passed its maxi-
mum before the latent period of the second was over. It will be
observed that the second curve is almost in all respects like the
first except that it starts, so to speak, from the first curve instead
of from the base-line. The second nervous impulse has acted on
the already contracted muscle, and made it contract again just as
it would have done if there had been no first impulse and the
muscle had been at rest. The two contractions are added together
and the lever raised nearly double the height it would have been
by either alone. A more or less similar result would occur if the
second contraction began at any other phase of the first. The
combined effect is, of course, greatest when the second contraction
begins at the maximum of the first, being less both before and
afterwards. If in the same way a third shock follows the second
at a sufficiently short interval, a third curve is piled on the top of
the second. The same with a fourth, and so on.

FIG. 7. MUSCLE THROWN INTO TETANUS, WHEN THE PRIMARY CURRENT or AN IN-
DUCTION-MACHINE IS EEPEATEDLT BROKEN AT INTERVALS OF SIXTEEN IN A SECOND.

To be read from left to right.

The upper Hue is that described by the muscle. The lower marks time, the
intervals between the elevations indicating seconds. The intermediate line shews
when the shocks were sent in, each mark on it corresponding to a shock. The lever,
which describes a straight line before the shocks are allowed to fall into the nerve,
rises almost vertically (the recording surface travelling in this case slowly) as soon

the first shock enters the nerve at a. Having risen to a certain height, it begins
to fall again, but in its fall is raised once more by the second shock, and that to a
greater height than before. The third and succeeding shocks have similar effects,
the muscle continuing to become shorter, though the shortening at each shock is
less. ^ After a while the increase in the total shortening of the muscle, though the
individual contractions are still visible, almost ceases. At b, the shocks cease to be
sent into the nerve ; the contractions almost immediately disappear, and the lever
forthwith commences to descend. The muscle being lightly loaded, the descent is
very gradual ; the muscle had not regained its natural length when the tracing was
stopped.

F. -i

50 TETANIC CONTRACTIONS. [BOOK i.

When however repeated shocks are given it is found that the
height of each contraction is rather less than the preceding one,
and this diminution becomes more marked the greater the number
of shocks. Hence after a certain number of shocks, the succeeding
impulses do not cause any further shortening of the muscle, any
further raising of the lever, but merely keep up the contraction
already existing. The curve thus reaches a maximum, which it
maintains, subject to the depressing effects of exhaustion, so long
as the shocks are repeated. When these cease to be given, the
muscle returns, in the usual way, at first very rapidly, and then
more slowly, to its natural length. When the shocks do not succeed
each other too rapidly, the individual contractions may readily be
traced along the whole curve, as is seen in Fig. 7, where the
primary current of the induction-machine was repeatedly broken
at intervals of sixteen in a second. When the shocks succeed
each other more rapidly, the individual contractions, visible at first,

FIG. 8. TETANUS PBODUCED WITH THE OBDINABY MAGNETIC INTEBEUPTOB OF AN IN-
DUCTION-MACHINE. (Eecording surface travelling slowly.) To be read from left to right.

The interrupted current being thrown in at a the lever ristes rapidly, but at b the
muscle reaches the maximum of contraction. This is continued till c, when the
current is shut off and relaxation commences.

may become fused together and lost to view as the tetanus con-
tinues and the muscle becomes tired. When the shocks succeed
each other still *more rapidly (the second contraction beginning in
the ascending portion of the first), it becomes difficult or impossible
to trace out the single contractions. The curve then described by
the lever is of the kind shewn in Fig. 8, where the primary current
of an induction-machine was rapidly made and broken by the
magnetic interrupter, Fig. 9. The lever, it will be observed, rises
at a after the latent period (which is not marked), first rapidly,
and then more slowly, in an apparently unbroken line to a maxi-
mum at about 6, maintains the maximum so long as the shocks
continue to be given, and when these cease to be given, as at c,
gradually descends to the base-line. This condition of muscle,
brought about by rapidly repeated shocks, this fusion of a number
of simple spasms into an apparently smooth, continuous effort, is
known as tetanus, or tetanic contraction. The above facts are most
clearly shewn when induction-shocks, or at least galvanic currents
in some form or other, are employed. They are seen, however,
whatever be the form of stimulus employed. Thus in the case of

CHAP, ii.]

THE CONTRACTILE TISSUES.

51

mechanical stimuli, while a single blow may cause a single spasm,
a pronounced tetanus may be obtained by rapidly striking suc-
cessively fresh portions of a nerve. With chemical stimulation, as
when a nerve is dipped in acid, it is impossible to secure a
momentary application; hence tetanus, generally irregular in
character, is the normal result of this mode of stimulation. In the
living body, the contractions of the striated muscles, brought about
either by the will or by reflex action, are generally tetanic in
character. Even very short sharp movements, such as a sudden
jerk of the limbs, are in reality examples of tetanus of short
duration.

FIG. 9. THE MAGNETIC INTERBUPTOE.

The figure is introduced to illustrate the action of this instrument as commonly
used by physiologists.

The two wires x and y from the battery are connected with the two brass pillars
a and d by means of screws. Directly contact is thus made the current, indicated
in the figure by the thick interrupted line, passes in the direction of the arrows, up
the pillar a, along the steel spring b, as far as the screw c, the point of which,
armed with platinum, is in contact with a small platinum plate on 6. The current
passes from b through c and a connecting wire into the primary coil p. Upon its
entering into the primary coil, an induced (making) current is for the instant de-
veloped in the secondary coil (not- shewn in the figure). From the primary coilp
the current passes, by a connecting wire, through the double spiral, m, and, did
nothing happen, would continue to pass from m by a connecting wire to the pillar d,
and so by the wire y to the battery. The whole of this course is indicated by the
thick interrupted line with its arrows.

As the current however passes through the spirals m, the iron cores of these are
made magnetic. They in consequence draw down the iron bar e, fixed at the end of
the spring 6, the flexibility of the spring allowing this. But when e is drawn down,
the platinum plate on the upper surface of 6 is also drawn away from the screw c,
and a similar platinum plate on the under surface of b is brought into contact with
the platinum-armed point of the screw /, the screws being so arranged that this
takes place. In consequence of this change the current can no longer pass from 6 to

52 TETANIC CONTRACTIONS. [BOOK i.

c. On the contrary, it passes from b to /, and so down the pillar d, in the direction
indicated by the thin interrupted line, and out to the battery by the wire y. Thus
the current is 'short- circuited' from the primary coil; and the instant that the
current is thus cut off from the primary coil, an induced (breaking) current is for the
moment developed in the secondary coil. But the current is cut off not only from
the primary coil, but also from the spirals m ; in consequence their cores cease to be
magnetised, the bar e ceases to be attracted by them, and the spring ft, by virtue of
its elasticity, resumes its former position in contact with the screw c. This return
of the spring however re-establishes the current in the primary coil and in the
spirals, and the spring is drawn down, to be released once more in the same manner
as before. Thus as long as the current is passing along x, the contact of 6 is
constantly alternating between c and/, and the current is constantly passing into
and being shut off from p, the periods of alternation being determined by the periods
of vibration of the spring 6. With each passage of the current into, or withdrawal
from the primary coil, an induced (making and, respectively, breaking) shock is de-
veloped in a secondary coil.

When it has once been realized that an ordinary tetanic
muscular movement is essentially a vibratory movement, that
the apparently rigid and firm muscular mass is really the subject
of a whole series of vibrations, a series namely of simple spasms, it
will be readily understood why a tetanized muscle, like all other
vibrating bodies, gives out a sound. That a contracting (tetanized)
muscle does give out a sound, the so-called muscular sound, is
easily proved by listening with a stethoscope to a contracted
biceps, or by stopping the ears and listening to the contractions
of one's own masseter and temporal muscles.

When a muscle is thrown into tetanus by interrupted shocks
applied directly to the nerve or to the muscle, the note is the same
as that of the interruptor determining the number of the shocks.
This is naturally the case, since the note of the muscle-sound is
determined by the rapidity of the spasms or vibrations which go to
make up the tetanus, and these are determined by the rapidity
with which the stimulus is repeated.

When a muscle is thrown into tetanus by the will or by reflex
action or by direct stimulation of the spinal cord, in fact, in any
way through the action of the central nervous system, the same
note is always heard, viz. one of 36 to 40 vibrations per second,
which however is probably a harmonic of a lower note indicating
that the muscle is really vibrating 19 or 20 times a second.

It need hardly be said that a single muscular contraction, a
single vibration, cannot cause a muscular sound.

The general observations which have been described in this
section may, when proper precautions are taken, be carried out on
a muscle-nerve preparation from a frog for a very considerable
time after its removal from the body. After some hours however,
or it may be days, the length of time varying according to
circumstances, it will be found that no stimulus, however powerful,
will cause any contraction, when applied either to the nerve or to
the muscle. Both muscle and nerve are then said to have lost
their irritability ; and a short time afterwards the muscle may be
observed to pass into a peculiar condition known as rigor mortis,

CHAP, ii.] THE CONTRACTILE TISSUES 53

in which it loses all the suppleness and extensibility characteristic
of the living irritable muscle. The causes of this loss of irritability
as well as the features and nature of this rigor mortis we shall
study in detail presently.

The muscles and nerves of a mammal, or indeed of any warm-
blooded animal, lose their irritability, and the muscles become
rigid in a very short time (it may be a few minutes) after removal
from the body. Hence these are less suitable for experiments
than the muscles and nerves of the frog, though their general
phenomena are exactly the same.

We must now attempt to study in greater detail the changes
which take place in a muscle and nerve during the contraction of
the former and the passage of an impulse along the latter, with a
view to the better understanding of both events.

SEC. 2. THE CHANGES IN A MUSCLE DURING
MUSCULAR CONTRACTION.

The Change in Form.

We have seen that at the close of the latent period the muscle
shortens, that is, each fibre shortens, at first slowly, then more
rapidly, and lastly more slowly again. The shortening (which in
severe tetanus may amount to three-fifths of the length of the
muscle) is accompanied by an almost exactly corresponding thicken-
ing, so that there is hardly any actual change in bulk. If a muscle
be placed horizontally, and a lever laid upon it, the thickening of
the muscle will raise up the lever, and cause it to describe on a
recording surface a curve exactly like that described by a lever
attached to the end of the muscle. There appears to be a minute
diminution of bulk not amounting to more than one thousandth.

If a long muscle of parallel fibres, poisoned with urari, so as to
eliminate the action of its nerves, be stimulated at one end, the
contraction may be seen, almost with the naked eye, to start from
the end stimulated, and to travel along the muscle. If two levers
be made to rest on, or be suspended from, two points of such a
muscle placed horizontally, the points being at a known distance
from each other and from the point stimulated, the progress of the
contraction may be studied. It is found that the contraction
starting from the spot stimulated, passes along the muscle in the
form of a wave diminishing in vigour as it proceeds. The velocity
with which this contraction wave travels in the muscles of the
frog is about 3 or 4 metres a second ; and since it takes, in round
numbers, from about 0-5 to *1 sec. for the contraction to pass over
any point of the fibre, the wave-length of the contraction wave
must be from about 200 to 400 mm.

In the muscles of a mammal laid bare for the purposes of
experiment the velocity does not seem to be very different from
that in the frog; but in the intact muscles in their normal con-

CHAP. IL]

THE CONTRACTILE TISSUES.

55

dition in the living body, it is probably somewhat greater, and the
wave also probably travels with undiminished velocity and vigour
to the end of the fibre. In general, the velocity with which the
contraction wave travels, like the duration and character of the con-
traction, varies under different circumstances, being much influenced
by temperature, by the action of drugs, and especially by those
complex intrinsic changes which we speak of as fatigue or ex-
haustion.

Seeing that the extreme limit of the length of a muscular fibre
is about 30 or 40 mm., it is evident that even when the stimulation
begins at one end and the wave travels at the more rapid rate,
the whole fibre is not only in a state of contraction at the same
time, but almost in the same phase of the contraction wave. In
an ordinary contraction occurring in the living body the stimulus
is never applied to one end of the fibre; the nervous impulse
which in such cases acts as the stimulus to the muscle, falls into
the fibre at about its middle, where the nerve ends in an end-plate,
and the contraction wave starting from the end-plate travels along
the muscular fibre in both directions. In such a case therefore,
still more even than in the urarised muscle stimulated artificially
at one end, must the whole fibre be occupied at the same time by
the wave of contraction.

Changes in microscopic structure. When portions of living
irritable muscle are examined under the microscope, contraction
waves similar to those just described, but feebler and of shorter

FlO. 10. MUSCULAB FIBRE UNDERGOING CONTRACTION.

The muscle is that of Telephones melanurus treated with osmic acid. The fibre
at c is at rest, at a the contraction begins, at 6 it has reached its maximum. The
right-hand side of the figure shews the same fibre as seen in polarized light. (After
Engelmann. )

56 THE CHANGE OF FORM. [BOOK T.

length, may be observed passing along the fibres. By appropriate
treatment with osmic acid or other reagents, these short contraction
waves may be fixed, and the structure of the contracted portion
compared at leisure with that of the portions of the fibre at rest.
In Fig. 10, representing a fibre of the muscle of an insect (in which
these changes can be more satisfactorily studied than in vertebrate
muscle), the contraction wave begins near a, and has reached
about its maximum at b, while at c the fibre is at rest, the
contraction wave not having reached it (or having passed over
it, for the beginning and end of the wave are exactly alike). It
will be seen that at b, each disc of the fibre is shorter and broader
than at c. Further, while at c the dim band oc is conspicuous, and
the light band y, with its accessory markings y ', is together lighter
than the dim band x, at b in the fully contracted part of the fibre
the dim band appears light as compared with the black line y
occupying the middle of the previously light band. In the
contracted muscle then there is a reversal of the state of things
in the resting muscle, the light band (or part of the light band)
of the latter in contracting becomes dark, and the dim band of
the latter becomes by comparison light. Between rest and full
contraction there is an intermediate stage, as at d, in which the
distinction between rHm and bright bands seems to be largely lost.
The subject however is one offering peculiar difficulties in the way
of investigation, and while most, though not all, observers agree in
the broad facts which have just been stated, there is great diversity
of opinion concerning further details and especially as to the
interpretation of the various appearances observed. The accessory
markings in the middle of the light band have, in particular, been
the subject of controversies into which we cannot enter here.

When the fibre is examined in polarised light it is seen that
the dim band is anisotropic, and the light band isotropic. This
is the case during all the phases of the contraction. At no period
is there any confusion between the anisotropic and isotropic material ;
these maintain their relative positions, both become shorter and
broader; but it will be observed that the isotropic substance
diminishes in height to a much greater extent than does the
anisotropic substance. The latter in fact appears to increase in
bulk at the expense of the former.

Relaxation. The shortening as we have seen is followed by a
relaxation, the muscle returning to its original length. When an
appropriate weight is attached to the muscle this return is generally
complete, the curve speedily rejoining, as shewn in Fig. 3, the base
line from which it started ; but when no load is used and the
muscle therefore is acted upon by its own weight and that of a
very light lever only, the return is incomplete ; the curve, though
descending near to, fails to touch the base line and runs nearly
parallel to it for some considerable distance. The relaxation
is therefore obviously assisted by the extending force of the load ;

CITAP. ii.] THE CONTRACTILE TISSUES. 57

but, nevertheless, is in the main the result of intrinsic processes
going on in the muscle, the reverse of those leading to the shorten-
ing. The return of the muscle to its elongated condition, is
not a mere passive stretching, after the causes leading to the
shortening have passed away; it like the shortening itself is a
manifestation of activity. And hence we find that the complete-
ness of the relaxation is dependent on the complex changes which
we speak of as the nutrition of the muscle. Thus in their natural
position in the living body, muscles, owing to their vigorous nu-
trition, assisted by the fact that their anatomical disposition keeps
them always on the stretch, return completely to their original
length, after even powerful and prolonged contractions. In a
muscle out of the body, on the other hand, even when loaded, re-
peated successive contractions frequently result in the failure to
achieve complete relaxation becoming very conspicuous ; and the
tetanus curves, Figs. 6 and 7, shew very strikingly this shortcoming,
which is often spoken of as the 'contraction remainder/

We may speak of the relaxation as the result of an elastic
reaction, but only in the sense that the elastic qualities of the
muscle, at any moment, are the expression of deep-seated and con-
tinually varying molecular changes going on in the muscular sub-
stance. And in this connection attention may be called to a peculiar
physical character of contracting muscle. Living muscle at rest
is very extensible, but when stretched returns after the extending
cause has been removed, rapidly and completely to its former
length. In physical language muscle is spoken of as possessing
slight but perfect elasticity. It might be imagined that during a
contraction this extensibility would be diminished in order that none
of the resistance which the muscle had to overcome, no part of the
weight for instance which had to be lifted, should be employed in
stretching the muscle itself and thus lead to an apparent waste of
energy. On the contrary we find that during a contraction there
is an increase of extensibility ; thus if a muscle at rest be loaded
with a given weight, say 50 grammes, and its extension observed,
and be then while unloaded thrown into tetanus, and the load
applied during the tetanus, the extension in the second case will
be distinctly greater than in the first. During the contraction
there is so to speak a greater mobility of the muscular molecules,
and though this greater mobility may have its advantages, the
loaded muscle has in contracting to overcome its own increased
tendency to lengthen on extension before it can produce any effect
on the weight which it has to lift.

The elasticity and extensibility of the muscular substance is how-
ever a complicated and difficult subject, and it will be sufficient to
reassert that it is essentially a vital property, being dependent, like
the irritability of the muscular substance, on certain nutritive factors.
As the muscular substance becomes weary with too much work or
impoverished by scanty nutrition, its elasticity suffers pari passu

58 MUSCLE CURRENTS. [BOOK i.

with its irritability. The exhausted muscle when extended does
not return so readily to its proper length as the fresh active muscle,
and, as we shall see, the dead muscle does not return at all.

Electrical Changes.

Muscle-currents. If a muscle be removed in an ordinary
manner from the body, and two non-polarisable electrodes1, con-

z.s
di.c

FlG. 11. NON-POLABISABLE ELECTRODES.

a, the glass tube; z, the amalgamated zinc slips connected with their respective
wires; z. s., the zinc sulphate solution; ch. c., the plug of china clay; c', the portion
of the china-clay plug projecting from the end of the tube; this can be moulded into
any required form.

nected with a delicate galvanometer of many convolutions, be
placed on two points of the surface of the muscle, a deflection of
the galvanometer will take place indicating the existence of a
current passing through the galvanometer from the one point of
the muscle to the other, the direction and amount of the deflection
varying according to the position of the points. The 'muscle-
currents' thus revealed are seen to the best advantage when the
muscle chosen is a cylindrical or prismatic one with parallel fibres,
and when the two tendinous ends are cut off by clean incisions at
right angles to the long axis of the muscle. The muscle then
presents a (artificial) transverse section at each end and a longi-
tudinal surface. We may speak of the latter as being divided
into two equal parts by an imaginary transverse line on its surface

1 These (Fig. 11) consist essentially of a slip of thoroughly amalgamated zinc
dipping into a saturated solution of zinc sulphate, which in turn is brought into
connection with the nerve or muscle by means of a plug or bridge of china-clay
moistened with normal sodium chloride solution ; it is important that the zinc should
be thoroughly amalgamated. This form of electrodes gives rise to less polarisation
than do simple platinum or copper electrodes. The clay affords a connection be-
tween the zinc and the tissue which neither acts on the tissue nor is acted on by the
tissue. Contact of any tissue with copper or platinum is in itself sufficient to de-
velope a current.

CHAP. IT.]

THE CONTRACTILE TISSUES.

59

called the * equator/ containing all the points of the surface midway
between the two ends. Fig. 12 is a diagrammatic representation of
such a muscle, the line ah being the equator. In such a muscle the
development of the muscle-currents is found to be as follows.

The greatest deflection is observed when one electrode is placed

FIG. 12. DIAGRAM ILLUSTRATING THE ELECTRIC CURRENTS OF NERVE AND MUSCLE.

Being purely diagrammatic, it may serve for a piece either of nerve or of muscle,
except that the currents at the transverse section cannot be shewn in a nerve. The
arrows shew the direction of the current through the galvanometer.

ab the equator. The strongest currents are those shewn by the dark lines, as
from a, at equator, to x or to y at the cut ends. The current from a to c is weaker
than from a to y, though both, as shewn by the arrows, have the same direction. A
current is shewn from e, which is near the equator, to /, which is farther from the
equator. The current (in muscle) from a point in the circumference to a point
nearer the centre of the transverse section is shewn at gh. From a to & or from
x to y there is no current, as indicated by the dotted lines.

at the mid-point or equator of the muscle, and the other at either
cut end ; and the deflection is of such a kind as to shew that posi-
tive currents are continually passing from the equator through the
galvanometer to the cut end, that is to say, the cut end is negative
relatively to the equator. The currents outside the muscle may be
considered as completed by currents in the muscle from the cut end
to the equator. In the diagram Fig. 12, the arrows indicate the
direction of the currents. If the one electrode be placed at the
equator ab, the effect is the same at whichever of the two cut ends x
or y the other is placed. If, one electrode remaining at the equator,
the other be shifted from the cut end to a spot c nearer to the
equator, the current continues to have the same direction, but is of
less intensity in proportion to the nearness of the electrodes to each
other. If the two electrodes be placed at unequal distances e and /,
one on either side of the equator, there will be a feeble current from
the one nearer the equator to the one farther off, and the current will
be the feebler, the more nearly they are equidistant from the equator.

60 MUSCLE CURRENTS. [BOOK i.

If they are quite equidistant, as for instance when one is placed on
one cut end x, and the other on the other cut end y, there will be
no current at all.

If one electrode be placed at the circumference of the transverse
section and the other at the centre of the transverse section, there
will be a current through the galvanometer from the former to the
latter; there will be a current of similar direction but of less intensity
when one electrode is at the circumference g of the transverse section
and the other at some point h nearer the centre of the transverse
section. In fact, the points which are relatively most positive and
most negative to each other are points on the equator and the two
centres of the transverse sections ; and the intensity of the current
between any two points will depend on the respective distances
of those points from the equator and from the centre of the
transverse section.

Similar currents may be observed when the longitudinal surface
is not the natural but an artificial one ; indeed they may be witnessed
in even a piece of muscle provided it be of cylindrical shape and
composed of parallel fibres. *

These 'muscle-currents' are not mere transitory currents dis-
appearing as soon as the circuit is closed; on the contrary they
last a very considerable time. They must therefore be maintained
by some changes going on in the muscle, by continued chemical
action in fact. They disappear as the irritability of the muscle
vanishes, and are connected with those nutritive, so-called vital
changes which maintain the irritability of the muscle.

Muscle-currents such as have just been described, may, we repeat,
be observed in any cylindrical muscle suitably prepared, and similar
currents, with variations which need not be discussed here, may be
seen in muscles of irregular shape with obliquely or otherwise ar-
ranged fibres. And du Bois-Reymond, to whom chiefly we are
indebted for our knowledge of these currents, has been led to re-
gard them as essential and important properties of living muscle.
He has moreover advanced the theory that muscle may be con-
sidered as composed of electro-motive particles or molecules, each
of which like the muscle at large has a positive equator and
negative ends, the whole muscle being made up of these molecules
in somewhat the same way, (to use an illustration which must not
however be strained or considered as an exact one) as a magnet
may be supposed to be made up of magnetic particles each with its
north and south pole.

There are reasons however for thinking that these muscle-currents
have no such fundamental origin, that they are in fact of surface
and indeed of artificial origin. Without entering largely into the
controversy on this question, the following important facts may be
mentioned.

1. When a muscle is examined while it still retains untouched
its natural tendinous terminations, the currents are much less than

CHAP, ii.] THE CONTRACTILE TISSUES. 61

when artificial transverse sections have been made; the natural
tendinous end is less negative than the cut surface. But the
tendinous end becomes at once negative when it is dipped in
water or acid, indeed when it is in any way injured. The less
roughly in fact a muscle is treated the less evident are the muscle-
currents, and it has been maintained that if adequate care be
taken to maintain a muscle in an absolutely natural condition no
such currents as those we have been describing exist at all.

2. Englemann has shewn that the surface of the uninjured in-
active1 ventricle of the frog's heart is isoelectric, i. e. that no current
is obtained when the electrodes are placed on any two points of the
surface. If however any part of the surface be injured, or if the
ventricle be cut across so as to expose a cut surface, the injured spot
or the cut surface becomes at once most powerfully negative towards
the uninjured surface, a strong current being developed which passes
through the galvanometer from the uninjured surface to the cut
surface or to the injured spot. The negativity thus developed in
a cut surface passes off in the course of some hours, but may be
restored by making a fresh cut and exposing a fresh surface.

Now, when a muscle is cut or injured the substance of the fibres
dies at the cut or injured surface. And many physiologists, among
whom the most prominent is Hermann, have been led by the above
and other facts to the conclusion that muscle-currents do not exist
naturally in untouched muscles, that the muscular substance is
naturally, when living, isoelectric, but that whenever a portion of
the muscular substance dies, it becomes while dying negative to the
living substance, and thus gives rise to currents. They explain the
typical currents (as they might be called) manifested by a muscle with
a natural longitudinal surface and artificial transverse sections, by
the fact that the dying cut ends are negative relatively to the rest
of the muscle.

Du Bois-Reymond and those with him offer special explanations
of the above facts and of other objections which have been urged
against the theory of naturally existing electro-motive molecules.
Into these we cannot enter here. We must rest content with the
statement that in an ordinary muscle currents such as have been
described may be witnessed, but that strong arguments may be
adduced in favour of the view that these currents are not ' natural '
phenomena but essentially of artificial origin. It will therefore be
best to speak of them as ' currents of rest/

Negative variation of the Muscle-current. The controversy
whether the " currents of rest " observable in a muscle be of natural
origin or not, does not affect the truth or the importance of the
fact that an electrical change takes place in a muscle whenever it
enters into a contraction. When currents of rest are observable in
a muscle these are found to undergo a diminution at the onset of a

1 Th* necessity of its being inactive will be seen subsequently.

62 NEGATIVE VARIATION. [BOOK i.

contraction, and this diminution is spoken of as 'the negative
variation' of the currents of rest. The negative variation may be
seen when a muscle is thrown into a single contraction, but is most
readily shewn when the muscle is tetanized. Thus if a pair of
electrodes be placed on a muscle, one at the equator, and the
other at or near the transverse section, so that a considerable
deflection of the galvanometer needle, indicating a considerable
current of rest, be gained, the needle of the galvanometer will,
when the muscle is tetanized by an interrupted current sent
through its nerve (at a point too far from the muscle to allow
any escape of the current into the electrodes connected with the
galvanometer), swing back towards zero ; it returns to its original
deflection when the tetanizing current is shut off.

Not only may this negative variation be shewn by the galvano-
meter, but it, as well as the current of rest, may be used as a
galvanic shock and so employed to stimulate a muscle, as in the
experiment known as ' the rheoscopic frog.' For this purpose the
muscles and nerves need to be very irritable and in thoroughly
good condition. Two muscle-nerve preparations A and B having
been made and each placed on a glass plate for the sake of insulation,
the nerve of the one B is allowed to fall on the muscle of the
other A in such a way that one point of the nerve comes in
contact with the equator of the muscle, and another point with
one end of the muscle or with a point at some distance from the
equator. At the moment the nerve is let fall and contact made, a
current, viz. the 'current of rest' of the muscle A, passes through
the nerve; this acts as a stimulus to the nerve, and so causes
a contraction in the muscle connected with the nerve. Thus the
muscle A acts as a battery, the completion of the circuit of which
by means of the nerve of B serves as a stimulus, causing the muscle
B to contract.

If while the nerve of B is still in contact with the muscle of A,
the nerve of the latter is tetanized with an interrupted current,
not only is the muscle of A thrown into tetanus but also that of
J5; the reason being as follows. At each spasm of which the
tetanus of A is made up, there is a negative variation of the
muscle-current of A. Each negative variation in the muscle-
current of A serves as a stimulus to the nerve of B, and is hence
the cause of a spasm in the muscle of B ; and the stimuli following
each other rapidly, as being produced by the tetanus of A they must
do, the spasms in B to which they give rise are also fused into
a tetanus in B. B in fact contracts in harmony with A. This
experiment shews that the negative variation accompanying the
tetanus of a muscle, though it causes only a single swing of the
galvanometer, is really made up of a series of negative variations,
each single negative variation corresponding to the single spasms
of which the tetanus is made up.

But an electrical change may be manifested even in cases when

CHAP, ii.] THE CONTRACTILE TISSUES. 63

no currents of rest exist. We have stated (p. 61) that the surface
of the uninjured inactive ventricle of the frog's heart is isoelectric,
no currents being observed when the electrodes of a galvanometer
are placed on two points of the surface. Nevertheless a most
distinct current is developed whenever the ventricle contracts.
This may be shewn either by the galvanometer or by the rheos-
copic frog. If the nerve of an irritable muscle-nerve preparation
be laid over a pulsating ventricle, each beat is responded to by
a spasm of the muscle of the preparation. In the case of ordinary
muscles too instances occur in which it seems impossible to regard
the electrical change manifested during the contraction as the
mere diminution of a preexisting current.

Accordingly Hermann and those who with him deny the
existence of 'natural' muscle-currents speak of a muscle as de-
veloping during a contraction a ' current of action,' occasioned as
they believe by the muscular substance as it is entering into the
state of contraction becoming negative towards the muscular
substance which is still at rest, or has returned to a state of
rest. In fact, they regard the negativity of muscular substance
as characteristic alike of beginning death and of a beginning
contraction. So that in a muscular contraction a wave of
negativity, starting from the end-plate when indirect, or from
the point stimulated when direct stimulation is used, passes
along the muscular substance to the ends or end of the fibre.
We cannot however enter more fully here into a discussion of this
difficult subject.

Whichever view be taken of the nature of these muscle-currents,
and of the electric change during contraction, whether we regard
that change as a ' negative variation ' or as a ' current of action,'
it is important to remember that it takes place entirely during the
latent period. It is not in any way the result of the change of
form, it is the forerunner of that change of form. Just as a
nervous impulse passes down the nerve to the muscle without any
visible changes, so a molecular change of some kind, unattended
by any visible events, known to us, at present, only by an electrical
change, runs along the muscular fibre from the end-plates to the
terminations of the fibre, preparing the way for the visible change of
form which is to follow. This molecular invisible change is the work
of the latent period, and careful observations have shewn that it,
like the visible contraction which follows at its heels, travels along
the fibre from a spot stimulated towards the ends of the fibres, in
the form of a wave having about the same velocity as the contrac-
tion, viz. about 3 metres a second1.

1 In the muscles of the frog; but as we have seen having probably a higher
velocity in the intact mammalian muscles, within the living body, and varying
according to circumstances.

64 CHEMICAL CHANGES. [BOOK i.

Chemical Changes.

Before we attack the important problem, What are the chemical
changes concerned in a muscular contraction? we must study in
some detail the chemical features of muscle at rest. And here we
are brought face to face with the chemical differences between
living and dead muscles. All muscles, within a certain time after
removal from the body, or while still within the body, after
'general' death of the body, lose their irritability. The loss of
irritability, even when rapid, is gradual, but is succeeded by an
"^event which is somewhat more sudden, viz. the entrance into the
condition known as rigor mortis, the occurrence of which is marked
by the following features. The muscle, previously possessing a

r certain translucency, becomes much more opaque. Previously very
extensible and elastic, it becomes much less extensible and at the
same time loses its elasticity; the muscle now requires considerable
force to stretch it, and when the force is removed, does not, as
before, return to its natural length. To the touch it has lost much
of its former softness, and becomes firmer and more resistent. The
entrance into rigor mortis is characterised by a shortening or con-
traction, which may, under certain circumstances, be considerable.
The energy of this contraction is not great, so that when opposed,
no actual shortening takes place. When rigor mortis has been fully
developed, no muscle-currents whatever are observed. The onset
of this rigidity may be considered as the token of the death of the
muscle itself. As we shall see, the chemical features of the dead
rigid muscle are strikingly different from those of the living
muscle.

If a dead muscle, from which all fat, tendon, fascia, and con-
nective tissue have been as much as possible removed, and which
has been freed from blood by the injection of saline solution, be
minced and repeatedly washed with water, the washings will
contain certain forms of albumin and certain extractive bodies,
of which we shall speak directly. When the washing has been
continued until the wash-water gives no proteid reaction, a large
portion of muscle will still remain undissolved. If this be treated
with a 10 p. c. solution of a neutral salt, ammonium chloride being
the best, a large portion of it will become imperfectly dissolved
into a viscid fluid which filters with difficulty. If the viscid
filtrate be allowed to fall drop by drop into a large quantity of
distilled water, a white flocculent matter will be precipitated.
This flocculent precipitate is myosin. It is a proteid, giving the
ordinary proteid reactions, and having the same general elementary
composition as other proteids. It is soluble in dilute saline solutions,
especially those of ammonium chloride, and may be classed in
the globulin family, though it is not so soluble as paraglobulin.
Dissolved in saline solutions it readily coagulates when heated, i.'e.

CHAP. IL] THE CONTRACTILE TISSUES. 65

is converted into coagulated proteid1, and it is worthy of notice
that it coagulates at a lower temperature, viz. 55° — 60° C., than
does serum-albumin, paraglobulin and many other proteids ; it is
precipitated and after long action coagulated by alcohol, and is
precipitated by an excess of sodium chloride. By the action
of dilute acids it is very readily converted into what is called
syntonin or acid-albumin2, by the action of dilute alkalis into
alkali-albumin. Speaking generally it may be said to be inter-
mediate in its character between fibrin and globulin. On keeping,
and especially on drying, its solubility is much diminished.

Of the substances which are left in washed muscle, from which
the myosin has thus been extracted by ammonium chloride solution,
little is known. If washed muscle be treated directly with dilute
hydrochloric acid, the greater part of the material of the muscle
passes at once into syntonin. The quantity of syntonin thus
obtained may be taken as representing the quantity of myosin
previously existing in the muscle. The portion insoluble in dilute
hydrochloric acid consists in part of the substance of the sarco-
lemma, of the nuclei, and of the tissue between the bundles, and in
part probably of certain structural elements of the fibres themselves.

If living contractile frog's muscle, freed as much as possible
from blood, be frozen3, and while frozen, minced, and rubbed
up in a mortar with four times its weight of snow containing
1 p. c. of sodium chloride, a mixture is obtained which at
a temperature just below 0° C. is sufficiently fluid to be filtered,
though with difficulty. The slightly opalescent filtrate, or muscle-
plasma as it is called, is at first quite fluid, but will when exposed
to the ordinary temperature become a solid jelly, and afterwards
separate into a clot and serum. It will in fact coagulate like
blood-plasma, with this difference, that the clot is not firm and
fibrillar, but loose, granular and flocculent. During the coagulation
the fluid, which before was neutral or slightly alkaline, becomes
distinctly acid.

The clot is myosin. It gives all the reactions of myosin obtained
from dead muscle.

The serum contains ordinary serum-albumin, one or more pe-
culiar proteids4 coagulating at a lower temperature than does serum-
albumin, and extractives. Such muscles as are red also contain a
small quantity of haemoglobin, to which indeed their redness is
due.

Thus while dead muscle contains myosin, serum-albumin, and
other proteids and extractives with certain insoluble matters and
certain gelatinous elements not referable to the muscle-substance

1 See Appendix. 2 Ibid.

3 Since, as we shall presently see, a muscle may be frozen and thawed again
without losing any of its vital powers, we are at liberty to regard the frozen muscle
as a still living muscle.

4 See Appendix.

F. 5

66 RIGOR MORTIS. [BOOK i.

[itself, living muscle contains no myosin, but some substance or
(substances which bear somewhat the same relation to myosin that
(the fibrin factors do to fibrin, and which give rise to myosin upon
(the death of the muscle.

"We may in fact speak of rigor mortis as characterised by a
coagulation of the muscle-plasma, comparable to the coagulation of
'blood-plasma, but differing from it inasmuch as the product is not
fibrin but myosin. The rigidity, the loss of suppleness, and the
diminished translucency appear to be at all events largely, though
probably not wholly, due to the change from the fluid plasma to the
solid myosin. We might compare a living muscle to a 'number of
fine transparent membranous tubes containing blood-plasma. When
this blood-plasma entered into the 'jelly' stage of coagulation, the
system of tubes would present many of the phenomena of rigor
mortis. They would lose much of their suppleness and translucency,
and acquire a certain amount of rigidity.

There is however one very marked and important difference
between rigor mortis of muscle and the coagulation of blood : blood
•during its coagulation undergoes only a slight change in its reaction ;
Ibut muscle during the onset of rigor mortis becomes distinctly acid.

A living muscle at rest is in reaction neutral, or, possibly from
some remains of lymph adhering to it, faintly alkaline. If on the
other hand the reaction of a thoroughly rigid muscle be tested, it
will be found to be most distinctly acid. This development of an
acid reaction is witnessed not only in the solid untouched fibre but
also in expressed muscle-plasma ; it seems to be associated in some
way with the appearance of the myosin.

The exact causation of this acid reaction has not at present
been clearly worked out. Since the coloration of the litmus pro-
duced is permanent, carbonic acid, which as we shall immediately
state, is set free at the same time, cannot be regarded as the active
acid, for the reddening of litmus produced by carbonic acid speedily
disappears on exposure. On the other hand it is possible to ex-
tract from rigid muscle a certain quantity of lactic acid, or rather
of a variety of lactic acid known as sarcolactic acid1; and it has
been thought that the appearance of the acid reaction of rigid
muscle is due to a new formation or to an increased formation of
this sarcolactic acid. But there is considerable doubt whether any
such increase of sarcolactic acid does actually take place in rigor
mortis. Hence though there can be no doubt that an acid reaction
is established, we are not yet in a position to affirm positively the
exact manner in which that reaction is produced, the complex
nature of the muscular substance suggesting to the chemist several
ways in which it might come about.

Coincident with the appearance of this acid reaction, though
as we have said, not the direct cause of it, a large development of
carbonic acid takes place when muscle becomes rigid. Irritable

1 Bee Appendix.

CHAP, ii.] THE CONTRACTILE TISSUES. 67

living muscular substance like all living protoplasm is continually
respiring, continually consuming oxygen and giving out carbonic
acid. In the body, the arterial blood going to the muscle gives up
some of its oxygen, and gains a quantity of carbonic acid, thus
becoming venous as it passes through the muscular capillaries.
Even after removal from the body, the living muscle continues to
take up from the surrounding atmosphere a certain quantity of
oxygen and to give out a certain quantity of carbonic acid.

At the onset of rigor mortis there is a very large and sudden!
increase in this production of carbonic acid, in fact an outburst as itl
were of that gas. This is a phenomenon deserving special attention.*
Knowing that the carbonic acid which is the outcome of the res-
piration of the whole body is the result of the oxidation of carbon-
holding subtances, we might very naturally suppose that the in-
creased production of carbonic acid attendant on the development
of rigor mortis is due to the fact that during that event a certain
quantity of the carbon-holding constituents of the muscle are
suddenly oxidized. But such a view is negatived by the following
facts. In the first place, the increased production of carbonic acid
during rigor mortis is not accompanied by any corresponding in-
crease in the consumption of oxygen. In the second place, a
muscle (of a frog for instance) contains in itself no free or loosely
attached oxygen : when subjected to the action of a mercurial air-
pump it gives off no oxygen to a vacuum, offering in this respect
a marked contrast to blood ; and yet, when placed in an atmosphere
free from oxygen, it will not only continue to give off carbonic
acid while it remains alive, but will also exhibit at the onset of
rigor mortis, the same increased production of carbonic acid that
is shewn by a muscle placed in an atmosphere containing oxygen.
It is obvious that in such a case the carbonic acid does not arise
from the direct oxidation of the muscle substance, for there is no
oxygen present at the time to carry on that oxidation. We are
driven to suppose that during rigor mortis, some complex body,
containing in itself ready formed carbonic acid so to speak, is split
up, and thus carbonic acid is set free, the process of oxidation by
which that carbonic acid was formed out of the carbon-holding
constituents of the muscle having taken place at some anterior date.

Living resting muscle then, is alkaline or neutral in reaction,
and the substance of its fibres contains a coagulable plasma. Dead
rigid muscle on the other hand is acid in reaction, and no longer
contains a coagulable plasma, but is laden with the solid myosin.
Further, the change from the living irritable condition to that of
rigor mortis is accompanied by a large and sudden development of
carbonic acid.

It is found moreover that there is a certain amount of parallel-
ism between the intensity of the rigor mortis, the degree of acid
reaction and the quantity of carbonic acid given out. If we
suppose, as we fairly may do, that the intensity of the rigidity is

5—2

68 CHEMICAL CHANGES. [BOOK i.

dependent on the quantity of myosin deposited in the fibres, and
the acid reaction to the development if not of lactic acid, at least
of some other substance, the parallelism between the three products,
myosin, acid-producing substance, and carbonic acid, would suggest
the idea that all three are the results of the splitting-up of the
same highly complex substance. But we have not at present
succeeded in isolating or in otherwise definitely proving the exist-
ence of such a body, and though the idea seems tempting, it may
in the end prove totally erroneous.

We may now return to the question, What are the chemical
changes which take place when a living resting muscle enters into
a contraction? These changes are most evident after the muscle
has been subjected to a prolonged tetanus ; but there can be no
doubt that the chemical events of a tetanus are, like the physical
events, simply the sum of the results of the constituent single
contractions.

In the first place, the muscle becomes acid, not so acid as in
rigor mortis, but still sufficiently so, after a vigorous tetanus, to
turn blue litmus distinctly red. The cause of the acid reaction
like that of rigor mortis is doubtful ; but is in all probability the
same in both cases.

In the second place, a considerable quantity of carbonic acid is
set free ; and the production of carbonic acid in muscular contrac-
tion is altogether similar to the production of carbonic acid during
rigor mortis. It is not accompanied by any corresponding increase
in the consumption of oxygen. This is evident even in a muscle
through which the circulation of blood is still going on, for though
the blood passing through a contracting muscle gives up more
oxygen than the blood passing through a resting muscle, the increase
in the amount of oxygen taken up falls below the increase in the
carbonic acid given out ; but it is still more markedly shewn in a
muscle removed from the body. For in such a muscle both the
contraction and the increase in the production of carbonic acid will
go on in the absence of oxygen. A frog's muscle suspended in an
atmosphere of nitrogen will remain irritable for some considerable
time, and at each vigorous tetanus an increase in the production of
carbonic acid may be readily ascertained.

Moreover there seems to be a correspondence between the
energy of the contraction and the amount of carbonic acid and
the degree of acid reaction produced, so that, though we are now
treading on somewhat uncertain ground, we are naturally led to the
view that the essential chemical process lying at the bottom of a
muscular contraction as of rigor mortis is the splitting up of some
highly complex substance. But here the resemblance between rigor
mortis and contraction ends. We have no evidence of the formation
jiuring a contraction of any body like myosin. Now the contracted
and rigid muscle differ essentially in the fact that while the former,
as compared with living resting muscle, increases in extensibility and

CHAP. IL] THE CONTRACTILE TISSUES. 69

loses none of its translucency, the latter becomes less extensible, less
elastic, and less translucent. Corresponding to this marked differ-
ence, we find myosin formed in the rigid muscle, but we cannot
find it in the contracted muscle.

The other chemical changes in muscle during a contraction
have not yet been clearly made out. Indeed our whole information
concerning the other chemical constituents of muscle is at present
imperfect.

The bodies which we have called extractives are numerous and
varied. Among the nitrogenous crystalline extractives the most
important is kreatin, which occurs to the extent of about '2 to
•3 p. c., is an invariable constituent of muscle, and is found elsewhere
only in nervous tissue, the kidney, and to a slight extent in the
blood. As we shall hereafter see, great interest is attached tot
this body inasmuch as it readily splits up into urea, and sarcosin, »
and accordingly has been regarded as one at least of the antecedents ?
of urea, which body is conspicuous by its absence from muscular \
tissue. The alkaline kreatinin into which kreatin is converted by
the action of acids, and which appears in the urine, is apparently
absent from muscle. The other nitrogenous crystalline bodies,
which need not detain us now, are karnin, hypoxanthin (or sarkin),
xanthin, inosinic acid, taurin and possibly uric acid1.

Fats are present in considerable quantities both in the adipose
tissue between the bundles of fibres and also as constituents of the
muscular substance within the sarcolemma.

The peculiar starch-like body, glycogen, of which we shall have
to speak more fully in a later part of this work, is especially
abundant in the muscles of the embryo at an early period, and
besides, is so continually met with in the muscles of the adult that
it may fairly be considered as a normal constituent of muscle to a
variable extent, possibly from '5 to 1 p. c. A dextrin-like body has
also been found, and at times glucose or an allied sugar. The
cardiac muscular tissue contains the peculiar sugar, inosit.

The ashes of muscle, like those of the red corpuscles, are cha-J
racterised by the preponderance of potassium salts and of phos-j
phates ; these form in fact nearly 80 p. c. of the whole ash.

The general composition of human muscle is shewn in the
following table of v. Bibra.

Water 744'5

Solids

Myosin and other matters, elastic ele-
ments, &c., insoluble in water ... 155*4

Soluble proteids 19'3

Gelatin 207

Extractives and Salts 37'1

Fats 23-0

255-5
1 See Appendix.

70 THERMAL CHANGES. [BOOK i.

Concerning the functional importance of these various bodies
we have very little exact knowledge.

Helmholtz shewed long ago that the effect of long continued
contraction is to diminish the substances in muscle which are
soluble in water, but to increase those which are soluble in
alcohol. In other words, during contraction some substance or
substances soluble in water are converted into another or other
substances insoluble in water but soluble in alcohol. During or
after rigor mortis, glycogen is converted into sugar, and it has been
contended that a similar change takes place during contraction;
but we are not, at present at all events, in a position to affirm that
such a conversion is a necessary and integral part of the chemical
transformations which lie at the bottom of a muscular contraction.

We shall have occasion to treat more fully and from a different
point of view, of the relations between muscular exercise and the
quantity of urea discharged by the kidneys. Meanwhile we may
state that not only does this all-important nitrogenous crystalline
body appear to be absent from normal muscle, both during rest
and after contraction, but we have as yet no adequate evidence
that the contraction of a muscle is followed by the appearance in
the substance of the muscle or in the blood passing through it of
any new nitrogenous product, or by any increase in any of the
nitrogenous extractives which we have mentioned as normally
present in muscle. In fact all we know at present is that a
contraction is followed by an increase in the discharge of carbonic
acid, and by certain changes which lead to an acid reaction.
Beyond this we are in the dark.

Thermal Changes.

The view however that chemical changes lie at the bottom of a
muscular contraction, that the energy which takes on the form of
muscular work arises from a metabolism of the muscular substance,
is supported by a variety of considerations and especially perhaps
by the fact, that the development of energy as muscular work, is
accompanied by a development of energy as heat.

Though we shall have hereafter to treat this subject more fully,
the leading facts may be given here. Whenever a muscle contracts,
its temperature rises, indicating that heat is given out. When a
mercury thermometer is plunged into a mass of muscles, such as
those of the thigh of the dog, a rise of the mercury is observed
upon the muscles being thrown into a prolonged contraction.
More exact results however are obtained by means of a thermopile,
by the help of which the rise of temperature caused by a few
repeated single contractions, or indeed by a single contraction, may
be observed and the amount of heat given out approximative^
measured.

CHAP, ii.] THE CONTRACTILE TISSUES. 71

The thermopile may consist either of a single junction in the form of
a needle plunged into the substance of the muscle ; or of several junctions
either in the shape of a flat surface carefully opposed to the surface of
muscle (Heidenhain) the pile being balanced so as to move with the con-
tracting muscle, and thus to keep the contact exact ; or in the shape of a
thin wedge (Fick) the edge of which comprising the actual junctions is
thrust into a mass of muscles and held in position by them. In all cases
the fellow junction or junctions must be kept at a constant temperature.

Fick calculated that the greatest heat given out by the muscles
of the thigh of a frog in a single contraction was 3*1 micro-units of
heat l for a gramme of muscle, the result being obtained by dividing
by five the total amount of heat given out in five successive single
contractions. It will however be safer to regard these figures as
illustrative of the fact that the heat given out is considerable
rather than as data for elaborate calculations. Moreover we have
no satisfactory quantitative determinations of the heat given out
by the muscles of warm-blooded animals, though there can be no
doubt that it is much greater than that given out by the muscles
of the frog.

There can hardly be any doubt that the heat thus set free is'
the product of chemical changes within the muscle, changes, which
though they cannot for the reasons given above be regarded as
simple and direct oxidations, may be spoken of in general terms as
a combustion. So that the muscle may be likened to a steam-
engine, in which the combustion of a certain amount of material
gives rise to the development of energy in two forms, as heat and
as movement, there being certain quantitative relations between
the amount of energy set free as heat and that giving rise to move-
ment. We must however carefully guard ourselves against pressing
this analogy too closely. In the steam-engine, we can distinguish
clearly between the fuel which through its combustion is the sole
source of energy, and the machinery, which is not consumed to
provide energy and only suffers wear and tear. In the muscle we
can make no such distinction ; though the whole matter is not
fully worked out, we have reason to think that the muscular fibre
is not to be regarded as a machine which takes so to speak a charge
of certain substances from the blood, and by inducing an explosion
of these substances in itself gives rise to the energy of heat and
movement. On the contrary the evidence goes to shew that it is
the living contractile substance as a whole which is continually
breaking down in an explosive decomposition and as continually
building itself up again out of the material supplied by the blood.
In a steam-engine only a certain amount of the total potential
energy of the fuel issues as work, the rest being lost as heat, the
proportion varying, but the work rarely exceeding one-tenth of the
total energy. In the case of the muscle we are not at present in a
position to draw up an exact equation between the latent energy

1 The micro- unit being a milligramme of water raised one degree centigrade.

72 CHANGES DURING A NERVOUS IMPULSE. [BOOK i.

on the one hand and the two forms of actual energy on the other.
"We have reason to think that the proportion between heat and
work varies considerably under different circumstances, the work
sometimes rising as high as one-fourth, sometimes possibly sink-
ing as low as one twenty-fourth of the total energy, and obser-
vations seem to shew that the greater the resistance which the
muscle has to overcome, the larger the proportion of the total
energy expended which goes out as work done. The muscle in
fact seems to be so far self-regulating, that the more work it has to
do, the greater, within certain limits, is the economy with which
it works.

Lastly it must be remembered that the giving out of heat by
the muscle is not confined to the occasions when it is actually con-
tracting. When, at a later period, we treat of the heat of the body
generally, evidence will be brought forward that the muscles even
when at rest are giving rise to heat, so that the heat given out at
a contraction is not some wholly new phenomenon, but a temporary
exaggeration of what is going on continually, at a more feeble
rate.

The Changes in a Nerve during the passage of a Nervous

Impulse.

The change in the form of a muscle during its contraction is a
thing which can be seen and felt; but the changes in a nerve
during its activity are invisible and impalpable. We stimulate one
end of a nerve, and since we see this followed by a contraction of
the muscle attached to the other end, we know that some changes
or other, constituting a nervous impulse, have been propagated
along the nerve ; but these are changes which we cannot see. Nor
have we satisfactory evidence of any chemical events or of any pro-
duction of heat, accompanying a nervous impulse. We may fairly
suppose that some chemical changes form the basis of a nervous
impulse, and that these changes set free a certain amount of heat ;
but these if they occur are too slight to be recognized satisfactorily
by the means at present at our disposal. In fact, beyond the
terminal results, such as a muscular contraction in the case of
a nerve going to a muscle, or some affection of the central
nervous system in the case of a nerve still in connection with
its nervous centre, there is one event and one event only which
we are able to recognize as the objective token of a nervous
impulse, and that is the so-called negative variation of the nerve-
current. For a piece of nerve removed from the body exhibits
nearly the same electric phenomena as a piece of muscle. It has
an equator which is electrically positive as compared to its two cut
ends. In fact the diagram Fig. 12, and the description which it
was used on p. 59 to illustrate, may be applied to nerve as well as

CHAP. IL] THE CONTRACTILE TISSUES. 73

to muscle, except that the currents are in all cases much more
feeble in the case of nerves than of muscles, and the special
currents from the circumference to the centre of the transverse
sections cannot well be shewn in a slender nerve; indeed it is
doubtful if they exist at all.

During the passage of a nervous impulse the ' natural nerve- \
current' undergoes a negative variation, just as the 'natural muscle-
current' undergoes a negative variation during a contraction.
There are however difficulties in the case of the nerve similar to
those in the case of the muscle, concerning the pre-existence of
any such 'natural' currents. It is maintained by many that
a nerve in an absolutely natural condition is like a muscle,
iso-electric ; hence we may say that in a nerve during the passage
of a nervous impulse, as in a muscle during a muscular contraction,
a ' current of action ' is developed.

This ' current of action ' or ' negative variation ' may be shewn
either by the galvanometer or by the rheoscopic frog. If the nerve
of the 'muscle-nerve preparation' B (see p. 62) be placed in an
appropriate manner on a thoroughly irritable nerve A (to which of
course no muscle need be attached), i.e. touching say the equator
and one end of the nerve, then single induction-shocks sent into
the far end of A will cause single spasms in the muscle of B, while
tetanization of A, i.e. rapidly repeated shocks sent into A, will
cause tetanus of the muscle of B.

That this current, whether it be regarded as an independent
4 current of action or as a negative variation of a ' pre-existing '
current, is an essential feature of a nervous impulse is shewn by
the fact that the degree or intensity of the one varies with that of
the other. They both travel too at the same rate. In describing
the muscle-curve, and the method of measuring the muscular latent
period, we have incidentally shewn (p. 47) how the velocity of the
nervous impulse is measured also, and stated that the rate in the
nerves of a frog is about 28 metres a second. Bernstein by means
of a special and somewhat complicated apparatus finds that the
current of action travels along an isolated piece of nerve at the
same rate. He also finds that it, like the molecular change in a
muscle preceding the contraction, and indeed like the contraction
itself, passes over any given spot of the nerve in the form of a
wave, rising rapidly to a maximum and then more gradually
declining again. He has been able to measure tne length of the
wave, and this he finds to be about 18 mm., taking *0007 sec. to
pass over any one point.

When an isolated piece of nerve is stimulated in the middle, the
current of action is propagated equally well in both directions, and
that whether the nerve be a chiefly sensory or a chiefly motor nerve,
or indeed if it be a nerve-root composed exclusively of motor or
of sensory fibres. Taking the current of action as the token of a
nervous impulse, we infer from this that when a nerve-fibre is

74 CHANGES DURING A NERVOUS IMPULSE. [BOOK i.

stimulated artificially at any part of its course, the nervous
impulse set going travels in both directions.

We used just now the phrase ' tetanization of a nerve/ meaning
the application to a nerve of rapidly repeated shocks such as would
produce tetanus in the muscle to which the nerve was attached,
and we shall have frequent occasion to employ the phrase. It will
however of course be understood that there is in the nerve as far
as we know no summation of nervous impulses comparable to the
summation of muscular contractions. The matter perhaps needs
fuller investigation, but as far as we know at present, we may
say that the series of shocks sent in at the far end of the nerve
start a series of impulses; these travel down the nerve and
reach the muscle as a series of distinct impulses; and the
first changes in the muscle, the molecular latent-period changes,
also form a series the members of which are distinct. It is
not until these molecular changes become transformed into visible
changes of form that any fusion or summation takes place.

Putting together the facts contained in this and the preceding
sections, the following may be taken as a brief approximate history
of what takes place in a muscle and nerve when the latter is
subjected to a single induction-shock. At the instant that the
induced current passes into the nerve, changes occur, of whose
nature we know nothing certain except that they cause a ' current
|of action' or 'negative variation of the natural' nerve-current.
These changes propagate themselves along the nerve in both
directions as a nervous impulse in the form of a wave, having
a wave-length of about 18 mm., and a velocity (in frog's nerve) of
about 28 m. per sec. Passing down the nerve-fibres to the muscle,
flowing along the branching and narrowing tracts, the wave at last
breaks on the end-plates of the fibres of the muscle. Here it is
transmuted into a muscle-impulse, with a shorter steeper wave,
and a greatly diminished velocity (about 3m. per sec.). This
muscle-impulse, of which we know hardly more than that it
:is marked by a current of action, travels from each end-plate
in both directions to the end of the fibre, where it appears to
be lost, at all events we do not know what becomes of it. As
it leaves the end plate it is followed by an explosive decomposition
of material, leading to a discharge of carbonic acid, to the appearance
of some substance or substances with an acid reaction, and probably
of other unknown things, with a considerable development of heat.
This explosive decomposition gives rise to the visible contraction-
wave, which travels behind the invisible muscle-impulse at about
the same rate, but with a vastly increased wave-length. The fibre,
as the wave passes over it, swells and shortens, bringing its two ends
nearer together, its molecules during the change of form arranging
themselves in such a way that the extensibility of the fibre is
increased.

SEC. 3. THE NATURE OF THE CHANGES THROUGH
WHICH AN ELECTRIC CURRENT IS ABLE TO GENE-
RATE A NERVOUS IMPULSE.

Action of the Constant Current.

In the preceding account, the stimulus applied in order to give
rise to a nervous impulse has always been supposed to be an
induction shock, single or repeated. This choice of stimulus has
been made on account of the almost momentary duration of the
induced current. Had we used a current lasting for some consider-
able time, the problems before us would have become more com-
plex in consequence of our having to distinguish between the
events taking place while the current was passing through the
nerve from those which occurred at the moment when the current
was thrown into the nerve or at the moment when it was shut
off from the nerve. These complications do arise when instead of
employing the induced current as a stimulus, we use a constant
current, i.e. when we pass through the nerve (or muscle) a current
direct from the battery without the intervention of any induction-
coil.

Before making the actual experiment, we might perhaps
naturally suppose that the constant current would act as a
stimulus throughout the whole time during which it was applied,
that, so long as the current passed along the nerve, nervous
impulses would be generated and thus the muscle thrown into
something at all events like tetanus. And under certain conditions
this does take place ; occasionally it happens that at the moment
the current is thrown into the nerve, the muscle of the muscle-
nerve preparation falls into a tetanus which is continued until the
current is shut off. But such a result is exceptional. In the vast

76 ACTION OF THE CONSTANT CURRENT. [BOOK i.

majority of cases what happens is as follows. At the moment that
the circuit is made, the moment that the current is thrown
into the nerve, a single spasm, a simple contraction, the so-called
making contraction, is witnessed ; but after this has passed away
the muscle remains absolutely quiescent in spite of the current
continuing to pass through the nerve, and this quiescence is
maintained until the circuit is broken, until the current is shut
off from the nerve, when another simple contraction, the so-
called breaking contraction, is observed. The mere passage of a
constant current of uniform intensity through a nerve does not
under ordinary circumstances act as a stimulus generating a
nervous impulse ; such an impulse is only set up when the
current either falls into or is shut off from the nerve. It is
the entrance or the exit of the current, and not the continuance of
the current, which is the stimulus.

The quiescence of the nerve and muscle during the passage of
the current is however dependent on the current remaining
uniform in intensity or at least not being suddenly increased
or diminished. Any sufficiently sudden and large increase or
diminution of the intensity of the current, will act like the
entrance or exit of a current, and by generating nervous impulses
give rise to contractions. If the intensity of the current however
be very slowly and gradually increased or diminished, a very wide
range of intensity may be passed through without any contraction
being seen. It is the sudden change from one condition to another,
and not the condition itself, which causes the nervous impulse.

In many cases, both a ' making ' and a ' breaking ' contraction,
each a simple spasm, are observed, and this is perhaps the
commonest event ; but when the current is very weak, and again
when the current is very strong either the breaking or the making
contraction may be absent, i.e. there may be a contraction only
when the current is thrown into the nerve or only when it is
shut off from the nerve.

Under ordinary circumstances the contractions witnessed with
the constant current either at the make or at the break, are of the
nature of a ' simple ' contraction, but, as has already been said, the
application of the current may give rise to a very pronounced
tetanus. Such a tetanus is seen sometimes when the current
is made, lasting during the application of the current, sometimes
when the current is broken, lasting some time after the current has
been wholly removed from the nerve. The former is spoken of as
a ' making/ the latter as a ' breaking ' tetanus. But these excep-
tional results of the constant current need not detain us now.

The great interest attached to the action of the constant
current lies in the fact, that during the passage of the current,
in spite of the absence of all nervous impulses and therefore
of all muscular contractions, the nerve is for the time both between
and on each side of the electrodes profoundly modified in a most

CHAP. IL]

THE CONTRACTILE TISSUES.

77

peculiar manner. This modification, important both for the light
it throws on the generation of nervous impulses and for its practical
applications, is known under the name of electrotonus.

Electrotonus. .The marked feature of the electrotonic con-
dition is that the nerve though apparently quiescent is changed in
respect to its irritability; and that in a different way in the
neighbourhood of the two electrodes respectively.

Suppose that on the nerve of a muscle-nerve preparation are
placed two (non-polarizable) electrodes (Fig. 13, a, Ic) connected
with a battery and arranged with a key so that a constant current
can at pleasure be thrown into or shut off from the nerve.
This constant current, whose effects we are about to study, may be
called the f polarizing current.' Let a be the positive electrode or
anode, and k the negative electrode or kathode, both placed at
some distance from the muscle, and also with a certain interval
between each other. At the point x let there be applied a pair of
electrodes connected with an induction-machine. Let the muscle
farther be connected with a lever, so that its contractions can
be recorded, and their amount measured. Before the polarizing
current is thrown into the nerve, let a single induction-shock
of known intensity (a weak one being chosen, or at least not
one which would cause in the muscle a maximum contraction) be
thrown in at a;. A contraction of a certain amount will follow.

B.

FIG. 13. MUSCLE-NERVE PREPARATIONS, with the nerve exposed in A to a descending
and in B to an ascending constant current.

In each a is the anode, k the kathode of the constant current, x represents the
spot where the induction-shocks used to test the irritability of the nerve are sent in.

That contraction may be taken as a measure of the irritability of
the nerve at the point x. Now let the polarizing current be
thrown in, and let the direction of the current be a descending
one, with the kathode or negative pole nearest the muscle,

78 ELECTROTONUS. [BOOK i.

as in Fig. 13^1. If while the current is passing, the same
induction-shock as before be sent through x, the contraction which
results will be found to be greater than on the former occasion.
If the polarizing current be shut off, and the point x after a
short interval again tested with the same induction-shock, the
contraction will be no longer greater, but of the same amount,
or perhaps not so great, as at first. During the passage of
the polarizing current, therefore, the irritability of the nerve at
the point x has been temporarily increased, since the same shock
applied to it causes a greater contraction during the presence than
in the absence of the current. But this is only true so long as the
polarizing current is a descending one, so long as the point x lies on
the side of the kathode. On the other hand, if the polarizing
current had been an ascending one, with the anode or positive pole
nearest the muscle, as in Fig. 135, the irritability of the nerve at
x would have been found to be diminished instead of increased by
the polarizing current. That is to say, when a constant current is
applied to a nerve, the irritability of the nerve between the polar-
izing electrodes and the muscle is, during the passage of the current,
increased when the kathode is nearest the muscle (and the polar-
izing current descending) and diminished when the anode is nearest
the muscle (and the polarizing current ascending). The same
result, mutatis mutandis, and with some qualifications which we
need not discuss, would be gained if x were placed not between
the muscle and the polarizing current, but on the far side of the
latter. Hence it may be stated generally that during the passage
of a constant current through a nerve the irritability of the nerve
is increased in the region of the kathode, and diminished in
the region of the anode. The changes in the nerve which give
rise to this increase of irritability in the region of the kathode
are spoken of as katelectrotonus, and the nerve is said to be
in a katelectrotonic condition. Similarly the changes in the
region of the anode are spoken of as anelectrotonus, and the nerve
is said to be in an anelectrotonic condition. It is also often usual
to speak of the katelectrotonic increase, and anelectrotonic decrease
of irritability.

This law remains true whatever be the mode adopted for
determining the irritability. The result holds good not only
with a single induction-shock, but also with a tetanizing inter-
rupted current, with chemical and with mechanical stimuli. It
further appears to hold good not only in a dissected nerve-muscle
preparation but also in the intact nerves of the living body. The
increase and decrease of irritability are most marked in the
immediate neighbourhood of the electrodes, but spread for a
considerable distance in either direction in the extrapolar regions.
The same modification is not confined to the extrapolar region,
but exists also in the intrapolar region. In the intrapolar region
there must be of course an indifferent point, where the katelectro-

CHAP, ii.] THE CONTRACTILE TISSUES. 79

tonic increase merges into the anelectrotonic decrease, and where
therefore the irritability is unchanged. When the polarizing
current is a weak one, this indifferent point is nearer the anode
than the kathode, but as the polarizing current increases in
intensity, draws nearer and nearer the kathode (see Fig. 14).

The amount of increase and decrease is dependent : (1) On the
strength of the current, the stronger current up to a certain limit
producing the greater effect. (2) On the irritability of the nerve,
the more irritable, better conditioned nerve being the more affected
by a current of the same intensity.

In the experiments just described the increase or decrease of
irritability is taken to mean that the same stimulus starts in the one
case a larger or more powerful and in the other case a smaller or
less energetic impulse ; but we have reason to think that the mere
propagation or conduction of impulses started elsewhere is affected
by the electrotonic condition. At all events anelectrotonus appears
to offer an obstacle to the passage of a nervous impulse.

These variations of irritability at the kathode and anode respec-
tively must be the result of molecular changes, brought about by
the action of the constant current. They are interesting theoreti-
cally because they shew that the generation of a nervous impulse
as the result of the making or breaking of a constant current is
dependent on the change of a nerve from its normal condition into
either katelectrotonus or anelectrotonus, or back again from one
of these phases into its normal condition. And certain results as
to the occurrence or absence of a contraction at the make or at
the break, according as the current is strong or weak, ascending,
or descending (results which need not detain us here but which
have been formulated as the co-called "law of contraction")

FIG. 14. DIAGRAM ILLUSTRATING THE VARIATIONS OF IRRITABILITY DURING ELECTRO-
TONUS, WITH POLARIZING CURRENTS OF INCREASING INTENSITY (from Pfliiger).

The anode is supposed to be placed at A, the kathode at B ; AB is consequently
the intrapolar district. In each of the three curves, the portion of the curve below
the base line represents diminished irritability, that above, increased irritability.
2/j represents the effect of a weak current; the indifferent point xl is near the
anode A. In yv a stronger current, the indifferent point x^ is nearer the kathode
B, the diminution of irritability in anelectrotonus and the increase in katelectro-
tonus being greater than in yl ; the effect also spreads for a greater distance along
the extrapolar regions in both directions. In */3 the same events are seen to be still
more marked.

80 ELECT ROTONIG CURRENTS. [BOOK i.

go far to shew that a nervous impulse is generated only when
a nerve passes suddenly from a normal condition into the phase of
katelectrotonus (making contraction) or returns from the phase of
anelectrotonus to a normal condition (breaking contraction), in
other words, when it passes suddenly from a phase of lower to
a phase of higher irritability.

The phenomena of electrotonus are also interesting practically
in as much as they shew that in the constant current appropriately
applied we have the means of changing at will the irritability of
this or that nerve, decreasing it when we wish to lessen pain or
spasm, increasing it when we wish to heighten sensibility or
muscular action. For the increase or decrease is observed in the
case of nervous impulses passing towards the central nervous system
as well as in those passing to muscles.

Electrotonic Currents. During the passage of a constant current
through a nerve, variations in the electric currents of the nerve analogous
in some respects to the variations of the irritability of the nerve may be
witnessed. Thus if a constant current supplied by the battery P
(Fig. 15) be applied to a piece of nerve by means of two non-polarizable
electrodes p, p, the " currents of rest " obtainable from various points of
the nerve will be different during the passage of the polarizing current
from those which were manifest before or after the current was applied;
and, moreover, the changes in the nerve-currents produced by the polariz-
ing current will not be the same in the neighbourhood of the anode (p)
as those in the neighbourhood of the kathode ( p'). Thus let G and H be
two galvanometers so connected with the two ends of the nerve as to
obtain good and clear evidence of the "currents of rest." Before
the polarizing current is thrown into the nerve, the needle of H will
occupy a position indicating the passage of a current of a certain
intensity from h to h' through the galvanometer (from the positive
longitudinal surface to the negative cut end of the nerve), the circuit
being completed by a current in the nerve from h' to h, i.e. the current
will flow in the direction of the arrow. Similarly the needle of G will
by its deflection indicate the existence of a current flowing from g to g'
through the galvanometer, and from g to g through the nerve, in the
direction of the arrow.

At the instant that the polarizing current is thrown into the nerve
at pp'j the currents at gg', hhf will suffer a "current of action" correspond-
ing to the nervous impulse, which, at the making of the polarizing
current, passes in both directions along the nerve, and may cause a
contraction in the attached muscle. The current of action is, as we
have seen, of extremely short duration, it is over and gone in a small
fraction of a second. It therefore must not be confounded with a
permanent effect which, in the case we are dealing with, is observed in
both galvanometers. This effect, which is dependent on the direction
of the polarizing current, is as follows: Supposing that the polarizing
current is flowing in the direction of the arrow in the figure, that is,
passes in the nerve from the positive electrode or anode p to the negative
electrode or kathode pft it is found that the current through the
galvanometer G is increased, while that through H is diminished. We

CHAP. IL]

THE CONTRACTILE TISSUES.

81

may explain this result by saying that the polarizing current has caused
the appearance in the nerve outside the electrodes of a new current,
the 'electrotonic' current, having the same direction as itself, which
adds to, or takes away from, the natural nerve-current or " current of
rest " according as it is flowing in the same or in an opposite direction.

.7

H

FIG. 15. DIAGRAM ILLUSTRATING ELECTROTOXIC CURRENTS.

P the polarizing battery, with k a key, p the anode, and p' the kathode. At the left
end of the piece of nerve the natural current flows through the galvanometer G
from g to g', in the direction of the arrows ; its direction therefore is the same
as that of the polarizing current; consequently it appears increased, as indicated
by the sign + . The current at the other end of the piece of nerve, from h to h',
through the galvanometer H, flows in a contrary direction to the polarizing
current ; it consequently appears to be diminished, as indicated by the sign — .

N.B. For simplicity's sake, the polarizing current is here supposed to be thrown
in at the middle of a piece of nerve, and the galvanometer placed at the two ends.
Of course it will be understood that the former may be thrown in anywhere, and the
latter connected with any two pairs of points which will give currents.

The strength of the electrotonic current is dependent on the strength
of the polarizing current, and on the length of the intrapolar region
which is exposed to the polarizing current. When a strong polarizing
current is used, the electromotive force of the electrotonic current may
be much greater than that of the natural nerve-current.

The strergth of the electrotonic current varies with the irritability,
or vital condition of the nerve, being greater with the more irritable
nerve; and a dead nerve will not manifest electrotonic currents. More-
over, the propagation of the current is stopped by a ligature, or by
crushing the nerve.

F. 6

82 ELECTROTONIC CURRENTS. [BOOK i.

We may speak of the conditions which give rise to this electrotonic
current as a physical electrotonus analogous to that physiological electro-
tonus which is made known by variations in irritability. The physical
electrotonic current is probably due to the escape of the polarizing
current along the nerve under the peculiar conditions of the living
nerve; but we must not attempt to enter here into this disputed
and difficult subject or into the allied question as to the exact con-
nection between the physical and the physiological electrotonus, though
there can be little doubt that the latter is dependent on the former.

An induction-shock is a current of very short duration developed
very suddenly and disappearing more gradually. Hence, when it
falls into a nerve, the nerve undergoes a sudden transition from its
normal condition to the katelectrotonic phase, and consequently a
nervous impulse giving rise to a contraction is the result. The
return from the anelectrotonic phase to the normal condition
appears from a number of considerations to be less effective as
a generator of nervous impulses than the change from the normal
condition to the katelectrotonic phase. Hence in the induced
current we have to deal with a ' making ' contraction only, the
breaking contraction being absent. This is true whether the induced
current be generated by the making or by the breaking of a con-
stant current.

The constant current applied directly to a muscle from which
the purely nervous element has been eliminated by urari poisoning,
has effects similar to and yet somewhat different from those which
it has upon a nerve. The efficacy of the rise of katelectrotonus
and the fall of anelectrotonus respectively in producing contraction
is the same as in a nerve. In one respect the muscle is more
striking, and offers a support of the hypothesis mentioned above.
The making contraction may under favourable circumstances be
seen to start from the kathode and the breaking contraction from
the anode. Besides the make and break spasm a partial tetanus
during the whole time of the passage of the current through a
muscle is very often seen. Another marked difference between
muscle and nerve is that in muscle the current must act for a
much longer time upon the tissue before it can call forth a con-
traction. This is what we might expect from the more sluggish
nature of the muscular impulse-wave. Hence muscular tissue
which has lost its nervous elements or does not possess them, is
far less readily affected by the almost momentary induction-shocks
than are nerves. -

SEC. 4. THE MUSCLE-NERVE PREPARATION AS A
MACHINE.

The facts described in the foregoing sections shew that a
muscle with its nerve may be justly regarded as a machine which,
when stimulated, will do a certain amount of work. But the
actual amount of work which a muscle-nerve preparation will do is
found to depend on a large number of circumstances, and conse-
quently to vary within very wide limits. These variations will be
largely determined by the condition of the muscle and nerve in
respect to their nutrition ; in other words, by the degree of irrita-
bility manifested by the muscle or by the nerve or by both. But
quite apart from the general influences affecting its nutrition and
thus its irritability, a muscle-nerve preparation is affected as
regards the amount of its work by a variety of other circumstances,
which we may briefly consider here, reserving to a succeeding
section the study of variations in irritability.

The nature and mode of application of the stimulus as affecting
the amount and character of the contraction.

We have seen that a nervous impulse is a molecular disturbance
travelling along the nerve in the form of a wave. We saw further
that the velocity with which this wave travels is in the frog about
28 inches per sec., and in the mammal somewhat higher, but that
it varies according to circumstances, being especially dependent on
temperature. The wave-length, that is, the total length of nerve
along which the disturbance is at any one instant taking place,
from the point nearer the muscle which the disturbance has just
reached, to the point farther from the muscle which the disturbance
has just left, may we have seen be put down (in the frog) as 18 mm.;
but possibly this too varies somewhat. The greatest and most
important variations however are those of the energy of the nervous
impulse, of the amount of disturbance which takes place in the
nerve or in the nerve fibre as the wave of the nervous impulse
passes over it ; this we might designate as the height of the wave.

6—2

84 THE MUSCLE-NERVE MACHINE. [BOOK i.

Thus a weak stimulus gives rise to a small disturbance, that is a
weak nervous impulse, and a strong stimulus gives rise to a large
disturbance, that is a powerful nervous impulse.

We are not in a position at present to speak definitely as to
the occurrence of other differences in the characters of nervous
impulses. As far as we know at present, nervous impulses what-
ever their origin are alike in nature l ; the impulses generated, in
a natural way, by the brain or spinal cord, or produced artificially
by mechanical stimuli, as by cutting or pinching, or by thermal
stimuli, as by touching the nerve with a red-hot wire, or by
chemical stimuli, or by electrical stimuli, may differ in intensity, and
in the rapidity with which they succeed each other, but, as far as
we know at present, not otherwise. Thus a drop of acid placed on
a nerve gives rise to tetanus in the muscle which differs from the
tetanus produced by repeated induction shocks applied to the nerve,
only so far as the tetanus is generally irregular, the individual
nervous impulses generated by the acid forming an irregular series,
not following each other at equal intervals and not being all of the
same intensity, whereas the impulses generated by the 'interrupted
current ' are generally of the same intensity and follow each other
at equal intervals. So also we are led at present to believe that
when muscles are thrown into action in a natural way in the living
body by the agency of the spinal cord, what goes 011 in the nerve
differs from what goes on in the same nerve when the interrupted
current is brought to bear on it, only in so far as in the former case
the impulses follow each other at a fixed rate (nineteen a second),
whereas in the latter, the rate of repetition varies according to
the rapidity with which in the induction-machine the shocks
follow each other; the individual impulses as far as we know at
present have the same characters in the two cases save only that
they may differ in intensity.

Supposing that the irritability of a nerve-muscle preparation
remains for the period of the experiment fairly constant, care
being taken to avoid the effects of exhaustion, and that the
stimulus be applied to the same part of the nerve, we find that the
intensity of the nervous impulse generated (as measured by the
muscular contraction) varies up to a certain limit according to
what we may call the strength of the stimulus. Thus taking a
single induction shock as the most manageable stimulus, we find
that if, before we begin, we slide the secondary coil (Fig. 1, sc.)
a certain distance from primary coil pr. c., no visible effect at all
follows upon the discharge of the induction shocks. The passage
of the momentary weak current is either unable to produce any
nervous impulse at all, or the weak nervous impulse to which it

1 It will be observed that we are speaking now exclusively of the nerve of a
muscle-nerve preparation, i.e. of what we shall hereafter term a motor nerve.
Whether sensory impulses differ essentially from motor impulses will be considered
later on.

CHAP, ii.] THE CONTRACTILE TISSUES. 85

gives rise is unable to stir the sluggish muscular substance to a
visible contraction. As we slide the secondary coil towards the
primary, sending in an induction shock at each new position, we
find that at a certain distance between the secondary and primary
coils, the muscle responds to each induction shock1 with a con-
traction which makes itself visible by the slightest possible rise
of the attached lever. This position of the coils, the battery
remaining the same and other things being equal, marks the
minimal stimulus giving rise to the minimal contraction. As the
secondary coil is brought nearer to the primary, the contractions
increase in height corresponding to the increase in the intensity
of the stimulus. Very soon however an increase in the stimulus
caused by continuing to slide the secondary coil over the primary
fails to cause any increase in the contraction. This indicates
that the maximal stimulus giving rise to the maximal contraction
has been reached; though the shocks increase in intensity as
the secondary coil is pushed further and further over the primary,
the contractions remain of the same height, until fatigue lowers
them. Sometimes however, after the contractions have for some
time remained of the same height, in spite of the stimulus, at
each fresh stimulation, being increased in strength, a point is
reached at which, with a further increase in the strength of the
stimulus, a new increase of contraction sets in; but we must not
attempt to explain here this paradoxical super-maximal contraction
as it is called.

With single induction shocks then the muscular contraction,
and by inference the nervous impulse, increases with an increase in
the intensity of the stimulus, between the limits of the minimal
and maximal stimuli; and this dependence of the nervous impulse
and so of the contraction on the strength of the stimulus may be
observed not only in electric but in all kinds of stimuli.

It may here be remarked that in order for a stimulus to
be effective, a certain abruptness in its action is necessary. Thus
we have seen that the constant current when it is passing through
a nerve with uniform intensity does not give rise to a nervous
impulse and that it may be increased or diminished to almost any
extent without generating nervous impulses, provided that the
change be made gradually enough ; it is only wrhen there is a
sudden change that the current becomes effective as a stimulus.
The current which is induced in the secondary coil of an induction-
machine at the breaking of the primary circuit, is more rapidly
developed, and has a steeper rise than the current which appears
when the primary circuit is made ; and accordingly we find that
the breaking induction shock is more potent as a stimulus than
the making shock. Similarly a sharp tap on a nerve will produce

1 In these experiments either the breaking or making shock must be used, not
sometimes one and sometimes the other, for the two kinds of shock differ in efficiency,
the breaking being the most potent.

86 THE MUSCLE-NERVE MACHINE. [Boom.

a contraction, when a gradually increasing pressure will fail to do
If so ; and in general the efficiency of a stimulus of any kind will
II depend in part on the suddenness or abruptness of its action.

A stimulus, in order that it may be effective, must have an
action of a certain duration, the time necessary to produce an effect
varying according to its strength and being different in nerve from
what it is in muscle. It would appear that an electric current
applied to a nerve must have a duration of at least about '0015 sec.
to cause any contraction at all, and needs longer than this to
produce its full effect. When the current is applied directly to a
muscle, whose nervous elements are placed hors de combat by
the action of urari, or by degeneration of the nerve-fibres this
period of necessary duration seems to be still longer, and to be
especially increased by deficient nutrition. And this may be
offered as an explanation of the well-known clinical fact that in
various cases of paralysis, muscles which have by degeneration
of their nerves, lost their nervous supply, more readily respond
to the break and make of the constant current than to induction
shocks, the duration of the former as stimuli being much greater
than that of the latter.

In the case of electric stimuli, the strength of the contrac-
tion, and by inference of the nervous impulse, depends on the
manner in which the current flows into the nerve. Though the
matter has been disputed, it appears that the current must
pass along some appreciable length of nerve-fibre in order to
produce an effect: a current which passes through a nerve in
an absolutely transverse direction being powerless to generate
impulses ; and further there is a connection between the efficiency
of the current and the angle at which it falls into the nerve.

It would also appear, at all events up to certain limits, and as
a general rule, that the longer the piece of nerve through which
the current passes, the greater is the effect of the stimulus.

When two pairs of electrodes are placed on the nerve of a long
and perfectly fresh and successful nerve-preparation, one near to
the cut end, and the other nearer the muscle, it is found that the
same stimulus produces a greater contraction when applied through
the former pair of electrodes than through the latter. Two inter-
pretations of this result are possible. Either the nerve at the part
farther away from the muscle is more irritable, i.e. that the
stimulus gives rise at the spot stimulated to a larger nervous
impulse ; or the impulse started at the farther electrodes gathers
strength, like an avalanche, in its progress to the muscle. The
latter view has been strongly urged by Pfluger, and is generally
known under the name of the 'avalanche theory'. Against it
may be urged that as far as we know, the progress of the current
of action along a nerve is marked by no such increase. It is
probable that the larger contraction produced by stimulation of
the portions of the nerve near the spinal cord is due to the

CHAP, ii.] THE CONTRACTILE TISSUES. 87

stimulus setting free a larger impulse, i.e. to this part of the
nerve being more irritable. It is possible that the irritability
of a nerve may vary considerably at different points of its course.

We have in a preceding section discussed at length the manner
in which a stimulus repeated sufficiently rapidly produces a com-
plete and uniform tetanus, during which the constituent single
contractions cannot be recognized either by the appearance of the
muscle itself or by any features in the curve which it may be
made to describe, though the 'muscular sound' shews that the
muscle is really in a state of vibration. If the frequency of
the stimulus be reduced the tetanus becomes incomplete and
a flickering of the muscle becomes obvious, and upon further
reduction of the frequency the flickering gives place to a rhythmic
series of single contractions. Since the height to which the lever
is raised, i.e. the amount of total shortening resulting from
any second contraction, is greater when that contraction starts
from the summit of the preceding curve than when it starts from
the decline, it is obvious that the amount of total contraction will
up to a certain limit increase with the frequency of repetition
of the stimulus. Thus a stimulus repeated rapidly will produce a
tetanus, shortening the muscle and raising the weight to a greater
extent than will the same stimulus less rapidly repeated. The
exact frequency of repetition required to produce complete tetanus
varies according to the condition of the muscle and is not the same
for all muscles, being dependent on the rapidity with which
the muscle executes each single contraction. In those animals
which possess two kinds of skeletal muscles, red and pale, the
red muscles (the single contractions of which are slow and long-
drawn) are thrown into complete tetanus with a repetition of much
less frequency than that required for the pale muscles. Thus,
ten stimuli in a second are quite sufficient to throw the red
muscles of the rabbit into complete tetanus, while the pale muscles
require at least twenty stimuli in a second.

When the stimulus is repeated more frequently than is
required to bring about a complete tetanus the constituent
contractions are still proportionately increased in frequency. This
is shewn by the increased pitch of the muscular sound. How
far the increase in the frequency of the constituent contractions
can be carried by increasing the frequency of the stimulus is
a question which presents considerable difficulties, and cannot be
discussed here.

The value of the muscle as a machine is also in part dependent
on the Load. It might be imagined that a muscle, which, when
loaded with a given weight, and stimulated by a current of a given
intensity, had contracted to a certain extent, would only contract
to half that extent when loaded with twice the weight and stimu-
lated with the same stimulus. Such however is not the case; the
height to which the weight is raised may be in the second instance

88 THE MUSCLE-NERVE MACHINE. [BOOK i.

as great, or even greater, than in the first. That is to say, the
resistance offered to the contraction actually augments the con-
traction, the tension of the muscular fibre increases the facility
with which the explosive changes resulting in a contraction take
place. And it has been observed by Heidenhain that the degree
of acid reaction, the amount of carbonic acid given off and the
rise of temperature are greater in a muscle contracting against
resistance than when the resistance is removed ; that is to say,
the tension increases the metabolism. There is, of course, a
limit to this favourable action of the resistance. As the load con-
tinues to be increased, the height of the contraction is diminished,
and at last a point is reached at which the muscle is unable (even
when the stimulus chosen is the strongest possible) to lift the load
at all.

In a muscle viewed as a machine we have to deal not merely
with the height of the contraction, that is with the amount of
shortening, but with the work done. And this is measured as the
height to which the load is raised multiplied into the weight of
the load. Hence it is obvious from the foregoing observations
that the work done must be largely dependent on the weight
itself. Thus there is a certain weight of load, with which in any
given muscle, stimulated by a given stimulus, the most work will
be done.

Since mere tension affects the changes going on in the muscular
fibres, it is desirable in experiments in which muscles are loaded, that
the weight should not bear upon the lever until the contraction actually
begins. This is easily managed by interposing between the end of the
muscle and the weight a lever with a support so arranged that, before
contraction takes place, the weight only extends the muscle to the
length natural to it during rest; but that the muscle directly it shortens
at once begins to pull on the weight. The muscle is then said to
be after-loaded1.

The value of a muscle as a machine is further determined by the
Size and Form of the Muscle. Since all known muscular fibres are
much shorter than the wave-length of a contraction, it is obvious
that the longer the fibre, the greater the height of the contraction
with the same stimulus. Hence in a muscle of parallel fibres, the
height to which the load is raised as the result of a given stimulus
applied to its nerve, will depend on the length of the fibres, while
the maximum weight of load capable of being lifted will depend
.on the number of the fibres, since the load is distributed among
them. Of two muscles therefore of equal length (and of the same
quality) the most work will be done by that which has the greater
sectional area; and of two muscles with equal sectional areas,
the most work will be done by that which is the longer. If
the two muscles are unequal both in length and sectional area,

1 This is perhaps the best equivalent of the German uberlastet.

CHAP, ii.] THE CONTRACTILE TISSUES. 89

the work done will be the greater in the one which has the
larger bulk, which contains the greater number of cubic units.
In speaking therefore of the work which can be done by a muscle,
we may use as a standard a cubic unit of bulk, or, the specific
gravity of the muscle being the same, a unit of weight.

Absolute power of a muscle. We have seen that with a given
weight a stimulus (induction shock) may be chosen of such a
strength that a contraction is only just visible. In such a case a
very slight increase of the weight would prevent even that
minimal contraction. Upon increasing the stimulus the minimal
contraction would reappear and vanish again upon a further
increase of the weight. Increasing the stimulus and weight in
this way we should be able to find out the weight which, with a
maximal stimulation, is just sufficient to prevent any visible con-
traction from taking place, a very slight diminution of weight at
once allowing a minimum contraction to make its appearance.
Such a weight is taken as the measure of what is called the
'absolute power' of the muscle; and from what has been said in the
previous paragraph, it is obvious that this will depend on the
number of fibres in, or more correctly, on the sectional area of, the
muscle. The absolute power of a square centimetre of a frog's
muscle has been in this way estimated at about -2800 to 3000 grms.:
of a square centimetre of human muscle at 6000 to 8000 grms.

It may be worth while to mention in this connection the
following interesting fact.

If the weight be determined which will stop a contraction
when applied directly the contraction begins, and also that which
stops any further contraction when applied at a moment when the
contraction is already partly accomplished, it will be found that
the second weight is much less than the first. It appears, in fact,
that the forces which cause the change in the form of the muscle
are at their maximum at the beginning of the shortening, and
thenceforwards decline until they become nothing when the short-
ening is complete.

ITie work done. We learn then from the foregoing paragraphs
that the work done, i.e. the weight of the load multiplied into the
height of the lift, will depend, not only on the activity of the nerve
and muscle as determined by their own irritability, but also on the
character and mode of application of the stimulus, on the kind
of contraction (whether a single spasm, or a slowly repeated tetanus
or a rapidly repeated tetanus) on the load itself, and on the size
and form of the muscle. Taking the most favourable circum-
stances, viz. a well nourished, lively preparation, a maximum
stimulus causing a rapid tetanus and an appropriate load, we may
determine the maximum work done by a given weight, say one
gramme, of muscle. This in the case of the muscles of the frog
has been estimated at about four gram-metres for one gramme
of muscle.

SEC. 5. THE CIRCUMSTANCES WHICH DETERMINE
THE DEGREE OF IRRITABILITY OF MUSCLES AND
NERVES.

A muscle-nerve preparation, at the time that it is removed
from the body, possesses a certain degree of irritability, it responds
by a contraction of a certain amount to a stimulus of a certain
strength, applied to the nerve or to the muscle. After a while,
the exact period depending on a variety of circumstances, the
same stimulus produces a smaller contraction, i.e. the irritability
of the preparation has diminished. In other words, the muscle
or nerve or both have become partially 'exhausted'; and the
exhaustion subsequently increases, the same stimulus producing
smaller contractions until at last all irritability is lost, no stimulus
however strong producing any contraction whether applied to the
nerve or directly to the muscle ; and eventually the muscle, as we
have seen, becomes rigid. The progress of this exhaustion is more
rapid in the nerves than in the muscles ; for some time after the
nerve-trunk has ceased to respond to even the strongest stimulus,
contractions may be obtained by applying the stimulus directly to
the muscle. It is much more rapid in the warm-blooded than in
the cold-blooded animals. The muscles and nerves of the former
lose their irritability, when removed from the body, after a period
varying according to circumstances from a few minutes to two or
three hours; those of cold-blooded animals (or at least of an
amphibian or a reptile) may under favourable conditions remain
irritable for two, three, or even more days. The duration of
irritability in warm-blooded animals may however be considerably
prolonged by reducing the temperature of the body before death.

CHAP, ii.] THE CONTRACTILE TISSUES. 91

If with some thin body a sharp blow be struck across a muscle which
has entered into the later stages of exhaustion, a wheal lasting for
several seconds is developed. This wheal appears to be a contraction
wave limited to the part struck, and disappearing very slowly, without
extending to the neighbouring muscular substance. It has been called
an 'idio-muscular' contraction, because it may be brought out even when
ordinarv stimuli have ceased to produce any effect. It may however be
accompanied at its beginning by an ordinary contraction. It is readily
produced in the living body on the pectoral and other muscles of persons
suffering from phthisis and other exJiausting diseases.

This natural exhaustion and diminution of irritability in
muscles and nerves removed from the body may be modified both
in the case of the muscle and of the nerve, by a variety of circum-
stances. Similarly, while the nerve and muscle still remain in the
body, the irritability of the one or of the other may be modified
either in the way of increase or of decrease by various events.
We have already seen (p. 78) how the constant current produces
the variations in irritability known as katelectrotonus and anelec-
trotonus. We have now to study the effect of more general
influences, of which the most important are, severance from the
central nervous system, and variations in temperature, in blood-
supply, and in functional activity.

The Effects of Severance from the Central Nervous System.

•When a nerve, such for instance as the sciatic, is divided in
situ, in the living body, there is first of all observed a slight
increase of irritability, noticeable especially near the cut end ; but
after a while the irritability diminishes, and gradually disappears.
Both the slight initial increase and the subsequent decrease begin
at the cut end and advance centrifugally towards the peripheral
terminations. This centrifugal feature of the loss of irritability is
often spoken of as the Bitter- Valli law. In a mammal it may be
two or three days, in a frog, as many, or even more weeks, before
irritability has disappeared from the nerve-trunk. It is maintained
in the small (and especially in the intramuscular) branches for still
longer periods.

This centrifugal loss of irritability is the forerunner in the
peripheral portion of the divided nerve of structural changes which
proceed in a similar centrifugal manner. The medulla suffers
changes similar to those seen in nerve-fibres after removal from the
body. Its double contour and its characteristic indentations be-
come more marked, it breaks up into small irregular fragments, or
drops, a separation apparently taking place between its proteid and
its fatty constituents. The latter are soon absorbed, but the
former remain for a longer time within the sheath of Schwann,
being in some cases scarcely, if at all, to be distinguished from the

92 VARIATIONS OF IRRITABILITY. [BOOK i.

swollen axis-cylinder. Meanwhile the nuclei which occur, one in
each segment of the nerve between each two nodes of Ranvier,
divide and multiply rapidly. Lastly the axis-cylinder breaks up
and disappears so that nothing remains of the original fibre
but the sheath of Schwann enclosing a proteid mass with many
nuclei. If no regeneration takes place these nuclei eventually
disappear.

In the central portion of the divided nerve similar changes may
be traced as far only as the next node of Ranvier. Beyond this
the nerve usually remains in a normal condition.

Regeneration, when it occurs, is apparently carried out by the

peripheral growth of the axis-cylinders of the intact central
portion. When the cut ends of the nerve are close together the
axis-cylinders growing out from the central portion run into and
between the sheaths of Schwann of the peripheral portion ; but
much uncertainty still exists as to the exact parts which the
proliferated nuclei referred to above, the proteid remnants of the
medulla, and the old axis-cylinders of the peripheral portion
respectively play in giving rise to the new structures of the
regenerated fibre.

This degeneration may be observed to extend down to the very
endings of the nerve in the muscle, including the end-plates, but
does not at first affect the muscular substance itself. The muscle,
though it has lost all its nervous elements, still remains irritable
towards stimuli applied directly to itself: an additional proof of
the existence of an independent muscular irritability.

For some time the irritability of the muscle, as well towards stimuli
applied directly to itself as towards those applied through the impaired
nerve, seems to be diminished; but after a while a peculiar condition
(to which we have already alluded on p. 86) sets in, in which the muscle
is found to be not easily stimulated by single induction shocks but to
respond readily to the make or break of a constant current. In fact it
is said to become even more sensitive to the latter mode of stimulation
than it was when its nerve was intact and functionally active. At the
same time it also becomes more irritable towards direct mechanical
stimuli, and very frequently fibrillar contractions, more or less rhythmic
and apparently of spontaneous origin, though their causation is ob-
scure, make their appearance. This phase of heightened sensitiveness
of a muscle, especially to the constant current, appears to reach its
maximum, in man at about the seventh week after nervous impulses,
from injury to the nerves or nervous centre, have ceased to reach the
muscle.

If the muscle thus deprived of its nervous elements be left to
itself its irritability however tested sooner or later diminishes, but
if the muscle be periodically thrown into contractions by artificial
stimulation with the constant current, the decline of irritability
and attendant loss of nutritive power may be postponed for some
considerable time. But as far as our experience goes at present

CHAP, ii.] TUE CONTRACTILE TISSUES. 03

the artificial stimulation cannot fully replace the natural one and
sooner or later the muscle like the nerve suffers degeneration, loses
all irritability and ultimately becomes replaced by connective
tissue.

The Influence of Temperature.

We have already seen that sudden heat applied to a limited
part of a nerve or muscle, as when the nerve or muscle is touched
with a hot wire, will act as a stimulus, and the same might
be said of cold when sufficiently intense. It is however much
more difficult to generate nervous or muscular impulses by ex-
posing a whole nerve or muscle to a gradual rise of temperature.
Thus according to most observers a nerve belonging to a muscle1
may be either cooled to 0° C. or below, or heated to 50° or even
100°C., without discharging any nervous impulses, as shewn by the
absence of contraction in the attached muscle. The contractions
moreover may be absent even when the heating has not been very
gradual.

A muscle may be cooled to 0° C. or below without any contrac-
tion being caused ; but when it is heated to a limit, which in the
case of frog's muscles is about 45°, of mammalian muscles about
50°, a sudden change takes place : the muscle falls, at the limiting
temperature, into a rigor mortis, which is initiated by a forcible
contraction or at least shortening. The rigor mortis thus brought
about by heat is often spoken of as rigor caloris.

Moderate warmth, ex. gr. in the frog an increase of temperature
up to somewhat below 45° C., favours both muscular and nervous
irritability. All the molecular processes are hastened and facili-
tated : the contraction is for a given stimulus greater and more
rapid, i.e. of shorter duration, and nervous impulses are generated
more readily by slight stimuli. Owing to the quickening of the
chemical changes, the supply of new material may prove insuffi-
cient ; hence muscles and nerves removed from the body lose their
irritability more rapidly at a high than at a low temperature.

The gradual application of cold to a nerve, especially when the
temperature is thus brought near to 0°, slackens all the molecular
processes, so that the wave of nervous impulse is lessened and pro-
longed, the velocity of its passage being much diminished, e.g. from
28 m. to 1 m. per sec. At about 0° the irritability of the nerve
disappears altogether.

When a muscle is exposed to similar cold, ex. gr. to a tempera-
ture very little above zero, the contractions are remarkably pro-
longed ; they are diminished in height at the same time, but not
in proportion to the increase of their duration. Exposed to a
temperature of zero or below, muscles soon lose their irritability,

1 The action of cold and heat on sensory nerves will be considered in the later
portion of the woik.

94 VARIATIONS OF IRRITABILITY. [BOOK i.

without however undergoing rigor mortis. After an exposure of
not more than a few seconds to a temperature not much below
zero, they may be restored, by gradual warmth, to an irritable con-
dition, even though they may appear to have been frozen. When
kept frozen however for some few minutes, or when exposed for a
less time to temperatures of several degrees below zero, their
irritability is permanently destroyed. When thawed, they enter
into rigor mortis of a most pronounced character.

The Influence of Blood-Supply.

When a muscle still within the body is deprived by any means
of its proper blood-supply, as when the blood-vessels going to it are
ligatured, the same gradual loss of irritability and final appearance
of rigor mortis are observed as in muscles removed from the body.
Thus if the abdominal aorta be ligatured, the muscles of the lower
limbs lose their irritability and finally become rigid. So also in
systemic death, when the blood-supply to the muscles is cut off by
the cessation of the circulation, loss of irritability ensues, and rigor
mortis eventually follows. In a human corpse the muscles of the
body enter into rigor mortis in a fixed order : first those of the jaw
and neck, then those of the trunk, next those of the arms, and
lastly those of the legs. The rapidity with which rigor mortis
comes on after death varies considerably, being determined both by
external circumstances and by the internal conditions of the body.
Thus external warmth hastens and cold retards the onset. After
great muscular exertion, as in hunted animals, and when death
closes wasting diseases, rigor mortis in most cases comes on rapidly.
As a general rule it may be said that the later it is in making its
appearance, the more pronounced it is, and the longer it lasts ; but
there are many exceptions, and when the state is recognized as
being fundamentally due to a coagulation, it is easy to understand
that the amount of rigidity, i.e. the amount of the coagulum, and
the rapidity of the onset, i.e. the quickness with which coagulation
takes place, may vary independently. The rapidity of onset after
muscular exercise and wasting disease is apparently dependent on
an increase of acid reaction, being produced under those circum-
stances in the muscle, for this seems to be favourable to the coagu-
lation of the muscle plasma. When rigor mortis has once become
thoroughly established in a muscle through deprivation of blood, it
cannot be removed by any subsequent supply of blood. Thus
where the abdominal aorta has remained ligatured until the lower
limbs have become completely rigid, untying the ligature will not
restore the muscles to an irritable condition ; it simply hastens the
decomposition of the dead tissues by supplying them with oxygen
and, in the case of the mammal, with warmth also. A muscle
however may acquire as a whole a certain amount of rigidity on
account of some of the fibres becoming rigid, while the remainder,

CHAP. Ji.] THE CONTRACTILE TISSUES. 95

though they have lost their irritability, have not yet advanced into
rigor mortis. At such a juncture a renewal of the blood-stream
may restore the irritability of those fibres which were not yet rigid,
and thus appear to do away with rigor mortis ; yet it appears that
in such cases the fibres which have actually become rigid never
regain their irritability, but undergo degeneration.

Mere loss of irritability, even though complete, if stopping short
of the actual coagulation of the muscle-substance, may be with
care removed. Thus if a stream of blood be sent artificially
through the vessels of a separated (mammalian) muscle, the irrita-
bility may be maintained for a very considerable time. On stopping
the artificial circulation, the irritability diminishes and in time
entirely disappears ; if however the stream be at once resumed,
the irritability will be recovered. By regulating the flow, the
irritability may be lowered and (up to a certain limit) raised at
pleasure. From the epoch however of interference with the nor-
mal blood-stream there is a gradual diminution in the responses
to stimuli, and ultimately the muscle loses all its irritability and
becomes rigid, however well the artificial circulation be kept up.
This failure is probably in great part due to the blood sent through
the tissue not being in a perfectly normal condition ; but we have
at present very little information on this point. Indeed with
respect to the quality of blood thus essential to the maintenance
or restoration of irritability, our knowledge is definite with regard
to one factor only, viz. the oxygen. If blood deprived of its oxygen
be sent through a muscle removed from the body, irritability, so
far from being maintained, seems rather to have its disappearance
hastened. In fact, if venous blood continues to be driven through
a muscle, the irritability of the muscle is lost even more rapidly
than in the entire absence of blood. It would seem that venous
blood is more injurious than none at all. If exhaustion be not
carried too far, the muscle may however be revived by a proper
supply of oxygenated blood.

The influence of blood-supply cannot be so satisfactorily studied
in the case of nerves as in the case of muscles ; there can however
be little doubt that the effects are analogous.

The Influence of Functional Activity.

This too is more easily studied in the case of muscles than of
nerves.

When a muscle within the body is unused, it wastes ; when
used it (within certain limits) grows. Both these facts shew that
the nutrition of a muscle is favourably affected by its functional
activity. Part of this may be an indirect effect of the increased
blood-supply which occurs when a muscle contracts. When a
nerve going to a muscle is stimulated, the blood-vessels of the
muscle dilate. Hence at the time of the contraction more blood

96 VARIATIONS OF IRRITABILITY. [BOOK i.

flows through the muscle, and this increased flow continues for
some little while after the contraction of the muscle has ceased.
But, apart from the blood-supply it is probable that the ex-
haustion caused by a contraction is immediately followed by a
reaction favourable to the nutrition of the muscle ; and this is a
reason, possibly the chief reason, why a muscle is increased by use,
that is to say, the loss of substance and energy caused by the
contraction is subsequently more than made up for by increased
metabolism during the following period of rest.

Whether there be a third factor, whether muscles for in-
stance are governed by so-called trophic nerves which affect their
nutrition directly in some other way than by influencing either
their blood-supply or their activity, must at present be left
undecided.

A muscle, even within the body, after prolonged action is
fatigued, i.e. a stronger stimulus is required to produce the same
contraction; in other words, its irritability may be lessened by
functional activity. Whether functional activity therefore is in-
jurious or beneficial depends on its amount in relation to the
condition of the muscle. It may be here remarked that as a
muscle becomes more and more fatigued, stimuli of short duration,
such as induction shocks, sooner lose their efficacy than do stimuli
of longer duration such as the break and make of the constant
current.

The sense of fatigue of which, after prolonged or unusual exertion,
we are conscious in our own bodies, is probably of complex origin,
and its nature, like that of the normal muscular sense of which we
shall have to speak hereafter, is at present not thoroughly under-
stood. It seems to be in the first place the result of changes in
the muscles themselves, but is possibly also caused by changes in
nervous apparatus concerned in muscular action, and especially
in those parts of the central nervous system which are concerned
in the production of voluntary impulses. In any case it cannot be
taken as an adequate measure of the actual fatigue of the muscles;
for a man who says he is absolutely exhausted may under excite-
ment perform a very large amount of work with his already weary
muscles. The will in fact rarely if ever calls forth the greatest
contractions of which the muscles are capable.

Absolute (temporary) exhaustion of the muscles, so that the
strongest stimuli produce no contraction, may be produced even
within the body by artificial stimulation; recovery takes place
on rest. Out of the body absolute exhaustion takes place readily.
Here also recovery may take place. Whether in any given case it
does occur or not, is determined by the amount of contraction
causing the exhaustion, and by the previous condition of the
muscle. In all cases recovery is hastened by renewal (natural or
artificial) of the blood-stream. The more rapidly the contractions
follow each other, the less the interval between any two con-

CHAP. IL] THE CONTRACTILE TISSUES. 97

tractions, the more rapid the exhaustion. A certain number of
single induction-shocks repeated rapidly, say every second or
oftener, bring about exhaustive loss of irritability more rapidly
than the same number of shocks repeated less rapidly, for instance
every 5 or 10 seconds. Hence tetanus is a ready means of pro-
ducing exhaustion.

In exhausted muscles the elasticity is much diminished ; the
tired muscle returns less readily to its natural length than does the
fresh one.

The exhaustion due to contraction may be the result : — Either
of the consumption of the store of really contractile material
present in the muscle. Or of the accumulation in the tissue
of the products of the act of contraction. Or of both of these
causes.

The restorative influence of rest may be explained by supposing
that during the repose, either the internal changes of the tissue
manufacture new explosive material out of the comparatively raw
material already present in the fibres, or the directly hurtful pro-
ducts of the act of contraction undergo changes by which they are
converted into comparatively inert bodies. A stream of fresh
blood may exert its restorative influence not only by quickening
the above two events, but also by carrying off the immediate waste
products while at the same time it brings new raw material. It is
not known to what extent each of these parts is played. That the
products of contraction are exhausting in their effects, is shewn by
the facts that the injection of a solution of the muscle-extractives
into the vessels of a muscle produces exhaustion and that exhausted
muscles are recovered by the simple injection of inert saline
solutions into their blood-vessels ; moreover lactic acid and indeed
other acids injected into a muscle cause rapid exhaustion; and
we may suppose that carbonic acid, with the other substances
which after a contraction tend to give rise to an acid reaction,
when generated too rapidly to be neutralized by the alkaline
lymph in which the fibres are bathed, in part at least determine
the exhaustion. But the matter has not yet been fully worked out.

One important element brought by fresh blood is oxygen. This,
as we have seen, is not necessary for the carrying out of the actual
contraction, and yet is essential to the maintenance of irritability.
It is probably of use as what may be called "intramolecular
oxygen " in preparing the explosive material whose decomposition
gives rise to the carbonic acid, and other products of contraction.

F.

SEC. 6. THE ENERGY OF MUSCLE AND NERVE, AND THE
NATURE OF MUSCULAR AND NERVOUS ACTION.

We may briefly recapitulate some of the chief results arrived at
in the preceding pages as follows.

A muscular contraction itself is essentially a translocation of
molecules, a change of form not of bulk. We cannot say however
anything definite as to the nature of this translocation or as to
the way in which it is brought about. Though it would appear
that the dim doubly refractive bands increase in bulk at the
expense of the bright singly refractive bands, we cannot satis-
factorily explain the connection between the striation of a muscular
fibre and a muscular contraction. Nearly all rapidly contracting
muscles are striated, and we must suppose that the striation is
of some use ; but it is not essential to the carrying out of a
contraction, for many muscles are not striated. But whatever
be the exact way in which the translocation is effected, it is
fundamentally the result of a chemical change, of an explosive
decomposition of certain parts of the muscle-substance. The
energy which is expended in the mechanical work done by the
muscle has its source in the latent energy of the muscle-substance
set free by that explosion. Concerning the nature of that ex-
plosion we only know at present that it results in the production
of carbonic acid and in an increase of the acid reaction, and that
heat is set free as well as the specific muscular energy. There is
a general parallelism between the extent of metabolism taking
place and the amount of energy set free. The greater the
development of carbonic acid, the larger is the contraction and
the higher the temperature.

It has not been possible hitherto to draw up a complete equa-
tion between the latent energy of the material and the two forms
of actual energy set free. The proportion of energy given out
as heat to that taking on the form of work probably varies
under different circumstances; and it would appear that on the
whole a muscle would be no more economical than a steam-engine
in respect to the conversion of chemical action into mechanical

CHAP, ii.] THE CONTRACTILE TISSUES. 99

work, were it not that in warm-blooded animals the heat given
out is not, as in the steam-engine, mere loss, but by keeping up the
animal temperature serves many subsidiary purposes. It might be
supposed that when in a contraction work is actually done, the
increase of temperature is less than when the same contraction
takes place without doing actual work, that is to say, that the
mechanical work is done at the expense of energy which otherwise
would go out as heat. Probable as this may seem it has not
yet been experimentally verified.

Of the exact nature of the chemical changes which underlie a
muscular contraction we know very little, the most important fact
being, that the contraction is not the outcome of a direct oxidation,
but the splitting up or explosive decomposition of some complex
substance. The muscle does consume oxygen, and the products of
muscular metabolism are in the end products of oxidation, but the
oxygen appears to be introduced not at the moment of explosion
but at some earlier date. There is no evidence of nitrogenous
products being given off as waste ; such nitrogenous crystalline
bodies as are present in muscle, kreatin, &c., may be regarded
rather as the wear-and-tear of the machine than as products of
the material consumed in the work. Yet it is hardly consonant
with what we know elsewhere, to suppose that the contraction
of a muscular fibre has for its essence the decomposition of a
non-nitrogenous substance ; and we may suppose that the explosion
does involve some nitrogenous products, which however are re-
tained within the tissue, and used up again. We may even go so
far as to entertain with Hermann the view that a single complex
substance, an hypothetical inogen, splits up partly into nitrogenous,
partly into non-nitrogenous factors, the former, possibly of the
nature of myosin, being rapidly built up again into new inogen,
while the latter, such as the carbonic acid, are discharged at once
from the muscle. But our knowledge of these matters is not yet
ripe enough for the construction of an adequate and wholly
satisfactory theory. It may be worth while to point out that
during even the most complete repose muscle is undergoing chemi-
cal changes, which, as far as we know, are the same in kind, and
only differ in degree from those characteristic of a contraction.
Thus carbonic acid is constantly being produced, as are probably
other substances, all being got rid of as they form, just as they are
got rid of in larger quantities during the repose which follows
contraction. Supposing the existence of a substance which splits
up into these various products, and which we may speak of as the
true contractile material, it is evident that this material being thus
constantly used up, must be as constantly repaired. Thus a stream
of chemical substances may be conceived of as flowing through
muscle, the raw material brought by the blood being gradually
converted into true contractile stuff, the breaking-down again of
which is- gentle and gradual so long as the muscle is at rest, but

7—2

100 MUSCULAR AND NERVOUS ACTION. [BOOK i.

becomes excessive and violent when a contraction takes place.
When rigor mortis sets in, the whole remaining contractile material
is decomposed.

While in muscle the chemical events are so prominent that we
cannot help considering a muscular contraction to be essentially a
chemical process, with electrical changes as attendant phenomena
only, the case is different with nerves. Here the electrical pheno-
mena completely overshadow the chemical. Our knowledge of the
chemistry of nerves is at present of the scantiest, and the little we
know as to the chemical changes of nervous substance is gained by
the study of the central nervous organs rather than of the nerves.
We find that the irritability of the former is closely dependent on
an adequate supply of oxygen, and we may infer from this that in
nervous as in muscular substance a metabolism, of in the main an
oxidative character, is the real cause of the development of energy;
and the axis-cylinder (which is probably the active element of a
nerve-fibre, the medulla being useful for its nutrition and protec-
tion only,) undoubtedly resembles in many of its chemical features
the substance of a muscular fibre. But we have as yet no satis-
factory experimental evidence that the passage of a nervous impulse
along a nerve is the result, like the contraction of a muscular fibre,
of chemical changes, and like it accompanied by an evolution of
heat.

On the other hand, the electric phenomena are so prominent
that some have been tempted to regard a nervous impulse as
essentially an electrical change. But it must be remembered that
the actual energy set free in a nervous impulse is so to speak in-
significant, so that chemical changes too slight to be recognized by
the means at present at our disposal would amply suffice to provide
all the energy set free. On the other hand, the rate of transmission
of a nervous impulse, putting aside other features, is alone sufficient
to prove that it is something quite different from an ordinary
electric current.

The curious disposition of the end-plates, and their remarkable
analogy with the electric organs which ai e found in certain animals,
has suggested the view that the passage of a nervous impulse from
the nerve-fibre into the muscular substance is of the nature of an
electric discharge. But these matters are too difficult and too
abstruse to be discussed here.

It may however be worth while to remind the reader that in
every contraction of a muscular fibre, the actual change of form is
preceded by invisible changes propagated all over the fibre and
occupying the latent period, and that these changes resemble in
their features the nervous impulse of which they are so to speak the
continuation rather than the contraction of which they are the
forerunners and to which they give rise. So that a muscle, even
putting aside the visible terminations of the nerve, is funda-
mentally a muscle and a nerve besides.

SEC. 7. OTHER FORMS OF CONTRACTILE TISSUE.

Unstriated Muscular Tissue. Our knowledge of the phenomena
of these structures is very imperfect since (in vertebrates) they do
not exist in isolated masses like the striated muscles, but occur as
constituents of complex organs, such as the intestine, ureter,
uterus, &c. They undergo rigor mortis : and what little informa-
tion we do possess concerning their chemical and physical features
leads us to believe that the processes which take place in them are
fundamentally identical with those occurring in striated muscle,
the two differing in degree rather than in kind. When stimulated,
they contract. If a stimulus, mechanical or electrical, be applied
to the intestine or ureter of a mammal, a circular contraction is
seen to take place at the spot stimulated. The contraction, which
is preceded by a very long latent period, lasts a very considerable
time, in fact several seconds, after which relaxation slowly takes
place. That is to say, over the circularly dispersed fibres of the
intestine (or ureter) at the spot in question there has passed a con-
traction-wave remarkable for its long latent period and for the slow-
ness of its development. From the spot so directly stimulated, the
contraction may pass as a wave (with a length of 1 cm. and a
velocity of from 20 to 30 millimetres a second in the ureter), along
the circular coat both upwards and downwards. The longitudinal
fibres at the spot stimulated are also thrown into contractions of
altogether similar character, and a wave of contraction may also
travel longitudinally along the longitudinal coat both upwards and
down wards. It is evident however that the wave of contraction of
which we are now speaking is in one respect different from the
wave of contraction treated of in dealing with striated muscle. In
the latter case the contraction-wave is a simple wave propagated

102\ I $*\ ;;'; ?';*»\ jStjJ-TJED MUSCLE. [BOOK i.

along the individual fibre ; in the case of the intestine or ureter,
the wave is complex, being the sum of the contraction-waves of
several fibres engaged in different phases and is propagated from
fibre to fibre, both in the direction of the fibres, as when the whole
circumference of the intestine is engaged in the contraction, or
when the wave travels longitudinally along the longitudinal coat,
and also in a direction at right angles to the axes of the fibres, as
when the contraction-wave travels lengthways along the circular
coat of the intestine, or when it passes across a breadth of the
longitudinal coat. Moreover, it is obvious that the contraction-
wave which passes along a single unstriated fibre differs from that
passing along a striated fibre, in the very great length both of its
latent period and of the duration of its contraction.

Waves of contraction thus passing along the circular and longi-
tudinal coats of the intestine constitute what is called peristaltic
action.

Like the skeletal muscles, whose nervous elements have been
rendered functionally incapable (p. 86), unstriated muscles are
much more sensitive to the making and breaking of a constant
current than to induction-shocks.

The unstriated muscles seem to be remarkably susceptible to
the influences of temperature. Thus the unstriated muscles of
the trachea are said not to contract at a temperature below 12°C.,
and are most active at a temperature above 21°C. So also the
movements of the intestine cease at a temperature below 19°C.

In striking contradistinction to what takes place in the striated
muscles, automatic movements are exceedingly common in struc-
tures built up of non-striated muscles ; these moreover exhibit a
great tendency to rhythmic action. Thus the peristaltic action of
the intestine and ureters, and the corresponding movements of the
uterus, are at once rhythmic, and largely automatic. What share
the nervous elements take in the automatism and the rhythm is
uncertain.

Cardiac Muscles. The most important features of this form of
contractile tissue will be studied when we come to deal with the
heart. It will be seen that they are intermediate between ordinary
skeletal and non-striated muscles.

Cilia. Ciliary movement consists in the rapid flexion (into a
sickle or hook-form) of the cilium and its less rapid return to its
previous straight form. The diminished velocity of the return
leads to the force of the ciliary action being exerted in the same
direction as the flexion. The cause of the flexion seems to be the
contraction of the cilium, and that of the return, an elastic reaction.
In the lower animals however many'varieties in the mode of move-
ment of cilia may be observed.

Various attempts to explain the movement by the presence of
special mechanisms at the base of the cilia have hitherto failed.
Some authors have attributed the movement to a' protoplasmic

CHAP, ii.] CONTRACTILE TISSUES. 103

contraction of the cell itself, the cilium acting merely as a minute
elastic rod ; and some such view as this is supported by the fact
that no movement has ever been observed in an isolated cilium.
It is difficult however to understand how the peculiar sickle-like
flexion of the cilium can be brought about unless the contractile
material is continued up into the cilium itself; and the tail of a
spermatozoon, which is practically a single cilium, may contract
even when separated from the head.

Ciliary movement appears therefore to differ from ordinary
muscular contraction chiefly in the size of the apparatus concerned.
The movement is rapid: thus Engelmann has estimated that
in the frog the flexions are repeated at least twelve times in a
second. The movement in fact is too rapid to be visible; it
can only be seen at a time when exhaustion and coming death
have begun to retard the action; Engelmann found that he was
first able to count them when their rapidity declined to eight in a
second.

In the vertebrate animal, cilia are, as far as we know, wholly
independent of the nervous system, and their movement is pro-
bably ceaseless. In such animals however as Infusoria, Hydrozoa,
&c. the movements in a ciliary tract may often be seen to stop
and go on again, to be now fast now slow, according to the needs
of the economy, and, as it almost seems, according to the will
of the creature ; indeed in some of these animals the ciliary move-
ments are clearly under the influence of the nervous system.

Observations with galvanic currents, constant and interrupted,
have not led to any satisfactory results, and, as far as we know at
present, ciliary action is most affected by changes of temperature and
chemical media. Moderate heat quickens the movements, but a
rise of temperature beyond a certain limit (about 40°C. in the case
of the pharyngeal membrane of the frog) becomes injurious ; cold
retards. Very dilute alkalis are favourable, acids are injurious.
An excess of carbonic acid or an absence of oxygen diminishes or
arrests the movements, either temporarily or permanently, according
to the length of the exposure. Chloroform or ether in slight doses
diminishes or suspends the action temporarily, in excess kills and
disorganises the cells.

Migrating Cells. We have already (p. 35) urged the view that
an amoeboid movement of a white corpuscle is essentially a form
of contraction.

All the circumstances which affect muscular contraction, heat,
absence or presence of oxygen and carbonic acid, &c., also affect
protoplasmic movements. The white corpuscles, like muscular
fibres, suffer rigor mortis, in which state they become spherical.

CHAPTER III.

THE FUNDAMENTAL PROPERTIES OF NERVOUS
TISSUES.

IN its simplest, and probably earliest form, a nerve is nothing more
than a thin strand of irritable protoplasm, forming the means of

FIG. 16. DIAGRAM TO ILLUSTRATE THE SIMPLEST FORMS OP A NERVOUS SYSTEM.

A. An ectoderm cell e.c., with its muscular process m.p., as in Hydra.

B. The ectoderm cell e.c. is connected with the muscle cell m.c. by means of the
primary motor nerve m.n.

C. The differentiated sensitive cell s.c. is connected by means of the sensory
nerve s.n. with the central cell c.c. , which is again connected by means of
the motor nerve m.n. with the muscle cell m.c.

CHAP, in] PBOPKRTIRS OF NERVOUS TISSUES. 105

vital communication between a sensitive ectodermic cell exposed
to extrinsic accidents, and a muscular, highly contractile cell (or a
muscular process of the same cell) buried at some distance from the
surface of the body, and thus less susceptible to external influences.
(Fig. 16, A, B.) If in Hydra, we imagine the junction of the
ectodermic muscular process with the body of its cell to be drawn out
into a thin thread (as is said to be the case in some other Hydrozoa),
we should have just such a primary nerve. Since there would be
no need for such a means of communication to be contractile and
capable of itself changing in form, but on the other hand an ad-
vantage in its remaining immobile, and in its dimensions being
reduced as much as possible consistent with the maintenance of
irritability, the primary nerve would in the process of development
lose the property of contractility in proportion as it became more
irritable, i.e. more apt in the propagation of the waves of disturb-
ance arising in the ectodermic cell.

We have already seen that automatism, i.e. the power of initiat-
ing disturbances or vital impulses, independent of any immediate
disturbing event or stimulus from without, is one of the fundamen-
tal properties of protoplasm. In simpler but less exact language,
such a mass of protoplasm as an amoeba, though susceptible in the
highest degree to influences from without, 'has a will of its own;'
it executes movements which cannot be explained by reference to
any changes in surrounding circumstances at the time being. A
hydra has also a will of its own ; and seeing that all the constituent
cells (beyond the distinction into ectoderm and endoderm) are alike,
we have no reason for thinking that the will resides in one cell
more than in another, but are led to infer that the protoplasm of
each of the cells (of the ectoderm at least) is automatic, the will
of the individual being the co-ordinated wills of the component
cells. In both Hydra and Amceba the processes concerned in
automatic or spontaneous impulses, though in origin independent
of, are subject to and largely modified by, influences proceeding
from without. Indeed the great value of automatic processes in a
living body depends on the automatism being affected by external
influences, and on the simple effects of stimulation being profoundly
modified by automatic action.

The next step of development beyond Hydra, is evidently to
differentiate the single (ectodermic) cell into two cells, of which
one, by division of labour, confines itself chiefly to the simple de-
velopment of impulses as the result of stimulation, leaving to the
other the task of automatic action, and the more complex trans-
formation of the impulses generated in itself. The latter, which
we may call the eminently automatic cell (though much of the
work which it has to do is of the kind we shall presently speak of
as reflex action), will naturally be withdrawn from the surface of
the body, while the other, which we may call the eminently sensitive
cell, will still retain its superficial position, so that it may most

106 SENSORY AND MOTOR NERVES. [BOOK i.

X readily be affected by all changes in the world without, Fig. 16 C.
And just as a primary motor nerve arises as a retained thread of
communication between a sensitive cell and its muscular process,
so a primary sensory nerve may be conceived of as arising as a
thread of communication between an eminently sensitive cell and
its twin the eminently automatic or central cell. By this arrange-
ment the sensitive cell, relieved of the heavy burden of spontaneous
action, is enabled to devote itself with greater vigour to the re-
ception of external influences ; while the automatic cell, no longer
hampered by the physical necessities of being which are imposed
on the superficial cell, exposed as this is to every wind and wave,
but secure in its internal retreat, is able with similar increased
energy, to devote itself either to the production of spontaneous
impulses, or to profoundly modifying the impulses which it receives
from the sensitive cell. Naturally the muscular process or muscu-
lar fibre would on the splitting of the original single cell remain in
connection with the more eminently automatic. We thus arrive
at that triple fundamental arrangement of a nervous system, in
its simplest form, viz. a sensitive cell on the surface of the body
connected by means of a sensory nerve with the internal automatic
central nervous cell, which in turn is connected by means of a
motor nerve with the muscular fibre-cell.

We have already seen that the physiology of the motor nerve
cannot without inconvenience be separated from that of the mus-
cular fibre. In the same way the physiology of the sensory nerve
cannot well be separated from those modifications of superficial
sensitive cells which constitute the organs of sense. We may add
that the special physiology of the central nervous cells can only
profitably be studied in connection with the sensory organs. In
the present chapter, therefore, we purpose to confine ourselves to
the consideration of the simplest and most general properties of
the central nervous cells.

These are arranged in the vertebrate body in two great systems :
the cerebro-spinal axis, and the various ganglia scattered over the
body ; we shall deal with such properties only as are more or less
common to the two systems. We may premise that as far as our
knowledge at present goes, the processes which are concerned in
the propagation of nervous impulses along a sensory nerve-trunk
are identical with those which take place in a motor nerve-trunk.
The phenomena of the natural nerve current, of the currents of
action during the passage of an impulse and of electrotons (and
these facts mark out, as we have seen, the limits of our information
on this matter,) are exactly the same, whether the piece of nerve-
trunk experimented on be a mixed nerve-trunk, or an almost
purely motor, or an almost purely sensory nerve-trunk, or an an-
terior or posterior nerve-root, or the special sensory nerve of a
particular sense, such as the optic nerve. In both sensory and
motor nerves the changes accompanying a nervous impulse are
transmitted equally well in both directions.

CHAP, in.] PROPERTIES OF NERVOUS TISSUES. 107

We seem justified in concluding that the events which occur in
a sensory nerve when it is an instrument of sensation, differ from
those which take place in a motor nerve when that is an instru-
ment of movement, only so far as the sensory impulses are gener-
ated by particular processes which bear the stamp of the sensory
cell in which they originated, while the motor impulses are gener-
ated by particular processes which bear the stamp of the central
nervous cells in which they in turn originated. All sensory im-
pulses appear to be tetanic iri nature, i. e. to be composed of a
series of constituent simple impulses ; and it is probable that
while the motor impulses which proceed from the central nervous
system to the muscles are composed of simple impulses repeated
with the same rapidity, and thus giving rise to the same muscular
note (p. 52), the sensory impulses which proceed from the periph-
eral sense organs to the central nervous system vary exceedingly as
to the way in which their constituent simple impulses are com-
bined. It is indeed possible that the complex sensory impulses
which give rise, for instance, to sight and touch respectively, may
differ only in the wave-length, so to speak, of their constituent
simple impulses, much in the same way as red light differs from
blue light.

In the scheme sketched out above, the same central nervous
cell is supposed to be engaged at once, both in originating auto-
matic actions and in modifying sensory impulses (i.e. impulses
proceeding from the superficial sensitive cells) previous to these
being passed on to the muscular fibre. It is evident that, where
two or more central nervous cells occur together, a further differen-
tiation would be of advantage : a differentiation into cells which,
though still susceptible of being influenced from without, should be
more especially restricted to automatic action, and into cells which
should forego their automatism for the sake of being more efficient
in modifying sensory impulses, with a view of transmuting them
into motor impulses, and so of giving rise to appropriate move-
ments. We thus gain the fundamental and primary differentiation
of the work of a central nervous system into automatic and into
reflex operations. These are very clearly manifested by the brain
and spinal cord, and probably also, though this is less certain, by
the sporadic ganglia.

Automatic Actions. In the vertebrate animal the highest form
of automatism, individual volition, with which conscious intelli-

fence is associated, is a function of certain parts of the brain,
'here are evidences of the existence in the brain of other forms of
automatism. All these will be considered in detail hereafter.

In the spinal cord separated from the brain by section of the
medulla oblongata, it becomes difficult to draw a line between
purely automatic and reflex actions. Thus, when we come to deal
with respiration, we shall see that while there can be no doubt that

108 AUTOMATIC ACTIONS. [BOOK i.

the muscular respiratory apparatus is kept at work by impulses
proceeding, in a rhythmic manner, from a group of nerve-cells, or
respiratory nervous centre, in the medulla oblongata it is an open
question whether those impulses, whose generation is certainly
modified by centripetal impulses passing to the centre along
various nerves, are absolutely automatic: i.e. whether they can
continue to make their appearance when no influences whatever
from without are brought to bear upon the centre. Similar doubts
hover round other automatic functions of the spinal cord. We
shall see hereafter reasons for speaking of the existence in the
medulla oblongata of a vaso-motor centre, that is of a group
of nerve-cells, whence impulses habitually proceed along the so-
called vaso-motor nerves to the muscular coats of the small
arteries, and keep these vessels in a state of semi-contraction or
tone. Here too it is doubtful whether these motor or efferent
impulses can be generated in the absence of all sensory or afferent
impulses. The posterior lymphatic hearts of the frog are connected
by the small tenth pair of spinal nerves with the grey matter of the
termination of the spinal cord, in such a manner that destruction of
that part of the spinal cord or section of the tenth nerves apparently
puts an end to the rhythmic pulsations of the lymphatic hearts. Here
it would seem as if rhythmic impulses were automatically generated
in the lower end of the cord, and proceeded along the efferent
nerves to the hearts, thus determining their rhythmic pulsations.
But if it be true, as asserted, that the rhythmic pulsations, though
arrested for a time by severance of the nerves, or destruction of the
lower end of the cord, are after a while resumed, then these too,
can be no longer counted among the automatic phenomena of the
cord. And so in other instances which we shall meet with in the
course of this book. The existence of automatism, then, even of
this comparatively simple character, is at least doubtful. That all
higher automatism comparable at least to that of the cerebral hemi-
spheres is absent, may be regarded as certain.

In the sporadic ganglia the evidence of automatic action seems
more clear, and yet is by no means absolutely decisive. The beat
of the heart is a typical automatic action : and, since the heart will
continue to beat for some time when isolated from the rest of the
body (that of a cold-blooded animal continuing to beat for hours,
or even days), its automatism must lie in its own structures.
When, however, we come to discuss the beat of the heart in detail,
we shall find that it is still an open question whether the automa-
tism is confined to the ganglia (either of the sinus venosus, auricles,
or auriculo-ventricular boundary), or shared in by the muscular
tissue : whether, in fact, the automatism is a muscular automatism
like that of a ciliated cell, or the automatism of a differentiated
nerve-ceil. And yet the heart is the case where the automatism of
the ganglia seems clearest.

The peristaltic contractions of the alimentary canal are auto-

CHAP. IIL] AUTOMATIC ACTIONS. 109

matic movements ; T,re cannot speak of them as being simply excited
by the presence of food in the canal, any more than we can say that
the beat of the heart is caused by the presence of blood in its
cavities. When absent they may be set agoing, and when present
may be stopped without any change in the contents of the canal.
They may, of course, be influenced by the contents, just as the beat
of the heart is, influenced by the quantity of blood in its cavities.
Throughout the intestines are found the nerve plexus of Auerbach
and that of Meissner ; to each or both of these the automatism of the
peristaltic movements has been referred. Yet in the ureter, whose
peristaltic waves of contraction closely resemble that of the intes-
tine, automatism is evident in the middle third of its length even
when completely isolated; in which region (in the rabbit at
least), according to Engelmann, ganglia, and indeed nerve-cells, are
entirely absent.

Thus, while in the spinal cord there is doubt whether purely
automatic, as stringently distinguished from reflex, actions take
place, in the case of the sporadic ganglia the uncertainty is whether
the clearly automatic movements of the organs with which the
ganglia are associated are due to the nerve-cells of the ganglia, or
to the muscular tissue itself.

Reflex Actions. The spinal cord offers the best and most
numerous examples of reflex action. In fact, reflex action may be
said to be, par excellence, the function of the spinal cord ; and the
grey matter of the spinal cord may be broadly considered as a
multitude of reflex centres. We have here to consider the cord
merely in its general aspects ; and must postpone the special con-
sideration of the particular forms of reflex action which it exhibits,
as they come before us in various connections, or until we have to
deal with it as part of the great central nervous machinery.

In its simplest form a reflex action is as follows. All the ma-
chinery it demands is (a) a sentient surface (external or internal),
connected by (6) a sensory, or — to adopt the more general and
better term — afferent nerve, with (c) a central nerve-cell or group
of connected nerve-cells, which is in relation by means of (d) a
motor, or efferent, nerve, or nerves, with (e) a muscle, or muscles,
or some other irritable tissue-elements, capable of responding by
some change in their condition, to the advent of efferent impulses.
The afferent impulses started in a, passing along 6, reach the
centre c, are there transmuted into efferent impulses, which,
passing along d, finally reach e, and there produce a cognisable
effect. The essence of a reflex action consists in the transmutation,
by means of the irritable protoplasm of a nerve-cell, of afferent into
efferent impulses. As an approach to a knowledge of the nature
of that transmutation, we jnay lay down the following propositions.

The number, intensity, character and distribution of the efferent
impulses are determined chiefly by the events which take place in the

110 REFLEX ACTIONS. [Boon i.

protoplasm of the reflex centre. It is not that the afferent impulse
is simply reflected in the nerve-cell, and so becomes with but little
change an efferent impulse. On the contrary, an afferent impulse
passing along a single sensory fibre may give rise to efferent im-
pulses passing along many motor nerves, and call forth the most
complex movements. An instance of this disproportion of the
afferent and efferent impulses is seen in the case where the contact
with the glottis of a foreign body so insignificant as a hair causes a
violent fit of coughing. Under such circumstances a slight contact
with the mucous membrane, such as could not possibly give rise to
anything more than few and feeble impulses, may cause the
discharge of so many efferent impulses along so many motor
nerves, that not only all the respiratory muscles, but almost all the
muscles of the body, are brought into action. Similar though less
striking instances of how incommensurate are afferent and efferent
impulses may be seen in most reflex actions. In fact, the afferent
impulse when it reaches the protoplasm of the nerve produces there
a series of changes, of explosive disturbances, which, except that the
nerve-cell does not in any way change its form, may be likened to
the explosive changes in a muscle on the arrival of an impulse along
its motor nerve1. The changes in a nerve-cell during reflex action,
we might say during any form of activity, far more closely resemble
the changes during a muscular contraction than those which
accompany the passage along a nerve of either an afferent or
efferent impulse. The simple passage along a nerve is accompanied
by little expenditure of energy ; it neither gains nor loses force to
any great extent as it progresses. The transmutation in a nerve-
cell is most probably (though the direct proofs are perhaps wanting)
accompanied by a large expenditure of energy, and a simple nervous
impulse in suffering the transmutation in a central nervous organ
may accumulate in intensity to a very remarkable extent, as in the
case of strychnia poisoning.

£^ The nature of the efferent impulses is, however, determined also
' by the nature of the afferent impulses. The nerve-centre remaining
in the same condition, the stronger or more numerous impulses will
give rise to the more forcible or more comprehensive movements.
Thus if the flank of a brainless frog be very lightly touched,
the only reflex movement which is visible is a slight twitching of
the muscles lying immediately underneath the spot of skin
stimulated. If the stimulus be increased, the movements will
spread to the hind-leg of the same side, which frequently will
execute a movement calculated to push or wipe away the stimulus.
By forcibly pinching the same spot of skin, or otherwise increasing
the stimulus, the resulting movements may be led to embrace the
fore-leg of the same side, then the opposite side, and finally, almost
all the muscles of the body. In other words, the disturbance

1 The question as to how far these processes in the central cells are connected
with the development of consciousness is here purposely passed over.

CHAP, in ] REFLEX ACTIONS. Ill

set going in the central nerve-cells, confined when the stimulus is
slight to a few nerve-cells and to a few nerve-fibres, overflows, so to
speak, when the stimulus is increased, on to a number of adjoining
and (we must conclude) connected cells, and thus throws impulses
into a larger and larger number of efferent nerves.

Certain relations may be observed between the sentient spot
stimulated and the resulting movement. In the simplest cases of
reflex action this relation is merely of such a kind that the muscles
thrown into action are those governed by a motor nerve which is the
fellow of the sensory nerve, the stimulation of which calls forth the
movement. In the more complex reflex actions of the brainless frog,
and in other cases, the relation is of such a kind that the resulting
movement bears an adaptation to the stimulus : the foot is with-
drawn from the stimulus, or the movement is calculated to push or
wipe away the stimulus. In other words, a certain purpose is
evident in the reflex action.

Thus in all cases, except perhaps the very simplest, the move-
ments called forth by a reflex action are exceedingly complex, com-
pared with those which result from the direct stimulation of a
motor trunk. When the peripheral stump of a divided sciatic
nerve is stimulated with the interrupted current, the muscles of
the leg are at once thrown into tetanus, continue in the same rigid
condition during the passage of the current, and relax immediately
on the current being shut off. When the same current is applied
for a second only, to the skin of the flank of a brainless frog, the
leg is drawn up and the foot rapidly swept over the spot irritated,
as if to wipe away the irritation ; but this movement is a complex
one, requiring the contraction of particular muscles in a definite
sequence, with a carefully adjusted proportion between the amounts
of contraction of the individual muscles. And this complex move-
ment, this balanced and arranged series of contractions, may be
repeated more than once as the result of a single stimulation of the
skin. When a deep breath is caused by a dash of cold water, the
same co-ordinated and carefully arranged series of contractions is
also seen to result, as part of a reflex action, from a simple stimulus.
And many more examples might be given.

In such cases as these, part of the complexity may be due to
the fact that the stimulus is applied to terminal sensory organs
and not directly to a nerve-trunk. As we shall see in speaking of
the senses, the impulses which are generated by the application of
a stimulus to a sensory organ are more complex than those which
result from the direct stimulation of a sensory nerve-trunk. Never-
theless, reflex actions of great if not of equal complexity may be
induced by stimuli applied directly to a nerve-trunk. We are
therefore obliged to conclude that in a reflex action, the processes
which are originated in the central nerve-cells by the arrival of even
simple impulses along afferent nerves may be highly complex; and
that it is the constitution and condition of the nerve-cells which

112 GANGLIA. [BOOK i.

determine the complexity and character of the movements which
are affected. In other words, the central nerve-cells concerned in
reflex actions are to be regarded as constituting a sort of molecular
machinery, the character of the resulting movements being deter-
mined by the nature of the machinery set going and its condition
at the time being, the character and amount of the afferent
impulses determining exactly what parts of and how far the central
machinery is thrown into action.

Actions of Sporadic Ganglia. Seeing that in the spinal cord
the nerve-cells undoubtedly are the central structures concerned in
the production of reflex action, it is only natural to infer that the
nerve-cells of the sporadic ganglia possess similar functions. Yet
the evidence of this is at present of very limited extent. With
regard to the ganglia on the posterior roots of the spinal nerves, all
the evidence goes to shew that these possess no power whatever of
reflex action. Of the larger ganglia visible to the naked eye, such
as the ciliary, otic, &c., we have indications of reflex action in
one only, viz. the submaxillary, and these indications are, as we
shall see in treating of the salivary glands, disputed. We have no
exact proof that the ganglia of the sympathetic chain, or of
the larger sympathetic plexuses, are capable of executing reflex
actions.

In fact, in searching for reflex actions in ganglia, we are
reduced to the small microscopic groups of cells buried in the
midst of the tissues to which they belong, such as the ganglia of
the heart, of the intestine, the bladder, &c. When a quiescent
frog's heart is stimulated by touching its surface, a beat takes
place. This beat is, as we shall see, a complex, co-ordinated move-
ment, very similar to a reflex action brought about by means of
the spinal cord; and in its production it is probable that the
cardiac ganglia are in some way concerned. When a quiescent
intestine is touched or otherwise stimulated, peristaltic action is
set up. Here again the ganglia present in the intestinal walls
may be supposed to play a part ; but this movement is much more
simple than the beat of the heart, and as regards it, and more
especially as regards the similar peristaltic action of the ureter, it
becomes difficult to distinguish between a movement governed by
ganglia, and one produced by direct stimulation of the muscular
fibres. We have seen that the great distinction between a reflex
action and a movement caused by direct stimulation of a nerve or
of a muscle lies in the greater complexity of the former ; and we
may readily imagine, that by continued simplification of the central
nervous machinery, the two might in the end become so much
alike as to be almost indistinguishable.

In the vertebrate animal then the chief seat of reflex action
is the spinal cord and brain. We say 'and brain' because, as
we shall see later on, the brain, in addition to its automatism,
is as busy a field of reflex action as the spinal cord.

CHAP, in.] PROPERTIES OF NERVOUS TISSUES. 113

Inhibition. In speaking of reflex action, we took it for granted
that the spinal cord was, at the moment of the arrival of the
afferent impulses at the central nerve-cells, in a quiescent state ;
that the nerve-cells themselves were not engaged in any auto-
matic action. We were justified in doing so, because as far as
the muscles generally of the body are concerned, the spinal cord
is in a brainless frog perfectly quiescent; an afferent impulse
reaching an ordinary nerve-cell of the spinal cord does not find
it preoccupied in discharging efferent impulses to the muscles with
which by means of nerve-fibres it is connected. But what happens
when afferent impulses reach a nerve-cell or a group of nerve-cells
already engaged in automatic action ?

We have already referred to an automatic respiratory centre
in the medulla oblongata. We may here premise, what we shall
shew more in detail hereafter, that the pneumogastric nerve is
peculiarly associated as an afferent nerve with this respiratory
centre. Now if the central end of the divided pneumogastric be
stimulated at the time when the respiratory centre is engaged
in its accustomed rhythmic action, sending out complex co-
ordinated impulses of inspiration (and of expiration) at regular
intervals, one of two things may happen, the choice of events
being determined by circumstances which need not be considered
here.

The most striking event, and the one which interests us now,
is that the respiratory rhythm is slowed or stopped altogether.
That is to say, afferent impulses which, under ordinary con-
ditions, would, on reaching a quiescent nervous centre, give rise
to movement, may, under certain conditions, when brought to
bear on an already active automatic nervous centre, check or stop
movement by interfering with the production of efferent impulses
in that centre. This stopping or checking an already present
action is spoken of as an ' inhibition ; ' and the effect of the
pneumogastric in this way on the respiratory centre is spoken of
as ' the inhibitory action of the pneumogastric on the respiratory
centre.'

The other event is that the respiratory rhythm is accelerated.
We shall hereafter discuss the explanation of the two events. We
may however state that according to one view the pneumo-
gastric contains among its afferent fibres two sets, which are either
of a different nature from each other, or are so differently connected
with the respiratory centre, that impulses arriving along one stop,
while those arriving along the other quicken, the action of that
centre. Hence, the one set are called ' inhibitory,' the other ' ac-
celerating' or 'augmenting' fibres. But we are concerned at present
only with the fact that the stimulation of a nerve may produce
either inhibitory or augmentative effects.

Similarly the vaso-motor centre in the medulla may, by im-
pulses arriving along various afferent tracts, be inhibited, during

jr. 8

114 INHIBITION. [BooK i. CHAP. in.

which the muscular walls of various arteries are relaxed ; or
augmented, whereby the tonic contraction of various arteries is
increased.

The most striking instance of inhibition is offered by the heart.
If when the heart is beating well and regularly, the pneumogastric
be divided, and the peripheral portion be stimulated even for a very
short time with an interrupted current, the heart is immediately
brought to a standstill. Its beats are arrested, it lies perfectly
flaccid and motionless, and it is not till after some little time that
it recommences its beat. Here again it is usually said that the
pneumogastric contains efferent cardio-inhibitory fibres, impulses
passing along which from the medulla stop the automatic actions
of the cardiac ganglia; the respiratory inhibitory fibres of the
same nerve are afferent, i.e. impulses pass along them up to the
medulla.

Though inhibition is most clearly seen in the case of automatic
actions, other actions may be similarly inhibited. Thus, as we
shall see later on, the reflex actions of the spinal cord may, by
appropriate means, be inhibited.

To sum up, then, the most fundamental properties of nervous
tissues.

Nerve-fibres are concerned in the propagation only, not in the
origination or transformation, of nervous impulses. As far as is at
present known, impulses are propagated in the same manner along
both sensory and motor nerves. Sensory impulses differ from
motor impulses inasmuch as the former are generated in sensory
organs and pass up to the central nervous cells, while the latter
pass from the central nervous cells to the muscles or to some
other peripheral organs.

The operations of the nerve-cells are either automatic or reflex.
In both an automatic and a reflex action, the diversity and the
co-ordination of the impulses are determined by the condition of
the nerve-cells. During the passage of an impulse along a nerve-
fibre, there is no augmentation of energy ; in passing through a
nerve-cell, the augmentation may be, and generally is, most con-
siderable.

When afferent impulses reach a centre already in action, the
activity of that centre may, according to circumstances, be either
depressed or exalted, may be ' inhibited ' or ' augmented.'

CHAPTEE IV.

THE VASCULAR MECHANISM.

IN order that the blood may be a satisfactory medium of com-
munication between all the tissues of the body, two things are
necessary. In the first place, there must be through all parts of
the body a flow of blood, of a certain rapidity and general con-
stancy. In the second place, this flow must be susceptible of both
general and local modifications. In order that any tissue or organ
may readily adapt itself to changes of circumstances (action,
repose, &c.), it is of advantage that the quantity of blood passing
to it should be not absolutely constant, but capable of variation.
In order that the material equilibrium of the body may be main-
tained as exactly as possible, it is desirable that the loading of the
blood with substances proceeding from the unwonted activity of
any one tissue, should be accompanied by a greater flow of blood
through some excretory or metabolic tissue by which these
substances may be removed. Similarly it is of advantage to
the body that the general flow of blood should in some circum-
stances be more energetic, and in others less so, than normal.

The first of these conditions is dependent on the mechanical
and physical properties of the vascular mechanism ; and the
problems connected with it are almost exclusively mechanical or
physical problems. The second of these conditions depends on
the intervention of the nervous system ; and the problems con-
nected with it are essentially physiological problems.

8—2

116 PHYSICAL PHENOMENA OF CIRCULATION. [BOOK i,

I. THE PHYSICAL PHENOMENA OF THE CIRCULATION.

The apparatus concerned in the Maintenance of the Normal
Flow is composed of the following factors :

1. The heart, beating rhythmically by virtue of its contractility
and intrinsic mechanisms, and at each beat discharging a certain
quantity of blood into the aorta. [For simplicity's sake we omit
for the present the pulmonary circulation.]

2. The arteries, highly elastic throughout, with a circular mus-
cular element increasing in relative importance as the arteries
diminish in size. It must not be forgotten that the muscular
element is also elastic.

When an artery divides, the united sectional area of the
branches is, as a rule, larger than the sectional area of the stem.
Thus the collective capacity of the arteries is continually (and
rapidly) increasing from the heart towards the capillaries. If all
the arterial branches were fused together, they would form a
funnel, with its apex at the aorta. The united sectional area of
the capillaries has been calculated by Vierordt to amount to
several (eight ?) hundred times that of the aorta.

3. The capillaries, channels of exceedingly small but variable
size. Their walls are elastic (as shewn by their behaviour during
the passage of blood-corpuscles through them), exceedingly thin
and permeable. They are permeable both in the sense of allowing
fluids to pass through them by osmosis, and also in the sense of
allowing white and red corpuscles to traverse them. The small
arteries and veins, which gradually pass into and from the capil-
laries properly so called, are similarly permeable, the more so, the
smaller they are.

4. The veins, less elastic than the arteries (the difference beiog
especially marked when both sets of vessels become distended) and
with a very variable muscular element. The united sectional area of
the veins diminishes from the capillaries to the heart, thus resem-
bling the arteries ; but the united sectional area of the venae cavae
at their junction with the right auricle is greater than that of the
aorta at its origin. (The proportion is nearly two to one.) The
total capacity of the veins is similarly much greater than that of
the arteries. The veins alone can hold the total mass of blood
which in life is distributed over both arteries and veins. Indeed
nearly the whole blood is capable of being received by what is
merely a part of the venous system, viz. the vena portaa and
its branches. Such veins as are for various reasons liable to a
reflux of blood from the heart towards the capillaries are provided
with valves.

SEC. 1. MAIN GENEBAL FACTS OF THE CIRCULATION.

1. The Capillary Circulation.

If the web of a frog's foot be examined with a microscope,
the blood, as judged of by the movements of the corpuscles, is seen
to be passing in a continuous stream from the small arteries
through the capillaries to the veins. The velocity is greater in the
arteries than in the veins, and greater in both than in the
capillaries. In the arteries faint pulsations, synchronous with the
heart's beat, are occasionally visible ; and not unfrequently varia-
tions in velocity and in the distribution of the blood, due to
causes which will be hereafter discussed, are witnessed from time
to time.

The flow through the smaller capillaries is very variable.
Sometimes the corpuscles are seen passing through the channel
in single file with great regularity; at other times, they may
be few and far between. Sometimes the corpuscle may remain
stationary at the entrance into a capillary, the channel itself being
for some little distance entirely free from corpuscles. Any one
of these conditions readily passes into another ; and, especially with
a somewhat feeble circulation, instances of all of them may be seen
in the same field of the microscope. It is only when the vessels
of the web are unusually full of blood that all the capillaries can be
seen equally filled with corpuscles. The long oval red corpuscle
moves with its long axis parallel to the stream, frequently rotating
on its long axis and sometimes on its short axis. The flexibility and
elasticity of a corpuscle are well seen when it is being driven into a

118 THE CAPILLARY CIRCULATION. [BOOK i.

capillary narrower than itself, or when it becomes temporarily lodged
at the angle between two diverging channels. The small mam-
malian corpuscles rotate largely as they are driven along.

In the web of the frog's foot the average velocity with which the
corpuscles move may be put down as about half a millimetre in a
second. In the human retina, the velocity of the capillary flow
has, by indirect methods, been estimated at "75 mm. per sec. The
movement of the blood in the capillaries is very slow, compared
with that in the arteries or even in the veins.

In the larger capillaries, and especially in the small arteries and
veins which permit the passage of several corpuscles abreast, it is
observed that the red corpuscles run in the middle of the channel,
forming a coloured core, between which and the sides of the
vessel all round is a layer, which has been called the ' inert layer,'
or better the 'plasmatic layer,' containing no red corpuscles. This
division into a plasmatic layer and an axial stream is due to the
fact that in any stream passing through a closed channel the
friction is greatest at the immediate sides, and diminishes towards
the axis. The corpuscles pass where the friction is least, in the
axis. A quite similar axial core is seen when any fine particles
are driven with a sufficient velocity in a stream of fluid through
a narrow tube. As the velocity is diminished the axial core
becomes less marked and disappears. In the plasmatic layer,
especially in that of the veins, are frequently seen white corpuscles,
sometimes clinging to the sides of the vessel, sometimes rolling
slowly along, and in general moving irregularly, and often in jerks.
The greater the velocity of the flow of blood, the fewer the white
corpuscles in the plasmatic layer, and with a very rapid flow they,
as well as the red corpuscles, may be all confined to the axial
stream. The presence of the white corpuscles in the plasmatic
layer has been attributed to their being specifically lighter than
the red corpuscles, it being affirmed that when fine particles of two
kinds, one lighter than the other, are driven through a narrow tube,
the heavier particles flow in the axis and the lighter in the more
peripheral portions of the stream. This however has been disputed,
and the phenomenon explained by the white corpuscles being dis-
tinctly more adhesive than the red, as is seen by the manner in
which they become fixed to the glass slide and cover-slip when
a drop of blood is mounted for microscopical examination. By
reason of this adhesiveness which possibly may vary with the
varying nutritive conditions of the corpuscles and of the blood-
vessels, the white corpuscles, it is urged, become temporarily
attached to the walls of the vessel, and consequently appear in
the plasmatic layer.

The resistance to the flow of blood thus caused by the friction
generated in so many minute passages, is one of the most important
physical facts in the circulation. In the large arteries the friction
is small; it increases as they divide, and receives a very great

CHAP, iv.] THE VASCULAR MECHANISM.

119

120 THE FLOW IN THE ARTERIES. [BOOK i.

FIG. 17. APPARATUS FOR INVESTIGATING BLOOD-PRESSURE.

At the upper right-hand corner, is seen, on an enlarged scale, the carotid artery,
clamped by the forceps bd, with the vagus nerve v lying by its side. The artery
has been ligatured at V and the glass cannula c has been introduced into the artery
between the ligature I' and the forceps bd, and secured in position by the ligature I.
The shrunken artery on the distal side of the cannula is seen at ca'.

p.b. is a box containing a bottle holding a saturated solution of sodium car-
bonate or a solution of sodium bicarbonate of sp. gr. 1083, and capable of being
raised or lowered at pleasure. The solution flows by the tube p.t. regulated by the
clamp c" into the tube t. A syringe, with a stop-cock, may be substituted for the
bottle, and attached at c". This indeed is in many respects a more convenient plan.
The tube t is connected with the leaden tube i, and the stopcock c with the mano-
meter, of which ra is the descending and ra' the ascending limb, and s the support.
The mercury in the ascending limb bears on its surface the float fl, a long rod
attached to which is fitted with the pen p, writing on the recording surface r. The
clamp cl. at the end of the tube t has an arrangement shewn on a larger scale
at the right hand upper corner.

The descending tube m of the manometer, and the tube t being completely filled
along its whole length with fluid to the exclusion of all air, the cannula c is filled
with fluid, slipped into the open end of the thick- walled india-rubber tube i, until it
meets the tube t (whose position within the india-rubber tube is shewn by the dotted
lines), and is then securely fixed in this position by the clamp cl.

The stopcocks c and c" are now opened, and the pressure-bottle raised or fluid
driven in by the syringe until the mercury hi the manometer is raised to the
required height. The clamp c" is then closed and the forceps bd removed from the
artery. The pressure of the blood in the carotid ca. is in consequence brought to
bear through t upon the mercury in the manometer.

addition in the minute arteries and capillaries. We may speak of
it therefore as the 'peripheral friction5 and the resistance which
it offers as the 'peripheral resistance.' It need perhaps hardly
be said that this peripheral friction not only opposes the flow of
blood through the capillaries themselves, but, working backwards
along the whole arterial system, has to be met by the heart at
each systole of the ventricle.

It is well known that when any portion of the skin is pressed
upon, it becomes pale and bloodless; this is due to the pressure
driving the blood out of the capillaries and minute vessels and
preventing any fresh blood entering into them. By carefully
investigating the amount of pressure necessary to prevent the
blood entering the capillaries and minute arteries of the web of the
frog's foot, or of the skin beneath the nail in man or elsewhere, the
internal pressure which the blood is exercising on the walls of the
capillaries and minute arteries and veins may be approximately
determined. In the frog's web this has been found to be equal to
about 7 or 11 mm. mercury.

2. The Flow in the Arteries.

When an artery is severed, the flow from the proximal section
is not equable, but comes in jets, which correspond to the heart-

CHAP, iv.] THE VASCULAR MECHANISM. 121

beats, though the flow does not cease between the jets. The blood
is ejected with considerable force; thus, in Dr Stephen Hales'
experiments, when the crural artery of a mare was severed, the jet,
even after much loss of blood, rose to the height of two feet. The
larger the artery and the nearer to the heart, the greater the force
with which the blood issues, and the more marked the intermittence
of the flow. The flow from the distal section may be very slight,
or may take place with considerable force and marked intermittence,
according to the amount of collateral communication.

Arterial pressure. If a mercury (or other) manometer,
Fig. 17m, m, be connected with a large artery, e.g. the carotid, in
such a way that while the blood is allowed to flow uninterruptedly
along the artery, there is free communication between the interior
of the artery and the proximal (descending) limb of the manometer,
the following facts are observed.

Immediately that communication is established between the
interior of the artery and the manometer, blood rushes from the
former into the latter, driving some of the mercury from the de-
scending limb into the ascending limb, and thus causing the level
of the mercury in the ascending limb to rise rapidly. This rise is
marked by jerks corresponding with the heart-beats. Having
reached a certain level, the mercury ceases to rise any more. It
does not, however, remain absolutely at rest, but undergoes oscilla-
tions ; it keeps rising and falling. Each rise, which is very slight
compared with the total height to which the mercury has risen,
has the same rhythm as the systole of the ventricle. Similarly,
each fall corresponds with the diastole.

If a float, swimming on the top of the mercury in the ascending
limb of the manometer, and bearing a brush or other marker, be
brought to bear on a travelling surface, some such tracing as that
represented in Fig. 18 will be described. Each of the smaller

FIG. 18. TRACING OF ARTERIAL PRESSURE WITH A MERCURY MANOMETER.

The smaller curves p p are the pulse-curves. The space from r to r embraces
a respiratory undulation. The tracing is taken from a dog, and the irregularities
visible in it are those frequently met with in this animaL

curves (p, p) corresponds to a heart-beat, the rise corresponding to
the systole and the fall to the diastole of the ventricle. The larger
undulations (r, r) in the tracing, which are respiratory in origin,

122 ARTERIAL PRESSURE, [BOOK i.

will be discussed hereafter. This observation teaches us that the
blood, as it is passing along the carotid artery, is capable of support-
ing a column of mercury of a certain height (measured by the
difference of level between the mercury in the descending limb,
and that in the ascending limb, of the manometer), when the
mercury is placed in direct communication with the side of the
stream of blood. In other words, the blood, as it passes through
the artery, exerts a lateral pressure on the sides of the artery, equal
to so many millimeters of mercury. In this lateral pressure we
have further to distinguish between the slighter oscillations corre-
sponding with the heart-beats, and a mean pressure above and
below which the oscillations range. A similar mean pressure with
similar oscillations is found, when any artery of the body is
examined in the same way. In all arteries the blood exerts a
certain pressure on the walls of the vessels which contain it. This
is generally spoken of as arterial pressure or arterial tension, and the
pressure in the aorta of any animal is usually spoken of as its blood-
pressure.

Description Of Experiment. The carotid, or other vessel, is laid
bare, clamped in two places and divided between the clamps. Into the
cut ends is inserted a hollow |— piece of the same bore as the artery, the
cross portion forming the continuation of the artery. The other portion
is connected by means of a non-elastic flexible tube with the descending
limb of the manometer. In order to avoid loss of blood, fluid is in-
jected into the flexible tube until the mercury in the manometer stands
a very little below what may be beforehand guessed at as the probable
mean pressure. The fluid chosen is a saturated solution of sodium car-
bonate or a solution of sodium bicarbonate of sp. gr. 1083, with a view to
hinder the coagulation of the blood in the tube. When the clamps are
removed from the artery the blood rushes through the cross of the f— piece.
Some passes into the side limb of the {— piece and continues to do so
until the mean pressure is quite reached. Thenceforward there is no more
escape ; but the pressure continues in the interior of the |— piece, is
transmitted along the connecting tube to the manometer, and the mercury
continues to stand at a height indicative of the mean pressure with
oscillations corresponding to the heart's beats. Practically the use of
the |— piece is found inconvenient. Accordingly the general custom is
to ligature the artery, to place a clamp on the vessel on the proximal
side of the ligature, and to introduce a straight cannula, Fig. 17 c,
connected with the manometer, into the artery between the ligature and
the clamp, and to secure it in that position. In this case, on loosing the
clamp, the whole column of blood in the artery is brought to bear on
the manometer, and the tracings taken illustrate the lateral pressure
not of the artery in which the cannula has been placed, hut of the vessel
(aorta &c. as the case may be) of which it is itself a branch.

Tracings of the movements of the column of mercury in the mano-
meter may be taken either on a smoked surface of a revolving cylinder
(Fig. 1), or by means of a brush and ink on a continuous roll of paper,
as iii the more complex kymograph (Fig. 19).

CHAP, iv.] THE VASCULAR MECHANISM.

123

In such a mercury manometer, the inertia of the mercury obscures
many of the features of the minor curves caused by the heart-beats.
When therefore these, rather than variations in the mean pressure, are
being studied, other methods have to be adopted.

The average pressure of the blood in the same body is greatest
in the largest arteries, and diminishes as the arteries get less ; but
the fall is a very gradual one until the smallest arteries are reached,
in which it becomes very rapid. In the carotid of the horse, the
mean arterial pressure varies from 150 to 200 mm. of mercury ; of
the dog from 100 to 175 ; of the rabbit from 50 to 90. In the
carotid of man it probably amounts to 150 or 200.

FIG. 19. LARGE KYMOGRAPH WITH CONTINUOUS ROLL OF PAPER.

The clock-work machinery, some of the details of which are seen, unrolls the
paper from the roll C, carries it smoothly over the cylinder B, and then winds it up
into the roll A.

Two electromagnetic markers are seen in the position in which they record their
movements on the paper as it - travels over B. The manometer, or any other
recording instrument used, can be fixed either in the notch immediately in front of
B or in any other position that may be desired.

Since in all arteries the blood is pressing on the arterial walls
with some considerable force, all the arteries must be in a state of
permanent distension, so long as blood is flowing through them
from the heart. When the blood-current is cut off, as by a
ligature, this expansion or distension disappears.

Not only is there a permanent expansion corresponding to the
mean pressure, but just as the mercury in the manometer rises
above the level of mean pressure at each systole of the heart, and

124 THE VELOCITY OF THE FLOW. [BOOK i.

falls below it at each diastole, so at any spot in the artery there is
for each heart-beat a temporary expansion succeeded by temporary
contraction, the diameter of the artery in its temporary expansions
and contractions oscillating, in correspondence with the oscillations
of the manometer, beyond and within the diameter of permanent
expansion. These temporary expansions constitute what is called
the pulse, and will be discussed more fully hereafter.

The velocity of the flow. When even a small artery is severed
a considerable quantity of blood escapes from the proximal cut end
in a very short space of time. That is to say, the blood moves in
the arteries from the heart to the capillaries, with a very con-
siderable velocity. By various methods, this velocity of the blood-
current has been measured at different parts of the arterial system;
the results, owing to imperfections in the methods employed, cannot
be regarded as satisfactorily exact, but may be accepted as approxi-
mately true. The velocity of the arterial stream is greatest in
the largest arteries, and diminishes from the heart to the capillaries,
pari passu with the increase of the width of the bed, i.e. with the
increase of the united sectional area.

Methods. The Hsemadromometer of Volkmann. An artery, e.g. a
carotid, is clamped in two places, and divided between the clamps. Two
cannulse, of a bore as nearly equal as possible to that of the artery, or of
a known bore, are inserted in the two ends. The two cannulse are con-
nected by means of two stop-cocks, which work together, with the two
ends of a long glass tube, bent in the shape of a U, and filled with normal
saline solution, or with a coloured innocuous fluid. The clamps on the
artery being released, a turn of the stop-cocks permits the blood to enter
the proximal end of the long U tube, along which it courses, driving the
fluid out into the artery through the distal end. Attached to the tube is
a graduated scale, by means of which the velocity with which the blood
flows along the tube may be read off. Even supposing the cannulss to
be of the same bore as the artery, it is evident that the conditions of
the flow through the tube are such as will only admit of the result thus
gained being considered as an approximative estimation of the real
velocity in the artery itself.

The Rheometer (Stromuhr) of Ludwig. This consists of two glass
bulbs A and 2i, Fig. 20, communicating above with each other and with
the common tube C by which they can be filled. Their lower ends are
fixed in the metal disc Z>, which can be made to rotate, through two
right angles, round the lower disc E. In the upper disc are two holes
a and b continuous with A and B respectively, and in the lower disc are
two similar holes a' and b', similarly continuous with the tubes H and G.
Hence, in the position of the discs shewn in the figure, the tube G is
continuous through the two discs with the bulb A and the tube H with
the bulb B. On turning the disc D through two right angles the tube G
becomes continuous with B instead of A, and the tube-ZT with .4 instead
of B. There is a further arrangement, omitted from the figure for the
sake of simplicity, by which when the disc D is turned through one

CHAP. iv.J THE VASCULAR MECHANISM. 125

instead of two right angles from either of the above positions, G becomes
directly continuous with H, both being completely shut off from the
bulbs.

FlG. 20. DIAGRAMMATIC REPRESENTATION OF LUDWIG'S SlEOMTJHR.

The ends of the tubes H and G are made to fit exactly into two
cannulae inserted into the two cut ends of the artery about to be experi-
mented upon, and having a bore as nearly equal as possible to that of
the artery.

The method of experimenting is as follows. The disc D, being placed
in the intermediate position, so that a and b are both cut off from
a and b', the bulb A is filled with pure olive oil up to the mark a?, and
the bulb B, the rest of A, and the junction C, with defibrinated blood;
and C is then clamped. The tubes H and G are also filled with de-
fibrinated blood, and G is inserted into the cannula of the central, H
into that of the peripheral, end of the artery. On removing the clamps
from the artery the blood flows through G to ff, and so back into the
artery. The observation now begins by turning the disc D into the
position shewn in the figure ; the blood then flows into A, driving the
oil there contained out before it into the bulb B, in the direction of the
arrow, the defibrinated blood previously present in B passing by H into
the artery, and so into the system. At the moment that the blood is
seen to rise to the mark cc, the disc D is with all possible rapidity turned
through two right angles; and thus -the bulb B, now largely filled with
oil, placed in communication with G. The blood-stream now drives the
oil back into A, and the new blood in A through H into the artery. As
soon as the oil has wholly returned to its original position, the disc is
again turned round, and A once more placed in communication with G,
and the oil once more driven from A to B. And this is repeated several
times, indeed generally until the clotting of the blood or the admixture
of the oil with the blood puts an end to the experiment. Thus the flow
of blood is used to fill alternately with blood or oil the space of the bulb A,
whose cavity as far as the mark x has been exactly measured; hence if
the number of times in any given time the disc D has to be turned round
be known, the number of times A has been filled is also known, and
thus the quantity of blood which has passed in that time through the

126 MEASUREMENTS OF VELOCITY OF FLOW. [BOOK r.

cannula connected with the tube G is directly measured. For instance,
supposing that the quantity held by the bulb A when filled up to the
mark x is 5 c.c., and supposing that from the moment of allowing the
first 5 c.c. of blood to begin to enter the tube to the moment when the
escape of the last 5 c.c. from the artery into the tube was complete, 100
seconds had elapsed, during which time 5 c.c. had been received 10
times into the tube from the artery (all but the last 5 c.c. being returned
into the distal portion of the artery), obviously '5 c.c. of blood had
flowed from the proximal section of the artery in one second. Hence
supposing that the diameter of the cannula (and of the artery, they
being the same) were 2 mm., with a sectional area therefore of 3'H
square mm., an outflow through the section of -o c.c. or 500 c.mm. in a
second would give (£JJ), a velocity of about 159 mm. in a second.

The Hsematachometer of Vierordt is constructed on the principle of
measuring the velocity of the current by observing the amount of devia-
tion undergone by a pendulum, the free end of which hangs loosely in
the stream. A square or rectangular chamber, one side of which is of
glass and marked with a graduated scale in the form of an arc of a circle,
is connected by means of two short tubes with the two cut ends of an
artery; the blood consequently flows from the proximal (central)
portion of the artery through the chamber into the distal portion of the
artery. Within the chamber and suspended from its roof is a short
pendulum, which when the blood-stream is cut off from the chamber
hangs motionless in a vertical position, but when the blood is allowed to
flow through the chamber, is driven by the force of the current out of
its position of rest. The pendulum is so placed that a marker attached
to its free end travels close to the inner surface of the glass side along
the arc of the graduated side. Hence the amount of deviation from a
vertical position may easily be read off on the scale from the outside.
The graduation of the scale having been carried out by experimenting
with streams of known velocity, the velocity can at once be calculated
from the amount of deviation.

An instrument based on the same principle has been invented by
Chauveau and improved by Lortet. In this the part which corresponds
to the pendulum in Vierordt's instrument is prolonged outside the
chamber, and thus the portion within the chamber is made to form the
short arm of a lever, the fulcrum of which is at the point where the wall
of the chamber is traversed and the long arm of which projects outside.
A somewhat wide tube, the wall of which is at one point composed of
an india-rubber membrane, is introduced between the two cut ends of an
artery. A long light lever pierces the india-rubber membrane. The
short expanded arm of this lever projecting within the tube is moved on
its fulcrum in the india-rubber ring by the current of blood passing
through the tube, the greater the velocity of the current, the larger being
the excursion of the lever. The movements of the short arm give rise
to corresponding movements in the opposite direction of the long arm
outside the tube, and these, by means of a marker attached to the end
of the long arm, may be directly inscribed on a recording surface. This
instrument is very well adapted for observing changes in the velocity of
the flow. In determining actual velocities, for which purpose it has to
be experimentally graduated, it is not so useful.

CHAP, iv.] THE VASCULAR MECHANISM. 127

In the horse, Volkmann found the velocity of the stream
to be in the carotid artery about 300 mm., in the maxillary artery
165 mm., and in the metatarsal artery 56 mm. in the second.
Chauveau determined the velocity in the carotid of the horse to
vary from 520 to 150 mm. per sec. at each beat of the heart, flow-
ing at the former rate during the height of each pulse-expansion,
and at the latter in the interval between each two beats. Ludwig
and Dogiel found the velocity in the dog and in the rabbit to vary
within very wide limits, not only in different arteries, but in the
same artery under different circumstances. Thus while in the
carotid of the rabbit it may be said to vary from 100 to 200 mm.
per sec., and in the carotid of the dog from 200 to 500 mm. per sec.,
both these limits were frequently passed.

3. The Flow in the Veins.

When a vein is severed, the flow from the distal cut end (i.e. the
end nearest the capillaries) is continuous, the blood is ejected with
comparatively little force, and with no great velocity.

When a vein is connected with a manometer, the lateral pressure
is found to be very small ; it is greater in the veins farther from
the heart than in those nearer the heart,. In the former it is much
less than that of the small arteries, and in the latter amounts only
to a few millimetres of mercury. Indeed in the immediate neigh-
bourhood of the heart the pressure may (during the inspiratory
movement) become negative, i.e. when the manometer is brought
into connection with the interior of the vein, the mercury in the
distal limb falls, instead of, as in the case of an artery, rising.

In the case of most veins, under ordinary circumstances the
mercury of a manometer connected with a vein does not shew any
of those pulse -oscillations which are so striking in the arteries. As
a general rule the pulse is seen on the arterial side only of the j J^
capillaries, though in special cases, under conditions which we shall
study presently, it may make its way through the capillaries from
the arteries to the small veins ; and it is probable that in general
a slight impulse does make its way right through the capil-
laries, but so feeble that it cannot be recognised by ordinary in-
struments save in special cases. Moreover, in the great veins near
the heart, under certain circumstances at all events, the movements
of that organ may make themselves felt as a so-called 'venous pulse'
transmitted in a backward direction along the veins from the heart.
But these exceptional instances and these recurrent oscillations do
not invalidate the truth of the general statement that the pulse is
absent from the veins. The exact determination of venous pressure
is attended with great experimental difficulties, and our knowledge in

128 THE FLOW IN THE VEINS. [BOOK i.

this direction is very incomplete ; but in all probability the pressure
in a vein varies within much wider limits than does the pressure in
the corresponding artery.

In the small veins the velocity of the current, measured in the
same way as in the case of the arteries, is very slight. It increases
• 'in the larger veins, corresponding to the diminution of the area of
'the bed' ; it is about 200 mm. per sec. in the jugular vein of the
dog.

Thus the flow in the veins presents strong contrasts with that
in the arteries. In the arteries, even in the smallest branches,
there is a considerable mean pressure. In the veins, even in the
small veins where it is largest, the mean pressure is very slight.
In other words, there is always a difference of pressure tending to
make the blood flow continuously from the arteries into the veins.
\^^A pulse is present in the arteries, but, with certain exceptions,
absent in the veins. The velocity of the stream of blood in the
tjj arteries is considerable ; in the small veins it is much less, but it
increases in the larger trunks; for in both arteries and veins it
corresponds with the area of the bed, diminishing in the former
from the heart to the capillaries, and increasing in the latter from
the capillaries to the heart.

Hydraulic Principles of the Circulation.

All the above phenomena are the simple results of an intermit-
tent force (like that of the systole of the ventricle) working in a
closed circuit of branching elastic tubes, so arranged that while the
individual tubes first diminish (from the heart to the capillaries)
and then increase (from the capillaries to the heart), the area of
the bed first increases and then diminishes, the tubes together
thus forming two cones placed base to base at the capillaries, with
their apices converging to the heart. To this it must be added
that the friction in the small arteries and capillaries, at the junction
of the bases of the cones, offers a very great resistance to the flow
of the blood through them. It is this peripheral resistance (in the
minute arteries and capillaries, for the resistance offered by the
friction in the larger vessels may, when compared with this, be
practically neglected), reacting through the elastic walls of the
arteries upon the intermittent force of the heart, which gives the
circulation of the blood its peculiar features.

Circumstances determining the character of the flow. When
fluid is driven by an intermittent force, as by a pump, through a
perfectly rigid tube (or system of tubes), there escapes at each
stroke of the pump from the distal end of the system just as much
fluid as enters it at the proximal end. The escape moreover takes
place at the same time as the entrance, since the time taken up by

CHAP, iv.] THE VASCULAR MECHANISM. 129

the transmission of the shock is so small, that it may be neglected.
This result remains the same when any resistance to the now is
introduced into the system. The force of the pump remaining the
same, the introduction of the resistance undoubtedly lessens the
quantity issuing at the distal end at each stroke, but it does so
simply by lessening the quantity entering at the proximal end;
the income and outgo remain equal to each other, and occur at
almost the same time. And what is true of the two ends, is also
true of any part of the course of the system, so far, at all events, as
the following proposition is concerned, that in a system of rigid
tubes, either with or without an intercalated resistance, the flow
caused by an intermittent force is, in every part of the tubes,
intermittent synchronously with that force.

In a system of elastic tubes in which there is little resistance to
the progress of the fluid, the flow caused by an intermittent force
is also intermittent. The outgo being nearly as easy as the
income, the elasticity of the walls of the tubes is scarcely at all
called into play. These behave practically like rigid tubes. When,
however, sufficient resistance is introduced into any part of the
course, the fluid, being unable to pass by the resistance as rapidly
as it enters the system from the pump, tends to accumulate on the
proximal side of the resistance. This it is able to do by expanding
the elastic walls of the tubes. At each stroke of the pump a
certain quantity of fluid enters the system at the proximal end.
Of this only a fraction can pass through the resistance during the
stroke. At the moment when the stroke ceases, the rest still
remains 011 the proximal side of the resistance, the elastic tubes
having expanded to receive it. During the interval between this
and the next stroke, the distended elastic tubes, striving to return
to their natural undistended condition, press on this extra quantity
of fluid which they contain and tend to drive it past the resistance.
Thus in the rigid system (and in the elastic system without
resistance) there issues, from the distal end of the system, at each
stroke, just as much fluid as enters it at the proximal end, while
between the strokes there is perfect quiet. In the elastic system
with resistance, on the contrary, the quantity which passes the
resistance is only a fraction of that which enters the system from
the pump, the remainder or a portion of the remainder continuing
to pass during the interval between the strokes. In the former
case, the system is no fuller at the end of the stroke than at the
beginning; in the latter case there is an accumulation of fluid
between the pump and the resistance, and a corresponding dis-
tension of that part of the system, at the close of each stroke — an
accumulation and distension, however, which go on diminishing
until the next stroke comes. The amount of fluid thus remaining
after the stroke will depend on the amount of resistance in relation
to the force of the stroke, and on the distensibility of the tubes ;
and the amount which passes the resistance before the next stroke

F.

130 INTERMITTENT FLOW. [BOOK T.

will depend on the degree of elastic reaction of which the tubes
are capable. Thus, if the resistance be very considerable in
relation to the force of the stroke, and the tubes very distensible,
only a small portion of the fluid will pass the resistance, the
greater part remaining lodged between the pump and the re-
sistance. If the elastic reaction be great, a large portion of this
will be passed on through the resistance before the next stroke
comes. In other words, the greater the resistance (in relation to
the force of the stroke), and the more the elastic force is brought
into play, the less intermittent, the more nearly continuous, will be
the flow on the far side of the resistance.

If the first stroke be succeeded by a second stroke before its
quantity of fluid has all passed by the resistance, there will be an
additional accumulation of fluid on the near side of the resistance,
an additional distension of the tubes, an additional strain on their
elastic powers, and, in consequence, the flow between this second
stroke and the third will be even more marked than that between
the first and the second, though all three strokes were of the same
force, the addition being due to the extra amount of elastic force
called into play. In fact, it is evident that, if there be a sufficient
store of elastic power to fall back upon, by continually repeating
the strokes a state of things will be at last arrived at, in which the
elastic force, called into play by the continually increasing dis-
tension of the tubes on the near side of the resistance, will be
sufficient to drive through the resistance, between each two strokes,
just as much fluid as enters the near end of the system at each
stroke. In other words, the elastic reaction of the walls of the
tubes will have converted the intermittent into a continuous flow.
The flow on the far side of the resistance is in this case not the
direct result of the strokes of the pump. All the force of the
pump is spent, first in getting up, and afterwards in keeping up,
the over-distension of the tubes on the near side of the resistance ; the
cause of the continuous flow lies in the over-distension of the tubes
which leads them to empty of themselves into the far side of the
resistance, at such a rate, that they discharge through the resistance
during a stroke and in the succeeding interval just as much as
they receive from the pump by the stroke itself.

This is exactly what takes place in the vascular system. The
friction in the minute arteries and capillaries presents a considerable
resistance to the flow of blood through them into the small veins.
In consequence of this resistance, the force of the heart's beat is
spent in maintaining the whole of the arterial system in a state
of over-distension, as indicated by the arterial pressure. The over-
distended arterial system is, by the agency of its elastic walls, con-
tinually emptying itself by overflowing through the capillaries into
the venous system, overflowing at such a rate, that just as much
blood passes from the arteries to the veins during each systole
and its succeeding diastole as enters the aorta at each systole.

CHAP, iv.] THE VASCULAR MECHANISM. 131

I It cannot be too much insisted upon that the whole arterial
system is over-distended. This is what is meant by the higlr
arterial pressure. On the other hand, the veins are much less
distended. This is shewn by the low venous pressure. The dis-
tended arteries are continually striving to pass their surplus in
a continuous stream through the capillaries into the veins, so as
to bring both venous and arterial pressure to the same level. As
continually the heart by its beat is keeping the arteries distended,
and thus maintaining the difference between the arterial and
venous pressure, and thus preserving the steady capillary stream.
When the heart ceases to beat, the arteries do succeed in emptying
their surplus into the veins, and when the pressure on both sides of
the capillaries is thus equalized, the flow through the capillaries
ceases.

In the facts just discussed, it makes no essential difference
whether the outflow on the far side of the resistance be an open
one, or whether, as is the case in the vascular system, the fluid be
returned to the pump, provided only that the resistance offered to
that return be sufficiently small. We shall see, in speaking of the
heart, that, so far from there being any resistance to the flow of
blood from the great veins into the auricle, the flow is favoured by
a variety of circumstances. We have seen moreover that, besides
the very sudden decrease in the immediate neighbourhood of the
capillaries, there is in passing along the whole vascular system from
the aorta to the venae cavse a gradual fall of pressure. A little
consideration shews that this must be the case. After what has
been said it is obvious that the movement of the blood may be
compared to that of a body of fluid, driven by pressure from the
ventricle through the vessels to its outflow in the auricle. Were the
pressure a continuous one, and were there no peripheral resistance,
there would be a gradual fall of pressure, from the part farthest
from the outfall, viz. the aorta, to the part nearest the outfall, viz.
the venaa cavae. The introduction of the peripheral resistance and
its attendant phenomena gives rise to the feature of a very sudden
and marked fall in the capillary region, but leaves untouched the
gradual character of the fall in the rest of the course, from the
aorta to the minute arteries, and from the minute veins to the
venae cavae.

To recapitulate : there are three chief factors in the mechanics
of the circulation, (1) the force and frequency of the heart-beat, (2)
the peripheral resistance, (3) the elasticity of the arterial walls.
These three factors, in order to produce a normal circulation, must
be in a certain relation to each other. A disturbance of these
relations brings about abnormal conditions. Thus, if the peripheral
resistance be reduced beyond certain limits, while the force and
frequency of the heart remain the same, so much blood passes
through the capillaries at each stroke of the heart that there is
not sufficient left behind to distend the arteries, and bring their

9—2

132 VARIATIONS IN VELOCITY. [BOOK i.

elasticity into play. In this case the intermittence of the arterial
flow is continued on into the veins. An instance of this is seen in
the experiments on the sub-maxillary gland, where sometimes the
resistance offered by the minute arteries of the gland is so much
lowered, that the pulse is carried right through the capillaries, and
the blood in the veins of the gland pulsates1. A like result occurs
when, the peripheral resistance remaining the same, the frequency
of the heart's beat is lowered. Thus the beats may be so
infrequent that the whole quantity sent on by a stroke has time to
escape before the next stroke comes. Lastly, if, while the heart's
beat and the peripheral resistance remain the same, the arterial
walls become more rigid, the arteries will be unable to expand
sufficiently to retain the surplus of each stroke or to exert sufficient
elastic reaction to carry forward the stream between the strokes ;
land in consequence more or less intermittence will become manifest.

Circumstances determining the velocity of the flow. We

have seen that the velocity of the blood-stream diminishes from
the aorta to the capillaries, and increases from the capillaries to
the great veins. Thus in the dog the velocity in the great arteries
may be stated at from 300 to 500 mm., in the capillaries at less
than 1 mm. ('5 to *75 mm.), and in the large veins at about 200 mm.
in a sec. In fact, the greater part of the time of the circuit is
taken up in the capillary region. An iron salt, injected into the
jugular vein of one side of the neck of a horse, makes its appear-
ance in the blood of the jugular vein of the other side in about
30 seconds.

Bering's mean result in the horse was 27'G sees. In the dog
Vierordt found it to be 15*2 sees.; in the rabbit 7 sees.

Without laying too much stress on this experiment, it may be
taken as a fair indication of the time in which the whole circuit
may be completed. It takes about the same time to pass through
about 20 mm. of capillaries. Hence, if any corpuscle had in its
circuit to pass through 10 mm. of capillaries, half the whole time
of its journey would be spent in the narrow channels of the

.capillaries. Since, however, the average length of a capillary
is about '5 mm., about one second is spent in the capillaries. In-
asmuch as the purposes served by the blood are chiefly carried out
in the capillaries, it is obviously of advantage that its stay in them

I should be prolonged.

The local differences in the velocity of the stream are directly
dependent on the area of the 'bed.' When a fluid is driven
by a uniform pressure through a narrow tube with an enlarge-
ment in the middle, the velocity of the stream diminishes in
the enlargement, but increases again when the tube once more
narrows. So a river slackens speed in a ' broad' but rushes on

1 See Book i. cap. i. sec. 2, on the Secretion of the Digestive Juices.

CHAP, iv.] THE VASCULAR MECHANISM. 133

rapidly again when the banks close in. Exactly in the same way
the velocity of the blood-stream slackens from the aorta to the
capillaries corresponding with the increased total bed, but hurries
on again as the numerous veins are gathered into the smaller bed
of the venae cavse. The loss of velocity in the capillaries, as com- '
pared with the arteries, is not due to there being so much more ;
friction in the narrow channels of the former than in the wide j
canals of the latter. For the peripheral resistance caused by the j
friction in the capillaries and small arteries is an obstacle not only
to the flow of blood through these small vessels where the resist-
ance is actually generated, but also to the escape of the blood from
the large into the small arteries, and indeed from the heart intoi
the large arteries. It exerts its influence along the whole arterial*
tract. And it is obvious that if it were this peripheral resistance
which checked the flow in the capillaries, there could be no re- [
covery of velocity along the venous tract. The rapidity of the flow
in arteries, capillaries, and veins, is in each case determined by the
total sectional area of the channels. There is, however, a loss of
velocity on the whole course. At each stroke as much blood enters
the right auricle as issues from the left ventricle ; but the sectional
area of the venae cavae is greater than that of the aorta, so that
even if the auricle were tilled in exactly the same time as the
ventricle is emptied, the blood must pass more rapidly through the
narrow aorta than through the broad venae cava?, in order that the
same quantity of blood should pass each in the same time. The
diastole of the auricle, however, is distinctly longer than the systole
of the ventricle; the time during which the auricle is being filled is
greater than that during which the ventricle is being emptied, and
hence the velocity of the venous flow into the auricle must be still \
less than that of the arterial blood in the commencing aorta.

The temporary variations of the velocity of the stream in any
given' channel, and these we have already (p. 127) seen to be very
considerable in the case of the arteries at least, are dependent on a
variety of circumstances. In a tube of constant calibre, the velo-
city with which fluid flows from one point to another, for instance
from the point a to the point 6, will be in main dependent on the
difference between the pressures existing at a and b. The lower
the pressure at b as compared with a the greater the rapidity with
which the fluid flows from a to 6. And temporary variations of
pressures form undoubtedly the main cause of the temporary varia-
tions observable in the velocity of the arterial flow. Thus with
each systole of the ventricle there is an increase of velocity in the
whole arterial flow followed by a diminution during the diastole.
So also if the peripheral resistance in the minute arteries into
which a larger artery divides be suddenly lowered (by the action of
vaso-motor nerves, in a manner which we shall presently discuss),
without the calibre of the larger artery itself being changed, the
pressure on the distal (peripheral) side of the artery may be much

134 VARIATIONS IN VELOCITY. [BOOK i.

diminished, while the pressure on the proximal (cardiac) side re-
mains at first .unaltered ; and this would necessarily cause an increase
in the rapidity of the stream through that artery. But, as we shall
see later on, from the complications of the vascular machinery
such problems as these become very intricate; and the results
of observations on variations in arterial velocity are not altogether
intelligible. It has been suggested that varying conditions of the
blood, by affecting the amount of adhesion between the blood and
the walls of the vessels, may be an important factor in determining
the variations in the velocity of the stream.

SEC. 2. THE HEART.

The heart is a pump, the motive power of which is supplied
by the contraction of its muscular fibres. Its action consequently
presents problems which are partly mechanical, and partly vital.
Regarded as a pump, its effects are determined by the frequency of
the beats, by the force of each beat, by the character of each beat
— whether, for instance, slow and lingering, or sudden and sharp —
and by the quantity of fluid ejected at each beat. Hence, with a
given frequency, force, and character of beat, and a given quantity
ejected at each beat, the problems which have to be dealt with are
for the most part mechanical. The vital problems are chiefly con-
nected with the causes which determine the frequency, force, and
character of the beat. The quantity ejected at each beat is governed
more by the state of the rest of the body, than by that of the
heart itself.

TJie Phenomena of the Normal Beat.

The visible movements. When the chest of a mammal is
opened and artificial respiration kept up, a complete beat of the
whole heart, or cardiac cycle, may be observed to take place. as
follows.

The great veins, inferior and superior vense cavse and pulmonary-
veins, are seen, while full of blood, to contract in the neighbourhood
of the heart : the contraction runs in a peristaltic wave towards the
auricles, increasing in intensity as it goes. Arrived at the auricles,
which are then full of blood, the wave suddenly spreads, at a rate
too rapid to be fairly judged by the eye, over the whole of those
organs, which accordingly contract with a sudden sharp systole. In
the systole, the walls of the auricles press towards the auriculc-

136 MOVEMENTS OF THE HEART. [BOOK i.

ventricular orifices, and the auricular appendages are drawn inwards,
becoming smaller and paler. During the auricular systole, the ven-
tricles may be seen to become more and more turgid. Then follows,
as it were immediately, the ventricular systole, during which the
ventricles become more conical. Held between the fingers they are
felt to become tense and hard. As the systole progresses, the aorta
and pulmonary arteries expand and elongate, and the heart twists
slightly on its long axis, moving from the left and behind towards
the front and right so that more of the left ventricle becomes dis-
played. As the systole gives way to the succeeding pause or
diastole, the ventricles resume their previous form, the aorta and
pulmonary artery contract and shorten, the heart turns back to-
wards the left, and thus the cycle is completed.

A more exact determination of the changes in the form and
position of the heart during a beat is attended with considerable
difficulties. The following experiment has been made with the
view of studying these changes without opening the chest and thus
without depriving the heart of its natural supports. If, in the un-
opened chest of a rabbit or dog, three needles be inserted through
the chest-wall so that their points are plunged into the substance
of the ventricle, one (B) at the base, close to the auricles, another
(A) through the apex, and a third (M) at about the middle of the
ventricle, all three needles will be observed to move at each beat of
the heart. The head of B will move suddenly upwards, shewing
that the point of the needle plunged in the ventricle moves down-
wards, whereas A will only quiver, and move neither distinctly up-
wards nor downwards. M will move upwards (and therefore its
point downwards), but not to the same extent as B. The nearer
to B, M is, the more it moves : the nearer to A, the less. After
the death of the animal, the needles, if properly inserted at first,
perpendicular to the chest, will be found with all their heads
directed downwards, indicating that the whole ventricle has been
drawn up by the contraction of the empty aorta and pulmonary
artery.

The behaviour of the needles during the beat has been in-
terpreted as follows. At the systole the whole heart is thrust
downward by the elongation of the aorta and pulmonary artery.
The needle A at the apex however does not move its place,
because this downward movement is compensated by an upward
movement due to a shortening, during systole, of the longitudinal
diameter of the ventricle. The base in which the needle B is
plunged, moves downwards and drawrs closer to A, i.e. to the apex,
partly by the downward thrust from the elongation of the great
arteries and partly from the shortening of the ventricle itself.
Naturally the behaviour of the needle M is intermediate in
character, its downward movement being the more conspicuous
the nearer it is to B. The experiment then is taken to
prove that during the systole the ventricle shortens in its

CHAP, iv.] THE VASCULAR MECHANISM. 137

longitudinal diameter, but that the apex remains stationary on
account of the compensating downward thrust of the whole
ventricle. It has been urged however that this method is untrust-
worthy, and that similar movements of needles thus placed might
be produced by the twisting of the heart on its long axis, com-
bined with an approximation of the heart to the chest-wall. And
different conclusions have been arrived at by taking plaster of
Paris models on the one hand of a dog's heart, which, while having
ceased beating but not yet become rigid, has been filled with blood
at a moderate pressure, and on the other hand of a heart of the
same size in which a condition simulating systolic contraction has
been brought about by immersing the empty heart in a saturated
solution of potassium bichromate at 50° C. The former is taken to
represent the diastolic and the latter the systolic form of the heart;
and the results are checked by measurements taken between marks
placed on various points of the surface of the heart as well as by
sections of a heart filled with blood and hardened in a cold solu-
tion of potassium bichromate and of one emptied and hardened in
the same solution warmed to 50°. A comparison of the two hearts
in these different conditions tends to shew that while both the
right-to-left and antero-posterior diameters are diminished during
systole, especially in the plane of the ostia venosa (whereby the
auriculo-ventricular orifices become narrowed) the longitudinal
diameter, at all events of the left ventricle, is not lessened, the
distance between the apex and the auriculo-ventricular groove
remaining unchanged. The right ventricle, the change of form of
which is complicated, does shorten to a certain extent, and there
is during systole a downward movement of the con us arteriosus
upon the plane of the ventricular base (which possibly may explain
the movement of the needle B in the above mentioned experiment)
so that the distance between the apex and the upper border of the
conus is less during systole than during diastole. This method
also confirms the view that the left ventricle in systole turns on
its long axis, towards the right, the movement increasing from the
base downwards so that the groove between the two ventricles
forms a closer spiral than during diastole.

Objections may be brought against this method also, and it
seems impossible to explain the movements of a lever placed upon
the heart unless we admit that during systole, the antero-posterior
diameter, of the middle portion of the ventricle at least is increased
instead of lessened. We may however probably go so far as to
conclude that as far as the ventricles are concerned the chief change
during systole is one from a roughly hemispherical to a more
conical form, effected without any marked diminution of the
distance between the apex and the ventricular base.

Cardiac Impulse. If the hand be placed on the chest, a
shock or impulse will be felt at each beat, and on examination

138 CARDIAC IMPULSE. [BOOK i.

this impulse, 'cardiac impulse,' will be found to be synchronous with
the systole of the ventricle. In man, the cardiac impulse may be
most distinctly felt in the fifth costal interspace, about an inch
below and a little to the median side of the left nipple. The same
impulse may be felt in an animal by making an incision through
the diaphragm from the abdomen, and placing the finger between
the chest-wall and the apex. It then can be distinctly recognized
as the result of the hardening of the ventricle during the systole.
And the impulse which is felt on the outside of the chest is the
same hardening of the stationary portion of the ventricle in contact
with the chest-wall, transmitted through the chest-wall to the
finger. In its flaccid state, during diastole, the apex is (in a
standing position at least) at this point in contact with the chest-
wall, lying between it and the tolerably resistant diaphragm.
During the systole, while being brought even closer to the chest-
wall, by the movement to the front and to the right of which
we have already spoken, it suddenly grows tense and hard. The
ventricles, in executing their systole, have to contract against
resistance. They have to produce within their cavities, tensions
greater than those in the aorta and pulmonary arteries, respectively.
This is, in fact, the object of the systole. Hence, during the swift
systole, the ventricular portion of the heart becomes suddenly
tense, just as a bladder full of fluid would become tense and hard
when forcibly squeezed. The sudden onset of this hardness gives
an impulse or shock both to the chest-wall and to the diaphragm,
which may be felt readily both on the chest- wall, and also through
the diaphragm when the abdomen is opened, and the finger
inserted. If the modification of the sphygmograph (see section
on Pulse), called the cardiograph, be placed on the spot where the
impulse is felt most strongly, the lever is seen to be raised during
the systole of the ventricles, and to fall again as the systole passes
away, very much as if it were placed on the heart directly. A
tracing may thus be obtained, of which we shall have to speak
more 'fully immediately. If the button of the lever be placed,
not on the exact spot of the impulse, but at a little distance
from it, the lever will be depressed during the systole. While
at the spot of impulse itself the contact of the ventricle
is increased during systole, away from the -spot the ventricle
retires from the chest-wall (by the diminution of its right-to-left
diameter), and hence, by the mediastinal attachments of the peri-
cardium, draws the chest-wall after it.

Endo-cardiac events. In order to study more fully the
changes going on in the heart during the cardiac cycle, it becomes
necessary to know something of what is taking place in the interior
of the cavities of the heart. Chauveau and Marey, by introducing
into the right auricle and ventricle respectively of the horse, through
the jugular vein, small elastic bags, each communicating with a

CHAP, iv.]

THE VASCULAR MECHANISM.

339

recording tambour, were enabled to take simultaneous tracings
of changes occurring in the two cavities. These results are
embodied in Fig. 21, of which the upper curve is a tracing taken

TC

V

FlG. 21. SIMULTANEOUS TRACINGS FROM THE INTERIOR OF THE RIGHT AURICLE, FROM
THE INTERIOR OF THE RIGHT VENTRICLE, AND OF THE CARDIAC IMPULSE, IN THE

HORSE. (AFTER CHAUVEAU AND MARF.Y.) To be read from left to right1.

The upper curve represents changes taking place within the auricle, the middle
curve changes within the ventricle. The lower curve represents the variations of
pressure transmitted to a lever outside the chest and constituting the cardiac
impulse. A complete cardiac cycle, beginning at the close of the ventricular
systole, is comprised between the thick vertical lines I and II. The thin vertical
lines represent tenths of a second. The explanation of the letters is given in
the text.

from the auricle, the middle curve a similar tracing taken from
the ventricle, while the lower curve is a cardiographic tracing
of the cardiac impulse. All these curves were taken simultaneously
on the same recording surface.

Method. A tube of appropriate curvature is furnished with two
small elastic bags, one at the extreme end and the other at such a
distance that when the former is within the cavity of the ventricle the
latter is in the cavity of the auricle ; such an instrument is spoken of
as a ' cardiac sound.' Each bag (Fig. 22 A) or 'ampulla' communicates
by a separate air-tight tube with an air-tight tambour (Fig. 22 B) on
which a lever rests so that any pressure on either bag is communicated
to the cavity of its respective tambour, the lever of which is raised in

1 It must be remembered that the curves in the diagram are intended merely
to illustrate the changes occurring at different times in the same chamber,
or to shew what changes in the one chamber are coincident in point of time with
changes in the other. They in no way indicate the amount of pressure exerted in the
auricle as compared with that in the ventricle.

140

ENDO-CARDIAC EVENTS.

[BOOK i.

proportion. The writing points of all three levers are brought to bear
on the same recording surface exactly underneath each other. The
tube is carefully introduced through the right jugular vein into the
right side of the heart until the lower (ventricular) bag is fairly in the

FIG. 22. MAREY'S TAMBOUR, WITH CARDIAC SOUND.

A. A simple cardiac sound such as may be used for exploration of the left
ventricle. The portion a of the ampulla at the end is of thin india-rubber, stretched
over an open framework with metallic supports above and below. The long tube b
serves to introduce it into the cavity which it is desired to explore.

B. The Tambour. The metal chamber ra is covered in an air-tight manner
with the india-rubber c, bearing a thin metal plate ra' to which is attached the lever Z
moving on the hinge h. The whole tambour can be placed by means of the clamp
cl at any height on the upright s'. The india-rubber tube t serves to connect the
interior of the tambour either with the cavity of the ampulla of A or with any other
cavity. Supposing that the tube t were connected with b, any pressure exerted on a
would cause the roof of the tambour to rise and the point of the lever would be pro-
portionately raised.

cavity of the right ventricle, and consequently the upper (auricular)
bag in the cavity of the right auricle. Changes of pressure on either
ampulla then cause movements of the corresponding lever. When the
pressure, for instance, on the ampulla in the auricle is increased, the
auricular lever is raised and describes on the recording surface an
ascending curve ; when the pressure is taken off the curve descends ;
and so also with the ventricle.

The ' sound ' may in a similar manner be readily introduced through
the carotid artery into the left ventricle and the changes taking place
in that chamber also explored; these are found to be very similar to
those of the right ventricle.

We may employ these curves as giving a general and useful
view of the sequence of events in the interior of the heart; but we
must bear in mind exactly what they mean. The tracings given

CHAP, iv.] THE VASCULAR MECHANISM. 141

by the auricular and ventricular levers really represent variations
in the pressure exerted on the respective ampullse, and so far are
instructive; but they must not be taken as representing variations
in the pressure exerted on the blood in' the several cavities. For
we can easily conceive that, in the systole of the ventricle for
instance, the contraction of the muscular walls might continue
after all the blood contained in the ventricle had been driven out.
In such a case the ventricle would continue to press upon the
ampulla, and this continued pressure would be transmitted to the
lever, and indicated on the curve; but we should be in error in
interpreting this part of the curve as meaning that the ventricle
was still continuing to exert pressure on the blood as yet remain-
ing in its cavity. With this caution, and with the remark that the
tracing of the cardiac impulse is very unlike the usual cardio-
graphic tracings taken from man, we may use the curves to deduce
the following conclusions.

A complete cardiac cycle is comprised between the vertical
lines I and II. The recording surface was travelling at such a
rate that the intervals between any two of the thin vertical lines
corresponds to one-tenth of a second. Hence in this case (the
heart being that of a horse) the whole cardiac cycle occupied
about f§ths of a second. Any point in the cycle might of course
be taken as its commencement. In the figure, the cycle is
supposed to begin shortly after the end of the ventricular systole,
and the beginning of the diastole.

On examining the three curves we see, at a, a steady rise of the
auricular, accompanied by similar gradual ascents of the ventricular
and also of the cardiograph lever. These may be interpreted as
indicating that the blood is pouring from the great veins into the
auricle, increasing the pressure there, and at the same time
passing on into the ventricle, increasing the internal pressure
there as well, a, and also by distending the ventricle, causing
it to press somewhat on the chest-wall and thus to raise the
cardiograph lever, a . This continues for about -j^ths of a second,
and is then followed by the sudden rise of auricular pressure b due
to the auricular systole, followed by a sudden fall as the blood
escapes into the ventricle and the systole ceases. The sudden
entrance of blood into the ventricle causes a sudden increase of the
pressure in the ventricle as indicated by the ventricular lever b', and
a sudden increase in the pressure on the chest-wall b". The
auricular systole is followed immediately by the sudden strong
ventricular systole c', the lever rising very abruptly. Owing to
the presence of the tricuspid valves, the pressure exerted by the
ventricular systole is kept off the auricle almost altogether; but
the chest-wall, as shewn by the tracing at c", feels the sudden
increase of the pressure of the ventricle against it. The most
important points concerning this rise of ventricular pressure are
that it is sudden in its onset and also rapid in its decline, and

142 THE MECHANISM OF THE VALVES. [BOOK i.

that it lasts for a comparatively long time; in the figure this
part of the curve embraces more than four-tenths of a second. These

[features, the sudden rise, the long duration, and the rapid fall
of the pressure exerted by the ventricle are seen in all tracings of
the ventricles engaged in a cardiac beat whatever be the method
employed. They mean of course that the muscular contractions
which constitute the ventricular systole come on suddenly, that
they last altogether a considerable time, and that relaxation is
also rapid. With the end of the ventricular systole the cycle
represented in figure ends, and a new cycle begins, repeating
the same changes. The meaning of the features on the curves
marked e and d, &c., as well as a more complete discussion of
the changes thus briefly described, we must defer till we have
spoken of

The Mechanism of the Valves.

The auriculo-ventricular valves present no difficulty. As the
blood is being driven by the auricular systole into the ventricle, a
reflux current is probably set up, by which the blood, passing along
the sides of the ventricle, gets between them and the flaps of the
valve (whether tricuspid or mitral). As the pressure of the
auricular systole diminishes, the same reflux current floats the
flaps up, until at or immediately after the close of the systole they
meet, and thus the orifice is at once and firmly closed, at the very
beginning of the ventricular beat. The increasing intraventricular
pressure serves only to render the valve more and more tense, and
in consequence more secure, the chordae tendineae (the slackening
of which through the change of form of the ventricle is probably
obviated by a regulative contraction of the papillary muscles) at
the same time preventing the valve from being inverted -or even
bulging into the auricle, and indeed, according to some observers,
keeping the valvular sheet actually convex to the ventricular
cavity, by which means the complete emptying of the ventricle
is more fully effected. Since the same papillary muscle is in
many cases connected by chordae with the adjacent edges of two
flaps, its contraction also serves to keep these flaps in more
complete apposition. Moreover the extreme borders of the valves,
outside the attachments of the chordae, are excessively thin, so
that when the valve is closed, these thin portions are pressed flat
together back to back ; hence while the tougher central parts of
the valves bear the force of the ventricular systole, the opposed
thin membranous edges, pressed together by the blood, more
completely secure the closure of the orifice.

CHAP, iv.] THE VASCULAR MECHANISM. 143

The semilunar valves are, during the ventricular systole, pressed
outwards towards but not close to the arterial walls, reflex currents
probably keeping them in an intermediate position, their orifice
forming an equilateral triangle with curved sides ; they thus offer
little obstacle to the escape of blood from the cavities of the
ventricles. The ventricle propels the blood with great force and
rapidity into the aorta and the whole contents are speedily ejected.
Now, when in a closed channel a rapid current suddenly ceases,
a negative pressure makes its appearance in the rear of the fluid,
and sets up a reflux current. So when the last portions of blood
leave the ventricle a negative pressure makes its appearance behind
them in the ventricle, and leads to a reflux current from the aorta
towards the ventricle. This alone would tend to bring the
valves together; but in all probability it is not till a short
(variable) time afterwards, that upon the commencing diastolic
relaxation of the ventricle, the elastic rebound of the arterial walls
completely fills and renders tense the pockets, causing their free
margins to come into close and firm contact, and thus entirely
blocking the way. The corpora Arantii meet in the centre, and the
thin membranous festoons or lunulse are brought into exact apposi-
tion. As in the tricuspid valves, so here, while the pressure of the
blood is borne by the tougher bodies of the several valves, each two
thin adjacent lunulsfi, pressed together by the blood acting on both
sides of them, are kept in complete contact, without any strain
being put upon them; in this way the orifice is closed in a
most efficient manner.

The ingenious view put forward by Briicke that during the ven-
tricular systole, the flaps are pressed back flat against the arterial walls,
and in the case of the aorta completely cover up the orifices of the
coronary arteries, so that the flow of blood from the aorta into the
coronary arteries can take place only during the ventricular diastole
or at the very beginning of the systole, and not at all during the systole
itself, has been disproved.

The Sounds of the Heart.

When the ear is applied to the chest, either directly or by
means of a stethoscope, two sounds are heard, the first a com-
paratively long dull booming sound, the second a short sharp
budden one. Between the first and second sounds, the interval
of time is very short, too short to be measurable, but between the
second and the succeeding first sound there is a distinct pause.
The sounds have been likened to the pronunciation of the syllables,
lubb, dup, so that the cardiac cycle, as far as the sounds are
concerned, might be represented by : — lubb, dup, pause.

144 THE SOUNDS OF THE HEART. [BOOK i.

The second short sharp sound presents no difficulties. It is
coincident in point of time with the closure of the semilunar
valves, and is heard to the best advantage over the second right
costal cartilage close to its junction with the sternum, i. e. at the
point where the aortic arch comes nearest to the surface. Its
characters are such as would belong to a sound generated by the
sudden tension of valves like the semilunar valves. It is obscured
and altered, replaced by ' murmurs ' when the semilunar valves are
affected by disease, the alteration being most manifest to the ear
at the above-mentioned spot when the aortic valves are affected.
When the aortic valves are hooked up by means of a wire intro-
duced down the arteries, the second sound is obliterated and
replaced by a murmur. These facts prove that the second sound
is due to the sudden tension of the aortic (and pulmonary) semi-
lunar valves.

The first sound, longer, duller, and of a more 'booming'
character than the second, heard with greatest distinctness at the
spot where the cardiac impulse is felt, presents many difficulties
in the way of a complete explanation. It is heard distinctly when
the chest-walls are removed. The cardiac impulse therefore can
have little or nothing to do with it. In point of time, and in the
position in which it may be heard to the greatest advantage (at
the spot of the cardiac impulse where the ventricles come nearest
to the surface), it corresponds to the closure of the auriculo-ven-
tricular valves. In point of character it is not such a sound as one
would expect from the vibration of membranous structures, but
has, on the contrary, many of the characters of a muscular sound.
In favour of its being a valvular sound, may be urged the fact that
it is obscured, altered, replaced by murmurs, when the tricuspid or
mitral valves are diseased ; and according to some authors clamp-
ing the great veins so as to shut off the blood supply stops the
sound though the beat continues. The first argument may be met
by the consideration that a murmur though itself undoubtedly of
valvular origin, might largely or completely hide a sound occurring
at the same time as the closure of the valves but due to other
causes ; and the second is directly contradicted by an experiment
of Ludwig and Dogiel. These observers tied in succession, in the
order of the flow of blood, the great veins and arteries of the heart
of a dog so as to completely deprive the heart of blood, and
listened to the heart both within the body and after removal.
For the short time that the heart continued to beat, the first sound
was heard, feeble but with its main characters recognisable. From
this they inferred that the sound was of muscular origin. But
there is a great difficulty in regarding the sound as a muscular
one, for a muscular sound is the result of a tetanic contraction,
the height of the note produced varying with the rate of re-
petition of the simple contractions which go to make up the

CHAP, iv.] THE VASCULAR MECHANISM. 145

tetanus. A simple contraction or spasm cannot possibly produce
a sound having the characters of the first cardiac sound. And the
evidence, though perhaps not conclusive, goes to shew that the beat
of the heart is a slow long-continued single spasm, intermediate
between the contraction of an ordinary striated and that of an
unstriated muscle, and not a tetanic contraction. We cannot, it
is true, now rely in support of this view on the fact that when the
nerve of a rheoscopic muscle-nerve preparation is placed on the
beating ventricle, each beat is followed by a single spasm of the
muscle, and not by a tetanus ; for we now know that many forms
of tetanus (e. g. those caused by the constant current, by strychnia,
and probably all natural voluntary contractions) give rise, in a
rheoscopic muscle-nerve preparation, to a single initial spasm and
not to a tetanus. But the general features of the beat, its long
latent period and the gradation of the ventricular systole through
the auricular systole into the rhythmic contractions of the un-
striated fibres of the walls of the great veins, render it difficult
to suppose that the beat is really a tetanus. Moreover the long
duration of the ventricular systole is readily explained by the
wave of contraction passing in a complicated peristaltic manner
over the different fibres in succession. But if the beat be a simple
contraction, it cannot give rise to a muscular sound, unless we
suppose that this sequence of simple contractions over various
parts of the ventricle in succession is adequate to produce such a
sound. This, however, does not seem very satisfactory.

On the other hand, if we reject the distinctly muscular origin of
the sound, we are almost driven to suppose that the abrupt systole
is able even in the absence of blood to produce such a sudden
tension of the valves, and of the ventricular walls, as to give rise to
a note. On such a view, the sound ought to vary in character
according as the ventricle is more or less filled, being low and
booming when it is full, and high and sharp when the contents are
scanty. And such is said to be the case. But the matter does not
at present seem ripe for any dogmatic statement.

In the normal state of things, the beats of the two ventricles
are so far synchronous with each other that practically only one
first sound and one second sound is heard. It sometimes happens
however that the synchronism fails to such an extent and the
closure of the pulmonary and aortic valves respectively are sepa-
rated by such an interval as to give the second sound a double
character.

10

146

SPECIAL CARDIAC PHASES.

[BOOK i.

On the relative duration and special characters of the
Cardiac events.

We may now return to a more detailed study of what is taking
place in the heart during a beat. We have already spoken of the
conclusions which may be drawn from Chauveau and Marey's curves,
and have incidentally (p. 138) referred to the cardiograph.

Various forms of cardiograph have been used to record the
cardiac impulse. In some the pressure of the impulse as in the
sphygmograph is transmitted directly to a lever which writes upon

FIG. 23. CARDIOGRAPHIC TRACING OF CARDIAC IMPULSE IN MAN (from Landois).

An entire beat occurs between a and /. The auricular systole is marked by b,
the end of the ventricular relaxation by/. At c, the highest point of the curve, the
blood begins to be propelled from the ventricle, d and e are considered by some to
indicate the closure of the aortic and semilunar valves respectively, see text. Five
cardiac beats are represented ; the convex curve which their base line forms is due to
the respiratory movements.

a travelling surface. In others the impulse is, by means of an
ivory button, brought to bear on an air-chamber, connected by
a tube with a tambour as in Fig. 22 ; the pressure of the cardiac
impulse compresses the air in the air-chamber, and through this
the air in the chamber of the tambour by which the lever is raised.
In such delicate and complicated movements as those of the
heart however, the use of long tubes filled with air is liable to
introduce various errors. A cardiographic tracing of ordinary
characters is given in Fig. 23.

Curves of the variations in internal pressure may be obtained
by passing a tube connected with a mercurial manometer (as in the
investigation of arterial pressure, p. 122) into the right ventricle
through the jugular vein or into the left ventricle through the
carotid artery. But this method, though useful for the purpose of
investigating generally the pressure exerted by the cardiac walls,
is, by reason of the inertia of the mercury, unsuitable for detecting
rapid and small changes.

CHAP, iv.]

THE VASCULAR MECHANISM.

147

Tracings of the movements of the ventricles themselves, corre-
sponding to the cardiac impulse and so to a certain extent to the
variations of internal pressure, may also be taken directly by
bringing a light lever to bear on the outside of the ventricles, the
chest having been previously opened and artificial respiration kept up.
A curve1 taken by this method is shewn in Fig. 24.

FIG. 24. Normal heart curve shewing changes in the antero-posterior diameter of
the ventricle obtained from the cat by a light recording lever moved by a button
which pressed gently on the anterior surface of the ventricle. The time curve gives
50 double vibrations per sec. and lines have been drawn to shew the duration of the
different phases of the ventricular movement, a to 6 corresponds to the distension of
the ventricle including the auricular systole, the wave-like rise during this period being
due to the increase in the diameter of the ventricle resulting from the entrance into it
of the contents of the auricle. The period from 6 to c corresponds to the time from
the commencement of the ventricular contraction to the moment when the organ
has completed its change in shape from a flattened to a more rounded form. The
highest part of the curve corresponds also in time with the opening of the semilunar
valves as well as the firm closure of the auriculo-ventrlcular valves. The duration of this

1 The majority of cardiograph ic, sphygmographic and other tracings shew certain
points which can be understood at a glance, but many characteristics can only
be learned by "measuring out the curve" as it is termed. This is done as follows.

Every tracing ought to bear on it an abscissa line, marked by a point which
remains motionless while the recording surface is travelling. Moreover, either
before or after taking a curve, while the paper or recording surface is at rest, the
point of the lever should be always moved up and down so as to describe a segment
of a circle of which the axis of the lever is the centre.

The tracing thus prepared, when it has to be measured, is pinned out on aboard,
and, by means of a pair of compasses, the distance between whose points has
previously been made equal to the distance between the axis and the point of
the lever used in making the experiment, the centre of the circle of which the
curved lines previously made as directed are segments is found and marked on the
paper. Through this centre, which of course corresponds to the position of
the axis of the lever, a horizontal line is drawn parallel to the abscissa line.

Keeping one of the compass points on this line, segments of circles are drawn in
succession through various points of the curve, the distance between the points of
the compass being fixed, but the centre of the circle described being shifted
backwards and forwards along the horizontal line. The points where these
segments cut the horizontal line are marked upon it, and the distances between them
measured as, for example, in Fig. 29, p. 166. If the curve of a tuning-fork, the
point of whose recording style was carefully placed on the same vertical line as the
point of the lever, be also present, the segments of circles may be continued until
they cut this, and the time corresponding to distances between them (as, for
instance, in Fig. 24 the intervals between a, 6, c, d,) thus directly measured off.

10—2

148 SPECIAL CARDIAC PHASES. [BOOK i.

.period in this ease is only about 3-50ths of a sec. The period from c to d is that
during which the ventricle having grasped its contents is emptying its cavity and
remaining contracted. It can be seen that only during the first half of this period
is there any marked descent of the lever point ; in other words the antero-posterior
diameter does not continue to diminish during the whole period of the systole,
indicating that little or no blood was thrown out during the second half of this
period, the ventricle remaining simply contracted after having emptied its cavity.
The period from d to a is that during which the ventricular muscle is relaxing.
Here, as is frequently the case, there is no period of pause between the close of
the relaxation of the ventricle and the commencement of the succeeding distension.
The tracing gives no evidence as to the time of closure of the semilunar valves.

The chief interest and the chief difficulties are attached to the* f
systole of the ventricles. In order to understand this, the most
important of the cardiac events, it must be borne in mind that,
as we have already seen, the pressure of the blood in the aorta
is always considerable. This pressure closes and keeps closed the
semilunar valves ; and it is not till the pressure in the ventricle
becomes greater than the pressure in the aorta that these valves
open to allow of the escape of the ventricular contents. The blood
therefore does not begin to pass from the left ventricle into the
aorta until some time, and that a variable time, after the commence-
ment of the systole of the ventricle ; and the same may be said of
the right ventricle and pulmonary artery, it being understood that
the arterial pressure on the right side is less than on the left. In
Fig. 24 the ventricular lever reaches its maximum c at once,
gradually declining afterwards till the more sudden fall begins,
and we may suppose that the escape of blood from the ventricle
begins at the moment when the maximum is attained; and this
view is confirmed by carefully comparing a tracing of the expansion
of an artery with the cardiac tracing. It is quite possible however
to conceive that owing to circumstances, such as an increasing con-
traction of the ventricular fibres or deficient expansion of the
arteries, the pressure might continue to increase even after blood
was escaping from the cavity of the ventricle. And indeed in some
curves, the ventricular lever after the first sudden leap continues
to rise gradually and does not reach the maximum point until
afterwards. In such cases the summit of the first rise must be
taken as marking the beginning of the flow from the ventricle.

By the sudden systole the blood is ejected with considerable
force and rapidity from the ventricle, and as the ventricle becomes
empty a negative pressure, as we have seen, makes its appearance
behind the column of blood which leaves the cavity and leads to
the closure of the semilunar valves. Much dispute has taken place
as to the exact condition of the ventricle at the moment of closure
of the semilunar valves. The slight rise e in Chauveau and
Marey's curves (Fig. 21) in the ventricular curve, seen also in the
auricle at e and in the cardiac impulse at e", and which has been
taken to indicate the shutting of the semilunar valves, appears quite
at the close of the descent of the ventricular lever. This would
mean that at the moment of the closure of the valves the ventricle

CHAP, iv.] THE VASCULAR MECHANISM. 149

had not only completed its contraction but was far advanced in
relaxation. Such a view is not only cb priori improbable but is
directly contradicted by the fact that when we compare a tracing
obtained by placing a lever directly on the heart or indeed a tracing
of the cardiac impulse with a pulse tracing, that is a tracing of the
expansion of an artery, we find that the ventricle continues con-
tracted after its contents have entirely left the cavity. That is to
say, the actual flow of blood takes place only during the middle
portion of the time during which the muscular fibres of the ven-
tricle are contracting and engaged in carrying on the systole.
During the first part, pressure is being got up, during the second
the blood is being propelled, during the third the ventricle continues
to remain empty and contracted. By this means the complete
emptying of the ventricle is effectually secured. And others have
urged that the closure of the semilunar valves, being entirely due
to the reflux spoken of above, follows close upon the emptying of
the ventricle ; in other words that it takes place while the ven-
tricle is still contracted. It is very difficult to point out indications
on the ventricular curve which indubitably correspond to this event.
In tracings of the cardiac impulse, and in tracings taken by a lever
placed directly on the heart, a notch, followed by a rise, is some-
times observed in that part of the curve which intervenes between
the first large rise and the final sudden fall ; and this secondary
rise has been taken to indicate the closure of the semilunar valves ;
but, if this be the case, the time during which the ventricle
remains contracted after the closure of the valves forms a very con-
siderable fraction of the whole period of the systole; and this
presents difficulties. Sometimes two such notches and peaks are
seen, and the occurrence of the two has been attributed to a want of
synchronism in the closure of the pulmonary and aortic semilunar
valves, the latter closing some little time before the former. But
it is by no means clear that these notches and peaks are thus due
to the closure of the valves; they may possibly have another
origin, they are not always present, and the attempt to fix the time
of the closure of the semilunar valves by them cannot be regarded
as satisfactory. On the other hand, the second sound of the heart
is undoubtedly due to the complete closure and sudden tension of
the semilunar valves ; and not only is this second sound separated
from the first sound by a distinctly appreciable interval (from which
we may infer either that the systole of the ventricle ceases before
the complete closure and sudden tension of the semilunar valves or
that the first sound does not last so long as the systole itself and
is therefore not a muscular sound) but the time elapsing between
the beginning of the first sound and the second sound is, as we shall
see, remarkably constant. Now we have reason to believe that the
quantity of blood expelled at any one beat, and hence the time
taken up in its escape, does vary very considerably ; whereas the
duration of the actual systole is probably much more constant.

150 ENDO-CARDIAC 2>RESSUPE. [BOOK i.

Hence we may infer, and the conclusion may be supported by other
arguments, that at the actual closure of the semilunar valves,
giving rise to the second sound, the ventricle has just finished its
systole and is beginning to relax. If this view be correct the time
of the closure of the valves is not indicated on the cardiographic
tracing by any special mark, but coincides with the commencement
of the more sudden and final fall of the lever as at d in Fig. 24.

Marey thought that the oscillations seen at d' in his curves and
obvious in the auricle and cardiac impulse as well, were due to
oscillations of the auriculo-ventricular valve, but in that case they
would be inverted in the auricular curve; whereas they are not.
It is difficult to say what gives rise to them. We may repeat that
many of the details of these curves vary considerably even with the
same method of investigation and when the same apparatus is
employed. In all probability the character and sequence of the
events are modified by various circumstances, such as the rate and
rapidity of the beat, the quantity of blood flowing into the heart,
and the pressure obtaining in the arteries.

Amount of Pressure. Although the instrument of Chauveau
and Marey may be experimentally graduated and has been used
to measure the amount of pressure in the several cavities of the
heart, it is, as we have said, open to objections. Better results may
be gained by passing through the jugular vein into the right auricle
and thence into the right ventricle, or through the carotid artery
into the left ventricle, a tube open at the end introduced into the
heart and connected at the other end with a manometer. Varia-
tions of pressure in the cardiac cavities are thus transmitted di-
rectly to the mercury column of the manometer in the same way
as those of an artery when arterial pressure is measured. The
inertia of the mercury column however prevents an exact response
to the rapid movements of the heart, and obscures the results ;
though by using maximum and minimum manometers, the
maximum and minimum pressures of the several cavities may be
determined.

The principle of the maximum manometer, Fig. 25, consists in the
introduction into the tube leading from the heart to the mercury
column, of a (modified cup-and-ball) valve, opening, like the aortic
semilunar valves, easily from the heart, but closing firmly when fluid
attempts to return to the heart. By reversing the direction of the
valve, the manometer is converted from a maximum into a minimum
instrument. When an ordinary manometer is connected with a ven-
tricular cavity, the movements of the mercury do not follow exactly the
rapid variations of pressure of the cavity, and the height of the column
fails to indicate both the highest and the lowest pressures.

In this way in the dog a maximum pressure has been observed
in the left ventricle of about 140 mm. (mercury), in the right
ventricle of about 60 mm. and in the right auricle of about 20 mm.

CHAP, iv.] THE VASCULAR MECHANISM.

151

Marey had previously, by means of his own instrument, determined
the pressure in the horse to be in the left ventricle about 150mm.,
in the right ventricle only about 30 mm., while that of the right
auricle he estimated at not more than a few mm.

FIG. 25. THE MAXIMUM MANOMETER OF GOLTZ AND GAULE.

At e a connection is made with the tube leading to the heart. When the screw
clamp k is closed, the valve v comes into action, and the instrument, in the position
of the valve shewn in the figure, is a maximum manometer. By reversing the
direction of v it is converted into a minimum manometer. When k is opened, the
variations of pressure are conveyed along a, and the instrument then acts like an
ordinary manometer.

It is interesting to observe that the minimum pressure may
fall below that of the atmosphere : thus in the left ventricle (of
the dog) a minimum pressure varying from — 52 to — 20 mm. may
be reached, the minimum of the right ventricle being from — 17 to
— 16 mm., and of the right auricle from — 12 to — 7 mm.1 Part of
this diminution of pressure in the cardiac cavities may be due, as
will be explained in a later part of this work, to the aspiration of
the thorax in the respiratory movements. But even when the
thorax is opened, and artificial respiration kept up, under which
circumstances no such aspiration takes place, the pressure in the
left ventricle may still sink as low as — 24 mm. The minimum ma-
nometer, which shews most distinctly the existence of this negative
pressure, obviously gives no information as to the exact phase of
the beat in which it occurs ; and there is some difference of opinion
as to the exact time at which it takes place. Goltz and Gaule, to

1 These numbers are to be considered merely as instances which have been
observed, and not as averages drawn from a large number of cases.

152 DURATION OF THE CARDIAC PHASES. [Boon i.

"whom we are indebted for the maximum and minimum manometer,
believed that the negative pressure appeared at the beginning of
the diastole and indeed that it was caused by the expansion of the
ventricle. Were this the case, the ventricle might be regarded not
only as a force pump driving blood into the arteries, but also as a
suction pump drawing blood from the auricles and great veins.

Others however find great difficulties in supposing that the
ventricular walls can, either by virtue of the elasticity of their
fibres, or by the contraction of special dilating fibres, or by
becoming suddenly injected with blood through the coronary
arteries, actually expand so as to exert any such suction power.
And they maintain that the negative pressure seen in the ventricle
is merely that same negative pressure due to the sudden emptying
of the ventricle which we have already described as serving to
close the semilunar valves. When the minimum manometer is
used, the lowest limit of negative pressure is not reached until after
several beats, indicating that its duration in any single beat must
be very brief. The negative pressure due simply to the cessation
of the flow is in fact almost immediately made away with by the
ventricular walls, in their continued contraction coming into com-
plete contact ; it passes off therefore before any blood can enter into
the ventricle from the auricle, and hence can exert no suction power.

Admitting this, however, it is still open for us to suppose that
after this negative pressure has passed away, a second negative
pressure is caused by the expansion of the ventricle in diastole ;
and that this, though also brief, does exert a suction power. And
indeed the view that the ventricle in expanding can produce such
a negative pressure is one which cannot as yet be regarded as
definitely disproved.

The duration of the several phases. The time-measurements
given in Fig. 21 afford a general idea of the relative duration of
the several events in the slowly beating heart of the horse. Thus
it is obvious that the longest phase (viz. about •£$ sec.) is that
occurring between the end of the ventricular systole at e to
the beginning of the auricular systole at b ; this is often spoken of
as the diastole, or as the " passive interval," since during this time
both auricles and ventricles are in diastole. The next longest phase
is the systole of the ventricles (viz. rather more than yL- sec.), and the
shortest (viz. rather less than T% sec.) is the systole of the auricles.

When we desire to arrive at more complete measurements, we
are obliged to make use of calculations based on various data;
and these give only approximate results. Naturally the most
interest is attached to the duration of events in the human heart.

The datum which perhaps has been most largely used is the
interval between the beginning of the first and the occurrence of
the second sound. This may be determined with approximative
correctness, and according to Bonders varies from '301 to '327 sec.,

CHAP, iv.] THE VASCULAR MECHANISM. 153

occupying from 40 to 46 p. c. of the whole period; and being fairly
constant for different rates of heart-beat.

The observer, listening to the sounds of the heart, made a signal at
each event on a recording surface, the difference in time between the
marks being measured by means of the vibrations of a tuning fork
recorded on the same surface. By practice it was found possible
to reduce the errors of observation within very small limits.

Now whatever be the exact causation of the first sound,
it is undoubtedly coincident with the systole of the ventricles,
though possibly the actual commencement of its becoming audible
may be slightly behind the actual beginning of the muscular con-
tractions. Similarly the occurrence of the second sound due to the
closure of the semilunar valves may, as we have seen, be taken to
mark the close of the ventricular systole. And thus the interval
between the beginning of the first and the occurrence of the second
sound has been regarded as indicating approximatively the duration
of the ventricular systole, i.e. the period during which the ventri-
cular fibres are contracting. If however we accept the view that
the ventricle still remains contracted for a brief period after the
valves are shut, then the second sound does not mark the end of
the systole, and the duration of the systole is rather longer than
the *3 sec. given above.

The propulsion of the blood into the aorta leads to an expansion
of the aorta walls, known as the pulse, which we shall study more
fully immediately. This pulse travels, as we shall see, along
the arteries at a certain rate : it is later at arterial points
more distant from the heart than at points nearer the heart. "We
can calculate with approximative correctness the time it takes for
the expansion to travel from the aortic valves to the radial artery
at the wrist, for example. Now when we record, as we may do on
the same recording surface, the exact moment at which the first
sound begins, or at which the lever of the cardiograph begins to
rise in the ventricular systole, and also the exact moment at which
the expansion of the corresponding pulse at the wrist begins, and
measure the interval of time between them, we find that the interval
is greater than is required for the expansion of the pulse-wave to
travel from the heart to the wrist. The difference gives the measure
of the time during which the ventricle by its contraction is getting
up an adequate pressure upon its contents, and during which, as yet,
blood has not escaped from the ventricular cavity and begun to ex-
pand the aorta : the measure in fact of what we called, a little while
ago, the first period of the ventricular systole. This may also be
estimated by directly measuring the time taken up by the upstroke
of the cardiographic tracing, and has been said to be on an average
about '085 sec. These measurements however are approximative
only and there can be no doubt that the time varies very largely,
being dependent on the quantity of blood in the ventricle, on the
blood-pressure in the aorta and on the condition of the heart.

154 DURATION OF THE CARDIAC PHASES. [BoOK T-

During the expansion of the artery and probably for some little
time beyond, viz. up to the occurrence of what in speaking of the
pulse-wave we shall callthe dicrotic notch, blood is being propelled
from the ventricle. By measuring this time or by deductions from
the curve of the cardiac impulse, it has been concluded that the time
during which blood is escaping from the ventricle or the duration
of the second phase of the ventricular systole, amounts to about
O'l sec.

Deducting these two periods from the total period of 0'3 sec.,
there would be left a period of O'l 15 sec., marking the third phase
of the systole, during which the ventricle, though empty, is con-
tinuing its contractions. Upon the view however that the closure
of the valves does not mark the end of the systole, this phase
must be taken as still longer.

In a heart beating 72 times a minute, which may be taken as
the normal rate, each entire cardiac cycle would last about 0'8 sec.,
and taking 0'3 sec. as the duration of the systole, the deduction of
this would leave 0'5 sec. for the whole diastole of the ventricle
including its relaxation.

At the close of this period, there occurs the systole of the
auricles, the exact duration of which it is difficult to determine, it
being hard to say when it really begins, but which perhaps may
be taken as lasting on an average O'l sec. The systole of the
ventricle follows so immediately upon that of the auricles, that
practically no interval exists between the two events.

We may sum up therefore the details of the duration of the more
important phases of the cardiac cycle in the following tabular form.

sees. sees.
Systole of ventricular previous to ~\

opening of semilunar valves . 0'085
Escape of blood into aorta . . O'lOO !-
Continued contraction of the

emptied ventricle . . . O'lloj
Total systole of the ventricle . . 0'3
Diastole of both auricle and ven- 1

tricle or "passive interval" . 0'400 j>
Systole of auricle . . . O'lOO J

Sum of above two, making the
diastole of ventricle or "pause"
between second and first sound . 0'5

Total Cardiac Cycle . . . .; (^8
Or selecting only the important facts out of the -£$ sec. occupying
the whole canfiac cycle, -^ sec. or possibly rather more are taken up
by the systole, and T% sec. or possibly rather less by the diastole of
the ventricle.

The following diagram may be useful as giving in a graphic
form a general idea of the sequence and duration of the several

CHAP, iv.] THE VASCULAR MECHANISM.

155

cardiac events. It will be understood of course that the diagram is
intended to shew merely the general relations of the several events
and not to represent exact measurements.

Fio. 26.

DIAGRAMMATIC KEPBESENTATION OF THE MOVEMENTS AND SOUNDS OP TUB
HEART DURING A CARDIAC PERIOD. (After Dr SHARPET.)

We may repeat that the details given above are at the best
approximative only, and, we may add, to a certain extent hypo-
thetical. We have given them at such length not on account
of their intrinsic importance, or because they are trustworthy data
for further calculations, but because the study of them may help
the reader in forming a more vivid image in his mind of what is
taking place in the heart during a beat. Moreover it must be
remembered that the figures quoted are those belonging to what
may be considered a normal rate of heart beat. The rate how-
ever at which the heart beats varies, as we shall see, under the
influence of circumstances, within very wide limits. With regard
to the duration of the several phases at different rates of heart
beat, the most important fact is perhaps that the pause varies
much more than does the systole of the ventricles. A quickly
beating heart differs from a slowly beating heart by reason of the
pause being shortened, much more than by each systole being of
less duration.

We may briefly recapitulate the main facts connected with
the passage of blood through the heart as follows. The right
auricle during its diastole, by the relaxation of its muscular fibres,
and by the fact that all pressure from the ventricle is removed by
the tension of the tricuspid valves, offers but little resistance to
the ingress of blood from the veins. On the other hand, the blood
in the trunks, of both the superior and inferior vena cava, is under a
pressure, which diminishing towards the heart and becoming within

156 DURATION OF THE CARDIAC PHASES. [BOOK i.

the thorax actually negative (as we shall see in speaking of
respirations), remains higher than the pressure obtaining in the
interior of the auricle; the blood in consequence flows into the
empty auricle, its progress in the case of the superior vena cava
being assisted by gravity. At each inspiration, this flow is favoured
by the increased negative pressure in the heart and great vessels
caused by the respiratory movements. Before this flow has gone on
very long, the diastole of the ventricle begins, its cavity dilates,
the flaps of the tricuspid valve fall back, and blood for some little
time flows in an unbroken stream from the venae cavse into the
ventricle. In a short time, however, probably before much blood
has had time to enter the ventricle, the auricle is full, and forth-
with its sharp sadden systole takes place. Partly by reason of the
onward pressure in the veins, which increases rapidly from the
heart towards the capillaries, partly from the presence of valves in
the venous trunks and at the mouth of the inferior vena cava, but
still more from the fact that the systole begins at the great veins
themselves and spreads thence over the auricle, the force of the
auricular contraction is spent in driving the blood, not back into
the veins, but into the ventricle, where the pressure is still ex-
ceedingly low. Whether there is any backward flow at all into the
great veins or whether by the progressive character of the systole
the flow of blood continues, so to speak, to follow up the systole
without break so that the stream from the veins into the auricle is
really continuous, is at present doubtful ; though a slight positive
wave of pressure- synchronous with the auricular systole, travelling
backward along the great veins has been observed at least in cases
where the heart is beating vigorously.

The ventricle thus being filled by the auricular systole, the
play of the tricuspid valves described above comes into action,
the auricular systole is followed by that of the ventricle and the
pressure within the ventricle, cut off from the auricle by the
tricuspid valves, is brought to bear entirely on the conus arteriosus
and the pulmonary semilunar valves. As soon as by the rapidly
increasing shortening of the ventricular fibres the pressure within
the ventricle becomes greater than that in the pulmonary artery,
the semilunar valves open and the still continuing systole discharges
the contents of the ventricle into that vessel.

As the ventricle thus rapidly and forcibly empties itself, a
transient negative pressure makes its appearance in the rear of the
ejected column of blood. This in return leads to a reflux of blood
towards the ventricle. The first act of this reflux however is, as
we have seen, to close the semilunar valves, and even if it be
urged that the exit of the ventricular contents does not always end
with sufficient abruptness to cause a negative pressure adequate
to produce this result, the elastic rebound of the arteries, upon
their receiving no fresh blood, has the same effect of closing the
semilunar valves, and thus of shutting off the blood in the over-

CHAP, iv.] THE VASCULAR MECHANISM. 157

distended arteries from the emptied ventricle. Coincidently with
this closure, the systole as we have seen probably ends and
relaxation begins ; then once more the cavity of the ventricle be-
comes unfolded and finally distended by the influx of blood from
the auricle.

During the whole of this time the left side has with still
greater energy been executing the same manoeuvre. At the same
time that the vense cavas are filling the right auricle, the pulmonary
veins are filling the left auricle. At the same time that the right
auricle is contracting, the left auricle is contracting too. The
systole of the left ventricle is synchronous with that of the right
ventricle, but executed with greater force ; and the flow of blood
is guided on the left side by the mitral and aortic valves in the
same way that it is on the right by the tricuspid valves and those
of the pulmonary artery.

The Work done.

We can measure with approximative exactness the intraven-
tricular pressure, the length of each systole, and the number of
times the systole is repeated in a given period, but perhaps the
most important factor of all in the determination of the work of
the vascular mechanism, the quantity ejected from the ventricle
into the aorta at each systole, cannot be accurately determined ;
we are obliged to fall back on calculations having many sources
of error. The mean result of these calculations gives about 180
grms. (6 oz.) as the quantity of blood which is driven from each
ventricle at each systole in a full-grown man of average size and
weight. It is evident that exactly the same quantity must issue at
a beat from each ventricle ; for if the right ventricle at each beat
gave out rather less than the left, after a certain number of beats
the whole of the blood would be gathered in the systemic circu-
lation. Similarly, if the left ventricle gave out less than the right,
all the blood would soon be crowded into the lungs. The fact that
the pressure in the right ventricle is so much less than that
in the left (probably 30 or 40 mm. as compared with 200 mm.
of mercury), is due, not to differences in the quantity of blood in
the cavities, but to the fact that the peripheral resistance which
has to be overcome in the lungs is so much less than that in the
rest of the body.

Various methods have been adopted for calculating the average
amount of blood ejected at each ventricular systole. It has been
calculated from the capacity of the recently removed and as yet not
rigid ventricle, filled with blood under a pressure equal to the calculated
average pressure in the ventricle. This method of course presupposes

158 THE WORK DONE BY THE II E ART. [BOOK i.

that the whole contents of the ventricle are ejected at each systole.
Yolkmann measured the sectional area of the aorta, and taking an
average velocity of the blood in the aorta (a very uncertain datum),
calculated the quantity of blood which must pass through the sectional
area in a given time. The number of beats in that time then gavo
him the quantity flowing through the area, and consequently ejected
from the heart, at each beat. The mean of many experiments on
different animals came out '0025 p. c. of the body weight, which in.
a man of 75 kilos would be 187*5 grms. Yierordt measured the mean
velocity and the sectional area in the carotid, and thence, from a
measurement of the sectional area of the aorta, and from a calculation
of the blood's mean velocity in it, based on the supposition that the
mean velocity in an artery was inversely as its sectional area, arrived
at the quantity flowing through the aortic sectional area in a given
time, and thus at the quantity passing at each beat. Both these
calculations are vitiated by the fact that the variations of velocity
in the aorta are so great, that any mean has really but little positive
value.

Pick by means of calculations based partly on the data gained by
observing the increase of the volume of the whole arm at each cardiac
systole, arrived at results much less than either of the above. In one
case he estimated the quantity ejected from the heart at each beat
at 53 grm., and in a second case at 77 grm.

It must be remembered that though it is of advantage to speak
of an average quantity ejected at each stroke, it is more than
probable that that quantity may vary within very wide limits.
Taking, however, 180 grms. as the quantity, in man, ejected at
each stroke at a pressure of 250 mm.1 of mercury, which is equiva-
lent to 3'21 metres of blood, this means that the left ventricle is
capable at its systole of lifting 180 grms. 3'21 m. high, i.e. it does
578 gram-metres of work at each beat. Supposing the heart to
beat 72 times a minute, this would give for the day's work of the
left ventricle, nearly 60,000 kilogram-metres ; calculating the work
of the right ventricle at one-fourth that of the left, the work of the
whole heart would amount to 75,000 kilogram-metres, which is
just about the amount of work done in the ascent of Snowdon by
a tolerably heavy man. A calculation of more practical value is
the following. Taking the quantity of blood as •£$ of the body
weight, the blood of a man weighing 75 kilos would be about
5,760 grms. If 180 grms. left the ventricle at each beat, a
quantity equivalent to the whole blood would pass through the
heart in 32 beats, i.e. in less than half a minute.

1 A high estimate is purposely taken here.

CHAP, iv.] THE VASCULAR MECHANISM. 159

Variations in the Heart's beat.

These are for the most part in reality vital phenomena, i.e.
brought about by events depending on changes in the vital
properties of some or other of the tissues of the body. It will
be convenient, however, briefly to review them here, though the
discussion of their causation must be deferred to its appropriate
place.

The frequency of the heart, i.e. the number of beats in any
given time, may vary. The average rate of the human pulse or
heart-beat is 72 a minute. It is quicker in children than in adults,
but quickens again a little in advanced age. It is quicker in the
adult female than in the adult male, in persons of short stature
than in tall people. It is increased by exertion, and thus is
quicker in a standing than in a sitting, and in a sitting than
in a lying posture. It is quickened by meals, and while varying
thus from time to time during the day, is on the whole quicker
in the evening than in early morning. It is said to be on the
whole quicker in summer than in winter. Even independently of
muscular exertion it seems to be quickened by great altitudes. It
is profoundly influenced by mental conditions.

The length of the systole may vary, indeed we have reason
to think that it does vary considerably, though as a general and
broad rule it may be stated that a frequent differs from an
infrequent pulse chiefly by the length of the diastole. Donders
found the length of the systole as measured by the interval
between the first and second sounds to be for ordinary pulses
remarkably constant in different persons, varying not more than
from '327 to '301 sec., and being therefore relatively to the whole
cardiac period less in slow than in quick pulses. •

The force of the beat may vary ; the ventricular systole may be
weak or strong. When the rate of beat is suddenly increased
there is a tendency for the individual beats to be diminished in
force, and on the other hand to be increased in force when the
rate is diminished. But there is no necessary connection between
rate and strength ; both a frequent and an infrequent pulse may
be either weak or strong.

The character of the beat may vary; the systole may be sudden
and sharp, rapidly reaching a maximum and rapidly declining, or
slow and lengthened, reaching its maximum only after some time
and declining very gradually; the latter being the slow pulse
(pulsus tardus) as distinguished from the infrequent pulse (pulsus
rams). The pulse is also sometimes spoken of as being slapping,
and sometimes as heaving. But, as we shall see immediately, the
features of the pulse are dependent not only on the heart beat but
also on the condition of the arteries.

160 VARIATIONS IN THE HEARTS BEAT. [BOOK I.

The rhythm may be intermittent or irregular. Thus in an
intermittent pulse, a beat may be so to speak dropped : the hiatus
occurring either regularly or irregularly. In an irregular rhythm
succeeding beats may differ in length, force; or character.

SEC. 3. THE

When the finger is placed on an artery, such as the radial, an
intermittent pressure on the finger, coming and going with the
beat of the heart, is felt. When a light lever such as that of the
sphygmograph is placed on the artery, the lever is raised at each
beat, falling between. The pressure on the finger, and the raising
of the lever, are expressions of the expansion of the elastic artery,
of the temporary additional distension which the artery undergoes
at each systole of the ventricle. This intermittent expansion is
called the pulse; it corresponds to the intermittent outflow of
blood from a severed artery, being present in the arteries only,
and except under particular circumstances, absent from the veins
and capillaries. The expansion is frequently visible to the eye,
and in some cases, as where an artery has a bend, may cause a
certain amount of locomotion of the vessel.

All the more important phenomena of the pulse may be
witnessed on an artificial scheme.

If two levers be placed on the arterial tubes of an artificial1
scheme, one near to the pump, and the other near to the peripheral
resistance, with a considerable length of tubing between them, and
both levers be made to write on a recording surface, one im-
mediately below the other, so that their curves can be more easily
compared, the following facts may be observed, when the pump is
set to work regularly.

1 By this is simply meant a system of tubes, along which fluid can be driven by a
pump worked at regular intervals. In the course of the tubes a (variable) resistance
is introduced in imitation of the peripheral resistance. The tubes on the proximal
side of the resistance consequently represent arteries; those on the distal side, veins.

F. 11

162

THE PULSE.

[BOOK

1. With each stroke of the pump, each lever (Fig. 27, L and II.)
rises to a maximum, la, 2a, and then falls again, thus describing a
curve, — the pulse-curve. This shews that the expansion of the

1 '• —

5ov\AAAAAAAAAAAAAAA/

FIG. 27. Pulse-curves described by a series of sphygmographic levers placed at
intervals of 20 cm. from each other along an elastic tube into which fluid is forced
by the sudden stroke of a pump. The pulse- wave is travelling from left to right, as
indicated by the arrows over the primary (a) and secondary (b, c) pulse- waves. The
dotted vertical lines drawn from the summit of the several primary waves to the
tuning-fork curve below, each complete vibration of which occupies ^sec., allow the
time to be measured which is taken up by the wave in passing along 20 cm. of the
tubing. The waves a are waves reflected from the closed distal end of the tubing ;
this is indicated by the direction of the arrows. It will be observed that in the
more distant lever VI. the reflected wave, having but a slight distance to travel,
becomes fused with the primary wave. (From Marey.)

tubing passes the point on which the lever rests in the form of
a wave. At one moment the lever is quiet: the tube beneath
it is simply distended to the normal permanent amount indicative

CHAP, iv.] THE VASCULAR MECHANISM. 163

of the mean arterial pressure; at the next moment the pulse
expansion reaches the lever, and the lever begins to rise, and
continues to do so until the top of the wave reaches it, after which
it falls again until it is once more at rest, the wave having
completely passed by.

The rise of each lever is somewhat sudden, but the fall is more
gradual, and is generally marked with some irregularities. The
suddenness of the rise is due to the suddenness with which the
sharp stroke of the pump expands the tube; the fall is more
gradual because the elastic reaction of the walls, whereby the tube
returns to its former condition after the expanding power of the
pump has ceased, is gradual in its action.

2. The size and form of each curve depend in part on the
amount of pressure exerted by the levers on the tube. If the
levers only just touch the tube in its expanded state, the rise
in each will be insignificant. If on the other hand they be pressed
down too firmly, the tube beneath will not be able to expand
as it otherwise would, and the rise of the levers will be proportion-
ately diminished. There is a certain pressure, depending on the
expansive power of the tubing, at which the tracings are best
marked.

3. If the points of the two levers be placed exactly one under
the other on the recording surface, it is obvious that, the levers
being alike except for their position on the tube, any difference in
time between the movements of the two levers will be shewn by
an interval between the beginnings of the curves they describe, if
the recording surface be made to travel sufficiently rapidly.

If the movements of the two levers be thus compared, it will be
seen that the far lever (Fig. 27, II.) commences later than the near
one (Fig. 27, 1.), the farther apart the two levers are, the greater is
the interval in time between their curves. Compare the series
I. to VI. (Fig. 27). This means that the wave of expansion, the
pulse-wave, takes some time to travel along the tube. By exact
measurement it would similarly be found that the rise of the near
lever began some fraction of a second after the stroke of the pump.

The velocity with which the pulse-wave travels depends chiefly
on the amount of rigidity possessed by the tubing. The more
extensible (with corresponding elastic reaction) the tube, the slower
is the wave ; the more rigid the tube becomes, the faster the wave
travels. The width of the tube is of much less influence, though ac-
cording to some observers the wave travels more slowly in the wider
tubes.

The rate at which the normal pulse- wave travels in the human
body has been variously estimated at from 10 to 5 metres per
second. In all probability the lower estimate is the more correct
one ; but it must be remembered that in all probability the rate
varies very considerably under different conditions. According to
all observers the velocity of the wave in passing from the groin to

11—2

164 THE PULSE. [BOOK i.

the foot is greater than that in passing from the axilla to the
wrist (6 m. against 5 m.). This is probably due to the fact that
the femoral artery with its branches is more rigid than the axil-
lary. So also in the arteries of children, the wave travels more
slowly than in the more rigid arteries of the adult ; and the velocity
appears to be increased by circumstances which heighten and
decreased by those which lessen the mean arterial pressure, since
with increasing or diminishing pressure the arterial walls become
more or less rigid.

4. When two curves taken at different distances from the
pump are compared with each other, the far curve will be found to
be shallower, with a less sudden rise, and with a more rounded
summit than the near curve : compare 5a with la, Fig. 27. In
other words, the pulse-wave as it travels onward becomes diminished
and flattened out. If a series of levers, otherwise alike, were
placed at intervals on a piece of tubing sufficiently long to convert
the intermittent stream into a continuous flow, the pulse-wave
might be observed to gradually flatten out and grow less until it
ceased to be visible.

Care must be taken not to confound the progression of the
pulse-wave with the progression of the fluid itself. The pulse-
wave travels over the moving blood somewhat as a rapidly moving
natural wave travels along a sluggishly flowing river, the velocity
of the pulse-wave being 9 metres per sec., while that of the current
of blood is not more than half a metre per sec. even in the large
arteries, and diminishes rapidly in the smaller ones.

Taking the duration of the pulse-wave, that is the time taken
by any point in the arterial tract, in expanding and returning to
its former calibre, so low as -^ of a second, it is evident that the
pulse-wave started by any one systole, even if it travels so slowly
as 5 m. per sec., will before it is completed have reached a
point y^ of 5m. = 2 in. distant from the ventricle. But even in the
tallest man the tips of the toes are not 2 m. distant from the heart.
In other words, the length of the pulse-wave is much greater
than the whole length of the arterial system, so that the beginning
of each wave has become lost in the small arteries and capillaries
some time before the end of it has finally passed away from the
beginning of the aorta.

The general causation of the pulse may then be summed up
somewhat as follows. The systole of the ventricle drives a
quantity of blood into the already full aorta. The sudden injection
of this quantity of blood expands the portion of the aorta next
to the heart, and thus gives rise to the sudden up-stroke of the
pulse-curve. The rapidity of the flow from the ventricle being
greatest at its beginning, the maximum of expansion is soon
reached, and the aortic walls, even while for a short time blood is
still, with diminishing rapidity, issuing from the ventricle, tend by
virtue of their elasticity to return to their former calibre. This

CHAP, iv.]

THE VASCULAR MECHANISM.

165

return continues after the flow has ceased, and the aortic valves
soon becoming closed, the elastic force thus brought into play serves
to drive the blood onward. The elastic recoil being slower than the
initial expansion, the down-stroke of the pulse-curve is more gradual
than the up-stroke. Of this portion of the aorta, which actually
receives the blood ejected from the heart, the part immediately
adjacent to the semilunar valves begins to expand first, and the ex-
pansion travels thence on to the end of this portion. In the same
way it travels on from this portion through all the succeeding portions
of the arterial system. For the total expansion required to make room
for the new quantity of blood cannot be provided by that portion
alone of the aorta into which the blood is actually received ; it is
supplied by the whole arterial system : the old quantity of blood
which is replaced by the new in this first portion has to find room
for itself in the rest of the arterial space. As the expansion
travels onward, however, the increase of pressure which each
portion transmits to the succeeding portion will be less than that
which it received from the preceding portion. For the whole
increase of pressure due to the systole of the ventricle has to
be distributed over the whole of the arterial system, and a fraction
of it must therefore be left behind at each stage of its progress ;
that is to say, the expansion is continually growing less, as the
pulse travels from the heart to the capillaries ; hence the diminished
height of the pulse-curve in the more distant arteries, and its
disappearance in the capillaries.

Secondary Waves and Dicrotism. In nearly all pulse tracings,
the curve of the expansion and contraction of the artery is broken

A/VVWl/WWWWV

FlG. 28. PULSE-TBACING FEOM CAROTID ARTERY OF HEALTHY MAN1 (from Moens).

x, commencement of expansion of the artery. A, summit of the first rise.

C , dicrotic secondary wave. B, predicrotic secondary wave, p notch preceding this.

D, succeeding secondary wave. The curve above is that of a tuning-fork with ten
double vibrations in a second.

1 It will be understood that in the case of this and the succeeding sphygmo-
graphic tracings (for the latter I am indebted to Dr Galabin and Dr Roy)
comparisons between the several curves can only be made in a limited
manner and with precautions, since the tracings are taken with different
amplifications, pressures, &c. — and are some from man, others from animals. They
are introduced simply to illustrate points treated of successively in the text.

166

THE PULSE.

[BOOK L

by two, three, or several smaller elevations and depressions:
secondary waves are imposed upon the fundamental wave. In the
sphygmographic tracing from the carotid and radial reproduced in
Figs. 28 and 29 and in many of the other tracings given, these
secondary elevations are marked as B, C, D. When one such

FIG. 29. PULSE-CURVE FROM RADIAL OP MAN.

Taken with extra vascular pressure of 70 mm. mercury. The vertical curved line
L, gives the tracing which the recording lever made when the blackened paper was
motionless. The horizontal line forms the abscissa of the tracing. The curved
interrupted lines shew the distance from one another in time of the chief phases of
the pulse wave, x = commencement and A close of expansion of artery, p, predi-
crotic notch, d, dicrotic notch. C, dicrotic crest. D, post-dicrotic crest. /, the
post-dicrotic notch.

secondary elevation only is conspicuous, so that the pulse-curve
presents two notable crests only, the primary crest and the second-
ary one, the pulse is said to be "dicrotic"; when two secondary
crests are prominent, the pulse is often called "tricrotic," where

FIG. 30. ANACROTIC PULSE-TRACING FROM THE CAROTID OF RABBIT.

several "polycrotic." As a general rule, the secondary elevations
appear only on the descending limb of the whole wave as in most
of the curves given, and the curve is then spoken of as "katacrotic."
Sometimes, however, the first elevation or crest is not the highest but

CHAP, iv.]

THE VASCULAR MECHANISM.

167

appears on the ascending portion of the main curve as in Fig. 30
and Fig. 33 : such a curve is spoken of as "anacrotic."

Of these secondary elevations, the most frequent, conspicuous
and important is the one which appears some way down on the
descending limb and is marked C on most of the curves. It is
more or less distinctly visible on all sphygmographic tracings and
may be seen in sphygmograms of the aorta as well as of other
arteries. Sometimes it is so slight as to be hardly discernible; at
other times it may be so marked as to give rise to a really double
pulse (Fig. 31), i.e. a pulse which can be felt as double by the finger ;
hence it has been called the dicrotic elevation or the dicrotic wave,
the notch preceding the elevation being spoken of as the "dicrotic

FlG. 31. TWO GBADES OF MARKED DICBOTISM IN RADIAL PULSE OF MAN.

(Typhoid Fever.)

notch." Neither it nor any other secondary elevations can be recog-
nised in the tracings of blood-pressure taken with a manometer.
This may be explained by the fact that the movements of the
mercury column are too sluggish to reproduce these finer variations;
but dicrotism is also conspicuous by its absence in the tracings
given by more delicately responsive instruments. Moreover, when
the normal pulse is felt by the finger, most persons find themselves
unable to detect any dicrotism. Hence some have been led to

FlG. 32. NOBMAL PULSE-CURVE IN THE AORTA FROM THE DOG.

maintain that this and the other secondary elevations do not really
exist in the normal pulse. But it seems difficult to maintain this
view in face of the experiment of Landois, in which the tracing
obtained by allowing the blood to spirt directly from an opened
small artery, such as the dorsalis pedis, upon a recording surface,
shewed in an unmistakeable manner the existence of the dicrotic
wave.

168

THE PULSE.

[BOOK i.

Less constant and conspicuous than the dicrotic wave but yet
appearing in most sphygmograms is an elevation which appears
higher up on the descending limb of the main wave; it is marked
B on some of the curves and is frequently called the predicrotic

FIG. 33. ANAGBOTIC SPHTGMOGBAPH TRACING FROM THE ASCENDING AORTA (Aneurism).

wave ; it may become very prominent. Sometimes other secondary
waves are seen following the dicrotic wave as at D in Fig. 28; but
these are very inconstant and usually even when present incon-
spicuous.

When tracings are taken from several arteries or from the same
artery under different conditions of the body, these secondary
waves are found to vary very considerably, giving rise to many
characteristic forms of pulse-curve. Moreover in the same artery,

FlG. 34. PULSE-TRACING FROM THE DORSALIS PEDIS.

and with the same instrument, the form and even the special features
of the curve vary according to the amount of pressure (expressed
either in ounces or in mm. of mercury) with which the lever is
pressed upon the artery. Figs. 35, 36 shew a series of changes
thus brought about by varying the pressure of the lever ; and Fig. 37
shews the effect of this extra vascular pressure on the form of a
fully dicrotic pulse. This effect of pressure in fact varies according
to the condition of the vascular system.

"Were we able with certainty to trace back the several features
of the curves to their respective causes, an adequate examination
of sphygmographic tracings would undoubtedly disclose much
valuable information concerning the condition of the body pre-
senting them. Unfortunately the problem of the origin of these
secondary waves is a most difficult and complex one ; so much so
that the detailed interpretation of a sphygmographic tracing is still
in most cases extremely uncertain.

CHAP, iv.]

THE VASCULAR MECHANISM.

169

Various causes have been suggested as bringing about the
secondary waves, and much discussion has arisen especially con-
cerning the dicrotic wave. When the tube of the artificial scheme
bearing two levers is blocked just beyond the far lever, the primary
wave is seen to be accompanied by a second wave, which at the far
lever is seen close to, and often fused into, the primary wave

Fra. 35. INFLUENCE OF CHANGES IN THE PRESSURE APPLIED TO THE EXTERIOR OF THE

VESSEL ON THE FORM OF THE CURVE.

a, From the Art. radialis of healthy man of 27 years of age with an extra arterial
pressure equal in a to 70 mm., in a' to 50mm., in a" to 30 mm. mercury.

(Fig. 27, VI. a'), but at the near lever is at some distance from it
(Fig. 27, I. a), being the farther from it, the longer the interval
between the lever and the block in the tube. The second wave is
evidently the primary wave reflected at the block and travelling
backwards towards the pump. It thus of course passes the far
lever before the near one. And it has been argued that the
dicrotic wave of the pulse is really such a reflected wave, started
either at the minute arteries and capillaries, or at the points
of bifurcation of the larger arteries, and travelling backwards to
the aorta. But if this were the case the distance between the
primary crest and the dicrotic crest ought to be less in arteries
more distant from the heart than in those nearer, just as in
the artificial scheme the reflected wave is fused with a primary

170

THE PULSE.

[BOOK i.

wave near the block, but becomes more and more separated
from it, the farther back we trace it. Now this is not the case
with the dicrotic wave. Careful measurements shew that the
distance between the primary and dicrotic crests is either greater

FlO. 36. NOBMAL PULSE-CURVE FBOM CAEOTID OF BABBIT J

shewing influence on height and form of curve of changes in the extra vascular
pressure which was in a 20 mm., in 6 30 mm., in c 40 mm., and d 50 mm. of mer-
cury.

or certainly not less in the smaller or more distant arteries than in
the larger or nearer ones. This feature indeed proves that the
dicrotic wave cannot be in any way a retrograde wave. Again, the
more rapidly the primary wave is obliterated or at least diminished
on its way to the periphery the less conspicuous should be the
dicrotic wave. Hence increased extensibility and increased elastic
reaction of the arterial walls which tend to use up rapidly the
primary wave, should also lessen the dicrotic wave. But as a
matter of fact these conditions are favourable to the prominence of

CHAP, iv.] THE VASCULAR MECHANISM. 171

the dicrotic wave. Besides the multitudinous peripheral division
would render one large peripherically reflected wave impossible.

But in addition to reflected waves, other waves which may be
called "waves of oscillation," make their appearance when a fluid is
driven through a system of tubes, by means of an intermittent
force. And different origins have been assigned to secondary waves
of this description.

FIG. 37. DICROTIC PULSE-CURVE DUE TO LOSS OF BLOOD.

From carotid of rabbit with, extra-vascular pressures in a of 50 mm., & of 40 mm.
c of 20 mm., and d of 10mm. of mercury.

Thus when the rapid flow of a fluid along a tube is suddenly
checked at a point of its course the inertia of the fluid will carry the
column of fluid still forwards so as to leave behind it a diminution
of pressure. This diminution will appear on a graphic record of
the pressure as a depression or notch ; and will be followed by a
secondary rise as a reflux of fluid takes place towards the point
where the pressure has become diminished. Both the depression
and the secondary rise will travel as a wave along the tube, being
frequently followed by other smaller waves of similar character and
similar origin. Waves thus originating have been appealed to as
explaining the secondary waves of the pulse-curve. Thus at the
moment when the ventricle, having emptied itself, ceases to throw
any more blood into the aorta, the blood which was last ejected
being carried forward by its inertia gives rise to a diminution of
pressure in the ventricle and at the root of the aorta. The aortic
walls forthwith contract upon this diminished pressure, and a reflux
of blood towards the semilunar valves takes place, leading to the
appearance of a depression or notch in the pulse-curve, which is
propagated forwards along the aorta. This reflux closes the semi-
lunar valves and at the same time leads to a recovery of pressure

172 THE PULSE. [BOOK i.

which similarly appears on the pulse-curve as an elevation succeed-
ing the notch.

Then again it has been argued that in any section of the
arterial tract, the inertia of the walls and of the contained blood,
in each expansion of the section, carries them on in their movement
of expansion some little time after the actual expanding force has
ceased to act. This leads to a falling back or contraction, which
again by reason of the same inertia overshoots its mark, and thus
through a series of oscillations, of which the first is the most
conspicuous, the artery settles down to its normal calibre before the
next expansion reaches it. The extent of such oscillations is
determined, not only by the character of the walls but by the
specific gravity of the contained fluid. In the artificial scheme
with the same elastic tubing the secondary waves thus caused are
much greater with mercury than with water, and disappear almost
wholly when air is employed. Such waves of oscillation may be
supposed to be generated in different degrees, in each and every
section of the arterial tract ; the waves due to a cessation of the
flow are on the contrary generated at the point where the inter-
mittence is effected, and may be seen in rigid as well as in elastic
tubes ; but these latter waves also are profoundly modified by the
nature of the walls of the tubes along which they are transmitted.

Lastly, it has been maintained that these secondary waves are
of active not passive origin; that is, that they are caused by a
rapid muscular contraction of the arterial walls following up so to
speak the arterial beat.

We have dwelt at so great a length on these secondary waves
of the pulse-curve because of the importance attached to them in
clinical medicine ; but it would be hardly profitable to enter more
fully into the discussion of these several contending views. As an
instance of the difficulty of the subject and the insufficiency of our
knowledge, we may point out that observers are not yet agreed as
to which part of the curve corresponds to the closure of the
semilunar valves. Thus some maintain that this event corresponds
to and indeed is indicated by the dicrotic wave, the dicrotic notch
representing the reflux towards the ventricle, and the dicrotic
elevation a new forward movement reflected from the closed
valves. But under this view, though it seems the more probable,
the predicrotic wave presents a difficulty; and indeed others
maintain that the moment of closure of the semilunar valves is
indicated by this the predicrotic, and not by the dicrotic wave.
Until this and other points are finally settled, all interpretations of
modifications of the pulse-curve must remain uncertain and un-
satisfactory.

The following facts however may be borne in mind as not only
of practical importance, but as necessary data for any judgments
concerning the pulse-curve.

CHAP, iv.] THE VASCULAR MECHANISM. 173

1. Whatever the origin of the dicrotic wave, its features may
be modified by changes taking place in the peripheral (arterial)
districts without any alteration in the central (cardiac) events.
Thus dicrotism may become conspicuous in one artery while re-
maining indistinct in others.

2. The prominence of the dicrotic wave, though favoured by
a sudden strong ventricular systole, is especially assisted by a
diminution of blood-pressure. Thus it is a marked characteristic
of the pulse in many cases of fever (Fig. 31) where blood-pressure

, is low. So also it may be brought on at once in an artery in which
it was previously insignificant by sudden lowering of the blood-
pressure as is shewn in Fig. 38. It may similarly be induced by

FIG. 38. TRACING FBOM RADIAL IN MAN ;

shewing change in form of pulse-curve accompanying a sudden fall in the blood-
pressure. The pulse, at first not markedly dicrotic, rapidly becomes so, and then
passes on into the condition known as hyperdicrotism, where the dicrotic notch
reaches a level lower than that from which the primary rise started.

section of the vaso-motor nerves belonging to the branches of the
artery; this, as we shall presently see, diminishes the peripheral
resistance, through an expansion of the minute arteries, and so
leads to a lowering of the blood-pressure in the main arteries. The
prominence of the dicrotic wave is further dependent on the amount
of extensibility and elastic reaction of the arterial walls. Hence
the dicrotic wave is not well marked in arteries which have become
rigid by disease or old age.

We may add that an anacrotic pulse, in which a crest followed
by a notch is visible on the ascending portion of the curve, before
the maximum of expansion is reached, though it may sometimes
be produced temporarily in healthy persons, is generally associated
with diseased conditions, usually such in which the arteries are abnor-
mally rigid. It has been interpreted as due to the pressure in the
aorta rising even after the first rapid rush from the ventricle. Under

174 THE PULSE. [BOOK i.

normal conditions, as we have already seen, the maximum expansion
is soon reached, but in cases where the arterial walls are unusually
rigid and the heart at the same time not abnormally weak, the
ventricle may continue to empty itself against a resistance which
increases rapidly with the amount of blood passing into the aorta,
so that in spite of the diminishing rapidity with which the blood
is leaving the ventricle the insufficient distensibility of the vessels
causes the pressure in their interior to continue to rise until nearly
the end of the outflow from the heart. An anacrotic pulse also
frequently accompanies hypertrophy and dilation of the left
ventricle.

The pulse then is the expression of two sets of conditions : one
pertaining to the heart, and the other to the arterial system. The
arterial conditions remaining the same, the characters of the pulse
may be modified by changes taking place in the beat of the heart ;
and again, the beat of the heart remaining the same, the pulse may
be modified by changes taking place in the arterial walls. Hence
the diagnostic use of the pulse-characters. It must however be
remembered that arterial changes may be accompanied by com-
pensating cardiac changes, to such an extent, that the same
features of the pulse may obtain under totally diverse conditions,
provided that these conditions affect both factors in compensating
directions.

Venous Pulse. Under certain circumstances the pulse may be
carried on from the arteries through the capillaries into the veins.
Thus when the salivary gland is actively secreting, the blood may
issue from the gland through the veins in a rapid pulsating stream.
The nervous events which give rise to the secretion of saliva, lead
at the same time, by the agency of vaso-motor nerves, of which we
shall presently speak, to a dilation of the small arteries of the gland.
This dilation of the small arteries diminishes the peripheral resist-
ance by allowing more blood to pass through them with less friction;
in consequence the elasticity of the arterial walls is brought into play
to a less extent than before, and this may in certain cases go so
far, that as in the case of the artificial apparatus, where the elastic
tubing has an open end (see p. 129), not enough elasticity is brought
into action to convert the intermittent arterial flow into a con-
tinuous one. A similar venous pulse is also sometimes seen in
other organs.

Careful tracings of the great veins in the neighbourhood of the
heart shew elevations and depressions, which appear due to the
variations of intracardiac pressure, and which may perhaps be
spoken of as constituting a "venous pulse"; but at present they
need further elucidation. In cases of insufficiency of the tricuspid
valves, the systole of the ventricle makes itself felt in the great
veins; and a distension travelling backwards from the heart be-

CHAP, iv.] THE VASCULAR MECHANISM. 175

comes very visible in the veins of the neck. This is sometimes
spoken of as a venous pulse.

Variations of pressure in the great veins due to the respiratory
movements are also sometimes spoken of as a venous pulse ; the
nature of these variations will be explained in treating of respi-
ration.

II. THE VITAL PHENOMENA OF THE CIRCULATION.

So far the facts with which we have had to deal, with the ex-
ception of the heart's beat itself, have been simply physical facts.
All the essential phenomena which we have studied may be re-
produced on a dead model. Such an unvarying mechanical
vascular system would however be useless to a living body whose
actions were at all complicated. The prominent feature of a living
mechanism is the power of adapting itself to changes in its in-
ternal and external circumstances. In such a system as we have
sketched above there would be but scanty power of adaptation.
The well-constructed machine might work with beautiful regu-
larity; but its regularity would be its destruction. The same
quantity of blood would always flow in the same steady stream
through each and every tissue and organ, irrespective of local and
general wants. The brain and the stomach, whether at work and
needing much, or at rest and needing little, would receive their
ration of blood, allotted with a pernicious monotony. Just the
same amount of blood would pass through the skin on the hottest
as on the coldest day. The canon of the life of every part for the
whole period of its existence would be furnished by the inborn
diameter of its blood-vessels, and by the unvarying motive power
of the heart.

Such a rigid system however does not exist in actual living
beings. The vascular mechanism in all animals which possess one
is capable of local and general modifications, adapting it to local
and general changes of circumstances. These modifications fall
into two great classes :

1. Changes in the heart's beat. These, being central, have of
course a general effect.

2. Changes in the peripheral resistance, due to variations in
the calibre of the minute arteries, brought about by the agency of
their contractile muscular coats. These changes may be either
local or general.

CHAP, iv.] THE VASCULAR MECHANISM. 177

To these may be added as subsidiary modifying events :

3. Changes in the peripheral resistance of the capillaries due
to alterations in the adhesiveness of the capillary walls or to
other influences arising out of the as yet obscure relations existing
between the blood within and the tissue without the thin per-
meable capillary walls, and depending on the vital conditions of the
one or of the other. Such changes causing an increase of peri-
pheral resistance are seen to a marked degree in the pathological
condition known as stasis.

4. Changes in the quantity of blood in circulation.

The two first and chief classes of events (and probably the
third) are directly under the dominion of the nervous system. It
is by means of the nervous system that the heart's beat and the
calibre of the minute arteries are brought into relation with each
other, and with almost every part of the body. It is by means of
the nervous system acting either on the heart, or on the small
arteries, or on both, that a change of circumstances affecting either
the whole or a part of the body is met by compensating or
regulative changes in the flow of blood. It is by means of the
nervous system that an organ has a more full supply of blood when
at work than when at rest, that the stream of blood through the
skin rises and ebbs with the rise and fall of the temperature of the
air, that the work of the heart is tempered to meet the strain of
overfull arteries, and that the arterial gates open and shut as the
force of the central pump waxes and wanes. Each of these vital
factors of the circulation must therefore be considered in connection
with those parts of the nervous system which are concerned in
its action.

F.

12

SEC. 4. CHANGES IN THE BEAT OF THE HEART.

We have already discussed the more purely mechanical pheno-
mena of the heart. We have therefore in the present section only
to inquire into the nature and working of the mechanism (chiefly
at least nervous) by which the beat of the heart is maintained,
varied, and regulated.

In studying closely the phenomena of the beat of the heart it
becomes necessary to obtain a graphic record of various movements.

1. In the frog or other cold-blooded animal, a light lever may be
placed directly on the ventricle (or on an auricle, <fec.) and changes of
form, due either to distension by the influx of blood, or to the systole,
will cause movements of the lever, which may be recorded on a
travelling surface. The same method may be applied to the mam-
malian heart, but difficulties are introduced by the locomotion of the
heart caused by the movements of the lungs.

2. Or, as in GaskelTs method, the heart may be fixed by a clamp
carefully adjusted round the auriculo-ventricular groove while the apex
of the ventricle and some portion of one auricle are attached by threads
to horizontal levers placed respectively above and below the heart.
The auricle and the ventricle each in its systole pulls at the lever
attached to it; and the times and extent of the contractions may thus
be recorded.

3. A record of intracardiac pressure may be taken in the frog or
tortoise, as in the mammal, by means of an appropriate manometer.
And in these animals at all events it is easy to keep up an artificial
circulation. A cannula is introduced into the sinus venosus and another
into the ventricle through the aorta. Serum or dilute blood (or any
other fluid which it may be desired to employ) is driven by moderate
pressure through the former; to the latter is attached a tube connected
by means of a side piece with a small mercury manometer. So long
as the exit tube is open at the end, fluid flows freely through the
heart and apparatus. Upon closing the exit tube at its far end, the
force of the ventricular systole is brought to bear on the manometer,

CHAP, iv.]

THE VASCULAR MECHANISM.

179

the index of which registers in the usual way the movements of
the mercury column. Newell Martin has succeeded in applying a
modification of this method to the mammalian heart.

4. The movements of the ventricle may be registered by introducing
into it through the auriculo- ventricular orifice a so-called 'perfusion'
cannula, Fig. 39 I., with a double tube, one inside the other, and tying the
ventricle on to the cannula at the auriculo-ventricular groove, or at any
level below that which may be desired. The blood or other fluid is
driven at an adequate pressure through the tube a, enters the ventricle,
and returns by the tube b. If b be connected with a manometer as in
method 3, the movements of the ventricle may be registered.

5. In the apparatus of Roy, Fig. 39 n., the exit tube is free but the
ventricle (the same method may be adopted for the whole heart) is
placed in an air-tight chamber filled with oil or partly with normal
saline solution and partly with oiL By means of the tube b the interior

FlG. 39. PUBELT DIAGRAMMATIC FIGURES OP

I. Perfusion cannula tied into frog's ventricle, a. entrance, &, exit, tube;
a, wall of ventricle; £, ligature.

II. Eoy's apparatus modified by Gaskell. a, chamber filled with saline solution
and oil, containing the ventricle a tied on to perfusion Ccinnula/. b, tube leading
to cylinder c, in which moves piston d, working the lever e.

of the chamber a is continuous with that of a small cylinder c in which
a piston d secured by thin flexible animal membrane works up and
down. The piston again bears on a lever e by means of which its
movements may be registered. When the ventricle contracts, and by
contracting diminishes in volume, there is a lessening of pressure in the
interior of the chamber, this is transmitted to the cylinder, and the
piston correspondingly rises, carrying with it the lever. As the
ventricle subsequently becomes distended the pressure in the chamber
is increased, and the piston and lever sink. In this way variations in
the volume of the ventricle may be recorded, without any interference
with the flow of blood or fluid through it.

TO O
*.£— ~*

180 THE CARDIAC MUSCLES. [BOOK i.

The Mechanism of the Normal Beat.

The cardiac Muscles. When a frog's heart which has ceased
to beat spontaneously is stimulated by touching it with a blunt
needle, a beat is frequently called forth ; this artificial beat differs
in no obvious characters from a natural beat. The latent period of
such an artificial beat is remarkably long, the length varying within
very wide limits. Thus the cardiac contraction is more like that
of an unstriated than of a striated muscle. The beat is in fact a
modified or peculiar form of peristaltic contraction. In the hearts
of some animals, the ventricle forms a straight tube ; and in these
the peristaltic character of the beat is obvious ; but in a twisted
tube like that of the vertebrate ventricle, ordinary peristaltic
action would be impotent to drive the blood onward, and is
accordingly so far modified that the peristaltic character of the beat
is recognised only when the action of the heart becomes slow and
feeble.

The cardiac, like the skeletal muscular fibre, after a contraction
returns by relaxation to its previous shape, and the whole ventricle
(or whole heart) regains after a beat the form natural to its qui-
escent state. This diastolic expansion, though increased by, is not
dependent on, the influx of fluid into the cavities of the heart.
Thus the cavity of the empty quiescent mammalian left ventricle,
though smaller than when it is distended with blood as in its
normal action, is larger than when it is in systole or when rigor
mortis has set in ; moreover if its dimensions be artificially less-
ened, as when it is squeezed with the hand, it returns by an elastic
reaction to its former volume when the pressure is removed.

The cardiac muscles in a healthy condition are, like the skeletal
muscles, very elastic. Their elasticity is however soon interfered
with by imperfect nutrition ; and a 'contraction remainder' (p. 57)
under certain circumstances is readily developed.

Under the influences of certain poisons, veratrin, digitalin. &c.,
the length of the beat is enormously prolonged, and the ventricle
is eventually thrown into a remarkable contracted condition, the
exact nature of which is perhaps not thoroughly understood,
though it is believed by many to be due to a deficiency of elastic
reaction.

One great feature of the cardiac beat produced by artificial
stimulation is the absence of that relationship between the strength
of the stimulus employed and the amount of contraction evoked
which is so striking in a skeletal muscle (p. 85). The beat with
which a heart responds to a stimulus, e.g. a single induction shock,
is, if there be any response at all, equally large when a feeble as
when a strong stimulus is used, though the strength of the beat
evoked either by a strong or a weak stimulus may vary con-
siderably within even a very short period of time.

CHAP, iv.] THE VASCULAR MECHANISM. 181

When a second induction shock is sent in at a certain interval
after a first, the beat due to the second shock is often larger than
the first, the beneficial effects of a "contraction (see p. 96) being
even still more manifest in the heart than in an ordinary skeletal
muscle. Frequently by successive shocks of equal intensity a
'staircase' of beats of successively increasing amplitude may be
produced.

When a second induction shock follows upon the first too
rapidly, it is apparently without effect ; no second beat is produced.
So also when a series of rapidly repeated induction shocks are sent
in, a certain number of them are thus 'ineffectual'; the application
of the ordinary interrupted current gives rise not to a tetanus but
to a rhythmic series of beats. The ' refractory period,' which is so
brief in the skeletal muscle (see p. 87), is very prolonged in the
cardiac muscle. So also in a spontaneously beating heart, induc-
tion shocks sent in at a certain phase of a cardiac cycle, e.g. the
commencement of the systole, are ineffectual, though they produce
forced beats when sent in at the other phases of the cycle.

As we shall immediately see, the beat of the heart, and even of
a part of the heart such as the ventricle, is not a mere muscular
contraction but a complex act, in which both nervous and muscular
elements intervene; and it is difficult in all cases to distinguish
the action of the one from that of the other. It is probable how-
ever that many of the features which we have just described are
due to peculiarities of the cardiac muscle.

Nervous mechanism of the Beat. The heart of a mammal or
of a warm-blooded animal ceases to beat almost immediately after
being removed from the body in the ordinary way ; and though by
special precautions and by means of an artificial circulation of blood,
an isolated mammalian heart may be preserved in a pulsating con-
dition for a considerable time, our knowledge of the exact nature
and of the causes of the cardiac beat is as yet almost entirely
based on the study of the hearts of cold-blooded animals, which
will continue to beat for hours, or under favourable circumstances
even for days, after they have been removed from the body with
only ordinary care. We have reason to think that the mechanism
by which the beat is carried on, varies in some of its secondary
features in even the cold-blooded animals: that the hearts, for
instance, of the snake, the tortoise and the frog, differ as to the
exact manner of carrying out the beat, both from each other and
from the bird and the mammal; but we may, at first at all
events, take the heart of the frog as illustrating the main and
important truths confirm' Tig the causes and mechanism of the
beat.

The heart of the frog, as we have just said, will continue to
beat for hours after removal from the body; and the beats are in
all important respects identical with the beats executed by the

182 NERVOUS MECHANISM OF THE BEAT. [BOOK i.

heart in its normal condition within the living body. Hence we
may infer that the beat of the heart is an automatic action : the
muscular contractions which constitute the beat are caused by
impulses which arise spontaneously in the heart itself.

The beat goes on even after the cavities have been cleared of
blood, and indeed when they are almost empty of all fluid. A beat
cannot therefore be, as was once thought, a reflex act excited by
the entrance of blood into the cavities of the heart.

In the frog's heart, as in that of the mammal, there is a distinct
sequence of events. First comes the beat of the sinus venosus,
preceded by a more or less peristaltic contraction of the large veins
leading into it, next follows the sharp beat of the two auricles
together, then comes the longer beat of the ventricle, and lastly
the beat of the bulbus arteriosus completes the cycle. If the
incisions, by which the heart is removed, be made carefully, so as
not to injure at all the sinus venosus, the beats will continue after
a very short pause, or sometimes without any real interruption,
with great vigour for a very considerable time. In order that
the frog's heart may beat after removal from the body with the
nearest approach in rapidity, regularity and endurance to the
normal condition, the removal must be carried out so as to leave
the sinus venosus intact.

When the incision is carried through the auricles so as to leave
the sinus venosus behind in the body, the result is different. The
sinus venosus beats forcibly and regularly, having suffered hardly
any interruption from the operation. The excised heart, however,
remains, in the majority of cases, for some time motionless.
Stimulated by a prick or an induction-shock, it will give one, two
or several beats, and then come to rest. But it will in the majority
of cases, the animal having previously been in a vigorous condi-
tion, recommence after a while its spontaneous beating, the systole
of the ventricle following that of the auricles ; but the rhythm of
beat will not necessarily be the same as that of the sinus venosus
left in the body, and the beats will not continue to go on for so
long a time as will those of a heart still retaining the sinus
venosus.

When the incision is carried through the auriculo-ventricular
groove, so as to leave the auricles and sinus venosus within the
body, and to isolate the ventricle only, the results are similar but
more marked. The sinus and auricles beat regularly and vigor-
ously, with their proper sequence, but the ventricle generally re-
mains for a long time quiescent. When stimulated however the
ventricle will give one, two or several beats, and after a while, in
many cases at least, will eventually set up a spontaneous pulsation
with an independent rhythm; and this may last for some consider-
able time, but the beats are not so regular and will not go on for
so long a time as will those of a ventricle to which the auricles are
still attached.

CHAP, iv.] THE VASCULAR MECHANISM. 183

If a transverse incision be carried through the ventricle at
about its upper third, leaving the base of the ventricle still
attached to the auricles, the portion of the heart left in the body
will go on pulsating regularly, with the ordinary sequence of
sinus, auricles, ventricle, but the isolated lower two-thirds of the
ventricle will not beat spontaneously at all however long it be
watched. Moreover in response to a single stimulus such as an
induction-shock or a gentle prick it gives, not as in the case of the
entire ventricle or of the ventricle to which the auricles are attached,
a series of beats, but a single beat.

Lastly, to complete the story we may add, that when the
heart is bisected longitudinally, each half continues to beat
spontaneously, with an independent rhythm, so that the beats of
the two halves are not necessarily synchronous, and this continuance
of spontaneous pulsations after longitudinal bisection may be seen
in the conjoined auricles and ventricle, or in the isolated auricles,
or in the isolated but entire ventricle. Moreover the auricles
may be divided in many ways and yet many of the segments
will continue beating; small pieces even may be seen under
the microscope pulsating, feebly it is true but distinctly and
rhythmically.

The various parts of the frog's heart thus form, as regards
the power of spontaneous pulsation, a descending series: sinus
venosus, auricles, entire ventricle, lower portions of ventricle,
the last exhibiting under ordinary circumstances no spontaneous
pulsations at all.

Now ganglia, containing nerve cells, are found in great abun-
dance in the sinus venosus, are seen in various parts of the auricles,
and occur as the so-called Bidder's ganglia at the junction of the
auricles and ventricle, from whence they also spread into the
upper part of the ventricle; in the lower two-thirds of the
ventricle they are entirely wanting. It is natural to infer from
this that the ganglia are in some way the agents of the spontaneous
pulsation.

The uncertainty, and in most cases temporary character of the
pulsations, occurring with seeming spontaneity, in the auricles or
ventricle separated from the sinus venosus, have led many to the
opinion that these are not really spontaneous, but of the nature of
reflex acts, induced by some obscurely acting stimuli, and that
really spontaneous pulsations proceed only from the sinus venosus.
And a view has been generally adopted which teaches that the
spontaneous beats of the frog's heart are due to rhythmic nervous
impulses started in the ganglia of the sinus venosus and spreading
thence to other parts, the ganglia of the auricles and of the
auriculo-ventricular groove acting in subordination to those of
the sinus, or behaving under certain circumstances independently
as reflex centres, or performing other functions which we shall
have to speak of immediately as of a restraining or inhibitory

184 INHIBITION OF THE BEAT. [BOOK i.

character. And the same view with possibly some slight modi-
fications has been supposed to hold good for the hearts of all
vertebrate animals.

Facts however are met with which appear to oppose this con-
ception. If the "perfusion" cannula previously described be
introduced into a frog's ventricle and secured by a ligature
carried round the ventricle some little distance below the base, the
lower part of the ventricle remains motionless and free from
pulsations in the same way as when it has been removed by
an incision. If however the cavity be regularly supplied with
serum or diluted blood (that of the rabbit being practically the
most useful), after a longer or shorter time, this portion of the
ventricle begins to pulsate with a more or less regular rhythm
and will continue these apparent spontaneous beats for an almost
indefinite time. It is usual to explain these pulsations, which
may be witnessed even when only the extreme tip of the ventricle
is tied on to the cannula, as not really spontaneous but as excited
by the serum or dilute blood, supplied under pressure, acting as a
stimulus; such an explanation is however hardly satisfactory.
Then again, though it is quite true that the beats of an isolated
frog's ventricle are uncertain and temporary, so much so as
perhaps to justify the view that they are not really spontaneous,
the isolated ventricle of the tortoise beats with such regularity and
for so long a time, that it seems almost impossible to avoid the
conclusion that in this animal, at all events, the ventricle by itself
possesses a real power of spontaneous pulsation. Moreover even
in the frog, section at various points, of the nerves with which the
ganglia are connected, may be effected and indeed Bidder's ganglia
carefully extirpated, without the natural sequence of beat of the
several parts being changed. And careful investigation has dis-
closed many other facts, which we cannot discuss here but which
go far to shew that the generation of the beat of the heart is
a very complex matter indeed. While we must admit that the
ganglia of the sinus venosus (in the frog, or what corresponds to
these in other animals) are prepotent in the work of producing
the beat, our knowledge will not at present allow us to make
a definite and consistent statement as to what it is they exactly
do, or as to the share in generating and carrying out the beat,
which is taken by the other ganglia, and their respective nerves, or
by the muscular fibres themselves.

Inhibition of the Beat. The beat of the heart may be
stopped or checked, i.e. may be inhibited by efferent impulses
descending the vagus nerve.

If while the beats of the heart of a frog are being care-
fully registered (Fig. 40) an interrupted current of moderate
strength be sent through one of the vagi, the heart is seen to stop
beating. It remains for a time in diastole, perfectly motionless

CHAP, iv.]

THE VASCULAR MECHANISM.

185

and flaccid. If the duration of the current be short and the
strength of the current great, the standstill may continue after the
current has been shut off; the beats when they reappear are
generally at first feeble and infrequent, but soon reach or even go
beyond their previous vigour and frequency. A wholly similar
inhibition may be seen in the mammal, and indeed in man:
Gzermak, by pressing his vagus against a small osseous tumour
in his neck, and thus mechanically stimulating the nerve, was able
to stop at will the beating of his own heart; it need hardly be
added that such an experiment is a dangerous one.

The effect is not produced instantaneously; if on the curve the
point be exactly marked as at a (Fig. 40), when the current is

IIWMJU

FIG. 40. INHIBITION OF FEOG'S HEABT BY STIMULATION OF THE VAGUS.
The contractions of the ventricle are registered by means of a simple lever, so
that each rise of the lever corresponds to a beat. The interrupted current was
thrown in at a, and shut off at 6. It will be seen that one beat occurred after a, and
that the pause continued for some time after 6. To be read from right to left.

thrown in it will frequently be found that one beat at least occurs
after the current has passed into the nerve. In other words, the
inhibitory action of the vagus has a long latent period; this has
been estimated by Bonders to last in the rabbit '16 sec. The in-
hibitory effect is at a maximum soon after the moment of applica-
tion of the current, and diminishes gradually onward; so much so
is this the case, that when the current is applied for more than a
very short time the heart recommences beating before the current
is removed.

It is obvious that the normal beat of the heart may be in-
terfered with in two distinct ways : on the one hand the systole of
the auricles and ventricle (or of either) may be diminished in
vigour, on the other hand the diastole or passive interval may be
prolonged. The vagus is able to act upon the heart in both these
directions; and sometimes the one, sometimes the other effect
is most prominent. Thus at times, as in the instance shewn in
Fig. 40, the most conspicuous result is the total suppression for
some time, of all visible contractions of the ventricle; and the
beats, when they appear again, are separated by diastolic intervals

186 INHIBITION OF THE BEAT. [BOOK i.

not much larger than the normal. At other times stimulation of
the vagus does not cause any disappearance of the beats, but the
intervals between the beats are much prolonged, so that the
rhythm is for a while very slow. It is possible that these two
different effects are brought about by more or less distinct
mechanisms.

We said just now that after the stimulation of the vagus has
ceased the beats may go beyond their previous vigour and fre-
quency. This is sometimes remarkably the case. We might be
tempted to speak of it as a reaction, were it not that no necessary
relation obtains between the amount of slowing or weakening and
the amount of succeeding acceleration or augmentation. Indeed
the latter effect may make its appearance without any previous
inhibition; that is to say, under certain circumstances stimulation
of the vagus may produce not inhibition but either augmentation
of the beats, or quickening of the rhythm, or both.

During the standstill, direct stimulation of the heart, as by
touching the auricle or ventricle, will produce a single beat;
though spontaneous pulsations are absent, the mechanism for the
production of a beat is capable of being put into action.

The stimulus need not be an interrupted current; mechanical
and chemical stimulation of the vagus also produces inhibition,
though less readily.

The stimulus may be applied at any part of the course of
either vagus (though it frequently happens in some animals, as in
the frog, that one vagus is more efficient than the other); but
perhaps the most marked effects are produced, when the electrodes
are placed on the boundary-line between the sinus venosus and the
auricles.

The effects of various poisons in reference to this inhibitory
action are very interesting. After atropin, even in a minute dose,
has been injected into the blood, stimulation of the vagus even
with the most powerful currents produces no inhibition whatever.
The heart continues to beat as if nothing were happening ; atropin
in some way or other does away with the normal inhibitory action
of the vagus.

In slight urari poisoning, the inhibitory action of the vagus
is still present; in the profounder stages it disappears, but even then
inhibition may be obtained by applying the electrodes to the sinus.
In order to explain this result it has been supposed that what
we may call the inhibitory fibres of the vagus terminate in an in-
hibitory mechanism (probably ganglionic in nature), seated in the
heart itself, and that the urari, while in large doses it may paralyse
the terminal fibres of the vagus, leaves this inhibitory mechanism
intact and capable of being thrown into activity by a stimulus ap-
plied directly to the sinus. After atropin has been given, inhibition
cannot be brought about by stimulation either of the vagus fibres
or of the sinus, or indeed of any part of the heart. Hence it is in-

CHAP, iv.] THE VASCULAR MECHANISM. 187

ferred that atropin, unlike urari, paralyses this intrinsic inhibitory
mechanism itself.

After the application of muscarin1 or pilocarpin, the heart stops
beating, and remains in diastole in perfect standstill. Its ap-
pearance is then exactly that of a heart inhibited by profound and
lasting vagus stimulation. This effect is not hindered by urari.
The application however of a small dose of atropin at once restores
the beat. These facts are interpreted as meaning that muscarin
(or pilocarpin) stimulates or excites the inhibitory apparatus
spoken of above, which atropin paralyses or places hors de combat.

There are many other effects of various poisons which have been
appealed to as throwing light on the action of the heart ; but we
must not enter into the discussion of these here. We may however
in this connection call attention to a remarkable experiment
known as that of Stannius. If a ligature be drawn tightly-
round the junction of the sinus venosus with the auricles, or if
the auricles be separated from the sinus by an incision carried
along the boundary-line between them, a standstill is produced
closely resembling a very prolonged vagus inhibition. Quiescence
thus induced may last a very considerable time. During the
standstill, a pulsation may be induced by a stimulus applied
directly to the heart, a whole series of beats being evoked when a
mechanical stimulus, such as the prick of a needle, is applied over
the seat of Bidder's ganglia at the junction of the auricles with the
ventricles, or to the ganglia in the auricles or to those in the
bulbus ; and when the ventricle is separated by an incision from
the auricles, the former will recommence beating, while the latter
remain as quiescent as before. The condition of the heart in
this experiment so closely resembles the standstill produced by
vagus stimulation, that the effect might be supposed to be caused
by the ligature (or section) stimulating the vagus fibres or the
inhibitory mechanism at the sinus; but this view is clearly dis-
proved by the fact that the experiment succeeds perfectly well
after atropin has been given. Another explanation attributes the
standstill to the section depriving the heart of the prepotent
ganglia in the sinus, and the recommencement of pulsation in the
ventricle after separation by incision or ligature from the auricles
to the incision or ligature acting as a stimulus to the ventricle but
not to the auricle. The experiment in fact is brought forward in
support of the views enunciated on p. 183. But these, as we have
said, are not satisfactory, and an adequate interpretation of the
experiment has yet to be supplied. Indeed, did it seem profitable,
we might relate many other puzzling results which have been
obtained in experimenting on the heart. We have already warned
the reader that the problem of the causes of the normal spon-
taneous beat is as yet far from being solved, and until we get

1 The poisonous effects of many mushrooms are probably in large measure due
to a similar action on the heart.

188 REFLEX INHIBITION. [BOOK i.

clearer views as to that main event we cannot expect to under-
stand exactly how inhibition is brought about. The conception
of an inhibitory mechanism, in which certain of the fibres of the
vagus end, must be regarded as a temporary hypothesis, useful
only until we gain further light; and we have ventured to
dwell on so obscure a topic at so great a length only because
inhibition of the heart through the vagus is not only a factor
of immense importance in the general operations of the economy,
and plays so prominent a part in the action of many drugs, but
because it is a type of other inhibitory processes in the nervous
system and elsewhere, which, perhaps even more than itself, con-
tribute to render the working of the complicated machine of the
animal body, at once both uniform when regularity is required
and delicately responsive when variety is needed.

Reflex inhibition. For it must not be thought that cardiac
inhibition by means of the vagus nerve is a mere experiment of
the laboratory; we have reason to think that it is an incident
continually recurring in daily life. For we have evidence
that the inhibitory action of the vagus may be brought about by
reflex action. If the abdomen of a frog be laid bare, and the
intestine be struck sharply, as with the handle of a scalpel, the
heart will stand still in diastole with all the phenomena of vagus
inhibition. If the nervi mesenterici or the connections of these
nerves with the sympathetic chain be stimulated with the inter-
rupted current, cardiac inhibition is similarly produced. If in
these two experiments both vagi are divided, or the medulla
oblongata destroyed, inhibition is not produced, however much
either the intestine or the mesenteric nerves be stimulated. This
shews that the phenomena are caused by impulses ascending along
the mesenteric nerves to the medulla, and so affecting a portion of
that organ as to give rise by reflex action to impulses which
descend the vagi as inhibitory impulses. The portion of the
medulla thus mediating between the afferent and efferent impulses
may be spoken of as the cardio-inhibitory centre. Reflex in-
hibition through one vagus may be brought about by stimulation
of the central end of the other.

If the peritoneal surface of the intestine be inflamed, very
gentle stimulation of the inflamed surface will produce marked
inhibition; and in general the alimentary tract seems in closer
connection with the cardio-inhibitory centre than other parts of
the body : the injurious, sometimes fatal effects of a violent blow
on the stomach are known to all. But apparently stimuli if suffici-
ently powerful will through reflex action produce inhibition from
whatever be the part of the body to which they are applied. Thus
crushing a frog's foot will stop the heart. In ourselves the fainting
from emotion or from severe pain is the result of a reflex inhibition
of the heart, the afferent impulses in the one case at least, and

CHAP, iv.] THE VASCULAR MECHANISM. 189

probably in both cases, reaching the medulla from the brain. In
succeeding pages we shall have occasion more than once in discuss-
ing the effects of stimulating a given nerve, to consider how far
those effects are due to a reflex inhibition of the heart; and probably
there are few events taking place in the body which have not a
tendency thus to affect the central vascular pump, though in many
cases the tendency is counteracted by interfering agencies. But
we must be careful to avoid falling into the error of supposing
that every arrest, or slowing or weakening of the heart, is due to
impulses descending the vagus fibres. In many instances cardiac
troubles are due to events originating in the heart itself, so far
independent of the inhibitory processes which we are studying
now, that they are in no way whatever counteracted by atropin.

Direct stimulation of the cardio-inhibitory centre itself, such as
occurs during the destruction of or results from injury to the
medulla, also produces inhibition.

And the question naturally arises, Has this cardio-inhibitory
centre any constant automatic action ?

In the dog, and also, though to a far less extent, in the rabbit,
section of both vagi is followed by a quickening of the heart's beat.
This result may be interpreted as shewing that the centre in the
medulla exercises a permanent restraining influence on the heart ;
that organ in fact being habitually curbed. The argument that
the effects of an artificial stimulation of the vagus soon wear off,
and that therefore a permanent stimulation of the vagi, leading to
permanent inhibitory action, would be impossible, may be met by
the reflection that a natural stimulation is, possibly, not wholly
identical with artificial stimulation, and its effects need not
necessarily wear off.

We need not now stay to discuss the question whether this
central action is really automatic, i.e. kept up by molecular pro-
cesses originating in certain nerve cells, or reflex, that is, maintained
by nervous impulses reaching it along certain or various afferent
nerves. Granting, however, the existence of a centre in the
medulla, which either automatically or otherwise is in permanent
action, it is obviously open to us to speak of reflex inhibition as
being brought about by influences which augment the action of
that centre. But we have seen that active nervous centres are
subject, not only to augmentative, but also to inhibitory influences.
Hence the cardio-inhibitory centre might itself be inhibited by
impulses reaching it from various quarters. In other words, the
beat of the heart might be quickened by a lessening of the normal
action of the inhibitory centre in the medulla. It is in fact
probable, that many cases of quickening of the heart's beat are
produced in this way ; though the matter requires further investi-
gation.

Accelerator nerves. The heart's beat may in the mammal be
quickened, even after division of both vagi, by direct stimulation

190

ACCELERATOR NERVES.

[BOOK

of the cervical spinal cord. The effects produced, however, are
very complex, and led, on their first being made known, to much
discussion, one outcome of which was the discovery of certain
nerves of a very peculiar character, which pass from the cervical
spinal cord, frequently along the nerve accompanying the vertebral
artery, and reach the heart through the last cervical and first
thoracic ganglia; these have been called the 'accelerator nerves.'
Their course is different in the rabbit and in the dog, see Figs. 41
and 42, and indeed varies even in the same kind of animal.
Stimulation of these nerves with the interrupted current causes a
quickening of the heart's beat, in which what is gained in rate is
lost in force, for the blood-pressure is not necessarily increased, but
may remain the same, or even be diminished ; apparently not only

Trad,

FIG. 41. THE LAST CERVICAL AND FIRST THORACIC GANGLIA IN THE BABBIT. (Left
side.) (Somewhat diagrammatic, many of the various branches being omitted.)

Track. Trachea. Ca. carotid artery. s&. subclavian artery, n. Vag. the
vagus trunk, n. rec. the recurrent laryngeal. sym. the cervical sympathetic nerve
ending in the inferior cervical ganglion, gl. cerv. inf. Two roots of the ganglion
are shewn, rad., the lower of the two accompanying the vertebral artery, A. vert.,
being the one generally possessing accelerator properties, gl. thor. pr. the first
thoracic ganglion. Its two branches communicating with the cervical ganglion
surround the subclavian artery forming the annulus of Vieussens. sym. thor. the
thoracic sympathetic chain, n, dep. depressor nerve, which, though running by the
side of the sympathetic, is really a branch of vagus, from which it separates higher
up. This is joined in its course by a branch from the lower cervical ganglion, there
being a small ganglion at their junction, from which proceed nerves to form a plexus
over the arch of the aorta. It is this branch from the lower cervical ganglion which
possesses accelerator properties— hence the course of the accelerator fibres is
indicated in <the figure by the arrows.

CHAP, iv.]

THE VASCULAR MECHANISM.

191

is the diastole diminished but the systole is actually shortened.
Our knowledge of these 'accelerator' nerves is however too im-
perfect to be dwelt upon here.

Other modifying agents. The beat of the heart may also be
modified by influences bearing directly on the nutrition of the
heart. The tissues of the heart, like all other tissues, need an
adequate supply of blood of a proper quality; if the blood vary
in quality or quantity the beat of the heart is correspondingly
affected. The excised frog's heart, as we have seen, continues to
beat for some considerable time, though apparently empty of blood.

FIG. 42. THE LAST CERVICAL AND FIRST THORACIC GANGLIA IN THE DOG.

The cardiac nerves of the Dog. The fignre is largely diagrammatic, and represents

the left side.

f. sym. the united vagus and cervical sympathetic nerves, gl. cerv. i. the
inferior cervical ganglion, n. v. the continuation of the trunk of the vagus.
ann. V. the two branches forming the annulus of Vieussens round the subclavian
artery, art. subcL, and joining gl. th. pr., the first thoracic or stellate ganglion (the
branch running in front of the artery is considered by Schmiedeberg to be an especial
channel of accelerator fibres), sym thorac. the sympathetic trunk in the thorax
r. vert, communicating branches from the cervical nerves running alongside the
vertebral artery, the rami vertebrales. n.. rec. the recurrent laryngeal. n. c. cardiac
branches from the lower cervical ganglion, accelerator nerves of Schmiedeberg. n'. c'.
cardiac branches from the first thoracic ganglion, accelerator nerves of Cyon. n". c".
cardiac branch from recurrent nerve, r. rec. branch from lower cervical ganglion to
the recurrent nerve, often containing accelerator fibres.

After a while however the beats diminish and disappear; and their
disappearance is greatly hastened by washing out the heart with a
normal saline solution, which when allowed to flow through the
cavities of the heart readily permeates the tissues on account of
the peculiar construction of the ventricular walls. If such a

192 MODIFYING AGENTS. [BOOK i.

'washed out' quiescent heart be fed in the manner described at
p. 179, with diluted blood (of the rabbit, sheep, &c.) it may be
restored to functional activity. A similar but less complete resto-
ration may be witnessed if serum be used instead of blood ; and a
heart fed regularly with fresh supplies of blood or even of serum
may be kept beating for a very great length of time. In treating
of the skeletal muscles we saw that in their case the exhaustion
following upon withdrawal of the blood-stream might be attributed
either to an inadequate supply of new nutritive material and
oxygen, or to an accumulation in the muscular substance of the
products of muscular metabolism, or to both causes combined.
And the same considerations hold good for the nervous and
muscular structures of the heart, though the subject has not yet
been sufficiently well worked out to permit any very definite
statements to be made. It seems probable however that an
important factor in the matter is the accumulation in the muscular
fibres and in the surrounding lymph of carbonic acid, and of the
substances which give rise to the acid reaction.

When the frog's heart is thus 'fed' with various substances
the interesting fact is brought to light that some substances,
such for instance as very dilute lactic acid, lead to increased
expansion, and others, such for instance as very dilute solutions of
sodium hydrate, to diminished expansion, or to continued con-
traction of the quiescent ventricle. It would appear that the
muscular fibres of the ventricle over and above their rhythmic
contractions are capable of varying in length, so that at one time
they are longer, and the ventricle when pressure is applied to it
internally dilates beyond the normal, while at another time they
are shorter, and the ventricle, with the same internal pressure is
contracted beyond the normal. Further, in the frog at least, when
the pause between two beats is lengthened the relaxation of the
ventricle goes on increasing, so that apparently the ventricle when
beating normally is already somewhat contracted when a new
beat begins. In other words, the ventricle possesses what we shall
speak of in reference to arteries as tonicity or tonic contraction,
and the amount of this tonic contraction, and in consequence the
capacity of the ventricle, varies according to circumstances.

When the frog's ventricle is thus artificially fed with serum or
even with blood, the beats, whether spontaneous or provoked by
stimulation, are apt to become intermittent and to arrange them-
selves into groups. This intermittence is possibly due to the
serum or blood being unable to carry on nutrition in a completely
normal manner, and to the consequent production of abnormal
chemical substances; and it is probable that cardiac intermittences
seen during life have often a similar causation. Various chemical
substances in the blood, natural or morbid, may thus affect the
heart's beat by acting on its muscular fibres, or its nervous
elements, or both, and that probably in various ways, modifying in

CHAP, iv.] THE VASCULAR MECHANISM. 193

different directions the rhythm, or the individual contractions, or
both.

The physical or mechanical circumstances of the heart also
affect its beat ; of these perhaps the most important is the amount
of the distension of its cavities. The contractions of cardiac
muscle, like those of ordinary muscle (see p. 87), are increased up
to a certain limit by the resistance which they have to overcome ;
a full ventricle will, other things being equal, contract more
vigorously than one less full ; though, as in ordinary muscle, the
limit at which resistance is beneficial may be passed, and an over-
full ventricle will cease to beat at all.

Under normal conditions the ventricle probably empties itself
completely at each systole. Hence an increase in the quantity of
blood in the ventricle would augment the work done in two ways ;
the quantity thrown out would be greater, and the increased
quantity would be ejected with greater force. Further, since the
distension of the ventricle is (at the commencement of the systole
at all events) dependent on the auricular systole, the work of the
ventricle (and so of the heart as a whole) is in a measure governed
by the auricle.

The relation of the heart's beat to blood-pressure. When
the blood-pressure is high, not only is the resistance to the
ventricular systole increased, but, other things being equal, more
blood flows (in the mammalian heart) through the coronary artery.
Both these events would increase the activity of the heart, and
we might expect that the increase would be manifest in the rate of
the rhythm as well as in the force of the individual beats. As a
matter of fact, however, we do not find this. On the contrary, as
Marey has insisted, the relation of heart-beat to pressure may
be put almost in the form of a law, that "the rate of the beat
is in inverse ratio to the arterial pressure ;" a rise of pressure being
accompanied by a diminution, and fall of pressure with an increase
of the pulse-rate. This however only holds good if the vagi
be intact. If these be previously divided, then in whatever
way the blood-pressure be raised — whether by injecting blood
or clamping the aorta, or increasing the peripheral resistance,
through that action of the vaso-motor nerves which we shall have
to describe directly — or in whatever way it be lowered, no such
clear and decided inverse relation between blood-pressure and
pulse rate is observed. It is inferred therefore that increased
blood-pressure causes a slowing of the pulse, when the vagi
are intact, because the cardio-inhibitory centre in the medulla
is thereby stimulated, and the heart in consequence to a certain
extent inhibited.

13

194

INHIBITION AND BLOOD-PRESSURE. [BOOK i.

The Effects on the Circulation of Changes in the Heart's Beat.

Any variation in the heart's beat directly affects the blood-
pressure unless some compensating influence be at work. The
most extreme case is that of complete inhibition. Thus if, while a
tracing of arterial pressure is being taken, the beat of the heart be
suddenly arrested, some such curve as that represented in Fig. 43
will be obtained. It will be observed that immediately after
the last beat, there is a sudden rapid fall of the blood pressure.

Fio. 43. TBACINCJ, SHEWING THE INFLUENCE or CARDIAC INHIBITION ON BLOOD-PBES-
BUBE. FBOM A BABBIT.

The current was thrown into the vagus at a and shut off at b. It will be
observed that one beat is recorded after the commencement of the stimulation.
Then follows a very rapid fall, continuing after the cessation of the stimulus.
With the returning beats, the mercury rises by leaps until the normal pressure
is regained.

At the pulse due to the last systole, the arterial system is at its
maximum of distension; forthwith the elastic reaction of the
arterial walls propels the blood forward into the veins, and
there being no fresh fluid injected from the heart, the fall of
the mercury is unbroken, being rapid at first, but slower afterwards,
as the elastic force of the arterial walls is more and more used up.
With the returning beats, the pressure correspondingly rises in
successive leaps until the normal mean pressure is regained. The
size of these returning leaps of the mercury may seem dispro-
portionately large, but it must be remembered that by far the
greater part of the force of the first few strokes of the heart is
expended in distending the arterial system, a small portion only
of the blood which is ejected into the arteries passing on into the
veins. As the arterial pressure rises, more and more blood passes
at each beat through the capillaries, and the rise of the pressure at
each beat becomes less and less, until at last the whole contents

CHAP, iv.] THE VASCULAR MECHANISM.

195

of the ventricle pass at each stroke into the veins, and the
mean arterial pressure is established. To this it may be added
that, as we have seen, the force of the individual beats may be
somewhat greater after than before inhibition. Besides, when the
mercury manometer is used, the inertia of the mercury tends to
magnify the effects of the initial beats.

STIMULATION VAGUS

FIG. 44. VAGUS STIMULATION.

Pulse-tracing from the carotid of rabbit, taken by a modification of the
sphygmograph. The period of Vagus stimulation is marked by the line below. One
beat occurs after stimulation has begun. Shews the fall of blood-pressure, and the
character of the first recommencing beats.

Complete arrest of the heart-beats is not necessary to produce a
fall of pressure. As is seen in Fig. 45, mere slowing of the beats
will lower the mean pressure. And, speaking generally, we may say

FIG. 45. STIMULATION OF VAGUS.

Blood-pressure curve taken with mercury manometer. The effect is to slow the
ythm ratber than to bring about complete standstill. With the slow pulse the
essure still continues to fall. The beginning of stimulation is marked by a.

that if while the force of the individual beats remains constant the
frequency is increased or diminished, and vice versa, if while the

13—2

196

INHIBITION AND BLOOD-PRESSURE. [BOOK i.

frequency remains the same the force is increased or diminished, the
result in both cases is that the pressure is proportionately increased
or diminished. This clearly must be the case ; but obviously it is
quite possible that the beats might, while more frequent, so lose in
force, or while less frequent, so increase in force, that no difference
in the mean pressure should result. And this indeed is not
unfrequently the case. So much so, that variations in the heart-
beat must always be looked upon as a far less important factor of
blood-pressure than variations in the peripheral resistance.

An increase in the quantity of blood ejected at each beat must
necessarily augment, and a decrease diminish, the blood-pressure,
other things remaining the same. But the quantity sent out
at each beat, on the supposition that the ventricle always empties
itself at each systole, will depend on the quantity entering into the
ventricle during each diastole, and that will be determined by the
circumstances not of the heart itself, but of some other part or
parts of the body.

SEC. 5. CHANGES IN THE CALIBRE OF THE MINUTE
ARTERIES. VASO-MOTOR ACTIONS.

The middle coat of all arteries contains circularly disposed
plain muscular fibres. As the arteries become smaller, the mus-
cular element becomes more and more prominent as compared
with the elastic element, until, in the minute arteries, the middle
coat consists entirely of a series of plain muscular fibres wrapped
round the elastic internal coat. Nerve-fibres belonging to the
sympathetic system are distributed largely to blood-vessels, but
their terminations have not as yet been clearly made out. By
galvanic, or still better by mechanical stimulation, this muscular
coat may, in the living artery, be made to contract. During
this contraction, which has the slow character belonging to
the contractions of all plain muscle, the calibre of the vessel
is diminished.

If the web of a frog's foot be examined under the microscope,
any individual small artery will be found to vary in calibre, being
sometimes narrowed and sometimes dilated. During the narrowing,
which is obviously due to a contraction of the muscular coat of the
artery, the attached capillary area and the corresponding veins
become less filled with blood, and paler. During the stage of
dilation, which corresponds to the relaxation of the muscular coat,
the same parts are fuller of blood and redder. It is obvious that,
the pressure at the entrance into any given artery remaining the
same, more blood will enter the artery when relaxation takes place
and consequently the resistance offered by the artery is lessened,
and less when contraction occurs and the resistance is consequently
increased. The blood always flows in the direction of least
resistance.

198 VASO- MOTOR NERVES. [BOOK i.

The small arteries frequently manifest what may be called
spontaneous variations in their calibre, and these variations are
very apt to take on a distinctly rhythmical character. If a small
artery in the web of the frog be carefully watched, it will be seen
from time to time to vary very considerably in width, without any
obvious change taking place in the heart's beat or any events
occurring in the general vaso-motor system. Similar variations may
be witnessed in the vessels of the mesentery of a mammal. The
most striking and most easily observed instance of rhythmical
constriction and dilation is to be found in the median artery of the
ear of the rabbit. If the ear be held up before the light, it will be
seen that at one moment the artery appears as a delicate, hardly
visible pale streak, the whole ear being at the same time pallid.
After a while the artery slowly widens out, becomes thick and red,
the whole ear blushing, and many small vessels previously invisible
coming into view. Again the artery narrows and the blush fades
away; and this may be repeated at somewhat irregular intervals
several times a minute. The extent and regularity of the rhythm
are usually markedly increased if the rabbit be held up by the ears
for a short time previous to the observation. Similar rhythmic
variations in the calibre of the arteries have been observed in
several places, ex. gr. in the saphena artery of the rabbit, in
the axillary artery of the tortoise, and in the small arteries
of the muscles of the frog ; probably they are widely spread. They
may be compared with the rhythmic movements of the veins in the
bat's wing and of the caudal vein of the eel.

The extent and intensity of the constriction or dilation which
may be observed in the frog's web are found to vary very largely.
Irregular variations of slight extent occur even when the animal
is apparently subjected to no disturbing causes; while as the
result of experimental interference the arteries may become
either constricted, in some cases almost to obliteration, or dilated
until they acquire double or more than double their normal
diameter. This constriction or dilation may be brought about
not only by treatment applied directly to the web, but also by
changes affecting the nerve of the leg. Thus section of the
sciatic nerve is generally followed by a dilation which may
be slight or which may be very marked, and which is sometimes
preceded by a passing constriction; while stimulation of the
peripheral stump of the divided nerve by an interrupted current
of moderate intensity generally gives rise to constriction, often
so great as almost to obliterate some of the minute arteries.

These facts shew that the contractile elements of the minute
arteries of the web of the frog's foot are capable by contraction or
relaxation of causing constriction or dilation of the calibre of the
arteries ; and that this condition of constriction or dilation may be
brought about through the agency of nerves.

CHAP, iv.] THE VASCULAR MECHANISM. 199

Vaso-motor nerves. In warm-blooded animals, though we
cannot readily, as in the frog, watch the circulation under the
microscope, we have abundant evidence of the influence of the
nervous system on the calibre of the arteries. Thus in the
mammal, division of the cervical sympathetic on one side of the
neck causes a dilation of the minute arteries of the head on the
same side, shewn by an increased supply of blood to the parts.
If the experiment be performed on a rabbit, the effect on the
circulation in the ear is very striking. The whole ear of the side
operated on is much redder than normal, its arteries are obviously
dilated, its veins unusually full, innumerable minute vessels before
invisible come into view, and the temperature may be more than a
degree higher than on the other side.

Division of the sciatic nerve in a mammal causes a similar
dilation of the small arteries of the foot and leg. Where the
condition of the circulation can be readily examined, as for instance
in the hairless balls of the toes, especially when these are not
pigmented, the vessels are seen to be dilated and injected ; and a
thermometer placed between the toes shews a rise of temperature
amounting, it may be, to several degrees.

The quantity of blood present in the blood-vessels of the mammal
may sometimes be observed directly, but has frequently to be determined
indirectly. The temperature of passive structures subject to cooling in-
fluences, such as the skin, is largely dependent on the supply of blood,
the more abundant the supply the warmer the part. Hence in these
parts variations in the quantity of blood may be inferred from varia-
tions of temperature ; but in dealing with more active structures there
are obviously sources of error in the possibility of the treatment
adopted, such as the stimulation of a nerve, giving rise to an increase of
temperature due to increased metabolism, independent of variations in
blood supply.

The quantity of blood may also be determined by the plethysmograph.
In this instrument, a part of the body, such as the arm is introduced into
a closed chamber tilled with fluid, ex. gr. a large glass tube, the opening
by which the arm is introduced being secured with a stout caoutchouc
membrane. An increase or decrease of blood sent into the arm
will lead to an increase or decrease of the volume of the arm, and
this will make itself felt by an increase or diminution of pressure in the
fluid of the closed chamber, which may be registered and measured iii
the usual way. We shall have to speak again of a modification of this
instrument when we are dealing with the kidney!

Division of the brachial plexus produces a similar dilation of
the blood-vessels of the front limb. Division of the splanchnic
nerve produces a dilation of the blood-vessels of the intestines and
other abdominal viscera. Division in the mammal of the hypo-
glossal nerve on one side causes a dilation of the vessels in the
corresponding half of the tongue. Division of a nerve supplying
a muscle causes a large and sudden increase in the venous flow

200 VASO-MOTOR NERVES. [BOOK i.

from the muscle, indicating that the muscular arteries have
become dilated; and in the frog this dilation, consequent on
section of the nerve, may be actually observed by placing a thin
muscle such as the mylo-hyoid under the microscope, and watching
the calibre of the small arteries and the circulation of the blood
through them while the nerve is being cut.

We find in fact that in almost all parts of the body certain
' vascular areas ' stand in such a relation to certain nerves that the
division of one of these nerves causes a dilation of the minute
arteries in, and consequently an increased supply of blood to, a
corresponding vascular area. We may speak of these nerves as
'vaso-motor' nerves, or more correctly, since in the vast majority
of cases the nerves in question have other functions than that of
governing arteries, as containing vaso-motor fibres, much in the
same way as an ordinary spinal nerve is spoken of as containing
sensory and motor fibres ; and from what has been said above it is
evident that these vaso-motor fibres are found sometimes in
sympathetic, sometimes in cerebro-spinal nerves.

Since division of a vaso-motor nerve, or nerve containing vaso-
motor fibres, leads to the dilation of the arteries of its appropriate
vascular area, it is obvious that previous to that division these arte-
ries were in a state of permanent constriction, due to a permanent
contraction of their muscular coats. This permanent constriction,
which may vary considerably in degree (the dilating effects of
section of the vaso-motor nerve correspondingly varying in a-
mount), is spoken of as ' tone/ ' arterial tone.' Arteries in such a
state of permanent constriction as under ordinary circumstances is
normal to arteries whose vaso-motor fibres have not been divided
and which are otherwise in a normal condition, are said to ' possess
tone.' When, as after division of the vaso-motor fibres, the constric-
tion gives place to dilation the arteries are said to have 'lost tone;'
and when, under various circumstances which we shall study
hereafter, the constriction becomes greater than normal, their tone
is said to be increased.

A very little consideration will shew that this arterial tone is
a most important factor in the circulation. In the first place the
whole flow of blood in the body is adapted to and governed
by what we may call the general tone of the arteries of the body at
large. In a normal condition of the body, if not all, at least
the great majority of the minute arteries of the body are in a
state of tonic, i.e. of moderate, constriction, and it is the narrowing
due to this constriction which forms a large item of that peripheral
resistance which we have seen (p. 129) to be one of the two great
factors of blood-pressure. The normal general blood-pressure, and
therefore the normal flow of blood, is in fact dependent on the
'general tone' of the minute arteries. In the second place, changes
in local tone, i.e. the tone of any particular vascular area, have very
decided effects on the circulation. These effects are both local
and general, as the following considerations will shew.

CHAP, iv.] THE VASCULAR MECHANISM. 201

Let us suppose that the artery A is in a condition of normal
tone, is midway between extreme constriction and dilation. The
How through A is determined by the resistance in A and in the
vascular tract which it supplies, in relation to the mean arterial
pressure, which again is dependent on the way in which the heart
is beating and on the peripheral resistance of all the small arteries
and capillaries, A included. If, while the heart and the rest of
the arteries remain unchanged, A be constricted, the peripheral
resistance in A will increase, and this increase of resistance will
lead to an increase of the general arterial pressure. This increase
of pressure will tend to cause the blood in the body at large to
flow more rapidly from the arteries into the veins. The con-
striction of A however will prevent any increase of the flow
through it, in fact will make the flow through it less than before.
Hence the whole increase of discharge from the arterial into the
venous system must take place through channels other than A.
Thus, as the result of the constriction of any artery there occur,
(1) diminished flow through the artery itself, (2) increased general
arterial pressure, leading to (3) increased flow through the other
arteries. If, on the other hand, A be dilated, while the heart and
other arteries remain unchanged, the peripheral resistance in A is
diminished. This leads to a lowering of the general arterial
pressure, which in turn causes the blood to flow less rapidly from
the arteries into the veins. The dilation of A however permits,
even with the lowered pressure, more blood to pass through it
than before. Hence the diminished flow tells all the more on the
rest of the arteries. Thus, as the result of the dilation of any
artery, there occur (1) increased flow of blood through the artery
itself, (2) diminished general pressure, and (3) diminished flow
through the other arteries. Where the artery thus constricted or
dilated is small, the local effect, the diminution or increase of flow
through itself, is much more marked than the general effects, the
change in blood-pressure and the flow through other arteries.
When, however, the area the arteries of which are affected is large,
the general effects are very striking. Thus if while a tracing of
the blood-pressure is being taken by means of a manometer
connected with the carotid artery, the splanchnic nerves be divided,
a conspicuous but steady fall of pressure is observed, very similar
to that which is seen in Fig. 46. The section of the splanchnic
nerves causes the mesenteric and other abdominal arteries to
dilate, and these being very numerous, a large amount of peripheral
resistance is taken away, and the blood-pressure falls accordingly ;
a large increase of flow into the portal veins takes place, and the
supply of blood to the face, arms, and legs is proportionally
diminished. It will be observed that the dilation of the arteries
is not instantaneous but somewhat gradual, the pressure sinking
not abruptly but with a gentle curve.

Arterial tone then, both general and local, is a powerful

202 VASO-MOTOR NERVES. [BOOK i.

instrument for determining the flow of blood to the various organs
and tissues of the body, and thus becomes a means of indirectly
influencing their functional activity. We should accordingly ex-
pect to find that the vaso-motor • nerves were connected with, and
arterial tone regulated by, the central nervous system, in order
that the calibre of the arteries of, and the supply of blood sent to,
this or that vascular area might be varied according to the varying
needs of the economy. And experiment proves this to be the
case.

We stated that section of the cervical sympathetic in the neck
causes dilation or loss of tone in the blood-vessels of the head and
face. This is true at whatever point of the course of the nerve
from the upper to the lower cervical ganglion, both included, the
section be made. No such dilation of the vessels of the head and
face takes place when the thoracic sympathetic chain is divided
anywhere below the upper thoracic ganglion; but dilation does
occur after division of certain of the rami communicantes connect-
ing the spinal cord with the cervical sympathetic through the
lower cervical or upper thoracic ganglion. Hence it is clear that
the normal tone of the arteries of the head and face is maintained
by influences (whose exact nature we shall study presently) pro-
ceeding from the central nervous system, passing through certain
rami communicantes (the exact path being somewhat uncertain or
possibly not constant) into the cervical sympathetic, and ascending
to the head and face by that nerve. In other words, the vaso-
motor fibres of the vessels of the head and face may be traced
down the sympathetic to the lower cervical ganglion, and thence
by rami communicantes into the spinal cord.

In a similar manner the vaso-motor fibres of the splanchnic
nerves governing the mesenteric and other abdominal arteries can
also be traced into the spinal cord, as may also those of the sciatic
governing the blood-vessels of the hind limb and of the brachial
nerves governing those of the fore limb. In fact all the vaso-
motor fibres (with certain special exceptions which will be discussed
presently) may thus be traced into the spinal cord ; they are all
connected with the central nervous system. There is at present
some uncertainty in certain cases a.s to the exact manner in which
the fibres pass from the spinal cord to this or that nerve, as, for
instance, along which nerve-roots the vaso-motor fibres eventually
joining the sciatic trunk run, whether they all pass on their way
into the abdominal sympathetic or no, and the like ; but these are
questions which need not delay us now; in whichever way they
may be settled, they do not affect the important fact that in some
way or other all vaso-motor fibres spring from the central nervous
system, and that (with certain special exceptions) what we have
called the normal tone of the various vascular areas is maintained
by influences proceeding from the central nervous system.

Far more important however than the maintenance of a normal

CHAP, iv.] THE VASCULAR MECHANISM. 203

tone, which indeed might be at once and for ever arranged for by
the proper natural calibre of the elastic blood-vessels, is the power
which the central nervous system possesses of varying the tone of
this or that artery or group of arteries, of increasing it or of
diminishing it, of producing constriction or dilation in those arteries,
and thus, as we have seen, of effecting changes in general or
local blood-pressure or in both, and consequently of determining a
flow of blood in this or that direction, according to the needs of the
economy. And the exercise of this carefully arranged manipulation
of the muscular walls of the arteries may be called forth in either
direction, in the way of constriction, or in the way of dilation (or
of both at the same time, one in one area and the other in others),
by means of nervous impulses either originating in the central
nervous system itself or started by afferent impulses passing up to
the central nervous system from some sentient surface.

Blushing is a familiar instance of vascular dilation brought
about by the action of the central nervous system. Nervous im-
pulses started in some parts of the brain by an emotion produce
certain changes in the central nervous system (the exact nature
and locality of these changes we shall discuss presently) which
have in turn an effect on the vaso-motor fibres of the cervical
sympathetic almost exactly the same as that produced by section
of the nerve. In consequence the muscular walls of the arteries of
the head and face relax, the arteries dilate and the whole region
becomes suffused. Sometimes an emotion gives rise not to blushing,
but to the opposite, viz. to pallor. In a great number of cases this
has quite a different cause, being due to a sudden diminution or
even temporary arrest of the heart's beats; but in some cases
it may occur without any change in the beat of the heart, and is
then due to a condition the very converse of that of blushing, that
is, to an increased arterial constriction; and this increased con-
striction, like the dilation of blushing, is effected through the
agency of the central nervous system and the cervical sympathetic.
These are familiar examples, but we have in abundance exact
experimental evidence of the effect of afferent impulses in inducing
through the central nervous system vaso-motor changes and thus
bringing about sometimes constriction, sometimes dilation, some-
times the two together. The action of the so-called depressor
nerve is a striking instance of reflex dilation as it may be called.

If in the rabbit while the pressure in an artery such as the
carotid is being registered, the depressor nerve, which is a branch
of the vagus running alongside the carotid artery and sympathetic
nerve (Fig. 41, n. dep.), be divided, and its central end (i. e. the one
connected with the brain) be stimulated with the interrupted
current, a gradual but marked fall of pressure in the carotid
is observed, lasting, where the period of stimulation is short,
some time after the removal of the stimulus (Fig. 46). Since the
beat of the heart is not markedly changed, the fall of pressure

204

VASO-MOTOR NERVES.

[BOOK i.

must be due to the diminution of peripheral resistance occasioned
by the dilation of some arteries. And there is evidence that the

./UUUUL/UUULAJl^^

FIG. 46.

TBACINO, SHEWING THE EFFECT ON BLOOD-PRESSURE OF STIMULATING THE
CENTRAL END OF THE DEPRESSOR NERVE IN THE KABBIT.

(To be read from right to left. )

T indicates the rate at which the recording surface was travelling ; the intervals
marked corresponds to seconds. G the moment at which the current was thrown
into the nerve ; 0 the moment at which it was shut off. The effect is some
time in developing and lasts after the current has been taken off. The larger
undulations are the respiratory curves ; — the pulse- oscillations are very small.

arteries thus dilated are chiefly if not exclusively those arteries of
the abdominal viscera which are governed by the splanchnic
nerve. For if both the splanchnic nerves are divided previous to
the experiment, the fall of pressure when the depressor is stimulated
is very small, in fact almost insignificant. The inference from this
is clear ; the afferent impulses passing along the depressor have so
affected some part of the central nervous system that the influences
which, in a normal condition of things, passing along the splanchnic
nerves keep the minute arteries of the abdominal viscera in
a state of moderate tonic constriction, fail altogether, and those
arteries in consequence dilate just as they do when the splanchnic
nerves are divided, the effect being possibly increased by the
similar dilation of other smaller vascular areas.

The condition of the splanchnic or other vascular areas may
moreover be changed, and thus the general blood-pressure modi-
fied, by afferent impulses passing along other nerves than the
depressor, the modification taking on, according to circumstances,
the form either of decrease or of increase.

Thus, if in an animal (dog) placed under the influence of urari
the central stump of the divided sciatic nerve be stimulated, an
increase of blood-pressure, almost exactly the reverse of the de-
crease brought about by stimulating the depressor, is observed.

CHAP, iv.]

THE VASCULAR MECHANISM.

205

The curve of the blood-pressure, after a latent period during which
no changes are visible, rises steadily without any corresponding
change in the heart's beat, reaches a maximum and after a while
slowly falls again, the fall sometimes beginning to appear before
the stimulus has been removed. There can be no doubt that the
rise of pressure is due to the constriction of certain arteries ; the
arteries in question being those of the splanchnic area certainly,
and possibly of other vascular areas as well. The effect is not
confined to the sciatic; stimulation of any nerve containing af-
ferent fibres may produce the same rise of pressure, and so constant
is the result that the experiment has been made use of as a
method for determining the existence of afferent fibres in any
given nerve and even the paths of centripetal impulses through
the spinal cord.

If, on the other hand, the animal be under not urari but
chloral, instead of a rise of blood-pressure a fall, quite similar to
that caused by stimulating the depressor, is observed when an
afferent nerve is stimulated. The condition of the central nervous
system seems to determine whether the reflex effect on the vaso-
motor fibres is in the direction of constriction leading to a rise, or
of dilation leading to a fall of blood-pressure.

FIG. 47. KISE OF BLOOD-PRESSURE FROM STIMULATION OF NOSTPIL WITH SMOKE.

The respiration and cardiac rhythm are at the same time rendered more slow.
The mark x indicates the time of stimulation.

Stimulation of a sentient surface in many cases causes a similar
rise in blood-pressure as shewn in Fig, 47, where a rise of blood-
pressure follows irritation of the nostrils. In this case however the
rise in blood-pressure is accompanied by changes in respiration and
in the cardiac rhythm.

206 VASO-MOTOR NERVES. [BOOK i.

In the instances just quoted, the effect of the stimulation of
the afferent nerve may be spoken of as a general one ; it is the
general blood -pressure which is diminished or increased ; though
in the case of the depressor at all events it is chiefly in the
splanchnic area that the constriction or dilation takes place.

There are however some remarkable cases where a local effect
can be readily distinguished from the general effect, because the
two are in opposite directions. Thus if in a rabbit under urari, the
central stump of the auricularis magnus nerve or of the auricularis
posterior be stimulated, the rise of general pressure which is
caused by the stimulation of this as of any other afferent nerve, is
accompanied by a dilation of the artery of the ear. That is to say,
the afferent impulses passing along the auricular nerve while
affecting the central nervous system in an ordinary way, so as to
cause constriction of many of the arteries of the body (but chiefly
probably the splanchnic vessels), at the same time so affect some
particular part of the central nervous system, more especially
connected with the vaso-motor fibres governing the artery of the
ear, as to lead to the dilation of that vessel.

So also in the same animal stimulation of branches of the
tibial nerve causes dilation of the saphena artery, together with
constriction of other arteries, as shewn by the concomitant rise of
pressure. And there are probably innumerable instances of the
same kind of action going on in the body during life, for it is
evident that the object of the local dilation, viz. the increased flow
of blood to the organ, must be assisted if a general constriction
is at the same time taking place in other regions.

The general effect may not always be obvious, may perhaps be
absent, so that the local dilation or constriction, as the case may
be, is the only obvious result of the vaso-motor action. When the
ear of the rabbit is gently tickled, the effect that is seen is a
blushing of the ear, and though this may be in part due, as we
shall see, to the action of a local mechanism, the case we have just
cited shews that the central nervous system must be largely
engaged. When the right hand is dipped in cold water, the
temperature of the left hand falls, on account of a reflex con-
striction of the vessels of the skin of that hand caused by the
stimulus applied to the other. Many more instances might be
quoted, and we shall again and again come upon examples. The
numerous pathological phenomena classed under sympathetic
action, such as the affection of one eye by disease in the other,
are probably in part at least the results of reflex vaso-motor
action.

We have said enough to shew that the calibre of the small
arteries, which by determining the peripheral resistance forms one
important factor regulating the flow of blood, is subject to in-
fluences proceeding from all parts of the body, and that these
influences reach the arteries in a reflex manner by means of the

CHAP, iv.] THE VASCULAR MECHANISM. 207

central nervous system, the afferent impulses being for the most part
carried by ordinary sensory nerves, while the efferent impulses pass
along special vaso-motor fibres, which, though the centre of the
reflex action lies in the cerebro-spinal axis, have a great tendency
to run in sympathetic tracts.

The afferent impulses of course need not start from the peri-
pheral nerve-endings. They may for instance arise in the brain.
Thus, as we have seen, an emotion originating in the cerebrum
may by vaso-motor action give rise either to blushing or to pallor.
Nay more, changes may be induced in the central nervous system
itself without the need of any impulses reaching it from without.
When we come to discuss the relations of respiration to the
circulation, we shall see reason to think that the vaso-motor action
of the central nervous system may be directly affected by the
condition of the blood passing through it, so that if the quantity of
oxygen in the blood be reduced, a general arterial constriction
takes place, and a rise of blood-pressure follows; while with a
return of oxygen to the blood, the vessels dilate and pressure falls.
And it is more than probable that many substances introduced
into the blood, or arising in the blood from natural or morbid
changes, may affect blood-pressure by acting directly on the
centres in the central nervous system. They may also however act
on the peripheral structures. We shall return to these phenomena
later on.

In many ways then, and to a varying degree and extent, the
central nervous system can bring about arterial constriction or
dilation, general or local. We have now to study the question,
What is more exactly the nature of the nervous influences
which lead to constriction and dilation respectively? How do
those which cause constriction differ from those which cause
dilation ?

In the fundamental experiment of the cervical sympathetic,
when arterial dilation has followed upon section of the nerve, if the
peripheral stump of the divided nerve be stimulated, the dilation
gives place to constriction, the blush is replaced by pallor. If the
stimulus be very strong the constriction is greater than normal, but
by carefully adjusting the strength of the stimulus, the circulation
may be brought to quite a normal condition, the ' loss of tone '
consequent on the severance of the vaso-motor fibres from the
central nervous system may be replaced, and not more than
replaced, by an artificial tone generated by the action of the
stimulus on the sympathetic nerve. The most natural interpreta-
tion therefore of the vaso-motor action in this case is to suppose
that the normal tone of the arteries of the face is maintained by
'tonic' constructive impulses of a certain intensity which pass
from the central nervous system along the sympathetic, and that
the dilation of the same arteries is due simply to a diminution or
absence of these constrictive impulses, an increased constriction or

208 VASO-MOTOR NERVES. [BOOK i.

pallor being similarly due to an increase beyond what is normal of
these same impulses. In other words, the nervous influences
leading to arterial dilation and constriction differ in degree only,
not in kind, and may be considered as being merely phases (of
decrease or of increase as the case may be) of the same action.
And if we turn to the splanchnic nerve we find a similar interpre-
tation equally valid. Stimulation of the splanchnic nerve causes
constriction of the arteries governed by that nerve, apparently
because the stimulation supplies artificially the constrictive im-
pulses which, so long as the nerve is intact, pass down it from the
central nervous system, giving the requisite tone to its vascular
area, and the loss of which by division of the nerve gives rise to
dilation. So that were we to stop our inquiries at this point, our
explanation of vaso-motor action would be very simple. We might
speak of constrictive impulses as passing from the central nervous
system to the various vascular areas, to such an extent as to
constitute normal tone, but as being susceptible either of in-
hibition, complete or partial, thus leading to greater or less
arterial dilation, or of augmentation, thus leading to excessive con-
striction.

But this simple view appears insufficient when we push our
studies further.

In the first place such a conception does not cover all the facts
connected even with the two nerves just mentioned. For the
dilation or loss of tone which follows upon section of the cervical
sympathetic (and the same is true of the splanchnic) is not
permanent ; after a while, it may be not until after several days, it
may be sooner, the dilation disappears and the arteries regain
their usual calibre. This recovery is not due to any regeneration
of vaso-motor fibres in the sympathetic, for it may be observed
when the whole length of the nerve including the superior cervical
ganglion is removed. When recovery of tone has thus taken place,
dilation or increased constriction may be occasioned by local treat-
ment : the ear may be made to blush or to pale by the application
of heat or cold, by gentle stroking or rough handling and the like ;
but neither the one nor the other condition can be brought about
by the intervention of the central nervous system. So also the
spontaneous rhythmic variations in the calibre of the arteries of
the ear of which we spoke on p. 198, though they cease for a time
after division of the cervical sympathetic, eventually reappear, even
if the superior cervical ganglion be removed. And the analogous
rhythmic variations of the veins of the bat's wing have been proved
experimentally to go on vigorously when all connection with the
central nervous system has been severed; they may continue in
fact in isolated pieces of the wing. From this it is clear that what
we have spoken of as the tone of the vessels of the face, though
influenced by and in a measure dependent on the central nervous
system, is not simply the result of an effort of that system. The

CHAP, iv.] THE VASCULAR MECHANISM. 209

muscular walls of the arteries are not mere passive instruments
worked by the cerebro-spinal axis through the cervical sympa-
thetic; obviously they have an intrinsic tone of their own, de-
pendent possibly on some local nervous mechanism, though in
the car at least no such mechanism has yet been found ; and it
seems natural to suppose that when the central nervous system
causes dilation or constriction of the vessels of the face, it makes
use, in so doing, of this intrinsic local tone. But if so, then the
simple view entertained above, that arterial dilation and constric-
tion are simply determined by the decrease or increase of tonic
constrictive impulses passing directly from the central nervous
system, is not a complete representation of the facts.

In the second place, if we turn from the sympathetic or
splanchnic to other nerves containing vaso-motor fibres, we meet
with still greater difficulties. To take, for instance, a nerve sup-
plying a muscle, such as that going, in the frog, to the mylo-hyoid
muscle. Here, as in the cervical sympathetic, section of the nerve
produces dilation, but that dilation is even more transient than in
the case of the sympathetic; the vessels speedily return to their
former calibre. And then it is found that stimulation of whatever
strength of the peripheral portion of the divided nerve brings about
not constriction but dilation. A similar dilation is seen when the
nerve of a mammalian muscle is stimulated, and probably occurs in
the case of all muscular nerves. There are therefore in the body
nerves, stimulation of which, as well as mere section, always brings
about arterial dilation.

There are other nerves in the body of a mixed character,
intermediate between the cervical sympathetic on the one hand,
and the muscular nerves on the other, stimulation producing now
constriction, now dilation. Such a nerve is the sciatic of a mam-
mal. We have already seen that section of this nerve produces
dilation of the vessels of the foot ; but the dilation so caused after
a few days disappears ; the foot on the side on which the nerve was
divided becomes not only as cool and pale, but frequently cooler
and paler than the foot on the sound side. If the peripheral por-
tion of the divided nerve be stimulated with an interrupted current,
immediately or very shortly after division, the dilation due to the
division gives place to constriction ; the sciatic acts then quite like
the cervical sympathetic, except perhaps that this artificial con-
striction cannot be maintained for so long a time, and is very apt
to be followed by increased dilation. If however the stimulation
be deferred for some days, until the dilation has given place to a
returning constriction, the effect is not constriction but dilation;
the nerve then acts, as far as its vaso-motor fibres are concerned,
like a muscular nerve and not like the cervical sympathetic. In
fact, by variations in the attendant circumstances, and in the mode
of stimulation, into the details of which we cannot enter now,
stimulation of the divided sciatic may at the will of the experi-

p. H

210 VASO-MOTOR NERVES. [BOOK i.

inenter be made to produce either arterial dilation or arterial con-
striction.

In all the above cases section of the nerve produces dilation,
whether the subsequent stimulation causes constriction or dilation;
the dilation after section may be sometimes not very marked, but
is always present to some extent or other. But there are certain
nerves, section of which produces no marked changes in the vascular
areas to which they are distributed, and yet stimulation of which
brings about dilation often of an extreme character. A striking
example of this is seen in the so-called nervi erigentes. The
erection of the penis is, putting aside the subsidiary action of
muscular bands in restraining the outflow through the veins, chiefly
due to the dilation of branches of the pudic arteries, whereby a
large quantity of blood is discharged into the venous sinuses.
Erection may in the dog be artificially produced by stimulating the
peripheral ends of the divided nervi erigentes, which are branches
from the first and second and sometimes from the third sacral nerve
passing across the pelvis. On applying the interrupted current to
the peripheral ends of these nerves, the corpora cavemosa at once
become turgid. And yet simple section of these nervi erigentes
will not in itself give rise to erection.

A similar case is presented by the submaxillary gland. As will
be explained more in detail in treating of secretion, this gland
is supplied by two nerves, by branches of the chorda tympani
reaching it along its duct, and by branches of the cervical sym-
pathetic reaching it along its arteries. Neither section of the
chorda tympani nor section of the cervical sympathetic produces
any very marked effect in the circulation of the gland. Yet stimu-
lation of the former will bring about a most striking dilation, of
the latter a no less striking constriction, of the arteries of the gland.

How can we construct a view of the action of vaso-motor nerves
which will be consistent with all these various facts?

In the first place, we must admit the existence of a local tone
in the several vascular areas, independent of the central nervous
system. In such cases as the corpora cavernosa of the penis,, and
the submaxillary gland, this independence is unmistakeable ; in
other regions it is not at first sight so apparent, but, as we have
already urged, must be admitted even for these.

In the second place, as is strikingly shewn by the case of the
submaxillary gland, there are nerves which, since stimulation of
them always causes dilation, may be called vaso-dilator nerves, and
nerves which, since stimulation of them always causes constriction,
may be called vaso-constrictor nerves. Examples of the first are
seen in the nervi erigentes, the chorda tympani, the nerves of
muscles, &c. ; of the second, in the cervical sympathetic, the
splanchnic, &c. Or to be more exact, we may say that the vaso-
motor fibres of the former are vaso-dilator, of the latter, vaso-con-
strictor.

CHAP, iv.] THE VASCULAR MECHANISM. 211

In the third place, the cases of the corpora cavernosa of the
penis and the submaxillary gland suggest the idea that dilation is
the result of the complete or partial loss of local tone, that in fact
vaso-dilators act by inhibiting, and vaso-constrictors by augmenting,
the activity of the local mechanism (whatever it be) which gives rise
to the local tone. The erection of the penis which follows stimula-
tion of the nervi erigentes, and the injection of the submaxillary
gland which follows stimulation of the chorda tympani, present a very
close analogy to the inhibition of the heart by stimulation of the
vagus. Just as the rhythmic contraction of the cardiac fibre is
stopped by the vagus, so the tonic contraction of the arterial fibre
(and this tonic contraction is indeed at bottom an obscure rhythmic
contraction) is stopped by the chorda or the nervi erigentes. And
it seems to be very natural to draw the conclusion that dilation is in
all cases mere inhibition, and constriction in all cases mere augmen-
tation, of local tone. But tempting as this view is, and useful perhaps
as it may be as a working hypothesis, it must not be regarded as
definitely proved. It is quite possible that dilation may be brought
about in different ways in different cases ; and so also with con-
striction.

Further, the occurrence of dilation after simple section of a
nerve raises an interesting question. Do the arteries in such a case
dilate because the very section of the nerve acts as a stimulus to
vaso-dilator fibres, or because the local tone is insufficient to keep
up an adequate arterial constriction unless it be supplemented by
additional tonic impulses reaching the local mechanism from the
central nervous system, which supplement is lost by section of the
nerve ? Obviously, if mere section behaves as a stimulus to vaso-
dilator fibres of such a potency as to give rise to a dilation lasting
hours or it may be days, all evidence of 'tonic' impulses proceeding
from the central nervous system is done away with. We can then
only speak of dilation and constriction as being the result of the action
of vaso-dilator and vaso-constrictor fibres respectively, both worked
in a reflex manner by the central nervous system. Into the dis-
cussion whether such an interpretation of the effects of simple
section is justified by facts or not, and into the allied controversy
concerning the reason why the vaso-motor effects of stimulating the
efferent fibres of the sciatic and other nerves vary so much under
different circumstances, we cannot enter here. We must content
ourselves with the general conclusion that though local tone may
exist independently of the central nervous system, the condition of
the various vascular areas, in the living body in a normal condition,
is arranged and modified to meet passing or permanent needs, by
the central nervous system, through the agency of vaso-motor nerves,
and that these vaso-motor nerves in some cases, since they are used
to give rise to dilation only, may be spoken of as vaso-dilator nerves,
or as containing vaso-dilator fibres, in other cases may similarly be
called vaso-constrictor, and in yet a third class of cases be regarded

14—2

212 VASO-MOTOR CENTRES. [BOOK i,

as mixed in character, since according to circumstances they give
rise either to dilation or to constriction.

The course of vaso-motor fibres. Leaving out of consideration
local vaso-motor mechanisms, such as those which may be sup-
posed to exist in the submaxillary gland, we may make the general
statement that vaso-motor influences may be traced back to the
spinal cord. The exact paths taken by the vaso-motor fibres have
not however as yet been fully worked out.

Most observers are agreed that the fibres leave the spinal cord
by the anterior roots of the spinal nerves ; but in the majority of
cases at all events as far as the mammal is concerned, the fibres do
not run in a direct course to their destination in company with the
ordinary motor fibres passing to the same structures as themselves.
Thus the vaso-motor fibres of the hind limbs do not pass directly
with the anterior roots into the sciatic nerve but, largely at all
events, turn aside, to join through the rami communicantes the
abdominal sympathetic ; and it is only after they have traversed a
certain length of sympathetic nerve that they again return to the
spinal nerves, enter into the sciatic plexus, and thus become
part of the nerves of the leg. So also the vaso-motor fibres for the
forelimb pass in large measure from the anterior roots of the upper
dorsal nerves to the thoracic sympathetic chain and thence by the
first thoracic ganglion to the brachial plexus and so on to the fore-
limb. And we have already seen that the vaso-motor fibres for the
head and face, pass from the lower cervical or lower dorsal spinal
cord to the first thoracic or to the last cervical ganglion and by the
cervical sympathetic upwards.

When, as in the case of the submaxillary gland, the presence of
distinct and antagonistic vaso-constrictor and vaso-dilator nerves is
conspicuous in the same organ, the dilator fibres are generally found
running in a cerebro-spinal and the constrictor fibres in a sympa-
thetic nerve, but we cannot at present say that such a contrast is
invariable. We cannot as yet trace out such distinct courses for
the dilator and constrictor fibres of either the fore or hind limb ;
and in the tongue while dilator fibres run into the lingual nerve,
constrictor fibres appear in the hypoglossal which is no less clearly
a spinal nerve than the fifth of which the lingual is a branch.

Vaso-motor centres. There remains the important question,
What part of the central nervous system is it which intermediates
as a nervous vaso-motor centre or centres either of purely reflex or
of partly reflex and partly automatic action, between various affer-
ent impulses and the efferent vaso-motor impulses leading either to
dilation or constriction ?

We have seen that stimulation of the central stump of the
divided sciatic gives rise, in an animal under urari, to an increase
of general blood-pressure, brought about chiefly, if not entirely, by
an augmentation of constrictive impulses passing along the splanch-
nic nerves. This increase of blood-pressure is manifested, with

CHAP, iv.] THE VASCULAR MECHANISM. 213

(in satisfactory experiments) undiminished intensity, even when the
whole of the brain, down to a certain limit in the medulla oblongata,
has been removed. But if the removal be carried beyond this
limit, or if a small area of the medulla oblongata lying above the
calamus scriptorius be removed, the effect on the general blood-
pressure of stimulating the central stump of the sciatic— we might
add, of any other afferent nerve — is comparatively insignificant. The
simplest view to take of these facts is to suppose that this small
portion of the medulla oblongata acts as a vaso-motor centre, by the
action of which ordinary afferent impulses coming from the sciatic
or any other afferent nerve, are transformed into vaso-motor
impulses of constructive (or as in the case of an animal under
chloral, of dilating) effect and so discharged along the splanchnic
nerves.

The lower limit of this region which we may call the medullary
vaso-motor centre has been placed in the rabbit at a horizontal
line drawn about 4 or 5 mm. above the point of the calamus
scriptorius, and the upper limit at about 4rnm. higher up, i.e.
about 1 or 2 mm. below the corpora quadrigemina. When trans-
verse sections of the brain are carried successively lower and
lower down, an effect on blood-pressure in the way of lowering it
and also of diminishing the rise of blood-pressure resulting from
stimulation of the sciatic, is first observed when the upper limit
is reached. On carrying the sections still lower, the effect of
stimulating the sciatic becomes less and less, until when the
lower limit is reached no effects at all are observed. The centre
appears to be bilateral, the halves being placed not in the middle
line but more sideways and rather nearer the anterior than the
posterior surface. It may perhaps be more closely defined as a
small prismatic space in the forward prolongation of the lateral
columns after they have given off their fibres to the decussating
pyramids. This space is largely occupied by a mass of grey
matter, called by Clarke the antero-lateral nucleus, and containing
large multipolar cells.

Whether this medullary vaso-motor centre has any distinct
automatic action, whether it may be regarded as continually gene-
rating out of its own molecular oscillations, and discharging along
the vaso-motor fibres, impulses whereby the general arterial tone
is maintained, is a question which, like the allied question mooted
on p. 188, need not be discussed here. Granting even the existence
of such automatic functions, they must be of secondary importance.
As we have already urged, the great use of the whole vaso-motor
system is not to maintain a general arterial tone, but to modify
according to the needs of the economy the condition of this or
that vascular area.

The impulses passing down the vaso-motor fibres of the cervical
sympathetic and of many other nerves may similarly be traced back
to this same region of the medulla oblongata. Whether all vaso-

214 VASO-MOTOR CENTRES. [BOOK i.

motor fibres are actually in functional connection with it may perhaps
be doubted; but at all events the fibres passing to so many vascular
areas, and those of such magnitude and importance, are by means
of it brought into functional relationship with so many afferent
nerves of the body, that it may fairly be spoken of as the general
vaso-motor centre.

But the use of this phrase must not be understood to imply
that this small portion of the medulla oblongata is the only part of
the central nervous system which can act as a vaso-motor centre.
In the frog reflex vaso-motor effects may be obtained by stimu-
lating various afferent nerves after the whole medulla has been
removed, and indeed even when only a comparatively small portion
of the spinal cord has been left intact and connected, on the one
hand, with the afferent nerve which is being stimulated and, on the
other, with the efferent nerves in which run the vaso-fibres whose
action is being studied. In the mammal such effects do not so
readily appear, but may with care and under special conditions be
obtained. Thus in the dog, when the spinal cord is divided in the
dorsal region, the arteries of the hind limbs and hinder part of the
body become dilated. This one would naturally expect as the
result of their severance from the general medullary vaso-motor
centre. But if the animal be kept in good condition for some time,
a normal or nearly normal arterial tone is after a while re-esta-
blished ; and the tone thus regained may be modified in the direc-
tion certainly of dilation, and possibly, but this is by no means so
certain, of constriction by afferent impulses reaching the lumbar
cord. Erection of the penis through the nervi erigentes may then
be still brought about by suitable stimulation of sensory surfaces,
and dilation of various vessels of the limbs readily produced by
stimulation of the central stump of one or another nerve.

These remarkable results, which though they are most striking
in connection with the lumbar cord hold good apparently for the
dorsal cord also and indeed for all parts of the spinal cord, naturally
suggest a doubt whether the explanation just given above of the
effects of section of the medulla oblongata, is a valid one. When
we come to study the central nervous system, we shall again and
again see that the immediate effect of operative interference with
these delicate structures is a temporary suspension of nearly all
their functions. This is often spoken of as ' shock ' and may be
regarded as an extreme form of inhibition. And the question may
fairly be put whether the effects of cutting and injuring the
structures which we have spoken of as the medullary vaso-motor
centre, are not in reality simply those of shock. The case of the
dog with the divided dorsal cord, and other similar cases, clearly
prove that parts of the spinal cord, other than the particular
region of the medulla oblongata of which we are speaking, may
act as vaso-motor centres. And we may very fairly at least put
forward the view, that the vascular dilation which follows upon

CHAP, iv.] THE VASCULAR MECHANISM. 215

sections of the so-called medullary vase-motor centre, comes about
because section of or injury to this region exercises a strong
inhibitory influence on all the vaso-motor centres situated in the
spinal cord below. Owing to the special function of the medulla
oblongata in carrying on the all-important work of respiration, a
mammal whose medulla has been divided cannot be kept alive for any
length of time. We cannot therefore put the matter to the simple
experimental test of extirpating the supposed medullary vaso-motor
centre and seeing what happens when the animal has completely
recovered from the effects of the operation : we have to be guided
in our decision by more or less indirect arguments. We must not
attempt to discuss the matter fully here, but may say that, after all
due weight has been attached to the play of inhibitory impulses,
there still remains a balance of evidence in favour of the view
that the. region of the medulla of which we are speaking does act
as a general vaso-motor centre. It is not however to be regarded
as the single vaso-motor centre, whither afferent impulses from all
parts of the body must always travel before they can start vaso-
motor impulses along this or that nerve. We are rather to suppose
that the spinal cord along its whole length, contains, interlaced
with the reflex and other mechanisms by which the skeletal muscles
are governed, vaso-motor centres and mechanisms of varied com-
plexity, the details of whose functions and topography have yet
largely to be worked out. As in the absence of the sinus venosus
the auricles and ventricle of the frog's heart may still continue to
beat, so in the absence of the medulla oblongata, these spinal vaso-
motor centres provide for the vascular emergencies which arise.
As however in the normal entire frog's heart, the sinus, so to speak,
gives the word and governs the work of the whole organ, so the
medullary vaso-motor centre rules and co-ordinates the lesser
centres of the cord, and through them presides over the chief
vascular areas of the body. It is possible moreover that the me-
dullary centre is specially connected with the splanchnic nerves and
thus with the capacious vascular area of the abdominal viscera, and
in consequence possesses an additional importance. By means of
these vaso-motor central mechanisms, by means of the head centre
in the medulla, and the subsidiary centres in the spinal cord, the
delicate machinery of the circulation, which determines the blood
supply, and so the activity of each tissue and organ, is able to
respond by narrowing or widening arteries to the ever-varying
demands and to meet by compensating changes the shocks and
strains of daily life.

Vase-motor nerves of the Veins. Although the veins are
provided with muscular fibres, and are distinctly contractile and
although rhythmic variations of calibre due to contractions may
be seen in the great veins opening into the heart, in the veins of

216 VASCULAR CONSTRICTION AND DILATION. [BOOK I.

the bat's wing, and elsewhere, and similar rhythmic variations, also
possibly due to active rhythmic contractions, but possibly also of
an entirely passive nature, have been observed in the portal veins,
very little is known of any nervous arrangements governing the
veins. When in the frog the brain and spinal cord are destroyed,
very little blood comes back to the heart as compared with the
normal supply, and the heart in consequence appears almost blood-
less and beats feebly. This has been interpreted as indicating the
existence of a normal tone in the veins dependent on the central
nervous system. "When the latter is destroyed, the veins become
abnormally distended and a large quantity of blood becomes lodged
and hidden as it were in them.

The Effects of Local Vascular Constriction or Dilation.

Whatever be determined ultimately to be the modus operandi
of vaso-motor mechanisms, the following fundamental facts remain
of prime importance.

The tone of any given vascular area may be altered, positively
in the direction of augmentation (constriction), or negatively in
the way of inhibition (dilation), quite independently of what is
going on in other areas. The change may be brought about by (1)
a stimulus applied to the spot itself, and acting either directly on
some local mechanism, or indirectly by reflex action through the
general central nervous system ; (2) by a stimulus applied to some
other sentient surface, and acting by reflex action through the
central nervous system ; (3) by a stimulus (chemical, arising in or
carried by the blood) acting directly on the central nervous system ;
(4) by some part of the central nervous system acting on the vaso-
motor centre, as in emotions.

The effects of local dilation are local and general.

The local effects are as follows. The arteries in the area being
dilated, offer less resistance than before to the passage of blood.
Consequently, more blood than usual passes through them, filling
up the capillaries and distending the veins. Owing to the diminu-
tion of the resistance, the fall of pressure in passing from the
arteries to the veins will be less marked than usual ; that in the
small arteries themselves will be lowered ; that in the corresponding
veins heightened. The lowering of the pressure in the arteries
means that their elastic coats are not put to the stretch as much
as usual ; i.e. their elasticity is not called into play to the same
extent as before. Now, as has been seen, every portion of the
arterial wall has its share in destroying the pulse by converting the

CHAP, iv.] THE VASCULAR MECHANISM. 217

intermittent into a continuous flow. Hence, the dilated arteries,
their elasticity not being called into play so much as before, will
not contribute their usual share towards destroying the pulsations
which -reach them at the cardiac side. The pulsations will travel
through them less changed than before, and may, in certain cases,
pass right on into the veins. This is frequently seen in the sub-
maxillary gland, when the chorda tympani is stimulated. The
channels being wider, resistance being less, and the force of the
heart behind remaining the same, more blood than before passes
through the area in a given time ; or, put differently, the same
quantity of blood passes through the area in a shorter time. The
blood, consequently, as it passes into the veins is less changed than
in the normal condition of the area. Usually the flow is so rapid
that the oxy-hsemoglobin of the corpuscles is deoxidised to a much
less extent than usual, and the venous blood still possesses an
arterial hue. On the other hand, since more blood passes in
a given time, there is an opportunity for an increase in the total
interchange between the blood and the tissue. Thus the total
work may be greater, though the share borne by each quantity of
blood is less.

The general effects of dilation are briefly these. Supposing
that the total quantity of blood issuing from the ventricle remains
the same, that is to say, supposing that the quantity of blood put
into circulation is constant, the surplus passing through the dilated
area must be taken away from the rest of the circulation. Con-
sequently the fulness of the dilated area will lead to an emptying
of the other areas. This is seen very clearly when the dilated area
is a capacious one. At the same time, local dilation causes a local
diminution of peripheral resistance. This in turn causes a lower-
ing of the general arterial pressure ; to this we have already called
attention.

The effects of local constriction, similarly local and general, are
naturally the reverse of those of dilation. In the vascular area
directly affected, less blood passes through the capillaries in a given
time, and in consequence less total interchange between the blood
and the tissues takes place, though each unit volume of blood which
does pass through is more deeply affected. The blood-pressure in
the corresponding arteries is increased, and, if the area be large, the
pressure in even distant arteries may be heightened.

Thus, to indicate results in a general manner, local dilation en-
courages a copious flow of blood through the area where the
dilation is taking place, and, by reducing the blood-pressure,
hinders the flow of blood into other areas. Local constriction, on
the other hand, lessens the flow of blood in the particular area, and
by heightening the blood-pressure tends to. throw the mass of the
blood on to other areas. Hence the great regulative value of the
vaso-motor system. By augmenting or inhibitory influences (con-
strictor or dilating) applied either to peripheral mechanisms or to

218 VASCULAR CONSTRICTION AND DILATION. [BOOK i.

cerebro-spinal centres, and called forth by stimuli either intrinsic
and acting through the blood, or extrinsic and acting through
nervous tracts, the supply of blood to this or that organ or tissue
may be increased or reduced : the surplus or deficit being carried
away to, or brought up from, either the rest of the body generally
or some other special organ or tissue.

SEC. 6. CHANGES IN THE CAPILLARY DISTRICTS.

We have already seen (p. 116) that the capillary channels vary
very much in width from time to time ; but the capillaries do not,
like the arteries, possess a distinct muscular coat, and the mechanism
by which they are brought now to a dilated now to a constricted
condition has not been worked out so thoroughly as in the case of
the arteries. On the one hand there can be no doubt that the
changes in their calibre are in part of a passive nature. They are
expanded when a large supply of blood reaches them through the
supplying arteries, and, by virtue of their elasticity, shrink again
when the supply is lessened or withdrawn.

On the other hand there is an increasing amount of evidence
that the capillary walls are really contractile. The constituent
epithelioid cells have been seen to change their form under the
influence of stimuli ; and there is much reason for believing that
the calibre of a capillary canal may vary, quite independently of
the arterial supply or the venous outflow, in consequence of changes
in form of the epithelioid cells, allied to the changes in a muscle-
fibre or muscle-cell which constitute a contraction. Though the
matter requires further investigation, it is probable that these
active changes play an important part in determining the quantity
of blood passing through a capillary area ; but there is as yet no
evidence that they, like the corresponding changes in the arteries,
are governed by the nervous system.

Over and above these changes of form, the capillaries and
minute vessels also possess other active properties, which cause
them to play an important part in the work of the circulation.
They are concerned in assisting to maintain a vital equilibrium
between the intra-vascular blood and the extra-vascular tissue, an

220 CHANGES IN THE CAPILLARIES. [BOOK i.

equilibrium which is the central fact of a normal capillary circula-
tion, of a normal interchange between the blood and the tissue, and
thus of a normal life of the tissue. The existence of this equi-
librium is best shewn when it is overthrown or modified, as in
inflammation and allied conditions.

If an irritant, such as a drop of chloroform or a little diluted
oil of mustard, be applied to a small portion of a frog's web, a frog's
tongue, or some other transparent tissue, the following changes may
be observed under the microscope. The first effect that is noticed
is a dilation of the arteries, accompanied by a quickening of the
stream. The capillaries become filled with corpuscles, and many
passages, previously invisible or nearly so on account of their con-
taining no corpuscles, now come into view. The veins at the same
time appear enlarged and full. The increase of width is most
marked in the arteries, next so in the veins, and least of all in
the capillaries. If the stimulus be very slight, this may all pass
away, the arteries gaining their normal constriction, and the capil-
laries and veins returning to their normal condition; in other
words, the effect of the stimulus in such a case is simply a tem-
porary blush. Unless however the chloroform or mustard be applied
with especial care the effects are much more profound and lasting.
In the case of the frog's web a condition is set up known under the
name of stasis. This has been considered as merely a phase of in-
flammation, since in the frog's web in which inflammation has been
largely studied, the agents which produce inflammation frequently
produce stasis. But in the frog's tongue and elsewhere true inflam-
mation may be set up and produce all its results without any stasis
making its appearance; and though the two conditions are in
several respects similar, they appear to be distinct: stasis being the
result of the profounder action of the irritant and the forerunner of
local death or necrosis.

It is this stasis which particularly illustrates the points to which
we wish to call attention. When as the result of the irritant, the
initial blush passes into stasis, the following events may be observed.
The quickening of the stream gives way to a slackening; this is
not due to any returning constriction of the arteries, for they still
continue dilated. It will further be observed that the red corpuscles,
instead of being in the larger capillaries and smaller arteries and
veins confined to the axial stream, are diffused and indeed crowded
over the whole width of the channels. The capillaries and veins
get more and more crowded with corpuscles, the white corpuscles
being scattered irregularly among the more numerous red ones;
and though the channels get wider and wider, becoming frequently
even enormously distended, the stream becomes slower and slower,
until at last the movement of the blood in the affected area ceases
altogether. The phase of accelerated flow has given place to stasis.
The capillaries, veins and small arteries are choked with corpuscles,
and it may now be remarked that the red corpuscles seem to run

CHAP, iv.] THE VASCULAR MECHANISM. 221

together, so that their outlines are no longer distinguishable ; they
appear to have become fused into a homogeneous mass. Except in
cases where the stimulus produces permanent mischief, this peculiar
condition after a while subsides. The outlines of the corpuscles
become once more distinct, those on the venous side of the block
gradually drop away into the neighbouring currents, little by little
the whole obstruction is removed, the current through the area is
re-established, and though the arteries and capillaries remain
dilated for some considerable time, they eventually return to their
normal calibre.

The stasis, the arrest of the current here seen, is not due to any
lessening of the heart's beat; the arterial pulsations, or at least the
arterial flow, may be seen to be continued down to the affected
area, and there to cease very suddenly. It is not due to any
increase of peripheral resistance caused by constriction of the small
arteries, for these continue dilated rather than constricted. It must
therefore be due to some new and unusual resistance occurring in
the capillary area itself. The increase of resistance is not caused
by any change confined to the corpuscles themselves ; for if after a
temporary delay one set of corpuscles has managed to pass away
from the affected area, the next set of corpuscles is subjected to the
same delay and the same apparent fusion. The cause of the resist-
ance must therefore lie in the capillary walls, or in the tissue
of which they form a part. We are driven to conclude that the
walls of the capillaries (and of the other vessels) exert in health a
certain attraction on the corpuscles, maintain a certain adhesiveness
between them and themselves, thereby determining the normal flow,
with its axial stream and plasmatic layer, and offering a normal
resistance to the pressure of the arterial system; and that, in stasis,
for reasons which we cannot as yet explain, this attraction, this
adhesiveness is largely and progressively increased. Hence the
early disappearance of the distinction between the axial stream and
plasmatic layer, the tarrying of the corpuscles in spite of the widen-
ing of their path, and finally their agglomeration and fusion in the
even enormously distended channels.

That the increased adhesion is due to the vascular walls and not
primarily to the corpuscles themselves is further shewn by the fact
that if in the frog, an artificial blood of normal saline solution to
which milk has been added be substituted for normal blood, a
stasis may by irritants be induced in which oil-globules play the
part of corpuscles, and by their aggregation bring about an arrest
of the flow through the capillaries.

In true inflammation the course of events is different. The
vessels become dilated, but the loss of distinction between the axial
stream and the plasmatic layer does not occur. On the contrary
the plasmatic layer appears even more striking on account of the
large number of white corpuscles which gather in it and become
adherent to the inner surface of the walls of the veins and venous

222 CHANGES IN THE CAPILLARIES. [BOOK i.

capillaries. In the normal circulation only a few white corpuscles
are from time to time seen in this situation slowly moving on
in jerks ; but now the walls of the veins seem to be more and
more thickly lined with white corpuscles, which are at first com-
pletely stationary. At the same time white corpuscles become
also very abundant in the capillaries. Very soon these white
corpuscles may be seen, either through stomata at the junctions of
the epithelioid cells forming the lining of the vessels, or by
temporary breaches which are rapidly repaired, making their way
through the walls of the veins and capillaries, and escaping into
the surrounding tissues. Through the walls of the capillaries and
smaller veinlets, red corpuscles pass as well as white. And this
takes place to such an extent that very soon the tissue around the
veins and capillaries becomes crowded with white corpuscles, and to
a less extent with red corpuscles which have made their way out
of the vessels. At the same time a large quantity of coagulable
lymph, which since it appears also to have passed from the blood-
stream through the walls of the blood-vessels is spoken of as exu-
dation, makes its appearance in the interstices of the inflamed
tissue. While however these changes are going on there is not, as
in stasis, a delay and final arrest of the blood-stream. On the
contrary, the flow through the widened channels continues during
the whole time to remain accelerated. By comparing the outflow
from the veins of the inflamed foot of a dog, with the outflow from
the veins of the healthy foot, it has been ascertained that a larger
(quantity of blood passes through the inflamed foot than through
the healthy foot in the same time.

We must not however pursue this subject of inflammation any
further. We have simply brought it forward as affording another
illustration of the action of the walls of the blood-vessels; for,
though the matter is perhaps not definitely settled, it seems pro-
bable that the aggregation, in inflammation, of the white corpuscles
upon the lining surface of the vessels is due to a special attraction
which the blood-vessels exert on the white corpuscles, without pro-
ducing that general adhesion of all the corpuscles which is the mark
of stasis, and that the migration of the corpuscles is also at least
facilitated by similar intrinsic changes in the vascular walls.

We cannot say at present whether the vascular walls are also
capable of modifying the passage of the fluid parts as distinguished
from the corpuscular elements of the blood, though we know by
experiment that the flow of fluid through capillary tubes may be
modified on the one hand by changes in the substance of which the
tubes are composed, and on the other hand by changes in the
chemical nature (even independent of the specific gravity) of the
iluid which is used. We have said enough to shew that the peri-
pheral resistance in the capillaries (and consequently all that depends
on that peripheral resistance) is not merely a matter of the mechani-
cal friction of the blood against the smooth walls of the blood-vessels,

CHAP, iv.] THE VASCULAR MECHANISM. 223

but is concerned with the vital condition of the tissues. When the
tissue is in health, a certain resistance is offered to the passage of
blood through the capillaries, and the whole vascular mechanism is
adapted to overcome this resistance to such an extent that a
normal circulation can take place. When the tissue becomes
affected, the disturbance of the equilibrium between the tissue
and the blood may as in inflammation so modify the flow as to lead
to the abnormal escape from the blood of various constituents, or as
in stasis so augment the resistance that the passage of the blood
becomes difficult or impossible. And it is quite open to us to
suppose that there are conditions the reverse of stasis, in which the
resistance may be lowered below the normal, and the circulation
in the area quickened.

Thus the vital condition of the tissue becomes a factor in the
maintenance of the circulation ; and it is possible, though not yet
proved, that these vital conditions are directly under the dominion
of the nervous system.

It is perhaps hardly necessary to observe that the considerations
urged above are quite distinct from what is sometimes spoken of under
the name of 'capillary' force, as an agent of the circulation. If by
capillary force it is intended to refer to the rise of fluids in capillary
tubes, it is evident that since such phenomena are the results of
adhesion, capillarity can only be a greater or less hindrance to the flow
of blood, seeing that this is propelled by a force (the heart's beat)
which has been proved by experiment to be equal to the task of
driving the blood from ventricle to auricle through the capillary regions.
If by capillary force it is meant that the tissues have some vital power
of withdrawing the fluid parts of the blood from the small arteries and
thus of assisting an onward flow, it becomes necessary also to assume
that they have as well the power of returning the fluid parts to the
veins. Both these assumptions are unnecessary and without foundation.

SEC. 7. CHANGES IN THE QUANTITY OF BLOOD.

In an artificial scheme, changes in the total quantity of fluid in
circulation will have an immediate and direct effect on the arterial
pressure, increase of the quantity heightening and decrease
diminishing it. This effect will be produced partly by the pump
being more or less filled at each stroke, and partly by the peri-
pheral resistance being increased or diminished by the greater
or less fulness of the small peripheral channels. The venous
pressure will under all circumstances be raised with the increase of
fluid, but the arterial pressure will be raised in proportion only so
long as the elastic walls of the arterial tubes are able to exert their
elasticity.

In the natural circulation, the direct results of change of quan-
tity are obscured by compensatory arrangements. Thus experi-
ment shews that when an animal with normal blood-pressure
is bled from one carotid, the pressure in the other carotid sinks so
long as the bleeding is going on1, and remains depressed for
a brief period after the bleeding has ceased. In a short time how-
ever it regains or nearly regains the normal height. This recovery
of blood-pressure, after haemorrhage, is witnessed so long as the
loss of blood does not amount to more than about 3 per cent, of

1 Chiefly in consequence of free opening in the vessel from which the bleeding
is going on, cutting off a great deal of the peripheral resistance, and so leading to a
general lowering of the blood-pressure.

CHAP, iv.] THE VASCULAR MECHANISM. 225

the body-weight. Beyond that, a large and frequently a sudden
dangerous permanent depression is observed.

The restoration of the pressure after the cessation of the
bleeding is too rapid to permit us to suppose that the quantity of
fluid in the blood-vessels is repaired by the withdrawal of lymph
from the extra-vascular elements of the tissues. In all probability
the result is gained by an increased action of the vaso-motor
nerves, increasing the peripheral resistance, the vaso-motor centres
being thrown into increased action by the diminution of their
blood-supply. When the loss of blood has gone beyond a certain
limit, this vaso-motor action is insufficient to compensate the
diminished quantity (possibly the vaso-motor centres in part
become exhausted), and a considerable depression takes place ; but
at this epoch the loss of blood frequently causes anaemic con-
vulsions.

Similarly when an additional quantity of blood is injected into
the vessels, no marked increase of blood-pressure is observed so
long as ~ the vaso-motor centre in the medulla oblongata is intact.
If however the cervical spinal cord be divided previous to the in-
jection, the pressure, which on account of the removal of the
medullary vaso-motor centre, is very low, is permanently raised by
the injection of blood. At each injection the pressure rises, falls
somewhat afterwards, but eventually remains at a higher level than
before. This rise continues until the amount of blood in the
vessels above the normal quantity reaches from 2 to 3 per cent,
of the body-weight. Beyond this point there is no further rise of
pressure.

These facts shew, in the first place, that when the volume of
the .blood is increased, compensation is effected by a lessening of
the peripheral resistance by means of a vaso-dilator action of the
vaso-motor centres, so that the normal blood-pressure remains con-
stant. They further shew that a much greater quantity of blood
can be lodged in the blood-vessels than is normally present in
them. That the additional quantity injected does remain in the
vessels is proved by the absence of extravasations, and of any con-
siderable increase of the extra-vascular lymphatic fluids. It has
already been insisted that, in health, the veins and capillaries must
be regarded as being far from filled, for were they to receive all the
blood which they can, even at a low pressure, hold, the whole quan-
tity of blood in the body would be lodged in them alone. In these
cases of large addition of blood, the extra quantity appears to
be lodged in the small veins and capillaries (especially of the
internal organs), which are abnormally distended to contain the
surplus.

We learn from these facts the two practical lessons, first, that
blood-pressure cannot be lowered directly by bleeding, unless the
quantity removed be dangerously large, and secondly, that there is

F. 15

226 CHANGES IN THE QUANTITY OF BLOOD. [BOOK i.

no necessary connection between a high blood -pressure and fulness
of blood or plethora, since an enormous quantity of blood may be
driven into the vessels without any marked rise of pressure.

SEC. 8. THE MUTUAL RELATIONS AND THE CO-ORDI-
NATION OF THE VASCULAR FACTORS.

The foregoing considerations shew how complicated, and
sensitive, and therefore how useful, is the vascular mechanism.
It may be worth while briefly to summarize the relations of the
different factors, and to point out the manner in which they are
made to work in harmony for the good of the body.

Two facts stand out prominent above all others: (1) the heart's
beat may be made slow by vagus inhibition, and, on the other
hand, quickened either by withdrawal of the constant inhibitory
influence exercised by the cardio-inhibitory centre, or by the direct
action of accelerating mechanisms. (2) The peripheral resist-
ance may be increased or diminished, the increase and decrease
being due either to increased or diminished action of the vaso-
motor centres which preside over arterial tone, or to the action of
special constrictor or dilator fibres.

These two facts are, by the mediation of the nervous system,
placed in mutual regulative dependence on each other. Thus, if
with a given peripheral resistance, and proportionate blood-pressure,
the heart begins to beat violently, afferent impulses passing up the
depressor nerves diminish peripheral resistance (by opening the
splanchnic flood-gates), and prevent the rise of blood-pressure
which would otherwise take place. In this way a delicate organ,
such for instance as the retina, is sheltered from the turbulence of
the heart by the flow of blood being diverted to the less noble

15—2

228 RELATIONS OF THE VASCULAR FACTORS. [BOOK i.

organs of the abdomen. Conversely, if peripheral resistance be in
any area increased, the general blood-pressure is prevented from
rising too high, by reason of the actual increase of blood-pressure
so affecting the medulla, that inhibitory impulses descend the
vagus, and, by producing a less frequent, possibly a weaker pulse,
tone down the distension of the arteries.

The more we learn of the working of the body, the more aware
we become of the fact that it is crowded with regulative and
compensating arrangements no less striking and exquisite than the
two we have just described. Some of these will be seen in the
following almost tabular statement of the various modifications of
the vascular factors, and of their causes.

A. The Beat of the Heart is affected

1. By the amount of distension of the ventricular cavities pre-
ceding the systole. This will depend on

a. The quantity of blood reaching the heart and passing into
its cavities during the diastole. This in turn is determined by
the flow of blood through the veins, the flow itself being influenced
by the arterial pressure, respiratory movements, &c. &c.

b. The force of the auricular contractions.

c. The amount of resistance which has to be overcome by the
systole. This is determined by the mean arterial pressure, and is
influenced by everything which influences that.

2. By the quantity of the blood passing through the coronary
arteries. In the frog the thin walls of the auricle and the spongy
texture of the ventricle permit the nourishment of the cardiac sub-
stance to be carried on by direct contact with the blood in the
cavities. In mammals this mode of nutrition must be insignificant.
In them the condition of the cardiac muscles and nervous ap-
pendages depends almost exclusively on the blood distributed by
the coronary arteries. The coronary circulation however is peculiar
and is largely determined by the action of the heart itself.

3. By the quality of the blood passing through the coronary
arteries, and acting upon simply the muscular tissue, or upon the
various nervous mechanisms, or upon both. This is illustrated by
the action of poisons. The quantitative relations of the normal,
and the presence of abnormal, constituents of the blood must of
necessity profoundly affect the heart's beat.

4. Through the inhibitory fibres of the vagus.

a. By the blood directly stimulating the endings of the vagus
fibres. This is only seen in the case of poisons.

b. By the blood directly affecting the cardio-mhibitory centre

CHAP, iv.] THE VASCULAR MECHANISM. 229

in the medulla oblongata, either positively by augmenting the
normal inhibitory influences and so slowing the heart, or negatively
by depressing those influences and so quickening the heart.

c. By reflex stimulation of the same centre. Cases of exalta-
tion through reflex stimulation have already been quoted. In-
stances of depression leading to quickening of the heart's beat are
not so clear. The afferent impulses may be started in any part of
the body; but, as we have seen, there seems to be a special
connection between this centre and the alimentary canal.

5. By the accelerator nerves. We have however, at present,
no very satisfactory evidence of the natural activity of these nerves.

B. The Peripheral Resistance is affected

1. By the vital i.e. the nutritive condition of the tissue of the
part. This is again influenced by

a. The quality (and quantity ?) of the blood brought to it.

b. Through the agency of the nervous system, as is seen in
cases of inflammation caused by nervous influences.

. Both these points are very obscure.

2. By the varying calibre (constriction, dilation) of the minute
arteries, brought about

a. By the blood or other stimulus acting directly on the peri-
pheral vaso-motor mechanism.

b. By the blood or other stimulus acting directly on the vaso-
motor centres in the central nervous system.

c. By reflex stimulation of the vaso-motor centres.

d. By the quantity of blood supplied to the vaso-motor centre,
this being in turn dependent on the blood-pressure in the arteries
supplying the centre. Thus a regulative mechanism is established
for cases when the quantity of blood, as distinguished from its
quality, is changed (see p. 225).

Through these intricate ties it comes to pass that an event
which takes place in one part of the body is felt, to a greater or
less extent, by all parts. To take a simple instance : a change in
the condition of the skin at any one spot, such as that produced by
the application of cold or heat, may lead,

a. By direct local action to a constriction or dilation of the
vessels of the part, giving rise to local pallor or suffusion.

/5. By reflex action through the central nervous system, to an
increase of the same local effects, and in addition to a change in

230 RELATIONS OF THE VASCULAR FACTORS. [BOOK i.

the calibre of the blood-vessels in other parts. This distant reflex
change may be of the same or the opposite nature as the local
change.

7. By reflex action to a quickening or slowing of the heart's
beat, though the heart is in this respect less intimately connected
with the skin than with other parts.

Out of these primary effects there may arise secondary effects ;
the constriction or dilation produced locally will affect the general
blood-pressure, which in turn will produce all its effects.

The modifications of the heart-beat will not only affect the general
blood-pressure, but in a reflex manner may affect the peripheral
resistance, and hence the flow of blood in particular areas (e.g. the
splanchnic area). The modifications of the flow through the area
directly, and also through those secondarily, affected, will influence
the temperature and chemical changes of the blood, and variations
in these will in turn produce their effects everywhere. And so on.

On the other hand, the turbulence which would be the natural
outcome of all these events is softened down, by the compensating
effects of which we have spoken, into the smoothness which we call
health. Still, the greatness of the possibilities of change which lie
hidden in the body are clearly enough shewn by the violence of
disease, when compensation fails of accomplishment.

BOOK II.

THE TISSUES OF CHEMICAL ACTION WITH THEIR
RESPECTIVE MECHANISMS. NUTRITION.

CHAPTEE I.
THE TISSUES AND MECHANISMS OF DIGESTION.

THE food in passing along the alimentary canal is subjected to the
action of certain juices which are produced by the secretory activity
of the epithelium-cells lining the canal itself or forming part of its
glandular appendages. These juices (viz. saliva, gastric juice,
bile, pancreatic juice, and the secretions of the small and large
intestines), poured upon and mingling with the food, produce
in it such changes, that from being largely insoluble it becomes
largely soluble, or otherwise modify it in such a way that the
larger part of what is eaten passes into the blood, either directly
by means of the capillaries of the alimentary canal or indirectly
by means of the lacteal system, while the smaller part is discharged
as excrement.

We have therefore to consider— First, the properties of the
various juices, and the changes they bring about in the food eaten.
Secondly, the nature of the processes by means of which the
various epithelium-cells of the various glands and various tracts of
the canal are able to manufacture so many various juices out of
the common source, the blood, and the manner in which the
secretory activity of the cells is regulated and subjected to the
needs of the economy. Thirdly, the mechanisms, here as elsewhere
chiefly of a muscular nature, by which the food is passed along the
canal, and most efficiently brought in contact with successive
juices. Fourthly and lastly, the means by which the nutritious
digested material is separated from the undigested or excremental
material, and absorbed into the blood.

SEC. 1. THE PROPERTIES OF THE DIGESTIVE JUICES.

Saliva.

Mixed saliva, as it appears in the mouth, is a thick, glairy,
generally frothy and turbid fluid. Under the microscope it is
seen to contain, besides the molecular debris of food (and fre-
quently cryptogamic spores), epithelium-scales, mucus-corpuscles
and granules, and the so-called saliva corpuscles. Its reaction in
a healthy subject is alkaline, especially when the secretion is
abundant. When the saliva is scanty, or when the subject suffers
from dyspepsia, the reaction of the mouth may be acid. Saliva
contains but little solid matter, on an average probably about
•5 p. c., the specific gravity varying from T002 to T006. Of these
solids, rather less than half, about "2 p. c., are salts (including a
small quantity of potassium sulphocyariate). The organic bodies
which can be recognised in it are chiefly mucin, with small
quantities of globulin and serum-albumin.

The chief purpose served by the saliva in digestion is to
moisten the food, and to assist in mastication and deglutition. In
some animals this is its only function. In other animals and in
man it has a specific solvent action on some of the food-stuffs.
Such minerals as are soluble in slightly alkaline fluids are dis-
solved by it. On fats it has no effect save that of producing a
very feeble emulsion. On proteids it has also no action. Its
characteristic property is that of converting starch into some form
of sugar.

CHAP. L] DIGESTION. 235

Action of Saliva on Starch. If to a quantity of boiled starch,
which is always more or less viscid and somewhat opaque or turbid,
a small quantity of saliva be added, it will be found after a short
time that an important change has taken place, inasmuch as the
mixture has lost its previous viscidity and become thinner and
more transparent. In order to understand this change, the reader
must bear in mind the existence of the following bodies (described
more fully in the Appendix) all belonging to the class of carbo-
hydrates : 1. Starch, which forms with water not a true solution
but a more or less viscid mixture, and gives a characteristic blue
colour with iodine. 2. Dextrin, differing from starch in forming a
clear solution and in giving a red colour with iodine. 3. Dextrose,
also called glucose or grape-sugar, giving no colouration with iodine,
but characterised by the power of reducing cupric and other
metallic salts; thus, when dextrose is boiled with a fluid often
known as Fehling's fluid, which is a solution of cupric sulphate with
an excess of sodium hydrate, the cupric salt is reduced and a red
or yellow deposit of cuprous oxide is thrown down. This reaction
serves with others as a convenient test for dextrose. Neither starch
nor dextrin, nor that commonest form of sugar known as cane-sugar,
give this reaction. 4. Maltose, very similar to dextrose, and like it
capable of reducing cupric salts. Besides having a slightly different
formula, it differs from dextrose, chiefly in its smaller reducing
power, i.e. a given quantity will not convert so much cupric oxide
into cuprous oxide as will the same weight of dextrose, and in having
a stronger rotatory action on rays of light (see Appendix). Besides
the above we may mention the peculiar body, achroodextrin, which
differs from dextrin in giving no colouration at all with iodine ; and
the so-called soluble starch, which like dextrin forms a clear solution
with water, but unlike dextrin gives a blue colour with iodine.

Hence when a quantity of starch is boiled with water we may
recognize in the viscid imperfect solution, on the one hand the
presence of starch, by the blue colour which the addition of iodine
gives rise to, and on the other hand the absence of sugar (dextrose,
maltose), by the fact that when boiled with Fehling's fluid no
reduction takes place and no cuprous oxide is precipitated. ,

If however the boiled starch be submitted for a while to the
action of saliva, especially at a somewhat high temperature such as
35° or 40° C., it is found that the subsequent addition of iodine
gives no blue colour at all, or very much less colour, shewing that
the starch has disappeared or diminished ; on the other hand the
mixture readily gives a precipitate of cuprous oxide when boiled
with Fehling's fluid, shewing that dextrose or maltose is present.
That is to say the saliva has converted the starch into dextrose
or maltose; and there are reasons, which we need not enter into
here, for thinking that while some dextrose is formed the greater
part of the sugar which appears is in the form of maltose. As
the conversion of the starch by the saliva is going on the addition

236 SALIVA. [BOOK n.

of iodine frequently gives rise to a red or violet colour instead of
a pure blue, but when the conversion is complete no colouration
at all is observed. The appearance of this red or violet colour
indicates the presence of dextrin.

The temporary appearance of dextrin shews that the action of
the saliva on the starch is somewhat complex; and this is still
further proved by the fact that even when the saliva has completed
its work the whole of the starch does not reappear as dextrose or
maltose. There are probably several other bodies formed out of
the starch besides these, the relative proportions varying according
to circumstances. The change therefore, though perhaps we may
speak of it in a general way as one of hydration, cannot be exhibited
under a simple formula, and we may rest content for the present
with the statement that starch when subjected to the action of
saliva is converted chiefly into the sugar known as maltose with a
comparatively small quantity of dextrose, dextrin appearing tempo-
rarily in the process, and other bodies on which we need not dwell
being formed at the same time.

Raw unboiled starch undergoes a similar change but at a much
slower rate. This is due to the fact that in the curiously formed
starch grain the true starch, or granulose, is invested with coats
of cellulose. This latter material, which requires previous treat-
ment with sulphuric acid before it will give the blue reaction,
on the addition of iodine, is apparently not acted upon by saliva.
Hence the saliva can only get at the granulose by traversing
the coats of cellulose, and the conversion of the former is thereby
much hindered and delayed.

The conversion of starch into sugar, and this we may speak of as
the amylolytic action of saliva, will go on at the ordinary tempera-
ture of the atmosphere. The lower the temperature the slower the
change, and at about 0° C. the conversion is indefinitely prolonged.
After exposure to this cold for even a considerable time the action
recommences when the temperature is again raised. Increase of
temperature up to about 35° — 40°, or even a little higher, favours
the change, and the greatest activity is said to be witnessed at
about 40°. Much beyond this, however, increase of temperature
becomes injurious, markedly so at 60° or 70°; and saliva which
has been boiled for a few minutes not only has no action on starch
while at that temperature, but does not regain its powers on
cooling. By being boiled, the amylolytic activity of saliva is per-
manently destroyed.

The action of saliva on starch needs for its development a
slightly alkaline or at least a neutral reaction of the mixture ;
it is hindered or arrested by a distinctly acid reaction. Indeed the
presence of even a very small quantity of free acid, at all events
of hydrochloric acid, at the temperature of the body not only
suspends the action but speedily leads to permanent abolition of
the -activity of the juice. The bearing of this will be seen later on.

CHAP, i.] DIGESTION. 237

The action of saliva is hampered by the presence in a concen-
trated state of the product of its own action, that is, of sugar. If
a small quantity of saliva be added to a thick mass of boiled starch,
the action will after a while slacken, and eventually come to almost
a stand-still long before all the starch has been converted. On
diluting the mixture with water, the action will recommence. If
the products of action be removed as soon as they are formed, a
small quantity of saliva will, if sufficient time be allowed, convert
into sugar a very large, one might almost say an indefinite,
quantity of starch. Whether the particular constituent on which
the activity of saliva depends is at all consumed in its action has
not at present been definitely settled.

On what constituent do the amylolytic virtues of saliva depend ?

If saliva, filtered and thus freed from mucus and other formed
constituents, be treated with ten or fifteen times its bulk of alcohol,
a precipitate takes place containing besides other substances all
the proteid matters. Upon standing under the alcohol for some
time (several days, or, better, weeks), the proteids thus precipitated
become coagulated and insoluble in water. Hence, an aqueous
extract of the precipitate, made after this interval, contains very
little proteid material, and yet is exceedingly active. Moreover
by other more elaborate methods there may be obtained from
saliva solutions which appear to be almost entirely free from
proteids and yet are intensely amylolytic. But even these probably
contain other bodies besides the really active constituent. Whatever
the active substance be in itself, it exists in such extremely small
quantities, that it has never yet been satisfactorily isolated; and
indeed the only evidence we have of its existence is the manifesta-
tion of its peculiar powers.

The salient features of this body, which we may call ptyalm, are
then 1st, its presence in minute and almost inappreciable quantity.
2nd, the close dependence of its activity on temperature. 3rd, its
permanent and total destruction by a high temperature and by
various chemical reagents. 4th, the want of any clear proof that it
itself undergoes any change during the manifestation of its powers;
that is to say, the energy necessary for the transformation which
it effects does not come oat of itself; if it is at all used up in
its action, the loss is rather that of simple wear and tear of a
machine, than that of a substance expended to do work. 5th, the
action which it induces is probably of such a kind (splitting up
of a molecule with assumption of water) as is effected by the agents
called catalytic, and by that particular class of catalytic agents
called hydrolytic.

These features mark out the amylolytic active body of saliva
as belonging to the class of ferments1 ; and we may henceforward
speak of the amylolytic ferment of saliva.

1 Ferments may, for the present at least, be divided into two classes, commonly
called organised and unorganised. Of the former, yeast may be taken as a well-

238 SALIVA. [BOOK n.

Mixed saliva, whose properties we have just discussed, is the
result of the mingling in various proportions of saliva from the
parotid, submaxillary, and sublingual glands with the secretion
from the buccal glands. These constituent juices have their own
special characters, and these are not the same in all animals.
Moreover in the same individual the secretion differs in composition
and properties according to circumstances ; thus, as we shall see in
detail hereafter, the saliva from the submaxillary gland secreted
under the influence of the chorda tympani nerve is very different
from that which is obtained from the same gland by stimulating
the sympathetic nerve.

In man pure parotid saliva may easily be obtained by introducing a
fine cannula into the opening of the Stenonian duct, and submaxillary
saliva, or rather a mixture of submaxillary and sublingual saliva, by
similar catheterisation of the Whartonian duct. In animals the duct
may be dissected out and a cannula introduced.

Parotid saliva in man is clear and limpid, not viscid ; the reaction
of the first drops secreted is often acid, the succeeding portions,
at all events when the flow is at all copious, are alkaline ; that is
to say the natural secretion is alkaline, but this may be obscured
by acid changes taking place in the fluid which has been retained
in the duct. On standing, it becomes turbid from a precipitate of
calcic carbonate, due to an escape of carbonic acid. It contains
globulin and some other forms of albumin, with little or no mucin.
Potassium sulphocyanate may also sometimes be detected, but
structural elements are absent.

Submaxillary saliva, in man and in most animals, differs from
parotid saliva in being more alkaline and, from the presence of
mucus, more viscid; it contains, often in abundance, salivary
corpuscles, and amorphous masses of proteid material. The so-
called chorda saliva in the dog, of which we shall presently speak, is
under ordinary circumstances thinner and less viscid, contains less
mucus, and fewer structural elements, than the so-called sympa-
thetic saliva, which is remarkable for its viscidity, its structural
elements, and for its larger total of solids.

Sublingual saliva is more viscid, and contains more mucin and
more total solids (in the dog 275 p. c.), than even the submaxillary
saliva.

The action of saliva varies in intensity in different animals.
Thus in man, the pig, the guinea-pig, and the rat, both parotid
and submaxillary and mixed saliva are amylolytic; the sub-
known example. The fermentative activity of yeast which leads to the conversion
of sugar into alcohol, is dependent on the life of the yeast-cell. Unless the yeast-
cell be living and functional, fermentation does not take place; when the yeast-
cell dies fermentation ceases ; and no substance obtained from yeast, by precipita-
tion with alcohol or otherwise, will give rise to alcoholic fermentation. The salivary
ferment belongs to the latter class; it is a substance, not a living organism
like yeast.

CHAP, i.] DIGESTION. 239

maxillary saliva being in most cases more active than the parotid.
In the rabbit, while the submaxillary saliva has scarcely any
action, that of the parotid is energetic. The saliva of the cat is
much less active than the above, and that of the dog still less ;
indeed the parotid saliva of the dog is wholly inert. In the horse,
sheep, and ox, the amylolytic powers of either mixed saliva, or of
any one of the constituent juices, are extremely feeble.

Where the saliva of any gland is active, an aqueous infusion of
the same gland is also active. The importance and bearing of this
statement will be seen later on. From the aqueous infusion of
the gland, as from saliva itself, the ferment may be approximately
isolated. In some cases at least some ferment may be extracted
from the gland even when the secretion is itself inactive.

The readiest method indeed of preparing a highly amylolytic
liquid tolerably free from proteid and other impurities, is to mince
finely a gland known to have an active secretion, such for instance
as that of a rat, dehydrate it by allowing it to stand under absolute
alcohol for some days, and then, having poured off most of the
alcohol, and removed the remainder by evaporation at a low tempe-
rature, to cover the pieces of gland with strong glycerine. A
mere drop of such a glycerine extract rapidly converts starch into
sugar.

Gastric Juice.

There is no difficulty in obtaining what may fairly be con-
sidered as a normal saliva ; but there are many obstacles in the
way of determining the normal characters of the secretion of the
stomach. When no food is taken the stomach is at rest and no
secretion takes place. When food is taken, the characters of the
gastric juice secreted are obscured by the food with which it is
mingled. The gastric membrane may it is true be artificially
stimulated, by touch for instance, and a secretion obtained. This
we may speak of as gastric juice, but it may be doubted whether
it ought to be considered as normal gastric juice. And indeed as
we shall see even the juice, which is poured into the stomach
during a meal, varies as digestion is going on. Hence the charac-
ters which we shall give of gastric juice must be considered as
having a general value only.

Gastric juice, obtained by artificial stimulation from the healthy
stomach of a fasting dog, by means of a gastric fistula, is a thin
almost colourless fluid with a sour taste and odour.

In the operation for gastric fistula, an incision is made through the
abdominal walls, along the linea alba, the stomach is opened, and the
lips of the gastric wound securely sewn to those of the incision in the
abdominal walls. Union soon takes place, so that a permanent opening

240 GASTRIC JUICE. [BOOK IT.

from the exterior into the inside of the stomach is established. A tube
of proper construction, introduced at the time of the operation, becomes
firmly secured in place by the contraction of healing. Through the
tube the contents of the stomach can be received, and the mucous
membrane stimulated at pleasure.

When obtained from a natural fistula in man, its specific
gravity has been found to differ little from that of water, varying
from rOOl to TO 10, and the amount of solids present to be
correspondingly small. In animals, pure gastric juice seems to be
equally poor in solids, the higher estimates which some observers
have obtained being probably due to admixture with food, &c.

Of the solid matters present about half are inorganic salts, chiefly
alkaline (sodium) chlorides, with small quantities of phosphates.
The organic material consists of pepsin, a body to be described
immediately, mixed with other substances of undetermined nature.
In a healthy stomach gastric juice contains a very small quantity
only of mucus, unless some submaxillary saliva has been swallowed.

The reaction is distinctly acid, and the acidity is normally due
to free hydrochloric acid. This is shewn by various proofs, among
which we may mention the fact that the amount of hydrochloric
acid is more than can be neutralized by the bases, and the excess
corresponds to the quantity of free acid present. Lactic and
butyric and other acids when present are secondary products,
arising either by their respective fermentations from articles of
food, or from the decomposition of their alkaline or other salts. In
man the amount of free hydrochloric acid in healthy juice may
be stated about '2 per cent., but in some animals it is probably
higher.

On starch gastric juice has per se no effect whatever ; indeed
the acidity of the juice tends to weaken, or may be sufficient to
arrest and even destroy, the amylolytic action of any saliva with
which it may be mixed.

On dextrose healthy gastric juice has no effect. And its power
of inverting cane-sugar seems to be less than that of hydrochloric
acid diluted to the same degree of acidity as itself. In an un-
healthy stomach however containing much mucus, the gastric
juice is very active in converting cane-sugar into dextrose. This
power seems to be due to the presence in the mucus of a special
ferment, analogous to, but quite distinct from, the ptyalin of
saliva. An excessive quantity of cane-sugar introduced into
the stomach causes a secretion of mucus, and hence provides for
its own conversion.

On fats gastric juice has at most a limited action. When
adipose tissue is eaten, the chief change which takes place in the
stomach is that the proteid and gelatiriiferous envelopes of the
fat-cells are dissolved, and the fats set free. Though there is
experimental evidence that emulsion of fats to a certain extent

CIIAP. L] DIGESTION. 241

does take place in the stomach, the great mass of the fat of a meal
is not so changed.

Such minerals as are soluble in free hydrochloric acid are for
the most part dissolved ; though there is a difference in this and in
some other respects between gastric juice and simple free hydro-
chloric acid diluted with water to the same degree of acidity as the
juice, the presence either of the pepsin or other bodies apparently
modifying the solvent action of the acid.

The essential property of gastric juice is the power of dissolving
proteid matters, and of converting them into a substance called
peptone.

Action of gastric juice on proteids. The results are essen-
tially the same whether natural juice obtained by means of a
fistula or artificial juice, i.e. an acid infusion of the mucous mem-
brane of the stomach, be used.

Artificial gastric juice "may be prepared in any of the following
ways.

1. The mucous membrane of a pig's or dog's stomach is removed
from the muscular coat, finely minced, rubbed in a mortar with
pounded glass and extracted with water. The aqueous extract filtered
and acidulated (it is in itself somewhat acid), until it has a free acidity
corresponding to '2 p. c. of hydrochloric acid, contains but little of the
products of digestion such as peptone, but is fairly potent.

2. The mucous membrane similarly prepared and minced, allowed
to digest at 35° C. in a large quantity of hydrochloric acid diluted
to "2 p. c. The greater part of the membrane disappears, shreds only
being left, and the somewhat opalescent liquid can be decanted and
filtered. The filtrate has powerful digestive (peptic) properties, but
contains a considerable amount of the products of digestion (peptone,
tfcc.), arising from the digestion of the mucous membrane itself1.

3. From the mucous membrane, similarly prepared and minced,
the superfluous moisture is removed with blotting paper, and the pieces
are thrown into a comparatively large quantity of concentrated
glycerine, and allowed to stand. The membrane may be previously
dehydrated by being allowed to stand under alcohol, but this is not
necessary. The decanted clear glycerine, in which a comparatively
small quantity of the ordinary proteids of the mucous membrane are
dissolved, if added to hydrochloric acid of "2 p. c. (about 1 c.c. of
glycerine to 100 c.c. of the dilute acid are sufficient), makes an artificial
juice tolerably free from ordinary proteids and peptone, and of remark-
able potency, the presence of the glycerine not interfering with the
results.

If a few shreds of fibrin, obtained by whipping blood, after
being thoroughly washed and boiled, be thrown into a quantity of
gastric juice, and the mixture be exposed to a temperature of from

1 These however may be removed by concentration at 40° C., and subsequent
dialysis.

F. 16

242 GASTRIC JUICE. [BOOK n,

35° to 40° C., the fibrin will speedily, in some cases in a few
minutes, be dissolved. The shreds first swell up and become
transparent, then gradually dissolve, being especially liable to fall
to pieces into flakes when the vessel containing them is shaken,
and finally disappear with the exception of some granular debris,
the amount of which, though generally small, varies according to
circumstances.

If small morsels of coagulated albumin, such as white of egg, be
treated in the same way, the same solution is observed. The
pieces become transparent at their surfaces ; this is especially seen
at the edges, which gradually become rounded down; and solution
steadily progresses from the outside of the pieces inwards.

If any other form of coagulated albumin (e.g. precipitated
acid- or alkali-albumin, suspended in water and boiled) be treated
in the same way, a similar solution takes place. The readiness
with which the solution is effected, will depend, ceteris paribus,
on the smallness of the pieces, or rather on the amount of surface
as compared with bulk, which is presented to the action of the juice.

Gastric juice then readily dissolves coagulated proteids, which
otherwise are insoluble, or soluble only, and that with difficulty, in
very strong acids.

Nature of the change as shewn by the products of the action.

If raw white of egg, largely diluted with water and strained, be
treated with a sufficient quantity of dilute hydrochloric acid, the
opalescence or turbidity which appeared in the white of egg on
dilution, and which is due to the precipitation of various forms of
globulin, disappears, and a clear mixture results. If a portion of
the mixture be at once boiled, a large deposit of coagulated albu-
min occurs. If, however, the mixture be exposed to 50° or 55° C.
for some time, the amount of coagulation which is produced by
boiling a specimen becomes less, and, finally, boiling produces no
coagulation whatever. By neutralisation, however, the whole of
the albumin (with such restrictions as the presence of certain
neutral salts may cause) may be obtained in the form of acid-
albumin or syntonin, the filtrate after neutralisation containing no
proteids at all (or a very small quantity). Thus the whole of the
albumin present in the white of egg is converted, by the simple
action of dilute hydrochloric acid, into acid-albumin or syntonin.

If the same white of egg be treated with gastric juice instead of
simple dilute hydrochloric acid, the events for some time seem the
same. Thus after a while boiling causes no coagulation, while
neutralisation gives a considerable precipitate of a proteid body,
which, being insoluble in water and in dilute sodium chloride
solutions, and soluble in dilute alkali arid acids, at least closely
resembles syntonin. But it is found that only a portion of the
proteids originally present in the white of egg can thus be regained
by precipitation. A great deal is still retained in the filtrate after

OHAP. i ] DIGESTION. 243

neutralisation, in the form of what is called peptone, and, on the
whole, the longer the digestion is carried on, the greater is the
proportion borne by the peptone to the precipitate thrown down
on neutralisation; indeed, in some cases at all events, all the
proteids are brought into the condition of peptone.

Peptone is a proteid, having the same approximate elementary
composition as other proteids, and giving most of the usual proteid
reactions.

It is distinguished from other proteids by the following marked
features :

1st. Though soluble in" distilled water and in neutral saline
solutions, even the most dilute, and therefore not precipitated
from its acid or alkaline solutions by neutralisation, it is not, like
the other similarly soluble proteids, coagulated by heat.

2nd. It is diffusible, passing through membranes with consider-
able ease. The diffusion is not so rapid as that of salts, sugar, and
other similar substances, but is very marked as compared with that
of other proteids ; these pass through membranes with the greatest
difficulty. (For the other less important reactions see Appendix.)

The neutralisation precipitate resembles, in its general charac-
ters, acid-albumin, or syntonin. Since, however, it probably is
distinguishable from the body or bodies produced by the action of
simple acid on muscle or white of egg, it is best to reserve for it
the name of parapeptone. Thus the digestion by gastric juice of
white of egg results in the conversion of all the proteids present
into peptone and parapeptone, of which the former must be
considered as the final and chief product, the latter a bye product
or initial product of variable occurrence and importance. The
gastric digestion of fibrin, either raw or boiled, and of all foims of
coagulated albumin, gives rise to the same products, peptone and
parapeptone. Milk when treated with gastric juice is first of all
coagulated or curdled. This is the result partly of the action of
the free acid but chiefly of the special action of a particular
constituent of gastric juice, of which we shall speak hereafter.
The coaguluna consists of a proteid, casein, and of fat ; and the casein
is subsequently dissolved with the same appearance of peptone and
parapeptone as in the case of other proteids. In fact, the digestion
by gastric juice of all the varieties of proteids consists in the con-
version of the proteid into peptone, with the concomitant appear-
ance of a certain variable amount of parapeptone.

Circumstances affecting gastric digestion. The solvent action
of gastric juice on proteids is modified by a variety of circum-
stances. The nature of the proteid itself makes a difference,
though this is determined probably by physical rather than by
chemical characters. Hence in making a series of comparative

16—2

244 GASTRIC JUICE. [BOOK n.

trials the same proteid should be used, and the form of proteid
most convenient for the purpose is fibrin. If it be desired simply
to ascertain whether any given specimen has any digestive powers
at all, it is best to use boiled fibrin, since raw fibrin is eventually
dissolved by dilute hydrochloric acid alone, probably on account of
some pepsin present in the blood becoming entangled with the fibrin
during coagulation. But in estimating quantitatively the peptic
power of two specimens of gastric juice under different conditions,
raw fibrin prepared by Griitzner's method is the most convenient.

Portions of well washed fibrin are stained with carmine and again
washed to remove the superfluous colouring matter. A fragment of
this coloured fibrin thrown into an active juice on becoming dissolved,
gives up its colour to the fluid, and if the same stock of coloured fibrin
be used in a series of experiments, the amount of fibrin dissolved may
be fairly estimated by the depth of tint given to the fluid. Fibrin thus
coloured with carmine may be preserved in ether.

Since, if sufficient time be allowed, even a small quantity of
gastric juice will dissolve at least a very large if not an indefinite
quantity of fibrin, we are led to take, as a measure of the activity
of a spe'cimen of gastric juice, not the quantity of fibrin which it
will ultimately dissolve, but the rapidity with which it dissolves a
given quantity.

The greater the surface presented to the action of the juice, the
more rapid the solution ; hence minute division and constant move-
ment favour digestion. And this is probably, in part at least, the
reason why a fragment of spongy filamentous fibrin is more readily
dissolved than a solid. clump of boiled white of egg of the same size.
Neutralisation of the juice wholly arrests digestion ; fibrin may be
submitted for an almost indefinite time to the action of neutralised
gastric juice without being digested. If the neutralised juice be
properly acidified, it may again become active ; in gastric juice
however which has been made alkaline, and kept at a temperature
of 35°, the solvent powers are not only suspended but actually
destroyed. Digestion is most rapid with dilute hydrochloric acid
of '2 p.c. (the acidity of natural gastric juice). If the juice con-
tains much more or much less free acid than this, its activity is
visibly impaired. Other acids, lactic, phosphoric, &c. may be sub-
stituted for hydrochloric; but they are not so effectual, and the
degree of acidity most useful varies with the different acids. The
presence of neutral salts, such as sodium chloride, in excess is
injurious. The action of mammalian gastric juice is most rapid at
35° — 40° C. ; at the ordinary temperature it is much slower, and at
about 0° C. ceases altogether. The juice may be kept however at
0°C. for an indefinite period without injury to its powers. The
gastric juice of cold-blooded vertebrates is relatively more active
at low temperatures than that of warm-blooded mammals or birds.

At temperatures much above 40° or 45° the action of the juice

CHAP, i.] DIGESTION. 245

is impaired^ By boiling for a few minutes the activity of the most
powerful juice is irrevocably destroyed. The presence in a con-
centrated form of the products of digestion hinders the process.
If a large quantity of fibrin be placed in a small quantity of juice,
digestion is soon arrested; on dilution with the normal hydro-
chloric acid ('2 p.c.), or if the mixture be submitted to dialysis to
remove the peptones formed, and its acidity be kept up to the
normal, the action recommences. By removing the products of di-
gestion as fast as they are formed, and by keeping up the acidity
to the normal, a given amount of gastric juice may be made to
digest a very large quantity of proteid material. Whether the
quantity is^really unlimited is disputed; but in any case the ener-
gies of the juice are not rapidly exhausted by the act of digestion.

Nature of the action. All these facts go to shew that the
digestive action of gastric juice on proteids, like that of saliva on
starch, is a ferment-action ; in other words, that the solvent action
of gastric juice is essentially due to the presence in it of a ferment-
body. To this ferment-body, which as yet has been only ap-
proximately isolated, the name of pepsin has been given. It is
present not only in gastric juice but also in the glands of the
gastric mucous membrane, especially in certain parts, and under
certain conditions which we shall study presently. The glycerine
extract of gastric mucous membrane, especially of that which has
been dehydrated, contains a minimal quantity of proteid matter,
and yet is intensely active. Other methods, such as the elaborate
one of Briicke, give us a material which, though containing nitrogen,
exhibits none of the ordinary proteid reactions, and yet in concert
with normal dilute hydrochloric acid' is peptic in the highest
degree. We seem therefore justified in asserting that pepsin is not
a proteid, but it would be hazardous to make any dogmatic state-
ment concerning a substance, obtained in small quantity only,
probably mixed with other bodies, and the chemical characters of
which we know as yet very little. At present the manifestation
of peptic powers is our only safe test of the presence of pepsin.

In one important respect pepsin, the ferment of gastric juice,
differs from ptyalin, the ferment of saliva. Saliva is active in a per-
fectly neutral medium, and there seems to be no special connection
between the ferment and any alkali or acid. In gastric juice,
however, there is a strong tie between the acid and the ferment,
so strong that some writers speak of pepsin and hydrochloric
acid as forming together a compound, pepto-hydrochloric acid.

In the absence of exact knowledge of the constitution of
proteids, we cannot state distinctly what is the precise nature of
the change into peptone. Judging from the analogy with the
action of saliva on starch, we may fairly suppose that the process
is at bottom one of hydration ; but we have no exact proof of
this, and it is at least quite as probable that peptone arises by a

246 GASTRIC JUICE. [BOOK n.

simple splitting up of larger proteid molecules. Peptone closely
resembling, if not identical with, that obtained by gastric di-
gestion, may be obtained by the action of strong acids, by the
prolonged action of dilute acids especially at a high temperature,
or simply by digestion with super-heated water in a Papin's
digester. The role of pepsin therefore is only to facilitate a change
which may be effected without it.

All proteids, so far as we know, are converted by pepsin into
peptone. Of its action on other nitrogenous substances not truly
proteid in nature, we need only say that mucin, nuclein, and the
chemical basis of horny tissues are wholly unaffected by it, but
that the gelatiniferous tissues are dissolved and changed into a
substance so far analogous with peptone, that the characteristic
property of gelatinisation is entirely lost. Chondrin and the
elastic tissues are also dissolved.

Action of gastric juice on milk. It has long been known that
an infusion of calves' stomach, called rennet, has a remarkable
effect in rapidly curdling milk, and this property is made use of in
the manufacture of cheese. Gastric juice has a similar effect ;
milk when subjected to the action of gastric juice is first curdled
and then digested. If a few drops of gastric juice be added to a
little milk in a test tube, and the mixture exposed to a tempera-
ture of 40°, the milk will curdle into a complete clot in a very
short time. If the action be continued the curd or clot will be
ultimately dissolved and digested. Milk contains, besides albumin,
fats, milk, sugar and various salines, a peculiar proteid called
casein1, a body allied to the so-called alkali-albumin. In natural
milk casein is present in solution, arid ' curdling ' consists essen-
tially in the casein becoming insoluble and being precipitated in a
solid form, a great deal of the fat being generally carried down
with it. Now casein is readily precipitated from milk upon the
addition of a small quantity of acid, and it might be supposed that
the curdling effect of gastric juice was due to its acid reaction.
But this is not the case, for neutralized gastric juice, or neutral
rennet, is equally efficacious. Moreover the substance thrown down
by an acid is not quite exactly the same as that which appears in
curdling.

The effect is closely dependent on temperature, being like the
peptic action of gastric juice favoured by a rise of temperature up
to about 40°. Moreover the curdling action is destroyed by
previous boiling of the juice or rennet. These facts suggest that a
ferment is at the bottom of the matter ; and indeed, all the
features of the action support this view. The ferment however is
not pepsin but some other body; and the two may be separated
by cautiously adding magnesium carbonate to gastric juice or to
an infusion of calves' stomach. The clear fluid, left above the pre-

1 See Appendix.

CHAP, i.] DIGESTION. 247

cipitate thus formed, readily curdles milk, but even when acidified
has no peptic action on proteids, shewing that the precipitate caused
by the addition of the magnesium carbonate has carried down all
the pepsin but left behind at least a good deal of the rennet-ferment.

Rennet-ferment seems to be present in variable quantity in the
gastric juice of most animals, and may also be obtained from the
gastric mucous membrane of many though not all animals. It is
especially abundant in the stomach of the calf.

It has been suggested that the ferment might act by inducing
a fermentation in the sugar of milk, giving rise to lactic acid,
which precipitates the casein by virtue of its being an acid. But
this view is disproved not only by the difference in the product
mentioned above, but also by the fact that casein precipitated
from milk by neutral salts, washed free from milk sugar and
redissolved, forms a fluid which is readily curdled by rennet like
natural milk. It seems probable that the ferment really acts on the
casein, converting it in some way from a soluble to an insoluble form.

Bile.

The quality of bile varies much, not only in different animals,
but in the same animal at different times. It is moreover affected
by the length of the sojourn in the gall-bladder ; bile taken direct
from the hepatic duct, especially when secreted rapidly, contains
little or no mucus; that taken from the gall-bladder, as of
slaughtered oxen or sheep, is loaded with mucus. The colour of
the bile of carnivorous and omnivorous animals, and of man, is a
bright golden red : of graminivorous animals, a golden green/ or a
bright green, or a dirty green, according to circumstances, being
much modified by retention in the gall-bladder. The reaction £
alkaline. The following may be taken as the average composition
of human bile (Frerichs).

In 1000 parts.
Water 859.2

Solids : —

Bile Salts ... ... .., ... ... 91-4

Fats, &c. . . . ... ... ... ... 9-2

Cholesterin ... ... ... 2'6

Mucus and Pigment 29*8

Inorganic Salts ... ... ... ... 7-3

~ 140-8

The entire absence of proteids is a marked feature of bile.
With regard to the inorganic salts, the points of interest are the
presence of a large quantity of sodium chloride ('2 to "27 per cent.),
the presence of phosphates, of iron (about '006 p. c.), manganese,
and occasionally, at all events, of copper. The ash contains soda in

248 BILE. [BOOK n.

a very large amount, and also sulphates, both coming from the
bile-salts. The peculiar body cholesterin is conspicuous by its
quantity and constancy, but its physiological functions are obscure.
The constituents which deserve chief attention are the pigments
and the bile-salts.

Pigments of Bile. The natural golden red colour of normal
human or carnivorous bile, is due to the presence of Bilirubin.
This, which is also the chief pigmentary constituent of gall-stones,
and occurs largely in the urine of jaundice, may be obtained in the
form either of an orange-coloured powder, or of well-formed
rhombic tablets and prisms. Insoluble in water, and but little
soluble in ether and alcohol, it is readily soluble in chloroform, and
in alkaline fluids. Its composition is C16H18N203. Treated with
oxidizing agents, such as nitric acid yellow with nitrous acid, it
displays a succession of colours in the order of the spectrum. The
yellowish golden red becomes green, this a greenish blue, then
blue, next violet, afterwards a dirty red, and finally a pale yellow.
This characteristic reaction of bilirubin is the basis of the so-called
Gmelin's test for bile-pigments. Each of these stages represents a
distinct pigmentary substance. An alkaline solution of bilirubin,
exposed in a shallow vessel to the action of the air, turns green,
becoming converted into Biliverdin (C16H20N2O5 or C16H]8N204
Maly), the green pigment of herbivorous bile. Biliverdin is also
found at times in the urine of jaundice, and is probably the body
which gives to bile which has been exposed to the action of gastric
juice, as in biliary vomits, its characteristic green hue. It is the
first stage of the oxidation of bilirubin in Gmelin's test. Treated
with oxidizing agents biliverdin runs through the same series of
colours as bilirubin, with the exception of the initial golden red.

The bile-salts. These consist, in man and many animals, of
sodium glycocholate and taurocholate : the proportion of the two
varying in different animals. In man both the total quantity of
bile-salts and the proportion of the one bile-salt to the other seem
to vary a good deal, but the glycocholate is said to be always the
more abundant. In ox-gall, sodium glycocholate is abundant, and
taurocholate scanty. The bile-salts of the dog, cat, bear, and other
carnivora, consist exclusively of the latter.

Insoluble in ether but soluble in alcohol and in water, the
aqueous solutions having a decided alkaline reaction, both salts
may be obtained by crystallisation in fine acicular needles. They
are exceedingly deliquescent. The solutions of both acids have a
dextro-rotatory action on polarized light.

Preparation. Bile, mixed with animal charcoal, is evaporated to
dryness and extracted with alcohol. If not colourless, the alcoholic
filtrate must be further decolorized with animal charcoal, and the

CHAP, i.] DIGESTION. 249

alcohol distilled off. The dry residue is treated with absolute alcohol,
and to the alcoholic filtrate anhydrous ether is added as long as any
precipitate is formed. On standing the cloudy precipitate becomes
transformed into a crystalline mass at the bottom of the vessel. If the
alcohol be not absolute, the crystals are very apt to be changed into a
thick syrupy fluid. This mass of crystals has been often spoken of as
bilin. Both salts are thus precipitated, so that in such a bile as that of
the ox or man bilin consists both of sodium glycocholate and sodium
taurocholate. The two may be separated by precipitation from their
aqueous solutions with sugar of lead, which throws down the former
much more readily than the latter. The acids may be separated from
their respective salts by dilute sulphuric acid, or by the action of lead-
acetate and sulphydric acid.

On boiling with dilute acids (sulphuric, hydrochloric), or caustic
potash, or baryta water, glycocholic acid is split up into cholalic
(cholic) acid and glycin. Taurocholic acid may similarly be split
up into cholalic acid and taurin. Thus

glycocholic acid cholalic acid glycin

CMH NO + H20 = C,4HW05 + C2H5N02

taurocholic acid cholalic acid taurin

C26H45NS07 + H20 = C24H<005 + C,H,NS03.

Both acids contain the same non-nitrogenous acid, cholalic acid ;
but this acid is in the first case associated or conjugated with the
important nitrogenous body glycin, or amido-acetic acid, that is a
compound formed out of ammonia, and one of the series of fatty
acids viz. acetic; and in the second case with taurin, or amido-
isethionic acid, that is a compound formed out of ammonia, a
member of the ethyl group, and sulphuric acid. The decom-
position of the bile acids into cholalic acid and taurin or glycin
respectively takes place naturally in the intestine, the glycin and
taurin being absorbed, so that from the two acids, after they have
served their purpose in digestion, the two ammonia compounds
are returned into the blood. Either of the two acids, or cholalic
acid alone, when treated with sulphuric acid and cane-sugar, gives
a magnificent purple colour (Pettenkofer's test) with a character-
istic spectrum. A similar colour may often be produced by the
action of the same bodies on albumin, amyl alcohol, and some
other organic bodies.

Action of Bile on Food. In some animals at least bile contains
a ferment capable of converting starch into sugar ; but its action
in this respect is wholly subordinate.

On proteids bile has no direct digestive action whatever, but
since it is at least often alkaline it tends to neutralise the acid
contents of the stomach as they pass into the duodenum and so
prepares the way for the action of the pancreatic juice. To peptic
action it is distinctly antagonistic; the presence of a sufficient
quantity of bile renders gastric juice inert towards proteids. More-

250 PANCREATIC JUICE. [BOOK n.

over when bile, or a solution of bile-salts, is added to a fluid con-
taining the products of gastric digestion, a precipitate takes place,
consisting of parapeptone, peptone and bile salts. The precipitate
however is redissolved in an excess of bile or solution of bile-salts.
Concerning the purpose of this precipitation, which actually takes
place in the duodenum, we shall speak hereafter.

With regard to the action of bile on fats, the following state-
ments may be made :

Bile has a slight solvent action on fats, as seen in its use by
painters. It has by itself a slight but only slight emulsifying
power: a mixture of oil and bile separate after shaking rather
less rapidly than a mixture of oil and water. With free fatty acids,
bile forms soaps. It is moreover a solvent of solid soaps, and it
would appear that the emulsion of fats is under certain circum-
stances at all events facilitated by the presence of soaps in solution.
Hence bile is probably of much greater use as an emulsion agent
when mixed with pancreatic juice than when acting by itself alone.
To this point we shall return. Lastly, the passage of fats through
membranes is assisted by wetting the membranes with bile, or
with a solution of bile-salts. Oil passes with considerable ease
through a filter-paper kept wet with a solution of bile-salts, where-
as it passes with extreme difficulty through one kept constantly
wet with distilled water.

Lastly bile possesses so-called antiseptic qualities. Out of the
body its presence hinders various putrefactive processes ; and when
it is prevented from flowing into the alimentary canal, the contents
of the intestine undergo changes different from those which take
place under normal conditions, and leading to the appearance of
various products, especially of ill-smelling gases.

These various actions of bile seem to be dependent on the bile
salts and not on the pigmentary or other constituents.

Pancreatic Juice.

Natural healthy pancreatic juice obtained by means of a tem-
porary pancreatic fistula differs from the preceding fluids in the
comparatively large quantity of proteids which it contains. Its
composition varies according to the rate of secretion, for, with the
more rapid flow, the increase of total solids does not keep pace
with that of the water, though the ash remains remarkably
constant.

By an incision through the linea alba the pancreatic duct (or ducts)
can easily be found either in the rabbit or in the dog, and a cannula se-
cured in it. There is no difficulty about a temporary fistula; but

CHAP, i.] DIGESTION. 251

Bernard found that with permanent fistulae the secretion altered in
nature, and lost many of its characteristic properties. Others, however,
have succeeded in obtaining permanent fistulse without any impairment
of the secretion.

Healthy pancreatic juice is a clear viscid fluid, frothing when
shaken. It has a very decided alkaline reaction, and contains few
or no structural constituents,

The average amount of solids in the pancreatic juice of the dog
when obtained from a temporary fistula is about 8 to 10 p. c. ; but
in the thoroughly active secretion from a permanent fistula it is
not more than about 2 to 5 p. c., *8 being inorganic matter,
and this is probably the normal amount. The important con-
stituents are albumin, a peculiar form of casein or alkali-albumin,
(precipitable by saturation with magnesium sulphate) peptone,
leucin and tyrosin, a small amount of fats and soaps, and a com-
paratively large quantity of sodium carbonate, to which the alkaline
reaction of the juice is due, and which seems to be peculiarly
associated with the albumin.

Since, as we shall presently see, pancreatic juice contains a
ferment acting energetically on proteid matters in an alkaline
medium, it rapidly digests itself; and, when kept, speedily changes
in character. Perfectly fresh juice appears to contain a substance
not unlike myosin giving rise to a sort of coagulation, but the
coagulum is soon dissolved. Perfectly fresh juice is also said to be
almost entirely free from leucin, tyrosin and peptone, which also
seem to be the products of self-digestion.

Action on food-stuffs. On starch, raw or boiled, pancreatic
juice acts with great energy, rapidly converting it into sugar
(chiefly maltose). All that has been said in this respect con-
cerning saliva might be repeated in the case of pancreatic juice,
except that the activity of the latter is far greater than that of the
former. .Pancreatic juice and the aqueous infusion of the gland
are always capable of converting starch into sugar, whether the
animal from which they were taken be starving or well fed.
From the juice, or, by the glycerine method, from the gland itself,
.an amylolytic ferment may be approximately isolated.

On proteids pancreatic juice also exercises a solvent action, so
far similar to that of gastric juice that by it proteids are converted
into peptone. If a few shreds of fibrin are thrown into a small
quantity of pancreatic juice, they speedily disappear, especially at
a temperature of 35° C., and the mixture is found to contain
peptone. The activity of the juice in thus converting proteids
into peptone, is favoured by increase of temperature up to 40° or
thereabouts, and hindered by low temperatures ; it is permanently
destroyed by boiling. The digestive powers of the juice in fact
depend, like those of gastric juice, on the presence of a ferment ; to
this ferment the name trypsin has been given. A glycerine extract

252 PANCREATIC JUICE. [BOOK n.

of pancreas, prepared in the same method as that of the gastric
mucous membrane, is (under appropriate conditions) active on
proteids, like the native juice.

The appearance of fibrin undergoing pancreatic digestion is
however different from that undergoing peptic digestion. In the
former case the fibrin does not swell up, but remains as opaque as
before, and appears to suffer corrosion rather than solution. But
there is a still more important distinction between pancreatic and
peptic digestion of proteids. Peptic digestion is essentially an
acid digestion ; we have seen that the action only takes place in
the presence of an acid, and is arrested by neutralisation. Pan-
creatic digestion, on the other hand, may be regarded as an alkaline
digestion ; the action is most energetic when some alkali is present;
and the activity of an alkaline juice is hindered or delayed by
neutralisation and arrested by acidification at least with mineral
acids. The glycerine extract of pancreas is under all circumstances
as inert in the presence of free mineral acid as that of the stomach
in the presence of alkalis. If the digestive mixture be supplied
with sodium carbonate to the extent of 1 p. c., digestion proceeds
rapidly, just as does a peptic mixture when acidulated with hydro--
chloric acid to the extent of '2 p. c. Sodium carbonate of 1 p. c.
seems in fact to play in pancreatic digestion a part altogether
comparable to that of hydrochloric acid of '2 p.c. in gastric di-
gestion. And just as pepsin is rapidly destroyed by being heated
to about 40° with a 1 p.c. solution of sodium carbonate, so trypsin
is rapidly destroyed by being similarly heated with dilute hydro-
chloric acid of '2 p.c. Alkaline bile, which arrests peptic digestion,
seems, if anything, favourable to pancreatic digestion.

Corresponding to this difference in the helpmate of the ferment,
there is in the two cases a difference in the nature of the products.
In both cases peptone is produced, and such differences as can be
detected between pancreatic and gastric peptones are comparatively
slight ; but in pancreatic digestion the bye-product is not, as in
gastric digestion, a kind of acid-albumin, but a body having more
analogy with alkali-albumin. Before solution has actually taken
place the fibrin becomes altered in character. It is soluble not
only in dilute acids and alkalis, but also in a 10 per cent, solution
of sodium chloride, and the solutions obtained by the latter reagent
are coagulable on boiling and on the addition of strong nitric acid.
The first action of the pancreatic juice therefore seems to be to
convert the proteid under digestion into a body intermediate
between alkali-albumin and ordinary native albumin.

But though the general characters of pancreatic and gastric
digestion are on the surface similar, it is more than probable
that profound differences do exist between them. This is shewn
by the appearance, in the pancreatic digestion of proteids, of two
remarkable nitrogenous crystalline bodies, leucin and ty rosin.
When fibrin (or other proteid) is submitted to the action of

CHAP, i.] DIGESTION. 253

pancreatic juice, the amount of peptone which can be recovered
from the mixture falls far short of the original amount of proteids,
much more so than in the case of gastric juice ; and the longer the
digestive action, the greater is this apparent loss. If a pancreatic
digestion mixture be freed from the alkali-albumin by neutral-
isation, and after concentration by evaporation be treated with
excess of alcohol, most of the peptone will be precipitated. The
alcoholic filtrate when concentrated, gives, on cooling, crystals of
tyrosin, and the mother liquor from these crystals will afford
abundance of crystals of leucin. Thus by the action of the pan-
creatic juice a considerable amount of the proteid, which is being
digested, is so broken up as to give rise to products which are no
longer proteid in nature. From this breaking up of the proteid
there arise leucin, tyrosin, and probably several other bodies, such
as fatty acids and volatile substances.

As is well known, leucin and tyrosin are the bodies which
make their appearance when proteids or gelatin are acted on by
dilute acids, alkalis, or various oxidising agents. Now leucin is
amido-caproic acid, and thus belongs distinctly to the fatty bodies ;
while tyrosin is a member of the aromatic group, being closely
related to benzoic acid. So that in pancreatic digestion we have
the large complex proteid molecule split up into its constituent
fatty acid and aromatic molecules, and into its other less distinctly
known components. In gastric digestion such a profound destruc-
tion of proteid material occurs to a much less extent or not at all ;
neither leucin nor tyrosin can at present be considered as natural
products of the action of pepsin.

Among the supplementary products of pancreatic digestion
may be enumerated a body which gives a violet colour with
chlorine water (this reaction is often seen in the juice itself), and
indol, to which apparently the strong and peculiarly faecal odour
which makes its appearance during pancreatic digestion is
due. Indol, however, unlike the leucin and tyrosin, is not a
product of pure pancreatic digestion, but of an accompanying
decomposition due to the action of organised ferments. A pan-
creatic digestive mixture soon becomes swarming with bacteria, in
spite of careful precautions, when natural juice or an infusion of
the gland is used. When isolated ferment is used, and atmospheric
germs are excluded, or when pancreatic digestion is carried on in
the presence of salicylic acid, which prevents the development of
bacteria and like organisms but permits the action of the trypsin,
no odour is perceived, and no indol is produced.

After long-continued digestion, especially when accompanied by
putrefactive decomposition, the amount of proteids which are
carried beyond the peptone stage and broken up, may be very
great.

On the gelatiniferous elements of the tissues in their normal
condition pancreatic juice appears to have no solvent action. In

254 PANCREATIC JUICE. [BOOK n.

this respect it affords a striking contrast to gastric juice. But
when they have been previously treated with acid or boiled so
as to become converted into actual gelatine, trypsin is able to
dissolve them, apparently changing them much in the same way
as does pepsin. Trypsin unlike pepsin, will dissolve mucin. Like
pepsin, it is inert towards nuclein, horny tissues, and the so-called
amyloid matter.

On Fats pancreatic juice has a twofold action: it emulsifies
them, and it splits up neutral fats into their respective acids and
glycerine. If hog's lard be gently heated till it melts and be then
mixed with pancreatic juice before it solidifies on cooling, a creamy
emulsion, lasting for almost an indefinite time, is formed. So also
when olive oil is shaken up with pancreatic juice, the separation
of the two fluids takes place very slowly, and a drop of the mixture
under the microscope shews that the division of the fat is very
minute. An alkaline aqueous infusion of the gland has similar
emulsifying powers. If perfectly neutral fat be treated with
pancreatic juice, especially at the body-temperature, the emulsion
speedily takes on an acid reaction, and by appropriate means not
only the corresponding fatty acids but glycerine may be obtained
from the mixture. When an alkali is present, the fatty acids thus
set free form their corresponding soaps. Pancreatic juice contains
fats, and is consequently apt after collection to have its alkalinity
reduced; and an aqueous infusion of a pancreatic gland (which
always contains a considerable amount of fat) very speedily becomes
acid.

Thus pancreatic juice is remarkable for the power it possesses
of acting on all the food-stuffs, on starch, fats and proteids.

The action on starch and on proteids, and the splitting up of
fatty acids appear to be due to the presence of three distinct
ferments, and methods have been suggested for isolating them.
The emulsifying power, on the other hand, is connected with the
general composition of the juice (or of the aqueous infusion of the
gland), being probably in large measure dependent on the alkali-
albumin present. The proteolytic ferment trypsin as ordinarily
prepared seems to be proteid in nature and capable of giving rise,
by digestion to peptones; but it may be doubted, as in the case of
pepsin &c. whether the pure ferment has yet been isolated. There
are no means of distinguishing the amylolytic ferment of the
pancreas from ptyalin. The term pancreatin has been variously
applied to many different preparations from the gland, and its use
had perhaps better be avoided.

The action of pancreatic juice, or of the infusion or extract of
the gland, on starch, is seen under all circumstances, whether the
animal be fasting or not. The same may probably be said of the
action on fats. On proteids the natural juice, when secreted in a
normal state, is always active. The glycerine extract or aqueous
infusion of the gland, on the contrary, differs at different times;

CHAP, i.] DIGESTION. 255

prepared from an animal some 4 to 10 hours after food has been
taken, it is very powerful; prepared from a fasting animal, it is
said to exhibit scarcely any action at all. To this point however
we shall return immediately.

Succus Entericus.

When, in a living animal, a portion of the small intestine is
ligatured, so that the secretions coming down from above cannot
enter its canal, while yet the blood-supply is maintained as usual,
a small amount of secretion collects in its interior. This is spoken
of as the succus entericus, and is supposed to be furnished by the
glands of Lieberkiihn. We have no exact knowledge howrever as
to the extent to which such a secretion takes place under normal
circumstances; and the statements with regard to its action are
conflicting. Probably it has no direct action on either fats or
proteids; but is amylolytic in some animals, though not in all.

A small quantity of fluid free from bile, gastric or pancreatic
juice, and which may be considered as pure succus entericus, may
also be obtained by the following method known as that of Thiry.
The small intestine is divided in two places at some distance apart.
By fine sutures the lower end of the upper section is united with the
upper end of the lower section, thus as it were cutting out a whole piece
of the small intestine from the alimentary tract. In successful cases,
union between the cut surfaces takes place, and a shortened but other-
wise satisfactory canal is re-established. Of the isolated piece the lower
end is carefully closed by sutures, while the upper is brought to the
wound in the abdominal wall and secured there. A fistula is thus
formed, leading into a short piece of intestine quite isolated from the
rest of the alimentary canal.

Succus entericus has also been said to change cane- into grape-
sugar, and by a fermentative action to convert cane-sugar into
lactic acid, and this again into butyric acid with the evolution of
carbonic acid and free hydrogen.

Of the possible action of other secretions of the alimentary
canal, as of the csecum and large intestine, we shall speak when we
come to consider the changes in the alimentary canal.

Concerning the secretion of Brunner's glands our information
is at present imperfect. The cells of the glands resemble the
central cells of the gastric glands; and an extract of the gland
is said to digest fibrin in an acid solution, but to have no distinct
amylolytic action.

SEC. 2. THE ACT OF SECRETION IN THE CASE OF THE

DIGESTIVE JUICES AND THE NERVOUS MECHANISMS

WHICH REGULATE IT.

The various juices whose properties we have just studied,
though so different from each other, are all drawn ultimately from
one common source, the blood, and they are poured into the ali-
mentary canal, not in a continuous flow, but intermittently as
occasion may demand. The epithelium cells which supply them
have their periods of rest and of activity, and the amount and
quality of the fluids which these cells secrete are determined by
the needs of the economy as the food passes along the canal. We
have therefore to consider how the epithelium cell manufactures
its special secretion out of the materials supplied to it by the
blood, and how the cell is called into activity by the presence of
food at some distance from itself, or by circumstances which do
not bear directly on itself. In dealing with these matters in
connection with the digestive juices, we shall have to enter at
some length into the physiology of secretion in general.

The question which presents itself first is : By what mechanism
is the activity of the secreting cells brought into play ?

While fasting, a small quantity only of saliva is poured into the
mouth; the buccal cavity is just moist and nothing more. When
food is taken, or when any sapid or stimulating substance, or
indeed a body of any kind, is introduced into the mouth, a flow is
induced which may be very copious. Indeed the quantity secreted
in ordinary life during 24 hours has been roughly calculated at as
much as from 1 to 2 litres. An abundant secretion in the absence

CHAP, i.] DIGESTION. 257

of food in the mouth may be called forth by an emotion, as when
the mouth waters at the sight of food, or by a smell, or by events
occurring in the stomach, as in some cases of nausea. Evidently
in these cases some nervous mechanism is at work. In studying
the action of this nervous mechanism, it will be of advantage to
confine our attention at first to the submaxillary gland.

The submaxillary gland (Fig. 48) is supplied with nerves from
two sources : from the cervical sympathetic along the submaxillary
arteries, and from the seventh or facial nerve by fibres, which, run-
ning in the chorda tympani, join the lingual branch of the fifth
nerve, from which they diverge under the lower jaw, and run as a
small nerve close beside the duct to the gland.

If a tube be placed in the duct, it is seen that when sapid
substances are placed on the tongue, or the tongue is stimulated
in any other way, or the lingual nerve is laid bare and stimulated
with an interrupted current, a copious flow of saliva takes place.
If the sympathetic be divided, stimulation of the tongue or lingual
nerve still produces a flow. But if the small chorda nerve spoken
of above be divided, stimulation of the tongue or lingual nerve
produces no flow.

Evidently the flow of saliva is a nervous reflex action, the
lingual nerve serving as the channel for the afferent and the small
chorda nerve for the efferent impulses. If the trunk of the
lingual be divided above the point where the chorda leaves it, as
at n. I' Fig. 48, stimulation of the tongue produces, under ordinary
circumstances, no flow. This shews that the centre of the reflex
action is higher up than the point of section; it lies in fact in
the brain.

In the angle between the lingual and the chorda, where the latter
leaves the former to pass to the gland, lies the small submaxillary gan-
glion (represented diagrammatically in Fig. 48 sm. gl.)t from which
branches pass to the lingual on the one hand and to the chorda on the
other ; branches may also be traced towards the ducts and glands and
towards the tongue. It has been much debated whether this ganglion
can act as a centre of reflex action, but no conclusive evidence that it
does so act has as yet been shewn.

Stimulation of the glossopharyngeal is even more effectual
than that of the lingual. Probably this indeed is the chief
afferent nerve in ordinary secretion. Stimulation of the mucous
membrane of the stomach (as by food introduced through a
gastric fistula) or of the vagus also produces a flow of saliva, as
indeed may stimulation of the sciatic, and probably of many other
afferent nerves. All these cases are instances of reflex action, the
cerebro-spinal system acting as a centre. We may further define
the centre as a part of the medulla oblongata, apparently not far
removed from the vaso-motor centre. When the brain is removed
down to the medulla oblongata, that organ being left intact, a flow

F. 17

258 SECRETION OF SALIVA. [BOOK n.

of saliva may still be obtained by adequate stimulation of various
afferent nerves ; when the medulla is destroyed no such action is
possible. And a flow of saliva may be produced by direct stimu-
lation of the medulla itself. When a flow of saliva is excited by
ideas, or by emotions, the nervous processes begin in the higher
parts of the brain, and descend thence to the medulla before they

FIG. 48. DIAGRAMMATIC KEPRESENTATION OF THE SUBMAXILLARY GLAND OF THE Doa
WITH ITS NERVES AND BLOOD-VESSELS.

(This is not intended to illustrate the exact anatomical relations of the several
structures.)

sm. gld. The submaxillary gland, into the duct (sm. d.) of which a cannula has
been tied. The sublingual gland and duct are not shewn.

n. l.,n.l'. The lingual branch nerve, ch. t.,ch. t'. The chorda tympani, pro-
ceeding from the facial nerve, becoming conjoined with the lingual at n.l' and after-
wards diverging and passing to the gland along the duct.

sm. (jl. The submaxillary ganglion with its several roots, n. I. The lingual
proceeding to the tongue.

a. car. The carotid artery, two branches of which, a. sm. a. and r. sm. p., pass to
the anterior and posterior parts of the gland, v. sm. the anterior and posterior veins
from the gland, falling into v. j. the jugular vein.

v. sym. The conjoined vagus and sympathetic trunks.

gl. cer. s. The super-cervical ganglion, two branches of which forming a plexus
(a.f.) over the facial artery, are distributed (n. sym. sm.) along the two glandular
arteries to the anterior and posterior portions of the gland.

The arrows indicate the direction taken by the nervous impulses during reflex
stimulation of the gland. They ascend to the brain by the lingual and descend by
the chorda tympani.

give rise to distinctly efferent impulses ; and it would appear that
these higher parts of the brain are called into action when a flow
of saliva is excited by distinct sensations of taste.

CHAP, i.] DIGESTION. 259

Considering then the flow of saliva as a reflex act the centre
of which lies in the medulla oblongata, we may imagine the
efferent impulses passing from that centre to the gland, either by
the chorda tympani or by the sympathetic nerve. Although it
would perhaps be rash to say that in this relation the sympathetic
nerve never acts as an efferent channel, as a matter of fact we
have no satisfactory experimental evidence that it does so ; and we
may therefore state that, practically, the chorda tympani is the
sole efferent nerve. Section of that nerve, either where the fibres
pass from the lingual nerve and the submaxillary ganglion to the
gland, or where it runs in the same sheath as the lingual, or
in any part of its course from the main facial trunk to the lingual,
puts an end, as far as we know, to the possibility of any flow being
excited by stimuli applied to the sensory nerves or sentient
surfaces of the mouth, or of other parts of the body.

The natural reflex act of secretion may be inhibited, like the
reflex action of the yaso-motor nerves, at its centre. Thus
when, as in the old rice ordeal, fear parches the mouth, it is
probable that the afferent impulses caused by the presence of food
in the mouth cease, through emotional inhibition of their reflex
centre, to give rise to efferent impulses.

In life, then, the flow of saliva is brought about by the advent

to the gland along the chorda tympani of efferent impulses, started

chiefly by reflex actions. The inquiry thus narrows itself to the

question : In what manner do these efferent impulses cause the in-

. crease of flow ?

If in a dog a tube be introduced into Wharton's duct, and the
chorda be divided, the flow, if any be going on, is from the lack of
efferent impulses arrested. On passing an interrupted current
through the peripheral portion of the chorda, a copious secretion
at once takes place, and the saliva begins to rise rapidly in the
tube ; a very short time after the application of the current the
flow reaches a maximum which is maintained for some time, and
then, if the current be long continued, gradually lessens. If the
current be applied for a short time only, the secretion may last for
some time after the current has been shut off. The saliva thus
obtained is but slightly viscid, and contains few salivary corpuscles
or protoplasmic lumps. If the gland itself be watched, while its
activity is thus roused, it will be seen that its arteries are dilated,
and its capillaries filled, and that the blood flows rapidly through
the veins in a full stream and of bright arterial hue, frequently
with pulsating movements. If a vein of the gland be opened, this
large ^increase of flow, and the lessening of the ordinary deoxy-
genation of the blood consequent upon the rapid stream, will be
still more evident. It is clear that excitation of the chorda largely
Mates the arteries ; the nerve acts energetically as a dilator nerve,
probably from acting on some local vaso-motor centre in the gland.

Thus stimulation of the chorda brings about two events: a

17—2

260 ACTION OF CHORDA TYMPANL [BOOK n.

dilation of the blood-vessels of the gland, and a flow of saliva.
The question at once arises, Is the latter simply the result of the
former or is the flow caused by some direct action on the secreting
cells, apart from the increased blood-supply? In support of the
former view we might argue that the activity of the epithelial
secreting cell, like that of any other form of protoplasm, is
dependent on blood-supply. When the small arteries of the gland
dilate, while the pressure in the arteries on the side towards the
heart is as we have seen in the last chapter correspondingly
diminished, the pressure on the far side in the capillaries and
veins is increased ; hence the capillaries become fuller, and more
blood passes through them in a given time. From this we might
infer that a larger amount of nutritive material would pass away
from the capillaries into the surrounding lymph-spaces, and so
into the epithelium cells, the result of which must be to quicken
the processes going on in the cells, and to stir these up to greater
activity. But even admitting all this it does not necessarily follow
that the activity thus excited should take on the form of secretion.
It is quite possible to conceive that the increased blood-supply
should lead only to the accumulation in the cell of the constituents
of the saliva, or of the raw materials for their construction^ and not
to a discharge of the secretion. A man works better for being fed,
but feeding does not make him work in the absence of any stimulus.
The increased blood-supply therefore, while favourable to active
secretion, need not necessarily bring it about. Moreover, the
following facts are distinctly opposed to such a view. When a
cannula is tied into the duct and the chorda is energetically
stimulated, the pressure acquired by the saliva accumulated in
the cannula and in the duct may exceed for the time being the
arterial blood-pressure, even that of the carotid artery ; that is to
say, the pressure of fluid in the gland outside the blood-vessels is
greater than that of the blood inside the blood-vessels. This
must, whatever be the exact mode of transit of nutritive material
through the vascular walls, tend to check that transit. Again,
if the head of an animal be rapidly cut off, and the chorda
immediately stimulated, a flow of saliva takes place far too copious
to be accounted for by the emptying of the salivary channels
through any supposed contraction of their walls. In this case
secretion is excited in the absence of blood-supply. Lastly, if a
small quantity of atropin be injected into the veins, stimulation of
the chorda produces no secretion of saliva at all, though the
dilation of the blood-vessels takes place as usual. These facts
prove that the secretory activity is not simply the result of vascular
changes, but may be called forth independently; they further
lead us to suppose that the chorda contains two sets of fibres,
one secreting fibres, acting directly on the epithelium cells only,
and the other vaso-motor or dilating fibres, acting on the blood-
vessels only, and further that atropin, while it has no effect on

CHAP, i.] DIGESTION. 261

the latter, paralyses the former just as it paralyses the inhibitory
fibres of the vagus. Hence when the chorda is stimulated, there
pass down the nerve, in addition to impulses affecting the blood-
supply, impulses affecting directly the protoplasm of the secreting
cells, and calling it into action, just as similar impulses call into
action the contractility of the protoplasm of a muscular fibre.
Indeed the two things, secreting activity and contracting activity,
are quite parallel. We know that when a muscle contracts, its
blood-vessels dilate ; and just as by atropin the secreting action of
the gland may be isolated from the vascular dilation, so by urari
muscular contraction may be removed, and leave dilation of the
blood-vessels as the only effect of stimulating the muscular nerve.
In both cases the greater flow of blood may be an adjuvant to, but
is not the exciting cause of, the activity of the protoplasm.

Since the chorda acts thus directly on the secreting cells, we
should expect to find an anatomical connection between the cells
and the nerve ; and some authors have maintained that the nerve-
fibres may be traced into the cells. But, save perhaps in the case of
certain glands of invertebrates (so called salivary glands of Blatta),
the evidence is as yet not convincing.

When the cervical sympathetic is stimulated, the vascular
effects are the exact contrary of those seen when the chorda
is stimulated. The small arteries are constricted, and a small
quantity of dark venous blood escapes by the vein. Sometimes,
indeed, the flow through the gland is almost arrested. The sym-
pathetic therefore acts as a constrictor nerve, and in this sense is
antagonistic to the chorda. We have already referred to the
probable existence of a local vaso-motor centre situated in the
gland itself, in which indeed there are found ganglionic cells in
abundance. The fact that section of the cervical sympathetic does
not cause complete dilation of the vessels of the gland — the dilating
effects of stimulation of the chorda being fully evident after pre-
vious section of the sympathetic — affords additional support to this
view. We may accordingly suppose that, while the chorda tympani
inhibits, the sympathetic exalts, the action of this local centre.

As concerns the flow of saliva brought about by stimulation of
the sympathetic, in the case of the submaxillary gland of the dog
the effects are very peculiar. A slight increase of flow is seen, but
this soon passes off, and so much saliva as is secreted is remarkably
viscid, of higher specific gravity, and richer in corpuscles and proto-
plasmic lumps, and is said to be more active on starch than the
chorda saliva. This action of the sympathetic is said not to be
affected by atropin.

In the submaxillary gland of the dog then the contrast between
the effects of chorda stimulation and those of sympathetic stimu-
lation are very marked : the former gives rise to vascular dilation
with a copious flow of limpid saliva, the latter to vascular
constriction with a scanty flow of viscid saliva. And in other

262 SECRETION OF GASTRIC JUICE. [BOOK 11.

animals a similar contrast prevails, though with minor differences.
Thus in the rabbit both chorda saliva and sympathetic saliva are
limpid and free from mucus, and in the cat, chorda saliva is more
viscid than sympathetic saliva; but in both these cases, as in the
dog, stimulation of the chorda causes a copious flow with dilated
blood-vessels, and stimulation of the sympathetic, a scanty flow
with vascular constriction. We shall return again presently to
these different actions of the two nerves ; meanwhile we have seen
enough of the history of the submaxillary gland to learn that
secretion in this instance is a reflex action, the efferent impulses of
which directly affect the secreting cells, and that the vascular phe-
nomena may assist, but are not the direct cause of, the flow. We
have dwelt long on this gland because it has been more fruitfully
studied than any other. But the nervous mechanisms of the other
secretions are in the main features similar.

Thus the secretion of the parotid gland, like that of the sub-
maxillary, is governed by two sets of fibres: one of cerebro-spinal
origin, running along the auriculo-temporal branch of the fifth
nerve but originating either in the glosso-pharyngeal or the facial,
and the other of sympathetic origin coming from the cervical
sympathetic. Stimulation of the cerebro-spinal fibres produces a
copious flow of limpid saliva, free from mucus, the secretion
reaching in the dog a pressure of 118 mm. mercury ; stimulation of
the cervical sympathetic gives rise in the rabbi t to a secretion free
from mucus but rich in organic matter and of greater amylolytic
power than the cerebro-spinal secretion, but in the dog little or no
secretion is produced, though, as we shall see later on, certain
changes are brought about in the gland itself. In both animals
the cerebro-spinal fibres are vaso-dilator and the sympathetic
fibres vaso-constrictor in action. Stimulation of the central end of
the glosso-pharyngeal produces by reflex action a secretion of the
parotid, but that of the lingual is said to be without effect,

Gastric juice. Though a certain amount of gastric juice may
sometimes be found in the stomachs of fasting animals, it may be
stated generally that the stomach, like the salivary glands, remains
inactive, yielding no secretion, so. long as it is not stimulated by
food or otherwise. The advent of food into the stomach however at
once causes a copious flow of gastric juice ; and the quantity secreted
in the twenty-four hours is probably very considerable, but we have
no trustworthy data for calculating the exact amount. So also when
the gastric mucous membrane is stimulated mechanically, as with a
feather, secretion is excited: but to a very small amount even when
the whole interior surface of the stomach is thus repeatedly stimu-
lated. The most efficient stimulus is the natural stimulus, viz. food ;
though dilute alkalis seem to have unusually powerful stimulating
effects ; thus the swallowing of saliva at once provokes a flow of
gastric juice. During fasting the gastric membrane is of a pale
grey colour, somewhat dry, covered with a thin layer of mucus, and

CHAP, i.] DIGESTION. 263

thrown into folds; during digestion it becomes red, flushed, and
tumid, the folds disappear, and minute drops of fluid appearing at
the mouths of the glands, speedily run together into small streams.
When the secretion is very active, the blood flows from the
capillaries into the veins in a rapid stream without losing its bright
arterial hue. The secretion of gastric juice is in fact accompanied
by vascular dilation in the same way as is the secretion of saliva,
but the vascular mechanism has not yet been fully worked out,
though there is evidence of the vagi nerves being concerned in
the matter.

Seeing that, unlike the case of the salivary secretion, food is
brought into the immediate neighbourhood of the secreting cells, it
is exceedingly probable that a great deal of the secretion is the
result of the working of a local mechanism ; and when a mechanical
stimulus is applied to one spot of the gastric membrane the secre-
tion is limited to the neighbourhood of that spot and is not excited
in distant parts. This local mechanism may be nervous in
nature or the effect of the stimulus may perhaps be conveyed
directly from cell to cell, from the mouth of the gland to its
extreme base without the intervention of any nervous elements ;
but the vascular changes at least would seem to imply the presence
of a nervous mechanism.

The importance of this local mechanism and the subordinate
value of any connection between the gastric membrane and the
central nervous system is further shewn by the fact that a secretion
of quite normal gastric juice will go on when both vagi, or when
the sympathetic nerves going to the stomach are divided,
or indeed when all the nervous connections of the stomach
are. severed. And all attempts to provoke or modify gastric
secretion by the stimulation of the nerves going to it, have
hitherto failed. On the other hand, in cases of gastric fistula, where
by complete occlusion of the oesophagus stimulation by the descent
of saliva has been avoided, the mere sight or smell of food has
been seen to provoke a lively secretion of gastric juice. This
must have been due to some nervous action ; and the same may
be said of the cases where emotions of grief or anger suddenly
arrest the secretion or prevent the secretion which would otherwise
have taken place as the result of the presence of food in the
stomach. So that much has yet to be learnt in this matter.

The contrast presented between the scanty secretion resulting
from mechanical stimulation and the copious flow which actual
food induces is interesting because it seems to shew that the
secretory activity of the cells is heightened by the absorption
of certain products derived from the portions of food first
digested. This is well illustrated by the following experiment of
Heidenhain. This observer, adopting the method employed
for the intestine (see p. 255), succeeded in isolating a portion
of the fundus from the rest of the stomach ; that is to say, he cut

S

/

~

264 SECRETION OF BILE. [BOOK n.

out a portion of the fundus, sewed together the cut edges of the
main stomach, so as to form a smaller but otherwise complete
organ, while by sutures he converted the excised piece of fundus,
into a small independent stomach opening on to the exterior by a
fistulous orifice. When food was introduced into the main stomach
secretion also took place in the isolated fundus. This at first sight
might seem the result of a nervous reflex act; but it was observed
that the secondary secretion in the fundus, was dependent on actual
digestion taking place in the main stomach. If the material intro-
duced into the main stomach were indigestible or digested with
difficulty, so that little or no products of digestion were formed
and absorbed into the blood, such ex gr. as pieces of ligamentum
nuchae, very little secretion took place in the isolated fundus. We
quote this now as bearing on the question of a possible nervous
mechanism of gastric secretion, but we shall have to return to it
under another aspect.

Bile. When the acid contents of the stomach are poured over
the orifice of the biliary duct, a gush of bile takes place. Indeed,
stimulation of this region of the duodenum with a dilute acid at
once calls forth a flow, whereas alkaline fluids so applied have
little or no effect. This, probably, is a reflex action leading to the
contraction of the muscular walls of the gall-bladder and ducts,
accompanied by a relaxation of the sphincter of the orifice;
it refers therefore to the discharge rather than to the secretion
of bile.

When the secretion of the bile is studied by means of a biliary
fistula (which, however, probably induces errors by the total with-
drawal from the body of the bile which should naturally flow into
the intestine), it is seen to rise rapidly after meals, reaching its
maximum in from four to ten hours. There seems to be an im-
mediate, sudden rise when food is taken, then a fall, followed
subsequently by a more gradual rise up to the maximum, and ending
in a final fall to the lowest point ; but it must be remembered that
the lowest point is not zero, since the secretion of the bile, unlike
that of the saliva and gastric juice, is continuous and even in
a fasting animal does not cease. It may be that these variations
are due to the action of the nervous system, but experiments have
hitherto failed to demonstrate clearly the existence of any distinct
nervous mechanism.

The pressure under which the bile is secreted is in general very
low. When a water manometer is connected with the gall-bladder
of a guinea-pig, the ductus choledochus being ligatured, the fluid
may rise in the manometer to about 200 mm. (equivalent to about
16 mm. mercury), but not much beyond. This is of course much
less than the arterial pressure in the same animal; but it must not
be forgotten that the liver receives its chief blood-supply from a
venous source, viz. from the portal vein; and it would appear from

CHAP. i.J

DIGESTION.

265

experiments on dogs that the pressure at which the bile is secreted
exceeds that of the blood in the mesenteric veins going to form the
portal vein. Hence, the limit of pressure, though so different from
that of the salivary glands, resembles it in this fundamental fact
that it exceeds the pressure of the blood in the capillaries of the
organ. The same peculiar vascular supply of the fiver renders it
difficult to draw any comparison between its vascular condition
during active secretion and that of the salivary glands, though
during digestion the liver is swollen and increased in weight,
apparently from an increase in the blood-supply.

The quantity of bile secreted in man in the twenty-four hours
has been estimated to be exceedingly great, but the calculations are
based on very imperfect data.

Pancreatic juice. In the dog the secretion of pancreatic juice
after food has been taken, follows the curve given in Fig. 49. There
is a sudden maximum rise immediately after food has been taken.
This at all events suggests very strongly some nervous action.
Then follows a fall, after which there is, as in bile, a secondary
rise, the causation of which may, or may not, be nervous in nature.
In the dog, there may be, during fasting, a complete cessation of

7V

-V

!2|3|4|5l6|7|8|9|iO|ll|l2il3l,l4ll5il6| I I2l3|4|5|6i7|8i9|l0

FIG. 49. DIAGRAM ILLUSTRATING THE INFLUENCE OF FOOD ON THE SECRETION OF
PANCREATIC JUICE. (N. 0. Bernstein.)

The abscissa) represent hours after taking food ; the ordinates represent in c.c.
the amount of secretion in 10 min. A marked rise is seen at B immediately after
food was taken, with a secondary rise between the 4th and 5th hours afterwards.
Where the line is dotted the observation was interrupted. On food being again
given at C, another rise is seen, followed in turn by a depression and a secondary
rise at the 4th hour. A very similar curve would represent the secretion of bile.

266 SECRETION OF PANCREATIC JUICE. [BOOK n.

secretion. The quantity secreted in 24 hours by man has been
calculated at 300 c.c. Like the salivary glands, the pancreas
while secreting is flushed, through dilation of its blood-vessels.

The secretion if present may be increased, or if absent may be
called forth, by stimulation of the medulla oblongata, and when
going on may be arrested by stimulation of the central end
of the vagus through a reflex act, the efferent channels of
which have not yet been made out; probably the arrest of the
secretion which is said to be caused by nausea or vomiting is thus
brought about by stimulation of the vagus endings. These facts
shew that the secretion is under the influence of the central
nervous system ; but we have no such satisfactory knowledge of the
exact working of the nervous mechanism as in the case of the
salivary glands.

SuccilS entericus. With regard to the secretion furnished by
the intestine itself our information is very limited. The secretion
of the isolated intestine appears to be not a constant one, but to
need for its production some stimulus (mechanical or other) which
probably acts in a reflex manner. After section of the nerves
going to a piece of intestine isolated after Thiry's method, a
copious flow of a dilute intestinal juice is said to take place.

Thus, while the influence of the nervous system is in the case
of the submaxillary gland tolerably clear, in the case of the other
secretions we have yet much to learn, and we must rest rather
on analogy with the submaxillary gland, than on any known facts.
We cannot, however, go far wrong, if we conclude that in all cases
secretion is essentially due to a direct activity of the epithelium
cells, and that variations in the blood-supply have a secondary
effect only.

We may now pass on to the second problem. What is the
exact nature of the activity which is thus called forth ?

Towards the solution of this problem much progress has been
made by the study of the microscopical changes in secreting glands
during various stages of activity and rest. And these are perhaps,
in some respects, best shewn in the pancreas.

It is possible, by special precautions, to examine with even
high powers of the microscope the pancreas of an animal such
as the rabbit, while still alive with the circulation intact; and
thus to watch the changes going on both when the animal has
been deprived of food for some time and the gland is therefore
at rest, and when the animal has been recently fed so that digestion
is going on and the pancreas in consequence is engaged in pouring
its secretion into the duodenum. In the former case, i.e. when the
pancreas is at rest and little or no secretion is being poured out,
the following appearances may be recognised. The outlines of
the individual cells forming an alveolus (Fig. 50 A) are very in-
distinct, and each cell is loaded with a number of small highly

CHAP, i.] DIGESTION. 267

refractive granules. These however are crowded towards the
inner side of the cell abutting on the lumen of the alveolus,
leaving the outer part of the cell next to the basement membrane

B.

FlG. 50. A PORTION OF THE PANCREAS OF THE EABBIT (E.CHNE AND SHERIDAN LEA),

A at rest, B in a state of activity.

a the inner granular zone, which in A is larger, and more closely studded with
fine granules, than in B, in which the granules are fewer and coarser.

b the outer transparent zone, small in At larger in B, and in the latter marked
with faint striae.

c the lumen, very obvious in B, but indistinct in A.

d an indentation at the junction of two cells, seen in B, but not occurring in A.

clear and hyaline. We can in fact distinguish in each cell two
zones, a smaller outer zone, free from granules, and a larger or
broader inner zone thickly studded with granules. At the same
time it may be remarked that the lumen of the alveolus* is
narrow and very obscure ; the blood-supply moreover is scanty,
the small arteries being constricted and the capillaries imperfectly
filled with corpuscles.

If, however, the same pancreas be examined while it is in a
state of activity, either from the presence of food in the stomach,
or from the injection of some stimulating drug such as pilocarpin,
a very different state of things is seen. The individual cells
(Fig. 50 B) have become smaller and much more distinct in outline
and the lumen of the alveolus is now wider and more conspicuous.
In each cell the granules have become much fewer in number and
as it were have retreated to the inner margin, so that the inner
granular zone is much narrower and the outer transparent zone
much broader than before ; the latter too is frequently marked at
its inner part by delicate striae running into the inner zone. At
the same time the blood-vessels are largely dilated and the stream
of blood through the capillaries is full and rapid.

These things, the disappearance of granules during activity
leading to a diminution of the inner granular zone and a widening
of the outer transparent zone, and the appearance of new granules
during rest leading to a restoration of the inner zone and its
consequent encroachment on the outer zone, may be witnessed in
the living pancreas of the rabbit, and the changes from the one

2G8 HISTOLOGICAL CHANGES. [BOOK IT.

condition to the other successively observed. And sections of the
prepared and hardened gland of this or of any other animal tell nearly
the same tale. Thus in the pancreas of a dog which has been
fasting for about 30 hours, each secreting cell is found to consist
of two zones : an inner zone, studded with fine granules, and a
smaller outer zone, which is homogeneous or marked with delicate
striae, the nucleus being placed partly in the one and partly in
the other zone. When however the pancreas of an animal in full
digestion (about six hours after food) is examined, though the
whole cell is smaller, the outer homogeneous zone is found to be
relatively much wider, the granular inner zone being narrower,
and in some cases actually disappearing. If the pancreas be ex-
amined at the end of digestion, when its activity has once more
ceased, and it has entered into a state of rest, the outer zone is
again found to be narrow, the granular inner zone occupying
the greater part of the cell, which has once more become larger.
Carmine stains the outer zone easily, the inner zone with difficulty.
Hence when, as during activity, the outer zone is relatively large,
the cell as a whole seems more deeply stained than when, as during
rest, the outer zone is small. During activity the nucleus is large
and round; during rest it often appears irregular, owing to its
being in such a condition that it shrinks under the influence of the
reagents employed.

Leaving aside for the present the changes in the nucleus, and
the matter of staining, we may say that the results of the two
methods are identical.

Before, however, we attempt to explain what these results mean,
it will be well to pay attention for a while to another type of
secreting gland, the so-called mucous glands. We have already
seen that some salivary glands, such as the submaxillary of the
dog, secrete a thick viscid saliva, the viscidity being due to the
presence of the body mucin (see Appendix), the essential con-
stituent of the so-called mucus ; while other salivary glands, such
as the parotid of most animals, secrete a thin limpid saliva free from
mucin. Glands of the latter kind, from the nature of their secre-
tion, receive the name of 'serous' glands. Glands, however, which
give rise to a viscid mucin-holding secretion, always contain a
certain number of cells of a distinct type. These cells are called
'mucous cells;' and the glands in which they are found are called
'mucous glands.' Sometimes the mucous cells are abundant form-
ing a large part of many or most of the alveoli; sometimes they are
scanty. Each ' mucous ' cell when examined in a fresh and natural
condition is loaded throughout with somewhat large granules;
but when treated with alcohol or other hardening reagents
(Fig. 51 A) appears to consist of two parts: of a small quantity of
what we may speak of as ordinary protoplasm, readily staining
with carmine, &c. and gathered round the nucleus, which is
placed towards the outside of the cell, generally close to the base-

CHAP.

DIGESTION.

269

ment membrane ; and of another different substance which occu-
pies the greater part of the cell. This latter substance is
composed of a loose network of fine fibres, the spaces of which
are occupied by a transparent material which does not stain
readily with carmine ; and upon examination is found to consist

c

FIG. 51. SECTION OF A. 'Mucous' GLAND, A in a state of rest, B after it has been for
some time actively secreting. (After Lavdowsky.)

a demilune cells, c leucocytes lying in the inter-alveolar spaces. The darker
shading hi both figures is intended to indicate the amount of staiaing.

largely of a material which is readily transformed into mucin,
and which may be spoken of as mucinogen or by abbreviation
mucigen. So that the ordinary mucous cell of a mucous gland
may be said to consist of a smaller portion of ordinary protoplasmic
substance and of a larger portion of a mucigenous substance.

Such a condition of things exists however only in a mucous
cell at rest. When the gland is actively secreting, or rather after
the gland has for some time been actively secreting, as for
instance after the submaxillary gland of the dog has been subjected
to long and powerful stimulation of the chorda, a different state of
things presents itself when prepared sections of the hardened gland
are examined. The alveolus is then found to be made up of
smaller cells (Fig. 51 B) almost wholly formed of protoplasmic
substance readily staining with carmine. In extreme cases hardly
a trace is left of the mucigenous substance spoken of above ; in
cases of moderate activity cells may be seen in which the muci-
genous substance has diminished, with an increase of the ordinary
protoplasmic substance, but has not entirely disappeared.

How are we to interpret these results ? obviously in this way.
The mucigenous basis is manufactured at the expense of the
ordinary protoplasm of the cell; the latter by its metabolism
produces the former and deposits it in the meshes of its own
framework, becoming as it were pregnant with mucigen. This
during the resting phase of the gland may go on to such an
extent, that only a small quantity of protoplasm is left to carry

270 HISTOLOGICAL CHANGES. [BOOK IT.

the large quantity of mucigen to which it has given rise ; that
is to say, the growth of new protoplasm does not keep pace with
the manufacture of protoplasm into mucigen. During activity
the mucigen is used up to provide the mucus of the saliva,
being probably converted into mucin and so discharged from the
cell, while at the same time the protoplasm takes a fresh start and
grows apace ; and thus a fresh supply of new, deeply-staining

Ctoplasm takes the place of the mucigenous matrix which has
n lost. We may remark incidentally that this rejuvenescence
of the protoplasm is marked as in the corresponding phase of the
pancreas, by the nucleus becoming round and conspicuous, whereas
when the mucigen is abundant it is of such a nature as to become
irregular in outline when acted upon by hardening reagents.

We have reason to think that in certain cases, where the activity
of the cell is long-continued and vehement, the whole cell may
disappear, and its place be taken by an entirely new cell supplied
by the so-called demilune cells lying on the outside of the alveolus
beneath the basement membrane. But in ordinary cases the
same cell probably, for a while at all events, continues to form and
discharge successive quantities of mucin without actually itself
disappearing.

In any case we see that in the mucous cell what takes place
in secretion is as follows. As the result of a period of rest there ac-
cumulates in the cell a quantity of mucigen, which is a product of
the metabolism of the protoplasm of the cell. During the active
phase, that is while the secretion is being poured forth, the
mucigen is converted into mucin and discharged from the cell.
A loss consequently accrues to the cell, but this is at once partly
made up by the protoplasm being stirred to a more active growth.
Subsequently during the succeeding rest the new protoplasm is
transformed into new mucigen, the cell wholly regains its former
dimensions and features and so the cycle is completed.

What relation do these changes in the mucous gland bear to
those of the pancreas ? To answer this question we must bring
the reader back to a statement made on p. 255, that in order to
obtain an actively proteolytic aqueous pancreatic extract, the
animal should be killed during full digestion. This statement now
requires modification.

If the pancreas of an animal, even in full digestion, be treated,
while still warm from the body, with glycerine, the glycerine
extract, as judged of by its action on fibrin in the presence of
sodium carbonate, is inert or nearly so as regards proteid bodies.
If, however, the same pancreas be kept for 24 hours before being
treated with glycerine, the glycerine extract readily digests fibrin
and other proteids in the presence of an alkali. If the pancreas,
while still warm, be rubbed up in a mortar for a few minutes
with dilute acetic acid, and then treated with glycerine, the
glycerine extract is strongly proteolytic. If the glycerine extract

CHAP, i.] DIGESTIOX. 271

obtained without acid from the warm pancreas, and therefore inert,
be diluted largely with water, and kept at 35° C. for some time!
it becomes active. If treated with acidulated instead of distilled
water, its activity is much sooner developed. If the inert glyce-
rine extract of warm pancreas be precipitated with alcohol in
excess, the precipitate, inert as a proteolytic ferment when fresh,
becomes active when exposed for some time in an aqueous solution,
rapidly so when treated with acidulated water. These facts shew
that a pancreas taken fresh from the body, even during full
digestion, contains but little ready-made ferment, though there is
present in it a body which, by some kind of decomposition, gives
birth to the ferment. ^ We may remark incidentally that though the
presence of an alkali is essential to the proteolytic action of the
actual ferment, the formation of the ferment out of its forerunner
is favoured by the presence of a small quantity of acid. To this
body, this mother of the ferment which has not at present been
satisfactorily isolated, the name of zymogen has been applied.
But it is better to reserve the term zymogen as a generic name
for all such bodies as not being themselves actual ferments, may
by internal changes give rise to ferments, for all 'mothers of
ferment' in fact; and to give to the particular mother of the
pancreatic proteolytic ferment, the name trypsinogen.

The pancreatic cell then contains trypsinogen ; and now comes
the important observation that the amount of trypsinogen in a
pancreas at any given time rises and sinks pari passu with the
granular inner zone, i.e. with the amount of granular substance in
the cell. The wider the inner zone and the more abundant the
granules the larger the amount, the narrower the zone and the
fewer the granules the smaller the amount, of trypsinogen ; and in
the cases of old-established fistulae, where the secretion is wholly
inert on proteids, the inner granular zone is absent from the
cells.

We have no corresponding satisfactory information concerning
the history of any zymogen which may be supposed to belong to
the amylolytic ferment of the pancreas or to the ferment which
acts upon fats. Nor on the other hand are we in a position to say
that the granules are wholly composed of trypsinogen; but it seems
clear that they contain trypsinogen, and that their abundance or
scarcity afford a measure of the quantity of that substance present
in the cell.

Hence we may draw a parallel between the mucous cell and
the pancreatic cell. Just as the protoplasm of the former by its
metabolism manufactures mucigen, so the protoplasm of the latter
by its metabolism manufactures trypsinogen, and just as the
mucigen gives rise to mucin which escapes from the cell to form
part of the actual secretion, so also the trypsinogen gives rise to
trypsin, which similarly forms part of the pancreatic juice. Just as
with the disappearance of the mucigen the protoplasm grows with

272 HISTOLOGICAL CHANGES. [BOOK n.

renewed vigour, so in the pancreas with the disappearance of the
granules from the inner zone, there is a rejuvenescence of the pro-
toplasm, to be followed both in the one case and the other by a
subsequent conversion of the protoplasm into a product, viz.
mucigen and trypsinogen respectively. In both cases the product
of the protoplasmic metabolism is deposited in the inner parts of
the cell, though the line of demarcation between the inner and
outer zone is much more distinct in the pancreas than in the
mucous gland. In the former abundance of granules is identical
with a broad inner zone, scarcity of granules with a broad outer
zone; and similarly the growth of the new protoplasm is most
obvious as an increase of the outer zone. In the mucous cell too
the mucigen appears on the inner side of the cell. This distinction,
however, between an inner and outer zone is not an essential
feature of the matter, though probably the growth of new proto-
plasm naturally tends to take place at a greater rate on the side
of the cell most exposed to the blood-stream, i.e. on the outer side
towards the basement membrane, and the deposition of zymogen or
mucigen tends to be greatest on the other side nearer to the lumen,
into which its products are about to be discharged.

When we come to study other glands, such as the serous
salivary glands, the glands of the stomach, and the hepatic cells,
we have evidence that in these also the same essential processes
are going on. Certain special features however are in various
instances met with, and, these becoming exaggerated by particular
modes of preparation, are apt to obscure the normal series of
events.

Thus in the case of the glands of the stomach, if we were
to trust exclusively to the indications given by sections of glands
hardened in alcohol, we should be led to make the following state-
ment. In an animal previous to taking a meal, the central or ' chief
(as distinguished from the ovoid, 'border,' or 'peptic') cells of the
gastric glands are pale, finely granular, and do not stain readily
with carmine and other dyes. During the early stages of gastric
digestion, the same cells are found somewhat swollen, but turbid
and more coarsely granular ; they stain much more readily. At a
later stage they become smaller and shrunken, but are even more
turbid and granular than before, and stain still more deeply.
This is true, not only of the central cells in the so-called peptic
glands, but also of the cells of which the glands of the pyloric end
of the stomach are built up. The ovoid or border cells appear
swollen during digestion, and project more on the outside of the
gland, but otherwise seem unchanged. This series of events is
different from that which we have seen to take place in the pancreas,
inasmuch as the cells appear to become more granular instead of less
granular during activity. But we have reason to think that the
granular character of the gastric cells thus seen during digestion
is due to some special material precipitated by the alcohol, where-

CHAP. L]

DIGESTION.

273

by changes really comparable to those of the pancreas are obscured.
For we find that in the newt the cells, when examined in a living
condition, are granular throughout when at rest but during activity
develope a clear outer zone, the granules becoming restricted to
the inner zone. And in many mammals similar changes may be
demonstrated by the use of osmic acid (Fig. 52). In some mammals

FIG. 52. GASTRIC GLAND OF MAMMAL (Mole) DURING ACTIVITY (Langley).

c, the mouth of the gland with its cylindrical cells.

n, the neck, containing conspicuous ovoid cells, with their coarse protoplasmic
network.

/, the body of the gland. The granules are seen in the central cells to be limited
to the inner portions of each cell, the round nucleus of which is conspicuous.

no very obvious difference between rest and activity can be made
out; and it is possible that in these a regeneration of granules
takes place during activity as well as during rest and that in pro-
portion as granules are being used up, so that the amount of
granules remains fairly constant.

Moreover we have evidence of the existence in the gastric
membrane of a zymogen, a mother of pepsin, a pepsinogen;
though owing to the facility with which apparently the conversion
of pepsinogen into pepsin takes place, the matter is not so clear as
in the analogous case of trypsinogen ; and it would appear that the
amount of pepsinogen and the abundance of visible granules in fresh
living cells run parallel to each other with considerable regularity.

F. 18

274

MUCOUS AND SEROUS GLANDS.

[BOOK ii.

In the case of the serous glands also the results are somewhat
different according as use is made of preparations hardened in
alcohol, or the gland is studied in a living state. Thus in the
parotid of the rabbit, which is a serous gland, even when a most
copious secretion has been called forth by stimulation of the auriculo-
temporal nerve, alcohol specimens shew an almost complete absence
of structural changes. When however the cervical sympathetic is
stimulated, either in the rabbit or the dog, very marked changes,
quite similar to those witnessed in the central cells of the gastric
glands, may be 'seen in the parotid hardened by alcohol, even though,
as occurs in the dog, no saliva whatever may be secreted. During
rest the cells of the parotid as seen in sections of the gland
hardened in alcohol (Fig. 53 A) are pale, transparent, staining with
difficulty, and the nuclei possess irregular outlines as if shrunken
by the reagents employed. After stimulation of the sympathetic,
the protoplasm of the cells becomes turbid (Fig. 53 B), and stains
much more readily, while the nuclei are no longer irregular in
outline but round and large, with conspicuous nucleoli, the whole
cell at the same time, at least after prolonged stimulation, becoming

A

FIG. 53. SECTION OF A 'SEROUS' GLAND: THE PAROTID OF THE RABBIT. A at
rest, B after stimulation of the cervical sympathetic. (After Heidenhain.)

distinctly smaller. When however we study the gland in a living
state, we find that the changes which take place during activity are
quite comparable to those of the pancreas. During rest (Fig. 54 A),
the cells are large, their outlines very indistinct, in fact almost
invisible and the protoplasm of the cell is studded with granules.

FIG. 51. ^ CHANGES IN THE PAROTID DURING SECRETION (Langley).
The figure which is somewhat diagrammatic represents the microscopic changes
which may be observed in the living gland. A. During rest. The obscure outlines
of the cells are introduced to shew the relative size of the cells, they could not be
readily seen in the specimen itself. B. After moderate stimulation. C. After
prolonged stimulation. The nuclei are diagrammatic, and introduced to shew their
appearance and position.

CHAP, i.] DIGESTION. 275

During activity (Fig. 54 B\ the cells become smaller, their outlines
more distinct, and the granules disappear especially from the outer
portions of each cell. After prolonged activity, as in Fig. 54 C, the
cells are still smaller with their outlines still more distinct, and the
granules have disappeared almost entirely, a few only being left at
the extreme inner margin of each cell abutting upon the conspicuous
almost gaping lumen of the alveolus. And upon special examina-
tion it is found that the nuclei are large and round. In fact we
might almost take the parotid as thus studied, to be more truly
typical of secretory changes than even the pancreas. For, as we
have already stated, the demarcation of an inner and outer zone is not
a necessary feature of the cell at rest. What is essential is that the
protoplasm manufactures granules, which for a while, that is during
rest, are deposited in the cell, and during activity these granules
are used up, their disappearance being earliest and most marked at
the outer portions of each cell, and progressing inwards towards the
lumen, the whole cell becoming smaller and as it were shrunken.

It would hardly be profitable to enter more fully into the
discussion of this matter, and especially of the differences, to which
we have just called attention, as occurring in different glands;
enough has been seen to justify us in the conclusion, which
further study will be found to strengthen, that the act of secretion
is not a mere filtration from the blood but a complicated business,
which we may picture to ourselves somewhat as follows.

The protoplasm of the secreting cell lives upon its 'internal
medium/ the lymph filling the lymph spaces by which the
alveolus is surrounded ; this lymph being constantly renewed from
the blood-stream. We have no reason to think that the main
nutritive constituents of the lymph in the interstices of a gland
are different from those in the interstices of a muscle ; but are led
to believe that the same substances are built up in the one
case into muscular and in the other into glandular protoplasm by
the specific activity of the already existing protoplasm which is
different in the one case and the other. The cell substance which
has thus built itself up out of the lymph materials sooner or later
breaks down again: the constructive metabolism is inevitably
followed by a destructive metabolism. In this downward path are
probably many steps, two of which become conspicuous: the
formation of some intermediate product or 'mesostate,' as we may
call it, such as zymogen or mucigen, and the conversion of the
zymogen into an actual ferment or of the mucigen into mucin, that
is of the mesostate into the final product, which is discharged as a
constituent of the secretion.

In what we may consider the common or typical case where
periods of rest alternate with periods of secretory activity, the
downward metabolism stops short at the formation of zymogen,
which becomes deposited, commonly in the form of granules in the
meshes of the protoplasm, the constructive metabolism or growth

18-2

276 THEORY OF SECEETION. [BOOK n.

of the latter languishing as the storage increases. Then generally
as the result of stimulation, changes takes place in the cell
by which the zymogen is converted into actual ferment, and this
ejected from the cell. This is the process which we sometimes
speak of as the act of secretion, and it obviously has many
analogies with a muscular contraction. Coincident with the dis-
turbances which thus give rise to the ejection of ferment, the
constructive metabolism of the cell is excited to greater activity,
and for a while there is an accumulation of new protoplasm in
great excess of zymogen. Soon, however, but slowly rather than
suddenly, this new protoplasm again breaks down into zymogen,
which in turn is stored up in the cell, and so the cycle is completed.

Such may be considered the more common mode of procedure ;
and in such a case we are enabled, as in the pancreas or mucous
gland, to watch the accumulation and disappearance of the zymo-
gen or mucigen, because this is alternately in excess of or less
than the actual protoplasm. But we can easily imagine .a case in
which all the various stages of the upward and downward
metabolism keep pace with each other, in which for instance when
any quantity of zymogen is converted into ferment which leaves
the cell, just that quantity of zymogen is replaced by a destruction
of protoplasm, and a new quantity of protoplasm appears just
sufficient to replace the old which has been broken down. In
such an instance of continuous changes it would be impossible, with
our present means at least to trace out the series of events, though
those at bottom would be identical with those where the changes
were discontinuous. And indeed it is obvious that this same plan of
secretion, if we may so call it, might be made to produce very
varied results, by variations in the proportions and rates of the
several steps.

Admitting, however, ihis view of what we may call the proto-
plasmic aspect of secretion, another feature has to be considered.
The juice secreted by any gland consists not only of the specific
ferments, trypsin etc. as the case may be, found only in it, but also
of a large quantity of water, and of various saline or other soluble
substances common to it and other juices. And the question arises,
Is this water, or are these salts and soluble substances furnished by
the same act as that which supplies the specific constituents ?

To this we may reply, that the very water is discharged by the
activity of the cell, and is not a mere filtration from the blood-
vessels. For, as we have seen in the case of the salivary glands,
when atropin is given, not only do the specific constituents cease
to be ejected in spite of the vessels becoming dilated, but the
discharge of water is also arrested: no saliva at all leaves the
gland. And what is true of the salivary glands probably holds
good with the other glands. Assuming then that even the escape
of water is the result of the activity of the cell, we cannot but feel
an increased interest in the fact mentioned some time ago, that in

CHAP, i.] DIGESTION. 277

the submaxillary gland of the dog, stimulation of the chorda
tympani produces a copious flow of thin limpid saliva, and stimu-
lation of the cervical sympathetic a scanty flow of thick viscid
saliva. That is to say, stimulation of the chorda affects chiefly the
discharge of water, which carries away with it various soluble
matters, while stimulation of the sympathetic chiefly affects the
conversion of mucigen into mucin. To this we may add the case
of the parotid of the dog. In this stimulation of a cerebro-spinal
nerve, the auriculo-temporal, produces a copious flow of limpid
saliva, while stimulation of sympathetic produces itself little or no
secretion at all ; but after previous stimulation of the sympathetic,
the saliva which flows upon stimulation of the cerebro-spinal nerve
is much richer in solid and especially in organic matter. And we
have already seen that while the microscopic changes after cerebro-
spinal stimulation are inappreciable, those following upon sym-
pathetic stimulation are very conspicuous. The latter gives rise to
certain constituents, while the former, so to speak, washes them
away into the duct.

These and other facts, on which we need not now dwell, have
led to the conception that the act of secretion consists of two
parts, both distinct efforts of the cell, which in one case may
coincide, in another may take place apart or in different pro-
portions. On the one hand, there is the discharge of water
carrying with it common soluble substances; on the other, the
escape of specific substances resulting from the profound meta-
bolism of the cell protoplasm. And it has been supposed that
two kinds of nerve fibres exist, one governing the former process
and preponderating in the chorda tympani, for instance, the other
governing the latter and preponderating in the branches of the
cervical sympathetic. Further hypotheses have been put forward
to explain the modus operandi of the discharge of water, such
as the existence of substances in the cell which absorb water from
the blood or lymph on the one side and give it up on the other
side into the lumen of the alveolus. But these matters are not
yet ripe for any distinct assertion, and though we have thought it
right to bring the matter before our readers, we must not pursue
the discussion any further. Whether there be two sets of fibres or
no, whether the two processes be absolutely distinct or merely
variations of the same fundamental changes, the proposition on
which we have so long dwelt — that the flow of juice from a
secreting gland is essentially the outcome of the activity of the
secreting cell — remains equally true.

Before we leave the mechanism of secretion there are one
or more accessory points which deserve attention.

In treating just now of the gastric glands we spoke as if
pepsin were the only important constituent of gastric juice,
whereas, as we have previously seen, the acid is equally essential.
The formation of the free acid of the gastric juice is very

278 THEORY OF SECRETION. [BOOK n.

obscure and many ingenious but unsatisfactory views have been
put forward to explain it. It seems natural to suppose that
it arises in some way from the decomposition of sodium chloride
drawn from the blood; and this is supported by the fact that
when the secretion of gastric juice is actively going on, the
amount of chlorides leaving the blood by the kidney is pro-
portionately diminished; but nothing definite can at present be
stated as to the mechanism of that decomposition, though an
organic acid such as lactic, which as we have seen appears in the
juice, might under certain conditions succeed in decomposing
chlorides. And even admitting that the sodium chloride of the
body at large is the ultimate source of the chlorine element of
the acid, it appears more likely that that element should be set
free in the stomach by the decomposition of some highly complex
and unstable chlorine compound previously generated, than that it
should arise by the direct splitting-up of so stable a body as
sodium chloride, at the time when the acid is secreted.

In the frog, while pepsin free from acid is secreted by the
glands in the lower portion of the oesophagus, an acid juice is
afforded by glands in the stomach itself, which have accordingly
been called oxyntic (6t;vveiv to sharpen, acidulate) glands ; but
these oxyntic glands appear also to secrete pepsin. In the
mammal the isolated pylorus secretes an alkaline juice; in fact
the appearance of an acid juice is limited to those portions
of the stomach in which the glands contain both 'chief or
'central,' and 'ovoid' or 'border' cells. Now there can be no
doubt that the chief cells do secrete pepsin. During life the
granules visible in the living chief cells abound or are scanty
according as pepsin is about to be or has been secreted, and
after death they contain pepsin (or pepsinogen), and that in
proportion to their richness in granules. No such correspondence
can be seen in the ' border ' or ' ovoid ' cells. Hence it has been
inferred that the border cells secrete acid; but the argument is one
of exclusion only, there being no direct proofs of these cells actually
manufacturing the acid.

The rennet ferment appears to be formed by the same cells
which manufacture the pepsin, that is, by the chief cells of the
fundus generally and to some extent by the cells of the pyloric
glands. We may add that we have evidence of the existence of a
zymogen of the rennet ferment analogous to the zymogen of pepsin
or trypsin.

The mucus which is present as a thin layer over the surface
of the fasting stomach, and which especially in herbivorous animals
is increased during digestion, comes from the mucous cells which line
the mouths of the several glands and cover the intervening surfaces.
We previously called attention to the fact that in the case of
the stomach the absorption of the products of digestion largely
increased the activity of the secreting cells. This has led to the

CHAP. i.J DIGESTION. 279

idea that one effect of food is to ' charge ' the gastric cells with
pepsinogen, and that certain articles of food might be considered
as especially peptogenous, i. e. conducive to the formation of pepsin.
Such a view is tempting, but needs as yet to be more fully
supported by facts.

Seeing the great solvent power of both gastric and pancreatic
juice, the question is naturally suggested, Why does not the
stomach digest itself? After death, the stomach is frequently
found partially digested, viz. in cases when death has taken place
suddenly on a full stomach. In an ordinary death, the membrane
ceases to secrete before the circulation is at an end. That there
is no special virtue in living things which prevents their being
digested is shewn by the fact, that the legs of a frog or the ear
of a rabbit introduced into a stomach through a fistula are readily
digested. It has been suggested that the blood-current keeps up an
alkalinity sufficient to neutralize the acidity of the juice in the
region of the glands themselves; but this will not explain why
the pancreatic juice, which is active in an alkaline medium, does
not digest the proteids of the pancreas itself, or why the digestive
cells of the bloodless actinozoon or hydrozoon do not digest them-
selves. We might add, it does not explain why the amoeba, while
dissolving the protoplasm of the swallowed diatom, does not dis-
solve its own protoplasm. We cannot answer this question at all
at present, any more than the similar one, why the delicate
protoplasm of the amoeba resists during life all osmosis, while a few
moments after it is dead, osmotic effects become abundantly evident.

The secretion of bile needs a few additional words. The analogy
of the other glands and what we already know of the microscopic
changes in the hepatic cells, leads us to believe that the secretion
of even such a complex fluid as the bile is in the main the result of
the direct metabolic activity of the protoplasm of the hepatic cells.
And this view is supported by the fact that after extirpation of the
liver, no accumulation of the biliary constituents is observed to take
place during the few hours of life remaining to the animal after the
operation. Still the great complexity of the secretion introduces
several very important considerations. In the first place, the liver,
unlike the other digestive glands, has a double supply of blood; and
vain attempts have been made to settle by direct experiment the
question whether the hepatic artery or the vena portse is the more
closely concerned in the production of bile. Ligature of the
hepatic artery has sometimes had no effect on the secretion, some-
times has interfered with it. Sudden ligature of the vena portse at
once stops the flow of bile; but gradual obliteration may be effected
without either causing death or even interfering with the secretion,
anastomotic branches forming a collateral circulation, and thus
maintaining an efficient flow of blood through the liver. The
problem, which is probably a barren one, cannot be settled in this way.

In the second place, the hepatic cells not only secrete bile, but,

280 SECRETION OF BILE. [BOOK n.

as we shall see later on, take an active part in other operations of
even greater importance. The consideration of the question in
what way these several functions of the hepatic cells are related to
each other must be deferred for the present.

In the third place, even if we maintain that the chief constitu-
ents of the bile are manufactured in the hepatic cells, and not
simply drained off from the blood, we are not thereby precluded
from admitting that the hepatic cells may avail themselves of
certain half-made materials, the arrival of which in the blood may,
so to speak, lighten their labours, or that they may even boldly seize
upon and pass off as their own handiwork any wholly manufactured
constituents which may be offered to them. Thus we have already
seen reasons for thinking that the bile-pigments are not made de novo
in the hepatic cells, but spring from haemoglobin, the change in the
liver being one of comparatively simple transformation. So also it is
quite possible, though not proved, that much if not all of the choles-
terin of bile is merely withdrawn by the liver from the body at large.
And even with the central components of bile, the bile-salts, we know
that in the case of taurocholic acid, taurin is normally present in
certain tissues, and that in the case of glycocholic acid, glycin, if not
a normal constituent of any tissue, is present in the body, since the
body can convert benzoic into hippuric acid, as we shall see in a
succeeding section ; so that the formation of these bodies by the
hepatic cells may be limited to the production of cholalic acid and
its conjugation with one or other of the above amido-acids. More-
over as a matter of fact, we find that the flow of bile from a biliary
fistula is much increased by the injection of bile into the small
intestine. This experiment renders it possible that some of the
bile which in natural digestion is poured into the intestine is re-
absorbed, and carried back to the liver to do duty over again.

In medical practice, distinction is drawn between jaundice by
suppression of the secreting functions of the liver and jaundice by
retention, brought about by an obstruction existing in some part of
the biliary passages. The gravity of the symptoms in the first class
of cases shews that an arrest or a too great diminution of the
normal functions of the hepatic cells is at least accompanied by the
presence in the blood of substances injurious to life ; but how far
the presence of those substances is due to a failure of the manufac-
ture of bile and the accumulation in the system of the materials for
the formation of bile, or to a failure of other functions of the hepatic
cells, must be regarded as at present undetermined. The presence
of the bile-pigment in this form of jaundice would seem to indicate
that the formation of the pigment, i. e. the transformation of haemo-
globin into bilirubin, in contrast to the formation of bile acids, re-
quires but little labour on the part of the cell, and may be carried
on even when the nutrition of the cell is highly deranged.

SEC. 3. THE MUSCULAR MECHANISMS OF DIGESTION.

From its entrance into the mouth until such remnant of it as is
undigested leaves the body, the food is continually subjected to
movements having for their object the trituration of the food as in
mastication, or its more complete mixture with the digestive juices,
or its forward progress through the alimentary canal. These various
movements may briefly be considered in detail.

Mastication. Of this it need only be said that in man it con-
sists chiefly of an up and down movement of the lower jaw, com-
bined, in the grinding action of the molar teeth, with a certain
amount of lateral and fore-and-aft movement. The lower jaw is
raised by means of the temporal, masseter, and internal pterygoid
muscles. The slighter effort of depression brings into action chiefly
the digastric muscle, though the mylohyoid and geniohyoid probably
share in the matter. Contraction of the external pterygoids pulls
forward the condyles, and thrusts the lower teeth in front of the
upper. Contraction of the pterygoids on one side will also throw
the teeth on to the opposite side. The lower horizontally placed
fibres of the temporal serve to retract the jaw.

During mastication the food is moved to and fro, and rolled
about by the movements of the tongue. These are effected by the
muscles of that organ governed by the hypoglossal nerve.

The act of mastication is a voluntary one, guided, as are so
many voluntary acts, not only by muscular sense but also by contact

282 DEGLUTITION. [BOOK n.

sensations. The motor fibres of the fifth cranial nerve convey
motor impulses from the brain to the muscles ; but paralysis of the
sensory fibres of the same nerve renders mastication difficult by
depriving the will of the aid of the usual sensations.

Deglutition. The food when sufficiently masticated is, by the
movements of the tongue, gathered up into a bolus on the middle
of the upper surface of that organ. The front of the tongue being
raised — partly by its intrinsic muscles, and partly by the stylo-
glossus — the bolus is thrust back between the tongue and the
palate through the anterior pillars of the fauces or isthmus faucium.
Immediately before it arrives there, the soft palate is raised by the
levator palati, and so brought to touch the posterior wall of the
pharynx, which, by the contraction of the upper margin of the
superior constrictor of the pharynx, bulges somewhat forward. The
elevation of the soft palate causes a distinct rise of pressure in the
nasal chambers ; this can be shewn by introducing a water mano-
meter into one nostril, and closing the other just previous to
swallowing. By the contraction of the palato-pharyngeal muscles
which lie in the posterior pillars of the fauces, the curved edges of
those pillars are made straight, and thus tend to meet in the middle
line, the small gap between them being filled up by the uvula.
Through these manoeuvres, the entrance into the posterior nares is
blocked, while the soft palate forms a sloping roof, guiding the bolus
down the pharynx. By the contraction of the stylo-pharyngeus
and palato-pharyngeus, the funnel-shaped bag of the pharynx is
brought up to meet the descending morsel, very much as a glove
may be drawn up over the finger.

Meanwhile in the larynx, as shewn by the laryngoscope, the
arytenoid cartilages and vocal cords are approximated : the latter
being also raised so that they come very near to the false vocal
cords : the cushion at the base of the epiglottis covers the rima
glottidis, while the epiglottis itself is depressed over the larynx.
The thyroid cartilage is now, by the action of the laryngeal muscles,
suddenly raised up behind the hyoid bone, and thus assists the
epiglottis to cover the glottis. This movement of the thyroid can
easily be felt on the outside. Thus, both the entrance into the
posterior nares and that into the larynx being closed, the impulse
given to the bolus by the tongue can have no other effect than to
propel it beneath the sloping soft palate, over the incline formed
by the root of the tongue and the epiglottis. The palato-glossi or
constrictores isthmi faucium, which lie in the anterior pillars of the
fauces, by contracting, close the door behind the food which has
passed them.

When the bolus of food is large, it is received by the middle
and lower constrictors of the pharynx which, contracting in
sequence from above downwards, thrust it into the oesophagus,
along which it is driven by a similar series of successive con-

CHAP. L] DIGESTIOX. 283

tractions which we shall speak of immediately as peristaltic
action. This comparatively slow descent of the food from the
pharynx into the stomach, may be readily seen if animals with
long necks such as horses and dogs be watched while swallowing.
Recent observations however seem to shew that when the morsel
is not large and especially when the substance swallowed is liquid,
the movement of the back part of the tongue is sufficient not
merely to introduce the food into the grasp of the constrictors
of the pharynx, but even to propel it rapidly, to shoot it in fact,
along the lax oesophagus before the muscles of that organ have
time to contract. In such a mode of swallowing the middle and
lower constrictors take little or no part in driving the food
onward, though they and the oesophagus appear to contract from
above downwards after the food has passed by them, as if to
complete the act and to ensure that nothing has been left behind.
Deglutition in this fashion still remains possible after the con-
strictors have become paralysed by section of their motor nerves.

Deglutition therefore, though a continuous act, may be regarded
as divided into three stages. The first stage is the thrusting of the
food through the isthmus faucium ; this may be either of long or
short duration. The second stage is the passage through the upper
part of the pharynx. Here the food traverses a region common
both to the food and to respiration, and in consequence the move-
ment is as rapid as possible. The third stage is the descent through
the grasp of the constrictors. Here the food has passed the respira-
tory orifice, and in consequence its passage may again become com-
paratively slow, or, as we have seen, may continue to be rapid.

The first stage in this complicated process is undoubtedly a
voluntary action. The raising of the soft palate and the approxi-
mation of the posterior pillars may also be, at times, voluntary,
since they have been seen, in a case where the pharynx was laid
bare by an operation, to take place before the food had touched
these parts; but the movement may take place without any
exercise of the will or presence of consciousness. And indeed the
second stage taken as a whole, though some of the earlier com-
ponent movements are, as it were, on the borderland between the
voluntary and involuntary kingdoms, must be regarded as a reflex
act. The third and last stage, whatever be the exact form which it
takes, is undoubtedly reflex ; the will has no power whatever over
it and can neither originate, stop, nor modify it.

Deglutition in fact as a whole is a reflex act ; it cannot take
place unless some stimulus be applied to the mucous membrane of
the fauces. When we voluntarily bring about swallowing move-
ments with the mouth empty, we supply the necessary stimulus
by forcing with the tongue a small quantity of saliva into the
fauces, or by touching the fauces with the tongue itself.

In the reflex act of deglutition the afferent impulses originated
in the fauces are carried up chiefly by the glosso-pharyngeal, but

284 MOVEMENTS OF THE (ESOPHAGUS. [BOOK u.

also by branches of the fifth, and by the pharyngeal branches
of the superior laryngeal division of the vagus. The efferent
impulses descend the hypoglossal to the muscles of the tongue, and
pass down the glosso-pharyngeal, the vagus through the pharyngeal
plexus, the fifth and the facial, to the muscles of the fauces and
pharynx: their exact paths being as yet not fully known, and
probably varying in different animals. The laryngeal muscles are
governed by the laryngeal branches of the vagus.

The centre of the reflex act lies in the medulla oblongata.
Deglutition can be excited, by tickling the fauces, in an animal
rendered unconscious by removal of the brain, provided the
medulla be left. If the medulla be destroyed, deglutition is
impossible. The centre for deglutition lies higher up than that
of respiration, so that the former act is frequently impaired or
rendered impossible while the latter remains untouched. It is
probable that, as is the case in so many other reflex acts, the
whole movement can be called forth by stimuli affecting the
centre directly, and not acting on the usual afferent nerves.

Movements of the (Esophagus. As we have already said, in
certain cases at all events, the food is carried down from the
pharynx to the stomach in a comparatively slow manner, by the
action of the muscular coat of the oesophagus itself. Contractions of
the circular fibres occur in succession from above downwards, driving
the food before them, very much as a fluid may be driven along a
tube by squeezing it. The movement is probably assisted by
a similarly progressive contraction of the longitudinal muscular
coat ; but the exact manner in which this acts is uncertain. Such
a progressive movement, of which we have already spoken on
p. 101, and which is much more pronounced in the small intestine
than in other parts of the alimentary canal, is spoken of as "peristaltic
action." These peristaltic movements of the oesophagus may, like
those of the intestine, be seen after removal of the organ from the
body ; and indeed may continue to appear upon stimulation, for an
unusual length of time. Nevertheless, in the intact body, the
movements of the oesophagus seem to be much more closely
dependent on the central nervous system than do those of the
intestines ; the contractions are not, as in the latter case, trans-
mitted from section to section of the tube, but afferent impulses
started in the pharynx and passing to the medulla oblongata, give
rise to reflex efferent impulses which descend along nervous tracts
to successive portions of the organ. If the oesophagus be cut
across some way down, or if a portion of the middle region be
excised, stimulation of the pharynx will produce a peristaltic
contraction, which travelling downwards will not stop at the
section but will be continued on into the lower disconnected
portion by means of the central nervous system. And it is stated
that ordinary peristaltic contractions of the lower part of the

CHAP, i.] DIGESTION. 285

oesophagus can be readily excited by stimulation of the pharynx,
but not by stimuli applied to its own mucous membrane. In
the reflex act which thus brings about the peristaltic contraction
of the oesophagus the afferent nerves are those of the pharynx,
viz. the superior laryngeal nerve, branches of the fifth, and in
some animals at least branches of the glossopharyngeal, but chiefly
the first. The centre lies in the medulla oblongata, being a part
of the general deglutition centre ; and the efferent impulses pass
along fibres of the vagus, reaching the upper part of the oesophagus
by the recurrent laryngeal nerves and the lower part through the
plexuses over the root of the lungs and the stomach, to which the
vagus gives origin. Section of the trunk of the vagus renders
difficult the passage of food along the oesophagus, and stimulation
of the peripheral stump causes cesophageal contractions. The
force of this movement in the oesophagus is considerable; thus
Mosso found that in the dog a ball pulling by means of a pulley
against a weight of 250 grammes was readily carried down from
the pharynx to the stomach.

The junction of the oesophagus with the stomach remains in a
more or less permanent condition of tonic or obscurely rhythmic
contraction, more particularly when the stomach is full of food, and
thus serves as a sphincter to prevent the return of food from the
stomach into the oesophagus. During the passage of the food
from the oesophagus into the stomach this sphincter becomes
relaxed, probably by a mechanism which will be described in
treating of vomiting.

Movements of the Stomach. These are at bottom peristaltic
in nature, though largely modified by the peculiar arrangement of
the gastric muscular fibres. When food first enters the stomach,
the movements are feeble and slight, but as digestion goes on
they become more and more vigorous, giving rise to a sort of
churning within the stomach, the food travelling from the cardiac
orifice along the greater curvature to the pylorus, and returning by
the lesser curvature, while at the same time subsidiary currents
tend to carry the food which has been passing close to the mucous
membrane toward the middle of the stomach, and vice versa. At
the pyloric end strong circular contractions are set up, by which
portions of food, more especially the dissolved parts, but also small
solid pieces, are carried through the relaxed sphincter into the
duodenum. As digestion proceeds, more and more material leaves
the stomach, which is thus gradually emptied, the last portions
which are carried through being those matters which are least
digestible, and foreign bodies which happen to have been swallowed.
The presence of food then leads to the development of obscurely
peristaltic rhythmic movements, the stomach when empty being
contracted, but quiescent; but evidently it is not the mere
mechanical repletion of the organ which is the cause of the move-

286 MOVEMENTS OF THE SMALL INTESTINE. [BOOK ir.

ments, since the stomach is fullest at the beginning when the
movements are slight, and becomes emptier as they grow more
forcible. The one thing which does increase pari passu with the
movements is the acidity, which is at a minimum when the
(generally alkaline) food has been swallowed, and increases steadily
onwards. It has not however been definitely shewn that the
increasing acidity is the efficient stimulus, giving rise to the
movements.

The nervous mechanism of the gastric movements is at present
very obscure. The stomach receives its nervous supply from the
vagi and also from the solar plexus, with which the splanchnics are
connected. When the vagi are divided, a spasmodic constriction of
the cardiac orifice takes place; in other words the tonic action of the
sphincter is increased, and food is thus prevented, for a time at least,
from leaving the oesophagus. In addition, the natural movements
of the stomach itself cease, or become uncertain and irregular, even
if food be present. Incomplete movements may be induced by
stimulation of the peripheral stumps of the vagi, when the stomach
is full, but not so readily if it be empty. The effects of section or
stimulation of the splanchnics or of the branches from the solar
plexus are uncertain. Nor do we know the exact mechanism by
which the pyloric sphincter is used to strain off gradually the
more digested portions of the food. The movements of even
a full stomach are said to cease during sleep.

Movements of the small Intestine. Though peristaltic move-
ments occur along the whole length of the alimentary canal, from
the oesophagus to the rectum, they are more pronounced in the
small intestine than elsewhere. When the intestines are watched,
after opening the abdomen, circular contractions, that is con-
tractions of the circular coat, may be seen travelling lengthways
along the intestine and often upwards as well as downwards.
Similarly longitudinal contractions, that is contractions of the longi-
tudinal coat, may also be seen to travel lengthways. The circular
coat being much thicker and stouter than the longitudinal coat, is
the more important of the two, and it is by the contractions
of the circular coat that in the normal state of things the
contents of the intestine are driven along toward the ileo-csecal
valve. The contractions of the longitudinal coat appear to be
chiefly of use in producing peculiar oscillating movements of the
pendent loops in which the intestine is arranged. The rhythmic
occurrence of these circular and to-and-fro movements, together
with the passive movements caused by the entrance of the fluid
contents into or their exit from the various loops, brings about the
peculiar writhing of the intestines which has given rise to the
phrase peristaltic action.

The movements, as we have said, take place from above down-
wards, and a wave beginning at the pylorus may be traced a long

CHAP, i.] DIGESTION. 287

way down. But contractions may, and in all probability oc-
casionally do, begin at various points along the length of the
intestine. In the living body the intestines have periods of rest,
alternating with periods of activity, the occurrence of the periods
depending on various circumstances.

With regard to the causation of the peristaltic movements of
the intestine, this much may be affirmed that they may 'occur, as
in a piece of intestine cut out from the body, wholly indepen-
dently of the central nervous system ; and the only nervous elements
which can be regarded as essential to their development are
the ganglia of Auerbach or those of Meissner in the intestinal
walls. Though the movements can readily be excited by stimuli,
applied either to the outside, or, more especially, to the inside of
the intestine, they are probably at bottom automatic. The
presence of „ food, especially of food in motion, may at times act
as a stimulus, and may in all cases be a condition affecting the
nature and extent of the movement; but cannot be regarded as
the real cause of the action. When any body is introduced into
the intestine, a contraction at first occurs, but soon passes off as
the intestine becomes accustomed to the presence of the body.
There is no reason why the intestine should not become equally
accustomed to the presence of food; and, as a matter of fact,
peristaltic movements are often absent when the intestines arc
full. The presence of food bears about the same relation to the
movements of the intestine, that the presence of blood bears to the
beat of the heart. Both are favouring but not indispensable
conditions: in both cases the action can go on without them.
We may add that just as the tension of a muscle increases up
to a certain extent the amount of its contraction, and a full heart
beats more strongly than an empty one, so distension of the
intestine largely increases peristaltic action. Hence in cases of
obstruction of the bowels, the movements become distressing by
their violence.

Among the chief circumstances affecting peristaltic action
may be mentioned in the first place the condition of the blood.
A lack of oxygen or an excess of carbonic acid in the blood excites
powerful movements. This is well seen in asphyxia, and the
powerful post-mortem peristaltic movements witnessed on opening
a recently-killed animal, as well as those which frequently occur
when in the living body, the blood-stream is cut off by com-
pression of the aorta, are probably due to the deficiency of oxygen
or the accumulation of carbonic acid in the blood and tissues of the
intestinal walls. Conversely, saturation of the blood with oxygen,
as in the peculiar condition known as apncea (see chapter on
Respiration), tends to check peristaltic movements.

In the second place, peristaltic action is largely influenced by
nervous influences passing along the splanchnic and vagus nerves.
The movements will go on after section of both these nerves ; but

288 MOVEMENTS OF THE LARGE INTESTINE. [BOOK n.

as a general rule, while stimulation of the splanchnic tends to
check, that of the vagus tends to excite them ; but much has
probably yet to be learnt about the exact manner in which these
nerves act. It is probably through the vagus that peristaltic
movements can be effected in an indirect manner, as in that in-
crease of the movements of the intestine in consequence of
emotions, which has given rise to the phrase ' my bowels yearned/

When the vagus is stimulated, peristaltic contraction is seen to
begin at the pylorus of the stomach and so to descend along the
intestine. When however the duodenum is mechanically stimu-
lated, both a peristaltic and an antiperistaltic wave, that is, a
wave of contraction passing upwards instead of downwards, may
be observed, the former passing downward and ceasing at the
ileo-csecal valve if not before, the latter passing up and ceasing
at the pylorus. And when in the exposed intestines a wave, as
occasionally happens, begins spontaneously in the duodenum, it
may sometimes be seen to pass both upwards and downwards. It
is worthy of notice that stimulation of the small intestine is said
not to cause movement either in tke stomach or large intestine,
.and stimulation of the large intestine or of the stomach causes
no movement of >the small intestine, the ileo-csecal valve and the
pylorus barring the .progress of the waves.

Certain drugs, such as nicotin, induce strong peristaltic action ;
the modus operandi of these and of the more specific purgative
drugs is at present uncertain.

Movements of the large Intestine. These are fundametally
the same as those of the small intestine, but distinct in so far as
the latter cease at the ileo-csecal valve, at which spot the former
normally begin. They are said, moreover, not to be inhibited by
stimulation of the splanchnics.

The fa3ces in their passage through the colon are lodged in the
sacculi during the pauses between the peristaltic waves. Arrived
at the sigmoid flexure, they are supported by the bladder and the
sacrum, so that they do not press on the sphincter ani.

Defsecation. This is a mixed act, being superficially the result
of an effort of the will, and yet carried out by means of an involun-
tary mechanism. Part of the voluntary effort consists in produ-
cing a pressure-effect, by means of the abdominal muscles. These
are contracted forcibly as in expiration, but the glottis being
closed, and the escape of air from the lungs prevented, the whole
force of the pressure is brought to bear on the abdomen itself, and
so drives the contents of the descending colon onward into the
rectum. The sigmoid flexure is by its position sheltered from this
pressure ; a body introduced per anum into the empty rectum is
not affected by even forcible contractions of the abdominal walls.

The anus is guarded by the sphincter ani, which is habitually
in a state of normal tonic contraction, capable of being increased or

CHAP, i.] DIGESTIOX. 239

diminished by a stimulus applied, either internally or externally,
to the anus. The tonic contraction is in part at least due to the
action of a nervous centre situated in the lumbar spinal cord. If
the nervous connexion of the sphincter with the spinal cord be
broken, relaxation takes place. If the spinal cord be divided in
the dorsal region, the sphincter, after the depressing effect of the
operation, which may last several days, has passed off, still main-
tains its tonicity, shewing that the centre is not placed higher up
than the lumbar region of the cord. The increased or diminished
contraction following on local stimulation is probably due to reflex
augmentation or inhibition of the action of this centre. The
centre is also subject to influences proceeding from higher regions
of the cord, and from the brain. By the action of the will,
by emotions, or by other nervous events, the lumbar sphincter
centre may be inhibited, and thus the sphincter itself relaxed ; or
augmented, and thus the sphincter tightened. A second item
therefore of the voluntary process in defecation is the inhibition of
the lumbar sphincter centre, and consequent relaxation of the
sphincter muscle. Since the lumbar centre is wholly efficient when
separated from the brain, the paralysis of the sphincter which occurs
in certain cerebral diseases is probably due to inhibition of this
centre, and not to paralysis of any cerebral centre.

Thus a voluntary contraction of the abdominal walls, accom-
panied by a relaxation of the sphincter, might press the contents
of the descending colon into the rectum and out at the anus.
Since however, as we have seen, the pressure of the abdominal
walls is warded off the sigmoid flexure, such a mode of defaecation
would always end in leaving the sigmoid flexure full. Hence the
necessity for these more or less voluntary acts being accompanied
by an entirely involuntary augmentation of the peristaltic action
of the large intestine and sigmoid flexure. Or rather, to describe
matters in their proper order, defaecation takes place in the
following manner. The sigmoid flexure and large intestine be-
coming more and more full, stronger and stronger peristaltic action
is excited in their walls. By this means the fseces are driven
against the sphincter. Through a voluntary act, or sometimes at
least by a simple reflex action, the lumbar sphincter centre is
inhibited and the sphincter relaxed. At the same time the
contraction of the abdominal muscles presses firmly on the descend-
ing colon, and thus the contents of the rectum are ejected.

It must however be remembered that, while in appealing to
our own consciousness, the contraction of the abdominal walls and
the relaxation of the sphincter seem purely voluntary efforts, the
whole act of defsecation, including both of these seemingly so
voluntary components, may take place in the absence of conscious-
ness, and indeed, in the case of the dog at least, after the complete
severance of the lumbar from the dorsal cord. In such cases the

F. 19

290 VOMITING. [BOOK 11.

whole act must be purely reflex, excited by the presence of faeces
in the rectum.

Vomiting". In a conscious individual this act is preceded by
feelings of nausea, during which a copious flow of saliva into the
mouth takes place. This being swallowed carries down with it a
certain quantity of air, the presence of which in the stomach,
by assisting in the opening of the cardiac sphincter, subsequently
facilitates the discharge of the gastric contents. The nausea is
generally succeeded at first by ineffectual retching in which a deep
inspiratory effort is made, so that the diaphragm is thrust down as
low as possible against the stomach, the lower ribs being at
the same time forcibly drawn in; since during this inspiratory
effort the glottis is kept closed, no air can enter into the lungs ;
but some is drawn into the pharynx, and thence probably descends
by a swallowing action into the stomach. In actual vomiting this
inspiratory effort is succeeded by a sudden violent expiratory
contraction of the abdominal walls, the glottis still being closed, so
that the whole force of the effort is spent, as in defecation, in
pressure on the abdominal contents. The stomach is therefore
forcibly compressed from without. At the same time, or rather im-
mediately before the. expiratory effort, by a contraction of its longi-
tudinal fibres the oesophagus is shortened and the cardiac orifice
of the stomach brought close under the diaphragm, while ap-
parently by a contraction of the fibres which radiate from the end
of the oesophagus over the stomach, the cardiac orifice, which is
normally closed, is somewhat suddenly dilated. This dilation opens
a -way for the contents of the stomach, which, pressed upon by the
contraction of the abdomen, and to a certain but probably only to
a slight extent by the contraction of the gastric walls, are driven
forcibly up the oesophagus, their passage along that channel being
possibly assisted by the contraction of the longitudinal muscles.
The mouth being widely open, and the neck stretched to afford as
straight a course as possible, the vomit is ejected from the body.
At this moment there is an additional expiratory effort which
serves to prevent the vomit passing into the larynx. In most
cases too the posterior pillars of the fauces are approximated,
in order to close the nasal passage against the ascending stream.
This however in severe vomiting is frequently ineffectual.

Thus in vomiting there are two distinct acts ; the dilation of
the cardiac orifice and the extrinsic pressure of the abdominal walls
in an expiratory effort. Without the former the latter, even when
distressingly vigorous, is ineffectual. Without the latter, as in
urari poisoning, the intrinsic movements of the stomach itself are
rarely sufficient to do more than eject gas, and, it may be, a very
small quantity of food or fluid* Pyrosis or waterbrash is probably
brought about by this intrinsic action of the stomach.

During vomiting the pylorus is generally closed, so that but
little material escapes into the duodenum. When the gall-bladder

CHAP, i.] DIGESTION, 291

is full, a copious flow of bile into the duodenum accompanies the
act of vomiting. Part of this may find its way into the stomach, as
in bilious vomiting, the pylorus then having evidently been opened.

The nervous mechanism of vomiting is complicated and in
many aspects obscure. The efferent impulses- which cause the
expiratory effort must come from the respiratory centre in the
medulla ; with these we shall deal in speaking of respiration. The
dilation of the cardiac orifice is caused, in part at least, by efferent
impulses descending the vagi, since when these are cut real
vomiting with discharge of the gastric contents is difficult, through
want of readiness in the dilation. The sympathetic abdominal
nerves coming from the coeliac ganglia and the splanchnic nerves
seem to have no share in the matter. The efferent impulses
which cause the flow of saliva in the introductory nausea descend
the facial along the chorda tympani branch. These various
impulses may best be considered as starting from a vomiting
centre in the medulla, having close relations with the respiratory
centre. This centre may be excited, may be thrown into action,
in a reflex manner, by stimuli applied to peripheral nerves, as
when vomiting is induced by tickling the fauces, or by irritation
of the gastric membrane, or by obstruction due to ligature, hernia,
etc., of the intestine. That the vomiting in the last instance is
due to nervous action, and not to any regurgitation of the intestinal
contents, is shewn by the fact that it will take place when the
intestine is perfectly empty and may be prevented by section of
the mesenteric nerves. The vomiting attending renal and biliary
calculi is apparently also reflex in origin. The centre however
may be affected directly, as probably in the cases of some poisons,
and in some instances of vomiting from disease of the medulla
oblongata. Lastly, it may be thrown into action by impulses
reaching it from parts of the brain higher up than itself, as in
cases of vomiting, produced by smells, tastes and emotions, and by
the memory of past occasions, and in some cases of vomiting due
to cerebral disease.

Many emetics, such as tartar emetic, appear to act directly on
the centre, since, introduced into the blood, they will produce
vomiting even when a bladder is substituted for the stomach.
Others again, such as mustard and water, act in a reflex manner
by irritation of the gastric mucous membrane. With others, again,
which cause vomiting by developing a nauseous taste, the reflex
action involves parts of the brain higher than the centre itself.

19—2

SEC. 4. THE CHANGES WHICH THE FOOD UNDERGOES
IN THE ALIMENTARY CANAL.

Having studied the properties of the digestive juices, and the
various mechanisms by means of which the food is brought under
their influence, we have now to consider what, as matters of fact,
are the actual changes which the food does undergo in passing
along the alimentary canal, what are the steps by which the
food is converted into faeces.

In the mouth the presence of the food, assisted by the move-
ments of the jaw, causes, as we have seen, a flow of saliva. By
mastication, and by the addition of mucous saliva, the food is
broken into small pieces, moistened, and gathered into a convenient
bolus for deglutition. In man some of the starch is, even during
the short stay of the food in the mouth, converted into sugar ; for
if boiled starch free from sugar be even momentarily held in the
mouth, and then ejected into water (kept boiling to destroy the
ferment), it will be found to contain a decided amount of sugar.
In many animals no such change takes place. The viscid saliva of
the dog serves almost solely to assist in deglutition ; and even the
longer stay which food makes in the mouth of the horse is in-
sufficient to produce any marked conversion of the starch it may
contain. During the rapid transit through the (BSOphagTlS no
appreciable change takes place.

In the stomach, the arrival of the food, the reaction of which
is either naturally alkaline, or is made alkaline, or at least is

CHAP, i.] DIGESTION. 293

reduced in acidity, by the addition of saliva, causes a flow of
gastric juice. This, already commencing while the food is as yet
in the mouth, increases as the food accumulates in the stomach,
and as, by the churning gastric movements, unchanged particles
are continually being brought into contact with the mucous
membrane. Moreover, the absorption of the earlier digested
portions gives rise to a further increase of secretion and especially
of pepsin. The percentage of pepsin in the gastric juice (in
the dog) varies considerably, actually sinking during the earlier
stages but rising rapidly afterwards and attaining a maximum
at about the fourth or fifth hour. The secretion of acid appears
to continue at a fairly constant rate; and consequently, unless
neutralized by fresh alkaline food, the reaction of the gastric
contents becomes more and more distinctly acid as digestion
proceeds. It would appear that in man, sometimes at least, the
contents of the stomach do not at first contain any free acid and
during this period the conversion of starch into sugar can still
go on. When the contents become acid, the conversion is arrested,
and indeed the amylolytic ferment probably destroyed. The fats
themselves probably remain in great measure unchanged ; though
it would appear that in the dog at least a certain amount of fat
can be digested, that is emulsionized, or even partly split up
into fatty acids, by the action of the gastric juice, and absorbed.
Moreover even in man, through the conversion of proteids into
peptone, not only are the more distinctly proteid articles of food,
such as meat, broken up and dissolved, but the proteid framework,
in which the starch and fats are frequently imbedded, is loosened,
the starch-granules are set free, and the fats, melted for the most
part by the heat of the stomach, tend to run together in large
drops, which in turn are more or less apt to be broken up into
an imperfect emulsion. The collagenous tissues are dissolved;
and hence the natural bundles of meat and vegetables fall asunder;
the muscular fibre splits up into discs, and the protoplasm is
dissolved from the vegetable cells. Milk is at once curdled by the
rennet ferment and the clotted casein subsequently dissolved.
Since peptone and the other products of artificial digestion with
gastric juice have been found in the contents of the stomach,
we have every reason to believe that natural digestion in the
stomach agrees with the results of laboratory experiments described
in a previous section. "While these changes are proceeding, the
thick turbid greyish liquid or chyme, formed by the imperfectly
dissolved food, is from time to time ejected through the pylorus,
accompanied by even large morsels of solid less-digested matter.
This may occur within a few minutes of food having been taken;
but the larger escape from the stomach probably does not in man
begin till from one to two, and lasts from four to five hours, after
the meal, becoming more rapid towards the end, and such pieces
as most resist the gastric juice being the last to leave the stomach.

294 CHANGES OF FOOD IN THE STOMACH. [BOOK n.

The time 'taken up in gastric digestion probably varies not only
\vith different articles of food but also with varying conditions of
the stomach and of the body at large. In different animals it
varies very considerably, being from 12 to 24 hours in the dog,
while the stomachs of rabbits are never empty but always remain
largely filled with food.

In a dog fed on an exclusively meat diet, nearly the whole of
the digestion is carried out by the stomach, very little work
apparently being left for the intestines. In man, especially on
a mixed diet, the case in all probability is different, a considerable
portion of the proteids as well as the greater part of the fats and
carbohydrates passing but little changed through the pylorus.
But our information on this matter is imperfect being chiefly
drawn from the study of cases of gastric or duodenal fistula, in
which probably the order of things is not normal or being in
large measure deductions from experiments on dogs, whose economy
in this respect must be largely different from our own.

In the presence of healthy gastric juice, and in the absence of
any nervous interference, the question of the digestibility of any
food is determined chiefly by mechanical conditions. The more
finely divided the material, and the less the proteid constituents
are sheltered by not easily soluble envelopes, such as those of
cellulose, the more rapid the solution. So also pieces of hard-
boiled egg, which have to be gradually dissolved from the outside,
are less easily digested than the more friable muscular fibre, the
repeated transverse cleavage of which increases the surface exposed
to the juice. Unboiled white of egg again, unless thoroughly
beaten up and mixed with air, is less digestible than the same
boiled. The unboiled white forms a viscid clotted mass, of low
diffusibility, into which the juice permeates with the greatest
difficulty. And so with the other instances. Beyond this me-
chanical aspect of digestibility, it is to be remembered that
different substances may differently affect the gastric membrane,
promoting or checking the secretion of the juice. Hence a
substance, the mass of which is readily dissolved by gastric juice,
and which offers no mechanical obstacles to digestion, may yet
prove indigestible by so affecting the gastric membrane through
some special constituent (or possibly in other ways) as to inhibit
the secretion of the juice.

That substances can be absorbed from the cavity of the stomach
into the circulation is proved by the fact that food when introduced
disappears very largely from the stomach of an animal, the pylorus
of which has been ligatured. But we cannot speak with certainty
as to what extent in ordinary life gastric absorption takes place, or
by what mechanism it is carried out. The presumption is, that
peptone and the diffusible sugars pass by osmosis direct into the
capillaries, and so into the gastric veins. In a dog fed on meat the
quantity of peptone present at any one time in the stomach has

CHAP, i.] DIGESTION. 295

been found fairly constant. From this it may fairly be inferred
that the peptone is absorbed in proportion as it is formed.

In the act of swallowing, no inconsiderable quantity of air is
carried down into the stomach, entangled in the saliva, or in the
food. This is returned in eructations. When the gas of eructation
or that obtained directly from the stomach is examined, it is found
to consist chiefly of nitrogen and carbonic acid, the oxygen of the
atmospheric air having been largely absorbed. In most cases the
carbonic acid is derived by simple diffusion from the blood, or from
the tissues of the stomach, which similarly take up the oxygen.
In many cases of flatulency, however, it may arise from a fermen-
tative decomposition of the sugar which has been taken as such in
food, or which has been produced from the starch, the gas being
either formed in the stomach or passing upwards from the intestine
through the pylorus.

The enormous quantity of gas which is discharged through the
mouth in cases of hysterical flatulency, even on a perfectly empty
stomach, and which seems to consist largely of carbonic acid,
presents difficulties in the way of explanation ; it is possible that it
may be simply diffused from the blood.

In the small intestine, the semi-digested acid food, or chyme,
as it passes over the biliary orifice, causes gushes of bile, and at the
same time, as we have seen (p. 265), the pancreatic juice, which
flowed freely into the intestine at the taking of the meal, is
secreted again with renewed vigour, when the gastric digestion is
completed. These two alkaline fluids tend to neutralize the
acidity of the chyme, but the contents of the duodenum do not
become distinctly alkaline until some distance from the pylorus is
reached. Even in the lower part of the ileum the chyme may be
acid ; possibly however in such cases it has been reacidified in con-
sequence of acid fermentations taking place in the intestinal
contents. The reaction of these contents appears to vary in fact
according to the nature of the food, the changes which it under-
goes, and other circumstances. Moreover it is probably not the
same in all animals. In a dog fed on starch and fat, the contents
of the intestine may remain acid throughout.

The conversion of starch into sugar, which as we have seen is
probably arrested in the stomach, is resumed with great activity
and indeed completed by the pancreatic juice, possibly assisted by
the succus entericus ; portions however of still undigested starch
may be found in the large intestine and even at times in the faeces.

The pancreatic juice, as we have seen, emulsifies fats, and also
splits them into their respective fatty acids and glycerine. Tlio
fatty acids thus set free become converted by means of the alkalino
contents of the intestine into soaps ; but to what extent saponifica-
tion thus takes place is not exactly known. Undoubtedly soaps
have to a small extent been found both in portal blood and in the

296 DIGESTION OF FATS. [BOOK n.

thoracic duct after a meal ; but there is no proof that any large
quantity of fat is introduced in this form into the circulation. On
the other hand, the presence of neutral fats, both in portal blood,
and especially in the lacteals, is a conspicuous result of the diges-
tion of fatty matters ; and in all probability saponification in the
intestine is a subsidiary process, intended rather to facilitate the
emulsion of neutral fats than to introduce soaps as such into the
blood. For the presence of soluble soaps favours the emulsion of
neutral fats. Thus a rancid fat, i.e. a fat containing a certain
amount of free fatty acid, forms an emulsion with an alkaline fluid
more readily than does a neutral fat. A drop of rancid oil let fall
on the surface of an alkaline fluid, such as a solution of sodium
carbonate of suitable strength, rapidly forms a broad ring of emul-
sion, and that even without the least agitation. As saponification
takes place at the junction of the oil and alkaline fluid currents
are set up, by which globules of oil are detached from the main
drop and driven out in a centrifugal direction. The intensity of
the currents and the consequent amount of emulsion depend on
the concentration of the alkaline medium and on the solubility of
the soaps which are formed ; hence some fats such as cod-liver oil
are much more easily emulsionized in this way than others. Now
the bile and pancreatic juice supply just such conditions as the
above for emulsionizing fats : they both together afford an alkaline
medium, the pancreatic juice gives rise to an adequate amount of
free fatty acid, and the bile in addition brings into solution the
soaps as they are formed. So that we may speak of the emulsion
of fats in the small intestine as being carried on by the bile and
pancreatic juice acting in conjunction ; and as a matter of fact the
bile and pancreatic juice do largely emulsify the contents of the
small intestine, so that the greyish turbid chyme is changed into a
creamy-looking fluid, which has been sometimes called chyle. It
is advisable however to reserve this name for the contents of the
lacteals.

This mutual help of bile and pancreatic juice in producing an
emulsion, explains to a certain extent the controversy which long
existed between those who maintained that the bile and those who
maintained that the pancreatic juice was necessary for the diges-
tion and absorption of fatty food. That the pancreatic juice does
produce in the intestine such a change as favours the transference
of neutral fats from the intestine into the lacteals, is shewn by the
fact that in diseases affecting the pancreas, much fatty food
frequently passes through the intestine undigested, and great
wasting ensues ; but it cannot be maintained that the pancreatic
juice is the sole agent in this matter, since in animals in which the
pancreatio ducts have been successfully ligatured chyle is still
found in the lacteals. On the other hand, that the bile is of use in
the digestion of fat is shewn by the prevalence of fatty stools in
cases of obstruction of the bile-ducts; and though the operation of

CHAP, i.] DIGESTION. 297

ligaturing the bile-ducts, and leading all the bile externally through
a fistula of the gall bladder, is open to .objection, since it so
exhausts the animal as indirectly to affect digestion, still the
results of Bidder and Schmidt, in which the resorption of fat was
distinctly lessened (the quantity of fat in the lacteals falling from
3*2 to *02 p.c.) by the ligature and fistula, obviously point to the
same conclusion. That in man the succus entericus possesses a
wholly insufficient emulsifying power is shewn by the observation
of Busch, in a case where the duodenum opened on the surface by
a fistula in such a way that the lower part of the intestine could
be kept free from the contents of the upper part containing the
bile and pancreatic juice and matters proceeding from the stomach.
Fats introduced into the lower part, where they could not be acted
upon either by the bile or by the pancreatic juice were but slightly
digested. Without denying the possible assistance of the succus
entericus, or even of gastric juice, we may conclude that the diges-
tion of fat is in the main carried out by the conjoint action of bile
and pancreatic juice.

We have seen that the addition of bile to a digesting mixture
gives rise to a precipitate consisting of parapeptone, and bile salts
with some pepsin, but that on the further addition of bile this pre-
cipitate is redissolved. In the upper part of the duodenum the
inner surface, if examined while digestion is going on, is found to be
lined by a coloured granular material, which is probably a precipi-
tate thus formed ; but the purpose of its formation does not seem
. clear. It is more important to remember that not only is bile anta-
gonistic to peptic digestion, but apparently pepsin is destroyed by
trypsin in an alkaline medium, so that with the flow of bile and
pancreatic juice into the duodenum the processes which have been
going on in the stomach come to an end. In fact it would seem
that the juices of the various districts of the alimentary canal are
mutually destructive; thus, while pepsin in an acid solution de-
stroys the active constituents of saliva, and of pancreatic juice (pro-
bably also those of the succus entericus), it is in its turn antagonized
or destroyed by the bile and the other alkaline juices of the intes-
tine. Hence pancreatic juice introduced through the mouth must
lose its powers in the stomach and can only be of use as an alkaline
medium containing certain proteid matters. On the other hand if,
as we have reason to believe, the contents of the stomach as they
issue from the pylorus still contain a large quantity of undigested
proteids, these must be digested by the pancreatic juice (with or
without the assistance of the succus entericus), the action of which
seems to be assisted or at least not hindered by bile. To what
stage the pancreatic digestion is carried, whether peptone is chiefly
formed, and when formed at once absorbed, or whether the pan-
creatic juice in the body, as out of the body, carries on its work
in the more destructive form, whereby the proteid material sub-
jected to it is broken dawn largely into leucin and tyrosin, is

298 DIGESTION OF FATS. [BOOK IT.

at present not exactly known. Leucin and tyrosin have been
found in the intestinal contents, and may therefore be formed
during normal digestion, but whether a large quantity or a small
quantity of the proteid material of food is thus hurried into
a crystalline form cannot be definitely stated. The extent to
which the action is carried is probably different in different
animals, and varies also according to the nature of the meal and
the condition of the body. Possibly when a large and unnecessary
quantity of proteid material is taken at a meal together with other
substances, no inconsiderable amount of the proteids undergo this
profound change, and, as we shall see, rapidly leave the body as
urea, without having been used by the tissues, their contribution
to the energy of the body being limited to the heat given out
during their formation. To this apparently wasteful use of
proteids we shall return in speaking of what is called the 'luxus
consumption ' of food.

Possibly also, in the intestines as in the laboratory, this
pancreatic digestion of proteids in excess is accompanied by a
considerable development of bacteria and other organized bodies,
which create trouble by inducing fermentative changes in the
accompanying saccharine constituents of the chyme. That fer-
mentative changes may occur in the small intestine is indicated
by the facts that the gas present there may contain free hydrogen,
and that chyme after removal from the intestine continues at
the temperature of the body to produce carbonic acid and hydrogen
in equal volumes. This suggests the possibility of the sugar of
the intestinal contents undergoing the butyric acid fermentation
(during which, as is well known, carbonic anhydride and hydrogen
are evolved) and thus, so to speak, put on its way to become fat ;
and we shall see hereafter that sugar is somewhere in the body
converted into fat. Moreover it is probable that by other fermen-
tative changes a considerable quantity of sugar is converted into
lactic acid, since this acid is found in increasing quantities as the
food descends the intestine.

Thus during its transit through the small intestine, by the
action of the bile and pancreatic juice, assisted possibly to some
extent by the succus entericus, the proteids are largely dissolved
and converted into peptone and other products, the starch is
changed into sugar, the sugar possibly being in part further con-
verted into lactic acid, and the fats are largely emulsified, and
to some extent saponified. These products, as they are formed,
pass into either the lacteals or the portal blood-vessels, so that the
contents of the small intestine, by the time they reach the ileo-
csecal valve, are largely but by no means wholly deprived of their
nutritious constituents. As far as water is concerned, the secretion
into the small intestine is about equal to the absorption from it, so
that the intestinal contents at the end of the ileum, though much
more broken up, are about as fluid as in the duodenum.

CHAP, i.] DIGESTION. 299

In the large intestine, the contents become once more distinct-
ly acid. This, however, is not caused by any acid secretion from
the mucous membrane : the reaction of the intestinal walls in the
large as in the small intestine is alkaline. It must therefore arise
from acid fermentations going on in the contents themselves ; and
that fermentations do go on is shewn by the appearance of marsh
gas as well as hydrogen in this portion of the alimentary canal.
The character and amount of fermentation probably depend
largely on the nature of the food and probably also vary in
different animals.

Of the particular changes which take place in the large
intestine we have no definite knowledge; but it is exceedingly
probable that in the voluminous caecum of the herbivora, a large
amount of digestion of a peculiar kind goes on. We know that in
herbivora a considerable quantity of cellulose disappears in passing
through the alimentary canal, and even in man some is probably
digested. It seems probable that this cellulose digestion is carried
on in the large intestine, though we know nothing of the nature of
the agency by which it is effected, and possibly the conversion may
take place elsewhere as well ; indeed recent evidence goes to shew
that in ruminants the change takes place in part in the stomach
and that it is effected by the saliva. The other digestive changes
are probably of a fermentative kind.

Be this as it may, whether digestion, properly so called, is all
but complete at the ileo-csecal valve, or whether important changes
still await the chyme in the large intestine, one great characteristic
of the work done in the colon is absorption. By the abstraction of
all the soluble constituents, and especially by the withdrawal of
water, the liquid chyme becomes as it approaches the rectum con-
verted into the firm solid faeces, and the colour shifts from the
bright orange, which the grey chyme gradually assumes after
admixture with bile, into a darker and dirtier brown.

In the faeces there are found in the first place the indigestible
and undigested constituents of the meal : shreds of elastic tissue,
hairs and other corneous elements, much cellulose and chlorophyll
from vegetable, and some connective tissue from animal food, frag-
ments of disintegrated muscular fibre, fat-cells, and not unfre-
quently undigested starch-corpuscles. The amount of each must of
course vary very largely, according to the nature of the food, and
the digestive powers, temporary or permanent, of the individual.
In the second place, to these must be added substances, not
introduced as food, but arising as part of, or as products of, the
digestive secretions. The fasces contain a ferment similar to
pepsin, and an amylolytic ferment similar to that of saliva or
pancreatic juice. They also contain mucus in variable amount,
sometimes albumin, cholesterin, butyric and other fatty acids, lime
and magnesia soaps, excretm (a non-nitrogenous crystalline body,

300 CHANGES OF FOOD IN THE FAECES. [BOOK n.

containing sulphur, obtained by Marcet), colouring matters, and
salts, especially those of magnesia. Cholalic acid (and dyslysin)
are found in very small quantities only, thus indicating that the
bile-salts have been in part at least destroyed (they may have
been in part reabsorbed, see p. 280), the less stable taurocholic
acid (of the dog) disappearing more readily than the glycocholic
acid (of the cow). The fact that the faeces become ' clay-coloured '
when the bile is cut off from the intestine shews that the bile-
pigment is at least the mother of the faecal pigment ; and a special
pigment, which has been isolated and called stercobilin, is said to
be identical with the substance called urobilin, which may be
formed from bilirubin1. We have already seen that during artificial
pancreatic digestion, a distinctly faecal odour due to the presence of
indol is generated ; and the fact that the presence of bacteria, or
other similar organisms, is essential to the production of this body,
does not preclude the possibility of it (or of the allied body skatol,
having an evil faecal odour, formed after prolonged putrefaction of
the pancreas and present in human excrement) being the chief
cause of the natural odour of faeces, for undoubtedly bacteria may
exist throughout the whole length of the intestinal canal. At the
same time it is quite possible, that specific odoriferous substances
may be secreted directly from the intestinal wall, especially from
that of the large intestine.

1 See Appendix.

V

SEC. 5. ABSORPTION OF THE PRODUCTS OF DIGESTION.

We have seen that absorption does, or at least may, take place
from the stomach. We have also stated that a large absorption,
especially of water, occurs along the whole large intestine. We
may add that absorption from the large intestine after injection
per anum or through a fistula has been observed not only in the
case of soluble peptone and sugar, but also in that of starch, white
of egg, and casein, though the exact changes undergone by the
latter previous to absorption are as yet unknown.

Nevertheless the largest and most important part of the digested
material passes away from the canal, during the transit of food
along the small intestine, partly into the lacteals, partly into the
portal vessels. The portal vessels are simply parts of the general
vascular system, but the lacteals, into which we may at once say
the greater part of the fat passes, need special attention.

The Lymphatics.

Characters of Chyle. In a fasting animal the contents of the
thoracic duct are clear and transparent ; shortly after a meal they
become milky and opaque, the change being entirely due to a
difference in the quality and quantity of the fluid brought to
the duct by the lacteals, that fluid also being, as seen by inspection

302 CHYLE. [BOOK n.

of the mesentery, transparent during fasting, and becoming milky
and opaque after a meal, especially after one containing much fat.
The contents of the thoracic duct therefore after a meal may be
taken as illustrative of the nature of the chyle present in the
lacteals, though strictly speaking the chyle of the thoracic duct
is mixed with lymph coming from the intestines and from the rest
of the body. During fasting the contents of the lacteals agree in
their general character with lymph obtained from other structures.

The contents of the thoracic duct may be obtained by laying bare
the junction of the subclavian and jugular veins and introducing a
caiinula into the duct as it enters into the venous system at that point.
The operation is not unattended with difficulties.

Chyle obtained from the thoracic duct, after a meal, is a white
milky-looking fluid, which after its escape coagulates, forming a
not very firm clot. The nature of the coagulation seems to be
exactly the same as that of blood. The surface of the clot after
exposure to air becomes pink, even though no blood be artificially
mixed with the chyle during the operation; the colour is due
to immature red corpuscles proper to the chyle. Examined micro-
scopically, the coagulated chyle consists of fibrin, a large number
of white corpuscles, a small number of developing red corpuscles,
an abundance of oil-globules of various sizes but all small, and
a quantity of fatty granules, too minute to be recognised under the
microscope as fatty in nature, forming the so-called ' molecular
basis.' Each oil-globule is invested with an albuminous envelope ;
this may be dissolved by the aid of alkalis, whereupon the globules
run together. The fibrin and white corpuscles are very scanty
(and the red corpuscles entirely absent) in lymph or chyle taken
from peripheral vessels; but they increase in quantity as the
lymph passes through the lymphatic glands.

. The composition of chyle varies considerably not only in differ-
ent animals but in the same animal at different times. The average
percentage of solids may perhaps be put down as about 9, that of
proteid material as about 4 or 5, and that of fat as about 3 or 4
(though the latter may sometimes rise as high as 14), the remainder
being extractives and salts. The fats occur chiefly in the form of
neutral fats, though some soaps or fatty acids are present. Some
amount of lecithin, and cholesterin in considerable quantity, are
also frequently present.

The proteids consist chiefly of serum-albumin, with a globulin,
probably paraglobulin, and a variable but small quantity of fibrin.
Among the extractives have been found sugar, urea, and leucin ;
since these are found in lymph as well as chyle they cannot be
regarded as derived exclusively from the intestinal contents. The
ash is remarkable for the abundance of sodium chloride and the
scantiness of phosphates. Iron is present in greater quantity than
can be accounted for by the presence of red corpuscles.

CHAP, i.] DIGESTION. 303

The nature of the fat is supposed to vary with that of the food,
but this has not been conclusively shewn.

The lymph taken from the duct during fasting differs chiefly
from that taken after a meal, in the much smaller quantity of fat,
the microscope shewing besides the white corpuscles only very few
oil-globules, and in the almost entire absence of the molecular basis.
Lymph in fact is, broadly speaking, blood minus its red corpuscles,
and chyle is lymph plus a very large quantity of minutely divided
neutral fat.

It has been calculated that a quantity equal to that of the
whole blood may pass through the thoracic duct in 24 hours, and of
this it is supposed that about half comes from food through the
lacteals and the remainder from the body at large ; but these cal-
culations are based on uncertain data.

Entrance of the Chyle into the Lacteals. The lacteal begins
as a club-shaped (or bifurcate) lymphatic space lying in the centre
of the villus, and connected with the smaller lymphatic spaces of the
adenoid tissue around it; it opens below into the submucous lymph-
atic plexus from which the lacteal vessels spring. The adenoid
tissue of the surrounding crypts of Lieberkiihn is by its lymphatic
spaces connected with the same lymphatic plexus. That the finely-
divided fat does pass from the intestine, through the epithelial
envelope of the villus, into the adenoid tissue, and so into the
lacteal chamber, is certain, but much discussion has arisen as to the
exact mechanism of the transit. Most observers agree that after a
meal the epithelium cells of the villus are loaded with fat and that
this fat is derived from the intestinal contents. Since the striation
of the hyaline border of the cells is not due to pores, as was once
thought, the particles must have entered into the cells very much
as foreign particles enter the body of an amoeba. The epithelium
may thus be said to eat the fat, and subsequently to pass it on
into the lymphatic spaces of the adenoid tissue of the villus and so
into the central lymphatic chamber. There would thus be a stream
of fatty particles through the cell from without inwards, a stream
in the causation of which the cell took an active part. In fact,
under this view, absorption by the cell might be regarded as a sort
of inverted secretion, the cell taking much material from the chyme
and secreting it, with little or ne change, into the villus. Other
observers however believe that the fat passes not through but be-
tween the epithelium-cells, being taken by the inter-epithelial pro-
cesses of the peculiar epitheloid-cells, described as forming a con-
tinuous protoplasmic reticulum, connecting the surface of the villus
with the central chamber. Along this reticulum the fat is sup-
posed to travel, the epithelium cells themselves having no active
share in absorption.

The passage is probably assisted by the movements of the in-
testine, though even in the contractions of strong peristaltic move-

304 MOVEMENTS OF CHYLE AND LYMPH, [BOOK n.

ments the pressure within the intestine is never very great. Of
more obvious use is the contraction of the villus itself. The longi-
tudinal muscular fibre-cells, in contracting, pull down the villus on
itself; the contents of the lacteal chamber are thus forced into the
underlying lymphatic plexus. When the fibre-cells relax, the
empty lacteal chamber is expanded ; the chyle cannot flow back
from the lymphatic channels by reason of the valves present in
them, and in consequence the lacteal chamber is filled from the
substance of the villus, and thus the entrance into the villus of
material from the intestine is facilitated. The villus in fact acts as
a kind of muscular suction-pump.

Movements of the Chyle. Having reached the lymphatic chan-
nels the onward progress of the chyle is determined by a variety of
circumstances. Putting aside the pumping action of the villi, the
same events which cause the movement of the lymph generally also
further the flow of the chyle ; and these are briefly as follows. In
the first place, the wide-spread presence of valves in the lymphatic
vessels causes every pressure exerted on the tissues in which they
lie to assist in the propulsion forward of the lymph. Hence a 1
muscular movements increase the flow. If a cannula be inserted
in one of the larger lymphatic trunks of the limb of a dog, the dis-
charge of lymph from the cannula will be more distinctly increased
by movements, even passive movements, of the limb than by any-
thing else. In addition to the valves along the course of the
vessels, the embouchement of the thoracic duct into the venous
system is guarded by a valve, so that every escape of lymph or chyle
from the duct into the veins becomes itself a help to the flow. In
the second place, we have already seen that the blood-pressure in
the capillaries and minute vessels is considerably greater than that
in the large veins, such as the jugular ; in fact this difference of
pressure is the cause of the flow of blood from the capillaries to the
heart. Now the lymph in the lymphatic spaces outside the capil-
laries and minute vessels undoubtedly stands at a lower pressure
than the blood inside the capillaries ; otherwise the transudation
from the blood into the tissues would be checked ; but the differ-
ence is probably not great. So that the lymph in the lymphatic
spaces of the tissues may still be considered as standing at a higher
pressure than the blood in the venous trunks, for instance in the
jugular vein. That is to say the lymphatic vessels as a whole form
a system of channels leading from a region of higher pressure, viz.
the lymphatic spaces of the tissues, to a region of lower pressure, viz.
the interior of the jugular and subclavian veins. This difference of
pressure will, as in the case of the blood-vessels, cause the lymph to
flow onward in a continuous stream. Further, this flow, caused by
the lowness of the mean venous pressure at the subclavian, will be
assisted at every respiratory movement, since at every inspiration
the pressure in the venous trunks becomes negative, and thus

CHAP, i.] DIGESTION. 305

lymph will be sucked in from the thoracic duct, while the increase
of pressure in the great veins during expiration is warded off from
the duct by the valve at its opening. In the third place, the flow
may possibly be increased by rhythmical contractions of the
muscular walls of the lymphatics themselves ; but this is doubtful,
since it is not clear whether the rhythmic variations which have
been observed in the lacteals of the mesentery of the guinea-pig are
active or simply passive, i.e. caused by the rhythmic peristaltic
action of the intestine, each contraction of the intestine filling the
lymph- channels more fully. Lastly, it is quite open for us to sup-
pose that just as osmosis may give rise to increased pressure on one
side of a diffusion septum, so the diffusion of substances from the in-
testines into the lacteals, or from the tissues into the lymphatics,
may be itself one of the causes of the flow of lymph. We have
at least, under all circumstances, one or other of these causes at
work promoting a continual flow from the lymphatic roots to the
great veins. We have no very satisfactory evidence that the flow of
lymph is in any way directly governed by the nervous system. We
cannot prove any direct connection between the nervous system
and absorption, though the phenomena of disease render such a
connection at least probable.

That the nervous system does exert an influence on absorption
is shewn by the following experiment, though probably in this
case the influence is an indirect one carried out through the medi-
ation of the vascular system. Of two frogs placed under the in-
fluence of urari so as to do away with muscular movements and
the action of the lymph-hearts, the brain and spinal cord are de-
stroyed in the one but in the other are left intact. Both animals
are suspended by the lower jaw ; chloride of sodium solution (75
per cent.) is poured into the dorsal lymphatic sacs of both ; and in
both the aorta is cut across. In the one where the nervous system
is intact, absorption from the lymphatic sac takes place copiously
and the heart pumps out large quantities of fluid by the aorta,
In the other, absorption does not occur; the heart, though beating,
remains empty, and the skin becomes dry. The experiment
probably shews the influence of the nervous system in maintaining
the tonicity of the blood-vessels and keeping up the connection of
the heart with the peripheral vessels, rather than any direct con-
nection between absorption proper and the nervous system.
When the nervous system is destroyed, dilation of the splanchnic
vascular area causes all the blood to remain stagnant in the portal
vessels, and probably these as well as other veins are rendered
unusually lax, so that the blood is largely retained in the venous
system, and very little reaches the heart; and with the enfeebled
circulation the absorption from the lymphatic sac is slight. So
long as the nervous system is still intact this stagnation does not
occur, the blood reaches the heart as usual, and with the more
vigorous circulation absorption from the lymphatic sac goes on

F. 20

306 LYMPH HEARTS. [BOOK n.

rapidly. As the blood is pumped away its place is renewed by the
lymph, supplied by the fluid in the sac, and thus the heart may be
made for a long time to pump away the fluid poured into the sac.

Lymph hearts. In frogs and some other animals the centri-
petal flow of lymph from the limbs is assisted by rhythmically
pulsating muscular lymph hearts, which present many curious
analogies with the blood-heart. In the frog, in which they have
been chiefly studied, their action as we have already stated (p. 108)
is in a measure dependent on the spinal cord. The posterior lymph
hearts belonging to the hind limbs are connected by means of the
delicate tenth pair of spinal nerves, with a region of the cord
opposite the sixth or seventh vertebra, in such a way that section
of the nerve or destruction of the particular region of the cord
suspends or destroys their activity. The anterior pair are similarly
connected with a region of the spinal cord opposite the third
vertebra. Each pair therefore seems to have a 'centre' in the spinal
cord; but it is probable, though observers are not wholly agreed,
that the hearts, after destruction of their spinal centre, ultimately
resume their rhythmic beats, so that the dependence of their
activity on the spinal centre, like the similar dependence of the
blood heart on the ganglia of the sinus venosus, is not an absolute
one. Like the blood heart, the lymph hearts may be inhibited,
and that in a reflex manner, the inhibition centre being moreover
in the medulla oblongata. If a frog be carefully observed, the
activity of the lymph hearts will be found to vary largely, and these
variations appear to be in part due to nervous influences ; so that
in this way the movement of lymph, and hence the processes of
absorption, are in this animal directly dependent on the nervous
system.

The course taken by the several products of digestion.

Digestion being, broadly speaking, the conversion of non-
diffusible proteids and starch into highly diffusible peptone and
sugar, and the emulsifying, or division into minute particles, of
various fats, it is natural to suppose that the diffusible peptone
and sugar pass by osmosis into the portal vessels and so directly
into the blood, and that the emulsified fats pass into the lacteals
and so indirectly into the blood. That a large part of the fat
which enters the body from the intestine does pass through the
lacteals, there can be no doubt ; and there can be but little doubt
that a considerable quantity of peptone and sugar does pass into
the portal blood. But the question as to how far the fat in its
difficult passage into the lacteal is accompanied by soluble peptone,

CHAP, i.] DIGESTION. 307

or by less diffusible forms of proteids arising as subsidiary products
of proteolytic digestion or by carbohydrate products, deserves
attention.

It cannot be a matter of indifference which course is taken by
the particular digestive products. For if they pass by the portal
vein they fall into the general blood-current after having undergone
only such changes as they may experience in the lymphatic system ;
while if they pass into the portal vein they are subjected to the
powerful influences of the liver before they find their way to the
right side of the heart. What those influences are we shall study
in a future chapter.

Fats. As we have seen, a special mechanism is provided for
the passage of fats into the lacteals. On the other hand, it is
difficult to suppose that solid particles of fat can pass into the
interior of the blood capillaries. So that we are led a priori to
the view that the whole of the fat takes the course of the lacteals.
But we cannot say that this is definitely proved. On the contrary,
a large deficit is observed when the quantity of fat disappearing
after a meal from the alimentary canal is compared with that
flowing out through a cannula placed in the end of the thoracic
duct; and if it be true, as is stated, that the blood of the portal
vein contains during digestion more fat than the general venous
blood, some of this deficit may be explained by the fat passing
into the blood capillaries, difficult as that passage may appear.
The portal blood, moreover, during digestion contains a small but
appreciable quantity of soaps. It may be however that the deficit
observed is due to some of the fat disappearing in some way, in
the glands for instance, from the interior of the- vessels in its
transit.

The fat thus entering the blood either directly or indirectly is
rapidly got rid of in some way or other, for from experiments on
dogs it would appear that the percentage of fat in the blood
after a meal rich in fat, does not, after the lapse of 20 hours
from the swallowing of the food, differ materially whether the
fat has been during the whole time shut off from the blood by
being allowed to flow out of a cannula placed in the thoracic duct,
or has been allowed to pass into the venous system in the usual
way.

Proteids. The question as to the course taken by the digested
proteids is complicated by the insufficiency of our knowledge con-
cerning the exact stages to which the digestion of proteids is
naturally carried in the alimentary canal. If we take it for
granted that the proteids taken as food are reduced to the
condition of soluble and diffusible peptone, it seems easy to
suppose that the proteids of food pass by diffusion as peptone into
the blood capillaries which as is well known are placed in the villus
between the epithelium and the lacteal chamber; though even

20—2

308 ABSORPTION OF PROTEIDS. [BOOK n.

on this view it is open for us to imagine that all the peptone
which passes through the epithelium is not intercepted by the
blood capillaries, but that some reaches and passes away by the
more centrally placed lacteal. It is difficult to imagine how
proteids in any other form than that of diffusible peptone can
pass through the walls of the blood capillaries ; though perhaps the
difficulty is not insurmountable, seeing that our conceptions of
nutrition are based on the assumption that the natural proteids of
the blood plasma pass from the interior of the vessels into the
extravascular elements of the tissues ; and we might imagine that
an accumulation of proteids in the same extravascular spaces
might cause a reversal of the proteid current, and thus lead
to proteids other than peptone passing through the vascular walls.
On the other hand it is at least open for us to ask the question, If
solid particles of fat can pass from the interior of the alimentary
canal into the lacteals, why should not various forms of proteids
pass in the same way into the lacteals, either in solution or even
as solid particles?

It would thus seem possible for some of the proteids to pass
into the lacteals and so into the system in a less digested form
than peptone; and it is further possible that the proteids thus
entering into the system in different forms may play different parts
in the nutritive labours of the economy.

But in all these considerations the fact must be borne in mind
that the intestinal walls undoubtedly possess a selective power of
absorption, which overrides the laws of diffusion and solubility.
This is shewn for instance by an observation made on a dog, in
which such fairly soluble and diffusible salts as sodium tauro-
cholate and glycocholate were found not to be absorbed by the
duodenum and upper jejunum even at a time when fat was being
rapidly absorbed in those regions, but to disappear in the ileum or
lower jejunum, the glycocholate apparently being absorbed by both
the ileum and lower jejunum, while the taurocholate passed away
in the ileum alone.

We cannot judge therefore of the course taken by the proteids,
or of the form in which they are absorbed, by deductions based on
solubility and diffusion. The problems we are discussing can only
be satisfactorily settled by direct experiment. And here we meet
with difficulties. If all proteids are converted into peptone, and
so pass into the lacteals or into the blood capillaries, we might
expect to find a quantity of peptone in the chyle or in portal
blood or in both after a proteid meal. Now all observers are
agreed that peptone is absent from chyle or at least that its
presence cannot be satisfactorily proved, in spite of the possi-
bility of its entering into the lacteals together with the fat. And
while some have succeeded in finding peptone in the blood after
food, but not during fasting, many have failed to demonstrate the
presence of peptone in the blood either of the portal vein or of the

CHAP, i.] DIGESTION. 309

vessels at large even after a meal containing large quantities
of proteids. Of course the quantity of peptone passing into the
portal blood at any moment might be small, and yet a considerable
quantity might so pass during the hours of digestion. We may
suppose moreover that that which does pass is immediately con-
verted, possibly by some ferment action, into one or other of the
natural proteids of the blood, or otherwise disposed of; and indeed
peptone injected carefully into a vein disappears from the blood,
though little or even none passes out by the kidney. And the
view that peptone is so changed, possibly in the very act of
absorption, is supported not only by the fact that peptone may be
found in the walls of the intestine even when it appears to be
absent from the blood, but also and especially by the following
observation. If an artificial circulation of blood be kept up in the
mesenteric arteries supplying a loop of intestine removed from the
body, the loop may be kept alive for some considerable time.
During this survival a considerable quantity of peptone placed in
the cavity of the loop, will disappear, i.e. will be absorbed, but
cannot be recovered from the blood which is being used for the
artificial circulation, and which escapes from the veins after
traversing the intestinal capillaries. The disappearance is not
due to any action of the blood itself, for peptones introduced into
the blood before it is driven through the mesenteric arteries in the
experiment may be recovered from the blood as it escapes from
the mesenteric veins. It would seem as if the peptone were
changed before it actually gets into the capillaries.

But the argument that the absence of peptone from the blood
is no proof that peptones are not absorbed into the blood may also
be applied to the chyle. We have however an indirect proof that
peptones do not pass into the chyle. We shall see hereafter that
the quantity of urea passing by the kidney may, with certain pre-
cautions, be taken as a measure of the quantity of proteid material
taken into the body. Now when a cannula is placed in the thoracic
duct of a dog so that all the chyle passes away and is lost to the
blood, the amount of urea leaving the body by the kidney does
not materially differ from the amount which, with the same food,
is passed, when all the chyle flows into the blood. Did any
large quantity of peptone (or proteid) pass by the chyle we
should expect to find the urea much diminished Hence except
on the very improbable view that proteids absorbed into the
lacteals of the villi escape from the lymphatic system before they
reach the thoracic duct, we must accept the view which seems to
follow legitimately from the results of artificial digestion, that
proteid food is converted into peptone and so passes from the
alimentary canal into the blood. And we know that artificially-
formed peptone is available for nutrition ; for dogs fed on peptone
and non-nitrogenous food may actually put on flesh and gain in
weight.

310 ABSORPTION BY DIFFUSION. [BOOK n.

Sugar. With regard to the path taken by the sugar, careful
inquiries shew that the percentage of sugar both in chyle and in
general blood is fairly constant, being to no marked extent in-
creased by even amylaceous meals ; but that a meal of sugar or
starch does temporarily increase the quantity of sugar in the
portal blood. From this we may infer that such portions of the
sugar of the intestinal contents as are absorbed as sugar pass
exclusively by the portal vein. But it must be remembered that
at present we have no accurate information as to how large a
proportion of the sugar resulting from a meal passes in this way
unchanged until it reaches the liver, and how much undergoes the
lactic acid or analogous fermentation. Nor do we know as yet
how much of the starch taken as food is removed from the
alimentary canal in the form not of sugar but of dextrin.

When a solution of sugar is injected into an empty isolated
loop of intestine a large quantity disappears, without the contents
of the loop becoming acid. In such a case it may fairly be
inferred that the sugar is directly absorbed without undergoing
any change. And where sugar is introduced in large quantities
into the alimentary canal, the percentage of sugar in the blood
may be temporarily increased; to such an extent indeed that
sugar may appear in the urine. But neither of these facts prove
that the sugar of an ordinary meal, passing as it does along the
intestine with the other portions of the food, and products of
digestion, and appearing as it does in most cases in comparatively
small quantities at a time owing to the more or less gradual con-
version of the starch of the meal, is similarly absorbed unchanged ;
while in order that the marked acidity of the contents of the
lower intestine should be kept up, a considerable quantity of
sugar must suffer lactic acid fermentation, if the acidity be due as
stated to lactic acid.

To sum up, the evidence is distinctly in favour of the fats
passing largely by the chyle, and of the proteids and sugar passing
largely by the portal vein ; but there still remains much doubt as
to the course and fate of a not inconsiderable portion of the fat,
and the question as to the exact form in which proteids and
carbohydrates leave the alimentary canal, cannot be answered in a
perfectly definite manner.

Absorption by diffusion. It is evident, from the discussion
just concluded, that simple diffusion is far from explaining the
whole transit of the digested food from the intestine into the
blood. Nevertheless, it must not be supposed that the great
and general property of diffusion does not make itself felt in the
process of absorption, however much it may, in the case of various
substances, be subordinated and held in check by more potent
influences. Thus the passage of water from the alimentary cavity
into the blood, or from the blood into the alimentary cavity, and

CHAP, i.] DIGESTION. 311

the behaviour of various inorganic salts, when taken as food or
medicine, illustrate very clearly the influence of osmosis. When
the intestine contains a large quantity of watery matter, the
surplus water passes by diffusion into the blood, just as it passes
through the membrane of a dialyser, with blood or serous fluid on
the one side, and water on the other. When an albuminous fluid
of the specific gravity of blood-serum is exposed in a dialyser to
water, about 200 parts of water pass through the membrane of the
dialyser from the water into the albuminous fluid for every one
part of the albumin which passes from the fluid into the water.
Moreover, in the living body, the blood in the mesenteric capillary,
thus diluted by diffusion from the intestinal contents, is con-
tinually being replaced by fresh blood concentrated by its passage
through the skin, lung, or kidney. By the help of the circulation
an almost unlimited quantity of water can be absorbed from the
alimentary canal.

It is a matter of common experience that such inorganic and
organic salts as are readily diffusible, pass with great rapidity into
the blood (and thus into the urine) when taken by the mouth ; and
the rapidity with which they are absorbed is in large measure pro-
portionate to their diffusibility. Of course, coincident with this
passage of the salt from the intestine into the blood, there is a
proportionate current of water in the contrary direction from the
blood into the intestine; but this, though opposed to, is, under
ordinary circumstances, too small to diminish to any serious extent
the passage of water from the intestine into the blood, of which we
spoke just now, as caused by the osmotic influence of the albuminous
constituents of the blood. But, under certain circumstances, the
former may overcome the latter. Thus, when a concentrated solu-
tion of a highly diffusible salt, such as magnesium sulphate, is in-
troduced into the alimentary canal, the flow of water from the blood
into the intestine accompanying the osmotic transit of the salt from
the intestine into the blood, is so great as largely to exceed the
current in the contrary direction ; and the intestine becomes filled
with water at the expense of the blood. This is probably the cause of
the purgative action of large doses of many saline substances. And
even the purgative action of more dilute solutions may be explained
in the same way, since in the case of some salts at least the transit
of water as compared with the transit of the salt is relatively more
rapid with very dilute solutions than with more concentrated solu-
tions. Salts such as these, which, when introduced into the intes-
tine, produces diarrhoea, bring about a contrary condition when
injected directly into the blood ; and magnesium sulphate, with its
higher endosmotic equivalent, is more purgative in its action than
sodium chloride with its lower equivalent.

CHAPTER II.
THE TISSUES AND MECHANISMS OF RESPIRATION.

WE have already seen (Introduction, p. 3) that one particular item
of the body's income, viz. oxygen, is peculiarly associated with one
particular item of the body's waste, viz. carbonic acid, the means
which are applied for the introduction of the former being also used
for the getting rid of the latter. Both are gases, and in consequence
the ingress of the one as well as the egress of the other is far more
dependent on the simple physical process of diffusion than on any
active vital processes carried on by means of tissues. Oxygen
passes from the air into the blood mainly by diffusion, and mainly
by diffusion also from the blood into the tissues ; in the same way
carbonic acid passes mainly by diffusion from the tissues into the
blood, and from the blood into the air. Whereas, as we have seen,
in the secretion of the digestive juices the epithelium-cell plays an
all-important part, in respiration the entrance of oxygen from the
lungs into the blood, and from the blood into the tissue, and the
passage of carbonic acid in the contrary direction, are affected, if at
all, in a wholly subordinate manner, by the behaviour of the pul-
monary, or of the capillary epithelium. What we have to deal with
in respiration then is not so much the vital activities of any par-
ticular tissue, as the various mechanisms by which a rapid inter-
change between the air and the blood is effected, the means by
which the blood is enabled to carry oxygen and carbonic acid to and

CHAP, ii.] RESPIRATION. 313

from the tissues, and the manner in which the several tissues take
oxygen from and give carbonic acid up to the blood. We have
reasons for thinking that oxygen can be taken into the blood, not
only from the lungs, but also from the skin, and, as we have seen,
occasionally from the alimentary canal also ; and carbonic acid cer-
tainly passes away from the skin, and through the various secretions,
as well as by the lungs. Still the lungs are so eminently the chan-
nel of the interchange of gases between the body and the air, that
in dealing at the present with respiration, we shall confine ourselves
entirely to pulmonary respiration, leaving the consideration of the
subsidiary respiratory processes till we come to study the secretions
of which they respectively form part.

SEO. 1. THE MECHANICS OF PULMONARY RESPIRATION.

The lungs are placed, in a semi-distended state, in the air-tight
thorax, the cavity of which they, together with the heart, great
blood-vessels and other organs, completely fill. By the contraction
of certain muscjes the cavity of the thorax is enlarged ; in conse-
quence the pressure of the air within the lungs becomes less than
that of the air outside the body, and this difference of pressure
causes a rush of air through the trachea into the lungs until an
equilibrium of pressure is established between the air inside and
that outside the lungs. This constitutes inspiration, tlpon the
relaxation of the inspiratory muscles (the muscles whose contraction
has brought about the thoracic expansion), the elasticity of the
lungs and chest-walls, aided perhaps to some extent by the contrac-
tion of certain muscles, causes the chest to return to its original
size | in consequence of this the pressure within the lungs now
becomes greater than that outside, and thus air rushes out of the
trachea until equilibrium is once more established. This consti-
tutes expiration ; the inspiratory and expiratory act together form-
ing a respiration. The fresh air introduced into the upper part of
the pulmonary passages by the inspiratory movement contains more
oxygen and less carbonic acid than the old air previously present in
the lungs. By diffusion the new or tidal air, as it is frequently
called, gives up its oxygen to, and takes carbonic acid from, the old
or stationary air, as it has been called, and thus when it leaves the
chest in expiration has been the means of both introducing oxygen

CHAP, ii.] RESPIRATION. 315

into the chest and of removing carbonic acid from it. In this way,
by the ebb and flow of the tidal air, and by diffusion between it
and the stationary air, the air in the lungs is being constantly
renewed through the alternate expansion and contraction of the
chest.

In ordinary respiration, the expansion of the chest never reaches
its maximum ; by more forcible muscular contraction, by what is
called laboured inspiration, an additional thoracic expansion can be
brought about, leading to the inrush of a certain additional quantity
of air before equilibrium is established. This additional quantity
is often spoken of as complemental air. In the same way, in
ordinary respiration, the contraction of the chest never reaches its
maximum. By calling into use additional muscles, by a laboured
expiration, an additional quantity of air, the so-called reserve or
supplemental air, may be driven out. But even after the most
forcible expiration, a considerable quantity of air, the residual air,
still remains in the lungs. The natural condition of the lungs in
the chest is in fact one of partial distension. The elastic pulmonary
tissue is always to a certain extent on the stretch ; it is always, so
to speak, striving to pull asunder the pulmonary from the parietal
pleura ; but this it cannot do, because the air can have no access to
the pleural cavity. When however the chest ceases to be air-tight,
when by a puncture of the chest-wall or diaphragm, air is introduced
into the pleural chamber, the elasticity of the lungs pulls the pul-
monary away from the parietal pleura, and the lungs collapse,
driving out by the windpipe a considerable quantity of the residual
air. Even then, however, the lungs are not completely emptied,
some air still remaining in the air-cells and passages. It need
hardly be added that when the pleura is punctured, and air can
gain free admittance from the exterior into the pleural chamber,
the effect of the respiratory movements is simply to drive air in
and out of that chamber, instead of in and out of the lung. There
is in consequence no renewal of the air within the lungs under
those circumstances.

In man the pressure exerted by the elasticity of the lungs alone
amounts to about 5 mm. of mercury. This is estimated by tying a
manometer into the windpipe of a dead subject and observing the
rise of mercury which takes place when the chest-walls are punc-
tured. If the chest be forcibly distended beforehand, a much larger
rise of the mercury is observed, amounting, in the case of a dis-
tension corresponding to a very forcible inspiration, to 30 mm. In
the living body this mechanical elastic force of the lungs is assisted
by the contraction of the plain muscular fibres of the bronchi ; the
pressure however which can be exerted by these probably does
not exceed 1 or 2 mm.

When a manometer is introduced into a lateral opening of the
windpipe of an animal, the mercury will fall, indicating a negative
pressure as it is called, during inspiration, and rise, indicating a

316

RHYTHM OF RESPIRATION.

[BOOK ii.

positive pressure, during expiration, both fall and rise being slight
and varying according to the freedom with which the air passes in
and out of the chest. When a manometer is fitted with air-tight
closure into the mouth, or better, in order to avoid the suction-
action of the mouth, into one nostril, the other nostril and the mouth
being closed, and efforts of inspiration and expiration are made, the
mercury falls or undergoes negative pressure with inspiration, and
rises, or undergoes positive pressure during expiration. It has been
found in this way that the negative pressure of a strong inspiratory
effort may vary from 30 to 74 mm., and the positive pressure of a
strong expiration from 62 to 100 mm.

The total amount of air which can be given out by the most
forcible expiration following upon a most forcible inspiration, that
is, the sum of the complemental, tidal and reserve airs, has been
called 'the vital capacity;' 'extreme differential capacity' is a better
phrase. It may be measured by a modification of a gas-meter called
a spirometer ; and though it varies largely, the average may be put
down at 3—4000 c.c. (200 to 250 cubic inches).

Of the whole measure of vital capacity, about 500 c.c. (30 c.
inch) may be put down as the average amount of tidal air, the
remainder being nearly equally divided between the complemental
and reserve airs. The quantity left in the lungs after the deepest
expiration amounts to about 1400 — 2000 c.c.

Since the respiratory movements are so easily affected by various
circumstances, the simple fact of attention being directed to the breath-
ing being sufficient to cause modifications both of the rate and depth of
the respiration, it becomes very difficult to fix the volume of an average
breath. Thus various authors have given figures varying from 53 c.c.
to 792 c.c. The statement made above is that given by Vierordt as the
mean of observations varying from 177 to 699 c.c.

The Rhythm of Respiration. If the movements of the column
of tidal air, or the movements of expansion and contraction, or the

FIG. 55. TRACING OF THORACIC EESPIRATORY MOVEMENTS OBTAINED BY MEANS OF
MAREY'S PNEUMATOGRAPH. (To be read from left to right.)

A whole respiratory phase is comprised between a and a ; inspiration, during which
the lever descends, extending from a to 6, and expiration from 6 to a. The
undulations at c are caused by the heart's beat.

CHAP, ii.] RESPIRATION. 317

fall and rise of the diaphragm, be registered, curves are obtained,
which, while differing in detail, exhibit the same general features,
and more or less resemble the curve shewn in Fig. 55.

The movements of the column of air may be recorded by introducing
a T piece into the trachea, one cross piece being left open or connected
with a piece of india-rubber tubing open at the end, and the other con-
nected with a Marey's tambour or with a receiver which in turn is con-
nected with a tambour, Fig. 22, p. 140, and Fig. 56. The movements of
the column of air in the trachea are transmitted to the tambour, the
consequent expansions and contractions of which are transmitted to the
recording drum by means of a lever resting on it. The movements of the
chest-walls may be recorded by means of the recording stethometer of
Burden-Sanderson. This consists of a rectangular framework constructed
of two rigid parallel bars joined at right angles to a cross piece. The free
ends of the bars, the distance between which can be regulated at pleasure,
are armed, the one with a tambour, the other simply with an ivory button.
The tambour also bears on the metal plate of its membrane (Figs. 22
and 56, m',) a small ivory button (in place of the lever shewn in
Figs. 22 and 56). When it is desired to record the changes occurring in
any diameter of the chest, e.g. an antero-posterior diameter from a point
in the sternum to a point in the back, the instrument is made to encircle
the chest somewhat after the fashion of a pair of callipers, the ivory
button at one free end being placed on the spine of a vertebra behind
and the tambour at the other on the sternum in front in the line of the
diameter which is being studied. The distance between the free ends of
the instrument being carefully adjusted so that the button of the tambour
presses slightly on the sternum, any variations in the length of the
diameter in question will, since the framework of the tambour is im-
mobile, give rise to variations of pressure within the tambour. These
variations of the 'receiving' tambour as it is called are conveyed by a
flexible tube containing air to a second or 'recording' tambour similar
to that shewn in Figs. 22 and 56, the lever of which records the varia-
tions on a travelling surface. For the purpose of measuring the extent
of the movements the instrument must be experimentally graduated.
In Marey's pneumatograph, a long elastic chamber is used as a pectoral
girdle. When the chest expands, the girdle is elongated, and the air
within it rarefied, and the lever of the tambour connected with it de-
pressed : and conversely, when the chest contracts, the lever is elevated.
The pneumatograph of Fick is somewhat similar. The movements of the
diaphragm may be registered by means of a needle, which is thrust
through the sternum so as to rest on the diaphragm, the head of the
needle being connected with a lever. Various modifications of these
several methods have been adopted by different observers.

As is shewn in Fig. 55, inspiration begins somewhat suddenly
and advances rapidly, being followed immediately by expiration
which is carried out at first rapidly, but afterwards more and
more slowly. Such pauses as are seen occur between the end of
expiration and the beginning of inspiration. In normal breathing,
hardly any such pause exists, but in cases where the respiration
becomes infrequent, pauses of considerable length may be observed.

318

RHYTHM OF RESPIRATION. [BOOK n.

CHAP. IL] RESPIRATION. 319

FIG. 56. APPARATUS FOR TAKING TRACINGS OF THE MOVEMENTS or THE
COLUMN OF AIR IN RESPIRATION.

The recording apparatus shewn is the ordinary cylinder recording apparatus. The
cylinder A covered with smoked paper is by means of the friction-plate B put into
revolution by the spring clock-work in C regulated by Foucault's regulator D. By
means of the screw E, the cylinder can be raised or lowered, and by means of the
screw F its speed may be increased or diminished.

The tracheotomy tube t fixed in the trachea of an animal is connected by india-
rubber tubing a with a glass T piece inserted into the large jar G. From the other
end of the T piece proceeds a second piece of tubing b, the end of which can be either
closed or partially obstructed at pleasure by means of the screw clamp c. From the
jar proceeds a third piece of tubing d, connected with a Marey's tambour TO (see
Fig. 22, p. 140), the lever of which I writes on the recording surface. When the tube
b is open the animal breathes freely through this, and the movements in the air of
G and consequently in the tambour are slight. On closing the clamp c, the animal
breathes only the air contained in the jar, and the movements of the lever of the
tambour become consequently much more marked.

Below the lever is seen a small time-marker n connected with an electro-magnet,
the current through which coming from a battery by the wires x and y is made and
broken by a clock-work or metronome.

In what may be considered as normal breathing, the respiratory
act is repeated about 17 times a minute ; and the duration of the
inspiration as compared with that of the expiration (and such pause
as may exist) is about as ten to twelve.

The rate of the respiratory rhythm varies very largely, and in
this as in the volume of each breath it is very difficult to fix
a satisfactory average, the figures given varying from 20 to 13 a
minute. It varies according to age and sex. It is influenced by
the position of the body, being quicker in standing than in lying,
and in lying than in sitting. Muscular exertion and emotional
conditions affect it deeply. In fact, almost every event which
occurs in the body may influence it. We shall have to consider in
detail hereafter the manner in which this influence is brought to
bear.

When the ordinary respiratory movements prove insufficient to
effect the necessary changes in the blood, their rhythm and
character become changed. Normal respiration gives place to
laboured respiration, and this in turn to dyspnoea, which, unless
some restorative event occurs, terminates in asphyxia. These
abnormal conditions we shall study more fully hereafter.

The Respiratory Movements.

When the movements of the chest during normal breathing are
watched, it is seen that during respiration an enlargement takes
place in the antero-posterior diameter, the sternum being thrown
forwards, and at the same time moving upward. The lateral width
of the chest is also increased. The vertical increase of the cavity
is not so obvious from the outside, though when the movements of

320 MOVEMENTS OF INSPIRATION. [BOOK 11.

the diaphragm are watched by means of an inserted needle, the
upper surface of that organ is seen to descend at each inspiration,
the anterior walls of the abdomen bulging out at the same time.
In the female human subject, the movement of the upper part of
the chest is very conspicuous, the breast rising and falling with
every respiration ; in the male, however, the movements are almost
entirely confined to the lower part of the chest. In laboured
respiration all parts of the chest are alternately expanded and
contracted, the breast rising and falling as well in the male as in
the female. We have now to consider these several movements in
greater detail, and to study the means by which they are carried
out.

Inspiration. There are two chief means by which the chest is
enlarged in normal inspiration, viz. the descent of the diaphragm
and the elevation of the ribs. The former causes that movement
in the lower part of the chest and abdomen so characteristic of
male breathing, which is called diaphragmatic ; the latter causes
the movement of the upper chest characteristic of female breath-
ing, which is called costal. These two main factors are assisted by
less important and subsidiary events.

The descent of the diaphragm is effected by means of the
contraction of its muscular fibres. When at rest the diaphragm
presents a convex surface to the thorax; when contracted it
becomes much flatter, and in consequence the level of the chest-
floor is lowered, the vertical diameter of the chest being pro-
portionately enlarged. In descending, the diaphragm presses on
the abdominal viscera, and so causes a projection of the flaccid ab-
dominal walls. From its attachments to the sternum and the false
ribs, the diaphragm, while contracting, naturally tends to pull the
sternum and the upper false ribs downwards and inwards, and the
lower false ribs upwards and inwards, towards the lumbar spine.
In normal breathing, this tendency produces little effect, being
counteracted by the accompanying general costal elevation, and by
certain special muscles to be mentioned presently. In forced
inspiration however, and especially where there is any obstruction
to the entrance of air into the lungs, the lower ribs may be
so much drawn in by the contraction of the diaphragm, that the
girth of the trunk at this point is obviously diminished.

The elevation of the ribs is a much more complex matter than
the descent of the diaphragm. If we examine any one rib, such as
the fifth, we find that while it moves freely on its vertebral arti-
culation, it inclines when in the position of rest in an oblique
direction from the spine to the sternum ; hence it is obvious that
when the rib is raised, its sternal attachment must not only
be carried upward, but also thrown forwards. The rib may in fact
be regarded as a radius, moving on the vertebral articulation as a
centre, and causing the sternal attachment to describe an arc of a

CHAP, ii.] RESPIRATION. 321

circle in the vertical plane of the body; as the rib is carried
upwards from an oblique to a more horizontal position, the sternal
attachment must of necessity be carried farther away in front of
the spine. Since all the ribs have a downward slanting direction,
they must all tend, when raised towards the horizontal position, to
thrust the sternum forward, some more than others according to
their slope and length. The elasticity of the sternum and costal
cartilages, together with the articulation of the sternum to the
clavicle above, permit the front surface of the chest to be thus
thrust forwards as well as upwards, when the ribs are raised.
By this action, the antero-posterior diameter of the chest is
enlarged.

Since the ribs form arches which increase in their sweep as
one proceeds from the first downwards as far at least as the seventh,
it is evident that when a lower rib such as the fifth is elevated so
as to occupy or to approach towards the position of the one above
it, the chest at that level will become wider from side to side,
in proportion as the fifth arch is wider than the fourth. Thus
the elevation of the rib increases not only the antero-posterior but
also the transverse diameter of the chest. Further, on account
of the resistance of the sternum, the angles between the ribs and
their cartilages are, in the elevation of the ribs, somewhat opened
out, and thus also the transverse as well ' as the antero-posterior
diameter, somewhat increased. In several ways, then, the elevation
of the ribs enlarges the dimensions of the chest.

The ribs are raised by the contraction of certain muscles. Of
these the external intercostals are the most important. Even in the
case of two isolated ribs such as the fifth and sixth, the contraction
of the external intercostal muscle of the intervening space raises
the two ribs, thus bringing them towards the position in which the
fibres of the muscle have the shortest length, viz. the horizontal
one. This elevating action is further favoured by the fact that
the first rib is less moveable than the second, and so affords a
comparatively fixed base for the action of the muscles between the
two, the second in turn supporting the third and so on, while the
scaleni muscles in addition serve to render fixed, or to raise, the
first two ribs. So that in normal respiration, the act begins
probably by a contraction of the scaleni. The first two ribs
being thus fixed, the contraction of the series of external inter-
costal muscles acts to the greatest advantage.

While the elevating i.e. inspiratory action of the external
intercostals is admitted by all authors, the function of the internal
intercostals has been much disputed. Haller may be regarded
as the leader of those who regard the internal intercostals as
inspiratory, while Hamberger was the first who successfully ad-
vocated the perhaps more commonly adopted view that while
those parts of them which lie between the sternal cartilages act
like the external intercostals as elevators, i.e. as inspiratory in

F. 21

322 LABOURED INSPIRATION. [BOOK n.

function, those parts which lie between the osseous ribs act as
depressors, i.e. as expiratory in function.

In the well-known model invented by Bernoulli and adopted
by Hamberger, consisting of two rigid bars, representing the ribs,
moving vertically by means of their articulations with an upright
representing the spine and connected at their free ends by a piece
representing the sternum, it is undoubtedly true that stretched
elastic bands attached to the bars in such a way as to represent
respectively the external and internal intercostals, viz. sloping in
the one case downwards and forwards and in the other downwards
and backwards, do, on being left free to contract, in the former
case elevate and in the latter depress the ribs. Such a model
however does not fairly represent the natural conditions of the
ribs, which are not straight and rigid, but peculiarly curved and of
varying elasticity, capable moreover of rotation on their own axes,
and having their movements determined by the characters of
their vertebral articulations. The mechanical conditions in fact
of these muscles are so complex, that a deduction of their actions
from simple mechanical principles, or from the direction of the
fibres, must be exceedingly difficult and dangerous. Actual experi-
ments on the cat and dog tend to shew that in these animals the
contraction of the internal intercostals, along their whole length,
takes place, in point of time, alternately with that of the
diaphragm, and thus afford an argument in favour of these muscles
being expiratory in function.

Next in importance to the external intercostals come the
levatores costarum, which, though small muscles, are able, from
the nearness of their costal insertions to the fulcrum, to produce
considerable movement of the sternal ends of the ribs. The
external intercostals and the levatores costarum with the scaleni
may fairly be said to be the elevators of the ribs, i.e. the chief
muscles of costal inspiration in normal breathing.

Additional space in the transverse diameter is afforded probably
by the rotation of the ribs on an antero-posterior axis; but this
movement is quite subsidiary and unimportant. When the chest
is at rest, the ribs are somewhat inclined with their lower borders
directed inwards as well as downwards. When they are drawn up
by the action of the intercostal muscles, their lower borders are
everted. Thus their flat sides are presented to the thoracic cavity,
which is thereby slightly increased in width.

Laboured Inspiration. When respiration becomes laboured,
other muscles are brought into play. The scaleni are strongly
contracted, so as to raise or at least give a very fixed support
to the first and second ribs. In the same way the serratus
posticus superior, which descends from the fixed spine in the lower
cervical and upper dorsal regions to the second, third, fourth, and
fifth ribs, by its contractions raises those ribs. In laboured breath-

CHAP, ii.] RESPIRATION. 323

ing a function of the lower false ribs, not very noticeable in easy
breathing, comes into play. They are depressed, retracted, and
fixed, thereby giving increased support to the diaphragm, and
directing the whole energies of that muscle to the vertical enlarge-
ment of the chest. In this way the serratus posticus inferior, which
passes upward from the lumbar aponeurosis to the last four ribs, by
depressing and fixing those ribs becomes an adjuvant inspiratory
muscle. The quadratus lumborum and lower portions of the sacro-
lumbalis may have a similar function.

All these muscles may come into action even in breathing
which, deeper than usual, can hardly perhaps be called laboured.
When however the need for greater inspiratory efforts becomes
urgent, all the muscles which can, from any fixed point, act in
enlarging the chest, come into play. Thus the arms and shoulder
being fixed, the serratus magnus passing from the scapula to the
middle of the first eight or nine ribs, the pectoralis minor passing
from the coracoid to the front parts of the third, fourth, and fifth
ribs, the pectoralis major passing from the humerus to the costal
cartilages, from the second to the sixth, and that portion of the
latissimus dorsi which passes from the hurnerus to the last three
ribs, all serve to elevate the ribs and thus to enlarge the chest.
The sterno-mastoid and other muscles passing from the neck to the
sternum, are also called into action. In fact, every muscle which
by its contraction can either elevate the ribs or contribute to the
fixed support of muscles which do elevate the ribs, such as the
trapezius, levator anguli scapulae and rhomboidei by fixing the
scapula, may, in the inspiratory efforts which accompany dyspnoea,
be brought into play.

Expiration. In normal easy breathing, expiration is in the
main a simple effect of elastic reaction. By the inspiratory effort
the elastic tissue of the lungs is put on the stretch ; so long as
the inspiratory muscles continue contracting, the tissue remains
stretched, but directly those muscles relax, the elasticity of the
lungs comes into play and drives out a portion of the air contained
in them. Similarly the elastic sternum and costal cartilages are by
the elevation of the ribs put on the stretch : they are driven into a
position which is unnatural to them. When the intercostal and
other elevator muscles cease to contract, the elasticity of the ster-
num and costal cartilages causes them to return to their previous
position, thus depressing the ribs, and diminishing the dimensions
of the chest. When the diaphragm descends, in pushing down the
abdominal viscera, it puts the abdominal walls on the stretch : and
hence, when at the end of inspiration the diaphragm relaxes, the
abdominal walls return to their place, and by pressing on the ab-
dominal viscera, push the diaphragm up again into its position of
rest. Expiration then is, in the main, simple elastic reaction ; but
there is probably some, though possibly in most cases, a very

21—2

324 FACIAL AND LARYNGEAL RESPIRATION. [BOOK n.

slight, expenditure of muscular energy to bring the chest
more rapidly to its former condition. This is, as we have
seen, supposed by many to be afforded by the internal inter-
costals acting as depressors of the ribs. If these do not act in
this way, we may suppose that the elastic return of the abdominal
walls is accompanied and assisted by a contraction of the abdominal
muscles. The triangularis sterni, the effect of whose contraction is
to pull down the costal cartilages, may also be regarded as an ex-
piratory muscle.

When expiration becomes laboured, the abdominal muscles
become important expiratory agents. By pressing on the contents
of the abdomen, they thrust them and therefore the diaphragm
also up towards the chest, the vertical diameter of which is
thereby lessened, while by pulling down the sternum and the
middle and lower ribs they lessen also the cavity of the chest in its
antero-posterior and transverse diameters. They are in fact the
chief expiratory muscles, though they are doubtless assisted by
the serratus posticus inferior and portions of the sacro-lumbalis,
since when the diaphragm is not contracting, the depression of the
lower ribs which the contraction of these muscles causes, serves
only to narrow the chest. As expiration becomes more and more
forced, every muscle in the body which can either by contracting
depress the ribs, or press on the abdominal viscera, or afford fixed
support to muscles having those actions, is called into play.

Facial and Laryngeal Respiration. The thoracic respiratory
movements are accompanied by associated respiratory movements
of other parts of the body, more particularly of the face and of the
glottis.

In normal healthy respiration the current of air which passes
in and out of the lungs, travels, not through the mouth but through
the nose, chiefly through the lower nasal meatus. The ingoing air,
by exposure to the vascular mucous membrane of the narrow and
winding nasal passages, is more efficiently warmed than it would be
if it passed through the mouth ; and at the same time the mouth
is thereby protected from the desiccating effect of the continual
inroad of comparatively dry air.

During each inspiratory effort the nostrils are expanded, pro-
bably by the action of the dilatores naris, and thus the entrance of
air facilitated. The return to their previous condition during expi-
ration is effected by the elasticity of the nasal cartilages, assisted
perhaps by the compressores naris. This movement of the nostrils,
perceptible in many people, even during tranquil breathing, becomes
very obvious in laboured respiration.

When the mouth is closed, the soft palate which is held some-
what tense, is swayed by the respiratory current, but entirely in a
passive manner, and it is not until the larynx is reached by the in-
going air that any active movements are met with. When the

CHAP, ii.] RESPIRATION. 325

larynx is examined with the laryngoscope, it is frequently seen that,
while during inspiration the glottis is widely open, with each expi-
ration the arytenoid cartilages approach each other so as to narrow
the glottis, the cartilages of Santorini projecting inwards at the
same time. Thus, synchronous with the respiratory expansion and
contraction of the chest, and the respiratory elevation and depres-
sion of the alse nasi, there is a rhythmic widening and narrowing
of the glottis. Like the movements of the nostril, this respiratory
action of the glottis is much more evident in laboured than in
tranquil breathing. Indeed in the latter case it is frequently
absent. The manner in which this rhythmic opening and narrow-
ing is effected will be described when we come to study the pro-
duction of the voice. Whether there exists a rhythmic contraction
and expansion of the trachea and bronchial passages effected by
means of the plain muscular tissue of those organs and synchronous
with the respiratory movements of the chest, is uncertain.

SEC. 2. CHANGES OF THE AIR IN RESPIRATION.

During its stay in the lungs, or rather during its stay in the
bronchial passages, the tidal air (by means of diffusion chiefly)
effects exchanges with the stationary air ; in consequence the ex-
pired air differs from inspired air in several important particulars.

1. The temperature of expired air is variable, but under
ordinary circumstances is higher than that of the inspired air. At
an average temperature of the atmosphere, for instance at about
20° C., the temperature of expired air is, in the mouth 33*9°, in the
nose 35*3°. When the external temperature is low, that of the ex-
pired air sinks somewhat, but not to any great extent, thus at
- 6*3° C. it is 29'8° C. When the external temperature is high, the
expired air may become cooler than the inspired, thus at 41 '9° it
was found by Valentin to be 38*1°. The exact temperature in fact
depends on the relative temperatures of the blood and inspired air,
and on the depth and rate of breathing.

2. The expired air is loaded with aqueous vapour. The point
of saturation of any gas, that is, the utmost quantity of water
which any given volume of gas can take up as aqueous vapour,
varies with the temperature, being higher with the higher
temperature. For its own temperature expired air is according
to most observers saturated with aqueous vapour.

3. When the total quantity of tidal air given out at any expira-
tion is compared with that taken in at the corresponding inspi-

CHAP, ii.] RESPIRATION. 327

ration, it is found that, both being dried and measured at the
same pressure, the expired air is less in volume than the inspired
air, the difference amounting to about ^th or ^th of the volume
of the latter. Hence, when an animal is made to breathe in
a confined space, the atmosphere is absolutely diminished, as
was observed so long ago as 1674 by Mayow. The approximate
equivalence in volume between inspired and expired air arises
from the fact that the volume of any given quantity of carbonic
acid is equal to the volume of the oxygen consumed to produce it;
the slight falling short of the expired air is due to the circum-
stance that all the oxygen inspired does not reappear in the
carbonic acid expired, some having formed other combinations.

4. The expired air contains about 4 or 5 p.c. less oxygen, and
about 4 p.c. more carbonic acid than the inspired air, the quantity
of nitrogen suffering but little change. Thus

oxygen. nitrogen. carbonic acid.

Inspired air contains 20*81 7915 '04

Expired „ „ 16*033 79'587 4'380

The quantity of nitrogen in the expired air is sometimes found
to be slightly greater, as in the table above, but sometimes less,
than that of the inspired air.

In a single breath the air is richer in carbonic acid (and poorer
in oxygen), at the end than at the beginning. Hence the longer
the breath is held, the greater the pause between inspiration and
expiration, the higher the percentage of carbonic acid in the
expired air. Thus by increasing the interval between two ex-
pirations to 100 seconds, the percentage may be raised to 7*5. When
the rate of breathing remains the same, by increasing the depth
of the breathing the percentage of carbonic acid in each breath is
lowered, but the total quantity of carbonic acid expired in a given
time is increased. Similarly, when the depth of breath remains
the same, by quickening the rate the percentage of carbonic acid
in each breath is lowered, but the quantity expired in a given
time is increased.

Taking, as we have done, at 500 c.c. the amount of tidal air
passing in and out of the chest of an average man, such a person
will expire about 22 c.c. of carbonic acid at each breath; this,
reckoning the rate of breathing at 17 a minute, would give over
500 litres of carbonic acid for the day's production. By actual
experiment, however, Pettenkofer and Voit, of whose researches we
shall have to speak hereafter, determined the total daily excretion
of carbonic acid in an average man to be 800 grins., i.e. rather
more than 400 litres (406), containing 218*1 grms. carbon, and
581*9 grms. oxygen, the oxygen actually consumed at the same
time being about 700 grms. This amount represents the gases
given out and taken in, not by the lungs only, but by the whole

328 CHANGES IN THE AIR. [BOOK n.

body; but the amount of carbonic acid given out by the skin is, as
we shall see, very slight (10 grms. or even less), so that 800 grms.
may be taken as the average production of carbonic acid by an
average man. The quantity however, both of oxygen consumed
and of carbonic acid given out, is subject to very wide variations ;
thus in Pettenkofer and Voit's observations, the daily quantity of
carbonic acid varied from 686 to 1285 grms., and that of the
oxygen from 594 to 1072 grms. These variations and their causes
will be discussed when we come to deal with the problems of
nutrition.

5. Besides carbonic acid, expired air contains various im-
purities, many of an unknown nature, and all in small amounts.
Traces of ammonia have been detected in expired air, even in that
taken directly from the trachea, in which case its presence could
not be due to decomposing food lingering in the mouth. When
the expired air is condensed by being conveyed into a cooled
receiver, the aqueous product is found to contain organic matter,
and rapidly to putrefy. The organic substances thus shewn to be
present in the expired air are the cause in part of the odour
of breath. It is probable that many of them are of a poisonous
nature; for an atmosphere containing simply 1 p.c. of carbonic
acid (with a corresponding diminution of oxygen) has very little
effect on the animal economy, whereas an atmosphere in which the
carbonic acid has been raised to 1 p.c. by breathing, is highly
injurious. In fact, air rendered so far impure by breathing that
the carbonic acid amounts to '08 p.c. is distinctly unwholesome,
not so much on account of the carbonic acid, as of the accom-
panying impurities. Since these impurities are of unknown
nature and cannot be estimated, the easily determined carbonic
acid is usually taken as the measure of their presence. We have
seen that the average man loads, at each breath, 500 c.c. of air
with carbonic acid to the extent of 4 p.c. He will accordingly at
each breath load 2 litres to the extent of 1 p.c.; and in one hour,
if he breathe 17 times a minute, will load rather more than 2000
litres to the same extent. At the very least then a man ought to
be supplied with this quantity of air hourly; and if the air is to be
kept fairly wholesome, that is with the carbonic acid reduced
below *1 p.c., he should have more than ten times as much.

SEC. 3. THE RESPIRATORY CHANGES IN THE
BLOOD.

While the air in passing in and out of the lungs is thus robbed
of a portion of its oxygen, and loaded with a certain quantity of
carbonic acid, the blood as it streams along the pulmonary capil-
laries undergoes important correlative changes. As it leaves the
right ventricle it is venous blood of a dark purple or maroon
colour; when it falls into the left auricle, it is arterial blood of a
bright scarlet hue. In passing through the capillaries of the body
from the left to the right side of the heart, it is again changed from
the arterial to the venous condition. We have to inquire, What are
the essential differences between arterial and venous blood, by
what means is the venous blood changed into arterial in the lungs,
and the arterial into venous in the rest of the body, and what
relations do these changes in the blood bear to the changes in the
air which we have already studied?

The facts, that venous blood at once becomes arterial on being
exposed to or shaken up with air or oxygen, and that arterial
blood becomes venous when kept for some little time in a closed
vessel, or when submitted to a current of some indifferent gas
such as nitrogen or hydrogen, prepare us for the statement that
the fundamental difference between venous and arterial blood is in
the relative proportion of the oxygen and carbonic acid gases
contained in each. From both, a certain quantity of gas can be
extracted by means which do not otherwise materially alter the
constitution of the blood ; and this gas when obtained from arterial

330 CHANGES IN THE BLOOD. [BOOK n.

blood is found to contain more oxygen and less carbonic acid than
that obtained from venous blood. This is the real differential
character of the two bloods ; all other differences are either, as we
shall see to be the case with the colour, dependent on this, or are
unimportant and fluctuating.

If the quantity of gas which can be extracted by the mercurial
air-pump from 100 vols. of blood be measured at ()°C., and a
pressure of 760 mm., it is found to amount, in round numbers, to
60 vols.

The vacuum produced by the ordinary mechanical air-pump is in-
sufficient to extract all the gas from blood. Hence it becomes necessary
to use either a large Torricellian vacuum or a Sprengel's pump. In the
former (Fig. 57) case two large globes of glass, one fixed and the other
moveable, are connected by a flexible tube; the fixed globe is made to
communicate by means of air-tight stopcocks alternately with a receiver
containing the blood, and with a receiver to collect the gas. When the
moveable globe filled with mercury is raised above the fixed one, the
mercury from the former runs into and completely fills the latter, the
air previously present being driven out. After adjusting the cocks, the
moveable globe is then depressed thirty inches below the fixed one,
in which the consequent fall of the mercury produces an almost
complete vacuum. By turning the proper cock this vacuum is put into
connection with the receiver containing the blood, which thereupon be-
comes proportionately exhausted. By again adjusting the cocks and
once more elevating the moveable globe, the gas thus extracted is
driven out of the fixed globe into a receiver. The vacuum is then
once more established and the operation repeated as long as gas continues
to be given off" from the blood. This form of pump, introduced by
Ludwig, or a modification of it, with drying apparatus, employed by
Pfliiger, or a similar form introduced by French observers, is the one
which has been hitherto most extensively used ; but a Sprengel's pump
is preferred by some.

The average composition of this gas in the two kinds of blood
is, stated in round numbers, as follows:

From 100 vols. m&y be obtained

Of oxygen, of carbonic acid, of nitrogen.

Of Arterial Blood, 20 vols. 40 vols. 1 to 2 vols.

Of Venous Blood, 8 to 12 vols. 46 vols. 1 to 2 vols.
all measured at 760 mm. and 0° C.

That is to say, venous blood, as compared with arterial blood,
contains 8 to 12 p.c. less oxygen and 6 p.c. more carbonic acid.
But the gases of venous blood are much more variable than those of
arterial blood.

It will be convenient to consider the relations of each of these
gases separately.

CHAP, n.]

RESPIRATION.

331

FIG. 57. DIAGRAMMATIC ILLUSTRATION OF LUDWIG'S MERCURIAL GAS PUMP.

A and B are two glass globes, connected by strong india-rubber tubes, a and 6,
with two similar glass globes A' and B'. A is further connected by means of the
stopcock c with the receiver C containing the blood (or other fluid) to be analysed,
and B by means of the stopcock d and the tube e with the receiver D for receiving
the gases. A and B are also connected with each other by means of the stopcocks
/ and g, the latter being so arranged that B also communicates with B' by the
passage g'. A' and B' being full of mercury and the cocks k, f, g, and d being open
but c and g' closed, on raising A' by means of the pulley p the mercury of A' fills A,
driving out the air contained in it, into B, and so out through e. When the mercury
has risen above g, f is closed, and g1 being opened, B' is hi turn raised till B is
completely filled with mercury, all the air previously in it being driven out through e.
Upon closing d, and lowering B', the whole of the mercury in B falls in B', and a
vacuum consequently is established in B. On closing g', but opening g, f, and k and
lowering A', a vacuum is similarly established in A and in the junction between
A and B. If the cock c be now opened the gases of the blood in C escape into the
vacuum of A and B. By raising A', after the closure of c, and opening of d, the
gases so set free are driven from A into B, and by the raising of B' from B, through
e into the receiver D, standing over mercury.

332 CHANGES IN THE BLOOD. [BOOK IL

The relations of Oxygen in the Blood.

When a liquid such as water is exposed to an atmosphere con-
taining a gas such as oxygen, some of the oxygen will be dis-
solved in the water, that is to say will be absorbed from the
atmosphere. The quantity which is so absorbed will depend on
the quantity of oxygen which is in the atmosphere above ; that is
to say on the pressure of the oxygen ; the greater the pressure of
the oxygen, the larger the amount which will be absorbed. If on
the other hand water, already containing a good deal of oxygen dis-
solved in it, be exposed to an atmosphere containing little or no
oxygen, the oxygen will escape from the water into the atmosphere.
The oxygen in fact which is dissolved in the water is in a state of
tension, the degree of tension depending on the quantity dissolved;
and when water containing oxygen dissolved in it is exposed to any
atmosphere, the result, that is whether the oxygen escapes from the
water into the atmosphere, or passes from the atmosphere into the
water, depends on whether the tension of the oxygen in the water is
greater or less than the pressure of the oxygen in the atmosphere.
Hence when water is exposed to oxygen, the oxygen either escapes
or is absorbed until equilibrium is established between the pressure
of the oxygen in the atmosphere above and the tension of the
oxygen in the water below. This result is, as far as mere absorption
and escape are concerned, quite independent of what other gases
are present in the water or in the atmosphere. Suppose a half-
litre of water were lying at the bottom of a two-litre flask, and that
the atmosphere in the flask above the water was one-third oxygen;
it would make no difference, as far as the absorption of oxygen by
the water was concerned, whether the remaining two-thirds of the
atmosphere was carbonic acid, or nitrogen, or hydrogen, or whether
the space above the water was a vacuum filled to one-third with
pure oxygen. Hence it is said that the absorption of any gas
depends on the partial pressure of that gas in the atmosphere to
which the liquid is exposed. This is true not only of oxygen and
water, but of all gases and liquicU which do not enter into chemical
combination with each other. Different liquids will of course
absorb different gases with differing readiness; but, with the same
gas and the same liquid, the amount absorbed will depend directly
on the partial pressure of the gas. It should be added that the
process is much influenced by temperature. Hence, to state the
matter generally, the absorption of any gas by any liquid, will
depend on the nature of the gas, the nature of the liquid, the pres-
sure of the gas, and the temperature at which both stand.

Now it might be supposed, and indeed was once supposed, that
the oxygen in the blood was simply dissolved by the blood. If this
were so, then the amount of oxygen present in any given quantity
of blood exposed to any given atmosphere, ought to rise and fall

CHAP, ii.] RESPIRATION. 333

steadily and regularly as the partial pressure of oxygen in that
atmosphere is increased or diminished. But this is found not to
be the case. If we expose blood containing little or no oxygen to
a succession of atmospheres containing increasing quantities of
oxygen, we find that at first there is a very rapid absorption of the
available oxygen, and then this somewhat suddenly ceases or
becomes very small ; and if on the other hand we submit arterial
blood to successively diminishing pressures, we find that for a long
time very little is given off, and then suddenly the escape becomes
very rapid. The absorption of oxygen by blood does not follow the
general law of absorption according to pressure. The phenomena
on the other hand suggest the idea that the oxygen in the blood is
in some particular combination with a substance or some sub-
stances present in the blood, the combination being of such a kind
that dissociation readily occurs at certain pressures and certain
temperatures. What is that substance or what are those sub-
stances ?

If serum, free from red corpuscles, be used in such absorption
experiments, it is found that as compared with the entire blood,
very little oxygen is absorbed, about as much as would be absorbed
by the same quantity of water; but such as is absorbed does follow
the law of pressures. In natural arterial blood the quantity of
oxygen which can be obtained from serum is exceedingly small ; it
does not amount to half a volume in one hundred volumes of the
entire blood to which the serum belonged. It is. evident that the
oxygen which is present in blood is in some way or other peculiarly
connected with the red corpuscles. Now the distinguishing feature
of the red corpuscles is the presence of haemoglobin. We have
already seen (p. 26) that this constitutes 90 per cent, of the dried
red corpuscles. There can be d priori little doubt that this must
be the substance with which the oxygen is associated ; and to the
properties of this body we must therefore direct our attention.

Hcemoglobin; its properties and derivatives.

When separated from the other constituents of the serum,
haemoglobin appears as a substance, either amorphous or crystal-
line, readily soluble in water (especially in warm water) and in
serum.

Since haemoglobin is soluble in serum, and since the identity of the
crystals observed occasionally within the corpuscles with those obtained
in other ways shews that the haemoglobin as it exists in the corpuscle is
the same thing as that which is artificially prepared from blood, it is
evident that some peculiar relationship between the stroma and the
haemoglobin must, in natural blood, keep the latter from being dissolved
by the serum. Hence in preparing haemoglobin it is necessary first of

334

HEMOGLOBIN.

[BOOK n.

FIG. 58. (After Preyer and Gamgee). THE SPECTRA OP OXY-HEMOGLOBIN IN
DIFFERENT GRADES OF CONCENTRATION, OF (REDUCED) HEMOGLOBIN AND OF CARBONIC-
OXIDE- HEMOGLOBIN.

1. Solution of Oxy-Haemoglobin containing less than -01 p.c.

2. ,, ,, ,, containing '09 p.c.

3. „ „ ,, „ -37 p.c.

4. ,, ,, „ ,, -8 p.c.

5. ,, (reduced) Haemoglobin containing about *2 p.c.

6. ,, carbonic oxide Haemoglobin.

CHAP, ii.] RESPIRATION. 335

In each oi' the six cases the layer brought before the spectroscope was 1 c.m. in
thickness.

The Letters (A, a &c.) indicate Frauenhofer's lines, and the figures wave-lengths
expressed in 100,000th of a millimetre.

all to break up the corpuscles. This may be done by the addition of
water, of ether, of chloroform or of bile salts, or by repeatedly freezing
and thawing. It is also of advantage previously to remove the alkaline
serum as much as possible so as to operate only on the red corpuscles.
The corpuscles being thus broken up, a solution of haemoglobin is
the result. The alkalinity of the solution, when present, being re-
duced by the cautious addition of dilute acetic acid, and the solvent
power of the aqueous medium being diminished by the addition of one
fourth its bulk of alcohol, the mixture, set aside in a temperature
of 0° C. in order still further to reduce the solubility of the haemo-
globin, readily crystallizes, when the blood used is that of the dog, cat,
horse, rat, guinea-pig, &c. In the case of the dog indeed it is simply
sufficient to add ether to the blood and then to let it stand in a cool
place; the mixture soon becomes a mass of crystals. The crystals may
be separated by filtration, redissolved in water and re-crystallized.

Haemoglobin from the blood of the rat, guinea-pig, squirrel,
hedgehog, horse, cat, dog, goose, and some other animals, crystal-
lizes readily, the crystals being generally slender four-sided prisms,
belonging to the rhombic system, and often appearing quite
acicular. The crystals from the blood of the guinea-pig are octa-
hedral, but also belong to the rhombic system; those of the
squirrel are six-sided plates. The blood of the ox, sheep, rabbit,
pig, and man, crystallizes with difficulty. Why these differences
exist is not known ; but the composition, and the amount of water
of crystallization, vary somewhat in the crystals obtained from
different animals. In the dog, the percentage composition of the
crystals is, according to Hoppe-Seyler, C. 53'85, H. 7'32, N. 1617,
O. 21-84, S. 0-39, Fe. '43, with 3 to 4 per cent, of water of crystal-
lization. It will thus be seen that haemoglobin contains, in
addition to the other elements usually present in proteid sub-
stances, a certain amount of iron; that is to say the element iron
is a distinct part of the hemoglobin molecule: a fact which of
itself renders haemoglobin remarkable among the chemical sub-
stances present in the animal body.

The crystals, when seen in a sufficiently thick layer under the
microscope, have the same bright scarlet colour as arterial blood
has to the naked eye ; when seen in a mass they naturally appear
darker. An aqueous solution of haemoglobin, obtained by dis-
solving purified crystals in distilled water, has also the same
bright arterial colour. A tolerably dilute solution placed before
tne spectroscope is found to absorb certain rays of light in a
peculiar and characteristic manner. A portion of the red end of
the spectrum is absorbed, as is also a much larger portion of the
blue end ; but what is most striking is the presence of two

336 HAEMOGLOBIN. [BOOK n.

strongly marked absorption bands, lying between the solar lines D
and E. (See Fig. 58.) Of these the one towards the red side,
sometimes spoken of as the band a, is the thinnest, but the
most intense, and in extremely dilute solutions (Fig. 58 1) is the
only one visible; its middle lies at some little distance to the blue
side of D. Its position may be more exactly defined by expressing
it in wave-lengths. As is well known the rays of light which
make up the spectrum differ in the length of their waves, diminish-
ing from the red end where the waves are longest to the blue end
where they are shortest. Thus Frauenhofer's line D corresponds
to rays having a wave-length of 589*4 millionths of a millimetre.
Using the same unit, the centre of this absorption band a of hsemo-

flobin corresponds to the wave-length 578; as may be seen in
ig. 58, where however the numbers of the divisions of the scale
indicate only 100,000 of a millimetre. The other, sometimes called
ft, much broader, lies a little to the red side of E, its blue-ward
edge, even in moderately dilute solutions (Fig. 58 2) coming close
up to that line; its centre corresponds to about wave-length 539.
Each band is thickest in the middle, and gradually thins away at
the edges. These two absorption bands are extremely characteristic
of a solution of haemoglobin. Even in very dilute solutions both
bands are visible (they may be seen in a thickness of 1 c.m. in a solu-
tion containing 1 grm. of haemoglobin in 10 litres of water), and
that when scarcely any of the extreme red end, and very little of the
blue end, is cut off. They then appear not only faint but narrow.
As the strength of the solution is increased, the bands broaden, and
become more intense ; at the same time both the red end, and still
more the blue end, of the whole spectrum, are encroached upon
(Fig. 58 3). This may go on until the two absorption bands become
fused together into one broad band (Fig. 58 4). The only rays
of light which then pass through the haemoglobin solution are
those in the green between the blueward edge of the united bands
and the general absorption which is now rapidly advancing from
the blue end, and those in the red between the united bands
and the general absorption at the red end. If the solution be still
further increased in strength, the interval on the blue side of the
united bands becomes absorbed also, so that the only rays which
pass through are the red rays lying to the red side of D; these are
the last to disappear, and hence the natural red colour of the solu-
tion as seen by transmitted light. Exactly the same appearances
are seen when crystals of haemoglobin are examined with a micro-
spectroscope. They are also seen when arterial blood itself
(diluted with saline solutions so that the corpuscles remain in as
natural condition as possible) is examined with the spectroscope, as
well as when a drop of blood, which from the necessary exposure to
air is always arterial, is examined with the micro-spectroscope. In
fact, the spectrum of haemoglobin is the spectrum of normal
arterial blood.

CHAP ii.] RESPIRATION. 337

When crystals of haemoglobin, prepared in the way described
above, are subjected to the vacuum of the mercurial air-pump, they
give off a certain quantity of oxygen, and at the same time they
change in colour. The quantity of oxygen given off is definite,
1 grm. of the crystals giving off 1'59 c.cm. of oxygen. In other
words, the crystals of haemoglobin over and above the oxygen
which enters intimately into their composition, (and which alone
is given in the elementary composition stated on p. 335), contain
another quantity of oxygen, which is in loose combination only,
and which may be dissociated from them by subjecting them to a
sufficiently low pressure. The change of colour which ensues when
this loosely combined oxygen is removed, is characteristic; the
crystals become darker and more of a purple hue, and at the same
time dichroic, so that while the thin edges appear green, the
thicker ridges are purple.

An ordinary solution of haemoglobin, like the crystals from
which it is formed, contains a definite quantity of oxygen in
a similarly peculiar loose combination; this oxygen it also gives up
at a sufficiently low pressure, becoming at the same time of
a purplish hue. This loosely combined oxygen may also be
removed by passing a stream of hydrogen or other indifferent gas
through the solution, whereby dissociation is effected. It may
also be got rid of by the use of reducing agents. Thus if a few
drops of ammonium sulphide or of an alkaline solution of ferrous
sulphate, kept from precipitation by the presence of tartaric acid,
be added to a solution of haemoglobin, or even to an unpurified
solution of blood corpuscles such as is afforded by the washings
from a blood clot, the oxygen in loose combination with the
haemoglobin is immediately seized upon by the reducing agent. This
may be recognised at once, by the characteristic change of colour ;
from a bright scarlet the solution becomes of a purplish claret colour,
when seen in any thickness, but green when sufficiently thin : the
colour of the reduced solution is exactly like that of the crystals
from which the loose oxygen has been removed by the air-pump.

Examined by the spectroscope, this reduced solution, or solution
of reduced haemoglobin as we may now call it, offers a spectrum
(Fig. 58. 5) entirely different from that of the unreduced solution.
The two absorption bands have disappeared, and in their place
there is seen a single, much broader, but at the same time much
fainter band whose middle occupies a position about midway be-
tween the two absorption bands of the unreduced solution, though
the red-ward edge of the band shades away rather farther towards
the red than does the other edge towards the blue; its centre
corresponds to about wave length 555. At the same time the
general absorption of the spectrum is different from that of the
unreduced solution ; less of the blue end is absorbed. Even when
the solutions become tolerably concentrated, many of the bluish-
green rays to the blue side of the single band still pass through.
F. 22

338 HMMOGLOBIN. [BOOK n.

Hence the difference in colour between haemoglobin which retains
the loosely combined oxygen1, and haemoglobin which has lost its
oxygen and become reduced. In tolerably concentrated solutions,
or tolerably thick layers, the former lets through the red and the
orange-yellow rays, the latter the red and the bluish-green rays.
Accordingly, the one appears scarlet, the other purple. In dilute
solutions, or in a thin layer, the reduced haemoglobin lets through
so much of the green rays that they preponderate over the red, and
the resulting impression is one of green. In the unreduced haemo-
globin or oxyhaemoglobin, the potent yellow which is blocked out
in the reduced haemoglobin makes itself felt, so that a very thin
layer of oxyhaemoglobin, as in a single corpuscle seen under the
microscope, appears yellow rather than red.

When the haemoglobin solution (or crystal) which has lost its
oxygen by the action either of the air-pump or of a reducing agent
or by the passage of an indifferent gas, is exposed to air containing
oxygen, an absorption of oxygen at once takes place. If sufficient
oxygen be present, the whole of the haemoglobin seizes upon its
complement, each gramme taking up in combination T59 c.cm. of
oxygen ; if there be an insufficient quantity of oxygen, a part only
of the haemoglobin gets its allowance and the remainder continues
reduced. If the amount of oxygen be sufficient, the solution (or
crystal), as it takes up the oxygen, regains its bright scarlet colour,
and its characteristic absorption spectrum, the single band being
replaced by the two. Thus if a solution of oxyhaemoglobin in a
test-tube after being reduced by the ferrous salt, and shewing the
purple colour and the single band, be shaken up with air, the
bright scarlet colour at once returns, and when the fluid is placed
before the spectroscope, it is seen that the single faint broad band
of the reduced haemoglobin has wholly disappeared, and that in its
place are the two sharp thinner bands of the oxyhaemoglobin. If
left to stand in the test-tube the quantity of reducing agent still
present is generally sufficient again to rob the haemoglobin of the
oxygen thus newly acquired, and soon the scarlet hue fades back
again into the purple, the two bands giving place to the one.
Another shake and exposure to air will however again bring back
the scarlet hue and the two bands ; and once more these may dis-
appear. In fact, a few drops of the reducing fluid will allow this
game of taking oxygen from the air and giving it up to the reducer
to be played over and over again, and at each turn of the game the
colour shifts from scarlet to purple, and from purple to scarlet,
while the two bands exchange for the one, and the one for the two.

Colour of venous and arterial Blood. Evidently we have in
these properties of haemoglobin an explanation of at least one-half

1 For brevity's sake we may call the haemoglobin containing oxygen in loose
combination, oxyhcemoglobin, and the haemoglobin from which this loosely combined
oxygen has been removed, reduced haemoglobin or simply haemoglobin.

CHAP, ii.] RESPIRATIOX. 339

of the great respiratory process, and they teach us the meaning of
the change of colour which takes place when venous blood becomes
arterial or arterial venous. In venous blood, as it issues from the
right ventricle, the oxygen present is insufficient to satisfy the
whole of the haemoglobin of the red corpuscles ; much reduced hae-
moglobin is present, hence the purple colour of venous blood.

When ordinary venous blood, diluted without access of oxygen,
is brought before the spectroscope, the two bands of oxyhsemo-
globin are seen. This is explained by the fact that in a mixture
of oxyhsemoglobin and (reduced) haemoglobin, the two sharp bands
of the former are always much more readily seen than the much
fainter band of the latter. Now in ordinary venous blood there is
always some loose oxygen, removable by diminished pressure or
otherwise ; there is always some, indeed a considerable quantity, of
oxyhsemoglobin as well as (reduced) haemoglobin. It is only in
the very last stages of asphyxia that all the loose oxygen of the blood
disappears ; and then the two bands of the oxyhaemoglobin vanish
too. So distinct are the two bands of even a small quantity of
oxyhaemoglobin in the midst of a large quantity of haemoglobin
that a solution of (completely reduced) haemoglobin may be used
as a test for the presence of oxygen.

As the blood passes through the capillaries of the lungs, this
reduced haemoglobin takes from the pulmonary air its complement
of oxygen, all or nearly all the haemoglobin of the red corpuscles
becomes oxyhaemoglobin, and the purple colour forthwith shifts
into scarlet.

The haemoglobin of arterial blood is saturated or nearly satu-
rated with oxygen. By increasing the pressure of the oxygen,
an additional quantity may be driven into the blood, but this,
after the haemoglobin has become completely saturated, is effected
by simple absorption. The quantity so added is extremely small
compared with the total quantity combined with the haemoglobin,
but its physiological importance is increased by its being present
at a high tension.

Passing from the left ventricle to the capillaries, some of the
oxyhaemoglobin gives up its oxygen to the tissues, becomes
reduced haemoglobin, and the blood in consequence becomes once
more venous, with a purple hue. Thus the red corpuscles by
virtue of their haemoglobin are emphatically oxygen-carriers.
Undergoing no intrinsic change in itself, the haemoglobin combines
in the lungs with oxygen, which it carries to the tissues; these,
more greedy of oxygen than itself, rob it of its charge, and the
reduced haemoglobin hurries back to the lungs in the venous
blood for another portion. The change from venous to arterial
blood is then in part (for as we shall see there are other events as
well) a peculiar combination of haemoglobin with oxygen, while
the change from arterial to venous is, in part also, a reduction of
oxyhaemoglobin; and the difference of colour between venous and

*)•) 9

340 COLOUR OF VENOUS AND ARTERIAL BLOOD. [BOOK 11.

arterial blood depends almost entirely on the fact that the reduced
haemoglobin of the former is of purple colour, while the oxy-
hsemoglobin of the latter is of a scarlet colour.

There may be other causes of the change of colour, but these
are wholly subsidiary and unimportant. When a corpuscle swells,
its refractive power is diminished, and in consequence the number
of rays which pass into and are absorbed by it are increased at the
expense of those reflected from its surface; anything therefore
which swells the corpuscles, such as the addition of water, tends to
darken blood, and anything, such as a concentrated saline solution,
which causes the corpuscles to shrink, tends to brighten blood.
Carbonic acid has apparently some influence in swelling the
corpuscles, and therefore may aid in darkening the venous blood.

We have spoken of the combination of haemoglobin with
oxygen as being a peculiar one. The peculiarity consists in the
facts that the oxygen may be associated and dissociated, without
any general disturbance of the molecule of haemoglobin, and that
dissociation may be brought about very readily. Haemoglobin
combines in a wholly similar manner with other gases. If car-
bonic oxide be passed through a solution of haemoglobin, a change
of colour takes place, a peculiar bluish tinge making its ap-
pearance. At the same time the spectrum is altered ; two bands
are still visible, but on accurate measurement it is seen that they
are placed more towards the blue end than are the otherwise
similar bands of oxyhaemoglobin (see Fig. 58. 6) ; their centres corre-
sponding respectively to about wave-lengths 572, and 533, while
those of oxyhaemoglobin as we have seen correspond to 578 and
539. When a known quantity of carbonic oxide gas is sent through
a haemoglobin solution, it will be found on examination that a
certain amount of the gas has been retained, an equal volume of
oxygen appearing in its place in the gas which issues from the
solution. If the solution so treated be crystallized, the crystals will
have the same characteristic colour, and give the same absorption
spectrum as the solution; when subjected to the action of the
mercurial pump, they will give off a definite quantity of carbonic
oxide, 1 grm. of the crystals yielding 1*59 c.cm. of the gas. ^In
fact, haemoglobin combines loosely with carbonic oxide just as it
does with oxygen ; but its affinity with the former is greater than
with the latter. While carbonic oxide readily turns out oxygen,
oxygen cannot so readily turn out carbonic oxide. Indeed,
carbonic oxide has been used as a means of driving out and
measuring the quantity of oxygen present in any given blood.
This property of carbonic oxide explains its poisonous nature.
When the gas is breathed, the reduced and the unreduced haemo-
globin of the venous blood unite with the carbonic oxide, and
hence the peculiar bright cherry-red colour observable in the blood
and tissues in cases of poisoning by this gas. The carbonic oxide
.haemoglobin, however, is of no use in respiration ; it is not an

CHAP, ii.] RESPIRATIOX. 341

oxygen-carrier, nay more, it will not readily, though it does so
slowly and eventually, give up its carbonic oxide for oxygen, when
the poisonous gas ceases to enter the chest and is replaced by pure
air. The organism is killed by suffocation, by want of oxygen, in
spite of the blood not assuming any dark venous colour. As
Bernard phrased it, the corpuscles are paralysed.

Haemoglobin similarly forms a compound, having a character-
istic spectrum, with nitric oxide, more stable even than that with
carbonic oxide.

It has been supposed by some that the oxygen thus associated
with haemoglobin is in the condition known as ozone ; but the
arguments urged in support of this view are inconclusive.

Although a crystalline body, haemoglobin diffuses with great
difficulty. This arises from the fact that it is in part a proteid
body; it consists of a colourless proteid, associated with a coloured
compound named hcematin. All the iron belonging to the haemo-
globin is in reality attached to the haematin. A solution of
haemoglobin, when heated, coagulates, the exact degree at which
the coagulation takes place depending on the amount of dilution ;
at the same time it turns brown from the setting free of the
haematin. If a strong solution of haemoglobin be treated with
acetic (or other) acid, the same brown colour, from the appearance
of haematin, is observed. The proteid constituent however is not
coagulated, but by the action of the acid passes into the state of
acid-albumin. On adding ether to the mixture, and shaking, the
haematin is dissolved in the supernatant acid ether, which it colours
a dark red, and which, examined with the spectroscope, is found to
possess a well-marked spectrum, the spectrum of the so-called acid
haematin of Stokes. The proteid in the water below the ether
appears in a coagulated form owing to the action of the ether. In
a somewhat similar manner alkalis split up haemoglobin into a
proteid constituent and haematin.

The exact nature of the proteid constituent of haemoglobin
has not as yet been clearly determined. It was supposed to
be globulin, (hence the name haematoglobulin contracted into
haemoglobin), but though belonging to the globulin family, has
characters of its own; it is possibly a mixture of two or more
distinct proteids. It has been provisionally named globin and is
said to be free from ash. Haematin when separated from its
proteid fellow, and purified, appears as a dark-brown amorphous
powder, or as a scaly mass with a metallic lustre, having the
probable composition of CS2, H^, N4, Fe, 06. It is fairly soluble
in dilute acid or alkaline solutions, and then gives characteristic
spectra.

An interesting feature in haematin is that its alkaline solution
is capable of being reduced by reducing agents, the spectrum
changing at the same time, and that the reduced solution will, like
the haemoglobin, take up oxygen again on being brought into

342 CARBONIC ACID IN THE BLOOD. [BOOK n,

contact with air or oxygen. This would seem to indicate that the
oxygen-holding power of haemoglobin is connected exclusively
with its haematin constituent. By the action of strong sulphuric
acid haematin may be robbed of all its iron. It still retains the
feature of possessing colour, the solution of iron-free haematin
being a dark rich brownish red ; but is no longer capable of com-
bining loosely with oxygen. This indicates that the iron is in
some way associated with the peculiar respiratory functions of
haemoglobin; though it is obviously an error to suppose, as was
once supposed, that the change from venous to arterial blood
consists essentially in a change from a ferrous to a ferric salt.

Though not crystallizable itself, haematin forms with hydro-
chloric acid a compound, occurring in minute rhombic crystals,
known as haemin crystals.

In conclusion, the condition of oxygen in the blood is as
follows. Of the whole quantity of oxygen in the blood, only a
minute fraction is simply absorbed or dissolved, according to the
law of pressures (the Henry-Dalton law). The great mass is in a
state of combination with the haemoglobin, the connection being of
such a kind that while the haemoglobin readily combines with the
oxygen of the air to which it is exposed, dissociation readily occurs
at low pressures, or in the presence of indifferent gases, or by the
action of substances having a greater affinity for oxygen than has
haemoglobin itself. The difference between venous and arterial
blood, as far as oxygen is concerned, is that while in the latter
there is an insignificant quantity of reduced haemoglobin, in the
former there is a great deal; and the characteristic colours of
venous and arterial blood are in the main due to the fact that the
colour of reduced haemoglobin is purple, while that of oxyhaemo-
globin is scarlet.

The relations of the Carbonic Acid in the Blood.

The presence of carbonic acid in the blood appears to be detei-
mined by conditions more complex in their nature and at present
not so well understood as those which determine the presence of
oxygen. The carbonic acid is not simply dissolved in the blood; its
absorption by blood does not follow the law of pressures. It exists
in association with some substance or substances in the blood, and
its escape from the blood is a process of dissociation. We cannot
however speak of it as being associated, to the same extent as is
the oxygen, with the haemoglobin of the red corpuscles. So far
from the red corpuscles containing the great mass of the carbonic
acid, the quantity of this gas which is present in a volume of serum

CHAP. IL] RESPIRATION. 343

is according to some observers actually greater than that which is
present in an equal volume of blood, i.e. an equal volume of mixed
corpuscles and serum.

When serum is subjected to the mercurial vacuum, by far the
greater part of the carbonic acid is given off; but a small additional
quantity (2 to 5 vols. per cent.) may be extracted by the subsequent
addition of an acid. This latter portion may be spoken of as 'fixed'
carbonic acid in distinction to the larger 'loose' portion which is
given off to the vacuum. When however the whole blood is subjected
to the vacuum, all the carbonic acid is given off, so that when
serum is mixed with corpuscles all the carbonic acid may be spoken
of as 'loose'; and it is stated that the excess of carbonic acid in
serum over that present in entire blood, corresponds to the fixed
portion in serum which has to be driven off by an acid. Moreover,
even those who maintain that the quantity of carbonic acid in blood
is less than that in an equal volume of serum, admit that the
tension of the carbonic acid in blood is greater than in serum.

If these statements be accepted it seems probable that the
carbonic acid exists associated with some substance or substances
in the serum, but that the conditions of its association (and therefore
of its dissociation) are determined by the action of some substance or
substances present in the corpuscles. It is further probable that
the association of the carbonic acid in the serum is with sodium as
sodium bicarbonate, and it is even possible that the haemoglobin of
the corpuscles plays a part in promoting the dissociation of the
sodium bicarbonate or even the carbonate, and thus keeping up the
carbonic acid tension of the entire blood. Other observers however
maintain that the serum does not hold this exclusive possession of
the carbonic acid, but that a considerable quantity of this gas is in
some way associated with the red corpuscles. Indeed further
investigations are necessary before the matter can be said to
have been placed on a satisfactory footing.

The relations of the Nitrogen in the Blood.

The small quantity of this gas which is present in both arterial
and venous blood seems to exist in a state of simple solution.

SEC. 4. THE RESPIRATORY CHANGES IN THE LUNGS.

The entrance of Oxygen.

We have already seen that the blood in passing through the
lungs takes up a certain variable quantity (from 8 to 12 vols. p. c.)
of oxygen. We have further seen that the quantity so taken
up, putting aside the insignificant fraction simply absorbed,
enters into direct but loose combination with the haemoglobin.
In drawing a distinction between the oxygen simply absorbed
and that entering into combination with the haemoglobin, it
must not be understood that the latter is wholly independent
of pressure. On the contrary all chemical compounds are in
various degrees subject to dissociation at certain pressures and
temperatures ; and the existence of the somewhat loose compound of
oxygen and hsemoglobin is dependent on the partial pressure of
oxygen in the atmosphere to which the haemoglobin is exposed. A
solution of hsemoglobin or a quantity of blood will either absorb
oxygen and thus undergo association or will undergo dissociation
and give off oxygen according as the partial pressure of oxygen
in the atmosphere to which it is exposed is high or low, and the
amount taken up or given off will depend on the degree of the
partial pressure. But the law according to which absorption or
escape thus takes place is quite different from that observed in the
simple absorption of oxygen by liquids. The association or dis-

CHAP. IL] RESPIRATION. 345

sociation is further especially dependent on temperature, a high
temperature favouring dissociation so that at a high temperature
less oxygen is taken up than would be taken up (or more given off
as the case may be than would be given off) at a lower
temperature, the partial pressure of the oxygen in the atmosphere
remaining the same.

Hence the question arises, Are the conditions in which haemo-
globin and oxygen exist in ordinary venous blood as it flows to the
lungs, of such a kind that the venous blood in passing through the
pulmonary capillaries will find the partial pressure of the oxygen
in the pulmonary alveoli sufficient to bring about the association of
the additional quantity of oxygen whereby the venous is converted
into arterial blood ?

The oxygen of expired air contains (in man) as we have seen
about 16 p. c. of oxygen. The air in the pulmonary alveoli must
contain rather less than this, since the expired air consists of tidal
air mixed by diffusion with the stationary air. How much less
it contains we do not exactly know, but probably the difference
is not very great. The question therefore stands thus, Will venous
blood, exposed at the temperature of the body to a partial pressure
of less than 16 p. c. of oxygen, take up sufficient oxygen (from 8 to
12 vols. p. c.) to convert it into arterial blood ? Numerous experi-
ments have been made (chiefly on the dog) to determine on the one
hand the oxygen-tension of both arterial and venous blood (i.e. the
partial pressure of oxygen in an atmosphere exposed to which the
arterial blood neither gives up nor takes in oxygen, and the same
for venous blood) and on the other hand the behaviour at the
temperature of the body or at ordinary temperatures of blood or of
solutions of haemoglobin (for the two behave in this respect very
much alike) towards an atmosphere in which the partial pressure
of oxygen is made to vary. Without going into detail, we may state
that these experiments shew that the partial pressure of oxygen
in the lungs is amply sufficient to bring about, at the temperature
of the body, the association of that additional amount of oxygen by
which venous blood becomes arterial. When a solution of haemo-
globin or when blood is successively exposed to increasing oxygen
pressures, as the partial pressure of oxygen is gradually increased,
the curve of absorption rises at first very rapidly but afterwards more
slowly, that is to say, the later additions of oxygen at the higher
pressures are proportionately less than the earlier ones, at the
lower pressures. And this is consonant with what appears to be
the fact that the haemoglobin of arterial blood though nearly
saturated with oxygen, i.e. associated with almost its full comple-
ment of oxygen, is not quite saturated. When arterial blood,
is thoroughly exposed to air, it takes up rather more than 1 vol. \
p. c. of oxygen; and that appears to represent the difference
between exposing blood to air as it enters the mouth in inspiration
and exposing blood to the air as it exists in the pulmenary alveoli.

346 EXIT OF CARBONIC ACID. [BOOK n.

The greater relative absorption at the lower pressures has a
beneficial effect in as much as it still permits a considerable quantity
of oxygen to be absorbed even when the partial pressure of oxygen
in the air in the lungs is largely reduced, as in ascending to great
heights.

The statements made so far refer to ordinary breathing, but
the question may be asked, What happens when the renewal of
the air in the pulmonary alveoli ceases, as when the trachea
is obstructed ? In such a case the oxygen in the alveoli is found
to diminish rapidly so that the partial pressure of oxygen in them
soon falls below the oxygen tension of ordinary venous blood. But
in such a case the blood is no longer ordinary venous blood ; instead
of containing a comparatively small amount, it contains a large and
gradually increasing amount, of reduced haemoglobin. And as the
reduced haemoglobin increases in amount, the oxygen tension of the
venous blood decreases ; it thus keeps below that of the air in the
lungs. Hence even the last traces of oxygen in the lungs are
taken up by the blood, and carried away to the tissues ; so that
with the last heart's beat, when the oxygen in the lungs has sunk
to a mere fraction, the bands of oxyhaemoglobin may still, it is said,
be detected for a moment in the blood of the left side of the heart
shewing that oxygen has even still been absorbed.

The exit of Carbonic Acid.

It seems natural to suppose that the carbonic acid would
escape by diffusion from the blood of the alveolar capillaries
into the air of the alveoli. But in order that diffusion should
thus take place, the carbonic acid tension of the air in the
pulmonary alveoli must always be less than that of the venous
blood of the pulmonary artery and indeed ought not to exceed
that of the blood of the pulmonary vein. There are however
many practical difficulties in the way of an exact determi-
nation of the carbonic acid tension of the pulmonary alveoli (for
though it must be greater than that of the expired air, it is
difficult to say how much greater), and of the carbonic acid tension
of the blood at the same time, so as to be in a position to compare
the one with the other. In the case of oxygen, there is always
present in the lungs a surplus of the gas, a portion only being
absorbed at each breath ; in the case of carbonic acid, the whole
quantity comes direct from the blood, and any modifications in
breathing seriously affect the amount given out. Thus when the
breath is held for some time the percentage of carbonic acid in the
expired air reaches 7 or 8 p.c., but we cannot take this as a measure
of the normal percentage of carbonic acid in the pulmonary alveoli,

CHAP, ir.] RESPIRATION. 347

since by the mere holding of the breath the carbonic acid in the
blood and in the pulmonary alveoli is increased beyond the normal.
The difficulties of the problem seem however to have been
overcome by an ingenious experiment in which there is introduced
into the bronchus of the lung of a dog a catheter, round which is
arranged a small bag ; by the inflation of this bag the bronchus,
whenever desired, can be completely blocked up. Thus, without any
disturbance of the general breathing, and therefore without any
change in the normal proportions of the gases of the blood, the ex-
perimenter is able to stop the ingress of fresh air into a limited
portion of the lung. At the same time he is enabled by means of
the catheter to withdraw a sample of the air of the same limited
portion, and, by analysis to determine its carbonic acid tension.
The blood passing through the alveolar capillaries of this limited
portion of the lung naturally possesses the same carbonic acid
tension as the rest of the venous blood flowing through the
pulmonary artery, a tension which, though varying slightly
from moment to moment, will maintain a normal average. On
the supposition that carbonic acid passes simply by diffusion
from the pulmonary blood into the air of the alveoli, because the
carbonic acid tension of the latter is normally lower than that of
the former, one would expect to find that the air in the occluded
portion of the lung would continue to take up carbonic acid
until an equilibrium was established between it and the carbonic
acid tension of the venous blood. Consequently if after an
occlusion, say of some minutes (by which time the equilibrium
might fairly be assumed to have been established), the carbonic
acid tension of the air of the occluded portion were determined, it
ought to be found to be equal to, and not more than equal to, the
carbonic acid tension of the venous blood of the pulmonary artery.
And this is the result which has been arrived at; it has been
found that the tensions of the carbonic acid of the occluded air and
of the venous blood of the right side of the heart are just about
equal, that of the occluded air being, if anything, slightly less than
that of the venous blood. So that the evidence so far as it goes is
distinctly in favour of the view that the escape of carbonic acid
from the blood into the pulmonary alveoli is simply due to diffusion,
and that there is no need to seek for any further explanation.
There is for instance no necessity to suppose that the epithelium
of the pulmonary alveoli has any specific secretory power of
discharging carbonic acid from the blood independently of or
in antagonism to the influence of pressures.

SEC. 5. THE RESPIRATORY CHANGES IN THE TISSUES.

In passing through the several tissues the arterial blood
becomes once more venous. A considerable quantity of the oxy-
hsemoglobin becomes reduced, and a quantity of carbonic acid
passes from the tissues into the blood. The amount of change
varies in the various tissues, and in the same tissue may vary at
different times. Thus in a gland at rest, as we have seen, the
venous blood is dark, shewing the presence of a large quantity of
reduced haemoglobin ; when the gland is active, the venous blood
in its colour, and in the amount of haemoglobin which it contains,
resembles closely arterial blood. The blood therefore which issues
from a gland at rest is more 'venous' than that from an active
gland ; though owing to the more rapid flow of blood which, as we
saw in an earlier section, accompanies the activity of the gland, the
total quantity of carbonic acid discharged into the blood from the
gland in a given time may be greater in the latter. The blood, on
the other hand, which comes from an active i.e. a contracting
muscle, is, in spite of the more rapid flow, not only richer in
carbonic acid, but also, though not to a corresponding amount,
poorer in oxygen than the blood which flows from a muscle
at rest.

In all these cases the great question which comes up for our
consideration is this: Does the oxygen pass from the blood into the
tissues, and does the oxidation take place in the tissues, giving rise
to carbonic acid, which passes in turn away from the tissues into

CHAP, ii.] RESPIRATION 349

the blood ? or do certain oxidizable reducing substances pass from
the tissues into the blood, and there become oxidized into carbonic
acid and other products, so that the chief oxidation takes place in
the blood itself?

There are, it is true, reducing oxidizable substances in the
blood, but these are small in amount, and the quantity of carbonic
acid to which they give rise when the blood containing them is
agitated with air or oxygen, is so small as scarcely to exceed the
errors of observation.

On the other hand, it will be remembered that in speaking of
muscle, we drew attention to the fact that a frog's muscle removed
from the body (and the same is true of the muscles of other animals)
contains no free oxygen whatever; none can be obtained from
it by the mercurial air-pump. Yet such a muscle will not only
when at rest go on producing and discharging a certain quantity,
but also when it contracts evolve a very considerable quantity, of
carbonic acid. Moreover this discharge of carbonic acid will go on
for a certain time in muscles under circumstances in which it is
impossible for them to obtain oxygen from without. Oxygen, it is
true, is necessary for the life of the muscle : when venous instead
of arterial blood is sent through the blood-vessels of a muscle, the
irritability speedily disappears, and unless fresh oxygen be ad-
ministered the muscle soon dies. The muscle may however,
during the interval in which irritability is still retained after the
supply of oxygen has been cut off, continue to contract vigorously.
The supply of oxygen, though necessary for the maintenance of
irritability, is not necessary for the manifestation of that irritability,
is not necessary for that explosive decomposition which developes
a contraction. A frog's muscle will continue to contract and to
produce carbonic acid in an atmosphere of hydrogen or nitrogen,
that is in the total absence of free oxygen both from itself and
from the medium in which it is placed.

Thus on the one hand the muscle seems to have the property
of taking up and fixing in some way or other the oxygen to which
it is exposed, of converting it into intra-molecular oxygen, in which
condition it cannot be removed by simple diminished pressure, so
that the tension of oxygen in the muscular substance may be con-
sidered as always nil ; while on the other hand the muscular sub-
stance is always undergoing a decomposition of such a kind that
carbonic acid is set free, sometimes, as when the muscle is at rest,
in small, sometimes, as during a contraction, in large quantities.
But if the oxygen tension of the muscular tissue be thus always
nil, the oxygen of the blood-corpuscles, in which it is at a com-
paratively high tension, will be always passing over, through the
plasma, through the capillary walls, the lymph spaces and the
sarcolemma, into the muscular substance, and as soon as it arrives
there will be hidden away as intra-molecular oxygen, leaving the
oxygen tension of the muscular substance once more nil. Con-

350 CHANGES IN THE TISSUES. [BOOK n.

versely, the carbonic acid produced by the decomposition of the
muscular substance will tend to raise the carbonic acid tension of
the muscle until it exceeds that of the blood ; whereupon it will
pass from the muscle into the blood, its place in the muscular
substance being supplied by freshly generated carbonic acid.
There will always in fact be a stream of oxygen from the blood to
the muscle and of carbonic acid from the muscle to the blood.
The respiration of the muscle then does not consist in throwing
into the blood oxidizable substances there to be oxidized into car-
bonic acid and other matters; but it does consist in the assumption
of oxygen (as intra-molecular oxygen), in the building up by help
of that oxygen of explosive decomposable substances, and in the
occurrence of decompositions whereby carbonic acid and other
matters are discharged first into the substance of the muscle and
subsequently into the blood. We cannot as yet trace out the steps
taken by the oxygen from the moment it slips into its intra-
molecular position to the moment when it issues united with carbon
as carbonic acid. The whole mystery of life lies hidden in the
story of that progress, and for the present we must be content
with simply knowing the beginning and the end.

Our knowledge of the respiratory changes in muscle is more
complete than in the case of any other tissue; but we have no
reason to suppose the phenomena of muscle are exceptional. On
the contrary, all the available evidence goes to shew that in all
tissues the oxidation takes place in the tissue, and not in the
adjoining blood. It is a remarkable fact, that lymph, serous fluids,
bile, urine, and milk contain a mere trace of free or loosely
combined oxygen, and saliva or pancreatic juice a very small quan-
tity only, while the tension of carbonic acid in peritoneal fluid and
probably in the tissues of the intestinal walls is higher than that
of venous blood, and in bile and urine is still greater. The tension
of carbonic acid in lymph, while higher than that of arterial blood,
is lower than that of the general venous blood ; but this probably
is due to the fact that the lymph in its passage onwards is largely
exposed to arterial blood in the connective tissues and in the
lymphatic glands, where the production of carbonic acid is slight
as compared to that going on in muscles. All these facts point to
the conclusion, that it is the tissues, and not the blood, which
become primarily loaded with carbonic acid, the latter simply
receiving the gas from the former by diffusion, except the (pro-
bably) small quantity which results from the metabolism of the
blood-corpuscles; and that the oxygen which passes from the
blood into the tissues is at once taken up in some combination, so
that it is no longer removable by diminished tension.

In further support of this view may be urged the fact that if, in
a frog, the whole blood of the body be replaced by normal saline solu-
tion, the total metabolism of the body is, for some time, unchanged.
The saline medium is able owing to the low rate of metabolism,

CHAP, ii.] RESPIRATIOX. 351

and large respiratory surface of the animal, to supply the tissues
with all the oxygen they need, and to remove all the carbonic acid
they produce. It is difficult to believe that, in such an experiment,
the oxidation took place in the saline solution itself while cir-
culating in the blood-vessels and tissue-spaces of the animal.

We may add, that the oxidative power which the blood itself
removed from the body is able to exert on substances which are
undoubtedly oxidized in the body is so small that it may be
neglected in the present considerations. If grape-sugar be added
to blood, or to a solution of haemoglobin, the mixture may be kept
for a long time at the temperature of the body, without undergoing
oxidation. Even "within the body a slight excess of sugar in the
blood over a certain percentage wholly escapes oxidation, and is
discharged unchanged. Many easily oxidized substances, such as
pyrogallic acid, pass largely through the blood of a living body
without being oxidized. The organic acids, such as citric, even
in combination with alkaline bases, are only partially oxidized;
when administered as acids, and not as salts, they are hardly
oxidized at all. It is of course quite possible that the changes
which the blood undergoes when shed might interfere with its
oxidative action, and hence the fact that shed blood has little
or no oxidizing power, is not a satisfactory proof that the un-
changed blood within the living vessels may not have such a
power. But did oxidation take place largely in the blood itself,
one would expect even highly diffusible substances to be oxidized
in their transit; whereas if we suppose the oxidation to take place
in the tissues, it becomes intelligible why such diffusible substances
as those which the tissues in general refuse to take up largely,
should readily pass unchanged from the blood through the secreting
organs.

We have seen that in muscle the production of carbonic acid
is not directly dependent on the consumption of oxygen. The
muscle produces carbonic acid in an atmosphere of hydrogen. What
is true of muscle is true also of other tissues and of the body
at large. Spallanzani and W. Edwards shewed long ago that
animals might continue to breathe out carbonic acid in an
atmosphere of nitrogen or hydrogen: and more recently Pfliiger
has shewn, by a remarkable experiment, that a frog kept at a
low temperature will live for several hours, and continue to
produce carbonic acid, in an atmosphere absolutely free from
oxygen. The carbonic acid produced during this period was made
by help of the oxygen inspired in the hours anterior to the com-
mencement of the experiment. The oxygen then absorbed was
stowed away from the haemoglobin into the tissues, it was made
use of to build up the explosive compounds, whose explosions later
on gave rise to the carbonic acid. Or, to adopt Pfliiger's simile, the
oxygen helps to wind up the vital clock; but once wound up the
clock will go on for a period without further winding. The frog

352 CHANGES IN THE TISSUES. [BOOK n.

will continue to live, to move, to produce carbonic acid for a while
without any fresh oxygen, as we know of old it will without any
fresh food; it will continue to do so till the explosive compounds
which the oxygen built up are exhausted ; it will go on till the
vital clock has run down.

To sum up, then, the results of respiration in its chemical
aspects. As the blood passes through the lungs, the low oxygen
tension of the venous blood permits the entrance of oxygen from
the air of the pulmonary alveolus, through the thin alveolar wall,
through the thin capillary sheath, through the thin layer of blood-
plasma, to the red corpuscle, and the reduced haemoglobin of the
venous blood becomes wholly, or all but wholly, oxyhsemoglobin.
Hurried to the tissues, the oxygen, at a comparatively high tension
in the arterial blood, passes largely into them. In the tissues, the
oxygen tension is always kept at an exceedingly low pitch, by the
fact that they, in some way at present unknown to us, pack away
at every moment into some stable combination each molecule of
oxygen which they receive from the blood. With much but not
all of its oxyhsemoglobin reduced, the blood passes on as venous
blood. How much haemoglobin is reduced will depend on the
activity of the tissue itself. The quantity of haemoglobin in the
blood is the measure of limit of the oxidizing power of the body
at large ; but within that limit the amount of oxidation is deter-
mined by the tissue, and by the tissue alone.

We cannot trace the oxygen through its sojourn in the tissue.
We only know that sooner or later it comes back combined in
carbonic acid (and other matters not now under consideration).
Owing to the continual production of carbonic acid, the tension
of that gas in the extravascular elements of the tissue is always
higher than that of the blood ; the gas accordingly passes from
the tissue into the blood, and the venous blood passes on not only
with its haemoglobin reduced, i.e. with its oxygen tension decreased,
bat also with its carbonic acid tension increased. Arrived at the
lungs, the blood finds the pulmonary air at a lower carbonic acid
tension than itself. The gas accordingly streams through the thin
vascular and alveolar walls, till the tension without the blood-vessel
is equal to the tension within. At the same time the blood finds
in the air of the pulmonary alveoli a supply of oxygen, more than
adequate to convert the greater part of the reduced haemoglobin
back again to oxyhaemoglobin. Thus the air of the pulmonary
alveoli, having given up oxygen to the blood and taken up carbonic
acid from the blood, having a higher carbonic acid tension and a
lower oxygen tension than the tidal air in the bronchial passages,
mixes rapidly with this by diffusion. The mixture is further assisted
by ascending and descending currents; and the tidal air issues from
the chest at the breathing out poorer in oxygen and richer in
carbonic acid than the tidal air which entered at the breathing in.

SEC. 6. THE NERVOUS MECHANISM OF RESPIRATION.

Breathing is an involuntary act. Though the diaphragm and
all the other muscles employed in respiration are voluntary muscles,
i.e. muscles which can be called into action by a direct effort of the
will, and though respiration may be modified within very wide
limits by the will, yet we habitually breathe without the interven-
tion of the will : the normal breathing may continue, not only in
the absence of consciousness, but even after the removal of all
the parts of the brain above the medulla oblongata.

We have already seen how complicated is even a simple respira-
tory act. A very large number of muscles are called into play.
Many of these are very far apart from each other, such as the
diaphragm and the nasal muscles ; yet they act in harmonious
sequence in point of time. If the lower intercostal muscles con-
tracted before the scaleni, or if the diaphragm contracted alternately
with the other chest-muscles, the satisfactory entrance and exit of
air would be impossible. These muscles moreover are coordinated
also in respect of the amount of their several contractions ; a gentle
and ordinary contraction of the diaphragm is accompanied by gentle
and ordinary contractions of the intercostals, and these are preceded
by gentle and ordinary contractions of the scaleni. A forcible con-
traction of the scaleni, followed by simply a gentle contraction of
the intercostals, would perhaps hinder rather than assist inspiration,
and at all events would be waste of power. Further, the whole com-
plex inspiratory effort is often followed by a less marked but still
complex expiratory action. It is impossible that all these so

F. 23

354 NERVOUS MECHANISM. [BOOK n.

carefully coordinated muscular contractions should be brought
about in any other way than by coordinate nervous impulses
descending along efferent nerves from a coordinating centre. By
experiment we find this to be the case.

When in a rabbit the trunk of a phrenic nerve is cut, the dia-
phragm on that side remains motionless, and respiration goes on
without it. When both nerves are cut, the whole diaphragm
remains quiescent, though the respiration becomes excessively
laboured.

When an intercostal nerve is cut, no active respiratory move-
ment is seen in that space, and when the spinal cord is divided
below the origin of the seventh cervical spinal nerve, costal
respiration ceases, though the diaphragm continues to act and
that with increased vigour. WThen the cord is divided just below
the medulla, all thoracic movements cease, but the respiratory
actions of the nostrils and glottis still continue. These however
disappear when the facial and recurrent laryngeal are divided. We
have already stated that after removal of the brain above the
medulla, respiration still continues very much as usual, the modifi-
cations which ensue from loss of the brain being unessential.
Hence, putting all these facts together, it is clear that the
respiratory movements are, as we suggested, brought about by
coordinated impulses which, originated in the medulla, find their
way thence along the several efferent nerves. The proof is completed
by the fact that the removal or extensive injury of the medulla
alone is, save in exceptional cases, at once followed by the cessation
of all respiratory movements, even though every muscle and every
nerve concerned be left intact. Nay more, if only a small portion
of the medulla, a tract whose limts are not as yet exactly fixed,
but which lies below the vaso-motor centre, between it and the
calamus scriptorius, be removed or injured, respiration ceases,
and death at once ensues. Hence this portion of the nervous
system was called by Flourens the vital knot, or ganglion of life,
nosud vital. We shall speak of it as the respiratory centre.

The nature of this centre must be exceedingly complex ; for
while even in ordinary respiration it gives rise to a whole group of
coordinate nervous impulses of inspiration followed in due sequence
by a smaller but still coordinate group of expiratory impulses, in
laboured respiration fresh and larger impulses are generated,
though still in coordination with the normal ones, the expiratory
events being especially augmented; and in the cases of more
extreme dyspnrea and asphyxia impulses overflow, so to speak,
from it in all directions, though only gradually losing their co-
ordination, until almost every muscle in the body is thrown into
contractions.

We must not however conceive of this centre as one of such a
kind that the impulses leave it fully coordinated and equipped so
that nothing remains for them but to travel, unchanged, along the

CHAP, n.j RESPIRATION. 355

several efferent nerve-fibres to their several muscular, destinations.
On the contrary we have reason to think that the respiratory motor
nerves, like other special nerves as they are about to issue from the
spinal cord, are connected with a nervous ganglionic machinery, —
a point which we shall consider more fully in treating of the spinal
cord ; and that the respiratory impulses pass into and are modified
by such spinal nervous machinery immediately before they issue
along the motor nerve-roots. Indeed recent observations shew
that under particular conditions, and especially in young animals,
respiratory movements may be carried out in the entire absence of
the medulla oblongata. Thus in a kitten, after removal of the
medulla, if the excitability of the spinal cord be heightened by
small doses of strychnia, not only may respiratory movements of
the chest be induced, in a reflex manner, by pinching or by
blowing on the skin, but even transient spontaneous efforts of
breathing may with care be observed. These are the excep-
tional instances mentioned above ; and they shew that the respi-
ratory nervous mechanism is not confined, as was once thought,
to the centre in the medulla, but also embraces other subsidiary
centres in the spinal cord below. The respiratory nervous sytem
seems in fact in many ways analogous to the vaso-motor nervous
system, with its head centre in the medulla, and secondary centres
elsewhere, and to the cardiac nervous system with its potent
ganglia in the sinus, and its secondary ganglia in the auricles, and
auriculo-ventricular groove. The matter is not at present thorough-
ly worked out, but we shall probably not greatly err in continuing
to speak of the centre in the medulla as being "the respiratory
centre" while admitting that it works through other nervous
machinery placed lower down in the spinal cord, and that this
subordinate machinery may, in exceptional cases, carry t>ut, though
inadequately, the work of the chief centre.

Admitting then the existence of this medullary respiratory
centre the question naturally arises, Are we to regard its rhythmic
action as due essentially to changes taking place in itself, or as due
to afferent nervous impulses cr other stimuli which affect it in a
rhythmic manner from without ? In other words, Is the action of
the centre automatic or purely reflex ? We know that the centre
may be influenced by impulses proceeding from without, and that
the breathing may be affected by the action of the will, or by an
emotion, or by a dash of cold water on the skin, or in a hundred
other ways ; but the fact that the action of the centre may be thus
modified from without, is no proof that the continuance of its
activity is dependent on extrinsic causes.

In attempting to decide this question we naturally turn to the
pneumogastric as being the nerve most likely to serve as the
channel of afferent impulses setting in action the respiratory centre.
If both vagi be divided, respiration still continues though in a
modified form. This proves distinctly that afferent impulses

2S-2

356 NERVOUS MECHANISM. [BOOK n;

ascending those nerves are not the efficient cause of the respiratory
movements. We have seen that when the spinal cord is divided
below the medulla, the facial and laryngeal movements still
continue. This proves that the respiratory centre is still in
action, though its activity is unable to manifest itself in any
thoracic movement. But when the cord is thus divided, the
respiratory centre is cut off from all sensory impulses, save those
which may pass into it from the cranial nerves ; and the division
of these cranial nerves by themselves, when the medulla and
spinal cord are left intact, does not destroy respiration. Hence
we may infer that the respiratory impulses proceeding from the
respiratory centre are not simply afferent impulses reaching the
centre along afferent nerves and transformed by reflex action in
that centre. They evidently start de now from the centre itself,
however much their characters may be affected by afferent impulses
reaching that centre at the time of their being generated. 'The
action of the centre is automatic, not simply reflex.

Among the afferent impulses which affect the automatic action
of the centre, the most important are those which ascend along
the vagi. If one vagus be divided, the respiration becomes slower;
if both be divided, it becomes very slow, the pauses between
expiration and inspiration being excessively prolonged. The
character of the respiratory movement too is markedly changed ;
each respiration is fuller and deeper, so much so indeed that,
according to some observers, what is lost in rate is gained in extent,
the amount of carbonic acid produced and oxygen consumed in a
given period remaining after division of the nerves about the
same as when these were intact. Without insisting too much on
the exactness of this compensation we may at least conclude from
the effects of section of the vagi, in the first place, that during life
afferent impulses are continually ascending the vagi and modifying
the action of the respiratory centre, and in the second place, that
the modification bears chiefly on the distribution in time of the
efferent respiratory impulses, and not so much on the amount to
which they are generated.

These afferent impulses are probably started in the lungs by
the condition of the blood in the pulmonary capillaries acting as a
stimulus to the peripheral endings of the nerves, though possibly
the altered air in the air-cells may also act as a stimulus to the
nerve-endings. It has further been suggested that the mere
movements of expansion and contraction may also serve as a
stimulus. Thus when air is mechanically driven into the chest, an
expiratory movement follows, and when air is drawn out, an in-
spiratory; and this not only with atmospheric air but with in-
different gases, such as nitrogen; when both vagi are cut, these
effects do not appear. So also, when in an animal, after division
of the spinal cord below the medulla, artificial respiration is kept
up, the respiratory movements of the nostrils follow the rhythm

CHAP, ii.] RESPIRATION. 357

of the artificial respiration so long as the vagi are intact; when
these are divided the movements of the nostrils exhibit a rhythm
independent of those of the chest. From this it is inferred that the
mere mechanical expansion of the lungs transmits along the vagus
an impulse tending to inhibit inspiration and to generate an ex-
piration, and the mechanical contraction of the lungs an impulse
tending to inhibit expiration and to generate an inspiration. That
is to say the very expansion of the lungs, which is the natural
effect of an inspiration, tends of itself to cut short that inspiration
and to inaugurate the sequent expiration, and similarly the
contraction of an expiration promotes the following inspiration.
The lungs in fact may be spoken of as being so far self-regulating.

The influence of the vagus is further shewn by the following
experiment. If the medulla oblongata be carefully divided in the
middle line respiration may continue to go on in quite a normal
fashion, indicating that the centre is composed of two lateral
halves placed one on each side of the median line. If however
one vagus be then divided, the respiratory movements both costal
and diaphragmatic, on the side of the body on which division of
the vagus has taken place, become slower than those on the other
side, so that the two sides are no longer synchronous. Obviously
the vagus influences primarily the respiratory centre of its own side ;
though under normal conditions the two halves of the centre work
in harmony and synchronism.

When after division of both vagi, the medulla being intact, the
central stump of one vagus is stimulated with a gentle interrupted
current, the respiration, which from the division of the nerves had
become slow, is quickened again; and with care, by a proper
application of the stimulus, the normal respiratory rhythm may
for a time be restored. Upon the cessation of the stimulus, the
slower rhythm returns. If the current be increased in strength,
the rhythm may in some cases be so accelerated that at last the
diaphragm is brought into a condition of prolonged tetanus, and
a standstill of respiration in an extreme inspiratory phase is the
result.

If the central end of the superior laryngeal branch of the vagus
be stimulated, whether the main trunk of the nerve be severed or
not, a slowing of the respiration takes place, and this may by
proper stimulation be earned so far that a complete standstill of
respiration in the phase of rest is brought about, i.e. the respiratory
apparatus remains in the condition which obtains at the close of
an ordinary expiration, the diaphragm being completely relaxed.
In other words, the superior laryngeal nerve contains fibres, the
stimulation of which produces afferent impulses whose effect is to
inhibit the action of the respiratory centre; while the main trunk
of the vagus contains fibres, the stimulation of which produces
afferent impulses whose effect is to accelerate or augment the
action of the respiratory centre. In some cases stimulation of the

358 NERVOUS MECHANISM. [BOOK n.

main trunk of the vagus also causes a slowing or even standstill of
the respiration, as for instance in deep chloral narcosis or when
the nerve has become exhausted by previous stimulation. Stimu-
lation of the superior laryngeal frequently produces not only a
complete cessation of all inspiratory movements, as indicated by
the perfectly lax diaphragm, but also contractions of the abdominal
muscles indicating an expiratory effort; and it is obvious that the
commencement of an expiration must be preceded by a cessation of
inspiratory effects, just as similarly inspiration must be preceded
by the cessation of expiration. Hence the influences which inhibit
inspiration are often spoken of as expiratory though they may not
go so far as to produce an actual expiration.

Corresponding to these antagonistic influences we may suppose
the existence of separate fibres, augmentative or inspiratory fibres,
the stimulation of which leads to inspiratory movements, and
inhibitory or expiratory fibres the stimulation of which checks
inspiration and subsequently gives rise to expiration. But it
must be remembered that the existence of these fibres is hypo-
thetical, and that some other explanation may eventually be given
of the facts which we have just described. Indeed we are not able
at present to give a wholly consistent and satisfactory explanation of
the nature and working of the respiratory centre. Apparently we
must conceive of its consisting of two parts, an inspiratory and
an expiratory: and direct stimulation of the medulla produces
sometimes inspiration, sometimes expiration; but the two parts
must be considered as co-ordinated in such a way as to act
alternately. Of the two the inspiratory centre is in ordinary life
the more important, the more sensitive and the more active, since
in normal breathing active expiratory effects are scanty, and the
emptying of the chest is chiefly the result of the cessation of
inspiration. Under conditions, however, which we shall speak of
presently under the name of dyspnoea, the expiratory centre
comes distinctly into play, since actual expiratory efforts come to
the front and, as we shall see, the greater the difficulty of breathing
the more and more prominent they become. We may picture to
ourselves, as Eosenthal has done, that the inspiratory centre is the
seat of two conflicting processes, one tending to the discharge of
inspiratory impulses and the other offering resistance to that
discharge, the former gathering head during a period of rest and so
at last overcoming the latter, and effecting an actual discharge.
After this the accumulation of inspiratory processes once more
begins, and once more terminates in a discharge, thus leading to
the rhythm of respiration. We may further suppose that the aug-
mentative impulses ascending the vagi, produce their effect by
diminishing the processes of resistance, and thus bring about move-
ments which are at once quicker and less ample. But we have to add
to this conception some view as to the relation of the expiratory to
the inspiratory centre in order to explain why the impulses inhibitory

CHAP, ii.] RESPIRATION. 359

to the latter should be augmentative to the former. Indeed the
whole matter becomes too complicated to be discussed any further
here ; and we have introduced the view not because we regard it as
an adequate explanation of the phenomena, but because it affords a
useful graphic conception of the molecular activity of these and
other automatic nervous centres. We may be at present content with
the knowledge that, as far as the vagus is concerned, the respiratory
centre as a whole may be influenced by augmentative or inspiratory
impulses which run chiefly in the trunk of the nerve and by inhibi-
tory or expiratory impulses which run certainly in the superior
laryngeal, apparently also in the recurrent laryngeal, and to a certain
extent in the trunk also ; in the latter case, however, their presence
is manifested under certain conditions only. And while, from the
results of simple section of the main trunk, it is clear that the ac-
celerating influences are continually at work, it is not so clear that
the inhibitory influences are always in action, since section even of
both superior laryngeals does not necessarily quicken respiration.

This double or alternate respiratory action of the vagi may be
taken as in a general way illustrative of the manner in which other
afferent nerves and various parts of the cerebrum are enabled to
influence respiration. As we know from daily experience, of all
the apsychical nervous centres, the respiratory centre is the one
which is most frequently and most deeply affected by nervous im-
pulses from various quarters. Besides the changes brought about
by the will (and when we breathe voluntarily we probably make
use to some extent of the normal nervous machinery of respiration,
working through this, rather than sending independent volitional
impulses direct to the diaphragm and other respiratory muscles),
we find that emotions, and painful sensations alter profoundly
the character of the respiratory movements. Sometimes the
breathing thereby becomes quicker and flatter, sometimes it is
deepened as well as hurried; at other times it may be slowed
or for a wrhile stopped altogether, while occasionally expiratory
efforts are made prominent. And though these effects may
be partly indirect, the emotion modifying the heart-beat, and
so influencing the flow of blood through the respiratory centre, they
are chiefly due to the direct actions of nervous impulses reaching
that centre from higher parts of the brain. So also impulses from
almost every sentient surface, or passing along almost every
sensory nerve, may modify respiration in one direction or another,
the slighter feebler impulses tending apparently to quicken, and
the stronger larger impulses to arrest or inhibit the respiratory
discharges. The influence in this way of stimuli applied to the
skin is well known to all; but perhaps next to the vagus the
nerve most closely connected with the respiratory centre is the
fifth nerve, branches of which guard the nasal respiratory channels ;
the slightest stimulation of the nostrils at once affecting the
breathing and most frequently arresting it. Thus the working of

360 NERVOUS MECHANISM. [BOOK n.

the respiratory centre is made to respond delicately to the varying
needs of the economy.

Besides these nervous influences, however, there is another
circumstance which perhaps above all others affects the respiratory
centre, and that is the condition of the blood in respect to its
respiratory changes ; the more venous (less arterial) the blood, the
greater is the activity of the respiratory centre. When by reason
either of any hindrance to the entrance of air into the chest, or of a
greater respiratory activity of the tissues, as during muscular
exertion, the blood becomes less arterial, more venous, i.e. with a
smaller charge of oxy-hoemoglobin and more heavily laden with
carbonic acid, the respiration from being normal becomes laboured.
We may speak of normal breathing as eupncea, and say that this,
when the blood is insufficiently arterialized, passes into dyspncea,
an intermediate stage in which the respiratory movements are
simply exaggerated being known as hyperpncea. This effect of
deficient arterialization of blood is very different from that of
section of the vagi: it is no mere change in the distribution of
impulses ; the breathing is quicker as well as deeper, there is an
increase in the sum of efferent impulses proceeding from the centre,
and the expiratory impulses, which in normal respiration are very
slight, acquire a pronounced importance. As the blood becomes,
in cases of obstruction, less and less arterial, more and more
venous, the discharge from the respiratory centre becomes more
and more vehement, and instead of confining itself to the usual
tracts, and passing down to the ordinary respiratory muscles, over-
flows into other tracts, puts into action other muscles, until there is
perhaps hardly a muscle in the body which is not made to feel it&
effects. And this discharge may, as we shall see in speaking
of asphyxia, continue till the nervous energy of the respiratory
centre is completely exhausted. The effect of venous blood then is
to augment these natural explosive decompositions of the nerve-
cells of the respiratory centre which give rise to respiratory
impulses; it increases their amount, and also quickens their
rhythm. The latter change however is much less marked than
the former, the respiration being much more deepened than
hurried, and the several respiratory acts are never so much
hastened as to catch each other up, and so to produce an in-
spiratory tetanus like that resulting from stimulation of the vagus.
On the contrary, especially as exhaustion begins to set in, the
rhythm becomes slower out of proportion to the weakening of the
individual movements.

On the other hand, the blood may be made not more but less
venous than usual. When we attempt to hold our breath, we find
that we can only do this for a limited time; sooner or later a
breath must come; but the time during which we can remain
without breathing may be much prolonged, if we first of all take a
series of deep breaths. .By this increased ventilation we bring our

CHAP, ii.j RESPIRATION. 361

respiratory centre into such a condition that it takes a much
longer time for the succeeding respiratory impulses to become
irresistible. A similar but even more pronounced condition may
be brought about in an animal by making it inspire oxygen,
or breathe ordinary air more rapidly and more forcibly than the
needs of the economy require. If in a xabbit artificial respiration
is carried on very vigorously for a while, and then suddenly
stopped, the animal does not immediately begin to breathe. For
a variable period no respiration takes place at all, and when it does
begin occurs gently and normally, only passing into dyspnoea if the
animal is unable to breathe of itself; and even then the transition is
quite gradual. Evidently during this period the respiratory centre
is in a state of complete rest, no explosions are taking place, no
respiratory impulses are being generated, and the quiet transition
from this condition to that of normal respiration shews that the
subsequent generation of impulses is attended by no great dis-
turbance. The cause of this state of things, which is known as
that of apncea, is to be sought for in the condition of the blood.
By the increased vigour of the artificial respiratory movements the
hemoglobin of the arterial blood, which in normal breathing is not
quite saturated, becomes almost completely so, and the quantity of
oxygen simply dissolved is increased, its tension being largely
augmented. Respiration is arrested because the blood is more
highly arterialized than usual. Thus we have in apnoea the
converse to dyspnoea; and both states point to the same con-
clusion, that the activity of the respiratory centre is dependent on
the condition of the blood, being augmented when the blood is less
arterial and more venous, being depressed when it is more arterial
and less venous than usual.

The question now arises, Does this condition of the blood affect
the respiratory centre directly, or does it produce its effect by
stimulating the peripheral ends of afferent nerves in various parts
of the body, and, by the creation there of afferent impulses,
indirectly modify the action of the centre ? Without denying the
possibility that the latter mode of action may help in the matter,
as regards not only the vagi, but all afferent nerves, it is clear from
the following reasons that the main effect is produced by the
direct action of the blood on the respiratory centre itself. If the
spinal cord be divided below the medulla oblongata, and both vagi
be cut, want of proper aeration of the blood still produces an
increased activity of the Tespiratory centre, as shewn by the
increased vigour of the facial respiratory movements. If the
supply of blood be cut off from the medulla by ligature of the
blood-vessels of the neck, dyspnoea is produced, though the opera-
tion produces no change in the blood generally, but simply affects
the respiratory condition of the medulla itself, by cutting off
its blood-supply, the immediate result of which is an accumulation
of carbonic acid and a paucity of available oxygen in the proto-

3G2 NERVOUS MECHANISM. [BOOK n.

plasm of the nerve-cells in that region. If the blood in the carotid
artery in an animal be warmed above the normal, dyspnoea is at
once produced. The overwarm blood hurries on the activity of
the nerve-cells of the respiratory centre, so that the supply of
blood, even though greater than normal owing to the blood-vessels
of the medulla becoming dilated by the increased temperature, is
yet insufficient for their needs. The condition of the blood then
affects respiration by acting directly on the respiratory centre itself.
Deficient aeration produces two effects in blood : it diminishes
the oxygen, and increases the carbonic acid. Do both of these
changes affect the respiratory centre, or only one, and if so, which ?
When an animal is made to breathe an atmosphere containing
nitrogen only, the exit of carbonic acid by diffusion is not affected,
and the blood, as is proved by actual analysis, contains no excess
of carbonic acid. Yet all the phenomena of dyspnoea are present.
In this case these can only be attributed to the deficiency of
oxygen. On the other hand, if an animal be made to breathe an
atmosphere rich in carbonic acid, but at the same time containing
abundance of oxygen, though the breathing becomes markedly
deeper and also somewhat more frequent, there is no culmination
in a convulsive asphyxia, even when the quantity of carbonic acid
in the blood, as shewn by direct analysis, is very largely increased.
On the contrary the increase in the respiratory movements after a
while passes off, the animal becoming unconscious, and appearing
to be suffering rather from a narcotic poison than from simple
dyspnoea. It does not seem certain that the increased respiratory
movements seen at first are the direct result of the action of the
carbonic acid on the respiratory centre; it is possible that the
carbonic acid may affect the respiratory centre in an indirect way,
by stimulating the respiratory passages, or by its action on higher
parts of the brain; and in all cases there is a marked contrast
between the slow development and evanescent character of the
hyperpncea of carbonic acid poisoning, and the rapid onset and
speedy culmination in convulsions and death of the dyspnoea due
to the absence of oxygen. There can in fact be no doubt that the
action of deficiently arterialized blood on the respiratory centre, as
manifested in an augmentation of the respiratory explosions, is due
primarily to a want of oxygen, and in a secondary manner only to
an excess of carbonic acid.

Cheyne-Stokes Respiration. A remarkable abnormal rhythm
of respiration, first observed by Cheyne but afterwards more fully
studied by Stokes and hence called by their combined names,
occurs in certain pathological cases. The respiratory movements
gradually decrease both in extent and rapidity until they cease
altogether, and a condition of apncea, lasting it may be for several
seconds, ensues. This is followed by a feeble respiration, succeeded
in turn by a somewhat stronger one, and thus the respiration

CHAP. IL] RESPIRATION. 363

returns gradually to the normal, or may even rise to hyperpnoea or
slight dyspnoea after which it again declines in a similar manner.
A secondary rhythm of respiration is thus developed, periods of
normal or slightly dyspnceic respiration alternating by gradual
transitions with periods of apncea. The cause of the phenomena
is not thoroughly understood. Stokes connected it with a fatty
condition of the heart, but it has been met with in various maladies.
Closely similar phenomena have been observed during sleep, under
perfectly normal conditions. It presents a striking analogy with
the 'groups' of heart-beats so frequently seen in the frog's ventricle
placed under abnormal circumstances.

c\

SEC. 7. THE EFFECTS OF RESPIRATION ON THE
CIRCULATION.

We have seen, while treating of the circulation, that the blood-
pressure curves are marked by undulations, which, since their
rhythm is synchronous with that of the respiratory movements, are
evidently in some way connected with respiration.

•_— v\

FIG. 59. COMPARISON OF BLOOD-PRESSURE CCRVE WITH CURVE OF INTRA-THORACIC
PRESSURE. To be read from left to right.

a is the blood-pressure curve, with its respiratory undulations, the slower beats
on the descent being very marked. 6 is the curve of intra-thoracic pressure
obtained by connecting one limb of a manometer with the pleural cavity. In-
spiration begins at i, expiration at e. The intra-thoracic pressure rises very
rapidly after the cessation of the inspiratory effort, and then slowly falls as the air
issues from the chest ; at the beginning of the inspiratory effort the fall becomes
more rapid.

ClIAP. II.]

RESPIRATION.

365

When these undulations of the blood-pressure curve are com-
pared carefully with the respiratory movements or with the
variations of intra-thoracic pressure, it is seen that while in general
the blood-pressure rises during inspiration and falls during expiration
neither the rise nor the fall of the former is exactly synchronous
with either inspiration or expiration. Fig. 59 shews two tracings
from a dog taken at the same time, one, a, being the ordinary
blood-pressure curve from the carotid, and the other, 6, representing
the condition of the intra-thoracic pressure as obtained by carefully
bringing a manometer into connection with the pleural cavity.
On comparing the two curves, it is evident that neither the
maximum nor the minimum of arterial pressure coincides exactly
either with inspiration or with expiration. At the beginning of
inspiration (i) the arterial pressure is seen to be falling ; it soon
however begins to rise, but does not reach the maximum until
some time after expiration (e) has begun ; the fall continues during
the remainder of expiration, and passes on into the succeeding
inspiration.

This suggests the idea that, while inspiration tends to increase
and expiration to diminish the blood-pressure, there are causes

EXPIR AT/O/V

INSPIRATION

FIG. 60. Influence of respiration on the form of the pulse- wave and the medium
blood-pressure. The upper curve gives the radial pulse from a healthy man of
27 years of age and with an extra- arterial pressure of 70 mm. mercury. The lower
curve gives the movements of the chest wall, the points of the recording levers of
both instruments being in the same vertical line. It can be seen that during
inspiration the pulse-waves diminish in height and become more dicrotic, while
during expiration the height of the pulse-waves is increased and their form tends
more towards that of the pulse-wave with a raised arterial pressure.

366 EFFECTS ON CIRCULATION. [BOOK n.

at work which in each case delay the effect. Extended observa-
tions however shew that such a relation as that shewn in
the figure though frequent is not constant. In fact the
effects of the respiratory movements on blood-pressure ' are
found to vary very widely according as the respiration is
quick or slow, easy and shallow or laboured and deep, and
especially as the air enters into the chest readily or with
difficulty. A similar variety of effect is seen in sphygmographic
tracings", and these further shew that the respiratory movements
bring about changes not only in the mean blood-pressure but in
the form and characters of each pulse-wave. In Fig. 60, which
represents a state of things frequently occurring, but which must
not be considered as illustrating what always takes place, it will
be seen that during the 'greater part of expiration the pulse-wave
is high and the dicrotic wave is not very prominent, while during
inspiration the height of the wave is diminished, and dicrotism
becomes much more marked ; the former indicates a higher and
the latter a lower blood-pressure.

These variations in the exact relations of the respiratory
undulations to the respiratory movements themselves will prepare
the reader for the statement that the causation of the undulations
is complex. Apparently the respiratory act affects the vascular
system in several different ways, and the general effect varies
according as one or other influence is predominant. These several
actions are sufficiently interesting and important to deserve dis-
cussion.

When the brain of a living mammal is exposed by the removal
of the skull, a rhythmic rise and fall of the cerebral mass, a
pulsation of the brain, quite distinct from the movements caused
by the pulse in the arteries of the brain, is observed; and upon
examination it will be found that these movements are synchronous
with the respiratory movements, the brain rising up during ex-
piration and sinking during inspiration. They disappear when the
arteries going to the brain are ligatured, or when the venous
sinuses of the dura mater are laid open so as to admit of a free
escape of the venous blood. They evidently arise from the ex-
piratory movements in some way hindering and the inspiratory
movements assisting the return of blood from the brain. We have
already (p. 127) stated that during inspiration the pressure of blood
in the great veins may become negative, i.e. sink below the pressure
of the atmosphere ; and a puncture of one of these veins may
cause immediate death by air being actually drawn into the vein
and thus into the heart during an inspiratory movement. When
the veins of an animal are laid bare in the neck and watched,
the so-called pulsus venosus may be observed in them, that is, they
swell up during expiration and diminish again during inspiration.
And indeed a little consideration will shew that the expansion and
contraction of the chest must have a decided effect on the flow of

CHAP, ii.] RESPIRATION. 367

blood through the thoracic portion of, and thus indirectly on that
through the whole of, the vascular system.

The heart and great blood-vessels are, like the lungs, placed in
the air-tight thoracic cavity, and are subject like the lungs to the
pumping action of the respiratory movements. Were the lungs
entirely absent from the chest, the whole force of the expansion of
the thorax in inspiration would be directed to drawing blood from
the extra-thoracic vessels towards the heart, and conversely the
effect of the contraction of the thorax in expiration would be to
drive the blood back again from the heart towards the extra-thoracic
vessels. In the presence of the lungs however the free entrance of
air into the interior of the chest tends to maintain the pressure
around the heart and great vessels within the thorax equal to the
ordinary atmospheric pressure on the vessels of the rest of the body
outside the thorax ; but it is unable completely to equalise the two
pressures. Did the air enter as freely into the lungs as it does into
the pleural cavities when wide openings are made in the thoracic
walls, the respiratory movements would have very little effect
indeed on the flow of blood to and from the heart, just as when
such free openings exist they are ineffectual in promoting the
entrance and exit of air to and from the lungs. But the air does
not pass into the pulmonary alveoli as freely as it would do into a
pleural cavity through an opening in the thoracic wall. Before the
inspired air can fill a pulmonary alveolus, the walls of the alveolus
have to be distended at the expense of the pressure which causes the
inspired air to enter. Part of the atmospheric pressure in fact
which causes the entrance of the air into the lung is spent in over-
coming the elasticity of the pulmonary passages and cells. Conse-
quently, any structure lying within the thorax but outside the
lungs, is never, even at the conclusion of an inspiration when the
lungs are filled with air, subject to a pressure as great as that of the
atmosphere. The pressure on such a structure always falls short of
the pressure of the atmosphere by the amount of pressure necessary
to counterbalance the elasticity of the pulmonary passages and cells.
And, since the fraction of the atmospheric pressure w^hich is thus
spent in distending the lungs increases as the lungs become more
and more stretched, it follows that the fuller the inspiration the
greater is the difference between the pressure on structures within
the thorax but outside the lungs and the ordinary pressure of the
atmosphere. Now we .have seen that the pressure necessary
to counterbalance the elasticity of the lungs, when they are com-
pletely at rest (in the pause between expiration and inspiration), is
in man about 5 to 7 mm. of mercury, and that when the lungs are
fully distended, as at the end of a forcible inspiration, the pressure
rises to as much as 30 mm. of mercury. Hence at the height of a
forcible inspiration the pressure exerted on the heart and great
vessels within the thorax is 30 mm. less than the ordinary atmo-
spheric pressure of 760 mm., and even when the chest is completely

368 EFFECTS ON CIRCULATION. [BOOK n.

at rest, at the end of an expiration, the pressure on the heart and
great vessels is slightly (by about 5 mm. mercury) below that of the
atmosphere.

During an inspiration then the pressure around the heart and
great blood-vessels becomes considerably less than that of the atmo-
sphere on the vessels outside the thorax. During expiration this
pressure returns towards that of the atmosphere, but in ordinary
breathing never quite reaches it. It is only in forcible expiration
that the pressure on the thoracic vascular organs exceeds that of
the atmosphere. But if during inspiration the pressure bearing on
the right auricle and the vense cavse becomes less than the pressure
which is bearing on the jugular, subclavian, and other veins out-
side the thorax, this must result in an increased flow from the
latter into the former. Hence, during each inspiration a larger
quantity of blood enters the right side of the heart. This probably
leads to a stronger stroke of the heart, and at all events causes
a larger quantity to be ejected by the right ventricle ; this
causes a larger quantity to escape from the left ventricle, and thus
more blood is thrown into the aorta, and the arterial tension
proportionately increased. During expiration the converse takes
place. The pressure on the intra-thoracic blood-vessels returns to
the normal, the flow of blood from the veins outside the thorax
into the venae cavse and right auricle is no longer assisted, and in
consequence less blood passes through the heart into the aorta,
and arterial tension falls again. During forced expiration, the
intra-thoracic pressure may be so great as to afford a distinct
obstacle to the flow from the veins into the heart.

The effect of the respiratory movements on the arteries is
naturally different from that on the veins. During inspiration the
diminution of pressure in the thorax around the aortic arch tends
to draw the blood from the arteries outside the thorax back to the
arch of the aorta, or, in other words, tends to check the onward
flow of blood. At the same time, and this is the point to which
we wish to call attention, the aortic arch itself tends to expand ; in
consequence the pressure of blood withm it, i. e. the arterial tension,
tends to diminish. During expiration, the increase of pressure
outside the aortic arch of course tends to increase also the blood-
pressure within it, acting in fact just in the same way as if the
coats of. the aorta themselves contracted. Thus as far as arterial
blood-pressure is concerned the effects of the respiratory move-
ments on the great veins and great arteries respectively are
antagonistic to each other ; the effect on the veins being to increase
arterial tension during inspiration and to diminish it during
expiration, while the^ effect on the arteries is to diminish arterial
tension during inspiration and to increase it during expiration.
But we should naturally expect the effect on the thin- walled veins
to be greater than that on the stout thick-walled arteries, so that
the total effect of inspiration would be to increase, and the total

CHAP, ii.] HESPIRATION. 369

effect of expiration to diminish, arterial tension. That is to say,
we should expect the blood-pressure to rise during inspiration
and to fall during expiration. This as we have seen is frequently the
case, and indeed when the breathing is deep and laboured the
influence in this direction on the blood-pressure curve of the
pumping action of the chest is unmistakeable.

In addition to the influence thus exerted by the thoracic move-
ments on the great veins leading to, and the great arteries leading
from the heart, we have to consider the behaviour of the pulmonary
vessels themselves under the varying thoracic pressure. These,
like the venae cavse and aorta, tend to expand under the influence
of the inspiratory expansion of the chest, and thus to become fuller
of blood, very much as they would if the whole lung were placed
under a large cupping-glass. The first effect of this increased filling
of the pulmonary vessels would be to retain for a while a certain
quantity of blood in the lungs and thus to lessen the amount falling
into the left auricle. But this would be temporary only ; and the
widening of the pulmonary vessels would speedily produce an
exactly contrary effect, namely, an increased flow through the lungs
due to the diminished resistance offered by the widened passages.
Conversely the first effect of expiration would be an increased flow
into the left auricle due to the additional quantity of blood driven
onwards by the partial collapse of the pulmonary vessels, followed
by a more significant diminished flow caused by the greater resis-
tance now offered by the narrower vascular channels. Thus the
effect of inspiration in this way would be first to diminish the flow
into the left auricle and so into the left ventricle and thus to
diminish for a brief initial period the blood-pressure in the aorta,
but afterwards, for the rest of the inspiration until the beginning of
expiration, to increase the flow into the ventricle and thus to raise
the arterial pressure ; while conversely the effect of expiration would
be first, for a brief period, to increase and afterwards, during the rest
of the movement, to diminish the flow of blood into the left ven-
tricle, and through that the amount of arterial pressure. Further,
while this may be considered as the effect on the pulmonary vessels,
large and small taken altogether, the influence both of the
thoracic negative pressure during inspiration, and the return
in a positive direction during expiration, will bear more on
the thin-walled pulmonary veins than on the stouter pulmonary
artery; that is to say, as inspiration becomes established,
there will be a diminution of pressure in the pulmonary veins
greater than that in the pulmonary artery, and this will be an
additional influence favouring the flow into the left ventricle; during
expiration a similar difference of effect will be felt in the contrary
direction. The general effect then of the movements of the chest on
the pulmonary vessels will be during the beginning of inspiration to
continue the lowering of arterial pressure which was taking place
during expiration but subsequently to raise the arterial pressure; and

F. 24

370 EFFECTS ON CIRCULATION. [BOOK n.

conversely at the beginning of expiration to continue the rise of
arterial pressure which was taking place during inspiration but sub-
sequently to lower arterial pressure. In ordinary breathing, as we
have seen, what may be considered as the normal relations of blood-
pressure to the respiratory movements are precisely of this kind ;
and it seems exceedingly probable that they are, to a large extent
at least, produced in this way.

In attempting however to estimate the action of the thorax, we
must bear in mind what is taking place in the abdomen. In easy
inspiration the descent of the diaphragm compresses the abdominal
viscera, and so, while at the very first it drives a quantity of
blood onward along the inferior vena cava, subsequently hinders
the upward flow from the abdomen and lower limbs ; at the same
time by compressing the abdominal aorta, it tends to raise
the pressure in the thoracic aorta and its branches. The effect
of easy expiration would be the converse of this ; but in forced
expiration the pressure of the contracting abdominal muscles would,
as in inspiration, first tend to drive the blood onward along the vena
cava but subsequently hinder the flow both along the vena cava and
the aorta. The effect of the abdominal movements therefore is
mixed and variable, and the influence on the blood-pressure in the
femoral artery must be different from that on the radial artery or
other branch of the thoracic aorta. It is difficult to predict what
in all cases the effect would be, but it is stated that section of the
phrenic nerves, leading to quiescence of the diaphragm, largely
diminishes, and sometimes causes the total disappearance of, even
the normal respiratory undulations.

Effects of the respiratory movements are seen not only in
natural but also in artificial respiration. When, for instance, in an
animal under urari, artificial is substituted for natural respiration,
undulations of the blood-pressure curve, synchronous with the
respiratory movements, are still observed (Fig. 61), though generally
less in extent than those seen under natural conditions. Now in
artificial respiration, the mechanical conditions, under which the
thoracic viscera are placed as regards pressure, are the exact
opposite of those existing during natural respiration ; for when air
is blown into the trachea to distend the lungs, the pressure within
the chest is increased instead of diminished.

Under these circumstances we should expect to find that
while the first effect of an artificial inspiration would be to drive
an additional quantity of blood out of the lungs into the left
ventricle, and thus to raise arterial pressure, this would be in turn
followed by a fall of arterial pressure due to the increased re-
sistance offered both to the passage of blood through the lungs
and to the entrance of blood through the venae cavse into the
right auricle. Conversely the effect of the succeeding expiration
would be an initial continuance of the fall of arterial pressure
succeeded by a rise. In other words we should expect to find in

CHAP. JL] RESPIRATION. 371

artificial respiration effects exactly the reverse of those which we
find in normal respiration ; and indeed in many curves of blood-
pressure taken during artificial respiration this is the case; but
here as in natural respiration the features of the blood-pressure
curve vary according as the breathing is hurried or slow, shallow
or deep.

We may add that another explanation than those given above
has been offered of these effects of the respiratory movements.
It has been suggested that when the lung is expanded, the
increase in the area of the wall of each pulmonary alveolus tends
to stretch and elongate the capillaries lying in the alveolar walls,
and in elongating them necessarily narrows them, just as an
india-rubber tube is narrowed when it is stretched lengthways.
This narrowing of the capillaries would present an obstacle to
the passage of blood through them ; and hence the expansion
of the alveoli in inspiration, other things being equal, would
be unfavourable to the flow of blood through the lungs. It has been
further suggested that the first effect of the expansion of the alveolus
and narrowing of the capillaries would be to drive out suddenly the
blood at the moment contained in them and thus for the instant to
produce a passing increase of flow; and conversely that the first effect
of the collapse of the alveolus and consequent widening of the
capillaries would be to find room for an extra quantity of blood, and
thus for a moment to check the flow. Whether in each case the
first or the second phase becomes predominant would depend on
the rate and depth of the breathing. There are difficulties however
in accepting this view and the one previously given seems to be
the more valid one.

From what has been said it is clear that the influences of
the respiratory movements are not only many but conflicting, and
that the exact effect at any one moment will vary according
as circumstances render one or other factor predominant. It will
hardly be profitable to make any further attempt to unravel
the complexity of the several cases.

The relations between respiration and circulation which we
have just discussed are of a mechanical nature, but there are also
ties of a nervous kind between the two systems. One striking
feature of the respiratory undulation in the blood-pressure curve
of the dog1 is the fact that the pulse-rate is quickened during the
rise of the undulation and becomes slower during the fall. The
quickening of the beat might be considered as itself partly
accounting for the rise, or on the other hand it might be urged
that the increased flow of blood which causes the rise, at the same
time leads to the quickening, were it not for one fact, viz. that the
difference is at once done away with, without any other essential

1 In the rabbit, the respiratory undulations, though well marked, present a very
small difference of pulse-rate in the rise and fall.

372 EFFECTS ON CIRCULATION. [BOOK n.

change in the undulations, by section of both vagi. Evidently the
slower pulse during the fall is caused by a coincident stimulation of
the cardio-inhibitory centre in the medulla oblongata, the quicker
pulse during the rise being due to the fact that, during that
interval, the centre is comparatively at rest. We have here most
important indications that, while the respiratory centre in the
medulla oblongata is at work, sending out rhythmic impulses of
inspiration and expiration, the neighbouring cardio-inhibitory
centre is, as it were by sympathy, thrown into an activity of such a
kind that its influence over the heart waxes and wanes with each
respiratory movement.

But if the cardio-inhibitory centre is thus synchronously
affected, ought we not to expect that the vaso-motor centre should
also be influenced ? We have indeed evidence that the action of
the vaso-motor centre is largely dependent on the respiratory
changes of blood.

When artificial respiration is stopped, a very large but steady
rise of pressure is observed. This may be in part due to the
increased force of the cardiac beat, caused by the increasingly
venous character of the blood ; but only in part, and that a small
part. The rise so witnessed is very similar to that brought about
by powerfully stimulating a number of vaso-constrictor nerves ; and
there can be no doubt that it is due to the venous blood stimu-
lating the vaso-motor centre in the medulla, and thus causing
constriction of the small arteries of the body, particularly perhaps
those of the splanchnic area. We say ' stimulating the medullary
vaso-motor centre,' because, though we must admit that, since a rise
of pressure follows upon dyspnoea when the spinal cord has been
previously divided below the medulla, the venous blood may
stimulate other vaso-motor centres in the spinal cord and possibly
even act directly on local peripheral mechanisms, or on the
muscular coats of the small arteries themselves, yet the fact
that the rise of pressure is much less under these circum-
stances shews that the medullary centre plays the chief part.
Upon the cessation of the artificial respiration, the respiratory
undulations cease also, so that the blood -pressure curve rises
at first steadily in almost a straight line ; yet after a while new
undulations, the so-called Traube or Traube-Hering curves, make
their appearance (Fig. 61. 2, 3), very similar to the previous ones,
except that their curves are larger and of a more sweeping
character. These new undulations, since they appear in the
absence of all thoracic or pulmonary movements, passive or active,
and are witnessed even when both vagi are cut, must be of vaso-
motorial origin; the rhythmic rise must be due to a rhythmic
constriction of the small arteries, and this probably is caused
by a rhythmic discharge from vaso-motor centres and especially
from the medullary vaso-motor centre. The undulations are main-
tained as long as the blood -pressure continues to rise. With the

CHAP. IT.]

RESPIRATION.

373

increasing venosity of the blood, however, both the vaso-motor
centres and the heart become exhausted ; the undulations disappear,
and the blood-pressure rapidly sinks.

< -' i / 1 / \ / '. ; I/ \ < • I II 1 1 \ I i

•Vl.VV« *.P'Ml

i

\

,T

h

I

i

j i

1

i

j

i

! i /

i

\

If

y

V

4

FIG. 61. TBAUBE-HEBING CTTBVES. To be read from left to right.

The curves 1, 2, 3, 4, 5 are portions selected from one long continuous tracing
forming the record of a prolonged observation, so that the several curves represent
successive stages of the same experiment. Each curve is placed in its proper position
relative to the base line, which, to save space, is omitted ; and it is obvious that,
starting from the stage represented by 1, the blood-pressure rises in stages
2, 3, and 4, but falls again in stage 5. Curve 1 is taken from a period
when artificial respiration was being kept up, and the undulations visible
are those the nature of which have been discussed; the vagi having been
cut the pulsations on the ascent and descent of the undulations do not differ.
When the artificial respiration was suspended these undulations for a while
disappeared, and the blood-pressure rose steadily while the heart-beats became
slower. Soon, as shewn in curve 2, new undulations appeared. A little later, the blood-
pressure was still rising, the heart-beats still slower, but the undulations still more
obvious (curve 3). Still later (curve 4), the pressure was still higher, but the heart-
beats were quicker, and the undulations flatter. The pressuie then began to fall
rapidly (curve 5), and continued to fall until some time after artificial respiration
was resumed.

The appearance of these Traube-Hering curves is not however
dependent on the cessation of the respiratory movements, and on
an abnormally venous condition of the blood. They sometimes
(Fig. 62) are seen in an animal whose breathing is fairly normal.
We need not discuss them any further now, and have introduced
them chiefly to illustrate the fact that the vaso-motor nervous
system is apt to fall into a condition of rhythmic activity. It has

374

EFFECTS ON CIRCULATION.

[BOOK ii.

been suggested that the normal respiratory undulations may be due
to a rhythmic rise and fall of the activity of the vaso-motor centre,
synchronous, like that of cardio-inhibitory centre, with the respi-

Fio. 62. BLOOD-PRESSUBE CURVE OF A BABBIT, RECORDED ON A SLOWLY MOVING

SURFACE, TO SHEW TRAUBE-HERING CURVES.

In each heart-beat the upward and downward stroke are very close
together but may be easily distinguished by the help of a lens. The undula-
tions of the next order are those of respiration. The wider sweeps are the
Traube-Hering curves, of which two complete curves and portions of two others are
shewn. Each Traube-Hering curve comprises about nine respiratory curves, and
each respiratory curve about the same number of heart-beats.

ratory movements. A review of all the evidence however goes to
shew that the respiratory variations in blood-pressure are due to
the mechanical conditions discussed above, and that vaso-motor
influences intervene but little if at all.

SEC. 8. THE EFFECTS OF CHANGES IN THE
AIR BREATHED.

The Effects of deficient Air. Asphyxia.

When, on account of occlusion of the trachea, or by breathing
in a confined space, a due supply of air is not obtained, normal
respiration gives place, through an intermediate phase of dyspnoea,
to the condition known as asphyxia; this, unless remedial measures
be taken, rapidly proves fatal.

Phenomena of Asphyxia. As soon as the oxygen in the
arterial blood sinks below the normal, the respiratory movements
become deeper and at the same time more frequent; both the
inspiratory and expiratory phases are exaggerated, the supple-
mentary muscles spoken of at p. 322 are brought into play, and the
rate of the rhythm is hurried. In this respect, dyspnoea, or hy-
perpncea as this first stage has been called, contrasts very strongly
with the peculiar respiratory condition caused by section of the
vagi, in which the respiratory movements, while much more pro-
found than the normal, are diminished in frequency.

As the blood continues to become more and more venous the
respiratory movements continue to increase both in force and fre-
quency, a larger number of muscles being called into action and
that to an increasing extent. Very soon, however, it may be
observed that the expiratory movements are becoming more
marked than the inspiratory. Every muscle which can in any way

376 ASPHYXIA. [BOOK n.

assist in expiration is in turn brought into play; and at last almost
all the muscles of the body are involved in the struggle. The
orderly expiratory movements culminate in expiratory convulsions,
the order and sequence of which are obscured by their violence and
extent. That these convulsions, through which dyspnoea merges
into asphyxia, are due to a stimulation of the medulla oblongata
by the venous blood, is proved by the fact that they fail to make
their appearance when the spinal cord has been previously divided
below the medulla, though they still occur after those portions of
the brain which lie above the medulla have been removed. It is
usual to speak of a 'convulsive centre' in the medulla, the stimu-
lation of which gives rise to these convulsions ; but if we accept
the existence of such a centre we must at the same time admit
that it is connected by the closest ties with the normal expiratory
division of the respiratory centre, since every intervening step
may be observed between a simple slight expiratory movement
of normal respiration and the most violent convulsion of asphyxia.
An additional proof that these convulsions are carried out by the
agency of the medulla is afforded by the fact that convulsions of
a wholly similar character are witnessed when the supply of
blood to the medulla is suddenly cut off by ligaturing the blood-
vessels of the head. In this case the nervous centres, being no
longer furnished with fresh blood, become rapidly asphyxiated
through lack of oxygen, and expiratory convulsions quite similar to
those of ordinary asphyxia, and preceded like them by a passing
phase of dyspnoea, make their appearance. Similar 'anaemic' con-
vulsions are seen after a sudden and large loss of blood from the
body at large, the medulla being similarly stimulated by the lack of
arterial blood.

Such violent efforts speedily exhaust the nervous system ; and
the convulsions after being maintained for a brief period suddenly
cease and are followed by a period of calm. The calm is one of
exhaustion; the pupils, dilated to the utmost, are unaffected by
light ; touching the cornea calls forth no movement of the eyelids,
and indeed no reflex actions can anywhere be produced by the
stimulation of sentient surfaces. All expiratory active movements
have ceased ; the muscles of the body are flaccid and quiet ; and
though from time to time the respiratory centre gathers sufficient
energy to develope respiratory movements, these resemble those of
quiet normal breathing, in being, as far as muscular actions are
concerned, almost entirely inspiratory. They occur at long intervals,
like those after section of the vagi; and like them are deep
and slow. The exhausted respiratory centre takes some time to
develope an inspiratory explosion; but the impulse when it is
generated is proportionately strong. It seems as if the resistance
which had in each case to be overcome was considerable, and
the effort in consequence, when successful, productive of a large
effect.

CHAP, ii.] RESPIRATION. 377

As time goes on, these inspiratory efforts become less frequent ;
their rhythm becomes irregular; long pauses, each one of which
seems a final one, are succeeded by several somewhat rapidly re-
peated inspirations. The pauses become longer, and the inspiratory
movements shallower. Each inspiration is accompanied by the
contraction of accessory muscles, especially of the face, so that
each breath becomes more and more a prolonged gasp. The in-
spiratory gasps spread into a convulsive stretching of the whole
body; and with extended limbs, and a straightened trunk, with
the head thrown back, the mouth widely open, the face drawn, and
the nostrils dilated, the last breath is taken in.

Thus we are able to distinguish three stages in the phenomena
which result from a continued deficiency of air : — (1) A stage of
dyspnoea, characterized by an increase of the respiratory movements
both of inspiration and expiration. (2) A convulsive stage, charac-
terized by the dominance of the expiratory efforts, and culminating
in general convulsions. (3) A stage of exhaustion, in which lin-
gering and long-drawn inspirations gradually die out. When
brought about by sudden occlusion of the trachea these events
run through their course in about 4 or 5 minutes in the dog, and
in about 3 or 4 minutes in the rabbit. The first stage passes
gradually into the second, convulsions appearing at the end of the
first minute. The transition from the second stage to the third
is somewhat abrupt, the convulsions suddenly ceasing early in the
second minute. The remaining time is occupied in the third
stage.

The duration of asphyxia varies not only in different animals
but in the same animal under different circumstances. Newly
born and young animals need much longer immersion in water
before death by asphyxia occurs than do adults. Thus while in
a full-grown dog recovery from drowning is unusual after 1J
minutes, a new-born puppy has been known to bear an immersion
of as much as 50 minutes. The cause of the difference lies in the
fact that in the quite young or rather just born animal the re-
spiratory changes of the tissues are much less active. These con-
sume less oxygen, and the general store of oxygen in the blood
has a less rapid demand made upon it. The respiratory activity of
the tissues may also be lessened by a deficiency in the circulation ;
hence bodies in a state of syncope at the time when the deprivation
of oxygen begins can endure the loss for a much longer period
than can bodies in which the circulation is in full swing. There
being the same store of oxygen in the blood in each case, the
quicker circulation must of necessity bring about the speedier
exhaustion of the store. In many cases of drowning, death is
hastened by the entrance of water into the lungs.

By training, the respiratory centre may be accustomed to bear
a scanty supply of oxygen for a much longer time than usual
before dyspnoea sets in, as is seen in the case of divers.

378 ASPHYXIA. [BOOK n.

The phenomena of slow asphyxia, where the supply of air is
gradually diminished, are fundamentally the same as those result-
ing from a sudden and total deprivation. The same stages are
seen, but their development takes place more slowly.

The circulation in Asphyxia. If the carotid or other artery
of an animal be connected with a manometer during the develop-
ment of the asphyxia just described, the following facts may be
observed. During the first and second stages the blood-pressure
rises rapidly, attaining a height far above the normal. During the
third stage it falls even more rapidly, repassing the normal and
becoming nil as death ensues. The respiratory undulations of the
pressure-curve are abrupt and somewhat irregular, the inspiratory
movements being accompanied by a fall of pressure. When the
animal has been previously placed under urari, so that the respira-
tory impulses cannot manifest themselves by any muscular move-
ments, the rise of the pressure curve, as we have already said, is at
first steady and unbroken, but after a variable period Traube's
curves make their appearance. As during the third stage the
pressure sinks, these undulations pass away.

The heart-beats are at first somewhat quickened, but speedily
become slow, while at the same time they acquire great force ; so
that the pulse-curves on the tracing are exceedingly bold and
striking, Fig. 61. Even while the blood-pressure is sinking, the
pulse-curves still maintain somewhat these characters; and the
heart continues to beat for some seconds after the respiratory
movements have ceased, the strokes at last rapidly failing in
frequency and strength.

If the chest of an animal be opened under artificial respiration,
and asphyxia brought on by cessation of the respiration, it will be
seen that the heart during the second and third stages becomes
completely gorged with venous blood, all the cavities as well as
the large veins being distended to the utmost. If the heart be
watched to the close of the events, it will be seen that the feebler
strokes which come on towards the end of the third stage are quite
unable to empty its cavities ; and when the last beat has passed
away its parts are still choked with blood. The veins spirt out
when pricked : and it may frequently be observed that the beats
recommence when the over-distension of the heart's cavities is
relieved by puncture of the great vessels. When rigor mortis
sets in after death by asphyxia, the left side of the heart is more
or less emptied of its contents ; but not so the right side. Hence
in an ordinary post-mortem examination in cases of death by
asphyxia, while the left side is found comparatively empty, the
right appears gorged.

These various phenomena of asphyxia are probably brought
about in the following way.

The increasingly venous character of the blood augments the

CHAP, ii.] RESPIRATION. 379

action of the general vaso-motor centre, and thus leads to a general
constriction of the small arteries This is the cause of the
markedly increased blood-pressure; though, as we have already
said, the venous blood may also act directly on the other spinal
vaso-motor centres and possibly on peripheral vaso-motor me-
chanisms or on the muscular arterial coats, or may even affect the
peripheral resistance by modifying the changes in the capillary
regions.

This increased peripheral resistance, while indirectly help-
ing to augment the force of the heart's beat, is a direct obstacle
to the heart emptying itself of its contents. On the other hand,
the increased respiratory movements favour the flow of venous
blood towards the heart, which in consequence becomes more and
more full. This repletion is moreover assisted by the marked
infrequency of the beats. This in turn depends in part on the
cardio-inhibitory centre in the medulla being stimulated by the
venous blood ; since when the vagi are divided the infrequency is
much less pronounced. It does not however disappear altogether ;
and we are therefore driven to suppose it is in part due to the
venous blood acting in an inhibitory manner directly on the heart
itself. The increased resistance in front, the augmented supply
from behind, and the long pauses between the strokes, all concur
in distending the heart more and more.

When the large veins have become full of blood the inspiratory
movements can no longer have their usual effect in increasing the
blood-pressure. The whole force of the chest movement, as far as
the circulation is concerned, is spent in diminishing the pressure
around the large arteries ; and hence the sinking of the blood- pres-
sure during each inspiratory movement.

The distension of the cardiac cavities, at first favourable to the
heart-beat, as it increases becomes injurious. At the same time
the cardiac tissues, which at first probably are stimulated, after a
while become exhausted by the action of the venous blood ; and
the strokes of the heart become feebler as well as slower.

On account of this increasing slowness and feebleness of the
heart's beat, the blood-pressure, in spite of the continued arterial
constriction, begins to fall, since less and less blood is pumped into
the arterial system ; the boldness of the pulse-curves at this stage
being chiefly due to the infrequency of the strokes. As the
quantity which passes from the heart into the arteries becomes
less second by second, the pressure gets lower and lower, the
descent being assisted by the exhaustion of the vaso-motor centre,
until almost before the last beats it has sunk to zero. Thus at the
close of asphyxia, while the heart and venous system are distended
with blood, the arterial system is less than normally full.

380 APNCEA. [BOOK n.

The Effects of an increased supply of Air. Apncea.

We have already (p. 861) seen that when artificial respiration
is carried on too vigorously, a condition of peculiar breathlessness
known as "apncea1" is brought about. We have further seen that
the essential feature of apncea consists in the blood containing
for the time being more oxygen than usual. In consequence of
this a longer time is needed before the deficiency of oxygen in the
blood of the capillaries of the medulla oblongata, or rather in the
nerve-cells constituting the respiratory centre, reaches the limit
which determines the discharge of a respiratory impulse. As we
have seen, the molecular processes of these cells are so arranged,
that whenever the oxygen which is available for their use sinks
below a certain level, respiratory explosions occur whereby a fresh
supply of oxygen is gained. We must suppose that the
changes going on in these cells, like those taking place in other
cells and tissues, are oxidative in character; but they possess this
peculiar feature, that the absence or diminution of oxygen acts as
it were as a stimulus, leading to an explosive decomposition. The
facts previously (p. 361) discussed lead us to adopt this view, though
we cannot explain why oxygen has this remarkable effect on these
particular cells. By increasing their available oxygen, the ex-
plosive action of the cells is deferred and diminished; that is,
apnoea is established. Similarly when the supply of oxygen is
diminished, the explosions are hastened and increased, that is,
dyspnoea is brought about. The different conditions of the respi-
ratory centre during apncea, normal breathing or eupncea, and
dyspnoea, are well shewn by the different effects produced by
stimulating the afferent fibres of the trunk of the vagus with the
same stimulus during the three stages. If the current chosen be
of such a strength as will gently increase the rhythm of normal
breathing, it will be found to have no effect at all in apncea, while
in dyspnoea it may produce almost convulsive movements. Indeed
in well-marked apncea even strong stimulation of the vagus may
produce no effect whatever.

The Effects of changes in the Composition of the Air breathed.

We have already discussed the effects of such changes as are
produced by the act of respiration itself, viz. a deficiency of oxygen
and an excess of carbonic acid. We have only to add, that the
result of an excess of oxygen, except in the cases of extreme
pressure to be mentioned immediately, is simply apncea, and that

1 It is to be regretted that this name is used by some medical authorities in a
sense almost identical with asphyxia. In its physiological sense, as here used, it is
the very opposite of asphyxia.

CHAP. IT.] RESPIRATION. 381

variations in amount of nitrogen have of themselves no effect, this
gas being eminently an indifferent gas as far as physiological pro-
cesses are concerned.

Poisonous gases. Carbonic oxide produces the same effects as
deficiency of oxygen, inasmuch as it preoccupies the haemoglobin
and so prevents the blood from becoming properly oxygenated, see
p. 340. Sulphuretted hydrogen produces similar effects, but in a
different manner ; it acts as a reducing agent, see p. 337. Some
gases are irrespirable, on account of their causing spasm of the
glottis, and this is said to be, to a certain extent, the case with
carbonic acid.

The Effects of changes in the Pressure of the Air breathed.

Gradual Diminution of Pressure. The symptoms are those of
deficiency of oxygen ; the animals die of asphyxia. The blood con-
tains less and less oxygen as the pressure is reduced, the quantity
present in the arterial blood soon becoming less than that in
normal venous blood. The quantity of carbonic acid in the blood
is also diminished. The increasing dyspnoea is accompanied by
great general feebleness ; and convulsions though frequent are not
invariable. The occurrence of these seems to depend on the
suddenness with which the oxygen of the blood is diminished.

Sudden Diminution. Death in these cases ensues from the
liberation of gases within the blood-vessels and the consequent
mechanical interference with the circulation. The gas which is
found in the blood-vessels on examination after death consists
chiefly of nitrogen.

Increase of Pressure. Up to a pressure of several atmospheres
of air, the only symptoms which present themselves are those
somewhat resembling narcotic poisoning. At a pressure however
of 4 atmospheres of oxygen, corresponding to 20 atmospheres of air,
and upwards, a very remarkable phenomenon presents itself. The
animals die of asphyxia and convulsions, exactly in the same way
as wheu oxygen is deficient. Corresponding with this it is found
that the production of carbonic acid is diminished. That is to say,
when the pressure of the oxygen is increased beyond a certain
limit, the oxidations of the body are diminished, and with a still
further increase of the oxygen are arrested altogether. The oxida-
tion of phosphorus is quite analogous ; at a high pressure of oxygen
phosphorus will not burn. Not only animals but plants, bacteria,
and organised ferments, are similarly killed by a too great pressure
of oxygen.

SEC. 9. MODIFIED RESPIRATORY MOVEMENTS.

The respiratory mechanism with its adjuncts, in addition to its
respiratory function, becomes of service, especially in the case of
man, as a means of expressing emotions. The respiratory column
of air, moreover, in its exit from the chest, is frequently made use
of in a mechanical way to expel bodies from the upper air-
passages. Hence arise a number of peculiarly modified and more
or less complicated respiratory movements, sighing, coughing,
laughter, &c. adapted to secure special ends which are not dis-
tinctly respiratory. They are all essentially reflex in character, the
stimulus determining each movement, sometimes affecting a
peripheral afferent nerve as in the case of coughing, sometimes
working through the higher parts of the brain as in laughter and
crying, sometimes possibly, as in yawning and sighing, acting on
the respiratory centre itself. Like the simple respiratory act, they
may with more or less success be carried out by a direct effort of
the will.

Sighing is a deep and long-drawn inspiration chiefly through
the nose followed by a somewhat shorter, but correspondingly large
expiration.

Yawning is similarly a deep inspiration, deeper and longer con-
tinued than a sigh, drawn through the widely open mouth, and
accompanied by a peculiar depression of the lower jaw and
frequently by an elevation of the shoulders.

Hiccough consists in a sudden inspiratory contraction of the
diaphragm, in the course of which the glottis suddenly closes, so

CHAP, ii.] RESPIRATION. 383

that the further entrance of air into the chest is prevented, while
the impulse of the column of air just entering, as it strikes upon
the closed glottis, gives rise to a well-known accompanying sound.
The afferent impulses of the reflex act are conveyed by the gastric
branches of the vagus. The closure of the glottis is carried out by
means of the inferior laryngeal nerve. See Voice.

In sobbing a series of similar convulsive inspirations follow each
other slowly, the glottis being closed earlier than in the case of
hiccough, so that little or no air enters into the chest.

Coughing consists in the first place of a deep and long-drawn
inspiration by which the lungs are well filled with air. This is fol-
lowed by a complete closure of the glottis, and then comes a
sudden and forcible expiration, in the midst of which the glottis
suddenly opens, and thus a blast of air is driven through the upper
respiratory passages. The afferent impulses of this reflex act are
in most cases, as when a foreign body is lodged in the larynx or by
the side of the epiglottis, conveyed by the superior laryngeal nerve ;
but the movement may arise from stimuli applied to other afferent
branches of the vagus, such as those supplying the bronchial
passages and stomach and the auricular branch distributed to
the meatus externus. Stimulation of other nerves also, such as
those of the skin by a draught of cold air, may develope a cough.

In sneezing the general movement is essentially the same,
except that the opening from the pharynx into the mouth is
closed by the contraction of the anterior pillars of the fauces and
the descent of the soft palate, so that the force of the blast is
driven entirely through the nose. The afferent impulses here
usually come from the nasal branches of the fifth. When sneezing
however is produced by a bright light, the optic nerve would seem
to be the afferent nerve.

Laughing consists essentially in an inspiration succeeded, not
by one, but by a whole series, often long continued, of short spas-
modic expirations, the glottis being freely open during the whole
time, and the vocal cords being thrown into characteristic vibrations.

In crying, the respiratory movements are modified in the same
way as in laughing; the rhythm and the accompanying facial
expressions are however different, though laughing and crying
frequently become indistinguishable.

CHAPTER III.
SECRETION BY THE SKIN.

WE have traced the food from the alimentary canal into the blood,
and, did the state of our knowledge permit, the natural course of
our study would be to trace the food from the blood into the
tissues, and then to follow the products of the activity of the
tissues back into the blood and so out of the body. This how-
ever we cannot as yet satisfactorily do ; and it will be more con-
venient to study first the final products of the metabolism of the
body, and the manner in which they are eliminated, and after-
wards to return to the discussion of the intervening steps.

Our food consists of certain food-stuffs, viz. proteids, fats and
carbohydrates, of various salts, and of water. In their passage
through the blood and tissues of the body, the proteids, fats and
carbohydrates are converted unto urea (or some closely allied body),
carbonic acid and water, the nitrogen of the urea being furnished
by the proteids alone. Many of the proteids contain sulphur, and
also have phosphorus attached to them in some combination or
other, and some of the fats taken as food contain phosphorus ;
these elements ultimately suffer oxidation into phosphates and
sulphates, and leave the body in that form in company with the
other salts.

Broadly speaking then, the waste products of the animal
economy are urea, carbonic acid, salts and water. Of these a large

CHAP, in.] CUTANEOUS SECRETION. 385

portion of the carbonic acid, and a considerable quantity of water,
leave the body by the lungs in respiration ; while all (or nearly all)
the urea, the greater portion of the salts, and a large amount of
water, with an insignificant quantity of carbonic acid, pass away
by the kidneys. The work therefore of the remaining excretory
tissue, the skin, is confined to the elimination of a comparatively
small quantity of salts, a little carbonic acid, and a variable but
on the whole large quantity of water in the form of perspiration.
The actual excretion by the bowel, that is to say, that portion of
the faeces which is not simply undigested matter, we have seen to
be very small.

The Nature and Amount of Perspiration.

The quantity of matter which leaves the human body by way
of the skin is very considerable. Thus it has been estimated that,
while 7 grains pass away through the lungs per minute, as much
as 11 grains escape through the skin. The amount however varies
extremely ; it has been calculated, from data gained by enclosing the
arm in a caoutchouc bag, that the total amount of perspiration
from the whole body in 24 hours might range from 2 to 20 kilos ;
but such a mode of calculation is obviously open to many sources
of error.

Of the whole amount thus discharged, part passes away at
once as watery vapour mixed with volatile matters, while part may
remain for a time as a fluid on the skin ; the former is frequently
spoken of as insensible, the latter as sensible perspiration. The
proportion of the insensible to the sensible perspiration will depend
on the rapidity of the secretion in reference to the dryness, tem-
perature, and amount of movement, of the surrounding atmosphere.
Thus, supposing the rate of secretion to remain constant, the drier
and hotter the air, and the more rapidly the strata of air in contact
with the body are renewed, the greater is the amount of sensible
perspiration which is by evaporation converted into the insensible
condition; and conversely when the air is cool, moist, and stagnant,
a large amount of the total perspiration may remain on the skin
as sensible sweat. Since, as the name implies, we are ourselves
aware of the sensible perspiration only, it may and frequently does
happen that we seem to ourselves to be perspiring largely, when in
reality it is not so much the total perspiration which is being in-
creased as the relative proportion of the sensible perspiration.
The rate of secretion may however be so much increased, that no
amount of dryness, or heat, or movement of the atmosphere, is
sufficient to carry out the necessary evaporation, and thus the
sensible perspiration may become abundant in a hot dry air. And
practically this is the usual occurrence, since certainly a high

25

386 CUTANEOUS RESPIRATION. [BOOK 11.

temperature conduces, as we shall point out presently, to an in-
crease of the secretion, and it is possible that mere dryness of the
air has a similar effect.

The total amount of perspiration is affected not only by the
condition of the atmosphere, but also by the nature and quantity
of food eaten, by the amount of fluid drunk, and by the amount of
exercise taken. It is also influenced by mental conditions, by
medicines and poisons, by diseases, and by the relative activity of
the other excreting organs, more particularly of the kidney.

The fluid perspiration, or sweat, when collected, is found to be
a clear colourless fluid, with a strong and distinctive odour varying
according to the part of the body from which it is taken. Besides
accidental epidermic scales, it contains no structural elements.
The reaction of the secretion of the sweat glands, apart from that
of the sebaceous glands, appears to be alkaline. This is well seen
when the sweat becomes abundant. An admixture of sebaceous
secretion may, when the sweat itself is scanty, give rise to an acid
reaction, probably from the sebaceous fats becoming converted into
fatty acids. The average amount of solids is about 1'81 p.c., of
which about two-thirds consist of organic substances. The chief
normal constituents are: (1) Sodium chloride with small quantities
of other inorganic salts. (2) Various acids of the fatty series,
such as formic, acetic, butyric, with probably propionic, caproic,
and caprylic. The presence of these latter is inferred from the
odour ; it is probable that many various volatile acids are present
in small quantities. Lactic acid, which Berzelius reckoned as a
normal constituent, is stated not to be present in health. (3)
Neutral fats, and cholesterin; these have been detected even in
places, such as the palms of the hand, where sebaceous glands are
absent. (4) Though some observers seem to have found a consider-
able quantity of urea (calculated at 10 grms. in the 24 hours for
the whole body) in sweat, the evidence goes to shew that neither
urea nor any ammonia compound exists in the normal secretion to
any extent ; apparently some small amount of nitrogen leaves the
body by the skin, but this is probably supplied by the epidermis.

In various forms of disease the sweat has been found to contain,
sometimes in considerable quantities, blood, albumin, urea (par-
ticularly in cholera), uric acid, calcium oxalate, sugar, lactic acid,
indigo, bile and other pigments. Iodine and potassium iodide,
succinic, tartaric, and benzoic (partly as hippuric) acids have been
found in the sweat when taken internally as medicines.

Cutaneous Respiration.

A frog, the lungs of which have been removed, will continue to
live for some time ; and during that period will continue not only
to produce carbonic acid, but also to consume oxygen. In other

CHAP, in.] CUTANEOUS SECRETION. 387

words, the frog is able to breathe without lungs, respiration being
carried on efficiently by means of the skin. In mammals and in
man this cutaneous respiration is, by reason of the thickness of the
epidermis, restricted to within very narrow limits; nevertheless,
when the body remains for some time in a closed chamber to
which the air passing in and out of the lungs has no access (as
when the body is enclosed in a large air-tight bag fitting tightly
round the neck, or where a tube in the trachea carries air to and
from the lungs of an animal placed in an air-tight box), it is found
that the air in the chamber loses oxygen and gains carbonic acid.
The amount of carbonic acid which is thus thrown off by the skin
of an average man in 24 hours amounts to about 10 grms., or accord-
ing to some observers to (no more than) about 4 grms., increasing
with a rise of temperature, and being very markedly augmented by
bodily exercise. It is stated that the amount of oxygen consumed
is about equal in volume to that of the carbonic acid given off, but
some observers make it rather less. It is evident that the loss
which the body suffers through the skin consists chiefly of water.

When an animal, such as a rabbit, is covered over with an
impermeable varnish such as gelatine, so that all exit or entrance
of gases or liquids by the skin is prevented, death shortly ensues.
This result cannot be due, as was once thought, to arrest of
cutaneous respiration, seeing how insignificant is the gaseous inter-
change by the skin as compared with that by the lungs. Nor are
the symptoms those of asphyxia, but rather of some kind of
poisoning, marked by a very great fall of temperature, which
however does not seem to be the result of diminished production
of heat, since it is said to be coincident with an actual
increase of the discharge of heat from the surface. The
animal may be restored, or at all events its life may be prolonged
with abatement of the symptoms, if the great loss of heat which is
evidently taking place be prevented by covering the body thickly
with cotton wool, or keeping it in a warm atmosphere. The
symptoms have not as yet been clearly analysed, but they seem to
be due in part to a pyrexia or fever possibly caused by the reten-
tion within or re-absorption into the blood of some of the con-
stituents of the sweat, or by the products of some abnormal meta-
bolism, and in part to a dilation of the cutaneous vessels which
causes an abnormally large loss of heat, even through the varnish.

The Secretion of Perspiration.

The skin contains, besides the ordinary sudoriparous glands, the
sebaceous glands, and the special odoriferous glands of the axilla,
anus, and other regions. With regard to the various volatile and
odoriferous substances peculiar to sweat, and especially with regard

25—2

388 NERVOUS MECHANISM. [BOOK n.

to those peculiar to the sweat of particular regions of the skin,
there can be no doubt that these are secreted by the epithelium of
the appropriate glands. There can be equally no doubt that the
fats which come to the surface of the skin from the sebaceous
glands arise from a metabolism of the cells of those glands. And
we shall probably not go far wrong in regarding the sweat as a
whole as supplied by the sweat-glands alone. For though it seems
evident that some amount of fluid must pass by simple transuda-
tion through the ordinary epidermis of the portions of skin inter-
vening between the mouths of the glands, yet on the whole it is
probable that the portion which so passes is a small fraction only
of the total quantity secreted by the skin ; and direct experiment
shews that even the simple evaporation of water is much greater
from those parts of the skin in which the glands are abundant than
from those in which they are scanty.

The nervous mechanism of Perspiration. The secreting ac-
tivity of the skin, like that of other glands, is usually accompanied
and aided by vascular dilation. In one of Bernard's early experi-
ments on division of the cervical sympathetic, it wras observed that
in the case of the horse, the vascular dilation of the face on the side
operated on was accompanied by increased perspiration. Indeed
the connection between the state of the cutaneous blood-vessels
and the amount of perspiration is a matter of daily observation.
When the vessels of the skin are contracted, the secretion of the
skin is diminished ; when they are dilated it becomes abundant.
And in this way, as we shall later on point out, the temperature of
the body is largely regulated. When the surrounding atmosphere
is warm, the cutaneous vessels are dilated, the amount of sweat
secreted is increased, and the consequently augmented evaporation
tends to cool down the body. On the other hand, when the
atmosphere is cold, the cutaneous vessels are constricted, perspira-
tion is scanty, and less heat is lost to the body by evaporation.

The analogy with the other secreting organs which we have
already studied leads us however to infer that there are special
nerves directly governing the activity of the sudoriparous glands,
independent of variations in the vascular supply. And not only is
this view supported by many pathological facts, such as the profuse
perspiration of the death agony, of various crises of disease, and
of certain mental emotions, and the cold sweats occurring in
phthisis and other maladies, in all of which the skin is anaemic
rather than hyperaemic ; but we have direct experimental evidence
of a nervous mechanism of perspiration as complete as the vaso-
motor mechanism.

If in the cat1 the peripheral stump of the divided sciatic nerve

1 The cat sweats freely in the hairless soles of the feet but not on any part
of the body covered with hairs. The dog also sweats in the same regions but
not so freely as the cat. Babbits and other rodents appear not to sweat at all. The
snout of the pig sweats freely ; and the often profuse sweating of the horse is known
to all.

CHAP, in.] CUTANEOUS SECRETION. 389

be stimulated with the interrupted current, a profuse sweat may
readily be observed to break out in the hairless sole of the foot on
that side. Not only may the secretion be observed when the
cutaneous vessels are thrown into a state of constriction by the
stimulus, but it also appears when the aorta or crural artery is
clamped previous to the stimulation, or indeed when the leg is am-
putated. Moreover when atropin has been injected, the stimula-
tion produces no sweat, though vaso-motor effects follow as usual.
The analogy between the sweat-glands of the foot and such a gland
•as the submaxillary is in fact very close, and we are justified in
speaking of the sciatic nerve as containing secretory fibres distri-
buted to the sudoriparous glands of the foot. Similar results
may be obtained with the nerves of the fore limb. And in our-
selves a copious secretion of sweat may be induced by tetanizing
through the skin the nerves of the limbs or the face.

If a cat in which the sciatic nerve has been divided on one side
be exposed to a high temperature in a heated chamber, the limb
the nerve of which has been divided remains dry, while the feet of
the other limbs sweat freely. This result shews that the sweating
which is caused by exposure of the body to high temperatures is
brought about not by a local action on the sweat-glands but by the
agency of the central nervous system. A high temperature up to
a certain limit increases the irritability of the epithelium of the
sweat-glands as it does that of other forms of protoplasm : thus
stimulation of the sciatic in the cat produces a much more abundant
secretion in a limb exposed to a temperature of 35° or somewhat
above, than in one which has been exposed to a distinctly lower
temperature, and in a limb which has been placed in ice-cold
water hardly any secretion at all can be gained ; but apparently
mere rise of temperature without nerve-stimulation will not give
rise to a secretory activity of the glands. The sweating caused
by a dyspnoeic condition of blood, and such appears to be the
sweat of the death agony, is similarly brought about by the
agency of the central nervous system. When an animal with the
sciatic nerve divided on one side is made dyspnceic, no sweat
appears in the hind limb of that side, though abundance is seen in
the other feet.

Sweating may be brought about as a reflex act. Thus when
the central stump of the divided sciatic is stimulated sweating is
induced in the other limbs, and in ourselves the introduction
of pungent substances into the mouth will frequently give rise to a
copious perspiration over the side of the face. We are thus led to
speak of sweat centres, analogous to the vaso-motor centres, as
existing in the central nervous system ; and as in the case of vaso-
motor centres, a dispute has arisen as to whether there is a
dominant sweat centre in the medulla oblongata or whether such
centres are more generally distributed over the whole of the spinal
cord.

390 ABSORPTION BY THE SKIN. [BOOK n.

It does not at present appear certain whether the sweating
caused by heat is carried out by direct action on the sweat centres,
or by the higher temperature affecting the skin and so producing
its effect in a reflex manner ; but in the case of dyspnoea at least
we may fairly suppose that the action of the venous blood is
chiefly if not exclusively on the nerve centres. Some drugs, such
as pilocarpin, which cause sweating, appear to produce their effect
chiefly by a local action on the glands since the action continues
after the division of the nerves (though pilocarpin at least has as
well some action on the nerve centres), and the antagonistic action
of atropin is similarly local. Nicotin appears to produce its
sweating action chiefly by acting on the central nervous system.

The sweat-fibres for the hind foot (in the cat) appear to leave
the spinal cord by the roots of the last dorsal and first two lumbar
or last two dorsal and first four lumbar nerves, pass along the rami
communicantes to the abdominal sympathetic, and thus reach the
sciatic nerve. Similarly the sweat-nerves for the fore foot leave
the spinal cord by the roots of the fourth (or fourth, fifth, and sixth)
dorsal nerves, pass into the thoracic sympathetic, thence into the
ganglion stellatum, and thus join the brachial plexus ; the course to
the foot is finally along the median and ulnar nerves respectively.
In the horse and pig the sweat-fibres for the side of face and snout
appear to run in branches of the fifth and not in the facial.

Absorption by the Skin.

Although under normal circumstances the skin serves only as
a channel of loss to the body, it has been maintained that
it may, under particular circumstances, be a means of gain.
Cases are on record where bodies are said to have gained in weight
by immersion in a bath, or by exposure to a moist atmosphere
during a given period, in which no food or drink was taken, or to
have gained more than the weight of the food or drink taken;
the gain in such cases must have been due to the absorption of
water by the skin. Direct experiments however throw doubt on
these statements, for they shew that under ordinary circumstances
such a gain by the skin is slight, being apparently due to mere imbibi-
tion of water by the epidermis. It is uncertain whether substances in
aqueous solution can be absorbed by the skin when the epidermis
is intact, the evidence on this point being contradictory. In the
case of the sound human skin the balance of conflicting evidence
is in favour of the view that soluble non-volatile substances are
not absorbed, and that volatile substances such as iodine which
may be detected in the system after a bath containing them are
absorbed not by the skin but by the mucous membrance of the
respiratory organs, the substance making its way to the latter by

CHAP, in.] CUTANEOUS SECRETION. 391

volatilisation from the surface of the bath. In the case of the
skin of the frog an absorption of water and of various soluble
substances would certainly appear to take place. The lymphatics
in the skin of a newborn infant have been found crowded with the
particles of the peculiar fatty secretion which covers the skin at
birth ; and solid particles rubbed into even the sound skin may,
especially when applied in a fatty vehicle, as ex. gr. in the well-
known mercury-ointment, find their way into the underlying
lymphatics. So that possibly absorption to a certain extent may
ordinarily take place in this way. By abraded surfaces, where the
dermis is laid bare and covered only by the lowest layers of
epidermis, absorption takes place very readily.

CHAPTER IV.
SECRETION BY THE KIDNEYS.

THE epithelium of the kidney, like that of the alimentary canal,
is a secreting tissue. The protoplasmic cells which line at least a
large portion of the tubuli uriniferi elaborate from the blood, in a
manner which we shall presently discuss, certain substances, and
discharge them into the channels of the tubules. Besides these
distinctly active secreting structures, however, the kidney exhibits
in its Malpighian bodies an arrangement very analogous to that
which obtains in the lungs. Just as in the latter the functions of
the alveolar epithelium are reduced to a minimum, and the en-
trance and egress of the gases of respiration are mainly carried on
by diffusion, so in the former the epithelium covering the glomerulus
has probably but little secreting activity, and the passage of
material from the interior of the convoluted blood-vessels into the
cavity of the tubule is chiefly carried on by processes which
more closely resemble ordinary filtration. What substances
pass in this way, and what substances are secreted by the
direct action of the epithelium of the secreting tubules, we
shall shortly consider. The various substances passing, in company
with a large amount of water, in either the one or the other way,
into the ducts of the gland, constitute the secretion called urine.
And since none of the substances so thrown out are of any further
use in the economy, but are at once carried away, urine is generally
spoken of as an excretion.

SEC. 1. COMPOSITION OF URINE.

The healthy urine of man is a clear yellowish slightly fluorescent
fluid, of a peculiar odour, saline taste, and acid reaction, having a
mean specific gravity of 1*020, and generally holding in suspension a
little mucus. The normal constituents may be arranged in several
classes.

1. Water.

2. Inorganic salts. These for the most part exist in urine in
natural solution, the composition of the ash almost exactly cor-
responding with the results of the direct analysis of the fluid ; in
this respect urine contrasts forcibly with blood, the ash of which is
largely composed of inorganic substances, which previous to the
combustion existed in peculiar combination with proteid and other
complex bodies. In the ash of urine there is rather more sulphur
than corresponds to the sulphuric acid directly determined; this
indicates the existence in urine of some sulphur-holding complex
body. And there are traces of iron, pointing to some similar iron-
holding substance. But otherwise, all the substances found in the
ash exist as salts in the natural fluid. The most abundant and
important is sodium chloride. There are found in smaller quanti-
ties, calcium chloride, potassium and sodium sulphates, sodium,
calcium and magnesium phosphates, with traces of silicates.
Alkaline carbonates are frequently found, and nitrates in small
quantity are also said to be sometimes present.

394 COMPOSITION OF URINE. [BOOK 11.

The phosphates are derived partly from the phosphates taken
as such in food, partly from the phosphorus or phosphates peculiarly
associated with the proteids, and partly from the phosphorus of
certain complex fats such as lecithin. When urine becomes alkaline,
the calcic and magnesic phosphates are precipitated, the sodium
phosphates remaining in solution. The sulphates are derived
partly from the sulphates taken as such in food and partly from
the sulphur of the proteids. The carbonates, when occurring in
large quantity, generally have their origin in the oxidation of such
salts as citrates, tartrates, &c. The bases present depend largely
on the nature of the food taken. Thus with a vegetable diet, the
excess of the alkalis in the food reappears in the urine ; with an
animal diet, the earthy bases in a similar way come to the front.

3. Nitrogenous crystalline bodies, derivatives of the metabo-
lism of the proteids of the body and food. First and foremost
come urea and its immediate ally, uric acid. These will be con-
sidered in detail hereafter; they are the typical products of the
metabolism of proteids. Existing in much smaller quantities are a
number of bodies more or less closely related to urea, which may for
the most part be regarded as less-completely oxidised products of
metabolism. Such are : kreatinin, xanthin, hypoxanthin, and
occasionally allantoin. To these may be added hippuric acid,
ammonium oxalurate, and, at times, taurin, cystin, leucin, and
tyrosin. These too we shall have to consider in dealing with the
metabolism of the body.

4. Non-nitrogenous bodies. These exist in very small quan-
tities, and many of them are probably of uncertain occurrence.
They are organic acids, such as lactic, succinic, formic, oxalic, phe-
nylic, &c. It has been maintained that minute quantities of sugar
are invariably present in even healthy urine ; this however has not
as yet been placed beyond all doubt.

5. Pigments. These are at present very imperfectly under-
stood. Whether the natural yellow colour of urine be due to a
single pigment, or to more than one, and what is the exact nature
of these pigments, must be left undecided. As was stated above
(p. 300), the urine frequently contains urobilin ; and the peculiar
red colour of some rheumatic urines is due to the presence of a
body called purpurin or uroerythrin. The urine of many animals,
especially of the dog, and occasionally of man, contains indican,
which under certain circumstances may give rise to the production
of indigo-blue.

6. Other bodies. When urine is treated with many times its
volume of alcohol, a granular or flocculent precipitate is thrown
down, consisting of phosphates, some substance or substances giving
proteid reactions and probably other bodies in small quantities.
An aqueous solution of the precipitate is both amylolytic and

CHAP, iv.] RENAL SECRETION. 395

proteolytic, from which it appears probable that some of the
ferments of the salivary glands, pancreas, stomach, &c., having done
their work, escape from the body by the urine.

7. Gases. Those gases which can be extracted from urine by
the mercurial pump are chiefly nitrogen and carbonic acid, oxygen
occurring in very small quantities or being wholly absent.
, The quantities in which these multifarious constituents are pre-
sent vary within very wide limits, being dependent on the nature
of the food taken, and on the conditions of the body. These
points will be considered in the succeeding chapter. What may be
called the average composition of human urine is shewn in the fol-
lowing table.

AMOUNTS OF THE SEVERAL URINARY CONSTITUENTS PASSED IN
TWENTY-FOUR HOURS. (After PAEKES.)

By an average Per 1 kilo

man of 66 kilos. of Body Weight.

Water 1500*000 grammes 23*0000 grammes

Total Solids 72-000 1*1000

Urea 33*180 '5000

Uric Acid '555 '0084

Hippuric Acid '400 '0060

Rreatinin '910 '0140
Pigment, and

other substances lO'OOO '1510

Sulphuric Acid 2'012 '0305

Phosphoric Acid 3*164 '0480

Chlorine 7*000 (8'21) '1260

Ammonia '770

Potassium 2*500

Sodium 11-090

Calcium -260

Magnesium "207

Acidity of Urine. The healthy urine of man is acid, owing
to the presence of acid sodium phosphate, the absence of free acid
being shewn by the fact that sodium hyposulphite gives no pre-
cipitate. The amount of acidity is about equivalent to 2 grms.
of .oxalic acid in twenty-four hours, but the degree of acidity at any
one time varies much during the day, being in an inverse ratio to
the amount of acid secreted by the stomach; thus it decreases
after food is taken, and increases as gastric digestion becomes
complete. It varies with the nature of the food; with a vege-
table diet the excess of alkalis secreted leads to alkalinity, or
at least to diminished acidity, whereas this effect is wanting with
an animal diet, in which the earthy bases preponderate. Hence
the urine of carnivora is generally very acid, while that of herbivora

396 CONSTITUENTS OF URINE. [BOOK n.

is alkaline. The latter, when fasting, are for the time being
carnivorous, living entirely on their own bodies, and hence their
urine becomes under these circumstances acid.

The natural acidity increases for some time after the urine has
been discharged, owing to the formation of fresh acid, apparently
by some kind of fermentation. This increase of acid frequently
causes a precipitation of urates, which the previous acidity has
been insufficient to throw down. After a while however the acid
reaction gives way to alkalinity. This is caused by a conversion
of the urea into ammonium carbonate through the agency of a
specific ferment. This ferment as a general rule does not make its
appearance except in urine exposed to the air ; it is only in un-
healthy conditions that the fermentation takes place within the
bladder.

Abnormal constituents of Urine. The structural elements
found in the urine under various circumstances are blood, pus and
mucus corpuscles, epithelium from the bladder and kidney, and
spermatozoa. Serum-albumin, fibrin (frequently as ' casts '), alkali-
albumin, globulin, a peculiar form of albumin (the so-called hemi-
albumose), fats, cholesterin, sugar, leucin, tyrosin, oxalic acid, bile
acids and bile pigment, may be enumerated as the most important
metabolic products abnormally present in urine. Besides these the
urine serves as the chief channel of elimination for various bodies,
not proper constituents of food, which may happen to have been
taken into the system. Thus various minerals, alkaloids, salts,
pigmentary and odoriferous matters, may be passed unchanged.
Many substances thus occasionally taken suffer changes in passing
through the body ; the most important of these will be considered
in a succeeding chapter.

SEC. 2. THE SECRETION OF URINE.

We have already called attention to the fact that the kidney,
unlike the other secreting organs which we have hitherto studied,
consists of two parts so distinct in structure that it seems im-
possible to resist the conclusion that their functions are different,
and that the mechanism by which the urine is secreted is of
a double kind. On the one hand the tubuli uriniferi with their
characteristic epithelium seem obviously to be actively secreting
structures comparable to the secreting alveoli of the salivary and
other glands. On the other hand the Malpighian capsules with
their glomeruli are organs of a peculiar nature with an almost
insignificant epithelium, and their structure irresistibly suggests
that they act rather as a filtering than as a truly secreting
mechanism. Hence the view put forward by Bowman long ago,
that certain constituents only of the urine are secreted after the
fashion of other secreting glands by the tubuli uriniferi, and that
the rest of the constituents, including a great * deal of the water
with such highly soluble and diffusible salts as preexist in con-
siderable quantity in the blood, are as it were filtered by the glome-
ruli of the Malpighian capsules. This view is moreover, as we
shall presently see, supported by direct experimental evidence.
Assuming for the present the truth of it, we may remark that
the passage of fluids and dissolved substances through membranes
being in large part directly dependent on pressure, the extent and
rapidity of that part of the whole process of the secretion of urine,

398 RELATIONS TO BLOOD-PRESSURE. [BOOK n.

which is a kind of filtration, will be directly affected by the amount
of arterial pressure in the renal arteries, while the effect of varia-
tions of arterial pressure on that part of the process which is a real
active secretion will be an indirect one only. Hence, the discharge
of urine by the kidneys must be to a much greater extent than is
the case with the secretion of saliva or of gastric juice a mere
matter of pressure ; and it will consequently be of advantage
to study the relations of urinary secretion to blood-pressure before
we enter upon the discussion of the active secretion itself.

The Relation of the Secretion of Urine to Arterial Pressure.

Eecent observations have shewn experimentally that the kidney
is supplied with a vaso-motor mechanism as well developed perhaps
as that of any other part of the body.

By means of a modification of the plethysmograph, we can readily
observe the variations which take place in the volume of the
kidney and the same method can be applied also to other internal
organs.

FIG. 63. BENAL ONCOMETER. Seen in section (semi-diagrammatic). K. kidney,
V. vessels and nerves imbedded in fat, &c. entering hilus of organ, O.C. and I.C.
outer and inner metal capsules screwed together by the screw S, and holding between

CHAP, iv.]

RENAL SECRETION.

399

them the edge of the membrane M which applies itself to the surface of the kidney,
and forms with the metal capsule two chambers a and B, one of which (B) is closed
by a plug filling the opening B, while the other (a) communicates by a tube T with
the recording instrument. The other opening C (which is closed by a small tap) is
for the purpose of filling the chamber a with warm oil, after the kidney has been
placed in the box, the other chamber B having been previously partly filled, the
quantity introduced into it depending upon the size of the kidney.

FIG. 64. SEMI-DIAGRAMMATIC SECTIONAL VIEW OF ONCOGBAPH. Half natural size.
K tube connecting instrument with oncometer. D piston floating on oil contained
in the cavity M ; the oil is prevented from escaping by the side of the piston, by the
delicate flexible membrane E, which does not interfere with the movements of the
piston. H, recording lever connected with the piston by a needle G passing through
the guides F, F*. The screw C is for the purpose of clamping the edge of the membrane
between the two ring-shaped surfaces at N, while the side tube L is for the purpose
of filling the instrument.

The instrument consists of two parts, one of which (Fig. 63) called
by Dr C. S. Roy, who introduced it, an oncometer lt is applied to the
organ about to be studied, while the other (Fig. 64), called the
oncograph, is the recording part of the apparatus. Any diminution
in the volume of the organ (Fig. 63, K), kidney, spleen, &c. as the case
may be, causes a diminution of the quantity of fluid in the
chamber a; this is transmitted through the tube T, continuous
with the tube K (Fig. 64) to the chamber M ; the piston D accordingly
falls and with it the lever H. Similarly an increase in the volume of
the organ causes the lever to rise.

The volume of the kidney may be increased by a swelling of its
constituent cells and other structural elements, by an accumulation
of lymph in its lymph spaces and by a distension of its blood-
vessels. Compared with the third, the two former causes are in
health so insignificant and problematical that they may be disre-
garded. Further the distension of the blood-vessels will in general

1 From oncos, bulk.

400 RELATIONS TO BLOOD-PRESSURE. [BOOK u

depend on the constriction or dilation of the renal arteries and their
ramifications, for distension due to venous obstruction will only
occur in special cases. Hence variations in the volume of the
kidney may be taken as a measure of variations in its vascular
supply, increase of volume indicating dilated renal vessels, and
decrease of volume indicating constriction of the renal vessels.

When by means of the instrument just described a tracing is
taken of the volume of a kidney in what may be considered
a normal condition, some such result as that shewn in Fig. 65 is
obtained.

BLOOD PRESSURE.

KIDNEY CURVE.

FIG. 65. BLOOD-PBESSUBE TBACING, AND CUBVE FBOM KENAL ONCOMETEB. Natural
size. The blood-pressure abscissa line has been raised 2*75 cm. (the actual medium
blood-pressure having been 115 mm. Hg.). The time-curve gives interruptions re-
curring every three seconds.

The volume of the kidney is seen to be so delicately responsive
to changes in the mean arterial pressure that the curve reproduces
almost exactly a blood-pressure curve, shewing not only the respira-
tory undulations, but even the rise and fall due to the individual
heart beats. With each rise of mean arterial pressure more blood
is driven into the renal vessels and the kidney swells: with each fall
of pressure less blood enters and the kidney shrinks. On other
tracings taken in the same way may often be seen the wider
variations corresponding to the Traube-Hering curves; but it will
be observed that in these the kidney shrinks with the rise of
pressure and swells with the fall. For as we have seen (p. 373) the
rise in the Traube-Hering undulation is due to an augmentation of
peripheral resistance caused by the constriction of minute arteries ;
and this constriction occurs in the kidney as elsewhere ; the renal
arterioles take their share in producing the result, and in consequence
of their constriction the kidney shrinks. Similarly the relaxation
of the renal vessels contributes to bring about the sequent fall.

Other variations in the volume of the kidney are seen to arise
from various influences. When respiration is stopped the in-
creasingly venous blood, acting on the medullary or spinal vaso-
motor centres, leads to constriction of the renal as well as of other

CHAP, iv.] RENAL SECRETION. 401

arteries, as shewn by the shrinking of the kidney. Stimulation of
the medulla oblongata causes a very marked shrinking of the
kidney, indicating powerful constriction of its arteries, as does also
stimulation of the splanchnic nerve; the effect when the splanchnic
on one side is stimulated frequently affects the kidney on the
opposite side as much as that on the same side. Stimulation of
a sensory nerve causes shrinking of the kidney, in spite of a rise
of mean pressure, which in itself would tend to swell the kidney,
taking place at the same time ; this is an instance of reflex con-
striction as that of stimulation of the splanchnic nerve is of direct
constriction. A direct constriction may also be brought about by
stimulation of the renal nerves. When all the renal nerves
are divided (an operation by no means easy), stimulation of nerves
in other parts of the body does not cause a constriction but an
expansion of the kidney, since it gives rise to an increase of
blood-pressure, through which the renal vessels are passively filled
to a greater extent.

The same method further shews that the vaso-motor mechanism
of the kidney is remarkably sensitive to changes in the chemical
constitution of the blood. The injection into the blood of even
a small quantity of water causes a shrinking of the kidney followed
by a more lasting expansion. The injection of urea and some
other diuretics produces the same effect to a more marked degree,
while the injection of normal saline solution and especially
of such diuretics as sodium acetate causes an expansion from the
very first, the primary shrinking being absent. It is moreover
worthy of note that these effects of diuretics and of chemical
changes in blood appear even after all the renal nerves have
apparently been completely severed, indicating that these bodies
induce vascular changes by acting either upon some peripheral
vaso-motor mechanism, or, even more directly, on the blood-vessels
themselves. It may be added that they will produce considerable
effects in the kidney itself without appreciably modifying the
general blood-pressure.

As yet this method has not disclosed any distinct vaso-dilator
fibres passing to the kidney from other parts, positive dilation
having been observed only as the result of chemical agents. But,
even if these prove eventually to be really absent, enough has been
said to shew that the kidney has an ample and well-developed
vaso-motor supply. In many of the observations referred to above,
the flow of urine was determined at the same time as the volume
of the kidney, by measuring the escape from the ureter of the kidney
experimented upon through a cannula tied into it. And it was
found that, unless special causes intervened, expansion of the
kidney was accompanied by an increase and contraction by a
decrease in the flow of urine. But before we attempt to illustrate
the working of the vaso-motor mechanism just described, it will be
as well to call attention to the fact that, as far as filtration is

v. 23

402 RELATIONS TO BLOOD-PRESSURE. [BOOK n.

concerned, the chief circumstance of the vascular condition of the
kidney which we have to consider is the extent of pressure present
in the small vessels of the renal glomeruli. The more the pressure
of the blood in these exceeds the pressure of the fluid in the
channels of the uriniferous tubules, the more rapid and extensive
will be the nitration from the one into the other.

This local blood-pressure in the small vessels of the glomeruli
may be increased —

1. By an increase of the general blood-pressure, brought about
— (a) by an increased force, frequency, &c. of the heart's beat,
(6) by the constriction of the small arteries supplying areas other
than the kidney itself.

2. By a relaxation of the renal artery, which, as we have pre-
viously pointed out (p. 216), while diminishing the pressure in the
artery itself, increases the pressure in the capillaries and small
veins which the artery supplies. It need hardly be added that
this local relaxation must either be accompanied by constriction in
other vascular areas, or at all events must not be accompanied by a
sufficiently compensating dilation elsewhere.

The same local pressure may similarly be diminished —

1. By a constriction of the renal artery and its branches, which,
while increasing the pressure on the cardiac side of the artery,
diminishes the pressure in the capillaries and veins which are
supplied by the artery. This again must either be accompanied by
dilation in other vascular areas, or at least not accompanied by a
compensating constriction.

2. By a lowering of the general blood-pressure, brought about
—(a) by diminished force, &c. of the heart's beat, (6) by a general
dilation of the small arteries of the body at large, or by a dilation
of vascular areas other than the kidneys.

Bearing these facts in mind, it becomes apparently easy to
explain many of the instances in which an increase or diminution
of urine is produced by natural or artificial means. Thus section
of the spinal cord below the medulla causes a great diminution, and
indeed in many cases a complete or almost complete arrest, of the
secretion of urine. This operation, as we have seen in discussing
the vaso-motor system, leads to a very general vascular dilation, in
consequence of which there ensues a great fall of the general blood-
pressure. At present it seems uncertain whether the renal arteries
really possess a normal tone like that of most other arteries ; and
we do not know whether they in consequence of the operation
share in the general dilation. Even if they do, their expansion
apparently is insufficient to compensate the great diminution of
general blood-pressure. It has been stated that the effect of section
of the medulla is so marked and constant that when, in the dog, the
blood-pressure sinks at least below 30 mm. mercury the secretion of
urine is invariably arrested. It would appear however that this is
not always the case, and that secretion is sometimes observed to

CHAP, iv.] RENAL SECRETIOtf. 403

continue when the blood-pressure sinks even below this point.
Section of the spinal cord in the dorsal region similarly depresses
the general blood-pressure and similarly arrests or diminishes the
secretion of urine. This is an operation however from which an
animal may, if duly tended, recover, and live for a long time with
the lumbar spinal cord quite separated from the brain and upper
parts of the spinal cord. In such a case the secretion of urine is
soon re-established; but the general blood-pressure is also re-
established, so that this condition of things also illustrates the
connection between blood-pressure and the secretion of urine.

Stimulation of the spinal cord below the medulla, though acting
in the converse direction, brings about the same result, arrest of
the secretion. By the stimulation the action of the vaso-motor
nerves is augmented, and constriction of the renal arteries as well
as of other arteries in the body is brought about. The increase of
general blood-pressure thus produced is insufficient to compensate
for the increased resistance in the renal arteries; and as a con-
sequence the flow of blood into the glomeruli is largely reduced.
We have seen that under these circumstances the kidney shrinks,
and indeed on inspection it is seen to become during the stimu-
lation pale and bloodless.

Section of the renal nerves is followed by a most copious
secretion, by what has been called hydruria or polyuria. The
section of the nerves, by interrupting the vaso-motor tracts, even if
it does not act in the way of destroying a normal tone (the existence
of which seems doubtful), prevents the advent of ordinary con-
stricting impulses, and thus indirectly leads to dilation of the renal
arteries, and so to increased pressure in the small vessels of the
glomeruli. If, after section of the renal nerves, the cord be divided
below the medulla, the polyuria disappears ; for the diminution of
general blood-pressure thus produced more than compensates for
the special dilation of the renal arteries. Conversely, if after
section of the renal nerves the cord be stimulated, the flow of urine
is still further increased, since the rise of general blood-pressure due
to the general arterial constriction caused by the stimulation tends
to throw still more blood into the renal arteries, on which, owing
to the division of their nerves, the spinal stimulation is powerless.
The section of the renal nerves sometimes leads to the appear-
ance of albumin in the urine, but this is probably due to some
other effects than those of variations in blood-pressure simply.

Section of the splanchnic nerves produces also an increased flow
of urine. But the augmentation in this case is smaller and less
certain than in the case of section of the renal nerves themselves,
partly because the vaso-motor tracts from the spinal cord to the
kidneys do not run exclusively in the splanchnic nerves but reach
the kidney along some other path or paths, and partly because the
splanchnic nerves govern the whole splanchnic area, and hence a
large portion of the increased supply of blood is diverted from the

26—2

404 ACTIVITY OF THE EPITHELIUM. [BOOK n.

kidney to other abdominal organs. On the other hand, stimulation
of the splanchnic nerves is able to arrest the flow of urine by
producing constriction of the renal arteries.

The experimental phenomena recorded above are thus seen to
receive a fairly satisfactory explanation when they are referred
exclusively to variations in blood-pressure. And many of the
natural variations in the flow of urine may be interpreted in the
same way. No fact in the animal economy is oftener or more
strikingly brought home to us than the correlation of the skin and
the kidney as far as their secretions are concerned ; and this seems
to be, in part at least, maintained by means of the vaso-motor
nervous mechanism. Thus when the skin is cold, its blood-vessels
are, as we know, constricted. This, by causing an increase of
general blood-pressure, will augment the flow through the kid-
neys, and conversely, the dilated condition of the arteries of a
warm skin, with the consequent diminution of general blood-
pressure, will give rise to a diminished renal discharge. It is
probable, however, that a more direct connection exists between
the skin and the kidneys, so that a warm skin leads to constriction
and a cold skin to dilation of the renal vessels ; and it is further
possible that the one may react on the other in another way, viz.,
by changes induced in the blood; Tjbe effects of emotions may
possibly also be explained as essentially vaso-motor phenomena.

Secretion by the Renal Epithelium.

While thus recognising the importance of the relations of the
flow of urine to blood-pressure, we must not be led into the error
of supposing that the work of the kidney is wholly a matter of
filtration. The glomerular mechanism, so specially fitted for filtra-
tion, is after all a small portion only of the whole kidney, and the
epithelium over a large part of the course of the tubuli uriniferi
bears most distinctly the characters of an active secreting epi-
thelium. These facts would lead us a priori to suppose that the
flow of urine is in part the result of an active secretion comparable
to that of the salivary or other glands which we have already
studied. And we have experimental and other evidence that such
is the case.

In the first place a flow of urine may be artificially excited
even when the natural flow has been arrested by diminution of
blood-pressure. Thus if, when the urine has ceased to flow in
consequence of a section of the medulla oblongata, certain sub-
stances, such as urea, sodium acetate, &c., be injected into the
blood, a more or less copious secretion is at once set up. This
secretion is, or at least may be, unaccompanied by any rise of

CHAP, iv.] RENAL SECRETION. 405

blood-pressure sufficient to account for the flow on the nitration
hypothesis. A very similar result is illustrated by the common
experience that the flow of urine is largely increased after taking
fluids especially in large quantities. We cannot explain this by a
reference to blood-pressure, since we have seen (p. 225) that the
quantity of blood may be increased largely without raising the
blood-pressure. On the other hand, observations with the on-
cometer have shewn us that the kidney is remarkably sensitive
to changes in the chemical constitution of the blood, an expansion,
preceded or not by a passing constriction, being caused by the
injection into the blood of even small quantities of water, sodium
chloride and other substances. We have further seen that the
expansion of the kidney, or rather the dilation of the renal vessels
which is the cause of that expansion, brought about in this way,
is dependent on a local peripheral action of some kind or other,
since it will take place after complete severance of all the renal
nerves. It is of course open for us to suppose that this very
dilation of the renal vessels is the cause of the increased flow at
the same time, since, the general blood-pressure remaining the
same, it will lead to increased pressure in the glomeruli. So that
the activity of the kidney which follows upon food and drink or
upon the injection of urea and other substances into the blood may
be taken as really illustrating the dependence of the flow of urine
on blood-pressure, though the vascular mechanism concerned is
limited to the kidney itself and variations of the general blood-
pressure play no part in the matter. But it is also open for us to
suppose that the presence of these substances in the blood excites
the renal epithelium cells to an unwonted activity, causing them-
to pour into the interior of the tubules a copious secretion, just
as the presence of pilocarpin in the blood will cause the salivary
cells to pour forth their secretion into the lumen of their ducts;
and that this activity of the epithelium cells is accompanied, also
as in the case of the submaxillary and other glands, by a vascular
dilation which, though adjuvant and beneficial, is not the distinct
cause of the activity. That this latter view is probably the true
one is shewn by the following remarkable experiment, from which
we learn that of the various substances finding their way into the
blood, some pass into the urine through the glomeruli while others
are distinctly secreted by the tubuli uriniferi, their discharge being
accompanied by an activity of the secreting cells indicated by the
flow of water taking place at the same time.

In the amphibia, the kidney has a double vascular supply : it
receives arterial blood from the renal artery, but there is also
poured into it venous blood from another source. The femoral
vein divides at the top of the thigh into two branches, one of
which runs along the front of the abdomen to meet its fellow
in the middle line and form the anterior abdominal vein, while the
other passes to the outer border of the kidney and branches in the

406 ACTIVITY OF THE EPITHELIUM, [BOOK n.

substance of that organ, forming the so-called renal portal system.
Now the glomeruli are supplied exclusively by the branches of the
renal artery, the renal vena portse only serving to form the ca-
pillary plexus around the tubuli urmiferi which is also sup-
plied by the efferent vessels of the glomeruli. From this it
is obvious that if the renal artery be tied, the blood is shut
off entirely from the glomeruli, actual observation of the kidney
of the newt having shewn that under these circumstances there
is no reflux from the capillary network surrounding the tubules
back to the glomeruli ; thus the kidney by this simple operation is
transformed into an ordinary secreting gland devoid of any special
filtering mechanism. We owe to Nussbaum the ingenious use of
such a kidney to ascertain what substances are excreted by the
glomeruli, and what by the tubules in some other part of their
course. It is found that sugar and peptones, which injected into
the blood readily pass through the untouched kidney and appear
in the urine, do not pass through a kidney the renal arteries
of which have been tied. These substances therefore are excreted
by the glomeruli. Urea on the other hand, injected into the
blood, gives rise to a secretion of urine, when the renal arteries are
tied ; this substance therefore is secreted by the epithelium of the
tubules, and in being so secreted gives rise at the same time to a
flow of water through the cells into the interior of the tubules.

Additional evidence in favour of the activity of the epithelium
cells is afforded by an observation for which we are indebted to
Heidenhain. Into the veins of animals in which the urinary flow
had been arrested by section of the spinal cord below the medulla,
this observer injected a quantity of colouring material known as
sodium sulphindigotate1. By killing the animals at appropriate
times after the injection of the material and examining the
kidneys microscopically and otherwise, he was enabled to ascer-
tain that the pigment so injected passed from the blood into
the renal epithelium, and from thence into the channels of the
tubules, where it was precipitated in a solid form. There being
no stream of fluid through the tubules, owing to the arrest of
urinary flow by means of the preliminary operation, the pigment
travelled very little way down the interior of the tubules, and
remained very much where it was cast out by the epithelium cells.
There were no traces whatever of the pigment having passed
by the glomeruli; and the cells which could be seen distinctly
to take up and eject it, were those lining such portions of the
tubules (viz. the so-called secreting tubules, intercalated tubules
and portions of the loops of Henle) as from their microscopic
features have been supposed to be the actively secreting portions
of the entire tubules. By varying the quantity injected and the
time which was allowed to elapse between the injection and subse-

1 Sometimes called indigo-carmine, though this name is more properly applied
to a crude impure preparation of potassium sulphindigotate.

CHAP, iv.] RENAL SECRETION. 407

quent inspection, Heidenhain was able to trace the material step
by step into the cells, out of the cells into the interior of the
tubules, and for some little distance along the tubules. The
advantage of the absence of a large flow of urine is obvious ; had
this been present, the pigment immediately that it issued from the
cells would have been rapidly washed away down the channels of the
tubules. One observation he made of a peculiarly interesting
character. After injecting a certain quantity of pigment, and
allowing such a time to elapse as he knew from previous experi-
ments would suffice for the passage of the material through the
epithelium to be pretty well completed, he injected a second
quantity. He found that the excretion of this second quantity
was most incomplete and imperfect. It seemed as if the cells were
exhausted by their previous efforts, just as a muscle which has
been severely tetanized will not respond to a renewed stimulation.

This observation may be objected to on the ground that this
colouring matter does not occur as a constituent of the blood either
in health or disease, and especially that the absence of any con-
comitant discharge of fluid from the cells excites suspicion that the
process observed was not really one of secretion ; for the injection
of such substances as urea or urates into the blood does cause
a copious flow of fluid, and indeed thus prevents the microscopic
tracking out of their passage, which in the case of urates might be done
much in the same way as with the sodium sulphindigotate. Moreover
other observers have maintained that the sodium sulphindigotate
does like ordinary carmine pass through the glomeruli ; but in the
case of the amphibian kidney when sodium sulphindigotate is injected
after ligature of renal arteries, no urine is found in the bladder,
but the pigment can be traced, through the epithelium of the
secreting portions of the tubuli. Without insisting too much on
the value of the sodium sulphindigotate experiments, they may
be taken as fairly supporting the view we are considering.

Experimental evidence then justifies the conception which the
structure of the kidney led us to adopt. The secretion of urine by
the kidney is a double process. It is partly a process of filtration,
whose object is to remove as rapidly as possible a quantity of
water from the body, and this part of the work of the kidney is
directly dependent on blood-pressure. It is also however a process
of active secretion by the epithelium of the tubuli. and this part of
the work of the kidney is, in an indirect manner only, dependent
on blood-pressure. Both processes may give rise to a discharge of
water from the blood, and both may give rise to the presence
of the solid constituents of the urine, in solution in that water. In
the first process the discharge of water is the primary object, and
the solid matters which escape at the same time are of secondary
importance; in the second process the excretion of the solid
substance is the primary object, and the accompanying water
of secondary importance. The first process is governed (mainly at

408 ACTIVITY OF THE EPITHELIUM. [BOOK n.

least) by the vaso-motor nervous system; the second process is
excited, as far as we know at present, by substances in the blood
acting directly as chemical stimuli to the epithelium ; but future
researches may disclose the existence of a secretory nervous me-
chanism analogous to that of other secretory glands. It must also
be left for further inquiries to determine exactly which of the two
processes, or to what relative extent each of them, is concerned in
bringing about the presence in the urine of its several constituents.

In one respect the kidney as a secreting organ differs markedly
from such a gland as the salivary. In the case of the latter, we
have seen that the saliva as it flows may cause a pressure in the
duct greater than the mean arterial pressure ; in the case of the
former when a manometer is connected with a cannula tied into the
ureter of a dog, the mercury may rise to 60 mm.,but not much beyond,
and often becomes stationary at lower level, shewing that the urine
cannot be secreted at a pressure greater than that probably
obtaining in the renal vessels ; or, at least, if secretion does
take place it is counterbalanced by an absorption taking place at
the same time. But in this respect the kidney has its fellow in
another secreting organ, the liver, for in this, as we have seen, the
secretion of bile is arrested when the pressure is raised too high.

One or two words of caution are necessary. In speaking of the
glomerulus as a filtering apparatus, it must not be understood that
it is thereby really compared to an ordinary filter made of dead
material, and that when filtration through it is spoken of, a process
exactly like that which takes place in the laboratory is meant. In
the glomerulus the elements of the blood have to pass through the
living wall of the capillary, and the covering layer of epithelium
cells ; and the transit must be affected by the condition of these
living structures. By virtue of their constitution they allow cer-
tain things to pass and not others; and when they become changed
the passage of material is changed also. The possible influence
of a mere layer of squamous epithelium is shewn by experiments on
the cornea, which acts absolutely differently as a filter according
as the epithelium of Descemet is retained or removed ; and in
speaking of the circulation we dwelt on the importance of the
physiological condition of the capillary walls. The nature of the
filtration taking place through the glomerulus will depend therefore
on the condition of the capillary walls and their epithelial invest-
ment. This is illustrated by the phenomena of albuminuria (or
the passage of albumin into the urine), especially as seen in the
following interesting experiment by Nussbaum on the artificial
production of albuminuria in the frog. The renal arteries being
tied, an injection of urea (1 cm. of a 10 p.c. solution) into the blood
gave rise to a flow of urine which was free from albumin. Upon
loosing the ligatures so as to re-establish the flow of blood through
the glomeruli, the urine at once became albuminous. The arrest
of the circulation through the glomeruli had damaged the capillary

CHAP, iv.] RENAL SECRETION. 409

walls, and so allowed the passage through them into the interior of
the Malpighian capsules of the natural proteids of the blood, which
in a normal condition of the capillaries cannot effect such a
passage. The injury however was temporary only; in a short time
the capillary walls were restored to health and the urine ceased to
be albuminous.

We may further quote as shewing the peculiar nature of
the nitration that ligature of the renal veins arrests the secretion
of urine. Apparently the effect which it should produce by
increasing the pressure in the glomeruli is more than counter-
balanced by other influences. Upon removal of the ligatures, the
urine is usually albuminous, shewing that in the interval the
glomeruli have become changed.

One consideration, of quite secondary importance in the glands
which have been previously studied, acquires great prominence
when the kidney is being studied. In studying the pancreas and
gastric glands, we concluded without much discussion that the
zymogen and pepsinogen were formed in the epithelium cells ; for
no great manufacture of these substances is going on in other parts
of the body. The kidney however is emphatically an excreting
organ : its great function is to get rid of substances produced by
the activity of other tissues ; its work is not to form but to eject.
There can be no doubt, to put forward a strong instance, that with
regard to urea it would be absurd to suppose that the whole series
of changes from the proteid condition to the urea stage is carried
on by the kidney. But there still remains the question, Are any
of the stages carried on in the kidney, and if so, what ? Is the
secreting activity of the renal epithelium confined to picking out the
already formed urea from the blood ? Or does the secreting cell of
the tubule receive from the blood some antecedent of urea, and in
the laboratory of its protoplasm convert that antecedent of urea
into urea itself ? and if so, what is that antecedent which comes to
the kidney in the blood of the renal artery ? And so with many
other of the urinary constituents.

In order to complete our study of renal activity, this question
ought to be considered now ; but for many reasons it will be more
convenient to defer the matter to the succeeding chapter, in which
we deal with the metabolic events of the body in general.

SEC. 3. MICTURITION.

The urine, like the bile, is secreted continuously ; the flow may
rise and fall, but, in health, never absolutely ceases for any length
of time. The cessation of renal activity, the so-called suppression
of urine, entails speedy death. The minute streams passing con-
tinuously, now more rapidly now more slowly, along the collecting
and discharging tubules, are gathered into the renal pelvis, whence
the fluid is carried along the ureters partly by pressure and gravity
and partly by the peristaltic contractions of the muscular walls
of those channels (see p. 101) into the urinary bladder. When a
ureter is divided in an animal, and a cannula inserted, the urine
may be observed to flow from the cannula drop by drop, slowly or
rapidly according to the rate of secretion. Frequently, after a
series of single drops at long intervals, several drops follow in
rapid succession, apparently urged by a peristaltic wave. In the
urinary bladder, the urine is collected, its return into the ureters
being prevented by the oblique entrance into the bladder and
valvular nature of the orifices of those tubes ; and its discharge from
thence in considerable quantity is effected from time to time by
a somewhat complex muscular mechanism, of the nature and
working of which the following is a brief account.

The involuntary muscular fibres forming the greater part of the
vesical walls are arranged partly in a more or less longitudinal
direction forming the so-called detrusor urinse, and partly in a
circular manner, the circular fibres being most developed round
the neck of the bladder and forming there the so-called sphincter

CHAP, iv.] RENAL SECRETION. 411

vesicse. After it has been emptied the bladder is contracted and
thrown into folds; as the urine gradually collects, the bladder
becomes more and more distended. The escape of the fluid is
however prevented by the resistance offered by the elastic fibres of
the urethra which keep the urethra channel closed. Some
maintain that a tonic contraction of the sphincter vesicae aids in or
indeed is the chief cause of this retention. The continuity of the
sphincter vesicse with the rest of the circular fibres of the bladder
suggests that it probably is not a sphincter, but that its use lies in
its contracting after the rest of the vesical fibres, and thus finish-
ing the evacuation of the bladder. On the other hand, the fact
that the neck of the bladder can withstand a pressure of 20 inches
of water so long as the bladder is governed by an intact spinal
cord, but a pressure of 6 inches only when the lumbar spinal cord
is destroyed or the vesical nerves are severed, affords very strong
evidence in favour of the view that the obstruction at the neck of
the bladder to the exit of urine depends on some tonic muscular
contraction maintained by a reflex or automatic action of the
lumbar spinal cord.

When the bladder has become full, we feel the need of making
water, the sensation being heightened if not caused by the
trickling of a few drops of urine from the full bladder into the
urethra. We are then conscious of an effort ; during this effort the
bladder is thrown into a long-continued contraction of an obscurely
peristaltic nature, the force of which is more than sufficient to
overcome the elastic resistance of the urethra, and the urine issues
in a stream, the sphincter vesicse, if it act as a sphincter, being at
the same time either relaxed after the fashion of the sphincter ani,
or at least overcome. In its passage along the urethra, the exit
of the urine is forwarded by irregularly rhythmic contractions of
the bulbo-cavernosus or ejaculator urinse muscle, and the whole
act is further assisted by pressure on the bladder exerted by
means of the abdominal muscles, very much the same as in defse-
cation.

We said just now, "when the bladder has become full," but this
must not be understood to mean, "when the bladder has received a
certain quantity of fluid." On the contrary, it is a matter of
common experience that we feel the desire to make water some-
times when a large quantity and sometimes when a small quantity
of urine has accumulated in the bladder. We have evidence that
the bladder possesses to a very high degree that obscure con-
tinuous contraction which we speak of as 'tone' ; and further that
the amount of its tone is exceedingly variable, the organ, quite
independently of distinct efforts at micturition, being at one time con-
tracted and at another flaccid and distended. When it is in a
contracted state, a small quantity of fluid may exert the same
pressure on the vesical walls as a larger quantity when the bladder
is flaccid. Hence the determining cause of the desire to make

412 MICTURITION. [BOOK n.

water is the pressure of the urine upon the vesical walls, the
quantity needed to produce fulness being dependent on the
amount of tonic contraction of the muscular fibres existing at the
time.

Micturition as sketched above seems at first sight, and espe-
cially when we appeal to our own consciousness, a purely voluntary
act. A voluntary effort throws the bladder into contractions, an
accompanying voluntary effort throws the ejaculator and abdominal
muscles also into contractions, and, the resistance of the urethra
being thereby overcome, the exit of the urine naturally follows. If
we adopt the view of a sphincter vesicaB being relaxed at the same
time, we have to add to the above simple statement the supposition
that the will, while causing the detrusor urinse to contract, also
lessens the tone of the sphincter, probably by inhibiting its centre
in the lumbar cord.

There are facts however which prevent the acceptance of so
simple a view. In the first place, in cases of urethral obstruction,
where the bladder cannot be emptied when it reaches its ac-
customed fulness, the increasing distension sets up fruitless but
powerful contractions of the vesical walls, contractions which are
clearly involuntary in nature, which wane or disappear, and
return again and again in a rhythmic manner, and which may
be so strong and powerful as to cause great suffering. It seems
that the fibres of the bladder, like all other muscular fibres, have
their contractions augmented in proportion as they are subjected
to tension. Just as a previously quiescent ventricle of a frog's
heart may be excited to a rhythmic beat by distending its cavity
with blood, so the quiescent bladder may, quite independent of
the will, be excited, by the distention of its cavity, to a peristaltic
action which in normal cases is never carried beyond a first effort,
since with that the bladder is emptied and the stimulus is removed,
but which in cases of obstruction is enabled clearly to manifest its
rhythmic nature.

In the second place it has been shewn that quite normal mictu-
rition may take place in a dog in which the lumbar region of the
spinal cord has been completely and permanently separated by
section from the dorsal region. In such a case there can be no
exercise of volition, and the whole process appears as a reflex
action. When under these circumstances the bladder becomes
full (and otherwise apparently the act fails) any slight stimulus,
such as sponging the anus or slight pressure on the abdominal
walls, causes a complete act of micturition : the bladder is entirely
emptied, and the stream of urine towards the end of the act
undergoes rhythmical augmentations due to contractions of the
ejaculator urinse. These facts can only be interpreted on the view
that there exists in the lumbar cord (of the dog) what we may
speak of as a micturition centre capable of being thrown into
action by appropriate afferent impulses, the action of the centre

CHAP, iv.] RENAL SECRETION. 413

being such as to cause a contraction of the walls of the bladder and
of the ejaculator urinse, and possibly at the same time to suspend
the tone of the sphincter vesicse.

Moreover we have, in the case both of man and of other
animals, experimental and other evidence that contraction of the
bladder is frequently brought about by reflex action. Thus the
pressure within the bladder when observed for any length of time
is found to be subject to considerable and manifold variations.
Over and above passive changes in pressure due to the respi-
ratory movements, when the bladder is pressed upon at each
descent of the diaphragm, active contractions, of a strength in-
adequate to bring about micturition, are from time to time
observed. These in some instances appear to be spontaneous, or
be the result of emotions, but they may be readily induced in a
reflex manner, by stimulating various sentient surfaces or sensory
nerves. And common experience affords many instances where
vesical contractions thus brought about in a reflex manner acquire
strength adequate to empty the bladder.

Observations of vesical pressure may be most conveniently carried
out by introducing into the bladder a catheter connected either with an
oncograph, or some other similar registering apparatus, so arranged as to
allow fluid to be driven into or received from the bladder at pleasure.

Involuntary micturition obviously of reflex nature has frequently
been observed in cases of paralysis from disease or injury of the
spinal cord ; and the involuntary micturition which is common in
children, as the result of irritation of the pelvis and genital
organs, and which sometimes occurs in the adult as the result
of emotions, or at least sensory impressions, appears to be the
result of reflex action. In these several cases we may fairly
suppose that the centre in the lumbar cord is affected by afferent
impulses reaching it along various sensory nerves or descending
from the brain. Hence we are led to the conception that when we
make water by a conscious effort of the will, what occurs is not a
direct action of the will on the muscular walls of the bladder, but
that impulses started by the will descend from the brain after
the fashion of afferent impulses and thus in a reflex manner throw
into action the micturition centre in the lumbar spinal cord.
Nor is this view negatived by the fact that paralysis of the
bladder, or rather inability to make water either voluntarily or in
a reflex manner, is a common symptom of cerebral or spinal disease
or injury. Putting aside the cases in which the reflex act is not
called forth because the appropriate stimulus has not been applied,
the failure in micturition under these circumstances may be
explained by supposing that the shock of the spinal injury or
some extension of the disease has rendered the lumbar centre
unable to act.

The so-called incontinence of urine in children is simply an

414 MICTURITION. [BOOK n. CHAP. iv.

easily excited and frequently repeated reflex micturition. In
cases of cerebral or spinal disease a form of incontinence is frequently
met with which seems to be of a different nature. The bladder
becoming full, but, owing to a failure in the mechanism of voluntary
or reflex micturition, being unable to empty itself by a complete
contraction, a continual dribbling of urine takes place through the
urethra, the fulness of the bladder being sufficient to overcome the
elastic resistance at the neck of the urethra. It is probable how-
ever that even in these cases the flow is partly caused by obscure,
unfelt, intrinsic contractions of the bladder.

CHAPTER V.
THE METABOLIC PHENOMENA OF THE BODY.

WE have followed the food through its changes in the alimentary
canal, and have seen it enter into the blood, either directly or by the
intermediate channel of the lacteals, in the form of peptone (or other-
wise modified albumin), sugar (lactic acid), and fats, accompanied
by various salts. We have further seen that the waste products
which leave the body are urea, carbonic acid and salts. We have
now to attempt to connect together the food and the waste pro-
ducts ; to trace out as far as we are able the various steps by which
the one is transformed into the other, and to inquire into the
manner in which the energy set free in this transformation is
distributed and made use of.

The master tissues of the body are the muscular and nervous
tissues ; all the other tissues may be regarded as the servants of
these. And we may fairly presume that, besides the digestive and
excretory tissues which we have already studied, many parts of the
body are engaged either in further elaborating the comparatively
raw food which enters the blood, in order that it may be as-
similated with the least possible labour by the master tissues, or in
so modifying the waste products which arise from the activity of
the master tissues that they may by removed from the body as
speedily as possible. There can be no doubt that manifold inter-
mediate changes of this kind do take place in the body ; but our
knowledge of the matter is at present very imperfect. In one or
two instances only can we localize these metabolic actions and
speak of distinct metabolic tissues. In the majority of cases we
can only trace out or infer chemical changes, without being able
to say more than that they do take place somewhere; and in
consequence, perhaps somewhat loosely, speak of them as taking
place in the blood.

SEC. 1. METABOLIC TISSUES.

The History of Olycogen.

The best known and most carefully studied example of
metabolic activity is the formation of glycogen in the hepatic cells.

Claude Bernard, in studying the history of sugar in the economy,
was led to compare the relative quantities of sugar in the portal
and hepatic veins, expecting to find that the sugar possibly
diminished during the passage of the blood through the liver; he was
astonished to discover that, on the contrary, the quantity appeared
to be greatly increased. He found, and anyone can make the obser-
vation, that when an animal living under ordinary conditions is killed,
the hepatic blood after death contains a considerable amount of sugar
(grape-sugar), even when there is little or none in the portal
blood; moreover a simple aqueous infusion of the liver is rich
in sugar. Not only so, but the sugar continues to be present in
the liver when all blood has been washed out of the organ by a
stream of water driven through the portal vein, and goes on
increasing in amount for some hours after death. Only one
interpretation of these facts is possible ; so far from the liver
destroying or converting the sugar brought to it by the portal
vein, it is clearly a source of sugar ; the hepatic tissue evidently
contains some substance capable of giving rise to the presence
of sugar. Bernard further found that when the liver was removed
from the body immediately after death, and, after being divided
into small pieces, was thrown into boiling water, the infusion or

CHAP, v.] NUTRITION. 417

decoction contained very little sugar, and that the small quantity
which was present did not increase even when the decoction was
allowed to stand for some time. The decoction, however, was
peculiarly opalescent, indeed milky in appearance; whereas the
decoction of a liver which had been allowed to remain exposed to
warmth for some time after death, before being boiled, and which
accordingly contained a large amount of sugar, was quite clear.
On adding saliva, or other amylolytic ferment, to the opalescent,
sugarless, or nearly sugarless, decoction and exposing it to a gentle
warmth (35° — 40°), the opalescence disappeared ; the fluid became
clear, and was then found to contain a considerable quantity of
sugar. Here again the explanation was obvious. The opalescence
of the decoction of boiled liver is due to the presence of a body
which is capable of being converted by the action of a ferment
into sugar, and is therefore of the nature of starch. At the
moment of death the liver must contain a considerable quantity
of this substance, which after death becomes gradually converted
into sugar, either through the action of some amylolytic ferment
present in the hepatic cells or in the blood of the hepatic vessels
or possibly by some special agency. Hence the post-mortem
appearance of a continually increasing quantity of sugar. By
precipitating the opalescent decoction with alcohol, by boiling the
precipitate with alcohol containing potash, whereby the proteid
impurities clinging to it were destroyed, and by removing adherent
fats by ether, Bernard was able to obtain this sugar-producing or
glycogenic substance in a pure state as a white amorphous powder,
with a composition of C6H10O5, and therefore evidently a kind of
starch. Its most striking differences from ordinary starch were
that it gave a deep red and not a blue colour with iodine, and that
when dissolved in water it formed a milky fluid. He gave to it the
name of glycogen.

Since Bernard's discovery glycogen has been recognized as a
normal constituent, variable in quantity, of hepatic tissue both in
vertebrate and invertebrate animals. That it is present in the
hepatic cells, and not simply contained in the hepatic blood, is
shewn by the fact that it remains in the liver after all blood has
been washed out of that organ. It has also been found in muscle,
of which indeed it is almost a constant constituent, in the placenta,
white corpuscles, testes, brain, and in other parts of the body ; the
tissues of the embryo at an early stage, especially before the liver
has become functionally active, are particularly rich in it.

We have some reasons for thinking that there are several
varieties of glycogen, and that the glycogen which exists in muscle is
not quite identical with that which occurs in the liver. Indeed there
seem to be intermediate stages between glycogen and starch or
dextrin. The physiological value of these differences has not yet
however been clearly determined, and, with this caution, we shall in
the discussions which follow, speak of glycogen as a single substance.

p. 27

418 GLYCOGEN. [BOOK n.

Formation and Uses of Glycogen. The amount of glycogen
present in the liver of an animal at any one time is largely
dependent on the amount and nature of the food previously taken.
When all food is withheld from an animal, the glycogen in the
liver diminishes, rapidly at first, but more slowly afterwards.
Even after some days' starvation a small quantity is frequently
still found; but in rabbits, at all events, the whole may eventually
disappear.

If an animal, after having been starved until its liver may
be assumed to be free or almost free from glycogen, be fed on
a diet rich in carbohydrates or on one consisting exclusively of
carbohydrates, the liver will in a short time be found to
contain a very large quantity of glycogen. Obviously the
presence of carbohydrates in food leads to an accumulation of
glycogen in the liver; and this is true both of starch and of dex-
trin and of the various forms of sugar, cane, grape and milk
sugar. The effect may be quite a rapid one, for glycogen has
been found in the liver in considerable quantity within a few
hours after the introduction of sugar into the alimentary canal of
a starving animal.

If an animal, similarly starved, be fed on an exclusively meat
diet a certain amount of glycogen is found in the liver. This
appears to be especially the case with dogs (probably with other
carnivorous animals also) ; and in his earlier researches Bernard
was led to regard the constant presence of glycogen in the livers of
dogs fed on meat, as an important indication of the conversion
within the body of nitrogenous into non-nitrogenous material.
But in the first place, the quantity of glycogen thus stored up in
the liver as the result of a meat diet, is much less than that which
follows upon a carbohydrate diet; and in the second place, ordinary
meat, especially horse-flesh on which dogs are ordinarily fed,
contains in itself a certain amount either of glycogen or some
form of sugar. Moreover when animals are fed not on meat but
on purified proteid, such as fibrin, casein or albumin, the quantity
of glycogen in the liver becomes still smaller, though according to
most observers remaining greater than during starvation. We may
infer therefore that part of the glycogen which appears in the liver
after a meat diet is really due to carbohydrate materials present in
the meat. Part however would appear to be the result of the actual
proteid food and we have similar evidence that gelatine taken as
food leads to the formation of some glycogen in the liver. But in
this respect these nitrogenous substances fall very far short indeed
of carbohydrate material.

With regard to fats, all observers are agreed that these lead to
no accumulation of glycogen in the liver; an animal fed on an
exclusively fatty diet has no more glycogen in its liver than a
starving animal.

Hence of the three great classes of food-stuffs, the carbohydrates

CHAP v.j NUTRITION. 419

stand out prominently as the substances which taken as food lead
to an accumulation of glycogen in the liver. As far as we know
at present the glycogen which thus appears in the liver as the
result of feeding either with any of the various forms of carbo-
hydrates, or with proteids, or with other substances, is of the same
kind and presents the same characters; at least we have no
evidence to the contrary.

The question naturally arises, What is the use and purpose of
this hepatic glycogen ? What ultimately becomes of the glycogen
thus for a while stored up in the liver ?

One view which has been put forward is as follows. We have
evidence, as we shall presently learn, that a great deal of the fat of
the body is not taken as such in the food, but is constructed anew
in the body out of other substances. Both carbohydrates and
proteids, taken in excess or under certain circumstances, lead to an
accumulation of fat, and we have reason to believe that carbo-
hydrates on the one hand and the carbon-holding portions of
various proteids, may by some process or other be converted into
fat. And it has been suggested that the glycogen in the liver is a
phase of a constructive fatty metabolism, that it is material on its
way to become fat.

The positive evidence in favour of this view is very scanty ; it
is almost limited to the facts that fat, sometimes in very large
quantity, is found in the hepatic cells, that while fat itself taken
as food leads to no increase in the hepatic glycogen, carbo-
hydrates, which are especially fattening, are most active producers
of glycogen, and that the fat present in the hepatic cells seems
to be increased by such diets as naturally increase the glycogen
in the liver. No evidence has been offered as to the several
steps of the conversion of glycogen into fat, nor indeed has
it been suggested what those steps are. The view indeed is
almost exclusively based on the supposed proof that the blood
of hepatic vein contains during life no sugar, or at least not
more than does the general blood or even the blood of the portal
vein. From this it is inferred that the glycogen in the liver is not
lost to the liver by becoming converted into sugar and so discharged
into the hepatic blood and therefore must be converted into some
other substance which substance is presumably fat. Bernard both
in his earlier and later researches maintained that the blood of
the hepatic vein under normal conditions is richer in sugar than
the blood of the portal vein or indeed of any other part of the vas-
cular system ; this he regarded as an indication that the liver is
always engaged in discharging a certain quantity of sugar into the
hepatic veins; and his views have been accepted by many observers.
On the other hand others maintain that the blood in the hepatic
vein, if care be taken to keep the animal in a perfectly normal
condition, contains no more sugar than does the blood of the right
auricle or of the portal vein, and indeed that the liver itself, if

27—2

420 GLYCOGEN. [BOOK n.

examined before any post-mortem changes have had time to de-
velope themselves, is absolutely free from sugar.

Normal hepatic blood was obtained by Pavy, by means of an in-
genious catheterisation. He introduced through the jugular vein, into
the superior, and so into the inferior vena cava, a long catheter, con-
structed in such a manner that he could at pleasure plug up the vena
cava below the embouchement of the hepatic veins, and draw blood ex-
clusively from the latter ; or vice versa.

Now the quantitative determination of sugar in blood by any
of the methods as yet suggested is open to many sources of error.
And when the quantity of blood which is continually flowing
through the liver is taken under consideration, it is obvious that
an amount of sugar, which in the specimen of blood taken for
examination fell within the limits of errors of observation, might
when multiplied by the whole quantity of blood, and by the
number of times the blood passed through the liver in a certain
time, reach dimensions quite sufficient to account for the conversion
into sugar of the whole of the glycogen present in the liver at any
given time. Hence we may safely conclude that the comparative
analysis of hepatic and portal blood, if they do not of themselves
prove that the liver is either continually or at intervals converting
some of its glycogen into sugar and discharging this sugar into the
general system, are at least not sufficiently trustworthy to disprove
the possibility of such a discharge of sugar being one of the normal
functions of the liver.

We may therefore regard the view that glycogen is simply a
stage in the formation of fat as not proved ; and indeed we shall
presently see reason to believe that fat is formed elsewhere.

Another view makes use of the formation of fat for the pur-
poses of analogy only. Seeing that adipose tissue serves as a
storehouse of fat which is not wanted by the body at the moment
but may be wanted presently, the question readily presents itself,
May not the hepatic glycogen have an analogous function ? May we
not regard the presence of glycogen in the liver as in large measure
due to the fact that it is deposited there simply as a store of carbohy-
drate material, being accumulated whenever amylaceous material is
abundant in the alimentary canal, and being converted into sugar
and so drawn upon by the body at large to meet the general
demands for carbohydrate material during the intervals when food
is not being taken ? And we can accept this view without being
able to say definitely what becomes of the sugar thus thrown into
the hepatic blood. Bernard believed that this sugar underwent an
immediate and direct oxidation, but we have already dwelt (p. 351)
on the objections to such a view. It is sufficient for us at the
present to admit that the sugar is made use of in some way or
other.

Now, many considerations lead us to believe that a certain

CHAP, v.] NUTRITION. 421

average composition is necessary for that great internal medium
the blood, in order that the several tissues may thrive upon it
to the best advantage, one element of that composition being a
certain percentage of sugar. It would appear that some at least if
not all of the tissues are continually drawing upon the blood for
sugar, and that hence a certain supply must be kept up to meet
this demand. On the other hand an excess of sugar in the blood
itself would be injurious to the tissues. And as a matter of fact
we find the quantity of sugar in blood is small but constant ; it
remains about the same when food is being taken as in the
intervals between meals. If sugar be injected into the jugular
vein in too large quantities or too rapidly a certain quantity
appears in the urine, indicating an effort of the system to throw
off the excess and so bring back the blood to its average con-
dition. The maintenance of such a constant percentage of sugar
would obviously be provided for or at least largely assisted by
the liver acting as a structure where the sugar might at once
and without much labour be packed away in the form of the
less soluble glycogen, at those times when, as during an amylaceous
meal, sugar is rapidly passing into the blood, and there is a
danger of the blood becoming loaded with far more sugar than
is needed for the time being ; and it may be incidentally noted
that a larger quantity of sugar may be injected into the portal
than into the jugular vein without any reappearing in the urine,
apparently because a large portion of it is in such a case retained
in the liver as glycogen. When on the other hand sugar ceases to
pass into the blood from the alimentary canal, we may suppose
that the average percentage in the blood is maintained by the
glycogen previously stored up becoming reconverted into sugar,
and slowly discharged into the hepatic blood.

Moreover, this view, that the glycogen of the liver is a reserve
fund of carbohydrate material, is strongly supported by the analogy
of the migration of starch in the vegetable kingdom. We know
that the starch of the leaves of a plant, whether itself having
previously passed through a glucose stage or not, is normally
converted into sugar, and carried down to the roots or other parts,
where it frequently becomes once more changed back again into
starch.

A similar argument may be drawn from the relations of
glycogen to muscle; that is to say, the glycogen in the muscle
may be regarded as a subsidiary store of carbohydrate material
laid up for the private use so to speak of the muscle. So fre-
quently is glycogen found in muscle that it may be regarded as
an ordinary though not an invariable constituent of that tissue ;
indeed it may almost be considered as a constituent of all con-
tractile tissues. The quantity varies very largely both in the dif-
ferent muscles of the same animal and in corresponding muscles of
different animals. It disappears readily upon starvation, even

422 GLYCOGEN. [BOOK n.

before the hepatic glycogen is exhausted ; at least this is the case
with most muscles. It is said to be increased in quantity when
the nerve of the muscle is divided, and the muscle thus brought
into a state of quiescence. On the other hand it diminishes or
even disappears when the muscle enters into rigor mortis. Some
have maintained that it diminishes during tetanus, but this
appears doubtful; and certainly muscles may be fully alive and
contractile from which glycogen is wholly absent. From this we
may infer, not that glycogen is a necessary chemical factor of
muscular metabolism, but that it can furnish materials for that
metabolism, and hence is stored up in the muscle so as to be ready
at hand for use.

Accepting then the view that the hepatic glycogen is simply
store glycogen, waiting to be converted into sugar little by little as
the needs of the economy demand, and not glycogen on its way to
take part, through the agency of the hepatic protoplasm, in the
formation of some more complex compound, such as fat, we have
next to deal with the question what is the exact origin of the
hepatic glycogen ? By what steps is it formed and what are
its immediate antecedents ? We have already seen that the
presence of glycogen in the liver is especially favoured by a
carbohydrate diet. Hence, if the use of the glycogen be such as
we have supposed, it seems only reasonable to conclude that the
glycogen which makes its appearance in the liver after an amy-
laceous meal arises from a direct conversion of the sugar carried
to the liver by the portal vein, the sugar becoming through some
action of the hepatic protoplasm dehydrated into starch, by a
process the reverse of that by which in the alimentary canal starch
is hydrated into sugar through the action of the salivary and
pancreatic ferments. Vegetable protoplasm can undoubtedly con-
vert both starch into sugar and sugar into starch ; and there are
no d priori arguments or positive facts which would lead us to
suppose that the activity of animal protoplasm cannot accomplish
the latter as well as the former of these changes. Again, as we
have incidentally mentioned, sugar injected into the jugular vein
readily gives rise to sugar in the urine; but a very considerable
quantity can be slowly injected into the portal vein without any
appearing in the urine. This suggests the idea that the liver, so
to speak, catches the sugar as it is passing through the hepatic
capillaries and at once dehydrates it into glycogen.

Upon such a view, the carbohydrate taken as food would be
converted in glycogen by the agency of the hepatic cell, without at
any time becoming an integral part of the protoplasm of the cell.
Such a view may be the true one ; but it is open for us to look at
the matter in another light. We may conceive of the hepatic cells
as being continually engaged in giving rise to carbohydrate
material, in the form either of sugar or of some other body, as a
product of the metabolism of their own protoplasm ; and we may

CHAP, v.] NUTRITION. 423

suppose that under certain circumstances, as in the absence of
adequate food, the carbohydrate material thus formed is at once
discharged into the hepatic blood, for the general use of the body,
but that under other circumstances as when an amylaceous meal
has been taken, the immediate wants of the economy being covered
by the carbohydrates of the meal, the carbohydrate products of the
hepatic metabolism are stored up as glycogen. Under such a view
the sugar of the meal is used up somewhere in the body and the
glycogen to which it gives rise comes direct from the hepatic
protoplasm. An argument against such a view is afforded by the
behaviour of the substance glycerine. This substance when taken
into the alimentary canal, or when injected into the portal vein,
gives rise to an increase of glycogen in the liver, but when it is
injected into the general venous system no such increase is ob-
served. But if the formation of glycogen were due to the glycerine
covering in some way or other the carbohydrate expenditure
of the body and thus sparing the products of hepatic metabolism,
we should expect to find an increase of glycogen in the latter case
as well as in the two former cases. From this not taking place
we infer that glycerine gives rise to glycogen by being in some
way or other transformed into glycogen by the agency of the
hepatic cell, or at all events by the glycerine producing changes in
the hepatic cell. And the small quantity of glycogen which
results from proteid food is probably in a similar way the product
of the direct action of the proteid on the hepatic protoplasm.
From these and similar cases we may conclude that sugar also and
the other carbohydrates give rise to glycogen, not by covering the
general carbohydrate expenditure, but by producing changes in the
liver itself. How far the sugar reaching the hepatic cell by the
portal capillaries enters into the upward and downward series of
the protoplasm of the cell, whether it is actually built up into the
protoplasm before its elements reappear in the course of the
destructive metabolism of the complex protoplasm as glycogen,
formed so to speak afresh, or whether the protoplasm simply
dehydrates the sugar as we just now suggested, while it is still
outside itself, we have not at present sufficient evidence to decide.
Though the former method seems to entail an unnecessary labour
there may be reasons why it should be adopted.

We have said that glycogen is readily converted by ferments
into sugar, and that, after death, a conversion into sugar goes on in
most cases with considerable rapidity and energy. An amylolytic
ferment may be extracted from the hepatic tissue and it seems pro-
bable that the post-mortem appearance of sugar in the liver is due to
the uncontrolled action of such a ferment. If this be the case,
the question may be asked, How is it possible for the glycogen
to remain as glycogen and become stored up in larger quantities
in the presence of such a ferment ? We can only answer that the
solution of this problem is of the same kind as that of the

424 DIABETES. [BOOK it.

problems, why blood does not clot in the living blood-vessels, why
the living muscle does not become rigid, and why the living
stomach or pancreas does not digest itself. It might be added,
bearing in mind the history of the fibrin ferment, that even ad-
mitting the presence of an amylolytic ferment after death, we have
no proof that such a ferment exists in the hepatic cells during life.
It is possible that the ferment which can be extracted after death
only makes its appearance as the result of post-mortem changes
which have taken place in the protoplasm of the hepatic cells.
Moreover it is stated that the sugar which makes its appearance
in the liver is dextrose whereas the sugar into which glycogen is
converted by the ordinary amylolytic ferments of saliva and pan-
creatic juice, is, as in the case of starch, largely maltose. This
would indicate that the conversion which takes place in the liver
is of a peculiar nature ; but the matter requires further investi-
gation.

Diabetes. Natural diabetes is a disease characterized by the
appearance of a large quantity of sugar in the urine. Into the
pathology of the various forms of this disease it is impossible to
enter here ; but a temporary diabetes, the appearance for a while
of a large quantity of sugar in the urine, may be artificially pro-
duced in animals in several ways. If the medulla oblongata of a
well-fed rabbit be punctured in the region which we have pre-
viously described (p. 212) as that of the vaso-motor centre (the
area marked out as the "diabetic area" agreeing very closely with
that defined as the vaso-motor area), though the animal need not
necessarily be in any other way obviously affected by the operation,
its urine will be found, in an hour or two, or even less, to be in-
creased in amount and to contain a considerable quantity of sugar.
A little later the quantity of sugar will have reached a maximum,
after which it declines, and in a day or two, or even less, the urine
will be again perfectly normal. The better fed the animal, or,
more exactly, the richer in glycogen the liver, at the time of the
operation, the greater the amount of sugar. If the animal be
previously starved so that the liver contains little or no glycogen,
the urine will after the operation contain little or no sugar. It
is clear that the urinary sugar of this form of artificial diabetes
comes from the glycogen of the liver. The puncture of the
medulla causes such a change in the liver that the previously
stored-up glycogen disappears, and the blood becomes loaded with
sugar, much if not all of which passes away by the urine. In
the absence of any proof to the contrary, we may assume that
in this form of artificial diabetes the glycogen previously present
in the liver becomes converted into sugar, just as we know that
it does become so converted by post-mortem changes. The glyco-
genic function of the liver is therefore subject to the influence
of the nervous system, and in particular to the influence of a

OHAP. v.] NUTRITION. 425

region of the cerebro-spinal centre which we already know as
the vaso-motor centre, or at least of a part of that region. The
path of the influence may be traced along the cervical spinal cord
(and not along the vagi, though the roots of these nerves lie so
close to the diabetic spot), as far down as (in rabbits) the level of
the third or fourth dorsal vertebra, or even a little lower, from
the spinal cord to the first thoracic ganglion, and from thence to
the liver by some channel or channels at present undetermined.
We cannot at present define clearly the nature of that influence.
We cannot say whether the temporary diabetes is a simple effect
of a dilation of the hepatic arteries which accompanies the diabetic
puncture or of some direct action of the nerves on the metabolic
activity of the hepatic protoplasm, though the latter view seems
the more probable one.

Artificial diabetes is also a prominent symptom of urari poison-
ing. This is not due to the artificial respiration, which is had
recourse to in order to keep the urarized animals alive ; because,
though disturbance of the respiratory functions sufficient to inter-
fere with the hepatic circulation may produce sugar in the urine,
artificial respiration may with care be carried on without any
sugar making its appearance. Moreover, urari causes diabetes in
frogs, although in these animals respiration can be satisfactorily
carried on without any pulmonary respiratory movements. The
exact way in which this form of diabetes is brought about has not
yet been clearly made out.

A very similar diabetes is seen in carbonic oxide poisoning;
and is one of the results of a sufficient dose of morphia or of amyl
nitrate.

There can be no doubt that in diabetes, arising from whatever
cause, the sugar appears in the urine because the blood contains
more sugar than usual. The system can only dispose (either by
oxidation, or as seems more probable in other ways) of a certain
quantity of sugar in a certain time. Sugar injected into the
jugular vein reappears in the urine, whenever the injection becomes
so rapid that the percentage of sugar in the blood reaches a certain
(low) limit. Sugar in the urine means an excess of sugar in the
blood. How in natural diabetes that excess arises, has not at
present been clearly made out. It may be that some forms of
diabetes resemble the artificial diabetes just described as resulting
from puncture of the medulla, and arise from a too rapid con-
version of the hepatic glycogen or from carbohydrate material
failing to be stored up as glycogen. All forms of diabetes how-
ever cannot be satisfactorily explained in this way; and it has
been suggested, though adequate proof has not yet been supplied,
that the sugar of diabetes is of a peculiar nature and accumulates
in the blood because it is unable to undergo those changes, what-
ever they be, which befall the normal sugar of the blood. We
must not pursue the subject any further; but there is much to

426 : ..FAT.- [BOOK ii.

be said in favour of the view that the sources of the excess of
sugar in the blood may be various, and hence that several dis-
tinct varieties of diabetes may exist. In one among many points,
the clinical history of diabetes throws light on the possible
sources of glycogen. While in many, especially of the less severe
cases of diabetes, withdrawal of all amylaceous food is followed
by a disappearance of sugar from the urine, in many instances
the sugar continues to be discharged even though the diet be
perfectly free from carbohydrates ; and in many other cases the
sugar in the urine is far in excess of the quantity which might be
derived from the food. In these cases the sugar must have some
non-amylaceous source ; from this we infer that glycogen also may
have a similar origin. And the fact that the urea is increased
(and that too in some cases in ratio with the sugar) in diabetes,
suggests that the sugar may arise from proteids which have been
split up into a nitrogenous (urea) and a non-nitrogenous moiety,
and so points out the way in which proteids may be a source of
glycogen.

As a sort of converse of diabetes we may mention that the
administration of arsenic in sufficient doses or for an adequate time
prevents an accumulation of glycogen in the liver and apparently
in the body generally, whatever be the diet used.

The History of Fat. Adipose Tissues.

Of all the tissues of the body adipose tissue is the most fluctu-
ating in bulk; within a very short space of time a large amount of
adipose tissue may disappear, and within an almost equally short
time the quantity present in a body may be several times multi-
plied. Histological inquiries teach us that when an animal is fatten-
ing the minute drops or specks of fat normally present in certain
connective-tissue corpuscles (either of a special kind, or certain
individuals of the ordinary kind) are seen to increase in number,
the protoplasm enlarging at the same time. As these specks
increase they coalesce into drops, which by similar coalescence
form larger drops, until, the protoplasm first ceasing to increase
and then diminishing, the original connective-tissue corpuscle is
transformed into a fat-cell, with a remnant only of protoplasm
gathered about the nucleus and forming an imperfect envelope
round the enlarged contents. When, on the contrary, an animal is
fasting, the fat seems in some way or other to escape from the cell,
which it may leave as a bag either filled with serous fluid or
empty and collapsed around the nucleus. These facts point to
the conclusion that the fat of adipose tissue is not simply and
mechanically collected in the cell, but is formed by the active
agency of the cell, being apparently the result of a breaking up of

CHAP, v.] NUTRITION. 427

the protoplasm; when formed, however, it appears to be dis-
charged from the cell in a more or less mechanical manner, as the
needs of the economy demand. And this view is supported by
the fact that protoplasm, wherever occurring, both during life and
after death (when it could not possibly be supplied with fat from
without), is subject to fatty degeneration, in which the fat evi-
dently arises, in large part at least, from the breaking up of
proteid compounds.

On the other hand, we have traced the fats taken as food, and
found that they pass with comparatively little change from the
alimentary canal, chiefly through the intermediate passage of the
lacteals, into the blood. We might infer from this that an excess
of fat thus entering the blood would naturally be simply stored up
in the available adipose tissue, without any further change, the
connective-tissue corpuscles eating the fat brought to them after
the fashion of an amoeba but not digesting it, simply keeping it
in store till it was wanted elsewhere.

Which of these views is the true one, or how far are both
these operations carried on in the animal body? In the first
place, it is evident that in an animal fattened on ordinary fattening
food, only a small fraction of the fat stored up in the body can
possibly come direct from the fat of the food. Long ago, in
opposition to the views of Dumas and his school, who taught that
all construction of organic material, that all actual manufacture of
protoplasm or even of its organic constituents, was confined to
vegetables and unknown in animals, Liebig shewed that the butter
present in the milk of a cow was much greater than could be
accounted for by the scanty fat present in the grass or other fodder
she consumed. He also urged, as an argument in the same
direction, that the wax produced by bees is out of all proportion to
the fat contained in their food, consisting as this does chiefly of
sugar. And Lawes and Gilbert have shewn by direct analysis that
for every 100 parts of fat in the food of a fattening pig, 472 parts
were stored up as fat during the fattening period. It is clear that
fat is formed in the body out of something which is not fat.

There are two possible sources of this manufactured fat. In
treating of digestion (p. 298), we referred to the possibility of
digested carbohydrates becoming by fermentation converted into
butyric acid; and we may imagine that when a member of
the fatty acid series had thus been formed, higher and more
complex members of the same series might be obtained out of it.
There can be no doubt indeed that a carbohydrate diet is most
efficacious in producing an accumulation of fat in the body : sugar
or starch, in some form or other, is always a large constituent of
ordinary fattening foods.

Another source of fat is to be found in the proteids. We have
seen that the urea of the urine practically represents the whole of
the nitrogen which passes through the body. Now in any given

428 FAT. [BOOK it

quantity of urea the amount of carbon is far less than that found
in the quantity of proteid containing the same amount of nitrogen.
Thus the percentage composition of the two being respectively,

Carbon. Hydrogen. Oxygen. Nitrogen. Sulpliur.

Urea 20'00 6'66 26'67 46*67

Proteid 53 7'30 23'04 15'53 113

100 grms. of urea contain about as much nitrogen as 300 grms. of
proteid; but the 300 grms. of proteid contain 139 grms. (159 — 20)
more carbon than do the 100 grms. urea. Hence the 300 grms. of
proteid in passing through the body and giving rise to 100 grms.
of urea, would leave behind 139 grms. of carbon, in some combi-
nation or other ; and this surplus of carbon, if the needs of the
economy did not demand that it should be immediately converted
into carbonic acid and thrown off from the body, might be deposited
somewhere in the form of fat. We have already seen, in treating
of the action of the pancreatic juice (p. 252), that there is evidence
of a fatty element (viz. leucin, which is amido-caproic acid, and
so belongs to the fatty acid series) being thrown off from the
complex proteid compound in the very process of digestion.

It is clear that a construction of fat does occur in the body
somewhere. What limits can we place on the degree to which
this construction is carried? In reference to this point it is worthy
of notice that the composition of fat varies in different animals.
The fat of a man differs from the fat of a dog, even if both feed on
exactly the same food, fatty or otherwise. Were the fat which is
taken as food stored up as adipose tissue directly and without
change, recourse being had to other sources of food for the con-
struction of fat only in cases where the fat in the food was de-
ficient, we should expect to find that the constitution of the fat of
the body would vary greatly with the food. So far from this being
the case, direct experiment shews that the fat of the dog is, as far
as composition is concerned, almost entirely independent of the
food, that the normal constituents of fat make their appearance as
usual, though some of them, such as stearin or olein, may wholly be
absent in the food, and that abnormal fats such as spermaceti
presented as food are not to be found in the fat which is stored up
in the body as a consequence of a large supply of that food.

Of course it is quite possible that in such cases as these, though
the stearin, or the olein, when absent from the food, was in some
way or other constructed anew, yet at the same time those con-
stituents which were present were simply stored up; but it is also
open for us to suppose that all the fat taken as food was in some
way or other disposed of, and that all the new fat which made its
appearance was constructed anew. And the latter view is supported
by the histological facts just mentioned, as well as by other con-
siderations, which we shall presently have to urge. At the pre~

CHAP, v.] NUTRITION. 429

sent, however, we may be content with the following conclusions.
1. Fat is actually formed in the animal body, and is not merely
stored up from the fat of the food. 2. The carbon elements of
.the newly-formed fat may be supplied either from amylaceous
food, or from the carbon surplus of proteid food, or from fats
taken as food which are not the natural constituents of the body-
fat. 3. The fat stored up appears as fat granules or drops de-
posited in the protoplasm of certain cells, and the increase of the
fat in the cells is accompanied first by a growth, and subsequently
by a decay of the protoplasm; but as in the analogous case
of glycogen there is no complete evidence to shew whether
the fat-granules which appear are simply deposited by the proto-
plasm in a more or less mechanical manner, without their forming
an integral portion of it, the chief stages of the manufacture
of the fat having been gone through elsewhere, or whether they
arise from a breaking up, a functional metabolism of the proto-
plasm of the fat-cell itself; the latter view is on the whole
however the most probable.

The Mammary Gland.

Since milk is a secretion, and indeed an excretion, the mam-
mary gland ought not to be classed as a metabolic tissue, in the
limited meaning we are now attaching to those words. Yet the
metabolic phenomena giving rise to the secretion of milk are so
marked and distinct, and have so many analogies with the purely
metabolic events in adipose tissue, that it will be more convenient
to consider the matter here, rather than in any other connection.

Human milk has a specific gravity of from 1/028 to T034, and
when quite fresh possesses a slightly alkaline reaction. It speedily
becomes acid, and cow's milk, even when quite fresh, is sometimes
slightly acid, the change of reaction taking place during the
stagnation of the milk in the mammary ducts.

The constituents of milk are :

1. Proteids, viz. casein1, and an albumin, agreeing in its gene-
ral features with ordinary serum-albumin. The casein may be sepa-
rated by curdling with rennet (p. 246) ; it may also be thrown down
by the careful addition of acetic acid, but a more complete precipita-
tion is effected by first adding to the milk a slight quantity of
acetic acid, and then passing through it a stream of carbonic acid.
From the nitrate the serum-albumin, which is present in small and
variable quantities, may be obtained by coagulation with heat,
or by precipitation with potassium ferrocyanide, &c.

1 Or, if we restiict the -word casein to the substance which appears in a solid
form in curdling, or which may be precipitated by acids, an antecedent of casein.

430 MILK. [BOOK 11.

*2. Fats. These are, in human milk, palmitin, stearin, and
olein. But other fats are also present in small quantities ; and the
composition of the fats of milk differ in different animals.

3. Milk-sugar, the conversion of which into lactic acid gives
rise to many of the features of milk.

4. Extractives, including, according to some observers, urea,
and salts. The last consists chiefly of potassium phosphate, with
calcium phosphate, potassium chloride, small quantities of mag-
nesium phosphate, and traces of iron.

The following is the composition of 1000 parts of
Human Milk. Cow's Milk.

Casein

39-24

48-28

Albumin

—

5-76

Fat

26-66

43-05

Sugar

43-64

40-37

Salts

1-38

5-48

Total Solids

110-92

142-94

Water

889-08

857-06

Milk is an emulsion, the fats existing in the form of globules of
various but minute size, each protected by a thin envelope of
casein or albumin. It is this condition of the fat which gives to
milk its peculiar white colour. The colostrum, or secretion of the
mammary gland at the beginning of lactation, differs from milk in
being very deficient in casein and proportionately rich in albumin.
It is said that the milk at the end of a long lactation again
becomes poor in casein and rich in albumin. Milk on standing
turns sour and curdles. This is generally due to the milk-sugar
becoming converted by a fermentative process into lactic acid, which
in turn precipitates the casein. Curdling may however as we have
already seen (p. 246) take place by the action of rennet ferment
quite independently of the production of any acid.

Milk, like the other secretions which we have studied, is the
result of the activity of certain protoplasmic secreting cells forming
the epithelium of the mammary gland. As far as the fat of milk
is concerned, the processes taking place in the gland are very
instructive, since the fat can be seen to be gathered in the
epithelium-cell, in the same way as in a fat-cell of the adipose
tissue, and to be discharged into the channels of the gland, either
by breaking away from the cell, or by a contractile extrusion very
similar to that which takes place when an amoaba ejects its digested
food. All the evidence we possess goes to prove that the fat
is formed in the cell through a metabolism of the protoplasm.
The microscopic history is thoroughly supported by other facts.
Thus the quantity of fat present in milk is largely and directly
increased by proteid, but not increased, on the contrary diminished,
by fatty food. This is quite intelligible when we know, as will be

CHAP, v.] NUTRITION. hi

shewn in a succeeding section, that proteid food increases, and
fatty food diminishes, the metabolism of the body ; and we have
already discussed the manner in which proteid material may give
rise to fat. A bitch fed on meat for a given period ;gave off more
fat in her milk than she could possibly have taken in her food, and
that too while she was gaining in weight, so that she could not
have supplied the mammary gland with fat at the expense of
fat previously existing in her body; she apparently obtained it
ultimately from the proteids of her food. In the 'ripening* of
cheese we have a similar conversion of proteids into fat, though
this appears to be effected by the agency of certain fungi.
We have also indications that the casein is, like the fat, formed in
the cells of gland, and not simply separated from the blood. When
the action of the cell is imperfect, as at the beginning or end of
lactation, the albumin in milk is in excess of the casein; but as
long as the cell possesses its proper activity the formation of casein
becomes prominent. When milk is kept at 35° C. out of the body
the casein is said to be increased at the expense of the albumin,
but the substance thus formed out of albumin is probably not real
casein but ordinary alkali-albumin, produced by the action of the
alkalis of the milk on the albumin. It has been suggested
that the casein may be formed by a splitting up of albumin by
some fermentative process, and a ferment capable of effecting this
is said to have been isolated. That the milk-sugar also is formed in
and by the protoplasm of the cell, is indicated by the facts that
it is found in no other part of the body, and that its presence in
milk is not dependent on carbohydrate food, for it is main-
tained in abundance in the milk of carnivora when these are fed
exclusively on meat, as free as possible from any kind of sugar or
glycogen. We thus have evidence in the mammary gland of the
formation, by the direct metabolic activity of the secreting cell, of
the representatives of the three great classes of food-stuffs, proteids,
fats and carbohydrates, out of the comprehensive substance proto-
plasm. And what we see taking place in the ^oammary cell is
probably a picture of what is going on in all protoplasmic bodies.
If the fat of the milk were not ejected from the mammary cell, the
mammary gland would become a mass of adipose tissue, especially
if, by a slight change in the metabolism, the production of fat were
exalted at the expense of the production of casein or milk-sugar. If,
again, by a similar slight change the milk-sugar were accumulated
rather than the fat or proteid, we should have a result which, by an
easy step, would bring us to glycogenic tissue. And, lastly, if the
proteid accumulation were greater than the fatty, or the saccharine,
these being earned off in some way or other, we should have an
image of the nutrition of an ordinary nitrogenous tissue.

That both the secretion and ejection of milk are under the
control of the nervous system is shewn by common experience,
but the exact nervous mechanism has not yet been fully worked

435 THE SPLEEN. [BOOK n.

out. While erection of the nipple ceases when the spinal nerves
which supply the breast are divided, the secretion continues, and
is not arrested even when the sympathetic as well as the spinal
nerves are cut.

The Spleen.

The Spleen may be wholly removed from an animal without
any obvious changes in the economy taking place : the functions of
the rest of the body appear to go on unimpaired. We are obliged
to assume that some compensating actions take place; but what
those actions are we do not know, and we are left at present by
these experiments almost completely in the dark as to the functions
of the spleen. The most that has been observed is a slight increase
in the lymphatic glands, and in the activity of the medulla of bones
(see p. 29), but even this is doubtful.

After a meal the spleen increases in size, reaching its maximum
about five hours after the taking of food ; it remains swollen for
some time, and then returns to its normal bulk. In certain diseases,
such as in the pyrexia attendant on fevers or inflammations, and
more especially in ague, a similar temporary enlargement takes
place. In prolonged ague a permanent hypertrophy of the spleen,
the so-called ague-cake, occurs.

The turgescence of the spleen seems to be due to a relaxation
both of the small arteries and of the muscular bands of the
trabeculse ; to be, in fact, a vaso-motor dilation accompanied by a
local inhibition of the tonic contraction of the other plain muscular
fibres entering into the structure of the organ, the latter, at all
events in some animals, being probably the more important of the
two. And the condition of the spleen, like that of other vascular
areas, appears to be regulated by the central nervous system,
the digestive turgescence being altogether comparable to the
flushed condition of the pancreas and of the gastric membrane
during their phases of activity.

The application of the plethysmographic method to the spleen,
carried out in the way which we described in speaking of the
kidney (p. 398), has revealed certain interesting phenomena.

A 'spleen curve* Fig. 66 taken in the same way as a 'kidney
curve' brings to light the following facts. The volume of the
spleen does not vary, as does that of the kidney with each pulse
wave. The kidney curve as we have seen, p. 400, gives clear
indications of each heart beat, but the spleen curve shews only
gentle undulations, obviously due to the respiratory movements.
This difference corresponds to the difference in the vascular

CHAP, v:] NUTRITION. 433

arrangements of the two organs. In the kidney the small arteries
are relatively numerous, and a large portion of the blood in the
kidney is contained in them ; in the spleen the small arteries are
relatively few, and the great bulk of the blood is contained in the
capillaries and in the meshes of the peculiar splenic tissue. Con-
sequently the blood-flow through the spleen is of a more even
character than that through the kidney, and the effects of variations
in the distension of the arteries, and of vaso-motor influences gene-
rally are less directly felt.

MWIilW^^

Fia. 66. NORMAL SPLEEJI CURVE FROM DOG.

The upper curve is the spleen curve shewing the rhythmic contractions and
expansions ; the smaller waves are due to the respiratory movements. The lower
curve is the blood-pressure curve and the point a of the spleen curve corresponds in
time to the point 6 of the blood-pressure curve. The marks on the tune curve
below indicate seconds.

Besides the respiratory undulations the spleen curve usually
shews, as seen in the figure, large slow variations of volume.
Rhythmic contractions and expansions, though not always present,
frequently make their appearance, each contraction with its fellow
expansion lasting in the cat and dog about a minute, and recurring
with great regularity for a long time. There can be little doubt but
that these variations in volume are due to rhythmic contractions,
with intervening relaxations, of the muscular trabeculse and capsule.
In many animals the contractility of the splenic tissue is shewn by
the white lines of constriction which appear when the electrodes
of an induction machine in action are drawn over its surface ; and
similar lines may be produced by mechanical stimulation with the
point of a needle. So that the spleen may be considered as a
muscular organ, now expanding to receive a larger quantity of
blood and now contracting to drive the blood on to the liver. We
have evidence moreover that the muscular activity of the spleen is
under the dominion of the nervous system. A rapid contraction of
the spleen may be brought about in a direct manner by stimulation
of the splanchnic or vagus nerves, or in a reflex manner by stimu-
lation of the central ends of a sensory nerve ; it may also be
p. 28

434 THE SPLEEN. [BOOK n.

caused by stimulation of the medulla oblongata with a galvanic
current or by means of asphyxia. Though the matter has not yet
been fully worked out, we have already sufficiently clear indi-
cations that the flow of blood through the spleen is, through
the agency of the nervous system, varied to meet changing needs.
At one time a small quantity of blood is passing through the
organ, and the blood is at such times probably confined to the
well-established capillary passages, the metabolic changes which
it undergoes in the transit being comparatively slight. At
another time a larger quantity of blood enters the organ, and then
probably is let loose, so to speak, into the splenic pulp, there
to undergo more profound changes, and afterwards to be ejected by
the rhythmic contractions of the muscular trabeculse.

Indeed, when the peculiar arrangements of the blood-vessels of
the spleen, with their large open venous networks, are borne in
mind, it seems in the highest degree probable that metabolic
events of great importance (possibly associated in some way with
the destruction or metamorphosis of the blood-corpuscles) take
place in the spleen, though at present we are unable to follow
them. And this view is supported by the somewhat peculiar
chemical characters of the spleen-pulp, which, in spite of its con-
taining a very large number of blood-corpuscles, differs markedly in
its chemical composition from either blood or serum. Thus a
special proteid of the nature of alkali-albumin holding iron in some
way peculiarly associated with it seems to be present. The occur-
rence of this ferruginous proteid, accompanied as it is by several
peculiar but at present little understood pigments, rich in carbon,
bears out the histological conclusions (see p. 30) concerning the dis-
appearance of the red corpuscles. The inorganic salts of the
spleen, or at least those of its ash, are remarkable for the large
amount of both soda and phosphates, and the small amount of
potash and chlorides which they contain, thus differing from blood -
corpuscles on the one hand, and from blood-serum on the other.
But perhaps the most striking feature of the spleen-pulp is its rich-
ness in the so-called extractives. Of these the most common and
plentiful are succinic, formic, acetic, butyric and lactic acids (these
may arise in part from the decomposition of haemoglobin), inosit,
leucin, xanthin, hypoxanthin and uric acid. Tyrosin apparently is
not present in the perfectly fresh spleen, though leucin is : both
are found when decomposition has set in. The constant presence
of uric acid is remarkable, especially since it has been found even
in the spleen of animals, such as the herbivora, whose urine
contains none. No less suggestive is the fact that the increase of
uric acid in the urine during ague, and during ordinary pyrexia,
seems to run parallel to the turgescence, and therefore presumably
to the activity, of the spleen. But these facts are at present
suggestive only ; they point to an active metabolism, associated in
some way with digestion, taking place in the spleen ; exact informa-

CHAP, v.] NUTRITION. 435

tion as to the nature of the metabolism is however wanting. The
thyroid and thyrnus bodies, often in descriptions associated with the
spleen, though different in structure, the former absolutely so, re-
semble the spleen somewhat, as far as their extractives are
concerned. The thymus contains leucin, xanthin and hypoxanthin,
with lactic and succinic acids ; uric acid seems to be absent. The
extractives of the thyroid are scanty, but apparently of the same
nature.

28 —2

SEC. 2. THE HISTORY OF UREA AND ITS ALLIES.

We may now return to the questions which we left unanswered
at p. 409. Where is urea formed ? what are its immediate ante-
cedents ? what are the various chemical links between it and the
proteid material of which it is the excretory representative ?

We have seen, p. 69, that the muscular tissues contain kreatin,
together with smaller quantities of allied nitrogenous crystalline
bodies, such as xanthin, hypoxanthin, &c. ; and we cannot go far
wrong in supposing that these bodies are in some way or other the
products of muscular metabolism. We do not know in what
quantities they are formed; but since they are such bodies as
would readily be carried away from the muscle by the blood-
stream, and yet are always to be found in the muscle, we infer that
they are continually being formed, and as continually being con-
verted into some other bodies and carried away. And we- may
further say, that since kreatin exists in muscle to the extent
of '2 or '4 p.c., and since muscle forms so large a portion of the
whole body, and must be continually undergoing some nitrogenous
metabolism, even if the energy of the muscle (see p. 99) have a
non-nitrogenous source, it is at least possible, if not probable, that
a considerable amount of kreatin passes within twenty-four hours
into the blood, on its way to become transformed by other tissues
into urea, or into some stage nearer to urea than itself. The urine,
it is true, contains a certain amount ('9grm. in 24 hours) of
kreatinin, into which kreatin is easily converted ; but this can be

CHAP, v.] NUTRITION. 437

considered as the normal form in which the kreatin of the muscles
passes out of the body. For the urinary kreatinin is exceedingly
variable in quantity, vanishing during starvation, and, though not at
all increased by exercise, is largely augmented by a flesh-diet ; and
kreatin injected into the blood, even in small quantities, reappears
as kreatinin in the urine. Without laying too much stress on the
last fact, we are led to conclude that the kreatinin or kreatin in
urine has an origin quite independent of that which is present in
the muscles, being probably derived directly from the food.

Of the metabolism of the nervous tissues we know little ; but
kreatin is found in the brain, in some cases in not inconsiderable
quantity. Moreover the bodies of the nerve-cells are undoubtedly
composed of protoplasm ; the axis-cylinders of the nerve-fibres are
also protoplasmic in nature, and it is at least possible that much of
the peculiar matrix of the cerebral and cerebellar convolutions, and
of the grey matter generally, is also in reality protoplasmic. Hence
we may, with a certain amount of reason, suppose that the
nervous, like the muscular tissues, are continually, but to a
much less extent, supplying an antecedent to urea in the form of
kreatin.

Lastly, the spleen contains a considerable quantity of kreatin,
as well as of xanthin, &a ; and these are present also in various
glandular organs.

We thus have evidence of a continual formation of kreatin,
possibly in large quantities, in various parts of the body. On the
other hand, urea is certainly not present in muscle (save in certain
exceptional cases) and its presence in nervous tissue is extremely
doubtful. It is absent from the spleen (of the occurrence of urea
in the liver we shall speak presently), the thymus, and thyroid
bodies, and from the lymphatic glands, though uric acid, as we
have seen, appears to be a normal constituent of the spleen. It
seems very tempting to jump at once from these facts to the
conclusion that kreatin is the natural antecedent of .urea, and that
as far as nitrogenous excretion is concerned the labour of the
kidney is confined to the simple transformation of kreatin into
urea. We have only to suppose that the kreatin passes from these
several tissues into the blood, in which it may be found, and
while circulating in the blood is seized upon by the renal epithelium
and converted into urea. And in support of this view it has been
urged that while ligature of the ureters leads to an accumulation
of urea in the various tissues and fluids of the body, kreatin takes
the place of urea when the kidneys are wholly extirpated, the ex-
planation given of the different results being that in the former
case the kidneys continue to perform their functions, and to manu-
facture urea out of kreatin, and the urea thus formed is thrown
back upon the blood, whereas in the latter case the kreatin-
converting organs are absent. Further observations however have
clearly shewn that whether the kidneys be wholly extirpated or the

438 UREA. [BOOK 11.

ureter simply ligatured, the result in both cases is the same, an
accumulation in the tissues and fluids of urea, or, in the case of
birds and snakes, &c., of uric acid. And indeed the ligature of the
ureters soon leads to such trouble in the renal epithelium as to
arrest their functional activity, so that the distinction between ex-
tirpation of the kidney and ligature of the ureters is an illusory
one. Hence, though we need not go so far perhaps as to say
that no part of the urea of urine is furnished by a transformation
of kreatin by the kidney itself, it is obvious that we cannot speak
of the main mass of urea, which passes from the body, as having
such an origin, and as having undergone such a transformation in
the kidney. Clearly the great part of the urea of the urine reaches
the kidney either as urea existing in the blood and has simply to be
passed through the epithelium cells, the healthy kidneys usually
performing their work so well as to leave behind in the blood only
such a slight amount of urea as to be with difficulty detected by the
means at present at our command, or as some substance, which
though not actually urea itself, is so nearly allied as to be capable
of being readily transformed into urea, and accumulated as urea
in the tissues and fluids, when the excreting power of the kidneys
is lost.

The kreatin of muscle and other tissues may, before it reaches
the kidney, be a source of this urea or antecedent of urea in the
blood, having undergone transformations whose seat and nature
are hidden from us or, as we have suggested, it may not be. There
are however other possible sources of urea besides the kreatin
formed in muscle and elsewhere. We have seen that one result of
the action of the pancreatic juice is the formation of considerable
quantities of leucin and tyrosin. In dealing with the statistics of
nutrition, our attention will be drawn to the fact that the intro-
duction of proteid matter into the alimentary canal is followed
by a large and rapid excretion of urea, suggesting the idea that a
certain part of the total quantity of the urea normally secreted
comes from a direct metabolism of the proteids of the food, without
these really forming a part of the tissues of the body. We do not
know to what extent normal pancreatic digestion has for its product
leucin, and its companion tyrosin; but if, especially when a meal
rich in proteids has been taken, a considerable quantity of leucin
is formed, we can perceive an easy and direct source of urea,
provided that the metabolism of the body is capable of converting
leucin into urea. That the body can effect this change is shewn by
the fact that leucin, when introduced into the alimentary canal in
even large quantities, does reappear in the urine as urea ; that is,
the urine contains no leucin, but its urea is proportionately in-
creased ; and the same is possibly the case with tyrosin, though
this is disputed. Now the leucin formed in the alimentary canal
is probably carried by the portal blood straight to the liver; and
the liver, unlike other glandular organs, does, even in a perfectly

CHAP, v.] -NUTRITION. 439

normal state of things, contain urea. We are thus led to the view
that among the numerous metabolic events which occur in the
hepatic cells, the formation of urea out of leucin or out of other
antecedents may be ranked as one. And in support of this view it
may be urged that a large quantity of urea seems to be present in
the liver of mammals, and of urates in the liver of birds. More-
over when a stream of fresh blood is passed several times through
the liver of an animal recently killed, the percentage of urea in
the blood so used is found to be decidedly increased. This however
is not conclusive, for the increased quantity in the blood which had
been circulated might have been simply urea which had been
washed out from the liver, where it had previously been staying.
Probable, therefore, as this view may seem, it has not as yet been
established as a fact. A strong presumption however in favour of
urea arising through the hepatic metabolism, from leucin as an
antecedent, is afforded by the fact that in cases of acute atrophy of
the liver, where the hepatic cells lose their functional activity, the
urea of the urine is replaced by leucin and tyrosin. And, lastly, it
may be remarked that not only are leucin and tyrosin found in
nearly all the tissues after death, especially in the glandular tissues,
but they also appear with striking readiness in almost all de-
compositions of proteids, and leucin is also a product of decompo-
sition of gelatiniferous substances.

The view that leucin is tranformed into urea lands us however
in very considerable difficulties. Leucin, as we know, is amido-
caproic acid; and, with our present chemical knowledge, we can
conceive of no other way in which leucin can be converted into
urea than by the complete reduction of the former to the ammonia
condition (the caproic acid residue being either elaborated into a
fat or oxidized into carbonic acid) and by a reconstruction of
the latter out of the ammonia so formed. We have a somewhat
parallel case in glycin. This, which is amido-acetic acid, when
introduced into the alimentary canal, also reappears as urea ; here
too a reconstruction of urea out of an ammonia phase must take
place. Moreover when ammonium chloride is given to a dog a
very large portion reappears as urea, i.e. there is an increase in the
urea of the urine corresponding to a large portion of the nitrogen
contained in the ammonium chloride. And there is a certain
amount of evidence into which we cannot enter here, leading to
the conception that the immediate antecedent of urea is ammonium
carbamate which by dehydration (and this it is stated may be
effected by electrolysis with rapidly alternating currents) is trans-
formed into urea. Or the antecedent which is dehydrated may be not
ammonium carbamate but ammonium carbonate (see Appendix); and
on the other hand, seeing how readily ammonium cyanate is trans-
formed into urea, it may be that the immediate antecedent is some
cyanogen compound. Leaving these matters for the present, and
indeed we have ventured to call attention to them, chiefly because

440 URIC ACID. [BOOK n.

they serve as a warning not to neglect the possible synthetic
operations of the animal body, we may sum up our imperfect
knowledge concerning the history of urea as follows. We have
evidence, not exactly complete but fairly satisfactory, that a part
at least of the urea is simply withdrawn from the blood by the
renal epithelium. The activity of the protoplasm of the secreting
cells must therefore, as far as this part of the urea is concerned,
be confined to absorbing the urea from the renal blood, and
to passing it on into the cavities of the renal tubules. The
mechanism by which this is effected we cannot at present
fathom, but it seems more comparable to a selection of food than
to anything else ; the cells appear to treat urea much in the same
way as they treat sodium sulphindigotate. The antecedents of the
urea in the blood are, we may at present suppose, partly the
kreatin formed in muscle and elsewhere, partly the leucin and
other like bodies formed in the alimentary canal as well as in
various tissues. The transformation of these bodies into urea may
take place in the liver and possibly in the spleen, but we have no
exact proof of this, nor can we say exactly in what way the
transformation is effected. There is no proof of any body existing
in the blood capable of effecting this transformation ; and we may
probably rest assured that in this, as in other metabolic events,
the activity exercised in the change comes from some tissue, and
cannot be manifested by simple blood plasma.

Lastly, it is possible that the kidney may, besides the simpler
duty of withdrawing ready formed urea from the blood, be exercised
in transforming various nitrogenous crystalline bodies to serve as
part of the supply of urea which passes from it.

Uric Acid. This, like urea, is a normal constituent of urine,
and, like urea, has been found in the blood, and in the liver
and spleen ; we have already, p. 434, referred to its relations with
this latter organ. In some animals, such as birds and most reptiles,
it takes the place of urea. In various diseases the quantity in the
urine is increased ; and at times, as in gout, uric acid accumulates
in the blood, and is deposited in the tissues. By oxidation a
molecule of uric acid can be split up into two molecules of urea,
and a molecule of mesoxalic acid. It may therefore be spoken of
as a less oxidised product of proteid metabolism than urea; but
there is no evidence whatever to shew that the former is a
necessary antecedent of the latter; on the contrary, all the facts
known go to shew that the appearance of uric acid is the result of
a metabolism slightly diverging from that leading to urea. And
we have no evidence to prove that the cause of the divergence lies
in an insufficient supply of oxygen to the organism at large ; on
the contrary, uric acid occurs in the rapidly breathing birds, as
well as in the more torpid reptiles. Nor can the fact that in the
frog urea again replaces uric acid be explained by reference to that
animal having so large a cutaneous in addition to its pulmonary

CHAP, v.] NUTRITION. 411

respiration. The final causes of the divergence are to be sought
rather in the fact that urea is the form adapted to a fluid, and uric
acid to a more solid excrement.

Hippnric Acid. In the urine of herbivora uric acid is for
the most part absent, being replaced by hippuric acid. In the
urine of omnivorous man, both acids may be present together.
The history of the hippuric acid of urine is very instructive ; for
though at first sight its presence might appear to indicate that the
metabolism of the herbivora is in some points fundamentally
different from that of carnivora, there can be little doubt that the
hippuric acid which appears in the urine of herbivora comes
directly from the ingested food. Hippuric acid is a compound of,
or rather a result of, the union or conjugation of benzoic acid and
glycin ; and when benzoic acid is introduced into the stomach of
an animal, whether herbivorous or not, it reappears not as benzoic
but as hippuric acid. It evidently meets, somewhere in the body,
with glycin ; and uniting with this becomes hippuric acid, in which
form it passes out by the urine. Nitrobenzoic acid in a similar
way becomes nitrohippuric acid; and many other bodies of the
aromatic class, by a like assumption of glycin, become conjugated
in their passage through the body.

The knowledge of the fact that benzoic acid is thus converted
into hippuric acid naturally suggested the idea that the food of
herbivora might contain either benzoic acid, or some allied body,
and that the presence of hippuric acid as a normal constituent of
urine might be thus accounted for. And it would appear
that all the hippuric acid of herbivorous urine is in reality
due to the presence in ordinary fodder (hay) of a particular
constituent containing a benzoic residue ; when this constituent is
withdrawn, the hippuric acid disappears from the urine.

The transformation or conjugation appears to take place chiefly
in the kidneys, for when blood containing benzoic acid is driven
through the vessels of a fresh, that is of a living, kidney, it is found
after the transit to contain hippuric acid. And indeed the same
change may be effected by simply mixing benzoic acid with
portions of fresh and still warm kidney, broken to pieces and as it
were mashed up, the mixture being exposed to the temperature of
the body. If the kidney be kept some time before the benzoic
acid is submitted to its action, the transformation fails, indicating
that the change is effected by certain elements, probably by the
renal epithelium cells, which retain this power so long only as they
remain alive after removal from the body.

A similar transformation of benzoic into hippuric acid is said
to take place in some animals at least in the liver, benzoic acid
injected into the portal vein reappearing as hippuric acid in the
blood of the hepatic vein. In both these cases it is worthy of note,
and the observation bears on the formation of urea just discussed,
that the change takes place even if no glycin be added with the

442 HIPPURIC ACID. [BOOK n.

benzole acid. Glycin must therefore be present in the kidney or
liver, and its presence in the liver is further shewn by the formation
of glycocholic acid from cholalic acid. But singularly enough, glycin,
though a common product of the decomposition of proteid and
gelatiniferous substances, has hitherto not been found as such in
any part of the living body.

Of the meaning of the appearance in the tissues of such bodies
as xanthin, &c., and of the exact nature of the metabolism which
they undergo, we know nothing. We cannot say whether they are
simply the accidental bye-products of nitrogenous metabolism, the
result of imperfect chemical machinery ; or whether they, though
small in quantity, serve some special ends in the economy.

SEC. 3. THE STATISTICS OF N CJTRITIOX.

The preceding sections have shewn us how wholly impossible
it is at present to master the metabolic phenomena of the body by
attempting to trace out forwards or backwards the several changes
undergone by the individual constituents of the food, the body or
the waste products. Another method is however open to us, the
statistical method. We may ascertain the total income and the
total expenditure of the body during a given period, and by com-
paring the two may be able to draw conclusions concerning the
changes which must have taken place in the body while the
income was being converted into the output. Many researches
have of late years been carried out by this method ; but valuable
as are the results which have been thereby gained, they must be
received with caution, since in this method of inquiry a small error
in the data may, in the process of calculation and inference, lead to
most wrong conclusions. The great use of such inquiries is to
suggest ideas, but the views to which they give rise need to be
verified in other ways before they can acquire real worth.

Composition of the Animal Body. The rirst datum we require
is a knowledge of the composition of the body, as far as the rela-
tive proportion of the various tissues is concerned. In the human
body the proportions by weight of the chief tissues are probably
somewhat as follows :

Adult man. Newborn baby.

Skeleton 15'9 p. c. 177 p. c.

Muscles 41-8 „ 22'9 „

Thoracic viscera 17 3'0

Abdominal viscera 7'2

Fat 18-2

Skin 6'9

Brain TO

11-5
20'0
15-8

444: THE STATISTICAL METHOD. [BOOK n.

An analysis of a cat has given the following result :

Muscles and tendons 45*0 p. c.

Bones 147 „

Skin 12-0 „

Mesentery and adipose tissue 3*8 „

Liver 4*8 „

Blood (escaping at death) 6*0 „

Other organs and tissues 13*7 „

One point of importance to be noticed in these analyses is that
the skeletal muscles form nearly half the body; and we have
already seen (p. 34) that about a quarter of the total blood in the
body is contained in them. We infer from this that a large
part of the metabolism of the body is carried on in the muscles.
Next to the muscles we must place the liver, for though far less in
bulk than them, it is subject to a very active metabolism, as
shewn by the fact that it alone may hold about a quarter of the
whole blood.

The Starving Body. Before attempting to study the influence
of food, it will be useful to ascertain what changes occur in a body
when all food is withheld. A cat was found to lose in a hunger
period of 13 days 734 grammes of solid material, of which 248*8
were fat and 118*2 muscle, the remainder being derived from the
other tissues. The percentages of dry solid matter lost by the more
important tissues during the period were as follows :

Adipose tissue 97'0 p. c.

Spleen 63'1

Liver 56*6

Muscles 30*2

Blood 17-6
Brain and spinal cord O'O

Thus the loss during starvation fell most heavily on the fat, indeed
nearly the whole of this disappeared. Next to the fat, the gland-
ular organs, the tissues which we have seen to be eminently
metabolic, suffered most. Then come the muscles, that is to say,
the skeletal muscles, for the loss in the heart was very trifling;
obviously this organ, on account of its importance in carrying on
the work of the economy, was spared as much as possible : it was
in fact fed on the rest of the body. The same remark applies to
the brain and spinal cord; in order that life might be prolonged
as much as possible, these important organs were nourished by
material drawn from less noble organs and tissues. The blood
suffered proportionally to the general body-waste, becoming gra-
dually less in bulk but retaining the same specific gravity; of
the total dry proteid constituents of the body 17'3 p. c. was lost,

CHAP, v.] NUTRITION. 445

which agrees very closely with the 17*6 p. c. lost by the blood. It
is worthy of remark that the tissues in general became more
watery than in health. We might infer from these data the con-
clusions that metabolism is most active first in the adipose tissue,
next in such metabolic tissues as the hepatic cells and spleen-pulp,
then in the muscles, and so on; but these conclusions must be
guarded by the reflection that because the loss of cardiac and
nervous tissue was so small, we must not therefore infer that their
metabolism was feeble; they may have undergone rapid metabolism,
and yet have been preserved from loss of substance by their
drawing upon other tissues for their material.

During this starvation-period, the urine contained in the form
of urea (for, as we shall see, the other nitrogenous constituents of
urine may for the most part be disregarded) 277 grammes of
nitrogen. Now the amount of muscle which was lost during the
period contained about 15'2 of nitrogen. Thus, more than half
the nitrogen of the output during the starvation-period must
have come ultimately from the metabolism of muscular tissue.
This is an important fact of which we shall be able to make use
hereafter. Bidder and Schmidt came to the conclusion, from their
observations on a starving cat, that the quantity of urea excreted
per diem, in all but the earlier days of the inanition period, bore a
fixed ratio to the body- weight. In the first two or three days of the
period, the daily quantity of urea was much in excess of this ratio.
They were thus led to distinguish two sources of urea : a quantity
arising from the functional activity of the whole body, and therefore
bearing a fixed ratio to the body-weight, and continuing until near
the close of life ; and a quantity arising from the amount of surplus
nitrogenous or proteid material which happened to be stored up in
the body at the commencement of the period, and which was
rapidly got rid of. The latter they regarded as not entering
distinctly into the composition of the tissues, but as, so to speak,
floating capital, upon which each or any of the tissues could draw.
They spoke of its direct metabolism as a luxus consumption. More
extended observations however have shewn that though the urea
of the first two or three days much exceeds that of the subsequent
days of a starvation-period, no such fixed relation of urea to body-
weight as that suggested obtains. To the question of a luxus con-
sumption we shall have again to refer.

The Normal Diet. What is the proper diet for a given animal
under given circumstances, can only be determined when the laws
of nutrition are known. Meanwhile it is necessary to gain an
approximate idea of what may be considered as the normal diet
for a body such as that of man under ordinary circumstances.
This may be settled either by taking a very large average, or by
determining exactly the conditions of a particular case. In the
table below is given both the average result obtained by Moleschott
from a large number of public diets, and the diet on which an

446 THE STATISTICAL METHOD. [Boon-it

observer (Ranke) found himself in good health, neither losing nor
gaining weight.

Public Diet (Moleschott). Eanke.

Proteids 30 100

Fat 84 100

Amyloids 404 240

Salts 30 25

Water 2800 2600

Of these two diets, which agree in many respects, that of
Rarike is probably the better one, since in public diets, the cheaper
carbohydrates are used to the exclusion of the dearer fats.

Comparison of Income and Output.

Method. We have now to inquire how the elements of such a
diet are distributed in the excreta, in order that, from the manner
of the distribution, we may infer the nature of the intermediate
stages which take place within the body. By comparing the
ingesta with the excreta, we shall learn what elements have been
retained in the body, and what elements appear in the excreta
which were not present in the food ; from these we may infer the
changes which the body has undergone through the influence of
the food.

In the first place, the real income must be distinguished from
the apparent one by the subtraction of the faeces. We have seen
that by far the greater part of the faeces is undigested matter, i. e.
food which, though placed in the alimentary canal, has not really
entered into the body. The share in the faeces taken up by matter
which has been excreted from the blood into the alimentary canal,
is so small that it may be neglected; certainly with regard to
nitrogen, the whole quantity of this element, which is present in
the faeces, may be regarded as indicating simply undigested nitro-
genous matter.

The income, thus corrected, will consist of so much nitrogen,
carbon, hydrogen, oxygen, sulphur, phosphorus, saline matters, and
water, contained in the proteids, fats, carbohydrates, salts, and
water of the food, together with the oxygen absorbed by the lungs,
skin, and alimentary canal. The output may be regarded as
consisting of (1) the respiratory products of the lungs, skin, and
alimentary canal, consisting chiefly of carbonic acid and water,
with small quantities of hydrogen and carburetted hydrogen, these
two latter coming exclusively from the alimentary canal ; (2) of
perspiration, consisting chiefly of water and salts, for the dubious
excretion (see p. 386) of urea by the skin may be neglected and

CHAP, v.] NUTRITION. 447

the other organic constituents of sweat amount to very little ; and
(3) of the urine, which is assumed to contain all the nitrogen really
excreted by the body, besides a large quantity of saline matters,
and of water. Where great accuracy is required the total nitrogen
of the urine ought to be determined; it is maintained, however,
that no errors of serious importance arise when the urea alone, as
determined by Liebig's method, is taken as the measure of the
total quantity of nitrogen in the urine, since, in this method, other
nitrogenous bodies besides urea are precipitated, and so contribute
to the quantitative result. It has been and indeed still is debated
whether the body may not suffer loss of nitrogen by other channels
than by the urine and faeces, whether nitrogen may not leave the
body by the skin or indeed in a gaseous state by the lungs. The
balance of the conflicting evidence seems however in favour of the
view that no such loss takes place. It would appear that though
nitrogen, the pivot, so to speak, of the chemical changes of living
beings, forms so large a portion of the atmosphere and moreover is
physically diffused through the bodies of both plants and animals,
free nitrogen is of no chemical use to either of them. It enters
into and remains in their bodies as an inert substance, and the
nitrogen which leaves a plant or animal, in a gaseous state, is simply
a part of the same inert supply and does not come from the break-
ing up of the nitrogenous substances of the body or of food.

Of these elements of the income and output, the nitrogen, the
carbon, and the free oxygen of respiration are by far the most
important. Since water is of use to the body for merely mechanical
purposes, and not solely as food in the strict sense of the word, the
hydrogen element becomes a dubious one ; the sulphur of the
proteids, and the phosphorus of the fats, are insignificant in
amount; while the saline matters stand on a wholly different
footing from the other parts of food, inasmuch as they are not
sources of energy, and pass through the body with comparatively
little change. The body-weight must of course be carefully
ascertained at the beginning and at the end of the period, cor-
rection being made where possible for the feces.

It will be seen that the labour of such inquiries is considerable.
The urine, which must be carefully kept separate from the faeces,
requires daily measurement and analysis. Any loss by the skin,
either in the form of sweat, or, in the case of woolly animals, of
hair, must be estimated or accounted for. The food of the period
must be as far as possible uniform in character, in order that the
analyses of specimens may serve faithfully for calculations involving
the whole quantity of food taken ; and this is especially the case
when the diet is a meat one, since portions of meat differ so much
from each other. But the greatest difficulty of all lies in the
estimation of the carbonic acid produced and the oxygen con-
sumed. In some of the earlier researches, this factor was
neglected and the variations occurring were simply guessed at,

448 THE STATISTICAL METHOD. [BOOK n.

through which very serious errors were introduced. No comparison
of income and output can be considered satisfactory unless at least
the carbonic acid produced be directly measured by means of a
respiration chamber. And in order that the comparison should be
really complete, the water given off by the skin and lungs must be
directly measured also ; but this seems to be more difficult than
the determination of the carbonic acid.

In the plan originally adopted by Regnault and Reiset and followed
by some other observers, the animal experimented on is allowed to
breathe a limited and measured atmosphere. The carbonic acid, as fast
as it is formed, is fixed and removed by a strong solution of caustic potash,
and the normal percentage of oxygen in the atmosphere is maintained
by a supply of this gas from a gasholder. In this way both the oxygen
consumed and the carbonic acid produced are directly determined, while
the continual supply of fresh oxygen prevents any evil effects due to
breathing a confined portion of air. In order however to avoid all
possible errors arising from a too restricted atmosphere a different method
has been adopted by Pettenkofer and Voit. Their apparatus consists
essentially of a large chamber, capable of holding a man comfortably.
By means of a steam-engine a current of pure air, measured by a gaso-
meter, is drawn through the chamber. Measured portions of the out-
going air are from time to time withdrawn and analysed ; and from the
data afforded by these analyses, the amounts of carbonic acid (and other
gases) and of water given off by the occupant of the chamber during a
given time are determined. The oxygen consumed may also be determined
by a comparison of the ingoing and outgoing air ; besides if the total
amounts of carbonic acid and of water given out by the lungs and skin
are thus ascertained and the amount of urine and faeces known, the
quantity of oxygen is determined by a simple calculation. For evidently
the difference between the terminal weight plus all the egesta and the
initial weight plus all the ingesta can be nothing else than the weight of
the oxygen absorbed during the period. This method in turn however is
also open to objections, since minute errors in the sample determinations
acquire by multiplication considerable dimensions. It seems moreover
undesirable to leave the quantity used of so important an element as
oxygen to be determined by indirect calculations.

Let us imagine, then, an experiment of this kind to have been
completely carried out, that the animal's initial and terminal
weights have been accurately determined, the composition of
the food satisfactorily known to consist of so much proteid, fat,
carbohydrates, salts, and water, and to contain so much nitrogen
and carbon, the weight of the faeces and the nitrogen they contain
ascertained, the nitrogen of the urine determined, the carbonic
acid and water given off by the whole body carefully measured,
and the amount of oxygen absorbed calculated — what interpreta-
tion can be placed on the results ?

Let us suppose that the animal has gained w in weight during
the period. Of what does w consist ? Is it fat or proteid material
which has been laid on, or simply water which has been retained,

CHAP, v.] NUTRITION. 449

or some of one and of the other? Let us further suppose that the
nitrogen of the urine passed during the period is less, say by x
grammes, than the nitrogen in the food taken, of course after
deduction of the nitrogen in the faeces. This means that x
grammes of nitrogen have been retained in the body ; and we may
with reason infer that they have been retained in the form of
proteid material. We may even go farther and say that they are
retained in the form of flesh, i.e. of muscle. In this inference we
are going somewhat beyond our tether, for the nitrogen might be
stored up as hepatic, or splenic, or any other form of protoplasm.
Indeed it might be for the while retained in the form of some
nitrogenous crystalline body; but this last event is unlikely; and
if we use the word 'flesh' to mean protoplasm of any kind,
contractile or metabolic, or of any other kind, we may without fear
of any great error reckon the deficiency of x grammes nitrogen
as indicating the storing up of a grammes flesh. There still
remain w — a grammes of increase to be accounted for. Let us
suppose that the total carbon of the egesta has been found to be
y grammes less than that of the ingesta ; in other words, that y
grammes of carbon have been stored up. Some carbon has been
stored up in the flesh with the nitrogen just considered ; this we
must deduct from y, and we shall then have y' grammes of carbon
to account for. Now there are only two principal forms in which
carbon can be stored up in the body : as glycogen or as fat. The
former is even in most favourable cases inconsiderable, and we
therefore cannot err greatly if we consider the retention of y'

rmmes carbon as indicating the laying on of 6 grammes fat.
a + b are found equal to w, then the whole chsnge in the
economy is known ; if w — (a + b) leaves a residue c, we infer that
in addition to the laying on of flesh and fat some water has been
retained in the system. If w — (a + b) gives a negative quantity,
then water must have been given off at the same time that flesh
and fat were laid on. In a similar way the nature of a loss of
weight can be ascertained, whether of flesh, or fat, or of water, and
to what extent of each. The careful comparison, the debtor and
creditor account of income and output, enables us, with the
cautions rendered necessary by the assumptions just now men-
tioned, to infer the nature and extent of the bodily changes. The
results thus gained ought of course, if an account is> kept of the
water taken in and given out, to agree with the amount of oxygen
consumed, and also to tally with the conclusions arrived at con-
cerning the retention or the reverse of water.

Having thus studied the method and seen its weakness as well
as its strength, we may briefly review the results which have been
obtained by its means.

Nitrogenous Metabolism. When a diet of lean meat, as free
as possible from fat, is given to a dog, which has previously been
deprived of food for some time, and whose body therefore is greatly
F. 29

450 NITROGEXUUti METABOLISM. [BOOK n.

deficient in flesh, it might be expected that the great mass of food
would be at once stored up, and only a small quantity be imme-
diately worked off as an additional quantity of urea, occasioned
by the increased labour thrown on the economy by the very
presence of the food. This however is not the case ; the larger
portion passes off as urea at once, and only a comparatively small
quantity is retained. If the diet be continued, and we are sup-
posing the meals given to be ample ones, the proportion of the
nitrogen which is given off in the form of urea goes on increasing
until at last a condition is established in which the nitrogen of
the egesta exactly equals that of the ingesta. This condition,
which is spoken of as nitrogenous equilibrium, is attained in dogs
with an exclusively meat diet only when large quantities of food
are given, and is not easily maintained for any length of time.
The exact quantity of meat required to attain nitrogenous equi-
librium varies with the previous condition of the dog ; it is fre-
quently seen when 1500 or 1800 grms. of meat are given daily.
Thus the most striking effect of a purely nitrogenous diet is largely
to increase the nitrogenous metabolism of the body. This result
has been explained by supposing that with the meat diet the
consumption of oxygen is largely increased ; in other words, that
the oxidizing activity of the body is directly augmented by a meat
diet. This in turn may be due in part to the fact that proteid
food largely increases the number of the red corpuscles, and so
augments the amount of oxygen with which the tissues are
supplied ; but as we have already urged more than once the
oxidative activity of the tissues is determined by the tissues
themselves rather than by the mere abundance of oxygen at their
disposal ; and probably other agencies are at work.

When nitrogenous equilibrium is established, it does not mean
that a body-equilibrium is established, that the body-weight
neither increases nor diminishes. On the contrary, when the meal
necessary to balance the nitrogen is a large one, the body may
gain in weight, and the increase is proved, both by calculation
from the income and output, and by actual examination of the
body, to be due to the laying on of fat. The amount so stored up
may be far greater than can possibly be accounted for by any fat
still adhering to the meat given as food. We are therefore driven
to the conclusion that the proteid food is split into a urea moiety
and a fatty moiety, that the urea moiety is at once discharged, and
that such of the fat as is not made use of directly by the body is
stored up as adipose tissue. And this disruption of the proteid
food at the same time explains why the meat diet so largely and
immediately increases the urea of the egesta. We have already
pointed out that possibly this disruptive metabolism of proteids is
largely carried on in the alimentary canal itself by the aid of the
pancreatic juice ; whether or to what extent other organs share in
the action we do not at present know,

CHAP, v.] NUTRITION. 451

The characteristic metabolic effects of proteid food are shewn
not only by these calculations of what is supposed to take place
in the body, but also by direct analysis. Lawes and Gilbert
laboriously analysing the body of a pig, which had been fed on a
known diet, and comparing the analysis with that of another pig of
the same litter, killed at the time when the first was put on the
fixed diet, found that of the dry nitrogenous material of the food
only 7'3-i p. c. was laid up as dry proteid material during the
fattening period, though the amount of proteid food was low ; in
the sheep the increase was only 4' 14 p. c.

It may be worth while to consider briefly here what is exactly
meant by the proteid metabolism of which we are speaking.
In the first place, in dealing with the changes taking place in the
body we may distinguish between morphological and physiological
destruction and renewal. We know that an epithelium cell, as
notably in the case of the skin, may be bodily cast off and its
place filled by a new cell ; and probably a similar disappearance of
and renewal of histological units takes place in all the tissues of
the body to a variable extent. But, in the adult body, these
histological transformations are, in the cases of most of the tissues,
slow and infrequent. A muscle for instance may suffer very
considerable wasting and recover from that wasting without any
loss or renewal of its elementary fibres. And it is obvious that
the metabolism of which we are now speaking does not involve any
such shifting of histological units. On the other hand we find
these histological units, the muscle-fibre or the gland-cell for
instance, living on their internal medium the blood, or rather on
the lymph which is the middleman between themselves and the
actual blood flowing in the vascular channels. Now we have
previously insisted at length on the view that no oxidative
changes on a large scale take place, as was once thought, in the
blood. The proteid metabolism which we are now considering or
rather the destructive part of that metabolism (and to avoid the
introduction of a new word we may venture, in using the word
metabolism, to leave the context to explain, whether the whole
series of changes constructive and destructive, or the constructive
changes alone, or the destructive changes alone, are intended) is
fundamentally oxidative in character; and we may therefore assume
that the large proteid metabolism which we are considering does
not go on in the blood. In other words, the metabolism of proteids
and the reduction of their nitrogenous residues into urea or into
immediate antecedents of urea is carried out by the agency of the
elements of the tissues. In a tissue unit however, such as a muscle-
fibre or gland-cell, we must distinguish between the actual living
protoplasm or modified protoplasm, the morphological framework so
to speak, and the material or substances, solid or in solution, which
are lodged in the spaces of the framework, which are not part of the
living unit but rather form a sort of internal medium to the unit

29—2

452 NITROGENOUS METABOLISM. [Boon 11.

itself. And we may readily conceive of the living unit effecting
changes, and even profound changes, in this its internal medium,
without the substances thus changed ever becoming an integral part
of the living unit itself. Moreover we can also conceive of the unit
as a whole producing changes in the lymph surrounding it, much
in the same way, as, according to some observers, the yeast-cell
produces changes in the molecules of sugar which surround it, but
which never become part of itself. We may therefore, in the case
of proteids, follow Voit and others in distinguishing between the
proteids 011 the one hand which actually become part of living
units and which may be called " tissue-proteids " or " morphotic
proteids," and those on the other hand which are found in the
internal meshes of the unit or in the surrounding lymph or in the
blood, and which, since they probably pass readily from one medium
to the other, may be spoken of as ''circulating proteids." By
older physiologists at a time when the energy of bodily movements,
of which we shall speak directly, was supposed to come from the
direct metabolism of the morphotic proteids of muscle, the increase
of urea due to food independent of exertion was regarded as simply
arising from proteids metabolized in the blood, and so cast out as
useless ; hence the phrase, to which we have already referred, of
luxus-consumption. We now know however, as will presently be
pointed out, that the energy of bodily movements does not come
from the metabolism of the proteids of muscle, and we have
already seen that oxidations on a large scale do not take place
in the blood. Hence this view of a luxus-consumption is no
longer tenable. There still remains, however, the difficulty of
supposing that every grain of urea which passes from the body
after a rich proteid meal is the issue of the metabolism of a
quantity of proteid previously existing as an integral part of some
tissue unit ; in other words, it seems unlikely that, simply as the
result of such a meal, the actual living proteid framework of the
body should be so largely renewed. Moreover the contrast between
that part of the daily urea which is variable and fluctuating and
that part which is more constant has to be explained. Hence has
arisen the view that the sources of urea are twofold, corresponding
to the metabolism of two distinct categories of the proteids of the
body. On the one hand, part of the urea, especially that which
appears as the immediate result of food, is supposed to be derived
from the metabolism of what we defined above as "circulating
proteids;" while, on the other hand, a certain (presumably smaller)
portion is really due to the metabolism of the "tissue-proteids,"
i.e. of the actual living framework of the body.

We must not attempt to discuss this view at length, and indeed
our knowledge is inadequate for the purpose. We have not as yet
a measure of the rate at which the metabolism of the living unit
does or may take place, and the arguments in favour of a metabolism
of circulating proteids are, at present, of a very indirect character.

CHAP, v.] NUTRITION. 4/53

Moreover it is possible that the rapid proteid metabolism indicated
by the great increase of urea which follows upon a meal rich in
proteids, may be, as we have hinted, merely a destructive digestion
of the proteids while they still are retained in the alimentary
canal.

We may however call attention to a possible analogy between
the history of proteids and that of fats and carbohydrates. The
uniform composition of the blood, which the body seems ever
striving to maintain, probably applies to its proteids as well as
to its other constituents. We have seen that* a surplus of non-
nitrogenous materials in the blood is withdrawn from the circula-
tion and stored up as fat or glycogen, and it is possible that an
excess of proteids might similarly be stored up in some tissue or
tissues, though from the facts previously mentioned it is obvious
that the power of storage is far less than in the case of fats
and carbohydrates. Such a store of proteid matter would re-
present a sort of circulating proteid, but nevertheless for its final
metabolism might have to form an integral part of some living
tissue unit.

The Effects of Fatty and of Carbohydrate Pood. Unlike
those of proteid food, the effects of fats and carbohydrates cannot
be studied alone. When an animal is fed simply on non-nitro-
genous food, death soon takes place ; the food rapidly ceases to be
digested, and starvation ensues. We can therefore only study the
dietetic effects of these substances when they are taken together
with proteid material.

When a small quantity of fat is taken, in company with a fixed
moderate quantity of proteid material, the whole of the carbon of
tha food reappears in the egesta. No fat is stored up.; some even
of the previously existing fat of the body may be consumed. As
the fat of the meal is increased, a point is soon reached at which
carbon is retained in the body as fat. So also with starch or sugar;
when the quantity of this is small, there is no retention of carbon;
as soon however as it is increased beyond a certain limit, carbon is
stored up in the form of fat or, to a smaller extent, as glycogen.
Fats and carbohydrates therefore differ markedly from proteid food
in that they are not so distinctly provocative of metabolism. This
is exceedingly well shewn in the results of Lawes and Gilbert, for
in the pig previously mentioned 472 parts of fat were laid on for
every 100 parts of fat taken as such in the food (which consisting
of barley-meal, &c. contained a very small amount of actual fat),
while of every 100 parts of the total dry non-nitrogenous food
including fat, starch, cellulose, &c. no less than 21 '2 parts were
retained in the body in the form of fat. No clearer proof
than this could be afforded that fat is formed in the body out of
something which is not fat.

As one might imagine, the presence of fat or carbohydrates in
the food is found to decrease the amount of proteid metabolism

454 FATTY AND CARBOHYDRATE FOOD. [Boon 11.

necessary to establish nitrogenous equilibrium. For instance, with
a diet of 800 grins, meat and 150 grins, fat, the nitrogen in the
egesta became equal to that in the ingesta in a dog, in whose case
1800 grms.. meat had to be given to produce the same result
in the absence of fats or carbohydrates.

On the other hand, it was found, that with a fixed quantity of
fatty or carbohydrate food, an increase of the accompanying proteid
led not to a storing up of the surplus carbon contained in the extra
quantity of proteid, but to an increase in the consumption of
carbon. Proteid food increases not only proteid but also non-
nitrogenous metabolism. This explains how an excess of proteid
food may, by the increase of metabolism, actually reduce the fat of
the body.

There can be no doubt then that both a proteid diet and a
carbohydrate diet may give rise to the formation of fat within the
body. And the question which we have already (p. 427) partly
discussed comes again before us, In what way is this fat so
formed ? Is the sugar, arising during digestion from the carbo-
hydrate, converted by a series of fermentative changes into fat ? Or
is the sugar directly consumed by the tissues in oxidative changes,
by which means the fatty derivatives of the metabolized proteids
are sheltered from oxidation and stored up as fat ? This is a vexed
question which has been hotly debated. Many observers hold
strongly to the latter view, and hence contend that all fattening
food must contain a supply of proteids adequate to provide, by
their decomposition, the carbon of the fat which it is desired to lay
up. The balance of evidence, however, seems to be in favour of
the view that carbohydrates may be, in some way, directly converted
into fat and that therefore fattening foods need not necessarily
contain any such definite proportion of proteids.

We have at present no exact information concerning the
nutritive differences between fats and carbohydrates, beyond the
fact that in the final combustion of the two, while carbohydrates
require sufficient oxygen to combine with their carbon only, there
being already sufficient oxygen in the carbohydrate itself to form
water with the hydrogen present, fats require in addition oxygen
to burn off some of their hydrogen. Hence in herbivora a larger
portion of the oxygen consumed reappears in the carbonic acid of
the egesta, than in carnivora, where more of it leaves the body as
formed water : the proportions of the oxygen in the carbonic acid
expired to the oxygen consumed being on an average 90 p. c. in
the former and 60 p. c. in the latter. When a herbivorous animal
starves, it feeds on its own fat, and under these circumstances the
oxygen proportion in the expired carbonic acid falls to the car-
nivorous standard. The carbohydrates are notably more digestible
than the fats, but on the other hand the fats contain more potential
energy in a given weight. As to the dietetic or rather metabolic
difference between starch and sugar, we know nothing very definite ;

CHAP, v.] NUTRITION. 455

it has been thought however that cane-sugar is rather more
fattening than starch.

The Effects of Gelatine Food. It is a matter of common
experience that gelatine will not supply the place of proteids as a
constituent of food. Animals fed on gelatine together with fat or
carbohydrates die very much in the same way as when they are fed
on non-nitrogenous material alone. Nevertheless it would appear,
as might be expected, that the presence of gelatine in food is not
without effect. Thus nitrogenous equilibrium is established at a
lower level of real proteid food when gelatine is added. In a dog,
moreover, fed on a diet of gelatine and fat the excess of nitrogen
in the excreta over that in the ingesta is less, than when the same
dog is fed on a diet of fat alone ; that is to say, the gelatine has
sheltered from metabolism some proteid constituents of the body ;
and the consumption of fat also seems to be lessened by the presence
of gelatine. These facts become intelligible if we suppose that
gelatine is rapidly split up into a urea and a fat moiety, in the
same way that we have seen a certain quantity of proteid material
to be. It is this direct destructive metabolism of proteid matter
which gelatine can take up ; it seems however unable to imitate
the other function of proteid matter, and to take part in the
formation of living protoplasm. What is the cause of this differ-
ence, we cannot at present say.

The Effects of Salts as Food. All food contains, besides the
potential substances which we have just studied, certain saline
matters, organic and inorganic, having in themselves little or no
latent energy, but yet either absolutely necessary or highly bene-
ficial to the body. These must have important functions in
directing the metabolism of the body : the striking distribution of
them in the tissues, the preponderance of sodium and chlorides in
blood-serum and of potassium and phosphates in the red corpuscles
for instance, must have some meaning ; but at present we are in
the dark concerning it. The element phosphorus seems no less
important from a biological point of view than carbon or nitrogen.
It is as absolutely essential for the growth of a lowly being like
Penicillium as for man himself. We find it probably playing an
important part as the conspicuous constituent of lecithin, we find
it peculiarly associated with the proteids ; but we cannot explain its
rdle. The element sulphur, again, is only second to phosphorus, and
we find it as a constituent of nearly all proteids; but we cannot
tell what exactly would happen to the economy if all the sulphur
of the food were withdrawn. We know that the various saline
matters are essential to health, that when they are not present in
proper proportions, nutrition is affected, as is shewn by certain
forms of scurvy; we are also aware that the properties and
reactions of various proteid substances are closely dependent on the
presence of certain salts ; but beyond this we know very little.

456 GELATINE AS FOOD. [Boos n.

Lastly, water has an effect on metabolism, as shewn by the fact
that when the water of a diet is increased, the urea is increased to
an extent beyond that which can be explained by the increase of
fluid increasing the facilities of mere excretion.

SEC. 4. THE ENERGY OF THE BODY.

Broadly speaking, the animal body is a machine for converting
potential into actual energy. The potential energy is supplied by
food ; this the metabolism of the body converts into the actual
energy of heat and mechanical labour. We have in the present
section to study what is known of the laws of this conversion, and
of the distribution of the energy set free.

The Income of Energy.

Neglecting all subsidiary and unimportant sources of energy,
we may say that the income of animal energy consists in the
oxidation of food into its waste products, viz. the oxidation of
proteids, fats and carbohydrates into urea, carbonic acid and water.
A principle laid down by the chemist teaches that the potential
energy of any body, considered in relation to any chemical change
in it, is the same when the final result is the same, whether that
result be gained at one leap or by a series of "steps; that, for
instance, the energy set free by the oxidation of 1 grm. of fat into
carbonic acid and water is the same, whatever the changes forwards
or backwards which the fat undergoes before it finally reaches the
stage of carbonic acid and water ; and similarly, that the energy
available for the body in 1 grm. of dry proteid is the energy given
out by the complete combustion of that 1 grm., less the energy
given out by the complete combustion of that quantity of urea to
which the 1 grm. of proteid gives rise in the body. Taking this as

458 THE EXPENDITURE OF ENERGY. [BOOK ir.

our guide we may easily calculate the total energy of any diet. The
following determinations, expressed both in gramme-degree (centri-
grade) units of heat, and kilogramme-metre units of work, may
serve as data.

The direct oxidation of the gives lisa to

following, dried at 100° C. gram.-deg. kilo.-met.

1 grm. Beef-fat 9069 3841

1 grm. Butter 7264 3077

1 grm. Arrowroot 3912 1657

1 grm. Beef-muscle purified with ether 5103 2161

1 grm. Urea 2206 934

Supposing that all the nitrogen of proteid food goes out as
urea, 1 grm. of dry proteid, such as dried beef-muscle, would give
rise to about J grm. of urea ; hence

gram.-deg. kilo.-met.
1 grm. Proteid 5103 2161

less
j grm. Urea 735 311

would give as
Available energy of Proteid "4368 1850

In a normal diet, such as Ranke's, p. 446, would be found :

gram.-deg. kilo.-met.

100 grm. Proteid 436800 185000

100 grm. Fat 906900 384100

240 grm. Starch 938880 397680

Total Income 2281580 966780

or, in round numbers, one million kilogramme-metres,

The Expenditure.

There are only two ways in which energy is set free from the
body: mechanical labour and heat. The body loses energy in
producing muscular work, as in locomotion, in all kinds of labour,
in the movements of the air, in respiration and speech, and, though
to a hardly recognizable extent, in the movements of the air or
contiguous bodies by the pulsations of the vascular system. The
body loses energy in the form of heat by conduction and radiation,
by respiration and perspiration, and by the warming of the urine
and faeces. All the internal work of the body, all the mechanical
labour of the internal muscular mechanisms with their accompany-
ing friction, all the molecular labour of the nervous and other
tissues, is converted into heat before it leaves the body. The

CHAP, v.] NUTRITION. 459

most intense mental action, unaccompanied by any muscular mani-
festations, the most energetic action of the heart or of the bowels,
with the slight exceptions mentioned above, the busiest activity of
the secreting or metabolic tissues, all these end simply in aug-
menting the expenditure of income in the form of heat.

A normal daily expenditure in the way of mechanical labour
can be easily determined by observation. Whether the work take
on the form of walking, or of driving a machine, or of any kind
of muscular toil, a good day's work may be put down at about
150,000 kilogramme-metres. The normal daily expenditure in
the way of heat cannot be so readily determined. Direct calori-
metric observations are attended with this difficulty, that the body
while within the calorimeter is placed in abnormal conditions,
which produce an abnormal metabolism. Hence results arrived at
by this method are of little value unless they be accompanied by a
comparison of the egesta and ingesta, so that the rate and nature
of the metabolism going on may be known. Many attempts have
been made to calculate the amount in an indirect manner. As
trustworthy as any is the plan of simply subtracting the normal
daily mechanical expenditure from the normal daily income. Thus,
150,000 k.-m. subtracted from one million k.-m. gives 850,000 k.-m.
as the daily expenditure in the form of heat ; i. e. between one-fifth
and one-sixth of the total income is expended as mechanical labour,
the remaining four-fifths or five-sixths leaving the body in the
form of heat.

The Sources of Muscular Energy. Liebig, satisfied with
having proved that the animal body was constructive as far as the
formation of fat was concerned, still held to the distinction between
nitrogenous or plastic and non-nitrogenous or respiratory food.
Put broadly, his view was that all the nitrogenous food went to
build up the proteid tissues, the muscular flesh, and other forms
of protoplasm, and that the nitrogenous egesta arose solely from
the functional metabolism of these tissues, while the non-
nitrogenous food was used with equal exclusiveness for respiratory
or calorific purposes, being either directly oxidized in the blood or,
if present in excess, stored up as fatty tissue. According to him
the two classes of income corresponded exactly to the two forms of
expenditure. "We have already urged several objections against
this view. We have seen that in the blood itself very little
oxidation takes place, that it is the active tissue, and not the
passive blood-plasma, which is the seat of oxidation. We have
further seen that proteid food may undoubtedly be in Liebig's
sense respiratory, and incidentally give rise to the storing-up of
fat. One division of Liebig's view is thereby overthrown. We
have now to inquire whether the other division holds good, whether
muscle or other protoplasm is fed exclusively on the proteid
material of food, and whether muscular energy comes exclusively

460 THE EXPENDITURE OF ENERGY. [BOOK n.

from the metabolism of the proteid constituents of muscle. We
have already seen (p. 70) that when the muscle itself is examined, we
find no proof of nitrogenous waste, but, on the other hand, clear
evidence of the production of non-nitrogenous bodies, such as
carbonic acid. And when we ask the question, Does muscular
exercise increase the urea given off by the body as a whole ? for
this, according to Liebig's theory, it certainly ought to do, the
evidence we can obtain, though somewhat conflicting, gives on the
whole a decidedly negative answer. Exercise, even severe, appears
not necessarily to increase the urea of the urine.

More than this, the experience of Fick and Wislicenus lands us
in an absurdity if we suppose the whole energy of muscular work
to arise from proteid metabolism. These observers performed a
certain amount of work (an ascent of the Faulhorn) on a non-
nitrogenous diet, and estimated the amount of urea passed during
the period. Assuming the urea to represent the oxidation of so
much proteid matter, which oxidation represented in turn so much
energy set free, they found that whereas the actual work done
amounted to 129026 and 148-656 kilogram. -kilometres, for each
respectively, the total energy available from proteid metabolism
during the period was in the case of the first 68'69, and of the
second 68'376 kilogram.-ldlometres. That is to say, the energy
set free by the proteid metabolism of the muscles engaged
in the work was at the most far less than that necessary to
accomplish the work actually done, besides having to provide
for the movements of respiration and circulation. Their muscular
energy therefore must have had other sources than proteid meta-
bolism.

That on the contrary the production of carbonic acid is at once
and largely increased by muscular exercise is beyond all doubt,
One hour's hard labour will increase fivefold the quantity of
carbonic acid given off within the hour. And in an experiment
directed to this point it was found that a man in 24 hours con-
sumed 954 grms. oxygen and produced 1284 gims. carbonic acid
when doing work, as against 708 grms. oxygen consumed and
911 grms. carbonic acid produced when remaining at rest, the
quantity of urea secreted being in the first case 37 grms., in the
second 37' 2 grms.

It is evident that the conclusions arrived at by the statistical
method entirely corroborate those gained by an examination of
muscle itself, viz. that during muscular contraction an explosive
decomposition takes place, the non-nitrogenous products of which
alone escape from the muscle and from the body, any nitrogenous
products which result being retained within the muscle. We must
therefore reject the second as well as the first division of Liebig's
view; not only is the muscle not fed exclusively on proteid
material, but also its energy does not arise from an exclusively
proteid metabolism.

CHAP, v.] NUTRITION. 461

The Sources and Distribution of Heat. We have already
seen that the conception of the non-nitrogenous portions of food
being solely calorifacient or respiratory proves to be unfounded
when we attempt to trace the history of the food on its way
through the body. The same view is still more strikingly shewn
to be inadequate when we study the manner in which the heat
of the body is produced. We may indeed at once affirm that
the heat of the body is generated by the oxidation, not of any
particular substances, but of the tissues at large. Wherever
metabolism of protoplasm is going on, heat is being set free. In
growth and in repair, in the deposition of new material, in the
transformation of lifeless pabulum into living tissue, in the con-
structive metabolism of the body, heat may be undoubtedly to
a certain extent absorbed and rendered latent: the energy of the
construction may be, in part at least, supplied by the heat present.
But all this, and more than this, viz. the heat present in a potential
form in the substances themselves so built up into the tissue, is lost
to the tissue during its destructive metabolism; so that the whole
metabolism, the whole cycle of changes from the lifeless pabulum
through the living tissue back to the lifeless products of vital
action, is eminently a source of heat.

Of all the tissues of the body the muscles not only from their
bulk, forming as they do so large a portion of the whole frame, but
also from the characters of their metabolism, must be regarded as
the chief sources of heat.

In treating (p. 70) of the thermal changes in muscle we have
seen that in the total energy expended in a muscular contraction,
the ratio of that which appears as heat to that which appears
as external work is variable. If we take what is somewhat below
the mean result and assume that the energy involved in the work
done in a muscular contraction is about one-tenth of the total
energy expended, the rest going out as heat, then, upon the
calculation that the total external work of the body is about
one-fifth of the total energy set free in the body, it is clear that the
heat given out by the muscles, even at those times only when they
are contracting, must form a very large part of the total heat
given out by the body. But the skeletal muscles, though
frequently, are not continually contracting ; they have periods,
at times long periods, of rest ; and during these periods of rest,
metabolism, of a subdued kind it is true, but still a metabolism
involving an expenditure of energy, is going on. This quiescent
metabolism must also give rise to a certain amount of heat ; and if
we add this amount, which in the present state of our knowledge
we cannot exactly gauge, to that given out during the movements
of the body, it is very clear, even in the absence of exact data, that
the metabolism of the muscles must supply a very large proportion
of the total heat of the body. They are par excellence the thermo-
genic tissues.

462 ANIMAL HEAT. [BOOK n.

Next to the muscles in importance come the various secreting
glands. In these the protoplasm, at the periods of secretion at all
events, is in a state of metabolic activity, which activity as else-
where must give rise to heat. In the case of the salivary gland of
the dog the temperature of the saliva secreted during stimulation
of the chorda has been found to be as much as 1° or 1'5° higher
than that of the blood in the carotid artery at the same time, and
in all probability the investigation of other' secreting glands would
lead to similar results. Of all these various glands, the liver
deserves special attention on account of its size and large supply
of blood, and because it appears to be continually at work. We
find indeed that the blood in the hepatic veins is the warmest
in the body. Thus in the dog a temperature of 4073° C. has been
observed in the hepatic vein, while that of the vena cava inferior
was 38-35° to 39'58, and that of the right heart 377. The fact
that the blood of the hepatic vein is warmer than that of either
the portal vein or the aorta, shews that the increased temperature
is not due simply to the liver being far removed from the surface of
the body.

The brain too may be regarded as a source of heat, since its
temperature is higher than that of the arterial blood with which it
is supplied; though from the smaller quantity of blood passing
through its vessels it cannot in this respect compare with either the
liver or the muscles as a source of heat to the body.

The blood itself cannot be regarded as a source of any
considerable amount of heat, since, as we have so frequently
urged, the oxidations or other metabolic changes taking place
in it are comparatively slight. The heat evolved by the in-
different tissues such as bone, cartilage and connective tissue
may be passed over as insignificant ; and we cannot even regard
the adipose tissue as a seat of the production of heat, since the fat
of the fat-cells is in all probability not oxidized in situ but simply
carried away from its place of storage to the tissue which stands in
need of it, and it is in the tissue that it undergoes the metabolism
by which its latent energy is set free. Some amount of heat is also
produced by the changes which the food undergoes in the ali-
mentary canal before it really enters the body.

Hence taking a survey of the whole body we may conclude
that since metabolism is going on to a greater or less extent every-
where, heat is everywhere being generated; but that, looked at
from a quantitative point of view, the muscles and the glandular
organs must be regarded as the main sources of the heat of the
body, the muscles being in all probability the more important of
the two.

But heat, while being thus continually produced, is as con-
tinually being lost, by the skin, the lungs, the urine and the faeces.
The blood passing from one part of the body to the other, and
carrying warmth from the tissues where heat is being rapidly

CIIAP. v.] NUTRITION. 463

generated, to the tissues or organs where heat is being lost by
radiation, conduction or evaporation, tends to equalize the tempera-
ture of the various parts; and thus maintains a "constant bodily
temperature."

When the production of heat is not great as compared with the
loss there is no great accumulation of heat within the body, the
temperature of which consequently is but slightly raised above
that of surrounding objects. Thus the temperature of the frog, for
instance, is rarely more than '04° to '05° C. above that of the atmo-
sphere, though in the breeding season the difference may amount
to 1°. Such animals, and they comprise all classes except birds
and mammals, are spoken of as cold-blooded. Exceptions among
them are not uncommon. Some fish, such as the tunny, are warmer
than the water in which they live, and in a species of Python (P.
bii'ittatus) a difference of as much as 12° C. has been observed.
Hliber found that in a beehive the temperature rose at times as
much as to 40° C. In the so-called warm-blooded animals, birds
and mammals, the loss and production of heat are so balanced
that the temperature of the body remains constant at, in round
numbers, 35° or 40° C., whatever be the temperature of the air.
The temperature of man is about 37'6° C. ; in some birds it is as
high as 44° C. (Hirundo) and in the wolf it is said to be as low as
35-24° C.

This temperature is with slight variations maintained through-
out life. After death the generation of heat rapidly diminishes,
and the body speedily becomes cold; but for some short time
immediately following upon systemic death, a rise of temperature
may be observed, due to the fact that, while the metabolism of the
tissues is still going on, the loss of heat is somewhat checked by
the cessation of the circulation. The onset of pronounced rigor
mortis causes a marked accession of heat, and when occurring after
certain diseases may give rise to a very considerable elevation of
temperature.

This mean bodily temperature of warm-blooded animals is,
during health, maintained, with slight variations of which we shall
presently speak, within a very narrow margin, a rise or indeed a
fall of much more than a degree above or below the limit given
above being indicative of some failure in the organism, or of some
unusual influence being at work. It is evident, therefore, that the
mechanisms which co-ordinate the loss with the production of heat
must be exceedingly sensitive. It is obvious, moreover, that these
mechanisms may act when the bodily temperature is tending to
rise, by either checking the production or by augmenting the loss
of heat ; and when the bodily temperature is tending to fall, by
either increasing the production or by diminishing the loss of heat.
As the regulation of temperature by variations in the loss of heat
is better known than regulation by variations in production, it will
be best to consider this first.

464 ANIMAL HEAT. [BOOK 11.

Regulation by variations in loss. Heat is lost to the body
by the warming of the faeces and of the urine, by the warming of
the expired air, by the evaporation of the water of respiration, by
conduction and radiation from the skin, and by the evaporation
of the water of perspiration. It has been calculated that the
relative amounts of the loss by these several channels are as
follows : In warming the faeces and urine about 3, or according to
others 6 per cent. By respiration about 20, or according to others
about 9 only per cent., leaving 77, or alternatively 85, per cent, for
conduction and radiation and evaporation by the skin.

The two chief means of loss then, which are at all susceptible
of any great amount of variation, and which can be used to regu-
late the temperature of the body, are the skin and the lungs.

The more air passes in and out of the lungs in a given time,
the greater will be the loss in warming the expired air, and in
evaporating the water of respiration. And in such animals as the
dog*, which do not perspire freely by the skin, respiration is a most
important means of regulating the., temperature. The changes
which give rise to this loss take place before the inspired air
reaches the pulmonary alveoli ; both the warming and the evapo-
ration being effected in the nasal and pharyngeal, and to some
extent in the bronchial passages. Some observers have maintained
that the left side of the heart is warmer than the right, and hence
argued that chemical changes leading to a considerable develop-
ment of heat take place in the pulmonary capillaries. It would
appear however that the right ventricle, owing to its lying
nearer to the liver, the high temperature of which has already
been mentioned, is in reality rather hotter than the left. And
indeed we have no satisfactory evidence of any large amount of
heat being produced by any pulmonary metabolism.

The great regulator however is undoubtedly the skin. The
more blood passes through the skin the greater will be the loss of
heat by conduction, radiation, and evaporation. Hence, any action
of the vaso-motor mechanism which, by causing dilation of the
cutaneous vascular areas, leads to a larger flow of blood through
the skin, will tend to cool the body ; and conversely, any vaso-
motor action which, by constricting the cutaneous vascular areas,
or by dilating the splanchnic vascular areas, causes a smaller flow
through the skin, and a larger flow of blood through the abdominal
viscera, will tend to heat the body. Besides this the special
nerves of perspiration will act directly as regulators of temperature,
increasing the loss of heat when they promote, and lessening the
loss when they cease to promote, the secretion of the skin. The
working of this heat-regulating mechanism is well seen in the case
of exercise. Since every muscular contraction gives rise to heat,
exercise must increase for the time being the production of heat ;
yet the bodily temperature rarely rises so much as a degree centi-
grade, if at all. By the exercise the respiration is quickened, and

CHAP, v.] NUTRITION. 465

the loss of heat by the lungs increased. The circulation of blood
is also quickened, and the cutaneous vascular areas becoming
dilated, a larger amount of blood passes through the skin. Added
to this, the skin perspires freely. Thus a large amount of heat is
lost to the body, sufficient to neutralise the addition caused by the
muscular contraction, the increase which the more rapid flow of
blood through the abdominal organs might tend to bring about
being more than sufficiently counteracted by their smaller supply
for the time. The sense of warmth which is felt during exercise
in consequence of the flushing of the skin, is in itself a token that
a regulative cooling is being carried on. In a similar way the ap-
plication of external cold or heat, either partially or completely,
defeats its own ends. Under the influence of external" cold the
cutaneous vessels are constricted, and the splanchnic vascular
areas dilated, so that the blood is withdrawn from the colder and
cooling regions to the hotter and heat-producing organs. This
vascular change may be used to explain the fact that stripping
naked in a cold atmosphere often gives rise to a distinct increase in
the mean temperature of the blood, as indicated by a thermometer
placed in the mouth, though possibly the effect may be partly
due to an actual increase of the production of heat. Under the
influence of external warmth, on the other hand, the cutaneous
vessels are dilated, a rapid discharge of heat takes place ; and if
the circumstances be such that the body can perspire freely, and
the perspiration be readily evaporated, the temperature of the
body may remain very near to the normal, even in an excessively
hot atmosphere. Thus, more than a century ago, Drs Fordyce and
Blagden were able to remain with impunity in a chamber heated
even. to 127° (260° Fahr.), and with ease in one so hot, that it
became painful for them to touch the metal buttons of their
clothing. It is unnecessary to give any more examples of this
regulation of temperature by variations in the loss of heat ; they
all readily explain themselves.

Regulation by variations in production. It is not however
solely by variations in the loss of heat that the constant tempera-
ture of the warm-blooded animal is maintained Variations in the
amount of heat actually generated in the body constitute an
important factor not only in the maintenance of the normal
temperature, but also probably in the production of the abnormally
high or low temperatures of various diseases. Many considerations
have long led physiologists to suspect the existence of a nervous
mechanism by which afferent impulses arising in the skin or
elsewhere might through the central nervous system originate
efferent impulses whose effect would be to increase or diminish the
metabolism of the muscles or other organs and thus to increase or
diminish the amount of heat generated for the time being in the
body. The existence in fact of a metabolic or thermogenic nervous
mechanism, comparable in many respects to the vaso-motor
p. 30

466 ANIMAL HEAT. [BOOK n.

mechanism or to the various secreting nervous mechanisms, seems
in itself d priori probable. And we have experimental evidence
that such a mechanism does really exist.

The warm-blooded animal is distinguished from the cold-blooded
animal by the fact that when it is exposed to cold or heat, it does not
like the latter become colder or hotter, as the case may be, but,
within certain limits, maintains its normal temperature. If the
maintenance of the temperature of the warm-blooded animal during
exposure to cold is assisted by an increased production of heat and
is not due simply to a diminished loss, we ought to find evidence of
an increased metabolism during that exposure. We ought to find
under these circumstances an increased production of carbonic
acid, and an increased consumption of oxygen, since it is to these
products, rather than to the nitrogenous factors, on the peculiar-
ities of which as uncertain signs of metabolism we have already
insisted, we must look for indications of the rise or fall of metabolic
activity. Of these two, the production of carbonic acid and the
consumption of oxygen, the latter is the more important and
trustworthy measure of metabolism, especially when observations
are made for short periods only at a time ; for as we have seen in
treating of respiration the exit of carbonic acid is more closely
dependent on the action of the respiratory mechanism than is the
income of oxygen, and carbonic acid can be retained in loose
combination and so temporarily stored up by various constituents
of the body.

Taking then the consumption of oxygen, and though with less
confidence the production of carbonic acid, as a measure of metabolic
activity and so of heat-production, Pfliiger, and his pupils, as well as
other observers, have shewn that a marked contrast in this respect
exists between cold-blooded and warm-blooded animals exposed to
changes of temperature. In the cold-blooded animal, cold dimin-
ishes and heat increases the metabolic activity of the body ; as the
temperature to which the animal is subjected rises or falls, so the
consumption of oxygen and production of carbonic acid is increased
or lessened. The body of a cold-blooded animal behaves in this
respect like a mixture of dead substances in a chemist's retort :
heat promotes and cold retards chemical action in both cases.
Very different is the behaviour of a warm-blooded animal. In
this case, within a lower and a higher limit, cold increases and heat
diminishes the bodily metabolism, as shewn by the increased or
diminished consumption of oxygen and production of carbonic
acid as the temperature falls or rises. In these animals there is
obviously a mechanism of some kind, counteracting and indeed
overcoming those more direct effects, which alone obtain in cold-
blooded animals. And that this mechanism is of a nervous nature,
is indicated by the following facts.

When an animal is poisoned by urari, the temperature falls
and the metabolism, measured by the consumption of oxygen and

CHAP, v.] NUTRITION. 467

the production of carbonic acid, sinks also ; and that the latter is
the cause not the effect of the former is shewn by the fact that
the metabolism continues to fall though loss of heat be prevented
by surrounding the animal with wrappings of cotton wool. In
such a urarized animal, exposure to higher temperatures augments
and exposure to lower temperatures diminishes metabolism ; the
urarized warm-blooded animal in fact behaves like a cold-blooded
animal. Similar, but perhaps not such striking results are gained
by division of the medulla oblongata. After this operation the
temperature of the body sinks, and the fall, though partly due to
increased loss of heat by the skin, caused by the dilated condition of
the cutaneous vessels, is also accompanied by diminished metabo-
lism and is therefore in part due to diminished production of heat.
And when an animal is in this condition, exposure to higher tem-
peratures increases and exposure to lower temperatures diminishes
the bodily metabolism. We can best explain these results by
supposing that, under normal conditions, the muscles, which as we
have seen contribute so largely to the total heat of the body, are
placed, by means of their motor nerves and the central nervous
system, in some special connection with the skin, so that a lowering
of the temperature of the skin leads to an increase, while a heigh-
tening of the temperature of the skin leads to a decrease, of the
muscular metabolism. Further, though the matter has not yet
been fully worked out, the centre of this thermotaxic reflex mecha-
nism appears to be placed above the medulla oblongata, possibly in
the region of the pons varolii. When urari is given, the reflex
chain is broken at its muscular end ; when the spinal cord is divided
the break is nearer the centre. Whether we should conclude that
the working of this reflex mechanism is of such a kind that cold to
the skin excites the centre to a heat-producing activity, or of such
a kind that warmth to the skin inhibits a previously existing auto-
matic activity of the centre, may be left for the present undeter-
mined.

We may add that the muscular metabolism which thus helps
to regulate temperature need not involve visible muscular con-
tractions, though the heat given out by a muscle will be temporarily
increased at every contraction; and that the regulative nervous
mechanism may apparently be overborne by an exposure to too
great heat or cold. When for instance the cold to which the
animal is exposed becomes excessive, the reaction of the thermo-
taxic nervous system is powerless against the depressing direct
effects, and the metabolism, together with the temperature, sinks.

Lastly, we have increasing evidence that the phenomena of
fever are due, not merely to a derangement of the regulation by
loss, though this may be a factor, but also, and indeed chiefly,
to an increased production of heat ; for in fever, the production of
carbonic acid, and the consumption of oxygen, that is to say, the
metabolic changes of the tissues, are increased.

30—2

468 ANIMAL HEAT. [BOOK n.

We may regard it then as established that such a thermotaxic
nervous mechanism does exist, and the importance of such a
mechanism in explaining not only the maintenance of the nor-
mal temperature but the abnormal variations of temperature in
disease can hardly be exaggerated. Much however still requires
to be learnt before we can speak with full confidence as to its
exact nature, or expound with certainty the details of its work.

By regulative mechanisms of this kind the temperature of the
warm-blooded animal is maintained within very narrow limits. In
ordinary health the temperature of man varies between 36° and
38°, the narrower limits being 36'25° and 37'5°, when the thermo-
meter is placed in the axilla. In th?. mouth the reading of the
thermometer is somewhat ('25° to 1*5°) higher; in the rectum it is
still higher (about *9°) than in the mouth. The temperature of
infants and children is slightly higher and much more susceptible
of variation than that of adults, and after 40 years of age the
average maximum temperature (of health) is somewhat lower than
before that epoch. A diurnal variation, independent of food or
other circumstances, has been observed, the maximum ranging
from 9 A.M. to 6 P.M. and the minimum from 1 1 P.M. to 3 A.M.
Meals cause sometimes a slight elevation, sometimes a slight
depression, the direction of the influence depending on the nature
of the food : alcohol seems always to produce a fall. Exercise and
variations of external temperature, within ordinary limits, cause
very slight change, on account of the compensating influences
which have been discussed above. The rise from even active
exercise does not amount to 1° C. ; when labour is carried to
exhaustion a depression of temperature may be observed. In
travelling from very cold to very hot regions a variation of less
than a degree occurs, and the temperature of tropical inhabitants
is practically the same as of those dwelling in arctic regions.

When external cold or warmth passes certain limits, or when
during the application of these agents the regulative mechanisms
are interfered with, the temperature of the body may be lowered
or raised until death ensues. When the cold or warmth applied is
not very great, as in cold and warm baths, it has been noticed that
the temperature is more easily raised by warmth than depressed
by cold. Death ensues from extreme cold by a depression of the
activities of all the tissues, more especially of the nervous; as-
phyxia is produced in animals when the fall of temperature is
rapid. Puppies can be recovered after the temperature in the
rectum has fallen to about 4° or 5° C., and hybernating mammals
may be cooled with impunity down to nearly freezing point.
When external warmth is brought to bear on a mammal in such a
way as to cause a rise of temperature in the body, death ensues
when an elevation of about 6° or 7° C. above the normal is reached.
The exact cause of the death has not been as yet sufficiently ex-

CHAP, v.] NUTRITION. 469

plained. It cannot be due, as has been suggested, to the muscles
entering into rigor caloris, for the animals frequently succumb
before this takes place. A high temperature makes the heart
irregular, and finally stops its beat, but probably other tissues are
also injuriously affected, so that death cannot be attributed to the
stoppage of the heart alone.

One of the most marked phenomena of starvation is the fall of
temperature, which becomes very rapid during the last days of life.
Indeed the low temperature of the body is a powerful factor in
bringing about death, for life may be much prolonged by wrapping
a starving animal in some bad conductor so as to economise the
bodily heat.

SEC. 5. THE INFLUENCE OF THE NEK VOUS SYSTEM
ON NUTRITION.

In the preceding sections we had more than once to refer to
the possibility of the nervous system having the power of directly
affecting the metabolic actions of the body, apart from any
irritable, contractile, or secretory manifestations. Thus the phe-
nomena of diabetes cannot, at present at all events, be satisfactorily
explained as a purely vaso-motor effect, and the production of heat
is, as we have seen, under the special guidance of the nervous
system. In the case of the salivary glands we meet with the
striking fact that when all the nerves of a gland have been divided
the gland enters into a peculiar condition during which it pours
forth a continuous, so-called 'paralytic' secretion, while ultimately
the tissue of the gland degenerates. This result differs perhaps
from the wasting of a muscle which follows upon severance of its
motor nerve, since this may be, partly at all events, explained by
the fact that the muscle is no longer functional ; and indeed, if the
muscle is rendered functional, if it is directly stimulated for
instance from time to time with a galvanic current, the atrophy
may be for a while at least postponed, though as we have seen
(p. 92) the postponement is probably not indefinite. But the
salivary gland at all events in the case in question is functional, it
does go on secreting; nevertheless in the absence of its usual

CHAP, v.] NUTRITION. 471

nervous guidance its nutrition becomes profoundly affected. We
are not justified in saying that in this case the nutrition of the
salivary cell is directly dependent on the nervous system, because
all biological studies teach us that the growth, repair, and repro-
duction of protoplasm may go on quite independently of any
nervous system, and the nutrition of the nervous system itself
cannot be dependent on the action of that system on itself; but
we may go so far as to infer that the nutrition of the salivary cell
is in the complex animal body so arranged to meet the constantly
recurring influences brought to bear on it by the nervous system,
that, when those influences are permanently withdrawn, it is thrown
out of equilibrium ; its molecular processes, so to speak, run loose,
since the bit has been removed from their mouths. And we might
expect that similar instances would be met with where nutrition
became abnormal after the removal of wonted nervous influences.
Such instances indeed are not uncommon. And there are many
pathological phenomena, inflammation itself to begin with, which
seem inexplicable, except when regarded as the result of nervous
action. As examples we might mention the rapid and peculiar
degeneration of and loss of contractility in the skeletal muscles in
certain affections of the spinal cord, the changes in the muscles
being more rapid and profound than in the nerves; the pheno-
mena of bed-sores, especially the so-called acute bed-sores of
cerebral apoplexy ; some at least of the cases of vesical affections
attendant on spinal or cerebral diseases or injuries ; the more
rapid atrophy and loss of contractility in muscles which follow
upon contusions of nerves as compared with the effects of simple
section of nerves; the occurrence of certain eruptions, such as
lichen, zona, ecthyma, &c., in various spinal or cerebral diseases,
frequently accompanied, as in maladies affecting the posterior
cornua, with intermittent pains ; and indeed the general phe-
nomena, and especially the topography of the eruption, of a
large number of cutaneous diseases. In all these cases, however,
there are many attendant circumstances to be considered before
we can feel justified in speaking of any direct influence of the
nervous system on nutrition, of any specific action of what have
been called 'trophic' nerves. Perhaps the instance which has
been best worked out is the connection of the nutrition of the eye
and face with the fifth or trigeminal nerve. When in a rabbit the
trigeminus is divided in the skull there is loss of sensation in those
parts of the face of which it is the sensory nerve. Very soon,
within twenty-four hours, the cornea becomes cloudy ; and this is
the precursor of an inflammation which may involve the whole eye
and end in its total disorganization. At the same time the nasal
chambers of the same side are inflamed, and very frequently ulcers
make their appearance on the lips and gums. Seeing how delicate
a structure the eye is, and how carefully it is protected by the

472 TROPHIC NERVES. [BOOK n.

mechanisms of the eyelids and tears, it seems reasonable to
suppose that the inflammation in question might simply be the
result of the irritation caused by dust and contact with foreign
bodies, to which the eye, no longer guided and protected by
sensations, these being destroyed by the section of the nerve,
became subject. In the same way the ulcers on the lips and
gums might be explained as injuries inflicted by the teeth on
those structures in their insensitive condition. And some ob-
servers maintain that the inflammation of the eye may be greatly
lessened or altogether prevented if the organ be carefully covered
np and in all possible ways protected from the irritating influences
of foreign bodies. Other observers however have failed to prevent
the inflammation in spite of every care. This negative result is in
itself no strong argument, but the question cannot yet be con-
sidered as entirely cleared up.

In a mammal division of both vagi is followed by pneumonia
(inflammation of the lungs) ending in death. This has been ad-
duced as an instance of the trophic action on the pulmonary tissues
of certain fibres of the vagi ; but the real explanation seems to be
that, owing to a paralysis of the oesophagus and larynx caused by
section of the vagi, food accumulating in the pharynx passes into
the air-passages and so sets up the pneumonia. In birds death
follows, sometimes from pneumonia of a similar causation, but more
frequently from inanition on account of the food not being able to
enter the stomach. The immediate cause of death however appears
in many cases at all events, both in birds and mammals, to be a
paralysis of the heart, and the histological changes (acute fatty
degeneration) observable in the cardiac muscles are of such a
character as to suggest a trophic action of the vagus fibres on that
tissue.

Other instances of nerves manifesting even a doubtful trophic
action as the result of experimental interference are rare; yet there
seems to be no reason why the fifth nerve or the vagus should be
conspicuous in possessing trophic fibres. When the sciatic nerve of
the frog is divided, no nutritive alterations beyond those explicable
as the result of loss of function are observed ; and indeed the ma-
jority of the effects on growth and nutrition resulting from the
section of nerves, or from paralysis, can be referred to the absence
of the usual functional activity, accompanied in some cases with an
altered vascular supply. It must be remembered however that
functional activity is itself the result of metabolic and therefore
nutritional changes ; and in cases of inhibition, as for instance in
the action of the vagus on the heart, we seem to have illustrations
of a nerve producing metabolic changes leading not to the exercise
but to the arrest of functional activity.

Taking all things into consideration, we may venture to say
that the numerous phenomena of disease, joined to the facts men-

CHAP, v.] NUTRITION. 473

tioned above, turn the balance of evidence in favour of the view
that some more or less direct influence of the nervous system on
metabolic actions, and so on nutrition, will be established by future
inquiries.

SEC. 6. DIETETICS.

We may sum up the main results of the previous sections some-
what in the following way. Although the body consists, like the
food, of proteids, fats and carbohydrates, yet the conversion of the
one into the other is not direct. Assimilation does not proceed in
such a way that the proteids of the food all become the proteids of
the body, the fats of the food the fats of the body, and the starch
and sugar of the food the glycogen, dextrin, and sugar of the body.
We cannot even say that the non-nitrogenous food supplies alone
the non-nitrogenous parts of the body, and that the nitrogenous food
remains as the sole source of the nitrogenous tissues. We have
seen that under all circumstances a certain quantity of proteid
food is immediately metabolized, probably while still within the
alimentary canal, and that an excess of proteid food may lead to
the accumulation of bodily fat. On the other hand, we find that
a large proportion of the carbonic acid of the egesta comes from
the metabolism taking place in nitrogenous tissues, such as
muscle ; and we have had proof that the energy set free by mus-
cular contraction may be far greater than could be supplied by the
proteid food taken, and that therefore the non-nitrogenous factors of
the metabolism which set free the energy must have ultimately come
from non-nitrogenous food. We have abundant evidence that the
various food-stuffs become more or less metabolized, and their ele-
ments more or less rearranged and mixed, before they appear as
constituents of the bodily tissues.

CHAP, v.] NUTRITION 475

We have seen that the oxidations of the body are, as in the
case of muscle, of a peculiar character, and carried on by the tissues
themselves. While at present we should be hardly justified in
denying that any oxidations at all take place in the blood-plasma,
such as do occur must be slight in amonnt as compared with those
going on in the tissues. We might also say that one body only,
viz. lactic acid, presents itself as a substance likely to be directly
oxidised in the blood itself; and even with regard to this the evi-
dence is as much against as for any such direct oxidation taking
place. The great mass of the oxidation of the body is of an
indirect kind, determined by the activity of the several tissues.
The blood serves as an oxygen carrier for the tissues ; and it is not
itself the large combustion agent it was once thought to be. The
tendency of all recent inquiries is to shew that the body cannot be
compared, either as a whole, or in its parts, to a furnace for the
direct combustion of combustible food. On the contrary, we are
driven nearer and nearer to the conclusion that all food which has
become absorbed into the blood must become tissue before it be-
comes waste product, and only becomes waste product through a
metabolism of the tissue. When we say " become tissue" we must
leave it at present wholly undecided how far the constant meta-
bolism which this view demands affects the so-called structural
elements of the more highly organized tissues ; it is quite open
however, as we have already suggested, for us to imagine that in
muscle, for instance, there is a framework of more stable material,
giving to the muscular fibre its histological features, and under-
going a comparatively slight and slow metabolism, while the
energy given out by muscle is supplied at the expense of more
fluctuating molecules which fill up so to speak the interstices
of the more durable frame-work, and the metabolism of which
alone is large and rapid.

The characteristic feature of proteid food is that it increases the
oxidative, metabolic activity of the tissues, leading to a rapid con-
sumption, not only of itself, but of non-nitrogenous food as well.
Where therefore a rapid renewal of the tissues is sought for, an
excess of proteid food may be desirable. But it must be borne in
mind that by the very nature of its rapid metabolism, proteid food
must tend to load the body with the so-called extractives, i.e. with
nitrogenous crystalline bodies. How far these are of use to the
body, and what part they play, is at present unknown to us. That
they are of some use is suggested by the beneficial effects of the
extractum carnis when taken as food in conjunction with non-nitro-
genous material, though it is possible that the dietetic value of
this preparation may be due to the small amount of non-crystalline
extractives which it contains. That when in excess these nitro-
genous products may be highly injurious is indicated by the little
we know of the connection between the symptoms of gout and the

476 DIETETICS. [BOOK n.

presence of uric acid. A large meal of proteid material must tax
the system to the utmost in getting rid of or stowing away the
nitrogenous crystalline bodies arising through changes either in
the alimentary canal or in the liver.

One value of fats and carbohydrates lies in their being sources
of energy, more than three-fourths of the normal income of poten-
tial energy coming from them (p. 458); and, as we have seen, they
are ultimate sources of muscular energy as well as of heat. But
their great characteristic is that they do not, like proteid food, excite
the metabolic activity of the body. Hence, to a far greater extent
than is the case with proteid food, they can be retained and stored
up in the body with comparative ease. The digested elements of
fatty or carbohydrate food which go to form the protoplasm of
adipose tissue, become part and parcel of a substance which can
perform its metabolism without any explosive expenditure of
energy, and which therefore, instead of giving rise to bodies de-
manding immediate excretion from the system, can deposit its
metabolic products as apparently little, but as we have seen in
reality greatly, changed fat. In this way the non-nitrogenous
food of to-day is rendered .available for future and even far distant
wants.

In comparing fats with carbohydrates, we can only point to the
much greater potential energy of the former than of the latter,
weight for weight (see p. 458).

A diet may be chosen either for the simple maintenance of
health, or for the sake of muscular energy, or for fattening purposes.
For the first purpose there is, we may suppose, a normal diet ; and
in the case of man, instinct and experience have probably not erred
far in choosing some such proportions as those given on p. 446. If,
as we have urged, all food becomes tissue before it leaves the body
as waste product, the dominant principle of all nutrition, and the
ultimate tribunal of all questions of diet, must be the individual
character of the tissue, the idiosyncrasy of the body. The same
mysterious qualities which cause the same blood-plasma to become
here a muscle, and there a secreting cell, convert the same food into
the body of a man or of a sheep. All the simpler and more general
laws of metabolism are made subservient to more intricate and
special laws of protoplasmic construction. We can only speak of a
normal diet in the same way that we speak of the average intelli-
gence of man.

In seeking to supply such a normal diet out of ordinary
articles of food, we must bear in mind that the nutritive value
of any substance, estimated in terms of the potential energy of
the proteids, fats or carbohydrates it contains, must of course
be corrected by its digestibility. One gramme of cheese has, as
far as potential energy is concerned, an exceedingly high value ;
but the indigestibility of cheese brings its nutritive value to a

CHAP, v.] NUTRITION. 477

very low level. Here too the factor of idiosyncrasy makes itself
exceedingly felt.

In feeding for fattening purposes the comparatively cheap
carbohydrates are of course chiefly depended on. If the view
mentioned on p. 454 be correct, that the fat really stored up all
comes from proteid metabolism, an equivalent of this food-stuff
must always be given. If, as seems probable, this view is a too
hurried generalisation, there still remains the possibility that for
economical fattening, with the least waste, a certain proportion
between the nitrogenous and non-nitrogenous foods must always be
maintained.

From what has been previously said it is evident that proteid
food is not the only food-stuff to be regarded in selecting a diet for
muscular labour. We should however equally err in the opposite
direction if we selected exclusively non-nitrogenous food on which
to do work, since, as we have seen, there is no evidence that the
fats or carbohydrates are the direct, though they may be in part
the ultimate source, of muscular energy. Considering how complex
a thing strength is, how much it depends on the vigour of parts of
the body other than the muscles, a normal diet, calculated to
develope equally all parts of the body, is probably the best diet for
active labour. It is possible however that an excess of proteid
food, by reason of the renewal of tissue caused by its metabolic
activity, may be, in such cases, of service.

Lastly, the several saline matters, including the extractives of
animal and vegetable food, are no less essential elements of a diet
than proteids, fats, or carbohydrates. Of use, not for the energy
they themselves possess, but by reason of their regulating the
energy of the food-stuffs more strictly so called, they are necessary
to life: the body in their absence fails to carry out its usual
metabolism, and disease if not death follows.

The dietetic superiority of fresh meat and vegetables depends
in part on their still retaining these various saline and extractive
matters. A diet from which phosphorus (or even possibly phos-
phates), or chlorides, or potash, or soda salts are absent, is, as soon
as the store of the substance in the body is exhausted, useless
for nutritive purposes. Calcium and magnesia may, to a certain
extent, be replaced by bases closely allied to them; but the
metabolic rdle of phosphorus or of sulphur cannot be taken up
by an analogous body ; and, as is illustrated by their distribution
in the body, the physiological functions of potash and soda are
widely different if not antagonistic, closely allied as are these two
alkalis when regarded from a chemical point of view. Like
medicines and poisons — and indeed they are in a manner natural
medicines — the action of these bodies depends in part on their
dose. Indispensable as are potash salts to the economy, a large
dose of them is injurious ; and a dog fed on nothing but Liebig's

478 DIETETICS. [BOOK 11.

extract dies sooner than a dog not fed at all, on account of the
potash salts of the extract exerting their deleterious influence in
the absence of the food whose metabolism their function is to
direct.

BOOK III.

THE CENTRAL NERVOUS SYSTEM AND ITS
INSTRUMENTS.

CHAPTER I.
SENSORY NERVES.

IN studying the phenomena of motor nerves we are greatly assisted
by two facts : — First, that the muscular contraction by which we
judge of what is going on in the nerve is a comparatively simple
thing, one contraction differing from another only by such features
as amount, rapidity, and frequency of repetition, and all such
differences being capable of exact measurement. Secondly, that
when we apply a stimulus directly to the nerve itself, the effects
differ in degree only from those which result when the nerve is set
in action by natural stimuli, such as the will. When we come, on
the other hand, to investigate the phenomena of afferent nerves,
our labours are for the time rendered heavier, but in the end
more fruitful, by the facts :— First, that we can only judge of
what is going on in an afferent nerve by the effects it produces
in some central nervous organ, in the way of exciting or modifying
reflex action, or modifying automatic action, or affecting conscious-
ness ; and we are consequently met on the very threshold of every
inquiry by the difficulty of clearly distinguishing the events which
belong exclusively to the afferent nerve from those which belong to
the central organ. Secondly, that the effects of applying a stimulus
to the peripheral end-organ of an afferent nerve are very different
from those of applying the same stimulus directly to the nerve-
trunk. This may be shewn by the simple experience of comparing
the sensation caused by the contact of any sharp body with a
nerve laid bare by a wound with that caused by contact of an intact
skin with the same body. These differences reveal to us a com-
plexity of impulses, of which the phenomena of motor nerves gave
us not so much as a hint ; but for the time being they increase the
difficulties of our study.

F. 31

482 SENSORY NERVES. [BOOK in.

An afferent impulse passing along an afferent nerve may in
certain cases simply produce a change in our consciousness
unaccompanied by any visible bodily movements; in other cases
it may give rise to reflex movements, or modify existing reflex
or automatic actions without causing any change in consciousness ;
in still other cases it may bring about both results at the same
time. An afferent nerve the stimulation of which gives rise to
a sensation, and so leads to a modification of consciousness, may be
more closely defined as a ' sensory ' nerve. There is however no
distinct proof, having regard to the difficulties just mentioned,
that the afferent fibres which in the body are commonly used to
cause or affect reflex action differ at all in kind from those whose
function it is to modify consciousness. On the contrary, such
evidence as we have goes to shew that an appropriate stimulus
of the same fibre may give rise to one or other or both events ; and
that whether the one or the other, or both, events occur depends
on the condition of the central organ, and on the relation of its
several parts to the afferent nerve. The stimulation of the same
nerve (and there are no positive facts which would preclude us
from saying ' of the same fibre ') may under certain circumstances,
as for instance when the brain has been removed, simply cause
a reflex action and under other circumstances give rise merely to a
sensation. Hence an afferent nerve is frequently spoken of as
a sensory nerve even under circumstances where there is no
evidence of consciousness being actually affected, because by a
slight change of circumstances the same stimulation of the same
nerve might give rise to a distinct sensation ; the substitution of
the specific for the general term being justified by the convenience
of the former.

All the spinal nerves are mixed nerves, composed of afferent
and efferent, of motor and sensory fibres. When a spinal nerve
is divided, stimulation of the peripheral portion causes muscular
contraction, of the central portion, a sensation (or a reflex action).
At the junction of the nerve with the spinal cord the sensory fibres
are gathered into the posterior and the motor fibres into the
anterior root. The proof of this, which was first made known
by Charles Bell and Majendie, their discoveries forming the founda-
tion of modern nervous physiology, is simply as follows.

When the anterior root is divided, the muscles supplied by the
nerve cease to be thrown into contractions either by the will, or by
reflex action, while the structures to which the nerve is distributed
retain their sensibility. During the section of the root, or when the
proximal stump, that connected with the spinal cord, is stimulated,
no sensory effects are produced. When the distal stump is stimu-
lated, the muscles supplied by the nerve are thrown into contractions.
When the posterior root is divided, the muscles supplied by the
nerve continue to be thrown into action by an exercise of the will,
or as part of a reflex action, but the structures to which the nerve

CHAP. L] SENSORY NERVES. 483

is distributed lose the sensibility which they previously possessed.
During the section of the root, and when the proximal stump is
stimulated, sensory effects are produced. When the distal stump
is stimulated no movements are called forth. These facts demon-
strate that sensory impulses pass exclusively by the posterior root
from the peripheral to the central organs, and that motor impulses
pass exclusively by the anterior root from the central to the
peripheral organs.

An exception must be made to the above general statement,
on account of the so-called recurrent sensibility which is witnessed
in conscious mammals, under certain circumstances. It often
happens that when the peripheral stump of the divided anterior
root is stimulated, signs of pain are witnessed. These are not
caused by the concurrent muscular contractions or cramp which
the stimulation occasions, for they remain if the whole trunk of
the nerve be divided some little way below the union of the roots
above the origins of the muscular branches, so that no contractions
take place. They disappear if the posterior root be also cut, and
they are not seen if the mixed nerve-trunk be divided close to the
union of the roots. The phenomena are probably due to the fact,
that bundles of sensory fibres of the posterior root after running a
short distance down the mixed trunk turn back and run upwards
in the anterior root, and by this recurrent course give rise to the
recurrent sensibility.

Concerning the ganglion on the posterior root, we may say defi-
nitely that it is neither a centre of reflex nor of automatic action.
Our knowledge concerning its function is almost limited to the
fact that it is in some way intimately connected with the nutrition
of the nerve. When a mixed nerve-trunk is divided, the peripheral
portion degenerates from the point of section downwards towards
the periphery. The central portion does not so degenerate, and if
the length of nerve removed be not too great, the central portion
uniting with the degenerating peripheral portion may grow down-
wards, and thus regenerate the nerve. This degeneration is
observed when the mixed trunk is divided in any part of its
course from the periphery to close up to the ganglion. When the
posterior root is divided between the ganglion and the spinal cord,
the portion attached to the spinal cord degenerates, but that
attached to the ganglion remains intact. When the anterior root
is divided, the proximal portion in connection with the spinal cord
remains intact, but the distal portion between the section and the
junction with the other root degenerates; and in the mixed nerve-
trunk many degenerated fibres are seen, which, if they be carefully
traced out, are found to be motor fibres. If the posterior root be
divided carefully between the ganglion and the junction with the
anterior root, the posterior root above the section remains intact,
but in the mixed nerve-trunk are seen numerous degenerated
fibres, which when examined are found to have the distribution of

31—2

484 ROOTS Of SPINAL NERVES. [Boon in.

sensory fibres. Lastly, if the posterior ganglion be excised, the
whole posterior root degenerates, as do also the sensory fibres of
the mixed nerve-trunk. Putting all these facts together, it would
seem that the growth of the motor and sensory fibres takes place
in opposite directions, and starts from different nutritive or
'trophic' centres. The sensory fibres grow away from the ganglion
either towards the periphery, or towards the spinal cord. The
motor fibres grow outwards from the spinal cord towards the
periphery. This difference in their mode of nutrition is frequently
of great help in investigating the relative distribution of motor
and sensory fibres. When a posterior root is cut beyond the
ganglion, or the ganglion excised, all the sensory nerves degenerate,
and the sensory fibres, by their altered condition, can readily be
traced in the mixed nerve-branches. Conversely, when the an-
terior roots are cut, the motor fibres alone degenerate, and can be
similarly diagnosed in a mixed nerve-tract. When the anterior
root is divided some few fibres in it do not, like the rest, degene-
rate, and when the posterior root is divided, a few fibres in the
anterior root are seen to degenerate like those of the posterior
root ; these appear to be the fibres which give to the anterior root
its "recurrent sensibility." By the same means in a mixed nerve
like the vagus, the fibres which spring from the real vagus root
may be distinguished from those proceeding from the spinal
accessory, by section of the vagus and spinal accessory roots
respectively ; and in the mixed vago-sympathetic trunk, met with
in many animals, the vagus fibres may be distinguished from the
sympathetic, since, after a section of the mixed trunk, the former
degenerate from above downwards, whereas the latter degenerate
in an upward direction from the inferior cervical ganglion below to
the superior cervical ganglion above; for the ganglia of the
sympathetic behave in this respect like the spinal ganglia of the
posterior roots. This method of diagnosis is often spoken of as
the Wallerian method, after A. Waller, to whom we are indebted
for the discovery of most of these facts.

In the cranial nerves the motor and sensory tracts are far less
mixed than in the spinal nerves. The olfactory, optic and acoustic
nerves are purely sensory nerves. The fifth, glosso-pharyngeal
and vagus are mixed nerves ; and it is stated that in the dog the
afferent and efferent fibres of the vagus are gathered into two
bundles so distinct that they may be separated by the knife,
the afferent bundle lying to the outside of the efferent bundle.
The facial and hypoglossal are for the most part motor (efferent)
nerves, but contain sensory (afferent) fibres. The third, fourth,
sixth and spinal accessory are exclusively motor (efferent) nerves.
These statements refer to what are commonly looked upon
as the trunks of the respective nerves. More exactly speaking,
the sensory fibres of the facial come from the fifth, pneumo-
gastric and glosso-pharyngeal nerves, so that the facial proper is in

CHAP, i.] SENSORY NERVES. 485

reality a purely motor nerve. So likewise is the hypoglossal, its
sensory fibres coming from the fifth, pneumogastric, and three
upper cervical nerves. The fifth is a mixed nerve entirely on the
plan of a spinal nerve, having distinct motor and sensory roots.
The glosso-pharyngeal seems to be essentially a sensory nerve, its
motor filaments springing from the fifth and facial nerves. Con-
cerning the vagus some have maintained that the pneumogastric
root proper is entirely sensory (afferent), and that all the efferent
functions of the vagus are dependent on the fibres of the spinal
accessory which join it. To this point we shall return when we
come to consider briefly the special functions of the several nerves.

We have already stated (p. 106) that isolated pieces of motor
and of sensory nerves behave exactly alike as far as all the physical
manifestations attendant on the passage of a nervous impulse are
concerned ; the current of action makes its appearance in the same
way and seems to have the same characters in both kinds of
nerves. The same is also true, as far as we know, of nerves within
the body.

Moreover, the rate at which nervous impulses travel appears to
be about the same in motor and sensory nerves ; at least we have
no evidence of any fundamental difference in this respect between
the two. We have seen that the velocity of a nervous impulse in
the motor-nerve of a frog is about 28 metres per sec. The velocity
of a motor impulse in man, as judged by the difference of the
latent period of the contraction of the thumb-muscles, when stimu-
lation is brought to bear on the motor-nerve at the wrist, or high
up in the arm, is about 33 metres per sec. In warm-blooded
animals, however, the rate of transmission of motor impulses is
very variable, being in particular closely dependent on temperature,
and probably also on other circumstances. Thus, it may range
from as low as 30 m. when the nerve is cooled to as high as 90 m.
when it is warmed. The velocity of a sensory impulse is estimated
by measuring the time taken between a stimulus being brought
to bear on some sentient surface, as the skin, and the making of a
signal by the individual experimented on at the instant that he
feels the stimulus. The time taken up in the sensory impulse
becoming converted into a sensation after reaching the nervous
central organs, in the mental operation of determining to make
the signal, and in the effort of making the signal, corresponds in a
way to the purely muscular portion of the latent period in the
experiment for determining the velocity of a motor impulse. The
application of the stimulus and the making of the signal (ex. gr.
closing a galvanic circuit) being both recorded on a rapidly
travelling surface, the time taken up in the whole operation
can be easily measured ; and the difference between the time taken
when the stimulus is applied to some spot separated from the
central nervous system by a short piece of nerve, ex. gr. the top of
the thigh, and that taken when a long piece of nerve intervenes, ex.

486 AFFERENT AND EFFERENT NERVE FIBRES. [BOOK in.

gr. when the stimulus Is applied to the toe, will give the time
required for the sensory impulse to pass along a piece of sensory
nerve as long as the difference of length between the above two
nerves ; from which the velocity can be calculated. Observations
carried on in this way have led to most discordant results, varying
from 26 metres to 94 metres, or even more, per sec. The difference
here is far too great to allow any value to be attached to an
average. When it is remembered how complex are all the central
nervous operations in these instances, as compared with the changes
going on in a muscle during the latent period of its contraction,
and how these central operations might vary according as one or
other spot of skin was stimulated, quite independently of the
length of nerve between the centre and the spot stimulated, these
discrepancies will not . be wondered at ; and it may fairly be
concluded that the velocity of a sensory impulse does not materially
differ from that of a motor impulse.

There are, however, certain phenomena which might at first
sight be interpreted as indicating that afferent and efferent nerve-
fibres behave differently towards stimuli. We have already (p. 93)
stated that according to most observers, when an ordinary motor
nerve, such as a nerve supplying a muscle, is heated, no indications
of the generation of nervous impulses, no contractions of the
muscle for instance, are observed. The heat does not act as a
stimulus; it may increase the irritability of the nerve for the
time being, but apparently cannot originate the explosive dis-
charge which we call an impulse. We have also seen that during
the passage of a constant current along the nerve of a muscle-
nerve preparation no contractions are visible, no impulses, save
in certain particular cases, are generated, so long as the current
is not suddenly varied in strength. But it has been found
that when afferent nerve-fibres, such as those in the central
stump of the divided sciatic or in the central stump of the
vagus, are heated to 45° or 50° events occur, clearly proving that
impulses are generated in the afferent fibres by the elevation of
temperature. In the case of the sciatic the animal shews sign
of pain, the blood-pressure is affected, &c. ; and in the case of the
vagus the heart is slowed by reflex inhibitory impulses passing
down the other, intact, vagus, though heating the peripheral
instead of the central stump of the divided vagus has no effect
whatever on the heart. Similarly when the same nerves or other
nerves containing afferent fibres are submitted to the action of the
constant current, there are like evidences of the continued genera-
tion of nervous impulses during the whole time of the passage of
the current, even though it be kept as uniform in strength as
possible. On the other hand many chemical substances which
act as powerful stimuli to motor nerves are ineffectual towards
afferent fibres, These results, however, until the contrary is
proved by further inquiries into the phenomena attending the

CHAP, i.] SENSORY NERVES. 487

generation and transmission of nervous impulses, may be taken
as indicating not so much that the afferent and efferent fibres
are themselves acted upon in a different way by heat or by the
constant current as that the molecular disturbances generated in
both cases have different effects according as they impinge upon a
central or a peripheral mechanism. We can readily imagine that
molecular disturbances which would be impotent to stir the
sluggish muscular substance to a contraction, and thus so to speak
be lost upon the muscle, might produce a very great effect on the
more sensitive and mobile material of the central nervous system.
We may for the present therefore conclude that there is no distinct
proof of an absolute difference between afferent and efferent fibres,
but we must at the same time be cautious not to consider the
grosser phenomena, presented by a muscle-nerve preparation, as
a satisfactory test of all the changes which may take place in a
nerve-fibre. The necessity of this caution will be almost im-
mediately illustrated from another point of view.

The apparent identity in function between afferent and efferent
fibres, taken into consideration with the facts just mentioned con-
cerning the regeneration of nerves, suggests the inquiry whether by
a change of the peripheral or central organs a motor nerve can be
converted into a sensory nerve, or vice versa. Experiments made
with a view of obtaining a functional union between purely motor
and sensory nerves have, in the hands of most observers, failed.
And though an apparent union between the central portion of a,
divided lingual (sensory) nerve and the peripheral portion of a
divided hypoglossal (motor) nerve has been accomplished, with the
result that stimulation of the lingual trunk produced movements in
the tongue, the case breaks down upon examination. In the first
place though the nerves appeared to have united, there was no
actual union between the lingual and hypoglossal fibres, but
degeneration of the latter, and a growth downward of the former ;
in the second place the movements of the tongue when the lingual
trunk was stimulated appear to have been brought about by stimu-
lation not of the sensory, true lingual, fibres, but of motor (chorda
tympani) fibres running in the lingual trunk.

We have already seen (p. 106) that a sensory nerve in its
simplest form may be regarded as a strand of eminently irritable
protoplasm, forming a link between a superficial cell which alone is
subject to extrinsic stimuli, and a central (reflex or automatic) cell
which receives stimuli, chiefly in the form of nervous impulses pro-
ceeding from the former along the connecting strand. In the
earliest stages of the developement of a sensory nervous system, the
superficial sensory cell is susceptible of stimuli of all kinds, pro-
vided they are sufficiently strong; and probably all the impulses
which it transmits to the central cell resemble each other very
closely, differing only in degree. It is obvious however that the
economy would gain by a further division of labour, by a differen-*

488 SPECIAL SENSES. [BOOK in.

tiatioii of the simple uniform superficial cell into a number of cells,
each of which was more susceptible to particular stimuli than its
fellows. Thus one cell, or rather one group of cells, would become
eminently susceptible to the influence of light : in them the impact
of rays of light would give rise to nervous impulses more readily
than in the other groups ; another group would develope a sensi-
tiveness to waves of sound, and so on. In this way the primary
homogeneous bodily surface would be differentiated into a series of
seme-organs, disposed and arranged among ectodermic cells, the
purpose of the latter being simply protective, and therefore not
demanding the existence of any direct connection with the central
nervous system. Similar but less highly marked differentiations
would be established in the endings of the afferent nerves connect-
ing the central nervous system with the internal surfaces and parts
of the body.

Moreover it is obvious that the sensory impulses transmitted to
the central nervous system by these differentiated sense-organs will
probably be themselves largely differentiated. Just as the impulses
which pass along a motor nerve differ according to the nature of the
stimulus which is applied to the nerve (whether, for instance, the
stimulus be a single induction-shock, or several shocks repeated
slowly, or several shocks repeated rapidly, and so on, the effect on
the muscle being in each case a different one), so also and even to a
much greater degree do the impulses generated by light in a visual
sense-organ in all probability differ from those generated by simple
pressure in a tactile sense-organ.

And since these various sensory impulses have much work to
perform on arriving at the central nervous system, in the way of
influencing the multitudinous molecular operations going on in the
central cells, and of affecting consciousness, this differentiation of
sensory organs and sensory impulses will naturally be accompanied
by a corresponding differentiation of those central cells which the
impulses first reach on arriving at the central organ. Those cells,
for instance, of the central nervous system, which first receive the
particular nervous impulses coming from the visual sense-organs,
will be set apart for the task of so modifying and preparing those
impulses as to adapt them in the best possible way for the work
which they have to do. Hence each peripheral sense-organ will be
united by means of its nerve with a corresponding central sense-
organ, the former being able to affect various parts of the central
nervous system only through the medium of the latter. And we
have evidence, at least as far as relates to all the central nervous
operations in which consciousness is concerned, that such central
sense-organs do really exist. For of the total characters which
belong to an affection of consciousness by means of any of the
sense-organs, i.e. which belong to any special sensations, we find
that while some are gained during the rise of the sensory impulses
in the peripheral sense-organ, others first appear in the central

CHAP, i.] SENSORY NERVES. 489

sense-organ in the course of the changes through which the sensory
impulses give rise to a sensation. Thus a stimulus of any kind
applied to the optic nerve along any part of its course, if it is able
to start any impulses at all, gives rise to a sensation of light, and
precisely the same stimulus applied to the acoustic nerve along any
part of its course gives rise to a sensation of sound; and so on. All
the evidence we possess goes against the view that a piece of optic
nerve, deprived of both its peripheral and central endings, differs in
function from a similarly isolated piece of acoustic nerve; such facts
as are within our knowledge go to shew that the disturbances
generated in a piece of optic nerve by a galvanic current are the
same as those generated in a piece of acoustic nerve. We are
therefore driven to the conclusion that the difference which appears
when the central endings are intact arises in the central organs.

In all these differentiated sensory mechanisms, or special senses
as they are called, we have then to deal with two elements : the
peripheral sense-organ, in which we have to study how the special
physical agent gives rise to special sensory impulses; and the
central sense-organs, in which our study is confined to the manner
in which these special impulses modify the operations of the
central nervous system. Inasmuch as in a normal body the
peripheral organ remains in connection with the central organ, and
our study of the special senses is carried on chiefly by subjective
observations in which we make use of our own consciousness, it
frequently becomes very difficult to distinguish in any given
sensation the peripheral from the central element. The two
become more distinct, the more complex the sense and the more
highly organised the sense-organs. For this reason it will be most
convenient to commence our study of the special senses with the
sense of vision.

CHAPTER II.
SIGHT.

A RAY of light falling on the retina gives rise to what we call a
sensation of light ; but in order that distinct vision of any object
may be gained, an image of the object must be formed on the
retina, and the better defined the image the more distinct will be
the vision. Hence in studying the physiology of vision, our first
duty is to examine into the arrangements by which the formation
of a satisfactory image on the retina is effected; these we may
call briefly the dioptric mechanisms. We shall then have to inquire
into the laws according to which rays of light impinging on the
retina give rise to sensory impulses, and those according to which
the impulses thus generated give rise in turn to sensations. Here
we shall come upon the difficulty of distinguishing between the
unconscious or physical and the conscious or psychical factors.
And we shall find our difficulties increased by the fact, that in
appealing to our own consciousness we are apt to fall into error by
confounding primary and direct sensations with states of conscious-
ness which are produced by the weaving of these primary sen-
sations with other operations of the central nervous system, or,
in familiar language, by confounding what we see with what we
think we see. These two things we will briefly distinguish as visual
sensations and visual judgments; and we shall find that both in
vision with one eye, but more especially in binocular vision, visual
judgments form a very large part of what we frequently speak of
as our sight.

SEC. 1. DIOPTRIC MECHANISMS.

The Formation of the Image.

The eye is a camera, consisting of a series of lenses and media
arranged in a dark chamber, the iris serving as a diaphragm ; and
the object of the apparatus is to form on the retina a distinct
image of external objects. That a distinct image is formed on
the retina, may be ascertained by removing the sclerotic from the
back of an eye, and looking at the hinder surface of the transparent
retina while rays of light proceeding from any external object are
allowed to fall on the cornea.

A dioptric apparatus in its simplest form consists of two
media separated by a (spherical) surface ; and the optical proper-
ties of such an apparatus depend upon (1) the curvature of the
surface, (2) the relative refractive power of the media. The eye
consists of several media, bounded by surfaces which are approxi-
mately spherical but of different curvature. The surfaces are all
centred on a line called the optic axis, which meets the retina at a
point somewhat above and to the inner (nasal) side of the fovea
centralis. In passing from the outer surface of the cornea to the
retina the rays of light traverse in succession the cornea, the
aqueous humour, the lens and the vitreous humour. Refraction
takes place at all the surfaces bounding these several media, but
particularly at the anterior surface of the cornea, and at both the
anterior and posterior surfaces of the lens. Since the anterior and
posterior surfaces of the cornea are parallel, or very nearly so, the
rays of light would suffer little or no change of direction in passing
through the cornea, if it were bounded on both sides by the same

492 SIGHT. [BOOK in.

medium. The direction of the rays of light in the aqueous
humour would therefore remain the same if the cornea were made
exceedingly thin, if in fact its two surfaces were made into one,
forming a single anterior surface to the aqueous humour; or,
which comes to the same thing in the end, since the refractive
power of the substance of the cornea is almost exactly the same
as that of the aqueous humour, the refraction at the posterior
surface of the cornea may be neglected altogether. Thus the two
surfaces of the cornea are practically reduced to one. The lens
varies in density in different parts, the refractive power of the
central portions being greater than that of the external layers;
but the refractive power of the whole may, without any serious
error, be assumed to be uniform. The refractive power of the
vitreous humour is almost exactly the same as that of the aqueous
humour.

Thus the apparently complicated natural eye may be simplified
into a 'diagrammatic eye/ in which the refracting surfaces are re-
duced to three, viz. (1) the anterior surface of the cornea, (2) the
anterior surface of the lens separating the lens from the aqueous
humour, and (3) the posterior surface of the lens separating the
lens from the vitreous humour. The media will similarly be
reduced to two ; the substance of the lens, and the aqueous or
vitreous humour. This 'diagrammatic eye' is of great use in the
various calculations which become necessary in studying physio-
logical optics ; for the magnitudes which are derived by calculation
from it represent the corresponding magnitudes in an average
natural eye with sufficient accuracy to serve for all practical
purposes. The values adopted by Listing for the constants of this
'diagrammatic eye,' and to him we are indebted for the intro-
duction of it, are as follow :

Radius of curvature of cornea 8 mm.

„ „ of anterior surface of lens 10 „

„ „ of posterior „ „ 6 „

Refractive index of aqueous or vitreous humour iff

Mean refractive index of lens -}-f

Distance from anterior surface of cornea to anterior

surface of lens 4 mm.

Thickness of lens 4 „

The calculated position of the principal posterior focus, i.e. the
point at which all rays falling on the cornea parallel to the optic
axis are brought to a focus, is in the diagrammatic eye 14'6470 mm.
behind the .posterior surface of the lens, or 22'6470 mm. behind the
anterior surface of the cornea. That is to say, the fovea centralis
must occupy this position in order that a distinct image of a
distant object may be formed upon it. It must be understood
that these values refer to the eye when at rest, i.e. when it is not
undergoing any strain of accommodation.

CHAP, ii.] SIGHT. 493

Accommodation.

When an object, a lens, and a screen to receive the image, are
so arranged in reference to each other, that the image falls upon
the screen in exact focus, the rays of light proceeding from each
luminous point of the object are brought into focus on the screen
in a point of the image corresponding to the point of the object.
If the object be then removed farther away from the lens, the rays
proceeding in a pencil from each luminous point will be brought to
a focus at a point in front of the screen, and, subsequently diverg-
ing, will fall upon the screen as a circular patch composed of a
series of circles, the so-called diffusion circles, arranged concentri-
cally round the principal ray of the pencil. If the object be
removed, not farther, but nearer the lens, the pencil of rays will
meet the screen before they have been brought to focus in a point,
and consequently will in this case also give rise to diffusion circles.
When an object is placed before the eye, so that the image falls
into exact focus on the retina, and the pencils of rays proceeding
from each luminous point of the object are brought into focus in
points on the retina, the sensation called forth is that of a distinct
image. When on the contrary the object is too far away, so that
the focus lies in front of the retina, or too near, so that the focus
lies behind the retina, and the pencils fall on the retina not as
points, but as systems of diffusion circles, the sensation produced
is that of an indistinct and blurred image. In order that objects
both near and distant may be seen with equal distinctness by the
same dioptric apparatus, the focal arrangements of the apparatus
must be accommodated to the distance of the object, either by
changing the refractive power of the lens, or by altering the
distance between the lens and the screen.

That the eye does possess such a power of accommodation is shewn
by every-day experience. If two needles be fixed upright some two
feet or so apart, into a long piece of wood, and the wood be held
before the eye, so that the needles are nearly in a line, it will be
found that if attention be directed to the far needle, the near one
appears blurred and indistinct, and that, conversely, when the near
one is distinct, the far one appears blurred. By an effort of the
will we can at pleasure make either the far one or the near one
distinct; but not both at the same time. When the eye is
arranged so that the far needle appears distinct, the image of
that needle falls exactly on the retina, and each pencil from each
luminous point of the needle unites in a point upon the retina;
but when this is the case, the focus of the near needle lies behind
the retina, and each pencil from each luminous point of this needle
falls upon the retina in a series of diffusion circles. Similarly,
when the eye is arranged so that the near needle is distinct,

494 ACCOMMODATION. [BOOK in.

the image of that needle falls upon the retina in such a way,
that each pencil of rays from each luminous point of the needle
unites in a point on the retina, while each pencil from each
luminous point of the far needle unites at a point in front of the
retina, and then diverging again falls on the retina, in a series
of diffusion circles. If the near needle be gradually brought nearer
and nearer to the eye, it will be found that greater and greater
effort is required to see it distinctly, and at last a point is reached
at which no effort can make the image of the needle appear any-
thing but blurred. The distance of this point from the eye marks
the limit of accommodation for near objects. Similarly, if the
person be short-sighted, the far needle may be moved away from
the eye, until a point is reached a,t which it ceases to be seen
distinctly, and appears blurred. In the one case, the eye, with all
its power, is unable to bring the image of the needle sufficiently
forward to fall on the retina : the focus lies permanently behind
the retina. In the other, the eye cannot bring the image suf-
ficiently backward to fall on the retina: the focus lies permanently
in front of the retina. In both cases the pencils of rays from the
needles strike the retina in diffusion circles.

The same phenomena may be shewn with greater nicety by
what .is called Schemer's Experiment. If two smooth holes be
pricked in a card, at a distance from each other less than the
diameter of the pupil, and the card be held up before one eye,
with the holes horizontal, and a needle placed vertically be looked
at through the holes, the following facts may be observed. When
attention is directed to the needle itself, the image of the needle
appears single. Whenever the gaze is directed to a more distant
object, so that the eye is no longer accommodated for the needle,
the image appears double and at the same time blurred. It also
appears double and blurred when the eye is accommodated for a
distance nearer than that of the needle. When only one needle
is seen, and the eye therefore is properly accommodated for the
distance of the needle, no effect is produced by blocking up one
hole of the card, except that the whole field of vision seems
dimmer. When, however, the image is double on account of the
eye being accommodated for a distance greater than that of the
needle, blocking the left-hand hole causes a disappearance of the
right-hand or opposite image, and blocking the right-hand hole
causes the left-hand image to disappear. When the eye is ac-
commodated for a distance nearer than that of the needle, blocking
either hole causes the image on the same side to vanish. The
following diagram will explain how these results are brought about.

Let a (Fig. 67) be a luminous point in the needle, and ae, af
the extreme right-hand and left-hand rays of the pencil of rays
proceeding from it, and passing respectively through the right-hand
e, and left-hand/, holes in the card. (The figure is supposed to be
a horizontal section of the eye.) When the eye is accommodated

CHAP, ii.]

SIGHT.

495

for a, the rays e and / meet together in the point c, the retina
occupying the position of the plane nn; the luminous point appears
as one point, and the needle will appear as one needle. When the
eye is accommodated for a distance beyond a, the retina may be
considered to lie * no longer at nn, but nearer the lens, at mm for
example ; the rays ae will cut this plane at p, and the rays of at
q; hence the luminous point will no longer appear single, but will

FIG. 67. DIAGRAM OF SCHEINER'S EXPERIMENT.

be seen as two points, or rather as two systems of diffusion circles,
and the single needle will appear as two blurred needles. The
rays passing through the right-hand hole e, will cut the retina at
p, i.e. ou the right-hand side of the optic axis; but, as we shall see
in speaking of the judgments pertaining to vision, the image on
the right-hand side of the retina is referred by the mind to an
object on the left-hand side of the person ; hence the affection
of the retina at p, produced by the rays ae falling on it there, gives

1 Of course, in the actual eye, as we shall see, accommodation is effected by a
change in the lens, and not by an alteration in the position of the retina ; but for
convenience sake, we may here suppose the retina to be moved.

496 ACCOMMODATION. [BOOK m.

rise to an image of the spot a at P, and similarly the left-hand
spot q corresponds to the right-hand Q. Blocking the left-hand
hole, therefore, causes a disappearance of the right-hand image,
and vice versa. Similarly when the eye is accommodated for a
distance nearer than the needle, the retina may be supposed to
be removed to II, and the right-hand ae and left-hand of rays, after
uniting at c, will diverge again and strike the retina at p' and q.
The blocking of the hole e will now cause the disappearance of the
image q' on the left-hand side of the retina, and this will be
referred by the mind to the right-hand side, so that Q will seem to
vanish.

If the needle be brought gradually nearer and nearer to the eye,
a point will be reached within which the image is always double.
This point marks with considerable exactitude the near limit of
accommodation. With short-sighted persons, if the needle be
removed farther and farther away, a point is reached beyond
which the image is always double; this marks the far limit of
accommodation.

The experiment may also be performed with the needle placed
horizontally, in which case the holes in the card should be vertical.

The adjustment of the eye for near or far distances may be
assisted by using two needles, one near and one far. In this case
one needle should be vertical, and the other horizontal, and the
card turned round so that the holes lie horizontally or vertically
according to whether the vertical or horizontal needle is being
made to appear double.

In what may be regarded as the normal eye, the so-called emme-
tropic eye, the near limit of accommodation is about 10 or 12 cm.
and the far limit may be put for practical purposes at an infinite
distance. The 'range of distinct vision' therefore for the emme-
tropic eye is very great. In the myopic, or short-sighted eye, the
near limit is brought much closer (5 or 6 cm.) to the cornea ; and
the far limit is at a variable but not very great distance, so that
the rays of light proceeding from an object not many feet away
are brought to a focus, not on the retina, but in the vitreous
humour. The range of distinct vision is therefore in the myopic
eye very limited. In the liypermetropic, or long-sighted eye, the
rays of light coming from even an infinite distance are, in the
passive state of the eye, brought to a focus beyond the retina.
The near limit of accommodation is at some distance off, and a far
limit of accommodation does not exist. The presbyopic eye,, or the
long sight of old people, resembles the hypermetropic eye in the
distance of the near point of accommodation, but differs from
it inasmuch as the former is an essentially defective condition
of the accommodation mechanism, whereas in the latter the power
of accommodation may be good and yet, from the internal arrange-
ments of the eye, be unable to bring the image of a near object on
to the retina. When a normal eye becomes presbyopic, the far

CHAP. IL] SIGHT. 497

limit may remain the same, but since the power of accommodating
for near objects is weakened or lost, the change is distinctly a
reduction of the range of distinct vision. In the normal emme-
tropic eye, when no effort of accommodation is made, the principal
focus of the eye lies on the retina, in the myopic eye in front of it,
and in the hypermetropic eye behind it.

Mechanism of Accommodation. In directing our attention
from a far to a very near object we are conscious of a distinct effort,
and feel that some change has taken place in the eye ; when we
turn from a very near to a far object, if we are conscious of any
change in the eye, it is one of a different kind. The former is the
sense of an active accommodation for near objects; the latter,
when it is felt, is the sense of relaxation after exertion.

Since the far limit of an emmetropic eye is at an infinite
distance, no such thing as active accommodation for far distances
need exist. The only change that will take place in the eye in
turning from near to far objects will be a mere passive undoing
of the accommodation previously made for the near object. And
that no such active accommodation for far distances takes place
is shewn by the facts — that the eye, when opened after being
closed for some time, is found not in medium state but adjusted
for distance ; that when the accommodation mechanism of the eye
is paralysed by atropin or nervous disease, the accommodation for
distant objects is unaffected; and that we are conscious of no
effort in turning from moderately distant to far distant objects.
The sense of effort often spoken of by myopic persons as being felt
when they attempt to see things at or beyond the far limit of their
range seems to arise from a movement of the eyelids, and not
from any internal changes taking place in the eye.

What then are the changes which take place in the eye, when
we accommodate for near objects ? It might be thought, and
indeed once was thought, that the curvature of the cornea was
changed, becoming more convex, with a shorter radius of curvature,
for near objects. Young, however, shewed that accommodation
took place as usual when the eye (and head) is immersed in water.
Since the refractive powers of aqueous humour and water are very
nearly alike, the cornea, with its parallel surfaces, placed between
these two fluids, can have little or no effect on the direction of
the rays passing through it when the eye is immersed in water.
And accurate measurements of the dimensions of an image on
the cornea have shewn that these undergo no change during
accommodation, and that therefore the curvature of the cornea
is not altered. Nor is there any change in the form of the bulb ;
for any variation in this would necessarily produce an alteration
in the curvature of the cornea, and pressure on the bulb would
act injuriously by rendering the retina anaemic and so less
sensitive. In fact, there are only two changes of importance
p. 32

498 ACCOMMODATION. [Boon m.

which can be ascertained to take place in the eye during accommo-
dation for near objects.

One is that the pupil contracts. When we look at near objects,
the pupil becomes small; when wo turn to distant objects, it
dilates. This however cannot have more than an indirect influence
on the formation of the image ; the chief use of the contraction of
the pupil in accommodation for near objects is to cut off the more
divergent circumferential rays of light.

The other and really efficient change is that the anterior
surface of the lens becomes more convex. If a light be held
before the eye, three reflected images may, with care and under
proper precautions, be seen by a bystander: one a very bright
one caused by the anterior surface of the cornea, a second less
bright, by the anterior surface of the lens, and a third very dim,
by the posterior surface of the lens ; when the images are those
of an object, such as a candle, in which a top and bottom can
be recognized, the two former images are seen to be erect, but
the third inverted. When the eye is accommodated for near
objects, no change is observed in either the first or the third of
these images; but the second, that from the anterior surface
of the lens, is seen to become distinctly smaller, shewing that
the surface has become more convex. When, on the contrary,
vision is directed from near to far objects, the image from the
anterior surface of the lens grows larger, indicating that the
convexity of the surface has diminished, while no change takes
place in the curvature either of the cornea or of the posterior
surface of the lens. And accurate measurements of the size of
the image from the anterior surface of the lens have shewn that
the variations in curvature which do take place, are sufficient to
account for the power of accommodation which the eye possesses.

The observation of these reflected images is facilitated by the simple
instrument introduced by Helmholtz and called a Phakoscope. It
consists of a small dark chamber, with apertures for the observed and
observing eyes ; a needle is fixed at a short distance in front of the
former, to serve as a near object, for which accommodation has to be
made ; and a lamp or candle is so disposed as to throw an image on
each of the three surfaces of the observed eye. Since the distance
between two images is more readily appreciated than is a simple change
of size of a single image, two prisms are employed so as to throw a
double image of the lamp on each of the three surfaces. When the
anterior surface of the lens becomes more convex the two images
reflected from that surface approach each other, when it becomes less
convex they retire from each other.

These observations leave no doubt that the essential change by
which accommodation is effected, is an alteration of the convexity of
the anterior surface of the lens. And that the lens is the agent of
accommodation, is further shewn by the fact that after removal of
the lens, as in the operation for cataract, the power of accommo-

CHAP, ii.] SIGHT. 499

dation is lost. In the cases which have been recorded, where eyes
from which the lens had been removed seemed still to possess
some accommodation, we must suppose that no real accommodation
took place, but that the pupil contracted when a near object was
looked at, and so assisted in making vision more distinct.

This increase of the convexity of the lens has been supposed
to be due to a compression of the circumference of the lens by a
contraction of the iris; but this is disproved by the fact that
accommodation may take place in eyes from which the iris is con-
genially absent. It has also been attributed to vaso-motor
changes, to increased fulness of the vessels of the iris or ciliary
processes, surrounding the lens ; but this also is disproved by the
fact that accommodation may be effected, after death in an eye
which is practically bloodless, by stimulating the ciliary ganglion
or ciliary nerves with an interrupted current or by other means.
The real nature of the mechanism seems to be as follows.

The lens when examined after removal from the eye is found
to be a body of considerable elasticity. When the curvature of
the anterior surface of the lens is determined, as may be done by
appropriate means, in its natural position in the eye at rest, and
then again determined, after the lens has been removed from the
eye, the anterior surface is found to be more convex in the latter
than in the former case. There seems to be, in the eye in its
natural condition, some agency at work, keeping the anterior
surface of the lens somewhat flattened. The suspensory liga-
ment, attached to the choroid and ciliary processes behind, and
passing over the front of the lens, is just such a structure as
would produce this effect. In the natural position of the choroid
this ligament is tense, and tends to flatten the front of the lens.
When the choroid is pulled forward, the ligament becomes slack
and the lens bulges out forward. Further the ciliary muscle
attached on the one hand to a fairly fixed region, the junction of
the sclerotic and cornea, and on the other to the looser and more
moveable choroid, would naturally, when thrown into contraction,
pull forward the choroid and so slacken the suspensory ligament,
and hence permit the elastic lens to bulge out forwards. And we
have experimental evidence, carried out on lower animals, that
stimulation of the ciliary ganglion or of its so-called radix brevis,
does lead on the one hand to a contraction of the ciliary muscle
and pulling forward of the choroid, and on the other hand to an
increased curvature of the anterior surface of the lens. Hence we
may conclude that accommodation for near objects consists essen-
tially in a contraction of the ciliary muscle, which, by pulling
forward the choroid coat and the ciliary process, slackens the sus-
pensory ligament, and allows the lens to bulge forward by virtue
of its elasticity, and so to increase the convexity of its anterior
surface.

Accommodation is in most cases a voluntary act ; since, however,

32—2

500 MOVEMENTS OF THE PUPIL. [BOOK in.

the change in the lens is always accompanied by movements in
the iris, it will be convenient to consider the latter, before we
discuss the nervous mechanism of the whole act.

Movements of the Pupil. Though by making the efforts
required for accommodation we can at pleasure contract or dilate
the pupil, it is not in our power to bring the will to act directly on
the iris by itself. This fact alone indicates that the nervous
mechanism of the pupil is of a peculiar character, and such indeed
we find it to be. The pupil is contracted (1) when the retina (or
optic nerve) is stimulated, as when light falls on the retina, the
brighter the light the greater being the contraction, (2) when we
accommodate for near objects. The pupil is also contracted when
the eyeball is turned inwards, when the aqueous humour is deficient,
in the early stages of poisoning by chloroform, alcohol, &c.; in nearly
all stages of poisoning by morphia, physostigmin, and some other
drugs, and in deep slumber. The pupil is dilated (1) when stimu-
lation of the retina (or optic nerve) is diminished or arrested as in
passing from a bright into a dim light or into darkness, (2) when
the eye is adjusted for far objects. Dilation also occurs when there
is an excess of aqueous humour, during dyspnoea, during violent
muscular efforts, as the result of a stimulation of sensory nerves, as
an effect of emotions, in the later stages of poisoning by chloroform,
&c. and in all stages of poisoning by atropin and some other drugs.

Contraction of the pupil is caused by contraction of the circular
fibres or sphincter of the iris. Dilation is caused by contraction of
the radial fibres of the iris; for though the existence of radial fibres
has been denied by many observers, the preponderance of evidence
is clearly in favour of their being really present.

Considering how vascular the iris is, it does not seem unreason-
able to interpret some of the variations in the condition of the pupil
as the results of simple vascular turgescence or of depletion brought
about by vaso-motor action or otherwise, the small or contracted
pupil corresponding to the dilated and filled, and the large or
dilated pupil to the constricted and emptied condition of the blood-
vessels. Thus slight oscillations of the pupil may be observed
synchronous with the heart-beat and others synchronous with the
respiratory movements. But the variations in the pupil seem too
marked to be merely the effects of vascular changes, and indeed that
constriction of the pupil cannot be wholly the result of turgescence,
nor dilation wholly the result of depletion of the vessels of the iris,
is shewn by the facts that both these events may be witnessed in a
perfectly bloodless eye, and that the movements of the pupil when
brought about by agents which also affect the blood-vessels, begin
some time before the changes in the calibre of the blood-vessels,
and indeed may be over before these have arrived at their maxi-
mum. Moreover the fibres of the sympathetic, which as we shall
see are concerned in causing dilation of the pupil, run a somewhat

CHAP, ii.] SIGHT. 501

different course from those which govern the blood-vessels of the eye.
We may therefore adhere to the view that the main changes of the
pupil in the direction of narrowing and widening are brought about
by contractions of the plain muscular fibres in the iris.

Muscular contractions leading to changes of the pupil may be
observed in the eye removed from the body, and indeed in the
extirpated iris. The plain muscular fibres of the iris like other
plain muscular fibres are remarkably sensitive to variations in tem-
perature. Besides this there seems to be in certain animals at
least a connection within the eye between the iris and retina of
such a kind, that light falling into an extirpated eye will lead to a
narrowing of the pupil. Putting aside however such exceptional
events we may lay down the broad principle that contraction of the
pupil, brought about by light falling on the retina, is a reflex act,
of which the optic is the afferent nerve, the third or oculo-motor
the efferent nerve, and the centre some portion of the brain lying
below the corpora quadrigemina in the front part of the floor of the
aqueduct of Sylvius. This is proved by the following facts. When
the optic nerve is divided, the falling of light on the retina no
longer causes a contraction of the pupil. When the third nerve is
divided, stimulation of the retina or of the optic nerve no longer
causes contraction ; but direct stimulation of the peripheral portion
of the divided third nerve causes extreme contraction of the pupil.
If the region of the brain spoken of above as a centre be carefully
stimulated contraction of the pupil will take place even in the
absence of light and after division of the optic nerve. After
removal of the same centre stimulation of the retina is ineffectual
in narrowing the pupil. But if the centre and its connections with
the optic nerve and third nerve be left intact and in thoroughly
sound condition, contraction of the pupil will occur as a result of
light falling on the retina, though all other nervous parts be
removed.

The nervous centre is not a double centre with two completely
independent halves, one for each eye ; there is a certain amount
of functional communion between the two sides, so that when one
retina is stimulated both pupils contract. It might be imagined
that this cerebral centre acted as a tonic centre, whose action was
simply increased not originated by the stimulation of the retina ;
but this is disproved by the fact that, if the optic nerve be
divided, subsequent section of the third nerve produces no further
dilation.

In considering the movements of the pupil, howrever, we have
to deal not only with a narrowing of the pupil thus brought about,
in a reflex way by contraction of the circular sphincter fibres, and
with the absence of such a narrowing, but also with active dilation
due to a contraction of the radial dilator fibres, and this renders the
whole matter much more complex than might be supposed to be the
case from the simple statement just made.

502

MOVEMENTS OF THE PUPIL. [BOOK in.

The iris is supplied, in common with the ciliary muscle and
choroid, by the short ciliary nerves (Fig. 68 s.c.) coming from the
ophthalmic or lenticular (ciliary) ganglion (I.e.) which is connected
by its roots with the third nerve (r.b.), the cervical sympathetic nerve
(sym.), and with the nasal branch of the ophthalmic division of the

FIG. 68. DIAGRAMMATIC REPRESENTATION OP THE NERVES GOVERNING THE PUPIL.

II. Optic nerve, l.g. lenticular ganglion, r.b. its short root from III. oc.in. third
or oculo-motor nerve. sym. its sympathetic root. r.l. its long root from
V. ophthm. the nasal branch of the ophthalmic division of the fifth nerve,
s.c. the short ciliary nerves from the lenticular ganglion. I.e. the long ciliary
nerve from the nasal branch of the ophthalmic division of the fifth nerve.

fifth nerve (r.l.) The short ciliary nerves are, moreover, accompanied
by the long ciliary nerves (I.e.) coming from the same nasal branch
of the ophthalmic division of the fifth nerve. What are the uses
of these several nerves in relation to the pupil ?

If the cervical sympathetic in the neck be divided, all other
portions of the nervous mechanism being intact, a contraction of
the pupil (not always very well marked) takes place, and if the
peripheral portion (i.e. the upper portion still connected with the

CHAP. IT.] SIGHT. 503

head) be stimulated, a well-developed dilation is the result. The
sympathetic has, it will be observed, an effect on the iris, the
opposite of that which it exercises on the blood-vessels ; when it is
stimulated the pupils are dilated while the blood-vessels are con-
stricted. This dilating influence of the sympathetic may, as in the
case of the vaso-motor action of the same nerve, be traced back
down the neck to the upper thoracic ganglion and thence along the
rami communicantes and roots of the lower cervical and first dorsal
or two first dorsal spinal nerves, to a region in the lower cervical
and upper dorsal cord (called by some authors the centrum cilio-
spinale inferius), and from thence up through the medulla oblongata
to a centre, which appears to be placed in the floor of the front part
of the aqueduct of Sylvius not far from and apparently on either
side of the centre for contraction of the pupil.

The dilation of the pupil which is witnessed in dyspnrea, and that
which results from stimulation of sensory nerves and from emotions,
appears to be brought about by the action of the sympathetic, the
venous blood, or the sensory impulses or the emotional impulses so
affecting the dilating centre as to augment the dilating impulses
proceeding from it along the sympathetic. The existence of the
subordinate centre in the cervical or dorsal cord, spoken of just
now, is supposed to be indicated by the fact that after division of
the medulla oblongata, and consequent severance of the efferent
paths from the centre in the aqueduct of Sylvius, dilation of the
pupil may still be brought about, in some animals at least, by
dyspnoea or by adequate stimulation of sensory nerves. A
question is raised here in fact somewhat similar to that raised in
connection with the medullary respiratory centre (p. 355) ; and
here as there we may probably conclude that the independent
action of such a spinal centre is of subordinate importance.

The pupil then seems to be under the. dominion of two antago-
nistic mechanisms : one a contracting mechanism, reflex in nature,
the third nerve serving as the efferent, and the optic as the afferent
tract ; the other a dilating mechanism, apparently tonic in nature,
but subject to augmentation from various causes, and of this the
cervical sympathetic is the efferent channel. Hence, when the
third or optic nerve is divided, not only does contraction of the
pupil cease to be manifest, but active dilation occurs, on account of
the tonic dilating influence of the sympathetic being left free to
work. When, on the other hand, the sympathetic is divided, this
tonic dilating influence falls away, and contraction results. When
the optic or third nerve is stimulated, the dilating effect of the
sympathetic is overcome, and contraction results ; and when the
sympathetic is stimulated, any contracting influence of the third
nerve which may be present is overcome, and dilation ensues.

But there are considerations which shew that the matter is still
more complex than this. A small quantity of atropin introduced
into the eye or into the system causes a dilation of the pupil. This

504 MOVEMENTS OF THE PUPIL. [BOOK in.

might be attributed to a paralysis of the third nerve, and indeed it
is found that after atropin has produced its effects the falling of
light on the retina no longer causes contraction of the pupil. A
difficulty however is introduced by the fact that when the third
nerve is divided, and when therefore the contracting effects of
stimulation of the retina are placed entirely on one side, and there
is nothing to prevent the sympathetic producing its dilating effects
to the utmost, dilation is still further increased by atropin. When
physostigmin is introduced into the eye or system, contraction of
the pupil is caused, whether the third nerve be divided or not ; and
when the dose is sufficiently strong the contraction is so great that
it cannot be overcome by stimulation of the sympathetic. The
dilation which is caused by a sufficient dose of atropin may be
greater than that which can ordinarily be produced by stimulation
of the sympathetic, and the contraction caused by a sufficient dose
of physostigmin may be greater than that which is ordinarily
produced in a reflex manner by stimulation of the optic nerve,
or even than that produced by direct stimulation of the third
nerve. Evidently these drugs act either directly on the plain
muscular fibres of the iris or on some local mechanism, the
One in such a way as to cause dilation, the other in such a way
as to cause contraction. Such a local mechanism cannot how-
ever lie in the ophthalmic ganglion, for both drugs continue to
produce these effects in a most marked degree after the ganglion
has been excised. We must suppose therefore that the mechanism
if it exists is situated in the iris itself or in the chorcid, where
indeed ganglionic nerve-cells are abundant. The movements of
the iris in the extirpated eye, spoken of just now, may perhaps
be attributed to the same local mechanism. Further it is stated
that with stimulation of the sympathetic, the latent period, i.e.
the period intervening between the beginning of stimulation and
the beginning of the movement of the iris, is much greater than
with stimulation of the third nerve, indicating that the former
acts through a local mechanism but the latter more directly on
the muscular fibres. The whole question however of this local
mechanism, and of the exact mode of action of the various drugs
and of the changes in the body which lead to contraction or
dilation respectively of the pupil, needs fuller discussion than
we can afford to give to it here. We may add that the local
action of atropin in contrast to any action on the cerebral centre
is well illustrated by applying atropin to one eye locally. The
pupil of that eye dilates widely ; in consequence more light falls
on the retina, and this so affects the cerebral centre, which as
we have. seen is not strictly unilateral but in communion with
its fellow, that increased constricting impulses pass from both
centres, and these, though ineffectual in the atropinized eye,
lead in the untouched eye to an increased narrowing of the pupil.
The share of the fifth nerve in the work of the iris seems to be

CHAP, ii.] SIGHT. 505

in part a sensory one ; the iris is sensitive, and the sensory impulses
which are generated in it pass from it along the fibres of the fifth
nerve. Moreover the fifth is peculiarly related to the dilating effects
of the sympathetic. For though the ophthalmic ganglion does
receive fibres directly from the cavernous plexus of the sympathe-
tic, the dilating action of the sympathetic would seem to be carried
out not by these fibres but by fibres joining the fifth nerve, and
passing to the iris not by the ganglion but by the ophthalmic
branch and the long ciliary nerves. The vaso-motor fibres of the
sympathetic, and those which dilate the iris, after running to-
gether in the main cervical sympathetic chain, part company
higher up, the latter passing to the Gasserian ganglion, and thus
reaching the nasal branch of the ophthalmic division of the fifth
nerve. Some observers maintain that in addition to these dilating
fibres of the sympathetic joined to it, the fifth contains fibres of its
own which also are able to dilate the pupil.

We may sum up the nervous mechanism of the pupil then
somewhat as follows. The salient and most frequently repeated
event, the contraction of the pupil, upon exposure to light, is a
reflex act, the centre of which is placed in the brain ; arid the
correlative widening of the pupil upon diminution of light is due
to the tonic action of the sympathetic making itself felt upon the
waning of its antagonist. The contraction of the pupil in the
earlier stages of the action of alcohol and chloroform and in
slumber is probably due to an increased action of the contracting
centre, but the narrow pupil caused by such drugs as morphia
and physostigmiii is due, chiefly at least, to a local action. The
dilating effects of such drugs as atropin are also largely due to a
local action, but in the widened pupil of the later stages of alcohol
poisoning and of dyspnoea we can probably trace the effects cf
an exhaustion of the cerebral contracting centre, assisted possibly
by an increased activity of the dilating centre.

There remains a wrord to be said concerning the contraction of
the pupil which takes place when the eye is accommodated for near
objects, and when the pupil is turned inwards (the two being
closely allied, since the eyes converge to see near objects), and the
return to the more dilated condition when the eye returns to rest
and regains the accommodation for far objects. These are instances
of what are called " associated movements." Two movements are
thus spoken of as " associated " when the special central nervous
mechanism employed in carrying out the one act is so connected
by nervous ties of some kind or other with that employed in
carrying out the other, that when we set the one mechanism
in action we unintentionally set the other in action also. The
ciliary muscles which bring about accommodation are governed in
this action by fibres which may be traced, through the ciliary
nerves and lenticular ganglion, along the third or oculo-motor
nerve, to a centre which lies (in dogs) in the hind part of the floor

506 DIOPTRIC IMPERFECTIONS. [BOOK HI.

of the third ventricle, and which is especially connected with the
most anterior bundles of the roots of the third nerve. This centre
is under the command of our will : when we wish to accommodate
for near objects we throw it into action, and it, when in action, calls
also into action by ' association ' the centre for the contraction of
the pupil ; when the action of the accommodation centre ceases and
the eye falls back to the condition of rest, in which it is accommo-
dated for far objects, the action of the pupil-contracting centre
ceases also, and the pupil therefore widens.

The mechanism of accommodation may also be affected in a
local manner. And the drugs which have a special action on the
pupil, such as atropin and calabar bean, also affect the mechanism
of accommodation. Atropin paralyses it, so that the eye remains
adjusted' for far objects ; and physostigmin throws the eye into a
condition of forced accommodation for near objects. This double
action has been explained by the supposition that while atropin
paralyses, physostigmin throws into tonic or tetanic contraction,
on the one hand the circular muscles of the iris and on the other
the ciliary muscles; but the phenomena, on inquiry, appear too
complicated to be explained in so simple a manner.

We can accommodate at will ; but few persons can effect the
necessary change in the eye unless they direct their attention to
some near or far object, as the case may be, and thus assist their
will by visual sensations. By practice, however, the aid of external
objects may be dispensed with; and it is when this is achieved
that the pupil may seem to be made to dilate or contract at
pleasure, accommodation being effected without the eye being
turned to any particular object.

Imperfections in the Dioptric Apparatus.

The emmetropic eye may be taken as the normal eye. The
myopic and hypermetropic eyes may be considered as imperfect
eyes, though the former possesses certain advantages over the
normal eye. An eye might be myopic from too great a convexity
of the cornea, or of the anterior surface of the lens, or from per-
manent spasm of the accommodation-mechanism, or from too great
a length of the long axis of the eyeball. The last appears to
be the usual cause. Similarly, most hypermetropic eyes possess
too short a bulb. Moreover in the strongly marked myopic eye
there is frequently hypertrophy of the longitudinal (meridional)
fibres of the ciliary muscle, often spoken of exclusively as the
ciliary muscle, and atrophy or absence of the circular fibres ; in the
hypermetropic eye on the other hand the circular fibres are well
developed and the meridional fibres scanty. The presbyopic eye

CHAP, ii.] SIGHT, 507

is, as we have seen, an eye normally constituted in which the
power of accommodation has been lost of is failing through in-
creasing weakness of the ciliary muscle or a loss of elasticity in
the lens, or through the parts becoming rigid.

Spherical Aberration. In a spherical lens the rays which
impinge on the circumference are brought to a focus sooner than
those which pass nearer the centre, and the rays proceeding from
a luminous point are no longer brought to a single focus at one
point but form a number of foci at different distances. Hence when
rays are allowed to fall on the whole of the lens, the image formed
on a screen placed in the -focus of the more central rays is blurred
by the diffusion-circles caused by the circumferential rays which
have been brought to a premature focus. In an ordinary optical
instrument spherical aberration is obviated by a diaphragm which
shuts off the more circumferential rays. In the eye the iris is an
adjustable diaphragm ; and when the pupil contracts in near vision
the more divergent rays proceeding from a near object, which tend
to fait on the circumferential parts of the lens, are cut off. As,
however, the refractive power of the lens does not increase regu-
larly and progressively from the centre to the circumference, but
varies most irregularly, the purpose of the narrowing of the pupil
cannot be simply to obviate spherical aberration ; and indeed the
other optical imperfections of the eye are so great, that such
spherical aberrations as are caused by the lens produce no obvious
effect on vision.

Astigmatism. We have hitherto treated the eye as if its
dioptric surfaces were all parts of perfect spherical surfaces. In
reality this is rarely the case, either with the lens or with the
cornea. Slight deviations do not produce any marked effect, but
there is one deviation, known as regular astigmatism, which, present
to a certain extent in most eyes, very largely developed in some,
frequently leads to very imperfect vision. This defect is due to the
dioptric surface being not spherical but more convex along one
meridian than another, more convex, for instance, along the vertical
than along the horizontal meridian. When this is the case the rays
proceeding from a luminous point are not brought to a single focus
at a point, but possess two linear foci, one nearer than the normal
focus and corresponding to the more convex surface, the other
farther than the normal and corresponding to the less convex
surface. If the vertical meridians of the surface be more convex
than the horizontal, then the nearer linear focus will be horizontal
and the farther linear focus will be vertical, and vice versa. (This
can be shewn much more effectually on a model, than in a diagram
in which we are limited to two dimensions.) Now, in order to see
a vertical line distinctly, it is much more important that the rays
which diverge from the line in a series of horizontal planes should
be brought to a focus properly than those which diverge in the

508 DIOPTRIC IMPERFECTIONS. [BOOK HI.

vertical plane of the line itself; and similarly, in order to see a
horizontal line distinctly it is much more important that the rays
whch diverge from the line in a series of vertical planes should be
brought to a focus properly than those which diverge in the
horizontal plane of the line itself. Hence a horizontal line held
before an astigmatic dioptric surface, most convex in the vertical
meridians, will give rise to the image of a horizontal line at the
nearer focus, the vertical rays diverging from the line being here
brought to a linear horizontal focus. Similarly, a vertical line
held before the same surface will give rise to an image of a vertical
line at the farther focus, the horizontal rays diverging from the
vertical line being here brought to a linear vertical focus. In
other words, with a dioptric surface most convex in the vertical
meridians, horizontal lines are brought to a focus sooner than are
vertical lines.

Most eyes are thus more or less astigmatic, and generally with
a greater convexity along the vertical meridians. If a set of
horizontal or vertical lines be looked at, or if the near point of
accommodation be determined by Schemer's experiment (p. 494),
for the needle placed first horizontally and then vertically, the
horizontal lines or needle will be distinctly visible at a shorter
distance from the eye than the vertical lines or needle. Similarly,
the vertical line must be farther from the eye than a horizontal
one, if both are to be seen distinctly at the same time. The cause
of astigmatism is, in the great majority of cases, the unequal
curvature of the cornea ; but sometimes the fault lies in the lens,
as was the case with Young.

When the curvature of the comea or lens differs not in two
meridians only but in several, irregular astigmatism is the result.
A certain amount of irregular astigmatism exists in most lenses,
thus causing the image of a bright point, such as a star, to be not
a circle but a radiate figure.

Chromatic Aberration. The different rays of the spectrum
are of different refrangibility, those towards the violet end of the
spectrum being brought to a focus sooner than those near the red
end. This in optical instruments is obviated by using compound
lenses made up of various kinds of glass. In the eye we have no
evidence that the lens is so constituted as to correct this fault ;
still the total dispersive power of the instrument is so small, that
such amount of chromatic aberration as does exist attracts little
notice. Nevertheless some slight aberration may be detected by
careful observation. When the spectrum is observed at some
distance the violet end will not be seen in focus at the same time
as the red. If a luminous point be looked at through a narrow
orifice covered by a piece of violet glass, which while shutting out
the yellow and green allows the red and blue rays to pass through,
there will be seen alternately an image having a blue centre with

CHAP, ii.]

SIGHT.

509

a red fringe, or a red centre with a blue fringe, according as the
image of the point looked at is thrown on one side or other of the
true focus. Thus supposing / (Fig. 69) to be the plane of the

FlG. 69. DlAOBAM ILLUSTRATING CHROMATIC ABERRATION.

hh is the dioptric surface, hv represents the blue, and 7<r the red rajs; V is the focal
plane of the blue, R of the red rays.

mean focus of A, the violet rays will be brought to a focus in the
plane V, and the red rays in the plane R. If the rays be supposed
to fall on the retina between V and /, the diverging or blue rays
will form a centre surrounded by the still converging red rays ;
whereas if the rays fall on the retina between / and 11, the con-
verging red rays will form a centre with the still diverging blue
rays forming a fringe round them. If the rays fall on the retina at
/, the two kinds of rays will be mixed together ; as will be seen
from the figure, the circumferential still converging red ray lir as
it cuts the plane of the retina is, in ordinary vision, accompanied
by the diverging violet ray hv, and thus by a sort of compensation,
we see together even the rays which differ most in refraction.

Entoptic Phenomena. The various media of the eye are not
uniformly transparent ; the rays of light in passing through them
undergo local absorption and refraction, and thus various shadows
are thrown on the retina, of which we become conscious as im-
perfections in the field of vision, especially when the eye is directed
to a uniformly illuminated surface. These are spoken of as
entoptic phenomena, and are very varied, many forms having been
described.

The most common are those caused by the presence of floating
bodies in the vitreous humour, the so-called muscce volitantes.
These are readily seen when the eye is turned towards a uniform
surface, and are frequently very troublesome in looking through a
microscope. They are especially obvious when divergent rays fall
upon the eye. They assume the form of rows and groups of
beads, of single beads, of streaks, patches and granules, and may
be recognised by their almost continual movement, especially when
the head or eye is moved up and down. When an attempt is
made to fix the vision upon them, they immediately float away.
Tears on the cornea, temporary unevenness on the anterior surface
of the cornea after the eyelid has been pressed on it, and imper-
fections in the lens or its capsule, also give rise to visual images.

510 DIOPTRIC IMPERFECTIONS. [BOOK m.

Not unfrequentlya radiate figure corresponding to the arrangement
of the fibres of the lens makes its appearance.

Imperfections in the margin of the pupil appear in the shadow
of the iris which bounds the field of vision ; and the movements
of the iris in one eye may be rendered visible by looking at a bright
point or luminous surface through a pin-hole in a card placed close
in the front of the eye, in the anterior focus in fact, and then
alternately closing and opening the other eye ; the field of the
first may be observed to contract when light enters, and to expand
when the light is shut off from the second. The media of the eye are
fluorescent : a condition which favours the perception of the ultra-
violet rays. If a white sheet or white cloud be looked at in day-
light through a Nicol's prism, a somewhat bright double cone or
double tuft, with the apices touching, of a faint blue colour, is
seen in the centre of the field of vision, crossed by a similar double
cone of a somewhat yellow darker colour. These are spoken of
as Haidinger's brushes ; they rotate as the prism is rotated, and
are supposed to be due to the unequal absorption of the polarized
light in the yellow spot. The prism must be frequently rotated,
as when the prism remains at rest the phenomena fade. Lastly,
the optical arrangements have a further imperfection in that the
dioptric surfaces are not truly centred on the optic axis.

SEC. 2. VISUAL SENSATIONS.

Light falling on the retina excites sensory impulses, and these
passing up the optic nerve to certain parts of the brain, produce
changes in certain cerebral structures, and thus give rise to what
we call a sensation. In a sensation we ought to be able to dis-
tinguish between the events through which the impact of the rays
of light on the retina is enabled to generate sensory impulses, and
the events, or rather series of events, through which these sensory
impulses (for, judging by the analogy of motor nerves, we have no
reason to think that they undergo any fundamental changes in
passing along the optic nerve), by the agency of the cerebral
arrangements, develope into a sensation. Such an analysis, how-
ever, is, at present at least, in most particulars, quite beyond our
power ; and we must therefore treat of the sensations as a whole,
distinguishing between the peripheral and central phenomena, on
the rare occasions when we are able to do so.

The Origin of Visual Impulses.

Of primary importance to the understanding of the way in
which luminous undulations give rise to those nervous changes
which pass along the optic nerve as visual impulses, is the fact that
the rays of light produce their effect by acting not on the optic
nerve itself but on its terminal organs (see p. 488). They pass
through the anterior layers of the retina apparently without induc-
ing any effect ; it is not till they have reached the region of the
rods and cones that they set up the changes concerned in the

512 VISUAL SENSATIONS. [BOOK HI.

generation of visual impulses; and the impulses here generated
travel back to the layer of fibres in the anterior surface of the
retina and thence pass along the optic nerve. That the optic fibres
are themselves insensible to light and that visual impulses begin in
the region of rods and cones is shewn by the phenomena of the
blind spot and of Purkinje's figures respectively.

Blind Spot. There is one part of the retina on which rays of
light falling give rise to no sensations ; this is the entrance of the
optic nerve, and the corresponding area in the field of vision is
called the blind spot. If the visual axis of one eye, the right for
instance, the other being closed, be fixed on a black spot in a white
sheet of paper, and a small black object, such as the point of a quill
pen dipped in ink, be moved gradually sideways over the paper
away to the outside of the field of vision, at a certain distance the
black point of the quill will disappear from view. On continuing
the movement still farther outward the point will again come into
view and continue in sight until it is lost in the periphery of the
field of vision. If the pen be used to make a mark on the paper at
the moment when it is lost to view, and at the moment when it
comes into sight again ; and if similar marks be made along the
other meridians as well as the horizontal, an irregular outline will
be drawn circumscribing an area of the field of vision within which
rays of light produce no visual sensation. This is the blind spot.
The dimensions of the figure drawn vary of course with the distance
of the paper from the eye. If this distance be known, the size as
well as the position of the area of the retina corresponding to the
blind spot may be calculated from the diagrammatic eye (p. 492).
The position exactly coincides with the entrance of the optic nerve,
and the dimensions (about 1'5 mm. diameter) also correspond.
While drawing the outline as above directed the indications of the
large branches of the retinal vessels as they diverge from the
entrance of the nerve can frequently be recognised. The existence
of the blind spot is also shewn by the fact that an image of light,
sufficiently small, thrown upon the optic nerve by means of the
ophthalmoscope, gives rise to no sensations.

The existence of the blind spot proves that the optic fibres
themselves are insensible to light; it is only through the agency
of the retinal expansion that these can be stimulated by luminous
vibrations.

Purkinje's Figures. If one enters a dark room with a candle,
and while looking at a plain (not parti-coloured) wall, moves the
candle up and down, holding it on a level with the eyes by the side
of the head, there will appear in the field of vision of the eye of the
same side, projected on the wall, an image of the retinal vessels,
quite similar to that seen on looking into an eye with the ophthal-
moscope. The field of vision is illuminated with a glare, and on

CHAP. ii.

SIGHT.

this the branched retinal vessels appear as shadows. In this mode
of experimenting the light enters the eye through the cornea, and
an image of the candle is formed on the nasal side of the retina ;
and it is the light emanating from this image which throws shadows
of the retinal vessels on to the rest of the retina. A far better
method is for a second person to concentrate the rays of light, with
a lens of low power, on to the outside of the sclerotic just behind
the cornea ; the light in this case emanates from the illuminated
spot on the sclerotic and passing straight through the vitreous
humour throws a direct shadow of the vessels on to the retina.
Thus the rays passing through the sclerotic at 6, Fig. 70, in the
direction bv, will throw a shadow of the vessel v on to the retina at
(S ; this will appear as a dark line at B in the glare of the field of
vision. This proves that the structures in which visual impulses
originate must lie behind the retinal vessels, otherwise the shadows
of these could not be perceived.

B A

FIG. 70. DIAGRAM ILLUSTRATING THE FORMATION OF PUKKINJE'S FIGURES WHEN THE
ILLUMINATION is DIRECTED THROUGH THE SCLEROTIC.

If the light be moved from b to a, the shadow on the retina will
move from # to a, and the dark line in the field of vision will move
from B to A. If the distance BA be measured when the whole
image is projected at a known distance, &B from the eye, k being
the optical centre1, then, knowing the distance k$ in the diagram-
matic eye, the distance fia can be calculated. But if the distance
(3a be thus estimated, and the distance ba be directly measured,
the distances (3v, av, bv, av can be calculated, and if the appearance
in the field of vision is really caused by the shadow of v falling on

1 For the properties of the optical centre, we must refer the reader to the various
treatises on optics. The optical centre of a lens is the point through which all the
principal rays, of the various pencils of rays falling on the lens, pass. The diagram-
matic eye of Listing (p. 492) has two optical centres, but the.e may, without serious
error, be further reduced for practical purposes to one lyijg in the lens near its
posterior surface, at about 15 mni. distance from the retina.

F. 33

514 VISUAL SENSATIONS. [BOOK in.

ft, these distances ought to correspond to the distances of the retinal
vessels v from the sclerotic b on the one hand, and from that part
of the retina /fif where visual impressions begin, on the other. H.
Miiller found that the distance fii> thus calculated corresponded to
the distance of the retinal vessels from the layer of rods and cones.
Thus Purkinje's figures prove in the first place that the sensory
impulses which form the commencement of visual sensations origi-
nate in some part of the retina behind the retinal vessels, i.e. some-
where between them and the choroid coat; and H. Miiller's calcula-
tions go far to shew that they originate at the most posterior
or external part of the retina, viz. the layer of rods and cones.
It must be admitted however that H. Miiller's results were not
sufficiently exact to allow any great stress to be placed on this
argument.

In the second method of experimenting, the image always moves
in the same direction as the light, as it obviously must do. In the
first method, where the light enters through the cornea, the image
moves in the same direction as the light when the light is moved
from right to left, provided the movement does not extend beyond
the middle of the cornea, but in the opposite direction to the light
when the latter is moved up and down. In Fig. 71, which repre-
sents a horizontal section of an eye, if a be moved to a, b will move
to /3, the shadow on the retina c to 7, and the image d to 8. If on
the other hand a be supposed to move a-bove the plane of the paper,
b will move below, in consequence o will move above, and d will
appear to move below, i.e. d will sink as a rises.

FIG. 71. DIAGRAM ILLUSTRATING THIS FORMATION OF PURKINJE'S FIGURES WUKN THE
ILLUMINATION is DIRECTED THROUGH THE CORNEA.

It is desirable in these cases to move the light to and fro, espe-
cially in the first method, as the retina soon becomes tired, and the
image fades away. Some observers can recognise in the axis of
vision a faint shadow corresponding to the edge of the depression
of the fovea centralis.

The retinal vessels may also be rendered visible by looking
through a small orifice such as a pin-hole in a card placed close
to the eye, at a bright field such as the sky, and moving the

CHAP. IL] SIGHT. 515

orifice very rapidly from side to side or up and down. If the
movement be from side to side, the vessels which run vertical will
be seen ; if up and down, the horizontal vessels. The fine capillary
vessels are seen more easily in this way than by Purkinje's method.
The same appearances may also be produced by looking through
a microscope from which the objective has been removed and the
eye-piece only left (or in which at least there is no object distinctly
in focus in the field), and moving the head rapidly from side to side
or backwards and forwards. Or the microscope itself may be
moved; a circular movement of the field will then bring both
the vertically and horizontally directed vessels into view at the
same time.

The Photochemistry of the Retina. In seeking to understand
how it is that rays of light falling upon the region of the rods and
cones can give rise to sensory, visual, impulses in the optic nerve, we
may adopt one or other of two views. On the one hand we may
suppose that the vibrations of the ether are able, through the means
of the retinal apparatus of the rods and cones for example, to give
rise in some way or other to molecular vibrations which are the
beginning of the nervous impulses in the optic nerve. No satis-
factory explanation of how such a change can be brought about has
been offered, and indeed the difficulties of such a conception are
very great. On the other hand we may more naturally turn to a
chemical explanation. We are familiar with the fact that rays of
light are able to bring about the decomposition of very many
chemical substances ; and we accordingly speak of these substances
as being sensitive to light. All the facts dwelt on in this book
illustrate the great complexity and corresponding instability of the
composition of protoplasm. And we might reasonably suppose that
protoplasm itself would- be sensitive to light; that is to say that
rays of light falling on even undifferentiated protoplasm might set
up a decomposition of that protoplasm and so inaugurate a mole-
cular disturbance ; in other words, that light might act as a direct
stimulus to protoplasm. As a matter of fact, however, such evi-
dence as we at present possess goes to shew that native undifferen-
tiated protoplasm is as a rule not sensitive to light (that is, to those
particular waves which when they fall on our retina give rise in us
to the sensation of light), though in the case of some lowly organ-
isms whose protoplasm exhibits very little differentiation and in
particular contains no pigment, a sensitiveness to light has been
observed. Nor can we be surprised at this indifference of proto-
plasm when we reflect that what we may call pure protoplasm is
remarkable for its transparency, that is to say the rays of light pass
through it with the slightest possible absorption. But in order
that light may produce chemical effects, it must be absorbed ; it
must be spent in doing the chemical work. Accordingly the first
step towards the formation of an organ of vision is the differentia^

33—2

516 VISUAL SENSATIONS. [BOOK in.

tion of a portion of protoplasm into a pigment at once capable of
absorbing light, and sensitive to light, i.e. undergoing decomposition
upon exposure to light. An organism, a portion of whose proto-
plasm had thus become differentiated into such a pigment, would
be able to react towards light. The light falling on the organism
would be in part absorbed by the pigment, and the rays thus
absorbed would produce a chemical action and set free chemical
substances which before were not present. We have only to sup-
pose that the chemical substances are of such a nature as to act as
a stimulus to the protoplasm of other parts of the organism, (and
we have manifold evidence of the exquisite sensitiveness of proto-
plasm in general to chemical stimuli,) in order to see how rays of
light falling on the organism might excite movements in it, or
modify movements which were being carried on, or might other-
wise affect the organism in whole or in part.

Such considerations as the foregoing may be applied to even
the complex organ of vision of the higher animals. If we suppose
that the actual terminations of the optic nerve are surrounded by
substances sensitive to light, then it becomes easy to imagine how
light falling on these sensitive substances should set free chemical
bodies possessed of the property of acting as stimuli to the actual
nerve-endings and thus give rise to visual impulses in the optic
fibres. We say "easy to imagine/' but we are, at present, far from
being able to give definite proofs that such an explanation of the
origin of visual impulses is the true one, probable and enticing as
it may appear.

One of the most striking features in the structure of the retina
is the abundance of black pigment in the retinal, or as it is some-
times called choroidal, epithelium. It is difficult to suppose that
the sole function of this pigment is to absorb the superfluous rays
of light, and that the rays thus absorbed are put to no use but
simply wasted. And indeed it has been shewn that the pigment is
sensitive to light; but the changes in it induced by light are ex-
cessively slow. Moreover its presence cannot be of fundamental
importance, since vision is not only possible but fairly distinct with
albinos in which -this pigment is absent.

Then again, in the vast majority of vertebrate animals, the
outer limbs of the rods are suffused with a purplish-red pigment,
the so-called visual purple, which is so eminently sensitive to light
that images of external objects may by appropriate means be
photographed in it on the retina. When the eye of a frog or of a
rabbit is examined in an ordinary way, with full exposure to light,
the retina appears colourless. But if the eye be kept in the
dark for some time before it is examined, the retina, if removed
rapidly, will be found to be of a beautiful purplish-red colour.
Upon exposure to light the colour changes to yellow and then
fades away, leaving however the retina, not only white but more
opaque than it was before. Upon examination with the microscope

. ii.] SIGHT. 517

it is found that the purple colour ia confined exclusively to the
rods and to the outer limbs of the rods, the inner limbs being wholly
devoid of it.

The colour of the rods is due to the presence of a distinct
pigment, the "visual purple," diffused through the substance of the
outer limbs ; and this may be extracted from the rods by dissolving
these in an aqueous solution of bile salts. A clear purple solution
is thus obtained, which is capable of being bleached by the action
of light, and in its general features and behaviour is similar to the
pigment as it naturally exists in the retina.

Visual purple is found as we have said exclusively in the outer
limbs of the rods; it has never yet been found in the cones,
and it is accordingly absent from "the retinas (such as those of
snakes) which are composed of cones only, and from the macula
lutea and fovea centralis of the retinas of man and the ape. The
intensity of the colouration varies in different animals, and the
retinas even of some animals possessing rods (bat, dove, hen) seem
to be wholly devoid of the visual purple; it is generally well
marked in retinas in which the outer limbs of the rods are well
developed. Its absence or presence is not dependent on nocturnal
habits, since the intense colour of the retina of the owl is in strong
contrast to the absence of colour in the bat. It has been found in
the retina of the embryo.

The visual purple is bleached not only by white but also by
monochromatic light, Of the various prismatic rays the mos't
active are the greenish-yellow rays, those to the blue side of these
coming next, the least active being the red. Now it is precisely
the greenish-yellow rays which are most readily absorbed by the
colour itself. A natural coloured retina or a solution of visual
purple gives a diffuse spectrum without any defined absorption
bands, and according to the amount of colouring material through
which the light passes, absorption is seen either to be limited to
the greenish-yellow part of the spectrum or to spread thence
towards the blue and, to a much less extent, towards the red.
Thus the various prismatic rays produce a photochemical effect on
the visual purple in proportion as they are absorbed by it. Under
the action of light the visual purple, whether in solution, or in its
natural condition in the rods, passes through a purplish orange to
a yellow, and finally becomes colourless ; and we appear to be
justified in speaking of a "visual yellow" and "visual white" as
products of the photochemical changes undergone by the visual
purple.

For the restoration of the visual purple, after it has been
destroyed by light, the maintenance of the circulation of the blood
through the tissues of the eye is not essential. The choroidal
epithelium has by itself, provided that it still retains its tissue life,
the power of regenerating the purple. If a portion of the retina
of an excised eye be raised from its epithelial bed, bleached, and

518 VISUAL SENSATIONS. [BOOK in.

then carefully restored to its natural position, the purple will
return if the eye be kept in the dark. The choroidal epithelium
may in fact be spoken of as a 'purpurogenous' membrane.

If the image of some bright object such as a lamp or a window
be thrown on to the retina, either of an eye in its natural position
or of one recently excised, care having been taken to keep the
retina for some time previous away from any rays of light, the
portion of the retina on which the rays have fallen will be found
to be bleached, the rest of the retina remaining purple. In fact
an " optogram " of external objects may thus be obtained ; and
if the retina be removed and treated with a 4p.c. solution of
potash alum before the choroidal epithelium has had time to
obliterate the bleaching effects, the retina may remain permanently
in that condition: the photochemical effect may, as the photo-
graphers say, be " fixed."

It seemed very tempting, especially upon the first discovery
of it, to suppose that this visual purple is directly concerned in
vision. If we suppose that visual purple itself is inert towards
the endings of the optic nerve, but that either visual yellow or
visual white, i.e. some product of the action of light on visual
purple, may act as a stimulus to those endings, the way seems
opened to understanding how rays of light can give rise to sensory
impulses in the optic nerve. Unfortunately visual purple is absent
from the cones, and from the fovea centralis which, as we shall
see, is the region of distinct vision ; it is further entirely wanting
in some animals which undoubtedly see very well ; and lastly
animals, such as frogs naturally possessing the pigment, continue
to see very well and even apparently to see colours when their
visual purple has been absolutely bleached, as it may be by
prolonged exposure of the eyes to strong light. We cannot there-
fore, at present at least, explain the origin of visual impulses by
the help of visual purple. At the same time its history suggests
that some substances, sensitive like it to light, but unlike it,
colourless and therefore escaping observation, may exist, and by
photochemical changes be the means of exciting the optic nerves.
And, as we shall see later on, one theory of colour vision is based on
the assumption that vision is carried on in some way or other by
changes in what may be called visual substances present in the
retina, these substances being used up and regenerated as vision is
going on.

But even admitting as probable the existence of these sensitive
visual substances, the changes in which lead to stimulation of the
real endings of the retinal nervous mechanism, we cannot at
present state anything definite concerning those nerve endings or
the manner of their stimulation. It may be that even the outer
limbs of the rods and cones, in spite of the apparent break of
continuity between the outer and inner limbs, are really nervous
in nature. It may be on the other hand that the outer limbs

CHAP, ii.] RIGHT. 519

are either purely dioptric in function, or are associated with the
sensitive visual substances in such a way that the purely nervous
structures must be considered as extending no further at least than
the inner limbs. We cannot as yet make any definite statement
in the one direction or the other.

In connection with the origin of visual impulses we may
perhaps call attention to the remarkable changes which the cells
of the retinal pigment epithelium undergo under the influence of
light. When an eye has been shut off from all light for some
little time the pigment is concentrated in the bodies of the
cells, and the remarkable filamentous processes of the cells, with
the pigment granules or crystals which they carry, extend a
slight distance only between the limbs of the rods and cones
(about one-third down the length of the outer limbs of the rods),
tinder the influence of light these processes loaded with pigment
thrust themselves a much longer way down towards the external
limiting membrane ; in consequence a considerable quantity of
pigment is found massed between the outer and even the inner
limbs of the rods and cones ; indeed the outer limbs of the rods
swelling at the same time become jammed as it were between the
masses of pigment, causing the epithelial layer to adhere very
closely to the layer of rods and cones.

The retina and optic nerve like other nervous structures de-
velope electric currents which may be spoken of as currents of
rest and currents of action. They may be shewn by placing one
electrode on the retina of a bisected eye, or on the cornea of
a whole one, and the other on the optic nerve, or hind part of the
eye ball or even on some distant part of the body. They are also
manifested by the isolated retina itself. The phenomena appear
somewhat complicated by the appearance now of positive, now of
negative variations ; but this fact comes out clearly that the in-
cidence of light on the irritable retina developes an electric
change, the magnitude of which is to a certain extent propor-
tionate to the intensity of the light acting as a stimulus. The
changes accordingly diminish and cease to appear as the retina
gradually loses its irritability after death. We may add that these
electric phenomena appear to be quite independent of the con-
dition of the visual purple.

Simple Sensations.

Relations of the Sensation to the Stimulus. If we put aside
for the present all questions of colour, we may say that light,
viewed as a stimulus affecting the retina, varies in intensity, that
is, in the energy of the luminous vibrations as manifested by their
amplitude, and in duration, that is, in the length of time a succes-
sion of waves continues to fall upon the retina. The effect of the

520 VISUAL SENSATIONS. [BOOK in.

light will also depend on the extent of retinal surface exposed to
the luminous vibrations' at the same time. Taking a luminous
point, in order to eliminate the latter circumstance, we may make
the following statements.

The sensation has a duration much greater than that of the
stimulus, and in this respect is comparable to a muscular contrac-
tion caused by such a stimulus as a single induction shock. The
sensation of a flash of light for instance lasts for a much longer time
than that during which luminous vibrations are falling on the
retina. Hence when two stimuli, such as two flashes of light,
follow each other at a sufficiently short interval, the two sensations
are fused into one ; and a luminous point moving rapidly round in
a circle gives rise to the sensation of a continuous circle of light.
This again is quite comparable to muscular tetanus. The interval
at which fusion takes place, that is the interval between successive
stimuli which must be exceeded in order that successive distinct
sensations may be produced, varies according to the intensity of the
light, being shorter with the stronger light ; with a faint light it is
about -fa sec., with a strong light ^ or -J^ sec. This may be shewn
by rotating rapidly before the eye a disc arranged with alternate
black and white sectors of equal width. With a faint illumination,
the flickering indicative of the successive sensations from the white
sectors not being completely fused, ceases when the rotation be-
comes so rapid that each pair of black and white sectors takes
only j1^ sec. in passing before the eye. When a brighter illumina-
tion is used the rapidity must be increased before the flickering
disappears. That part of the sensation which is recognised as
lasting after the cessation of the stimulus is frequently spoken of
as the 'after-image.'

Though the duration of the after-image is longer with the
stronger light (that caused by looking even momentarily at the
sun lasting for some time) the commencement of the decline of
the sensation begins relatively earlier, hence the greater difficulty
in the complete fusion of successive sensations with the stronger
light. The interval at which fusion takes place differs with different
colours, being shortest with yellow, intermediate with red, and
longest with blue.

The duration of a stimulus necessary to call forth a sonsation is
exceedingly short ; thus the shortest possible flash, such as that
of an electric spark, gives rise to a sensation of light.

Objects in motion when illuminated by a single electric spark
appear motionless, the stimulus of the light reflected from them
ceasing before they can make an appreciable change in their posi-
tion. When a moving body is illuminated by several rapid flashes
in succession, several distinct images corresponding to the positions
of the body during the several flashes are generated : the images of
the body corresponding to the several flashes fall on different parts
of the retina.

CHAP, ii.] SIGHT. 521

The intensity of the sensation varies with the luminous inten-
sity of the object ; a wax candle appears brighter than a rushlight.
The ratio, however, of the sensation to the stimulus is not a simple
one. If the luminosity of an object be gradually increased from a
very feeble stage to a very bright one, it will be found that though
the corresponding sensations likewise gradually increase, the incre-
ments of the sensations due to increments of the luminosity
gradually diminish ; and at last an increase of the luminosity
produces no appreciable increase of sensation; a light, when it
reaches a certain brightness, appears so bright that we cannot tell
when it becomes any brighter. Hence it is much easier to distin-
guish a slight difference of brightness between two feeble lights
than the same difference between two bright lights; we can easily
tell the difference between a rushlight and a wax candle ; but two
suns, or even two bright lamps one of which differed from the
other merely by just the number of luminous rays which a wax
candle emits in addition to those sent forth by a rushlight, would
appear to us to have exactly the same brightness. In a darkened
room an object placed before a candle will throw what we consider
a deep shadow on a sheet of paper, or any white surface. If,
howrever, sunlight be allowed to fall on the paper at the same
time from the opposite side, the shadow is no longer visible. The
difference between the total light reflected from that part of the
paper where the shadow was, and which is illuminated by the sun
alone, and that reflected from the rest of the paper which is
illuminated by the candle as well as by the sun, remains the same;
yet we can no longer appreciate that difference.

On the other hand, if using two rushlights we throw two
rhadows on a white surface and move one rushlight away until the
shadow caused by it ceases to be visible ; and, having noted the
distance to which it had to be moved, repeat the same experiment
with two wax candles; we shall find that the wax candle has to
be moved just as far as the rushlight. In fact, it is found by
careful observation, that within tolerably wide limits, the smallest
difference of light which we can appreciate by visual sensations
is a constant fraction (about TJoth) of the total luminosity employed.
The same law holds good with regard to the other senses as well.
The smallest difference in length we can detect between two lines,
one an inch long and the other a little less than an inch, is the
p.ame fraction of an inch, that the smallest difference in length
we can detect between a line a foot long and one a little less than
a foot, is of a foot. Put in a more general form then, the law,
which is often called Weber's law *, is as follows : When a stimulus
is continually increased, the increase of stimulus necessary to call
forth the smallest appreciable increase of sensation always bears
the same proportion to the whole stimulus.

1 From which Fechner, by an assumption, obtained a mathematical expression
cr formula, which is sometimes incorrectly spoken of as Fechner's law.

522 VISUAL SENSATIONS. [BOOK in.

Distinction and Fusion of Sensations. When light falls on a
large portion of the retina the total sensation produced is greater
in amount than when a small portion only of the retina is affected ;
a large piece of white paper produces a greater total effect on our
consciousness than a small one, though, if the surfaces be uniformly
and equally illuminated, the intensity of the sensation is in each
case the same ; the small piece of paper appears as bright or as
' white ' as the large one. If the images of two luminous objects
fall on the retina at sufficient distances apart, the consequent
sensations are distinct, and the intensity of each sensation will
depend solely upon the luminosity of the corresponding object. If
however the two objects are made to approach each other, a point
will be reached at which the two sensations are fused into one.
When this occurs the intensity of the total sensation produced will
be greater than that of either of the sensations caused by the
single objects. A number of luminous points scattered over a wide
surface would appear each to have a certain brightness ; each would
give rise to a sensation of a certain intensity. If they were all
gathered into one spot, that spot would appear far brighter than
any of the previous points ; the intensity of the sensation would be
greater. We may therefore suppose the retina to be divided into
areas corresponding to sensational units. If the images from two
luminous objects fall on separate visual areas, if we may so call
them, two distinct sensations will be produced ; if, on the contrary,
they both fall on the same visual area, one sensation only will be
produced. Where the sensations are separate, the intensity of the
one (with exceptions hereafter to be mentioned) is not affected by
the presence of the other; but where they become fused the
intensity of the united sensations is greater than either of, though
not equal to the sum of, the single sensations. The existence of
these sensational units is the basis of distinct vision. When we
speak of the smallest size visible or distinguishable, we are referring
to the dimensions of the retinal areas corresponding to these sen-
sational units. The retinal area must be carefully distinguished
from the sensational unit, for the sensation is, as we have seen, a
process whose arena stretches from the retina to certain parts of
the brain, and the circumscription of the sensational unit, though
it must begin as a retinal area, must also be continued as a
cerebral area in the brain, the latter corresponding to, and being
as it were the projection of, the former. With most people two
stars appear as a single star when the distance between them sub-
tends an angle of less than 60 seconds ; and the best eyes generally
fail to distinguish two parallel white streaks when the distance
between the two, measured from the middle of each, subtends an
angle of less than 73 seconds. Some however can distinguish
objects 50 seconds distant from each other. An angle of 73 seconds
in an object corresponds in the diagrammatic eye (see p. 492) to the

CHAP. IL] SIGHT. 523

length of 5'36^ in the retinal image1, and one of 50 seconds to
3-65 p.

In the human eye 50 cones may be counted along a line of
200 fj, in length drawn through the centre of the yellow spot ; this
would give 4 //. for the distance between the centres of two ad-
joining cones in the yellow spot, the average diameter of a cone at
its widest part being 3 //, and there being slight intervals between
neighbouring cones. Hence if we take the centre of a cone as the
centre of an anatomical retinal area, these anatomical areas cor-
respond very fairly to the physiological visual areas as determined
above. That is to say, if two points of the retinal image are less
than 4 //, apart, they may both lie within the area of a single cone ;
and it is just when they are less than about 4 /j, apart that they
cease to give rise to two distinct sensations. It must be remem-
bered, however, that the fusion or distinction of the sensations is
ultimately determined by the brain and not by the retina. Two
points of the retinal image less than 4 //, apart might lie both
within the area of a single cone; but the reason why, under such
circumstances, they give rise to one sensation only is not because
one cone-fibre only is stimulated. Two points of a retinal image
might lie, one on the area of one cone and another on the area of
an adjoining cone, and still be less that 4 fi apart ; in such a case
two cone-fibres would be stimulated, and yet only one sensation
would be produced. So also in the less sensitive peripheral parts
of the retina two points of the retinal image might stimulate two
cones a considerable distance apart, and yet give rise to one sensa-
tion only.

In the case where the two points lie entirely within the area of
a single cone, it is exceedingly probable that, even if the adjacent
cones or cone-fibres in the retina are not at the same time stimu-
lated, impulses radiate from the cerebral ending of the excited cone
into the neighbouring cerebral endings of the neighbouring cones ;
in other words, the sensation-area in the brain does not exactly
correspond to and is not sharply defined like the retinal area, but
gradually fades away into neighbouring sensation-areas. We may
imagine two points of the retinal image so far apart that even the
•extreme margins of their respective cerebral sensation-areas do not
touch each other in the least ; in such a case there can be no doubt
about the two points giving rise to two sensations. We might,
however, imagine a second case where two points were just so far
apart that their respective sensation-areas should coalesce at their
margins, and yet that, in passing from the centre of one sensation-
area to the centre of the other, we should find on examination
a considerable fall of sensation at the junction of the two areas ; and
in a third case we might imagine the two centres to be so close to
each other that in passing from one to the other no appreciable
diminution of sensation could be discovered. In the last case there

1 By fj. is meant one-thousandth of a millimetre.

524 COLOUR SENSATIONS. [BOOK in.

would be but one sensation, in the second there might still be two
sensations if the marginal fall were great enough, even though the
areas partially coalesced. Thus, though the mosaic of rods and
cones is the basis of distinct vision, the distinction or fusion of
two visual impulses is ultimately determined by the disposition
and condition of the cerebral centres. Hence the possibility of
increasing by exercise the faculty of distinguishing two sensations,
since by use the cerebral sensation-areas become more and more
differentiated. This however is even more strikingly shewn in
touch than in sight.

Colour Sensations.

When we allow sunlight reflected from a cloud or sheet of
paper to fall into the eye, we have a sensation which we call a
sensation of white light. When we look at the same light through
a prism, and allow different parts of the spectrum to fall in
succession into the eye, we have sensations which we call respec-
tively sensations of red, orange, yellow, green, blue, violet, &c. light.
In other words, rays of light falling on the retina give rise to different
sensations, according to the wave-lengths of the rays. Though
we speak of the spectrum as consisting of a few colours, such as
red, orange, &c., there are an almost infinite number of intermediate
tints in the spectrum itself; and we perceive in external nature a
large number of colours, such as purple, brown, grey, &c., which do
not correspond to any of the colour sensations gained by regarding
the successive parts of the spectrum. We find however, on exami-
nation, that certain distinct colour sensations, not corresponding to
any of the colours of the spectrum, may be obtained by the fusion
of the sensations caused by two or more of the prismatic colours.
Thus purple, which is not present in the spectrum, may be at once
produced by fusing the sensations of blue and red in proper
proportions. Moreover many of the various tints and shades
of nature may be imitated by fusing a particular colour sensation
with the sensation of white, or by allowing a certain quantity of
light of a particular colour to fall sparsely over the area of the retina,
which is at the same time protected from the access of any other
light, i.e. as we say, by mixing the colour with black. Thus the
browns of nature result from various admixtures of yellow, red,
white, and black ; and a small quantity of white light, scattered
over a large area of the retina, i.e. white largely mixed with black,
forms a grey. In fact, the qualities of a colour depend (1) on the
nature of the prismatic colour or colours, i.e. on the wave-lengths of
the constituent rays, falling on a given area of the retina ; (2) on
the amount of this coloured light which falls on the area of
the retina in a given time ; and (3) on the amount of white light

CHAP, ii.] SIGHT. 525

falling on the same area at the same time. When rays corre-
sponding to a prismatic colour fall upon the retina unaccompanied
by any white light, the colour is said to be 'saturated'; and
a colour is spoken of as more or less saturated according as
it is mixed with less or more white light. When we are led
to describe a colour as being of such a tint or hue, we are guided
by the first of the above conditions. But we have no common
phrases by which we distinguish the second of the above conditions
from the third. The word 'pale/ it is true, is most frequently used
to express a colour very slightly saturated ; but the words 'rich' or
'deep' are used sometimes as meaning highly saturated, sometimes
as meaning simply that a large quantity of light of the particular
hue is passing into the eye. So also with the phrase 'bright'; this
we often use when a large amount of coloured and white light fall
at the same time on the same retinal area, but we sometimes also
use it to express the mere intensity of the sensation.

The best method of fusing colour sensations is that adopted by
Maxwell, of allowing two different parts of the spectrum to fall on the
same part of the retina at the same time. The use of the pure prismatic
colours eliminates errors which arise when pigments, the colours of which
are not pure, but mixed, are employed. And where pigments are used,
it is the sensations to which the pigments give rise which must be mixed
and not the pigments themselves. Thus while the sensations gained bv
looking at gamboge yellow and indigo respectively when fused give rise
to a sensation of white, gamboge and indigo themselves when mixed
appear green. The colour of the mixed pigment is due to the fact that
the rays which reach the eye from the mixture are those which are least
absorbed by the two pigments. The gamboge absorbs the blue rays very
largely, but the green to a much less extent ; while the indigo absorbs
the red and yellow rays very largely, but also absorbs very little of the
green. Hence green is the predominant hue of the mixture. When
pure pigments, i.e. pigments corresponding as closely as possible to the
prismatic colours, are used, satisfactory results may be gained, either by
using the reflected image of one pigment, and arranging so that it falls
on the retina at the same spot as the direct image of the other pigment,
or by allowing the image of one pigment to fall on the retina before the
sensation produced by the other has passed away. The first result is
easily reached by Helmholtz's simple method of placing two pieces of
coloured paper a little distance apart on a table, one on each side of a
glass plate inclined at an angle. By locking with one eye down on the
glass plate the reflected image of the one paper may be made to coincide
with the direct image of the other, the angle which the glass plate makes
with the table being adjusted to the distance between the pieces
of paper. In the second method, the 'colour top' is used; sectors of
the colours to be investigated are placed on a disc made to rotate very
rapidly, and the image of one colour is thus brought to bear on the
retina so soon after the image of another, that the two sensations
are fused into one.

When the sensations corresponding to the several prismatic

526 COLOUR SENSATIONS. [BOOK in.

colours are fused together in various combinations, the following
remarkable results are brought about.

1. When red and yellow in certain proportions are mixed
together the result is a sensation of orange, quite indistinguishable
from the orange of the spectrum itself. Now the latter is produced
by rays of certain wave-lengths, whereas the rays of red and of
yellow are respectively of quite different wave-lengths. The orange
of the spectrum cannot be made up by any mixture of the
red and the yellow of the spectrum in the sense that the red
and yellow rays can unite together to form rays of the same wave-
lengths as the orange rays ; the three things are absolutely different.
It is simply the mixed sensation of the red and yellow which is so
like the sensation of orange ; the mixture is entirely and absolutely
a physiological one. In the same way we may by appropriate
mixtures produce the sensations corresponding to other parts of the
spectrum. Now we must suppose that rays of different wave-
lengths give rise to different sensory impulses, that, for instance, the
sensory impulses generated by orange rays are different from those
generated by red and by yellow rays. Hence we are led by
the fact of mixed sensations being identical with other apparently
simple sensations to infer that the sensory impulses which any
ray originates are either themselves of a complex character, or in
becoming converted into sensations give rise to complex or mixed
sensations ; that, for instance, the impulse or sensation which a ray
in the middle of the orange gives rise to, is not a simple impulse or
sensation answering exclusively to the colour of that ray, but
that the ray gives rise either to a complex impulse which becomes
converted into a complex sensation, or to a simple impulse which
eventually developes into a mixed or complex sensation, into the
composition of which in each case other orange tints and shades
of red and yellow enter.

2. When certain colours are mixed together in pairs in certain
definite proportions, the result is white. These colours are

Red (near a)1, and Blue-Green (near F),

Orange (near C), and Blue (between F and G),

Yellow (near D), and Indigo-Blue (near G),

Green- Yellow (near E), and Violet (between G and H),

and are said to be 'complementary' to each other. To these might
be added the peculiar non-prismatic colour purple, which with
green also gives white.

3. If we select arbitrarily any three colours corresponding to
any three parts of the spectrum sufficiently far apart, say for
instance red, green, and blue, we can, by a proper adjustment of
the proportions of each, produce white. Further, these three

1 These letters refer to Frauenhofer's lines.

CHAP, ii.] SIGHT. 027

colours can be taken in such proportions as with a proper addition,
if necessary, of white to produce the sensations of all other colours1.
That is to say, given three standard sensations, all the other
sensations may be gained by the proper mixture of these.

It is obvious from the foregoing that our real colour sensations
are much fewer in number than those which we appear to have
when we look on the colours of the spectrum or of nature; that
rays of light awake in us certain simple sensations, which mixed in
various proportions reproduce all our sensations. And the question
arises, what is the nature or what are the characters of these simple
sensations ?

When we examine our own sensations of light we find that
certain of these seem to be quite distinct in nature from each
other, so that each is something sui generis, whereas we easily
recognise all other sensations as various mixtures of these. Thus
red and yellow are to us quite distinct: we do not recognise any
thing common to the two ; but orange is obviously a mixture of red
and yellow. The sensations caused by different kinds of light
which thus appear to us distinct, and which we may speak of as
'fundamental sensations/ are white, black, red, yellow, green, blue.
Each of these seems to us to have nothing in common with any of
the others, whereas in all other colours we can recognise a mixture
of two or more of these.

This result of common experience suggests the idea that these
fundamental sensations are the primary or simple sensations,
spoken of above as those out of which all other sensations may be
supposed to be compounded. And a theory has been proposed to
reconcile the various facts of colour vision, with the supposition
that we possess these six fundamental sensations. This theory,
known as that of Hering, is somewhat as follows. The six sensa-
tions readily fall into three pairs, the members of each parr having
analogous relations to each other. White and black naturally go
together, the one being the antagonistic or correlative of the other.
There is a similar connection between red and green, the one being
the complementary of the other, and between yellow and blue
which are similarly complementary. We saw reason, a short time
back (p. 518), for believing that vision originates in the changes
taking place in certain visual substances (or a visual substance) in
the retina. And the theory of which we are speaking supposes that
there exist in the retina, or at least somewhere in the visual appa-
ratus, three distinct visual substances which are continually under-
going a double metabolism, one constructive, of assimilation or
building up, and the other destructive, of dissimilation or breaking
down. One of these substances is further of such a nature that

1 A few highly saturated colours cannot be so reproduced, but a mixture of any
one of them with white can. We may perhaps therefore speak of these saturated
colours as being reproduced by a proper combination of the three arbitrarily selected
colours, with the subtraction of white.

528 COLOUR SENSATIONS [BOOK in.

when dissimilation is in excess of assimilation, \ve have a sensation
of white, and when assimilation is in excess a sensation of black.
With a second substance excess of dissimilation provokes red, of
assimilation green ; and with the third substance, yellow and blue
respectively. When in the latter two substances dissimilation and
assimilation are exactly equal, 110 effect is produced ; but with the
first substance, this condition produces in us the effect of grey.
Further these substances are of such a kind that while the first or
white-black substance is influenced by rays along the whole range
of the spectrum, the two other substances are differently influenced
by rays of different wave-length. Thus in the part of the spectrum
which we call red, the rays promote a rapid dissimilation of the
red-green substance with comparatively slight effect in either di-
rection on the yellow-blue substance ; hence our sensation of red.
In that part of the spectrum which we call yellow the rays effect
a marked dissimilation of the yellow-blue substance but their
action on the red-green substance is equal in the direction of both
assimilation and dissimilation ; hence our sensation of yellow.
The green rays, again, promote assimilation of the red-green
substance, leaving the assimilation of the yellow-blue substance
equal to the dissimilation, and similarly blue rays cause assimila-
tion of the yellow-blue substance, and leave the red-green sub-
stance neutral. Finally at the extreme blue end of the spectrum,
the rays once more provoke dissimilation of the red-green sub-
stance. When orange rays fall on the retina, there is a:i excess of
dissimilation of both the red-green and the yellow-blue substance ;
when greenish-blue rays are perceived there is an excess of assimi-
lation of both these substances ; and other intermediate tints
correspond to variable amounts of dissimilation or assimilation of
two or more of these substances.

When all the rays together fall on the retina^the red-green and
yellow-blue substance remain in equilibrium, but the white-black
substance is violently dissimilated ; and we say the light is white.

Another theory (known as the Young-Helmholtz theory, be-
cause it was introduced by Young and more fully elaborated by
Helmholtz) strives to reduce the matter to still further simplicity.
Starting from the fact mentioned a short time since, that all colour
sensations, including the sensation of white, may be obtained by
the appropriate mixture of three standard sensations, this theory
teaches that our visual apparatus is so constituted as, when excited,
to give rise to three primary sensations, and that these primary
sensations are called forth in different degrees by different rays of
light, so that each ray gives rise to a different mixture of the three.
Several sets of three such primary sensations might be chosen,
which would satisfy the conditions of giving rise, by appropriate
mixture, to all sensations of colour including white ; but for reasons,
into which we cannot enter fully here, the sensations which may
thus be taken as primary sensations appear to correspond to our

CHAP, ii.]

SIGHT.

529

sensations of red, green, and blue or violet. Such a view of three
primary colour sensations is represented in the diagram (Fig. 72).
Thus the red primary sensation, excited to a certain extent by the
rays at the extreme red end, is most powerfully affected by the
rays at a little distance from the end, the rays from this point
onwards towards the blue end producing less and less effect. The
curve of the green primary sensation begins later and reaches its
maximum in the green of the spectrum, while the blue or violet
primary sensation is still later and only reaches its maximum
towards the blue end of the spectrum. Each ray calls forth each
sensation but to a different degree, and the total result of each ray,
or of each group of rays, is determined by the proportionate amount
of the three sensations. Thus the sensation of orange (0 in the
figure) is brought about by a mixture of a great deal of the primary
red with much less of the primary green, and hardly any of the
primary blue ; the orange sensation is converted into a yellow
sensation by diminishing the primary red and largely increasing
the primary green, the primary blue undergoing also some slight
increase. And similarly with all the other sensations. When
each of the primary sensations is excited to a maximum, as when
ordinary light falls on the retina, the result is a sensation of white.
According to this theory, black is simply the absence of sensation
from the visual apparatus.

FIG. 72. DIAGRAM OF THREE PRIMARY COLOUR SENSATIONS.

1 is the so-called ' red,' 2 'green, 'and 3 ' violet ' primary colour sensation. R,0, Y, &c.
represent the red, orange, yellow, &c., colour of the spectrum, and the diagram
shews, by the height of the curve in each case, to what extent the several
primary colour sensations are respectively excited by vibrations of different
wave-lengths.

In the view, as originally put forward by Young, the three
primary sensations were supposed to be represented by three sets of
fibres, each set of fibres being differently affected by different rays of
light, and the impulses passing to the brain along each set awaken-
ing a distinct sensation. No such distinction of fibres can be found
in the retina ; but an anatomical basis of this kind is not necessary
for the theory ; we can easily conceive of the same fibre trans-
p. 34

530 COLOUR SENSATIONS, [BOOK m.

mitting three distinct kinds of impulses ; or we may suppose that
the visual substances are three in number instead of six, the
changes in each substance provoking a primary sensation.

Such are the two main theories of colour vision ; and much may
be said in favour of both of them ; at the same time both of them
present many difficulties. To discuss them fully, is a task beyond
the limits of this book, and to discuss them in any but a full manner
would be unsatisfactory. We must be satisfied therefore with the
foregoing simple statement of the two views. Independently of any
theory, however, we may remember (1) that all the sensations
which we experience under the action of light of whatever kind
may be reduced to six, white, black, red, yellow, green and blue ;
and (2) that these may be all reproduced by various mixtures of
three standard sensations, if black be allowed to indicate the
absence of all sensation. These are matters of fact : what is at
present debated is whether the six fundamental sensations are
the outcome of three primary sensations or whether they represent
six distinct conditions of the visual apparatus.

Colour Blindness. Persons vary much in their power of
appreciating and discriminating colour, i.e. in the intensity and
accuracy of their colour sensations; and some people regard
as similar, colours which to most people are glaringly distinct ;
these latter are said to be ' colour blind.' The most common form
of colour blindness is that of persons unable to distinguish green
and red from each other. As in the case of Dalton, they tell a red
gown lying on a green grass plot, or a red cherry among the green
leaves, by its form, and not by its colour. They confound not only
red, green, and certain forms of brown, but also rose, purple,
and blue. Such persons are often spoken of as ' red blind.' On the
Hering theory they lack the red-green visual substance; hence,
all the colour sensations they possess must be those of yellow and
blue freed from all mixture of red or green ; and such accounts as
have been given of their sensations by those persons who are
'red-blind' in one eye, but possess normal vision with the other,
accord with this conclusion. On the Young-Helmholtz theory,
such persons lack the primary red sensation; and hence the
sensations which they have must be mixtures of green and blue
alone, our yellow appearing to them a bright green, and our green-
blue a kind of grey.

All such red-blind people ought, on either theory, to be
less affected than are persons with normal eyes, by the red end
of the spectrum : this ought with them to be shortened and obscure.
In a certain number of persons who confound red and green, this is
the case ; but in some instances no such lack of appreciation of the
red end of the spectrum can be ascertained. Such cases have been
supposed to be green-blind, that is lacking the primary sensation
of green. According to the Hering theory green blindness apart

CHAP, ii.] SIGHT. 531

from red blindness is impossible, the only two possible colour
defects being red-green and blue-yellow blindness. And the
existence of distinct green blindness has been held to contradict
that theory. On the other hand the Hering theory admits the
possibility of total colour blindness, i. e. the inability to see anything
but white and black ; and this, on the Young-Helmholtz theory, is
impossible, since for vision to exist at all, one of the three primary
sensations must be present ; a man to see at all must see things
in various shades of either red, or of green, or of violet, though he
may confound this single-coloured vision with the normal vision of
white of different intensities. But indeed a full examination of
colour blindness rather increases than diminishes the difficulties of
deciding between the two rival theories.

Influence of the pigment of the yellow spot. In the macula
lutea, which part of the retina we use chiefly for vision, images
falling on other parts of the retina being said to give rise to
'indirect vision,' the yellow pigment absorbs some of the greenish-
blue rays. Hence the sensation which .we receive from objects
which we are in the habit of calling white is that which, if this
pigment were absent, we should receive from objects more or less
yellow. We may use this feature of the yellow spot for the purpose
of making the spot, so to speak, visible to ourselves, by an experi-
ment suggested by Maxwell. A solution of chrome alum, which
only transmits red and greenish-blue rays, is held up between the
eye and a white cloud. The greenish-blue rays are absorbed by the
yellow spot, and here the light gives rise to a sensation of red ;
whereas in the rest of the field of vision, the sensation is that
ordinarily produced by the purplish solution. The yellow spot is
consequently marked out as a rosy patch. This very soon however
dies away.

In speaking of sensation as a function of the stimulus, p. 520,
we referred to white light only; but the different colours are
unequal in the relations borne by the intensity of the stimulus,
to the amount of sensation produced. Thus the more refrangible
blue rays produce a sensation more readily than the yellow or red
rays. Hence in dim lights, as those of evening and moonlight,
the blues preponderate, and the reds and yellows are less obvious.
So also when a landscape is viewed through a 3rellow glass,
the yellow hue suggests to the mind bright sunlight and summer
weather, although the actual illumination which reaches the eye is
diminished by the glass. Conversejy when the same landscape is
viewed through a blue glass the idea of moonlight or winter
is suggested.

The theory of three primary colour sensations may be used
to explain why any coloured light, if made sufficiently intense,
appears white. Thus a violet light of moderate intensity appears
violet because it excites the primary sensation of violet much more

34—2

532 COLOUR SENSATIONS. [BOOK in.

than those of green and red. If the stimulus be increased the
maximum of violet stimulation will be reached, while the stimula-
tion of green will continue to be increased and even that of red to
a slight degree. The result will be that the light appears violet
mixed with green, that is blue. If the stimulus be still further
increased while the green and violet are both excited to the
maximum, the red stimulation may be increased until the result is
violet, green, and red in the proportions which make white light.
And so with light of other colours.

After-images. We have already seen that in vision the
sensation lasts much longer than the stimulus. Under certain
circumstances, such as particular conditions of the eye, an intense
stimulus, &c., the sensation is so prolonged, that it is spoken of as
an after-image. Thus, if the eye be directed to the sun, the image
of that body is present for a long while after; and if, on early
waking, the eye be directed to the window for an instant and then
closed, an image of the window with its bright panes and darker
sashes, the various parts being of the same colour as the object, will
remain for an appreciable time. These images, which are simply
continuations of the sensation, are spoken of as positive after-
images. They are best seen after a momentary exposure of the eye
to the stimulus.

When, however, the eye has been for some time subject to a
stimulus, the sensation which follows the withdrawal of the sti-
mulus is of a different kind ; what is called a negative after-image,
or negative image, is produced. If, after looking stedfastly at a
white patch on a black ground, the eye be turned to a white
ground, a grey patch is seen for some little time. A black patch
on a white ground similarly gives rise on a grey ground to a
negative image in the form of a white patch. This may be
explained as the result of exhaustion. When the white patch
has been looked at steadily for some time, that part of the retina
on which the image of the patch fell becomes tired; hence the
white light, coming from the white ground subsequently looked
at, which falls on this part of the retina, does not produce so much
sensation as in other parts of the retina; and the image, con-
sequently, appears grey. And so in the other instance, the whole
of the retina is tired, except at the patch; here the retina is
for a while most sensitive, and hence the white negative image.

When a red patch is looked at, the negative image is a green
blue, that is, the colour of the negative image is complementary to
that of the object. Thus also orange produces a blue, green a
pink, yellow an indigo-blue, negative image ; and so on. This too
can be explained as a result of exhaustion on either hypothesis of
colour vision. When the coloured patch is looked at, one of the
three primary colour sensations is much exhausted, and the other
two less so, in varying proportions, according to the exact nature of

CHAP, ii.] SIGHT. 533

the colour of the patch; and the less exhausted sensations become
prominent in the after-image. Thus, the red patch exhausts the
red sensation, and the negative image is made up chiefly of green
and blue sensations, that is, appears to be greenish blue, or bluish
green, according to the tint of the red. On the other hypothesis,
we may suppose that, owing to the continued effect of looking at
the red patch, dissimilation of the red-green substance becomes
less and less, leading to a prominence and indeed to an actual
increase of the process of assimilation of the same substance;
hence the sensation of green dominating in the negative image.

Similarly, when the eye, after looking at a coloured patch, is
turned to a coloured ground, the effects may easily be explained
by reference to the comparative exhaustion of the colour sensations
excited by the patch and the ground respectively; if a yellow
ground be chosen after looking at a green object, the negative
image will appear of a reddish yellow, and so on.'

The theory of three primary sensations does not so readily
explain why negative images should make their appearance with-
out any subsequent stimulation of the retina. When the eyes are
shut and all access of light, even through the eyelids, carefully
avoided, the field of vision is not absolutely dark; there is still a
sensation of light, the so-called 'proper light' of the retina. If a
white patch on a black ground be looked at for some time, and the
eyes then shut, a negative (black) image of the spot will be seen
on the ground of the 'proper light' of the retina, having in its
immediate neighbourhood a specially bright corona. So also, if a
window be looked at and the eyes then closed, the positive after-
image with bright panes and dark sashes gives rise to a negative
after-image with bright sashes and dark panes ; and similar effects
appear with colours. These and similar facts have been largely
used in support of the Hering theory. When the eye has been
looking at red, and so has caused dissimilation of the red-green
substance mere rest, as on shutting the eyes, favours assimilation of
the same substance and thus leads to a sensation of green. And
the rhythmic oscillations from one colour to its correlative and
back again, frequently observed under these conditions and which
point to assimilation and dissimilation alternately gaining the
upper hand, are not without analogies in other common instances
of protoplasmic metabolism.

SEC. 3. VISUAL PERCEPTIONS.

Hitherto we have studied sensations only, and have considered
an external object, such as a tree, as simply a source of so many
distinct sensations, differing from each other in intensity and kind
(colour). In the mind these sensations are coordinated into a per-
ception. We are not only conscious of a number of sensations of
bright and dim lights, of green, brown, black, &c., but these sen-
sations are so related to each other and by virtue of cerebral pro-
cesses so fashioned into a whole, that we 'see a tree/ We some-
times, in illustration of such an effect, speak of an image or picture
in the mind corresponding to the physical image on the retina.

When we look upon the external world, a variety of images
are formed at the same time on the retina, and give rise to a
number of contemporaneous visual sensations. The sum of these
sensations constitutes 'the field of vision,' which varies of course
with every movement of the eye. This field of vision, being in
reality an aggregate of sensations, is of course a subjective matter;
but we are in the habit of using the same phrase to denote the
sum of external objects which give rise to the aggregate of visual
sensations; in common language the field of vision is 'all that we
can see' in any position of the eye, and we have a field of vision
for each eye separately and for the two eyes combined.

Using for the present the words in their subjective sense, we
may remark, that we are able to assign to each constituent
sensation its place among the aggregate of sensations constituting
the field of vision ; we can, as we say, localise the sensation. We
can say whether it belongs to (what we regard as) the right-hand
or left-hand, the upper or the lower part, of the field of vision. We
are able to distinguish the relative positions of any two distinct

CHAP, ii.] SIGHT. 535

sensations; and the relative positions, together with the relative
intensities and qualities (colour) of the sensations arising from any
object determine our perception of the object. It need hardly be
remarked that this localisation is purely subjective. We simply
determine the position of the sensation in the field of vision
(which is itself a wholly subjective matter) ; we do not determine
the position of the object. The connection between the position of
the object in the external world and the position of the sensation
in the field of vision, cannot be determined by visual observation
alone. All the information which can be gained by the eye is
limited to the field of vision, and provided that the relative position
of the sensations in the field of vision remained the same, the
actual position of external objects might, as far as vision. is con-
cerned, be changed without our being aware of it.

As a matter of fact the field of vision in one important par-
ticular does not correspond to the field of' external objects. The
image on the retina is inverted ; the rays of light proceeding from
an object which by touch we know to be on what we call our right
hand, fall on the left-hand side of the retina. If therefore the field
of vision corresponded to the retinal image, the object would be
seen on the left hand. We however see it on the right hand,
because we invariably associate right-hand tactile localisation with
left-hand visual localisation ; that is to say, our field of vision, when
interpreted by touch, is a re-inversion of the retinal image.

The dimensions of the field of vision of a single eye are about
145° for the horizontal and 100° for the vertical meridian, the
former being distinctly greater than the latter. The horizontal
dimension of the field of vision for the two eyes is about 180°.
By movements of the eyes, however, even apart from those of the
head, the extent may be considerably increased.

The satisfactory perception of external objects requires distinct
vision ; and of this, as we have already said, the formation of a
distinct image on the retina is an essential condition. We can
receive visual sensations of all kinds with the most imperfect
dioptric apparatus, but our perception of an object is precise in
proportion to the clearness of the image on the retina.

Region of Distinct Vision. If we take two points, such as
two black dots, only just so far apart that they can be seen dis-
tinctly as two when placed near the axis of vision, and then,
keeping the axis fixed, move the two points out into the circum-
ferential parts of the field of vision, it will be found that the two
soon appear as one. The two sensations become fused, as they
would do if brought nearer to each other in the centre of the field.
The farther away from the centre of the field, the farther apart
must two points be in order that they may be seen as two. In
other words, vision is much more distinct in the centre of the field
than towards the circumference. Practically the region of distinct

536 VISUAL PERCEPTIONS. [BOOK in.

vision may be said to be limited to the macula lutea, or even to
the fovea centralis ; by continual movements of the eye we are
constantly bringing any object which we wish to see in such a
position that its image falls on this region of the retina.

The diminution of distinctness does not take place equally from
the centre to the circumference along all meridians. The outline
described by a line uniting the points where two spots cease to be
seen as two when moved along different radii from the centre, is a
very irregular figure.

The sensations of colour are much more distinct in the centre
of the retina, than towards the circumference. If the visual axis
be fixed and a piece of coloured paper be moved towards the out-
side of the field of vision, the colour undergoes changes and is
eventually lost, red disappearing first, and blue last, the object re-
maining visible, though with very indistinct outlines, when its
colour can be no longer recognised. A purple colour becomes
blue, and a rose colour a bluish white. In fact, there seems to be
a certain amount of red-blindness in the peripheral parts of all
retinas.

Modified Perceptions.

Since our perception of external objects is based on the dis-
tinctness of the sensations which go to form the perception, it
might be expected that when an image of an object is formed on
the retina the sensory impulses would correspond to the retinal
image, the sensations correspond to the sensory impulses and the
perception correspond to the sensations, and that therefore the
mental condition resulting from our looking at any object or view
would correspond exactly to the retinal image. We find, however,
that this is not the case. The sensations and probably even the
simple sensory impulses produced by an image react upon each
other, and these reactions modify our perceptions, independently of
the physical conditions of the retinal image. There arise certain
discrepancies* between the retinal image and the perception, some
having their source in the retina, some in the brain, and others
being of such a nature, that it is difficult to say where the
irrelevancy is introduced.

Irradiation. A white patch on a dark ground appears larger,
and a dark patch on a white ground smaller, than it really is.
This is especially so when the object is somewhat out of focus, and

CHAP, n.] SIGHT. 537

may, in this case, be partly explained by the diffusion circles which,
in each case, encroach from the white upon the dark. But over
and beyond this, any sensation, coming from a given retinal area,
occupies a larger share of the field of vision, when the rest of the
retina and central visual apparatus are at rest, than when they are
simultaneously excited. It is as if the neighbouring, either retinal
or cerebral, structures were sympathetically thrown into action at
the same time.

Contrast. If a white strip be placed between two black strips,
the edges of the white strip, near to the black, will appear whiter
than its median portion ; and if a white cross be placed on a black
background, the centre of the cross will appear sometimes so dim,
compared with the parts close to the black, as to seem shaded.
This occurs even when the object is well in focus ; the increased
sensation of light which causes the apparent greater whiteness of
the borders of the cross is the result of the 'contrast' with the
black placed immediately close to it. Still more curious results
are seen with coloured objects. If a small piece of grey paper be
placed on a sheet of green paper, and both covered with a sheet of
thin tissue paper, the grey paper will appear of a pink colour, the
complementary of the green. This effect of contrast is far less
striking, or even wholly absent, when the small piece of paper is
white instead of grey, and generally disappears when the thin
covering of tissue paper is removed. It also vanishes if a bold
broad black line be drawn round the small piece of paper, so as to
isolate it from the ground colour. If a book, or pencil, be placed
vertically on a sheet of white paper, and illuminated on one side
by the sun, and on the other by a candle, two shadows will be
produced, one from the sun which will be illuminated by the
yellowish light of the candle, and the other from the candle which
will in turn be illuminated by the white light of the sun. The
former naturally appears yellow ; the latter, however, appears not
white but blue ; it assumes, by contrast, a colour complementary
to that o'f the candle-light which surrounds it. If the candle be re-
moved, or its light shut off by a screen, the blue tint disappears,
but returns when the candle is again allowed to produce its shadow.
If, before the candle is brought back, a vision be directed through a
narrow blackened tube at some part falling entirely within the
area of what will be the candle's shadow, the area, which in the
absence of the candle appears white, will continue to appear white
when the candle is made to cast its shadow, and it is not until the
direction of the tube is changed so as to cover part of the ground
outside the shadow, as well as part of the shadow, that the latter
assumes its blue tint.

Filling up the Blind Spot. Though, as we have seen, that
part of the retina which corresponds to the entrance of the optic

538 VISUAL PERCEPTIONS. [BOOK m.

nerve is quite insensible to light, we are conscious of no blank in the
field of vision. When in looking at a page of print we fix the
visual axis so that some of the print must fall on the blind spot, no
gap is perceived. We could not expect to see a black patch, be-
cause what we call black is the absence of the sensation of light
from structures which are sensitive to light ; we must have visual
organs to see black. But there are no visual organs in the blind
spot, and consequently we are in no way at all affected by the
rays of light which fall on it. There is in our subjective field of
vision no gap corresponding to the gap in the retinal image. We
refer the sensations coming from two points of the retina lying on
opposite margins of the blind spot to two points lying close
together, since we have no indication of the space which separates
them. Concerning the effects which are produced when an object
in the field of view passes into the region of the blind spot there
has been much discussion. In ordinary vision of course, the exist-
ence of the blind spot is of little moment since it is outside the
region used for distinct vision, and besides the image of an object
does not fall on the blind spots of both eyes at the same time.

Ocular Spectra. So far from our perceptions exactly corre-
sponding to the arrangements of the luminous rays which fall on
the retina, we may-have visual sensations and perceptions in the
entire absence of light. Any stimulation of the retina or of the
optic nerve sufficiently intense will give rise to a visual sensation.
Gradual pressure on the eyeball causes a sensation of rings of colour-
ed light, the so-called phosphenes ; a sudden blow on the eye causes
a sensation of flashes of light, and the seeming identity of the
visual sensations so 'brought about with visual sensations produced
by light is well illustrated by the statement once gravely made in
a German court of law, by a witness who asserted that on a pitch
dark night he recognised an assailant by help of the flash of light
caused by the assailant's hand coming in violent contact with his
eye. Electrical stimulation of the eye or optic nerve will also give
rise to visual sensations.

The sensations which may arise without any light falling on the
retina need not necessarily be undefined; on the contrary they
may be most clearly defined. Complex and coherent visual images
or perceptions may arise in the brain without any corresponding
objective luminous cause. These so-called ocular spectra or phan-
toms, which are the result of an intrinsic stimulation of some
(probably cerebral) part of the visual apparatus, have a distinctness
which gives them an apparent objective reality quite as striking as
that of ordinary visual perceptions. They may occasionally be
seen with the eyes open (and therefore while ordinary visual per-
ceptions are being generated) as well as when the eyes are closed.
They sometimes become so frequent and obtrusive as to be dis-

CHAP. IL] SIGHT. 539

tressing, and form an important element in some kinds of delirium,
such as delirium tremens.

Appreciation of apparent size. By the eye alone we can only
estimate the apparent size of an object, we can only tell what space
it takes in the field of vision, we can only perceive the dimensions
of the retinal image, and therefore have a right only to speak of
the angle which the diameter of the object subtends. The real
size of an object must be determined by other means. But our
perception of even the apparent size of an object is so modified by
concurrent circumstances that in many cases it cannot be relied
on. The apparent size of the moon must be the same to every
eye, and yet while some persons will be found ready to compare
the moon in mid heavens with a threepenny piece, others will
liken it to a cart-wheel ; that is to say, the angle subtended by the
moon seems to the one to be about equal to that subtended by a
threepenny piece held at the distance from the eye at which it is
most commonly looked at, and to the other about equal to that sub-
tended by a cart-wheel similarly viewed at the distance at which
it is most commonly looked at. If a line such as AC, Fig. 73, be
divided into two equal parts AB, BC, and AB be divided by
distinct marks into several parts, as is shewn in the figure, while
BG be left entire, the distance AB will always appear greater than
CB. So also, if two equal squares be marked, one with horizontal
and the other with vertical
alternate dark and light bands,

the former will appear higher, •

and the latter broader, than it

really is. Hence short persons affect dresses horizontally striped
in order to increase their apparent height, and very stout persons
avoid longitudinal stripes. Two perfectly parallel lines or bands,
each of which is crossed by slanting parallel short lines, will appear
not parallel, but diverging or converging according to the direction
of the cross-lines.

Again, when a short person is placed side by side with a tall
person, the former appears shorter and the latter taller than each
really is. The moon on the horizon appears larger than when at
the zenith, because in the first position it can be most easily com-
pared with terrestrial objects. The absence of comparison may,
however, contribute to an opposite effect, as when a person looks
larger in a fog ; being seen indistinctly, he is judged to be farther
off than he really is, and so appears larger than he naturally would
do at the distance at which he is supposed to be. So, conversely,
distant mountains when seen distinctly in a clear atmosphere
appear small, because on account of their distinctness they are
judged to be nearer than they really are. Indeed, our daily life is
full of instances in which our direct perception is modified by
circumstances. Among those circumstances previous experience is

540 VISUAL PERCEPTIONS. [BOOK in.

one of the most potent, and thus simple perceptions become
mingled with what are in reality judgments, though frequently
made unconsciously. But this intrusion of past experience into
present perceptions and sensations is most obvious in binocular
vision, to which we now turn,

SEC. 4. BINOCULAR VISION.

Corresponding or Identical Points.

Though we have two eyes, and must therefore receive from
every object two sets of sensations, our perception of any object is
under ordinary circumstances a single one ; we see one object, not
two. By putting either eye into an unusual position, as by squint-
ing, we can render the perception double; we see two objects
where one only exists. From which it is evident that singleness of
perception depends on the image of the object falling on certain
parts of each retina at the same time, these parts being so related
to each .other, that the sensations from each are blended into one
perception ; and it is also evident that the movements of the eye-
balls are adapted to bring the image of the object to fall on these
'corresponding' or 'identical* parts, as they are called, of each
retina.

When we look at an object with one eye the visual axis of that
eye is directed to the object, and when we use two eyes the visual
axes of the two eyes converge at the object, the eyeballs moviDg
accordingly. The corresponding points of the two retinas are those
on which the two images of the object fall when the visual axes
converge at the object. Thus in Fig. 74, if Cc, Ccl be the two
visual axes, c, cl being the centres of the foveae centrales of the two
eyes, then, the object AGE being seen single, the point a on the
one retina will ' correspond ' to or be ' identical ' with the point av
on the other, and the point b in the one to the point bl in the other.

542

BINOCULAR VISION.

[BOOK in.

Hence a point lying anywhere on the right side of one retina, has
its corresponding point on the right side of the other retina, and
the points on the left of one correspond with those on the left of

FIG. 74. DIAGRAM ILLUSTRATING CORRESPONDING POINTS.

L the left, E the right eye, K the optical centre, av &,, CL are points in the
right eye corresponding to the points a, b, c in the left eye. The two figures below
are projections of L the left and E the right retina. It will be seen that a on the
malar side of L corresponds to «lf on the nasal side of R.

the other. Thus, while the upper half of the retina of the left eye
corresponds to the upper half of the retina of the right eye, and the
lower to the lower, the nasal side of the left eye corresponds with
the malar side of the right, and the malar of the left with the
nasal side of the right.

The blending of the two sensations into one only occurs when
the two images of an object fall on these corresponding points of
the two retinas. Hence it is obvious that in single vision with two
eyes the ordinary movements of the eyeballs must be such as to
bring the visual axes to converge at the object so that the
two images may fall on corresponding points. When the visual
axes do not so converge, and when therefore the images do not fall
on corresponding points, the two sensations are not blended into
one perception and vision becomes double.

Movements of the Eyeballs.

The eye is virtually a ball placed in a socket, the bulb and the
orbit forming a ball and socket-joint. In its socket-joint the optic
ball is capable of a variety of movements, but it cannot by any
voluntary effort be moved out of its socket, It is stated that by a
very forcible opening of the eyelids the eyeball may be slightly

CHAP, ii.] SIGHT. 543

protruded; but this trifling locomotion may be neglected. By
disease, however, the position of the eyeball in the socket may be
materially changed.

Each eyeball is capable of rotating round an immobile centre of
rotation, which has been found to be placed a little (177 mm.) be-
hind the centre of the eye ; but the movements of the eye round
the centre are limited in a peculiar way. The sho alder-joint is
also a ball and socket-joint; and we know that we can not only
move the arm up and down round a horizontal axis passing through
the centre of rotation of the head of the humerus, and from side
to side round a vertical axis, but we can also rotate it round its own
longitudinal axis. When, however, we come to examine closely
the movements of the eyeball we find, that though we can move it
up and down round a horizontal axis, as when with fixed head we
direct our vision to the heavens or to the ground, and from side to
side, as when we look to left or right, and though by combining
these two movements we can give the eyeball a variety of in-
clinations, we cannot, by a voluntary effort, rotate the eyeball
round its longitudinal visual axis. The arrangement of the muscles
of the eyeball will permit of such a movement, but we cannot by
any direct effort of will bring it about by itself. In certain move-
ments of the eye, rotation of the eyeball does take place ; and by
bringing about these movements, we can indirectly cause rotation ;
but we cannot rotate the eyeball except thus indirectly as a part
of these movements.

If, when vision is directed to any object, the head be moved
from side to side, the eyes do not move with it; they appear
to remain stationary, very much as the needle of a ship's compass
remains stationary when the head of the ship is turned. The
change in the position of the visual axes to which the movement
of the head would naturally give rise is met by compensating
movements of the eyeballs; were it not so, steadiness of vision
would be impossible.

There is one position of the eyes which has been called the
primary position. It corresponds to that which may be attained
by looking at the distant horizon with the head vertical and the
body upright; but its exact determination requires special pre-
cautions. The visual axes are then parallel to each other and to
the median plane of the head. All other positions of the eyes are
called secondary positions.

Muscles of the Eyeball. The eyeball is moved by six muscles,
the recti inferior, superior, intemus, and externus, and the obliqui
inferior and superior. It is found by calculation from the attach-
ments and directions of the muscles, and confirmed by actual obser-
vation, that the six muscles may be considered as three pairs, each
pair rotating the eye round a particular axis. The relative attach-
ments and the axes of rotation are diagrammatically shewn in

544 BINOCULAR VISION. [Boon m.

Fig. 75. The rectus superior and the rectus inferior rotate the eye
round a horizontal axis, which is directed from the upper end of
the nose to the temple; the obliquus superior and obliquus in-
ferior round a horizontal axis directed from the centre of the eye-

r.ext. r.sup. r.inf
r.inf.

FIG. 75. DIAGRAM OF THE ATTACHMENTS OF THE MUSCLES OF THE EYE, AND OF THEIR
AXES OF KOTATION, the latter being represented by dotted lines. The axis of
rotation of the rectus externus and internus, being perpendicular to the plane
of the paper, cannot be shewn. (After Fick.)

ball to the occiput; and the rectus internus and rectus externus
round a vertical axis (which, being at right angles to the plane of
the paper, cannot be shewn in the diagram), passing through
the centre of rotation of the eyeball parallel to the median plane
of the head when the head is vertical. Thus the latter pair acting
alone would turn the eye from side to side, the other straight pair
acting alone would move the eye up and down, while the oblique
muscles acting alone would give the eye an oblique movement.
The rectus externus acting alone would turn the eye to the malar
side, the internus to the nasal side, the rectus superior upwards,
the rectus inferior downwards, the oblique superior downwards and
outwards, and the inferior upwards and outwards. The recti
superior and inferior in moving the eye up and down also turn it
somewhat inward and at the same time give it a slight amount of
rotation; but this is corrected if the oblique muscles act at the
same time; and it is found that the rectus superior acting with the
obliquus inferior moves the eye upwards, and the rectus inferior
with the obliquus superior downwards in a vertical direction. In
oblique movements also, the obliqui are always associated with the
recti. Hence the various movements of the eyeball may be ar-
ranged as follows :

CHAP, ii.] SIGHT. 545

Elevation. Rectus superior and obliquus inferior

g. f Elevation. Rectus superior and obliquus inferior

-g Depression. Rectus inferior and obliquus superior.

At0

extemu,

f Elevation with Rectus superior and internus with obliquus

^ I adduction. inferior.

o> -g | Depression Rectus inferior and internus with obliquus

.£T | I with adduction. superior.

Elevation with Rectus superior and externus with obliquus

abduction. inferior.

Depression Rectus inferior and externus with obliquus

with abduction. superior.

Coordination of Visual Movements. Thus even in the move-
ments of a single eye, a considerable amount of coordination takes
place. When the eye is moved in any other than the vertical and
horizontal meridians, impulses must descend to at least three
muscles, and in such relative energy to each of the three as to pro-
duce the required inclination of the visual axis. But the co-
ordination observed in binocular vision is more striking still. If
the movements of any person's eyes be watched it will be seen that
the two eyes move alike. If the right eye moves to the right, so
does also the left; and, if the object looked at be a distant one,
exactly to the same extent; if the right eye looks up, the left eye
looks up also, and so in every other direction. Very few persons
are able by a direct effort of the will to move one eye inde-
pendently of the other; though some, and among them one
distinguished both as a physiologist and an oculist, have acquired
this power. In fact, the movements of the two eyes are so arranged
that in the various movements the images of any object should fall
on the corresponding points of the two retinas, and that thus single
vision should result. We cannot by any direct effort of our will
place our eyes in such a position that the rays of light proceeding
from any object shall be brought to a focus on parts of the two
retinas which do not correspond, and thus give rise to two distinct
visual images. We can bring the visual axes of the two eyes from
a condition of parallelism to one of great convergence, but we
cannot, without special assistance, bring them from a condition
of parallelism to one of divergence. The stereoscope will enable us
to create a divergence. If in a stereoscopic picture the distance
between the pictures be increased very gradually so as carefully to
maintain the impression of a single object, the visual axes may be
brought to diverge. Similarly if a distant object be looked at
with a prism before one eye, and the image of the object be kept
carefully single, while the prism is turned very slowly up or down,
then on suddenly removing the prism a double image is for a
F. 35

546 BINOCULAR VISION [BOOK in.

moment seen; shewing that the eye before which the prism was
placed had moved in disaccordance with the other. The double
image however in a few seconds after the removal of the prism
becomes single, on account of the eyes coming into accordance.

It is only when loss of coordination occurs, as in various
diseases and in alcoholic or other poisoning, that the movements of
the two eyes cease to agree with each other. It is evident then
that when we look at an object to the right, since we thereby
abduct the right eye and adduct the left, we throw into action the
rectus externus of the right eye and the rectus internus of the left;
and similarly when we look to the left we use the rectus externus
of the left and the rectus internus of the right eye. On the other
hand when we look at a near object, and therefore converge
the visual axes, we use the recti interni of both eyes ; and when we
look at a distant object, and bring the axes from convergence
towards parallelism, we use the recti externi of both eyes. In the
various movements of the eye there is therefore, so to speak,
the most delicate picking and choosing of the muscular instruments.
Bearing this in mind, it cannot be wondered at that the various
movements of the eye are dependent for their causation on visual
sensations. In order to move our eyes, we must either look at or
for an object; when we wish to converge our axes, we look at some
near object real or imaginary, and the convergence of the axes
is usually accompanied by all the conditions of near vision, such as
increased accommodation and contraction of the pupil. And so with
other movements. The close association of the movements of the
eye may be illustrated by the following case. Suppose the eyes, to
start with, directed for the far distance, and that it is desired
to direct attention to a nearer point lying in the visual line of the
right eye. In this case no movement of the right eye is required ;
all that is necessary is for the left eye to be turned to the right,
that is, for the rectus internus of the left eye to be thrown
into action. But in ordinary movements the contraction of
this muscle is always associated with either the rectus externus of
the right eye, as when both eyes are turned to the right, or
the rectus internus of that eye, as in convergence ; the muscle
is quite unaccustomed to act alone. This would lead us to suppose
that in the case in question the contraction of the rectus internus
of the left eye is accompanied by a contraction of both recti externus
and internus of the right eye, keeping that eye in lateral equi-
librium. And the peculiar oscillating movements seen in the right
eye, as well as the sense of efforts in the right eye which is felt by
the person, shew this to be the case.

Such a complex coordination requires for its carrying out
a distinct nervous machinery; and we have reasons for thinking
that such a machinery exists in certain parts of the corpora quadri-
gemina or in the underlying structures. In the nates, there
appears to be a common centre for both eyes, stimulation of the

CHAP, ii.]

SIGHT.

547

right side producing movements of both eyes to the left, of the left
side movements to the right ; while stimulation in the middle line
behind causes a downward movement of both eyes with convergence
of the axes, and in the front an upward movement with return to
parallelism, both accompanied by the naturally associated move-
ments of the pupil. Stimulation of various parts of the nates causes
various movements, depending on the position of the spot stimu-
lated. After an incision in the middle line, stimulation of the
nervous centre on one side produces movements in the eye of the
same side only.

The Horopter.

When we look at any object we direct to it the visual axes, so
that when the object is small, the ' corresponding ' parts of the two

FIG. 76. DIAGRAM ILLUSTRATING A SIMPLE HOROPTEK.

\Yhen the visual axes converge at C, the images a a of any point A on the
circle drawn through C and the optical centres k k, will fall on corresponding points.

retinas, on which the two images of the object fall, lie in their
respective fovese centrales. But while we are looking at the
particular object the images of other objects surrounding it fall
on the retina surrounding the fovea, and thus go to form what
is called indirect vision. And it is obviously of advantage
that these images also should fall on 'corresponding' parts in
the two eyes. Now for any given position of the eyes there exists
in the field of vision a certain line or surface of such a kind
that the images of the points in it all fall on corresponding points
of the retina. A line or surface having this property is called
a Horopter. The horopter is in fact the aggregate of all those
points in space which are projected on to corresponding points
of the retina; hence its determination in any particular case
is simply a matter of geometrical calculation. In some instances it

35—2

548 BINOCULAR VISION. [BOOK m.

becomes a very complicated figure. The case whose features are
most easily grasped is a cii^le drawn in the plane of the two
visual axes through the point of the convergence of the axes and
the optic centres of the two eyes. It is obvious from geometrical
relations that in Fig. 76 the images of any point in the circle will
fall on corresponding points of the two retinas. When we stand
upright and look at the distant horizon the horopter is (approxi-
mately, for normal emmetropic eyes) a plane drawn through
our feet, that is to say, is the ground on which we stand; the
advantage of this is obvious.

SEC. 5. VISUAL JUDGMENTS.

Binocular vision is of use to us inasmuch as the one eye is able
to fill up the gaps and imperfections of the other. For example,
over and above the monocular filling up of the blind spot, of which
we spoke in page 537, since the two blind spots of the two eyes, being
each on the nasal side, are not 'corresponding' parts, the one eye
supplies that part of the field of vision which is lacking in the other.
And other imperfections are similarly made good. But the great use
of binocular vision is to afford us means of forming visual judgments
concerning the form, size, and distance of objects.

Judgment of Distance and Size. The perceptions which we
gain simply and solely by our field of vision, concern two dimensions
only. We can become aware of the apparent size of any part of the
field corresponding to any particular object, and of its topographical
relations to the rest of the field, but no more. Had we nothing
more to depend on, our sight would be almost valueless as far as any
exact information of the external world was concerned. By
association of the visual sensations with sensations of touch, and
with sensations derived from the movements of the eyeballs
required to make any such part of the field as corresponds to
a particular object distinct, we are led to form judgments, i.e. to
draw conclusions concerning the external world by means of
an interpretation of our visual perceptions. Looking before us, we
say we see a certain object of a certain colour nearly in front of us,
or much on our right hand or much on our left ; that is to say, we
judge such an object to be in such a position because from

550 VISUAL JUDGMENTS. [BOOK in.

the constitution of our brain, strengthened by all our experience,
we associate such a part of our field of vision with such an object.
The subjective visual complex sensation or perception is to us
a symbol of the external object.

Even with one eye we can, to a certain extent, form a judgment,
not only as to the position of the object in a plane at right angles
to our visual axis, but also as to its distance from us along the
visual axis. If the object is near to us, we have to accommodate
for near vision; if far from us, to relax our accommodation
mechanism so that the eye becomes adjusted for distance. The
muscular sense (of which we shall speak presently) of this effort
enables us to form a judgment whether the object is far or near.
Seeing the narrow range of our accommodation, and the slight
muscular effort which it entails, all monocular judgments of distance
must be subject to much error. Everyone who has tried to thread
a needle without using both eyes, knows how great these errors
may be. When, on the other hand, we use two eyes, we have still
the variations in accommodation, and in addition have all the
assistance which arises from the muscular effort of so directing the
two eyes on the object that single vision shall result. When the
object is near, we converge our visual axes ; when distant, we bring
them back towards parallelism. This necessary contraction of the
ocular muscles affords a muscular sense, by the help of which we form
a judgment as to the distance of the object. Hence, when by any
means the convergence which is necessary to bring the object into
single vision is lessened, the object seems to become more distant,
when increased, to move towards us: as may be seen in the
stereoscope.

The judgment of size is closely connected with that of distance.
Our perceptions, gained exclusively from the field of vision, go no
farther than the apparent size of the image, i. e. of the angle sub-
tended by the object. The real size of the object can only be
gathered from the apparent size of the image when the distance of
the object from the eye is known. Thus perceiving directly the
apparent size of the image, we judge the distance of the object
giving the image, and upon that come to a conclusion as to its
size. And conversely, when we see an object, of whose real size
we are otherwise aware, or are led to think we are aware, our
judgment of its distance is influenced by its apparent size. Thus
when^in our field of vision there appears the image of a man,
knowing otherwise the ordinary size of a man, we infer, if the
image be very small, that the man is far off. The reason of the
image being small may be because the man is far off, in which
case our judgment is correct ; it may be, however, because the
image has been lessened by artificial dioptric means, as when the
man is looked at through an inverted telescope, in which case
our judgment becomes a delusion. So also an image on a screen
when gradually enlarged seems to come forward, when gradually

CHAP, ii.]

SIGHT.

551

diminished seems to recede. In these cases the influence on our
judgment of the muscular sense of binocular adjustment, or
monocular accommodation, is thwarted by the more direct influence
of the association between size and distance.

Judgment of Solidity. When we look at a small circle all
parts of the circle are at the same distance from us, all parts are
equally distinct at the same time, whether we look at it with one
eye or with two eyes. When, on the other hand, we look at a
sphere, the various parts of which are at different distances from

FIG. 77.

us, a sense of the accommodation, but much more a sense of the
binocular adjustment, of the convergence or the opposite of the two
eyes, required to make the various parts successively distinct,
makes us aware that the various parts of the sphere are unequally
distant ; and from that we form a judgment of its solidity. As
with distance of objects, so with solidity, which is at bottom a
matter of distance of the parts of an object, we can form a judg-
ment with one eye alone ; but our ideas become much more exact
and trustworthy when two eyes are used. And we are much
assisted by the effects produced by the reflection of light from the
various surfaces of a solid object ; so much so, that raised surfaces
may be made to appear depressed, or vice versa, and flat surfaces
either raised or depressed, by appropriate arrangements of shadings
and shadow.

Binocular vision, moreover, affords us a means of judging of the
solidity of objects, inasmuch as the image of any solid object which
falls on to the right eye cannot be exactly like that which falls on
the left, though both are combined in the single perception of the
two eyes. Thus, when we look at a truncated pyramid placed in
the middle line before us, the image which falls on the right eye is
of the kind represented in Fig. 77 E, while that which falls on the
left eye has the form of Fig. 77 L; yet the perception gained
from the two images together corresponds to the form of which
. Fig. 77 B is the projection. Whenever we thus combine in one
perception two dissimilar images, one of the one, and the other of
the other eye, we judge that the object giving rise to the images is
solid.

This is the simple principle of the stereoscope, in which two
slightly dissimilar pictures, such as would correspond to the vision
of each eye separately, are, by means of reflecting mirrors, as in

552 VISUAL JUDGMENTS. [BOOK in.

Wheats-tone's original instrument, or by prisms, as in the form
introduced by Brewster, made to cast images on corresponding
parts of the* two retinas so as to produce a single perception.
Though each picture is a surface of two dimensions only, the
resulting perception is the same as if a single object, or group of
objects, of three dimensions had been looked at.

It might be supposed that the judgment of solidity which
arises when two dissimilar images are thus combined in one per-
ception, was due to the fact that all parts of the two images cannot
fall on corresponding parts of the two retinas at the same time, and
that therefore the combination of the two needs some movement
of the eyes. Thus, if we superimpose E on L (Fig. 77), it is
evident that when the bases coincide the truncated apices will not,
and vice versa; hence, when the bases fall on corresponding parts,
the apices will not be combined into one image, and vice versa; in
order that both may be combined, there must be a slight rapid
movement of the eyes from the one to the other. That, however,
no such movement is necessary for each particular case is shewn
by the fact that solid objects appear as such when illuminated by
an electric spark, the duration of which is too short to permit of
any movements of the eyes. If the flash occurred at the moment
that the eyes were binocularly adjusted for the bases of the pyra-
mids, the two apices not falling on exactly corresponding parts
would give rise to two perceptions, and the whole object ought to
appear confused. That it does not, but, on the contrary, appears a
single solid, must be the result of cerebral operations, resulting in
what we have called a judgment.

Struggle of the two Fields of Vision. If the images of two
surfaces, one black and the other white, are made to fall on corre-
sponding parts of the eye, so as to be united into a single percep-
tion, the result is not always a mixture of the two impressions, that
is a grey, but, in many cases, a sensation similar to that produced
when a polished surface, such as plumbago, is looked at : the surface
appears brilliant. The reason probably is because when we look at
a polished surface the amount of reflected light which falls upon
the retina is generally different in the two eyes ; and hence we as-
sociate an unequal stimulation of the two retinas with the idea of
a polished surface. So also when the impressions of two colours
are united in binocular vision, the result is in most cases not a
mixture of the two colours, as when the same two impressions are
brought to bear together at the same time on a single retina, but a
struggle between the two colours, now one, and now the other, be-
coming prominent, intermediate tints however being frequently
passed through. This may arise from the difficulty of accommo-
dating at the same time for the two different colours (see p. 508) ;
if two eyes, one of which is looking at red, and the other at blue,
be both accommodated for red ravs, the red sensation will over-

CHAP. IT.] SIGHT. 553

power the blue, and vice versa. It may be however that the ten-
dency to rhythmic action, so manifest in other simpler manifesta-
tions of protoplasmic activity, makes its appearance also in the
higher cerebral labours of binocular vision.

SEC. 6. THE PROTECTIVE MECHANISMS OF THE EYE.

The eyeball is protected by the eyelids, which are capable of
movements called respectively opening and shutting the eye. The
eye is shut by the contraction of the orbicularis muscle, carried out
either as a reflex or voluntary act, by means of the facial nerve.
The eye is opened chiefly by the raising of the upper eyelid,
through the contraction of the levator palpebrae carried out by
means of the third nerve. The upper eyelid is also raised and the
lower depressed, the eye being thus opened, by means of plain
muscular fibres existing in the two eyelids and governed by the
cervical sympathetic. The shutting of the eye as in winking is in
general effected more rapidly than the opening.

The eye is kept continually moist partly by the secretion of the
glands in the conjunctiva, and of the Meibomian glands, but chiefly
by the secretion of the lachrymal gland. Under ordinary circum-
stances the fluid thus formed is carried away by the lachrymal
canals into the nasal sac and thus into the cavity of the nose.
When the secretion becomes too abundant to escape in this way it
overflows on to the cheeks in the form of tears.

If a quantity of tears be collected, they are found to form
a clear faintly alkaline fluid, in many respects like saliva, contain-
ing about 1 p.c. of solids, of which a small part is proteid in nature.
Among the salts present sodium chloride is conspicuous.

The nervous mechanism of the secretion of tears, in many
respects, resembles that of the secretion of saliva. A flow is usually
brought about either in a reflex manner by stimuli applied to the

CHAP. ii.J SIGHT. 555

conjunctiva, the nasal mucous membrane, tongue, optic nerve, &c.
or more directly by emotions. Venous congestion of the head
is also said to cause a flow. The efferent nerves belong either
to the cerebro-spinal system, (the lachrymal and orbital branches
of the fifth nerve,) or arise from the cervical sympathetic, the
afferent nerves varying according to the exciting cause.

The act of blinking undoubtedly favours the passage of tears
through the lachrymal canals into the nasal sac, and hence when
the orbicularis is paralysed tears do not pass so readily as usual
into the nose ; but the exact mechanism by which this is effected
has been much disputed. According to some authors, the con-
traction of the orbicularis presses the fluid onwards out of the
canals, which, upon the relaxation of the orbicularis, dilate and
receive a fresh quantity. Others maintain that a special arrange-
ment of muscular fibres keeps the canals open even during the
closing of the lids, so that the pressure of the contraction of the
orbicularis is able to have full effect in driving the tears through
the canals.

CHAPTER III.
HEARING, SMELL, AND TASTE.

SEC. 1. HEAEING.

As in the eye, so in the ear, we have to deal first with a nerve of
special sense, the stimulation of which gives rise to a special sensa-
tion; secondly with terminal organs through which the physical
changes proper to the special sense are enabled to act on the nerve ;
and thirdly with subsidiary apparatus, by which the usefulness of
the sense is increased. The central connections of the auditory
nerve are such that whenever the auditory fibres are stimulated,
whether by means of the terminal organs in the usual way or by
the direct application of stimuli, electrical, mechanical, &c., the
result is always a sensation of sound. Just as stimulation of the
optic fibres produces no other sensation than that of light, so
stimulation of the auditory fibres produces no other sensation than
that of sound1. The terminal organs of the auditory nerve are of
two kinds : the complicated organ of Corti in the cochlea, and the
epithelial arrangements of the maculae and cristse acusticse in other
parts of the labyrinth. Waves of sound falling on the auditory
nerve itself produce no effect whatever; it is only when by the
medium of the endolymph they are brought to bear on the delicate
and peculiar epithelium cells which constitute the peripheral ter-
minations of the nerve, that sensations of sound arise. Such
delicate structures are for the sake of protection naturally with-
drawn from the surface of the body where they would be subject to
injury. Hence the necessity of an acoustic apparatus, forming the
middle and external ear, by which the waves of sound are most
advantageously conveyed to the terminal organs.

1 It will be seen later on that there are reasons for thinking that impulses
passing along the auditory nerve may give rise to other effects than auditory
sensations.

CHAP, in.] HEARING, SMELL, AND TASTE. 557

The Acoustic Apparatus.

Waves of sound can and do reach the endolymph of the
labyrinth by direct conduction through the skull. Since however
sonorous vibrations are transmitted with great difficulty from the
air to solids and liquids, and most sounds come to us through the
air, some special apparatus is required to transfer the aerial vibra-
tions to the liquids of the internal ear. This apparatus is supplied
by the tympanum and its appendages.

The concha. The use of this, as far as hearing is concerned, is
to collect the waves of sound coming in various directions, and to
direct them on to the membrana tympani. In ourselves of moderate
service only, in many animals it is of great importance.

The membrana tympani. It is a characteristic property of
stretched membranes that they are readily thrown into vibration by
aerial waves of sound. The membrana tympani, from its peculiar
conformation, being funnel-shaped with a depressed centre sur-
rounded by sides gently convex outwards, is peculiarly susceptible
to sonorous vibrations, and is most readily thrown into correspond-
ing movements when waves of sound reach it by the meatus. It
has moreover this useful feature, that unlike other stretched
membranes, it has no marked note of its own. It is not thrown into
vibrations by waves of a particular length more readily than
by others. It answers equally well within a considerable range, to
vibrations of very different wave-lengths. Had it a fundamental
tone of its own, we should be distracted by the prominence of this
note in most of the sounds we hear. When sounds impinge on the
solids of the head, as when a watch is held between the teeth, the
membrana tympani is still functional. Vibrations are conveyed
from the temporal bone to it and hence pass in the usual way,
in addition to those transmitted directly from the bone to the peri-
lymph.

The auditory ossicles. The malleus, the handle of which de-
scending forwards and inwards, is attached to the membrana tym-
pani, and the incus, whose long process is connected by means of its
os orbiculare or lenticular process and the stapes to the fenestra
ovalis, form together a body which rotates round an axis, passing
through the short process of the incus, the bodies of the incus and
malleus, and the processus gracilis of the malleus. When the mal-
leus is carried inwards, the incus moves inwards too, and when the
malleus returns to its position, the incus returns with it, the peculiar
saddle-shaped joint with its catch teeth permitting this movement
readily, but preventing the stapes being pulled back when the mem-
brana tympani with the malleus is, for any reason, pushed outwards
more than usual ; the joint then gapes, so as to permit the malleus
to be moved alone. Various ligaments, the superior or suspensory,

558 THE TYMPANUM. [BOOK m.

anterior, and external, also serve to keep the malleus in place. The
whole series of ossicles may be regarded as a single-armed lever,
moving on the ligamental attachment of the short process of
the incus to the posterior wall of the tympanum, the weight
being brought to bear at the end of the long process of the incus,
and the power at the end of the handle of the malleus. The
long, malleal arm of this lever is about 9 \ mm., the short, stapedial,
6J mm. in length; hence the movements of the stapes are less
than those of the tympanum; but the loss in amplitude is made up
by a gain of force, which is in itself an obvious advantage.

Thus every movement of the tympanic membrane is trans-
mitted through this chain of ossicles to the membrane of the
fenestra ovalis, and so to the perilymph of the labyrinth; the
vibrations of the tympanic membrane are conveyed with increased
intensity, though with diminished amplitude, to the latter. That
the bones thus move en masse has been proved by recording their
movements in the usual graphic method. A very light style
attached to the incus or stapes is made to write on a travelling
surface; when the membrana tympani is thrown into vibrations by
a sound, the curves described by the style indicate that the chain
of bones moves with every vibration of the tympanum. On the
other hand, the comparatively loose attachments of the several
bones is an obstacle to the molecular transmission of sonorous
vibrations through them. Moreover, sonorous vibrations can only
be transmitted to or pass along such bodies as either are very long
compared to the length of the sound-waves, or, as in the case
of membranes and strings, have one dimension very much smaller
than the others. Now the bones in question are not especially
thin in any one dimension, but are in all their dimensions ex-
ceedingly small compared with the length of the vibrations of even
the shrillest sounds we are capable of hearing ; hence they must
be useless for the molecular propagation of vibrations.

The tensor tympani muscle even in a quiescent state is of use
in preventing the membrana tympani being pushed out far. When
it contracts it renders the membrana tympani more tense and
hence has been supposed to act as a damper lessening the
amount of vibration of the membrane in the case of too powerful
sounds; it is said to be readily thrown into contraction at the
commencement of a sound or noise, but to return to rest during
the continuance of a musical note. Efferent impulses reach it
through fibres of the fifth nerve, and its activity is regulated by
a reflex action. In some persons the muscle seems to be partly
under the dominion of the will, since a peculiar crackling noise
which these persons can produce at pleasure appears to be caused
by a contraction of the tensor tympani.

The so-called laxator tympani is considered to be not a muscle
at all, but a part of the ligamentous supports of the malleus.

CHAP, in.] HEARING, SMELL, AND TASTE. 559

The stapedius muscle is supposed to regulate the movements
of the stapes, and especially to prevent its base being driven too far
into the fenestra ovalis during large or sudden movements of the
membrana tympani. It is governed by fibres from the facial
nerve.

The Eustachian tube. This serves to maintain an equi-
librium of pressure between the external air and that within the
tympanum, and to serve as an exit for the secretions of that cavity.
Were the tympanum permanently closed the vibrations of the
membrana tympani would be injuriously affected by variations of
pressure occurring either inside or outside. The Eustachian tube
is undoubtedly open during swallowing, but it is still disputed
whether it remains permanently open, or is opened only at in-
tervals; probably it is, at most times, neither widely open nor
closely shut.

Auditory Sensations.

Each vibration communicated by the stapes to the perilymph
travels as a wave over the vestibule, the semicircular canals, and
other parts of the labyrinth; and from the perilymph is transmitted
through the membranous walls to the endolymph. From the
vestibule it passes on into the scala vestibuli of the cochlea, and
descending the scala tympani, ends as an impulse against the
membrane of the fenestra rotunda. In the regions of the maculae
and cristae the vibrations of the endolymph are supposed to throw
into corresponding vibrations the so-called auditory hairs. In the
cochlea the vibrations of the perilymph are supposed to throw into
vibrations the basilar membrane with the superimposed organ of
Corti, consisting of the rods of Corti with the inner and outer hair-
cells. The vibrations thus transmitted to these structures give rise
to nervous impulses in the terminations of the auditory nerves, and
these impulses reaching certain parts of the brain produce what we
call auditory sensations. We are accustomed to divide our auditory
sensations into those caused by noises and those caused by musical
sounds. It is the characteristic of the latter that the vibrations
which constitute them are periodical; they occur and recur at regular
intervals. When no marked periodicity is present in the vibrations,
when the repetition of the several vibrations is irregular, or the
period so complex as not to be readily appreciated, the sensation
produced is that of a noise. There is however no abrupt line be-
tween the two. Between a pure and simple musical sound pro-
duced by a series of vibrations each of which has exactly the same
wave-length, and a harsh noise in which no consecutive vibrations
may be alike, there are numerous intermediate stages.

In both noises and musical sounds we recognise a character
which we call loudness. This is determined by the amplitude of

560 A UDITOR Y SENS A TIONS. [BOOK HI.

the vibrations; the greater the disturbance of the air (or other
medium) the louder the sound. In a musical sound we recognise
also a character which we call pitch. This is determined by the
wave-length of the vibrations; the shorter the wave-length, the
larger the number of consecutive vibrations which fall upon the ear
in a second, the higher the pitch. We are able to speak of a whole
series of tones or musical sounds of different pitch, from the lowest
to the highest audible tone. And even in many noises we can, to
a certain extent, recognise a pitch, indicating that among the
multifarious vibrations there is a periodicity of certain groups of
vibrations.

Lastly, we distinguish musical sounds by their quality; the
same note sounded on a piano and on a violin produce very
different sensations, even when a series of vibrations having in each
case the same period of repetition is set going. This arises from
the fact that the musical sounds generated by most musical in-
struments are not simple but compound vibrations. When the
note C in the treble for instance is struck on the piano, and we
analyse the total sound, we find that it can be resolved partly into
a series of vibrations with a period characteristic of the pure tone
of the treble 0, and partly into other series of vibrations with
periods characteristic of the C in the octave above, of the G above
that, of the C in the next octave, and of the E above that. And
the sensation which we associate with the sound of the treble C on
the piano is determined by the characters of the complex vibration
arising out of these several constituent simple vibrations. Almost
all musical sounds are thus composed of what is called a 'funda-
mental tone' accompanied by a number of 'overtones.' And the
overtones varying in number and relative prominence in different
instruments, give rise to a difference in the sensation caused by the
whole tone. So that while the fundamental tone determines the
pitch of the sound, the quality of the sound is determined by the
number and relative prominence of the overtones. In a somewhat
similar way we distinguish the quality of noises, such as a banging,
crackling, or rustling noise, by an appreciation of sudden or
irregular changes in the amplitude and period of the constituent
vibrations.

Since we have a very considerable appreciation, capable by
exercise of astonishing enlargement, of the loudness, pitch, and
quality of a wide range of noises and musical sounds, it is clear
that, within the limits of hearing, each vibration or series of
vibrations must produce its effect on the auditory nerves, according
to the measure of its intensity and period. Out of those effects, out
of the sensory impulses to which the several vibrations thus give
rise, are generated our sensations of the noise or of the sound.

The vibrations of a musical sound (and since noises are so im-
perfectly understood-, we may, with benefit, chiefly confine ourselves
to musical sounds), as they pass through the air (or other medium)

CHAP, in.] HEARING, SMELL, AND TASTE. 561

are not discrete ; the vibrations corresponding to the fundamental
tone and overtones do not travel as so many separate waves ; they
all together form one complex disturbance of the medium; and it
is as one composite wave that the sound falls on the membrana
tympani, and passing through the auditory apparatus, breaks on
the terminations of the auditory nerve. And when two or more
musical sounds are heard at the same time, the same fusion of the
waves occurs. Since we can distinguish several tones reaching our
ear at the same time, it is clear that we must possess in our minds
or in our ears some means of analysing these composite waves
of sound which fall on our acoustic organs, and of sorting out their
constituent vibrations.

There is at hand a simple and easy physical method of analysing
composite sounds. If a person standing before an open piano sings
out any note, it will be observed that a number of the strings of
the piano will be thrown into vibration, and on examination it will
be found that those strings which are thus set going correspond in
pitch to the fundamental tone and to the several overtones of the
note sung. The note sung reaches the strings as a complex wave,
but these strings are able to analyse the wave into its constituent
vibrations, each string taking up those vibrations and those vibra-
tions only which belong to the tone given forth by itself when
struck. If we suppose that each terminal fibril of the auditory
nerve is connected with an organ so far like a piano-string that it
will readily vibrate in response to a series of vibrating impulses of
a given period and to none other, and that we possess a number of
such terminal organs sufficient for the analysis of all the sounds
which we can analyse, and that each terminal organ so affected by
particular vibrations gives rise to a sensory impulse and thus to a
sensation of a distinct character — if we suppose these organs to
exist, our appreciation of sounds is in a large measure explained.
In the organ of Corti we find structures the arrangement of which
irresistibly suggests to us that these are the organs we are seeking.
We have only to suppose that of the long series of rods of Corti,
varying regularly as these do from the bottom to the top of the
spiral, in length and in the span of their arch, each pair will
vibrate in response to a particular tone, and the whole matter
seems explained. But the more the subject is inquired into, the
more complex and difficult it appears; and we are obliged to
conclude that the part played by the rods of Corti is only a sub-
ordinate part of the function of the whole organ of Corti.

In the first place, it is difficult to see how the rods of Corti,
even if they are thrown into vibration, can originate sensory
impulses, for the fibrils of the auditory nerve terminate in the
inner and outer hair-cells, and it is in these cells, and not along the
course of the fibrils as they pass under and between the rods
of Corti, that the sensory impulses must begin. In the second
place, the variation in length of the fibres along the series is

F. 36

562 AUDITORY SENSATIONS. [BOOK HI.

insufficient for the work assigned to them. Moreover, they ap-
pear not to be elastic. Lastly, they are wholly absent in birds,
who very clearly can appreciate musical sounds. This last fact
proves indubitably that the rods in question are not absolutely
essential for the recognition of tones. In the face of these diffi-
culties it has been suggested that the basilar membrane, which is
present in birds as well as in mammals, and which, being tense
radially but loose longitudinally, i. e. along the spiral of the cochlea,
may be considered as consisting of a number of parallel radial
strings, each capable of independent vibrations, is the sought-for
organ of analysis; for it may be shewn mathematically that a
membrane so stretched in one direction only is capable of vibrating
in such a manner. And the radial dimensions of the basilar
membrane give a much greater range of difference than do the
rods of Corti, diminishing in man downwards from '495 mm. at
the hamulus to "04125 mm. near the bottom of the spiral, whereas
the difference in length of the latter is simply that between "048
and '085 mm. for the inner, and between *019 and '085 for the outer
fibres. According to this view, a particular simple vibration
reaching the scala tympani of the cochlea throws into sympathetic
vibrations a small portion of the basilar membrane, the vibrations
of which in turn so affect the structures overlying it, that sensory
impulses are generated. These sensory impulses reaching the brain
give rise to a corresponding sensation of a particular tone.

The remarkable reticular membrane which has such peculiar
relations with the hair-cells, and through them with the basilar
membrane, must, one might imagine, have some special function ;
but it is impossible at present to assign to it any satisfactory duty.
The structural arrangements seem, if anything, to indicate that when
a segment of the basilar membrane is thrown into vibrations, the
overlying hair-cells, reticular membrane, and rods of Corti vibrate
en masse together with it. But this renders the whole matter still
more difficult. Indeed the whole subject is in the highest degree
obscure, and the most we can say is that the organ of Corti as
a whole seems to be in some way connected with the appreciation
of tones, but that at present it is very hazardous to attempt to
explain how it acts, or to assign particular functions to particular
parts. The distinction between the inner and outer hair-cells
seems to be very parallel to that between the rods and the cones of
the retina ; but even this analogy may be a fallacious one.

It has been observed that among the auditory hairs of the
Crustacea, some will vibrate to particular notes ; but the auditory
hairs of the mammal are far too much of the same length to permit
the supposition that they can act as organs of analysis.

If the organ of Corti is the means by which we appreciate
tones, it is evident that by it also we must be able to estimate
loudness, for the quality of a musical sound is dependent on the
relative intensity, as well as on the nature, of the overtones. And

CHAP, in.] HEARING, SMELL, AND TASTE. 563

since noise is at best but confused music, the cochlea must be a
means of appreciating noises as well as sounds. But this would
leave nothing whatever for the rest of the labyrinth to do in
respect to the appreciation of sound save so far as the difference in
structure between the hair-cells of Corti, with their short thick
rods, and the hair-bearing structures in the maculae and cristse
with their thin delicate hairs, may possibly indicate a difference of
function, the latter being more susceptible to the irregular vibra-
tions of noises. That the vestibule and semicircular canals are
however concerned in hearing is shewn by its being the only audi-
tory organ in the ichthyopsida, unless we suppose that in the
higher vertebrates its function has been wholly transferred to the
cochlea. That the semicircular canals may have duties apart from
hearing we shall shew later on.

Concerning the function of the other parts of the internal ear
we know very little. The otoliths have been supposed to intensify
the vibrations of the endolymph ; but since apparently they are
lodged in a quantity of mucus it is probable that they really act as
dampers. A similar damping action has been suggested for the
membrane of Corti (membrana tectoria) overhanging the fibres and
hair-cells; and some writers have supposed that muscular fibres
present in the planum semilunare may by tightening the basilar
membrane serve as a sort of accommodation mechanism.

It must however be borne in mind that even making the fullest
allowance for the assistance afforded us by the organ of Corti, the
appreciation of any sound is ultimately a mental act The analysis
of the vibrations by the fibres of Corti or the basilar membrane is
simply preliminary to a synthesis of the sensory impulses so gene-
rated into a complex sensation. We do not receive a distinct
series of specific auditory impulses resulting in a specific sensation
for every possible variation in the wave-length of sonorous vibra-
tions any more than we receive a distinct series of specific visual
impulses for every possible wave-length of luminous vibrations.
In each case we have probably a number of primary sensations,
from the various mingling of which, in different proportions, our
varied complex sensations arise; the difference between the eye
and the ear being that whereas in the former the number of
primary sensations appears to be limited to three or at least to six,
in the latter, thanks to the organ of Corti, the number is very
large ; what the exact number is we cannot at present tell. Our
appreciation of a sound is at bottom an appreciation of the com-
bined effect produced by the relative intensities to which the
primary auditory sensations are, with the help of the organ of
Corti, excited by the sound.

Whatever be the explanation of the manner in which our
distinct auditory sensations arise, the range and precision of our
appreciation of musical sounds is very great. Vibrations with a

36—2

564 A UDITORY SENSATIONS. [BOOK in.

recurrence below 30 a second1 are unable to produce a sensation of
sound ; if the waves are powerful enough we may feel them, but
we do not hear them if the vibrations are simple, and such as
would give rise to a pure tone ; if the fundamental tone is accom-
panied by overtones we may hear these, and are thus apt to say we
hear the former when in reality we only hear the latter. The note
of the 16-feet organ pipe, 33 vibrations a second, gives us the sen-
sation of a droning sound. A tone of 40 vibrations is however
quite distinct. In the other direction it is possible to hear a note
caused by 38,000 vibrations a second, though the limit for most
persons is far lower, about 16,000. Some persons hear grave
sounds more easily than high ones, and vice versa. This may be so
pronounced as to justify the subjects being spoken of as deaf to
grave or high tones respectively. The range in different animals
is very different.

The power of distinguishing one note from another varies, as is
well known, in different individuals, according as they have or have
not a ' musical ear.' A well-trained ear can distinguish the differ-
ence of a single or even of a half vibration a second, and that
through a long range of notes. The range of an ordinary apprecia-
tion of tones lies between 40 and 4000 vibrations a second, i.e. be-
tween the lowest bass C (Ox 33 vibrations) and the highest treble
C (C5 4224 vibrations) of the piano ; tones above and below these,
even when audible, being distinguished from each other with great
difficulty.

When two consecutive sounds follow each other at a sufficiently
short interval the sensations are fused into one. In this respect
auditory sensations are of shorter duration than ocular sensations.
When ocular sensations are repeated ten times in a second they
become fused (p. 520), whereas the ticks of a pendulum beating
100 in a second are readily audible as distinct sounds. When two
tuning-forks not quite in tune are struck together the interference
of the vibrations gives rise to an alternating rise and fall of the
sound, known as 'beats.' When the beats follow each other as
rapidly as 132 in a second they cease to be recognised, that is to
say, the sensations which they cause become fused. Before
they disappear they give a peculiar disagreeable roughness to the
sound. The pleasure given by musical sounds depends largely on
the absence of this incomplete fusion of sensations.

Corresponding to entoptic phenomena there are various entotic
phenomena, sensations or modifications of sensations originating in
the tympanum or in the labyrinth ; moreover sensations of sound
may rise in the auditory nerve or in the brain itself, without any
vibration whatever falling on the labyrinth.

1 By some authors the limit is placed as low as 24 or even 15 a second.

CHAP, in.] HEARING, SMELL, AND TASTE. 565

Auditory Judgments.

In seeking for the cause of our visual sensations we invariably
refer to the external world. The sensation caused by a direct
stimulation of the optic nerve or retina by a blow or a galvanic
current, we identify with that caused by a flash of light. A sensa-
tion arising from any stimulation of the left side of our retina we
regard as caused by some object on the right-hand side of our ex-
ternal visible world. In a similar way, but to a less extent, we
project our auditory sensations into the world outside us, and when
the auditory nerve is affected we seek the cause in vibrations start-
ing at a greater or less distance from us. We do not think of the
sound as originating in the ear itself.

This mental projection of the sound is much more complete
when the ear is stimulated by vibrations reaching it through the
membrana tympani than when the vibrations are conducted by the
solids of the head directly to the perilymph of the labyrinth.
When the meatus externus is filled with fluid and the vibrations
of the membrana tympani are in consequence interfered with, the
apparent outwardness of sounds is to a very large extent lost;
sounds, however caused, seem under these circumstances to arise in
the ear. Hence it would seem that the vibrations of the mem-
brana tympani, or possibly the action of the muscles attached
to the ossicula, give rise to obscure sensations of which, by them-
selves, we are not distinctly conscious, but which nevertheless lead
us to judge that the sounds heard by means of the tympanum
come from outside the ear.

Our judgment of the distance of sounds is very limited. A
sound whose characters we know appears to us near when it is loud,
and far off when it is faint. A blindfold person will be unable to
distinguish between the difference of intensity produced on the
one hand by a timing-fork being held before him, first with the
broad edge of the fork toward him and then with the narrow edge,
and the difference on the other hand caused by the removal of the
tuning-fork to a distance. We can on the whole better appreciate
the distance of noises than of musical sounds.

Our judgment of the direction of sounds is also very limited.
Our chief aid in this is the position in which we have to place the
head in order that we may hear the sound to the best advantage.
If a tuning-fork be held in the median vertical plane over the
head, though it is easy to recognise it as being in the median plane,
it becomes very difficult when the eyes are shut to say what is its
position in that plane, i.e. whether it is more towards the front or

566 A UDITORT SENS A TIONS. [BOOK in.

back of the head. In this respect, too, our appreciation is more
accurate in the case of noises than of musical sounds, with the
exception of those given out by the human voice, the direction of
which can be judged better than even that of a noise.

SEC. 2. SMELL.

Odorous particles present in the inspired air passing through
the lower nasal chambers diffuse into the upper nasal chambers,
and falling on the olfactory epithelium produce sensory impulses
which, ascending to the brain, give rise to sensations of smell. We
may presume that the sensory impulses are originated by the con-
tact of the odorous particles with the peculiar rod-shaped olfactory7
cells described by Max Schultze ; but we are as much in the dark
about this matter as about the development of visual sensory im-
pulses in the rods and cones or of auditory sensory impulses in the
organ of Corti.

The subsidiary apparatus of smell is exceedingly meagre. By
the forced nasal inspiration, called sniffing, we draw air so forcibly
through the nostrils that currents pass up into the upper as well as
the lower nasal chambers ; and thus a more complete contact of the
odorous particles with the olfactory membrane than that supplied
by mere diffusion is provided for.

We have every reason to think that any stimulus applied to the
olfactory nerve will produce the sensation of smell ; but the proof
of this is not so clear as in the case of the optic and auditory
nerves. We are, however, subject to sensations of smell not caused
by objective odours. The olfactory membrane is the only part of
the body in which odours as such can give rise to any sensations ;

568 SMELL. [BOOK in.

and the sensations to which they give rise are always those
of smell. The mucous membrane of the nose is however also an
instrument for the development of afferent impulses other than the
specific olfactory ones. Chemical stimulation of the olfactory
membrane by pungent substances such as ammonia gives rise to a
sensation distinct from that of smell, a sensation which affords us
no information concerning the chemical nature of the stimulus,
and which is indistinguishable from the sensations produced by
chemical stimulation of other parts of the nasal membrane as well
as of other surfaces equally sensitive to chemical action. It is
probable that these two kinds of sensations thus arising in the ol-
factory membrane are conveyed by different nerves, the former by
the olfactory, the latter by the fifth nerve.

For the developement of smell it appears necessary that the
odorous particles should be conveyed to the nasal membrane in a
gaseous medium, or at least that the surface of the membrane
should not be exposed at the same time to the action of fluids.
Thus, when the nostril is filled with rose-water, the odour of roses
is not perceived ; and simply filling the nostrils with distilled water
suspends for a time all smell, the sense returning gradually after
the water has been removed ; the water apparently acts injuriously
on the delicate olfactory cells.

Each substance that we smell causes a specific sensation, and
we are not only able to recognise a multitude of distinct odours,
but also to distinguish individual odours in a mixed smell.

As in the previous senses, we project our sensation into the
external world ; the smell appears to be not in our nose, but some-
where outside us. We can judge of the position of the odour how-
ever even less definitely than we can of that of a sound.

The sensation takes some time to develope after the contact of
the stimulus with the olfactory membrane, and may last very long.
When the stimulus is repeated the sensation very soon dies out :
the sensory terminal organs speedily become exhausted. Mental
associations cluster more strongly round sensations of smell than
round any other impressions we receive from without. And reflex
effects are very frequent, many people fainting in consequence of
the contact of a few odorous particles with their olfactory cells.

Apparently the larger the surface the more intense the sen-
sation; animals with acute scent having a proportionately large
area of olfactory membrane. The quantity of material required to
produce an olfactory sensation may be, as in the case of musk,
almost immeasurably small.

When two different odours are presented to the two nostrils, an
oscillation of sensation similar to that spoken of in binocular vision
(p. 552) takes place.

The assertion that the olfactory nerve is the nerve of smell has
been disputed. Cases have been recorded of persons who appeared
to have possessed the sense of smell, and yet in whom the olfactory

CHAP, in.] HEARING, SMELL, AND TASTE. 569

lobes were found after death to be absent. Direct experiments on
animals however shew that loss of the olfactory lobes entails loss of
smell. On the other hand, it is stated that section or injury of the
fifth nerve causes a loss of smell though the olfactory nerve remains
intact ; but in these cases it has not been shewn that the olfactory
membrane remains intact, and it is quite possible that, as in the
case of the eye, changes may take place in the nasal membrane as
the result of the injury to the fifth nerve, sufficient to prevent its
performing its usual functions.

SEC. 3. TASTE.

The word taste is frequently used when the word smell ought
to be employed. We speak of 'tasting' odoriferous substances, such
as an onion, wines, &c., when in reality we only smell them as we
hold them in our mouth; this is proved by the fact that the
so-called taste of these things is lost when the nose is held, or the
nasal membrane rendered inert by a catarrh.

The terminal organs of the sense of taste thus more strictly de-
nned, are the endings of the glossopharyngeal and lingual nerves in
the mucous membrane of the tongue and palate, those nerves serving
as the special nerves of taste. Whether the so-called gustatory
buds can be regarded as specific organs of taste, appears doubtful.
The subsidiary apparatus is confined to the tongue and lips, which
by their movements assist in bringing the sapid substances into
contact with the mucous membrane of the mouth.

Though we can hardly be said to project our sensation of taste
into the external world, we assign to it no subjective localisation.
When we place quinine in our mouth, the resulting sensation of
taste gives us no information as to where the quinine is, though we
may learn that by concomitant general sensations arising in the
buccal mucous membrane.

We recognise a multitude of distinct tastes, which may be
broadly classified into acid, saline, bitter and sweet tastes. Sapid
substances have the power of producing these sensations by virtue
of their chemical nature. But other stimuli will also give rise to
sensations of taste. When the tongue is tapped, a taste is felt ;
and when a constant current is passed through the mouth, an
alkaline or, in some persons, a bitter metallic taste is developed
when the anode, and an acid taste when the kathode, is placed on
the tongue. It is probable that in these cases the terminal organs
are indirectly affected by the current. When hot or pungent
substances are introduced into the mouth, sensations of general
feeling are excited, which obscure any strictly gustatory sensations
which may be present at the same time.

Though analogy would lead us to suppose that a stimulus
applied to any part of the course of the real gustatory fibres of

CHAP, in.] HEARING, SMELL, AND TASTE. 571

either the glossopharyngeal or lingual nerves, would give rise to a
sensation of taste and nothing else, the proof is not forthcoming ;
since both these nerves are mixed nerves containing other afferent
fibres as well as those of taste.

When the constant current is used as a means of exciting taste,
gustatory sensations are found to be developed in the back, edges
and tip of the tongue, the soft palate, the anterior pillar of the
fauces, and a small tract of the posterior part of the hard palate.
They are absent from the anterior and middle dorsal, and under
surface of the tongue, the front portion of the hard palate, the
posterior pillars of the fauces, the gums and the lips. Sapid
substances are unsuitable as a test for this purpose, on account of
their rapid diffusion. Bitter substances produce most effect when
placed on the back of, and sweet substances when placed on the tip
of the tongue ; but the tasting power of the tip of the tongue varies
very much in different individuals and in many seems almost
entirely absent. It is said that acids are best appreciated by the
edge of the tongue.

It is essential for the developement of taste, that the substance
to be tasted should be dissolved ; and the effect is increased by
friction. The larger the surface the more intense the sensation.
The sensation takes some time to develope, and endures for a long
time, though this may be in part due to the stimulus remaining in
contact with the terminal organs. A temperature of about 40° is
the one most favourable for the production of the sensation. At
temperatures much above or below this, taste is much impaired.
The nerves of taste are, as we have said, the glossopharyngeal and
the lingual or gustatory. The former supplies the back of the
tongue, and section of it destroys taste in that region. The latter
is distributed to the front of the tongue, and section of it similarly
deprives the tip of the tongue of taste. There is no reason for
doubting that the gustatory fibres in the glossopharyngeal are
proper fibres of that nerve ; but it has been urged by many, that
the gustatory fibres of the lingual are derived from the chorda
tympani, and that those fibres of the lingual which come from the
fifth are employed exclusively in the sensations of touch and
feeling; the evidence in favour of this view is however incon-
clusive.

CHAPTER IV.
FEELING AND TOUCH.

SEC. 1. GENERAL SENSIBILITY AND TACTILE
PERCEPTIONS.

WE have taken the foregoing senses first in the order of discussion
on account of their being eminently specific. The eye gives us
only visual sensations, the ear only auditory sensations. The sen-
sations are produced in each case by specific stimuli: the eye
is only affected by light and the ear only by sound. Moreover, the
information they afford us is confined to the external world ; they
tell us nothing about ourselves. The various visual sensations
which arise in our retina are referred by us not to the retina itself,
but to some real or imaginary object in the world without (in-
cluding as part of the external world such portions of our own
bodies as are visible to ourselves). Such also with diminishing
precision is the information gained by hearing, taste and smell.

All the other afferent nerves of the body, centripetal impulses
along which are able to affect our consciousness, are the means of
conveying to us information concerning ourselves. The sensations,
arising in them from the action of various stimuli, are referred by
us to appropriate parts of our own body. When any body comes
in contact with our finger, we know that it is our finger which has
been touched ; from the resultant sensation we not only learn the
existence of certain qualities in the object touched, but we also are
led to connect the cognizance of these qualities with a particular
part of our own body.

Like the more specific senses previously studied, the sensations
of which we are now speaking, and which may be referred to under
the name of touch, using that word for the present in a wide

CHAP, iv.] FEELING AND TOUCH. 573

meaning, require for their production terminal organs; and the
chief but not exclusive organ of touch is to be found in the epider-
mis of the skin and certain underlying nervous structures. For
the developement of specific tactile sensations these terminal organs
are as essential as are the terminal organs of the eye for sight or of
the ear for hearing. Contact of the skin with a hard or with
a hot body gives rise to a distinct sensation, whereby we recognise
that we have touched a hard or a hot body. But the application of
either body or of any other stimulus to a nerve-trunk gives rise to
a sensation of general feeling only, corresponding to the simple
sensation of light which is produced by direct stimulation of the
optic nerve. We have no more tactile perception of a body which
is in contact with a nerve-trunk than we could have visual per-
ception of any luminous object, the rays proceeding from which
were strong enough to excite sensory impulses when directed on to
the optic nerve instead of on to the retina, supposing such a thing
to be possible. It is further characteristic of these ordinary nerves
of general feeling, that the sensations caused by any stimulation of
them beyond a certain degree develope that state of consciousness
which we are in the habit of speaking of as 'pain.' Putting aside
the general feeling which many parts of the eye possess, a very
strong luminous stimulation of the retina is required to produce a
sensation of pain, if indeed it can be at all brought about; whereas
a very moderate stimulation of the skin, and almost every stimu-
lation of an ordinary nerve-trunk, is said by us to be painful.

Though the skin is the chief organ of touch, the mucous mem-
brane lining the various passages of the body also serves as an
instrument for the same sense, but only for a short distance from
the respective orifices. We can recognise hard or hot bodies with
our lips or mouth, but a hot liquid, when it has reached the oeso-
phagus or stomach, simply gives rise to a sensation of pain : we
cannot distinguish the sensation caused by it from the sensation
caused by a draught of a too acid fluid.

From parts and tissues of the body other than the skin and the
portions of mucous membrane just mentioned we have obscure
sensations of general feeling, by which we are made vaguely
aware of the general condition of our body, though our judgments
in this matter are chiefly influenced by what we shall have to
speak of directly as a muscular sense. In all parts of the body,
however, on occasions all too frequent, this general feeling may
become prominent as pain.

The stimuli which, when applied to the skin, give rise to tactile
perceptions are of two kinds only : (1) mechanical, that is, the con-
tact of bodies exerting varying degrees of pressure ; and (2) thermal,
i.e. the raising or lowering of the temperature of the skin by the
approach or contact of hot or cold bodies. We can judge of the
weight and of the temperature of a body, because we can, through
touch, perceive how much it presses when allowed to rest on

574 TACTILE SENSATIONS. [BOOK in.

our skin or how hot it is. But we can through touch derive
no other perceptions and form no other judgments. An electric
shock sent through the skin will give rise to a sensation, but
the sensation is an indefinite one, because the electric current acts
not on the terminal organs of touch, but on the fine nerve-branches
of the skin. We cannot distinguish the sensation so caused from a
mechanical prick of similar intensity, we cannot perceive that the
sensation is caused by an electric current. Similarly certain
chemical substances such as a strong acid will give rise to a
sensation, but we cannot perceive the acid, we can form no judg-
ment of its nature such as we could if we tasted it ; and if the acid
does not permeate the skin so as to act directly and chemically on
the fine nerve-fibres, we cannot distinguish the acid from any
other liquid giving rise to the same simple contact impressions.
The terminal organs of the skin are such as are only affected
by pressure or by temperature. Conversely pressure or a variation
in temperature brought to bear on a nerve-trunk, instead of on the
terminal organs, produces no specific tactile sensations of pressure
or temperature, but merely general sensations of feeling rapidly
rising into pain.

SEC. 2. TACTILE SENSATIONS.

Sensations of Pressure.

As with visual, so with tactile and indeed with all other sen-
sations, the intensity of the sensation maintains that general
relation to the intensity of the stimulus which we spoke of at
p. 521 as being formulated under Weber's law. We can distinguish
the difference of pressure between one and two grammes as readily
as we can that between ten and twenty or one hundred and two
hundred.

When two sensations follow each other in the same spot at a
sufficiently short interval they are fused into one; thus, if the
finger be brought to bear lightly on a rotating card having a series
of holes in it, the holes cease to be felt as such when they follow
each other at a rapidity of about 1500 in a second. The vibrations
of a cord cease to be appreciable by touch when they reach the
same rapidity. When sensations are generated at points of the
skin too close together they become fused into one ; but to this
point we shall return presently.

The sensation caused by pressure is at its maximum soon after
its beginning, and thenceforward diminishes. The more suddenly
the pressure is increased, the greater the sensation; and if the
increase be sufficiently gradual, even very great pressure may be
applied without giving rise to any sensation. A sensation in any
spot is increased by contrast when the surrounding areas are not
subject to pressure. Thus if the finger be dipped into mercury the
pressure will be felt most at the surface of the fluid ; and if the
finger be drawn up and down, the sensation caused will be that of
a ring moving along the finger.

576 TACTILE SENSATIONS. [CHAP. iv.

All parts of the skin are not equally sensitive to pressure; small
differences of simple pressure are more readily appreciated when
brought to bear on the palmar surface of the finger, or on the
forehead, than on the arm or on the sole of the foot. In making
these determinations all muscular movements should be avoided in
order to eliminate the muscular sense of which we shall speak
presently; and the area stimulated should be as small and the
surfaces in contact as uniform as possible. In a similar manner
small consecutive variations of pressure, as in counting a pulse, are
more readily appreciated by certain parts of the skin than by
others ; and the minimum of pressure which can be felt differs in
different parts. In all cases variations of pressure are more easily
distinguished when they are successive than when they are simul-
taneous.

Sensations of Temperature.

When the temperature of the skin is raised or lowered in any
spot we receive sensations of heat and cold respectively ; and by
these sensations of the temperature of our own skin we form judg-
ments of the temperature of bodies in contact with it. Bodies of
exactly the same temperature as the region of the skin to which
they are applied produce no such thermal sensations, though we
can, from the very absence of sensations, form a judgment as
to their temperature; and good conductors of heat appear re-
spectively hotter and colder than bad conductors raised to the same
temperature.

We may consider the skin as having at any given time and in
any given spot a normal temperature at which the sensation
of temperature is at zero ; for under ordinary circumstances we are
not directly conscious of the temperature of our skin ; it is only
when the normal temperature at the spot is raised or lowered that
we have a sensation of heat or cold respectively. This normal
temperature may be at the same time different in different parts of
the body ; thus at a time when neither the forehead nor the hand
are giving rise to any sensation of temperature, we may, by putting
the hand to the forehead, frequently feel the former hot or cold
because the normal temperatures of the two parts differ. The
normal temperature in any spot may also vary from time to time.
Thus when the hand is placed in a warm medium for some time,
the sensation of warmth ceases ; a new normal temperature is
established with the zero of sensation at a higher level, a depression
or elevation of this new temperature giving rise however as before
to sensations of heat and cold respectively. That it is the changed
condition, and not the change itself, of which we are conscious is
shewn by the fact that when a portion of skin is cooled, by brief
contact with a cold metal for instance, we are still conscious of the

CHAP, iv.] FEELING AND TOUCH. 577

spot being cold after the cooling agent has been removed, that is
at a time when the cooled spot is in reality being heated by the
surrounding warmer tissues.

The change in temperature of the skin necessary to produce a
sensation must have a certain rapidity ; and the more gradual the
change the less intense the sensation. The repeated dipping of the
hand into hot water produces a greater sensation than when the
hand is allowed to remain all the time in the water, though in the
latter case the temperature of the skin is most affected. The
effects of contrast are also seen in these sensations as in those of
pressure.

We can with some accuracy distinguish variations of tempera-
ture, especially those lying near the normal temperature of the
skin. These sensations, in fact, follow Weber's law, though
apparently sensations of slight cold are more vivid than those
of slight heat, the range of most accurate sensation seeming to lie
between 27° and 33°.

The regions of the skin most sensitive to variations in tempera-
ture are not identical with those most sensitive to variations
in pressure. Thus the cheeks, eyelids, temples and lips, are more
sensitive than the hands. The least sensitive parts are the legs,
and front and back of the trunk.

The simplest view which can be taken with regard to the
distinction between pressure sensations and temperature sensations,
and which is suggested by the facts just mentioned, is to suppose
that two distinct kinds of terminal organs exist in the skin, one of
which is affected only by pressure, and the other only by variations
in temperature ; and that the two kinds of peripheral organs are
connected with different parts of the central sensory organs by
separate nerve-fibres. Certain pathological cases have been quoted
as shewing not only that this is the case, but that the two sets of
fibres pursue different courses in the spinal cord. Thus in certain
diseases or injuries to the brain or spinal cord, hypersesthesia
as regards temperature has been observed unaccompanied by an
augmentation of sensitiveness to pressure ; and conversely instances
have been seen where the patient could tell when he was touched,
but could not distinguish between hot and cold. On the other
hand there are facts which shew a close dependence between the
sensations of pressure and temperature. When each stimulus is
brought to bear on a very limited area, the two sensations are fre-
quently confounded, especially in those regions of the body where
sensations are not acute. So also a penny cooled down nearly
to zero and placed on the forehead will be judged by most
people to be as heavy or even heavier than two pennies of the
temperature of the forehead itself; and conversely a body warmer
than the skin will often appear heavier than a body of the same
weight but of the same temperature as the skin. Moreover cases
have been recorded where a hot body, such as a heated spoon,

F. 37

578 SENSATIONS OF TEMPERATURE. [Boon in.

was felt, though the application of the same spoon at the
temperature of the body produced no sensations, and yet the
heated spoon was not recognised as a hot body but appeared
to be simply something touching the skin. It may be argued
that these instances shew nothing more than the changes in
the skin whatever they be, which give rise to sensations of
pressure, are modified by the temperature of the skin for the time
being, whereby the judgment as to the pressure which is being
exerted is rendered faulty ; but they may also be taken to indicate
that variations in pressure and temperature affect the same
terminal organs, and the same nerve-fibres, though affecting them
in a different way and generating nervous impulses so far different
that they give rise to different sensations. And we may here note
that we certainly cannot speak of nerves of warmth in the same
sense in which we speak of nerves of sight or of hearing. A
stimulus (of whatever kind) applied to an optic or auditory
nerve, if adequate, gives rise, as we have seen, to a sensation of
light or of sound; a stimulus, on the other hand, applied to the
trunk of a cutaneous nerve gives rise only to general feeling or
pain; though the nerve certainly contains fibres by which sen-
sations of pressure and of temperature reach the brain, the general
feeling which stimulation of the trunk causes is akin neither to
sensations of pressure nor to those of warmth.

The rapidity with which hot or cold bodies brought into contact
with the skin give rise to sensations of temperature, suggests that the
terminal apparatus for generating these sensations, whatever be its
nature, is placed in the epidermis, and indeed as near as possible to
the surface. Pressure on the other hand can be readily transmitted
through even a thick layer of skin. And those who maintain the
existence of different terminal organs for pressure and temperature,
regard the nerve-endings in the epidermis as the latter and the
corpuscula tactus, end-bulbs and allied organs as the former. But
the evidence we possess concerning this matter is at present incon-
clusive.

SEC. 3. TACTILE PERCEPTIONS AND JUDGMENTS.

When a body presses on any spot of our skin, or when the tem-
perature of the skin at that spot is raised, we are not only conscious
of pressure or of heat, but perceive that a particular part of our
body has been touched or heated. We refer the sensations to
their place of origin, and we thus by touch perceive the relations to
ourselves of the body which gives rise to the tactile sensations, in
the same way as in our visual perception of external objects we
refer to external nature the sensations originating in certain parts
of the retina. When we are touched on the finger and on the back
we refer the sensations to the finger and to the back respectively,
and when we are touched at two places on the same finger at the
same time we refer the sensations to two points of the finger. In
this way we can localize our sensations, and are thus assisted
in perceiving the space relations of objects with which we come in
contact.

This power of localizing pressure-sensations varies in different
parts of the body. The following table from Weber gives the
distance at which two points of a pair of compasses must be held
apart, so that when the two points are in contact with the skin,
the two consequent sensations can be localized with sufficient
accuracy to be referred to two points of the body, and not
confounded together as one.

Tip of tongue ... ... ... ... I'l mm.

Palm of last phalanx of finger ... ... 2*2 „

Palm of second „ „ 4'4 „

Tip of nose 6'6 „

White part of lips 8'8 „

Back of second phalanx of finger ... Ill „

Skin over malar bone ... ... ... 15'4 „

Back of hand 29'8 „

Forearm 39'6 „

Sternum ... ... ... ... 44'0 „

Back 66-0 „

37—2

580 TACTILE PERCEPTIONS. [Boon in.

And an analogous distribution has been observed in reference to
the localisation of sensations of temperature. As a general rule it
may be said that the more mobile parts are those by which we can
thus discriminate sensations most readily. The lighter the pressure
used to give rise to the sensations, the more easily are two sen-
sations distinguished ; thus two points which, when touching the skin
lightly, appear as two, may, when firmly pressed, give rise to one
sensation only. The distinction between the sensations is obscured
by neighbouring sensations arising at the same time. Thus two
points brought to bear within a ring of heavy metal pressing on
the skin, are readily confused into one. And it need hardly be
said that these tactile perceptions, like all other perceptions, are
immensely increased by exercise.

Our 'field of touch,' if we may be allowed the expression,
is composed of tactile areas or units, in the same way that our field
of vision is composed of visual areas or units. The tactile sensation
is, like the visual sensation, a symbol to us of some external event,
and we refer the sensation to its appropriate place in the field of
touch. All that has been said (p. 523) concerning the subjective
nature of the limits of visual areas, applies equally well, mutatis
mutandis, to tactile areas. When two points of the compasses are
felt as two distinct sensations, it is not necessary that two and only
two nerve-fibres should be stimulated ; all that is necessary is that
the two cerebral sensation-areas should not be too completely
fused together. The improvement by exercise of the sense of
touch must be explained not by an increased development of the
terminal organs, not by a growth of new nerve-fibres in the skin,
but by a more exact limitation of the sensational areas in the
brain, by the development of a resistance which limits the radiation
taking place from the centres of the several areas.

By a multitude of simultaneous and consecutive tactile sensa-
tions thus converted into perceptions we are able to make ourselves
acquainted with the form of external objects. We can tell by
variations of pressure whether a surface is rough or smooth, plane
or curved, what variations of surface a body presents, and how far
it is heavy or light ; and from the information thus gained we
build up judgments as to the form and nature of objects, judgments
however which are most intimately bound up with visual judg-
ments, the knowledge derived by one sense correcting and com-
pleting that obtained by the other. As in other senses so in this,
our sensations may mislead us and cause us to form erroneous
judgments. This is well illustrated by the so-called experiment of
Aristotle. It is impossible in an ordinary position of the fingers to
bring the radial side of the middle finger and the ulnar side of the
ring finger to bear at the same time on a small object such
as a marble. Hence when with the eyes shut we cross one finger
over the other, and place a marble between them so that it touches
the radial side of the one and the ulnar side of the other, we

CHAP. iv.J FEELING AND TOUCH. 581

recognise that the object is such as could not under ordinary
conditions be touched at the same time by these two portions
of our skin, and therefore judge that we are touching not one but
two marbles. Upon repetition however we are able to correct our
judgment and the illusion disappears.

Distinct tactile sensations are, as we have seen, produced only
when a stimulus is applied to a terminal organ. When sensations or
affections of general sensibility other than the distinct tactile sen-
sations are developed in the termination of a nerve, we are still able,
though with less exactitude, to refer the sensation to a particular
part of the body. Thus when we are pricked or burnt, we can feel
where the prick or burn is. When a sensory nerve-trunk is
stimulated, the sensation is always referred to the peripheral
terminations of the nerve. Thus a blow on the ulnar nerve at the
elbow is felt as a tingling in the little and ring fingers correspond-
ing to the distribution of the nerve, and sensations started in the
stump of an amputated limb are referred to the absent member.
When cold is applied to the elbow it is felt as cold in the skin
of the elbow : but a cooling of the ulnar nerve at this spot, since
stimulation of a nerve-trunk gives rise to general sensations only,
simply gives rise to pain which is referred to the ulnar side of
the hand and arm.

SEC. 4. THE MUSCULAR SENSE.

When we come into contact with external bodies we are
conscious not only of the pressure exerted by the object on our
skin, but also of the pressure which we exert on the object. If we
place the hand and arm flat on a table, we can estimate the
pressure exerted by bodies resting on the palm of the hand, and
so come to a conclusion as to their weights ; in this case we are
conscious only of the pressure exerted by the body on our skin. If
however we hold the body in the hand, we not only feel the
pressure of the body, but we are also aware of the muscular
exertion required to support and lift it. We possess a muscular
sense ; and we find by experience that when we trust to this
muscular sense as well as to sensations of pressure, we can form
much more accurate judgments concerning the weight of bodies than
when we rely on sensations of pressure alone. When we want to tell
how heavy a body is, we are not in the habit of allowing it simply to
press on the hand laid flat on a table ; we hold it in our hand and
lift it up and down. We appeal to our muscular sense to inform
us of the amount of exertion necessary to move it, and by help of
that, judge of its weight. And in all the movements of our body
we are guided, even to an astonishing degree of accuracy, as is well
seen in the discussions concerning vision, by an appreciation, more
or less distinctly conscious, of the amount of the contraction to
which we are putting our muscles. In some way or other we are
made aware of what particular muscles or groups of muscles are
being thrown into action, and to what extent that action is being

CHAP, iv.] FEELING AND TOUCH. 583

carried. We are also conscious of the varying condition of our
muscles, even when they are at rest ; the tired and especially the
paralysed limb is said to 'feel' heavy. In this way the state of our
muscles largely determines our general feeling of health and
vigour, of weariness, ill health and feebleness.

It has been suggested that since muscle possesses little or no
general sensibility, comparatively little pain being felt for instance
when muscles are cut, our muscular sense is chiefly derived from
the traction of the contracting muscle on its attachments; and
undoubtedly in many instances of cramp, the pain is chiefly felt
at the joints; and, as we know, Pacinian bodies are abundant
around the joints. Afferent nerves, however, having a different
disposition from the ordinary motor nerves which terminate in
end-plates, have been described as present in muscle ; and analogy
would lead us to suppose that these afferent fibres, though possess-
ing a low general sensibility, might be easily excited in a specific
manner by a muscular contraction ; but further investigations are
necessary before these can be accepted as the true nerves of the
muscular sense.

In favour of the view that the muscular sense is peripheral and
not central in origin, may be urged the fact that the sense is felt
when the muscles are thrown into contraction by direct galvanic
stimulation instead of by the agency of the will. Many authors,
even while admitting the existence of a muscular sense of peripheral
origin, contend that wre also possess and are very largely guided in
our movements by what might be called a ' neural ' sense of central
origin. That is to say, the changes in the central nervous system
involved in initiating and carrying out a movement of the body, so
affect our consciousness, that we have a sense of the effort itself.

It has been observed that when the posterior roots are divided,
movements become less orderly, as if they lacked the guidance of a
muscular sense ; and although the impairment of the movements
may be due in part to the coincident loss of tactile sensations, it is
probable that it is increased by the loss of the muscular sense.
There is a malady or rather a condition attending various diseased
states of the central nervous system called locomotor ataxy, the
characteristic feature of which is that, though there is no loss of
direct power over the muscles, the various bodily movements are
effected imperfectly and with difficulty, from want of proper
co-ordination. In such diseases the pathological mischief is fre-
quently found in the posterior columns of the spinal cord and the
posterior roots of the spinal nerves, that is in distinctly afferent
structures ; and the phenomena seem in certain cases at least to be
due to inefficient co-ordination caused by the loss both of the
muscular sense and of ordinary tactile sensations. The patients
walk with difficulty, because they have imperfect sensations both of
the condition of their muscles and of the contact of their feet with
the ground. In many of their movements they have to depend largely

584 MUSCULAR STRENGTH. [BOOK in.

on visual sensations ; hence when their eyes are shut, they become
singularly helpless. In other cases again ataxy may be present
without any impairment of touch; but a discussion of the varied
phenomena of this class of maladies cannot be entered into here.

CHAPTER V.
THE SPINAL CORD.

SEC. 1. AS A CENTRE OR GROUP OF CENTRES OF
REFLEX ACTION.

OF the several functions of the spinal cord perhaps the most
striking and important is that of carrying out reflex actions. As
we have already said, the spinal cord is par excellence the organ
of reflex action; in by far the greater number of the reflex move-
ments of the body, the centre is supplied by some part of the spinal
cord. We have already (Book i. Chap, in.) touched on the
general features of reflex actions, and elsewhere have incidentally
dwelt on particular instances ; we may therefore confine ourselves
now to certain points of special interest.

Reflex movements are perhaps best studied in the frog and
other cold-blooded animals, where the phenomena are less ob-
scured by the working of the other so-called higher parts of the
central nervous system. They obtain however in the warm-blooded
mammal also, but in these special precautions are necessary to
secure their full development.

In the frog the shock which follows upon division of the spinal
cord, and which, as we shall presently see, for a while inhibits reflex
activity, soon passes away; within a very short time after the
medulla oblongata for instance has been divided the most com-
plicated reflex movements can be carried on by the frog's spinal
cord when the appropriate stimuli are applied. With the mammal
the case is very different. For days even after division of the
spinal cord the parts of the body supplied by nerves springing
from the cord below the section exhibit very feeble reactions only.

586 REFLEX ACTIONS. [BOOK in.

In the dog, for instance, after division of the spinal cord in the
lower dorsal region, the hind limbs hang flaccid and motionless,
and pinching the hind foot evokes as a response either slight
irregular movements or none at all. Indeed were our observations
limited to this period we might infer that the reflex actions of the
spinal cord in the mammal were but feeble and insignificant. If
however the animal be kept alive for a longer period, for weeks or
better still for months, though no union or regeneration of the
spinal cord takes place, reflex movements of a powerful, varied and
complex character manifest themselves in the hind limbs and
hinder parts of the body ; a very feeble stimulus applied to the
skin of these regions promptly gives rise to extensive and yet co-
ordinate movements. Compared with the reflex actions of the
frog, the movements carried out by the lower portion of the spinal
cord of the mammal while they are more energetic have hitherto
been regarded as being less definite and complete and less
purposeful ; but it would be dangerous to insist on this, for recent
experience tends to shew that, in the case of most mammals, the
powers of the spinal cord have been unduly underrated. It is
worthy of attention that the reflex phenomena in mammals vary
very much not only in different species but also in different in-
dividuals and in the same individual under different circumstances.
Race, age, and previous training, seem to have a marked effect in
determining the extent and character of the reflex actions which
the spinal cord is capable of carrying out ; and these seem also to
be largely influenced by passing circumstances, such as whether food
has been recently taken or no. And it is asserted that the spinal
cord of the rabbit, which has been the subject of so many experi-
ments, is, as compared with that of the dog and many other
mammals, singularly deficient in the power of carrying out complex
reflex movements.

Both in the cold-blooded and warm-blooded animals the salient
feature of ordinary reflex actions is their purposeful character,
though every variety of movement may be witnessed, from a simple
spasm to a most complex manoauvre ; and in all reflex movements,
both simple and complex, we can recognise certain determining
causes, the influences of which more or less directly contribute
to the shaping of this purposeful character.

Thus the features of any movement taking place as part of a
reflex action are in part determined by the nature of the afferent
impulses. Simple nervous impulses generated by the direct
stimulation of afferent nerve-fibres generally evoke as reflex
movements merely irregular spasms in a few *nuscles ; whereas
the more complicated differentiated sensory impulses generated
by the application of the stimulus to the skin, readily give rise
to large and purposeful movements. It is easier to produce a
complex reflex action by a slight pressure on the skin than by
even a strong single induction-shock applied directly to a nerve-

CHAP, v.] THE SPINAL CORD. 587

trunk. If, in a brainless frog, the area of skin supplied by one of
the dorsal cutaneous nerves be separated by section from the rest
of the skin of the back, the nerve being left attached to the piece
of skin and carefully protected from injury, it will be found that
slight stimuli applied to the surface of the piece of skin easily
evoke reflex actions, whereas the trunk of the nerve may be stimu-
lated with even strong currents without producing anything more
than irregular movements. In ordinary mechanical and chemical
stimulation of the skin it is a series of impulses and not a single
impulse which passes upwards along the sensory nerve, the changes
in which may be compared to the changes in a motor nerve during
tetanus. In every reflex action, in fact, the central mechanism
may be looked upon as being thrown into activity through a
summation of the afferent impulses reaching it. Hence while a
reflex action is readily called forth by even feeble single induction-
shocks applied to the skin if they be repeated sufficiently rapidly,
a solitary induction-shock is ineffectual unless it be strong enough
to cause profound changes in the skin or nerves.

When a muscle is thrown into contraction in a reflex action,
the note which it gives forth does not vary with the stimulus, but
is constant, being the same as that given forth by a muscle thrown
into contraction by the will. From which we infer that in a reflex
action the afferent impulses do not simply pass through the centre
in the same way that they pass along afferent nerves, but are
profoundly modified. And this explains why a reflex action takes
always a considerable time, and frequently a very long time, for its
development. When the toes of a brainless frog are dipped in
dilute sulphuric acid, several seconds may elapse before the feet
are withdrawn. Making every allowance for the time needed for
the acid to develope sensory impulses in the peripheral endings of
the afferent nerve, a very large fraction of the period must be
taken up by the molecular actions going on in the nerve-cells. In
other words, the interval between the advent at the central organ
of afferent, and the exit from it of efferent impulses, is a busy time
for the nerve-cells of that organ; during it many processes, of
which we have at present very little exact knowledge, are being
carried on.

The character of the movement forming part of a reflex
action is also influenced by the intensity of the stimulus. A
slight stimulus, such as gentle contact of the skin with some
body, will produce one kind of movement ; and a strong stimulus,
such as a sharp prick applied to the same spot of skin, will
call forth quite a different movement. When a decapitated
snake or newt is suspended and the skin of the tail lightly
touched with the finger the tail bends towards the finger; when
the skin is pricked or burnt, the tail is turned away from the
offending object. And so in many other instances. Further we
have already pointed out (p. 110) that while the effects of a weak

588 REFLEX ACTIONS. [BOOK in.

stimulus applied to an afferent nerve are limited to a few, those of
a strong stimulus may spread to many efferent nerves. Granting
that any particular afferent nerve is more especially associated with
certain efferent nerves than with any others, so that the reflex
impulses generated by afferent impulses entering the cord by the
former, pass with the least resistance down the latter, we must
evidently admit further that other efferent nerves are also, though
less directly, connected with the same afferent nerve, the passage
into the second efferent nerve meeting with an increased but not
insuperable resistance. When a frog is poisoned with strychnia,
a slight touch on any part of the skin may cause convulsions of the
whole body ; that is to say, the afferent impulses passing along any
single afferent nerve may give rise to the discharge of efferent im-
pulses along any or all of the efferent nerves. This proves that a
physiological if not an anatomical continuity obtains between
all the nerve-cells of the spinal cord which are concerned in reflex
action, that the nerve-cells with their processes form a functionally
continuous protoplasmic network. This network however we must
suppose to be marked out into tracts presenting greater or less re-
sistance to the progress of the impulses into which afferent impulses,
coming from this or that afferent nerve, are transformed on their
advent at the network; and accordingly the path of any series
of impulses in the network will be determined largely by the
energy of the afferent impulses. And the action of strychnia may
be in part explained by supposing that it reduces and equalises the
normal resistance of this network, so that even weak impulses
travel over all its tracts with great ease.

Further, the movement forming part of a reflex action varies
in character, according to the particular area of the skin or
the locality of the body to which the stimulus is applied.
Pinching the folds of skin surrounding the anus of the frog
produces different effects from those witnessed when the flank
or toe is pinched; and, speaking generally, the stimulation
of a particular spot calls forth particular movements. In the
case of the simpler reflex movements, it appears to be a
general rule that a movement started by the stimulation of a
sensory surface or region on one side of the body, is developed
on the same side of the body, and if it spreads to the other side,
still remains most intense on the same side ; the movement on the
other side moreover is symmetrical with that on the same side. It
has been maintained that 'crossed' or diagonal reflex movements,
as where stimulation of one fore-foot leads to movements of the
opposite hind-limb, do not occur unless some portion of the medulla
oblongata be left attached to the spinal cord. Seeing that loco-
motion in four-footed animals is largely effected by diagonal move-
ments of the limbs, one would rather have expected to find the
spinal cord itself provided with mechanisms to assist in carrying
them out ; and indeed it is affirmed that in the case of cold-

CHAP, v.] THE SPINAL CORD. 589

blooded animals and of many young mammals, after division of the
spinal cord below the medulla, a gentle stimulation will provoke a
diagonal movement, slight pressure on one fore-foot for example
giving rise to movements in the opposite hind-leg; a strong
stimulus however will produce an ordinary one-sided movement.

From these and similar phenomena we may infer that the proto-
plasmic network spoken of above is, so to speak, mapped out into
nervous mechanisms by the establishment of lines of greater or less
resistance, so that the disturbances in it generated by certain
afferent impulses are directed into certain efferent channels. But
the arrangement of these mechanisms is not a fixed and rigid one.
We cannot always predict exactly the nature of the movement
which will result from the stimulation of any particular spot, be-
cause the result will vary according to the condition of the spinal
cord, especially in relation to the strength of the stimulus. More-
over, under a change of circumstances a movement quite different
from the normal one may make its appearance. Thus when a
drop of acid is placed on the right flank of a frog, the right foot is
almost invariably used to rub off the acid ; in this there appears
nothing more than a mere 'mechanical' reflex action. If however
the right leg be cut off, or the right foot be otherwise hindered
from rubbing off the acid, the left foot is, under the exceptional
circumstances, used for the purpose. This at first sight looks like
an intelligent choice. A choice it evidently is; and were there
many instances of choice, and were there any evidence of a
variable automatism, like that of a conscious volition, being mani-
fested by the spinal cord of the frog, we should be justified in
supposing that the choice was determined by an intelligence.
It is however, on the other hand, quite possible to suppose that the
lines of resistance in the spinal protoplasm are so arranged as to
admit of an alternative, though still mechanical, action ; and seeing
how few and simple are the apparent instances of choice witnessed
in a brainless frog, and how absolutely devoid of spontaneity
or irregular automatism is the spinal cord of the frog, this seems
the more probable view. Moreover this conclusion is supported by
the behaviour of other animals. Thus similar vicarious reflex
movements may be witnessed in mammals, though not perhaps to
such a striking extent as in frogs. In dogs, in which partial removal
of the cerebral hemispheres has apparently heightened the reflex
excitability of the spinal cord, the remarkable scratching move-
ments of the hind leg which are called forth by stimulating a particu-
lar spot on the loins or side of the body, are executed by the leg
of the opposite side, if the leg of the same side be gently held.
In this case the vicarious movements are ineffectual and can
hardly be considered as betokening intelligence. Again the
'mechanical' nature of reflex actions is well illustrated by the
behaviour of a decapitated snake. When the body of the animal
in this condition is brought into contact at several places with any

590 REFLEX ACTIONS. [BOOK in.

object such as an arm or a stick, complex reflex movements
are excited, the obvious purpose as well as effect of which is to
twine the body round the object. A decapitated snake will how-
ever with equal and fatal readiness twine itself round a red-hot bar
of iron.

It may be added that the movements evoked by even a
segment of the cord may be purposeful in character; hence we
must conclude that every segment of the protoplasmic network is
mapped out into mechanisms.

Lastly, the characters of a reflex movement are, as we need
hardly say, dependent on the condition of the cord. The action of
strychnia just alluded to is an instance of an apparent augmen-
tation of reflex action best explained by supposing that the
resistances in the cord are lessened. There are probably however
cases in which the explosive energy of the nerve-cells is positively
increased above the normal. Conversely, by various influences of
a depressing character, as by various anaesthetics or other poisons,
reflex action may be lessened or prevented ; and this again may
arise either from an increase of resistance, or from a diminished
action of the nerve-cells themselves.

In actual life reflex movements, in by far the greater number
of instances, are occasioned by stimulation of the skin or of the
mucous membrane. They may however occur as the result of
stimulation of the organs of special sense. A sound or a flash
of light readily produces a start, a bright light causes many
persons to sneeze, and reflex movements may even result from a
taste or smell.

Inhibition of Reflex Action. The reflex actions of the spinal
cord, like other nervous actions, may be totally or partially inhibited,
that is may be arrested or hindered in their developement by
impulses reaching the centre while it is already in action. Thus
if a decapitated snake be suspended, slow rhythmic pendulous
movements, which appear to be reflex in nature, soon make their
appearance, and these may be for a while arrested by slight
stimulation, as by gently stroking the tail. We have already seen
that the action of such nervous centres as the respiratory and vaso-
motor centres, which frequently at all events is of a reflex nature,
may be either inhibited or augmented by afferent impulses. The
micturition centre in the mammal, which is also largely a reflex centre,
may be easily inhibited by impulses passing downward to the lumbar
cord from the brain, or upward along the sciatic nerves. In the case
of dogs, whose spinal cord has been divided in the dorsal region,
micturition set up as a reflex act by simple pressure on the
abdomen, or by sponging the anus, is at once stopped by sharply
pinching the skin of the leg. And it is a matter of common
experience that micturition may be suddenly checked by an
emotion or other cerebral event. The erection centre in the

CHAP. v.J THE SPINAL CORD. 591

lumbar cord also, in large measure a reflex centre, is similarly
susceptible of being inhibited by impulses reaching it from various
sources. And indeed many similar instances of the inhibition
of reflex movements might readily be quoted.

Several apparent instances of the inhibition of reflex acts are
not really such : in these cases all the nervous processes of the
act may take place in their entirety and yet fail to produce their
effect on account of a failure in the muscular part of the act.
Thus when we ourselves stop or inhibit the reflex movements
which otherwise would be produced by tickling the soles of the
feet, we achieve this to a large extent by throwing voluntarily
into action certain muscles, the contractions of which antagonise
the action of the muscles engaged in carrying out the reflex
movements. But it may be doubted even in these cases, whether
inhibition is always or wholly to be explained in this way ; and
certainly in very many instances of reflex inhibition, no such
muscular antagonism is present, and the reflex act is checked at
its nervous centre.

It is a remarkable fact that when the brain of a frog is re-
moved, reflex actions are developed to a much greater degree than
in the entire animal. This suggests the idea that there must be
in the brain some mechanism or other for preventing the normal
developement of the spinal reflex actions. And we learn by experi-
ment that stimulation of certain parts of the brain has a remark-
able effect on reflex action. If a frog, from which the cerebral
hemispheres only have been removed (the optic thalami, optic
lobes, medulla oblongata and spinal cord being left intact), be
suspended by the chin, and the toes of the pendent legs be from
time to time dipped into very dilute sulphuric acid, a certain
average time will be found to elapse between the dipping of the
toe and the resulting withdrawal of the foot. If, however, the
optic lobes or optic thalami be stimulated, as by putting a crystal
of sodium chloride on them, it will be found on repeating the
experiment while these structures are still under the influence
of the stimulation, that the time intervening between the action of
the acid on the toe and the withdrawal of the foot is very much
prolonged. That is to say, the stimulation of the optic lobes has
caused impulses to descend to the cord, which have there so inter-
fered with the action of the nerve-cells engaged in reflex action as
greatly to retard the generation of reflex impulses ; in other words,
the stimulation of the optic lobes has inhibited the reflex action of
the cord. And similar results may be obtained in mammals by
stimulating certain parts of the corpora quadrigemina, which
bodies are analogous to the optic lobes of frogs. From this it has
been inferred that there is present in this part of the brain a
special mechanism for inhibiting the reflex actions of the spinal
cord, the impulses descending from this mechanism to the
various centres of reflex action being of a specific inhibitory

592 REFLEX ACTIONS. [BOOK m.

nature. But, as we have already seen, impulses of an ordinary
kind, passing along ordinary sensory nerves, may inhibit reflex
action. We have quoted instances where a slight stimulus, as in
the pendulous movements of the snake, and where a stronger
stimulus as in the case of the micturition of the dog, may produce
an inhibitory result ; we may add that adequately strong stimuli
applied to any afferent nerve will in the frog inhibit, i.e. will retard
or even wholly prevent reflex action. If the toes of one leg are
dipped into dilute sulphuric acid at a time when the sciatic of the
other leg is being powerfully stimulated with an interrupted
current, the period of incubation will be found to be much pro-
longed, and in some cases the reflex withdrawal of the foot will
not take place at all. And this holds good, not only in the
complete absence of the optic lobes and medulla oblongata, but
also when only a portion of the spinal cord, sufficient to carry out
the reflex action in the usual way, is left. There can be no
question here of any specific inhibitory centres, such as have been
supposed to exist in the optic lobes.

Hence it is clear that inhibition may be brought about by
impulses which are not in themselves of a specific inhibitory
nature, and accordingly we may hesitate to accept the view that
a special inhibitory mechanism in the sense of one giving rise to
nothing but inhibitory impulses is present in the optic lobes of frogs.
Nor is there adequate proof that the exaltation of reflex actions
which is manifest in decapitated animals is due to the withdrawal
of such a specific inhibitory mechanism. We shall have occasion
again to return to these inhibitory phenomena of the central nervous
system. We have seen enough to shew that the spinal cord, and
the same holds good, as we shall see, for the whole central nervous
system, may be regarded as an intricate mechanism in which the
ciirect effects of stimulation or automatic activity are modified and
governed by the checks of inhibitory influences. Seeing that in the
ordinary actions of life the spinal cord is to a large extent a mere
instrument of the cerebral hemispheres, we may readily expect that
among the many impulses passing from the latter to the former,
some under certain circumstances should result in an inhibition of
spinal activity, while others, or the same under different circum-
stances, should lead to an exaltation of the same spinal activity.
The experiments quoted above shew that the optic lobes when
stimulated are especially prone to give rise to inhibitory results;
but we have as yet much to learn before we can speak with
certainty as to the exact manner in which such an inhibition is
brought about.

CHAP, v.] THE SPINAL CORD. 593

The Time required for Reflex Actions.

When one eyelid is stimulated with a sharp electrical shock,
both eyelids blink. Hence, if the length of time intervening
between the stimulation of the right eyelid and the movement of
the left eyelid be measured, this will give the total time required for
the various processes which make up a reflex action. It has been
found to be from '0662 to '0578 sec. Deducting from these figures
the time required for the passage of afferent and efferent impulses
along the fifth and facial nerves to and from the medulla, and for
the latent period of the contraction of the orbicularis muscle,
there would remain *0555 to '0471 sec. for the time consumed in
the central operations of the reflex act. The calculations, however,
necessary for this reduction, it need not be said, are open to sources
of error. Blinking thus produced is a reflex act of the very simplest
kind; but as we have seen in the preceding pages, reflex acts
differ very widely in nature and character; and we accordingly
find, as indeed we have incidentally mentioned, that the time
taken up by a reflex movement varies very largely. This indeed
is seen in the blinking itself. When the blinking is caused not by
an electric shock applied to the eyelid, but by a flash of light
falling on the retina, in which case complex visual processes are
involved, the time is exceedingly prolonged ; moreover the results
in different experiments of such a kind are not nearly so uniform
as when the blinking is caused by stimulation of the eyelid.

In general it may be said that the time required for any
reflex act varies very considerably with the strength of the
stimulus employed, being less for the stronger stimuli; this we
should -expect, seeing that the efferent impulses of the reflex act
are not simply afferent impulses transmitted through the central
organ, but result from internal changes in the central organ started
by the afferent impulse or impulses ; and these internal changes
will naturally be more intense and more rapidly effective when the
afferent impulses are strong. It is stated that when the movement
induced is on the same side of the body as the surface stimulation
of which starts the act, the time taken up is less than when the
movement is on the other side of the body, allowance being made
for the length of central nervous matter involved in the two cases ;
that is to say the central operations of a reflex act are propagated
more rapidly along the cord than across the cord. The rapidity
of the act varies of course with the condition of the spinal

F. 38

594 RAPIDITY OF REFLEX ACTIONS. [BOOK in.

cord, being greatly prolonged when the cord becomes exhausted.
The time thus occupied by purely reflex actions must not be
confounded with the interval required for mental operations; of
the latter we shall speak presently.

SEC. 2. AS A CENTRE OR GROUP OF CENTRES OF
AUTOMATIC ACTION.

Irregular automatism, i.e. a spontaneity comparable to our own
volition, is wholly absent from the spinal cord. A brainless frog
placed in a condition of complete equilibrium in which no stimulus
is brought to bear on it — protected from sudden passing changes in
temperature, from a too rapid evaporation and the like — remains
perfectly motionless till it dies. Such apparently spontaneous
movements as are occasionally witnessed are so few and seldom,
that we can hardly do otherwise than attribute them to some
stimulus, internal or external, which has escaped observation. In
the mammal (dog) after division of the spinal cord in the dorsal
region regular and apparently spontaneous movements may be ob-
served in the parts governed by the lumbar cord. When the
animal has thoroughly recovered from the operation the hind limbs
rarely remain at rest for any long period ; they move restlessly in
various ways; and when the animal is suspended by the upper
part of the body, the pendent hind limbs are continually being
drawn up and let down again with a monotonous rhythmic regu-
larity, highly but perhaps falsely suggestive of automatic rhythmic
discharges from the central mechanisms of the cord. In the newly
born mammal too, after removal of the brain, apparently spon-
taneous movements are frequently observed. This greater prone-
ness to activity is however just what might be expected, when
we take into consideration the more rapid metabolic changes and
the consequent greater molecular mobility of the whole nervous
system of the mammal. The movements, even when most highly
developed, are wholly different from the movements irregular in
their occurrence, but orderly and purposeful in their character,
which result from the working of volition.

38—2

596 AUTOMATIC ACTION. [BOOK in.

Of the various regular automatic centres, both the numerous
ones in the medulla oblongata, such as the vaso-motor, respiratory,
&c., and the more sparse ones in other regions of the cord, such as
those connected with micturition, defsecation, erection, parturition,
and so on, we have treated or shall have to treat so fully in
reference to their respective mechanisms, and discussed how far
they are purely automatic, or in reality merely reflex in nature,
that nothing more need be said here.

It has been much disputed whether the spinal cord exercises
over the skeletal muscles a tonic action comparable to that of the
vaso-motor centres over the smooth muscles of the arteries. The
arguments which were once brought forward as proving the exist-
ence of such a tone are invalid. It is true that when a muscle is cut
across in the living body, the section gapes ; but this is because all
the muscles of the body are slightly stretched beyond their normal
length. Again, when one side of the face is paralysed the mouth
is drawn to the opposite side, not because the paralysed muscles
have lost tone, but because there are on the paralysed side no con-
tractions to antagonise the effect of the continually repeated con-
tractions of the sound side. And indeed the existence of such a
tone seems distinctly disproved by the fact that, according to most
observers, when in the living body the nerve going to a muscle is
cut no permanent lengthening of the muscle is caused. On the
other hand, when the sciatic plexus of one leg of a brainless frog is
cut, and the animal is suspended, that leg hangs down more help-
lessly than the other ; that is to say the sound leg is rather more
flexed than the other. The difference which is sometimes marked,
but sometimes hardly visible, disappears entirely when the whole
cord is destroyed. But the same flaccidity is observed in a leg
in which the posterior roots only of the sciatic plexus have been
divided. Hence it is to be regarded as an instance not so much of
automatic tone, as of feeble reflex action occasioned by afferent
impulses.

Though however the view of a real tone lacks adequate support,
several considerations favour the idea that the condition of a
muscle, apart from its being in a state of contraction or at rest, is
closely dependent on influences proceeding from the spinal cord.
We saw, in treating of muscle and nerve (p. 92), that the irritability
of a muscle is markedly affected by the section of its nerve, i.e.
by severance from the central nervous system ; and more recently,
(p. 471) in speaking of the so-called trophic action of the nervous
system, we referred to changes in the nutrition of muscles oc-
casioned by diseases of the nervous system. An instance of a
similar action is afforded by the so-called ' tendon-phenomena.' It
is well known that when the leg is placed in an easy position, as
when resting on the other leg, a sharp blow on the patellar tendon
will cause a sudden jerk forward of the leg, brought about by a
contraction of the quadriceps femoris. Similarly the muscles of the

CHAP, v.] THE SPINAL CORD. 597

calf may be thrown into action by tapping the tendo Achillis ; and
in some cases the same muscles may be made to execute a series of
rhythmic contractions, by suddenly pressing back the sole of the
foot so as to put them on the stretch. These, and other instances
of a like kind, at first sight appear to be, and indeed it has been
maintained that they are, cases of reflex action, due to afferent
impulses started in the tendon; hence they have been frequently
spoken of as 'tendon-reflex.' But the evidence, on the whole,
shews that they are not reflex, but due to direct stimulation
of the muscles. Nevertheless, and this is the interesting point,
they are closely dependent on the integrity of the spinal cord, and
of the connections between the cord and the muscles. In the case
of animals they disappear when the spinal cord is destroyed, or the
nerves going to the muscles are severed or even when the posterior
roots only are divided. And in the case of man they are diminished
or wanting in certain diseases of the spinal cord (locomotor ataxy),
and exaggerated in others ; so much so indeed that they have be-
come of practical clinical importance as a means of diagnosis. With-
out discussing the matter any further, we may say that such pheno-
mena indicate that the nutrition and the irritability of a muscle
are in some way governed by influences of one kind or another
which proceed from the spinal cord, and which, in certain cases at
all events, are the result of, or are determined by, influences of a
similarly obscure nature reaching the cord from the muscles by the
posterior roots of the spinal nerves.

SEC. 3. AS A CONDUCTOR OF AFFERENT OR EFFERENT

IMPULSES.

When we feel something touching our foot, or when we move
our foot, afferent or efferent impulses must evidently pass along the
whole length of the spinal cord on their way to and from the brain.
We may say at once that it is impossible that sensory impulses
should be conveyed straight along a fibre from the periphery to
the sensorium, and volitional impulses straight along another
fibre from the 'organ of the will' to the muscular fibre; the
number of fibres in the cord is wholly insufficient for such a
purpose. Moreover not only anatomical but physiological con-
siderations shew that conduction along the cord is not simple, but
carried out by a more or less intricate system of relays.

The phenomena of reflex action have shewn us that the cord
contains a number of more or less complicated mechanisms capable
of producing, as reflex results, coordinated movements altogether
similar to those which are called forth by the will. Now it must
be an economy to the body, that the will should make use of these
mechanisms already present, rather than that it should have
recourse to a special apparatus of its own of a similar kind. It is
therefore a priori probable that when the foot is pricked the
sensory impulses so generated, on reaching the cord pass into the
grey matter there to undergo a certain amount of transformation
and thence to be transmitted, either by direct and simple, or by
indirect and complicated, paths to the brain. Similarly, we may
suppose that when the leg is moved by an effort of the will,
volitional impulses starting from the brain, pass by a more or less
direct path to certain portions of grey matter in the lumbar cord,

CHAP, v.]

THE SPINAL CORD.

599

with which the motor fibres of the nerves of the leg are specially
connected, and induce such changes in this grey matter as to lead
to the discharge of the appropriate impulses along those motor fibres.
And such a view is strongly supported by the anatomical fact, as
illustrated by Figs. 78 — -80, that along the length of the spinal cord,
the amount of grey matter varies according to the number of fibres
passing into the cord, indicating that the fibres as they pass into the
cord have a certain amount of grey matter allotted to them. More-
over, though the course which the fibres of the posterior roots take
immediately upon entering the cord has perhaps yet not been
satisfactorily determined, the fibres of the anterior root have been
definitely traced to the nerve cells of the anterior cornu; and
according to recent observations, in the frog at all events, the
cells of the anterior cornu are equal in number to the fibres of the
anterior root.

I XII XI X IX VIII VII VI V IV III II I VIII VII VI V IV III U

FIG. 78. DIAGRAM SHEWING THE RELATIVE SECTIONAL AREAS OF THE SPINAL NERVES,

AS THEY JOIN THE SPINAL COBD.

V IV II! II I V IV III II I XI XI X IX VIII VII VI V IV III II I VIII VII VI V IV III II I

FIG. 79. DIAGRAM SHEWING THE UNITED SECTIONAL AREAS OP THE SPINAL NERVES,
PROCEEDING FROM BELOW UPWABDS.

V IV III II I V IV III II I XII XI X IX Viil VII VI V IV III II I via VII VI V IV HI II I

FIG. 80. DIAGRAM SHEWING THE VARIATIONS IN THE SECTIONAL AREA OF THE GREY
MATTER OF THE SPINAL CORD, ALONG ITS LENGTH.

All three figures are to read from left (the bottom of the cord) to right (top of
the cord), the numerals indicating successively the sacral, lumbar, dorsal and
cervical nerves. The figures are not drawn to the same scale.

600 CONDUCTION OF IMPULSES. [BOOK in.

But admitting this, there still remains the question, How do
volitional and sensory impulses travel along the cord, between the
brain on the one hand and the grey matter belonging to this
or that nerve root on the other ?

Our information concerning the conduction of impulses along
the spinal cord is derived partly by anatomical deduction, partly
from experiment and partly from pathological observation. These
several methods have their advantages and disadvantages. We
have just now brought forward a very general anatomical de-
duction. More detailed inferences are afforded by the Wallerian
method (see p. 484). When the spinal cord is diseased or injured at
any point, tracts of degenerated fibres may at times be traced on
the one hand upwards towards the brain, or on the other down-
wards in a peripheral direction. The former may be taken as
being sensory or afferent, and the latter, together with tracts of
degeneration in the cord which are found associated with disease of
the brain, as motor or efferent. Again, when the development of
the spinal cord is studied, it is found that the fibres of different
tracts assume their medullary sheaths at different times; and by
this means the longitudinal fibres of the cord may be differentiated
into tracts having different terminal connections, some tracts being
thus traced into the crura cerebri, others into the cerebellum, while
others appear to terminate in the medulla oblongata, or both to
begin and end in the cord itself. These different distributions
obviously suggest different functions. But all such anatomical de-
ductions must here, as elsewhere, be received with caution.

When experiments are used as a means of inquiry, we
are met with the danger of confounding the immediate and
temporary effects of the operation, such as those produced by
shock, with the more real and lasting effects. It is difficult too in
such cases to determine the existence of sensations, and to dis-
tinguish between reflex and purely voluntary movements. The
difficulty of recognizing, and especially of quantitatively estimating
the value of, signs of sensation has however been met by an
ingenious use of variations in blood-pressure. We have seen that,
at all events in an animal under urari, afferent impulses occasion a
rise of blood-pressure. If, having determined the amount of rise
due to a definite stimulation of a sensory nerve, such as the
sciatic, we make an incision into the spinal cord of the dorsal
region, dividing for instance part of the lateral column on one side,
and afterwards find that the same stimulus applied in the same
way to the sciatic nerve, leads to a greatly diminished rise of
blood-pressure, we are justified in inferring that the afferent
impulses affecting blood-pressure are largely conducted through the
part of the lateral column which has been divided. We may
thus obtain a definite measure, in millimetres of mercury, of the
effect produced by the injury. On the other hand, the value of
this precise measurement is diminished by the doubt whether we

CHAP, v.] THE SPINAL CORD. 601

have a right to conclude that the afferent impulses which affect
blood-pressure take the same course as those which give rise to
sensations, and affect consciousness. And further, in all experi-
mental results on animals we must bear in mind the probability
that the functions of the spinal cord may vary in different animals,
possibly to a very considerable extent.

In pathological cases we have the advantage of being able
clearly to define sensation and volition, but this is frequently more
than counterbalanced by the diffuse nature of the injury or disease,
and the want of exact anatomical verification. When these facts
are borne in mind, it will easily be understood that in no part of
physiology are the statements of investigators more conflicting and
unsatisfactory.

One salient fact comes out in all observations, whether ex-
perimental or pathological, viz. that between the brain, where
volitional impulses are started, or where conscious sensations are
perfected, and the muscle which carries out the movement or the
sentient surface where the sensory impulses begin, there is a
complete crossing or decussation of all impulses whether sensory or
motor. When the right side of the brain is injured or diseased,
when for instance damage is done to the right corpus striatum and
optic thalamus, it is on the left side of the body, in the left limbs,
and in the left face, that the paralysis and loss of sensation appear ;
it is on the left side that sensory impulses fail to 'affect conscious-
ness, it is on the left side that the muscles can no longer be
reached by volitional impulses. Kesults other than these indicate
complications involving the other side of the brain.

Further, all observers are agreed that as far as the spinal
nerves are concerned (and since we are now treating of the spinal
cord we may for the present leave out of consideration the cranial
nerves), the decussation is complete at about the level of the
upper part of the medulla oblongata and pons Varolii when the
paths are traced upwards ; that is to say, all the sensory impulses
coming from, and all the volitional impulses passing to, the left
side of the body, make their way along the right cms cerebri.
Nearly all observers again are agreed that the sensory impulses
cross over lower down in the spinal cord than do the volitional
impulses; but opinions differ as to the exact difference in the
paths of the two kinds of impulse. Experiments conducted by
some observers have seemed to shew that transverse division of the
lateral half of the cord in any part of its course below the medulla
oblongata is followed on the same side, below the injury, by loss of
voluntary movement, accompanied by no loss of sensation, but
even by increased sensitiveness or hypersesthesia, and on the
opposite side by loss of sensation without any affection of voluntary
movement. From these and other experiments these authors
conclude that sensory impulses entering into the cord at a posterior
root immediately cross to the other side of the cord and so ascend

602 CONDUCTION OF IMPULSES. [BOOK in.

to the brain, whereas efferent impulses of volition cross wholly in
the region of the medulla oblongata, and afterwards keep to the
same side of the cord along its whole length. Other observers, and
these perhaps are deserving of the greater confidence, find that a
section of a lateral half of the cord affects both volitional and
sensory impulses of both sides, though to different degrees, the
loss both of sensation and motion being greater on the side operated
on than on the other. Hence they maintain that the decussation
of both kinds of impulses is gradual, extending some distance
along the cord. Thus they hold that the volitional impulses
for the hind limb, while crossing over largely in the upper part
of the cord, continue to cross over right down to the lumbar
region, and similarly that the sensory impulses from the hind limb,
while crossing largely in the lumbar region of the cord, continue to
cross in the dorsal or even in the cervical region.

Admitting this latter view as the one most in accordance with
facts, we have still to ask what are the exact paths taken by the
volitional and sensory impulses in their respective courses, that is
to say, What are the particular parts of the spinal cord which serve
to conduct volitional impulses on the one hand and sensory
impulses on the other ? Upon the discovery of the distinctive
functions of the anterior and posterior roots, it seemed natural to
conclude that the anterior columns with which the anterior roots
are more directly connected, should serve as the path for volitional
impulses, and similarly that the posterior columns should afford a
path for sensory impulses. But this view was soon found to be
untenable ; and it became modified into the conception that sensory
impulses pass along the posterior columns and the grey matter,
while volitional impulses descend in the antero-lateral columns.
Further, this somewhat general statement has been reduced to
greater definiteness by some authors in the following way. They
hold that the impulses which when they reach the brain give rise
to feelings of general sensibility only or of pain, and the impulses
which form part of the chain of a reflex act, as when the fore leg or
hind leg moves in response to a stimulus applied to the hind leg or
fore leg respectively, are transmitted by the grey matter, and by all
parts of the grey matter and that in any direction. Distinct tactile
sensations on the other hand, they contend, travel exclusively by
the posterior columns, and distinct volitional impulses by the antero-
lateral columns. That these several kinds of impulse should travel
by separate paths, does not in itself seem improbable, and is to a
certain extent suggested by pathological experience. For carefully
observed cases have been recorded of disease of the cord, and ap-
parently of the cord alone, in which the patient could appreciate
even a slight touch but felt no pain when a needle was thrust
into the skin, or when the skin was otherwise treated in a way
which, under normal circumstances, would give rise to pain. Con-
versely the sense of touch has been found to be absent, while pain

CHAP, v.]

THE SPINAL CORD.

603

was still felt. Similarly, as was stated on p. 577, cases have been
recorded where the sensation of pressure was retained but that of
temperature impaired or lost, and vice versa. Such cases however
have not as yet afforded any clear insight as to what are the actual
paths of the respective sensory impulses. While they do not oppose
they do not distinctly confirm the view we are speaking of as to the
particular paths of these several kinds of impulse. Nor indeed can
this view, either in its more general or in its more elaborate form,
be considered as adequately supported by experimental evidence.

For the investigations of other observers, especially the more
recent ones, including those conducted by the blood-pressure
method, largely concur in shewing that along the cord, at all
events in the dorsal region, both volitional and sensory impulses,
indeed we might say impulses of all kinds passing between the
brain and various parts of the spinal cord, or between distinct
parts of the cord itself, run in the lateral columns. This view is
further supported by the anatomical facts that the lateral
columns (Fig. 81) increase in bulk from below upwards to a much
greater degree than do either the anterior or posterior columns
(Figs. 82, 83), and that after certain diseases or injuries of the brain

v iv in ii i v iv 111 ii i xii xi x ix vni vu vi v iv in n i VIH vii vi v iv

Fro. 81. DIAGRAM SHEWING THE VARIATIONS IN THE SECTIONAL AREA OP THE LATERAL

COLUMNS OF THE SPINAL CORD, ALONG ITS LENGTH.

.1

V IV III II | V IV III II I XII XI X IX VIII VII VI V IV III II I VIII VII VI V IV III II |

. 82. DIAGRAM SHEWING THE VARIATIONS IN THE SECTIONAL AREA. OF THE ANTERIOR

COLUMNS OF THE SPINAL CORD, ALONG ITS LENGTH.

0.

I V iv in n i v iv in u i xii xi x ix v::i vn vi v ii/ in n i vm vu vi v iv m n i

FIG. 83. DIAGRAM SHEWING THE VARIATIONS IN THE SECTIONAL AREA OF THE POSTERIOR
COLUMNS OF THE SPINAL CORD, ALONG ITS LENGTH.

604 CONDUCTION OF IMPULSES. [BOOK in.

or cord tracts of degeneration travel downwards and upwards re-
spectively in the lateral columns (though accompanied by degenera-
tion in other parts); moreover the method of development spoken
of at p. 600 teaches that a large part of each lateral column is asso-
ciated with the pyramids (and hence sometimes called pyramidal
tracts) and so with the crura cerebri and the brain. It may
be added that the decussation of the pyramids in the medulla
oblongata is chiefly a decussation of the lateral columns, though
obviously, from what has been said before, decussation of impulses
does not take place exclusively here. And such pathological evidence
as is forthcoming also to a certain extent supports this same view.
For while disease of the posterior cornua and posterior columns
seems to affect the sensory impulses passing along the nerves which
pass into the cord at the diseased part, and disease of the anterior
cornua and (though this is less clear) of the anterior columns is
similarly confined in its action to motor impulses passing out by
the nerves belonging to the diseased part, disease of the lateral
columns seems to affect chiefly the transmission of impulses along
the length of the cord and especially the transmission of volitional
impulses, for the evidence as to the interference in the conduction of
sensations by disease other than of the posterior columns and
cornua is by no means large or conclusive.

Accepting this view provisionally we may form some such
conception as follows of the conduction of volitional and sensory
impulses. Volitional impulses cross, to a considerable extent in
the medulla oblongata, but continue to cross probably to a less
and less extent all the way down. In either case they appear to
travel along the cord in the lateral columns. Eventually they
become connected (possibly through part at least of the anterior
columns) with the grey matter of the anterior cornua, where
they join the local nervous mechanisms of which we have spoken
above. From the grey matter the impulses proceed by the anterior
roots to the appropriate muscles. Similarly sensory impulses make
their way, with the intervention possibly of the posterior columns,
first into the grey matter of the posterior cornua, and thence
into the lateral columns, and so up to the brain, decussation being
effected at first largely, and afterwards to a less extent, though
continued upwards for some distance.

It must be remembered however that such a conception
can only be regarded as provisional. And indeed continued
experimental investigations teach us that this view also is in
turn beset with many difficulties. We have already called and
shall have occasion again to call attention to the importance
of distinguishing between the immediate and the more permanent
effects of any operation on the central nervous system. Now
cases have been recorded where section of the lateral columns on
both sides in the dorsal region, has had for its immediate effect
loss of sensibility and voluntary power in the hind legs, but where

CHAP, v.] THE SPINAL CORD. 605

without any regeneration in the divided tracts, recovery has ulti-
mately taken place, the return of voluntary power being nearly if
not absolutely complete. So also cases have been recorded in which
the section of a lateral (say right) half of the lower dorsal cord has
led to an impairment of sensibility and voluntary power in the hind
legs, most marked on the same side, but in which the impairment
has in the course of time completely or nearly completely dis-
appeared without any regeneration of the cord taking place, and
further in which a second lateral section higher up in the cord, and
this time of the other (left) half, has again led to impairment, again
to be followed by complete or nearly complete recovery. Gases of
this kind, carefully conducted and observed by competent persons,
place us in considerable difficulties. If we admit that the imme-
diate effects of the operation are largely due to 'shock' and inhibi-
tory processes, and that after the lateral section of the right half of
the cord, sensory volitional impulses passed to and from the hind
legs by the left half, then the recovery from the second operation
shews that these impulses must have crossed between the two
sections from the left to the right side. From which we might infer
that impulses travelling along the cord were continually passing in
a zigzag fashion from one lateral half to the other ; and an analo-
gous series of experiments in which the anterior and posterior
halves were divided at different heights would lead us to infer in
addition that the impulses also crossed in a similar zigzag fashion
from front to back and back to front. But then the serious
question is started, Is this serpentine path the normal one, or an
artificial one forced upon the impulses by the abnormal condition
of the cord ? Finding their usual path blocked, did they make for
themselves new tracts ? But if such alternative passages be pos-
sible how can we trust to either experiment or disease to shew us
the normal paths, or what right have we to speak of normal paths
at all?

It will be seen from the foregoing that the time is not yet ripe
for making any dogmatic statement concerning the conduction of
impulses along the cord ; and indeed the controversies concerning
it have perhaps acquired a factitious importance. If we might
venture to deduce any distinct lesson from all the various conflicting
statements and results, it would be that the complexity and per-
fection of the nervous mechanisms of the spinal cord itself has been
underrated rather than overrated. We spoke at the beginning of
this section of a system of relays ; we insisted on the existence of
mechanisms with which the anterior and posterior roots were
respectively in immediate connection; and the results of experi-
ment as well as of pathological experience seem to shew that im-
pulses, whether of volition or of sensation, work their way along
the cord through a whole series of such and similar mechanisms,
rather than through simple direct straightforward tracts of con-
tinuous fibres whether in the lateral columns or elsewhere.

606 CONDUCTION OF IMPULSES [BOOK in.

In connection with this, a curious apparent contradiction
between the results of pathological observation and experimental
investigation may be mentioned. On the one hand pathological
observation clearly teaches that a limited disease of the cord
affects the conduction of volitional impulses much more distinctly
than it does that of sensory impulses. A segment of the cord may be
very largely diseased, causing a large or complete block to volitional
impulses, and may yet serve to conduct sensory impulses, which
however are in that case generally retarded as if the impulses were
making progress upwards by a roundabout and difficult route. On
the other hand, in the case of experiments, after various sections of
the cord, the recovery of voluntary power is generally more speedy
and more complete than that of distinctly conscious sensations, even
when both are primarily affected by the operation. The contradic-
tion may partly perhaps be explained by the difficulty, in the case
of animals, of any objective quantitative determination of sensation,
but not wholly. Both facts point to the possibility of both sensory
and volitional impulses making their way by changed paths under
changed circumstances.

We may conclude our observations on this difficult but probably
pregnant topic by the following statement. While we appear to have
evidence that sensory and motor impulses are connected, at their
entrance into and exit from the cord with complicated mechanisms,
in which the grey matter undoubtedly, and possibly portions of the
posterior and anterior columns, are involved, the paths along the
cord are not clearly known. We have some reason to think that
they pass largely along the lateral columns, but probably not in a
direct straightforward manner, the whole cord being functionally a
series of mechanisms, for which the white matter supplies com-
missural connections. And the view that the paths may shift
according to circumstances is not without a certain support.

As was stated above, after unilateral section of the spinal cord,
the sensation on the same side below the injury, so far from being
diminished or lost has in a certain number of cases, though by no
means always, been observed to be increased ; the parts are then
said to suffer from hyperaesthesia. Since the hypersesthesia appears
immediately after the operation, it cannot be due to any inflam-
matory process. Nor can it be explained as simply the result of
the increased supply of blood to the peripheral terminations of
the sensory nerves, caused by the section involving vaso-motor
tracts ; since the simple section of a vaso-motor tract, as when the
cervical sympathetic is divided, does not give rise to hypersesthesia.
Nor can we explain it as due to a one-sided hyperhsemia of the
spinal cord itself, for we have no evidence that such a state of
things is brought about. Since it lasts for a very considerable
time it cannot be due to any passing exciting effect of the operation.
It has been suggested that the section in such cases has removed
previously existing influences which descending the cord exercised

CHAP, v.] THE SPINAL CORD. 607

an inhibitory action on the generation of sensory impulses, more
particularly of those more complex impulses which we have
supposed to arise in the local mechanism of grey matter with
which the posterior roots are connected. In other words, this
one-sided exaltation of sensation may be compared to the general
increase of reflex action which occurs in the spinal cord after
removal of the brain. But we cannot enter into the full discussion
of this matter here.

Much discussion has arisen on the question whether the spinal
cord itself is irritable towards stimuli other than nervous, that
is whether it can be excited by electric and other stimuli applied
directly to it. Undoubtedly, the cord, as a whole, is irritable ;
if two electrodes be plunged into it, and a current sent through
it, muscular movements, arterial constriction, and other results,
follow. But in such a case, the current may fall into nerve-
roots, which are as irritable, at least, as the nerve-trunks. But
even if the nerve-roots be eliminated, the white matter at
least is irritable; for it has been found that movements result
when the anterior columns are isolated for some way down and
stimulated with an electric current. With regard to the grey
matter it has been maintained that though it will convey both
motor and sensory impulses, it cannot originate them. It has
accordingly been spoken of as kinesodic and cesthesodic, as simply
affording paths for motor and sensory impulses. But the argu-
ments urged in support of this view cannot be regarded as
conclusive.

CHAPTER VI.
THE BRAIN.

SEC. 1. ON THE PHENOMENA EXHIBITED BY AN ANIMAL
DEPRIVED OF ITS CEREBRAL HEMISPHERES.

A FEOG from which the cerebral lobes have been removed, even
though all the rest of the brain has been left intact, seems to
possess no volition. The apparently spontaneous movements which
it executes are so few and seldom that it is much more rational
to attribute those which do occur to the action of some stimulus
which has escaped observation, than to suppose that they are the
products of a will acting only at long intervals and in a feeble
manner.

By the application however of appropriate stimuli, such an
animal can be induced to perform all the movements which an
entire frog is capable of executing. It can be made to swim, to
leap, and to crawl. When placed on its back, it immediately
regains its natural position. When placed on a board, it does not
fall from the board when the latter is tilted up so as to displace
the animal's centre of gravity : it crawls up the board until it
gains a new position in which its centre of gravity is restored to
its proper place. Its movements are exactly those of an entire
frog except that they need an external stimulus to call them forth.
They inevitably follow when the stimulus is applied ; they come
to an end when the stimulus ceases to act. By continually varying
the inclination of a board on which it is placed, the frog may
be made to continue crawling almost indefinitely ; but directly
the board is made to assume such a position that the body of
the frog is in equilibrium, the crawling ceases ; and if the position
be not disturbed the animal will remain impassive and quiet for
an almost indefinite time. When thrown into water, the creature

CHAP, vi.] THE BRAIN. 609

begins at once to swim about in the most regular manner, and will
continue to swim till it is exhausted, if there be nothing present on
which it can come to rest. If a small piece of wood be placed on
the water the frog will when it comes in contact with the wood
crawl upon it, and so come to rest. Such a frog, if its flanks be
gently stroked, will croak ; and the croaks follow so regularly and
surely upon the strokes that the animal may almost be played up-
on like a musical instrument. Moreover, the movements of the
animal appear to be influenced by light ; if it be urged to move in
any particular direction, it seems to avoid in its progress objects
casting a strong shadow. In fact, even to a careful observer the
differences between such a frog and an entire frog which was
simply very stupid or very obstinate, would appear slight and
unimportant except in one point, viz. that the animal without its
cerebral hemispheres was obedient to every stimulus, and that
each stimulus evoked an appropriate movement, whereas with the
entire animal it would be impossible to predict whether any result
at all, and if so what result, would follow the application of this or
that stimulus. Both are machines ; but the one is a machine and
nothing more, the other is a machine governed and checked by a
dominant volition.

Now such movements as crawling, leaping, swimming, and in-
deed, to a greater or less extent, all bodily movements, are carried
out by means of coordinate nervous motor impulses, influenced,
arranged, and governed by coincident sensory or afferent impulses.
We have already seen that muscular movements are determined
by the muscular sense ; they are also directed by means of sensory
impulses passing centripetally along the sensory nerves of the skin,
the eye, the ear, and other organs. Independently of the afferent
impulses, which acting as a stimulus call forth the movement, all
manner of other afferent impulses are concerned in the generation
and coordination of the resultant motor impulses. Every bodily
movement such as those of which we are speaking is the work of a
more or less complicated nervous mechanism, in which there are
not ^only central and efferent, but also afferent factors. And,
putting aside the question of consciousness, with which we have
here no occasion to deal, it is evident that in the frog deprived of
its cerebral hemispheres all these factors are present, the afferent
no less than the central and the efferent. The machinery for all
the necessary and usual bodily movements is present in all its
completeness. The share therefore which the cerebral hemispheres
take in executing the movements of which the entire animal is
capable, is simply that of putting this machinery into action. The
relation which the higher nervous changes concerned in volition
bear to this machinery is not unlike that of a stimulus. We
might almost speak of the will as an intrinsic stimulus. Its
operations are limited by the machinery at its command. The
cerebral hemispheres in their action can only give shape to a

*• 39

610 THE BRAINLESS FROG. [BOOK m.

bodily movement by throwing into activity particular parts of the
nervous machinery situated in the lower encephalic structures;
and precisely the same movement may be initiated in their
absence, by applying such stimuli as shall throw precisely the same
parts of that machinery into the same activity.

Very marked is the contrast between a frog which, though de-
prived of its cerebral hemispheres, still retains the optic lobes, cere-
bellum and medulla oblongata, and one which possesses a spinal
cord only. The latter when placed on its back makes no attempt
to regain its normal position ; in fact, it may be said to have com-
pletely lost its normal position, for even when placed on its feet it
does not stand with its fore feet erect, as does the other animal,
but lies flat on the ground. When thrown into water, instead of
swimming it sinks like a lump of lead. When pinched, or other-
wise stimulated, -it does not crawl or leap forwards ; it simply
throws out its limbs in various ways. When its flanks are stroked
it does not croak ; and when a board on which it is placed is
inclined sufficiently to displace its centre of gravity it makes no
effort to regain its balance, but falls off the board like a lifeless
mass. Though, as we have seen, there is in all parts of the spinal
cord of the frog a large amount of coordinating machinery, it is
evident that a great deal of the more complex machinery of this
kind, especially all that which has to deal with the body as a
whole, and all that which is concerned with equilibrium and is
specially governed by the higher senses, is seated not in the spinal
cord but in the brain including the medulla oblongata; and
apparently a great deal of this more complex machinery is con-
centrated in the optic lobes. The point however to which we wish
now to call special attention is that the nervous machinery re-
quired for the execution, as distinguished from the origination, of
bodily movements even of the most complicated kind, is present
after complete removal of the cerebral hemispheres, though these
movements are such as to require the cooperation of highly
differentiated afferent impulses.

Our knowledge of the phenomena presented by the bird or
mammal from which the cerebral hemispheres have been removed
is not so exact as in the case of the frog. Under such circum-
stances movements apparently spontaneous in character are more
common with the bird or mammal than with the frog. This
might be expected, seeing that the more complicated brain of the
former affords, even in the absence of the cerebral hemispheres,
much more opportunity for the origination of stimuli within the
nervous system itself, and for the play of stimuli however origi-
nating, than does that of the latter. It would be hazardous to
regard such apparently spontaneous movements as indications of
volition, and indeed it seems a priori improbable that the will
should be confined to the cerebral hemispheres in the frog, and yet
so to speak diffused among other parts of the brain in the more

CHAP, vi.] THE BRAIN. 611

highly differentiated bird or mammal. On the other hand, when
the cerebral hemispheres are bodily removed by the knife, the
portions of the brain left behind are so profoundly affected by the
' shock ' of the operation, are for a while so obviously in an ab-
normal condition, that no just deductions can then be made as to
what are their normal functions. And the animals generally die
before they have entirely recovered from these immediate effects of
the operation.

In the case of the bird, it has been found possible to keep the
creature alive for months, after apparently complete removal of
the hemispheres, and the following phenomena have then been ob-
served. The bird is able to maintain a completely normal posture,
and will balance itself on one leg, after the fashion of a bird which
has in a natural way gone to sleep. In fact, its appearance and be-
haviour are strikingly similar to those of a bird sleepy and stupid.
Left alone in perfect quiet, it will remain impassive and motionless
for a long, it may be for an almost indefinite, time. When stirred
it moves, shifts its position ; and then on being left alone returns
to a natural, easy posture. Placed on its side or its back it will
regain its feet ; thrown into the air, it flies with considerable pre-
cision for some distance before it returns to rest. It frequently
tucks its head under its wings, and at times may be seen to
clean its feathers and to pick up corn or to drink water presented
to its beak. It may be induced to move not only by ordinary
stimuli applied to the skin, but also by sudden sharp sounds, or
flashes of light ; and it is evident that its movements are to a
certain extent guided by visual sensations, for in its flight it will,
though imperfectly, avoid obstacles. Save that all clear signs of
distinct volition are absent, that all satisfactory indications of
intelligence are wanting, and that the movements are on the
whole clumsy, resembling rather those of a stupid drowsy bird
than those of one quite wide awake, there is very little to dis-
tinguish such a bird from one in full possession of its cerebral
hemispheres.

In a mammal, during the few hours which intervene between
the sudden removal of the whole of both hemispheres and death,
very much the same phenomena may be observed. The rabbit, or
rat, operated on can stand, run and leap ; placed on its side or
back it at once regains its feet. Left alone, it remains as motion-
less and impassive as a statue, save now and then when a passing
impulse seems to stir it to a sudden but brief movement. Such a
rabbit will remain for minutes together utterly heedless of a carrot
or cabbage-leaf placed just before its nose, though if a morsel be
placed in its mouth it at once begins to gnaw and eat. When
stirred, it will with perfect ease and steadiness run or leap forward ;
and obstacles in its course are very frequently, with more or less
success, avoided. It will often follow by movements of the head a
bright light held in front of it (provided that the optic nerves and

39—2

612 - THE BRAINLESS MAMMAL. [BOOK in.

tracts have not been injured during the operation), and starts
when a shrill and loud noise is made near it. When pinched it
cries, often with a long and seemingly plaintive scream. Evidently
its movements are guided and may be originated by tactile, visual,
and auditory sensations1. But there is no satisfactory evidence
that it possesses either visual or other perceptions, or that the
sensations it experiences give rise to ideas. Its avoidance of
objects depends not so much on the form of these as on their inter-
ference with light. No image, whether pleasant or terrible,
whether of food or of an enemy, produces an effect on it, other
than that of an object reflecting more or less light. And though
the plaintive character of the cry which it gives forth when
pinched suggests to the observer the existence of passion, it is pro-
bable that this is a wrong interpretation of a vocal action ; the cry
appears plaintive simply because, in consequence of the complete-
ness of the reflex nervous machinery and the absence of the usual
restraints, it is prolonged. The animal is able to execute all its
ordinary bodily movements, but in its performances nothing is ever
seen to indicate the retention of an educated intelligence. With
the removal of that part of the brain which lies between the
hemispheres and the medulla a large number of these coordinate
movements disappear. The animal can no longer balance itself, it
lies helpless on its side, and though various movements of a
complex character, including cries, may be produced by appropriate
stimuli, they are much more limited than when these cerebral
structures are intact.

When in a dog, the cerebral convolutions are removed piece-
meal at several operations, the animal may be kept alive and in
good health for a long time, many months at least, though these
parts of the brain have been reduced to very small dimensions.
In such a case the indications of volition are much more prominent
and numerous. We do not wish now to discuss whether the residues
of volition and of intelligence then observed are to be ascribed to
the small portion of the cerebral hemispheres still left, or whether
they result from the working of other parts of the brain. To do this
we should have to attempt to define with greater exactness than we

1 Here we come upon a difficulty, which we shall meet with again in the present
chapter. Are we justified in speaking of 'sensation' in cases where we have reason
to think that consciousness is absent, or where, as in the present instance, we have
no evidence to shew whether consciousness is present or not ? In treating of the
senses we called attention to the fact, that we must suppose in the case, for instance,
of vision, the visual peripheral organ to be connected with a visual central organ in
such a way that the sensory impulses originating in the former become modified in
the latter before they affect consciousness. In the peripheral organ and along the
nerve of sense, the affection of the nervous tissue may be spoken of as a sensory
impulse; but after the affection has traversed the central organ and become modified
it is no longer a simple sensory impulse. We must then either call it a sensation
irrespective of whether any change of consciousness intervenes or no, or we must
give it a new name. Not wishing to introduce a new name, we have ventured to use
the word 'sensation' in a sense which neither affirms nor denies the coexistence of
consciousness.

CHAP, vi.] THE BRAIN. 613

have hitherto done, the meaning of the words ' volition ' and ' in-
telligence ;' and should probably in the end come to the conclusion
that the discussion is a barren one. The more we study the pheno-
mena exhibited by animals possessing a part only of their brain,
the closer we are pushed to the conclusion that no sharp line can
be drawn between volition and the lack of volition, or between the
possession and absence of intelligence. Between the muscle-nerve
preparation at the one limit, and our conscious willing selves at
the other, there is a continuous gradation without a break; we
cannot fix on any linear barrier in the brain or in the general
nervous system, and say ' beyond this there is volition and in-
telligence but up to this there is none.'

This however is not the question with which we are now deal-
ing. What we want to point out is that in the higher am' mala,
including mammals, as in the frog, after the removal of the cerebral
hemispheres (or rather of the cerebral convolutions, for interference
with the corpora striata and optic thai ami is apt to induce disorders
of which we shall speak presently), even though volition and in-
telligence appear to be largely, if not entirely, lost, the body is
still capable of executing all the ordinary movements which the
animal in its natural life is wont to perform, in spite of these
movements necessitating the cooperation of various afferent
impulses ; and that therefore the nervous machinery for the
execution of these movements lies in some part of the brain
other than the cerebral hemispheres. We have reasons for
thinking that it is situated in the structures forming the middle
or hind brain.

SEC. 2. THE MECHANISMS OF COORDINATED
MOVEMENTS.

When in a pigeon the horizontal membranous circular canal
of the internal ear is . cut through, the bird is observed to be
continually moving its head from side to side. If one of the
vertical canals be cut through, the movements are up and down.
The peculiar movements may not be witnessed when the bird is
perfectly quiet, but they make their appearance whenever it is
disturbed, or attempts in any way to stir. When one side only
of the head is operated on, the condition after a while passes away.
When the canals of both sides have been divided, it becomes much
exaggerated, lasts longer, and sometimes remains permanently.
And it is then found that these peculiar movements of the head
are associated with what appears to be a complete want of co-
ordination of all bodily movements. If the bird be thrown into
the air, it nutters and falls down in a helpless and confused
manner; it appears to have totally lost the power of orderly
flight. If placed in a balanced position, it may remain for some
time quiet, generally with its head in a peculiar posture; but
directly it is disturbed, the movements which it attempts to
execute are irregular and fall short of their purpose. It has great
difficulty in picking up food and in drinking; and in general
its behaviour very much resembles that of a person who is exceed-
ingly dizzy.

It can hear perfectly well, and therefore the symptoms cannot
be regarded as the result of any abnormal auditory sensations, such
as ' a roaring ' in the ears. Besides, any such stimulation of the
auditory nerve as the result of the section, would speedily die away,
whereas these phenomena may be permanent.

CHAP, vi.] THE BRAIN. 615

The movements are not occasioned by any partial paralysis, by
any want of power in particular muscles or group of muscles. Nor
on the other hand are they due to any uncontrollable impulse;
a very gentle pressure of the hand suffices to stop the movements
of the head, and the hand in doing so experiences no strain. The
assistance of a very slight support enables movements otherwise
impossible or most difficult, to be easily executed. Thus, though
when left alone the bird has great difficulty in drinking or picking
up corn, it will continue to drink or eat with ease if its beak be
plunged into water, or into a heap of barley ; the slight support of
the water or of the grain being sufficient to steady its movements.
In the same way, it can, even without assistance, clean its feathers
and scratch its head, its beak and foot being in these operations
guided by contact with its own body.

In mammals (rabbits) section of the canals produces a loss of
coordination similar to that witnessed in birds ; but the movements
of the head are not so marked, peculiar oscillating movements of
the eye-balls (nystagmus), differing in direction and character
according to the canal or canals operated upon, becoming however
very prominent. In the frog no deviations of the head are seen,
but there is, as in other animals, a loss of coordination in the
movements of the body.

Injury to the bony canals alone is insufficient to produce the
symptoms ; the membranous canals themselves must be divided or
destroyed.

How are we to explain these remarkable phenomena ? Let us
for a while turn aside to ourselves and examine the coordination of
the movements of our own bodies. When we appeal to our own
consciousness we find that our movements are governed and guided
by what we may call a sense of equilibrium, by an appreciation of
the position of our body and its relations to space. When this
sense of equilibrium is disturbed we say we are dizzy, and we then
stagger and reel, being no longer able to coordinate the move-
ments of our bodies or to adapt them to the position of things
arouad us. What is the origin of this sense of equilibrium? By
what means are we able to appreciate the position of our body ?
There can be no doubt that this appreciation is in large measure
the product of visual and tactile sensations; we recognize the
relations of our body to the things around us in great measure by
sight and touch ; we also learn much by our muscular sense. But
there is something besides these. Neither sight nor touch nor
muscular sense would help us when, placed perfectly flat and at
rest on a horizontal rotating table, with the eyes shut and not a
muscle stirring, we attempted to determine whether the table
and we with it were moved or no, or to ascertain how much it
and we were turned to the right or to the left. Yet under such
circumstances we are not only conscious of a change in our position
but some observers have been able to pass a tolerably successful

616 THE SEMI-CIRCULAR CANALS. [BOOK in.

judgment as to the angle through which they have been moved.
What are the data on which such a judgment can be formed?
It is possible that the mere displacement of blood or of the more
fluid parts of the tissues in various regions of the body, by giving
rise to affections of general sensibility, may contribute to these
data ; but the peculiar features of the semi- circular canals suggest
that these are special agents in this matter. The three canals are,
as we know, placed in the head in planes nearly at right angles to
one another. Hence the pressure of the endolymph on the walls
of the canal (including the maculae of the ampullae) in any given
position of the head, and variations of that pressure due to move-
ments of the head, or the movements of the endolymph within the
canals accompanying movements of the head, would be different
in the three canals; a sonorous wave on the other hand would
affect all the ampullae equally. If we suppose that the pressure of
the endolymph or variations in that pressure, or the movements of
the endolymph can give rise to afferent impulses which, though
passing up to the brain along the auditory nerve, are not of
the nature of auditory impulses, we appear to have the data for
which we are seeking; for it is quite possible to conceive that
the impulses thus generated in the ampullae by movements of
the head, should by becoming transformed into sensations enter
into the judgment which we form, of the movements which have
given rise to them.

But if ampullar sensations, if we may so call them, thus enter
into our appreciation of the position of our body and thus form, in
part, the basis of our sense of equilibrium, it is obvious that when
these are absent or deranged, the sense of equilibrium will be
affected and the coordination of movements interfered with. And
it has been urged that the phenomena attendant on injury to the
semi-circular canals are due either to the absence of normal or to
the influence of abnormal ampullar sensations. There are how-
ever difficulties in the way of giving a satisfactory explanation of
these phenomena. If, as some observers state, both auditory
nerves may be completely and permanently severed, without any
effect on the coordination of movements, it is obvious that the
incoordination which follows upon section of the auditory canals is
due to some irritation set up by the operation and not to the
absence of any normal impulses passing up from those organs to the
brain, to the lack of what we called just now ampullar sensations.
But if the effects are those of irritation, it is difficult to understand
how they can, as according to certain observers they certainly do,
become permanent. It has however been strongly urged that in
such cases of permanent incoordination, the operation has set up
secondary mischief in the brain, in the cerebellum for instance, and
that the permanent effects are really due t6 the disease going on here;
and we have reason as we shall see to think that the cerebellum
is concerned in the coordination of movements. But the matter is

CHAP. VL] THE BRAIN. 617

one on which it does not as yet seem possible to make a dogmatic
statement.

We compared the condition of a pigeon after injury to the
semi-circular canals to that of a person who is dizzy, and indeed
one great characteristic of vertigo or dizziness is an inability on the
part of the subject to maintain a due equilibrium ; he cannot co-
ordinate his movements properly or adapt them to the circum-
stances around him, and in consequence staggers and reels. Vertigo
may be brought about in various ways. It may be the result
simply of unusual and powerful visual sensations, such as those
produced by water falling rapidly from a great height or by objects
moving swiftly across the field of vision. It may arise from
changes taking place in the brain itself, and is a common symptom of
many maladies and of the action of many poisons. As is well known,
a most severe vertigo may be at once produced by rapidly rotating
the body ; and a very curious form may be induced by passing an
electric constant current of adequate strength through the head
from ear to ear. All cases of vertigo, however produced, have this
common subjective feature, that one or more of the sets of sensa-
tions which form the basis of our appreciation of the relation of our
body to external things disagree, and are in conflict with, the rest
of the sensations which go to make up the same appreciation.
Thus in the vertigo after rapid rotation of the body, while we seem
to see the whole world whirling round us, this conclusion is contra-
dicted by other sensations. Corresponding to this subjective feature
of vertigo is the objective feature of the failure of motor coordina-
tion ; and there can be no doubt that the two are connected
together as cause and effect. The exact manner in which the
vertigo is developed, i.e. the sequence and relation of the various
factors of it, will naturally vary according to the nature of the
exciting cause, and the course of events appears to be not only
different in different forms, but in many cases complex. When
vertigo comes on from rapidly rotating the body with the eyes
open, an element of discord is introduced by the eye-balls not
keeping pace with the movements of the head but following ir-
regularly, executing the oscillatory movements known as nystagmus,
movements which continue after the body has come to rest, and
then give rise to the false sensation that external objects are
moving rapidly. But in this vertigo of rotation there are other
factors at work, for the dizziness comes on, though less readily,
when the eyes are kept shut all the time. It has been suggested
that false ampullar sensations arise from the rotation of the body
exciting the semi-circular canals ; and the form of vertigo^ which is
the salient symptom of the so-called Meniere's malady, has been
ascribed to disease of the semi-circular canals. But it must be re-
membered that the canals are frequently diseased without any
vertigo appearing; and if, as some observers state, vertigo by rotation
may be readily induced in rabbits after section of both auditory

618 VERTIGO. [BOOK in.

nerves, it is clear that the semi-circular canals can have little share
in this form of vertigo. And indeed, even admitting this as a contri-
bution to the total effect, it seems probable that changes in the brain
due to the displacement of the blood or even of the brain-substance
itself caused by the too rapid rotation, are at work. It is difficult
otherwise to explain the unconsciousness which may ensue if the
rotation be rapid and long-continued ; and the vertigo resulting
from various poisons seems to be distinctly of central origin.

Whether we accept the view of ampullar sensations just dis-
cussed or not, and whatever be the exact share which false ampul-
lar sensations take in the causation of vertigo, this at all events is
clear, that afferent impulses of various kinds so far contribute to
the building up of the coordinating mechanisms that changes in
these impulses tend to throw the mechanisms into disorder, or at
least to impair their proper working. It is not necessary that
these afferent impulses should directly affect consciousness (or, to
speak more correctly, should affect that complete consciousness
which is associated with volition), and so develope into distinct
perceptions. We have seen that a bird from which the cerebral
hemispheres have been removed is perfectly able to fly ; and that
therefore the coordinating nervous mechanism necessary for flight
is situated in the parts of the brain lying behind the cerebral
hemispheres. We have also dwelt on the fact that all the chief
coordinating mechanisms of the frog lie in the hind parts of the
brain ; yet in the frog, as in the bird, and we may add, as in the
mammal, injury to the hinder parts of the brain produces loss
of coordination whether the hemispheres be present or not. Now,
we have no satisfactory reasons for either asserting or denying that
what we call consciousness, i.e. a distinct consciousness similar to
our own consciousness, exists in animals deprived of their cerebral
hemispheres. When signs of volition are present, we may safely
take these signs as indications of consciousness also ; but we are not
justified in saying that all consciousness is absent when satisfactory
signs of volition are wanting. We cannot form any just judgment
on the matter without some more trustworthy and objective tokens
of consciousness than we at present possess. But what we may
safely assert is, that the coordinating mechanism, the retention of
which is so striking a feature of an animal deprived of its cerebral
hemispheres, is constructed out of divers afferent impulses of
various kinds arriving at the coordinating centre from various
parts of the body, that in fact the coordination taking place at the
centre is the adjustment of efferent to afferent impulses. Many, if
not all, of these afferent impulses are such that in the presence of
consciousness they would give rise to perceptions and ideas ; but
we have no reason for thinking that the complete development of
the afferent impulse into a perception or an idea is always necessary
to the carrying out of coordination. We may say that we have a
sense of equilibrium by means of the semi-circular canals, and

CHAP, vi.] THE BRAIN. 619

when that sense is deranged, we feel giddy and cannot stand. We
have no reason, however, for thinking that the failure to keep
upright is due to the feeling of giddiness, in the sense of being
a direct result of the condition of the consciousness. On the con-
trary, since the peculiar movements characteristic of vertigo may
take place in the absence of consciousness without the vertigo
being actually felt, we may with security assert that the failure to
stand upright and the feeling of giddiness are both concomitant
effects of the same disarrangement of the coordinating mechanism.

It cannot be too much insisted upon that for every bodily
movement of any complexity afferent impulses are as essential as
the executive efferent impulses. Our movements, as we have
already urged, are guided not only by the muscular sense, but also
by contact sensations, auditory sensations, visual sensations, and
visual perceptions (for the remarks made above concerning the
relations of the coordinating mechanism to consciousness do not
exclude the possibility of consciousness affecting the mechanism,
indeed not only may perceptions enter into the causation of vertigo,
but even an imaginary idea may be the sole exciting cause of this
condition); and when we say 'they are guided,' we mean that with-
out the sensations the movements become impossible. In studying
vision we saw repeatedly that the movements of the eyes were
directly dependent on vision, and every ball-room affords abundant
evidence of the ties between sensations of sound and motions of the
limbs. So essential, in fact, are afferent impulses to the develop-
ment of complex bodily movements, that we are almost justified in
considering every such movement in the light of a reflex action
made up of afferent and efferent impulses and central actions, and
set going by the influence of some dominant afferent impulse, or
by the direct action of those nervous changes, whose psychical cor-
relative is what we call the will, on the centre itself. All day long
and every day multitudinous afferent impulses, from eye, and ear,
and skin, and muscle, and other tissues and organs, are streaming
into our nervous system ; and did each afferent impulse issue as its
correlative efferent motor impulse, our life would be a prolonged
convulsion. As it is, by the checks and counterchecks of cerebral
and spinal activities, all these impulses are drilled and marshalled,
and kept in hand in orderly array till a movement is called for ; and
thus we are able to execute at will the most complex bodily
manoeuvres, knowing only why, and unconscious or but dimly
conscious how, we carry them out.

We have ventured to use the phrase ' coordinating centre,' but
it must be understood that we have no right to attach more than a
general meaning to the words. We cannot, at present at least,
define such a centre in the same way that we can the vaso-motor
or respiratory centre. When the optic lobes as well as the cerebral
hemispheres are removed from the frog, the power of balancing
itself is lost ; when such a frog is thrown off its balance by inclining

620 COORDINATING MECHANISMS. [BOOK in.

the plane on which it is placed, it falls down. The special coordi-
nating mechanism for balancing must therefore in this animal be
situated in the optic lobes ; but after removal of these organs, the
animal is still capable of a great variety of coordinate movements :
unlike a frog retaining its spinal cord only, it can swim and leap,
and when placed on its back immediately regains the normal posi-
tion. The cerebellum of the frog is so small, and in removing it
injury is so likely to be done to the underlying parts, that it becomes
difficult to say how much of the coordination apparent in a frog
possessing cerebellum and medulla is to be attributed to the former
or to the latter ; probably, however, the part played by the former
is small. In the mammal, as we have stated, removal of the whole
middle and hind brain does away with the most marked of these
coordinating mechanisms. Removal of the pons Varolii alone has
the same effect. Injury to, or disease of, the more superficial parts
of the corpora quadrigemina or of the cerebellum, does not appear
to influence the movements of the body at large to any striking
extent ; but there are many pathological cases, as well as experi-
mental observations, tending to associate the coordinating mechan-
isms of which we are speaking with the deeper parts of the cere-
bellum. It would be hazardous, in the present state of our know-
ledge, to make any definite statement concerning the share taken
by these several cerebral structures in the various coordinations.

Forced Movements.

All investigators who have performed experiments on the brain,
have observed as the result of injury to various parts of it remark-
able compulsory movements. One of the most common forms is
that in which the animal rolls incessantly round the longitudinal
axis of its own body. This is especially common after section of
one of the crura cerebri, more particularly of the external and
superior parts, or after unilateral section of the pons Varolii, but
has also been witnessed after injury to the medulla oblongata and
corpora quadrigemina. Sometimes the animal rotates towards and
sometimes away from the side operated on. Another form is that
in which the animal executes 'circus movements/ i.e. continually
moves round and round in a circle, sometimes towards and some-
times away from the injured side. This may be seen after several
of the above-mentioned operations, but is perhaps particularly com-
mon after injuries to the corpora striata and optic thalami. "There
is a variety of the circus movement said to occur frequently after
lesions of the nates, in which the animal moves in a circle, with the
longitudinal axis of its body as a radius, and the end of its tail for

CHAP, vi.] THE BRAIN. 621

a centre. And this form again may easily pass into a simply rolling
movement. In yet another form the animal rotates over the trans-
verse axis of its body, tumbles head over heels in a series of somer-
saults; or it may run incessantly in a straight line backwards or
forwards until it is stopped by some obstacle. These latter forms
of forced movements are frequently seen after injury to the corpora
striata even when a very limited portion of their grey matter is
affected. Lastly, many, if not all, these various forced movements
may result from injuries which appear to be limited to the cerebral
cortex.

Attempts have been made to explain the rotatory movements
by reference to unilateral paralysis or to spasm of various muscles
of the body caused by the cerebral injury ; and in the case of the
'circus' movements with partial hemiplegia, which follow upon
injury to the corpora striata or other parts, the explanation that
the animal in progressing forward naturally bears on its paralysed
or weak side seems a valid one; but the movements may frequently
be witnessed in the complete absence of either paralysis or spasm,
and cannot therefore be always so explained. On the other hand,
if the views urged just now concerning the nature of the coordina-
ting mechanisms of the brain are true, it is evident that they afford
a general explanation of the phenomena, though our present know-
ledge will not permit us to explain the genesis of each particular
kind of movement. Such gross injuries as are involved in dividing
cerebral structures or in injecting corrosive substances into the
midst of cerebral organs, must of necessity, either by irritation or
otherwise, seriously affect the transmission not only of afferent
impulses in their cerebral course, but also of central impulses, in-
hibitory and the like, passing from one part of the brain to another;
and must therefore seriously affect the due working of the general
coordinating mechanisms. The fact that an animal can, at any
moment, by an effort of its own will, rotate on its axis or run
straight forwards, shews that the nervous mechanism for the execu-
tion of those movements is ready at hand in the brain, waiting only
to be discharged ; and it is easy to conceive how such a discharge
might be affected either by the substitution of some potent intrinsic
afferent impulse for the will or by some misdirection of the volitional
impulses. Persons who have experienced similar forced movements
as the result of disease report that they are frequently accompanied,
and seem to be caused, by disturbed visual or other sensations;
thus when they suddenly fall forward they say that they do
so because the ground in front of them appears to sink away
beneath their feet. Without trusting too closely to the interpreta-
tions the subjects of these disorders give of their own feelings, we
may at least conclude that the disorderly movements are in many
cases due, not to any paralytic or other failing of the simple muscu-
lar instruments of the nervous system, but to a disorder of the
coordinating mechanism, which in many cases is itself the result of

622 FORCED MOVEMENTS. [BOOK in.

disordered sensory impulses. And this view is supported by the
fact that many of these forced movements are accompanied by a
peculiar and wholly abnormal position of the eyes, which alone
might perhaps explain many of the phenomena.

SEC. 3. THE FUNCTIONS OF THE CEREBRAL
CONVOLUTIONS.

Using the word cerebral hemisphere for brevity's sake to
denote the cortical substance of the cerebrum (for we have no
reason to think that the fibres of the white matter serve for
any other than conducting functions, and it is advisable to keep
apart the consideration of the corpora striata) we have endeavoured
to shew that in respect to function a broad line separates these
structures from the rest of the brain. We have seen reason to
think that will and intelligence are associated with the former,
while the latter are concerned in elaborating and coordinating
afferent and efferent impulses in such a way as to furnish a com-
plicated nervous machinery of which the former makes use in
carrying out the voluntary and intelligent movements of the body.
It is not uncommon to speak of the cerebral hemispheres as 'the
seat of will and intelligence. Such a phrase is however open to
objection. It suggests that if the cerebral hemispheres could be
kept alive quite isolated from the rest of the brain, the processes of
volition and intelligence, though unable to manifest themselves by
any outward show, would still go on. But we are not in a position
to accept, without hesitation, such an assumption. All we know
is that the existence of volition and intelligence are dependent
on the connection of the cerebral cortex with the rest of the
brain. When that connection is broken they disappear; and it
may be that what we call volition and intelligence are the product
of both the cerebral hemispheres and other parts of the brain
working together by virtue of their connections and ceasing so to
work when the connections fail; on the other hand it may
be that they are generated in the former alone, and that the
connections only serve to allow the former to make use of the
machinery of the latter. Our present knowledge will not allow us

624 CEREBRAL CONVOLUTIONS [BOOK in.

to decide between these two views ; meanwhile it will be well not
to consider the latter as the only possible one.

With this preliminary caution we may now proceed to inquire
whether we can attribute different functions to different parts
of the cerebral cortex. All the older observers, Flourens and others,
agreed that when the cerebral cortex was gradually removed,
piece by piece or slice by slice, no obvious effects manifested
themselves, either in the intelligence or volition of the animal,
when the first small portions were taken away ; but that, as the
removal was repeated, the animal became more and more dull and
stupid, until at last both intelligence and volition seemed to be entirely
lost. It has been frequently observed that in case of wounds of
the skull large portions of the brains of men might be removed
without any marked effect on the psychical condition of the
patients. The brain when exposed was found not to be sensitive ;
and ordinary stimuli applied to the surface of the convolutions of
animals failed in the hands of most experimenters to produce any
clearly recognizable effect. Hence it became very common to deny
the existence of any localization of functions in the convolutions of
the hemisphere, and to speak of the brain as * acting as a whole,'
whatever that might mean. On the other hand, pathological
observation seemed clearly to shew that diseased conditions limited
to different areas of the convolutions, produced different effects. It
was found that in the case of circumscribed lesions confined to
parts of the cerebral cortex, the effects whether in the way of
paralysis or of convulsive movements, were frequently confined to
certain regions of the body or were even limited to particular
groups of muscles. One set of phenomena in particular spoke very
strongly in favour of definite convolutions, i.e. definite parts of the
cerebral cortex having definite functions. In certain cases of cere-
bral disease the patient is unable to speak at all or speaks imper-
fectly or incorrectly. It is obvious that the failure to speak or to
speak properly may be brought about in various ways; the fault
may be simply in the tongue or hypoglossal nerve, or it may lie in
one or other of the series of central and cerebral processes which
issue in coordinate impulses being sent to the organs of speech.
Using the word aphasia, as is usually done, in its general sense to
denote the partial or complete loss of articulate speech, due to
cerebral causes, we may say that aphasia was found to be so closely
associated with disease of a definite part of the brain, viz. the
posterior portion of the third frontal convolution, Fig. 86 (9) (10),
as to afford almost irresistible proof that this particular part of
the brain must be specially connected with the faculty of speech.
Moreover the disease occurs in so great a majority of cases on one
side of the brain only, namely the left (aphasia being frequently a
symptom accompanying right hemiplegia, or paralysis of the right
side of the body, the disease in such cases affecting other parts of
the brain as well), as to suggest the idea that in the act of speech,

CHAP. vi.

THE BRAIN.

625

one side of the brain only is used. On this point however we
must not dwell now; we cannot here discuss the question of
unilateral cerebral activity, or the exact nature of the failings
which lead to the loss of, or to errors in, speech, or with what
particular link or links in the chain of cerebral events leading
to speech, whether mainly afferent or mainly efferent ones, this
portion of the cortex is associated ; we simply quote these cases of
aphasia, as affording proof of the localization of function in the
cerebral cortex.

FIG. 84.

THE ABEAS OF THE CEBEBRAL CONVOLUTIONS or THE DOG, ACCORDING TO
HITZIG AND FBITSCH.

(1) A The area for the muscles of the neck. (2) -p The area for the extension
and adduction of the fore limb. (3) + The area for the flexion and rotation of the
fore limb. (4) £{: The area for the hind limb. Kunning transversely towards and
separating (1) and (2) from (3) and (4) is seen the crucial sulcus. (5) Q The facial

For a while then the teachings of pathology and experiment were
contradictory ; but continued experimental inquiry shewed that the
former were in the right. Hitzig and Fritsch were the first to shew
that the local application of the constant galvanic current to par-
ticular convolutions and to particular parts of convolutions gave rise
to definite coordinate movements of various groups of muscles. Thus
while the stimulation of one spot (Fig. 84) caused movements in the
muscles of the neck, another caused extension with adduction of
the fore leg, a third movements of the hind leg, a fourth movements
of the eye and other parts of the face. In fact, they and Ferrier,
who using chiefly the interrupted or faradaic current, repeated and
extended their observations, were able to map out the convolutions
of the front and middle parts of the hemisphere of the dog (Figs. 84,
85), cat, monkey (Figs. 86, 87), and other animals, into a number

F.

40

626 CEREBRAL CONVOLUTIONS. [BOOK m.

FIG. 85. THE AREAS OJP THE CEREBRAL CONVOLUTIONS OF THE DOG, ACCORDING

TO FERRIER.

0. The Olfactory Lobe. A. The Fissure of Sylvius. B. The Crucial Sulcus.

Stimulation by the interrupted current of the areas indicated by the several
circles produces the following results.

(1) The hind leg is advanced as in walking. (3) Lateral or wagging motion of
the tail. (4) Eetraction and adduction of the opposite forelimb. (5) Elevation of
the shoulder of, and extension forwards of, the opposite forelimb. (7) Closure of
the opposite eye caused by combined action of the orbicular and zygomatic muscles.
(8) Extraction and elevation of the opposite angle of the mouth. (9) The mouth is
opened and the tongue moved, sometimes barking is produced. (11) Extraction of
the angle of the mouth. (12) Opening of the eyes and dilation of the pupils; the
eyes and then the head turning to the opposite side. (13) The eyeballs move to the
opposite side. (14) Pricking or sudden retraction of the opposite ear. (15) Torsion
of the nostril on the same side. (16) Elevation of the lip and dilation of the
nostril (?).

of precisely limited areas, the stimulation of each area producing a
distinct and limited movement, while stimulation of a large surface
produced general convulsions. The movements were so precise that
they answered each to the spot stimulated almost as completely as
a note answers to a key struck on the piano. A somewhat similar
relationship has also been observed between various regions of the
cortex and the secretion of saliva, the beat of the heart, the con-
dition of the pupil, the action of vaso-motor nerves, and other
organic functions.

These experiments, which have not only been confirmed by
many observers, but may, with due care, be successfully repeated
by any one, clearly shew, in spite of some discordance among
various authors as to the exact position and extent of the several
'areas,' that there is a connection between electric stimulation of
certain areas of the brain-surface and certain bodily movements. The
areas in question have been spoken of by some authors as 'motor
centres.' Such a term is however undesirable, since it suggests
that the brain-surface in a given area is largely occupied in giving
rise to the coordinate nervous impulses which carry out the
movement resulting from stimulation of the area; whereas, as
we have already seen from the behaviour of an animal deprived of

CHAP, vi.]

THE BRAIN.

627

FIG. 86.

FIGS. 86 AND 87. SIDE AND UPPER VIEWS OF THE BRAIN OF MAN, WITH THE
ABEAS OF THE CEREBRAL CONVOLUTIONS, ACCORDING TO FERRIEB.

The figures are constructed by marking on the brain of man, in their respective
situations, the areas of the brain of the monkey as determined by experiment,
and the description of the effects of stimulating the various areas refers to the brain of
the monkey.

(1) (On the postero-parietal [superior parietal] lobule). Advance of the opposite
hind limb as in walking. (2), (3), (4) (Around the upper extremity of the fissure of
Rolando). Complex movements of the opposite leg and arm, and of the trunk, as in
swimming, (a), (fc), (c), (d) (On the postero-parietal [posterior central] convolution).
Individual and combined movements of the fingers and wrist of the opposite hand.
Prehensile movements. (5) (At the posterior extremity of the superior frontal con-
volution). Extension forward of the opposite arm and hand.

(6) (On the upper part of the antero-parietal or ascending frontal [anterior
central] convolution). Supination and flexion of the opposite foiearm. (7) (On
the median portion of the same convolution). Retraction and elevation of the
opposite angle of the mouth by means of the zygomatic muscles. (8) (Lower
down on the same convolution). Elevation of the ala nasi and upper lip with de-
pression of the lower lip, on the opposite side. (9), (10) (At the inferior extremity
of the same convolution, Broca's convolution). Opening of the mouth with (9) pro-
trusion and (10) retraction of the tongue; region of Aphasia, bilateral action.

(11) (Between (10) and the inferior extremity of the postero-parietal convolution).
Retraction of the opposite angle of the mouth, the head turned slightly to one side.

(12) (On the posterior portions of the superior and middle frontal convolutions).
The eyes open widely, the pupils dilate, and the head and eyes turn towards the
opposite side. (13), (13') (On the supra-marginal lobule and angular gyrus). The
eyes move towards the opposite side with an upward (13) or downward (13')
deviation. The pupils generally contracted. (Centre of vision.) (14) (On the

40—2

628

CEREBRAL CONVOLUTIONS.

[BOOK in.

FIG. 87.

infra-marginal or superior [first] temporo-sphenoidal convolution). Pricking of the
opposite ear, the head and eyes turn to the opposite side, and the pupils dilate
largely. (Centre of hearing.) Ferrier moreover places the centres of taste and
smell at the extremity of the temporo-sphenoidal lobe, and that of touch in the
gyrus uncinatus and hippocampus major.

its cerebral hemispheres, coordination is effected in parts of the
brain other than the surface of the cerebral hemispheres; and all
that the areas in question do is to make use in some way or other
of these lower coordinating mechanisms.

As will be seen from an inspection of the figures the areas,
stimulation of which gives rise to definite movements, are dis-
tributed over a part only of the surface of the hemispheres.
Over large tracts of the surface electric stimulation gives rise to no
movements at all. It has been supposed that the stimulation
of these parts gives rise to various psychical states, of such a nature
that they do not manifest themselves by any movements as do the
psychical states brought about by stimulation of the so-called
motor areas; and hence these tracts have been supposed to be

CHAP, vi.] THE BRAIN. 629

composed of so-called 'sensory 'centres, a term even more objection-
able than 'motor' centres.

Confining ourselves for the present to the areas, stimulation of
which produces movements, the question naturally presents itself,
Do events of importance take place in the grey matter itself
when stimulated, or is it that either by stimulation of the fibres of
the white matter, or by simple escape downwards of the current
employed as a stimulus, the parts below, such as the corpora striata,
are stimulated, and that the shaping of the movements according
to the locality operated on is effected in these lower parts and not
at the surface itself? On this point considerable controversy
has taken place. On the one hand it seems clear that localization
of function, that is to say the occurrence of definite movements as
the result of stimulation of definite parts, may take place in the
regions of the brain below the cortex, since the appropriate move-
ments follow upon stimulation of the several cortical areas, when
the grey matter has been removed, or rendered functionally incapa-
ble by treatment with acids and the like, or separated functionally
from the white matter below by an incision parallel with the surface;
and definite movements have been even obtained by stimulation
of definite parts of the surface of the corpora striata. On the
other hand, we have adequate evidence that when movements in a
muscle or group of muscles are produced by stimulation of an area of
the surface of the cerebrum, the movements differ in character, for
instance in the length of the latent period, the form of the muscle
curves, &c. according as the stimulus is applied to the intact cortex
or to the underlying white matter. Further the irritability of the
grey matter, falling and rising with the condition of the animal,
is much more variable than is that of the white matter ; and while
under certain circumstances stimulation of the grey matter is apt
to give rise to general epileptiform convulsions, stimulation of the
white matter rarely if ever produces such an effect. Without
discussing the matter any more fully we may say that the preponde-
rating evidence seems clearly in favour of the view that when the
grey matter is stimulated, some events of an important kind do
take place in the grey matter itself; in other words, we have
evidence of a localization of function in the cortex, inasmuch as
when a given area of the cortex is stimulated the movements in a
definite group of muscles which result are in part at least due to
changes taking place in the grey matter itself of that area.

If such is the case, if events of importance having an especial
connection with certain muscles result from the stimulation of
a given area, it is only reasonable to conclude that in actual life
more or less similar events, having similar relations to the muscles,
take place in the area from time to time. Further it seems also
reasonable to suppose that these events are of such a kind that the
area may be regarded as a 'point d'appui' by which will and
intelligence are brought to bear on the muscles corresponding

630 CEREBRAL CONVOLUTIONS. [BOOK in.

to the area. We may very fairly imagine that when a dog wills to
extend the forelimb, the cerebral changes are of such a kind that
eventually processes are set up in the grey matter of the area for
extension of the forelimb similar to those which arise from stimu-
lation of the area. But if this be the case, then removal of the
area ought permanently to remove also, from the dominion of the
will, the muscles employed in extension of the limb; the chain of
events leading down from the inception of the voluntary effort to
the actual contraction of the appropriate muscles ought to be
broken in the link constituted by the events occurring in the
cortical area; the dog ought thereafter to be unable to extend his
forelimb by any direct effort of the will. The results of experiment
however shew that this is not the case. Immediately after the
operation by which the area is removed, more or less paralysis it is
true may be observed in the corresponding muscles. But this soon
passes away, and complete power over the muscles may be re-
gained. The temporary paralysis seems to be a sort of inhibitory
effect due to the injury caused by the operation; and, though the
experiment confirms the view that some special connection exists
between the cortical area and the appropriate group of muscles, it
disproves the view that the area serves as a direct instrument
of the will. Nor can we take refuge in the idea that some other
area has taken up vicariously the duties of the lost area. This is
disproved by the observations of many inquirers which go to shew
that not only many different parts of the brain, but a very large
portion of the whole brain, may be removed without any clear and
definite paralysis of any group of muscles being occasioned. In the
experiments of Goltz, which we shall mention directly, the loss of a
large mass of the cerebral convolutions diminishes the movements
of the body inasmuch as it curtails the general action of the
intelligent will which brings them about, but does not withdraw
any particular sets of muscles from the influence of the so to speak
shortened will which is left to the animal. Indeed we have reason
to think that when in such operations directed solely to the
removal of the cerebral convolutions, paralysis of any particular
group of muscles occurs, mischief must unwittingly have been done
to other parts of the brain.

What then can we conclude as to the nature of the events
which take place in the several .cortical areas ? To this question
unfortunately no clear answer can yet be given; for the results
of different inquirers are so far irreconcilably opposed.

On the one hand, one observer (Munk) states that the re-
moval of a certain area in the posterior lobes produces no other
effect whatever but blindness. He further states that removal
of small portions of the area leads to partial blindness, that is
to the formation so to speak of artificial blind spots in the field of
vision corresponding to the spots of cerebral cortex removed; so
that the retinal image may be conceived of as projected as it were

CHAP, vi.] THE BRAIN. 631

on to the 'visual area of* the cerebral convolutions. Munk has
moreover been led, for reasons which we cannot enter into here, to
believe that removal of part of this area (the circumferential part)
leads to what may be called 'absolute blindness,' i.e. the inability
to gain conscious sensations of the images falling on the retina,
whereas removal of another part (the central part) leads to what may
be called 'psychical blindness/ i.e. the inability to form an intelligent
comprehension of the visual impressions received. The latter, he
maintains, may eventually be recovered from by processes which
may be crudely spoken of as the deposition of new visual experiences
in the visual area. We cannot discuss these results in detail here,
but we may add that Munk has similarly been led from his experi-
ments to conclude that the rest of the cerebral surface may be
parcelled out into auditory, olfactory, tactile, &c. areas, in fact that
all the sensory impulses which stream upon the living body are
projected as sensations on to the cerebral convolutions in definite
order, being there elaborated into perceptions and experiences, this
reception and elaboration being the special work of the cerebral
cortex. And one author (Schiff) has from the first maintained
that the cortical 'motor' areas associated with movements in
particular regions of the body, have to do with the tactile
sensations arising in those regions, and that the movements
arising from stimulation of the areas are tactile reflex actions
started in the cortex of the brain instead of in the periphery
of the body.

On the other hand another observer (Goltz) maintains that the
whole of the posterior lobes may be removed without affecting
vision any more directly than does the removal of the anterior or
middle lobes. In fact this author in his latest, as in his earlier
researches, insists most strongly that he can no more obtain distinct
evidence of localization in reference to vision or other sensations
than in reference to movements. When in a dog the lesions are
slight the recovery from imperfections of vision, of the other senses,
and of general sensibility which follow immediately on the opera-
tion, may be complete. When a larger portion of brain is removed,
whatever be the region of the hemisphere acted on, certain
peculiar imperfections of sight and other sensations, corresponding
to the psychical blindness spoken of just now as observed by Munk,
become striking, and may remain permanent. In the case of
vision the salient character of this imperfection is that though the
animal evidently can see, and uses his sight successfully in avoiding
obstacles and guiding his movements, yet what he sees does not
produce its usual effect on him; he obviously fails to recognize
many things, and has become indifferent to scenes which formerly
affected him strongly. Thus a dog from which portions of the
cerebral hemispheres have been removed, fails to recognize his
food by sight; when he is threatened with the whip, he is not
cowed; when the hand is held out for his paw he makes no

632 CEREBRAL CONVOLUTIONS. [BOOK in.

response; and though before the operation he became violently
excited when the laboratory servant dressed in a fantastic garb was
presented to him, he remains after the operation perfectly in-
different to the same image. Another striking character of this
imperfection of vision is that recovery from it to a considerable
extent is, under certain circumstances, possible by means of
educational exercise; the dog, which at first could not recognize
his food by sight and was indifferent to the whip, learns after
a while to know the one and to respect the other. It would
be hazardous however to insist upon the view that in such a case
the failure was of distinctly psychical origin, due to the want
of intelligent power to fully appreciate the crude sensations. It
might be that the sensations were themselves imperfect, and
unable to give rise to sufficiently definite perceptions, all things
possibly appearing to the dog as if seen through a gauze with
all their colours washed out. With such an imperfect vision a dog
might readily fail to recognize meat by sight and might easily
regard with unconcern any figure however fantastically dressed.

According then to the views advocated by Goltz, barring some
possible difference in the extent to which the intellect or the
emotions are respectively affected according to the part of the
brain operated on, removal of the brain gives no evidence as to
any part of the mind (using that word in a wide sense) being
connected with any particular part of the cerebral cortex.
According to the views advocated by Munk, all the sensations
which form the basis of psychical activity, are very definitelv
associated with distinct areas of the convolutions; and nearly
all those, Ferrier and others, who have urged the doctrine of
localization of function in the cerebral cortex have been led to
entertain conceptions more or less similar to those of Munk.
The time is not yet ripe to decide dogmatically between these
conflicting views, though it appears to us that of the two, the
former one is the nearer the truth. All the more so since there
are some reasons for thinking that in these operations which appear
to be confined to the cortex and the white matter immediately
beneath this, damage is not unfrequently done to more central
parts of the brain, such as the corpora striata and optic thalami ;
and it is quite possible that where blindness becomes a prominent
symptom after these operations, the immediate cause of that blind-
ness is not in the cortex but in the optic thalami.

But if we accept Goltz's conclusions there still remains at least
an apparent contradiction between these and the conclusions
we reached just now concerning the results of stimulation of the
surface ; but this we must leave for further inquiries to clear up.

Before leaving the subject of the cerebral convolutions we wish
to call attention to certain remarkable results which have been
observed to follow upon stimulation of the cerebral cortex, under
various circumstances, more particularly in different stages of the

CHAP, vi.] THE BRAIN. 633

influence of narcotic drugs such as morphia. In certain stages of
narcotism by morphia, the dose required varying according to the
individual, but generally being large, the irritability of the cortex
is diminished ; currents which previously readily produced contrac-
tions in the muscles corresponding to the area stimulated, now
produce little or none at all ; and indeed the cortex may be thus
brought to such a condition that even very strong currents produce
no movements at all. In such cases, movements may, at times at all
events, be brought about by removing the cortex and applying the
electrodes directly to the underlying white matter, thus shewing
that the morphia produces its effects, in part at least, by acting
directly on the cortex itself. From this we gain an additional ar-
gument in favour of the independent irritability of the cortex.

On the other hand in certain stages of the action of morphia
the irritability of the cortex is not diminished, but on the contrary
increased. It is well known that an animal under the influence of
morphia frequently manifests an increase of reflex excitability,
being for instance remarkably sensitive, and readily responding to
the stimuli of sounds and noises ; and a similar exaltation has been
observed in reference to the influence of electric stimuli applied to
the cortical areas. At times this increased excitability may become
so developed that the application of even a moderate stimulus
leads to epileptiform convulsions lasting for some considerable
time. Not unfrequently indeed, experiments of this kind have
to be suspended on account of the appearance of these convulsions.
When any particular 'motor area' is being stimulated the con-
vulsive contractions generally appear first in the appropriate group
of muscles and thence spread first over the same side and then over
the- other side of the body until sometimes the whole frame is
convulsed. When the cortex is removed, and the electrodes are
applied directly to the subcortical white matter, these convulsions
are not nearly so readily produced, and when they appear are not
exactly of the same character, being generally limited to one side of
the body. It would thus appear that the convulsions, though carried
out by the nervous machinery of the lower parts of the brain and
more especially perhaps by the so-called 'convulsive centre' in the
medulla oblongata, originate and to a large extent are fashioned by
changes in the cerebral cortex ; and, though this is a matter into
which we must not go more fully here, pathological and clinical
observations similarly tend to shew that epilepsy itself, in certain
cases at all events, is the product of an abnormal action of the
cerebral convolutions.

From what has been said in previous sections, more particularly
in reference to the reflex actions of the spinal cord (p. 592) and co-
ordinating mechanisms (p. 619), the reader will be prepared for the
observation that the phenomena of these convulsions suggest the
idea that they arise not so much from a positive increase in the
explosive, discharging energy of the central nervous mechanisms as

634 CEREBRAL CONVOLUTIONS. [BOOK in.

from a withdrawal of certain normal restraining inhibitory influences.
We have already more than once insisted that almost any event in
the central nervous system is to be regarded not as the result of
the activity of some one isolated nervous machine, but as the out-
come of various conflicting processes, some positive, tending to bring
out the event, others negative, offering a resistance or bringing
inhibitory influences to bear. And it would seem that this is even
more true perhaps of the cerebral convolutions than of any other
part of the nervous system. Such a view is at all events strongly
supported by some observations lately made by Heidenhain. If in
an animal under morphia, the contractions in a muscle resulting
from the stimulation of the appropriate ' motor area/ by a current
of known strength, be recorded, the sciatic nerve then divided or
torn or otherwise irritated, and the motor area again stimulated
with the same strength of current, the contractions will be much
less in height, and the latent period will be much longer. This of
course is nothing more than an instance of somewhat ordinary inhi-
bition. But, in certain stages of the influence of morphia, the fol-
lowing remarkable result makes its appearance. If a subminimal
stimulus be found, that is a current of such intensity that ap-
plied to a motor area it will produce no movement, but if
increased ever so slightly will give a feeble contraction of the
appropriate muscles, it may be observed that a slight stimulus,
such as gently stroking the skin over the muscles in question,
or indeed some other part of the body, will render the previous
subminimal stimulus effective, and so call forth a movement.
Thus if the area experimented on be that connected with the
lifting of the forepaw, and the subminimal stimulus be applied to
the area at intervals, after several ineffective applications, a gentle
stroke or two over the skin of the paw will lead to the paw being
lifted the next time the stimulus is applied to the area. On the
other hand, in certain other stages of the influence of morphia, the
convolutions and the rest of the nervous system are in such a
condition that the application of even a momentary stimulus to an
area leads to a long-continued tonic contraction of the appropriate
muscles. Under these circumstances, a gentle stimulus, such as
stroking the skin, or blowing on the face, applied immediately
after the application of the electric stimulus to the area, suddenly
cuts short the contraction, and brings the muscles at once to rest
and normal flaccidity. Thus according to the condition of the
central nervous system (and in these instances the effect appears
to be dependent largely though not wholly on the condition of the
cerebral cortex) the same kind of stimulus, and indeed we might
almost say the same stimulus, will lead now to exaltation, now to
inhibition of a nervous action. We must not dwell on these matters
any further, though we might point out the interesting even if
partial light which they throw on the phenomena known as Hyp-
notism. We have introduced them chiefly to emphasize the view

CHAP, vi.] THE BRAIN. 635

that the nervous system is not to be considered as a collection of
isolated organs each fulfilling its functions independently of its
fellow, but as a large machine, integrated into a whole, the consti-
tuent parts of which are in almost all its actions acting and react-
ing on each other in various ways. So much so does this appear to
be the case, that the secondary influences, often of the kind called
inhibitory, of outlying parts prove as important to the due function
of any particular structure as its own more direct action.

SEC. 4. THE FUNCTIONS OF OTHER PARTS OF THE

BRAIN.

If the views just expressed are true then it is clear that the
proper method to study the brain is to trace out a cerebral
operation along its chain of events rather than to seek to attach
readily definable functions to the cerebral anatomical components.

We may therefore be permitted to summarise very briefly what
can be fairly placed under this heading.

Corpora Striata and Optic Thalami. These two bodies, often
spoken of as 'the basal ganglia/ are undoubtedly the great means
of communication between the cerebral hemispheres on the one
hand and the crura cerebri on the other. Though some fibres appear
to pass from the crura by or through the ganglia to the cerebral
convolutions without being connected with the nerve-cells of those
ganglia, the great mass of the peduncular fibres are probably con-
nected with the superficial grey matter of the hemispheres in an
indirect manner only, the lower or anterior fibres (crusta) passing
first into the corpora striata, and the upper or posterior fibres (teg-
mentum) into the optic thalami. This anatomical disposition would
lead us to suppose that these bodies have important functions in
mediating between the psychical operations of the cerebral convo-
lutions on the one hand, and the sensori-motor machinery of the
middle and hind brain on the other; and the separate courses taken
by the peduncular fibres would further lead us to expect that the
functions of the corpora striata differ fundamentally from those of
the optic thalami.

When in the human subject a lesion occurs involving both
these bodies, on one side of the brain, the result is a loss of sensa-
tion in, and voluntary power over, the opposite side of the body
and face, a so-called hemiplegia, which may be absolutely complete
without any impairment whatever of the intellectual faculties.
The will and the psychical power to receive impressions are present
in their entirety, but neither efferent nor afferent impulses can

CHAP, vi.] THE BRAIN. 637

make their way to or from the peripheral organs and the cerebral
convolutions. The injury to the basal ganglia blocks the way. In
the great majority of cases, the anaesthesia (or loss of sensation)
and akinesia (or loss of movement) are absolutely confined to the
opposite side of the body ; and the cases in which a lesion of the
basal ganglia of one side of the brain affects the same side of the
body or both sides, must be regarded as exceptional, and explicable
as the results of the action of one side of the brain on the other
side either of the brain or of some region of the cerebro-spinal axis.
The results of experiments on animals agree entirely with the
general experience of pathologists, that lesions of the corpora
striata and optic thalami produce their effect on the opposite side
of the body. Whatever be the view taken concerning the de-
cussations of sensory and motor impulses in the spinal cord (see
p. 601), it must be admitted that both kinds of impulses cross
over completely somewhere during their transmission to and from
the basal ganglia and the peripheral organs.

When however we have admitted that these bodies act, as it
were, the part of middlemen between the cerebral convolutions
and the rest of the brain, we have gone almost as far as facts will
support us. We are not at present in a position to state dogmati-
cally what is the nature of the mediation which either body
respectively effects. A very tempting hypothesis is one which
suggests that the corpora striata are concerned in the downward
transmission and elaboration of efferent volitional impulses, and
the optic thalami in a similar upward transmission and elaboration
of afferent sensory impulses ; and there are many facts which may
be urged in favour of this view.

The evidence in this matter afforded by pathology is perhaps the
most consistent, but not wholly so. A number of cases may be cited
to shew not only that lesions of a corpus striatum may be accom-
panied by akinesia without anaesthesia, but that lesions of an optic
thalamus may cause anaesthesia without actual akinesia, that is
without any further interference with the execution of voluntary
movements than is occasioned by the loss of the coordinating
sensations. Of these two classes of cases, the latter is the more
valuable, since all clinical experience shews that any lesion more
readily interferes with volitional movements than with the reception
of sensory impressions. Convulsions are not common when the lesions
are confined to these bodies; but when witnessed they can generally
be referred to the corpora striata rather than to the optic thalami ;
like the paralysis, the convulsions are generally limited to the
opposite side of the body, though feeble movements may occasion-
ally be seen on the same side as well. But it would be dangerous
to trust too much to evidence of this kind; for numerous cases
have been recorded where an injury apparently confined to one
corpus striatum has had as part of its results anaesthesia of the
opposite side of the body; and others where disease apparently

638 CORPORA QUADRIGEMINA. [BOOK m.

confined to an optic thalamus has caused loss of movement as well
as of sensation.

The evidence obtained by means of experiments on animals is
still more discordant. Some observers have found that stimulation,
either mechanical or electrical, of the corpora striata gives rise to
convulsive movements, while stimulation of the optic thalami does
not ; and have seen in these results a confirmation of the view we
are discussing. Such a confirmation is, at best, a feeble one, and
moreover is not supported by the results of all observers. Some
observers again have found that removal or destruction, by the
injection of corrosive substances, of both nuclei lenticular es (the
extra-ventricular portions of the corpora striata) leads to a sup-
pression of voluntary movements almost as complete as if both
hemispheres were removed, whereas after removal or destruction of
both nuclei caudati (intra-ventricular portions of the same bodies)
voluntary movements still persist ; and it has been affirmed that
the removal or destruction of the optic thalami may with care be
effected without the animal appearing any the worse. In the
absence of more exact knowledge it is useless to attempt to form
any clear judgment ; and the view we stated above as to the motor
functions of the corpora striata and sensory functions of the optic
thalami may be allowed to stand as neither definitely disproved
nor satisfactorily proved, and as in any case affording an inadequate
expression of the part played by these masses in the general work
of the brain. Two points we may venture to call attention to,
which as far as they go may be used as arguments in support of
the above view. Almost all observers agree that after injuries
to the corpora striata, more particularly after one-sided or after
partial injuries, and especially after injuries of the nuclei caudati,
forced movements such as those of which we spoke on p. 620 are
very apt to make their appearance. With regard to the optic
thalami on the other hand there is an agreement both of experi-
mental and pathological evidence in favour of the view (which as
the very name of the bodies shews is an old one) that these
structures are in some way or other concerned in vision. Where
the optic thalami are directly involved in an injury to or disease of
the brain, blindness or at least some imperfection of vision is a
frequent result ; and there are reasons for thinking that in some at
all events of the cases where blindness has resulted from removal
of the cerebral cortex of the hinder part of the hemispheres, the
optic thalami have been either directly or secondarily affected.

Corpora Quadrigemina. We have already seen that the centre
of coordination for the movements of the eyeballs (p. 546), and that
for the contraction of the pupil (p. 501), lie in the neighbourhood of
the upper or anterior pair of the corpora quadrigemina. These
two centres are associated together in such a way that when the
eyeballs are voluntarily directed inwards and downwards, as for near

CHAP, vi.] THE BRAIN. 639

vision, the pupils are at the same time contracted ; and when the
eyeballs are directed upwards, and return to parallelism, the pupils
are dilated to a corresponding extent; when both eyeballs are
moved together sideways the pupils remain unchanged. We have
seen (p. 546) that the various movements of the eyeballs may be
brought about by direct stimulation of particular parts of the
anterior corpora quadrigemina, and are then also accompanied by
the appropriate changes in the pupils. The association therefore
of the movements of the pupil and of the ocular muscles is not
simply psychical in nature but is dependent on the close connection
of their respective centres. From the fact of the movements of
the eyeball and pupil being so readily and variously excited by
stimulation of the anterior corpora quadrigemina it has been
inferred that the centres for these movements lie in those bodies ;
it would appear however that what may be called the real or im-
mediate centres of these movements lie beneath the corpora quad-
rigemina, in the front part of the floor of the aqueduct of Sylvius,
and therefore are affected in an indirect manner only when the
corpora quadrigemina are stimulated.

It was long ago observed that unilateral extirpation of the
corpora quadrigemina in mammals or of the optic lobes in birds
produced blindness in the opposite eye ; and the same result has
been gained by many subsequent observers. We have seen more-
over that both frogs, birds, and mammals continue to receive and
within limits to react upon visual impressions after the total
removal of the cerebral hemispheres. From these facts we infer
that visual sensory impulses become transformed into visual sensa-
tions in the corpora quadrigemina ; or, in other words, that these
nervous structures are centres of sight. But they are so in a limited
sense only. We have seen that destruction or injury of the cerebral
hemispheres profoundly affects vision ; even admitting that in such
cases the results may be in part at least due to concomitant failures
in the optic thalami, we may still venture to say that in the absence
of the cerebral convolutions, a crude vision, devoid of distinct visual
perceptions, is probably all that is possible. The processes consti-
tuting distinct and perfect vision, in fact, begin in the retina, are
partially elaborated in the corpora quadrigemina and further de-
veloped in the optic thalami, but do not become perfected until the
cerebral convolutions have been called into operation. Anatomical
considerations lead us to suppose that the anterior pair of the
corpora quadrigemina are alone connected with the optic tract,
and so with the external corpus geniculatum and optic thalamus.
Hence we may infer that it is the anterior pair alone which are
thus concerned in vision and that the posterior pair have some
other function.

In those animals (ex. gr. rabbits) in which unilateral destruction
of the corpora quadrigemina entails blindness of the opposite eye,
and yet does not affect at all the visual sensory impulses originating

640 CEREBELLUM. [BOOK in.

in the eye of the same side, it is obvious that complete decussation
of the sensory impulses must take place before the centre is
reached. The question however whether the decussation of fibres
(and consequently of impulses) in the optic chiasma is complete or
incomplete, whether the optic tract of one side is the continuation
of the fibres in the optic nerve of the opposite side exclusively or
whether it is composed of representatives of the optic nerves of both
sides, is one which has been much debated, both from an anatomical
and a physiological standpoint. In the case of mammals the evidence
goes to shew that in some kinds of animals (rabbits) the decussation
is complete, but in others (dogs) more or less incomplete. In man
a peculiar affection of vision, which may be spoken of under the
general name of hemiopia, is a frequent symptom of diseases of the
brain. In this affection portions of the field of vision are wanting ;
thus a patient sometimes can see nothing in the right half or the
upper half of the fields of vision of both eyes ; looking at a man or a
house he can only see half the object, the left half or the lower half
as the case may be. Hemiopia of both eyes has been observed in
cases in which disease was apparently limited to one side of the
brain; and these cases added to other evidence lead to the con-
clusion that in man the decussation is incomplete.

Many observers have noticed that injury or removal of the
corpora quadrigemina on one side frequently caused forced move-
ments, and that removal of the whole mass led to great want of co-
ordination. These results are quite in harmony with the fact men-
tioned above (p. 610) concerning the coordinating functions of the
optic lobes in frogs. But at present we have no exact knowledge
concerning the nature of the coordination, and what relations are
borne in this respect by the corpora quadrigemina to the cere-
bellum, crura cerebri, and pons Yarolii.

Various observers have witnessed as the result of stimulation of
the corpora quadrigemina movements of the several parts of the
alimentary canal, and of the urinary bladder, changes in blood-
pressure, and alterations in the working of the respiratory mecha-
nism, indicating that these bodies have a special connection with
the centres (in the medulla oblongata and spinal cord respectively)
concerned in carrying on these movements.

Cerebellum. We have already referred to the cerebellum as
being probably concerned in the coordination of movements. It
was long ago observed that when a small portion of the cerebellum
was removed from a pigeon, the animal's gait became unsteady ;
when larger portions were taken away its movements became much
more disorderly, and when the whole of the organ was removed an
almost total loss of coordination supervened. When the portion
removed was small, the disorderly movements which at first ap-
peared eventually vanished, but when a large portion was re-
moved the loss of coordination became permanent. Subsequently

CHAP, vi.] THE BRAIN, 641

observers have obtained similar results in other animals ; and it has
in general been found that lateral or unsymraetrical lesions and
incisions produce a greater effect than those which are median or
symmetrical. Section of the middle peduncle on one side almost
invariably gives rise to a forced movement, the animal rolling
rapidly round its own longitudinal axis ; the rotation is generally
though not always towards the side operated on; and is accompanied
by nystagmus, i.e. by peculiar rolling movements of the eyes sug-
gestive of vertigo ; frequently one eye is moved in one direction, ex.
gr. inwards and downwards, and the other in a different or opposite
direction, ex. gr. outwards and upwards. As we have already said
the permanent effects which follow upon injury to the semicircular
canals, have been attributed by some to secondary mischief being
set up in the cerebellum. The clinical evidence is discordant, for
though unsteadiness of gait has been frequently witnessed in cases
of cerebellar disease, many histories have been recorded in which
extensive disease, amounting at times to almost complete destruc-
tion, of the cerebellum has existed without any obvious disturbance
of the coordination of movements. Still the experimental evidence
is so strong, that we must consider the cerebellum as an important
organ of coordination, though we are unable at present to define its
functions more exactly.

In this connection we may observe that the history of the
developement of the spinal cord (see p. 600) tends to connect a
definite portion of the lateral columns of the spinal cord with the
cerebellum ; but the meaning of this connection is obscure.

Attempts have been made to connect the cerebellum with the
sexual functions ; but there is no satisfactory evidence of any such
relation. As we shall see later on, the nervous centres connected
with the sexual and generative organs are seated, in the case of
dogs at least and probably of all animals, in the lumbar spinal cord;
and all or nearly all sexual phenomena may be witnessed in animals,
in which the lumbar spinal cord has been isolated by section
from the rest of the cerebro-spinal system. Galvanic stimulation
of the cerebellum produces no change in the generative organs, and
when erection of the penis is caused by emotions, the tract con-
necting the cerebral convolutions with the erection-centre in the
spinal cord must be supposed to pass straight along the crura cerebri
and medulla, for it has been observed that stimulation of these parts
in the dog will produce erection.

Crura Cerebri and Pons Varolii. Though from the grey
matter abundant in both these organs we may infer that they
possess important functions, we hardly know more concerning
them than that the former serve as the great means of communi-
cation between the spinal cord and the higher parts of the brain,
and that both are intimately connected with the coordination of
movements, since either forced or disorderly movements are the

F. 41

642 MEDULLA OBLONGATA. [BOOK in.

frequent results of section of either of them ; and as we have seen,
the possession of these parts, in the absence of the cerebral
hemispheres, and even of the corpora striata and optic thalami, is
sufficient to carry out the most complex bodily movements. ^

Since the paralysis of the face seen in cases of hemiplegia from
disease of one corpus striatum is on the same side as that of the
limbs, it follows that the impulses proceeding along the cranial
nerves cross over like those of the spinal nerves; and when the
nucleus of origin of such a nerve as the facial is stimulated on one
side, the movements which result are on the opposite side. Hence
when paralysis of the face occurs on the opposite side to that of the
body, it may be inferred that the injury or disease has affected
the cranial nerve (or nerves) in a part of its course before
decussation has taken place ; and pathological observations support
this view, unilateral disease or injury of the pons Varolii not
unfrequently involving the facial nerve of the same side in its
comparatively superficial course before decussation has taken place,
and so causing paralysis of the muscles of the same side of the
face as the disease, and the opposite side to the paralysis of the
limbs. It is probable that the decussation which we have seen
to take place partly in the spinal cord, is gradually completed as
the impulses pass through the medulla and pons Varolii. There
does not appear to be adequate support for the view of those who
maintain that volitional impulses cross suddenly and completely at
the decussation of the pyramids.

Medulla Oblongata. We have so often spoken of this link
between the brain and the spinal cord, that it is hardly necessary
here to do more than recall the fact, that the majority of the
' centres ' for various organic functions are situated in it.

These we may briefly recapitulate as follows : The respiratory
centre with its neighbouring convulsive centre. The vaso-motor
centre. The cardio-inhibitory centre. The diabetic centre, or
centre for the production of artificial diabetes. The centre for
deglutition. The centre for the movements of the oesophagus
and stomach, with its allied vomiting centre. The centre for
reflex excitation of the secretion of the saliva, with which may
be associated the centre through which the vagus influences the
secretion of pancreatic juice, and possibly of the other digestive
juices.

In the frog, as we have urged, p. 610, the medulla is undoubt-
edly largely concerned in the coordination of movements, and it is
exceedingly probable that in the mammal also a considerable
portion of work of this kind falls to its lot.

SEC. 5. ON THE RAPIDITY OF CEREBRAL OPERATIONS.

We have already seen (p. 593) that a considerable time is
taken up in a purely reflex act, such as that of winking, though
this is perhaps the most rapid form of reflex movement. When
the movement which is executed in response to a stimulus involves
mental operations a still longer time is needed ; and the interval
between the application of the stimulus and the commencement of
the muscular contraction varies according to the nature of the
mental labour involved.

The simplest case is that in which a person makes a signal
immediately that he perceives a stimulus, ex. gr. closes or opens a
galvanic circuit the moment that he feels an induction shock
applied to the skin, or sees a flash of light, or hears a sound. By
arrangements similar to those employed in measuring the velocity
of nervous impulses, the moment of the application of the stimulus
and the moment of the making of the signal are both recorded
on the same travelling surface, and the interval between them
is carefully measured. This interval, which has been called 'the
reaction period,' consists of three portions: (1) the passage of
afferent impulses from the peripheral sensory organ to the central
nervous system, including the possible latent period of the gene-
ration of the impulses in the sensory organ ; (2) the transformation,
by the operations of the central nervous system, of the afferent into
efferent impulses ; and (3) the passage of the efferent impulses to
the muscles, including the latent period of the muscular contractions.
If the time required for the first and third of these events be
deducted from the whole, the ' reduced reaction period,' as it may be
called, gives the time taken up exclusively by the operations going
on in the central nervous system.

41—2

644 RAPIDITY OF CEREBRAL OPERATIONS. [BOOK in.

The reaction period, both reduced and unreduced, varies
according to the nature and disposition of the peripheral organs
stimulated. The reaction period of vision has long been known
to astronomers. It was early found that when two observers
were watching the appearance of the same star, a considerable
discrepancy existed between their respective reaction periods ; and
that the difference, forming the basis of the so-called 'personal
equation/ varied from time to time according to the personal
conditions of the observers.

In general it may be said that tactile sensations produced by
the stimulus of an electric shock applied to the skin, are followed
by a shorter reaction period than are auditory sensations, while the
period of these is in turn shorter than that of visual sensations
produced by luminous objects; on the other hand, the shortest
period of all is that of visual sensations produced by direct electrical
stimulation of the retina. Roughly speaking we may say that the
reaction period or physiological time is for feeling nj-th, for hearing
Jth, and for sight Jth of a second. But even with the same
stimulus, the reaction period will vary according to circumstances,
such as the time of year, weather, &c., and according to the
condition of the individual, previous practice, fatigue, and the like.

The calculations involved in ' reducing ' the reaction period are
obviously open to much error; in general the reduced reaction
period may be said to be less than -j-^th of a second, that is to say
an intelligent person takes about this time to perceive and to will.

The reaction period just given belongs to cases where a
single stimulus is used, and all that the person experimented
on has to do is to perceive the stimulus, and to make an
effort in accordance. If, however, the stimulus, instead of being
applied to a part of the body determined by previous arrange-
ment, as for instance to the left foot, were applied either
to the left or the right foot, without the person being told
which it was to be, and it was arranged that he should make
a signal when the left foot, but not when the right foot was
stimulated, additional mental exertions would be necessary; and
it is found that in such a case the reaction period is considerably
prolonged. The difference between a simple reaction period, and
one in which a mental decision has to be carried out before the
voluntary effort to make the signal is initiated, gives the time
required for a person to ' make up his mind ' in accordance with
the nature of the sensation which he receives ; this is found to be,
roughly speaking, from £ to -£$ of a second.

SEC. 6. THE CIRCULATION IN THE BRAIN.

The supply of blood to the brain seems at first sight not to
correspond to the importance of this the chief organ of the body.
In the rabbit it would appear that not much more than one per
cent, of the total quantity of the blood of the body is present at
any one time in the brain, a quantity distinctly less than that
which is found in the kidneys; and of the total weight of the
organ, the weight of blood in the brain at any one time amounts to
about five per cent., being about the same as in the muscles, whereas
in the kidney it amounts to nearly twelve per cent, and in the liver
to as much as nearly thirty per cent. Making every allowance for
the relative small size and functional importance of the rabbit's brain,
the blood-supply of even the human brain must still be small. In
other words, the metabolism of the brain-substance is of importance,
not so much on account of its quantity as of its special qualities.

We have seen (p. 366) in speaking of respiration that when
the brain is exposed the quantity of blood in the brain and so the
total volume of the brain rises and falls, in a conspicuous manner,
with the respiratory movements. And observations by the plethys-
mographic method, a portion of the skull being removed for the
purpose or advantage being taken of a natural deficiency, have shewn
the existence of more rapidly repeated movements, of a swelling
and shrinking synchronous with and due to the beats of the heart,
as well as of variations, larger and slower than the respiratory
undulations, and brought about by various causes such as the
position of the head in relation to the trunk, movements of the
limbs, modifications of the respiratory movements, and apparently
phases of activity of the brain itself, as in waking and sleeping

646 THE CIRCULATION IN THE BRAIN. [BOOK m.

In certain respects the circulation in the brain is peculiar.
The skull forms a fairly complete inextensible envelope, presenting
a strong contrast to the extensible elastic capsules which invest
such organs as the spleen and kidney. As a consequence of this,
when at any time an extra quantity of blood is sent from the
heart to the brain, room must be made for it by the increased exit
of the fluids already present. For any pressure on the brain-
substance beyond a certain limit is injurious to its welfare and
activity, as is seen in certain maladies, where blood passing by
rupture of the blood-vessels out of its normal channels remains
effused on the surface of the brain or elsewhere, and thus taking
up the room of the proper brain-substance leads, by ' compression '
as it is called, to paralysis, loss of consciousness, or death. Within
the limits of the normal cerebral circulation, the characteristic venous
sinuses serve to regulate the internal pressure ; they form temporary
reservoirs from which a comparatively large quantity of blood can
be rapidly discharged from the cranium, the flow from the sinuses
being greatly assisted by the inspiratory movements of the chest.

The arterial supply of the brain as a whole is undoubtedly
regulated by vaso-motor nerves, and in all probability the special
distribution of blood to the various parts of the brain is determined
by the same agents. When the head is suddenly shifted from the
erect to a hanging position, there must be a tendency for the blood
to accumulate in the cranial cavity, and conversely when the head
is suddenly shifted from a hanging to an erect position, there must
be a tendency for the supply of blood within the cranium to be for
a while less than normal. Either change of position, and especially
perhaps the latter, would thus lead to cerebral disturbances
which would in ourselves be revealed by affections of our con-
sciousness. That a perfectly healthy, and especially young organism
whose vaso-motor mechanisms are at once effective and delicately
responsive, can pass swiftly from one position of the head to the
other without inconvenience, whereas those in whom the vaso-
motor mechanisms by age or otherwise have become imperfect are
giddy when they attempt such rapid changes, is in itself adequate
evidence of the importance of the vaso-motor arrangements of the
brain. But our information concerning this matter, is at present of
a very vague and general character. As yet we have no detailed
knowledge, and are especially ignorant as to how far special
parts of the brain are supplied with independent vaso-motor
mechanisms.

Many writers have insisted on the mechanical importance of
the cerebro-spinal fluid. By the foramen of Majendie at the apex
of the roof of the fourth ventricle, the fluid within the various
ventricular cavities of the brain is continuous with the fluid in the
subarachnoid labyrinth of the spinal cord. And it has been argued
that when an extra quantity of blood is driven into the skull, the
transference of a corresponding quantity of cerebro-spinal fluid

CHAP, vi.] THE BRAIN. 647

through the foramen of Majendie, from the cranium into the spinal
canal, the walls of which are less rigidly complete, prevents any
injurious intracranial compression. Experimental evidence how-
ever, as far as it goes, does not lend any very great support to this
view ; and though removal of the fluid by aspiration is said to lead
to haemorrhage from the pia mater and to various nervous disorders,
the value of the cerebro-spinal fluid depends in all probability more
on its physiological properties as lymph, than on its mechanical
properties as a mere fluid.

SEC. 7. THE CRANIAL NERVES.

Though we have incidentally dwelt on the functions of all these
nerves, it may be as well to recapitulate them in a tabular form.

1. Olfactory. Nerve of smell.

2. Optic. Nerve of sight.

3. Oculo-motor. Motor nerve to the levator palpebrse superi-
oris and all the muscles of the eye, except the obliquus superior
and the rectus externus. Efferent nerve for the contraction of the
pupil and for the muscles of accommodation. Hence when the
nerve is divided or otherwise paralysed the upper eyelid falls
(ptosis) ; the eye, which is turned outwards, is capable of partial
movements only, viz. such as can be produced by the rectus
externus and obliquus superior ; when the head is moved, the eye
moves with it, the inferior oblique not being able to execute the
usual compensating movements of the eyeball ; the pupil is
dilated, and the eye cannot accommodate for near distances. The
root of the nerve shews recurrent sensibility, due to fibres from
the fifth, but is otherwise a purely motor nerve.

4. Trochlear or Pathetic. Motor nerve to the obliquus
superior. When the nerve is paralysed, no marked difference is
observed in the position of the eye, but the patient sees double
when he attempts to look straight forward or towards the paralysed
side ; the images however coalesce when he turns his head to the
sound side. When the head is moved from side to side the eye
moves with it, the usual compensating movement of the eye which
accompanies the movements of the head failing in consequence of
the superior oblique not acting. It is a purely motor nerve, but
receives recurrent fibres from the fifth.

CHAP, vi.] THE BRAIN. 649

5. Trigeminus. A mixed efferent and afferent nerve, with
distinct motor and sensory roots, the latter bearing the ganglion of
Gasser.

Efferent Fibres. Motor fibres to the muscles of mastication,
temporal, masseter, two pterygoids (mylo-hyoid, anterior belly of
digastric), to the tensor palati, and tensor tympani; vaso-motor
fibres to various parts of the head and face ; secretory fibres to the
lachrymal gland, and according to some authors to the parotid and
submaxillary glands by fibres joining the facial. Trophic (?)
fibres to eye, nose, and other parts of the face. Efferent fibres for
the dilation of the pupil.

Afferent Fibres. General nerve of sensation of the skin of
head and face, and of the mucous membrane of the mouth, except
the back part of the tongue, the posterior pillars of the fauces, and
a large part of the pharynx, these parts being supplied by the
glossopharyngeal and vagus; the back of the head is chiefly
supplied by branches from the cervical nerves, and the external
meatus and concha are supplied chiefly by the auricular branch of
the vagus. Nerve of special sense of taste for the front part of
the tongue.

6. Abducens. Motor nerve to the rectus externus. When
the nerve is divided or otherwise paralysed, the eye is turned
inwards. It probably receives recurrent sensory fibres from the fifth.
It is also joined by fibres coming from the cervical sympathetic ;
when this latter nerve is divided in the neck, the action of the
muscle is said to be weakened.

7. Facial. Motor nerve to the muscles of the face; hence
nerve of expression. Supplies also stylohyoid, posterior belly of
the digastric, buccinator, stapedius, muscles of the external ear,
platysma, some muscles of the palate, viz. the levator palati and
probably others. Secretory nerve of submaxillary and parotid
gland. Receives afferent, possibly efferent, fibres from trigeminus
and also from vagus. It is said by some to contain vaso-motor
fibres for the tongue and side of the face. The effects of paralysis
of the facial, from the inability of the orbicularis to close the eye,
the drawing of the face to the sound side, and the smoothness of
the paralysed side, are very striking.

8. Auditory Nerve. Special nerve of hearing ; afferent nerve
for impulses other than auditory proceeding from the semi-circular
canals.

9. Olosso-pharyngeal. Motor nerve for levator palati, azygos
uvulae, stylo-pharyngeus, constrictor faucium medius; the motor
functions of this nerve have been disputed. Special nerve of taste
for the back of the tongue. General nerve of sensation for the
root of the tongue, the soft palate, the pharynx (being here
associated with the vagus), the Eustachian tube and the tympanum.

650 CRANIAL NERVES. [BOOK m.

10. Pneumogastric. Vagus.

Efferent Fibres. Motor nerve for the muscles of the pharynx,
for the movements of the oesophagus, of the stomach, of the
intestines, for the muscles of the larynx, possibly for the plain
muscular fibres of the trachea and bronchial divisions. Vaso-
motor fibres for lungs. Inhibitory nerve of the heart. Trophic
fibres for lungs and heart.

Afferent Fibres. Sensory nerve of the respiratory passages,
and of the pharynx, oesophagus and stomach. Afferent nerve,
augmenting and inhibiting, of the respiratory centre, afferent
inhibitory nerve (depressor branch) of the medullary vaso-motor
centre, afferent nerve producing salivary secretion, inhibiting

rcreatic secretion. It is stated that in the rabbit the vagus may
easily dissected into two strands, an outer one containing the
afferent, and an inner one containing the efferent fibres.

11. Spinal accessory. Motor nerve to the sterno-mastoid and
trapezius muscles. It receives recurrent sensory fibres from the
cervical nerves. Part of the spinal accessory blends with the
pneumogastric, and the efferent effects (such as the movements of
the larynx, pharynx, &c., and cardiac inhibition) of the united
trunk seem to be largely due to the spinal accessory fibres con-
tained in them. It is stated however that division of the spinal
accessory before it joins the pneumogastric, does not entirely do
away with either swallowing or the movements of the larynx. In
the movements of the oesophagus and stomach, brought about by
the vagus acting as an efferent nerve, the accessory fibres seem to
have no share. The cardiac inhibitory fibres seem to be distinctly
of accessory origin.

12. Hypoglossal. Motor nerve for the muscles of the tongue,
and for all the muscles connected with the hyoid bone except the
digastric, stylo-hyoid, mylo-hyoid, and middle constrictor of the
pharynx ; it also supplies the sterno-thyroid. It receives sensory
fibres from the fifth and vagus, and is also connected with the
three upper cervical nerves as well as with the sympathetic.

CHAPTER VII.

SPECIAL MUSCULAR MECHANISMS.

SEC. 1. THE VOICE.

A BLAST of air, driven by a more or less prolonged expiratory
movement, throws into vibrations two elastic membranes — the
chordce vocales. These impart their vibrations to the column of
air above them, and so give rise to the sound which we call the
voice. Since the sound is generated in the vocal cords, we may
speak of them and of those parts of the larynx which decidedly
affect their condition as constituting the essential vocal apparatus ;
while the chamber above the vocal cords, comprising the ventricles
of the larynx with the false vocal cords, the pharynx and the
cavity of the mouth, the latter varying much in form, constitute a
subsidiary apparatus of the nature of a resonance-tube, modifying
the sound originating in the vocal cords. In the voice, as in other
sounds, we distinguish : (1) Loudness. This depends on the
strength of the expiratory blast. (2) Pitch. This depends on the
length and tension of the vocal cords. Their length may be
regarded as constant, or varying only with age. It consequently
determines the range only of the voice, and not the particular note
given out at any one time. The shrill voice of the child is
determined by the shortness of the cords in infancy, and the
voices of a soprano, tenor and baritone are all dependent on the
respective lengths of their vocal cords. Their tension is on the
contrary variable; and the chief problems connected with the
voice refer to variations in the tension of the vocal cords. (3)

652

THE VOICE.

[BOOK in.

Quality. This depends on the number and character of the over-
tones accompanying any fundamental note sounded, and is deter-
mined by a variety of circumstances, chief among which is the
physical quality of the cords.

The vocal cords, attached in front to the thyroid cartilage, end
behind in the processus vocales of the arytenoid cartilages. Hence
a distinction has been drawn between the rima vocalis, i.e. the

FIG. 88. THE LARYNX AS SEEN BY MEANS OF THE LARYNGOSCOPE IN DIFFERENT
CONDITIONS OF THE GLOTTIS. (From Quain's Anatomy after Czermak.)

A while singing a high note ; B in quiet breathing ; C during a deep inspiration.
The corresponding diagrammatic figures A', B', C', illustrate the changes in
position of the arytenoid cartilages, and the form of the rima vocalis and
rima respiratoria in the above three conditions.

I the base of the tongue ; e the upper free part of the epiglottis ; e' the
tubercle or cushion of the epiglottis ; ph. part of the anterior wall of the
pharynx behind the larynx; w swelling in the aryteno-epiglottidean fold
caused by the cartilage of Wrisberg ; s swelling caused by the cartilage of
Santorini ; a the summit of the arytenoid cartilage ; cv the true vocal cords ;
cvs the false vocal cords ; tr the trachea with its rings j 6 the two bronchi at
their commencement.

opening bounded laterally by the vocal cords, and the rima
respiratoria, or space between the arytenoid cartilages behind the
processus vocales; these names however are not free from ob-
jections. In quiet breathing (Fig. 88 £) the two form together a
V-shaped space, which, as we have seen (p. 325), in deep inspiration

CHAP. VIL] SPECIAL MUSCULAR MECHANISMS. 653

is widened into a rhomboidal opening by the divergence of the
processus vocales (Fig. 88 C). When a note is about to be uttered,
the vocal cords are by the approximation of the processus vocales
brought into a position parallel to each other, and the whole rima
is narrowed (Fig. 88-4). By their parallelism and by the narrow-
ness of the interval between them the cords are rendered more
susceptible of being thrown into vibration by a moderate blast of
air. The problems we have to consider are, first, by what means
are the cords brought near to each other or drawn asunder as
occasion demands ; and secondly, by what means is the tension of
the cords made to vary. We may speak of these two actions as
narrowing or widening of the glottis, and tightening or relaxation
of the vocal cords.

of the Glottis. The change of form of the glottis is
best understood when it is borne in mind that each arytenoid
cartilage is, when seen in horizontal section (Fig. 88), somewhat of
the form of a triangle, with an internal or median, an external,
and a posterior side, the processus vocalis being placed in the
anterior angle at the junction of the median and external sides.
When the cartilages are so placed that the processus vocales are
approximated to each other, and the internal surfaces of the
cartilages nearly parallel, the glottis is narrowed. When on the
contrary the cartilages are wheeled round on the pivots of their
articulations, so that the processus vocales diverge, and the inter-
nal surfaces of the cartilages form an angle with each other, the
glottis is widened.

There are several muscles forming together a group, which has
been called by Henle the sphincter of the larynx. These are (1)
the thyro-ary-epiglotticus, proceeding from the inner surface of the
thyroid cartilage and from the arytenoid epiglottidean ligament,
and sweeping round the outer ridge of the arytenoid cartilage of
its own side to be inserted into the processus muscularis of the
arytenoid cartilage of the other side: (2) the thyro-arytenoideus
externus, passing from the reentrant angle of the thyroid cartilage
to be inserted into the outer edge of the arytenoid cartilage of the
same side : (3) the thyro-arytenoideus intemus, passing from the
angle of the thyroid cartilage to the processus vocalis and outer
side of the arytenoid cartilage : (4) the arytenoideus (posticus),
passing transversely from one arytenoid cartilage to another. All
these muscles, when they act together, grasp round the glottis and
tend to close it up : and each of them, acting alone, has, with the
exception of the last-named (arytenoideus), the same effect. In
addition to these, the crico-arytenoideus lateralis, which passes
from the lateral border of the cricoid cartilage upwards and back-
wards to the outer angle of the arytenoid,- by pulling this outer
angle forwards throws the processus vocalis inwards, and so also
narrows the glottis.

654 THE VOICE. [BOOK in.

Widening of the Glottis. The crico-arytenoideus posticus
passing from the posterior surface of the cricoid cartilage to the
outer angle of the arytenoid cartilage behind the attachment of
the lateral crico-arytenoideus, pulls back this outer angle, and so
causing the processus vocalis to move outwards, widens the glottis.
The arytenoideus posticus, acting alone, has a similar effect.

Tightening of the Vocal Cords. The crico-thyroideus pulls
the thyroid downwards and forwards, and so increases the distance
between that cartilage and the arytenoids when the latter are
fixed. Supposing then the arytenoideus and crico-arytenoideus.
posticus to fix the arytenoids, the effect of the contraction of the
crico-thyroideus would be to tighten the vocal cords.

Slackening of the Vocal Cords. This is effected by the whole
sphincter group just mentioned, but more especially by the thyro-
arytenoidei externus and internus ; these acting alone, supposing
the arytenoid cartilages to be fixed, would pull the thyroid car-
tilage upwards and backwards, and so shorten the distance between
the processus vocales and that body.

Thus almost every movement of the larynx is effected not by
one muscle only but by several, or at least by more than one,
acting in concert. The movements which give rise to the voice
are preeminently combined and coordinate movements. When
we remember how a very slight variation in the tension of the
vocal cords must give rise to a marked difference in the pitch of
the note uttered, and yet what a multitude of fine differences of
pitch are at the command of a singer of even moderate ability, it
appears exceedingly probable that the various muscular com-
binations required to produce the possible variations in pitch are
of such a kind that frequently a part only, possibly a few fibres
only, of a particular muscle, may be thrown into contraction, while
all the rest of the muscle remains quiet. Taking into view
moreover the great range of pitch possessed by even common
voices, as compared with the possible variations of tension of
which the vocal cords in their natural length are capable, it has
been suggested that some of the fibres of the thyro-arytenoideus
internus, which passing either from the thyroid or from the
arytenoid, appear to end in the vocal cords themselves, may, by
fixing particular points of the cords, so to speak, 'stop' them ; and
by thus artificially shortening the length actually thrown into
vibration, produce higher notes than the cords in their natural
length are capable of producing. It has been also suggested that
the processus vocales may overlap each other, and thereby shorten
the length of cord available for vibration.

These various muscles are supplied by the vagus nerve, or
rather by spinal accessory fibres running in the vagus trunk. The
superior laryngeal is the afferent nerve supplying- the mucous
membrane, but it also contains the motor fibres distributed to the

CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 655

crico-thyroid muscle ; hence when this nerve is divided on one
side the corresponding vocal cord is relaxed and high notes become
impossible. It is worthy of notice that this, the chief tensor, and
therefore the most important, muscle of the larynx, has a separate
and distinct nervous supply. According to some authors the
arytenoideus posticus also receives its nervous supply from this
nerve ; but this is denied by others.

The inferior laryngeal or recurrent branch supplies all the other
muscles. When this nerve is divided the voice is lost, since the
approximation and parallelism of the vocal cords can no longer be
effected. When in a living animal both recurrent nerves are
divided, the glottis is seen to become immobile and partially
dilated, the vocal cords assuming the position in which they are
found in the body after death, and which may be considered as the
condition of equilibrium between the dilating and constricting
muscles. During forcible inspiration the glottis passes from this
condition in the direction of more complete dilation; during
forcible expiration, the change is one of constriction. When the
peripheral portion of one recurrent nerve is stimulated, the vocal
cord of the same side is approximated to the middle line ; when
both nerves are stimulated, the vocal cords are brought together
and the glottis is narrowed. Though the nerve is distributed to
both dilating and constricting muscles, the latter overcome the
former when the nerve is artificially stimulated. In the complete
closure of the glottis, which is so important a part of the act of
coughing (p. 383), the group of muscles which we have spoken of
as constituting a sphincter is thrown into forcible contractions by
the recurrent laryngeal nerve.

Though fundamentally a voluntary act, the utterance of a given
note is not effected by the direct passage of simple volitional im-
pulses down to the laryngeal muscles. So complex and coordinate
a movement as that of sounding even a simple and natural note,
requires a coordinating nervous mechanism in which, as in other
complex muscular actions, afferent impulses play an important part.
Auditory sensations, if not as important for an accurate manage-
ment of the voice as are visual sensations for the movements of the
eye, are yet of prime importance. This is recognized when we say
that such and such a one whose power over his laryngeal muscles is
imperfect, 'has no ear.'

A person may speak or sing in two kinds of voice. In the
one the sounds are full and strong, and the resonance chamber which
is supplied by the trachea, bronchi and indeed by the whole chest,
is thrown into powerful and palpable vibrations ; hence this voice
is spoken of as the chest-voice. The other kind of voice, called the
falsetto, is thin and poor, deals chiefly with high notes, and is not
accompanied by the same conspicuous vibrations of the chest.
Much controversy has taken place as to the exact manner in which
these two voices are respectively produced. The prevailing opinion

656 THE VOICE. [BOOK in.

teaches that in the chest-voice the vocal cords are somewhat thick,
their substance being thrust inward towards the median line by
the contraction of the thyro-arytenoidei externi muscles, and the
opening between them, sometimes so narrow as to be almost linear,
extends along their whole length. In the falsetto voice, on the other
hand, the vocal cords are said to be thin and membranous, and the
note to be given forth by a vibration, not of the whole width of the
cords as in the chest voice, but of the extreme edges only, the lateral
parts though not absolutely at rest vibrating with a different rhythm.
Though the whole larynx in the falsetto voice is stretched in the
antero-posterior direction and the vocal cords correspondingly elon-
gated, the rima vocalis does not extend along their whole length ;
at their posterior part the cords are in contact, and indeed according
to some authors, the high falsetto notes are produced by a sort of
'stopping' of the cords. The sense of effort which accompanies
the falsetto voice indicates that the changes in the larynx which
bring it about, are effected by some special muscular manoauvres,
as is also suggested by the fact that the ease with which falsetto
notes can be uttered is readily increased by practice. The change
from the chest to the falsetto voice is an abrupt one, and the com-
bined range may be very extensive, as in the case of persons who
can carry on a duet, singing alternately, for instance, in a tenor
(chest) and a soprano (falsetto) voice.

The ventricles of Morgagni are apparently of use in giving the
vocal cords sufficient room for their vibrations, and perhaps supply
a secretion by which the vocal cords are kept adequately moist.
The purpose of the false vocal cords is not exactly known. Some
authors think that in the falsetto voice they are brought down into
contact with, and thus serve to stop, the true vocal cords.

At the age of puberty a rapid development of the larynx takes
place, leading to a change in the range of the voice. The peculiar
harshness of the voice when it is thus 'breaking' seems to be due
to a temporary congested and swollen condition of the mucous mem-
brane of the vocal cords accompanying the active growth of the
whole larynx. The change in the mucous membrane may come on
quite suddenly, the voice 'breaking' for instance in the course of a
night.

SEC. 2. SPEECH.
Vowels.

Every sound, or every note (for all vocal sounds when considered
by themselves are musical sounds), caused by the vibrations of the
vocal cords, besides its loudness due to the force of the expiratory
blast, and its pitch due to the tension of the cords, has a quality of
its own, due to the number and relative prominence of the over-
tones which accompany the fundamental tone. Some of these
features which make up the quality are imposed on the note by
the nature of the vocal cords, but still more arise from various modi-
fications which the relative intensities of the overtones undergo
through the resonance of the cavity of the mouth and throat.
Whenever we hear a note sounded by the larynx we are able to
recognize in it features which enable us to state that one or other
of the 'vowels' is being uttered. Vowel sounds are in fact only
extreme cases of quality, extreme prominence of certain overtones
brought about by the shape assumed by the buccal and pharyngeal
passages and orifices, as the vibrations pass through them. Each
vowel has its appropriate and causative disposition of these parts.
When i (ee in feet) is sounded, the sounding-tube of the upper air
passages is made as short as possible, the larynx is raised and the
lips are retracted, the whole cavity of the mouth taking on the form
of a broad flask with a narrow neck. During the giving out of e
(a in fat) the shape of the mouth is similar, but somewhat longer.
For the production of a (as in father) the mouth is widely open, so
that the buccal cavity is of the shape of a funnel with the apex at
the pharynx. With o, the buccal cavity is again flask-shaped, with
F. 42

658 SPEECH. [BOOK in

the mouth more closed than in a, but the lips, instead of being re-
tracted as in i and e, are somewhat protruded, so that the sounding
tube is prolonged. The greatest length of the tube is reached in u,
(oo), in which the larynx is depressed and the lips protruded as
much as possible. While the two latter vowels are being uttered,
the general form of the buccal cavity is that of a flask with a
short neck and a small opening, the orifice being smaller for u than
for o.

Each of these various 'vowel' forms of the mouth possesses a
note of its own, one towards which it acts as a resonance chamber.
Thus if several tuning-forks of various pitch be held while sounding
before a mouth which has assumed the particular form necessary
for sounding U, it will be found that the resonance will be particu-
larly great with the fork having the pitch of the bass 6-flat. Simi-
larly other and higher notes will be intensified when the mouth is
moulded to utter the other vowels. And it is the experience of
singers that each vowel is sung with peculiar ease on a note having
a prominent overtone corresponding to the tone proper to the
mouth when moulded to utter the vowel. The precise nature of
the vowel sounds is however still disputed.

As the vibrations are travelling through the pharyngeal and
buccal cavities, the posterior nares are closed by the soft palate;
and it may be shewn, by holding a flame before the nostril, that no
current of air issues from the nose when a vowel is properly said or
sung. When the posterior nares are not effectually closed the
sound acquires a nasal character. The same happens when the
anterior nares are closed, as when the nose is held between the
fingers, the nasal chamber then forming a cavity of resonance.

Consonants.

^ Vowels are, as their name implies, the only real vocal sounds ;
it is only on a vowel that a note can be said or sung. Our speech
however is made up not only of vowels but also of consonants, i.e.
of sounds which are produced not by the vibrations of the vocal
cords but by the expiratory blast being in various ways interrupted
or otherwise modified in its course through the throat and mouth.

The distinction between the two is however not an absolute one,
since, as we have seen, the characters of the several vowels depend
on the form of the mouth, and in the production of some conso-
nants (B, D, M, N, &c.) vibrations of the vocal cords form a neces-
sary though adjuvant factor.

Consonants have been classified according to the place at which

CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 659

the characteristic interruption or modification takes place. Thus it
may occur,

1. At the lips, by the movement or position of the lips in
reference to each other or to the teeth, giving rise to labial conso-
nants.

2. At the teeth, by the movement or position of the front part
of the tongue in reference to the teeth or the hard palate, giving
rise to dental consonants.

3. In the throat, by the movement or position of the root of
the tongue in reference to the soft palate or pharynx, giving rise to
guttural consonants.

Among the dentals again may be distinguished the dentals
commonly so called, such as T, the sibilants such as S, and the
lingual L, all differing in the relative position of the tongue, teeth,
and palate.

Consonants may also be classified according to the character of
the movements which give rise to them. Thus they may be either
explosive or continuous.

1. Explosives. In these the characters are given to the sound
by the sudden establishment or removal of the appropriate inter-
ruption. Thus, in uttering the labial P, the lips are first closed,
then an expiratory current of air is driven against them, and upon
their being suddenly opened, the sound is generated. Similarly,
the dental T is generated by the sudden removal of the interruption
caused by the approximation of the tip of the tongue to the front
of the hard palate, and the guttural K by the sudden removal of
the interruption caused by the approximation of the root of the
tongue to the soft palate.

The labial B differs from P, inasmuch as it is accompanied by
vibrations of the vocal cords (that is, a vowel sound is uttered at
the same time), and these vibrations continue after the removal of
the interruption. Hence B is often spoken of as being uttered with
voice and P without voice ; and D and G (hard) with voice bear
the same relation to T and K without voice.

The continuous consonants may further be divided into

2. Aspirates. In these the sound is generated by a rush of
air through a constriction formed by the partial closure of the lips,
or by the raising of the tongue against the hard or soft palate, &c.
Thus F is sounded when the lips are brought into partial, and not
as in P and B into complete approximation, and a current of air is
driven through the narrowed opening. F is uttered without any
accompanying vibration of the vocal cords, i.e. without voice. With
voice it becomes V.

The sibilant S is formed by a rush of air past an obstruction
caused by the partial closure of the teeth, the front of the tongue

42—2

660 CONSONANTS. [BOOK in.

being depressed at the same time ; and S accompanied with vibra-
tions of the vocal cords becomes Z.

In Sh the dorsal surface of the tongue is raised so as to narrow
the passage between that organ and the palate for a considerable
portion of its length.

Th is formed by placing the tongue between the two partially
open rows of teeth ; and the hard and soft Th bear to each other
the same relation as do P and B.

L is produced when the passage is closed in the middle by
pressing the tip of the tongue against the hard palate and the air
is allowed to escape at the sides of the tongue.

When the constriction in an aspirate is formed by the approxi-
mation of the root of the tongue to the soft palate, we have the
guttural CH (as in loch) without voice and GH (as in lough) with
voice.

3. Resonants or Nasals. In these, all of which must have
vibrations of the vocal cords as a basis, the usual passage through
the mouth is closed either in a labial, dental, or guttural, fashion
and the peculiar character is given to the sound by the nasal
chambers acting as a resonance cavity. Thus in M, the passage is
closed by the approximation of the lips, in N, by the approximation
of the tongue to the hard palate, and in NG by the approximation
of the root of the tongue to the soft palate.

4. The various forms of R are often spoken of as vibratory, the
characteristic sounds being caused by the vibration of some or
other of the parts forming a constriction in the vocal passage.
Thus the ordinary R is produced by vibrations of the point of the
tongue elevated against the hard palate, the guttural R by the
vibrations of the uvula or other parts of the walls of the pharynx ;
and in some languages there seems to be an R produced by the
vibrations of the lips.

H is caused by the rush of air through the widely open glottis.
When, in sounding a vowel, the sound coincides with a sudden
change in the position of the vocal cords from one of divergence to
one of approximation, the vowel is pronounced with the spiritus
asper. When the vocal cords are brought together before the
blast of air begins, the vowel is pronounced with the spiritus lenis.
The Arabic H is produced by closing the rima vocalis, the epi-
glottis and false vocal cords being depressed, and sending a blast of
air through the rima respiratoria.

On many of the above points however, there are great dif-
ferences of opinion, the discussion of which as well as of other more
rare consonantal sounds would lead us too far away from the
purpose of this book. The following tabular statement must
therefore be regarded as introduced for convenience only.

CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 661

EXPLOSIVES. Labials, without voice, P.

„ with voice, B.

Dentals, without voice, T.

„ with voice, D.

Gutturals, without voice, K (hard C).

„ with voice, G (hard).

ASPIRATES. Labials, without voice, F.

„ with voice, V.

Dentals, without voice, L.

S. (soft C),Sh,Th (hard).

„ with voice, Z, Zh (in azure, the

French j),Th(soft).

Gutturals, without voice, CH (as in loch).

„ with voice, GH (as in lough}.

RESONANTS. Labial, ; M.

Dental, N.

Guttural, NG.

VIBRATORY. Labial, not known in European speech.
Dental, R (common).
Guttural, R (guttural).

Whispering is speech without any employment of the vocal
cords, and is effected chiefly by the lips and tongue. Hence in
whispering the distinction between consonants needing and those
not needing voice, such as B and P, becomes for the most part lost.

SEC. 3. LOOOMOTOR MECHANISMS.

The skeletal muscles are for the most part arranged to act on
the bones and cartilages as on levers, examples of the first kind of
lever being rare, and those of the third kind, where the power
is applied nearer to the fulcrum than is the weight, being more
common than the second. This arises from the fact that the
movements of the body are chiefly directed to moving com-
paratively light weights through a great distance, or through a
certain distance with great precision, rather than to moving heavy
weights through a short distance. The fulcrum is generally
supplied by a (perfect or imperfect) joint, and one end of the
acting muscle is made fast by being attached either to a fixed
point, or to some point rendered fixed for the time being by
the contraction of other muscles. There are few movements of
the body in which one muscle only is concerned ; in the majority
of cases several muscles act together in concert; nearly all our
movements are coordinate movements. Where gravity or the
elastic reaction of the parts acted on does not afford a sufficient
antagonism to the contraction of a muscle or group of muscles,
the return to the condition of equilibrium is provided for by the
action either elastic or contractile of a set of antagonistic muscles ;
this is seen in the case of the face.

The erect posture, in which the weight of the body is borne by
the plantar arches, is the result of a series of contractions of the
muscles of the trunk and legs, having for their object the keeping
the body in such a position that the line of gravity fails within
the area of the feet. That this does require muscular exertion

CHAP. VIL] SPECIAL MUSCULAR MECHANISMS. 663

is shewn by the facts, that a person when standing perfectly at
rest in a completely balanced position falls when he becomes
unconscious, and that a dead body cannot be set on its feet.
The line of gravity of the head falls in front of the occipital
articulation, as is shewn by the nodding of the head in sleep.
The centre of gravity of the combined head and trunk lies at
about the level of the ensiform cartilage, in front of the tenth
dorsal vertebra, and the line of gravity drawn from it passes
behind a line joining the centres of the two hip-joints, so that the
erect body would fall backward were it not for the action of the
muscles passing from the thighs to the pelvis assisted by the
anterior ligaments of the hip-joints. The line of gravity of the
combined head, trunk and thighs falls moreover a little behind
the knee-joints, so that some, though little, muscular exertion is
required to prevent the knees from being bent. Lastly, the line of
gravity of the whole body passes in front of the line drawn
between the two ankle-joints, the centre of gravity of the whole
body being placed at the end of the sacrum ; hence some exertion
of the muscles of the calves is required to prevent the body falling
forwards.

In walking, there is in each step a moment at which the body
rests vertically on the foot of one, say the right leg, while the other,
the left leg, is inclined obliquely behind with the heel raised and
the toe resting on the ground. The left leg, slightly flexed to avoid
contact with the ground, is then swung forward like a pendulum
the length of the swing or step being determined by the length of
the leg ; and the left toe * is brought to the ground. On this left
toe as a fulcrum, the body is moved forward, the centre of gravity
of the body describing a curve the convexity of which is upward
and the left leg necessarily becoming straight and rigid. As the
body moves forward, a point will be reached similar to that with
which we supposed the step to be started, the body resting
vertically on the left foot, and the right leg being directed behind
in an oblique position. The movement on the left foot however
carries the body beyond this point, and in doing so swings the
right leg forward until it is the length of a step in advance of its
previous position, and its toe in turn forms a fulcrum on which the
body, and with it the left leg, is again swung forward. Hence
in successive steps the centre of gravity, and with it the top of the
head, describes a series of consecutive curves, with their convexities
upwards, very similar to the line of flight of many birds.

Since in standing on both feet the line of gravity falls between
the two feet, a lateral displacement of the centre of gravity is
necessary in order to balance the body on one foot. Hence in
walking the centre of gravity describes not only a series of vertical,

1 This indicates perhaps what should be done rather than the actual practice;
most people put the heel to the ground first, the contact with the toe coming later.

664 LOCO MOTOR MECHANISMS. [BOOK m.

bat also a series of horizontal curves, inasmuch as at each step the
line of gravity is made to fall alternately on each standing foot.
While the left leg is swinging, the line of gravity falls within the
area of the right foot, and the centre of gravity is on the right side
of the pelvis. As the left foot becomes the standing foot, the
centre of gravity is shifted to the left side of the pelvis. The
actual curve described by the centre of gravity is therefore a
somewhat complicated one, being composed of vertical and
horizontal factors. The natural step is the one which is de-
termined by the length of the swinging leg, since this acts as
a pendulum; and hence the step of a long-legged person is
naturally longer than that of a person with short legs. The
length of the step however may be diminished or increased by a
direct muscular effort, as when a line of soldiers keep step in spite
of their having legs of different lengths. Such a mode of marching
must obviously be fatiguing, inasmuch as it involves an unnecessary
expenditure of energy.

In slow walking there is an appreciable time during which,
while one foot is already in position to serve as a fulcrum, the
other, swinging, foot has not yet left the ground. In fast walking
this period is so much reduced, that one foot leaves the ground the
moment the other touches it ; hence there is practically no period
during which both feet are on the ground together.

When the body is swung forward on the one foot acting as a
fulcrum with such energy that this foot leaves the ground before
the other, swinging, foot has reached the ground, there being
an interval during which neither foot is on the ground, the person
is said to be running, not walking.

In jumping this propulsion of the body takes place on both feet
at the same time ; in hopping it is effected on one foot only.

The locomotion of four-footed animals is necessarily more com-
plicated than that of man. The simple walk, such as that of the
horse, is executed in four times, with a diagonal succession : thus,
right fore leg, left hind leg, left fore leg, right hind leg. In the
amble, such as that of the camel, the two feet of the same side are
put down at one and the same time, this movement being followed
by a similar movement of the other two legs ; it corresponds there-
fore very closely to human walking. In the trot, which corresponds
to human running, the two diagonally opposite feet are brought to
the ground at the same time, and the body is propelled forwards on
them. Concerning this however, as well concerning the still more
complicated gallop and canter observers are not agreed and much
discussion has arisen.

The other problems connected with the action of the various
skeletal muscles of the body are too special to be considered here.

BOOK IV.

THE TISSUES AND MECHANISMS OF REPRODUCTION,

THE TISSUES AND MECHANISMS OF REPRODUCTION.

MANY of the individual constituent parts of the body are capable
of reproduction, i.e. they can give rise to parts like themselves; or
they are capable of regeneration, i.e. their places can be taken by
new parts more or less closely resembling themselves. The ele-
mentary tissues undergo during life a very large amount of re-
generation. Thus the old epithelium scales which fall away from
the surface of the body are succeeded by new scales from the
underlying layers of the epidermis ; old blood-corpuscles give place
to new ones ; worn-out muscles, or those which have failed from
disease, are renewed by the accession of fresh fibres; divided nerves
grow again ; broken bones are united ; connective tissue seems to
disappear and appear almost without limit ; new secreting cells
take the place of the old ones which are cast off; in fact, with the
exception of some cases, such as cartilage, and these doubtful ex-
ceptions, all those fundamental tissues of the body, which do not
form part of highly differentiated organs, are, within limits fixed
more by bulk than by anything else, capable of regeneration.
That regeneration by substitution of molecules, which is the
basis of all life, is accompanied by a regeneration by substitution
of mass.

In the higher animals regeneration of whole organs and mem-
bers, even of those whose continued functional activity is not
essential to the well-being of the body, is never witnessed, though
it may be seen in the lower animals ; the digits of a newt may be
restored by growth, but not those of a man. And the repair
which follows even partial destruction of highly differentiated
organs, such as the retina, is in the higher animals very imperfect.

668 TISSUES OF REPRODUCTION. [BOOK iv.

In the higher animals the reproduction of the whole individual
can be effected in no other way than by the process of sexual
generation, through which the female representative element or
ovum is, under the influence of the male representative or sperma-
tozoon, developed into an adult individual.

We do not purpose to enter here into any of the morphological
problems connected with the series of changes through which the
ovum becomes the adult being; or into the obscure biological
inquiry as to how the simple all but structureless ovum contains
within itself, in potentiality, all its future developments, and as to
what is the essential nature of the male action. These problems
and questions are fully discussed elsewhere ; they do not properly
enter into a work on physiology, except under the view that all
biological problems are, when pushed far enough, physiological
problems. We shall limit ourselves to a brief survey of the more
important physiological phenomena attendant on the impregnation
of the ovum, and on the nutrition and birth of the embryo.

CHAPTER I.

MENSTRUATION.

FROM puberty, which occurs at from 13 to 17 years of age, to the
climacteric, which arrives at from 45 to 50 years of age, the human
female is subject to a monthly discharge of ova from the ovaries,
accompanied by special changes, not only in those organs but also
in the Fallopian tubes and uterus, as well as by general changes in
the body at large, the whole constituting 'menstruation.' The
essential event in menstruation is the escape of an ovum from its
Graaffian follicle. The whole ovary at this time becomes con-
gested, and the ripe follicle bulges from its surface. The most
projecting portion of the wall of the follicle, which has previously
become excessively thin, is now ruptured, and the ovum, which
having left its earlier position, is lying close under the projecting
surface of the follicle, escapes, together with the cells of the discus
proligerus, into the Fallopian tube. How the entrance of the
ovum into the Fallopian tube is secured is not exactly known.
Some maintain that the ovary is grasped by the trumpet- shaped
fimbriated mouth of the Fallopian tube, itself turgid and con-
gested ; the movements necessary to bring this about being effected
by the plain muscular fibres present in the mouth of the tube.
Others, rejecting this view, and asserting that the turgescence
of the tube does not occur until after the ovum has become
safely lodged in the tube, suggests that the ovum is carried in the
proper direction by currents in the peritoneal cavity set up by the
action of the ciliated epithelium lining the tube, currents whose
direction and strength seem, as shewn by experiment, to be
adequate to carry into the uterus particles present in the perito-
neal fluid. Arrived in the tube, the ovum travels downwards, very

670 MENSTRUATION. [BOOK iv.

slowly, by the action probably of the cilia lining the tube, though
possibly its progress may occasionally be assisted by the peristaltic
contractions of the muscular walls. The stay of the ovum in the
Fallopian tube may extend to several days. There is an effusion of
blood into the ruptured follicle, which is subsequently followed by
histological changes in the coats of the follicle resulting in a corpus
luteum. The discharge of the ovum is accompanied not only by a
congestion or erection of the ovary and Fallopian tube, but also by
marked changes in the uterus, especially in the uterine mucous
membrane. While the whole organ becomes congested and en-
larged, the mucous membrane, and especially the uterine glands,
are distinctly hypertrophied. The swollen internal surface is
thrown into folds which almost obliterate the cavity ; and a
h^emorrhagic discharge, often considerable in extent, constituting
the menstrual or catamenial flow, takes place from the greater
part of its surface. The blood as it passes through the vagina
becomes somewhat altered by the acid secretions of that passage,
and when scanty coagulates but slightly ; when the flow however is
considerable, distinct clots may make their appearance. The
swollen and hypertrophied mucous membrane then undergoes a
rapid degeneration, and is shed, passing away sometimes in distinct
masses, forming the latter part of the menstrual flow. The loss of
the mucous membrane is so complete, that the bases only of the
uterine glands are left, and from the epithelial cells lining these
the regeneration of the new membrane is said to take place. It is
not certain that menstruation, in the human subject at all events,
is always accompanied by a discharge of an ovum ; indeed cases
have been recorded in which menstruation continued after what
appeared to be complete removal of both ovaries. And it seems
probable also that under certain circumstances, ex. gr. coitus, a dis-
charge of an ovum may take place at other times than at the
menstrual period. Since however the time during which both the
ovum and the spermatozoon may remain in the female passages
alive and functionally capable is considerable, probably extending
to some days, coitus effected either some time after or some time
before the menstrual escape of an ovum might lead to impregna-
tion and subsequent development of an embryo; hence the fact
that impregnation may follow upon coitus at some time after or
before menstruation is no very cogent argument in favour of the
view that such a coitus has caused an independent escape of an
ovum. The escape of the Ovum is said to precede, rather than
coincide with or follow, the catamenial flow. If no spermatozoa
come in contact with the ovum it dies, the uterine membrane
returns to its normal condition, and no trace of the discharge of an
ovum is left, except the corpus luteum in the ovary.

It is obvious that in these phenomena of menstruation we have
to deal with complicated reflex actions affecting not only the
vascular supply but, apparently in a direct manner, the nutritive

CHAP, i.] MENSTRUATION. 671

changes of the organs concerned. Our studies on the nervous
action of secretion render it easy for us to conceive in a general
way how the several events are brought about. It is no more
difficult to suppose that the stimulus of the enlargement of a
Graaffian follicle causes nutritive as well as vascular changes in the
uterine mucous membrane, than it is to suppose that the stimulus
of food in the alimentary canal causes those nutritive changes in
the salivary glands or pancreas which constitute secretion. In the
latter case we can to some extent trace out the chain of events ; in
the former case we hardly know more than that the maintenance
of the lumbar cord is sufficient, as far as the central nervous
system is concerned, for the carrying on of the work. In the case
of a dog in which the spinal cord had been completely divided in
the dorsal region while the animal was as yet a mere puppy, 'heat'
or menstruation took place as usual.

CHAPTER II.

IMPREGNATION.

IN coitus the discharge of the semen containing the spermatozoa is
most probably effected by means of the peristaltic contractions of
the vesiculse seminales and vasa deferentia. assisted by rhythmical
contractions of the bulbo-cavernosus muscle, the whole being a
reflex act, the centre of which appears to be in the lumbar spinal
cord. In the dog, emission of semen can be brought about by
stimulation of the glans penis after complete division of the spinal
cord in the dorsal region. The emission of semen is preceded by
an erection of the penis. This we have already seen, p. 210, is in
part at least due to an increased vascular supply brought about by
means of the nervi erigentes; it is probable, however, that the
condition is further secured by a compression of the efferent veins
of the corpora cavernosa by means of smooth muscular fibres
present in those bodies. The semen being received into the female
organs, which are at the time in a state of turgescence resembling
the erection of the penis, but less marked, the spermatozoa find
their way into the Fallopian tubes, and here (probably in its upper
part) come in contact with the ovum. In the case of some animals
impregnation may take place at the ovary itself. The passage of
the spermatozoa is most probably effected mainly by their own
vibratile activity; but in some animals a retrograde peristaltic
movement travelling from the uterus along the Fallopian tubes has
been observed ; this might assist in bringing the semen to the
ovum, but inasmuch as these movements are probably parts of the
act of coitus and impregnation may be deferred till some time after
that event, no great stress can be laid upon them.

CHAP, ii.] IMPREGNATION. 673

As the result of the action of the spermatozoa on the ovum, the
latter, instead of dying as when impregnation fails, awakes to great
nutritive activity accompanied by remarkable morphological
changes ; it enlarges and develops into an embryo. No sooner, how-
ever, have these changes begun in the ovum than correlative changes,
brought about probably by reflex action, but at present most
obscure in their causation, take place in the uterus. The mucous
membrane of this organ, whether the coitus resulting in im-
pregnation be coincident with a menstrual period or not, becomes
congested, and a rapid growth takes place, characterized by a rapid
proliferation of the epithelial and subepithelial tissues. Unlike the
case of menstruation, however, this new growth does not give way
to immediate decay and haemorrhage, but remains; and may be
distinguished as a new temporary lining to the uterus, the so-called
decidua. Into this decidua the ovum, on its descent from the
Fallopian tube, in which it has probably already undergone some
developmental changes, is received; and in this it becomes em-
bedded, the new growth closing in over it. Meanwhile the rest of
the uterine structures, especially the muscular tissue, become also
much enlarged; as pregnancy advances a large number of new
muscular fibres are formed. As the ovum continues to increase in
size, it bulges into the cavity of the uterus, carrying with it the
portion of the decidua which has closed over it. Henceforward,
accordingly, a distinction is made in the now well-developed
decidua between the decidua reflexa, or that part of the membrane
which covers the projecting ovum, and the decidua vera, or the
rest of the membrane lining the cavity of the uterus, the two being
continuous round the base of the projecting ovum. That part of
the decidua which intervenes between the ovum and the nearest
uterine wall is frequently spoken of as the decidua serotina. As
the ovum developes into the foetus with its membranes, the decidua
reflexa becomes pushed against the decidua vera; about the end
of the third month, in the human subject, the two come into com-
plete contact all over, and ultimately the distinction between them
is lost. In the region of the decidua serotina the allantoic vessels
of the foetus develope a placenta. For an account of the various
changes by which these events are brought about, as well as of the
history of the embryo itself, we must refer the reader to anatomical
treatises.

IT. 43

CHAPTER III.

THE NUTRITION OF THE EMBRYO.

DURING the development of the chick within the hen's egg the
nutritive material needed for the growth first of the blastoderm,
and subsequently of the embryo, is supplied by the yolk, while the
oxygen of the air passing freely through the porous shell, gains
access to all the tissues both of the embryo and yolk, either directly
or by the intervention of the allantoic vessels. The mammalian
embryo, during the period which precedes the extension of the
allantoic vessels into the cavities of the uterine walls to form the
placenta, must be nourished by direct diffusion, first from the con-
tents of the Fallopian tube, and subsequently from the decidua ;
and its supply of oxygen must come from the same sources. All
analogy would lead us to suppose that, from the very first, oxida-
tion is going on in the blastodermic and embryonic structures ; but
the amount of oxygen actually withdrawn from without is probably
exceedingly small in the early stages, seeing that nearly the whole
energy of the metabolism going on is directed to the building up
of structures, the expenditure of energy in the form of either heat
or external work being extremely small. The marked increase of
bulk which takes place during the conversion of the mulberry mass
into the blastodermic vesicle, shews that at this epoch a relatively
speaking large quantity of water at least, and probably of nutritive
matter, must pass from without into the ovum ; and subsequently,
though the blastoderm and embryo may for some time draw the
material for their continued construction at first hand from the
yolk-sac or umbilical vesicle, both this and they continue probably
until the allantois is formed to receive fresh material from the
mother by direct diffusion.

As the thin-walled allantoic vessels come into closer and fuller

CHAP, in.] THE NUTRITION OF THE EMBRYO. 675

connection with the maternal uterine sinuses, until at last in the
fully formed placenta the former are freely bathed in the blood
streaming through the latter, the nutrition of the embryo becomes
more and more confined to this special channel. The blood of the
foetus flowing along the umbilical arteries effects exchanges with
the venous blood of the mother, and leaves the placenta by the
umbilical vein richer in oxygen and nutritive material and poorer
in carbonic acid and excretory products than when it issued from
the foetus.

As far as the gain of oxygen and the loss of carbonic acid are
concerned these are the results of simple diffusion. Venous blood,
as we have already seen, always contains a quantity of oxyhaemo-
globin, and the quantity of this substance present in the blood of
the uterine veins is sufficient to supply all the oxygen that the em-
bryo needs ; the blood of the foetus, containing less oxygen than
even the venous blood of the mother, will take up a certain though
small quantity. The foetal blood travelling in the umbilical artery
must, in proportion to the extent of the nutritive changes going on
in the embryo, possess a higher carbonic tension than that in the
umbilical vein or uterine sinus ; and by diffusion gets rid of this
surplus during its stay in the placenta. The blood in the umbilical
arteries and veins is therefore, relatively speaking, venous and arte-
rial respectively, though the small excess of oxyhsemoglobin in the
blood of the umbilical vein is insufficient to give it a distinctly arterial
colour, or to distinguish it as sharply from the more venous blood
of the umbilical artery, as is ordinary arterial from ordinary venous
blood. Thus the foetus breathes by means of the maternal blood,
in the same way that a fish breathes by means of the water in which
it dwells.

The blood of the foetus is very poor in haemoglobin correspon-
ding to its low oxygen consumption. When the mother is asphyxi-
ated, the foetus is asphyxiated too, the oxygen of the latter passing
back again into the blood of the former ; and the asphyxia thus pro-
duced in the foetus is much more rapid than that which results
when the oxygen is used up by the tissues of the foetus alone,
as when the umbilicus is ligatured and the foetus not allowed to
breathe.

If oxygen and carbonic acid thus pass by diffusion to and from
the mother and the foetus, one might fairly expect that diffusible
salts, proteids, and carbohydrates would be conveyed to the latter,
and diffusible excretions carried away to the former, in the same
way; and if fats can pass directly into the portal blood during
ordinary digestion, there can be no reason for doubting that this
class of food-stuffs also would find its way to the foetus through the
placental structures. We do know from experiment that diffusible
substances will pass both from the mother to the foetus, and from
the foetus to the mother ; but we have no definite knowledge as to
the exact form and manner in which, during normal intra-uterine

43—2

676 FCETAL METABOLISM, [BOOK iv.

life, nutritive materials are conveyed to or excretions conveyed from
the growing young. The placenta is remarkable for the great de-
velopment of cellular structures, apparently of an epithelial nature,
on the border-land between the maternal and foetal elements ; and
it has been suggested that these form a temporary digestive and
secretory (excretory) organ. But we have no exact knowledge of
what actually does take place in these structures. From the coty-
ledons of ruminants may be obtained a white creamy-looking fluid,
which from many features of its chemical composition might be
almost spoken of as a 'uterine milk/

Speaking broadly, the foetus lives on the blood of its mother,
very much in the same way as all the tissues of any animal live
on the blood of the body of which they are the parts.

For a long time all the embryonic tissues are 'protoplasmic' in
character; that is, the gradually differentiating elements of the
several tissues remain still embedded, so to speak, in undifferen-
tiated protoplasm ; and during this period there must be a general
similarity in the metabolism going on in various parts of the body.
As differentiation becomes more and more marked, it obviously
would be an economical advantage for partially elaborated material
to be stored up in various foetal tissues, so as to be ready for
immediate use when a demand arose for it, rather than for a
special call to be made at each occasion upon the mother for
comparatively raw material needing subsequent preparatory changes.
Accordingly, we find the tissues of the foetus at a very early period
loaded with glycogen. The muscles are especially rich in this
substance, but it occurs in other tissues as well. The abundance
of it in the former may be explained partly by the fact that they
form a very large proportion of the total mass of the foetal body, and
partly by the fact that, while during the presence of the glycogen
they contain much undifferentiated protoplasm, they are exactly
the organs which will ultimately undergo a large amount of
differentiation, and therefore need a large amount of material for
the metabolism which the differentiation entails. It is not until
the later stages of intra-uterine life, at about the fifth month,
when it is largely disappearing from the muscles, that the glycogen
begins to be deposited in the liver. By this time histological
differentiation has advanced largely, and the use of the glycogen
to the economy has become that to which it is put in the ordinary
life of the animal ; hence we find it deposited in the usual place.
Besides being present in the foetal, glycogen is found also in the
placental structures; but here probably it is of use, not for the
foetus, but for the nutrition and growth of the placental structures
themselves. We do not know how much carbohydrate material
finds its way into the umbilical vein; and we cannot therefore
state what is the source of the foetal glycogen ; but it is at least
possible, not to say probable, that it arises, in part at all events,
from a splitting up of proteid material.

CHAP, in.] THE NUTRITION OF THE EMBRYO. 677

Concerning the rise and development of the functional activities
of the embryo, our knowledge is almost a blank. We know
scarcely anything about the various steps by which the primary
fundamental qualities of the protoplasm of the ovum are differen-
tiated into the complex phenomena which we have attempted in
this book to expound. We can hardly state more than that while
muscular contractility becomes early developed, and the heart
probably, as in the chick, beats even before the blood-corpuscles
are formed, movements of the foetus do not, in the human subject,
become pronounced until after the fifth month; from that time
forward they increase and subsequently become very marked.
They are often spoken of as reflex in character ; but only a pre-
conceived bias would prevent them from being regarded as largely
automatic. The digestive functions are naturally, in the absence
of all food from the alimentary canal, in abeyance. Though
pepsin may be found in the gastric membrane at about the fourth
month, it is doubtful whether a truly peptic gastric juice is
secreted during intra-uterine life ; trypsin appears in the pancreas
somewhat later, but an amylolytic ferment cannot be obtained
from that organ till after birth. The date however at which these
several ferments make their appearance in the embryo appears to
differ in different animals. The excretory functions of the liver
are developed early, and about the third month bile-pigment and
bile-salts find their way into the intestine. The quantity of bile
secreted during intra-uterine life, accumulates in the intestine and
especially in the rectum, forming, together with the smaller secre-
tion of the rest of the canal, and some desquamated epithelium,
the so-called meconium. Bile salts, both unaltered and variously
changed, the usual bile pigments, and cholesterin, are all present
in the meconium. The distinct formation of bile is an indication
that the products of foetal metabolism are no longer wholly carried
off by the maternal circulation ; and to the excretory function of
the liver there are now added those of the skin and kidney. The
substances escaping by these organs find their way into the
allantois or into the amnion, according to the arrangement of the
foetal membranes in different classes of animals; in both these
fluids urea or allied bodies have been found as well as the ordinary
saline constituents ; the latter may or may not have been actually
secreted. From the allantoic fluid of ruminants the body allan-
toin has been obtained, and human and other amniotic fluids have
been found to contain urea. It is maintained by some however
that the fluid in the amnion is secreted by the mother and that
hence the substances present in it are of maternal origin.

About the middle of intra-uterine life, when the foetal circula-
tion is in full development, the blood flowing along the umbilical
vein is carried chiefly by the ductus venosus into the inferior vena
cava and so into the right auricle. Thence it is directed by the
valve of Eustachius through the foramen ovale into the left

678 F(ETAL CIRCULATION. [BOOK iv.

auricle, passing from which into the left ventricle it is driven into
the aorta. Part of the umbilical blood, however, instead of passing
directly to the inferior cava, enters by the portal vein into the
hepatic circulation, from which it returns to the inferior cava by
the hepatic veins. The inferior cava also contains blood coming
from the lower limbs and lower trunk. Hence the blood which
passing from the right auricle into the left auricle through the
foramen ovale is distributed by the left ventricle through the
aortic arch, though chiefly blood coming direct from the placenta,
is also blood which on its way from the placenta has passed
through the liver and blood derived from the tissues of the lower
part of the body of the foetus. The blood descending as foetal
venous blood from the head and limbs by the superior vena cava
does not mingle with that of the inferior vena cava, but falls into
the right ventricle, from which it is discharged through the ductus
arteriosus (Botalli) into the aorta, below the arch, whence it flows
partly to the lower trunk and limbs, but chiefly by the umbilical
arteries to the placenta. A small quantity only of the contents
of the right ventricle finds its way into the lungs. Now the blood
which comes from the placenta by the umbilical vein direct into
the right auricle is, as far as the foetus is concerned, arterial blood ;
and the portion of umbilical blood which traverses the liver
probably loses at this epoch very little oxygen during its transit
through that gland, the liver being at this period a simple ex-
cretory rather than an actively metabolic organ. Hence the blood
of the inferior vena cava, though mixed, is on the whole arterial
blood; and it is this blood which is sent by the left ventricle
through the arch of the aorta into the carotid and subclavian
arteries. Thus the head of the foetus is provided with blood
comparatively rich in oxygen. The blood descending from the
head and upper limbs by the superior vena cava is distinctly
venous ; and this passing from the right ventricle by the ductus
arteriosus is driven along the descending aorta, and together with
some of the blood passing from the left ventricle round the aortic
arch falls into the umbilical arteries and so reaches the placenta.
The fcetal circulation then is so arranged, that while the most
distinctly venous blood is driven by the right ventricle back to the
placenta to be oxygenated, the most distinctly arterial (but still
mixed) blood is driven by the left ventricle to the cerebral struc-
tures, which have more need of oxygen than have the other tissues.
Contrary to what takes place afterwards, the work of the right
ventricle is in the foetus greater than that of the left; and, ac-
cordingly, that greater thickness of the left ventricular walls,
so characteristic of the adult, does not become marked until close
upon birth.

In the later stages of pregnancy the mixture of the various
kinds of blood in the right auricle increases preparatory to the
changes taking place at birth. But during the whole time of

CHAP. HI.] THE NUTRITION OF THE EMBRYO. 679

mtra-uterine life the amount of oxygen in the blood passing from
the aortic arch to the medulla oblongata is sufficient to prevent
any inspiratory impulses being originated in the medullary
respiratory centre. This during the whole period elapsing between
the date of its structural establishment, or rather the consequent
full development of its irritability, and the epoch of birth, remains
dormant; the oxygen-supply to the protoplasm of its nerve-cells
is never brought so low as to set going the respiratory molecular
explosions. As soon however as the intercourse between the
maternal and umbilical blood is interrupted by separation of the
placenta or by ligature of the umbilical cord, or when, as by the
death of the mother, the umbilical blood ceases to be replenished
with oxygen by the maternal blood, or when in any other way
blood of sufficiently arterial quality ceases to find its way by the
left ventricle to the medulla oblongata, the supply of oxygen in
the respiratory centre sinks, and when the fall has reached a
certain point an impulse of inspiration is generated and the foetus
for the first time breathes. This action of the respiratory centre
may be assisted by adjuvant impulses reaching the centre along
various afferent nerves, such as those started by exposure of the
body to the air, or to cold ; but these are subordinate, not essential.
A retarded first breath may be hurried on by dashing water on the
face of the new-born infant; but on the other hand, the foetus,
upon the cessation of the placental circulation, will make its first
respiratory movements while it is still invested with the intact
membranes and thus sheltered from the air and indeed from all
external stimuli.

Before this first breath is taken the pulmonary alveoli contain
no .air, and the lungs when thrown into water sink at once; they
are then said to be 'atelectatic.' After the first breath, the alveoli
contain air and the lungs float when thrown into water. A
striking difference however exists between the lungs of a new-born
infant and those of an older person. When the pleural cavity of
the former is opened, the lungs do not collapse, no air is driven
out by the trachea; that partial distension of the lungs, and
negative thoracic pressure, which we studied (p. 367) in treating of
respiration, appears not to be established immediately upon birth.
That portion of the residual air (p. 315) in the lungs of the adult,
which, remaining after the most forcible expiration, is still driven
from the lungs upon the pleural cavity being laid open, and which
might be called 'collapse air,' is wanting in the new-born infant.
When the change from one condition to the other is effected is
not at present known ; it may possibly arise from the growth of
the chest outstripping that of the lungs.

When the first breath is taken, as under normal circumstances
it is, with free access to the atmosphere, and the lungs become
filled with air, the scanty supply of blood which at the moment
was passing from the right ventricle along the pulmonary artery

680 F(ETAL CIRCULATION. [BOOK iv.

returns to the left auricle brighter and richer in oxygen than ever
was the foetal blood before. With the diminution of resistance in
the pulmonary circulation caused by the expansion of the thorax,
a larger supply of blood passes into the pulmonary artery instead
of into the ductus arteriosus, and this derivation of the contents
of the right ventricle increasing with the continued respiratory
movements, the current through the latter canal at last ceases
altogether, and its channel shortly after birth becomes obliterated.
Corresponding to the greater flow into the pulmonary artery, a
larger and larger quantity of blood returns from the pulmonary
veins into tiie left auricle. At the same time the current through
the ductus venosus from the umbilical vein having ceased, the flow
from the inferior cava has diminished ; and the blood of the right
auricle finding little resistance in the direction of the ventricle,
which now readily discharges its contents into the pulmonary
artery, but finding in the left auricle, which is continually being
filled from the lungs, an obstacle to its passage through the fora-
men ovale, ceases to take that course. Any return of blood from
the now vigorous and active left auricle into the right auricle
is prevented by the valve which, during the latter stages of intra-
uterine life, has been growing up in the left auricle over the
foramen ovale. At birth the edge of this valve is to a certain
extent free so that, in case of an emergency, as when the pulmonary
circulation is obstructed, a direct escape of blood into the left
auricle from the over-burdened right auricle can take place.
Eventually, in the course of the first year, adhesion takes place,
and the separation of the two auricles becomes complete. With
its larger supply of blood and greater work the left ventricle
acquires the greater thickness characteristic of it during life. Thus
the foetal circulation, in consequence of the respiratory movements
to which its interruption gives rise, changes its course into that
characteristic of the adult.

CHAPTER IV.
PARTURITION.

IN spite of the increasing distension of its cavity, the uterus remains
quiescent, as far as any marked muscular contractions are concerned,
until a certain time has been run. In the human subject the period
of gestation generally lasts from 275 to 280 days, i.e. about 40
weeks, the general custom being to expect parturition at about
280 days from the last menstruation. Seeing that, in many cases,
it is uncertain whether the ovum which developes into the embryo
left the ovary at the menstruation preceding or succeeding coitus,
or, as some have urged, independent of menstruation, by reason of
the coitus itself, an exact determination of the duration of preg-
nancy is impossible.

In the cow the period of gestation is about 280 days, in the mare
about 350, sheep about 150 days, dog about 60 days, rabbit about 30
days.

The extrusion of the foetus is brought about, partly by rhyth-
mical contractions of the uterus itself, and partly by a pressure
exerted by the contraction of the abdominal muscles, similar to that
described in defaecation. The contractions of the uterus are the
first to appear, and their first effect is to bring about a dilation of
the os uteri; it is not till the later stages of labour, while the foetus
is passing into the vagina, that the abdominal muscles are brought
into play.

The whole process of parturition may be broadly considered as
a reflex act, the nervous centre being placed in the lumbar cord.
In a dog, whose dorsal cord had been completely severed, parturi-
tion took place as usual ; and the fact that, in the human subject,

682 UTERINE CONTRACTIONS. [BOOK iv.

labour will progress quite naturally while the patient is unconscious
from the administration of chloroform, shews that in woman also
the whole matter is an involuntary action, however much it may be
assisted by direct volitional efforts. That the uterus is capable of
being thrown into contractions through reflex action, excited by
stimuli applied to various afferent nerves, is well known. The con-
traction of the uterus, which is so necessary for the prevention of
haemorrhage after delivery, may frequently be brought about by
exerting pressure or by dashing cold water on the abdomen, by the
introduction of foreign bodies into the vagina, and especially by
putting the child to the nipple. And we learn from experiments
on animals that rhythmic contractions of the uterus resemblingr at
least those of parturition may be brought about in a reflex manner
by stimulating various afferent nerves. Similar movements may
be induced by direct stimulation of the spinal cord along its whole
length, as well as of various parts of the brain; but there are
reasons for thinking that in these cases, the impulses started in the
brain, and upper part of the spinal cord, produce their effects by
working upon what may be called a 'parturition' centre in the
upper lumbar regions of the cord. And it would appear that' the
uterine contractions which are induced by such drugs as ergot as
well as those caused by asphyxia, are, at all events in part, brought
about by the agency of the same lumbar centre. From this centre
the paths for the efferent impulses appear (in the dog) to be two-
fold: one along sympathetic tracts, by nerves passing from the
inferior mesenteric ganglion to the hypogastric plexus, and the
other along spinal tracts by branches of the sacral nerves to the
same plexus. It is stated that the characters of the movements
induced by stimulating these two tracts are somewhat different
and moreover that the sympathetic tract is vaso-constrictor and the
spinal tract vaso-dilator in nature; but the matter has not yet been
fully worked out.

We are however hardly justified in considering the rhythmical
contractions of the uterus during parturition as simple reflex acts
excited by the presence of the foetus. We are utterly in the dark
as to why the uterus, after remaining apparently perfectly quiescent
(or with contractions so slight as to be with difficulty appreciated)
for months, is suddenly thrown into action, and within it may be a
few hours or even less gets rid of the burden it has borne with
such tolerance for so long a time; none of the various hypotheses
which have been put forward can be considered as satisfactory.
And until we know what starts the active phase, we shall remain
in ignorance of the exact manner in which the activity is brought
about. The peculiar rhythmic character of the contractions, each
'pain' beginning feebly, rising to a maximum, then declining, and
finally dying away altogether, to be succeeded after a pause by a
similar pain just like itself, pain following pain like the tardy
long-drawn beats of a slowly beating heart, suggests that the cause

CHAP, iv.] PARTURITION. 683

of the rhythmic contraction is seated, like that of the rhythmic beat
of the heart, in the organ itself. And this view is supported by the
fact that contractions of the uterus, similar to those of parturition,
have been observed in animals even after complete destruction of
the spinal cord ; and the movements induced by asphyxia seem in
part, and those caused by some drugs such as ammonia, seem to
be wholly due to an intrinsic action of the uterus itself. Neverthe-
less general evidence supports the conclusion that, in a normal
state of things at all events, the contractions of the uterus, like
those of the lymph-hearts, are largely dependent on the spinal
cord.

The occurrence of contractions in consequence of an asphyxiated
condition of the blood, explains why when pregnant animals are
asphyxiated, an extrusion of the foetus frequently takes place. There
is no evidence however that the onset of labour is caused by a
gradual diminution of oxygen in the blood, reaching at last to a
climax. Nor are there sufficient facts to connect parturition with
any condition of the ovary resembling that of menstruation.

The action of the abdominal muscles in parturition is, on the
other hand, obviously a reflex act carried out by means of the spinal
cord, the necessary stimulus being supplied by the pressure of the
foetus in the vagina, or by the contractions of the uterus. Hence
the whole act of parturition may with reason be considered as a
reflex one.

Whether it be wholly a reflex or partly an automatic one, the
act can readily be inhibited by the action of the central nervous
system. Thus emotions are a very frequent cause of the progress
of parturition being suddenly stopped; as is well known, the
entrance into the bedroom of a stranger often causes for a time the
sudden and absolute cessation of 'labour' pains, which previously
may have been even violent. Judging from the analogy of mictu-
rition, between which and parturition there are many points of
resemblance, we may suppose that this inhibition of uterine con-
tractions is brought about by an inhibition of the centre in the
lumbar cord.

After the expulsion of the foetus, the foetal placenta separates
from the uterine walls, and is, together with the remnants of the
membranes, expelled after it. The uterus then falls into a firm
tonic contraction, similar to that of the emptied bladder, by which
means haemorrhage from the vessels torn by the separation of the
placenta is avoided. The lining membrane of the uterus is gradually
restored, the muscular elements are reduced by a rapid fatty de-
generation, and in a short time the whole organ has returned to its
normal condition.

CHAPTER V.

THE PHASES OF LIFE.

THE child has at birth, on an average, rather less than one-third
the maximum length, and about one-twentieth the maximum
weight, to which in future years it will attain.

The composition of the body of the new-born babe, as compared
with that of the adult, will be seen from the following table, in
which the details are more full than those given on p. 443.

Weight of organ in

adult, as compared

with that of new-born

babe taken as 1.

17
37
12
12
13-6

Weight of organ in percentage
of Body- weight

New-born babe.

Eye

•28

Brain

14-34

Kidneys

•88

Skin

11-3

Liver

4-39

Heart

•89

Stomach and|
Intestine j

2-53

Lungs

216

Skeleton

167

Muscles, &c.

23'4

Testicle

•037

Adult.

•028
2-37
•48
6'3
277
•52

2-34

2-01

15-35

43-1

•8

15
20

20
26
28
60

It will be observed that the brain and eyes are, relatively to
the whole body-weight, very much larger in the babe than in the
adult, as is also, though to a less extent, the liver. This dispro-
portion is a very marked embryonic feature, and as far as the brain

CHAP, v.] THE PHASES OF LIFE. 685

and eye are concerned at least, has a morphological or phylogenic,
as well as a physiological or teleological, significance. Inasmuch
as the smaller body has relatively the larger surface, the skin is
naturally proportionately greater in the babe. It is chiefly by the
accumulation of muscle or flesh, properly so called, that the child
acquires the bulk and weight of the man, the skeletal framework,
in spite of its being specifically lighter in its earlier cartilaginous
condition, maintaining throughout life about the same relative
weight.

The increase in stature is very rapid in early infancy,
proceeding however by decreasing increments. During or shortly
before puberty, there is again a somewhat sudden rise, with a
subsequent more steady but diminishing increase up to about
the twenty-fifth year. From thence to about fifty years of age the
height remains stationary, after which there may be a decrease,
especially in extreme old age.

The increase in weight is also very rapid at first, and proceed-
ing, like the height, with diminishing increments, may continue
till about the fortieth year. After the sixtieth year a decline
of variable extent is generally witnessed. It is a remarkable
fact, however, that in the first few days of life, so far from
there being an increase, there is an actual decrease of weight,
so that, even on the seventh day the weight still continues to be
less than at birth.

The saliva of the babe is active on starch, and its gastric juice,
unlike that of many new-born animals, has good peptic powers,
from which we may infer that its digestive processes in general are
identical with that of the adult ; but the faeces of the infant con-
tain, besides considerable quantity of undigested food (fat, casein
&c.), unaltered bile-pigment, and undecomposed bile-salts.

The heart of the babe (see Table, p. 684) is, relatively to its
body-weight, larger than the adult, and the frequency of the heart--
beat much greater, viz. about 130 or 140 per minute, falling to
about 110 in the second year, and about 90 in the tenth year.
Corresponding to the smaller bulk of the body, the whole circuit of
the blood system is traversed in a shorter time than in the adult
(12 seconds as against 22); and consequently the renewal of
the blood in the tissues is exceedingly rapid. The respiration of
the babe is quicker than that of the adult, being at first about 35
per minute, falling to 28 in the second year, to 26 in the fifth
year, and so onwards. The respiratory work, while it increases
absolutely as the body grows, is, relatively to the body-weight,
greatest in the earlier years. It is worthy of notice, that the ab-
sorption of oxygen is said to be relatively more active than the
production of carbonic acid ; that is to say, there is a continued
accumulation of capital in the form of a store of oxygen-holding
explosive compounds (see p. 349). This, indeed, is the striking
feature of infant metabolism. It is a metabolism directed largely

686 CHILDHOOD. [BOOK iv.

to constructive ends. The food taken represents, undoubtedly, so
much potential energy; but before that energy can assume a
vital mode, the food must be converted into tissue ; and, in such a
conversion, morphological and molecular, a large amount of energy
must be expended. The metabolic activities of the infant are
more pronounced than those of the adult, for the sake, not so much
of energies which are spent on the world without, as of energies
which are for a while buried in the rapidly increasing mass of flesh.
Thus the infant requires over and above the wants of the man, not
only an income of energy corresponding to the energy of the flesh
actually laid on, but also an income corresponding to the energy
used up in making that living sculptured flesh out of the dead amor-
phous proteids, fats, carbohydrates and salts, which serve as food.
Over and above this, the infant needs a more rapid metabolism to
keep up the normal bodily temperature. This, which is no less,
indeed slightly ('3°) higher, than that of the adult, requires a
greater expenditure, inasmuch as the infant with its relatively far
larger surface, and its extremely vascular skin, loses heat to a
proportionately much greater degree than does the grown-up man.
It is a matter of common experience that children are more
affected by cold than are adults.

This rapid metabolism is however not manifest immediately
upon birth. During the first few days, corresponding to the loss
of weight mentioned above, the respiratory activities of the tissues
are feeble; the embryonic habits seem as yet not to have been
completely thrown off, and, as was stated on p. 377, new- born
animals bear with impunity a deprivation of oxygen, which would
be fatal to them later on in life.

The quantity of urine passed, though scanty in the first two
days, rises rapidly at the end of the first week, and in youth the
quantity of urine passed is, relatively to the body-weight, larger
than in adult life. This may be, at least in quite early life, partly
due to the more liquid nature of the food, but is also in part the
result of the more active metabolism. For not only is the quantity
of urine passed, but also the amount of urea and some other
urinary constituents excreted, relatively to the body-weight,
greater in the child than in the adult. The presence of uric, of
oxalic, and according to some, of hippuric acids in unusual quantities
is a frequent characteristic of the urine of children. It is stated
that calcic phosphates, and indeed the phosphates generally, are
deficient, being retained in the body for the building up of the
osseous skeleton.

Associated probably with these constructive labours of the
growing frame is the prominence of the lymphatic system. Not
only are the lymphatic glands largely developed and more active
(as is probably shewn by their tendency to disease in youth), but
the quantity of lymph circulation is greater than in later years.
Characteristic of youth is the size of the thymus body, which

CHAP, v.] THE PHASES OF LIFE. 687

increases up to the second year, and may then remain for a while
stationary, but generally before puberty, has suffered a retro-
gressive metamorphosis, and frequently hardly a vestige of it
remains behind. The thyroid body is also relatively greater
in the babe than in the adult; the spleen, on the other
hand, which grows rapidly in early infancy, is not only absolutely,
but also relatively, greater in the adult. It need hardly be
said that the recuperative power of infancy and early youth is
very marked.

It would be beyond the scope of this work to enter into the
psychical condition of the babe or the child, and our knowledge
of the details of the working of the nervous system in infancy
is too meagre to permit of any profitable discussion. It is hardly
of use to say that in the young the whole nervous system is
more irritable or more excitable than in later years ; by which
we probably to a great extent mean that it is less rigid, less
marked out into what, in preceding portions of this work, we
have spoken of as nervous mechanisms. It may be mentioned
that stimulation of the various cerebral areas, in new-born animals,
does not give rise to the usual localized movements. The sense
of touch, both as regards pressure and temperature, appears
well developed in the infant, as does also the sense of taste,
and possibly, though this is disputed, that of smell. The pupil
(larger in the infant than in the man) acts fully, and Bonders
observed normal binocular movements of the eyes in an infant
less than an hour old. The eye is (in man) from the outset
fully sensitive to light, though of course visual perceptions are
imperfect. As regards hearing, on the other hand, very little
reaction follows upon sounds, i.e. auditory sensations seem to be
dull during the first few days of life ; this may be partly at least
due to absence of air from the tympanum and a tumid condition
of the tympanic mucous membrane. As the child grows up his
senses rapidly culminate, and in his early years he possesses a
general acuteness of sight, hearing, and touch, which frequently
becomes blunted as his psychical life becomes fuller. Children
however are said to be less apt at distinguishing colours than in
sighting objects ; but it does not appear whether this arises from
a want of perceptive discrimination or from their being actually
less sensitive to variations in hue. A characteristic of the nervous
system in childhood, the result probably of the more active meta-
bolism of the body, is the necessity for long or frequent and deep
slumber.

Dentition marks the first epoch of the new life. At about seven
months the two central incisors of the lower jaw make their way
through the gum, followed immediately by the corresponding teeth
in the upper jaw. The lateral incisors, first of the lower and then
of the upper jaw, appear at about the ninth month, the first molars
at about the twelfth month, the canines at about a year and a half,

688 PUBERTY. [BooK iv.

and the temporary dentition is completed by the appearance of the
second molars usually before the end of the second year.

About the sixth year the permanent dentition commences by
the appearance of the first permanent molar beyond the second
temporary molar; in the seventh year the central permanent
incisors replace their temporary representatives, followed in the
next year by the lateral incisors. In the ninth year the temporary
first molars are replaced by the first bicuspids, and in the tenth
year the second temporary molars are similarly replaced by the
second bicuspids. The canines are exchanged about the eleventh
or twelfth year, and the second permanent molars are cut about the
twelfth or thirteenth year. There is then a long pause, the third
or wisdom tooth not making its appearance till the seventeenth, or
even twenty-fifth year, or in some cases not appearing at all.

Shortly after the conclusion of the permanent dentition (the
wisdom teeth excepted) the occurrence of puberty marks the begin-
ning of a new phase of life ; and the difference between the sexes,
hitherto merely potential, now becomes functional. In both sexes
the maturation of the generative organs is accompanied by the
well-known changes in the body at large ; but the events are much
more characteristic in the typical female than in the aberrant male.
Though in the boy, the breaking of the voice and the rapid growth
of the beard which accompany the appearance of active spermato-
zoa, are striking features, yet they are after all superficial. The
curves of his increasing weight and height, and of the other events
of his economy, pursue for a while longer an unchanged course ; the
boy does not become a man till some years after puberty ; and the
decline of his functional manhood is so gradual that frequently it
ceases only when disease puts an end to a ripe old age. With the
occurrence of menstruation, on the other hand, at from thirteen to
seventeen years of age, the girl almost at once becomes a woman,
and her functional womanhood ceases suddenly at the climacteric
in the fifth decennium. During the whole of the child-bearing
period her organism is in a comparatively stationary condition.
While before the age of puberty up to about the eleventh or
twelfth year, the girl is lighter and shorter than the boy of the
same age, in the next few years her rate of growth exceeds his ; but
she has then nearly reached her maximum, while he continues to
grow. Her curve of weight from the nineteenth year onward to
the climacteric, remains stationary, being followed subsequently by
a late increase, so that while the man reaches his maximum of
weight at about forty, the woman is at her greatest weight about
fifty.

Of the statical differences of sex, some, such as the formation
of the pelvis, and the costal mechanism of respiration, are directly
connected with the act of child-bearing, while others have only an
indirect relation to that duty ; and indications at least of nearly all
the characteristic differences are seen at birth. The baby boy is

CHAP, v.] THE PHASES OF LIFE. 689

heavier and taller than the baby girl, and the maiden of five
breathes with her ribs in the same way as does the matron of forty.
The woman is lighter and shorter than the man, the limits in the
case of the former being from 1*444 to 1*740 metres of height and
from 39*8 to 93*8 kilos of weight, in the latter from 1*467 to
1*890 of height, and from 49*1 to 98*5 kilos of weight. The muscu-
lar system and skeleton are both absolutely and relatively less in
woman, and her brain is lighter and smaller than that of man,
being about 1272 grammes to 1424. Her metabolism, as measured
by the respiratory and urinary excreta, is also not only absolutely
but relatively to the body- weight less, and her blood is not only
less in quantity but also of lighter specific gravity and contains a
smaller proportion of red corpuscles. Her strength is to that of
man as about 5 to 9, and the relative length of her step as 1000 to
1157.

From birth onward (and indeed from early intra-uterme life)
the increment of growth progressively diminishes. At last a point is
reached at which the curve cuts the abscissa line, and the increment
becomes a decrement. After the culmination of manhood at forty
and of womanhood at the climacteric, the prime of life declines
into old age. The metabolic activity of the body, which at first
was sufficient not only to cover the daily waste, but to add new
material, later on is able only to meet the daily wants, and at last
is too imperfect even to sustain in its entirety the existing frame.
Neither as regards vigour and functional capacity, nor as regards
weight and bulk, do the turning-points of the several tissues and
organs coincide either with each other or with that of the body at
large. We have already seen that the life of such an organ as the
thymus is far shorter than that of its possessor. The eye is in its
dioptric prime in childhood, when its media are clearest and its
muscular mechanisms most mobile, and then it for the most part
serves as a toy ; in later years, when it could be of the greatest
service to a still active brain, it has already fallen into a clouded
and rigid old age. The skeleton reaches its limit very nearly at
the same time as the whole frame reaches its maximum of height,
the coalescence of the various epiphyses being pretty well completed
by about the twenty-fifth year. Similarly the muscular system in
its increase tallies with the weight of the whole body. The brain,
in spite of the increasing complexity of structure and function to
which it continues to attain even in middle life, early reaches its
limit of bulk and weight. At about seven years of age it attains
what may be considered as its first limit, for though it may increase
somewhat up to twenty, thirty, or even later years, its progress is
much more slow after than before seven. The vascular and digestive
organs as a whole may continue to increase even to a very late
period. From these facts it is obvious that though the phenomena
of old age are, at bottom, the result of the individual decline of the
several tissues, they owe many of their features to the disarrange-
F. 44

690 OLD AGE. [BOOK iv.

ment of the whole organism produced by the premature decay or
disappearance of one or other of the constituent bodily factors.
Thus, for instance, it is clear that were there no natural intrinsic
limit to the life of the muscular and nervous systems, they would
nevertheless come to an end in consequence of the nutritive dis-
turbances caused by the loss of the teeth. And what is true of the
teeth is probably true of many other organs, with the addition that
these cannot, like the teeth, be replaced by mechanical contrivances.
Thus the term of life which is allotted to a muscle by virtue of its
molecular constitution, and which it could not exceed were it always
placed under the most favourable nutritive conditions, is, in the
organism, determined by the similar life-terms of other tissues;
the future decline of the brain is probably involved in the early
decay of the thymus.

Two changes characteristic of old age are the so-called cal-
careous and fatty degenerations. These are seen in a completely
typical form in cartilage, as, for instance, in the ribs; here the
protoplasm of the cartilage-corpuscle becomes hardly more than an
envelope of fat globules, and the supple matrix is rendered rigid
with amorphous deposits of calcic phosphates and carbonates, which
are at the same time the signs of past and the cause of future
nutritive decline. And what is obvious in the case of cartilage is
more or less evident in other tissues. Everywhere we see a dis-
position on the part of protoplasm to fall back upon the easier task
of forming fat rather than to carry on the more arduous duty of
manufacturing new material like itself; everywhere almost we see
a tendency to the replacement of a structured matrix by a deposit
of amorphous material. In no part of the system is this more
evident than in the arteries ; one common feature of old age is the
conversion by such a change of the supple elastic tubes into rigid
channels, whereby the supply to the various tissues of nutritive
material is rendered increasingly more difficult, and their intrinsic
decay proportionately hurried.

Of the various tissues of the body the muscular and nervous are
however those in which functional decline, if not structural decay,
becomes soonest apparent. The dynamic coefficient of the skeletal
muscles diminishes rapidly after thirty or forty years of life, and a
similar want of power comes over the plain muscular fibres also ;
the heart, though it may not dimmish, or even may still increase
in weight, possesses less and less force, and the movements of the
intestine, bladder, and other organs, diminish in vigour. In the
nervous system, the lines of resistance, which, as we have seen, help
to map out the central organs into mechanisms, and so to produce
its multifarious actions, become at last hindrances to the passage of
nervous impulses in any direction, while at the same time the
molecular energy of the impulses themselves becomes less. The
eye becomes feeble, not only from cloudiness of the media and
presbyopic muscular inability, but also from the very bluntness of

CHAP, v.] THE PHASES OF LIFE. 691

the retina ; the sensory and motor impulses pass with increasing
slowness to and from the central nervous system, and the brain
becomes a more and more rigid mass of protoplasm, the molecular
lines of which rather mark the history of past actions than serve as
indications of present potency. The epithelial glandular elements
seem to be those whose powers are the longest preserved; and
hence the man who in the prime of his manhood was a ' martyr to
dyspepsia' by reason of the sensitiveness of gastric nerves and
the reflex inhibitory and other results of their irritation, in his
later years, when his nerves are blunted, and when therefore his
peptic cells are able to pursue their chemical work undisturbed by
extrinsic nervous worries, eats and drinks with the courage and
success of a boy.

Within the range of a lifetime are comprised many periods of
a more or less frequent recurrence. In spite of the aids of a com-
plex civilisation, all tending to render the conditions of his life
more and more equable, man still shews in his economy the effects
of the seasons. Some of these are the direct results of varying
temperature, but some probably, such as the gain of weight in
winter and the loss in summer, are habits acquired by descent.
Within the year, an approximately monthly period is manifested in
the female by menstruation, though there is no exact evidence of
even a latent similar cycle in the male. The phenomena of recur-
rent diseases, and the marked critical days of many other maladies,
may be regarded as pointing to cycles of smaller duration than that
of the moon's revolution, unless we admit the view urged by some
authors that in these cases the recurrence is to be attributed rather
to periodical phases in the disease-producing germ itself, than to
variations in the medium of the disease.

Prominent among all other cyclical events is the fact that most
animals possessing a well-developed nervous system, must, night
after night, or day after day, or at least time after time, lay them
down to sleep. The salient feature of sleep is the cessation of the
automatic activity of the brain ; it is the diastole of the cerebral
beat. But the condition is not confined to the cerebral hemi-
spheres; all parts of the body either directly or indirectly take
share in it. The phenomena of sleep are perhaps seen in their
simplest form in the winter-sleep or hybernation, to which especially
cold-blooded animals, but also to some extent warm-blooded animals,
are subject. In these cases the cold of winter slackens the vibra-
tions and lessens the explosions of the protoplasm, not only of
nervous but also of muscular and glandular structures ; indeed the
activity of the whole body is lowered, in some respects almost to
actual arrest. At the same time that the labour of the cerebral
molecules becomes insufficient to develop consciousness, the respi-
ratory centre is either wholly quiescent or discharges feeble im-
pulses at rare intervals, and the heart beats with a slow infrequent
stroke, not by reason of any inhibitory restraint, but because its

44—2

692 SLEEP. [BOOK iv.

very substance in its slow molecular travail can gather head for
explosions only after long pauses of rest. And such few and distant
beats as do occur are amply sufficient to meet the needs of the
feeble metabolism of the several tissues. The sleep of every day
differs from the sleep of winter-cold chiefly because the slackening
of molecular activities is due in the former not to extrinsic but to
intrinsic causes, not to changes in the medium, but to exhaustion
of the subject, and because the phenomena are largely confined to
the cerebral hemispheres. It is true that the whole body shares in
the condition. The pulse and breathing are slower, the intestine
and other internal muscular mechanisms are more or less at rest,
the secreting organs are less active, some apparently being wholly
quiescent, and the sleeper on waking rubs his eyes to bring back
to his conjunctiva its needed moisture. Indeed the whole meta-
bolism and the dependent temperature of the body are lowered ;
but we cannot say at present how far these are the indirect results
of the condition of the nervous system, or how far they indicate a
partial slumbering of the several tissues.

Thoracic respiration is said to become more prominent than
diaphragmatic respiration during sleep, and the Cheyne-Stokes
rhythm of respiration (see p. 362) is frequently observed. During
sleep the pupil is contracted, during deep sleep exceedingly so ; and
dilation, often unaccompanied by any visible movements of the limbs
or body, takes place when any sensitive surface is stimulated ; on
awaking also the pupils dilate. The eye-balls have been generally
described as being during sleep directed upwards and converging,
or according to some authors, diverging ; but others maintain that
in true sleep the visual axes are parallel and directed to the far
distance. The eyes of children have been described as continually
executing during sleep movements, often irregular and unsymme-
trical and unaccompanied by changes in the pupils.

We are not at present in a position to trace out the events
which culminate in this inactivity of the cerebral structures. It
has been urged that during sleep the brain is ansemic ; but even if
this anaemia is a constant accompaniment of sleep, it must, like the
vascular condition of a gland or any other active organ, be regarded
as an effect, or at least as a subsidiary event, rather than as a
primary cause. Nor can the view which regards sleep as the result
of a shifting of the mechanical arrangements of the cranial circu-
lation be considered as satisfactory. The explanation of the con-
dition is rather to be sought in purely molecular changes ; and the
analogy between the systole and diastole of the heart, and the
waking and sleeping of the brain, may be profitably pushed to a
very considerable extent. The sleeping brain in many respects
closely resembles a quiescent but still living ventricle. Both are
as far as outward manifestations are concerned at rest, but both
may be awakened to activity by an adequately powerful stimulus.
Both, though quiescent, are irritable, in both the quiescence will

CHAP, v.] THE PHASES OF LIFE. 693

ultimately give place to activity, and in both an appropriate
stimulus applied at the right time will determine the change from
rest to action. Just as a single prick will under certain circum-
stances awake a ventricle, which for some seconds has been
motionless, into a rhythmic activity of many beats, so a loud noise
will start a man from sleep into a long day's wakefulness. And
just as in the heart the cardiac irritability is lowest at the beginning
of the diastole and increases onwards till a beat bursts out, so is
sleep deepest at its commencement after the day's labour ; thence
onward slighter and slighter stimuli are needed to wake the sleeper.
For judging of the depth of ordinary nocturnal sleep by the inten-
sity of the noise required to wake the sleeper, it may be concluded
that, increasing very rapidly at first, it reaches its maximum within
the first hour ; from thence it diminishes, at first rapidly, but after-
wards more slowly.

We cannot, however, at present make any definite statements
concerning the nature of the molecular changes which determine
this rhythmic rise and fall of cerebral irritability. The fact that
the products of protoplasmic activity when they accumulate within
the protoplasm appear to become in the end an obstruction to
that activity, has suggested the idea that the presence in the
cerebral tissue of an excess of the products of nervous metabolism
is the cause of sleep. Indeed lactic acid, the increase of which
was supposed to be the cause of the acid reaction of muscular
and nervous tissues after exercise, has been especially pointed to
in this connection; but, as we have seen, the acid reaction in
question appears not to be due to any increased production of
lactic acid. Besides, if the accumulation of metabolic products of
any kind were the cause of sleep, it is not clear why we should
ever have any hope of waking. More may be said in favour of
the conception that during the waking hours the expenditure of
oxygen exceeds the income and that the quiescence, which we call
sleep, comes from the exhaustion of the body's store of oxygen,
more especially of that ' intramolecular ' oxygen of which we spoke,
in dealing with the respiration of the tissues. But to this view
must be added some hypothesis, such as the byplay of some
inhibitory mechanism, whereby the respiratory centre is not roused
to increased activity by this lack of oxygen, for as we have seen
the breathing shares in the slumber of the body, though continuing
to play with an amount of energy, which permits a gradual
restoration of the lost store of oxygen and so finally brings on
the awakening which ends the sleep. And the necessity for such
a complication indicates that the explanation is, at present at
least, inadequate.

The phenomena of sleep shew very clearly to how large an
extent an apparent automatism is the ultimate outcome of the
effects of antecedent stimulation. When we wish to go to sleep we
withdraw our automatic brain as much as possible from the influ-

694 SLEEP. [BOOK iv.

ence of all extrinsic stimuli ; and an interesting case is recorded of
a lad whose connection with the external world was, from a compli-
cated anaesthesia, limited to that afforded by a single eye and a
single ear, and who could be sent to sleep at will, by closing the
eye and stopping the ear.

The cycle of the day is however manifested in many other ways
than by the alternation of sleeping and waking, with all the in-
direct effects of these two conditions. There is a diurnal curve of
temperature (see p. 468), apparently independent of all immediate
.circumstances, the hereditary impress of a long and ancient sequence
of days and nights. Even the pulse, so sensitive to all bodily
changes, shews, running through all the immediate effects of the
changes of the minute and the hour, the working of a diurnal in-
fluence which cannot be accounted for by waking and sleeping, by
working and resting, by meals and abstinence between meals. And
the same may be said concerning the rhythm of respiration, and
the products of pulmonary, cutaneous and urinary excretion. There
seems to be a daily curve of bodily metabolism, which is not the
product of the day's events. Within the day we have the narrower
rhythm of the respiratory centre with the accompanying rise and
fall of activity in the vaso-motor centres. And lastly, there stands
out the fundamental fact of all bodily periodicity, that alternation of
the heart's systole and diastole which ceases only at death. Though,
as we have seen, the intermittent flow in the arteries is toned down
in the capillaries to an apparently continuous flow, still the con-
stantly repeated cycle of the cardiac shuttle must leave its mark
throughout the whole web of the body's life. Our means of inves-
tigation are, however, still too gross to permit us to track out its
influence. Still less are we at present in a position to say how far
the fundamental rhythm of the heart itself, that rhythm which is
influenced, but not created, by the changes of the body of which
it is the centre, is the result of cosmical changes, the reflection as
it were in little of the cycles of the universe, or how far it is the
outcome of the inherent vibrations of the molecules which make up
its substance.

CHAPTER VI.
DEATH.

WHEN the animal kingdom is surveyed from a broad stand-point, it
becomes obvious that the ovum, or its correlative the spermatozoon,
is the goal of an individual existence : that life is a cycle beginning
in an ovum and coming round to an ovum again. The greater part
of the actions which, looking from a near point of view at the
higher animals alone, we are apt to consider as eminently the pur-
poses for which animals come into existence, when viewed from the
distant outlook whence the whole living world is surveyed, fade
away into the likeness of the mere byplay of ovum-bearing organ-
isms. The animal body is in reality a vehicle for ova ; and after
the life of the parent has become potentially renewed in the off-
spring, the body remains as a cast-off envelope whose future is but
to die.

Were the animal frame not the complicated machine we have
seen it to be, death might come as a simple and gradual dissolution,
the 'sans everything' being the last stage of the successive loss of
fundamental powers. As it is, however, death is always more or
less violent; the machine comes to an end by reason of the disorder
caused by the breaking down of one of its parts. Life ceases not
because the molecular powers of the whole body slacken and are
lost, but because a weakness in one or other part of the machinery
throws its whole working out of gear.

We have seen that the central factor of life is the circulation
of the blood, but we have also seen that blood is not only useless,
but injurious, unless it be duly oxygenated ; and we have further
seen that in the higher animals the oxygenation of the blood can
only be duly effected by means of the respiratory muscular mechan-
ism, presided over by the medulla oblongata. Thus the life of a
complex animal is, when reduced to a simple form, composed of
three factors ; the maintenance of the circulation, the access of air
to the haemoglobin of the blood, and the functional activity of the

696 DEATH. [BOOK iv.

respiratory centre ; and death may come from the arrest of either
of these. As Bichat put it, death takes place by the heart or by
the lungs or by the brain. In reality, however, when we push the
analysis further, the central fact of death is the stoppage of the
heart, and the consequent arrest of the circulation; the tissues then
all die, because they lose their internal medium. The failure of the
heart may arise in itself, on account of some failure in its nervous or
muscular elements, or by reason of some mischief affecting its me-
chanical working. Or its stoppage may be due to some fault in its
internal medium, such for instance as a want of oxygenation of the
blood, which in turn may be caused by either a change in the blood
itself, as in carbonic oxide poisoning, or by a failure in the mechan-
ical conditions of respiration, or by a cessation of the action of the
respiratory centre. The failure of this centre, and indeed that of
the heart itself, may be caused by nervous influences proceeding
from the brain, or brought into operation by means of the central
nervous system ; it may, on the other hand, be due to an imperfect
state of blood, and this in turn may arise from the imperfect or
perverse action of various secretory or other tissues. The modes of
death are in reality as numerous as are the possible modifications
of the various factors of life ; but they all end in a stoppage of the
circulation, and the withdrawal from the tissues of their internal
medium. Hence we come to consider the death of the body as
marked by the cessation of the heart's beat, a cessation from which
no recovery is possible ; and by this we are enabled to fix an exact
time at which we say the body is dead. We can, however, fix
no such exact time to the death of the individual tissues. They
are not mechanisms, and their death is a gradual loss of power.
In the case of the contractile tissues, we have apparently in rigor
' mortis a fixed term, by which we can mark the exact time of their
death. If we admit that after the onset of rigor mortis recovery
of irritability is impossible, then a rigid muscle is one permanently
dead. In the case of the other tissues, we have no such objective
sign, since the rigor mortis of simple protoplasm manifests itself
chiefly by obscure chemical signs. And in all cases it is obvious
that the possibility of recovery, depending as it does on the skill
and knowledge of the experimenter, is a wholly artificial sign of
death. Yet we can draw no other sharp line between the seemingly
dead tissue whose life has flickered down into a smouldering ember
which can still be fanned back again into flame, and the handful of
dust, the aggregate of chemical substances into which the decom-
posing tissue finally crumbles.

Moreover, the failure of the heart itself is at bottom loss of
irritability, and the possibility of recovery here also rests, as far
as is. known at present, on the skill and knowledge of those who
attempt to recover. So that after all the signs of the death of the
whole body are as artificial as those of the death of the constituent
tissues.

APPENDIX.

APPENDIX.

ON THE CHEMICAL BASIS OF THE ANIMAL BODY.

THE animal body, from a chemical point of view may be regarded
as a mixture of various representatives of three large classes of
chemical substances, viz. proteids, carbohydrates and fats, in associa-
tion with smaller quantities of various saline and other crystalline
bodies. By proteids are meant bodies containing carbon, oxygen,
hydrogen and nitrogen in a certain proportion, varying within narrow
limits, and having certain general features ; they are frequently spoken
of as albuminoids. By carbohydrates are meant starches and sugars
and their allies. We have also seen that the animal body may be
considered as an assemblage of protoplasm under various modifications
and of numerous products of protoplasmic activity. We do not at
present know anything definite about the molecular composition of
active living protoplasm ; but when we submit protoplasm to chemical
analysis, in which act it is killed, we always obtain from it a considerable
quantity of the material spoken of as proteid. And many authors go
so far as to speak of protoplasm as being purely proteid in nature : they
regard the living protoplasm as proteid material, which in passing from
death to life, has assumed certain characters and presumably has
been changed in construction, but still is proteid matter ; they some-
times speak of protoplasm as ' living proteid ' or ' living albumin.' It is
worthy of notice however that even simple forms of protoplasm, like that
constituting the body of a white corpuscle, forms of protoplasm which
we may fairly consider as native protoplasm, when they can be obtained
in sufficient quantity for chemical analysis, are found to contain some

700 CHEMICAL BASIS [Apr.

representatives of carbohydrates and fats as well as of proteids. We
might perhaps even go as far as to say, that in all forms of living proto-
plasm, the proteid basis is found upon analysis to have some carbohydrate
and some kind of fat associated with it. Further, not only does the
normal food which is eventually built up into protoplasm consist of all
three classes, but, as we have seen in the sections on nutrition, proto-
plasm gives rise by metabolism to members of the same three classes ;
and as far as we know at present, carbohydrates and fats, when formed
in the body out of proteid food, are so formed by the agency of living
protoplasm, by some living tissue. Hence there is at least some
reason for thinking it probable that the molecule of protoplasm, if
we may use such a phrase, is far more complex than a molecule of
proteid matter, that it contains in itself residues so to speak not only of
proteid but also of carbohydrate and fatty material.

Be this as it may, for no dogmatic statement can at present be made,
when we examine the various tissues and fluids of the animal body from
a chemical point of view we find present in different places, or at different
times, several varieties and derivatives of the three chief classes ; we
find many forms of proteids, and bodies closely allied to proteids, in the
forms of mucin, gelatine, &c. ; many varieties of fats ; and several kinds
of carbohydrates.

We find moreover many other bodies which we may regard as
stages in the constructive or destructive metabolism of both native and
differentiated protoplasm, and which are important not so much from
the quantity in which they occur in the animal body at any one time as
from their throwing light on the nature of animal metabolism ; these
are such bodies as urea, other organic crystalline bodies, and the ex-
tractives in general.

In the following pages the chemical features of the more important
of these various substances which are known to occur in the animal
body will be briefly considered, such characters only being described as
possess or promise to possess physiological interest. The physiological
function of any substance must depend ultimately on its molecular
(including its chemical) nature; and though at present our chemical
knowledge of the constituents of an animal body gives us but little
insight into their physiological properties, it cannot be- doubted that
such chemical information as is attainable is a necessary preliminary to
all physiological study.

APP.] OF THE ANIMAL BODY. 701

PBOTEIDS.

These form the principal solids of the muscular, nervous, and gland-
ular tissues, of the serum of blood, of serous fluids, and of lymph. In
a healthy condition, sweat, tears, bile and urine contain mere traces, if
any, of proteids. Their general percentage composition may be taken as

O. H. N. C. S.

From 20-9 6-9 15-2 51-5 0-3

to 23-5 to 7-3 to 17-0 to 54-5 to 2-0

(Hoppe-Seyler l. )

These figures are obtained from a consideration of numerous analyses, slight
differences in the various results being immaterial, where the purity of the substance
operated upon cannot be definitely determined.

In addition to the above constituents, proteids leave on ignition a variable
quantity of ash. In the case of egg-albumin the principal constituents of the ash
are chlorides of sodium and potassium, the latter greatly exceeding the former in
amount. The remainder consists of sodium and potassium, in combination with
phosphoric, sulphuric, and carbonic acids, and very small quantities of calcium,
magnesium and iron, in union with the same acids. There is also a trace of silica2.
The ash of serum-albumin contains an excess of sodium chloride, but the ash of the
proteids of muscle contains an excess of potash salts and phosphates. The nature
of the connection of the ash with the proteid is still a matter of obscurity. Globin
from hasmoglobin is said to leave no ash on ignition.

Proteids as met with in the animal body are all amorphous ; some
are soluble, some insoluble in water, and all are for the most part insoluble
in alcohol and ether; they are all soluble in strong acids and alkalis,
but in becoming dissolved mostly undergo decomposition. Their solutions
possess a left-handed rotatory action on the plane of polarisation, the
amount depending on various circumstances, and being, with one ex-
ception, viz. peptones, changed by heating.

Crystals into whose composition certain proteid (especially globulin)3 elements
enter were long since observed in the seeds of many plants; as yet they have not
been obtained sufficiently isolated or in quantities large enough to permit any
accurate analysis to be made. A method of isolating in quantity and recrystallizing
these substances has however4 been indicated, and it seems probable that analysis
of these may lead to interesting information on the subject of the constitution and
combinations of proteids.

The presence of proteids may be determined by the following tests.

1. Heated with strong nitric acid, they or their solutions turn
yellow, and this colour is, on the addition of ammonia, or caustic soda
or potash, changed to a deep orange hue. (Xanthoproteic reaction.)

1 Hdb. Phys. Path. Chem. Anal., Ed. rv. (1875) S. 223.

2 See Gmelin, Hdb. Org. Chem., Bd. vin. S. 235.

3 Vines, Jl. of Physiol. Vol. in. (1880) p. 93.

4 Drechsel, Journ. f. prakt. Chem., N. F. Bd. xix. (1879) S. 331.

702 PROTEIDS. [App.

2. With Millon's reagent they give, when present in sufficient
quantity, a precipitate, which turns red on heating. If they are only
present in traces, no precipitate is obtained, but merely a red colouration
of the solution.

3. If mixed with some concentrated solution of sodic hydrate,
and one or two drops of a solution of cupric sulphate, a violet colour is
obtained, which deepens in tint on boiling.

The above serve to detect the smallest traces of all proteids. The
two following tests may be used when there is more than a trace
present, but do not hold for every kind of proteid.

4. Render the fluid strongly acid with acetic or other acid, and
add a few drops of a solution of ferrocyanide of potassium ; a pre-
cipitate shews the presence of proteids.

5. Bender the fluid, as before, strongly acid with acetic acid, add
an equal volume of a concentrated solution of sodic sulphate, and
boil. A precipitate is formed if proteids are present.

This last reaction is useful, not only on account of its exactness, but also
because the reagents used produce no decomposition of other bodies which may be
present ; and hence after filtration the same fluid may be further analysed for other
-substances. Additional methods of freeing a solution from proteids are : acidulating
with acetic acid and boiling, avoiding any excess of the acid; precipitation by excess
of alcohol; in the latter case the solution must be neutral or faintly acid. Hoppe-
Seyler1 recommends the employment of a saturated solution of freshly precipitated
ferric hydrate, in acetic acid ; this is added to the solution, and on boiling the
whole of the proteids are precipitated as well as the ferric salt, the latter as a basic
acetate. Briicke's method of removing the last traces of proteids from glycogen
solutions is also of use (see glycogen). Precipitation of the last traces of proteids by
means of hydrated oxide of lead at a boiling temperature 2 may be also employed.

Proteids may be conveniently divided into classes.

CLASS I. Native Albumins.

Members of this class, as their name implies, occur in a natural
condition in animal tissues and fluids. They are soluble in water, are
not precipitated by very dilute acids, by carbonates of the alkalis, or
by sodium chloride. They are coagulated by heating in solution to a
temperature of about 70° C. If dried at 40° C., the resulting mass is of
a pale yellow colour, easily friable, tasteless, inodorous and soluble.

1. Egg-albumin.

Forms in aqueous solution a neutral, transparent, yellowish fluid.
From this it is precipitated by excess of strong alcohol. If the alcohol
be rapidly removed the precipitate may be readily redissolved in water;

1 Op. cit. S. 227.

2 Hofmeister, Zeitsch. f. pliysiol. Chem., Bd. n. (1878) S. 288.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 703

if subjected to lengthier action a coagulation occurs, and the albumin is
then no longer thus soluble. Strong acids, especially nitric acid, cause
a coagulation similar to that produced by heat or by the prolonged
action of alcohol; the albumin becomes profoundly changed by the
action of the acid and does not dissolve upon removal of the acid.
Mercuric chloride, argentic nitrate, and lead acetate, precipitate the
albumin, forming insoluble compounds of variable composition with it,:
the precipitant may be removed by means of sulphuretted hydrogen and
the albumin again obtained, apparently unaltered, in solution.

Strong acetic acid in excess gives no precipitate, but when the
solution is concentrated the albumin is transformed into a transparent
jelly. A similar jelly is produced when strong caustic potash is added
to a concentrated solution of egg-albumin. In both these cases the
substance is profoundly altered becoming in the one case acid — in the
other alkali-albumin.

The specific rotatory power of egg-albumin in aqueous solution is,
for yellow light, - 35 -5°. Hydrochloric acid, added until the reaction is
strongly acid, increases this rotation to -37 '7°. The formation of the
gelatinous compound with caustic potash is at first accompanied with an
increase, but this is followed by a decrease of rotation.

Preparation. White of hen's egg is broken up with scissors into
small pieces, diluted with an equal bulk of water, and the mixture
shaken strongly in a flask till quite frothy ; on standing, the foam rises
to the top, and carries all the fibres in whose meshwork the albumin
was contained. The fluid, from which the foam has been removed, is
strained, and treated carefully with dilute acetic acid as long as any
precipitate is formed; the precipitate is then filtered off, and the filtrate
after neutralisation concentrated at 40° to its original bulk.

2. Serum -albumin.

This form of albumin resembles, to a great extent, the one previously
described. The following may suffice as distinguishing features.

1. The specific rotation of serum-albumin is — 5G°; that of egg-
albumin is - 35'5°, both measured for yellow light.

2. Serum-albumin is not coagulated by being shaken up with ether,
egg-albumin is.

3. Serum-albumin is not very readily precipitated by strong hydro-
chloric acid, and such precipitate as does occur is readily redissolved on
further addition of the acid ; the exact reverse of these two features
holds good for egg-albumin.

4. Precipitated or coagulated serum-albumin is readily soluble,
egg-albumin is with difficulty soluble, in strong nitric acid.

704 PROTEIDS. [App.

5. Egg-albumin if injected subcutaneously or into a vein, reappears
unaltered in the urine1 ; serum-albumin similarly injected does not thus
normally pass out by the kidney.

Serum-albumin is found not only in blood-serum, but also in lymph,
both that contained in the proper lymphatic channels and that diffused
in the tissues; in chyle, milk, transudations and many pathological
fluids.

It is this form in which albumin generally appears in the urine.

In addition to the above, Scherer2 has described two closely related bodies, to
which he gives the names Paralbumin and Metalbumin. The first he obtained from
ovarian cysts ; its alkaline solutions are remarkable for being very ropy. It seems
doubtful whether this body is a proteid; it differs sensibly in composition from
these. Haerlin3 gives as its composition, 0. 26'8, H. 6'9, N. 12-8, C. 51-8, S. 1'7 p.c.
It seems to be associated with some body like glycogen, capable of being converted
into a substance giving the reactions of dextrose. Metalbumin, found in a dropsical
fluid, resembles the preceding, but is not precipitated by hydrochloric acid, or by
acetic acid and ferrocyanide of potassium; it is precipitated, but not coagulated, by
alcohol ; its solution is scarcely coagulated on boiling.

Albumins are generally found associated with small but definite
amounts of saline matter. A. Schmidt4 says that they may be freed
from these by dialysis, and that they are then not coagulated on boiling.
From this it might be inferred that the albumin and the saline matters
were peculiarly related, and that the latter played some special part during
the coagulation of the former by heat. Schmidt's observations however
have not been conclusively corroborated by subsequent observers.

CLASS II. Derived Albumins (Albuminates).
1. Acid-albumin.

When a native albumin in solution, such as serum-albumin, is treated
for some little time with a dilute acid such as hydrochloric, its proper-
ties become entirely changed. The most marked changes are (1) that
the solution is no longer coagulated by heat ; (2) that when the solution
is carefully neutralized the whole of the proteid is thrown down as a
precipitate; in other words, the serum-albumin which was soluble in
water, or at least in a neutral fluid containing only a small quantity of
neutral salts, has become converted into a substance insoluble in water
or in similar neutral fluids. The body into which serum-albumin thus
becomes converted by the action of an acid is spoken of as acid-albumin.
Its characteristic features are that it is insoluble in distilled water, and

1 Stokvig, Eech. exp. sur Us condlt. patJwl. de Valbuminurie, Bruxelles, 1867 ; also
Lehmann, Arch. f. path. Anat. Bd.xxx. (1864), S. 593.

2 Ann. der Chem. und Pharm., Bd. 82, S. 135.

3 Chem. Centralblatt, 1862, No. 56.
* Pniiger's Archiv, xi. (1875), S. 1.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 705

in neutral saline solutions, such as those of sodic chloride, that it
is readily soluble in dilute acids or dilute alkalis, and that its solutions
in acids or alkalis are not coagulated by boiling. When suspended, in
the undissolved state, in water, and heated to 70° C, it becomes coagulated,
and is then undistinguishable from coagulated serum-albumin, or indeed
from any other form of coagulated proteid. It is evident that the sub-
stance when in solution in a dilute acid is in a different condition from
that in which it is when precipitated by neutralisation. If a quantity
of serum- or egg-albumin be treated with dilute hydrochloric acid, it
will be found that the conversion of the native albumin into acid-
albumin is gradual ; a specimen heated to 70° C immediately after the
addition of the dilute acid, will coagulate almost as usual ; and another
specimen taken at the same time will give hardly any precipitate on
neutralisation. Some time later, the interval depending on the pro-
portion of the acid to the albumin, on temperature, and on other
circumstances, the coagulation will be less, and the neutralisation
precipitate will be considerable. Still later the coagulation will be absent,
and the whole of the proteid will be thrown down on neutralisation.

If finely-chopped muscle, from which the soluble albumins have been
removed by repeated washing, be treated for some time with dilute
(•2 per cent.) hydrochloric acid, the greater part of the muscle is dis-
solved. The transparent acid filtrate contains a large quantity of
proteid material in a form which, in its general characters at least,
agrees with acid-albumin. The acid solution of the proteid is not
coagulated by boiling, but the whole of the proteid is precipitated on
neutralisation ; and the precipitate,, insoluble in neutral sodic chloride
solutions, is readily dissolved by even dilute acids or alkalis. The
proteid thus obtained from muscle has been called syntonin, but we
have at present no satisfactory test to distinguish the acid-albumin (or
syntonin) prepared from muscle from that prepared from egg- or serum-
albumin. When coagulated albumin or other coagulated proteid or
fibrin is dissolved in strong acidsr acid-albumin is formed ; and when
fibrin or any other proteid is acted upon by gastric juice, acid-albumin
is one of the first products; and these acid-albumins cannot be dis-
tinguished from acid-albumin prepared from muscle or native albumin.
Though hydrochloric acid is perhaps the most convenient acid for
forming acid-albumin, other acids may also be used for the purpose of
preparing it. Acid-albumin is soluble not only in dilute alkalis, but
also in dilute solutions of alkaline carbonates ; its solutions in these are
not coagulated by boiling.

If sodic chloride in excess is added to an acid solution of acid-
albumin, the acid-albumin is precipitated : this also occurs on adding
sodic acetate or phosphate.

F. 45

706 PROTEIDS. [App.

As special tests of acid-albumin may be given : 1. Partial coagu-
lation of its solution in lime-water on boiling. 2. Further precipitation
of the same solution sifter boiling, on the addition of calcic chloride,
magnesic sulphate, or sodic chloride.

Dissolved in very dilute hydrochloric acid, acid-albumin (syntonin)
-prepared from muscle possesses a specific laevo -rotatory power of -72° for
yellow light, this being independent of the concentration1. On heating
the solution in a closed vessel in a water-bath, the rotatory power rises
to -84-8°.

The body known as parapeptone which makes its appearance during
the peptic digestion of proteids is closely allied to the substances just
described. (See p. 243).

2. Alkali-albumin.

If serum- or egg- albumin or washed muscle be treated with dilute
alkali instead of with dilute acid, the proteid undergoes a change quite
similar to that which was brought about by the acid. The alkaline
solution, when the change has become complete, is no longer coagulated
by heat, the proteid is wholly precipitated on neutralisation, and the
precipitate, insoluble in water and in neutral sodic chloride solutions,
is readily soluble in dilute acids or alkalis. Indeed in a general way
it may be said that acid-albumin and alkali-albumin are nothing more
than solutions of the same substance in dilute acids and alkalis
respectively. When the precipitate obtained by the neutralisation of
a solution of acid-albumin in dilute acid is dissolved in a dilute alkali,
it may be considered to become alkali- albumin ; and conversely when
the precipitate obtained from an alkali-albumin solution is dissolved in
dilute acid, it may be regarded as acid-albumin.

It is stated 2 as a characteristic reaction of this modified or derived
albumin that it is not precipitated when its alkaline solutions are
neutralised in the presence of alkaline phosphates; solutions of acid-
albumin on the contrary are said to be precipitated on neutralisation in
the presence of alkaline phosphates, and this difference is considered
to be a distinguishing feature of the two proteids. But doubt has been
cast on this statement *.

Alkali-albumin may be prepared by the action not only of dilute
alkalis but also of strong caustic alkalis on native albumins as well as
on coagulated albumin and other proteids. The jelly produced by the
action of caustic potash on white of egg, spoken of in Class I. 1, is
alkali-albumin ; the similar jelly produced by strong acetic acid is acid-

1 Hoppe-Seyler, Hdb. Phys. Path. Chem. Anal. Ed. iv. (1875), S. 246.
• 3 Hoppe-Seyler, loc. cit. S. 245.
3 Soyka. Pfltiger's Arch. Bd. xn. (1876), S. 347.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 707

albumin. One of the most productive methods of obtaining alkali-
albumin is that introduced by Lieberkiihn1, and consists in adding a
strong solution of caustic potash to purified white of egg until the
above-mentioned jelly is obtained. This is then cut into small pieces,
and dialysed until quite white. The lumps are then dissolved by
heating on the water-bath, and the alkali-albumin precipitated by the
careful addition of acetic acid.

Both alkali- and acid-albumin are with difficulty precipitated by
alcohol from their alkaline or acid solutions. The neutralisation pre-
cipitate however becomes coagulated under the prolonged action of
alcohol.

The body 'protein,' described by Mulder appears, if it exists at all, to be closely
connected with this body. All subsequent observers have however failed to confirm
his views.

The rotatory power of alkali-albumin varies according to its source ;
thus when prepared by strong caustic potash from serum-albumin, the
rotation rises from - 56° (that of serum albumin) to — 86°, for yellow
light. Similarly prepared from egg-albumin, it rises from — 38-5° to
— 47°, and if from coagulated white of egg, it rises to — 58'8°. Hence
the existence of various forms of alkali-albumin is probable.

In addition to the methods given above, alkali-albumin may be also readily ob-
tained by shaking milk with strong caustic soda solution and aether, removing the
aetherial solution, precipitating the remaining fluid with acetic acid and washing the
precipitate with water, cold alcohol and aether.

The most satisfactory method of regarding acid- and alkali-albumin
is to consider them as respectively acid and alkali compounds of the
neutralisation precipitate. We have reason to think that when the
precipitate is dissolved in either an acid or an alkali, it does enter into
combination with them. The neutralisation precipitate is in itself
neither acid- nor alkali-albumin, but may become either, upon solution
in the respective reagent.

It is probable that several derived albumins exist2, differing according to the
proteid from which they are formed or possibly according to the mode of their pre-
paration, and that each of these may exist in its correlative forms of acid- and alkali-
albumin; but the whole subject requires further investigation.

Acid-albumin, prepared by the direct action of dilute acids on native
albumins or on muscle-substance, contains sulphur, as shewn by the
brown colouration which appears when the precipitate is heated with
caustic potash in the presence of basic lead acetate. Alkali albumin,
at all events as prepared by the action of strong caustic potash or soda,

1 Poggendorff's Annalen, Bd LXXXVI. S. 118.

2 Morner. Pfluger's Arch. Bd, xvii. (1878), S. 468.

45—2

708 PROTEIDS. [Apr.

does not contain any sulphur ; and the acid-albumin, prepared by the
solution in an acid of the neutralisation precipitate from such an alkali-
albumin solution, is similarly free from sulphur.

3. Casein.

This is the well-known proteid existing in milk. When freed from
fat, and in the moist condition, it is a white, friable, opaque body. In
most of its reactions it corresponds closely with alkali-albumin ; thus it
is readily soluble in dilute acids and alkalis, and is re-precipitated on
neutralisation; if, however, potassic phosphate is present, as is the
case in milk, the solution must be strongly acid before any precipitate
is obtained.

Various reactions have at different times been assigned to casein as distinguishing
it from the closely allied body alkali- albumin. Later researches have however in
most cases cast so much doubt on these differences that the identity or non-identity
of casein and alkali-albumin must still be left an open question, the discussion of
which would be out of place here.

Casein, as occurring in milk, has had several reactions ascribed to it, as character-
istic; but these lose their importance on considering that milk contains, in addition
to casein, other substances such as potassic phosphate, and a number of bodies
which yield acids by fermentation. The presence of potassic phosphate has an
especial influence on the reactions of casein. In the entire absence of this salt,
acetic acid in the smallest quantities, as also carbonic anhydride, gives a precipitate;
but if this salt is present, carbonic anhydride gives no precipitate, and acetic acid
one only when ihe solution is acid from the presence of free acid, and not from
that of acid potassic phosphate1.

When prepared from milk by magnesic sulphate (see below), freed
by aether from fats, and dissolved in water, casein possesses a specific
rotatory power of - 80° for yellow light ; in dilute alkaline solutions, of
-76°; in strong alkaline solutions, of — 91°; in dilute hydrochloric acid,
of -87°.

Casein has been asserted to occur in muscle, in serous fluids, and in
blood-serum (Serum-casein). In many cases it has probably been
confounded with globulins (see Class III.); but blood-serum and muscle-
plasma undoubtedly contain an alkali-albumin in addition to whatever
globulin may be present, but the usual doubt exists as to the identity-
of this with true casein. Its presence may be shewn by adding dilute
acetic acid to blood-serum which has been freed from globulin by a
current of carbonic anhydride ; a distinct precipitate is thrown down.
A substance similar to casein has also been described as existing in
unstriated muscle and in the protoplasm of nerve-cells.

Preparation. Dilute milk with several (10 to 15) times its bulk of
water, add dilute acetic acid till a precipitate begins to appear, then pass

1 See Kiihne, Lehrb. d. Physiol. Chem., 1868, S. 5G5.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 709

a current of carbonic anhydride, filter, and wash the precipitate with
water, alcohol and aether : the complete removal of the fat carried
down with the casein presents some difficulties. Magnesic sulphate
added to saturation also precipitates casein from milk ; the precipitate
as thus formed is readily soluble on the addition of water.

CLASS III. Globulins.

Besides the native albumins there are a number of native proteids
which differ from the albumins in not being soluble in distilled water;
they need for their solution the presence of an appreciable, though it may
be a small, quantity of a neutral saline body such as sodic chloride.
Thus they resemble the albuminates in not being soluble in distilled
water, but differ from them in being soluble in dilute sodic chloride
or other neutral saline solutions. Their general characters may be
stated as follows.

They are insoluble in water, soluble in dilute (1 p.c.) solutions of
sodic chloride ; they are also soluble in dilute acids and alkalis, being
changed on solution into acid- and alkali-albumin respectively unless
the acids and alkalis are exceedingly dilute. The saturation with solid
sodic chloride of their solutions in dilute sodic chloride, precipitates
most members of this class.

1. Globulin (Crystallin}.

If the crystalline lens be rubbed up with fine sand, extracted with
water and filtered, the filtrate will be found to contain at least three
proteids. On passing a current of carbonic anhydride a copious precipi-
tate occurs ; this is globulin.

The addition of dilute acetic acid to the filtrate from the globulin, gives a pre-
cipitate of alkali-albumin1 ; and the filtrate from this if heated gives a further pre-
cipitate, due to serum-albumin.

In its general reactions globulin corresponds almost exactly with
the next members of this class (paraglobulin and fibrinogen), but has no
power to form or promote the formation of fibrin in fluids containing
the above-mentioned bodies, and possesses the following special features.
1. According to Lehmann, its oxygenated, neutral solutions become
cloudy on heating to 73° C., and are coagulated at 93° C. 2. It is readily
precipitated on the addition of alcohol. According to Hoppe-Seyler, it
is not precipitated on saturation with sodic chloride, resembling
vitellin in this respect.

1 But see also Pfluger's Arch. Bd. xm. (1876), S. G31.

710 PEOTEIDS. [A PP.

According to Kuhne1 and Eiehwald2 a globulin with properties identical with
those just given may be precipitated from dilute serum by the cautious addition of
acetic acid. This body is stated by Weyl3 to be th6 same as paraglobulin (fibrino-
plastin), the latter differing from it only by a small admixture of fibrin-ferment.

2. Paraglobulin (Fibrinoplastin).

Preparation. Blood-serum is diluted ten-fold with water, and a
brisk current of carbonic anhydride is passed through it. The first-formed
cloudiness soon becomes, a flocculent precipitate, which is finally quite
granular, and may easily be separated by decantation and filtration : it
should be washed on the filter with water containing carbonic acid.

It has usually been stated that paraglobulin may be separated from
$erum by saturation with sodic chloride. But Hammarsten4 has shown
that this is only in part true, a considerable portion of the globulin
remaining unprecipitated. The separation may however be completely
effected by saturation with magnesic sulphate. When determined
by this method the amount of paraglobulin in serum is very con-
siderable, amounting, in some cases according to Hammarsten, to as
much as 4 '5 6 5 p. c. (reckoned on 100 cc. of serum). The quantity
seems to vary in different animals, the precipitation being much more
complete in serum from ox-blood than in that from the blood of horses.
From its solution in dilute sodic chloride, paraglobulin may be pre-
cipitated by a current of carbonic anhydride or the addition of exceedingly
dilute (less than 1 pro mille) acetic acid. If the acid is strong, the
precipitated proteid becomes immediately changed into acid-albumin
(Class II. 1 .). In pure water, free from oxygen, paraglobulin is insoluble,
but on shaking with air or passing a current of oxygen, solution readily
takes place ; from this it may be reprecipitated by a current of carbonic
anhydride. Very dilute alkalis dissolve this body without change ; if,
however, the strength of the alkali be raised even to 1 p. c. the para-
globulin is changed into alkali-albumin (Class II. 2.).

According to Kiihne and A. Schmidt the solutions of this body in
water containing oxygen or in very dilute alkalis are not coagulated on
heating. The sodic chloride solutions do however coagulate when
heated to 68°— 70° C.5, and if the substance itself be suspended in
water and heated to 70° C. it is coagulated. Although insoluble in
alcohol, its solutions are with difficulty precipitated by this reagent.

Paraglobulin occurs not only in blood-serum, but it is also found in
white corpuscles, in the stroma of red corpuscles (to some extent at

1 Lekrb. d. Physiol. Chem. 1868. S. 175.

2 Beitrdge zur Chem., d. gewebebild. Subst. Berlin, 1873. Hf. i.

3 Zeitschr.f. Physiol. Chem., Bd. i. (1878) S. 79.

4 Pniiger's Archiv, Bd. xvn. (1878) S. 446. Bd. xvm. (1878), S. 38.
6 Hammarsten, op. cit.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 711

least), in connective tissue, the cornea, aqueous humour, lymph, chyle,
and serous fluids.

For the occurrence of globulin in urine see Edlefsen l and Senator2.
3. Fibrinogen.

The general reactions of this body are identical with those of
paraglobulin. The most marked difference between the two is
the point at which coagulation of their solutions takes place.
Hammarsten3 has shewn that fibrinogen in a 1 — 5 p. c. solution of
sodic chloride coagulates at from 52° — 55° C., whereas, as stated above,
paraglobulin (fibrinoplastin) coagulates first at from 68° — 70° C. This
however is disputed by A. Schmidt who holds that the substance
coagulating at 52° — 55° C. is not fibrinogen but a sort of nascent fibrin.
There is also a marked difference in the precipitability of the two bodies
by sodic chloride. (See below.) Other differences between the two
may be thus enumerated : — In precipitating fibrinogen by a current
of carbonic anhydride, the containing fluid must be much more strongly
diluted, and the gas must pass for a much longer time. The pre-
cipitate thus obtained differs from that of paraglobulin in that it
forms a viscous deposit, adhering more closely to the sides and bottom
of the containing vessel ; there is also no flocculent stage previous
to the viscous precipitate.

Eibrinogen occurs in blood, chyle, serous fluids, and in various
transudations. The relations of fibrinogen and paraglobulin to the
formation of fibrin have been discussed in the text, p. 18.

Preparation4. Salted plasma, obtained by centrifugalising blood
whose coagulation is prevented by the addition of a certain proportion
of magnesic sulphate, is mixed with an equal volume of a saturated
(35-87 p.c. at 14° C.)5, solution of sodic chloride; the fibrinogen is thus
precipitated while the paraglobulin remains in solution. The adhering
plasma may be removed by washing with a solution of sodic chloride
and the fibrinogen finally purified by being several times dissolved in
and reprecipitated by sodic chloride.

There is no proof that the whole of the substance thrown down by
carbonic anhydride from diluted blood-serum is fibrinoplastic, indeed we
know that a true globulin devoid of fibrinoplastic properties may be
prepared from serum6. Weyl7 considers that there is only one globulin

1 Centralblatt f. d. med. Wiss. Jahrg. 1870, S. 367. Also Arch. f. klin. Med. Bd.
vii., S. 69.

2 Virchow's Archiv, Bd. LX., S. 476.

3 Upsala Ldkareforenings forhandlingar. Bd. xi. 1876.

4 See Hammarsten, Nov. Act. Reg. Soc. Sci. Upsala, Ser. in. Vol. x. (1875),.-
p. 31. Also Pfliiger's Archiv, Bd. xix. (1879) S. 563, and Bd. xxn. (1880), S. 431.

5 Poggiale, Ann. Chim. Phys (3) Vol. vm. p. 469.

6 Kiihne and Eichwald, loc. cit. 7 Loc. cit.

712 PROTEIDS. [Apr.

in serum, which he characterises by the name of 'serum-globulin/ and
regards fibrinoplastin as a mixture of this body with a portion of fibrin-
ferment. "We know for certain (see p. 16) that the whole of the fibrino-
plastic precipitate, used to cause the coagulation of a fibrinogenous fluid,
does not enter into the composition of the fibrin produced ; we also know
that such a precipitate may lose its fibrinoplastic powers without any
marked change in its general reactions. It would seem advisable
therefore to speak of the deposit produced by carbonic anhydride in
dilute serum, or by saturation with sodic chloride in undiluted serum,
as globulin, and to distinguish it as fibrinoplastic globulin when it is
able to give rise to fibrin. Fibrmogeii similarly might be spoken of as
fibrinogenous globulin. The name crystallin rather than globulin
might then be given to the substance obtained from the crystal-
line lens.

4. Myosin.

This is the substance which forms the chief proteid constituent
of dead, rigid muscle ; its general properties and mode of preparation
have been already described at p. 64. In the moist condition, it forms
a gelatinous, elastic, clotted mass ; dried, it is very brittle, slightly
transparent and elastic. From its solution in sodic chloride it is pre-
cipitated, either by extreme dilution, or by saturation with the solid
salt. When precipitated by dilution and submitted to the prolonged
action of water myosin loses its property of being soluble in solutions
of sodic chloride1. The sodic chloride solution, if exposed to a rising
temperature, becomes milky at 55° C., and gives a flocculent precipitate
at 60° C. This precipitate is however no longer myosin, for it is in-
soluble in a 10 p. c. sodic chloride solution, and does not, until after
many days' digestion, yield syntonin on treatment with hydrochloric
acid ('1 p. c.). It is in fact coagulated proteid (see Class V.).

Myosin is excessively soluble in dilute acids and alkalis. Advan-
tage may be taken of its solubility in the former to extract it from
muscles2. But if the reagents are at all concentrated, myosin under-
goes in the act of solution a radical change, becoming in the one case
acid-albumin or syntonin, in the other alkali-albumin (Class II.).

Like fibrin, it can in some cases decompose hydrogen dioxide, and oxidise guaiacum
with formation of a blue colour.

5. Vitellin.

As obtained from yolk of egg, of which it is the chief proteid con-
stituent, vitellin is a white granular body, insoluble in water, but very
soluble in dilute sodic chloride solutions; it surpasses myosin in this

1 Weyl, Zeitschr.f.physioL Chem.~B&. i. (1878) S. 77.

2 Danilewsky, Zeitsch. /. pJnjsioL Chem. Bd. v. (1831), S. 158.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 713

respect, for the solution may be easily filtered. Its coagulation tempera-
ture is higher than that of myosin, lying according to Weyl1, between
70° C. and 80° C. Saturation with solid sodic chloride gives no precipi-
tate ; in this respect it differs from most other members of this class.
In yolk of egg vitellin is always associated with, and probably exists
in combination with, the peculiar complex body lecithin (see p. 743).

Denis, and after him, Hoppe-Seyler, have shewn that vitellin before the treatment
requisite to free it from lecithin, possesses properties quite different from other
proteids.

A theory has been advanced that vitellin is really a complex body
like haemoglobin, and on treatment with alcohol splits up into coagulated
proteid and lecithin. When well purified it contains -75 p. c. sulphur,
but no phosphorus. Dilute acids or alkalis readily convert it in its un-
coagulated form into a member of Class II.

Fremy and Valenciennes2 have described a series of proteids, viz. ichthin,
ichthidin, &c., derived from fish and amphibia. They appear to be either identical
with, or closely related to, vitellin.

Preparation. Yolk of egg is treated with successive quantities of
aether, as long as this extracts any yellow colouring matter ; the residue
is dissolved in moderately strong (10 p. c.) sodic chloride solution, and
filtered. The filtrate on falling into a large excess of water is
precipitated. In this state it is mixed with lecithin and nuclein, and in
order to free it from these it was usually treated with alcohol. This,
as above stated, entirely changes the vitellin into a coagulated form.
It seems probable that the separation of vitellin from the other bodies
with which it is mixed in the yolk of egg may be effected by precipitat-
ing the sodic chloride solution by the addition of excess of water ; the
precipitate is then re-dissolved in 10 p. c. solution of sodic chloride and
the process repeated as rapidly as possible3.

6. Globin.

Globin, stated by Preyer4 to be the proteid residue of the complex body haemo-
globin (see p. 341), ought probably to be considered as an outlying member of this
class. It is however not readily soluble either in dilute acids or sodic chloride
solutions. It is said to bs absolutely free from ash.

CLASS IV. Fibrin.

Insoluble in water and dilute sodic chloride solutions; soluble
with difficulty in dilute acids and alkalis, and more concentrated
neutral saline solutions.

1 Op. cit. - Compt. Rend. T. xxxvm., pp. 469 and 525.

s Weyl, op. cit. S. 74. •* Die Blutknjstalle (1871), S. 160.

7U PROTEIDS. [Apr.

Fibrin, as ordinarily obtained, exhibits a filamentous structure, the
component threads possessing an elasticity much greater than that of
any other known solid proteid.

If allowed to form gradually in large masses, the filamentous structure is not so
noticeable, and it resembles in this form pure india-rubber. Such lumps of fibrin
are capable of being split in any direction, and no definite arrangement of parallel
bundles of fibres can be made out.

At ordinary temperatures fibrin is insoluble in water, being dissolved
only at very high temperatures, and then undergoing a complete change
in its characters. In hydrochloric acid solutions of 1 — 5 p. c. fibrin
swells up and becomes transparent, but is not dissolved1. In 'this
condition the mere removal of the acid by an excess of water,
neutralisation, or the addition of some salt, causes a return to the
original state. If, however, the acid be allowed to act for many days
at ordinary temperatures or for a few hours at 40° — 60° C., solution takes
place, and the resulting proteid is syntonin. In dilute alkalis and
ammonia, fibrin is much more readily soluble, though in this case also
the solution is greatly aided by warming; the resulting fluid contains
no longer fibrin, but alkali-albumin. This property is not distinctly
characteristic of fibrin, although it dissolves perhaps more readily in
both dilute acids and alkalis than do coagulated proteids. None of
these solutions can be coagulated on heating, which is intelligible when
it is remembered that they no longer contain fibrin, but either acid or
alkali-albumin. In addition to the above, fibrin is soluble, though with
difficulty and only after a considerable time, in 10 p. c. solutions of
sodic chloride, potassic nitrate or sodic sulphate, the solution being
often accompanied by putrefactive changes. These solutions may be
coagulated by a temperature of 60°C., and are precipitated by dilution
with water or saturation with solid sodic chloride; in fact, by the
action of the neutral saline solutions the fibrin has become converted
into a body exceedingly like myosin or globulin2.

On ignition of fibrin a residue of inorganic matter is always
obtained; it is, however, considered that sulphur is the only one of
these elements which enters essentially into its composition. In other
respects fibrin corresponds entirely in general composition with other
proteids.

Suspended in water and heated to 70° C., it loses its elasticity, and be-
comes opaque ; it is then indistinguishable from other coagulated proteids.

A peculiar property of this body remains yet to be mentioned, viz. its power of
decomposing hydrogen dioxide. Pieces of fibrin placed in this fluid, though them-

1 Complete solution may however take place if the fibrin, as is frequently the
case, contains any adherent pepsin.

2 Gautier, Compt. Rend. T. LXXIX. (1874), p. 227.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 715

selves undergoing no change, soon become covered with babbles of oxygen; and
guaiacum is turned blue by fibrin in presence of hydrogen dioxide or ozonised tur-
peutine.

Preparation. By vigorously stirring blood with a bundle of twigs
and then washing with water until it is quite white. If required per-
fectly pure and colourless it should be prepared from plasma free from
corpuscles. If the blood, before stirring, be diluted with an equal bulk
of water, the subsequent, washing of the fibrin is much facilitated, and
it may readily be obtained quite white. Any adherent fats may be re-
moved by aether.

When globulin, myosin, and fibrin are compared each with the other,
it will be seen that they form a series in which myosin is intermediate
between globulin and fibrin. Globulin is excessively soluble in even
the most dilute acids and alkalis ; fibrin is almost insoluble in these ;
while myosin, though more soluble than fibrin, is less soluble than
globulin. Globulin again dissolves with the greatest ease in a very
dilute solution of sodic chloride. Myosin, on the other hand, dissolves
with difficulty ; it is much more soluble in a 10 per cent, than in a one
per cent, solution of sodic chloride; and even in a 10 per cent.
solution the myosin can hardly be said to be dissolved, so viscid is the
resulting fluid and with such difficulty does it filter. Fibrin again
dissolves with great difficulty and very slowly in even a 10 per cent,
solution of sodic chloride, and in a one per cent, solution it is
practically insoluble. When it is remembered that fibrin and myosin
are, both of them, the results of coagulation, their similarity is in-
telligible. Myosin is in fact a somewhat more soluble form of fibrin,
deposited not in threads or filaments but in clumps and masses.

CLASS V. Coagulated Proteids.

These are insoluble in water, dilute acids and alkalis, and neutral
saline solutions of all strengths. In fact they are really soluble only in
strong acids and strong alkalis, though prolonged action of even dilute
acids and alkalis will effect some solution, especially at high tempera-
tures. During solution in strong acids and alkalis a destructive decom-
position takes place, but some amount of acid- or alkali-albumin is
always produced.

Very little is known of the chemical characteristics of this class.
They are produced by heating to 70° C., solutions of egg- or serum-
albumin, globulins suspended in water or dissolved in saline solutions ; by
boiling for a short time fibrin suspended in water or dissolved in saline
solutions, or precipitated acid- and alkali-albumin suspended in water.
They are readily converted at the temperature of the body into peptones,

716 PROTEIDS. [Apr.

by the action of gastric juice in an acid, or of pancreatic juice in an
alkaline medium.

All proteids in solutions are precipitated by an excess of strong
alcohol. If the precipitant be rapidly removed they are again soluble
in water, but if the precipitated proteids are subjected for some time to
the action of the alcohol they are, with the exception of peptones,
coagulated and lose their solubility. It appears however that the
proteids contained in the aleurone-grains of plants are exceedingly
resistant to this coagulating action of alcohol !.

It seems scarcely necessary to point out the distinction in the use of the word
' coagulation ' as applied to blood- or muscle-plasma on the one hand and to the
action of heat and alcohol upon proteids on the other. The difference is obvious
when it is remembered that in the first case the coagulation leads to the formation
of fibrin (Class iv.), or myosin (Class m.), and that these bodies may then further
be coagulated by heat or alcohol as described above.

CLASS VI. Peptones.

Very soluble in water, and not precipitated from their aqueous
solutions by the addition of acids or alkalis, or by boiling. Insoluble
in alcohol, they are precipitated with difficulty by this reagent, and aro
unchanged in the process ; they differ from all other proteids in not being
coagulated by prolonged exposure to alcohol. They are not precipitated
by cupric sulphate, ferric chloride, or, except in the instances to be
mentioned presently, by potassic ferrocyamde, and acetic acid. In
these points they differ from most other proteids. On the other hand,
precipitation is caused by chlorine, iodine, tannin, mercuric chloride,
nitrates of mercury and silver, and both acetates of lead ; also by bile-
acids in an acid solution. In common with all proteids, these bodies
possess a specific laevo-rotatory power over polarised light; but they
differ from all other proteids in the fact that boiling produces no change
in the amount of rotation.

A solution of peptones, mixed with a strong solution of caustic
potash, gives, on the addition of a mare trace of cupric sulphate, a pink
colour. An excess of the cupric salt gives a violet colour, which
deepens in tint on boiling, in fact the ordinary proteid reaction. Other
proteids simply give the violet colour. But the most characteristic
feature of peptones is their relatively great diffusibility, a property which
they alone, of all the proteids, may be said to possess, since all other forms
of proteids pass through membranes with the greatest difficulty, if at all.

The diffusibility of peptones is however absolutely small as compared with that
of crystalline bodies such as sodic chloride; in fact solutions of peptones may be
freed from salts by dialysis, a process employed in their preparation.

1 See Vines, JL of PhysioL Vol. in. p. 108.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 717

Notwithstanding their probable formation in large quantities in the
stomach and intestine, to judge from the results of artificial digestion, a
very small quantity only can be found in the contents of these organs
They are probably absorbed as soon as formed. Another point of
interest is their reconversion into other forms of proteids, since this
must occur to a great extent in the body. We are however as yet
ignorant of the manner in which this reverse change is effected.

Production. All proteids, with the exception of lardacein (see p. 720),
yield peptones (and other products) on treatment with acid gastric or
alkaline pancreatic juice, most readily at the temperature of the human
body. Peptones are likewise produced, in the absence of pepsin and
trypsin, by the action of dilute and moderately strong acids at medium
temperatures, also by the action of distilled water at high temperatures
under pressure. For various methods of preparing peptones, see Haly l
Aclamkiewicz2, Henninger3, and Pekelharing4.

It appears possible to reobtain ordinary coagulable proteids from peptones by
the action of either prolonged heating to 140°— 170° C. or of dehydrating agents5.

No difference in percentage composition between peptones and the
proteid from which they are formed has, at present, been definitely
established.

We have used the phrase 'peptones' in the plural number because
we have reason to think that more than one kind of peptone exists.
Meissner6 described three peptones, naming them respectively A- B-
and C-peptone. He distinguished them as follows. A-peptone is
precipitated from its aqueous solutions by concentrated nitric acid, and
also by potassic ferrocyanide in the presence of even Aveak acetic
acid. B-peptone is not precipitated by concentrated nitric acid, nor
will potassic ferrocyanide give a precipitate unless a considerable
quantity of strong acetic acid be added at the same time. C-peptone is
precipitated neither by nitric acid nor by potassic ferrocyanide and
acetic acid, whatever be the strength of the acetic acid. In place how-
ever of speaking of all' these as peptones, it is better to consider C-
peptone as the only real peptone, and the A- and B-peptones as not
peptones at all. Nevertheless we have reason, from the researches of
Kiilme, to speak of more than one peptone, viz. of a hemipeptone which
is capable under the action of trypsin of being converted into leucin and
tyrosin, and of an antipeptone which resists such a decomposition. The
name antipeptone is given to the latter on account of this resistance which

1 Pfliiger's Arch. Bd. ix. (1874) S. 585.

2 Die Natur u. Ndhrwerth d. Ptptons (1877), S. 33.

3 De la Nature et du Role physiologique des Peptones, Paris, 1878.
PflUger's Arch., Bd. xxn. (1882), S. 185.

5 Henninger, loc. cit., Hofmeister, Zeitsch.f.physioL Chem., Bd. n. (1878), S. 206.
Pekelharing, loc. cit.

6 Zeitschr. f. rat. J/«7., Bde. vii., YIII., x., xii. und xiv.

718 P ROTE IDS. [A PP.

it offers towards trypsin ; the name hemipeptone, given to the former,
signifies that this peptone is the twin or correlative half of antipeptone.

We have seen (p. 243) that when any proteid is digested with
pepsin, what we may preliminarily call a bye-product makes its appear-
ance. This bye product, which has many resemblances to acid-
albumin or syntonin, appearing as a neutralisation precipitate soluble
in dilute acids and alkalis but insoluble in distilled water, is generally
spoken of as parapeptone. According to Finkler1 this neutralisation
precipitate is especially abundant if the pepsin be previously modified
by exposure to a temperature of 40° to 60° C. The pepsin thus modified
is spoken of by Finkler as 'isopepsin.' Many authors regard parapep-
tone, syntonin, and acid-albumin as being the same thing. Meissner
however gave the name parapeptone to a body, which need not and
probably does not make its appearance during normal natural digestion
or during artificial digestion with a thoroughly active pepsin, but which
is formed when proteid s are subjected to the action of weak hydrochloric
acid, either alone or in company with an imperfectly-acting pepsin, and
which in certain characters is quite distinct from ordinary syntonin or
acid-albumin. Its distinguishing feature is that it cannot be changed
into peptone by the action of even the most energetic pepsin, though it
is readily so converted under the influence of trypsin ; otherwise it very
closely resembles syntonin. We have here an indication that the simple
characters by which we have described acid-albumin may be borne
by bodies having marked differences from each other. The researches
of Kiihne2 have thrown an important light on these differences. The
fundamental notion of Kuhne's view is that an ordinary native albumin
or fibrin contains within itself two residues, which he calls respectively
an anti-residue and a hemi-residue. The result of either peptic or
tryptic digestion is to split up the albumin or fibrin, and to produce on
the part of the anti-residue antipeptone, and on the part of the hemi-
residue hemipeptone, the latter being distinguished from the former by
its being susceptible of further change by tryptic digestion into leucin,
tyrosin, &c. Antipeptone remains as antipeptone even when placed
under the action of the most powerful trypsin, provided putrefactive
changes do not intervene.

Before the stage of peptone (whether anti- or hemi-) is reached,
there is an intermediate stage corresponding to the formation of synto-
nin. In both normal peptic and tryptic digestion antipeptone is
preceded by an anti-album ose, and hemipeptone by a hemi-albumose.
Of these the anti-albumose is closely related to syntonin, and has

3 Pfliiger's Archiv, xiv. (1877), S. 128.

2 Only a short account of these has as yet been published. Verhand. d.
hist-Med. Ver-Heidelbg. Ed. i. Hf. 4, 1876.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 719

hitherto been regarded as syntonin. The hemi-albumose has not
been so frequently observed ; it was however isolated by Meissner ; it
is apparently the body called by him A-peptone. It possesses several
peculiar features. If its solutions are heated they partially coagulate
at about 60 — 65° C. ; the precipitate is soluble at about 70° C. and is
-re-precipitated as th.e temperature again falls. It also yields a precipitate
with nitric acid and potassic ferrocyanide and this also is soluble at the
higher temperature reprecipitating on cooling. In these respects it
closely resembles a proteid body observed by Bence-Jones in the urine
of osteomalacia. It approaches myosin in being readily soluble in a
10 per cent, solution of sodic chloride.

If however albumin be digested with in sufficient or with imperfectly
active pepsin, or simply with dilute hydrochloric acid at 40° C., anti-
albumose is not formed, but in its place a body makes its appearance
which Kiihne calls anti-albumate l. Its characteristic property is that it
cannot be converted by peptic digestion into peptone, though it can be so
changed by tryptic digestion. It is in fact the parapeptone of Meissner.
It may perhaps be advisable, now that Meissner's parapeptone is
cleared up, to reserve the name parapeptone for the initial products of
both peptic and tryptic digestion, and to speak of anti-albumose and hemi-
albumose as being both parapeptones. But in this sense parapeptone
will be an intermediate and not a collateral product of digestion.

Meissner also described a particularly insoluble form of his parapep-
tone as dyspeptone, and another intermediate product as metapeptone ;
but further investigation of both these bodies, as well as of his B-peptone,
is necessary. Under the influence of dilute hydrochloric acid, anti-
albumate becomes changed into a body which Kiihne calls anti-albumid
and which seems identical with the very insoluble proteid described by
Schiitzenberger as 'hemiprotein,' and probably with Meissner's dyspep-
tone. The same body is produced at once in company with products
belonging to the hemi-group by the action of 3 to 5 per cent, sulphuric
acid on native albumin or fibrin. The following tables shew the
relations and genesis of the bodies we have just described. The several
products (antipeptone, &c.) are given in duplicate, on the hypothesis
(which though not proved is probable) that the changes of digestion are
essentially hydrolytic changes2, accompanied by a deduplication ; that
just as a molecule of starch splits up into at least two molecules
of dextrose, or as a molecule of cane-sugar splits up into a molecule of
dextrose and a molecule of levulose, so a molecule of antialbumose, for
instance, splits up into two molecules of antipeptone, and so on. But
the whole scheme is of course only provisional.

1 An albumate must not be confounded with an albuminate.

2 Henninger, loc. cit. p. 49.

720 PROTEIDS. [Apr.

DECOMPOSITION OF PROTEIDS BY DIGESTION.

Albumin. .S

( Antialbumose. Hemialbumose.

, J . J — .-,

Antipeptone. Antipeptone. Hemipeptone. Hemipeptone.

Leucin. Tyrosin. Leucin. Tyrosin.
etc. etc. f

DECOMPOSITION BY ACIDS.

1.
By -25 p. c. HC1 at 40° C.

Albumin.

I

Antialbumate. Hemialbumose.

Antialbumid. Hemipeptone. Hemipeptone.

2.

By 3—5 p. c. H2S04 at 100° C.
Albumin.

Antialbumid. Hemialbumose.

Hemipeptone. Hemipeptone.
Leucin. Tyrosin. etc. Leucin. Tyrosin. etc.

CLASS VIL Lardacein, or the so-called amyloid substance.

The substance to which the above name is applied, is found
as a pathological deposit in the spleen and liver, also in numerous other
organs, such as the blood-vessels, kidneys, lungs, <fec.

It is insoluble in water, dilute acids and alkalis, and neutral saline
solutions.

In centesimal composition it is almost identical with other proteids1,
viz. : —

0. and S. H. N. C.

24-4 7-0 150 53-6

The sulphur in this body exists in the oxidised state, for boiling
with caustic potash gives no sulphide of the alkali. The above results of

1 C. Schmidt, Ann. d. Chem. u. Pharm. Bd. ex., S. 250, and Friedreich and
Kekule, Virchow's Archiv, Bd. xvi., S. 50.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 721

analysis would lead at once to the ranking of lardacein as a proteid, and
this is strongly supported by other facts. Strong hydrochloric acid
converts it into acid-albumin, and caustic alkalis into alkali-albumin.
On the other hand, it exhibits the following marked differences from other
proteids: — It wholly resists the action of ordinary digestive fluids; it is
coloured red, not yellow, by iodine, and violet or pure blue by the joint
action of iodine and sulphuric acid. From these last reactions it has
derived one of its names, ' amyloid,' though this is evidently badly chosen ;
for not only does it differ from the starch group in composition, but by
no means can it be converted into sugar : this latter is one of the crucial
tests for a true member of the carbohydrate group. According to
Heschl1 and Cornil2 anilin-violet (methyl-anilin) colours lardaceous
tissue rosy red, but sound tissue blue.

The colours mentioned above, as being produced by iodine and sulphuric acid,
are much clearer and brighter when the reagents are applied to the purified lardacein.
When the reagents are applied to the crude suhstance hi its normal position in the
tissues, the colours obtained are always dark and dirty-looking.

Purified lardacein is readily soluble in moderately dilute ammonia,
and can, by evaporation, be obtained from this solution in the form of
tough, gelatinous flakes and lumps ; in this form it gives feeble reactions
only with iodine. If the excess of ammonia is expelled, the solution
becomes neutral, and is precipitated by dilute acids.

Preparation. The gland or other tissue containing this body
is cut up into small pieces, and as much as possible of the surrounding
tissue removed. The pieces are then extracted several times with wator
and dilute alcohol, and if not thus rendered colourless, are repeatedly
boiled with alcohol containing hydrochloric acid. The residue after
this operation is digested at 40° C., with good artificial gastric juice in
excess. Everything except lardacein, and small quantities of muciii,
nuclein, keratin, together with some portion of the elastic tissue, will
thus be dissolved and removed3. From the latter impurities it may be
separated by decantation of the finely-powdered substance.

The chief products of the decomposition of proteids are ammonia, car-
bonic anhydride, leucin and tyrosin. Several other bodies, for the most
part, like leucin, amidated acids, such as aspartic acid, gtutamic acid,

1 Wien. med. Wochenschr. No. 32, S. 714.

2 Compt. Rend. T. LXXX. (1875), p. 1288.

3 RUhne und Eudneff, Virchow's Arch. Bd. xxxnr. (1865), S. 66.

F 46

722 PROTEIDS. [Apr.

&c., have also been obtained; also by tryptic digestion, hypoxanthin
and perhaps xanthin. But urea has never yet been derived by direct
decomposition from proteid material, the statements to this effect
having been based on errors. In spite of numerous researches, we
cannot at present state definitely what is the real constitution of
a proteid, or in what manner these several residues are contained in the
undecomposed substance. It is unnecessary to give here any of
the formulae, nearly all empirical, which have been made to represent
a proteid ; they all give with equal exactitude the percentage compo-
sition, but beyond this they are untrustworthy. Of the various attempts
which have been made to assign to proteids some definite molecular
structure, none appear, at the present stage of information, sufficiently
reliable for general acceptance.

Among the most elaborate labours in this direction may be mentioned tbose of
Hlasiwetz and Haberman. In their first publication1, starting from the general
similarity of the products of decomposition of the proteids and carbohydrates, they
tried to establish a definite relation between the two classes of bodies. In this they
were not successful, and in their second research2 they come to the conclusion
that the carbohydrates take no part in the formation of the proteids.

Other experiments in the same direction have been made by Scliiitzenberger3. He
shews that albumin can be decomposed into carbonic anhydride and ammonia, and
that the ratio of these two is the same as though urea had been the body on which
he operated. From this he concludes that "the molecule of albumin contains the
grouping of urea and represents a complex ureide." In his second publication4 he
confirms his previous results, stating that the ammonia, carbonic anhydride and
oxalic acid, produced by the decomposition of proteids, are so connected quanti-
tatively as to be capable of derivation from varying proportions of urea and oxamide.
He also obtained from the decomposition of proteids a nitrogenous residue which
could be formulated as giving rise to all the amidated acids and other bodies spoken
of above. Thus according to him, albumin, built up as a complex ureide, decomposes
into ammonia, carbonic, oxalic, and acetic acids, and this nitrogenous body : this
last then gives rise to the other products of decomposition5.

It will be noticed that in the general description of the various
proteids, distinctive reactions for each could not be given, but that
varying solubilities were the chief means at our disposal for distinguishing
them. They may be arranged according to their solubilities in the
following tabular form.

Soluble in distilled water :

Aqueous solution not coagulated on boiling Peptones.

Aqueous solution coagulated on boiling Albumins.

1 Ann. d. Chem. u. Pharm. Bd. 159, S. 304.

2 Ibid. Bd. 169, S. 150.

3 Comptes Rendus, T. 80 (1875), p. 232. Bull, de la Soc. chim. xxin. 161, 193,
216, 242, 385, 433, xxiv. 2 et 145.

4 Compt. Rend. T. 81, p. 1108. Bull de la Soc. chim. xxv. 147.

6 See also Schutzenberger, Ann. de Chem. et de Phys. T. xvi. (1879), p. 280.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 723

Insoluble in distilled water :

Soluble in NaCl solution 1 per cent Globulins.

Insoluble „ „ „

( Acid- and Alkali-
Soluble in HC1 '1 per cent, in the cold „

Insoluble in HC1 '1 per cent, in the cold, but]

( Fibrin.
soluble at 60°

Insoluble in HC1 '1 per cent, at 60° ; soluble in strong acids.

Soluble in gastric juice Coagulated albumin.

Insoluble ,, „ Lardacein.

Such a classification is however obviously a wholly artificial one,
useful for temporary purposes, but in no way illustrating the natural
relations of the several members. Nor is a division into 'native'
and 'derived' proteids much more satisfactory. It is true that we may
thus put together serum- and egg-albumin, with vitellin, myosin.
and fibrin, on the one hand; and peptones, coagulated proteids,
accl acid- with alkali-albumin, on the other. But in what light are we
to consider casein, seeing that though a natural product, it has so many
resemblances to alkali-albumin ? Moreover the system of classification
must be useless which would place fibrinoplastic globulin and fibrinogen
in the same class as fibrin, and yet we can hardly speak of either of the
two former bodies as derived proteids. If the view be true that when
fibrin is converted into peptone the large molecule of the former is split
up, with assumption of water, into two smaller molecules of the latter,
one belonging to the 'anti' and the other to the 'hemi' group, we might
speculate on a possible classification of all proteids into hemi-proteids,
anti-proteids and holo-proteids. Thus serum- and egg-albumin, myosin,
and fibrin would be undoubtedly holo-proteids, peptones either anti- or
hemi-proteids, and we should have to distinguish probably in the
heterogeneous group of derived albumins both anti-, hemi- and holo-
proteid members. It is possible, moreover, that fibrinoplastic and
fibrinogenous globulin and casein may be natural hemi- or anti-proteids
and not holo-proteids. But we have at present no positive knowledge
on these points.

NITROGENOUS NON-CRYSTALLINE BODIES ALLIED TO PROTEIDS.

These resemble the proteids in many general points, but exhibit
among themselves much greater differences than do the proteids. As
regards their molecular structure nothing satisfactory is known. Their
percentage composition approaches that of the proteids, and like these
they yield, under hydrolytic treatment, large quantities of leucin and in
some cases tyrosin. They are all amorphous.

46—2

724 MUG IN, GELATIN, ETC. [Apr.

Mucin. (O, 35-75. H, 6-81. N, 8-50. C, 48-94.)1

The characteristic component of mucus. Its exact composition is
not yet known, the figures given above being merely an approximation.

As occurring in the normal condition it gives to the fluids which
contain it the well-known ropy consistency, and can be precipitated
from these by acetic acid, alcohol, alum and mineral acids ; the latter,
if in excess, redissolve the precipitate, but this is not the case with
acetic acid. In its precipitated form it is insoluble in water, but swells
up strongly in it, and this effect is increased by the presence of many
alkali salts. Alkalis and alkaline earths dissolve it readily. Its
solutions do not dialyse ; they give the proteid reactions with Millon's
reagent and nitric acid, but not that with sulphate of copper, and are
precipitated by basic lead acetate only when neutral or faintly alkaline.
According to Eichwald2, when heated with dilute mineral acids,
inucin yields acid-albumin, and another body which in many of its
properties closely resembles a sugar, inasmuch as it reduces solutions
of cupric sulphate. Prolonged boiling with sulphuric acid gives leucin
and about 7 p. c. of tyrosin.

Preparation*. Ox-gall or an aqueous extract of finely-chopped
submaxillary gland is acidulated with acetic acid; the precipitated
mucin is then washed with water, dissolved in dilute sodic carbonate
and finally precipitated with acetic acid. It may also be obtained from
snails4.

Chondrin. (0, 31-04. H, 6-76. N, 13-87. C, 47-74. S,
•60 p. c.)5

This is usually regarded as forming the essential part of the matrix
of hyaline cartilage, and is contained in the interstices of the fibres in
elastic cartilage. A similar substance can be prepared from the cornea.
Boiled with water, it dissolves slowly, forming an opalescent solution,
which is precipitated by acetic acid, lead acetate, dilute mineral acids,
alum, and salts of silver and copper ; an excess of the last four reagents
redissolves the precipitate. Solutions of this body gelatinise on
standing, even if very dilute; the solid mass is insoluble in cold
water, readily soluble in hot water, alkalis and ammonia.

The aqueous and alkaline solutions of chondrin possess a left-handed
rotatory power on polarised light of— 213-5°; in presence of excess of
alkali this becomes - 552-0°, both measured for yellow light8.

1 Eichwald, Ann. d. Chem. u. Pharrn. Bd. 134, S. 193. 2 Op. cit.

3 Eichwald, op. cit. and Chem. Centralb., 1866, No. 14. Staedeler, Ann. de Chem.
u. Pharm. Bd. Ill, S. 14. Landwehr, Zeitscli. f. physiol. Chem. Bd. v. (1881),
S. 371.

4 Landwebr, Zeitsch. f. physiol. Chem. Bd. vi. (1882), S. 75.
8 I. v. Mering, Beitrag zur Chemie des Knorpels, 1873.

8 Hoppe-Seyler, Hdb. phys. path. chem. Anal 4 Aufl. 1875, S, 262.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 725

It seems, according to the observations of many, that chondrin can,
by heating with hydrochloric acid, be converted into a body whose
reactions resemble those of syntonin, and another substance, which like
the similar product from mucin, so far resembles grape-sugar that it
reduces cupric salts in alkaline solution1 ; it appears however to contain
nitrogen. The existence of chondrin as a distinct substance has however
been denied2 on the supposition that it is in all cases a mere mixture of
other bodies. It is stated that a substance having all the reactions of the
so-called chondrin, may at any time be produced by a mixture of mucin,
glutin and inorganic salts. The extreme similarity in the reactions of
chondrin and mucin point to a close relationship between the two. The
whole subject, however, requires more complete investigation. With
alkalis or dilute sulphuric acid chondrin gives leucin, but no tyrosin or
glycin. Whether chondrin exists as such in cartilage is uncertain;
it seems probable that it does not, since its extraction from cartilage
requires an amount of boiling with water much greater than that
requisite to dissolve dried chondrin.

Preparation. From cartilage by extracting with water, and
precipitating with acetic acid.

Gelatin or Glutin3. (O, 23-21. H, 7-15. N, 18-32. C, 50-76.
S, -56 p. c.)

This is the substance which is yielded when connective tissue fibres
are heated for several days with very dilute acetic acid, at a temperature
of about 15° C., or by the prolonged action of water in a Papin's digester.
The elastic elements of connective tissue are unaffected by the above
treatment

As obtained in this way glutin is when heated a thin fluid, solidi-
fying on cooling to the well-known gelatinous form. When dried it is
a colourless, transparent, brittle body, swelling up, but remaining undis-
solved in cold water; heating, or the addition of traces of acids or
alkalis, readily effects its solution. When dissolved in water it
possesses a Isevo-rotatory power of— 130°, at 30° C. ; the addition of
strong alkali or acetic acid reduces this to -112° or -114°, both
measured for yellow light4. Its solutions will not dialyse.

Mercuric chloride and tannic acid are the only two reagents which
yield insoluble precipitates with this body. Its presence prevents the
action of Trommer's sugar test, since it readily dissolves up the
precipitated cuprous oxide. The proteid reactions of glutin are so
feeble that they are probably due merely to impurities. Heated with
sulphuric acid it yields ammonia, leucin and glycin, but no tyrosin.

1 De Bary, Hoppe-Seyler's Untersuch. Hft. i. S. 71.

2 Morochowetz, Verhand. naturhist. med. Ver. Heidelberg. Bd. I. (1876) Hft. 5.

3 Not to be confounded with the vegetable proteid 'gluten.'

4 Hoppe-Seyler, Hbd. d. phys. path. diem. Anal. 4 Aufl. 1875, S. 222.

726 MUCIX, GELATIN, ETC. [App.

It appears improbable that glutin exists ready formed in connective
tissue fibres, since these do not swell up in water, and only yield glutin
after prolonged treatment with boiling water; to which it may be added
that while glutin is acted upon by trypsin, the connective tissue fibres
in their natural condition resist its action (see p. 253). When glutin is
submitted for some time to the action of dilute hydrochloric acid, at
38° C., and the change is brought about even more readily by the action
of pepsin, it loses its power of gelatinising and is now diffusible through
porous membranes ; the name of gelatin-peptone has been given to the
product thus obtained1.

Elastin. (0, 20-5. H, 74. N, 16-7. C, 55-5 p. c.)

This characteristic component of elastic fibres is left on the removal
of all the glutin, mucin, &c. from such tissues as " ligamentum nuchoe,"
advantage being taken of its not being altered when it is heated with
water, even under pressure, with strong acetic acid, or with dilute
alkalis. When moist it is yellow and elastic, but on drying becomes
brittle. It is soluble in strong alkalis at boiling temperatures, and
concentrated sulphuric and nitric acids dissolve it even in. the cold ; it
is also dissolved by the action of papaya juice. It is precipitated from
solutions by tannic acid, but not by the addition of ordinary acids.
Notwithstanding that it closely approaches the proteids in its per-
centage composition, and gives distinct although feeble proteid reactions,
any very close relationship between the two appears improbable, since
elastin when treated with sulphuric acid, yields leucin (30 — 40 p.c.)
only and no tyrosin.

Hilger2 has obtained a similar body from the shell membrane of
snakes' eggs.

Keratin3. (0, 20-7—25-0. II, G-4-7-0. N, 16-2—17-7. C,
50-3—52-5. S, -7—5-0 p.c.)

This body, though somewhat resembling the proteids in general
composition, differs from them and also from the preceding bodies so
widely in other properties, that its description is placed here for
convenience rather than anything else. Hair, nails, feathers, horn, and
epidermic scales consist for the most part of keratin. Heated with
water in a digester at 150° C. keratin is partially dissolved with evolution
of sulphuretted hydrogen ; the solution then gives with acetic acid and
ferrocyanide of potassium a precipitate soluble in excess of the acid.
Prolonged boiling with alkalis and acids, even acetic, dissolves keratin ;
the alkaline solutions evolve sulphuretted hydrogen on treatment with

1 Hofmeister, Zeitsch. f. physiol. Chem. Bd. n. (1878), S. 299.

2 Ber. d. deutsch. chem. Gesellsch. 1873, S. 166. But see also next reference.

8 Lindwall, "Nagra bidragtiil kann. om. Ker. Upasala Lfikarefs. fork, xvi. (1881),
p. 546.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 727

acids. The sulphur in keratin is evidently very loosely united to the
substance, and in all its reactions there appears to be a want of
similarity between keratin and either proteids, mucin or gelatin. The
most common of its products of decomposition are leucin (10 p.c.), and
tyrosin (3 '6 p.c.), and some aspartic acid; no glycin is formed. What
is generally known as keratin is probably a compound body, which has
not yet been resolved into its components.

Ewald and Kiihne l have described a new body to which, since it occurs as a
constituent of nervous tissue (both of nerves and of the central nervous system),
and is yet closely identical with ordinary horny tissue, they give the name of neuro-
keratin. It is prepared in quantity from the brain by extracting this tissue with
alcohol and aether, and subjecting the residue to the action of pepsin and trypsin.
The final residue is neuro-keratin, and amounts to 15 — 20 p.c. of the original tissue.

Nuclein. C^ H^ N9 P3 O^

Discovered by Miescher2 in the nuclei of pus corpuscles and in the
yellow corpuscles of yolk of egg. Other observers have subsequently
obtained it from yeast, from semen, from the nuclei of the red blood-cor-
puscles of birds and amphibia, from hepatic cells, and it is probably
present in all nuclei.

"When newly prepared it is a colourless amorphous body, soluble to a
slight extent in water, readily soluble in many alkaline solutions; but
its solubilities alter on keeping. If added gradually in sufficient
quantity to a solution of caustic alkali it first neutralises the solution
and then renders it acid. It seems to possess an indistinct xantho-
proteic reaction, but gives no reaction with Millon's fluid. It yields
precipitates with several salts, e.g. zinc chloride, argentic nitrate, and
cupric sulphate.

Preparation3. Since nuclein is very resistent to the action of
pepsin, it may be obtained from the granular residue consisting chiefly
of nuclei, which occurs after digesting pus with pepsin. The most
remarkable feature of this body is its large percentage of phosphorus,
9-59 per cent. This phosphorus is readily separated by boiling with
strong hydrochloric acid or caustic alkalis; the same occurs when
solutions of nuclein are acidulated and allowed to stand.

Chitin. CuHagN.Ojo4.

Although not found as a constituent of any mammalian tissue, this
substance composes the chief part of the exoskeleton of many inverte-
brates. It may probably be regarded as the animal analogue of the

1 Verhand. naturhist. med. Ver Heidelberg. Bd. i. (1876), Heft 5.

2 Med. Chem. Untersuch. Hoppe-Seyler, Heft 4, 1872, S. 441 und 502.

3 See Kossel, Zeitsch. f. physiol. Chem. Bd. in. (1879), S. 284 iv. (1880), S. 290.
vn. (1883), S. 7. "Untersuch. iiber d. Nuclein u. ihre Spaltungsprod," Strassb.,
1881.

4 Ledderhose, Zeitsch. f. physiol. Chem. Bd. n. (1878), S. 213.

728 CARBOHYDRATES. [App.

cellulose of plants, and from this point of view it possesses considerable
morphological interest. Both cellulose and chitin appear to yield some
form of sugar when treated with strong acids.

"When purified, chitin is a white amorphous body, often retaining the
shape of the tissue from which it has been prepared. It is insoluble in
all reagents except strong mineral acids, the best solvents being sulphuric
or hydrochloric acids. The immediate addition of water to these solu-
tions reprecipitates the chitin in an unaltered form ; but the prolonged
action of sulphuric acid causes a decomposition resulting, according to
some observers, in the formation of an amorphous fermentible carbo-
hydrate ; and when hydrochloric acid is used an amidated carbohydrate
is obtained to which the name of glycosamin l has been given.

Preparation 2. The cleaned exoskeleton of a lobster is thoroughly
extracted with dilute hydrochloric acid and then with caustic soda. To
purify it finally it is submitted to prolonged boiling with a solution of
potassic permanganate.

CARBOHYDRATES.

Certain members only of this class occur in the human body ; of
these, the most important and wide-spread are those known as glycogen
and the two sugars, grape-sugar or dextrose (glucose), with which
diabetic sugar seems to be identical3 and maltose. Next to these comes
milk-sugar. Inosit is another body of this class, although it differs in
many important points from the preceding two.

Sugars are often considered to be polyatomic alcohols. Several of them
stand in peculiar relation to mannit, and may be converted into that substance by
the action of sodium amalgam4.

1. Dextrose (Grape-sugar). C6 H12 O6 + H2 O.

Occurs in the contents of the alimentary canal to a variable extent
dependent on the nature of the food taken. It is also a normal con-
stituent of blood, chyle,- and lymph. Concerning its presence in the
liver, see p. 419. The amniotic fluid also contains this body. Bile
in the normal condition is free from sugar, so also is urine, though
this point has given rise to great dispute5. The disease diabetes is
characterized by an excess of dextrose in the fluids and tissues of the
body (see p. 424).

1 Ledderhose, loc. cit. Bd. iv. (1880), S. 139.

2 Biitschli, Arch. f. Anat. u. Phijsiol. Jahrg. 1874, S. 362.

3 The question, however, whether several varieties of sugar occurring in the
animal body have not been confounded together under the common name of dextrose
or glucose may be considered at present an open one.

4 Linnemann, Ann. d. Chem. u. Pharm. Bd. 123, S. 136.
6 See Seegen, Der Diabetes Mellitus, 2 Ed. S. 196.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 729

When pure, dextrose is colourless and crystallises from its aqueous
solution in six-sided tables or prisms, often agglomerated into warty
lumps. The crystals will dissolve in their own weight of cold water,
requiring however some time for the process; they are very readily
soluble in hot water. Dextrose is somewhat sparingly soluble in alcohol,
and crystallises from anhydrous alcohol in prisms free from water of
crystallisation ; it is moreover insoluble in aether.

The freshly prepared cold aqueous solution of the crystals possesses a dextro-
rotatory power of + 104° for yellow light. This, quickly on heating, more slowly on
standing, falls to + 56°, at which point it remains constant.

Dextrose readily forms compounds with acids and many salts ; the latter are very
unstable, decomposition rapidly ensuing on heating them. When its metallic com-
pounds are decomposed the decomposition is in many cases accompanied by the
precipitation of the metals, e.g. silver, gold, mercury, bismuth. Caustic alkalis
readily decompose them, as also does ammonia.

Dextrose is readily and completely precipitated by lead acetate and
ammonia.

An important property of this body is its power of undergoing fer-
mentations. Of these the two principal are : (1) Alcoholic. This is
produced in aqueous solutions of dextrose, under the influence of yeast.
The decomposition is the following : C6 H12 O6 = 2 C2 H6 O + 2 CO^,
yielding (ethyl) alcohol and carbonic anhydride. Other alcohols of the
acetic series are found in traces, as also are glycerine, succinic acid and
probably many other bodies. The fermentation is most active at about
25°C. Below 5°C. or above 45°C. it almost entirely ceases. If the
saccharine solution contains more than 1 5 per cent, of sugar it will not
all be decomposed, as excess of alcohol stops the reaction. (2) Lactic.
This occurs in the presence of decomposing nitrogenous matter, especially
of casein, and is probably the result of the action of a specific ferment1.
The first stage is the production of lactic acid, C6 H]0 O6 = 2 C3 H6 O3.
In the second butyric acid is formed with evolution of hydrogen and
carbonic anhydride: 2 C3 H6O3 = C4H8O2 + 2 CO2 + 2 H2. The above
changes, the first of which is probably undergone by sugar to a consider-
able extent in the intestine, are most active at 35°C. ; the presence of
alkaline carbonates is also favourable. It is moreover essential that the
lactic acid should be neutralized as fast as it is formed, otherwise the
presence of the free acid stops the process.

The preparation, detection and estimation of dextrose are so fully
given in various books that they need not be detailed here.

1 Lister, Path. Soc. Trans. Vol. for 1873, p. 425, also Quart. Jl. of Micros.
Science, Vol. xviu. (1878), p. 177.

730 CA R BO HYDRA TES. [App.

2. Maltose. C12 H23 On + H2 O.

This form of sugar was first described by Dubrunfaut1 as a product
of the action of malt extract on starch. Its existence was for a long time
doubted until O'Sullivan2 repeated and confirmed the previous experi-
ments. According to him it crystallises in fine acicular crystals,
possesses a specific rotatory power of + 150° and a reducing power which
is only one-third as great as that of dextrose. It seems probable that
this is the chief sugar obtained by the action not only of diastase but of
ptyalin and pancreatic ferment upon starch and perhaps also upon
glycogen3; although some dextrose may at the same time be formed.
Musculus and Gruber4 have shewn that maltose may also be formed by
the action of dilute sulphuric acid on starch, and that it is capable of
undergoing alcoholic fermentation.

Preparation. See Musculus and Gruber (loc. cif.).

3. Milk-sugar. Ci2H22011 + H2O.

Also known as Lactose. It is found in milk, and is characteristic
of this secretion. It is said however to occur abnormally in the urine of
lying-in women5.

It yields, when pure, hard colourless crystals, belonging to the
rhombic system (four-sided prisms). It is less soluble in water than
dextrose, requiring for solution six times its weight of cold, but only
two parts of boiling, water; it is entirely insoluble in alcohol and aether.
It is fully precipitated from its solutions by the addition of lead acetate
and ammonia.

When freshly dissolved, its aqueous solution possesses a specific dextro-rotatory
power of +93-1° for sodium light: this diminishes, slowly on standing, rapidly on
boiling, until it finally remains constant at +52 '5°. The amount of rotation is
independent of the concentration of the solution.

Lactose unites readily with bases, forming unstable compounds ; from its metallic
compounds the metal is precipitated in the reduced state on boiling ; it reduces
copper salts as readily as dextrose but to a less extent viz. in the ratio of 70 : 100.

Lactose is generally stated to admit of no direct alcoholic fermenta-
tion ; this may however sometimes be induced by the prolonged action
of yeast. By boiling with dilute mineral acids lactose is converted into
galactose, which readily undergo alcoholic fermentation and possess a
greater rotatory power than lactose.

It may be remarked here that though isolated lactose is incapable of direct
alcoholic fermentation, milk itself may be fermented; Berthelot was unable in this

1 Ann. Chim. Phys. (3) xxi. (1847), p. 178.

2 Jl. Chem. Soc. Ser. 2, Vol. x. (1872), p. 579.

3 Musculus u. v. Mering, Zeitsch.f. physiol Chem. Bd. n. (1878), S. 403.

4 Zeitschr. f. physiol. Chem. Bd. n. (1878), S. 177.

5 Hofmeister, Ibid. Bd. i. (1877), S. 101.

APR.] CHEMICAL BASIS OF THE ANIMAL BODY. 731

direct alcoholic fermentation to detect any intermediate change of the lactose into
any other fermentable sugar.

Lactose is however directly capable of undergoing the lactic and
butyric fermentations ; the circumstances and products are the same as
in the case of dextrose (see above). The action is generally productive
of a collateral small quantity of alcohol.

Lactose is thus distinguished from dextrose by its smaller solubility
in water, insolubility in alcohol, crystalline form, lower cupric oxide re-
ducing power and its incapability of undergoing direct alcoholic fermen-
tation.

Preparation. After the removal of the casein and other proteids of
the milk, the mother liquor is evaporated to the crystallising point ; the
crystals are purified by repeated crystallisation from warm water.

4. Inosit. C6 H12 OG + 2H2 O.

This substance occurs but sparingly in the human body; it was
found originally by Scherer1 in the muscles of the heart. Cloetta shewed
its presence in the lungs, kidneys, spleen and liver2, and Miiller in the
brain3. It occurs also in diabetic urine, and in that of 'Bright's disease,'
and is found in abundance in the vegetable kingdom.

Pure inosit forms large efflorescent crystals (rhombic tables); in
microscopic preparations it is usually obtained in tufted lumps of fine
crystals. Easily soluble in water, it is insoluble in alcohol and sether.
It possesses no action on polarised light, and does not reduce solutions
of metallic salts.

It admits of no direct alcoholic, but is capable of undergoing the
lactic fermentation; according to Hilger4 the acid formed is sarcolactic.
It is unaltered by heating with dilute mineral acids.

Preparation. It may be precipitated from its solutions by the action
of basw lead acetate and ammonia ;. the lead is then removed by sulphu-
retted hydrogen and the inosit precipitated with excess of alcohol.

As a special test (Scherer's} may be mentioned the production of a
bright violet colour by careful evaporation to dryness on platinum foil,
with a little ammonia and calcium chloride.

5. Dextrin. CUH10O5.

By boiling starch-paste with dilute acids, or by the action of fer-
ments, the starch is converted into an isomeric body, to which, from its
action on polarised light, the name dextrin has been given. It is soluble

1 Ann. d. Chem. u. Pharm. Bd. 73, S. 322. 2 Ibid. Bd. 99, S. 289.

8 Ibid. Bd. 103, S. 140. •» Ibid. Bd. 160, S. 333.

732 CARBOHYDRATES. [APP.

in water, but is precipitated by alcohol. It does not undergo alcoholic
fermentation until after it has been changed into dextrose, nor can it
reduce metallic salts. It yields a reddish port-wine colour with iodine,
which disappears on warming and does not return on cooling. Further
action of acids or of ferments converts dextrin into dextrose. Dextrin
is present in the contents of the alimentary canal after a meal containing
starch, and has also been found in the blood.

There is not the least doubt that several modifications of dextrin
exist and may be obtained by the action of acids and ferments on starch.
Of these two of the best known are those described by Briickei under
the name of erythrodextrin and achroodextrin, the former giving a red
colour with iodine, the latter not yielding any colour at all. Erythro-
dextrin may be readily converted into a sugar by the action of ferments,
and thus is not found as a product of the complete action of ptyalin on
starch. Achroodextrin on the other hand is not thus converted by
ferments, and therefore remains in solution, together with the sugar
formed by the action of ptyalin on starch. Achroodextrin may be con-
verted into dextrose by boiling with dilute hydrochloric acid.

6. Glycogen. C6H10O5.

Belongs to the starch division of carbohydrates. Discovered by
Bernard in the liver and other organs (see p. 416).

Glycogen is, when pure, an amorphous powder, colourless, and taste-
less, readily soluble in water, insoluble in alcohol and sether. Its
aqueous solution is generally though not always strongly opalescent, but
contains no particles visible microscopically ; the opalescence is much
reduced by the presence of free alkalis. The same solution possesses,
according to Hoppe-Seyler, a very strong dextro-rotatory power, about
three times as great as that of dextrose8; it dissolves hydrated cupric
oxide ; but this is not reduced on boiling.

By the action of dilute mineral acids (except nitric) it is partially
converted into a form of sugar very closely resembling, though probably
differing somewhat from true dextrose, and the same conversion is also
readily effected by the action of amylolytic ferments. The sugar into
which the glycogen of the liver is naturally converted after death (see
p. 424), appears to be true dextrose3; so also the sugar of diabetes.
The result of the action of diastase, or salivary or pancreatic ferment,
upon glycogen is however according to Musculus and v. Mering4 a

1 Sitzber. d. Wien. AJcad. 1872, in. AUli. Also Vorlesungen 2. Aufi. 1875, Bd. i.
S. 224.

2 See Kiilz, Pfliiger's Arch. Bd. xxiv. (1881), S. 85.

s Pfliiger's Arch. Bd. xix. (1879), S. 106, and xxn. (1880), S. 206. Also Kiilz,
Ibid. Bd. xxiv. (1881), S. 52.

* Zeitschr. f. physiol. CJiem. Bd. n. (1878), S. 403.

Arr.] CHEMICAL BASIS OF THE ANIMAL BODY. 733

mixture of achroodextrin and maltose ; the quantity of dextrose making
its appearance at the same time being very small.

Opalescent solutions of glycogen usually become clear on the addition
of caustic alkali : Yintschgau and Dietl1 have shewn that this is accom-
panied on boiling by a change which converts a portion of the glycogen
into a substance to which they give the name of /S.-glycogen-dextrine.
(Kiihne2 had previously described a body to which he gave the name gly-
cogen-dextrin. That described by Yintschgau and Dietl differs slightly
from Kiihne's body, hence the name.) According to these authors one-
fifth of the glycogen is at the same time changed into some other, at pre-
sent undetermined, substance. Normal lead acetate gives a cloudiness,
the basic salt a precipitate, in solutions of glycogen.

As tests for this body may be used the formation of a port-wine
colour with iodine ; this disappears on warming but returns on cooling.
The same colour is produced by the action of iodine on dextrin, but
this does not reappear on cooling after its disappearance by warming.

Preparation of Glycogen. The following is Briicke's3 method. The
filtered or simply strained decoction of perfectly fresh liver or other gly-
cogenic tissue is, when cold, treated alternately with dilute hydrochloric
acid, and a solution of the double iodide of potassium and mercury4,
as long as any precipitate occurs. In the presence of free hydrochloric
acid, the double iodide precipitates proteid matters so completely as to
render their separation by filtration easy. The proteids being thus got
rid of, the glycogen is precipitated from the filtrate by adding alcohol to
the extent of between 60 and 70 p. c. Too much alcohol is to be
avoided, since other substances as well as glycogen are thereby pre-
cipitated. The glycogen is now washed with alcohol first of 60 and
then of 95 per cent, afterwards with aether, and finally with absolute
alcohol. It is then dried over sulphuric acid.

Tunicin. (C6H10O5)U.

This body is regarded by many observers as identical with the true
cellulose of plants, while others have ascribed to it properties differing
from those of cellulose sufficiently to justify its receiving a distinct name.
It appears to be more resistent to the action of chemical reagents than
plant-cellulose.

It constitutes the chief part of the integument of the Ascidia or

1 Pfluger's Arch. Bd. xvn. (1878), S. 154.

2 Lehrb. d. physiol. Chem. (1868), S. 63.

3 Sitzungsber. d. Wiener Akad. Bd. 63 (1871), n. Abth.

4 This may be prepared by precipitating potassic iodide with mercuric chloride
and dissolving the washed precipitate in a hot solution of potassic iodide as long
as it continues to be taken .up. On cooling, some amount of precipitate occurs,
which must be filtered off; the nitrate is then ready for use.

734 FATTY ACIDS. [App.

Tunicata. As prepared from this source it is when pure quite white and
usually retains the shape of the tissue. It is unacted upon by any
reagent except strong acids and alkalis, and by the action of the former
it yields some form of sugar.

FATS, THEIR DERIVATIVES AND ALLIES.

THE ACETIC ACID SERIES.

General formula Cn H3n O3 (monobasic).

This, which is one of the most complete homologous series of organic
chemistry, runs parallel to the series of monatomic alcohols. Thus formic
acid corresponds to methyl alcohol, acetic acid to ethyl (ordinary)
alcohol, and so on. The several acids may be regarded as being derived
from their respective alcohols by simple oxidation : thus ethyl alcohol
yields by oxidation acetic acid :— C2 H6 O + O2 = C2 H4 O2 + H3 O. The
various members differ in composition by CHg, and the boiling points
rise successively by about 19° C. Similar relations hold good with regard
to their melting points and specific gravities. The acid properties are
strongest in those where n has the least value. The lowest members of
the series are volatile liquids, acting as powerful acids; these succes-
sively become less and less fluid, and the highest members are colour-
less solids, closely resembling the neutral fats in outward appear-
ance. Consecutive acids of the series present but very small differences
of chemical and physical properties, hence the difficulty of separating
them: this is further increased in the animal body by the fact that
exactly those acids which present the greatest similarities usually occur
together.

The free acids are found only in small and very variable quantities
in various parts of the body ; their derivatives on the other hand form
most important constituents of the human frame, and will be considered
further on.

Formic acid. CHO . OH,

When pure is a strongly corrosive, fuming fluid, with powerful irri-
tating odour, solidifying at 0°C., boiling at 100° C., and capable of
being mixed in all proportions with water and alcohol. It has been
obtained from various parts of the body, such as the spleen, thymus,
pancreas, muscles, brain, and blood ; in the latter its presence may be
due to the action of acids on the haemoglobin. According to some
authors1 it occurs also in urine.

1 Buliginsky, Hoppe-Seyler's Med. chem. Mittheilung. Heft. 2, S. 240. Tlmdichum,
Journ. of the Chem. Soc. Vol. 8, p. 400.

APP.] CHEMICAL BASIS OF THE AXIMAL BODY. 735

Heated with sulphuric acid it yields carbonic oxide and water ; with
caustic potash it gives hydrogen and oxalic acid.

Acetic acid. C2 H3 O . OH.

Is distinguished by its characteristic odour; its boiling point is
117°C. ; it solidifies at 5° and is fluid at all temperatures above 15°C.
It is soluble in all proportions in alcohol and water.

It occurs in the stomach as the result of fermentative changes in the
food, and is frequently present in diabetic urine. In other organs and
fluids it exists only in minute traces.

With ferric chloride it yields a blood-red solution, decolourized by hydrochloric
acid. (It differs in this last reaction from sulphocyanide of iron.) Heated with
alcohol and sulphuric acid, the characteristic odour of acetic aether is obtained. It
does not reduce silver nitrate.

Propionic acid. C3 H5 O . OH.

This acid closely resembles the preceding one. It possesses a very
sour taste and pungent odour; is soluble in water, boils at 141°C.,
and may be separated from its aqueous solution by excess of calcic
chloride.

It occurs in small quantities in sweat, in the contents of the stomach,
and in diabetic urine when undergoing fermentation. It is similarly
produced, mixed however with other products, during alcoholic fermen-
tation, or by the decomposition of glycerine. It partially reduces silver
nitrate solution on boiling.

Butyric acid. C4 H7 O . OH.

An oily colourless liquid, with an odour of rancid butter, soluble in
water, alcohol, and aether, boiling at 162°C. Calcic chloride separates
it from its aqueous solution.

Found in sweat, the contents of the large intestine, faeces, and in
urine. It occurs in traces in many other fluids, and is plentifully
obtained when diabetic urine is mixed with powdered chalk and kept at
a temperature of 35° C. It exists, as a neutral fat, in small quantities
in milk.

This is the principal product of the second stage of lactic fermenta-
tion. (See Dextrose.)

Valerianic acid. C5 H9 O . OH.

An oily liquid, of penetrating odour and burning taste ; soluble in
30 parts of water at 12°C., readily soluble in alcohol and sether. Boils
at 175° C. Possesses, in free and combined form, a feeble right-handed
rotation of the plane of polarisation.

736 FATTY ACIDS. [App.

It is found in the solid excrements, and is formed readily by the de-
composition, through putrefaction, of impure leucin, ammonia being at
the same time evolved; hence its occurrence in urine when that fluid
contains leucin, as in cases of acute atrophy of the liver.

Caproic acid. C6 Hu O . OH.

Caprylic „ C8H15O.OH.

Capric (Rutic) acid C10H19O . OH.

These three occur together (as fats) in butter, and are contained in
varying proportions in the faeces from a meat diet. The first is an oily
fluid, slightly soluble in water, the others are solids and scarcely soluble
in water ; they are soluble in all proportions in alcohol and aether.
They may be prepared from butter, and separated by the varying solu-
bilities of their barium salts.

Laurostearic acid. C12 H23 0 . OH.
Myristic „ CUH27O. OH.

These occur as neutral fats in spermaceti, in butter and other fats.
They present no points of interest,

Palmitic acid. C16 H31 0 . OH.
Stearic „ C18H35O.OH.

These are solid, colourless when pure, tasteless, odourless, crystalline
bodies, the former melting at 62° Q, the latter at 69 -2° C. In water
they are quite insoluble ; palmitic acid is more readily soluble in cold
alcohol than stearic : both are readily dissolved by hot alcohol, aether, or
chloroform. Glacial acetic acid dissolves them in large quantity, the
solution being assisted by warming. They readily form soaps with the
alkalis, also with many other metals. The varying solubilities of their
barium salts afford the means of separating them when mixed l : this
may also be applied to many others of the higher members of this
series.

These acids in combination with glycerin (see below), together with
the analogous compound of oleic acid, form the principal constituents of
human fat. As salts of calcium they occur in the faeces and in
'adipocire/ and probably in chyle, blood and serous fluids, as salts of
sodium. They are found in the free state in decomposing pus, and in
the caseous deposits of tuberculosis.

The existence of margaric acid, intermediate to the above two, is not now
admitted, since Heintz 2 has shewn that it is really a mixture of palmitic and stearic
acid. Margaric acid possesses the anomalous melting point of 59'9° C. A mixture
of 60 parts stearic and 40 of palmitic acids, melts at 60-3°.

1 Heintz, Annal. d. Phy*. it. Chcm. Ed. 92, S. 588. 2 Op. cit. -

APP."| CHEMICAL BASIS OF THE ANIMAL BODY. 737

• ACIDS OF THE OLEIC (ACRYLIC) SERIES. H (CM H2n_3) Os (monobasic).

Many acids of this series occur as glycerine compounds in various
fats. They are very unstable, and readily absorb oxygen when exposed
to the air. The higher members are decomposed on attempting to
distil them. Their most peculiar property is that of being converted
by traces of NO2 into solid, stable metameric acids, capable of being
distilled. They bear an interesting relation to the acids of the acetic
series, breaking up when heated with caustic potash into acetic acid and
some other member of the same series : — thus,

Oleic acid. Potassic acetate. Potassic palmitate.

H01.HMOt + 2KHO = KCiHaOf + KCl6 H3l O, + H9.

Oleic acid. C18H33O . OH.

This is the only acid of the series which is physiologically important.
It is found united with glycerin in all the fats of the human body.

When pure it is, at ordinary temperatures, a colourless, odourless,
tasteless, oily liquid, solidifying at 4°C. to a crystalline mass. Insoluble
in water, it is soluble in alcohol and aether. It cannot be distilled
without decomposition. It readily forms with potassium and sodium
soaps, which are soluble in water: its compounds with most other bases
are insoluble. It may be distinguished from the acids of the acetic
series by its reaction with NOg and by the changes it undergoes when
exposed to the air.

THE NEUTRAL FATS.

These may be considered as aethers formed by replacing the exchange-
able atoms of hydrogen in the triatomic alcohol glycerin (see below), by
the acid radicles of the acetic and oleic series. Since there are three
such exchangeable atoms of hydrogen in glycerin, it is possible to form
three classes of these aethers; only those, however, which belong to the
third class occur as natural constituents of the human body : those of
the fi rst and second are of theoretical importance only.

They possess certain general characteristics. Insoluble in water and
cold alcohol, they are readily soluble in hot alcohol, aether, chloroform,
&c. ; they also dissolve one another. They are neutral bodies, colourless
and tasteless when pure; are not capable of being distilled without
undergoing decomposition, and yield as a result of this decomposition,
solid and liquid hydrocarbons, water, fatty acids, and a peculiar body,
acrolein. (Glycerin contains the elements of one molecule of acrolein,
and two molecules of water.)

They possess no action on polarised light.

They may readily be decomposed into glycerin and their respective
fatty acids by the action of caustic alkalis, or of superheated steam.
F. 47

38 FATS, ETC. [APP.

Palmitin (Tri-palmitin). 'JP&L <V

The following reaction for the formation of this fat is typical for all
the others :

Glycerin. Palmitic acid. Palmitin.

C*H4o+3C'«H"°io- °°H<
Hj°'+ H /0-(C16H3,

Palmitin is slightly soluble in cold alcohol, readily so in hot alcohol,
or in jether; when pure it crystallises in fine needles; if mixed with
stearin, it generally forms shapeless lumps, although the mixture may at
times assume a crystalline form, and was then regarded as a distinct body,
namely margarin. It possesses three different melting points, according
to the previous temperatures to which it has been subjected. It solidifies
in all cases at 45° C.

Preparation. From palm oil, by removing the free palmitic acid
with alcohol, and crystallising repeatedly from aether.

Stearin (Tri-steariu). /r,C*?' A O..

(Ujgll^Us)!

This is the hardest and least fusible of the ordinary fats of the
body; is also the least soluble, and hence is the first to crystallise out
from solutions of the mixed fats. It crystallises usually in square
tables. It presents peculiarities in its fusing points similar to those of
palm it in.

Preparation. From mutton suet, its separation from palmitin and
olein being effected by repeated crystallisation from aether, stearin being
the least soluble.

Olein (Tri-olein). Q8

^3^5 j

Is obtained with difficulty in the pure state, and is then fluid at
ordinary temperatures. It is more soluble than the two preceding ones.
It readily undergoes oxidation when exposed to the air, and is converted
by mere traces of N02 into a solid isomeric fat. Olein yields, on dry
distillation, a characteristic acid, the sebacic, and is saponified with much
greater difficulty than are palmitin and stearin.

Preparation. From olive oil, either by cooling to 0° 0. and pressing
out the olein that remains fluid ; or by dissolving in alcohol and cooling,
when the olein remains in solution while the other fats crystallise out.

Glycerin C^F 5| 0..

This principal constituent of the neutral fats may. as above stated,
be looked upon as a triatoniic alcohol.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 739

When pure, glycerin is a viscid, colourless liquid, of a well-known
sweet taste. It is soluble in water and alcohol in all proportions,
insoluble in aether. Exposed to very low temperatures it becomes almost
solid ; it may be distilled in close vessels without decomposition, between
275°— 280° C.

It dissolves the alkalis and alkaline earths, also many oxides, such
as those of lead and copper; many of the fatty acids are also soluble in
glycerin.

It possesses no rotatory power on polarised light.

It is easily recognized by its ready solubility in water and alcohol,
its insolubility in aether, its sweet taste, and its reaction with bases.
The production of acrolein is also characteristic of glycerin.

C3H808- 2H,O = C,H4O (Acrolein).

Preparation. By saponification of the various oils and fats. It is
also formed in small quantities during the alcoholic fermentation of
sugar1.

Soaps. These may be formed by the action of caustic alkalis on fats.
The process consists in a substitution of the alkali for the radicle of
glycerin, the latter combining with the elements of water to form
glycerin. Thus
Tristearin. Potassic stearate. Glycerin.

(o»H.o),i 0 ,K) _ gcg^.01 eystt

C3HS j°'+3H/C K P H,}0"

Pancreatic juice can split up fats into glycerin and free fatty acids (see p. 254),
and the bile is known to be capable of saponifying these fatty acids. The amount
of soaps formed in the alimentary canal is however small and unimportant.

ACIDS OF THE GLY COLIC SERIES.

Running parallel to the monatomic alcohols (C^H^^O) is the series
of diatomic alcohols or glycols (CnHn+2O2). Thus corresponding to ethyl
alcohol is the diatomic alcohol, ethyl-glycol. As from the monatomic
alcohols, so from the glycols, acids may be derived by oxidation ; from
the latter (glycols) however two series of acids can be obtained, known
respectively as the glycolic and oxalic series. The iirst stage of oxi-
dation of the glycol gives a member of the glycolic series, thus :

Ethyl-glycol. Glycolic- acid.

C2H6O2 + O2 = C2H4O3 + H2O, or more generally
C.H^ A + 02 p. CJF^O, + H20.

1 Pasteur, Ann. d. Chem. u. Pharm. Bd. 106, S. 338.

47—2

740

LACTIC ACIDS.

[App.

By further oxidation a member of the glycolic series can be converted
into a member of the oxalic series, thus :

Glycolic acid. Oxalic acid.

C2H4O3 + O2 = C2H2O4 + H2O, or more generally

CroH2n03 + 02 = CnH2re_204 + H20.

The acids of the glycolic series are diatomic but monobasic ; those of
the oxalic series are diatomic and diabasic.

The following table may be given to shew the general relationships
of alcohols and acids :

Eadicle.

Alcohol.

Acid.

Glycols.

Acid I.

Acid II.

Formic.

Carbonic.

Methyl (CH8)

CH,(OH)

HCH02

I*

H2C03

Ethyl (C2H5)

C2H5(OH)

Acetic.
HC2H302
Propionic.

Ethyl-glycol
C2H4(OH)2
Propyl-glocol

Glycolic.
HC2H303
Lactic.

Oxalic.
H2C204
Malonic.

Propyl (C3H7)

C3H7(OH)

HC3H502

C3H6(OH)2

HC3H503

H2C3H204

Butyl (C4H9)

C4H9(OH)

Butyric.
HC4H702

Butyl-glycol
C,H8(OH)2

Oxybutyric.
HC5H703

Succinic.
H2C4H404

GLYCOLIC ACID SERIES.
Lactic acid. C3H603.

Next to carbonic acid, the most important member of this series, as
far as physiology is concerned, is lactic acid.

Lactic acid exists in four isomeric modifications, but of these only
three have been found in the human body. These three all form sirupy,
colourless fluids, soluble in all proportions in water, alcohol and jether.
They possess an intensely sour taste, and a strong acid reaction. When
heated in solution they are partially distilled over in the escaping
vapour. They form salts with metals, of which those with the alkalis
are very soluble and crystallise with difficulty. The calcium and zinc
salts are of the greatest importance, as will be seen Liter on.

1. Ethylidene-lactic acid. This is the ordinary form of the
acid, obtained as the characteristic product of the well-known 'lactic fer-
mentation.' It occurs in the contents of the stomach and intestines.
According to Ileintz1 it is found also in muscles, and according to
Gscheidlen 2 in the ganglionic cells of the grey substance of the brain.
In many diseases it is found in urine, and exists to a large amount in
this excretion after poisoning by phosphorus 8.

1 Ann. d. Chem. u. Pharm. Bd. 157, S. 320.

2 Pfluger's Archiv, 3d. vm. (1873—74) S. 171.

3 Schultzen and Eiess, Ueber acute PhospJiorvcrgiftung. Chem. Ccntralb. 1869, S.
681.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 741

It may be prepared by the general methods of slowly oxidising the corresponding
glycol or by acting on monochlorinated propionic acid with moist silver oxide.
In obtaining it from the products of lactic fermentation, the crusts of zinc lactate
are purified by several crystallisations, and the acid liberated from the compound by
the action of sulphuretted hydrogen.

2. Ethylene-lactic acid. This acid is found accompanying the
next to be described, in the watery extract of muscles. From this it is
separated by taking advantage of the different solubilities in alcohol
of the zinc salts of the two acids. It seems probable, however, that
it has not yet been prepared in the pure state by this method.

TVislicenus first obtained this acid by heating hydroxycyanide of ethylene with
aqueous solutions of the alkalis1.

The same observer found it also in many pathological fluids.

3. Sarcolactic acid. This acid has not yet been procured syn-
thetically. As its name implies, it is that form of the acid which
chiefly occurs in muscles, and hence exists in large quantities in Liebig's
' extract of meat.' It is often found also in pathological fluids. This
is the only acid of the series which possesses any power of rotating the
plane of polarised light; it is otherwise indistinguishable from the
preceding ethylidene-lactic acid, and is generally represented by the
same formula. The free acid has dextro-, the anhydride Isevo-rotatory
action. The specific rotation for the zinc salt in solution is -7' 65° for
yellow light.

The zinc and calcium salts of sarcolactic acid are more soluble both
in water and alcohol, than those of ethylidene-lactic acid, but less so
than those of ethylene-lactic acid, and the same salts of ethylene-lactic
acid contain more water of crystallisation than those of the other two.

Heintz2 has compared the above acids to the modifications capable of existing in
tartaric acid3.

Hydracrylic acid, the fourth in this series of lactic acids, is distinguished by the
nature of its decomposition on heating. It is never found as a constituent of
animal bodies.

OXALIC ACID SERIES.

Oxalic acid. H2 C2 O4.

In the free state this acid does not occur in the human body. Cal-
cic oxalate, however, is a not unfrequent constituent of urine, and
enters into the composition of many urinary calculi, the so-called mul-
berry calculus consisting almost entirely of it. It may occur in fseces,
and in the gall bladder, though this is rarely observed.

1 Ann. d. Chem, u. Pharm. Bd. 128, S. 6.

2 Op. cit.

3 See further, Wislicenus, op. cit. Also Ann. d. Chem. u. Pharm. Bd. 166, S. 3,
Bd. 167, S. 302, and Zeitschr. f. Chem. Bd. xm. S. 159.

742 ACIDS OF THE OXALIC SERIES, [App.

As ordinarily precipitated from solutions of calcic salts by am-
raonic oxalate, calcic oxalate is quite amorphous, but in urinary
deposits it assumes a strong characteristic crystalline form, viz. that of
rectangular octohedra. In some cases it presents the anomalous forms
of rounded lumps, dumb-bells, or square columns with pyramidal ends.
It is insoluble in water, alcohol and aether, also in ammonia and acetic
acid. Mineral acids dissolve this salt readily, as also to a smaller extent
do solutions of sodic phosphate or urate. All the above characteristics
serve to detect this salt ; its microscopical appearance, however, is gene-
rally of most use for this purpose.

The pure acid is prepared either by oxidising sugar with nitric acid,
or decomposing ligneous tissue with caustic alkalis.

Succinic acid. H2 C4 H4 O4.

This is the third acid of the oxalic series, being separated from oxalic
acid by the intermediate malonic acid, H2C3H2O4. It occurs in the
spleen, the thymus, and thyroid bodies, hydrocephalic and hydrocele
fluids.

According to Meissner and Shepard1 it is found as a normal constituent of urine.
This is contested by Salkowsld2, and also by von Speyer. It seems probable how-
ever that since wines and fermented liquors contain succinic acid, and this latter
passes unchanged into the urine, that it may thus be occasionally present in this
excretion.

Succinic acid crystallises in large rhombic tables, also at times in the
form of large prisms : they are soluble in 5 parts of cold water, and 2*2
of boiling, slightly soluble in alcohol, and almost insoluble in aether.
The crystals melt at 180° 0., and boil at 235° C., being at the same time
decomposed into the anhydride and water. The alkali salts of this acid
are soluble in water, insoluble in alcohol and aether.

Preparation. Apart from the synthetic methods, it may readily be
obtained by the fermentation of calcic malate, acetic acid being produced
simultaneou sly.

Its presence is recognised by the microscopic examination of its
crystals, and its characteristic reaction with normal lead acetate. With
this it gives a precipitate, easily soluble in excess of the precipitant, but
coming down again on warming and shaking3.

CHOLESTERIN. (C^H^O.)

This is the only alcohol which occurs in the human body in the free
state. (The triatomic alcohol glycerin is almost always found combined

1 Untersuch. uber d. Entsteh. d. Hippursaure. Hannover, 1866.

2 Pfluger's Archiv, Bd. n. (1869) S. 367, and Bd. iv. (1871) S. 95.

3 For further particulars see Meissner, op. cit. and Meissner arid Solly, Zeitschr.
/. rat. Med. (3) Bd. xxiv. S. 97.

APP.] CHEMICAL BASIS OF THE AXIMAL BODY. 743

'as in the fats; and cetyl alcohol, or eethal, is obtained only from sperma-
ceti.) It is a white crystalline body, crystallising in fine needles from
its solution in aether, chloroform or benzol ; from its hot alcoholic solu-
tions it is deposited on cooling in rhombic tables. When dried it melts
at 145°, and distils in closed vessels at 360° C. It is quite insoluble in
water and cold alcohol ; soluble in solutions of bile salts.

Solutions of cholesterin possess a left-handed rotatory action on
polarised light, of - 32° for yellow light, this being independent of con-
centration and of the nature of the solvent

Heated with strong sulphuric acid it yields a hydrocarbon ; with
concentrated nitric it gives cholesteric acid and other products. It is
capable of uniting with acids and forming compound aethers.

Cholesterin occurs in small quantities in the blood and many tissue*,
and is present in abundance in the white matter of the cerebro- spinal
axis and in nerves. It is a constant constituent of bile, forming fre-
quently nearly the whole mass of some gall-stones. It is found in many
pathological fluids, hydrocele, the fluid of ovarial cysts, &c,

Preparation. From gall-stones by simple extraction with boiling
alcohol, and treatment with alcoholic potash to free from extraneous
matter.

As tests for this substance may be given : — With concentrated sul-.
phuric acid and a little iodine a violet colour is obtained, changing
through green to red or blue. This is applicable to the microscopic
crystals. After dissolving in chloroform a blood-red solution is formed
on the addition of an equal volume of concentrated sulphuric acid; this
solution if exposed to the air in an open dish turns, blue, green and
finally yellow; the sulphuric acid under the chloroform has a green
fluorescence. After evaporation to dry ness with nitric acid, the residue
turns red on treating with ammonia.

This body is described here rather for the sake of convenience than from its
possessing any close relationship to the substances immediately preceding.

COMPLEX NITROGENOUS FATS.

Lecithin. C« Hw NP09.

Occurs widely spread throughout the body. Blood, bile, and serous
fluids contain it in small quantities, while it is a conspicuous component
of the brain, nerves, yolk of egg, semen, pus, white blood-corpuscles, and
the electrical organs of the ray.

When pure, it is a colourless, slightly crystalline substance, which
can be kneaded, but often crumbles during the process. It is readily

744 NITROGENOUS FATS. [APP.

soluble in cold, exceedingly so in hot alcohol ; sether dissolves it freely
though in less quantities, as also do chloroform, fats, benzol, carbon di-
sulphide, &c. It is often obtained from its alcoholic solution, by eva-
poration, in the form of oily drops. It swells up in water and in this
state yields a flocculent precipitate with sodium chloride.

Lecithin is easily decomposed : not only does this decomposition set
in at 70° C., but the solutions, if merely allowed to stand at the ordinary
temperature, acquire an acid reaction, and the substance is decomposed.
Acids and alkalis, of course, effect this much more rapidly. If heated
with baryta water it is completely decomposed, the products being
neurin, glycerinphosphoric acid, and baric stearate. This may be thus
represented : —

Lecithin. Stearic acid. Glyceringaosphoric

3H20 = 2018H3803 + 03H9P06 + C5H15N02.
When treated in an sethereal solution with dilute sulphuric acid, it is
merely split up into neurin and distearyl-glycerinphosphoric acid. Hence
Diakonow l regards lecithin as the distearyl-glycerinphosphate of neurin,
two atoms of hydrogen in the glycerinphosphoric acid being replaced by
the radicle of stearic acid. It appears also that there probably exist
other analogous compounds in which the radicles of oleic and palmitic
acids take part.

Preparation. Usually from the yolk of egg, where it occurs in union
with vitellin. Its isolation is complicated, and the reader is referred to
Hoppe-Seyler*.

Glycerinphosphoric acid. C3H9P06.

Occurs as a product of the decomposition of lecithin, and hence is
found in those tissues and fluids in which this latter is present : in
leukhsemia the urine is said to contain this substance. It has not been
obtained in the solid form. It has been produced synthetically by
heating glycerin and glacial phosphoric acid ; it may be regarded as
formed by the union of one molecule of glycerin with one of phosphoric
acid, with elimination of one molecule of water. It is a dibasic acid ;
its salts with barium and calcium are insoluble in alcohol, soluble in cold
water. Solutions of its salts are precipitated by lead acetate.

Protagon. (0lt50H3a8N5P033?)

A crystalline body, containing nitrogen and phosphorus, obtained by
Liebreich3 from the brain substance and regarded by him as its principal

1 Hoppe-Seyler's Med. Chem. Untersuch, Heft. n. (1867), S. 221, Heft. in. (1868),
3. 405. Centralb. f. d. med. Wiss. (1868), Nr. 1. 7 u. 28.
3 Med. Chem. Untersuch. Heft. n. (1867), S. 215.
3 Ann. d. Chem. u. Pharm. Bd. 134, S. 29.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 745

constituent The researches of Hoppe-Seyler and Diakonow tended to
shew that protagon was merely a mixture of lecithin and cerebrin. A
repetition of Liebreich's experiments has however led Gamgee and Blan-
kenhorn1 to confirm the truth of his results. Protagon appears to separate
out from warm alcohol on gradual cooling in the form of very small
needles, often arranged in groups : it is slightly soluble in cold, more
soluble in hot alcohol, and aether. It is insoluble in water, but swells
up and forms a gelatinous mass. It melts at 200° C. and forms a
brown sirupy fluid.

Preparation. Finely divided brain substance, freed from blood and
connective tissue, is digested at 45° C. with alcohol (85 p. c.) as long as
the alcohol extracts anything from it. The protagon which separates
out from the nitrate is well washed with aether to get rid of all
cholesterin and other bodies soluble in aether, and finally purified by
repeated crystallisation from warm alcohol.

N eurin (Cholin). C8 H15 ISTOa.

Discovered by Strecker8 in pig's-gall, then in ox-gall. It does not
occur in the free state except us a product of the decomposition of lecithin.
It is a colourless fluid, of oily consistence, possesses a strong alkaline re-
action, and forms with acids very deliquescent salts. The salts with
hydrochloric acid and the chlorides of platinum and gold are the most
important.

Neurin is a most unstable body, mere heating of its aqueous solution
sufficing to split it up into glycol, trimethylamin and ethylene oxide.

Preparation. From yolk of egg. For this see Diakonow *.

Wurtz4 has obtained it synthetically, first by the action of glycol hydrochloride
on trimethylamin, and then by that of ethylene oxide and water on the same
substance. The above, together with the mode of its decomposition, point to the
idea that neurin may be regarded as trimethyl-oxyethyl-ammonium hydrate,
N(CH3^3(C2H50)OH.

Cerebrin. C17 H^ N03 (?)

Is found in the axis cylinder of nerves, in pus corpuscles, and
largely in the brain. In former times many names were given to the
substance when in an impure state ex.gr. cerebric acid, cerebrote, &c.
W. Miiller5 first prepared it in the pure form, and constructed the
above formula from his analysis; the mean of these is O, 15 '85. H,
11 '2. N, 4*5. C, 6845. Great doubts are however thrown upon

1 Zeitschr. f. physiol. Chem. Bd. ra. (1879) S. 260, and Jl. of Physiol. Vol. n.
(1879) p. 113.

2 Ann. d. Chem. u. Pharm. Bd. 123, S. 353, Bd. 148, S. 76.

3 Op. cit. (sub. Lecithin).

* Ann. d. Chem. u. Pharm. Sup. Bd. 6, S. 116 u. 127.
c Ann. d. Chem. «. Phat-m. Bd. 105, S. 361.

746 UREA AND ITS ALLIES. [App.

its purity, by the researches of later observers. According to Liebreich1
and Diakonow2, it is a glucoside3.

Cerebrin is a light, colourless, exceedingly hygroscopic powder, which
swells up strongly in water, slowly in the cold, rapidly on heating.
When heated to 80° C. it turns brown, and at a somewhat higher tempe-
rature melts, bubbles up and finally burns away. It is insoluble in cold
alcohol, or aether; warm alcohol dissolves it easily. Heated with
dilute mineral acids, cerebrin yields a sugar-like body, possessing left-
handed rotation, but incapable of fermentation.

Preparation. Eor this see W. Miiller*.

NITROGENOUS METABOLITES.
THE UREA GROUP, AMIDES, AND SIMILAR BODIES.

Urea. (NH2)2 CO.

The chief constituent of normal urine in mammalia, and some other
animals; the urine of birds also contains a small amount. Normal
blood, serous fluids, lymph and the liver, all contain the same body in
traces. It is not found in the muscles, as a normal constituent, but
may make its appearance there under certain pathological conditions.

When pure it crystallises from a concentrated solution in the form
of long, thin glittering needles. If deposited slowly from dilute
solutions, the form is that of four-sided prisms with pyramidal ends;
these are always anhydrous. It possesses a somewhat bitter cooling
taste, like saltpetre. It is readily soluble in water and alcohol, the
solutions being neutral. In anhydrous aether it is insoluble. The
crystals may be heated to 120°C. without being decomposed; at a
higher temperature they are first liquefied and then decompose, leaving
no residue. Heated with strong acids or alkalis, decomposition ensues,
the final products being carbonic anhydride and ammonia. The same
decomposition may also occur as the result of the action of a specific
ferment on urea in an aqueous solution5. Nitrous acid at once decom-
poses it into carbonic anhydride and free nitrogen. It readily forms
compounds with acids and bases; of these the following are of im-
portance.

Nitrate of urea. (NH2)2 CO. HNO3.

Crystallises in six-sided or rhombic tables. Insoluble in aether and
nitric acid, soluble in water, slightly soluble in alcohol.

1 Arcli. f. patkol. Anat. Bd. 39 (1867).

2 Centralb. f. d. med. Wiss. 1868, Nr. 7.

3 See also, Geogheghan, Zeitsch.f. physiol. Chem. Bd. in. (1879) S. 332.

4 Op. cit.

6 Musculus, Pfliiger's Archiv, Bd. xu. (1876) S. 214. Jaksch. Zeitsch.f. physiol.
Chem. Bd. v. (1881) S. 395.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 747

Oxalate of urea. [(NH2)2 CO]2 . H2 C2 04 + H3 O.

Often crystallises in long thin prisms, but under the microscope is
obtained in a form closely resembling the nitrate; it is slightly soluble
in water, less so in alcohol.

With mercuric nitrate urea yields three salts, containing respectively,
4, 3 and 2 equivalents of mercuric oxide to one of urea. The first is the
precipitate formed in Liebig's quantitative determination of urea and
may be represented by the formula 2N2 H4 CO . Hg (NO3)2 3HgO. The
exact constitution of these salts has not yet been determined.

Preparation. Ammonic sulphate and potassic cyanate are mixed to-
gether in aqueous solution, and the mixture is evaporated to dry ness.
The residue when extracted with absolute alcohol yields urea. From
urine, either by evaporating to dryness, having previously precipitated
the urine with normal and basic lead acetate in succession and removed
the lead by sulphuretted hydrogen, and then extracting with alcohol; or
concentrating only to a syrup, and then forming the nitrate of urea;
this is washed with pure nitric acid and decomposed with baric
carbonate.

Detection in Solutions. In addition to the microscopic appear-
ance of the crystals obtained on evaporation, the nitrate and oxalate
should be formed and examined. Another part should give a precipitate
with mercuric nitrate, in the absence of sodic chloride, but not in the
presence of this last salt in excess. A third portion is treated with
nitric acid containing nitrous fumes ; if urea is present, nitrogen and
carbonic anhydride will be obtained. To a fourth part nitric acid in
excess and a little mercury are added, and the mixture is warmed. In
presence of urea a colourless mixture of gases (N and C02) is given off.
A fifth portion is kept melted for some time, dissolved in water, and
cupric sulphate and caustic soda are added; a red or violet colour, due
to biuret, is developed.

Quantitative determination. For this some special manual
must be consulted '. It will suffice here to point out that the determina-
tion is made either with a solution of mercuric nitrate of known strength
(Liebig) ; by decomposing the urea by means of sodic hypobromite into
nitrogen, carbonic anhydride and water and measuring the nitrogen
(Knop) [N2 H4 CO + SNaBrO = SNaBr + CO2 + 2H2 O + NJ or by heating
the urea with caustic baryta in a sealed tube, the urea being determined
by the weight of baric carbonate formed (Bun sen).

Urea is generally considered to be an amide of carbonic acid i.e. car-
bamide. The amide of an acid is formed when water is removed from the
ammonium salt of the acid ; if the acid be dibasic and two molecules of
1 Neubauer and Vogel, Analyse des Harris, vin. Aufl. 1881. S. 264.

nS UREA AND ITS ALLIES. [App.

water be removed, the result is often spoken of as a diamide. Thus if
from ammonic carbonate, (NH4)2CO3, two molecules of water, 2H2O, be
removed, carbonic acid being a dibasic acid, the result is urea; thus :

(NH4)2 C03 - 2H20 = (NH2)2 CO,

which may be written either according to the ammonia type as
CO

H

or as CO

two atoms of amidogen (NH2) being substituted for two atoms of hy-
droxyl (HO).

This connection between carbonic acid and urea is shewn by the fact
that ammonic carbonate may be formed out of urea by hydration, as
when urea is subjected to the specific ferment mentioned above.
Regarded then as a diamide of carbonic acid, urea may be spoken
of as carbamide. Bat the theoretical derivation of urea from ammonic
carbonate by dehydration cannot be realised in practice, whereas urea
can readily be formed from ammonic carbarnate, and Kolbe is inclined
to regard it, not as the diamide of carbonic acid, but as the amide of
carbamic acid. Ammonium carbamate, C02N2H6 minus H20, gives urea,
CO, N2, H4 — which, if carbamic acid be written as CO, OH, NH2, may
be written as CO, NH2, NH,, one atom of amidogen being substituted
for one atom of hydroxyl, and not two, as when the substance is re-
garded as derived from carbonic acid. Drechsel's experiments indicate
a ready derivation of urea from ammonic carbamate. He has obtained
urea by the electrolysis of a solution of this salt with rapidly alternating
currents thus removing the elements of water from the carbamate by
such alternating processes of oxidation and reduction as may be supposed
to take place in the body. The reaction is expressed as follows :

i. NH . CO . O . NH4 + O - NH2 . CO . O . NH2 + H2O.
ii. NH2 . CO . ONH2 + H, = NH2 . CO . NH2 + H2O.

Wanklyn and Gamgee2 however, since urea when heated with a
large excess of potassic permanganate gives off all its nitrogen in
a free state and not in the oxidized form of nitric acid, as do all other
amides, conclude that it is not an amide at all, that it is isomeric only
and not identical with carbamide.

It is important to remember that urea is also isomeric with ammonic

(N
cyanate, C j Q-J^JJ and indeed was first formed artificially by Wohlei

(1828) from this body. We thus have three isomeric compounds, am-
monium cyanate, urea, and carbamide, related to each other in such a way
1 Arch.f. Physiol. 1880, S. 550. 2 Journ. Chem. Soc. 2, Vol. vr. p. 25.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 749

' that urea may be obtained readily either from ammonium cyanate or from
ammonic carbamate, and may with the greatest ease be converted into
ammonic carbonate1. Now urea is a much more stable body than
amnionic cyanate, and in the transformation of the latter into the
former, energy is set free; and it is worthy of notice that though the
presence of sulphocyanides in the saliva probably indicates the existence
of cyanic residues in the body, the nitrogenous products of the decom-
position of proteids belong chiefly to the class of amides, cyanogen
compounds being rare among them. Pfliiger2 has called attention to the
great molecular energy of the cyanogen compounds, and has suggested
that the functional metabolism of protoplasm by which energy is set
free, may be compared to the conversion of the energetic unstable
cyanogen compounds into the less energetic and more stable amides. In
other words, ammonium cyanate is a type of living, and urea of dead
nitrogen, and the conversion of the former into the latter is an image of
the essential change which takes place when a living proteid dies.

Compound Ureas. The hydrogen atoms of urea can be replaced by alcohol and
acid radicles. The results are compound ureas or ureides when the hydrogen is
replaced by an acid radicle. Many of them are called acids, since the hydrogen
from the amide group, if not all replaced as above, can be replaced by a metal.
Thus the substitution of oxalyl (oxalic acid) gives parabanic acid,

CO

/

N2 H2

a

Ic2o2

of tartronyl (tartronic acid), dialuric acid, CO, NH2, N.C3H203; of rnesoxalyl
(mesoxalic acid), alloxan, CO, NE^, N . C303. These bodies are interesting as being
also obtained by the artificial oxidation of uric acid. (See below).

Uric acid. C5H4N403.

The chief constituent of the urine in birds and reptiles ; it occurs
only sparingly in this excretion in man and most mammalia. It is
normally present in the spleen, and traces of it have been found in
the lungs, muscles of the heart, pancreas, brain and liver. Urinary
and renal calculi often consist largely of this body, or its salts. In gout,
accumulations of uric acid salts may occur in various parts of the body,
forming the so-called gouty concretions.

It is when pure a colourless, crystalline powder, tasteless, and with-
out odour. The crystalline form is very variable, but usually tends to-

1 The following literature is interesting in connection with the question of the
cyanic or amide origin of urea. Drechsel: Ber. d. k. s. Gesell. d. Wiss. Leipzig:
Sitz. 25. Juli. 1875; Arch. f. PhysioL, 1880, S. 550. v. Knieriem: Zt.f. Biol.t Bd.
x. (1874), S. 263. Munk: Zt. f. physiol. Chem., Bd. 11. (1878), S. 29. . E. Salkow-
ski : Centralb. f. d. Med. Wiss.\ 1875. No. 58 ; Ber. d. dtutsch. Chem. Gesell., 1875,
S. 116; Zeitsch. f. physiol. Chem., Bd. I. (1877), Sn. 1. u. 374; Bd. rv. (1880), Sn.
54. u. 103. Schmiedeberg: Arch. f. exp. PathoL, Bd. vni. (1877), S. 1.

2 Pfliiger's Archiv, Bd. x. (1875) S. 337.

750 UREA AND ITS ALLIES. [APP.

wards that of rhombic tables1. When impure it crystallises readily,
but then possesses a yellowish or brownish colour. In water it is very
insoluble (1 in 14,000 or 15,000 of cold water); aether and alcohol
do not dissolve it appreciably. On the other hand, sulphuric acid takes
it up without decomposition, and it is also readily soluble in many salts
of the alkalis, as in the alkalis themselves. Ammonia however scarcely
dissolves it.

Salts of Uric acid. Of these the most important are the acid
urates of sodium, potassium, and ammonium. The sodium salt crystallises
in many different forms, these not being characteristic, since they are
almost the same for the corresponding compounds of the other two
bases. It is very insoluble in cold water (1 in 1100 or 1200), more
soluble in hot (1 in 125). It is the principal constituent of several
forms of urinary sediment, and composes a large part of many calculi ;
the excrement of snakes contains it largely. The potassium resembles
the sodium salt very closely, as also does the compound with
ammonium ; the latter occurs generally in the sediment from alkaline
urine.

Preparation. Usually from guano, or snake's excrement. From
guano by boiling with caustic potash (1 part alkali to 20 of water) as
long as ammonia is evolved. In the nitrate a precipitate of acid urate
of potassium is formed by passing a current of carbonic anhydride ;
this salt is then washed, dissolved in a caustic potash and decomposed
by carefully pouring its solution into an excess of hydrochloric acid.

The presence of uric acid is recognized by the following tests. The
substance having been examined microscopically, a portion is evaporated
carefully to dry ness with one or two drops of nitric acid. The residue
will, if uric acid is present, be of a red colour, which on the addition of
ammonia turns to purple. This is the murexide test, and depends
on the presence of alloxan and alloxantin in the residue. Schiff2 has
given a delicate reaction for uric acid. The substance is dissolved
in sodic carbonate, and dropped on paper moistened with a silver
salt. If uric acid be present a brown stain is formed, due to the
reduction of the carbonate of silver. An alkaline solution of uric acid
can, like dextrose, reduce cupric sulphate, with precipitation of the
cuprous oxide.

Uric acid resists very largely the action of even strong acids and
alkalis, exhibiting in this respect a marked difference from urea. It
might therefore perhaps be supposed that urea residues do not pre-exist
in uric acid ; nevertheless by oxidation uric acid does give rise not only

1 See Ultzmann and K. B. Hoffman, Atlas der Harnsedimente, Wien, 1872.

2 Ann. d. Chem. u. Pharm. Bd. 109, S. 65.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 751

to ordinary urea, but also, and at the same time, to the compound ureas
(ureides) spoken of above. Thus by oxidation with acids,

Uric acid. Alloxan. Urea.

C5H4N403 + H20 + O = C4N2H2O4 + C£T2H4O.

Now alloxan, as was stated above, is a compound urea, viz. mesoxal yl-
urea, and by hydration can be converted into mesoxalic acid and urea,

thus:

Alloxan. Mesoxalic. Urea.

C4N2H204 + 2H20 = C2 H2 O6 + CN2H4O ;

and by the action of chlorine uric acid can be split up directly into a
molecule of mesoxalic acid and two molecules of urea :
Uric acid. Mesoxalic acid. Urea.

C5H4N4O3 + C12 + 4H2O = C3 H2 O5 + 2CN2H4OC + 2HC1.
By oxidation with alkalis, uric acid is converted into allantoin and

carbonic acid,

Uric acid. Allantoin.

C5H4N403 + H20 + O = C4H6N403 + CO2 ;
and allantoin, by hydration, becomes allanturic or lantanuric acid and

urea,

Allantoin. Urea. Allanturic acid.

C4H6N4O3 + H2O - CH4N20 + C3H4N2O.

Now allanturic acid is a compound urea, with a residue of glyoxylic
acid. By other oxidations of uric acid, parabanic acid (oxalyl-urea),
oxaluric acid (which is hydrated parabanic acid), and dialuric acid
(tartronyl-urea) are obtained. In fact all these decompositions of a
molecule of uric acid lead to the production of urea and of a carbon acid
of some kind or other. The relation of uric acid to urea as illustrated
by the above reactions is brought very prominently into view by the
synthesis of uric acid which has recently been performed1. It is
obtained by simply fusing together glycocine (amido-acetic acid,) and
urea at a temperature of 200° — 230° C. The converse formation of gly-
cocine from uric acid with the simultaneous production of ammonia and
carbonic anhydride has been known for some time. Since in this latter
reaction the ammonia and carbonic anhydride are in the proportions in
which they would be obtained from cyanic or cyanuric acid, uric acid
has been regarded as built up from residues of cyanuric acid and glycin,
just as hippuric acid is formed from glycin and benzoic acid. It was
also at one time supposed that uric acid might be regarded as tartronyl
cyanamide.

N2 (ON),

IH,
1 Horbaczewski, Ber. d. deutsch. chem. Gesell. Jahrg. 1882, S. 2678.

752 UREA AND ITS ALLIES, [App.

If the existence of some cyanogen residue is thus assumed in the
molecule of uric acid, then it must be supposed that before urea can be
obtained from it a molecular change takes place by which a portion at
least of the nitrogen of the uric acid is converted into the same condition
as the rest of the nitrogen, viz., into the amide state.

If this be so, since the metabolism of the animals in which uric acid
replaces urea cannot be supposed to be fundamentally different from
that of the urea-producing animals, we may infer that the antecedent
of both uric acid and urea in the regressive metabolism of proteids
is, as we suggested above, a body containing some at least of its nitrogen
in the form of cyanogen1.

Kreatin. C4 H. N3 O2.

Occurs as a constant constituent of the juices of muscles, though
possibly it may be formed during the process of extraction by the
hydration of kreatinin. Kreatin is not a normal constituent of urine,
but it is said to occur in traces in several fluids of the body. When
found in urine its presence is probably due to the conversion of
kreatinin, a constant constituent of urine, into kreatin during its
extraction, since Dessaignes3 has shewn that the more rapidly the
separation is effected, the less is the quantity of kreatin obtained, and
the greater the amount of kreatinin.

In the anhydrous form it is white and opaque, but crystallises with
one molecule of water in colourless transparent rhombic prisms. It
possesses a somewhat bitter taste, is soluble in cold, extremely soluble in
hot water, is less soluble in absolute than in dilute alcohol, and is soluble
in aether.

It is a very weak base, scarcely neutralising the weakest acids. It
forms crystalline compounds with sulphuric, hydrochloric and nitric
acids.

Preparation. From extract of muscle by precipitating completely
with basic lead acetate, and crystallising out the kreatin, mixed with
kreatinin. From this latter it is separated by the formation of the
zinc-salt of kreatinin, kreatin not readily yielding a similar compound.

Kreatin may be converted into kreatinin under the influence of acids, the trans-
formation being one of simple dehydration.

Kreatin may be decomposed into sarcosin (methyl-glycin) and urea :
C4H9N302 + HaO = C3H7N02 + CH4N3O ;

1 See V. Knieriem, Zeitsch. f. Biol Bd. xm. (1877), S. 36. Schroder, Zeitsch. /.
Physiol. Chem. Bd. n. (1878), S. 228.

2 J. Pharm. (3) Bd. xxxn. S. 41.

APR] CHEMICAL BASIS OF THE ANIMAL BODY. 753

it maybe formed synthetically1 by tlie action of sarcosin and cyanamide:

C3H7NO2 + CH2N2 - C4H9N3O.

Sarcosin is glycin in which one atom of hydrogen has been replaced by
the alcohol radicle methyl, thus :

C0H30 ) C2H2(CH3)O ) _

like glycin, Farcosin has not been found in a free state in the body.

Kreatinin. C4H7N,O.

This, which is simply a dehydrated form of kreatin, occurs normally
as a constant constituent of urine and of muscle extract. It crystallises
in colourless shining prisms, possessing a strong alkaline taste and
reaction. It is readily soluble in cold water (1 in 11 -5), also in alcohol,
but is scarcely soluble in aether. It acts as a powerful base, forming
with acids and salts compounds which crystallise well. Of these the
most important is the salt with zinc chloride (C4H7N3O)2Zn CLy It is
formed when a concentrated solution of the chloride is added to a not
too dilute solution of kreatinin. Since the compound is very little
soluble in alcohol, it is better to use alcoholic rather than aqueous
solutions. It crystallises in warty lumps composed of aggregated
masses of prisms, or fine needles.

Preparation. Either by the action of acids on kreatin, or from
human urine by concentrating, and precipitating with lead acetate; in
the nitrate from this, a second precipitate is caused by the addition of
mercuric chloride, and consists of a compound of this salt with kreatinin.
The mercury is removed by sulphuretted hydrogen, and the kreatinin
purified by the formation of the zinc salt, and washing with alcohol.

Kreatinin-zinc chloride may he converted into kreatin, by the action of hydrated
oxide of lead on its boiling aqueous solution.

Allantoin. C4H6N403.

The characteristic constituent of the allantoic fluid of the foetus; it
occurs also in the urine of animals for a short period after their birth.
Traces of it are sometimes detected in this excretion at a later date.

It crystallises in small, shining, colourless prisms, which are taste-
less and odourless. They are soluble in ] 60 parts of cold, more soluble
in hot water, insoluble in cold alcohol and aether, soluble in hot alcohol.
Carbonates of the alkalis dissolve them, and compounds may be formed
of allantoin with metals but not with acids.

Allantoin, as already stated, p. 750, is one of the products of the
oxidation of uric acid, and by further oxidation gives rise to urea.

1 Sitzungsber. d. bvjersch. Akad. 1868, Hft 3, S. 472.
F. 48

:754 UREA AND ITS ALLIES. [Arp.

Preparation. This is best can led out by the careful oxidation of uric
acid either by means of potassic permanganate or ferrocyanide, or by
plumbic oxide.

Hypoxanthin or Sarkin. C5H4N4O.

Is a normal constituent of muscles, occurring also in the spleen,
liver, and medulla of bones. In leukhsemia it appears in the blood and
urine. It crystallises in fine needles which are soluble in 300 parts of
cold, more soluble in hot water, insoluble in alcohol, soluble in acids and
alkalis. It forms crystalline compounds with acids and bases. It is
precipitated by basic acetate of lead, the precipitate being soluble in a
solution of the normal acetate. Its preparation from muscle-extract
depends on its precipitation first by basic acetate of lead, and then by an
ammoniacal solution of silver nitrate after the removal of kreatin.

Both hypoxanthin aud the next hody, xanthin, can also be obtained from
proteids by the action of putrefactive changes, of water at boiling temperature, of
dilute hydrochloric acid (-2 p.c.) at 40° C, and by the action of gastric and pancreatic
ferments1. Chittenden has noticed a peculiar difference between fibrin and egg-
albumin when submitted to the above processes ; he finds that the latter does not
yield hypoxanthin when treated with boiling water, with dilute hydrochloric acid, or
gastric ferment, while the former does. Egg-albumin on the other hand yields
hypoxanthin by the action of pancreatic ferment in alkaline solution but not so
readily as fibrin does.

Xanthin. C5H4N4O3.

First discovered in a urinary calculus, and called xanthic oxide.
More recently it has been found as a normal, though scanty, constituent
of urine, muscles, and several organs, such as the liver, spleen,
thymus, <fec.

When precipitated by cooling from its hot, saturated, aqueous
solution it falls in white flocks, but if the solution be allowed to
evaporate slowly it is obtained in small scales. When pure it is a
colourless powder, very insoluble in water, requiring 1500 times its
bulk for solution at 1 00° 0. Insoluble in alcohol and aather, it readily
dissolves in dilute acids and alkalis, forming crystallisable compounds.

Hypoxanthin by oxidation becomes xanthin. Both these bodies, as
well as the following, guanin and carnin, are evidently closely allied to
uric acid; indeed, uric acid by the action of sodium-amalgam may be
converted into a mixture of xanthin and hypoxanthin.

Preparation. It is obtained from urine and the aqueous extract of
muscle by a process similar to that for hypoxanthin, and is then

1 Salomon, Zeitschr. f. physiol. Chem. Bd. n. (1878-1879), S. 60. Krause, Inaug.
Diss., Berlin, 1878. Chittenden, Journ. of Physiol. Vol. n. (1879), p. 28. See also
Drechsel, Ber. d. deutsch. Chem. Gesell. Jahrg. xin. (1880), S. 240. Salomon,
Ibid. S. 1160. Kossel, Zeitsch.f. physiol. Chem. Bd. v. (1881), Sn. 152 u. 267.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 755

separated from the latter by the action of dilute hydrochloric acid; this
separation depends on the different solubilities of the hydrochlorides of
the two bodies. For further information see Neubauer and Vogel1.

Carnin . C7 H8 N4 O3.

Discovered by Weidel2 in extract of meat, of which it constitutes
about one per cent.

It crystallises in white masses composed of very small irregular
crystals; it is soluble with difficulty in cold, more easily soluble in hot
water, insoluble in alcohol and aether. Its aqueous solution is not
precipitated by normal lead acetate, but is by the basic acetate of this
metal. It unites with acids and salts forming crystalline compounds.

Preparation. Is found in the precipitate caused in extract of meat
by basic acetate of lead3.

This body possesses an interesting relation to hypoxanthin, into which it maybe
converted by the action either of nitric acid or, still better, of bromine.

Guanin. C5H5lSr50.

First obtained from guano, but recently observed as occurring in
small quantities in the pancreas, liver and muscle extract.

It is a white amorphous powder, insoluble in water, alcohol, aether
and ammonia. It unites with acids, alkalis and salts to form crystallis-
able compounds.

Preparation. From guano by boiling successively with milk of
lime and caustic soda, precipitating with acetic acid, and purifying by
solution in hydrochloric acid and precipitation by ammonia.

Guanin may, by the action of nitrous acid, be converted into xanthin.
By oxidation it can be made to yield principally guanidine and parabanic
acid, accompanied however by small quantities of urea, xanthin and
oxalic acid. Capranica has given several reactions characteristic of
this body4.

Its separation from hypoxanthin and xanthin depends on its in-
solubility in water and behaviour with hydrochloric acid.

Kynurenic acid. C20 H]4 1ST2 Od + 2H2 O.

Found in the urine of dogs, and first described by Liebig5. When
pure it crystallises in brilliant white needles, insoluble in cold, soluble
in hot alcohol. The only salt of this body which crystallises well is

1 Ham- Analyse, Ed. vm. (1881), S. 26. Also the literature quoted above on
hypoxanthin.

2 Ann. d. Chem. v. Pliarm. Bd. 158, S. 365.

3 See Weidel, op. cit. 4 Zeitsch.f. physiol. Chem. Bd. rv. (1880), S. 240.
5 Ann. d. Chem. u. Pharm. Bd. 86, S. 125, and Bd. 108, S. 354.

48—2

756 UREA AND ITS ALLIES. [AFP.

that formed with barium. For preparation and other particulars see
Liebig1 and Schultzen and Schmiedeberg2.

Glycin. C2 H2 (NHa) 0 (OH). Also called Glycocoll and Glycocine.

Does not occur in a free state in the human body, but enters into
the composition of many important substances, ex. gr. hippuric and bile
acids. It crystallises in large, colourless, hard rhombohedra, which are
easily soluble in water, insoluble in cold, slightly soluble in hot alcohol,
insoluble in aether. It possesses an acid reaction, but a sweet taste. It
has also the property of uniting with both acids and bases, to form
crystallisable compounds. In this it exhibits its amide nature, and that
it is an amide is rendered evident from the methods of its synthetic
preparation; thus mono-chlor-acetic acid and ammonia give glycin and
ammonic chloride :— CaH,Cl O2 + 2NH3 = C2H2(NH2)0(OH) + NH4CL It
is amido-acetic acid. Heated with caustic baryta it yields ammonia
and methylamine.

Preparation. From glutin by the action of acids or alkalis; from
hippuric acid by decomposing it with hydrochloric acid at a boiling
temperature and removing by precipitation the simultaneously formed
benzoic acid.

Taurin. C2H7NO.S.

In addition to entering into the composition, of taurocholic acid (see
p. 763) taurin is found in traces in the juices of muscle and in the lungs.

It crystallises in colourless, regular, six-sided prisms; these are
readily soluble in water, less so in alcohol. The solutions are neutral.
It is a very stable compound, resisting temperatures of less than 240° 0;
it is not acted on by dilute alkalis and acids, even when boiled with
them. It is not precipitated by metallic salts.

Taurin is amido-isethionic aoid; and may be synthetically prepared
from isethionic (ethyl- sulphuric) acid by the action of ammonia; thus:

S04 + NH3 S03 * HA

Preparation. As a product of the decomposition of bile, and is
purified by removing any traces of bile acids by means of lead acetate,
and then successively crystallising from water.

Leucin. C6H13N02.

Is one of the principal products of the decomposition of nitrogenous
matter, either under the influence of putrefaction or of strong acids and
alkalis. It occurs however normally in the pancreas, spleen,

1 Op. cit. 2 Ann. d. Cherr.. u. Pharm. Bd. 164, S. 155.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 757

thyroid, salivary glands, liver, &c., and is one of the products of the
tryptic (pancreatic) digestion of proteids; in acute atrophy of the liver
it is present in the urine in large quantity, in company with tyrosin.

As usually obtained in an impure form it crystallises in rounded
lumps which are often collected together and sometimes exhibit radiating
striation. When pure, it forms very thin, white, glittering flat crystals.
These are easily soluble in hot water, less so in cold water and alcohol,
insoluble in aether. They feel oily to the touch, and are without smell
and taste. Acids and alkalis dissolve them readily, and crystallisable
compounds are formed.

Carefully heated to 170° C. it sublimes, but at a higher temperature is decom-
posed, yielding amylamin, carbonic anhydride and ammonia. In the presence of
putrefying animal matter it splits up into valeric acid and ammonia.

Leucin is amido-caproic acid, and may be represented thus :

Preparation. From horn shavings by boiling with sulphuric acid,
neutralising with baryta and separating from tyrosin by successive crys-
tallisation. See also Kiihne1, who prepares it by the action of pancreatic
ferment (trypsin) on proteids.

Scherer has given the following test for leucin. The suspected sub-
stance is evaporated carefully to dryness with nitric acid ; the residue,
if it is leucin, will be almost transparent and turn yellow or brown on
the addition of caustic soda. If this be again very carefully concen-
trated with the alkali an oily drop is obtained, which is quite character-
istic of this substance. Leucin if not too impure, may be easily recog-
nized by its subliming on being heated; a characteristic odour of
amylamin is at the same time evolved

Asparagine. C4H8N2O3.

Is not found as a constituent of the animal body but appears- to be
formed by the decomposition of proteids, notably during the germinative
changes of the proteids in leguminous seeds 2. It is a crystalline body,
and when boiled with acids or alkalis is readily converted into aspartic
acid.

Aspartic (or asparaginic) acid. C4H7NO4.

This acid has been obtained in small quantities among the products
of the pancreatic digestion of fibrin3 and vegetable glutin4, although not

1 Virchow's Archiv, Bd. 39, S. 130.
8 Landwirthsch. Versuchs Stationen. Bd. xvm. 1.

3 Kadzieje-wski u. Salkowski, Ber. d. deutsch. cTiem. GeselL Jahrg. vn. (1874),
S. 1050.

* V. Kuieriem, Zeitscli.f. Bio!. BJ. xi. (1875), S. 198.

758 UREA AND ITS ALLIES. [APP.

occurring as a constituent of any animal tissue or secretion. It is on the
other hand found normally in plants, notably in beet-sugar molasses. It
arises also as a constant product of the action of alkalis and other reagents
on both vegetable and animal proteids, and of acids on gelatine1. It thus
possesses considerable interest in respect of its relation to the proteids
(see p. 721). It crystallises in rhombic prisms which are but sparingly
soluble in cold water or alcohol, readily soluble in boiling water. Its
acid solutions are dextrorotatory, its alkaline laevorotatory and reduce
Fehling's fluid. It forms a characteristic readily crystallisable compound
with copper. Nitrous acid converts it into malic acid.

Glutaminic acid. C5H9N04.

The circumstances and conditions under which this body occurs are
in general the same as for the aspartic acid, and hence as a product of
proteid decomposition it acquires some importance. It has not however
as yet been obtained by the action of pancreatic ferments on proteids
and in this it differs from the preceding body.

It crystallises in rhombic tetrahedra or octahedra; is not very soluble
in cold, but readily soluble in hot water; insoluble in alcohol and
aether. Its acid solutions possess a strong dextrorotatory power and it
reduces Fehling's fluid.

Cystin. C3H7NS02.

Is the chief constituent of a rarely occurring urinary calculus in men
and dogs. It may also occur in renal concretions, and in gravel, and is
occasionally found in urina

From calculi it is obtained, by extraction with ammonia, as colour-
less six-sided tables or rhombohedra, which are neutral and tasteless.
It is insoluble in water, alcohol and aether, soluble in ammonia and the
other alkalis, and also in mineral acids. The fact that this body is one
of the few crystalline substances, occurring physiologically, which
contain sulphur, renders its detection very easy. Apart from its
insolubility in water, &c., it yields with caustic potash and salts of
either silver or lead, a brown colouration due to the presence of the
sulphides of these metals.

According to Dewar and Gamgee2 cystin is amido-sulpho-pyruvic acid, and its
formula is C3H5NS02— pyruvic being lactic acid minus two atoms of hydrogen.

1 Horbaczewski, Sitxb. d. k. Akad. d. Wiss. Wien, 1890. 2 Abth. Juui-Heft.
a Journ. of Anat. and PJtysioL, Nov. 1S70, p. 143.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 759

THE AROMATIC SERIES.

Benzole acid. HC7 F5 O2.

This is not found as a normal constituent of the body, but owes its
presence in. urine to the fermentative decomposition of hippuric acid,
whereby glycin and benzoic acid are formed :

Hippuric acid. Glycin. Benzoic acid.

C, H4 (C7 H5 O) N02 + H2 0 - a H3 K02 + C7 H6 O2.

The sublimed acid is generally crystallised in fine needles, which are
light and glistening ; any odour they possess is not due to the acid, but
to an essential oil, with which they are mixed. When precipitated from
solution, the crystalline form is always indistinct. This acid is soluble
in 200 parts cold, or 25 parts of boiling water, but is easily soluble
in alcohol or aether. It sublimes readily at 145° C. ; it also passes off
in the vapours arising from its heated solutions.

Preparation. Either as above from hippuric acid by fermentation,
by boiling the hippuric acid with acids or alkalis or by sublimation from
gum-benzoin.

Ty rosin. C9HnN03.

Generally accompanies leucin, and is perhaps found normally in small
quantities in the pancreas and spleen. It is also usually obtained in
large quantities by the decomposition of proteid matter, either by
putrefaction or the action of acids.

The researches of Kadziejewsky1 render it probable that tyrosin does not occur
normally in any part of the human organism, except as a product of pancreatic
digestion.

All attempts to synthetise tyrosin were for some time fruitless,
although evidence was obtained sufficient to indicate the probable
existence in its molecule of some aromatic (phenyl) radicle2. More
recently the synthesis has been performed3, and we now have every
reason for regarding tyrosin as para-hydroxy-pheiiyl-a alanine. This
synthesis as well as that of uric acid, referred to above, is of considerable
importance, since the more definite the knowledge which is possessed
of the true molecular structure of the products of proteid decomposition
the more reason is there for expecting that the synthesis of a proteid
itself may be realisable in the not very remote future.

1 Archiv. f. path. Anat. Bd. 36, S. 1. Zeitsch. f. anal. Ghent. Bd. 5, S. 466.

2 Barth., Chum. Centralb. 1865. S. 1029. 1869. S. 761. 1872. S. 830. Hufner,
Ibid. 1869. S. 159. Beilstein u. Kiihlberg, Ibid. 1872, S. 830.

3 Erlenmeyer u. Lipp., Per. d. deutsch. Chem. Gesell. Jahrg. XT. (1882), S. 1544.

760 THE AROMATIC SERIES. [App.

Tyrosin crystallises in exceedingly fine needles which are usually
collected into feathery masses. The crystals are snow-white, tasteless and
odourless, almost insoluble in cold water, readily soluble in hot water,
acids and alkalis, insoluble in alcohol and aether. If crystallised from
an alkaline solution tyrosin often assumes the form of rosettes composed
of fine needles arranged radiately.

Tyrosin does not sublime by heating, but is decomposed with an
odour of phenol and nitrobeuzol. On boiling with Millon's reagent
it gives a reaction almost identical with, but much more marked than,
that for proteids (Hoffman's test). If tyrosin is treated on a watch-
glass with one or two drops of strong sulphuric acid, then diluted with
a little water, neutralised with calcic carbonate and the solution filtered,
a characteristic violet colour is obtained on the addition of a drop of
acid-free ferric chloride (Piria's test).

Preparation. By means similar to those employed for leucin, the
separation of the two depending on their widely differing solubilities.
According to Kuhne's method1 large quantities are easily obtained as
the result of pancreatic digestion.

Hippuricacid. C9H9NO3. Or Benzoyl-glycin. C2H4(C7H50)N02.

Is found in considerable quantities in the urine of herbivora, and
also, though to a much smaller amount, in the urine of man. It is
formed in the body by the union with dehydration of glycin and benzoic
acid, see p. 441.

Crystallised from a saturated aqueous solution, it assumes the form
of fine needles ; if from a more dilute solution, white, semitransparent
four-sided prisms are obtained. These when pure are odourless, with a
somewhat bitter taste. They are soluble in 600 parts of cold water,
readily soluble in boiling water, readily soluble in alcohol, less so in
sether. All the solutions redden litmus.

Hippuric acid is monobasic, and forms salts which are readily
soluble in water (except the iron salts); from these, if in sufficiently
concentrated solutions, excess of hydrochloric acid precipitates the acid
in fine needles. When heated with concentrated mineral acids it is
resolved into benzoic acid and glycin. The same decomposition occurs
in presence of putrefying bodies. Strong nitric acid produces an odour
of nitrobenzol.

Preparation. Fresh urine of horses or cows is treated with milk of
lime, in order to form calcic hippurate and thus prevent the decom-
position of the hippuric acid, filtered, and the filtrate evaporated to a

1 Op. cit. (sub Leucin).

APP.] CHEMICAL BASIS OF THE AXIMAL BODY. 761

small bulk ; the hippuric acid is then precipitated by adding an excess of
hydrochloric acid ; the acid is then purified by several crystallisations
from boiling water.

When heated in a small tube, hippuric acid gives a sublimate of
benzoic acid and ammonic benzoate, accompanied by an odour like that
of new hay, while oily, red drops are observed in the tube. This is very
characteristic, and distinguishes it from benzoic acid.

Phenylic (Carbolic) acid or Phenol. C6 H6 O.

This body is undoubtedly obtained as the result of the putrefactive
decomposition of proteids, notably in putrefactive pancreatic digestions \
It may be obtained from the distillate of such digestive mixtures. It
is also found in the contents of the alimentary canal under the same
conditions which give rise to indol. When so occurring a portion of it
may be obtained from the fseces while the rest reappears in the urine 2.

Buliginsky3 says the urine of many animals, of cows and horses always, contains
a substance insoluble in alcohol, and not precipitated by lead acetate and ammonia^
which by the action of dilute mineral acids gives carbolic acid. The same acid
applied to the body externally or internally also passes into the urine4. Similarly
benzol (C6H6) when taken into the stomach appears as carbolic acid in the urine 5.

The pure acid crystallises in long, colourless prismatic needles; they
melt at 35° C., and boil at 180°C. It is readily soluble in alcohol and
aether, slightly soluble in water (1 part in 20). In most cases it acts as
a weak acid, forming crystalline salts with the alkalis. With nitric acid
it yields picric acid. Its solutions reduce silver and mercury salts.

Preparation. By the dry distillation of salicylic acid, also from the
acid products of the distillation of coal. It is obtained in the last
portions of the distillate when preparing indol, and is separated by
forming a compound with bromine C6H3Br3O.

THE BILE SERIES.

Cholalic (or dtolic) acid. H . C24 H^ O5 + H2 O.

Occurs in traces in the small intestine, in larger quantities in the
contents of the large intestine, and the fseces of men, cows and dogs.

1 Baumann, Zeitsch. f. physiol. Chem. Bd. i. (1877), S. 60.

2 Salkowski, Ber. d. deutsch. Chem. Gesell. ix. (1876), S. 1595. Centralb. f. d.
med. Wiss. 1876, S. 818. Ber. d. deutsch. Chem. Gesell. x. (1877), S. 842. Virchow's
Arch. Bd. LXXII. (1878), S. 409. See also Centralb. f. d. med. Wiss. 1878, Nos. 30,
31, 34, 42, and Zeitsch. f. physiol. Chem. Bd. n. (1878), S. 241.

3 Hoppe-Seyler, Med. chem. Untersuch. Heft 2 (1867), S. 234.

4 Alme'n, Neues Jahrb. d. Pliarm. Bd. 34, S. 111. Salkowski, Pfluger's Archiv,
Bd. v. (1871-72), S. 335.

6 Schultzen and Naunyn, Reichert u. Du-Bois Keymond's Archiv, 1867, Heft 3,
S. 349.

762 THE BILE SERIES. [App.

In icterus, the urine often contains traces of this acid. But its principal
interest lies in its being the starting point for the various bile acids
(see below). The pure acid may be amorphous, or crystalline, in
the latter case crystallising from hot alcoholic solutions in tetrahedra.
These crystals are insoluble in water and tether. In the amorphous
form, it is somewhat soluble in water and aether. Heated to 200° C., it
is converted into water and dyslysin (C24H43Oo).

This acid possesses, in the anhydrous condition, a specific rotatory
power of + 50° for the yellow light : when it crystallises with H2O, the
rotation is 4- 35°. The rotatory power of the alkali salts is always less
than the above, and when in solution in alcohol, the rotation is
independent of the concentration. For the alcoholic solution of the
sodium salt, the rotation is + 314°.

Preparation. By the decompositions of bile acids by means of acids,
alkalis, or fermentative changes.

Bayer1 has examined the bile-acids obtained from human bile, and has pre-
pared from them cholalic acid. To this he assigns the formula C18H0804. If
this be so, then cholalic acid of human bile would seem to be a body entirely
different from that obtained from ox bile, and analysed by Strecker. Bayer's
results however require further confirmation.

Pettenkofer's test 2.

This well-known, test for bile acids depends on the reaction of
cholalic acid in presence of sugar and sulphuric acid. If to a solution of
the acid a little sugar be added, and then sulphuric acid, keeping the
temperature below but not much below 70° C., a beautiful reddish purple
is obtained. If diluted with alcohol this solution gives a characteristic
spectrum with two absorption bands, one between D and E, nearest to E,
the other close to F 011 the red side of F.

The reaction is much impeded by the presence of colouring matters;
moreover proteids, and other bodies easily decomposed by sulphuric
acid such as amyl-alcohol and oleic acid, give a similar result, the
colouring matter produced from these bodies does not however give the
absoiption bands described above 3.

Glycocholic acid. C26H43NO6.

This body was first obtained in the crystalline form and described by
Gmelin (1826), who gave it the name of 'cholic' acid.

1 Zeitschr. f. physiol Cliem. Bd. n. (1878-79), S. 358.

2 Pettenkofer, Annalen. d. Chem. u. Pharm. Bd. LII. (1844), S. 90.

3 For further information on this subject see: Bischoff, Zeitsch.f. rat. Med. Ser.
3, Bd. 21, S. 126. Schulze, Ann. d. Chem. u. Pharm. LXXI. (1849), S. 266. Schenk,
Anatom. physiol. Untersuch. Wien, 1872, S. 47. Adamkiewicz, Pfliiger's Arch. Bd.
is. (1874), S. 156.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 7G3

To avoid confusion it is now best to use the term 'cholic' as a synonym for
' cholalic,' Demarcay who first (1838) described the cholalic acid as a product of the
decomposition of bile acids having given it the name of cholic acid. The name
cholalic is perhaps the best, since it indicates the method by which the bile acids are
split up, viz. by treatment with alkali.

This is the principal bile-acid of ox gall; it is also present in the
bile of man, but has so far not been observed in that of carnivora. In
icterus, the urine may contain traces of this acid.

It crystallises in fine, glistening needles. These are slightly soluble
in cold water, readily so in hot water and alcohol but insoluble in sether.
They possess a bitter and yet sweet taste, aud a strong acid reaction.

The salts of this acid are readily soluble in water and crystallise
well. The salts, as well as the free acid, exert right-handed polarisation
amounting to + 29*0° for the acid, and + 257° for the sodium salt, both
measured for yellow light.

Glycocholic acid is a compound of glycin and cholalic acid ; thus :
Cholalic acid. Glycin. Glycocholic acid.

C»H^OB + C.2NH502 - H20 = CJEJ^NO,

Prolonged boiling with dilute mineral acids or caustic alkalis decomposes gly-
cocholic acid into glycin and cholalic acid ; if dissolved in concentrated sulphuric
acid and then warmed, glycocholic acid by the removal of one molecule of water
yields cholonic acid, C26H41N05. The barium salt of this last acid is insoluble in
water, which fact is of importance, since cholonic acid possesses nearly the same
specific rotatory power as glycocholic acid.

Preparation. From ox gall, by evaporating to a syrup, decolorising
with animal charcoal, extracting with strong alcohol, and precipitating
by a large excess of sether. Its separation from taurocholic acid depends
on its precipitation by normal lead acetate, taurocholic acid not being
precipitated by this reagent

Taurocholic acid. C^H^NSO^

Occurs also in ox-gall, but is found especially plentiful in human
bile and that of carnivora, notably of the dog.

It crystallises with difficulty in very fine needles which are exceed-
ingly deliquescent. When dried it is an amorphous powder, with
pure bitter taste, easily soluble in water and alcohol, insoluble in sether.
All its salts are soluble in water, and are precipitated by basic lead
acetate in the presence of free ammonia. The sodium salt dissolved
in alcohol has a specific rotatory power of + 24*5°; if dissolved in water
this rotation is less, and in this respect it resembles glycocholic acid.

This acid is far more unstable than the preceding one, being decom-
posed if boiled with water. The products of decomposition are tauriu
and cholalic acid.

764 BILE PIGMENTS. [App.

Taurocholic acid is a compound of taurin and cholalic acid; thus:
Cholalic acid. Taurin. Taurocholic acid.

C24H4005 + C2H7N03S - H20 = C^NO.S.

Preparation. From the bile of dogs by a process similar to that for
glycocholic acid. It is separated from traces of this latter and from
cholalic acid by precipitation with basic lead acetate and ammonia l.

BILE PIGMENTS.
These have been very briefly described on p. 248.

Bilirubin . C16 H18 N2 03.

It is found chiefly in the fresh bile of man and carnivora, to which it
gives the characteristic dark golden-red colour. It frequently constitutes
a considerable part of some kinds of gall-stones, not however as free
bilirubin but as a compound with earthy matter, chiefly chalk : the gall-
stones of oxen and pigs often contain 40 p. c. of this compound2. These
are therefore the best material from which to prepare bilirubin.

Preparation. The gall-stones are treated with strong acetic or
dilute hydrochloric acid to separate the earthy matter and the residue
is thoroughly washed with water and alcohol and dried. From this
residue the prolonged action of hot chloroform extracts the bilirubin,
which may either be obtained in the amorphous form by precipitation
with alcohol of its solution in chloroform, or as well-defined crystals by
the slow evaporation of the chloroform solution.

The most usual form of the crystals is that of rhombic prisms ; they
are readily soluble in chloroform and alkaline solutions only.

By treatment with oxidising agents such as nitrous acid bilirubin
takes up oxygen and becomes biliverdin, the colour at the same time
changing to green. The possible oxidation does not end here, and if
continued a series of products are obtained each with a characteristic
colour as in the well known Gmelin's test3. Of these only the final
product of the oxidation has been obtained in a state of sufficient purity
to enable any definite statements to be made of its characteristics4.
This is the body known as Choletelin (see below).

Biliverdin. C16 H18 N2 O4. 5

This product of the oxidation of bilirubin gives the characteristic
colour to the bile of herbivora, and to biliary vomits. It occurs also
probably at times in the urine of jaundice and in the pigmentary matter

1 Parke, Tubing. Med.-chem. Unters. Bd. i., S. 160.

2 Maly, Sitzber. d. Wien Akad. LVII. 1868, ir. Abth. Febr. Hft.

3 Tiedemann und Gmelin, Die Verdauung, 1826, S. 79.

4 Heynsius und Campbell, Pfliiger's Arch. Bd. rv. (1871), S. 497.
0 Maly, Sitzb. d. Wisn. Akad. LXX. (1874), in. Abth.

APP.] CHEMICAL BASIS Of1 THE ANIMAL BODY. 765

of the placenta. It is not found, or occurs in traces only, in gall-
stones.

Preparation. An impure product is obtained by precipitating
ordinary herbivorous bile with baric chloride, washing the precipitate
with water and alcohol and decomposing it with hydrochloric acid.
The biliverdin thus obtained is washed with aether and dissolved in
alcohol. From its solution in the latter itis obtained as an amorphous
green powder by slow evaporation. Pure biliverdin is best prepared by
the slow oxidation in the air of bilirubin dissolved in dilute caustic
soda.

It does not crystallise, and is insoluble in aether or chloroform ; readily
soluble in alcohol. When oxidised it gives the same play of colours as
does bilirubin, with the formation of the same final and intermediate
products.

Neither this body nor bilirubin gives any characteristic absorption
bands.

There seems now no reason for doubting that the bile pigments are
derived ultimately from the colouring matter of the blood. (See p. 30.)
Yirchow has described1 the gradual changes in old blood-clots,
as of cerebral haemorrhage, which lead to the presence of the so-called
haematoidin crystals. Though these have not been obtained in sufficient
quantities to enable their composition to be finally fixed by a chemical
analysis2, still the identity of their crystalline form with that of bilirubin
and the fact that they both give the same play of colours when oxidised,
as in Gmelin's test, justify the assumption that haematoidin and bilirubin
are identical3. Moreover the balance of experimental evidence distinctly
supports the view that a liberation from the corpuscles of the colouring
matter of the blood in the blood-vessels by an injection of chloroform,
water &c., leads generally to the appearance of bile-pigments in the urine4.
The occurrence of bilirubin crystals in the urine has frequently been ob-
served after the operation of transfusion of blood in man. The chemical
possibility of the conversion of haemoglobin into biliverdin is readily
seen by a comparison of the formulae of haematin (see p. 341) and
bilirubin. The former has, according to Hoppe-Seyler5, the composition
indicated by the formula 2 (CM H^ N4 Fe 05) while that of bilirubin is
C16H18N2O3. Although the conversion has not as yet been directly
effected the following facts are significant. If bilirubin is treated with
sodium amalgam the substance known as hyclrobilirubin (see below) is

1 Arch. f. path. Anat. Bd. i., S. 383.

2 Robin, Ann. d. Chem. u. Pharm. Bd. cxvi. S. 89.

3 But see also Preyer, Die Blutkrystalle, 1871, S. 187.

Tarchanofif, Pfliiger's Arch. Bd. ix. (1874), S. 53. See also Bd. x. (1875)

6 Physiologisclie Chemie, 1879, S. 395.

76G BILE PIGMENTS. [App.

obtained. If hsematin is dissolved in caustic soda and treated with
sodium amalgam or in hydrochloric acid solution with zinc dust, a
substance is obtained which is now recognised as identical with hydro -
bilirubin1. This is the most direct chemical evidence of the relation of
the colouring matters of the blood and bile.

Choletelin. C16 H18 Na O6 (?) 2.

This substance is obtained as the final product of the oxidation of
either bilirubin or biliverdin. It is best prepared by acting upon
bilirubin with nitrous acid in presence of alcohol ; the various colours
of Gmelin's reaction are observed and the final reddish-yellow solution,
if poured into water, yields a precipitate of choletelin. It is not
crystalline and is soluble in alcohol, sether and chloroform. When
freshly prepared it seems to give an uncertain absorption band if
examined in an acid solution. On this account some observers3 have
been led to regard it as identical with hydrobilirubin (urobilin). There
is however no doubt that they are quite distinct bodies4.

Hydrobilirubin . C32 H40 N4 O7.

This body was first described by Maly5 as resulting from the action
of sodium amalgam on an alkaline solution of bilirubin. When the
reaction is complete, the solution is precipitated with hydrochloric acid,
the precipitate dissolved in ammonia, again precipitated by acid, and the
substance thus finally obtained is washed with water. It is readily
soluble in alcohol, less so in sether. Its alkaline solutions are yellow,
and these turn pink on the addition of acid. Both its acid and alkaline
solutions, the latter especially on the addition of a few drops of chloride
of zinc, give a characteristic absorption band between b and F. 6 In the
colours of its alkaline and acid solutions and the greenish fluorescence
of its ammoniacal solution on the addition of chloride of zinc, and in" its
absorption spectrum hydrobilirubin shews its close relation to urobilin
(see below), with which indeed it is now considered to be identical. It
is also identical with a body named stercobilin7 which had previously
been described, as a product of the alteration of the bile pigments in the

1 Hoppe-Seyler, Med.-chem. Untersuch. Hft. iv. 1871, S. 523. Ber. d. deutsch.
cJiem. Gesell. vn. (1874), S. 1065.

2 Maly, Sitzb. d. Wien A kad. Bd. LVII. (1868), 2 Abth. Febr. und Bd. LIX. 1869,
2 Abth. April. See also Heynsius and Campbell, loc. cit.

3 Heynsius and Campbell, loc. cit. Stokvis, Centralb. f. d. med. Wiss. No. 14
(1873), S. 211.

4 Maly, Centralb. f. d. med. Wiss. No. 21 (1875), S. 321. Liebermann, Pfliiger's
Arch. Bd. xi. (1875), S. 181.

5 Centralb. f. d. med. Wiss. No. 54, 1871. Annal. d. Chem. Bd. CLXIII. (1872),
S. 77.

« Vierordt, Zeitsch.f. BioL Bd. ix. (1873), S. 160.

7 Vanlair and Masius, Centralb. f. d. med. Wiss. No. 24, 1871.

App.J CHEMICAL BASIS OF THE ANIMAL BODY. 767

"alimentary canal, occurring in fbeces. There is no difficulty in seeing
how this change (hydrogenation) can be brought about in the intestine
since it is known that a considerable quantity of hydrogen may make
its appearance by fermentative processes in the intestine, and in its
nascent state might readily produce the simple change which is known
to occur when bilirubin is converted into hydrobilirubin.

PIGMENTS OF URINE.

Our knowledge of these bodies is at present limited and imperfect.
Most probably1 they are numerous, but only two appear sufficiently well
characterised to deserve mention here.

Urobilin . C32 H^ N4 O7.

As stated above, this is now regarded as identical with hydrobilirubin.
It was first described by Jaffe2 as a well-characterised normal urinary
pigment and its identity with hydrobilirubin subsequently determined3.

Normal urine contains only small quantities of urobilin but there is
present a substance (chromogen) which under the influence of acids,
with absorption of oxygen, yields urobilin. The urine of fever fre-
quently contains a considerable amount of actual urobilin as such.

The properties described above for hydrobilirubin are identical with
those of urobilin. Its preparation from urine is somewhat difficult and
for this some special manual must be consulted4.

Uroerythrin

Is considered to be the substance which gives to the urine of
rheumatism its characteristic colour. Yery little is known of its
chemical properties5. It appears to be an amorphous reddish body with
an acid reaction, slowly soluble in water, alcohol and aether. When
treated with caustic alkali it turns green. Urine containing this body
takes on a characteristic reddish-yellow colour on the addition of con-
centrated hydrochloric acid.

Thudichum considers that normal urine contains only one pigment, which he calls
urochrome6. Maly is inclined to regard this as the same as urobilin7. More recently
Thndichum has upheld his former views8.

1 Vierordt, Die quantitative Spectralanalyse, &c. Tubingen, 1876, S. 81.

2 Centralb. f. d. med. Wis*. 1868, S. 243. Virchow's Arch. Bd. XLVII. (1869),
S. 405.

3 Maly, Ann. d. Clitm..u. Pharm. Bd. CLXIII. (1872), S. 77.

4 Vide Neubauer and Vogel. Harnanalyse, ed. vm. (1881), S. 81.

5 Heller's Archiv. (2) Bd. in. (1854), S. 361.

6 Brit. Med. Jl N. S., No. 201, 1864, p. 509.

7 Maly, Ann. d. Chem. u. Pharm., loc. cit. 1872, S. 90.

8 Jl. chem. Soc. Ser. 2. Vol. xin. (1875), pp. 397, 401.

768 THE INDIGO SERIES. [App.

THE INDIGO SERIES.

Indican. C8H7NS04.

A body was long ago described * as occurring in the urine and sweat
of men and other animals which yielded by the action of acids the
blue colouring matter indigo as one of the products of its decom-
position. Schunk considered this substance to be identical with the
indican known to occur in several plants (Indigofera, Isatis). Hoppe-
Seyler2 on the other hand, having regard to the greater ease with which
the indican from plants undergoes decomposition, regarded them as most
probably different substances. Bauinann has shown3 that the two
are really different, and has confirmed his earlier statements in a more
recent publication4. According to him, the indican obtained from
urine is not a glucoside (so also Hoppe-Seyler) and yields sulphuric
acid by the action of hydrochloric acid. He assigns to it the formula
C8H6N.O.SO2.OH, and regards it as indoxylsulphuric acid. The acid
itself is not yet known in the free state, but it yields stable salts such
as that of potassium, C8H6N.S04K. It occurs largely in the urine
as the result of the presence of indol in the alimentary canal. In this
way Baumann and Brieger5 were enabled to obtain large quantities by
giving indol to a dog. For its preparation their original paper must be
consulted.

When treated in aqueous solution with hydrochloric acid in presence
of oxygen it yields indigo blue

2C8H6NS04K + Oa~ 2C8H5NO + 2KHS04.
It is always estimated in urine by conversion into indigo blue.
Indigo. C8H5NO.

It is formed, as stated above, from indican, and gives rise to the
bluish colour sometimes observed in sweat and urine.

It may, by slow formation from indican, be obtained in fine
crystals; these are insoluble in water, slightly soluble, with a faint violet
colour, in alcohol and aether. Chloroform also dissolves them to a slight
extent. Indigo is soluble in strong sulphuric acid, forming at the same

1 Schunk, Phil. Mag. Vol. x. p. 73; xiv. p. 228; xv. pp. 29, 117, 183. Chem.
Centralb. 1856, S. 50; 1857, S. 957; 1858, S. 225. Hoppe-Seyler, Arch. f. path.
Anat. Bd. xxvii. S. 388. Jaffe", Pfliiger's Arch. Bd. in. (1870), S. 448.

2 Handb. d. path. chem. Anal. Ed. iv. (1875), S. 191.

3 Pfliiger's Arch. Bd. xm. (1876), S. 301. Zeitschr. f. physiol. Chem. Bd. i.
(1877—78), S. 60.

4 Zeitschr. f. physiol. Chem. Bd. m. (1879), S. 254.

5 Zeitsch. f. physiol. Chem. Bd. in. (1879), S. 254. See also Ber. d. deutsch.
Chem. Gesell, xii. (1879), Sn. 1098, 1192 ; 2166, ami xm. (1880), S. 408.

APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 769

time two compounds with this acid; these are soluble in water. It
possesses a pure blue colour; when pressed with a hard body a reddish
copper-coloured mark is left, and the crystals exhibit the same colour if
seen in reflected light.

The soluble compounds with sulphuric acid give an absorption band
in the spectrum which lies close to the D line and to the red side of it.
This may be used to detect indigo.

Treated with reducing agents, indigo is decolorised, being reduced to
indigo- white. The latter contains two atoms more hydrogen than indigo.

Indol. C8H7N.

To this body the specific odour of the faeces is partly due. It is
obtained as the final product of the reduction of indigo ; and also by the
distillation of proteid matter with caustic alkalis l.

It often occurs among the products of the action of pancreatic
ferment on proteids ; its presence in such cases appears however to be
due, not to the action of the trypsin, but to a simultaneous putrefaction
under the influence of bacteria, etc.' If the pancreatic digestion be
carried on in the presence of salicylic acid, indol does not make its
appearance. Indol is a crystalline body, soluble in boiling water,
alcohol and sether. It passes over in the steam when its aqueous
solution is boiled. It is characterised by the following reactions. A
strip of pine-wood moistened with hydrochloric acid is coloured bright
crimson when dipped into a solution of indol. Its alcoholic solution
turns red when treated with nitrous acid and its aqueous solution gives
a copious red precipitate with the same reagent. It also yields a
characteristic crystalline compound with picric acid.

Skatol. C9H9N (?). Noticed by Brieger8 as one of the products of
putrefactive changes in the small intestine. Secretan4 had previously
described a similar substance as arising from the putrefaction of
albumin.

Skatol is crystalline and contains nitrogen; it is more soluble in
water than indol and does not give rise to any red colouration with
nitrous acid.

Skatol readily passes into the urine when it occurs in the alimentary
canal, and then gives a violet-red reaction with strong hydrochloric acid.

v. Nencki5 prepares this substance by the putrefaction of a mixture

1 Kiihne, Ber. d. deutsch. chem. Gesell. VHI. (1875), S. 206.

2 Kiihne, Verhand. d. Heidlb. naturhist med. Ver. N.S. Bd. i. Hft. 3. Bericht
d. Deutschen chem. Gesellschaft, 1875, S. 206.

3 Ber. d. Deutsch. chem. Gesell., Jahrg. x. (1877), S. 1027.

4 Recherches sur putrefaction de Valbumine. Geneva, 1876.

5 Centralb.f. d. med. Wiss., 1878, S. 849.

F 49

770 THE INDIGO SERIES. [App.

of finely divided pancreas and muscle substance. After the addition of
acetic acid the mass is distilled, when the skatol readily passes over.
From the distillate it is precipitated by picric acid, aud the precipitate
when again distilled with ammonia gives off pure skatol which may be
finally purified by crystallisation.

INDEX.

NOTE : — Eeferences to the appendix have an italic a after them.

An asterisk attached to a number denotes that a diagram will be found
at the page indicated.

Abducens nerve, 649

Absorption of the products of digestion,

301

,, from alimentary canal, 306
,, by diffusion, 310
by the skin, 390
Accelerator nerves, 189, 190
Accommodation, power of, possessed by

the eye, 493
„ limits of, how determined,

494

„ mechanism of, 497

,, associated with move-

ments of the pupil, 505
Acetic acid, 735a
Acetic acid series, 734a
Achroo-dextrin, 235
Acid-albumin, characters of, 704a
Acid, reaction in rigid muscle, 66
Acidity of gastric juice, 240
Acids,

„ acetic series, 734a
,, bile series, 761a
„ glycolic series, 739a
,, oleic series, 737a
„ oxalic series, 741a
Acoustic apparatus, 556
Adipose tissue, 426
Adult, composition of, 684
After images, 532
Air in respiration, 326
complemental, 315
residual, 315
stationary, 314
supplemental, 315
tidal, 314

changes of, in respiration, 326
inspired and expired, composition of,

327

,, effects of deficient, 375
Air, effect of increased supply of, 380
., effect of changes in composition
of, 380

Air, effects of changes in pressure of

breathed, 381
Albuminates, 704a
Albumin, 'tests for, 701a
Albumins, native, 702a
,, derived, 704a
Alimentary canal, changes which the

food undergoes in the, 292
Alkali-albumin, characters of, 706a
Allantoin, 753a
Amosba, features of, 1
Amphibia, renal circulation in, 405
Anacrotic pulse, 166, 168, 173
Animal Body, composition of, 443
Anti-albumate, 719a
Anti-albumid, 719a
Anti-albumose, 719a
Anti-peptone, 718a
Antiseptic qualities of bile, 250
Apnoea, 361, 380

Apparent size, appreciation of, 539
Aristotle's experiment, 580

Arterial blood,

Arterial flow, intermittent, converted

into a continuous, 128
Arterial pressure, tracing of, with a
Mercury manometer,

121*

„ features of, 121

,, methods of estimat-

ing, 122
„ amount of, in various

animals, 123
Arterial tone, 200

Arteries, as factors in circulation, 116
„ blood velocity in, 124, 127
,, changes in calibre of, 197
,, rhythmic pulsations in, 197
Artificial respiration, effects on blood-
pressure, 370
Asparagine, 757a
Aspartic acid, 757a

49—2

772

INDEX.

Asphasia, 674

Asphyxia, phenomena of, 375

,, stages of, 376

,, in new-born animal, 376

,, effects of, on circulation, 378
Aspirates, 659, 661
Astigmatism, 507
Atropin, effect of, on heart, 186

,, action on the pupil of the eye,

503

Anelectrotonus, 78
Auditory judgments, 565

„ nerve, 649

,, sensations, 559
Auriculo-ventricular valves, mechanism

of, 142
Automatic actions, 107

,, ,, in spinal cord, 595

Avalanche, theory of nervous impulse,

Bacteria, in intestine, 298

Basilar membrane of the ear, uses of,

562

Benzoic acid, 759<x
Bile, composition of, 247
,, pigments of, 248, 764a
,, pigments, in connection with red

corpuscles, 31
„ action on food, 249
„ tests for, 249
,, antiseptic qualities of, 250
,, nervous mechanism of secretion of,

264

,, action of, in intestine, 297
,, the nature of the act of secretion,

279

Bile-acid series, 761a
Bile-salts, 248

,, ,, preparation of, 248
Bile-secretion, 279
Bilirubin, 31, 764a

,, in bile, 248
Biliverdin, 248, 764a
Binocular vision, 541
Bladder urinary, tone of, 411

,, ,, movements of, 413

Blind Spot, the, 512

„ filling up of, 537
Blindness, psychical, 631
Blood, 1—34

,, an internal medium, 12
,, phenomena of coagulation, 13
„ why fluid in living blood- vessels, 19
„ origin of fibrin-factors from cor-
puscles of, 22
„ composition of, 24
„ the corpuscles, 26, 27, 28
,, quantity in body, 33
„ distribution in body, 34
„ influence of supply on irritability

of nerve and muscle, 94
,, changes in quantity of, 224
„ respiratory changes in the, 329
„ venous and arterial, nature of, 330
„ gases of, 330

Blood, gases of, method of obtaining, 330
,, relations of oxygen in, 332
,, venous and arterial, colour of,

338

,, causes of change of colour of, 338
,, relations of carbonic acid in, 342
,, ,, ,, nitrogen acid, 343

,, entrance of oxygen into, 344
,, oxygen in, relations to pressure,

344

,, exit of carbonic acid from, 346
,, oxidation in, 351
Blood-pressure, apparatus for investi-
gating, 120*

„ ,, in arteries, 123
,, „ in veins, 128
,, ,, in capillaries, 120
,, ,, relation of heart's-beat

to, 193

„ „ effect of cardiac inhibi-
tion on, 194*

„ „ influence of stimulation
of sensory nerves on,
205

,, ,, effects of changes in
quantity of blood on,
224

,, ,, curve, respiratory undu-
lations of, 364

,, ,, curve and curve of intra-
thoracic pressure, 364*
,, ,, effects of artificial respi-
ration on, 370
Blushing, 203
Body, the metabolic phenomena of the,

415

,, changes in, during starvation, 444
,, energy of the, 457
,, temperature of, 463, 465
Brain, visual areas in the, 523
,, movements of, 644
,, circulation in the, 645
,, weight of, 684

Breath, causes leading to the first, 679
Brunner's gland, secretion of, 255
"Buffy coat" in blood, 14
Butyric acid, 735a

Calibre of the minute arteries, changes

in the, 197
Capillaries, as factors in circulation,

116

,, velocity of flow in, 118
,, plasmatic or inert layer, 118
,, blood-pressure in, 120
,, changes in, 219
Capillary walls, action of, 222
Capric acid, 736a
Caproic acid, 736a
Caprylic acid, 736a
Carbohydrate food, a source of fat, 472

„ „ effects of, 453

Carbohydrates, 728a
Carbolic acid, 761a
Carbonic acid in the blood, 342

exit from blood, 346

INDEX.

773

Carbonic acid tension of in blood and

•lungs, 347
Carbonic oxide Haemoglobin, 340

„ „ poisoning, artificial dia-
betes in, 425
Cardiac events, general characters of,

146

„ ,, duration of, 152, 154

„ impulse, 137
„ inhibition, effect on circulation,

194
Cardiac muscles, 102

„ ,, characteristics of, 180

Cardiograph, 138, 146
Cardiographic tracings, 146*
Cardio- inhibitory centre, 188
Carnin, 755a

Casein, characters of, 708a
Central Sense-organ, 488
Cerebellum functions of, 640
Cerebral convolutions, functions of, 623
,, ,, motor areas in,

625

„ „ of the dog, areas

of, 625*, 626*

„ ,, of man, 627*,

628*
,, ,, sensory areas in,

628

,, ,, effects of stimu-

lation of, their
nature, 629

,, ,, effects of re-

moval of mo-
tor areas of,
638
,, „ visual areas in

the, 631

„ ,, varying irrita-

bility of, under
morphia, 632

„ „ activity of, modi-

fied by gentle
stimuli, 634

Cerebral hemispheres, nature of the move-
ments of frog in
absence of, 609

„ ,, behaviour of bird

in absence of, 611

„ „ behaviour of mam-

mal in absence
of, 611

,, operations, rapidity of, 643
Cerebrin, 745a
Cerebro-spinal fluid, 645
Chemical basis of the animal body, 699a

,, changes in muscle, 64
Chest-movements, influence on flow of
blood to and from
the heart, 367

,, ,, influence on flow of

blood from the
lungs, 369
Chest voice, 655

Cheyne- Stokes, respiration, 362
Chitin. 727a

Cholalic acid, 249
Cholesterin, 742a

,, in red corpuscles, 26

Choletelin, 766a
Cholic acid, 761a
Cholin, 745a
Chondrin, 7'24a

Chorda saliva and sympathetic saliva, 262
Chorda Tympani, action of, on sub-

maxillary gland, 259
Choroidal epithelium, behaviour towards

light, 519

Chromatic aberration, 508, 509*
Chyle, characters of, 301

,, entrance of, into lacteals, 303
,, movements of, 304
Chyme, formation of, 293
Cilia, 102

Circulating proteids, 452
Circulation, physical phenomena of, 116
,, chief factors enumerated,

116

,, phenomena of capillary, 117

„ hydraulic principles of, 128

,, vital phenomena of, 176

„ chief causes of modifications

of, 176
,, effect of changes in the

heart's beat on, 194
,, effect of cardiac inhibition

on, 194

,, effects of respiration on, 364

,, effects of asphyxia on, 378

in the brain, 644
foetal, 177

,, changes in, at birth, 679

Circus movements, 621
Coagulated proteids, 25
Coagulation of blood, 13
,, nature of, 18

„ (artificial), of serous fluids,

17

Cold increases metabolism of body, 467
Cold and Heat, lethal effects of, 468
Colostrum, 430
Colour Blindness, 530
Colour sensations, 524

,, ,, methods of mixing,

525

,, ,, fundamental or pri-

mary, 527

,, ,, diagram of three pri-

mary, 529*

Colour vision, the Hering theory of, 527
,, ,, Young-Helmholtz theory

of, 528
Colours, complementary, 526

,, nomenclature of, 524
Complemental air, 315
Complementary colours, 526
Concha, use of, 557
Consonants, nature of, 658
Constant current, action on muscle and

nerve, 75

Constriction, effects of local vascular,
216

774

INDEX.

Contractile Tissues, 35

Contraction, simple muscular, 39

Contraction of muscle affected by load,
87

Contrast, phenomena of, in vision, 537

Coordinated movements, mechanism of,
614

Coordinating nervous mechanisms, na-
ture and seat of, 618

Coordination of visual movements, ner-
vous machinery of, 546

Corpora quadrigemina, functions of, 638

Corpora striata, functions of, 636

Corpuscles of the blood, 11, 12, 22, 26,
27, 29

Corresponding points, 541, 542*

Corti, organ of, use in the analysis of
sounds, 561

Crassamentum, or blood clot, 13

Cranial nerves, 648

,, ,, motor and sensory, 484

Crura Cerebri, functions of, 641

Crying, 383

Curdling of milk, 430

Cutaneous respiration, 386

Cyclical changes in body, 691

Cystin, 758a

Diabetes, 424
Diagrammatic Eye, 492
Diagrams :

Apparatus for experiments with mus-
cle and nerve, 42
The muscle-nerve preparation with

clamp, electrodes &c, 43
Muscle-curve obtained by means of

the pendulum myograph, 43
The pendulum myograph, 44
Curves illustrating the measurement of

the velocity of a nervous impulse, 46
Tracing of a double muscle curve, 48
Muscle thrown into Tetanus, 49
Tracing produced with the ordinary

magnetic interrupter of an induction

machine, 50

Magnetic interrupter, 51
Muscular fibre undergoing contraction,

55

Non-polarisable electrodes, 58
Electric currents of nerve and muscle,

59

Muscle-nerve preparation, 77
Variations of irritability during elec-

trotonus, 79

Electrotonic currents, 81
Simplest forms of a nervous system,

104

Apparatus for investigating blood-
pressures, 120
Tracing of arterial pressure with a

mercury manometer, 121
Large kymograph with continuous

roll of paper, 123
Ludwig's stromuhr, 125
Simultaneous tracings from the in-
terior of the right auricle, from the

Diagrams:

interior of the right ventricle, and
of the cardiac impulse in the horse,
139
Marey's tambour, with cardiac sound,

140

Cardio-graphic tracing of cardiac im-
pulse in man, 146
Normal heart curve, 147
Goltz and Gaule's maximum mano-
meter, 151
Movements and sounds of the heart

during a cardiac period, 155
Pulse curves, 162
Pulse tracing from carotid artery of

healthy man, 165

Pulse-curve from radial of man, 166
Anacrotic pulse-tracing from the ca-
rotid of rabbit, 166

Dicrotism in radial pulse of man, 167
Normal pulse-wave in aorta of frog, 167
Anacrotic sphymograph tracing from

the ascending aorta, 168
Pulse tracing from the dorsal pedis,

168

Influence of changes in the pressure
applied to the exterior of the vessel
on the form of the curve, 169
Normal pulse-curve from carotid of

rabbit, 170
Dicrotic pulse-curve due to loss of

blood, 171

Tracing from radial of man, 173
Perfusion canula tied into frog's ven-
tricle ; Koy's apparatus modified by
Gaskell, 179

Inhibition of frog's heart by stimula-
tion of the vagus, 185
Last cervical and first thoracic ganglia

in the rabbit, 190
Last cervical and first thoracic ganglia

in the dog, 191
Influence of cardiac inhibition on

blood-pressure, 194
Vagus stimulation, 195
Effect on blood-pressure of stimu-
lating the depressor nerve in the
rabbit, 204

Rise of blood-pressure from stimula-
tion of nostril with smoke, 205
Submaxillary gland of the dog with its

nerves and blood-vessels, 258
Influence of food on the secretion of

pancreatic juice, 265
Pancreas of the rabbit, 267
Section of a 'mucous' gland, 269
Gastric gland of mammal, 273
Section of a serous gland, the parotid

of the rabbit, 274

Changes in the parotid during secre-
tion, 274
Thoracic respiratory movements by

Marey's pneumatograph, 316
Apparatus for taking tracings of the
movements of the column of air in
respiration, 319

INDEX.

775

Diagrams :

•Ludwig's mercurial gas pump, 331
Spectra of Oxy-haemoglobin, 334
Curves of blood and intra-thoracic

pressure, 364
Influence of respiration on the form of

the pulse-wave, 365
Traube-Hering curves, 373
Blood-pressure, curve of a rabbit's, 374
Renal oncometer, 398
Semi-diagrammatic sectional view of

oncograph, 399
Blood-pressure tracing and curve with

renal oncometer, 400
Normal spleen-curve from dog, 433
Schemer's experiment, 495
Nerves governing the pupil, 502
Chromatic aberration, 509
Formation of Purkinje's figures from
illumination through the sclerotic,
513

The same through the cornea, 514
Three primary colour sensations, 529
Appreciation of apparent size, 539
Corresponding points, 542
Attachments of the muscles of the
eye, and of their axes of rotation, 544
The Horopter, 547
Judgment of solidity, 551
Eelative sectional areas of the spinal
nerves, as they join the spinal cord,
599

United sectional areas of the spinal
nerves, proceeding from below up-
wards, 599

Variations in the sectional area of the
grey matter of the spinal cord, 599
Variations in the sectional area of
the lateral, anterior, and posterior
columns of the spinal cord, 603
Cerebral convolutions of the dog, Hitzig

and Fritsch, 625
Cerebral convolutions of the dog,

Ferrier, 626

Side view of brain of man, with areas
of cerebral convolutions, Ferrier, 627
Upper view of the same, Ferrier, 628
Larynx as seen by the laryngoscope in
different conditions of the Glottis, 652
Death, 695

Decay of the body, 689
Decussation of sensory and volitional

impulses, 601
Defaecation, 288
Deglutition, 282

,, nervous mechanism of, 283

Dental consonants, 659, 661
Dentition, 687
Depressor nerve, 204
Derived albumins, 704a
Dextrin, 235, 731a
Dextrose, 235, 728a

Diaphragm, action of, in inspiration, 321
Dicrotic pulse, 166, 167, 169, 171
Diet, the normal, 445
,, general features of proteid, 475

Dietetics, 474

Digestion, tissues and mechanisms of,

233

„ circumstances affecting gas-
tric, 243

„ muscular mechanisms of, 281
,, absorption of the products

of, 301
,, course taken by the several

products of, 306
,, decomposition of proteids by,

720a

Digestive juices, properties of the, 234
Dilation, effect of local vascular, 216
Dioptric apparatus, imperfections in the,

506

Dioptric mechanisms, 491
Distance and size, judgment of, 549
Distribution of blood in the body, 34
Diurnal changes in the body, 694
Dyspeptone, 719a
Dyspnoea, 360

Ear, organ of Corti, 561

,, basilar membrane of the, 562
Egg-albumin, characters of and pre-
paration, 702a
Elastin, 726a

Electric currents in retina, 519
Electrical phenomena attending nervous

impulse, 72

Electrodes, non-polarisable, 58*
Electrotonic currents, 80, 81*
Electrotonus, 77

,, variations of irritability

during, 79*
Embryo, nutrition of, 674

,, respiration of, 674
Emmetropic eye, its features, 496, 506
Emetics, action of, 291
Endo-cardiac events, 138

„ pressure, amount of, 150

„ tracings, Chauveau and

Marey, 139*

Energy, muscular and nervous, 98
income of, 457

,, how determined, 457
expenditure of, 458

„ how determined

459

sources of muscular, 459
muscular, not due to proteids

alone, 460
Entotic phenomena, 509, 564
Equilibrium, nitrogenous, 450

,, sense of, how gained, 615

Erect posture, maintenance of, 662
Expiration, movements of, 323

„ laboured, 324

Expired air, composition of, 327
Explosive consonants, 652, 661
Extractives in serum, 25
„ in muscle, 69
in milk, 430

Eye, the, as a dioptric apparatus, 491
,, ,, diagrammatic, 492

776

INDEX.

Eye, the, diagrammatic values of, 492
,, power of accommodation possessed

by the, 493

„ the emmetropic, 496, 506
„ the myopic, 496, 506
,, the hypermetropic, 496, 506
„ the presbyopic, 496, 506
„ protective mechanisms of the, 554

Eyeballs, movements of, 542
,, rotation of, 543
,, muscles of, their action, 543

Ethylene-lactic acid, 741a

Ethylidene-lactic acid, 740a

Eupnoea, 360

Eustachian tube, uses of, 559

Facial nerve, 649

,, and Laryngeal respiration, 324
Faeces, characters of, 299
Fallopian tube, descent of ovum into

the, 669

Falsetto voice, 655

Fat, deposition in Adipose Tissue, 426
,, formed from carbohydrate food, 427
,, < ,, „ proteid food, 427
Fats in serum, 25

„ action of gastric juice on, 240
,, action of bile on, 250
,, action of pancreatic juice on, 254
, , emulsification of, in small intestine ,

296
„ absorption of, from alimentary

canal, 307
„ in milk, 430
,, complex nitrogenous, 743a
,, their derivatives and allies, 734a
,, the neutral, 737 a
Fatty food, effects of, 453
Feeling and Touch, 572
Ferment of pancreatic juice, 251
,, in fresh pancreas, 271
Ferments, 18, 237
Fibrin, characters of, 13, 14, 713a
Fibrin factors, origin from corpuscles of

blood, 22

Fibrin Ferment, 18
Fibrinogen, 16, 71la
Field of Touch, 580
Fields of Vision, struggle of the two,

552

Fo3tus, characters of blood of, 675
,, secretory functions of, 677
,, circulation of, 677
Food, action of bile on, 249

,, action of pancreatic juice on, 251
,, and the secretion of pancreatic

juice, 265*
,, changes in the mouth, 292

oesophagus, 292
stomach, 292
small intestine, 295
large intestine, 299
influence of on deposition of

glycogen, 418

fatty and carbohydrate, effects of,
453

Food, effects of gelatine as, 455

,, effects of salts as, 455
Forced movements, 620
Formic acid, 734a
"Frog, the rheoscopic," 62
Functional activity, influence of, on

irritability of nerve and muscle, 95

Ganglia, action of sporadic, 112

,, cervical and thoracic in Kabbit

and Dog, 190*, 191*
Gases in Stomach, 295
Gases of blood, 330

,, poisonous, 381
Gastric digestion of proteids, nature of,

242, 245
,, ,, circumstances affecting,

243

,, ,, duration of, 294

,, ,, conditions affecting, 294

,, fistula, formation of, 239
,, gland of mammal, 273*
,, glands, histological changes dur-
ing activity, 272
,, juice, nature of, 239
,, ,, acidity of, 240
,, ,, action of, on starch and

fats, 240

,, ,, action of, on proteids, 241
,, ,, preparation of artificial.

241

,, ,, action on milk, 246
„ „ nervous mechanism of se-
cretion of, 262

,, ,, formation of acid of, 278
Gelatine or glutin, 725a
Gelatine as food, 455
General sensibility, 572
Gestation, period of, 681
Glands, gastric, 272, 273*
mucous, 268
oxyntic, 278
parotid, 274*
salivary, 268
serous, 268, 274*
Globin, characters of, 713a
Globulin, characters of, 709a
Globulins, 709a
Glomeruli of Kidney, pressure in, how

varied, 402

Glomerulus as a filtering apparatus, 408
Glosso-pharyngeal nerve, 649
Glottis, narrowing of, 653

,, widening of, 654
Glycerin, 738a

Glyceriuphosphoric acid, 744a
Glycin, 249, 756a
Glycocholic acid, 249, 762a
Glycogen, 416, 732a

preparation of, 417

influence of food on, 418

deposition of, 418

use of, 419

the liver a storehouse of, 420

in muscle, 421

conversion after death, 423

INDEX.

777

Glycogen, present in embryonic tissues,

676

Glycolic acid series, 739a
Glutaminic acid, 758a
Goltz and Gaule's maximum manometer,

151*

Grape-sugar, 728a
Growth, arrest and decline of, 689
Griitzner's method of measuring peptic

powers, 244
Guanin, 755a
Guttural consonants, 659, 661

Hasmadromometer of Volkmann, 124
Haamatachometer of Vierordt, 126
Haematin, 341

,, reduction of, 341
Haemoglobin, in the corpuscles, 26,

333

„ spectra of, 334*, 335

„ reduction, of 337

„ reduced, spectrum of, 347

Hearing, 556

„ power of distinguishing notes,

564

Heart, as a factor in circulation, 116
,, normal beat of, 135
,, visible movements of, 136
„ change of form during systole,

136

,, sounds of, 143
„ first sound, 144
,, second sound, 144
,, Sounds and movements during a

cardiac period, 155*
,, work done by, 157
„ means of recording beat of, 178
„ mechanism of the normal beat of,

180
, , characteristics of cardiac muscles,

180

„ nervous mechanism of beat, 181
„ of Frog, effect of various sec-
tions, 182

„ inhibition of the beat of, 184
„ of Frog, inhibition of, by stimula-
tion of the vagus, 185
,, effect of atropin on, 186
,, effect of urari on, 186
,, effect of muscarin on, 187
,, effect of pilocarpin on, 187
„ Stannius' experiment on beat of,

187

,, reflex inhibition of, 188
,, accelerator nerves of, 189
„ agents, modifying beat of, 191
Heart's beat, variations in, 159

,, relation of blood-pressure

to, 193
,, effects on the circulation of

changes in the, 194
„ what affected by, 228
Heat of the Body, sources and distribu-
tion of, 461

„ „ muscles, chief source

of, 461

Heat of the body, channels of, loss of,

464

Heat and cold, lethal effects of, 468
Hemi-albumose, 719a
Hemi-peptoue, 718a
Hemiprotein, 719a
Hering, theory of colour vision, 527
Hiccough, 382
Hippuric acid, 760a

„ how formed in body, 441

Hoematoidin, 30
Horopter, the, 547*
Hydraulic principles of the circulation,

128

Hydrobilirubin, 766a
Hyperaesthesia after section of spinal

cord, 606

Hypermetropic eye, its features, 496, 506
Hyperpncea, 360
Hypoglossal nerve, 650
Hypoxanthin, 754a

Identical points, 541

Image, formation of the retinal, 491

Impregnation of ovum, 672

Income and output, method of deter-
mining, 446

„ ,, „ deductions from,
448

Indican, 767a

Indigo series, 767a

Indol, 253, 769a

Induction Machine, 39, 41*

Inflammation, 221

Inhibition, general nature of, 113

Inhibition of the Heart's beat, 184

Inogen, 29

Inosit, 731a

Insensible perspiration, 385

Inspiration, movements of, 320
„ action of ribs in, 320

,, action of diaphragm in, 320

„ laboured, muscles employed

in, 322

Inspired air, composition of, 327

Intestine, bile action of, in, 297
,, bacteria in, 298
,, large, movements of, 288
,, large, changes in, 299
,, small, movements of, 286
,, ,, changes of food in, 295

,, emulsification of fats in,

296
,, ,, absorption from, 298

Intra-molecular oxygen, 349

Irradiation in vision, 536

Irritability muscular and nervous, 37, 90
„ independent muscular, 38

Isopepsin, 718a

Katacrotic pulse, 166
Katelectrotonus, 78
Keratin, 726a
Kidneys, secretion by the, 392

, , double character of function of,
397

778

INDEX.

Kidneys, variations in volume of, how
measured, oncometer and
oncograph, 398

,, variations in volume of, due to
variations in blood supply,
400

,, how brought about, 401
,, curve, 400
Kreatin, 752a

,, its relation to urea, 436
Kreatinin, 753a
Kymograph, with continuous roll of

paper, 123*
Kynurenic acid, 75 5a

Labial consonants, 659, 661

Lacteals, entrance of the chyle into the,

303'

Lactic acid, 740a
Lactose, 730a

Lardacein, or the so-called amyloid sub-
stance, 728a

Laryngeal and facial respiration, 324
Larynx, as seen by the laryngoscope,

652*

,, action of muscles of, 653
,, nerves of, 654
Latent period, 46
Laughing, 383
Laurostearic acid, 736a
Leucin, 756a

,, origin of urea from, 439
,, and Tyrosin, products of pan-
creatic digestion, 252
Lecithin, 743a

,, in red corpuscles, 26
Liver, a storehouse of glycogen, 420
Living blood-vessels, blood fluid in, 19
Local constriction, 217

„ dilation, 216

Localization of pressure sensations, 579
Locomotor ataxy and muscular sense,

583

,, mechanisms, 662
Ludwig's mercurial gas pump, 331*

,, stromuhr, 125
Lungs, pressure exerted by elasticity of,

315

,, respiratory changes in the, 344
,, self-regulating action of, 356
,, of new born infant, condition of,

679

,, condition of foetal, 679
Lymph-hearts, 306

„ movements of, 304

„ influence of nervous system on

movements of, 305
Lymphatics, the, 301

Magnetic interrupter, 51*
Maltose, 235, 730a
Mammary gland, 429

,, „ formation of milk in,

430

Manometer for arterial pressure, 122, 123
,, maximum, 151*

Marey's tambour, 150*
Mastication, 281
Mechanisms of digestion, 233

,, of respiration, 312

Medulla oblongata, functions of, 641
Medullary vaso-motor centre, 213
Membrana tectoria, uses of, 563
Membrana tympani, uses of, 557
Meniere's malady, 617
Menstruation, 669
Mercurial gas pump, 331*
Metabolic phenomena of the body,

415

Metabolic tissues, 416
Metapeptone, 719a
Metabolism, nitrogenous, 449

„ proteid, exact nature of, 451

,, of the body, -increased by

cold, 467
Micturition, 410
Migrating cells, 103
Milk, action of gastric juice on, 246
,, action of rennet on, 246
,, constituents of, 429
,, formation in mammary gland, 430
,, influence of nerves on secretion

and ejection of, 431
Milk-sugar, 430, 730a
Morphia, producing irritability of cere-
bral convolutions, 632
Motor cranial nerves, 484

, , nerves, behaviour towards stimuli
different from that of sensory
nerves, 487
,, and sensory nerves, differences

between, 106

,, and sensory nerves, union of, 487
Movements and sounds of the heart,
during a cardiac period,
155*

,, of chest, their influence on

the flow of blood to and
from the Heart, 367
,, ,, chest, influence on flow of

blood through the lungs,
369

,, the Brain, 644
Mucigen, 269
Mucin, 724a
Mucous glands, characters of, 268

,, gland in a state of rest and

activity, 269*

Muscarin, effect of, on heart, 187
Muscle thrown into tetanus, 49*, 52
„ change in form during contrac-
tion, 54
,, change in microscopic structure

during contraction, 55
,, relaxation after contraction, 56
,, elasticity of, 57
„ electric currents of, 59*
,, neutral or alkaline reaction of

living, 66

,, chemical changes during con-
traction, 68
,, extractives p^f, 6(J

INDEX.

779

Muscle, composition of, 69
" „ thermal changes in during con-
traction, 70
„ action of constant current upon,

75

„ value of, as a machine, dependant
on the load, 87 ; further deter-
mined by the size and form of
the muscle, 88
,, absolute power of, 89
,, work done by, 89
„ influence of tempera ture on irri-
tability of, 93

„ influence of blood-supply on irri-
tability of, 94
,, influence of functional activity

on irritability of, 95
,, energy of, 98
„ properties of unstriated, 101
,, glycogen in, 421
„ acid reaction of dead, 66
Muscle-currents, 58

, , , , negative variation of, 6 1
Muscle-curve, 42*, 48*
Muscle nerve preparation, 77*

,, ,, ,, as a machine, 83

Muscle-plasma, 65
Muscle and nerve, phenomena of, 37
Muscles, cardiac, 102

,, characteristics of cardiac, 180
„ employed in inspiration, 322
,, chief source of heat of body,

461

„ of the eyebaU, 543, 544*
„ of the Larynx, 653
„ use of glycogen in foetal, 676

weight of, 684
Muscular action, nature of, 98

,, contraction compared with
amoeboid move-
ment, 35
„ ,, phenomena of a

simple, 39

M I* as affected by na-

ture of stimulus,
83

„ energy, 459
„ fibre undergoing contraction,

55*

„ irritability, 37
,, mechanisms of digestion, 281
„ mechanisms, special, 651
„ sense, the, 582
Musical sounds, analysis of, 560
Myopic eye, its features, 496, 506
Myosin, 64, 712a
Myristic acid, 736a

Negative variation of the muscle current,

61

,, ,, nerve current, 73

Nerve, electric current of, 59*

„ changes during the passage of

a nervous impulse, 72
,, action of constant current upon,
75

Nerve changes caused by severance from
central nervous system in a, 91
,, influence of temperature on irri-
tability of, 93
,, and muscle, influence of blood

supply on irritability of, 94
„ and muscle, influence of func-
tional activity on, 95
Nerve, influence of rest on, 97
,, energy of, 98

„ and muscle, phenomena of, 37
Nerves, circumstances determining irri-
tability of, 90
,, differences between motor and

sensory, 106
„ accelerator, 189
,, vaso-motor, 199
,, vaso-dilator, 210
,, vaso-constrictor, 210
„ vaso-motor, of the veins, 215
,, their influence on secretion and

ejection of milk, 413
„ their influence on the spleen,

433

„ trophic, 471
,, sensory, 481
,, spinal, 482
„ cranial, 484, 648
,, fibres, degeneration of, after

section, 448
,, governing the pupil of the eye,

502

Nervi erigentes, 210
Nervous action, nature of, 98
Nervous impulses, definition of, 38

„ ,, rate of propagation,

47
„ „ curves illustrating

their velocity, 46*
„ „ electrical phenomena

attending, 72
„ „ avalanche theory of,

86

Nervous irritability, 37

Nervous mechanism, of Heart beat, 181

„ „ of secretion of

gastric juice, 262

,, „ of secretion of bile,

264

,, ,, of respiration, 353

,, ,, of perspiration, 388

„ „ nature and seat

of co-ordinating,

618

„ system, simplest form of, 104*
„ ,, influence on nutrition,

470
Nervous tissues, fundamental properties

of, 104
Neurin, 745a

New-born infant, respiration of, 679
,, ,, circulation of, 679

„ composition of, 684
„ „ growth of, 685

„ „ function of, 685

„ metabolism of, 685

780

INDEX.

New-born infant, psychical characters of,

687

Nitrate of urea, 746a
Nitrogen in the blood, 343
Nitrogenous equilibrium, 150
Nitrogenous Fats, 743a

,, metabolism, 449

,, metabolites, 746a

, , non-crystalline bodies allied

to Proteids, 723a
Non-polarisable electrodes, 58*
Nuclein, 727a
Nutrition, 233

,, statistics of, 443
,, influence of the nervous
system on, 470

Ocular spectra, 538

Oculo-motor nerve, 648

(Esophagus, movements of, 284

Old age, characteristics of, 689

Oleic acid series, 737a

Olein, 738a

Olfactory nerve and sensation of smell,

567

Olfactory nerve, 648
Oncograph, 399*
Oncometer, 398*
Optic axis, the, 491
,, lobes, inhibitory of reflex action,

591

„ nerve, 648

„ Thalami, functions of, 636
Ossicles, auditory, uses of, 557
Otoliths, 563

Output and income, method of deter-
mining, 446
Ovum, descent of, into Fallopian tube,

669

,, impregnation of, 672
Oxalate of urea, 747a
Oxalic acid series, 741a
Oxidation in blood, 351
Oxygen in the blood, 332

„ entrance of, into blood, 344

,, tension of, in blood and lungs,

345

,, influences respiratory centre, 362
Oxyhaemoglobin, spectrum of, 335

,, ,, and Hasmoglobin, dif-

ference in colour of,
338
Oxyntic glands, 278

Pain, 573

Palmitic acid, 736a

Palmitin, 738a

Pancreas, histological changes during

••activity and rest, 267*
Pancreatic digestion, characters of, 252
„ juice, characters of, 250
action on food, 251
action on proteids, 251

„ fats, 254
„ ,, starch, 254
act of secretion of, 265

Paraglobulin, 16, 25; characters of,

710a

Parapeptone, 243, 719a
Parotid glands during secretion, 274*
Parturition, 681
Pathetic nerve, 648
Pendulum Myograph, 44*
Peristaltic contractions, 284, 286
Pepsin, action on proteids, 246
Pepsinogen, 273
Peptic action, theories of nature of,

720a

Peptic digestion, 252
Peptone, characters of, 243

,, proteids converted into, by

pepsin, 246

„ characters of, 716a
,, theories as to nature of, 717a
Perfusion Cannula, 179*
Peripheral Eesistance, 118

„ ,, what affected by,

229

,, sense-organ, 488

Perspiration, amount of, 385

„ sensible and insensible, 385

,, characters of, 386

„ secretion of, 387

,, nervous mechanism of, 388

Pettenkofer's test for Bile acids, 762a
Phakoscope, 498
Phases of Life, 684
Phenol, 769a
Pherjylic acid, 761a
Photo-chemistry of the retina, 515
Physical electrotonus, 82
Physiological electrotonus, 82
Physical phenomena of circulation, 116
Pigments of Bile, 764a

,, ,, Urine, 767a
Pilocarpin, effect of, on heart, 187
Placenta, respiratory function of, 675

,, nutritive functions of, 676
Plasmine, 16
Pneumogastric nerve, 650

,, ,, in respiration, 355

Poisonous gases, 381
Poisons, effect of, on heart, 186, 187
Polycrotic pulse, 166
Pons Varolii, functions of, 641
Predicrotic pulse-wave, 168
Presbyopic eye, its features, 496, 506
Pressure of air breathed, effects of

changes in, 381
Pressure-sensations, characters of, 575

,, ,, localization of, 579

Pressure and temperature sensations,
separate nerves and nerve endings for,
577

Propionic acid, 735a
Protagon, 744a

Proteid diet, general features of, 475
Proteids, in serum, 25

„ „ red corpuscles, 26

,, action of gastric juice on, 241

,, ,, ,, pancreatic juice on,

251

INDEX.

781

Proteids, absorption of, from alimentary

canal, 307

„ a source of fat, 427
,, composition of, 428
,, characters of, 701a
,, coagulated, characters of, 715a
„ decomposition of, by digestion,

720a
„ products of decomposition* of,

721a
,, theory of composition of,

722a
Protoplasm, fundamental Phenomena

of, 1—3

„ composition of, 699a

Psychical blindness, 631

,, characters of new-born infant,

687

Ptyalin, 237

Puberty, phenomena attending on, 688
Pulmonary alveoli, determination of car-
bonic acid tension in, 347
Pulse, 161

., waves produced on artificial

scheme, 161
,, rate at which it travels, 163

circumstances determining,

163

„ general causation of, 164
„ secondary waves in, 165, 171
„ dicrotic, 166
,, tricrotic, 166
„ polycrotic, 166
„ anacrotic, 166, 173
„ katacrotic, 166
,, causes of dicrotic wave of, 167,

169

„ predicrotic wave of, 168
,, dicrotic wave, variations in, 173
,, venous, 174
„ rate, as influenced by respiratory

movement, 371

Pulse- waves, sphygmographic tracings,
162*, 165*, 1(56*, 167*, 168*, 169*,
170*, 171*, 173*
Pupil, movements of, 500
„ by what contracted, 500
„ ,, „ dilated, 500
,, diagrammatic representation of

nerves governing the, 502*
, , nervous mechanism of contraction

of, 507
„ by what means dilated, 503

relations of cervical sympathetic

to, 503

„ action of atropin on, 503
„ relation of fifth nerve to, 506
,, accommodation associated with

movements of the, 505
Purkinje's figures, 512, 513*, 514*

Quadrupeds, locomotion of, 664

Reaction, period, 644

„ ,, reduced, 644

Recurrent sensibility, 483

Red corpuscles, composition, 26

„ number in the blood, 28

„ proportion to white cor-

puscles, 29
„ origin of, 29

„ destruction of, 30

,, connection with bile

pigment, 31
Reflex actions, nature of determinants

of, 10J

„ dependent on nature of

afferent impulses, 586

„ dependent on intensity

of stimulus, 587
, , varying with area of skin

stimulated, 588
„ in the mammal, 586

„ indicating choice, 589

,, inhibition of, 590

„ time taken up in, 593

Reflex inhibition of heart, 188
Regeneration of tissues and organs, 667
Reproduction, tissues and mechanisms

of, 667

Renal circulation in amphibia, 405
,, epithelium, share in secretion of

urine, 404

,, nerves, result of section of, 403
Rennet, action of, 246
Residual air, 315

Resonant or Nasal consonants, 660. 661,
Respiration, nature of, 312

„ mechanisms of pulmonary,

314

„ rhythm of, 316

,, Facial and Laryngeal, 324

,, changes of air in, 326

„ chemical aspects of, 352

,, nervous mechanism of, 353

,, effects of pneumogastric on,

355
,, inhibition of, by superior

laryngeal nerve, 357
,, Cheyne- Stokes, 362

, , effects of, on the circulation,

364

,, influence on the pulse-wave

and median blood-pres-
sure, 365*

,, effects of artificial, on blood-

pressure, 370
„ cutaneous, 386

,, of new-born infant, 679

Respiratory centre, 354

,, ,, theory of action of,

358

,, ,, action of, modified by

various influences ,
359

,, ,, action of dependant

on condition of
blood, 360
,, ,, influenced by loss of

oxygen, 362

Respiratory changes in the blood, 329
„ ,, in the lungs, 344

782

INDEX.

Bespiratory changes in the tissues, 348
, , movements , pressure exerted

by, 315

„ „ recorded by

means of
Marey'sPneu-
matograph,
316*

,, ,, method of re-

cording, 316,
319*
,, ,, characters of,

317, 319
,, ,, influencing pulse

rate, 371

,, „ modified, 382

Best, influence of, on Nerve and Muscle,

97

Eetina, electric currents in, 519
,, Photochemistry of, 515
,, visual areas in the, 523
Kheometer of Ludwig, 124
"Bheoseopic frog," 62
Ehythm of respiration, 316
Bibs, action of, in inspiration, 321
Bigor Mortis, 64, 66
Bima respiratoria, 652

,, vocalis, 652

Boots of spinal nerves, functions of, 482
Bunning, 664
Butic acid, 736a

Saline matters in serum, 25
„ „ uses of, 477
Saliva, properties of, 234

„ action of, on starch, 235
„ parotid, 238
,, submaxillary, 238
„ sublingual, 238
,, mixed, 238
,, secretion of, 256
,, chorda and sympathetic, 262
Salivary secretion, nervous mechanism

of, 257

,, ,, inhibition of, 259

,, ,, vascular changes dur-

ing, 259
Salivary gland, histological changes

during activity of, 268
Salts as food, 455
Salts of uric acid, 750a
Sarcolactic acid, 741a
Sarkin, 754a

Schemer's experiment, 494, 495*
Secretion, theory of the nature of, 275
„ by the skin, 384
„ by the kidneys, 392
,, of perspiration, 387
,, of urine, 397
Semicircular canals, result of injury to,

614

Semilunar valves, 143
Sensations, visual, 511

„ of pressure, 575

,, of temperature, 576

Sense organs, 488

Sensible perspiration, 385
Sensory impulses, velocity of, 485
,, cranial nerves, 484
,, nerves, 481

,, nerves, behaviour towards sti-
muli different from that of
motor nerves, 486
Sensory and motor nerves, differences

between, 106
,, and motor nerves, union of,

487
Serum-albumin, 25

,, ,, characters of 703a

Serous fluids, artificial coagulation of,

17

Serous glands, 268, 274*
Serum, composition of, 25
Sex, difference of bodily constants in,

688

Shock, 214
Sighing, 382
Sight, 490

Size and distance, judgment of, 549
Skatol, 769a
Skin, secretion by the, 384

,, absorption by, 390
Sleep, phenomena of, 691

,, causes of, 692
Smell, 567

,, olfactory nerve, and, 567
Sneezing, 383
Soaps, 739a
Sobbing, 383
Sodium glycocholate, 248
Sodium sulphindigotate, secretion of, by

epithelium of kidney, 406
Sodium taurocholate, 248
Solidity, judgment of, 551
Soluble starch, 235
Sounds, judgment of direction of, 565

of the heart, 143, 144
Spectra of Hasmoglobin, 334*
Speech, 657

Spherical aberration, 507
Spinal cord, 585

,, ,, of frog, evidences of choice

in, 589

,, ,, automatic actions in, 595
,, ,, tonic action of, 596
,, „ conduction of impulses in,

598

,, „ relation of grey matter to

roots of spinal nerves, 599

„ ,, decussation of sensory and

volitional impulses in,

601

,, ,, sectional areas of the late-
ral, anterior and posterior
columns of the, 603*
,, ,, paths in, as determined by
anatomical investigation,
600

„ ,, transmission of impulses a-
long the grey matter,
lateral, anterior and pos-
terior columns, 602

INDEX.

783

Spinal cqrd, vicarious transmission of

impulses, 605
„ ,, hyperaesthesia after section

of the, 606

Spinal ganglia, functions of, 483
Spinal accessory nerve, 650
Spinal nerves, function of roots, 482

„ ,, sectional areas of, 599*
Spirometer,the, 316
Spleen, destruction of red corpuscles in

the, 30

,, variations in size of, 432
,, curve, features of, 433*
,, influence of nerves on, 433
,, circulation in, 434
,, substances present in, 434
,, presence of uric acid in, 434
Stannius' experiment, 187
Stapedius muscle, uses of, 559
Starch, action of saliva on, 235, 236
,, action of gastric juice on, 240
„ action of pancreatic j uice on, 25 1 ,

254

Starvation, changes in body during, 444
Stasis, 220
Stationary air, 314
Stearic acid, 736a
Stearin, 738a
Stereoscope, the, 545
Stimulus, definition of, 37
Stimulus affecting muscular contraction,

83
Stomach, why it does not digest itself,

279

,, movements of, 285
,, absorption from, 294
,, gases in, 295

Submaxillary gland, nerves of, 257, 258*

,, ,, action of chorda

tympani on, 259

,, ,, action of cervical

sympathetic on,
261

Succinic acid, 742a
Succus entericus, 255

„ ,, Thiry's method of

obtaining, 255
,, ,, act of secretion of,

266
Sugar in saliva, 237

, , action of succus entericus on cane ,

255

,, absorption of, from intestine, 310
Supplemental air, 315
Sympathetic and chorda saliva, 262
Sweat, characters of, 386
„ centres, 389
,, nerves, course of, 390

Tactile judgments, 579

,, perceptions, 572

„ sensations, 575
Taste, 570
Taurin, 249, 756a
Taurocholic acid, 249, 763a
Tears, 654

Temperature, influence of, on irritability
of nerve and muscle, 93
„ normal constant, of the

body, 463
„ of the body, regulated by

the skin, 464

,, of the body, regulated by

variations hi produc-
tion, 465

„ sensations, 576

„ and pressure sensations,

separate nerves and
nerve endings for, 577
Tendon phenomena, 596
Tension of oxygen in blood and lungs, 345
,, of carbonic acid in blood and

lungs, 347

Tensor tympani muscle, uses of, 558
Tetanic contractions, 48, 50
Tetanus produced with magnetic inter-
rupter, 50*

Thermal changes in muscle during con-
traction, 70
Thinking and willing, time taken up by,

644

Tidal air, 314
Tissue-proteids, 452
Tissues, the fundamental, 5
Tissues and mechanisms of digestion, 233
„ ,, ,, reproduc-

tion,

667

,, „ of respi-

ration,
312

„ respiratory changes in, 348
„ absence of free oxygen from, 349
Tone of arteries, 200
Tonic action in spinal cord, 596
Touch, nerve endings essential to, 573

field of, 580

Traube-Hering curves, 372, 373*, 374*
Tricrotic pulse, 166
Trigeminal nerve, 649
Trochlear on Pathetic nerve, 648
Trophic nerves, 471
Trypsin, 251
Trypsinogen, 271
Tryptic action, theories of nature of,

720a

Tunicin, 733a
Tyrosin, 759a

„ product of pancreatic digestion,
252

Unstriated muscular tissue, properties

of, 101
Urari, effect of, on heart, 186

„ poisoning, artificial diabetes, a

prominent symptom of, 426
Urea, composition of, 428, 746a
„ its relation to kreatin, 436
,, origin of, in body, 437
,, ,, from leucin, 439

„ secretion of, by epithelium of kid-
ney, 406

'84

INDEX.

Urea, nitrate of, 746a
,, oxalate of, 747a
,, detection in solutions, 747a
,, quantitative determination, 747a
Uric acid in the spleen, 434
„ origin in body, 440
„ , 749a
„ salts of, 750a
Urine, composition of, 3D3
„ characters of, 393
,, quantity of constituents passed

in 24 hours, 395
,, acidity of, 395
,, abnormal constituents of, 396
,, secretion of, 397
,, secretion, in relation to blood-
pressure, 398, 402

„ „ effects of section of

spinal cord, and of
nerves upon, 403

,, ,, by the renal epithe-

lium, 404

,, incontinence of, 413
,, of infants, 686
,, pigments, 767fl
Urobilin, 767a
Uroerythrin, 767a
Uterus, movements of, 682

,, changes in, after impregnation,

673
,, condition of, in menstruation, 670

Vagus nerve, 650

,, stimulation, 195*
Valerianic acid, 735a
Valves, auriculo-ventricular, 142

,, semilunar, 143

Vascular constriction and dilation, 199
,, ,, effects of local, 216

,, factors, mutual relations of, 227
„ mechanism, 115
Vaso-constrictor nerves, 210
Vaso-dilator nerves, 210
Vaso-motor actions, 197

,, ,, nature of, 207

,, centres, 212

„ medullary centre, 213

,, nerves, 199

,, ,, course of, 212

,, ,, of the veins, 215

Veins, as factors in circulation, 116
,, blood-pressure in, 128
,, velocity of blood in, 128
,, vaso-motor nerves of the, 215
Velocity of Blood in arteries, how mea-
sured, 124
,, in various arteries,

127
,, ,, on what dependent,

124

,, „ in veins, 128

„ ,, circumstances deter-

mining, 132

Venous blood, colour of, 338

,, ,, nature of, 330

,, pulse, 174
Vertigo, 617

Vibratory consonants, 660, 661
Vierordt's Haematachometer, 126
Vision, influence of yellow spot on, 531

,, dimensions of field of, 535

,, region of distinct, 535

„ irradiation in, 536

,, contrast in, 537

,, binocular, 541

,, struggle of the two fields of, 552
Visual areas in the retina and in the
brain, 523

,, ,, in the cerebral convolu-
tion, 631

Visual impulses, origin of, 511
Visual judgments, 549
Visual movements, co-ordination of, 545
Visual perceptions, 534
Visual purple, 517
Visual sensations, 511

,, ,, duration of, 520

,, ,, their relations to the

stimulus, 521

,, „ fusion and distinction

of, 522

Visual white, 517
,, yellow, 517

Vital phenomena of the circulation, 176
Vitellin, character of, 712a
Vocal cords, 652

,, ,, how tightened, 654

,, ,, ,, slackened, 654
Voice, 651

,, characters of, on what dependent,
651

,, breaking of, 656
Volkmann's Haemadromometer, 124
Vomiting, 290
Vowels, nature of, 657

Walking, 663

Wallerian Method, 484

Weber's law, 521

Weight of organs of the body, 684

Whispering, 661

White corpuscles, composition of, 27

,, ,, proportion to red cor-

puscles, 29

,, ,, origin of, 31

., ,, use of, 31

Xanthin, 754a

Yawning, 382

Yellow spot, influence of, on vision, 531
Young-Helmholtz, theory of colour vision,
528

Zymogen, 271

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