PUBLIC HEALTH LIBRARY

Health Lib

HANDBOOK

OF

PHYSIOLOGY

BLDDD- SPECTRA COMPARED WITH SPECTRUM DP ARGANQ- LAMP

1 Spectrum Qp Arg and -I amp with Fraunhafers lines in position.

2 Spectrum aP Dxyhsmadlabin in diluted bland.
.'3 Spectrum nP Reduced HEmc^labin.

4 Spectrum aP Carbonic nxide Hsmprjlabin.

5 Spectrum of Acid Hsmatm in ethErial aalu

6 Spectrum af^ Alkaline Hsmatm.

7 Spectrum oF DblarnFarm extract nf acidulated Dx-Bile.

8 Spectrum of MethsmnglDhin.

9 Spectrum oF HsmDchramDi^Gn.
10 Spectrum op HaEmEtnpnrphyrin.

Moat of the abow Spectra have been drawn fivm observations by bFWtepra/k F.C.S.

KIRKES' HANDBOOK

OF

PHYSIOLOGY

Revised and Rewritten by

CHARLES WILSON GREENE, A. M., Ph. D.

PROFESSOR OF PHYSIOLOGY AND PHARMACOLOGY, UNIVERSITY OF MISSOURI

Sevcntl) .American

WITH FIVE HUNDRED AND SEVEN ILLUSTRATIONS,
INCLUDING MANY IN COLORS

NEW YORK
WILLIAM WOOD AND COMPANY

MDCCCCXIII

COPYRIGHT, 1910
BY WILLIAM WOOD AND COMPANY

THE. MAPLE. PRESS. YORK. PA

PREFATORY NOTE.

THE features of the Handbook of the last edition have been retained
and extended. Considerable new material has been introduced with a
view to keeping pace with the rapid strides of progress of the subject. The
newer discoveries of Cannon on the acid control of the valves of the stomach
and of Rettger on blood clotting have been incorporated. The chapter
on the Chemical Composition of the Body has been entirely rewritten
and the chemical discussions throughout the volume have been carefully
revised. I am indebted to my colleagues Dean C. M. Jackson, for valuable
criticisms of the chapter on the Nervous System, and Dr. R. B. Gibson, for
the revision of the chemical discussions.

CHAS. W. GREENE.

COLUMBIA, Mo., June i, 1910.

PUBLIC
HEALTH
UBRABX

BLIG
HEALTH
LIBRARY

CONTENTS.

CHAPTER I— THE PHENOMENA OF LIFE; Properties of Protoplasm,

Structure of Protoplasm i

CHAPTER II— CELL DIFFERENTIATION AND THE STRUCTURE OF THE
ELEMENTARY TISSUES; The Structure of the Cell, The Structure of
the Elementary Tissues. I. The Epithelial Tissues. II. The
Connective Tissues. III. Muscular Tissue. IV. Nervous Tissue, 18

CHAPTER III— THE CHEMICAL COMPOSITION OF THE BODY; The
Nitrogenous Substances, The Proteins, Classification of the Pro-
teins, Characteristics of the Proteins, The Fats, The Carbo-
hydrates; Inorganic Substances of the Body, Laboratory Experi-
ments 79

CHAPTER IV— THE BLOOD; Quantity of the Blood, Coagulation of
the Blood, Morphology of the Blood, Chemical Composition of the
Blood, Globulocidal and Other Properties of Serum, The Character
and Composition of Lymph, Laboratory Experiments 117

CHAPTER V — THE CIRCULATION OF THE BLOOD; Anatomical Con-
siderations, The Action of the Heart, The Regulative Influence of
the Central Nervous System, The Circulation through the Blood-
vessels, The Pulse, The Peripheral Regulation of the Flow of Blood,
Vaso-constrictor and Vaso-dilator Nerves for Individual Organs,
Laboratory Experiments 161

CHAPTER VI— RESPIRATION; The Respiratory Apparatus, The
Movements of the Respiratory Mechanism, Respiratory Changes in
the Air Breathed, The Respiratory Changes in the Blood, The
Nervous Regulation of the Respiratory Apparatus, The Effect of
Respiration on the Circulation, Laboratory Experiments in
Respiration 266

CHAPTER VII— SECRETION IN GENERAL; Organs and Tissues of
Secretion, Secreting Glands, The Process of Secretion, Influence

of the Nervous System on Secretion 316

vii

Vlll CONTENTS.

PAGE

CHAPTER VIII— FOOD AND DIGESTION; Food and Food Principles,
The Process of Digestion, Digestion in the Mouth, Deglutition,
Nervous Mechanism of Deglutition, Digestion in the Stomach,
Movements of the Stomach, Digestion in the Intestines, Moveme ts
of the Intestines, Laboratory Experiments in Digestion, Saliva and
Salivary Digestion, Gastric Juice and Gastric Digestion, Pancreatic
Juice and Pancreatic Digestion 322

CHAPTER IX — ABSORPTION; Absorption in the Stomach, Absorption

in the Intestines, Absorption from the Skin, the Lungs, etc. . . .388

CHAPTER X— EXCRETION; Structure and Function of the Kidneys,
General Structure, The Urine, The Method of Excretion of Urine,
The Discharge of the Urine, The Structure and Excretory Func-
tions of the Skin, Laboratory Experiments in Excretion 398

CHAPTER XI — METABOLISM, NUTRITION, AND DIET; Metabolism of
Proteids, The Metabolism of Fats, the Metabolism of Carbohy-
drates, Requisites of a Normal Diet, The Influence of the Duct-
less Glands on Metabolism 431

CHAPTER XII — ANIMAL HEAT; Heat-producing Organs, Variation in
the Loss of Heat, Variation in the Production of Heat, Influence of
the Nervous System on Heat Production 461

CHAPTER XIII— MUSCLE-NERVE PHYSIOLOGY; Chemical Composi-
tion of Muscle, The Properties of Living Muscle, Single Muscle Con-
tractions, Conditions which Affect the Irritability of the Muscle and
the Character of the Contraction, Tetanic and Voluntary Muscular
Contractions, The Type of Contraction in Involuntary Muscle and
in Cilia, The Function of Nerve Fiber, Some Special Coordinated
Motor Activities, Locomotion, The Production of the Voice,
Laboratory Experiments on Muscle and Nerves 470

CHAPTER XIV— THE NERVOUS SYSTEM; Function of the Nerve Cell;
Specific Energy of the Nerve Impulse, Structure and the Function
of the Spinal Cord, Tracts of the Cord, The Functions of the Cord.
The Brain, The Medulla Oblongata and Pons, Structure, Func-
tions of the Medulla, The Cerebellum, The Midbrain, The
Peduncles of the Cerebrum, Corpora Quadrigemina, Corpora
Geniculata, Corpora Striata, The Cerebrum, Structure of the
Cortex, General Function of the Cerebrum, Localization of the
Motor Function, Localization of Sensory Function, Association
Centers, The Cranial Nerves, The Physiology of Sleep. The
Sympathetic System 534

CONTENTS. IX

PAGE

CHAPTER XV— THE SENSES; I. The Senses of Touch, Pain, Tem-
perature, and the Muscle Sense. II. Taste and Smell, The Sense
of Taste, The Sense of Smell. III. Hearing and Equilibration,
The Anatomy of the Ear, The Physiology of Hearing, The Sense of
Equilibrium. IV. The Sense of Sight, The Eye, The Optical
Apparatus, Accommodation, Defects in the Optical Apparatus,
Visual Sensations from Excitation of the Retina, Color Sensations,
Binocular Vision, Visual Judgments, Laboratory Directions for
Experiments on the Sense Organs 629

CHAPTER XVI— THE REPRODUCTIVE ORGANS; The Reproductive
Organs of the Male, The Reproductive Organs of the Female,
Ovulation and Menstruation, Menstrual Life 715

CHAPTER XVII— DEVELOPMENT; Changes which Occur in the
Ovum Prior to Impregnation, Changes Following Impregnation,
Circulation of Blood in the Fetus, Parturition, Lactation 727

INDEX 739

HANDBOOK OF PHYSIOLOGY,

CHAPTER I
THE PHENOMENA OF LIFE

PHYSIOLOGY is the science which treats of the various processes or changes
which take place in the organs and tissues of the body during life. These
processes, however, must not be considered as by any means peculiar to the
human organism, since, putting aside the properties which serve to distin-
guish man from other animals, the changes which go on in the tissues of man
go on in much the same way in the tissues of all other animals as long as they
live. Furthermore, it is found that similar changes proceed in all living
vegetable tissues; they indeed constitute what are called vital phenomena,
and are those properties which mark out living from non-living material.

The lowest types of life, whether animal or vegetable, are found to con-
sist of minute masses of a substance generally known under the name of
protoplasm. Each such living mass is called a cell, so that these minute
elementary organisms are designated unicellular.

Just as in the lowest types of life the morphological unit of organization
is the cell, so also are the most complex organisms composed of cells. The
tissues and organs of the higher plants and animals are great aggregates of
differentiated cells. The phenomena of life are exhibited in cells, whether
existing alone or developed into the organs and tissues of animals and plants.
It must be at once evident that a correct knowledge of the nature and activi-
ties of the cell forms the very foundation of physiology; cells being, in fact,
physiological no less than morphological units.

The prime importance of the cell as an element of structure was first
established by the researches of the botanist Schleiden, and his conclusions,
drawn from the study of vegetable histology, were at once extended by Theo-
dor Schwann to the animal kingdom. The earlier observers defined a cell
as a more or less spherical body limited by a membrane, and containing a
smaller body termed a nucleus, which in its turn incloses one or more still
smaller bodies or nucleoli. Such a definition applied admirably to most vege-
table cells, but the more extended investigation of animal tissues soon
showed that in many cases no limiting membrane or cell wall could be
demonstrated.

THE PHENOMENA OF LIFE

"Space contain-
ing liquid.

"""Protoplasm.

——Nucleus.

Cell wall.

FIG. i.— Vegetable Cells.

The presence or absence of a cell wall, therefore, was then regarded as
quite a secondary matter, while at the same time the cell substance came
gradually to be recognized as of primary importance. Many of the lower
forms of animal life, the Rhizopoda, were found to consist almost entirely
of matter very similar in appearance and chemical composition to the cell

substance of higher forms; and this from its
chemical resemblance to flesh was termed
Sarcode by Dujardin. When recognized in
vegetable cells it was called Protoplasm by
Mulder, while Remak applied the same name
to the substance of animal cells. As the
presumed formative matter in animal tissues
it was termed Blastema, and in the belief that,
wherever found, it alone of all substances has
to do with generation and nutrition, Beale has
named it Germinal matter or Bioplasm. Of
these terms the one most in use at the present
day as we have already said, is protoplasm, and
inasmuch as all life, both in the animal and
vegetable kingdoms, is associated with proto-
plasm, we are justified in describing it, with
Huxley, as the "physical basis of life," or simply "living matter."

Properties of Protoplasm. — Protoplasm is a semifluid substance,
which absorbs, but does not mix with water. It is transparent and gener-
ally colorless, with refractive index higher than that of water, but lower than
that of oil. It is neutral or weakly alkaline in reaction, but may under
special circumstances be acid,
as, for example, after activity.
It undergoes heat coagulation at
a temperature of about 54. 5° C.
(130° F.), and hence no organ-
ism can live when its own tem-
perature is raised above that
point. It is also coagulated
and therefore killed by alcohol,
by solutions of many of the
metallic -salts, by Strong acids FlG- 2.— Semidiagrammatic Representation of

... a Human Ovum, showing the parts of an animal

and alkalies, and by many other ce\^ (Cadia.)

chemical substances.

Under the microscope it is seen almost universally to be granular, the
granules consisting of different substances, albuminous, fatty, or carbo-
hydrate matter. The granules are not equally distributed throughout the
whole cell mass, as they are sometimes absent from the outer part or layer

Vitelline mem-
brane.

CHARACTERISTICS OF PROTOPLASM 3

and very numerous in the interior. In addition to granules, protoplasm
generally exhibits spaces or vacuoles, usually globular in shape, except-
ing during movement, when they may be irregular, and filled with a watery
fluid. These vacuoles are more numerous and pronounced in vegetable
than in animal cells. Gas bubbles also sometimes exist in cells.

It is impossible to make any definite statement as to the exact chemical
composition of living protoplasm, since the methods of chemical analysis
necessarily imply the death of the cell; it is stated, however, that protoplasm
contains 75 to 85 per cent, of water, and of the 15 to 25 per cent, of solids the
most important part belongs to the class of substances called proteins or al-
bumins. Proteins contain the chemical elements carbon, hydrogen, nitrogen,
oxygen, sulphur, and phosphorus, the last two in very small quantities only.
A protein-like substance, nuclein, found in the nuclei of cells, contains phos-
phorus in greater abundance. In the cell nucleus a compound of nuclein

FIG. 3. — Phases of Ameboid Movement.

with protein, called nucleoprotein, forms the most abundant protein sub-
stance. Other bodies are frequently found associated with the proteins, such
as glycogen, starch, cellulose, which contain the elements carbon, hydrogen,
and oxygen, the last two in the proportion to form water, and hence are
termed carbohydrates; fatty bodies, containing carbon, hydrogen, and oxygen,
but not in proportion to form water; lecithin, a complicated fatty body con-
taining phosphorus; cholesterin, a monatomic alcohol; chlorophyll, the color-
ing matter of plants; inorganic salts, particularly the chlorides and phos-
phates of calcium, sodium, and potassium; ferments, and many special
substances.

The Physiological Characteristics of Protoplasm. — The properties
of protoplasm may be well studied in the microscopic animal called the
ameba, a unicellular organism found chiefly in fresh water. These proper-
ties may be conveniently studied under the following heads:

The Power of Spontaneous Movement. — When an ameba is observed
with a high power of the microscope, it is found to consist of an irregular mass
of protoplasm containing one or more nuclei, the protoplasm itself being
more or less granular and vacuolated. If watched for a minute or two, an
irregular projection is seen to be gradually thrust out from the main body;
other masses are then protruded until gradually the whole protoplasmic sub-
stance is, as it were, drawn over to a new position, and when this is repeated

4 THE PHENOMENA OF LIFE

several times we have locomotion in a definite direction, together with a con-
tinual change of form. These movements, figures 3 and 4, are observed in
such cells as the colorless blood corpuscles of higher animals, in the branched
corneal cells of the frog and elsewhere, and are termed ameboid.

The remarkable movement of pigment granules observed in the branched
pigment cells of the frog's skin by Lister are also probably due to ameboid
movement. These granules are seen at one time distributed uniformly
through the body and branched processes of the cell, while at another time
they collect in the central mass leaving the branches quite colorless.

This movement within the pigment cells might also be considered an ex-
ample of the so-called streaming movement not infrequently seen in certain
of the protozoa, in which the mass of protoplasm extends long and fine proc-
esses, themselves very little movable, but upon the surface of which freely

6.

FiG. 4. — Changes of Form of a White Corpuscle, Sketched at Brief Intervals. The figures
show also the ingestion of two small granules. (Schafer.)

moving or streaming granules are seen. A gliding movement has also been
noticed in certain animal cells; the motile part of the cell being composed of
protoplasm bounding a central and more compact mass. By means of the
free movement of this layer, the cell may be observed to move along.

In vegetable cells the protoplasmic movement can be well seen in the
hairs of the stinging-nettle and Tradescantia and in the cells of Vallisneria
and Chara; it is marked by the movement of the granules nearly always em-
bedded in it. For example, if part of a hair of Tradescantia, figures 5 and 6,
be viewed under a high magnifying power, streams of protoplasm containing
crowds of granules hurrying along, like the foot passengers in a busy street,
are seen flowing steadily in definite directions, some coursing round the film
which lines the interior of the cell wall, and others flowing toward or away
from the irregular mass in the center of the cell cavity. Many of these streams
of protoplasm run together into larger ones and are lost in the central mass,
and thus ceaseless variations of form are produced. The movement of
the protoplasmic granules to or from the periphery is sometimes called

CHARACTERISTICS OF PROTOPLASM 5

vegetable circulation, whereas the movement of the protoplasm round the
interior of the cell is called rotation.

The first account of the movement of protoplasm was given by Rosel in
1755, as occurring in a small Proteus, probably a large fresh-water ameba.
His description was followed twenty years later by Corti's demonstration of
the rotation of the cell sap in characeae, and in the earlier part of the last
century by Meyer in Vallisneria, 1827; Robert Brown, 1831, in "Staminal
Hairs of Tradescantia." Then came Dujardin's description of the granular
streaming in the pseudopodia of Rhizopods and movements in other cells of
animal protoplasm (Planarian eggs, von Siebold, 1841; colorless blood
corpuscles, Wharton Jones, 1846).

The Power of Response to Stimuli, or Irritability. — Although the move-
ments of the ameba have been described above as spontaneous, yet they
may be increased under the action of external agencies which excite them
and are therefore called stimuli. If the movement has ceased for the time,
as is the case if the temperature is lowered beyond a certain point, move-
ment may be set up again by raising the temperature. Contact with foreign

FIG. 5. — Cell of Tradescantia Drawn at Successive Intervals of Two Minutes. — The
cell contents consist of a central mass connected by many irregular processes to a peripheral
film, the whole forming a vacuolated mass of protoplasm, which is continually changing
its shape. (Schofield.)

bodies, gentle pressure, certain salts, and electricity produce or increase the
movement in the ameba. The protoplasm is, therefore, sensitive or irritable
to stimuli, and shows its irritability by movement or contraction of its mass.
The effects of some of these stimuli may be thus further detailed:

a. Changes of Temperature. — Moderate heat acts as a stimulant; the
movement stops below o° C. (32° F.), and above 40° C. (104° F.); between
these two points the movements increase in activity; the optimum tempera-
ture is about 37° to 38° C. Exposure to a temperature even below o° C.
stops the movement of protoplasm, but does not prevent its reappearance if
the temperature is raised; on the other hand, prolonged exposure to a tem-
perature of over 40° C. kills the protoplasm and causes it to enter into a
condition of coagulation or heat rigor.

b. Mechanical Stimuli. — When gently squeezed between a cover and

THE PHENOMENA OF LIFE

object-glass under proper conditions, a colorless blood corpuscle contracts
and ceases its ameboid movement.

c. Nerve Influence. — By stimulation of the nerves of the frog's cornea,
contraction of certain of its branched cells has been produced.

d. Chemical Stimuli. — Water generally stops ameboid movement, and by
imbibition causes great swelling and finally bursting of the cells. In some
cases, however (myxomycetes), protoplasm can be almost entirely dried up,
but remains capable of renewing its movements when again moistened.
Dilute salt solution and many dilute acids and alkalies stimulate the move-
ments temporarily. Strong acids or alkalies permanently stop the move-
ments; ether, chloroform, veratrum, and quinine also stop it for a time.

Movement is suspended in an atmosphere of hydrogen or carbonic acid
and resumed on the admission of air or oxygen, but complete withdrawal of
oxygen will after a time kill the protoplasm.

e. Electrical. — Weak currents stimulate protoplasmic movement, while

strong currents cause the cells to assume a
spherical form and to become motionless.

The Power of Digestion, Respiration, and
Nutrition. — This consists in the power which
is possessed by the ameba and similar animal
cells of taking in food, modifying it, building
up tissue by assimilating it, and rejecting what
is not assimilated. These various processes
are effected in some one-celled animals by the
protoplasm simply flowing around and en-
closing within itself minute organisms such as
diatoms and the like. From these it extracts
what it requires, and then rejects or excretes the
remainder, which has never formed part of the
body. This latter proceeding is done by the
cell withdrawing itself from the material to be
excreted. The assimilation constantly taking
place in the body of the ameba is for the
purpose of replacing waste of its tissue conse-
quent upon manifestation of energy. The
respiratory process of absorbing oxygen goes
on at the same time.

The processes which take place in cells, both animal and vegetable, are
summed up under the term metabolism (from ^era/foVr;, change). The
changes which go on are of two kinds, viz., assimilation, or building up, and
dis assimilation, or breaking down; they may be also called, using the nomen-
clature of Gaskell, anabolism or constructive metabolism, and catabolism or
destructive metabolism. In the direction of anabolism two processes occur,

-.d

FIG. 6. — Cells from the Stam-
inal Hairs of Tradescantia. A,
Fresh in water; B, the same cell
after slight electrical stimula-
tion; a, b, region stimulation;
c, d, clumps and knobs of con-
tracted protoplasm. (Kiihne.)

CHARACTERISTICS OF PROTOPLASM 7

viz., the building up of special though non-living substances from materials
which it takes in, and secondly, the building up of its own living substance
from those or other materials. As we shall see in a subsequent paragraph,
the process of anabolism differs to some extent in vegetable and animal
cells. The catabolism of the cell consists in the disintegrative chemical
changes which occur in the cell substance itself or in substances in contact
with it.

The destructive metabolism of a cell is increased by its activity, but goes
on also during quiescence. It is probably of the nature of oxidation, and re-
sults in the evolution of carbon dioxide and water on the one hand, and in the
formation of various more complex chemical substances on the other, some of
which may be stored up in the cell for future use, and are called secretions,
and others, like carbon dioxide, for example, and bodies containing nitrogen,
are eliminated as excretions.

The Power of Growth. — In protoplasm it is seen that the two processes of
waste and repair go on side by side, and so long as they are equal the size
of the animal remains stationary. If, however, the building up exceed the

FIG. 7. — Diagram of an Ovum (a) Undergoing Segmentation. In (6) it has divided
into two, in (c) into four; and in (d) the process has ended in the production of the so-called
"mulberry mass." (Frey.)

waste, then the animal grows; if the waste exceeds the repair, the animal
decays; and if decay goes on beyond a certain point, life becomes impossi-
ble, and the animal dies.

The power of increasing in size, although essential to our idea of life, is
not, it must be recollected, confined to living beings. A crystal of common
salt, for example, if placed under appropriate conditions for obtaining fresh
material, will increase in size in a fashion as definitely characteristic and as
easily to be foretold as that of a living creature; but the growth of a crystal
takes place merely by additions to its outside; the new matter is laid on par-
ticle by particle, and layer by layer, and, when once laid on, it remains un-
changed. In a living structure, where growth occurs, it is by addition of
new matter, not to the surface only, but throughout every part of the mass,
and this matter becomes an intimate part of the living substance.

The Power of Reproduction. — The ameba, to return to our former illus-
tration, when the growth of its protoplasm has reached a certain point, mani-
fests the power of reproduction, by splitting up into (or in some other way
producing) two or more parts, each of which is capable of independent
existence. The new amebae manifest the same properties as the parent,

8 THE PHENOMENA OF LIFE

perform the same functions, grow and reproduce in their turn. This cycle
of life is being continually passed through.

In more complicated structures than the ameba, the life of individual
protoplasmic cells is probably very short in comparison with that of the organ-
ism they compose; and their constant decay and death necessitate constant
reproduction. The mode in which this takes place has long been the sub-
ject of controversy.

It is now very generally believed that every cell is descended from some
pre-existing mother cell. This derivation of cells from cells takes place by
gemmation, which essentially consists in the budding off and separation of
a portion of the parent cell; or by fission or division.

The exact manner of the division of cells is a matter of some difficulty,
and will not be described until the subject of the structure of protoplasmic
cells has been considered.

STRUCTURE OF PROTOPLASM.

Elemental Structure. — Protoplasm was formerly thought to be homo-
geneous. It is now generally found to consist of the elemental divisions
called cells. Each cell, from a morphological point of view, consists of dif-
ferentiated parts, the most constant of which are the cell nucleus and the cell
cytoplasm. The cytoplasm is differentiated further into two substances,
spongioplasm and hyaloplasm. The spongioplasm or reticulum forms a fine

^ _ Membrane of nucleus.

Cell membrane. —

Achromatic substance of

Cell reticulum. — Chromatic substance of

nucleus.

FIG. 8. — Cell with its Reticulum Disposed Radially; from the intestinal epithelium of a

worm. (Carnoy.)

network, increases in relative amount as the cell grows older, and has an
affinity for staining reagents. The hyaloplasm is less refractile, elastic, or
extensile, and has little or no affinity -for stains; it predominates in young cells,
is thought to be fluid, and fills the interspaces of the reticulum. The nodal
points of the reticulum, with the granular microsomes, found in the proto-
plasm, cause the granular appearance.

The arrangement of the reticulum varies considerably in different cells,
and even in different parts of the same cell. Sometimes, for example, figure

STRUCTURE OF PROTOPLASM 9

8, the mesh work has an elongated radial arrangement from the nucleus; at
others, the mesh work is more evenly disposed, as in figure 9. At the junc-
tions of the fibrils there are usually slight enlargements or nodes.

In some^cells, particularly in plants, but also in some animal cells, there
is a tendency toward a formation of a firmer external envelope, constituting
in vegetable cells a membrane distinct from the more central and more fluid
part of the protoplasm. In such cases the reticulum at the periphery of
the cell is made up of very fine meshes. The membrane when formed is
usually pierced with pores by which fluid may pass in, or through which
protrusion of the protoplasmic filaments forming the cell's connection with
other cells surrounding it may take place.

It is an exceedingly interesting question whether in cells the one part of
the protoplasm can exist without the other. Schafer summarizes the mat-
ter thus: "There are cells, and unicellular organisms both animal and vege-

FIG. 9. — A: The Colorless Blood Corpuscle, Showing the Intracellular Network, and
two nuclei with intranuclear network. B: Colored blood corpuscle of newt showing the
intracellular network of fibrils. Also oval nucleus composed of limiting membrane and
fine intranuclear network of fibrils. X 800. (Klein and Noble Smith.)

table, in which no reticular structure can be made out, and these may be
formed of hyaloplasm alone. In that case, this must be looked upon as the
essential part of protoplasm. So far as ameboid phenomena are concerned
it is certainly so; but whether the chemical changes which occur in many
cells are effected by this or by spongioplasm is another matter."

The Cell Nucleus. — All cells at some period of their existence pos-
sess nuclei. The origin of a nucleus in a cell is the first trace of the differentia-
tion of protoplasm. The existence of nuclei was first pointed out in the
year 1833 by Robert Brown, who observed them in vegetable cells. They
are either small transparent vesicular bodies containing one or more smaller
particles called nucleoli, always when in the resting condition bounded by
a well-defined envelope. In their relation to the life of the cell they are
certainly hardly second in importance to the cytoplasm itself, and thus Beale is
fully justified in comprising both under the term " germinal matter." They
control the nutrition of the cell, and probably initiate the process of sub-

IO

THE PHENOMENA OF LIFE

division. If a cell be mechanically divided, that portion not containing
the nucleus dies.

Histologists have long recognized certain important characters of nuclei.
One is their power of resisting the action of various acids and alkalies, particu-
larly acetic acid, by which their outlines are more clearly denned, and they
are rendered more easily visible. Another is their quality of staining in solu-
tions of carmine, hematoxylin, etc. This indicates some chemical difference
between the cytoplasm of the cells and their nuclei, as the former is destroyed
by these reagents.

Nuclei are most commonly oval or round and do not necessarily conform
to the diverse shapes of the cells; they are altogether less variable elements
than cells, even in regard to size, of which fact one may see a good example

a.

FIG. 10. — Akinesis, Amitosis, or Direct Cell Division. A, Constriction of nucleus; B,
division of nucleus and constriction of cell body; C, daughter nuclei still connected by a
thread, division being delayed; D, division of cell body nearly complete. (After Arnold.)

in the uniformity of the nuclei in cells so multiform as those of epithelium.
But sometimes nuclei occupy almost the whole of the cell, as in the lymph
corpuscles of lymphatic glands, and in some small nerve cells. Their
position in the cell is very variable. In many cells, especially where active
growth is progressing, two or more nuclei are present.

Cell Division and Growth. — The division of a cell is preceded by
division of its nucleus, which may be either direct or indirect. Direct or
simple division, amitosis or akinesis, see figure 10, occurs without any change
in the arrangement of the intranuclear network. A constriction develops at
the center of the nucleus, possibly preceded by division of the nucleoli, and
gradually divides it into two equal daughter nuclei. A similar constriction
of the protoplasm of the cell occurs between the daughter nuclei and divides
it into two parts.

Indirect division, mitosis, or karyokinesis is the usual method, and con-

DIFFERENCES BETWEEN ANIMALS AND PLANTS

II

sists of a series of changes in the arrangement of the intranuclear network,
resulting in the exact division of the chromatic fibers into two parts, which
form the chromoplasm of the daughter nuclei. The changes follow a closely
similar course in both plant and animal cells.

Differences between Animals and Plants. — Having considered at
some length the vital properties of protoplasm, as shown in cells of animal
as well as of vegetable organisms, we are now in a position to discuss the ques-
tion of the differences between plants and animals. It might at the outset
of our inquiry have seemed an unnecessary thing to recount the distinctions
which exist between an animal and a vegetable as they are in many cases so
obvious, but, however great the differences may be between the higher ani-
mals and plants, in the lowest of them the distinctions are much less plain.

FIG. ii. — Karyokinesis, Mitosis, or Indirect Cell Division (diagrammatic). A, Cell
with resting nucleus; B, wreath, daughter centrosomes and early stage of achromatic
spindle; C, chromosomes; D, monaster stage, achromatic spindle in long axis of nucleus,
chromosomes dividing; E, chromosomes moving toward centrosomes; F, diaster stage,
chromosomes at poles of nucleus, commencing constriction of cell body; G, daughter nuclei
beginning return to resting state; H, daughter nuclei showing monaster and wreath; 7,
complete division of cell body into daughter cells whose nuclei have returned to the resting
state. (After Bohm and von Davidoff.)

In the first place, it is important to lay stress upon the differences between
vegetable and animal cells, first as regards their structures and next as re-
gards their functions.

It has been already mentioned that in animal cells an envelope or cell wall
is by no means always present. In adult vegetable cells, on the other hand,
a well-defined wall is highly characteristic; this is composed of cellulose,
is non-nitrogenous, and thus differs chemically as well as structurally from
the contained protoplasmic mass. Moreover, in vegetable cells, figure 12,
B, the protoplasmic contents of the cell fall into two subdivisions: i, a con-
tinuous film which lines the interior of the cellulose wall; and, 2, a reticulate

12

THE PHENOMENA OF LIFE

mass containing the nucleus and occupying the cell cavity. The inter-
stices are filled with fluid. In young vegetable cells such a distinction does
not exist; a finely granular protoplasm occupies the whole cell cavity, figure
12, A. As regards the respective functions of animal and vegetable cells,
one of the most important differences consists in the power which vegetable
cells possess of being able to build up new complicated nitrogenous and
non-nitrogenous bodies out of very simple chemical substances obtained
from the air and from the soil. They obtain from the air oxygen, carbon
dioxide, and water, as well as traces of ammonia gas; and from the soil they
obtain water, ammonium salts, nitrates, sulphates, and phosphates in com-
bination with such bases as potassium, calcium, magnesium, sodium, iron,
and others. The majority of plants are able to work up these elementary
compounds into other and more complicated bodies. This they are able

FIG. 12.— A. Young Vegetable Cells, Showing Cell Cavity Entirely Filled with Gran-
ular Protoplasm Enclosing a Large Oval Nucleus, with one or more Nucleoli. B. Older
cells from same plant, showing distinct cellulose wall and vacuolation of protoplasm.

to do in consequence of their containing a certain coloring matter called
chlorophyll, the presence of which is the cause of the green hue of plants.
In all plants which contain chlorophyll two processes are constantly going
on when they are exposed to light: one, which is called true respiration and
is a process common to animal and vegetable cells alike, consists in the
taking of the oxygen from the atmosphere and the giving out of carbon
dioxide; the other, which is peculiar apparently to bodies containing chloro-
phyll, consists in the taking in of carbon dioxide and the giving out of oxygen.
It seems that the chlorophyll is capable of decomposing the carbon dioxide
gas and of fixing the carbon in the structures in the form of new compounds,
one of the most rapidly formed of which is starch.

Vegetable protoplasm by the aid of its chlorophyll is able to build up a
large number of bodies besides starch, the most interesting and important
being protein or albumin. It appears to be a fact that the power which
bodies possess of being able to synthesize is to a large extent dependent
upon the chlorophyll they contain. Thus the power is present to a marked
extent only in the plants in which chlorophyll is found, and is absent in

DIFFERENCES BETWEEN ANIMALS AND PLANTS 13

those which do not possess it. It is probably present only in slight degree
as one of the properties of animal protoplasm.

It must be recollected, however, that chlorophyll without the aid of the
light of the sun can do nothing in the way of building up substances, and a
plant containing chlorophyll when placed in the dark, while it continues to
live, and that is not as a rule long, acts as though it did not contain any of
that substance. It is an interesting fact that certain of the bacteria have the
chlorophyll replaced by a similar pigment which is able to decompose carbon
dioxide gas.

Animal cells do not possess the power of building up or synthesizing from
simple materials; their activity is chiefly exercised in the opposite direction,
viz., they have brought to them as food the complicated compounds pro-
duced by the vegetable kingdom. With these foods they are able to perform
their complex functions, setting free energy in the direction of heat, motion,
and electricity, and at the same time eliminating such bodies as carbon di-
oxide and water, and producing other bodies, many of which contain nitrogen
but are derived from decomposition.

With reference to the substance chlorophyll it is necessary to say a few
words. It has been noted that the synthetical operations of vegetable cells
are peculiarly associated with the possession of chlorophyll and that these
operations are dependent upon the light of the sun. It has been further
shown that a solution of chlorophyll has a definite absorption spectrum
when examined with the spectroscope, and that it is particularly those parts of
the solar spectrum corresponding to these absorption bands which are chiefly
active in the decomposition of carbon dioxide. In the synthetical processes
of the plant, then, by aid of its chlorophyll, the radiant energy of the sun's
rays becomes stored up or rendered potential in the chemical products
formed. The potential energy is set free, or is again made kinetic, when
these products by simple combustion produce heat, or when they are taken
into the animal organism and used as food and to produce heat and motion.

The influence of light is not an absolute essential to animal life; indeed,
it is said not to increase the metabolism of animal tissue to any great extent,
and the animal cell does not receive its energy directly from the sun's light
nor yet to any extent from the sun's heat, but from the potential energy of the
food stuffs. But it must be always kept in mind that anabolism is not pecu-
liar to vegetable, or katabolism to animal cells; both processes go on in each.
Some of the lowest forms of vegetable life, e.g., the bacteria, will live only in a
highly albuminous medium, and in fact seem to require for their growth
elements of food stuffs which are essential to animal life. In their metabo-
lism, too, they very closely approximate animal cells, not only requiring an
atmosphere of oxygen, but giving out carbon dioxide freely, and secreting
and excreting many very complicated nitrogenous bodies, as well as forming
protein, carbohydrates, and fat, requiring heat but not light for the due per-

14 THE PHENOMENA OF LIFE

formance of their functions. Certain bacteria grow only in the absence of
oxygen.

There is, commonly, a difference in general chemical composition be-
tween vegetables and animals, even in their lowest forms; for associated
with the protoplasm of the former is a considerable amount of cellulose, a
substance closely allied to starch and containing carbon, hydrogen, and
oxygen only. The presence of starch in vegetable cells is very character-
istic, though, as we have seen above, it is not distinctive, and a substance,
glycogen, similar in composition to starch, is very common in the organs and
tissues of animals.

Inherent power of movement is a quality which we so commonly consider
an essential indication of animal nature that it is difficult at first to conceive
of its existence in any other. The capability of simple motion is now known,
however, to exist in so many vegetable forms that it can no longer be held
as an essential distinction between them and animals, and ceases to be a mark
by which one can be distinguished from the other. Thus the zoospores of
many of the Cryptogams exhibit ciliary or ameboid movements of a like
kind to those seen in amebae; and even among the higher orders of plants,
many, e.g.,Dionxa muscipula (Venus's fly-trap), and Mimosa sensitiva (Sensi-
tive plant) exhibit such motion, either at regular times or on the applica-
tion of external irritation, as might lead one, were this fact taken by itself, to
regard them as sentient beings. Inherent power of movement, then, al-
though especially characteristic of animal nature, is, when taken by itself, no
proof of it.

Cell Differentiation and the Functions of Organized Cells. — As we
proceed upward in the scale of life from the unicellular organisms, we find
another phenomenon exhibited in the life history of the higher forms, namely,
that of development. The one-celled ameba comes into being derived from
a previous ameba; it manifests the properties and performs the functions of
its life which have been already enumerated. In the higher organisms it is
different. Each, indeed, begins as a single cell, but the cells which result
from division and subdivision do not form so many independent organisms,
but adhere in one differentiated community which ultimately forms the
complex but co-ordinated whole, in man the human body.

Thus, from the ovum, or germ cell which forms the starting-point of ani-
mal life, in a comparatively short time there is formed a complete membrane
of cells, polyhedral in shape from mutual pressure, called the Blastoderm;
and this speedily differentiates into two and then into three layers, chiefly
from the rapid proliferation of the cells of the first single layer. These layers,
figure 13, are called the Epiblast, the Mesoblast, and the HypoUast. In the
further development of the animal it is found that from each of these layers is
produced a very definite part of the completed body. For example, from
the cells of the epiblast are derived, among other structures, the skin and the

CELL DIFFERENTIATION 15

central nervous system; from the mesoblast the muscles and connective
tissue of the body, and from the hypoblast the epithelium of the alimentary
canal, some of the chief glands, and so on.

It is obvious that the tissues and organs so derived will exhibit in a varying
degree the primary properties of protoplasm. The muscles, for example,
derived chiefly from certain cells of the mesoblast are particularly contractile
and respond to stimuli readily, while the cells of the liver, although possibly
contractile to a certain extent, have to do chiefly with the processes of
nutrition.

As the cells of the embryo increase in number in development there is a
corresponding differentiation of function among the groups of cells. The
various functions which the original cell may be supposed to discharge, and
the various properties it may be supposed to possess, become divided among
groups of cells in which the work of each group is specialized. As a result

FIG. 13. — Transverse Section through Embryo Chick (26 hours), a, Epiblast; b,
mesoblast; c, hypoblast; d, central portion of mesoblast, which is here fused with epiblast;
e, primitive groove;/, dorsal ridge. (Klein.)

of this division of labor the functions and properties are developed and made
more perfect, with a view to the more economic and effective accomplishment
of the activities of the body as a whole.

In studying the functions of the human body it is necessary first of all to
know of what it is composed, of what tissues and organs it is made up; this
can of course be ascertained only by the dissection of the dead body, and thus
it comes that Anatomy, the science which treats of the structure of organized
bodies, is closely associated with physiology, which treats of the function of
the same structures. So close, indeed, is the association that Histology,
which is especially concerned with the minute or microscopic structure of the
tissues and organs of the body and which is, strictly speaking, a department
of anatomy, is often included in works on physiology. There is much to be
said in favor of such an arrangement, since it is impossible to consider the
changes which take place in any tissue during life, apart from the knowledge
of the structure of the tissues themselves. There is indeed an almost insep-
arable relation between the structure and the function of the differentiated

1 6 THE PHENOMENA OF LIFE

animal body in which the one is made the means to a knowledge of the other
as an end, and vice versa, according to the aims and purposes of the student.

An equally important essential to the right comprehension of the changes
which take place in the living organism is a knowledge of the chemical com-
position of the body. Here, however, we can deal directly only with the
composition of the dead body, and it is well at once to admit that there may
be many chemical differences between living and non-living tissues; but as it
is impossible to ascertain the exact chemical composition of the living tissues,
the next best thing which can be done is to find out as much as possible about
the composition of the same tissues after they are dead. This is the assist-
ance which the science of Chemistry can afford to the physiologist.

Having mastered the structure and composition of the body, we are
brought face to face with physiology proper, and have to investigate the vital
changes which go on in the tissues, the various actions taking place as long
as the organism is at work. The subject includes not only the observation
of the manifest processes which are continually taking place in the healthy
body, but the conditions under which these are brought about, the laws
which govern them and their effects.

Sources and Utilization of Physiological Material. — It may be well
to mention as a preliminary that the physiological information which we have
at our disposal has been derived from many sources, the chief of which are
as follows: From actual observation of the various phenomena occurring in
the human body from day to day, and from hour to hour, as, for example, the
estimation of the amount and composition of the ingesta and egesta, the res-
piration, the beat of the heart, and the like; from observations upon ether
animals, the bodies of which we are taught by comparative anatomy approxi-
mate the human body in structure and may be supposed to be similar in func-
tion; from observations of the changes produced by experiment upon the
various processes in such animals, or in the organs and tissues of animals;
from observations of the changes in the working of the human body produced
by diseases; from observations upon the gradual changes which take place in
the functions of organs when watched in the embryo from their earliest
beginnings to their completed development.

The physiologist, in order to utilize the sources of material, must be
familiar with the gross structure of the animals or parts of animals which he
proposes to use in experimental procedure. So simple a matter as the deter-
mination of arterial blood pressure involves familiarity with extensive ana-
tomical structure. Experimental procedure must also draw on the field of
microscopic structure or histology, and many of the most instructive bodies of
physiological knowledge have come directly from the utilization of the facts
of comparative anatomy and of biology. The problems in animal nutrition
which are under such extensive investigation at the present time require for
their solution not only the use of the most complex methods of chemistry,

SOURCES AND UTILIZATION OF PHYSIOLOGICAL MATERIAL 17

both analytical and synthetical, but also the principles and methods of phys-
ics. Indeed, since the work of Helmholz, the interpretation of physio-
logical phenomena by means of physical laws and methods has contributed
more than any other means toward the prominent scientific position of
physiology at the present time. In a word, physiology must utilize the
facts of anatomy, histology, biology, physics, and chemistry to interpret the
phenomena of life.

CHAPTER II

CELL DIFFERENTIATION AND THE STRUCTURE OF THE
ELEMENTARY TISSUES

A CAREFUL examination of the human body shows that the functional unit
for the various and complicated life phenomena is the microscopical structure,
the cell. The cell, alone or in combination, is capable of all the activities
manifested by the living body. As a basis for brief review of the elementary
structures of the body we shall first discuss the structure and development of
the cell.

THE STRUCTURE OF THE CELL.

The typical tissue cell is a spherical or ovoid mass of protoplasm. Its
structure is quite complex, but the most general differentiation is into the cell-
mass or cytoplasm, and its contained nucleus. The cytoplasm is sometimes
bounded by a definite cell membrane, but in differentiated animal tissues this
membrane is usually not present.

The Cell Body. — The cell body or cytoplasm is a complex semi-fluid
mass, the detailed structure of which has presented problems of many
difficulties. It is usually described as having a framework of spongioplasm or
formed elements, and a homogeneous hyaloplasm. In some cells there are
formed materials resulting from the cellular activity called metaplasm, figure
14. These structural features are made more evident by their affinity for
certain staining reagents.

The spongioplasm or reticulum varies greatly in different types of cells,
and even in different parts of the same cell. It has considerable affinity for
stains which exhibit a fine network, the reticulum. It increases in amount
in older cells and also in constancy in the type of arrangement.

The hyaloplasm is more fluid, less refractile, and stains with great diffi-
culty. It fills the interspaces of the spongioplasm. In this material may
be embedded such substances as the metaplasts mentioned above.

Structure of the Nucleus. — The nucleus when in a condition of rest
is bounded by a distinct membrane, the nuclear membrane, possibly derived
from the spongioplasm of the cell, which encloses the nuclear contents, nucleo-
plasm or karyoplasm. The membrane consists of an inner, or chromatic,
and of an outer, or achromatic layer, so called from their reaction to stains.
The nucleoplasm is made up of a reticular network, or chromoplasm, whose
interspaces are filled by the karyolymph, or nuclear matrix, a homogeneous

18

CELL MULTIPLICATION

substance which is rich in proteins, has but slight affinity for stains, and is
supposed to be fluid.

The network is composed of limn or achromatin, a transparent unstain-
able framework; and of chromatin, which stains deeply. It is supported by
the linin, and occurs sometimes in the form of granules, but usually as irreg-
ular anastomosing threads, both thicker primary fibers and thinner connect-
ing branches. The threads often form thickened nodes, karyosomes or
false nucleoli, at their points of intersection. It is now quite generally be-

Cell membrane.

Metaplasm gran- <-
ules.

Karyosome or net- —
knob.

Hyaloplasm. „

Spongioplasm. —

Linin network. »*

Nucleoplasm. -'

Attraction sphere.
Centrosome.

Plastids.

... Chromatin network

•- Nuclear membrane

'* Nucleolus.

— Vacuole.

FIG. 14. — Diagram of a Typical Cell. (Bailey.)

lieved that the chromatin occurs as short, rod-like, and highly refractive
masses, which are embedded in the linin in a regular series.

The nucleoli, or plasmosomes, are spherical bodies which stain deeply, and
may either lie free in the nuclear matrix or be attached to the threads of
the network.

The Centrosome and Attraction Sphere. — In addition to the nucleus,
a minute spherical body called the centrosome is believed to be constantly
present in animal cells, though sometimes too small to be demonstrated.
The centrosome is smaller than the nucleus, close to which it lies, and exerts a
peculiar attraction for the protoplasmic filaments and granules in its vicinity,
so that it is surrounded by a zone of fine radiating fibrils, forming the attrac-
tion sphere or archoplasm. Some authorities assert that the centrosome
lies within the nucleus in the resting state, and passes into the cell proper only
in the earlier stages of cell division. The attraction sphere is most distinctly
seen in cells about to divide. It plays an important role in nuclear division,
but it is doubted if it gives the initial impulse to the process.

Cell Multiplication. — Cells increase in number by a process known
as cell division, of which the first act is nuclear division, In fact the nucleus
is the center of control of the cell mass in the process of division. Cell multi-

20

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

plication takes place by two recognized methods, direct (amitosis), in which
there is little disturbance of the nuclear network, and indirect (mitosis), in
which there is a complex series of nuclear network changes. These mitotic
changes result in the division of the chromatin fila-
ments into the two new parts which form the chromo-
plasm of the daughter nuclei.

The process may be divided into the following
stages:

Prophase. — The resting nucleus becomes somewhat
enlarged, and the centrosome (according to those who
regard it as lying normally within the nucleus) migrates
into the cell protoplasm. The centrosome then divides
into two daughter centrosomes which lie near the nucleus
but are separated by a considerable interval. Each is
surrounded by the radiating fibrils of the attraction
sphere, and some of these fibrils pass continuously from
one centrosome to the other, forming the achromatic
spindle. At the same time the intranuclear network be-
comes converted into a fine convoluted coil, the spirem or
skein, which may be either continuous or else broken up into several threads.
The thread or threads then shorten and become thicker, while the convolu-
tions, which have become less numerous, arrange themselves in a series of
connecting loops, forming the wreath. The nuclear membrane and the
nucleolus disappear, the latter passing at times into the cell protoplasm and
disintegrating. The wreath then breaks up into V-shaped segments, the
chromosomes, of which each species of animal has a constant and character-
istic number. This varies in the different animals, but is sixteen in man.

The two centrosomes migrate to the poles of the nucleus, while the achro-
matic spindle which connects them occupies the long axis of the nucleus.

A B

FIG. 15. — Leuco-
cyte of Salamander
Larva, Showing At-
traction Sphere.
(After Flemming.)

FIG. 16.— Early Stages of Karyokinesis. A. The thicker primary fibers remain and
the achromatic spindle appears. B. The thick fibers split into two and the achromatic
spindle becomes longitudinal. (Waldeyer.)

The chromosomes, becoming much shorter and thicker, gather around the
spindle in its equatorial plane, with their angles directed toward the center,
forming the aster or monaster.

Metaphase. — The actual division of the nucleus is begun at this time by the
splitting of each chromosome longitudinally into halves which lie at first close

CELL MULTIPLICATION

21

together so that each seems doubled. Soon afterward the fibrils of the
achromatic spindle begin to contract, and thus separate the halves of the
chromosomes in such a way that one-half of each is turned toward one pole,
and the other half toward the other. As this continues, the two groups,

centred, __.
}3<xrticle>

clear area,
of nucleus

FIG. 17. — Monaster Stage of Karyokinesis. (Rabl.)

which are equal in size, draw away from each other and from the equator,
each group being formed of daughter chromosomes.

Anaphase. — The two groups (daughter chromosomes) now gradually ap-
proach their respective poles, or centrosomes, and the equator becomes free.
On reaching the pole, each group gathers in a form which is similar in arrange-
ment to the monaster and is known as the diaster. During this time the cell
ABC

FIG. 18. — Stages of Karyokinesis. (Rabl.) A. Commencing separation of the split
chromosomes. B. The separation further advanced. C. The separated chromosomes
passing along the fibers of the achromatic spindle.

body becomes slightly constricted by a circular groove at its equatorial plane.
Telophase. — Soon afterward the fibrils of the chromatic spindle which
connect the two groups begin to grow dim and finally disappear. The daugh-
ter chromosomes assume the form of threads twisted in a coil and develop
each a nuclear membrane and a nucleolus, forming a daughter nucleus.
The nuclei enlarge and the nuclear threads assume the appearance of the
resting state of the nucleus. Meanwrhile, the constriction about the body
of the cell has become deeper and deeper until the protoplasm is divided into
two equal parts, or daughter cells, each with its daughter nucleus, and the
process of karyokinesis is completed.

22 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

The Cell Types. — All of the elementary tissues consist of cells and of
their altered equivalents. It will be as well therefore to indicate some of the
differences between the cells of the body. They are named in various ways,
according to their shape, origin, and functions.

From their shape, cells are described as spherical or spheroidal, which is
the typical shape of the free cell; this may be altered to polyhedral when the
pressure on a mass of cells in all directions is nearly the same; of this the
primitive segmentation cells afford an example. The discoid form is seen
in blood corpuscles, and the scale-like form in superficial cells. Some cells
have a jagged outline and are then called prickle cells. Cells of cylindrical ,
conical, or prismatic form occur in various places in the body. Such cells
may taper at one or both ends into fine processes, in the former case being
caudate, in the latter fusiform. They may be greatly elongated so as to
become fibers. Cells with hair-like processes, or cilia, projecting from their

Remains of spindle.

-» Lighter substance
' of nuc.eus.

------ Hilus.

FIG. 19. — Final Stages of Karyokinesis. In the lower figure the changes are still more
advanced than in the upper. (Waldeyer.)

free surfaces, are a special variety. The cilia vary greatly in size, and may
even exceed in length the cell itself. Finally, cells may be branched or stellate
with long outstanding processes.

From theirfunction cells are called secreting, protective, sensitive, contractile,
and the like.

From their origin cells are called epiblastic and mesoblastic and hypoblastic
(ectodermic, mesodermic, and endodermic).

Modes of Cell Connection.— Cells are connected together to form
tissues in various ways.

They are connected by means of a cementing intercellular substance.
This is probably always present as a transparent, colorless, viscid, albu-
minous substance, even between the closely apposed cells of epithelium;
while in the case of cartilage it forms the main bulk of the tissue, and the cells
only appear as embedded in, not as cemented together by, the intercellular
substance. This intercellular substance may be either homogeneous or
fibrillated. In many cases, e.g., the cornea, it can be shown to contain a
number of irregular branched cavities, which communicate with each other ?

THE EPITHELIAL TISSUES 23

and in which branched cells lie. Nutritive fluids can find their way through
these branching spaces into the very remotest parts of a non-vascular tissue.
The basement membrane (membrana propria) must be mentioned as a special
variety of intercellular substance which is found at the base of the epithelial
cells in most mucous membranes, and especially as an investing tunic of
gland follicles which determines their shape.

Cells are connected by anastomoses of their processes. This is the usual
way in which stellate cells, e.g., of the cornea, are united. The individuality
of each cell is thus to a great extent lost by its connection with its neighbors
to form a reticulum. As an example of a network so produced we may cite
the anastomosing cells of the reticular tissue of lymphatic glands.

Derived Elements. — Besides the cell, which may be termed the primary
tissue element, there are materials which may be termed secondary or derived
elements or formed materials. Examples of this type of structure are found
in the matrix of cartilage, the fibers of connective tissue, bone, etc.

Decay and Death of Cells. — There are two chief ways in which the
comparatively brief existence of cells is brought to an end, by mechanical
abrasion and by chemical transformation.

The various epithelia furnish abundant examples of mechanical abrasion.
As it approaches the free surface, the cell becomes more and more flattened
and scaly in form and more horny in consistency, till at length it is simply
rubbed off as in the epidermis. Hence we find free epithelial cells in the
mucus of the mouth, intestine, and in the genito-urinary tract.

In the case of chemical transformation the cell contents undergo a
degeneration wrhich, though it may sometimes be pathological, is very often
a normal process. Thus we have cells by fatty metamorphosis producing
oil globules in the secretion of milk, fatty degeneration of the muscular fibers
of the uterus after the birth of the fetus. Calcareous degeneration is common
in the cells of many cartilages.

THE STRUCTURE OF THE ELEMENTARY TISSUES.

There are certain elementary structures formed in the process of dif-
ferentiation which alone or when combined in varying proportions form the
whole of the organs and tissues of the body. These elementary tissues are:
The Epithelial, The Connective, The Muscular, and The Nervous Tissues.
To these four some would add a fifth, looking upon the Blood and Lymph,
containing, as they do, formed elements in a fluid menstruum, as a distinct
tissue.

I. THE EPITHELIAL TISSUES.

Epithelium is a tissue composed almost wholly of cells, with a very
small amount of intercellular substance which glues the cells together.
In general it includes all those cellular membranes which cover either an

24 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

external or an internal free surface, together with the cellular portions of the
glands which are connected with, or developed from, these free surfaces.

Epithelium clothes (i) the whole exterior surface of the body, forming
the epidermis with its appendages; becoming continuous at the chief orifices
of the body — nose, mouth, anus, and urethra — with (2) the epithelium which
lines the whole length of the respiratory, alimentary, and genito-urinary
tracts, together with the ducts and secretory cells of their various glands.
Epithelium also lines the cavities of (3) the brain and the central canal of the
spinal cord, (4) the serous and synovial membranes, and (5) the interior of
blood vessels and lymphatics.

Epithelial cells vary in size and shape, pressure being the main factor in
this variation. The protoplasm may be granular, reticular, or fibrillar in
appearance. The nucleus is spherical or oval, usually there is only one, but
there may be two or more present.

Epithelial tissues are non-vascular, that is to say, do not contain blood
vessels, but in some varieties minute channels exist between the cells of
certain layers. Nerve fibers are supplied to the cells of many epithelia.

CLASSIFICATION OF EPITHELIA.

As to form and arrangement of cells.

I. Epithelia in the form of membranes (covering surfaces).

1. Simple epithelium. Cells only one layer in thickness.

(1) Squamous or pavement. Cells flattened.

(a) Non-ciliated. Alveoli of lungs, also includes endothelium,
lining the blood vessels, and mesothelium, lining the large
serous spaces.

(b) Ciliated. The peritoneum of some forms at breeding season.

(2) Cubical epithelia. Cells with the three dimensions approxi-

mately equal, mainly glandular.

(a) Non-ciliated. The usual type. It is found lining both
ducts and secretory portions of most glands, the pigmented
layer of the retina, etc.

(b) Ciliated. Not common. Lining of some of the smaller
bronchial tubes.

(3) Columnar. Cells may be cylindrical, conical, or goblet-shaped.

(a) Non-ciliated. Intestinal.

(b) Ciliated. Fallopian tube and uterus.

(c) Pseudo-stratified. Smaller bronchi, nasal duct, etc.

2. Stratified epithelia. Cells more than one layer in thickness,
(i) Squamous. Surface cells flattened.

(a) Non-ciliated. Skin, mouth, vagina, etc.

(b) Ciliated. Pharynx of embryo.

SIMPLE EPITHELIUM 25

(2) Columnar. Surface cells columnar.

(a) Non-ciliated. Portions of male urethra.

(b) Ciliated. Trachea, bronchi, etc.

II. Epithelia not in the form of membranes, but in solid masses or cords,
usually glandular.

(1) Cells spheroidal, ova.

(2) Cells polyhedral, liver, suprarenal, etc.

Epithelia, classified mainly as to function.

I. Protective. Skin, mouth, alimentary canal.

1. Corniiied. Skin, nails, hair.

2. Cuticular border. Columnar cells of intestine.
II. Glandular.

1. Secretory. Cells of salivary glands, pancreas, etc.

2. Excretory. Cells of kidney.

3. Absorptive. Cells of alimentary canal.

III. Sensory Epithelium. Cells of olfactory membrane, organ of Corti,

taste buds, etc.

IV. Reproductive. Sex cells.

V. Pigmented. Pigmented layer of retina.
VI. Ciliated. Trachea, uterus, Fallopian tube, etc.

Only a few of the more important of the above-mentioned types of epithe-
lium will be described here.

Simple Epithelium. — Simple Squamous. — This form of epithelium
is found arranged in a single layer of flattened cells, for example, the lining of
the alveoli of the lungs and of the descending arm of Henle's loop of the
kidney tubule. Aside from endothelium as mesothelium it has very limited
distribution in man. Endothelium and mesothelium are typical simple

FIG. 20. — The Endothelium of a Small Blood Vessel. Silver- nitrate stain. X 350.

squamous epithelia. They consist of much flattened cells with clear or
slightly granular protoplasm and oval bulging nuclei, the edges of the cells
are peculiarly wavy or serrated.

The presence of endothelium in any locality may be demonstrated by
staining with silver nitrate, which brings into view the intercellular cement

26

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

substance. When a small portion of a perfectly fresh serous membrane,
for example, figure 20, is immersed for a few minutes in a solution of silver
nitrate, and exposed to the action of light, the silver is precipitated in the in-

FiG. 21. — Abdominal Surface of Central Tendon of the Diaphragm of Rabbit, showing the
general polygonal shape of the endothelial cells; each cell is nucleated. (Klein.) X 300.

tercellular cement substance, and the endothelial cells are thus mapped out
by fine, dark, and generally sinuous lines of extreme delicacy.

Endothelial cells in certain situations may be ciliated, e.g., those of the
mesentery of the frog, especially during the breeding season.

On those portions of the peritoneum and other serous membranes in
which lymphatics abound, apertures, figure 22, are found surrounded by
small, more or less cubical, cells. These apertures are called stomata. They
are particularly well seen in the anterior wall of the great lymph sac of the

FIG. 22. — Peritoneal Surface of a Portion of the Septum of the great Lymph Sac of Frog.
The stomata, some of which are open, some collapsed, are surrounded by endothelial cells
(Klein.) X 160.

frog, figure 22, and in the omentum of the rabbit. These are really the open
mouths of lymphatic vessels or spaces, and through them lymph corpuscles
and the serous fluid from the serous cavity pass into the lymphatic system.

Simple Non-ciliated Columnar Epithelium, figure 23, lines, a, the mucous
membrane of the stomach and intestines as a single layer, from the cardiac

SIMPLE EPITHELIUM

orifice of the stomach to the anus, and b, wholly or in part all the ducts of the
glands opening on its free surface, and c, many gland ducts in other regions
of the body, e.g., mammary, salivary, etc. The intracellular and intra-
nuclear networks are well developed, and in some cases the spongioplasm is

FIG. 23. — Simple Columnar Epithelial Cells from the Human Intestinal Mucous
Membrane, a, Mucous (goblet) cell; b, basement membrane; c, cuticle; d, leucocyte
nucleus; e, germinating cell. (Bailey.)

arranged in rods or longitudinal striae at one part of the cell, as in the cells of
the ducts of salivary glands. The protoplasm of columnar cells may be
vacuolated and may also contain fat or other substances seen in the form of
granules. Certain columnar cells transform a large part of their protoplasm
into mucin, goblet cells, figure 24, which is discharged by the open mouth

FIG.

FIG.

FIG. 24.— Goblet Cells. (Klein.)

FIG. 25.— Cross-section of a Villus of the Intestine, e, Columnar epithelium with
striated border; g, goblet cell, with its mucus partly extruded; I, lymph corpuscles between
the epithelial cells; b, basement membrane; c, sections of blood capillaries; m, section of
plain muscle fibers; c I, central lacteal. (Schafer.)

of the goblet, leaving only a nucleus surrounded by the remains of the proto-
plasm in its narrow stem. This transformation is a normal process which
is continually going on during life, the cells themselves being supposed to
regenerate into their original shape.

28

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Stratified Epithelium. — The term stratified epithelium is employed
to describe the type found in the skin or its derivatives in which the cells
forming the epithelium are arranged in a considerable number of superim-
posed layers. The shape and size of the cells of the different layers, as well
as the number of layers, vary in different situations. Thus the superficial
cells may be either squamous or columnar in shape and the deeper cells
range from polygonal to columnar in form.

Stratified Squamous. — The intermediate cells are polygonal in shape and
approach more to the flat variety the nearer they are to the surface, and to the

FIG. 26. — Squamous Epithelium Scales from the Inside of the Mouth. X 260. (Henle.)

columnar as they approach the lowest layer. In many of the deeper layers
of epithelium in the mouth and skin, the outline of the cells is very irregular,
in consequence of processes passing from cell to cell across these intervals.
Such cells, figure 28, are termed "prickle" cells. These "prickles" are the
intercellular bridges which run across from cell to cell, the interstices being
filled by the transparent intercellular lymph. When this increases in quan-

FIG. 27.— Vertical Section of the Stratified Epithelium Covering the Front of the
Cornea. Highly magnified. (Schafer.) c, Lowermost columnar cells; p, polygonal cells
above these;/, flattened cells near the surface. The intercellular channels, bridged by
minute cell processes, are well seen.

tity in inflammation the cells are pushed further apart, and the connecting
fibrils or "prickles" are elongated and more clearly visible.

The columnar cells of the deepest layer are distinctly nucleated; they
multiply rapidly by division; and as new cells are formed beneath, they press
the older cells forward, to be in turn pressed forward themselves toward the
surface, gradually altering in shape and chemical composition until they
die and are cast off from the surface.

STRATIFIED EPITHELIUM

29

Stratified squamous epithelium is found in the following situations: i.
Forming the epidermis, covering the whole of the external surface of the body;
2. Covering the mucous membrane of the nose, tongue, mouth, pharynx, and
esophagus; 3. As the conjunctival epithelium, covering the cornea; 4.
Lining the vagina and the vaginal part of the cervix uteri.

Stratified Columnar Epithelium. — In this type of epithelium, the surface
cells alone are columnar, the deeper cells being irregular in shape. From

FIG. 28. — Epithelial Cells from the Stratum Spinosum of the Human Epidermis, Showing
''Intercellular Bridges." X 700. (Szymonowicz.)

the surface cells long processes extend down among the underlying cells.
This type of epithelium is usually ciliated, as in the trachea, bronchi, etc.,
but may be non-ciliated, as in portions of the human male urethra.

Transitional Epithelium. — This is a stratified epithelium consisting of
only three or four layers of cells. The superficial cells are large and flat,

FIG. 29. — Stratified Columnar Ciliated Epithelium from the Human Trachea,
(goblet) cell also is present.

A mucous

often containing two nuclei. The under surfaces of these cells are hollowed
out, and into these depressions fit the large ends of the pyriform cells which
form the next layer. Beneath the layer of pyriform cells are from one to
four layers of polyhedral cells. This type of epithelium occurs in the bladder,
ureter, and pelvis of the kidney.

30 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Specialized Epithelium. — Glandular epithelium forms the active secreting
agent in the glands; the cells are usually spheroidal, but may be polyhedral
from mutual pressure, or even columnar; their protoplasm is generally oc-
cupied by the materials which the gland secretes. Examples of glandular

w • w : -^ ;$jj

FIG. 30.— Transitional Epithelium from the Human Bladder. (Bailey.)

epithelium are to be found in the liver, figure 31, in the secreting tubes of
the kidney, and in the salivary, figure 32, and gastric glands.

Ciliated epithelium consists of cells which are generally cylindrical in form,
figures 29, 30, but may be spheroidal or even squamous.

This form of epithelium lines: a. The mucous membrane of the respira-
tory tract beginning just beyond the nasal aperture, and completely covers
the nasal passages, except the upper part to which the olfactory nerve is

FIG. 31.

FIG.

FIG. 31. — A Small Piece of the Liver of the Horse. (Cadiat.)

FIG. 32. — Glandular Epithelium. Small lobule of a mucous gland of the tongue,
showing nucleated glandular cells. X 200. (V. D. Harris.)

distributed, and also the sinuses and ducts in connection with it and the
lachrymal sac, the upper surface of the soft palate and the naso-pharynx,
the Eustachian tube and tympanum, the larynx, except over the vocal cords,
to the finest subdivisions of the bronchi. In part of this tract, however,
the epithelium is in several layers, of which only the most superficial is ciliated,

STRATIFIED EPITHELIUM

31

so that it should more accurately be termed transitional, page 24, or stratified.
b. Some portions of the generative apparatus in the male, viz., lining the
'vasa efferentia" of the testicle, and their prolongations as far as the lower
end of the epididymis, and much of the vas deferens; in the female, c, com-
mencing about the middle of the neck of the uterus, and extending throughout

FIG. 33. — Specialized Pigmented Epithelial Cells of Retina.

the uterus and Fallopian tubes to their fimbriated extremities, and even for
a short distance on the peritoneal surface of the latter, d. The ventricles of
the brain and the central canal of the spinal cord are clothed with ciliated
epithelium in the child, but in the adult this epithelium is limited to the cen-
tral canal of the cord.

FIG. 34.

FIG. 35.

FIG. 34. — Spheroidal Ciliated Cells from the Mouth of the Frog. X 300 diameters.
(Sharper.)

FIG. 35. — Ciliated Epithelium from the Human Trachea, a, Large, fully formed cell
b, shorter cell; c, developing cells with more than one nucleus. (Cadiat.)

The cilia themselves are fine rounded or flattened homogeneous processes.
According to some observers, these processes are connected with longitudinal
fibers which pass to the other end of the cell, but which are not connected
with the nucleus.

32 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Functions of Epithelium. — According to function,
epithelial cells may be classified as: i, protective, e.g., in
the skin, mouth, blood vessels, etc. ; 2, protective and motive,
ciliated epithelium; 3, secreting, glandular epithelium; 4,
germinal, as epithelium of testicle producing spermatozoa;
5, absorbing and secreting, e.g., epithelium of intestine; 6,
sensory, e.g., olfactory cells, organ of Corti.

Epithelium forms a continuous smooth investment
over the whole body, being thickened into a hard, horny
tissue at the points most exposed to pressure, and develop-
ing various appendages, such as hairs and nails. Epithe-
lium lines also the sensorial surfaces of the eye, ear, nose,
and mouth, and thus serves as the medium through which
all impressions from the external world — touch, smell,
taste, sight, hearing — reach the delicate nerve endings,
whence they are conveyed to the brain.

The ciliated epithelium which lines the air passages
serves to promote currents of the air in the bronchial tubes
and to propel fluids and minute particles of solid matter
out of the body. In the case of the Fallopian tube, the
cilia assist the progress of the ovum toward the cavity of
FIG. 36.— Cili- the uterus.
Intestine of a The epithelium of the various glands, and of the whole

Mollusk. (En- intestinal tract, has the power of secretion, i.e., of produc-
gelmann.) . , . -11 <• , i T

ing certain materials by processes of metabolism m its

protoplasm.

Epithelium is likewise concerned in the processes of transudation,
diffusion, and absorption.

II. THE CONNECTIVE TISSUES.

This group of tissues forms the skeleton with its various connections —
bones, cartilages, and ligaments — and also affords a supporting framework
and investment to the various organs composed of nervous, muscular, and
glandular tissue. Its chief function is the mechanical one of support, and
for this purpose it is so intimately interwoven with nearly all the textures of
the body that if all other tissues could be removed, and the connective tissues
left, we should have a wonderfully exact model of almost every organ and
tissue in the body.

General Structure of Connective Tissue. — The connective tissue is
made up of two chief elements, namely, cells and intercellular or formed
substance.

Cells. — The cells are usually of an oval shape, often with branched
processes, which are united to form a network. They are most readily

THE CONNECTIVE TISSUE 33

observed in the cornea, in which they are arranged, layer above layer, parallel
to the free surface. They lie in spaces in the intercellular or ground sub -
stance, which form by anastomosis a system of branching canals freely
communicating, figure 37.

The flattened tendon corpuscles which are arranged in long lines or rows
parallel to the fibers belong to this class of cells, figure 39.

These branched cells often contain pigment granules, giving them a dark
appearance; they form one variety of pigment cell. Pigment cells of this
kind are found in the outer layers of the choroid. In many of the lower ani-

FIG. 37. — Horizontal Preparation of the Cornea of Frog, Stained in Gold Chloride;
showing the network of branched corneal corpuscles. The ground substance is completely
colorless. X 400. (Klein.)

mals, such as the frog, they are found widely distributed not only in the skin,
but also in internal parts, the mesentery, sheaths of blood vessels, etc. Under
the action of light, electricity, and other stimuli, the pigment granules become
massed in the body of the cell, leaving the processes quite hyaline; if the
stimulus be removed, they will gradually be distributed again throughout
the processes. Thus the skin in the frog is sometimes uniformly dusky and
sometimes quite light colored, with isolated dark spots.

Intercellular Substance. — This isfibrillar, as in the fibrous tissues and in
certain varieties of cartilage; or homogeneous, as in typical mucoid tissue.

The fibers composing the former are of two kinds, white fibrous and
yellow elastic tissue.

The chief varieties of connective tissues may be thus classified:

White fibrous.

Elastic.

Areolar.

Gelatinous.

34

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Adenoid or retiform.
Adipose.
Neuroglia.
Cartilage.

1. Hyaline.

2. White fibrous.

3. Elastic.
Bone and dentine.

The White Fibrous Tissue. — It is found typically in tendon; also in
ligaments, in the periosteum and perichondrium, the dura mater, the peri-
cardium, the sclerotic coat of the eye, the fibrous sheath of the testicle, in the
fasciae and aponeuroses of muscles, and in the sheaths of lymphatic glands.

Structure. — To the naked eye, tendons and many of the fibrous mem-
branes, when in a fresh state, present an appearance as of watered silk.

FIG. 38.

FIG. 39.

FIG. 38. — Mature White Fibrous Tissue of Tendon, Consisting Mainly of Fibers with a
Few Scattered Fusiform Cells. (Strieker.)

FIG. 39. — Caudal Tendon of Young Rat, Showing the Arrangement, Form, and
Structure of the Tendon Cells. X 300. (Klein.)

This is due to the arrangement of the fibers in wavy parallel bundles. Under
the microscope the tissue appears to consist of long, often parallel, bundles
of fibers of different sizes. The cells in tendons, figure 39, are arranged
in long chains in the ground substance separating the bundles of fibers, and
are more or less regularly quadrilateral with large round nuclei containing
nucleoli, generally placed so as to be contiguous in two cells. Each of
these cells consists of a thick body from which processes pass in various
directions into, and partially fill up the spaces between, the bundles of
fibers. The rows of cells are separated from one another by lines of cement
substance.

Yellow Elastic Tissue. — Yellow elastic tissue is found chiefly in the
ligamentum nuchae of the ox, horse, and other animals; the ligamenta sub-

GELATINOUS TISSUE

35

flava of man; the arteries, constituting the fenestrated coat of Henle; the
veins iri the lungs and trachea; the stylo-hyoid, thyro-hyoid, and crico-
thyroid ligaments; in the true vocal cords; and in areolar tissue.

Structure. — Elastic tissue occurs in various forms, from a structureless,
elastic membrane to a tissue whose chief constituents are bundles of fibers
crossing each other at different angles; when seen in bundles elastic fibers are
yellowish in color, but individual fibers are not
so distinctly colored. The varieties of the tissue
may be classified as follows:

a. Fine elastic fibrils, which branch and anas-
tomose to form a network. This variety of elastic
tissue occurs chiefly in the skin and mucous
membranes, in subcutaneous and submucous
tissue, in the lungs and true vocal cords.

b. Thick fibers, sometimes cylindrical, some-
times flattened, which branch, anastomose and
form a network: these are seen most typically in
the ligamenta subflava and also in the ligamentum
nuchae of such animals as the ox and horse, in
which that ligament is largely developed, figure 40.

A certain number of connective-tissue cells
found in the ground substance between

are

FIG. 40. — Elastic Fibers
from the Ligamenta Sub-
flava. X 200. (Sharpey.)

the elastic fibers which make up this variety of
connective tissue, page 34.

Areolar Tissue. — This variety of fibrous tissue has a very wide dis-
tribution and constitutes the subcutaneous, subserous, and submucous tis-
sue. It is found in the mucous membranes, in the true skin, and in the outer
sheaths of the blood vessels. It forms sheaths for muscles, nerves, glands,
and the internal organs, and, penetrating into their interior, supports and con-
nects the finest parts.

Structure. — To the naked eye it appears, when stretched out, as a fleecy,
white, and soft meshwork of fine fibrils, with here and there wider films join-
ing in it, the whole tissue being evidently elastic. The openness of the mesh-
work varies with the locality from which the specimen is taken. Under the
microscope it is found to be made up of fine white fibers, which interlace in a
most irregular manner, together with a variable number of elastic fibers.
On the addition of acetic acid, the white fibers swell up, and become gelatin-
ous in appearance; but as the elastic fibers resist the action of the acid, they
may still be seen arranged in various directions, sometimes appearing to pass
in a more or less circular or spiral manner round a small gelatinous mass of
changed white fiber. The cells of areolar tissues are connective-tissue
corpuscles.

Gelatinous Tissue. — Gelatinous connective tissue forms the chief'

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

part of the bodies of such marine animals as the jelly-fish. It is found in
many parts of the human embryo. It may be best seen in the " Whartonian
jelly" of the umbilical cord and in the enamel organs of developing teeth.

FIG. 41.

FIG. 42.

FIG. 41. — Mucous Connective Tissue from the Umbilical Cord, a, Cells; b, fibrils.

FIG. 42. — Part of a Section of a Lymphatic Gland, from which the corpuscles have
been for the most part removed, showing the Adenoid Reticulum. (Klein and Noble
Smith.)

Structure. — It consists of cells, which in the jelly of the enamel organ
are stellate, embedded in a soft jelly-like intercellular substance which forms
the bulk of the tissue.

Adenoid or Lymphoid Tissue. — Distribution. — This variety of tissue
makes up the stroma of the spleen and lymphatic glands, and is found also

FlG. 43. — Portion of Submucous Tissue of Gravid Uterus of Sow. a, Branched cells,
more or less spindle-shaped; b, bundles of connective tissue. (Klein.)

in the thymus, in the tonsils, and in the follicular glands of the tongue; in
Peyer's patches, in the solitary glands of the intestines, and in the mucous
membranes generally.

Structure. — Adenoid or retiform tissue consists of a very delicate network

ADENOID OR LYMPHOID TISSUE 37

of minute fibrils, figure 46. The network of fibrils is concealed by being
covered with flattened connective-tissue corpuscles, which may be readily
dissolved in caustic potash, leaving the network bare. The network con-
sists of white fibers, the interstices of which are filled with lymph corpuscles.
The cement substance of adenoid tissue is very fluid.

Neuroglia. — This form of connective tissue found in the nervous system
is described on page 78.

Development of Fibrous Tissues. — In the embryo the place of the fibrous
tissues is at first occupied by a mass of roundish cells, derived chiefly from
the mesoderm, but also from ectoderm and from entoderm. These develop
either into a network of branched cells or into groups of fusiform cells,
figure 43.

The cells are embedded in a semifluid albuminous substance derived
probably from the cells themselves. Later this formed material is converted
into fibrils under the influence of the cells. The process gives rise to fibers
arranged in the one case in interlacing networks, areolar tissue, in the other

FIG. 44. — Blood Vessels of Adipose Tissue. A, Minute flattened fat lobule, in which
the vessels only are represented, a, The terminal artery; v, the primitive vein; b, the fat
vesicles of one border of the lobule separately represented. X 100. B, Plan of the
arrangement of the capillaries, c, On the exterior of the vesicles; more highly magnified.
(Todd and Bowman.)

in parallel bundles, white fibrous tissue. In the mature forms of purely
fibrous tissue not only the remnants of the cell substance, but even the nuclei,
may disappear. The embryonic tissue, from which elastic fibers are devel-
oped, is composed of fusiform cells and a structureless intercellular sub-
stance. The fusiform cells dwindle in size and eventually disappear so
completely that in mature elastic tissue hardly a trace of them is to be found;
meanwhile the elastic fibers steadily increase in size.

Adipose Tissue. — In almost all regions of the human body a larger

38 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

or smaller quantity of adipose or fatty tissue is present. Adipose tissue is
almost always found seated in areolar tissue, and forms in its meshes little
masses of unequal size and irregular shape, to which the term lobules is com-
monly applied.

Structure. — Adipose tissue consists essentially of cells which present
dark, sharply defined edges when viewed with transmitted light; each con-
sisting of a structureless and colorless membrane or bag formed of the re-
mains of the original protoplasm of the cell, filled with fat. A nucleus

FIG. 45. — A Lobule of Developing
Adipose Tissue from an Eight-months
Fetus, a, Spherical or, from pressure,
polyhedral cells with large central nu-
cleus, surrounded by a finely reticulated
substance staining uniformly with hema-
toxylin. b, Similar cells with spaces
from which the fat has been removed
by oil of cloves, c, Similar cells showing
how the nucleus with enclosing proto-
plasm is being pressed toward periphery.
d, Nucleus of cndothelium of investing
capillaries. (McCarthy.) Drawn by
Treves.

FIG. 46. — Branched Connective-
tissue Corpuscles, Developing
into Fat Cells. (Klein.)

is always present in some part or other of the cell protoplasm, but in the
ordinary condition of the loaded cell it is not easily or always visible. This
membrane and the nucleus can generally be brought into view by extracting
the fat with ether and by staining the tissue.

The ultimate cells are held together by capillary blood vessels, figure 44;
while the little clusters thus formed are grouped into small masses, and
held so, in most cases, by areolar tissue. The oily matter contained in the
cells is composed chiefly of the compounds of fatty acids with gylcerin, olein,
stearin, and palmitin.

Development of Adipose Tissue. — Fat cells are developed from connective-
tissue corpuscles. In the infra-orbital connective tissue there are cells ex-

CARTILAGE

39

hibiting every intermediate gradation between an ordinary branched connect-
ive-tissue corpuscle and mature fat cells. Their developmental appearance
is as follows: a few small drops of oil make their appearance in the proto-
plasm, and by their confluence a larger drop is produced, figure 45. This
gradually increases in size at the expense of the original protoplasm of the
cell, which becomes correspondingly diminished in quantity till in the mature
cell it forms only a thin crescentic film with a nucleus closely pressed against
the cell wrall. Under certain circumstances this process may be reversed.

A large number of blood vessels are developed in adipose tissue, which
subdivide until each lobule of fat contains a fine meshwork of capillaries
ensheathing each individual fat globule, figure 44.

Adipose tissue serves as a storehouse of combustible matter which may
be reabsorbed into the blood when occasion requires, and, being used up
in the metabolism of the tissues, may help to preserve the heat of the body.
That part of the fat which is situated beneath the skin must, by its want of
conducting power, assist in preventing undue waste of the heat of the body
by escape from the surface.

CARTILAGE.

All kinds of cartilage are composed of cells embedded in a substance
called the matrix. The apparent differences of structure met with in the

FIG. 47. — Hyaline Articular Cartilage (Human). The cell bodies entirely fill the spaces in
the matrix. X 340 diams. (Schafer.)

various kinds of cartilage are more due to differences in the character of
the matrix than of the cells. With the exception of the articular variety,
cartilage is invested by a thin but tough firm fibrous membrane called the
perichondrium.

4O CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Cartilage exists in three different forms in the human body, viz., hyaline
cartilage, yellow elastic cartilage, and white fibro- cartilage.

Hyaline Cartilage. — This variety of cartilage is met with largely in
the human body where it invests the articular ends of bones, and forms the
costal cartilages, the nasal cartilages, and those of the larynx with the ex-

FIG. 48.— Fresh Cartilage from the Triton. (A. Rollett.)

ception of the epiglottis and cornicula laryngis, the cartilages of the trachea
and bronchi.

Structure. — Like other cartilages, it is composed of cells embedded in a
matrix. The cells are irregular in shape, generally grouped together in

FIG. 49. — Costal Cartilage from an Adult Dog, showing the Fat Globules in the Cartilage

Cells. (Cadiat.)

patches, figure 47. The patches are of various shapes and sizes and placed
at unequal distances apart. They generally appear flattened near the free
surface of the mass of cartilage, and more or less perpendicular to the surface
in the more deeply seated portions.

ELASTIC AND WHITE FIBRO-CARTILAGE 41

The intercellular substance of hyaline cartilage, when viewed fresh or
after ordinary fixation, appears homogeneous. However, when subjected
to special methods, the seemingly homogeneous intercellular substance can
be shown to be made up of fibers, comparable with those found in white
fibrous tissue, embedded in the homogeneous matrix.

In the hyaline cartilage of the ribs the cells are mostly larger than in
the articular variety, and there is a tendency to the development of fibers

FIG. 50. — Yellow Elastic Cartilage of the
Ear. Highly magnified. (Hertwig.)

FIG. 51. — White Fibro-cartilage.
(Cadiat.)

in the matrix, figure 49. The costal cartilages also frequently become
calcified in old age, as also do some of those of the larynx.

In the fetus cartilage is the material of which the bones are first con-
structed; the " model" of each bone being laid down, so to speak, in this
substance. In such cases the cartilage is termed temporary. It closely
resembles the ordinary hyaline cartilage, but the cells are more uniformly
distributed throughout the matrix.

Elastic and White Fibro-cartilage. — The first variety is found in
the cartilage of the external ear; the latter in portions of the joints, the inter-
vertebral cartilages, etc.

Structure. — Elastic and white fibro-cartilage are composed of cells and a
matrix; the latter being made up almost entirely of fibers closely resembling
those of fibrous connective tissue.

Development of Cartilage. — Cartilage is developed out of mesoblast cells
with a very small quantity of intercellular substance. The cells multiply by
fission within the cell capsules.

42 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

BONE.

The characteristic of bone is that the matrix is solidified by a deposit of
earthy salts, chiefly calcium phosphate, but some magnesium phosphate and
calcium carbonate.

To the naked eye there appear two plans of structure in different bones,
and in different parts of the same bone, namely, the dense or compact, and
the spongy or cancellous tissue. In a longitudinal section of a long bone,
as the humerus, the articular extremities are found capped on their surface
by a thin shell of compact bone, while their interior is made up of the spongy
or cancellous tissue. The shaft is formed almost entirely of a thick layer
of the compact bone which surrounds a central canal, the medullary cavity,
so called from its containing the medulla, or marrow. In the flat bones, the
parietal bone or the scapula, a layer of cancellous structure lies between
two layers of the compact tissue. In the short and irregular bones, as those
of the carpus and tarsus, the cancellous tissue alone fills the interior, while
a thin shell of compact bone forms the outside.

FIG. 52. — Cells of the Red Marrow of the Guinea-pig, highly magnified, a, A large
cell, the nucleus of which appears to be partly divided into three by constrictions; b, a cell,
the nucleus of which shows an appearance of being constricted into a number of smaller
nuclei; c, a so-called giant cell, or myeloplaxe, with many nuclei; d, a smaller myeloplaxe,
with three nuclei; e-i, proper cells of the marrow. (Schafer.)

The Marrow. — There are two distinct varieties of marrow — the red and
the yellow.

Red marrow is that variety which occupies the spaces in the cancellous
tissue; it is highly vascular, and thus maintains the nutrition of the spongy
bone, the interstices of which it fills. It contains a few fat cells and a large
number of marrow cells, many of which are undistinguishable from
lymphoid corpuscles, and has for a basis a small amount of fibrous tissue.
Among the cells are some nucleated cells containing hemoglobin like the
blood corpuscles. There are also a few large cells with many nuclei, termed
giant cells or myeloplaxes, which are probably derived from the ordinary
marrow cells, figure 52.

THE PERIOSTEUM AND NUTRIENT BLOOD VESSELS

43

Yellow marrow fills the medullary cavity of long bones, and consists
chiefly of fat cells with numerous blood vessels. Many of its cells are in
every respect similar to lymphoid corpuscles.

From these marrow cells, especially those of the red marrow, the red
blood corpuscles are derived.

The Periosteum and Nutrient Blood Vessels. — The surfaces of
bones, except the part covered with articular cartilage, are clothed by a

FIG. 53. — Transverse Section of Compact Bone (of humerus). Three of the Haver-
sian canals are seen, with their concentric rings; also the lacunas, with the canaliculi extending
from them across the direction of the lamellae. The Haversian apertures were filled with
debris in grinding down the section, and therefore appear black in the figure, which
represents the object as viewed with transmitted light. The Haversian systems are so
closely packed in this section, that scarcely any interstitial lamellce are visible. X 150.
(Sharpey.)

tough, fibrous membrane, the periosteum, which is closely attached to the
surface of the bone. Blood vessels are distributed in this membrane, and
minute branches from these periosteal vessels enter the Haversian canals
to supply blood to the solid part of the bone. The long bones are supplied
also by a proper nutrient artery which, entering at some part of the shaft
so as to reach the medullary canal, breaks up into branches for the supply
of the marrow, from which again small vessels are distributed to the interior
of the bone. Other small nutrient vessels pierce the articular extremities
for the supply of the cancellous tissue.

44 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Microscopic Structure of Bone. — Notwithstanding the differences
of arrangement just mentioned, the structure of all compact bone substance
is found under the microscope to be essentially the same.

Examined with a rather high power its substance is found to contain a
multitude of small irregular spaces, approximately fusiform in shape, called
lacuna, with very minute canals or canaliculi, as they are termed, leading

FIG. 54. — Longitudinal Section from the Human Ulna, Showing Haversian Canals,
Lacunae, and Canaliculi. (Rollett.)

from them, and anastomosing with similar prolongations from other lacunae,
figure 53. In very thin layers of bone, no other canals than these may be vis-
ible; but on making a transverse section of the compact tissue of a long bone,
as the humerus or ulna, the arrangement shown in figure 53 can be seen.
The bone seems mapped out into small circular districts, at or about the
center of each of which is a hole, around which are concentric layers, the
lamella, the lacuna and canaliculi following the same concentric distribution
around the center, with which indeed they communicate.

On making a longitudinal section, the central holes are shown to be
simply the cut extremities of small canals which run lengthwise through
the bone, anastomosing with each other by lateral branches, figure 54, and
are called Haversian Canals, after the name of the physician, Clopton Havers,
who first accurately described them.

The Haversian Canals. — The average diameter of the Haversian canals
is 5o/£. They contain blood vessels, and by means of them blood is con-
veyed to even the densest parts of the bone; the minute canaliculi and lacunae

MICROSCOPIC STRUCTURE OF BONE 45

absorbing nutrient matter from the Haversian blood vessels and conveying
it still more intimately to the very substance of the bone which they traverse.
The blood vessels enter the Haversian canals both from without from the
periosteum, and from within from the medullary cavity or from the can-
cellous tissue. The arteries and veins usually occupy separate canals.

The lacuna are occupied by branched cells, the bone cells or bone corpus-
cles, figure 55, which very closely resemble the ordinary branched connective-
tissue corpuscles. The processes of the bone cells extend into the canaliculi.
Each cell controls the nutrition of the bone immediately surrounding it.
Each lacunar corpuscle communicates with the others in its surrounding

FIG. 55. — Bone Corpuscles with their Processes as seen in a Thin Section of Human Bone.

(Rollett.)

district, and with the blood vessels of the Haversian canals by means of the
ramifications just described.

It will be seen from the above description that bone bears a very close
structural resemblance to what may be termed typical connective tissue.
The bone corpuscles with their processes occupying the lacunae and canalic-
uli correspond exactly to the cornea corpuscles lying in the branched spaces.

TheLamellcB of Compact Bone. — In the shaft of a long bone three distinct
sets of lamellae can be clearly recognized: General or fundamental lamellae,
which are just beneath the periosteum and parallel with it, and around the
medullary cavity; Special or Haversian lamellae, which are concentrically
arranged around the Haversian canals to the number of six to eighteen
around each; Interstitial lamellae, which connect the systems of Haversian
lamellae, filling the spaces between them, and consequently attaining their
greatest development where the Haversian systems are few.

The ultimate structure of the lamellae appears to be fibrous. A thin
film peeled off the surface of a bone, from which the earthy matter has been
removed by acid, is composed of a finely reticular structure, formed ap-

46

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

parently of very slender fibers decussating obliquely, but coalescing at the
points of intersection, as if here the fibers were fused rather than woven
together. The reticular lamellae are perforated by the perforating fibers of
Sharpey, which bolt the neighboring lamellae together, and may be drawn
out when the latter are torn asunder, figure 56. These perforating fibers
originate from ingrowing processes of the periosteum, and in the adult still
retain their connection with it.

FIG. 56. — Lamellae Torn off from a Decalcified Human Parietal Bone at some Depth
from the Surface, a, a, Lamellae, showing reticular fibers; b, b, darker part, where several
lamellae are superposed; c, perforating fibers. Apertures through which perforating fibers
had passed, are seen especially in the lower part, a, a, of the figure. (Allen Thomson.)

Development of Bone. — From the point of view of their development
all bones may be subdivided into two classes:

Those which are ossified directly in membrane or fibrous tissue, e.g., the
bones forming the vault of the skull, parietal, frontal, and a certain portion
of the occipital bones.

Those whose form, previous to ossification, is laid down in hyaline carti-
lage, e.g., humerus, femur, etc.

The process of development, pure and simple, may be best studied in
bones which are not preceded by cartilage, i.e., membrane-formed. Without
a knowledge of ossification in membrane it is difficult to understand the much
more complex series of changes' through which such a structure as the carti-
laginous femur of the fetus passes in its transformation into the bony femur
of the adult (ossification in cartilage}.

Ossification in Membrane. — The membrane, afterward forming the
periosteum, from which such a bone as the parietal is developed, consists
of two layers, an external fibrous and an internal cellular or osteo genetic.

OSSIFICATION IN CARTILAGE 47

The external layer consists of ordinary connective tissue, with branched
corpuscles here and there between the bundles of fibers. The internal layer
consists of a network of fine fibrils with nucleated cells and ground or cement
substance between the fibrous bundles. It is more richly supplied with
capillaries than the outer layer. The relatively large number of its cellular
elements, together with the abundance of blood vessels, clearly mark it as
the portion of the periosteum which is immediately concerned in the for-
mation of bone.

In such a bone as the parietal there is first an increase in vascularity,
followed by the deposition of bony matter in radiating spicula, starting
from a center of ossification. These primary bony spicula are osteogenetic
fibers, composed of osteogen, in which calcareous granules are deposited.
Calcareous granules are deposited also in the interfibrillar matrix. By
the junction of the osteogenetic fibers and their resulting bony spicula a
meshwork of bone is formed. The osteoblasts, being in part retained within
the bone trabeculae thus produced, form bone corpuscles. Lime salts are
deposited in the circumferential part of each osteoblast, and thus a ring
of osteoblasts gives rise to a ring of bone with the remaining uncalcified
portions of the osteoblasts embedded in it as bone corpuscles. At the same
time the plate increases at the periphery by the extension of the bony spicula
and by deposits taking place from the osteogenetic layer of the periosteum.
The bulk of the primitive spongy bone is gradually converted into compact
bony tissue of the Haversian systems.

Ossification in Cartilage.— Under this heading, taking the femur as
a typical example, we may consider the process by which the solid cartilag-
inous rod which represents the bone in the fetus is converted into the hollow
cylinder of compact bone with expanded ends formed of cancellous tissue
in the adult long bone.

The fetal cartilage is sheathed in a membrane termed the perichondrium,
which resembles the periosteum described above. Thus, the differences
between the fetal perichondrium and the periosteum of the adult are such
as usually exists between the embryonic and mature forms of connective
tissue.

There are several steps in the transformation of the fetal cartilage to the
adult bone, due to the fact that there is first an impregnation of the cartilage
with lime salts, followed later by the resorption of this entire material with
formation of the embryonic spongy bone, which is later replaced by the per-
manent bone. The complicated phenomenon takes place in steps or stages
as follows :

Stage of Proliferation and Calcification. — The cartilage cells in and[near
the center of ossification become enlarged, proliferate, and arrange them-
selves in rows in the long axis of the fetal cartilage, figure 57. Lime salts are
next deposited in fine granules in the hyaline matrix of the cartilage,;and this

48

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

gradually becomes transformed into calcined trabeculae, figure 57. The en-
larging cartilage cells become more transparent, and finally disintegrate, the
spaces occupied by them forming the primordial marrow cavities. During
this stage the perichondrium has become the periosteum, and is beginning
to deposit bone on the outside of the cartilage.

FIG. 57. — Developing Bone of Femur of the Rabbit. X 350. a, Cartilage cells;
6, cartilage cells enlarged in the region of calcifying matrix; c, d, trabeculae of calcifying
cartilage covered with e, osteoblasts; /, osteoclasts eroding the trabeculse; g, h, disap-
pearing cartilage cells. The osteoblasts are seen to be depositing layers of bony sub-
stance. Loops of blood vessels extend to the limit of the region in which the bone is
forming. (Schafer, from Klein.)

Stage of V ascularization of the Cartilage. — Processes from the osteo-
genetic layer of the periosteum containing blood vessels break through the
bone into the primordial marrow cavities and form the primary marrow,
beginning at the centers of ossification, and spreading chiefly up and down
the shaft.

Stage of Substitution of Embryonic Spongy Bone for Calcified Cartilage. —
The cells of the primary marrow arrange themselves as a continuous epi-

OSSIFICATION IN CARTILAGE

49

thelium-like layer on the calcified trabeculae and deposit a layer of bone,
and ensheath them. The encased trabeculae are gradually absorbed by
the osteodasts of Kolliker.

These stages are precisely similar to what goes on in the growing shaft
of a bone which is increasing in length by the advance of the process of ossifi-

/c,

sv.

FIG. 58. — Transverse Section through the Tibia of a Fetal Kitten, semidiagrammatic.
X 60. P, Periosteum. O, Osteogenetic layer of the periosteum, showing the osteoblasts
arranged side by side, represented as pear-shaped black dots on the surface of the newly
formed bone. B, The periosteal bone deposited in successive layers beneath the peri-
osteum and ensheathing E, the spongy endochondral bone; represented as more deeply
shaded. Within the trabeculse of endochondral spongy bone are seen the remains of the
calcined cartilage trabeculae represented as dark wavy lines. C, The medulla, with V, V,
veins. In the lower half of the figure the endochondral spongy bone has been completely
absorbed. (Klein and Noble Smith.)

cation into the intermediary cartilage between the diaphysis and epiphysis.
In this case the cartilage cells become flattened and, multiplying by division,
are grouped into regular columns at right angles to the plane of calcification
while the process of calcification extends into the hyaline matrix between
them.

50 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

The embryonic spongy bone, formed as above described, is simply a tem-
porary tissue occupying the place of the fetal rod of cartilage; the preceding
stages show the successive changes at the center of the shaft. Periosteal
bone is at the same time deposited in successive layers beneath the perios-
teum at the circumference of the shaft, exactly as described in the section
on ossification in membrane, and thus a casing of periosteal bone is formed
around the embryonic endochondral spongy bone. The embryonic spongy
bone is absorbed, through the agency of the osteoclasts, until the trabeculae
are replaced by one great cavity, the medullary cavity of the shaft.

FIG. 59. — Transverse Section of Femur of a Human Embryo about Eleven Weeks Old.
a, Rudimentary Haversian canal in cross-section; b, in longitudinal section; c, osteoblasts;
d, newly formed osseous substance of a lighter color; e, that of greater age;/, lacunae with
their cells; g, a cell still united to an osteoblast. (Frey.)

Stage of Formation of Compact Bone. — The transformation of spongy
periosteal bone into compact bone is effected in a manner exactly similar
to that which has been described in connection with ossification in mem-
brane, page 46. The irregularities in the walls of the spongy periosteal
bone are absorbed by the osteoclasts, while the osteoblasts which line them
are developed in concentric layers, each layer in turn becoming ossified
till the comparatively large space in the center is reduced to a well-formed
Haversian canal, figure 59. When once formed, bony tissue grows to some
extent inter stitially, as is evidenced by the fact that the lacunae are rather
further apart in full-formed than in young bone.

THE TEETH 51

It will be seen that the common terms ossification in cartilage and ossifi-
cation in membrane are apt to mislead, since they seem to imply two processes
radically distinct. The process of ossification, however, is in all cases one
and the same, all true bony tissue being formed from membrane, perichon-
drium or periosteum; but in the development of such a bone as the femur,
lime salts are first of all deposited in the cartilage; this calcified cartilage,
however, is gradually and entirely reabsorbed, replaced by bone formed
from the periosteum. Thus calcification of the cartilaginous matrix pre-
cedes the real formation of bone. We must, therefore, clearly distinguish
between calcification and ossification. The former is simply the infiltration
of an animal tissue with lime salts, while ossification is the formation of
true bone.

Growth of Bone. — Bones increase in length by the advance of the
process of ossification into the cartilage intermediate between the diaphysis
and epiphysis. The increase in length indeed is due entirely to growth
at the two ends of the shaft. Increase in thickness in the shaft of a long
bone occurs by the deposition of successive layers beneath the periosteum.
If a thin metal plate be inserted beneath the periosteum of a growing bone
it will soon be covered by osseous deposit, but if it be put between the fibrous
and osteogenetic layers it will never become enveloped in bone, for all the
bone is formed beneath the latter.

THE TEETH.

During the course of his life, man, in common with most other mammals,
is provided with two sets of teeth; the first set, called the temporary or milk-
teeth of infancy, are shed and replaced by the second or permanent set.

Temporary Teeth.

MIDDLE LINE OF JAW.

Molars. Canine. Incisors. Incisors. Canine. Molars.

212

The figures indicate in months the age at which each tooth appears:

', First molar and

Upper incisors ' lower lateral Canines Second molar

incisors

incisors

6 to 9 8 to 12 12 to 15 i8to24 24 to 30

52 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Permanent Teeth.

MIDDLE LINE OF JAW.

PJSffiT Canine' Incisors'

Incisors. Canine. g^SSi

2 I 2

or Tru
Mol

3

212

3

The age at which each permanent tooth is cut is indicated in this table in years :

First molars

Incisors

Bicuspids or
premolars

Canines

Second

molars

Third
molars or
wisdoms

Centrals

Laterals

First

Second

6

7

8

9

10

12 to 14

12 to 15

17 to 25

Structure. — A tooth is generally described as possessing a crown, neck,
and root or roots. The crown is the portion which projects beyond the
level of the gum. The neck is that constricted portion just below the crown
which is embraced by the free edges of the gum, and the root includes all
below this.

On making longitudinal and transverse sections through its center, figure
61, A, B, a tooth is found to be principally composed of a hard superficial

FIG. 60. — Normal Well-formed Jaws, from which the Alveolar Plate has been in great
part removed, so as to expose the Developing Permanent Teeth in their Crypts in the Jaws.
(Tomes.)

material, dentine or ivory, which is hollowed out into a central cavity which
resembles in general shape the outline of the tooth, and is called the pulp
cavity.

The tooth pulp is composed of fibrous connective tissue, blood vessels,
nerves, and large numbers of cells of varying shapes. On the surface in

DENTINE OR IVORY 53

close connection with the dentine there is a specialized layer of cells called
odontoblasts , which are elongated columnar cells with a large nucleus at the
tapering ends farthest from the dentine. The cells are all embedded in a
mucoid gelatinous matrix.

The blood vessels and nerves enter the pulp through a small opening
at the apical extremity of each root.

A layer of very hard calcareous matter, the enamel, caps the dentine of
the crown; beneath the level of the gum is a layer of true bone, called the
cement or crusta petrosa. The enamel and cement are very thin at the neck
of the tooth where they come in contact, the cement overlapping the enamel.
The enamel becomes thicker toward the crown, and the cement toward
the lower end or apex of the root.

FIG. 61. — A. — A Longitudinal Section of a Human Molar Tooth, c, Cement; d,
dentine; e, enamel; v, pulp cavity (Owen). B. — Transverse section. The letters indicate
the same as in A.

Dentine or Ivory. — Dentine closely resembles bone in chemical com-
position. It contains, however, rather less animal matter.

Structure. — Dentine is finely channelled by a multitude of delicate tubes,
which by their inner ends communicate with the pulp cavity, and by their
outer extremities come into contact with the under part of the enamel and
cement, and sometimes even penetrate them for a greater or less distance,
figures 63, 64. The matrix in which these tubes lie is composed of " a retic-
ulum of fine fibers of connective tissue modified by calcification, and,
where that process is complete, entirely hidden by the densely deposited
lime salts" (Mummery).

The tubules of the dentine contain fine prolongations from the tooth
pulp, which gives the dentine a certain faint sensitiveness under ordinary
circumstances and, without doubt, have to do also with its nutrition. They
are probably processes of the dentine cells or odontoblasts lining the pulp

54

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

cavity. The relation of these processes to the tubules in which they lie is
precisely similar to that of the processes of the bone corpuscles to the canalic-

Dentine. —

Periosteum of
alveolus.

Cement.

Enamel.

— * Cement.

Lower jaw hone.

FIG. 62. — Premolar Tooth and Surrounding Bone of Cat.

uli of bone. The outer portion of the dentine, underlying the cement and
the enamel, figure 63, b, c, contains cells like bone corpuscles.

FIG. 63. — Section of a Portion of the Dentine and Cement from the Middle of the Root
of an Incisor Tooth, a, Dental tubuli ramifying and terminating, some of them in the
interglobular spaces b and c, which somewhat resemble bone lacunae; d, inner layer of the
cement with numerous closely set canaliculi; e, outer layer of cement;/, lacunas; g, canalic-
uli. X 350. (Kolliker.)

Enamel. — The enamel, which is by far the hardest portion of a tooth,
is composed chemically of the same elements that enter into the composition

ENAMEL

55

of dentine and bone, but the animal matter amounts only to about 2 or 3
per cent. It contains a larger proportion of inorganic matter and is harder
than any other tissue in the body.

Structure. — Enamel is composed of fine hexagonal fibers, figures 64, 65.

FIG. 64.

FIG. 64. — Thin Section of the Enamel and a Part of the Dentine, a, Cuticular pellicle
of the enamel (Nasmyth's membrane); b, enamel fibers, or columns with fissures between
them and cross striae; c, larger cavities in the enamel, communicating with the extremities
of some of the dentinal tubuli (d). X 350. (Kolliker.)

FIG. 65. — Section of the Upper Jaw of a Fetal Sheep. A. — i, Common enamel germ
dipping down into the mucous membrane; 2, palatine process of jaw; 3, rete Malpighi.
(Waldeyer.) B. — Section similar to A, but passing through one of the special enamel germs
here becoming flask-shaped; c, c, epithelium of mouth;/, neck;/', body of special enamel
germ. (Rose.) C. — A later stage; c, outline of epithelium of gum; /, neck of enamel
germ; /', enamel organ; p, papilla; s, dental sac forming;/^, the enamel, germ of perma-
nent tooth; m, bone of jaw; v, vessels cut across. (Kolliker.) Copied from Quain's
" Anatomy."

These are set on end vertical to the surface of the dentine, and fit into cor-
responding depressions in the same.

Like the dentine tubules, they are disposed in wavy and parallel curves.

56 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

The fibers are thus marked by transverse lines. They are mostly solid,
but some of them may contain a very minute canal.

The enamel prisms are connected together by a trace of hyaline cement
substance.

Development. — The first step in the development of the teeth consists
in a downward growth, figure 65, A, i, from the deeper layer of stratified
epithelium of the mouth, which first becomes thickened in the neighborhood
of the maxillae or jaws, now also in the course of formation. This epidermal
papilla grows downward into a recess of the imperfectly developed tissue of
the embryonic jaw. It forms the primary enamel organ or enamel germ, and
its position is indicated by a slight groove in the mucous membrane of the
jaw. The next step consists in the elongation and the inclination outward

FIG. 66. — Part of Section of Developing Tooth of a Young Rat, showing the Mode
of Deposition of the Dentine. Highly magnified, a, Outer layer of fully formed dentine;

b, uncalcified matrix with one or two nodules of calcareous matter near the calcified parts;

c, odontoblasts sending processes into the dentine; d, pulp; e, fusiform or wedge-shape cells
found between odontoblasts; /, stellate cells of pulp in fibrous connective tissue. The
section is stained in carmine, which colors the uncalcified matrix but not the calcified part .
(E. A. Schafer.)

of the deeper part, figure 65, B,/', of the enamel germ, followed by an in-
creased development at certain points corresponding to the situations of the
future milk-teeth. The enamel germ becomes divided at its deeper portion,
or extended by further growth, into a number of special enamel germs corre-
sponding to each of the milk-teeth, and connected to the common germ by a
narrow neck. Each tooth is thus placed in its own special recess in the
embryonic jaw, figure 65, c, /'.

As these changes proceed, there grows up from the underlying tissue
into each enamel germ, figure 65, c, p, a distinct vascular papilla, dental
papilla, and upon it the enamel germ becomes molded, and presents the
appearance of a cap of two layers of epithelium separated by an interval,
figure 65, c, /'. While part of the subepithelial tissue is elevated to form
the dental papillae, the part which bounds the embryonic teeth forms the
dental sacs, figure 65, c, s; and the rudiment of the jaw sends up processes
forming partitions between the teeth. The papilla, which is really part of
the dental sac, is composed of nucleated cells arranged in a meshwork, in

ENAMEL

57

the outer layer of which are the columnar cells called odontoblasts. The
odontoblasts form the dentine, while the remainder of the papilla forms the
pulp. The method of the formation of the dentine from the odontoblasts
is said to be as follows: The cells form elongated processes at their outer
surfaces which are directly converted into the tubules of dentine, figure 66, c,
and into the contained fibrils.

Each papilla early takes the shape of the crown of the tooth to which
it corresponds, but as the dentine increases in thickness and papilla dimin-
ishes until when the tooth is cut only a small amount remains as the pulp. It
is supplied by vessels and nerves which enter at the end of the root. The
roots are not completely formed at the time of the eruption of the teeth.

FIG. 67. — Vertical Transverse Section of the Dental Sac, Pulp, etc., of a Kitten, a,
Dental papilla or pulp; b, the cap of dentine formed upon the summit; c, its covering of
enamel; d, inner layer of epithelium of the enamel organ; e, gelatinous tissue; /, outer
epithelial layer of the enamel organ; g, inner layer, and h, outer layer of dental sac. X 14
(Thiersch.)

The enamel cap is formed by the enamel cells, by the deposit of a keratin-
like substance, which subsequently undergoes calcification. Other layers
are formed in the same manner meanwhile.

The temporary or milk-teeth are speedily replaced by the growth of the
permanent teeth.

The development of the temporary teeth commences about the sixth
week of intrauterine life, after the laying down of the bony structure of
the jaws. Their permanent successors begin to form about the sixteenth
week of intra-uterine life.

58 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

III. MUSCULAR TISSUE.

There are two chief kinds of muscular tissue, differing both in minute
structure as well as in mode of action, viz., (i) the smooth or non- striated, and
(2) the striated.

SMOOTH OR NON-STRIATED MUSCLE.

Non-striated muscle forms the proper muscular coats of the digestive
canal from the middle of the esophagus to the internal sphincter ani; of
the uterus and urinary bladder; of the trachea and bronchi; of the ducts

FIG. 68. — Isolated Smooth Muscle Cells from Human Small Intestine. X 400. Rod-
shaped nucleus surrounded by area of finely granular protoplasm; longitudinal striations
of cytoplasm.

of glands; of the gall-bladder; of the vesiculae seminales; of the uterus and
Fallopian tubes; of the blood vessels and lymphatics; and of the iris and
some other parts of the eye. This form of tissue also enters largely into the
composition of the tunica dartos of the scrotum. Unstriped muscular tissue

FIG. 69. — Smooth Muscle from Intestine of Pig, Showing Syncytial Structure, a,
Protoplasmic process connecting two muscle fibers; b, end-to-end union of two muscle
fibers, showing the continuity of protoplasm and myofibrils; c, nucleus of muscle fiber;
d, granular protoplasm at the end of muscle nucleus; e, coarse myofibril;/, fine myofibril;
g, connective-tissue cell with connective-tissue fibrils surrounding it; h, elastic fiber. (New
figure by Caroline McGill.)

occurs largely also in the true skin generally, being especially abundant in the
interspaces between the bases of the papillae, and, when it contracts, the
papillae are made unusually prominent, giving rise to the peculiar roughness
of the skin termed cutis anserina, or eoose flesh. It also occurs in all parts

STRUCTURE

59

where hairs occur, in the form of flattened roundish bundles which lie along-
side the hair follicles and sebaceous glands.

Structure. — Unstriated muscle fibers are elongated, spindle-shaped,

FIG. 70. — Transverse Section through Muscular Fibers of Human Tongue. The
deeply stained nuclei are situated at the inside of the sarcolemma. Each muscle fiber
shows "Cohnheim's fields," that is, the sarcous elements in transverse section separated
by clear (apparently linear) interstitial substance. X 450. (Klein and Noble Smith.)

mononucleated cells, 7 to 8>tj. in diameter by 40 to 200/4 in length, figures
68 and 69. The protoplasm of each cell, the contractile substance, is
marked by longitudinal striations representing fibrils which have been
described as contractile. The nucleus is an oblong mass placed near the

FIG. 71.

FIG. 7:

FIG. 71. — Muscle Fiber Torn Across; the sarcolemma still connects the two parts of the
fiber. (Todd and Bowman.)

FIG. 72. — Part of a Striped Muscle Fiber of a Water Beetle prepared with Absolute
Alcohol. A, Sarcolemma; B, Krause's membrane. The sarcolemma shows regular
bulgings. Above and below Krause's membrane are seen the transparent "lateral discs."
The chief mass of a muscular compartment is occupied by the contractile disc composed
of sarcous elements. The substance of the individual sarcous elements has collected more
at the extremity than in the center hence this latter is more transparent. The optical
effect is that the contractile disc appears to possess a "median disc" (Disc of Hensen).
Several nuclei, C and D, are shown, and in them a minute network. X 300. (Klein and
Noble Smith.)

center of the cell. It is covered by a nuclear membrane which encloses a
network of anastomosing fibrils.

Development. — In the pig the smooth muscle of the alimentary canal
originates in the syncytium of the mesodermal cells which surround the

60 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

entoderm. The cells soon begin to grow into the adult spindle-shape form
and the fibrils make their appearance. Even in the adult muscle the syn-
cytial connections are retained, according to Dr. McGill.

STRIATED MUSCLE.

Striated or striped muscle constitutes the whole of the muscular apparatus
of the skeleton, of the walls of the abdomen, the limbs, etc. — the whole
of those muscles which are under the control of the will and hence termed
voluntary; also the muscle of the heart.

For the sake of description, striated muscular tissue may be divided
into two classes, (a) skeletal, which comprises the whole of the striated mus-
cles of the body except (b) the heart.

"£

A

**

^ <l sm

m i ifg

*-»-: i *- •*»

?S ! !i» »
tea i * jji/

a i I S!

pi II w\

&

FIG. 73. — 4, Portion of a Medium-sized Human Muscle Fiber. B, Separated bundles
of fibrillae equally magnified; a, a, larger, and b, b, smaller collections; c, still smaller; d, d,
the smallest which could be detached, possibly representing a single series of sarcous
elements. X 800. (Sharpey.)

Skeletal Muscle. — The muscle fibers of the skeletal muscles are usually
grouped in small parallel bundles, fasciculi. The fasciculi extend through
the muscle, converging to their tendinous insertions. Connective-tissue
sheaths, endomysium, surround the fasciculi and support the blood vessels,
while a stronger sheath, the perimysium, encases the entire muscle.

The unit of muscular structure is the fiber. Each muscle fiber is a long
cylinder with fusiform ends. The fibers vary in diameter from 10 to ioo/*,
while the length may reach as much as 40 mm. Each fiber is enclosed in

SKELETAL MUSCLE

6l

a distinct sheath, the sarcolemma. The sarcolemma is a transparent structure,
less sheath of great resistance which surrounds each fiber, figure 71.

The substance of the fiber enclosed A
by the sarcolemma, the contractile
substance, contains a number of oval
nuclei distributed along the length of
the fiber and lying just under or
through the sarcolemma. Each nu-
cleus is accompanied by a small mass
of granular protoplasm at its poles.
The main mass of the fiber is charac-
terized by transverse light and dark
bands, figure 73, from which the name
striated muscle arises.

Longitudinal striation is also ap-
parent under certain modes of treat-
ment, figure 81. The muscle fibers
can be split longitudinally into fibrils,
called sarcostyles, figures 73 and 74
each of which exhibits the character-
istic striation of the whole fiber.
Under certain treatment the sarco-
styles break transversely into smaller discs by cleavage at the line of
Krause's membrane.

The sarcostyle is, therefore, composed of a number of smaller elements

A' R n (A

K

S.E.

K - -,

FIG. 74. — Diagram of Segment of Muscle
Fiber, showing Sarcostyle A, Sarcous
element B, Krause's line C, Hensen's
line D.

S.E.

FIG. 75.

FIG. 76.

FIG. 75. — Sarcostyles from the Wing Muscles of a Wasp. A, A', Sarcostyles showing
degrees of retraction; B, a sarcostyle extended with the sarcous elements separated into two
parts; C, Sarcostyles moderately extended (semidiagrammatic). (E. A. Schafer.)

FIG. 76. — Diagram of a Sarcomere in a Moderately Extended Condition, B. K, K,
Krause's membranes; H, plane of Henson; S, E, poriferous sarcous element. (E. A.
Schafer.)

joined end to end. These are the sarcous elements of Bowman. The sar-
cous element has a highly refractive denser middle piece surrounded by a

62

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

less refractive more fluid material. The polarizing microscope reveals the
fact that the middle piece which corresponds in position to the dark trans-
verse band is doubly refractive, isotropic, while the surrounding material,
the light band, is singly refractive, anisotropic.

In transverse section, figure 70, the area of the muscle substance is
mapped out into small polygonal areas by a network of clear lines called Cohn-
heim's areas. The lines represent the substance between the sarcostyles.
This substance probably represents the less differentiated contractile sub-
stance, called sarcoplasm. In figure 81
the interfibrillar sarcoplasm is indicated
by the longitudinal and transverse lines.
Heart Muscle. — The muscle sub-
stance of the heart is composed of

FIG. 77. FIG. 78.

FIG. 77. — A Section of Cardiac Muscle, Diagrammatic. (From E. A. Schafer, after
Heidenhain.)

FIG. 78. — Intercellular Continuity of Muscle Fibrils in Cardiac Muscle. (From E. A.
Schafer after Przewosky.)

mononucleated masses of protoplasm, cardiac muscle cells, in which the
substance of the cell presents the transversely striated appearance char-
acteristic of the voluntary muscle just described. But the heart muscle is
physiologically much more like an involuntary muscle. The cells are rather
small, two to four times as long as thick, and the nucleus is usually situated
near the middle of the cell, figure 79. There is no sarcolemma; on the other
hand, the cells present branched and irregular outlines, but adjacent cells
interlock in close-fitting contact.

Certain observers have described fibrils as extending across the so-called
cell boundary and noted that not all such boundaries enclose nuclei. These

BLOOD AND NERVE SUPPLY 03

observations suggest that cardiac muscle belongs to the group of tissues
possessing a syncytium. However, the section of cardiac tissue may very
possibly cut many cells without enclosing a nucleus. The continuity of
fibrils is an important observation from the physiological point of view; see
Circulation chapter.

In certain parts of the heart, the cardiac tissue is not completely differ-
entiated and retains in the adult somewhat embryonic characters; for ex-
ample, the bundle of His running in the septum from the auricles to the
ventricles and the cells containing Purkinje's fibers lying immediately under
the endocardium.

FIG. 79.

FIG. 80.

FIG. 79. — Muscular Fiber Cells from the Heart. (E. A. Schafer.)

FIG. 80. — From a Preparation of the Nerve Termination in the Muscular Fibers of a

Snake, a, End-plate seen only broad-surfaced: b, end-plate seen as narrow surface.

(Lingard and Klein.)

Blood and Nerve Supply. — The muscles are freely supplied with blood
vessels; the capillaries form a network with oblong meshes around the fibers.
Nerves also are supplied freely to muscles; the striated voluntary muscles
receiving them from the cerebro- spinal nerves, and the cardiac muscle from
both the cerebro-spinal and the sympathetic nerves.

In striped muscle the nerves end in motor end-plates. The nerve fibers
are medullated; and when a branch passes to a muscle fiber, its primitive
sheath becomes continuous with the sarcolemma, and the axis-cylinder
forms a network of its fibrils on the surface of the muscle fiber. This net-
work lies embedded in a flattened granular mass containing nuclei of several
kinds; this is the motor end-plate, figures 80 and 81. There is considerable
variation in the exact form of the nerve end- plate in the muscle. In batrachia
the nerve fiber ends in a brush of branching nerve fibrils which are accom-
panied here and there by attached oval nuclei.

64

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Development. — The striated muscle of the voluntary variety is usually
developed from the mesoderm. The embryonic cells increase enormously
in size, the nuclei multiply by fission and distribute themselves beneath the

FIG. 81.

FIG. 82.

FIG. 81. — Two Striped Muscle Fibers of the Hyoglossus of Frog, a, Nerve end-plate;
!) , nerve fibers leaving the end-plate; c, nerve-fibers terminating after dividing into branches;
d, a nucleus in which two nerve fibers anastomose. X 600. (Arndt.)

FIG. 82. — Developing Striated Muscular Fibers, Showing Different Stages of Develop-
ment and Different Positions of the Unstriated Protoplasm. A. — Elongated cell with
two nuclei; the longitudinal striation is beginning to show on the right side. From a fetal
sheep. (Wilson Fox.) B. — -Developing muscular fiber, showing * both longitudinal
and transverse striations at the periphery, and a central unstriated cylinder of protoplasm
containing several nuclei. From a human fetus near the third month. (Ranvier.) n,
Nucleus (there is usually a mass of glycogen near each nucleus); p, central unstriated
protoplasm; s, peripheral striated substance. C. — Developing muscular fiber, showing a
lateral position of the unstriated protoplasm. From a three months' human fetus.
(Ranvier.) n, Nucleus; g, unstriated protoplasm at one side of the fiber; s, striated sarcous
substance with longitudinal and transverse striations.

sarcolemma. There is a differentiation of the cell protoplasm which takes
place by the formation of sarcostyles. This begins nearest the surface of
the cells and proceeds toward the center of the mass.

NERVOUS TISSUE 65

The sarcolemma is apparently produced from embryonic connective
tissue.

The cardiac muscle cells are at first spindle-shaped embryonic cells
which elongate more and more. In further differentiation their protoplasm
exhibits faint striations which pervade the cell as it grows in the great increase
in size. The rhythmic contractions begin long before the striations appear.

IV. NERVOUS TISSUE.

Nervous tissue has usually been described as being composed of two
distinct substances, nerve fibers and nerve cells. The modern view of the
nature of nerve tissue is, however, that the nerve cell and the nerve fibers
are to be considered together as one unit, called the neurone. The neurone

FIG. 83. — Diagram Showing the Arrangement of the Neurones or Nerve Units in the
Architecture of the Nervous System. (Raymdn y Cajal.) A, Pyramidal neurone of
-cerebral cortex; B, anterior horn motor cell of spinal cord; D, collateral branches of A; E,
medullary neurone with ascending axone; F, spinal-ganglion neurones; G, sensory axones
of F; I, collaterals of F in the cord.

is embedded in, and supported by, a substance called neuroglia. This neurone
consists of a cell body, a number of branching processes termed dendrites,
and a long process running out from it, the neuraxone, or axone, which be-
comes eventually a nerve fiber. The nerve cell and the nerve fiber are parts
of the same anatomical unit, and the nervous centers are made up of those
units, arranged in different ways throughout the nervous system, figure 83.
5

66

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

NERVE FIBERS.

While the nerve fiber is really to be considered
as a process of the nerve cell, it is convenient to de-
scribe it separately. Nerve fibers are of two kinds,
medullated or white fibers, and non-medullated or
gray fibers.

Medullated Fibers. — Each medullated nerve
fiber is made up of the following parts: An ex-
ternal sheath, called the primitive sheath, neuri-
lemma, or nucleated sheath of Schwann; an inter-
mediate, known as the medullary or myelin sheath,
or white substance of Schwann; and a central
thread, the axis-cylinder, or axial fiber.

The Primitive Sheath. — This is a pellucid mem-
brane forming the outer investment of the nerve
fiber. The sheath is constricted at intervals of a
millimeter or less, the nodes of Ranvier. Each in-
ternodal segment bears a single nucleus surrounded by a variable amount
of protoplasm. This membrane is described as having its origin in the

FIG. 84. — Two Nerve
Fibers of the Sciatic
Nerve. A, Node of Ran-
vier; B, axis-cylinder;
C, sheath of Schwann
with nuclei. X 300.
(Klein and Noble
Smith.)

FIG. 85. — A Node of Ranvier in a Medullated Nerve Fiber, viewed from above. The
medullary sheath is interrupted and the primitive sheath thickened. Copied from Axel
Key and Retzius. X 750. (Klein and Noble Smith.)

FIG. 86. — Gray, Pale, or Gelatinous Nerve Fibers. A, From a branch of the olfactory
nerve of the sheep; two dark-bordered or white fibers from the fifth pair are associated
with the pale olfactory fibers, B, from the sympathetic nerve. X 450. (Max Schultze.)

mesoblastic cells, and the nuclei are the indications of the cellular nature
of each nodal segment.

The Medullary or Myelin Sheath.— This is the part to which the peculiar

NON-MEDULLATED FIBERS

67

opaque white aspect of medullated nerves is due. The thickness of this
layer of nerve fiber varies considerably. It is a semifluid, fatty substance
of high refractive power. It possesses a fine reticulum (Stilling, Klein), in
the meshes of which is embedded the fatty material. It stains well with
osmic acid.

The Axis- cylinder. — -The central thread of a medullated nerve fiber is
the axis- cylinder. It is the prolongation of a nerve cell and extends un-
interrupted for the full length of the fiber. It consists of a large number of
primitive fibrilla, as shown in the cornea, where the axis- cylinders of nerves
break up into minute fibrils which form terminal networks. From various
considerations, such as its invariable presence and unbroken continuity in
all nerves, there can be no doubt that the axis-cylinder is the essential con-

FIG. 87. — Transverse Section of a Portion of the Sciatic Nerve of the Rabbit, Hardened
in Chromic Acid and Stained with Picro-carmine, to show medullated fibers in end view.
X 275. a, Perifascicular connective tissue; b, lamellar sheath; e, axis-cylinder.

ducting part of the fiber, the other parts having the subsidiary function of
support and possibly of insulation.

The size of the nerve fibers varies, figure 87. The largest fibers are
found within the trunks and branches of the spinal nerves, in which the
majority measure from 14^ to igjj. in diameter. In the so-called visceral
or autonomic nerves of the brain and spinal cord medullated nerves are
found, the diameter of which varies from i . S/j. to 3 . 6 p.. In the hypoglossal
nerve they are intermediate in size, and generally measure 7 . 2/j. to 10. 8/*.

Non-medullated Fibers.— The fibers of the second kind, figure 86,
which are also called fibers of Remak, constitute the principal part of the
trunk and branches of the sympathetic nerves, the whole of the olfactory

68

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

nerve, and are mingled in various proportions in the cerebro-spinal nerves.
They differ from the preceding chiefly in not possessing the outer layer of
medullary substance; their contents being composed exclusively of the axis-
cylinder.

FIG. 88. — Transverse Section of the Sciatic Nerve of a Cat, about X 100. It consists
of bundles (funiculi) of nerve fibers ensheathed in a fibrous supporting capsule, epineurium,
A,- each bundle has a special sheath (not sufficiently marked out from the epineurium in
the figure) or perineurium, B, the nerve fibers, Nf; L, lymph spaces; Ar, artery; V, vein;
F, fat. Somewhat diagrammatic. (V. D. Harris.)

The non-medullated nerves are only about one-third to one-half as
large as the medullated nerves, they do not exhibit the double contour, and

FIG. 89. — Small Branch of a Motor Nerve of the Frog, near its Termination, Showing
Divisions of the Fibers: a, into two; 6, into three. X 350. (Kolliker.)

NERVE COLLATERALS

69

they are grayer than the medullated nerves. The non-medullated fibers
frequently branch.

It is worthy of note that in the fetus, at an early period of development,
all nerve fibers are non-medullated.

Nerve Trunks. — Each nerve trunk is composed of a variable number
of different-sized bundles, funiculi, of nerve fibers which have a special
sheath, perineurium. The funiculi are enclosed in a firm fibrous sheath,
epineurium; this sheath also sends in processes of connective tissue which
connect the bundles together. In the funiculi between the fibers is a delicate
supporting tissue, the endoneurium. There are numerous lymph spaces
both beneath the connective tissue investing individual nerve fibers and
also beneath that which surrounds the funiculi.

FIG. 90. — Terminal Ramifications of a Collateral Branch Belonging to a Fiber of the
Posterior Column in the Lumbar Cord of an Embryo Calf.

Bundles of fibers run together in the nerve trunk, but they merely lie
in approximation to each other, they do not unite. Even when nerves anas-
tomose, there is no union of fibers, but only an interchange of fibers between
the anastomosing bundles. Although each nerve fiber is thus single through
most of its course, yet, as it approaches the region in which it terminates, it
may break up into several subdivisions before its final ending.

Nerve Collaterals. — It has been discovered through the researches of
Golgi, and confirmed by the further studies of Cajal and other anatomists,

7o

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

that each individual nerve fiber in the central nervous system gives off in its
course branches which pass out from it at right angles for a short distance,
and then may run in various directions. These branches are called collaterals.
They end in fine, brush-like terminations known as end-brushes, or in little

FIG. 91.

FIG. 92.

FIG. 91. — Nerve Cell with Short Axis-cylinder from the Posterior Horn of the Lumbar
Cord of a 0.55 cm. Embryo Calf. (After Van Gehuchten.)

FIG. 92. — Scheme of Lower Motor Neurone. The cell body, protoplasmic processes,
axone, collaterals, and terminal arborizations in muscle are all seen to be parts of a single
cell. and together constitute the neurone. (Barker.) c, Cytoplasm of cell body containing
chromophilic bodies, neurofibrils, and perifibrillar substance; n', nucleus; n, nucleolus; d,
dendrites; ah, axone hill free from chromophilic bodies; ax, axone; sf, side fibril (collateral);
m, medullary sheath; nR, node of Ranvier where side branch is given off; si, neurilemma
and incisures of Schmidt; m, striated muscle fiber; tel, motor end-plate.

bulbous swellings which come in close contact with other nerve cells,
figures 83 and 90.

In the nerve centers, that is, in the brain and spinal cord, the different
nerve fibers end just as the collaterals do, by splitting up into fine branches
which form the end-brushes. Collaterals of the nerve fibers and end-brushes

NERVE COLLATERALS

71

are chiefly found in the nervous centers. The nerve fibers of the peripheral
nerves end in the muscles, glands, or special sensory organs, such as the
eye and ear, each by its own special type of ending. Here, however, some

FIG. 93. — Large Nerve Cells with Processes, from the Ventral Cornua of the Cord of
Man. X 350. On the cell at the right two short processes of the cell body are present,
one or the other of which may have been an axis-cylinder process (Deiters). A similar
process appears also on the cell at the left.

FlG. 94. — Multipolar Nerve Cell of the Cord of an Embryo Calf.

analogy to the end-brush can also be discovered. As the peripheral nerve
fibers approach their terminations, they lose their medullary sheath, and
consist then merely of an axis-cylinder and primitive sheath. They may
even lose the latter, and only the axis-cylinder be left. Finally, the axis-

72 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

cylinder breaks up into its elementary fibrillae, to end in various ways to
be described later.

THE NERVE -CELL BODY.

The nerve-cell body is the nodal and important part of the neurone, and
from it are given off the dendrites and axis-cylinder process or axone. It
consists of a mass of protoplasm, of varying shape and size, containing within
it a nucleus and nucleolus. All nerve cells give off one or more processes
which branch out in various directions, dividing and subdividing like the
branches of a tree, but never anastomosing with each other or with other cells.

FIG. 95. — Ganglion Cells, Showing Neurofibrils. A, Anterior-horn cells of human; B, cell
from the facial nucleus of rabbit; C, dendrite of anterior horn cell of human. (Bethe.)

These branches are what have already been referred to as the dendrites of
the cell. They were formerly called the protoplasmic processes, figures 91,
93. It is thus seen that the neurone or nerve unit consists of a number of
subdivisions, namely, the cell body, with its nucleus and nucleolus, the
dendrites or protoplasm processes, and the axone or axis-cylinder process.

The protoplasm of the cells is shown by various dyes to consist of neuro-
fibrils, perifibrillar substance) and in most cells chromophilic bodies. Apathy
and others have demonstrated that a network of interlacing and anasto-
mosing fibrils traverses both the cell body and its branches, figure 95.

The perifibrillar substance is a fluid or semifluid substance in which the
fibrils are embedded. By treating nerve cells with special stains granular
bodies varying in size are found embedded in the cytoplasm. These bodies
are the chromophilic bodies, figure 96.

THE NERVE-CELL BODY

73

Ganglion cells are generally enclosed in a transparent membranous
capsule similar in appearance to the external nucleated sheath of nerve
fibers; within this capsule is a layer of small flattened cells.

*

M^*T

FIG. 96. — Cell of the Anterior Horn of the Human Spinal Cord, Stained by Nissl's Method,
showing chromophiles. (After Edinger.)

A

C~

FIG. 97. — An Isolated Sympathetic Ganglion Cell of Man, Showing Sheath with
Nucleated Cell Lining, B. A, Ganglion cell, with nucleus and nucleolus; C, branched
process or dendrite; D, unbranched process or axone. (Key and Retzius.) X 750.

74 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

Nerve Terminations.

Nerve fibers terminate peripherally in four different ways: i, by the ter-
minal subdivisions which pass in between epithelial cells, and are known as
interepithelial arborizations; 2, by motor- plates which lie in the muscles;
3, by special end-organs, connected with the sense of sight, hearing, smell,
and taste; and, 4, by various forms of tactile corpuscles.

FIG. 98. — Sensory Nerve Terminations in Stratified Pavement Epithelium. Golgi's rapid
method. (After G. Retzius.)

The Interepithelial Arborizations. — This forms a most common
mode of termination of the sensory nerves of the body. The nerve fibers
to the surface of the skin or mucous membrane lose their neurilemmse and
myelin sheaths, the bare axis-cylinder divides and subdivides into minute
ramifications among the epithelial cells of the skin and mucous membrane.
In the various glands of the body this form of termination also prevails.
The hair bulbs, the teeth, and the tendons of the body are supplied by this
same process of terminal arborization, figures 98, 99.

FIG. 99. — Sensory Nerve Termination in the Epithelium of the Mucosa of the Inferior
Vocal Cord and in the Ciliated Epithelium of the Subglottic Region of the Larynx of a
Cat Four Weeks Old. (After G. Retzius.) Golgi's rapid method. «, Nerve fibers rising
from the connective-tissue layer into the epithelial layer, where they terminate in ramified
and free arborizations.

The motor nerves to the muscles end in what are known as muscle plates,
the details of whose structure have been already described.

The special sensory end-organs will be described later in the chapter
on the Special Senses.

A fourth form of termination consists of corpuscles that are more or less
encapsulated, and these are known as the corpuscles of Pacini, the tactile

THE TACTILE CORPUSCLES OF MEISSNER

75

corpuscles of Meissner, the tactile corpuscles of Krause, the tactile menisques,
and the corpuscles of Golgi.

The Pacinian Corpuscles.— These nerve endings, named. after their
discoverer Pacini, are elongated oval bodies situated on some of the cerebro-
spinal and sympathetic nerves. They occur on the cutaneous nerves
of the hands and feet, the branches of the large sympathetic plexus about
the abdominal aorta, the nerves of the mesentery, and have been observed
also in the pancreas, lymphatic glands, and thyroid glands, figure 100.
Each corpuscle is attached by a narrow pedicle to the nerve on which it is

FIG.

FIG. 101.

FIG. 100. — Pacinian Corpuscle of the Cat's Mesentery. The stalk consists of a nerve
fiber, n, with its thick outer sheath. The peripheral capsules of the Pacinian corpuscle are
continuous with the outer sheath of the stalk. The intermediary part becomes much
narrower near the entrance of the axis-cylinder into the clear central mass. A hook-
shaped termination with the end-bulb, a, is seen in the upper part. (Ranvier.)

FIG. 101. — Summit of a Pacinian Corpuscle of the Human Finger, showing the
Endothelial Membranes Lining the Capsules. X 220. (Klein and Noble Smith.)

situated, and is formed of several concentric layers of fine membrane, each
layer being lined by endothelium, figure 101. A single nerve fiber passes
through its pedicle, traverses the several concentric layers, enters a central
cavity, and terminates in a knob-like enlargement or in a bifurcation.

The physiological import of these bodies is still obscure.

The Tactile Corpuscles of Meissner. — They are found in the papillae
of the skin of the fingers and toes or among its epithelium. When simple
they are small, slightly flattened transparent bodies composed of nucleated
cells enclosed in a capsule. When compound, the capsule contains several

76

CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

small cells. The nerve fiber penetrates the corpuscles, loses its myelin
sheath, and divides and subdivides to form a series of arborizations. The
terminal arborizations occupy the central part of the corpuscle, and are

FIG. 102. — Tactile Corpuscle of Meissner, Tactile Cell, and Free Nerve Ending.
(Merkel-Henle.) a. Corpuscle proper, outside of which is seen the connective-tissue
capsule; b, fiber ending on tactile cell; c, fiber ending freely among the epithelial cells.

surrounded by a great number of marginal cells. The tactile corpuscles
of Meissner serve for the special purpose of touch.

The Corpuscles of Krause or End-bulbs.— These exist in great

I,...

FIG. 103. FIG. 104.

FIG. 103. — End-bulb of Krause. a, Medullated nerve fiber; &, capsule of corpuscle.
FIG. 104. — A Termination of a Medullated Nerve Fiber in Tendon, lower half with
Convoluted Medullated Nerve Fiber. (Golgi.)

numbers in the conjunctiva, the glans penis, clitoris, lips, skin, and in tendon
of man. They resemble the corpuscles of Pacini, but have much fewer
concentric layers to the corpuscle, and contain a relatively voluminous central

THE CORPUSCLES OF GOLGI.

77

mass composed of polyhedral cells. In man these corpuscles are spherical
in shape, and receive many nerve fibers which wind through the corpuscles
and end in the free extremities, figure 103.

Tactile Menisques. — In different regions of the skin of man, one meets,
in the superficial layers and in the Malpighian layers, nerves which, after
having lost their myelin sheath, divide and subdivide to form extremely
beautiful arborizations. The branches of these arborizations are the tactile
menisques. These menisques, which simulate the form of a leaf, represent a
mode of terminal nervous arborization (Ranvier).

The Corpuscles of Golgi. — These are small terminal plaques placed
at the union of tendons and muscles, but belonging more properly to the

FIG. 105. — Neuroglia Cells in the Cord of an Adult Frog. (After Cl. Sala.) A,
Ependyma cells with their peripheral extremities atrophied and ramified; B, C, D, neuroglia
cells in different degrees of emigration and separation from the ependymal canal; their
central extremity is atrophied and much contracted; their peripheral extremity, on the
other hand, is greatly extended; the ramifications of the latter, terminating in conical
buttons, /, end under the pia mater.

tendon. They are fusiform in shape and are flattened upon the surface of
the tendon close to its insertion into the muscular fibers. They are composed
of a granular substance, enveloped in several concentric hyaline membranes
which contain some nuclei. The nerve fiber passes into this little corpuscle,
splitting itself up into fine terminals. The corpuscles of Golgi are believed
to be related to the muscular sense, figure 104.

7 8 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES

THE NEUROGLIA.

The neuroglia, while not a nervous tissue, is closely mingled with it and
forms an important constituent of the nervous system. It consists of cells
giving off a fine network of richly branching fibers. Neuroglia is a form
of connective tissue, and it is in its functions strictly comparable to the con-
nective tissue which supports the special structures of other organs, like the
lungs and kidneys, figure 106. In the adult animal the neuroglia tissue is

FIG. 1 06. — Different Types of Neuroglia Cells. (After Van Gehuchten.) b, Neuroglia
cells of the white substance, and c, of the gray substance of the cord of an embryo calf.

composed of cells from which are given off immense numbers of fine proc-
esses. These extend out in every direction, and intertwine among the nerve
fibers and nerve cells, figure 105. The neuroglia cell differs in size and shape
very much in different parts of the nervous system in accordance with the
arrangement of the nervous structures about it. The cell is composed of
granular protoplasm, and lying in it is a large nucleus, within which is a
nucleolus. The body of the cell is small in proportion to the nucleus.

CHAPTER III.
THE CHEMICAL COMPOSITION OF THE BODY

OF the eighty chemical elements which have been isolated, no less than
seventeen combine in varying quantities to form the chemical basis of the
animal body. The substances which contribute the largest share are the
non-metallic elements, Nitrogen, Oxygen, Carbon, and Hydrogen — oxygen
and carbon making up altogether about 85 per cent, of the whole. The
most abundant of the metallic elements are Calcium, Sodium, and Potassium*

These elements do not exist in the animal body in the free state, but are
combined into complex chemical compounds.

The first step in the act of separating the composition products of proto-
plasm produces changes which destroy the chemical and physical relations
of these products which maintain the state of life. Dead protoplasm, how-
ever, yields a number of substances wrhich must be very directly derived
from the living protoplasm. On the other hand, certain products can be
isolated from the animal body which are evidently not a part of the proto-
plasm itself, but products of protoplasmic activity. Some of these, like fat,
glycogen, etc., are constructive products, others are disintegration products
of protoplasmic activity.

THE NITROGENOUS SUBSTANCES.

The nitrogenous substances in the body consist chiefly of the proteins
or of substances which are derived from the proteins. Nitrogenous sub-
stances occur in the solid tissues of the body and are found also to a con-
siderable extent in the circulating fluids (the blood and lymph) and in the
secretions and excretions.

* The following table represents the relative proportion of the various elements in
the body. (Marshall.)

Oxygen 72.0 Fluorine o . 08

Potassium . o. 026

Iron . .

Carbon 13.5

Hydrogen 9.1

Nitrogen 2.5

o. 01

Magnesium 0.012

Calcium 1.3 Silicon o . 0002

Phosphorus 1.15 (Traces of copper, lead, and alu-

Sulphur o . 1476 minum)

Sodium o.i

Chlorine 0.085 IO°

8o THE CHEMICAL COMPOSITION OF THE BODY

THE PROTEINS.

These nitrogenous substances constitute the most important and com-
plex compounds in the body. They are essentially the organic basis of all
living substance. At the same time they are the most important of our
organic food stuffs. The proteins are necessary as food material for the
continuance of life and cannot be replaced in the diet by any other organic
or inorganic substances. Without them all life, whether animal or vegetable,
is impossible.

The proteins are substances containing carbon, hydrogen, and oxygen
(which are present in fats and carbohydrates). The proteins also contain
nitrogen and sulphur. Phosphorus and certain metallic elements are present
as constituents of some proteins. The elementary composition of most
protein substances falls within the following percentages:

Carbon from 50 to 55.0 per cent.

Hydrogen from 6 to 7.3 per cent.

Oxygen from 19 to 24.0 per cent.

Nitrogen from 15 to 19.0 per cent.

Sulphur from 0.3 to 2.5 per cent.

Phosphorus, when present from 0.4 to 0.8 per cent.

The individual protein substances are chemical entities. As individuals
of a group they differ in elementary composition and in the derivatives
which they yield on cleavage of the protein molecule.

Chemical Structure of Proteins. — Proteins are combinations of
a-amino acids, the simplest example of which is glycocoll or a-amino acetic
acid. Acetic acid has the formula CH3COOH; if the NH2 group is sub-
stituted for one of the H's in the CH3 radical it is an amino acid. The
introduction of the amino group in this way yields bodies which combine
both with acids and with bases. It is also possible for the amino acids to
combine with one another, with the elimination of water. The reaction,
however, can only be brought about under certain conditions. For instance,
glycocoll can be combined with itself as a dipeptid or combined with any
other amino acid. The combination may be indicated by the following:

CH2 - NH2 - CO I OH +H j HN - CH2 - COOH=

glycocoll plus glycocoll

CH2 - NH2 - CO - NH - CH2 - COOH + H2O

glycyl-glycine plus water

A glance at the chemical formulae of the resulting dipeptid indicates
that in this new substance there is still an amino group (NH2) and a carboxyl
group (COOH) which are not combined. Another amino acid may be
joined on to the carboxyl root, and yet a fourth. on to the remaining amino

THE PROTEINS

8l

group, so that the still more complex peptids can be formed. When this is
done there is yet a carboxyl and an amino group to which other amino acids
can similarly be joined. The structure of the protein molecule accordingly
may be represented as follows:

H

H

I

H

- OC - C - NH - OC - C - NH - OC - C - NH -

R"tS
j\.

In which R indicates here the rest of the formula for any of the a-amino
acids entering into the constitution of protein.

At least eighteen amino acids have been found to enter into the composi-
tion of the proteins. The list includes glycocoll, alanine, serine, phenyl-
alanine, tryosin, tryptophane, cystine, leucine, isoleucine, aspartic acid, gluta-
minic acid, proline, oxyproline, histidine, argenine, lysine, and tryhydroxy-
dodecanoic acid. The chemical formulae for the more important of these
are given below :

NH2

H-C-COOH
H

Glycocoll.

H NH2

I I
H-C-C-COOH

I !

H H

Alanine.

H NH2

C - C-C-COOH

/\ I
HC CH H H

I I
HC CH

C
N
H

Phenylalamne.

(amino acetic acid.) (a-amino proprionic acid.) (Phenyl a-amino proprionic acid.)

OH NH,

HC CH H H
H-C-C-COOH |

HC CH
H H

C

H NH2

C - C-C-COOH H H

I I

H-C-S-S-C-H

H-C-NH2H-C-NH.

COOH

COOH

Serine.

(a-amino /3-hydroxy
proprionic acid.)
6

OH

Tyrosine.

(p-oxyphenyl a-amino
proprionic acid.)

Cystine.

82

THE CHEMICAL COMPOSITION OF THE BODY

H

C H NH2

/\ I

HC C C - C - C - COOH

I I I
HC C CH H H

C NH
H

Tryptophane.
(Indol amino proprionic acid.)

CH3NH.

H-C-C-COOH

I I
CH3H

Valine.
(a-amino isovalerianic acid.)

NH,

NH.

CH3H NH2

H-C-C-C- COOH
CH3H H

Leucine.
(a-amino isobutylacetic acid.)

H NH0

H-C-COOH
H-C-COOH
H

=C-C-C-COOH

I I I

HN N H H

C
H

Histidine.
(a-amino /?-imidazol proprionic acid.)

H-C-COOH
H-C-H
H-C-COOH
H

A spar tic acid. Glutaminic acid.

(amino succinic acid.) (a-amino normal glutaric

acid).

H H H NH2

I I

H-N-C-C-C-C-COOH

I I I

NH=C H H H H

I
NH2

Arginine.
(guanidine a-amino valerianic acid.)

NH2H H H NH2

I I
H-C-C-C-C-C- COOH

I I
H H H H H

Lysine.
(a-e-diamino caproic acid.)

The amino acids belong either to what is known in organic chemistry as
the aliphatic, carbocyclic, or heterocyclic series; that is, they are derivations
either of the hydrocarbons, of benzene or of closed-ring compounds not
composed wholly of carbon atoms, but in which one or more of the links
in the closed chain are supplied by other polyvalent elements (in the proteins
by nitrogen). Thus tyrosine and phenylalanine are carbocyclic compounds;
histidine, proline, and tryptophane are heterocyclic compounds, and the
remaining members of the list are aliphatic derivatives.

Of the elements of the protein molecule, nitrogen is by far the most im-

THE PROTEINS 83

portant. The animal organism cannot build up protein material from nitro-
gen of the atmosphere or from combinations, such as ammonia, nitrates, and
nitrites. Plants, however, have the property of synthesizing proteins from
inorganic nitrogen. The nitrogen in the protein is directly utilizable by the
body, so that the animals are ultimately dependent upon plants for their
protein supply.

Nitrogen in the protein molecule occurs in four different forms:

1. The monamino acid nitrogen, or the nitrogen that is in the NH2 (amino)
group of the a position.

2. The diamino acid nitrogen, or the basic nitrogen, as shown in the
amino group in lysine.

3. Amide nitrogen; the OH of the second COOH group in the dibasic
glutaminic and aspartic acids in protein may be replaced by the amino group.
On cleavage, the NH2 is split off from the acid amide as ammonia.

4. The guanidine residue as in arginine.

The distribution of nitrogen in the protein accordingly depends on the
amino acids entering into its composition.

Sulphur of the protein is present in the amino acid cystine.

It has been stated that the amino acids are combined together in a pro-
tein molecule, carboxyl with amino radical. On boiling the proteins with
mineral acids, the reaction is reversed and the protein substances are split,
with the combining of water, into the individual amino acid components.
This change is termed a "hydrolytic cleavage." The qualitative and quan-
titative determination of the products thus obtained have shown us that the
proteins differ chemically both as to the individual amino acids which enter
into the complex protein molecule and the amount of each acid present.
Proteins, then, which may give exactly the same percentage composition and
elementary analysis and which show practically the same physical prop-
erties are found to be actually different individuals of the protein group
when the products of their hydrolytic cleavage are investigated. For exam-
ple, the following tables give the elementary composition and the amino
acids obtained from three proteins which are present in wheat flour.

ELEMENTARY COMPOSITION OF WHEAT PROTEINS.

Gliadin

Glutenin

Leucosin

Carbon
Hydrogen

52.72
6.86

52.34
6.8s

53-02
6.84

Nitrogen

17 66

I 7.40

1 6 80

Sulphur
Oxygen

1.03

21-73

i. 08
22.26

1.28
22.06

100.00

IOO.OO

100.00

84 THE CHEMICAL COMPOSITION OF THE BODY

AMINO ACIDS OBTAINED ON HYDROLYTIC CLEAVAGE OF WHEAT PROTEIN,

Percent of Gliadin

Glutenin

Leucosin

Glycocoll ! o.oo
Alanin 2 oo

0.89
46 >

0.94

44. ^

Amino valerianic acid 0.21
Leucine 5-6i

0.24

r.n r

0.18

I I 34.

Proline 7.06

4-2 3

3.18

Phenylalanine j 2.35
Aspartic acid 0-58
Glutaminic acid 37-33
Serine i o 13

1.97
0.91
23.42
O 74.

3.83

3.35

6.73

o oo

Tyrosine ; 1.20
Cystine 045

4-25
O O2

3-34
o . oo

Lysine o.oo
Histidine o 61

1.92
1.76

2.75

2.8}

Arginine 3 • T 6
Ammonia 5 1 1

4.72

4 01

5-94
i .41

Tryptophane present

present

present

It has been indicated that the synthesis in very simple proteins can be
attained by combining amino acids. A synthesis, however, can be brought
about by the reversible action of the digestive enzymes. Recently Taylor
has been able to synthesize a simple protein, a protamine, by the reversible
action of a trypsin on amino acids which were previously obtained by the
digestion of the protamine. Cleavage by enzymes is a hydrolysis of the
same type as that mentioned above by the use of the mineral acids. In
the concentration of the products of a digestion the enzymes act in the
reverse manner and resynthesize these substances on which they have pre-
viously acted. Robertson has demonstrated a similar reversible action of
pepsin on paranuclein derived from a digestion of casein. The reversible
action may be indicated by the equation:

PROTEIN + WATER +± AMINO ACIDS.

These experiments lend a new stimulus to the efforts to build up proteins
in the chemical laboratory along the lines of catalytic action of enzymes.
The proteins of the various tissues of the body are quite different in character
and chemical constitution and are different from the protein of the diet.
In digestion there is a breaking down of the protein in the food into simple
combinations of amino acids or the acids themselves, and subsequently
there is a selection of certain amino acids and resynthesis of characteristic
proteins by the cells of the tissues.

THE PROTEINS 85

It is customary to assign to a compound having an unknown molecular
mass, i.e., relative weight in units of the weight of an atom of hydrogen, a
formula representing the least mass which the substance could have and
preserve its characteristic properties. The simplest formula for oxyhemoglo-
bin, the compound protein of the red blood cells, is C658H1181N207S2FeO210.
This formula is based on the relative proportion that the C, H, N, S,
and O bear to the Fe as determined by analysis. This protein contains
iron, and the least Fe that one molecule can contain is one atom. By addi-
tion of the atomic masses of the total number of atoms of each element, the
least possible molecular mass for oxyhemoglobin is about 15,000. It might
just as well be 30,000 with two atoms of iron in the compound. The follow-
ing formulae have been proposed for ovalbumin and seralbumin:

Ovalbumin, C239H386N58S2O78
Seralbumin, C450H720N116S6O140

the molecular masses being in the neighborhood of 5000 and 6000, re-
spectively.

Besides the amino acids other radicals are present in some proteins. A
carbohydrate moiety is evidently present in certain proteins and phosphoric
acid in others (as in the milk protein casein). Such proteins are to be dis-
tinguished from those which exist as combinations with definite chemical
entities, as hematin, nucleic acid, amino sugars, lecithins, etc.

Properties of Protein. — Many proteins have been prepared in crys-
talline form, especially the reserve proteins from various seeds. Only three
animal proteins have ever as yet been crystallized — seralbumin, lactalbumin,
and ovalbumin.

The majority of the proteins are soluble in water or in dilute solutions
of neutral salts of strong bases with alkalies. The proteins do not form
solutions as do; for instance, the inorganic salts, but are to be regarded as a
suspension of the molecules or molecular aggregates. Such a solution is
known as a colloidal solution, and the proteins are frequently spoken of as
colloids. Colloidal solutions of the heavy metals can be formed by the
interrupted contact of metal electrodes under water. The metallic colloidal
solutions and the protein solutions have many properties in common.

When a true solution of a chemical substance of relatively small molecular
weight is placed within a parchment or animal membrane, and the whole
immersed in water, the substance in solution will diffuse through the pores
of the membrane into the water external to it; similarly, water will pass
through the membrane to the interior. After some time the system will
come into equilibrium. The force which drives the dissolved substance from
the more concentrated to the less concentrated solution is known as osmotic
pressure. The large protein molecules and molecular aggregates cannot
pass through the pores of the membrane, or, in other words, they are not

86 THE CHEMICAL COMPOSITION OF THE BODY

diffusible. Their osmotic pressure is very slight. Some of the simpler
derived proteins, however, are diffusible.

Proteins in aqueous solution rotate polarized light to the left. The
specific rotation of the individual proteins varies. The compound proteins,
hemoglobin and nucleoproteins are dextrorotatory.

Proteins chemically are rather unstable bodies and are easily hydrolyzed,
through heating and standing in alcohol, into modifications which differ only
slightly from the original substances. This change is ordinarily termed
coagulation.

Proteins may be precipitated from their solutions by the addition of the
neutral inorganic salts in high concentration or to saturation. This pre-
cipitation is essentially a physical one, the protein remaining unchanged.
Salting out is, then, a most valuable method for the separation and purifica-
tion of the protein substances. The proteins form insoluble combinations
with the so-called alkaloidal reagents; phosphotungstic acid, phospho-
molybdic acid, picric acid, trichloracetic acid, potassium mercuric iodide,
and tannic acid. The protein also forms insoluble albuminates with the
salts of the heavy metals.

The color reactions for the proteins, which are given in the laboratory
experiments at the end of this chapter are due to a reaction between some
one or more of the constituent radicals of the complex protein molecule and
the chemical reagent or reagents used. Thus certain color tests are due
to the presence of individual amino acids in the protein molecule, and the
intensity of the reaction obtained will vary with the amount of the amino
acids present. The negative results for a certain test will indicate the ab-
sence of the particular amino acid in the molecular complex. The color
tests, then, are important because they throw light on the chemical consti-
tution of the protein under observation.

CLASSIFICATION OF THE PROTEINS.

The following classification is that adopted by the American Physio-
logical Society and the American Society of Biological Chemists:

I. Simple Proteins. — Protein substances which yield only a-amino acids
or other derivatives on hydrolysis.

a. Albumins. — Soluble in pure water; e.g., ovalbumin, seralbumin, and
the vegetable albumins.

b. Globulins.. — Insoluble in pure water, but soluble in neutral solutions
of strong bases with strong acids; e.g., ovoglobulin, edestin, and other vege-
table globulins.

c. Glutelins. — Simple proteins insoluble in neutral solvents, but readily
soluble in very dilute acids and alkalies. These substances occur abundantly
in the seeds of cereals.

CLASSIFICATION OF THE PROTEIXS 87

All of the above are coagulable by heat.

d. Prolamins or Alcohol- soluble Proteins, — Soluble in 70 to 80 per cent,
alcohol; insoluble in water, absolute alcohol, and other neutral solvents; e.g.,
zein from corn, gliadin from wheat, and hordein from barley.

e. Albuminoids. — Simple proteins characterized by a pronounced in-
solubility in all neutral solvents. These form the principal organic con-
stituents of the connective tissues of animals including their external covering
and its appendages. Examples: elastin, collagen, and keratin.

The above sub-classes are characterized by physical rather than by
chemical differences. When the protein, for instance, is termed a globulin
it means that it is a typical simple protein with certain characteristic solu-
bilities. Proteins intermediate in character between albumins and globulins
are met with, and the use of these terms as a hard-and-fast classification
has led to considerable confusion.

/. Histones. On hydrolysis these yield a large number of amino acids,
among which the basic ones predominate. The histones stand chemically
between the typical, simple proteins and the following group of protamins.
Examples are: globin, thymus histone, scombrone.

g. Protamines. — Simpler polypeptids than the proteins included in the
preceding groups. They yield comparatively few amino acids, among which
the basic ones predominate. They are the simplest natural proteins.
Examples are: salmin, sturine, clupeine, and scombrine.

II. Conjugated Proteins. — Substances which contain the protein mole-
cule united to some other molecule or molecules otherwise than as a salt.

a. Nudeoproteins. — Compounds of one or more protein molecules with
nucleic acid; e.g., nucleohistone.

b. Glycoproteins. — Compounds of the protein molecule with a substance
or substances containing a carbohydrate group other than a nucleic acid;
e.g., mucins and mucoids.

c. Phospho proteins. — Compounds of the protein molecule writh phos-
phorous containing substances other than a nucleic acid or lecithin; e.g.,
casein, ovovitellin.

d. Hemoglobins. — Compounds of a protein molecule with hematin or
some similar substance. These include the respiratory pigments; e.g.,
hemoglobin and hemocyanin.

e. Lecithoproteins. — Compounds of the protein molecule with the lipoid
lecithin; e.g., lecithans, phosphatides.

III. Derived Proteins. Class i. Primary Protein Derivatives. —
Derivatives of the protein molecule apparently formed by hydrolytic changes
which involve only slight alteration of the protein molecule.

/. Proteans. — Insoluble products which apparently result from the in-
cipient action of water, from dilute acids or enzymes; e.g., myosan, edestan.
g. Metaproteins. — Products of the further action of acids and alkalies

88 THE CHEMICAL COMPOSITION OF THE BODY

whereby the molecule is so far altered as to form products soluble in very
weak acids and alkalies, or insoluble in neutral solutions; e.g., acid meta-
protein, acid albuminate, alkali metaprotein or alkali albuminate.

h. Coagulation Proteins. — Insoluble products resulting from i, the action
of heat on protein in solution or, 2, the action of alcohol on the protein.

Class 2. Secondary Protein Derivatives. — Products of more extensive
hydrolytic cleavage of the protein molecule than that in the preceding class.

i. Proteases. — Soluble in water, non-coagulable by heat, and precipitated
by saturating their solutions with ammonium or zinc sulphate.

/. Peptones. — Soluble in water, non-coagulable by heat, and not pre-
cipitated by saturating their solutions with ammonium sulphate.

k. Peptides. — Definitely characterized combinations of two or more
amino acids, the carboxyl group of one being united with the amino group
of the other with the elimination of a molecule of water.

CHARACTERISTICS OF THE VARIOUS CLASSES OF PROTEINS.

Albumins. — Albumins constitute the first class of simple proteins.
They may be defined as simple proteins which are coagulable by heat and
are soluble in pure (salt-free) water. As a rule, they are not precipitated on
saturating their solutions with sodium chloride or magnesium sulphate,,
unless the solution be then acidified with dilute acid. They do not coagu-
late out on heating their solution unless a trace of a salt is present. Some
albumins have been prepared in crystalline form; e.g. ovalbumin, serum-
albumin, and lactalbumin. Crystallization is obtained on adding ammonium
sulphate to the protein solution until slight turbidity results, then clearing
the solution by adding a little water and acidifying slightly with acetic acid.
The albumins, as a rule, are precipitated on saturating with neutral ammo-
nium sulphate. Zinc sulphate may be employed when it is desired not to
introduce ammonium salts into the precipitation. The proteins are pre-
cipitated and subsequently coagulated by the addition of an excess of alco-
hol. They remain in solution on dialysis.

On heating a solution of an albumin (or a globulin) the turbidity and
flocking out of the coagulun occur at a temperature which is more or less
characteristic for the individual protein. However, the coagulation tem-
perature can be varied according to the concentration of the protein solu-
tion, the presence of inorganic salts, and by the reaction of the solution. The
coagulation temperatures, then, cannot be given as definite characters for
individual proteins unless the conditions under which the figures were ob-
tained are comparable.

The albumins differ among themselves in the cleavage products they
yield on hydrolysis, in their elementary composition, and in the specific
rotation and coagulation temperatures. The serum albumin and lact-

ALBUMINOIDS 89

albumin are quite closely related chemically, though differing in their specific
rotation of polarized light. The albumins contain, as a rule, more sulphur
than do the other classes of proteins.

Globulins. — The globulins are simple proteins which are insoluble in
pure (salt-free) water, but which are soluble in neutral solutions of salts of
strong bases with strong acids. Most globulins are precipitated from
their solutions on slight acidification and on saturation with sodium chloride
and magnesium sulphate. They are precipitated also from other solutions
on adding equal volume of saturated ammonium sulphate solution; this
precipitation is commonly termed " precipitation at half saturation ammon-
ium sulphate." Since they are insoluble in pure water, dilution of the
weak salt solution containing protein causes precipitation. The globulins
are especially predominant in the vegetable kingdom. They occur in rela-
tively large amounts as the reserve protein in seeds of various sorts. There
are, however, no essential differences as a class between the globulins of
animal and of vegetable origin.

The globulins are precipitated from weak salt solutions on dialysis in
pure water. The inorganic salts diffuse through parchment, and with the
reduction in salt content the globulins are precipitated. Many of the
vegetable globulins can be obtained in crystalline form by precipitating
them in this way.

As a class the globulins are relatively less stable than the albumins.
They are converted over into proteans on successive reprecipitation or
simply by standing under water.

Albuminoids. — The albuminoids yield similar amino acids on hydrol-
ysis to those obtained from the simple proteins. They possess essentially
the same general chemical structure. They differ from all other proteins in
that they are insoluble in neutral solvents. The classification, then, is based
purely on this property, though they are characterized by their occurrence as
the principal organic constituents in the structure of the supporting tissues
of the body and of the skin and its appendages. The individual albumin-
oids differ from each other fundamentally in certain chemical character-
istics. The albuminoids also are differentiated along with the morphologi-
cal variations of the connected tissues in which they occur. For example,
the keratins occur in the skin and its appendages. Collagen is the principal
albuminoid of white fibrous tissue, though found also in cartilage and bone.
Elastin characterizes the yellow elastin tissue, as, for instance, the nuchal
tendon, the elastic tendon so well developed in the neck of the ox.

Keratins. — The epidermis of the skin, the nails, hair and horn, feathers,
tortoise shell, silk, and the supporting neuroglia of nervous tissue may be
considered to be keratins in relatively pure form. The keratins take the
form of the tissue from which they are prepared. On heating they are
decomposed with the odor of burnt horn. They are insoluble in water,

QO THE CHEMICAL COMPOSITION OF THE BODY

alcohol, and ether, and in the ordinary protein solvents. They are not
acted upon by gastric or pancreatic juices. On heating to 150 to 200° C.
in water the protein is hydrolyzed and dissolves. The keratins are also
soluble in the caustic alkalies, especially on heating. Keratins from any
source may be prepared in pure form by treating with artificial gastric juice,
artificial pancreatic juice, boiling alcohol, and boiling ether, from twenty-
four to forty-eight hours being devoted to each process. Several keratins,
so far as their chemical structure is concerned, exist.

Collagen. — Collagen can be most satisfactorily prepared from the tendo
achillis of the ox. It forms the principal organic constituent of this and
other white fibrous tissues, as shown by the analysis given in the following
table:

CHEMICAL COMPOSITION OF THE WHITE FIBROUS TISSUE: Tendo Achillis

(BERG AND GIES).

Water 62.87 per cent.

Solids 37 .13 per cent.

Inorganic matter 0.47

Organic matter 36.66

Fatty substance (ether-solu-
ble) i . 04

Coagulable protein 0.22

Mucoid i .28

Elastin 1-63

Collagen 3 1 • 59

Extractives, etc o . 90

The collagen from various sources in common with the keratin is not
identical in composition. It differs from the keratin in containing less
sulphur. It does not give the reaction for tryptophane and contains but
little tyrosin. It is dissolved by pepsin and hydrochloric acid, but not by
pancreatic juice.

The general characteristic of collagen is that it is hydrolyzed into gelatin
by boiling with water or dilute acid. Gies has shown that ammonia is
liberated by this procedure. Gelatin is soluble in hot wrater, but its solutions
form a jell when cooled. Inasmuch as tyrosin and tryptophane are not
present in the gelatin molecule, this albuminoid is not a satisfactory substi-
tute for the protein constituents in the normal diet.

Elastin. — Elastin is the principal solid constituent of yellow elastic
tissue; e.g., the ligamentum nuchce. It gives the ordinary protein color re-
actions. It contains, however, a relatively small amount of sulphur. Elas-
tin is dissolved by pepsin hydrochloric acid and by pancreatic juice, and
unlike collagen it is not converted into gelatin on prolonged boiling with
water or dilute acids.

PROTAMINES 91

COMPOSITION OF YELLOW ELASTIC TISSUE: Ligamentum nuchce (BERG AND

GIES).

Water 57-57 Per cent.

Solids 42 .43 per cent.

Inorganic matter Q-47

Organic matter 41 .96

Fatty substance (ether-solu-
ble) 1. 12

Coagulable protein 0.62

Mucoid o . 53

Elastin 31 .67

Collagen 7 .23

Extractives, etc o . 80

Histones. — The histories are proteins which stand in their chemical
structure between the true proteins and the protomines. On hydrolysis
they yield a large number of amino acids, among which the basic ones pre-
dominate. The basicity, however, is only slight. They are precipitated
by dilute ammonia and this precipitate is soluble in an excess of ammonia
in the absence of ammonium salts. They are precipitated by nitric acid,
the precipitate dissolving on heating and again appearing on cooling. They
give precipitates with solutions of other proteins. On heating, the histones
yield a coagulum which is easily soluble in very dilute acids.

The histones are found in the nuclei of the red blood cells of birds, the
unripe testis in salmon and mackerel and in the ripe spermatozoon of the
sea-urchin. The thymus contains histone. The liver, kidneys, ox pan-
creas, and testis of mammals contain no histone-like substances. The
globin of the compound protein hemoglobin is to be regarded as a histone.

Protamines. — The protamines are basic proteins which are combined
with nucleic acid and form the chief constituent of the spermatozoa of the
salmon and other fish. They are relatively simple proteins yielding com-
paratively few amino acids on hydrolysis, among which the basic ones
predominate. From elementary analyses the following formula has been
suggested for the platinum salt of salmine. C30H57N17O6.4HC1.2PtCl4.
As seen from the formula, the protamines are extremely rich in nitrogen
which comprises from 25 to 32 per cent, of their weight. The protamines
dissolve in water and give a faintly alkaline reaction. They are precipitated
in acid solution by platinic chloride. The protamines, after the addition of
ammonia, precipitate true proteins, proteoses, and nucleic acid. On hy-
drolysis all protamines yield relatively large amounts of argenine and varying
amounts of histone, lysin, proline, alanine, valine, leucin, tyrosin, and ap-
parently also tryptophane. Protamines also do not contain sulphur or a
carbohydrate moiety. They are not changed by digestion with pepsin
hydrochloric acid.

92 THE CHEMICAL COMPOSITION OF THE BODY

Conjugated proteins consist of a protein molecule united with some
other molecule or molecules otherwise than as a salt. There are nucleo-
proteins, glycoproteins, phosphoproteins, hemoglobins or chromoproteins and
lecithoproteins — five classes of conjugated proteins.

Nucleoproteins. — Nucleoproteins contain phosphorus and in most
instances iron. They are combinations of simple proteins with a substance
known as nucleic acid. On boiling with strong acids they undergo hydroly-
tic cleavage, yielding the ordinary protein cleavage products from the pro-
tein in the combination, and purine and pyrimidine bases, carbohydrates
and phosphoric acid from the nucleic acid moiety. Nucleoproteins are
differentiated from the phosphoproteins in that the latter do not yield purine
and pyrimidine bases on hydrolytic cleavage. Nucleoproteins are the es-
sential organic constituents of cell nuclei. They go into solution when the
tissues are extracted with cold water or dilute salt solution. They are pre-
cipitated from these extracts by careful acidification and dissolved if an
excess of acid is added. The solutions of nucleoproteins coagulate on
heating. They give the color reactions of proteins.

By boiling nucleoproteins with water or very dilute acetic acid, some
of the protein is split off. There result substances which are precipitated
by very dilute acids. These bodies are known as /?- nucleoproteins and
have a smaller carbon and higher phosphorus content than the original nu-
cleoprotein. On digestion of the original nucleoprotein or of the /?-nucleo-
protein with pepsin hydrochloric acid, a precipitate of nuclein is obtained.
On further digestion with pepsin hydrochloric acid, or with trypsin, or on
cleavage with acids and alkalies, there is a further splitting away of the
protein, and substances are formed known as nucleic acids. The structure
and cleavage of the nucleoprotein is indicated in the following diagram.

Nucleoprotein

on boiling with water or on digestion
with pepsin hydrochloric acid yields

Nuclein Protein

On long boiling with water, i
per cent, hydrochloric acid, or
dilute alkalies gives

i i

Nucleic acid Protein

Nucleic acids are not merely known as cleavage products of nucleopro-
tein, but occur preformed in the cell nuclei. A special group of nucleic
acids are bound with protamines to form the principal constituent of the
spermatozoa.

PYRIMIDINES 93

Nucleic acids are white amorphous substances containing 9 to 10 per cent,
phosphorus. According to Schmeideberg, the composition corresponds to
C40H56NUO162P2O5. Nucleic acids give none of the protein reactions. They
are precipitated, however, by tannic acid, picric acid, and phosphotungstic
acid. They are, therefore, basic besides being acids. Nucleic acids combine
with proteins in water and in dilute hydrochloric acid to form difficultly
soluble combinations which in some measure have the character of acids and
form soluble salts with alkalies. The alkali salt of a combination of nucleic
acid and a histone is the nucleohistone of the thymus gland.

On boiling of nucleic acids with strong acids the purine bases are split
off, leaving a substance known as nucleotinic acid. On boiling with strong
sulphuric acid this is split into the pyrimidine bases, carbohydrate (pen-
toses) and phosphoric acid.

Nucleic acid
treated with strong acids

Nucleotinic acid Purine bases

on boiling with 30 per cent, sulphuric acid

Pyrimidines, pentoses, and phosphoric acid

The structure of nucleic acid is then extremely complex. For the tritico-
nucleic acid of the wheat embryo, T. B. Osborne has suggested the following
formula where X is an unresolved residue.

HO pentose X OH guanine (purine base)

\/ I ' I /

P -O - P - O -P-O- P— pentose

/\ l\ l\ \

HO pentose OH uracil OH uracil OH adenine (purine base)

(pyrimidine
base)

Pyrimidines. — The mother substance of the pyrimidine bases in the nucleic
acid is pyrimidine. The skeleton structure of the pyrimidine is a ring con-
sisting of the elements of a molecule of urea and closed with three carbon atoms.
The elements of the ring are numbered to determine the position of substituted
radicals in the compounds derived from pyrimidine.

'N-C6 N = CH

2C C5 HC CH

3N-C* N-CH

Pyrimidine ring. Pyrimidine.

94

THE CHEMICAL COMPOSITION OF THE BODY

Three derivatives of pyrimidine, cytosin, uracil, and thy mine, were obtained

These derivatives have all

by Kossel and his co-workers from nucleic acids,
been prepared synthetically.

N=C-NH2 HN-C=0

0=C CH 0=C CH

HN-CH HN-CH

Cytosine. Uracil.

(2-oxy- 6-amino pyrimidine.) (2-6-dioxypyrimidine.)

HN-C=0

o-A L

CH3

HN-CH

Thymine.

(2-6-dioxy- 5-methyl-
pyrimidine.)

Purines. — To the purines belong a number of extremely important animal
and plant substances, including adenine, guanine, hypoxanthine, xanthine,
and uric acid, and the methyl purines caffeine, theobromine, and theophylline.

The mother substance of the purines is known as purine, which has the
following structure :

'N-C6

2C C5-N\

I ! >c8

3N-C4-N9/
Purine ring.

N = CH
HC C-NH

iCH

N-C-N
Purine.

Adenine and guanine may be converted into hypoxanthine and xanthine,
respectively, when added to extracts of tissues, such as the liver and the thymus,
spleen and pancreatic glands. The "deamidization" is brought about by
specific enzymes or non-living ferments which have been termed adenase and
guanase. On slight oxidation, hypoxanthine is converted into xanthine, and
the latter into uric acid. This change can also be brought about in the body
by oxidizing enzymes. The relation of the purine bases to uric acid is indicated
in the following scheme:

>

H(

IN

(6-
i=(

: (
r-c

Adenine.
amino purine.)

:-NH2

+ H20

H

(6
HP

H(

j

;y/>0;
-oxy
^-(

: (

1-c

xanthine.
purine.)

:=o
:-NH

)CH

:-N

:-NH

-NH3

>CH

:-N

on oxi-

dation

HN-C=O

+ H20

H2N-C C-NH ;— 0=C C-NH

-NH,

>CH >CH

N-C-N HN-C-N

Guanine. Xanthine.

(2-amino 6-oxypurine.) (2-6di-oxypurine.)

HN-C=O HN-C=O

on oxidation

> 0=C C-NH

-

HN-C-NH

Uric acid.
( 2-6-8-trioxypurine.)

METAPROTEINS 95

Glycoproteins. — The glycoproteins are to be considered as compounds
of protein and a carbohydrate complex. The carbohydrate group can be
split from the protein by boiling with mineral acids or by the action of alka-
lies. The group of glycoproteins includes a number of proteins, of which the
mucines and mucoids are the most important.

Mucines are very widely distributed. They give the mucilaginous
character to many secretions and are formed and discharged through the
respiratory, digestive, and other tracts, partly by mucous cells and in part by
the mucous glands, especially by the submaxillary and sublingual sali-
vary glands, and in the bile passages. On hydrolysis the mucines are split,
the carbohydrate moiety yielding glucose amine or galactose amine.

Mucoids occur in the connecting tissues along with the albuminoids.
They are found especially in the tendon, bone, and cartilage. They are
combinations of protein and a carbohydrate containing ethereal sulphuric
acid known as chondroitin sulphuric acid. On cleavage, besides the products
formed from the protein, they yield sulphates and a reducing substance.

Phosphoproteins. — The phosphoproteins, sometimes called nucleo-
albumins, are compounds of the protein molecule with some as yet unde-
fined phosphorus-containing substance other than a nucleic acid or lecithin.
While the phosphorus content of these substances is quite similar to that
of the nucleoproteins, they do not yield any purine or pyrimidine bases on
hydrolytic cleavage. Two of the best known phosphoproteins are the
casein of milk, and vitellin of the egg yolk. The phosphorus is apparently
present as a phosphoric acid ester.

Hemoglobins. — These are compounds of the simple protein histone,
with an iron- or copper-containing pigment substance. The hemoglobins
are more fully discussed in the chapter on the Blood.

Lecithoproteins. — These are combinations of proteins and a fat-like
substance, lecithin. Lecithin is a compound of fatty acids, glycerin, phos-
phoric acid, and an ammonium-like organic base, choline. The combination
of lecithin and protein is apparently a loose one: the lecithin ordinarily can
be split off by boiling alcohol. The lecithoproteins include substances
commonly termed lecithans and phosphatids.

The derived proteins are formed as intermediate products in the hydro-
lytic cleavage of the original protein molecule. The primary protein de-
rivatives are (l apparently formed through hydrolytic changes which involve
only slight alteration of the protein molecule."

Metaproteins. — These are formed from the simple proteins by the
action of weak acids and alkalies. This class comprises what have com-
monly been termed acid and alkali albuminates. The metaproteins are
soluble in acid or alkaline solution, but are insoluble in neutral solutions. In
the formation of alkali metaproteins, the sulphur in organic combination

96 THE CHEMICAL COMPOSITION OF THE BODY

is split off. Thus the alkali metaprotein differs from the acid metaprotein
in that the former contains little or no sulphur. It is impossible, then, to
transform an alkali metaprotein into an acid metaprotein, though the acid
metaprotein can be changed into the other modification. Acid metaproteins
are the first products formed in the pepsin hydrochloric acid digestion of
proteins.

Coagulated Proteins. — Unaltered typical simple proteins in solution are
altered when heated or by long standing under alcohol. They are transformed
into a coagulated modification no longer soluble in water or dilute salt solu-
tions. A similar change occurs when solutions of the proteins are con-
tinuously shaken or by the action of enzymes, as in the formation of fibrin
from fibrinogen in the clotting of the blood. On treating coagulated proteins
with acids or alkalies they are converted into the respective metaproteins.

Secondary Protein Derivatives. — Secondary protein derivatives are
intermediary cleavage products which result from a more profound change
than occurs in the formation of the primary derived protein.

Proteases or albumoses are intermediate products in the digestion of
proteins by proteolytic enzymes or in the cleavage with acids. Peptones
are yet more simple products than the proteoses and are to be regarded
as relatively simple polypeptides which still retain some of the protein
characteristics. A number of proteoses and peptones have been described.
However, there is no sharp dividing line between the more simple proteoses
and more complex peptones, or between the simple peptones and the peptides.
(The term peptide as at present understood designates only those combina-
tions of amino acids possessing a known definite structure.) The peptones
differ from the proteoses in being more diffusible, being non-precipitable
on saturation with ammonium sulphate, and by their failure to give certain
protein reactions. As a class, proteoses and peptones are relatively very
soluble and are non-coagulable by heat.

Melanins are the pigmentary substances found in the hair, feathers, skin,
the choroid coat of the eye, and in some tumors. Products similar to the
naturally occurring melanins are obtained on hydrolizing nearly all proteins
with acids. The melanins are sulphur- containing acid-like substances, and
seem to be combinations of amino-sugars (glucosamine) with certain amino-
acids, especially tyrosine, tryptophane, and lysine. Iron is found in some of
the melanins.

THE FATS.

Fats occur very widely distributed in the plant and animal kingdom, and
constitute one of the four classes of food stuffs. Fats are esters or ethereal
salts consisting of an organic radical (glycerol) united with the residue of an
organic acid. Ethyl alcohol may be combined as an ester with acetic acid.

C2H5OH + CH3COOH = C2H5OOCCH3+ H2O

Alcohol Acetic acid Ethyl acetate.

THE FATS 97

Similarly the triatomic alcohol glycerol may be combined with the
higher fatty acids to form the true fats.

CH2OH CH2-OOCC15H31

CHOH + 3C15H31COOH = CH- OOCC15H31 + 3H2O

CH2OH CH2- OOCCi5H31

Glycerol Palmitic acid Tri-palmitin

The animal fats are for the most part mixtures of tri-palmitin, tri-stearin,
and tri-olein, the last two being esters of glycerol with stearic acid, C17H35
COOH, and the unsaturated oleic acid, C17H33 COOH. Human fat con-
sists of a mixture of which tri-palmitin and tri-stearin comprise three-fourths
of the whole. The fat in milk and butter is in part tri-butyrin, the ester
of glycerol with butyric acid,C2H5COOH. The percentage of any in-
dividual fat in animal tissue depends on, and is characteristic of, the particular
species of animal from which the fat was obtained. Ordinary mutton fat
contains more tri-stearin and less tri-olein than pork fat, and the mutton
fat is stiffer because the melting-point of the tri-stearin is the highest of
the fats.

The pure fats are odorless, tasteless, and generally colorless. They
are insoluble in water and cold alcohol, but are dissolved by acetone, hot
alcohol, benzol, chloroform, and ether. When shaken with water, protein
solutions, soap, or gum arabic, the fats assume a finely divided condition
known as an emulsion. The suspension in water is only temporary, while
the emulsions are permanent.

The fats are hydrolyzed or saponified by superheated steam into glycerol
and the fatty acids, the reaction being the reverse of that indicated in the
equation above. On boiling with caustic alkalies, they are similarly saponi-
fied; the fatty acids are then combined with the bases to form salts or soaps.

Lecithins are tri-glycerides in which the H atom of two instead of three
groups of the glycerol is replaced by a fatty acid radical; for the H of the
third hydroxyl (OH) group there is substituted an ester-like combination
of phosphoric acid with a nitrogen-containing organic base, choline.

CH2OOCC17H35

CHOOCC17H35 C2H4OH

I / '

CH2O - O P - O C2H4 N=(CH3)3

\ \

(CH3)3=N OH

OH

HO

Lecithin Choline

98 THE CHEMICAL COMPOSITION OF THE BODY

On saponification the di-stearyl lecithin molecule above combines with
three molecules of water and is split into two molecules of stearic acid, one
of phosphoric acid and one of choline.

The lecithins are soluble in alcohol, benzene, chloroform, and ether.
They are precipitated from chloroform or alcohol-ether solution by
acetone.

The lecithins are found in nearly all animal and vegetable tissues, espe-
cially in nervous tissues. They are essential constituents of the cell.

Cholesterol is a complex alcohol with the elementary formula C27H45OH.
Accordingly, it cannot be saponified. It crystallizes in the form of thin,
colorless, transparent plates usually notched in one corner. It exists in the
tissues in part in the form of esters with the complex fatty acids. Choles-
terol is an essential cell constitutent; it is present in relatively large
amounts in nervous tissue. It occurs also in wool fat, eggs, milk, and
blood plasma.

Cholesterol and the lecithins are often termed lipoids or fat-like
substances.

CARBOHYDRATES.

The carbohydrates contain carbon and hydrogen and oxygen in the
proportion to form water. Other substances, such as acetic acid, CH3-
COOH, lactic acid, CH3CHOHCOOH, and inosit, (CHOH)6, which con-
tain hydrogen and oxygen in the proportion to form water, are not carbohy-
drates. Certain true carbohydrates also do not fulfill this condition. Chem-
ically, the carbohydrates are aldehyde or ketone derivatives of complex
alcohols; i.e., they have the structure

1 <i R-CHOH-CHO or R-CO-CH2OH

Aldose Ketose

Accordingly, the carbohydrates are termed aldoses or ketoses. They
are commonly classified by the number of carbon atoms in the molecule;
e.g., pentoses are those containing five carbon atoms, and hexoses have six
carbons. Each member of the carbohydrate class, with the exception of
the pentoses, may be regarded as containing the saccharide group, C6H10O5.
The monosaccharides are then C6H10O5+H2O; the di-saccharides contain
two saccharide groups with water, (C6H10O5)2 +H2O, while the poly-
saccharides contain this group taken a large number of times, (C6H10O5)n.
In general, the solubility of the saccharides varies inversely with the
number of saccharide groups present: the mono-saccharides, as a class,
being the most soluble and the poly-saccharides being the least so. On
boiling in the autoclave or with mineral acids, and by the action of amylo-

CARBOHYDRATES 99

lytic and inverting enzymes, the poly-saccharides are, as a rule, hy-
drolyzed into the simple carbohydrates. The reaction may be indicated

(C6H1005)n + nH20 . : nC6H1206
Poly-saccharide Water Mono-saccharide

Simple poly-saccharides, and di-saccharides are formed as intermediate
products in the cleavage and in turn these are further hydrolyzed.

C12H220U + H20 , 2C6H1206

Di-saccharide Water Mono-saccharide

The color reactions with iodine, fermentation with yeast and bacteria,
the formation of characteristic crystalline osazones with phenylhydrazine
and the reducing of alkaline solutions of the oxides of metals like copper,
bismuth, mercury, and ammoniacal silver solutions, are the most widely
used reactions for testing and differentiating the carbohydrates. The
reduction of alkaline solutions of the metallic oxides is due to the easily
oxidized aldehyde and ketone structure of the sugar.

The more common carbohydrates may be listed as follo\vs:

1. Mono-saccharides.

Hexoses, C6H12O0— dextrose, levulose, galactose.

Pentoses, C5H10O5 — arabinose, xylose, rhamnose (methylpentose,

C6H1205). '

2. Di-saccharides, C12H22On,

Maltose, saccharose (cane-sugar), lactose.

3. Poly-saccharides, (C6H10O5)n.

Dextrin group — dextrins.

Starch group — starch, inulin, lichenin, glycogen.

Cellulose group — cellulose.

Dextrose (glucose, grape-sugar) is an aldose found in honey and
in many fruit juices where it is usually associated with levulose. It is
present in the blood in small amounts, o.i to 0.15 per cent., in normal
urine in minute traces, and in diabetic urine. It is not as sweet as cane-
sugar. Glucose is produced on boiling starch with dilute acids. It is very
soluble in water and is slightly soluble in alcohol. It crystallizes from
water in leaves or plates and from alcohol in anhydrous needles. Dextrose
rotates the plane of polarized light to the right — its specific rotation is given
by the expression [a]d = +52.5°. It forms a characteristic glucosazone
when boiled with phenylhydrazine in the presence of acetic acid; the osazone
crystallizes from the hot solution. Glucose reduces metallic oxides in

100 THE CHEMICAL COMPOSITION OF THE BODY

alkaline solution. It undergoes alcoholic fermentation with yeast and acid
fermentation with certain bacteria.

CH2OH CH2OH

I I

CHOH CHOH

I I

CHOH CHOH

I !

CHOH CHOH

I I

CHOH CO

!

CHO CH2OH

Dextrose. Levulose.

Levulose (fructose) is a ketose and is found associated with dextrose
in many fruits, the mixture probably being produced by the hydrolysis of, or
preceding the synthesis of, cane-sugar. It may be prepared by the hydrolysis
of inulin and, along with dextrose, by the inversion of cane-sugar on boiling
with dilute mineral acids or through the action of specific enzymes. It is
levorotatory, [a]d = —92°. Levulose may be crystallized with difficulty in
needles. It has a sweet taste. It reduces alkaline solutions of the
metallic oxides, but not so much as dextrose, and yields an osazone identical
with glucosazone. It undergoes fermentation, but less readily than dextrose.

Galactose is obtained with dextrose from milk-sugar or lactose on
boiling with dilute mineral acids. It is less soluble in water than levulose
or glucose. It reduces metallic oxide in alkaline solution, forms a charac-
teristic osazone which melts at 193-4° C. and it undergoes slow fermentation
by yeast. It is dextrorotatory.

It is also obtained on hydrolysis of cerebrin, a glucoside occurring in
nervous tissue.

Maltose (malt-sugar) is produced by the action of amylolytic enzymes
on starch and glycogen. It crystallizes in small needles, is strongly dextro-
rotatory, [a]d = +140.6°, reduces alkaline copper solutions much feebler
than dextrose, and does not reduce bismuth oxide. It forms a characteris-
tically crystalline osazone, melting at 206° C. It is readily soluble in water
and only slightly soluble in alcohol. Maltose is not so sweet as cane-sugar.
It does not undergo alcoholic fermentation with yeast unless first split into
dextrose. On boiling with dilute mineral acids or through the action of
inverting enzymes, it is hydrolyzed into dextrose.

Saccharose (cane-sugar) is obtained from many plants, such as the
sugar beet and sugar cane, and from the sap of certain trees, as the sugar
maple. It crystallizes in prisms, is soluble in water, and only very slightly
soluble in alcohol. Cane-sugar is not directly fermentable by yeast. It is
levorotatory. Saccharose has no reducing action on alkaline copper solution

CARBOHYDRATES IOI

— the dextrose and levulose yielded on inversion probably being united
together by the aldehyde and ketone radicals, respectively. Similarly, it does
not form an osazone. In strong solutions, saccharose acts as a food pre-
servative against bacterial or other decomposition through organic agencies.
On boiling with dilute mineral acids or through. the action of inverting en-
zymes, one molecule of saccharose yields one molecule of dextrose and one
molecule of levulose,.

Lactose (milk-sugar) is present as the chief carbohydrate of milk. It
may be separated from the whey — the product remaining after skimming
milk and precipitating the proteins therein. It can be prepared in large
hard crystals. It is much less soluble in water than cane-sugar, and has but
a slightly sweet taste. Lactose is strongly dextrorotatory, [a]d = +52.5°.
It reduces alkaline copper solution and forms a characteristic osazone. It
is not fermented by ordinary yeast; certain bacteria easily convert it into
lactic and other simple organic acids. The inverted milk-sugar undergoes
alcoholic fermentation readily, and kumiss and kephir, made from mare's
and cow's milk, respectively, are prepared in this way. On hydrolyzing by
boiling with mineral acids or through the action of inverting enzymes, the
lactose is split into dextrose and galactose.

Dextrins are a series of intermediate poly-saccharides between the di-
saccharides and the starches. They are non-crystalline, are soluble in
water, and are precipitated on the addition of alcohol in excess. They are
dextrorotatory and are not fermented by yeast. Their power to reduce
alkaline copper solution has been questioned, but they yield osazones which
are relatively soluble. They have a slightly sweet taste. The more com-
plex dextrins give a red reaction with iodine.

Starch is found in various parts of plants, especially in the tubers and
seeds. It is a form of storage carbohydrate, and serves as a source of ma-
terial for the development of the young plant. Starch is obtained commer-
cially from potatoes, rice, corn, and wheat. It constitutes the greater pro-
portion of our food.

Starch as obtained is a soft white powder which on microscopic examina-
tion is found to consist of small granules. These are often characteristic in
shape and size according to the origin of the material. The granules appear
to be built up of concentric layers. They are covered with a sheath of
starch cellulose. This sheath is ruptured by boiling the aqueous suspension
of starch granules and an opalescent solution or starch paste is obtained.
On standing in dilute solution, the opalescent material settles to the bottom,
but the clear fluid above still gives the blue reaction writh iodine. This
color is characteristic for starch; it disappears on heating, but returns when
the liquid cools. Starch will not diffuse through a semi-permeable mem-
brane. On boiling with dilute mineral acids starch is hydrolyzed to dex-
trose. The dextrins and maltose are formed as intermediate products.

102

THE CHEMICAL COMPOSITION OF THE BODY

With amylolytic enzymes, the change practically only goes as far as the
maltose stage.

Glycogen (animal starch) is the reserve form of carbohydrates in
animals. It is synthesized from dextrose and can again be hydrolyzed to
dextrose for transportation or for oxidation to yield energy to the tissues.
The following table shows the per cent, and distribution of glycogen in the
various tissues of the dog (Schondorff) :

Organ

Per cent, glycogen

Per cent, of total
glycogen.

Blood

o . 0041

o . 01 ^

Liver

7.297

37-97

Muscles

0-7599

44-23

Bones

0.2736

9-25

Viscera

o . 2024

3.81

Skin

0.0859

4-49

Heart ,

0.231

0.17

Brain

o . 1984

0.09

It occurs in relatively large amounts in some invertebrates, especially
in moluscs and in intestinal worms. The adductor muscle of the scallop
(Pecten irradians) is very rich in this substance.

Glycogen resembles starch in forming opalescent solutions. It may be
prepared from the liver or muscle of a freshly killed animal by boiling the
tissue to coagulate the proteins, grinding with sand, boiling with water
slightly acidified with acetic acid and precipitating the filtrate with an excess
of alcohol; dilute or concentrated solutions of caustic alkalies may be used
to extract all the glycogen. Glycogen is a white, tasteless, and amorphous
powder. It gives a maroon color with iodine, and does not reduce alkaline
copper sulphate solution. It is completely precipitated by saturating its
solution with solid ammonium sulphate, by tannic acid, or by ammoniacal
basic lead acetate. On hydrolysis with mineral acids or on digestion with
amylolytic enzymes it yields the same series of products as ordinary starch.

Inulin is the reserve carbohydrate of the Composite, occurring in the
tubers of the artichoke and dahlia and in the roots of the dandelion and bur-
dock. On hydrolysis with acids or the enzyme inulase, it yields levulose.
Inulin is slightly soluble in cold and easily soluble in hot water. It is precipi-
tated from its solution by an excess of alcohol. The starch-digesting enzymes
of the body do not act on inulin.

Lichinin is obtained from the Cetraria Islandica (Iceland moss) . It forms
a difficultly soluble jelly in cold water and an opalescent solution in hot water.
On hydrolysis with dilute acids, it yields dextrines and dextrose. The
ordinary digestive enzymes have no action on lichinin.

INORGANIC SUBSTANCES OF THE BODY 103

Cellulose forms a large portion of the cell wall or the woody structure
of plants. It is extremely insoluble. Chemically, it is more complex than
the common starch molecule. The hydrochloric and hydrofluoric acid
extracted (ash-free) filter-papers and absorbent cotton are examples of prac-
tically pure cellulose.

INORGANIC SUBSTANCES OF THE BODY.

Salt. — The inorganic principles of the human body are numerous.
They are derived, for the most part, directly from food and drink and pass
through the system unaltered. Some radicals are newly formed by oxi-
dation within the body, as, for example, a part of the sulphates and car-
bonates from the sulphur of the proteins and the carbon of protein, fat, and
carbohydrate.

Much of the inorganic saline matter found in the body is a necessary
constituent of its structure, as necessary in its way as protein or any other
organic principle. Another part is important in regulating or modifying
various physical processes, as absorption, solution, and the like. A part
must be reckoned only as matter which is, so to speak, accidentally present,
whether derived from the food or the tissues, and which will, at the first
opportunity, be excreted from the body. The principal salts present in
the body are:

Sodium and Potassium Chlorides. — These salts are present in nearly all
parts of the body. The former seems to be especially necessary, judging
from the instinctive craving for it on the part of animals in whose food it
is deficient, and from the condition which is consequent on its withdrawal.
The quantity of sodium chloride in the blood is greater than that of all its
other saline ingredients taken together, but it is present chiefly in the fluids
of the body. In the tissues, the muscles for example, the quantity of sodium
chloride is less than that of the chloride of potassium, which forms a constant
ingredient of protoplasm.

Calcium Fluoride. — It is present in minute amount in the bones and
teeth, and traces have been found in the blood and some other fluids.

Calcium, Potassium, Sodium, and Magnesium Phosphates. — These phos-
phates are found in nearly every tissue and fluid. In some tissues — the bones
and teeth — the phosphate of calcium exists in very large amount. The phos-
phate of calcium is intimately incorporated with the organic basis or matrix,
but it can be removed by acids without destroying the general shape of the
bone. After the removal of its inorganic salts, a bone is left soft, tough,
and flexible.

Potassium and sodium phosphates, with the carbonates, maintain the
alkalinity of the blood.

Calcium Carbonate. — It occurs in bones and teeth, but in much smaller

IO4 THE CHEMICAL COMPOSITION OF THE BODY

quantity than the phosphate. It is found also in some other parts. The
small concretions of the internal ear (otoliths) are composed of crystalline
calcium carbonate, and form the only example of inorganic crystalline
matter existing as such in the body.

Potassium and Sodium Carbonates and Sulphates. — These are found in
the blood and most of the secretions and tissues.

Silicon. — A very minute quantity of silica exists in the urine and in
the blood. Traces of it have been found also in bones, hair, and some
other parts.

Iron. — The especial place of iron is in hemoglobin, the coloring- matter
of the blood, of which a full account will be given with the chemistry of the
blood. Iron is found, in very small quantities, in the ashes of bones, mus-
cles, and many tissues, and in lymph and chyle, albumin of serum, fibrin,
bile, milk, and other fluids.

Iodine occurs as an iodized protein in the thyroid gland. Biologically,
it is found as a tri-iodotyrosin in sponges and the Gorgonian corals.

Water. — Water forms a large proportion, more than two-thirds, of
the weight of the whole body. Its relative amount in some of the principal
solids and fluids of the body is shown in the following table (from Robin
and Verdeil) :

Quantity of Water in Per Cent.

Teeth 10.0 Bile 88.0

Bones 13.0 Milk 88.7

Cartilage 55.0 Pancreatic juice. ... 90.0

Muscles 75-o Urine 93 . 6

Ligament 76.8 Lymph 96.0

Brain 78.9 Gastric juice 97.5

Blood 79-5 Perspiration 98 . 6

Synovia 80 . 5 Saliva 99-5

In all the fluids and tissues of the body — blood, lymph, muscle, gland,
etc. — water acts the part of a general solvent, and by its means alone circula-
tion of nutrient matter is possible. It is the medium also in which all fluid
and solid aliments are dissolved before absorption, as well as the means by
which all, except gaseous, excretory products are removed. All the various
processes of secretion, transudation, and nutrition depend of necessity on
its presence for their performance.

The greater part, by far, of the water present in the body is taken into
it as such from without, in the food and drink. A small amount, however,
is the result of the chemical union of hydrogen with oxygen in the oxidations
of the body.

The loss of water from the body is intimately connected with excretion

LABORATORY EXPERIMENTS 105

from the lungs, skin, and kidneys, and, to a less extent, from the alimentary
ca.nal. The loss from these various organs may be thus apportioned (quoted
by Dalton from various observers) :

From the alimentary canal (feces) 4 per cent.

From the lungs 20 per cent.

From the skin (perspiration) 30 per cent.

From the kidneys (urine) 46 per cent.

100

LABORATORY EXPERIMENTS ON THE CHEMISTRY OF THE

BODY.

THE PROTEINS.

i. Preparation of Proteins. — The most convenient source of proteins
for laboratory work are blood serum, egg white, or commercial preparations
of the milk protein casein. Protein may also be prepared from various
plant seeds, especially cereals Hempseed contains a globulin, edestin,
which is very easily isolated in the laboratory.

a. Preparation of Edestin. — Grind up some hemp-seed in an ordinary
meat chopper and extract the resulting meal with 5 per cent, salt solution,
warming to 60°. The solution should not be heated above 65° because
the protein will be coagulated. Filter while hot. On cooling slowly the
edestin will crystallize out. Examine some of the precipitate with a micro-
scope and sketch the crystals. The edestin is soluble in 10 per cent, salt
solution without warming, and solutions for laboratory use can be prepared
in this way.

b. Preparation of Egg Albumin. — The yolk should be separated from
the white of fresh eggs and the reticulum in the egg white broken up with
a wire egg-beater. Egg white can then be diluted as desired and the pre-
cipitate globulin filtered off. Crystals of ovalbumin can be prepared as
follows :

The egg white, beaten as directed, is strained through gauze and an
equal volume of saturated ammonium sulphate solution is added. After
twenty-four hours the globulin precipitate is filtered off and concentrated
ammonium sulphate solution added until the mixture becomes turbid.
Then distilled water is added very carefully until turbidity has disappeared.
The solution is then acidified with acetic acid, which has been saturated
with ammonium sulphate, until a precipitate is obtained. The precipitate
is at first amorphous, and on standing becomes crystalline. Examine the
crystals under the microscope and sketch them.

c. Other Protein Crystals. — Crystals of hemoglobin may be demon-
strated by adding a drop of ether to diluted dog blood on the microscope

106 THE CHEMICAL COMPOSITION OF THE BODY

slide and allowing the mixture to dry around the edge. Hemoglobin crys
tals may be observed under the microscope to have formed where the solu-
tion has concentrated and dried.

Crystals of seralbumin and of lactalbumin can be obtained in essen-
tially the same manner already described for ovalbumin.

2. Elementary Composition of the Proteins. — a. Nitrogen. — Make
an intimate mixture of some dry protein, preferably a casein preparation,
with sodalime and place it in a dry test-tube. Warm gently over a Bunsen
flame. Hold a piece of moistened red litmus-paper over the mouth of
the test-tube. The ammonia split off from the protein will color the
litmus blue.

Warm together carefully in a dry test-tube a few particles of dry protein
and a small cube of metallic sodium. (Do not place the tube in the flame.)
When the fusion is complete and the tube is cooled somewhat, plunge the
end into a small amount of water in a casserole. The glass of the test-tube
will probably break. When the fused mass has dissolved, filter, and to the
nitrate add a few drops of ferric chloride and ferrous sulphate solution.
On acidifying writh hydrochloric acid a precipitate of Prussian blue is ob-
tained. Sodium ferricyanide is formed in the reaction and in consequence
gives a Prussian blue with the excess of iron present.

b. Carbon. — Place some desiccated casein in the end of a piece of glass
tubing, tap it down gently so that the lumen of the tube will not be obstructed.
Heat the casein gently over a small Bunsen flame, inclining the tube so that
there will be a slight current of air passing upward through it. The casein
will char, indicating the presence of carbon.

c. Hydrogen. — Note the clear fluid that has condensed in the upper
portion of the tubing from the preceding experiment. If a little anhydrous
copper sulphate is introduced into the tube, the fluid of condensation coming
in contact with it will become blue, indicating that water has been formed
in the charring of the casein. Hydrogen in protein has been oxidized to form
water.

d. Sulphur. — Boil some casein or some egg-white solution with sodium
hydroxide after adding a few drops of lead acetate solution. The presence
of sulphur is shown by the formation of a black-lead sulphide. On adding
hydrochloric acid the lead sulphide formed will be decomposed and the odor
of hydrogen sulphide will be noted.

e. Phosphorus. — Heat some casein, preferably in a nickel crucible, with
a fusion mixture composed of three or four parts of caustic soda and one part
of potassium nitrate, warming cautiously until the mass becomes colorless.
Dissolve the residue when cool in a small volume of water, neutralize and
acidify with nitric acid slightly, and add about 5 c.c. of ammonium molyb-
date solution. Warm for some minutes at 80°. A yellow precipitate of
ammonium phosphomolybdate is obtained.

COLOR REACTIONS OF THE PROTEINS 107

3. Color Reactions of the Proteins. — a. Millon's Reaction. — To about
5 c.c. of a dilute solution of egg albumin in a test-tube add a few drops of
Millon's reagent. A white precipitate forms which turns red when heated.
This test can be used with advantage on solid proteins. In this case the
reagent is added to suspensions of the solid substance. Such proteins as are
not precipitated by the mineral acids yield a red solution instead of a red
precipitate. Millon's reagent consists of one part mercury dissolved in two
parts by weight of concentrated nitric acid; the resulting solution is diluted
with two volumes of water.

This reaction is due to the presence of the hydroxyphenyl group or
C6H5OH in the protein molecule. Accordingly, certain non-protein sub-
stances give this reaction; i.e., tyrosin, phenol (carbolic acid), thymol, etc.
The reaction 'given by the protein is due to the presence of the amino acid
tyrosin, and it is evident that the test is really an indication of the presence
of the tyrosin complex in the protein molecule.

b. Xanthoproteic Reaction. — To 2-3 c.c. of egg- albumin solution or of
some dry casein in the test-tube, add concentrated nitric acid and heat until
the protein dissolves, forming a yellow solution. Cool the solution and care-
fully add ammonium hydroxide in excess. The yellow7 color changes to an
orange. This reaction is due to the presence in the protein molecule of the
phenyl group in phenyalanine, tyrosine, or tryptophane; with the phenyl
group nitric acid forms certain nitro-derivatives of benzene.

c. Adamkiewicz or Hopkins-Cole Reaction. — Mix a couple of c.c. of con-
centrated sulphuric acid with 4 or 5 c.c. of glacial acetic acid in a test-tube.
Add a few drops of egg-albumin solution and warm gently. A reddish-
violet color is produced. This reaction is due to the presence of trypto-
phane in the protein and the test depends on the presence of glyoxylic acid
(CHOH2COOH) in the acetic acid. The Hopkins-Cole reagent, a glyoxylic
acid solution, may be used instead of the glacial acetic acid. The reagent
is prepared by adding sodium amalgam to a saturated solution of oxalic
acid and allowing the mixture to stand until the evolution of gas ceases.
In making the test the protein solution and Hopkins-Cole reagent are mixed
thoroughly in a test-tube, and concentrated sulphuric acid poured gently
into the tube which has been inclined somewhat so that it forms a layer in
the bottom of the test-tube. The acid and protein solutions will be strati-
fied and a reddish-violet ring is developed where the two fluids come in
contact.

This reaction is due to the presence of tryptophane in the protein mole-
cule. Gelatin does not respond to this test, for it does not yield this sub-
stance as a cleavage product.

d. Liebermanri* s Reaction. — Add a few drops of egg-white solution or a
little dry casein to about 5 c.c. of concentrated hydrochloric acid in a test-
tube and boil the mixture until a pinkish-violet color results. It was for

108 THE CHEMICAL COMPOSITION OF THE BODY

merly thought that this reaction indicated the presence of a carbohydrate
group in the protein molecule, but this is now considered uncertain.

e. Biuret Reaction. — To 2 or 3 c.c. of egg-white solution in a test-tube an
equal volume of concentrated potassium hydroxide solution is added and
mixed thoroughly. Very dilute (2 per cent.) copper sulphate solution is
added until a purplish-violet or pinkish-violet color is produced. This
reaction is given by substances containing two amino groups in the molecule,
these groups being joined directly together or through a single atom of
nitrogen or carbon. Non-protein substances that contain the necessary
groups will of course respond to this test, which derives its name from the
fact that it is given by biuret, a substance formed on heating urea to 180°.

NH2

NH2 CO

/ /

2C=O NH + NH3

\ \

NH2 CO

I
NH2

Urea. Biuret. Ammonia.

Proteins give this reaction since there are more than one CONH2 group
in the protein molecule. Proteoses and peptones give a pink biuret re-
action, gelatin a rather blue reaction, and the ordinary proteins a purple.

/. Molisch Reaction. — This reaction is really a carbohydrate test, but is
given by some proteins and interpreted as indicating that such proteins
contain a carbohydrate moiety. The test is made as follows:

Place about 5 c.c. of the solution to be tested in a test-tube, and add a
couple of drops of a 15 percent, alcoholic solution of a-naphthol. Incline
the tube and pour very carefully down the side about 5 c.c. of concentrated
sulphuric acid so that the two solutions are stratified. A blue or violet-red
ring is obtained in the area of contact of the solutions.

4. Precipitation Reactions of the Proteins. — a. Precipitation with
Concentrated Mineral Acids. — Prepare four test-tubes which contain about
5 c.c. of egg-white solution. To these respectively add drop by drop con-
centrated sulphuric acid, hydrochloric acid, nitric acid, and acetic acid.
Note that the mineral acids precipitate the protein. The precipitation with
nitric acid is a frequently used protein reaction, and when carried out as
follows is known as Heller's ring test. The solution to be tested is placed
in a test-tube, the tube is inclined and about 5 c.c. of concentrated nitric
acid is poured carefully down the side of the tube so that the solution and
acid stratify. A white zone of precipitated protein is obtained between the
strata. An instrument known as the albumiscope has been devised to

PRECIPITATION REACTIONS OF THE PROTEINS IO9

facilitate the making of the ring tests. Heller's ring test is most commonly
used to determine the presence of protein in urine.

b. Precipitation with Heavy Metals. — Proteins form insoluble compounds
with the metals when mercuric chloride, lead acetate, copper sulphate,
silver nitrate, etc., are added to protein solutions.

c. Acetic Acid and Potassium Ferrocyanide Test. — To about 5 c.c. of egg-
white solution in a test-tube add five to ten drops of acetic acid and then
potassium ferrocyanide drop by drop until a precipitate forms. This
test is very delicate.

d. Precipitation with the Alkaloidal Reagents. — Prepare six tubes contain-
ing about 3 c.c. egg-white solution. To the first add picric acid drop by
drop until excess of the reagent has been added, noting the changes with
care. Repeat the experiment with trichloracetic acid and tannic acid.
Acidify the remaining tubes with hydrochloric acid, and repeat the experi-
ment with phosphotungstic acid, phosphomolybdic acid, and potassium
mercuric iodide.

e. Heat Coagulation. — Take about 10 c.c. of egg-white solution in a test-
tube and heat to boiling. Then add a few drops of dilute acetic acid. The
protein will be coagulated. The acetic acid should be added after heating,
since otherwise acid metaprotein might be formed. The presence of
some neutral inorganic salts tends to give a sharper test. The addition of
the acid also will dissolve the earthy phosphates which are often precipi-
tated from the urine on heating. Proteoses, peptones, the casein of milk,
and a few other proteins are not coagulated by heat.

/. Precipitation by Alcohol. — Add some 95 per cent, alcohol to a test-tube
containing about 3 c.c. of egg-white solution. The protein is precipitated,
and on standing it is coagulated so that it can no longer be dissolved in
neutral solvent.

g. Salting-out Experiments. — Add to some diluted blood-serum in a small
beaker, crystals of magnesium sulphate until no more of the salt will go
into solution. After standing for a few minutes, filter and test the filtrate
and residue for protein by some of the precipitation or color reactions given
above. It is found that the filtrate still contains some protein. Further,
that this protein can be precipitated on adding a few drops of dilute acetic
acid. When the blood serum is similarly saturated with ammonium sul-
phate, there will be no protein found in the filtrate. If to the blood serum
an equal volume of saturated ammonium sulphate solution is added, the
result will be the same as that already obtained with magnesium sulphate.
Some proteins then are precipitated on saturating their solutions with mag-
nesium sulphate or by adding an equal volume of saturated ammonium
sulphate solution; albumins, globulins, and proteoses, however, are all pre-
cipitated by saturation with the more soluble ammonium sulphate.

110 THE CHEMICAL COMPOSITION OF THE BODY

ALBUMINS AND GLOBULINS.

5. Properties of Albumins and Globulins. — Try out the solubility
and the precipitation tests indicated in the following table for a solution of
ovalbumin, and on edestin furnished by the instructor.

Soluble in Precipitated

Coagulated
by

C

t/3

• G+-

en

<u

•3

in

1

la,

1** i P

1?

o

rt

*g

G>

|

o3

•+-> ^ 3^1

flj'^r

(U

'Q

Protein

3

i

!

1

1^

5S ! fffi

11

eg

1

Cj

£

|

0

>

Q i O

°^ 1 3'1

o|

<

1

Albumin

(ovalbumin)

i 1

Globulin

1

(edestin)

1

ALBUMINOIDS.

6. Keratin. — Horn shavings are most conveniently used for the experi-
ments with keratin.

a. Try the solubility of keratin in water, 10 per cent, salt solution, dilute
hydrochloric acid, and dilute potassium or sodium hydroxide.

b. Make a test for loosely combined sulphur as in experiment 2, d,
page 1 06.

c. Try Milieu's reaction and the biuret reaction.

d. Try the solubility of keratin in the artificial gastric and pancreatte
juice furnished by the instructor.

7. Collagen. — The tendo achillis of the ox may be used for the prepara-
tion of collagen.

a. Clean the tendon and cut it into small pieces. Wash the pieces in
dilute salt solution in order to remove the soluble protein, and then wrash
with distilled water. Transfer the pieces of washed tendon to a flask and
add 100 c.c. of saturated lime-water and same amount of distilled water.
The flask should be shaken at intervals for twenty-four hours. The lime-
water dissolves the mucoid in the tendon. Filter off the pieces of tendon
and save the filtrate for a later experiment. The residue of the tendon con-
sists of the albuminoid collagen and a little elastin. We may consider the
tests to follow as being made upon collagen.

b. Cut the collagen into very fine pieces and try the solubility as in 6 a
above.

* If not precipitated, acidify and note result.

t See page 89.

% On standing under alcohol.

GLYCOPROTEINS III

c. Test for loosely combined sulphur in collagen. Heat with the alkali
until the large piece of collagen used is partly decomposed, then add one or
two drops of lead acetate and again heat to boiling.

d. Try Millon's reaction, the biuret test, the xanthoproteic reaction, and
the Hopkins-Cole reaction.

e. Formation oj gelatin jrom collagen. Transfer the remainder of the
collagen to a casserole, fill about two-thirds with water, and boil for several
hours, replacing the water that is lost by evaporation. Filter and cool.
Collagen is transformed into gelatin and the characteristic gel is obtained.
Try this experiment also with some cartilage from the trachea and with some
0.2 per cent. HC1 extracted bone.

/. The properties oj gelatin. Try the solubility as in a above on some
gelatin furnished by the instructor. Try the solubility also in hot water.

g. Try the tests for loosely combined sulphur. Try Millon's Hopkins-
Cole, and the biuret reactions. Try the solubility in artificial gastric and
pancreatic juices.

8. Elastin. — a. Preparation of Elastin. — Cut the ligamentum nuch(E of
the ox into strips and run it through a meat chopper. Wash the finely
divided material with salt solution and in running water for some hours.
Transfer it to a flask and add about 200 c.c. of half- saturated lime-water and
extract for forty-eight hours. Filter off the lime-water which has dissolved
the mucoid present, saving the filtrate, and wash the residue and tendon with
water. Boil the material in dilute acetic acid for some hours to convert the
collagen present into gelatin. Wash the residue thoroughly with water. It
may be dried by washing it with boiling alcohol, pressing it out between
filters, and manipulating it in the air.

b. Try the solubility of elastin as in a. Test for loosely combined
sulphur. Try Millon's, biuret, and the Hopkins-Cole reactions. Try the
solubility in artificial gastric and pancreatic juices.

c. Make a table comparing the properties of keratin, collagen, and elastin.

GLYCOPROTEINS.

9. Mucoid. — a. Unite the lime-water of filtrates obtained in the extraction
of the tendons in the preceding experiment and acidify them with dilute
acetic acid until precipitation occurs. The mucoid is precipitated. Avoid
adding excessive acid or the mucoid will again go into solution. Allow the
mucoid precipitate to settle and decant the supernatant fluid and filter off
the precipitate.

b. Try the biuret test on a portion of the mucoid.

c. Place the remainder of the mucoid in a beaker, add about 25 c.c. of
water and 2 c.c. of dilute hydrochloric acid; boil until the solution becomes
dark. To a portion of the mixture add a few drops of barium chloride. A

112 THE CHEMICAL COMPOSITION OF THE BODY

white precipitate shows the presence of sulphate. Neutralize to litmus-paper
with solid potassium or sodium hydroxide and test for sugar with Fehling's
solution (see Experiment 12, d). The mucoid has been split by boiling with
acid into protein, protein cleavage products, and carbohydrate or a reducing
substance. The presence of oxidized sulphur in the molecule has also
been shown.

DERIVED PROTEINS.

10. Metaproteins. — a. Acid Metaproteins or Acid Albuminate. — Acid
metaprotein or acid albumin may be prepared as follows:

To some chopped lean meat in a flask add .4 per cent, hydrochloric
acid. Allow it to stand for some time, shaking it occasionally. Filter
and neutralize the nitrate. A precipitate of acid metaprotein is obtained.
The acid albuminate then is insoluble in neutral dilute salt solutions, but
it dissolves in acidified solutions. Filter off some of the precipitated acid
albuminate and test it for loosely combined sulphur.

b. Alkali metaprotein is formed on treating proteins with alkali. To
some undiluted egg white in an evaporating dish add some protein hy-
droxide solution slowly with constant stirring. The mixture forms a
stiff gel known as Lieberkiihn's jelly. Wash the gel, which has been broken
into small pieces, with running water until the excess of alkali is removed.
Warm it in a small amount of \vater and dissolve by heating gently.
Neutralize the solution carefully with acid, noting the odor of the hydrogen
sulphide that is given off. The precipitate which appears when the neutral
point is reached is alkali metaprotein or alkali albuminate. Filter off the
precipitate, wash it in water, and try the test for loosely combined sulphur.
A weak reaction or negative result shows that the loosely combined sulphur
has been split off by treating the protein with the alkali, a change which has
not occurred in the formation of the acid albuminate above.

SECONDARY PROTEIN DERIVATIVES.

11. Proteose and Peptone. — Commercial proteose-peptone prepara-
tions, such as Witte peptone or Armour's peptone, may be employed for
the separation of proteoses and peptones.

a. Take about 5 grams of the proteose-peptone mixture and dissolve it in
100 c.c. of water.

Try the biuret reaction, Millon's reaction, and Heller's ring test. Do
the proteoses and peptones coagulate on heating ?

b. Place the remainder of the solution in the beaker and add dry ammonium
sulphate in excess. Note that before the solution is completely saturated with
the salt, the precipitation of the primary proteoses (proto proteose and hetero
proteose). Completely saturate the solution with the ammonium sulphate,
warming it gently to facilitate the separation. At full saturation the second-

CARBOHYDRATES 113

ary proteoses (deutero-proteoses) are precipitated. The peptones remain
in solution. Try the biuret test on the precipitate and on the nitrate con-
taining the peptone, in the latter instance making the solution strongly alka-
line with solid sodium or potassium hydroxide.

d. From what you have learned of the properties of the derived proteins
in the text and in the laboratory, prepare a chart (Exp. 5) in which the
properties of these substances are indicated. Compare the results in this
chart and the results in this table with the similar one that you made for
the albumins and globulins.

CARBOHYDRATES.

12. Starch. — a. Examine under the microscope and sketch the starch
granules obtained by grinding some potato scrapings in a mortar with a
little water; examine and sketch also the granules of corn, wheat (flour),
and arrowroot starch.

b. Starch Paste. — Make a suspension of i gram of arrowroot starch in a
little distilled water by grinding in a mortar, and pour slowly into some
boiling water. Heat for a few minutes longer, cool and make up to
100 c.c.

c. Iodine Test. — Shake up three or four drops of dilute iodine solution
with 2 c.c. starch. A deep blue color appears. The color is discharged in
dilute alkali and reappears on acidifying again. Heat also discharges
the color.

d. Fehling's Test. — Fill a test-tube about a fourth full of Fehling's
solution and heat to boiling for a minute or two. Add a few drops of starch
paste. The red precipitate of copper (cuprous) oxide should not be obtained,
for pure starch does not reduce Fehling's solution.

e. Hydrolysis of Starch. — Boil starch solution with 5 per cent, sulphuric
acid for fifteen minutes. Test with Fehling's solution, first neutralising the
excess of acid. A copious precipitate of cuprous oxide sho\vs that the starch
has been converted to reducing sugar.

13. Dextrins. — Make a 5 per cent, solution of dextrin in distilled water
and try:

a. Iodine Test. — This gives a red which is characteristic.

b. Fehling's Test.

. 14. Dextrose. — Test a 5 per cent, solution of dextrose:

a. Iodine Test. — No reaction.

b. Fehling's Test.

15. Glycogen. — Use i per cent, solution of glycogen. Note the char-
acteristic opalescence of the solution.

a. Iodine Test. — A wine-red, somewhat like that given by dextrin.

b. Fehling's Test. — Glycogen does not reduce the copper solution.

c. Hydrolysis. — Test as in e. The glycogen is hydrolyzed to dextrose.

114 THE CHEMICAL COMPOSITION OF THE BODY

FATS.

16. Neutral Fat. — a. Melting-point. — Compare neutral olive oil, some
fresh rendered lard, and some tallow. The former is fluid at ordinary
room temperature. Determine the melting-points of the lard and of the
tallow by the method of Wiley. Fill a test-tube one-half full of water and
add a two-inch top layer of alcohol. Prepare a thin flake of fat and suspend
it in the test-tube at the dividing line of the water and alcohol. Insert the
bulb of a thermometer at the same level. Mount the test-tube with the
thermometer in a beaker on a ring stand, fill the beaker with water above the
level of the content of the test-tube, and gradually heat with stirring of the
water in the beaker. At the melting temperature the flake of fat will run
into a round drop.

b. Solubility. — Fat is insoluble in water, but soluble in acetone, ether,
chloroform, benzol, and in alcohol.

c. Saponification. — Heat some fat in an evaporating-dish, add sodium
hydrate, and boil. Saponification takes place. The soap is soluble in water.
Add 25 per cent, sulphuric acid to some of the soap, the fatty acid is liberated
and collects on the surface of the solution.

17. Fatty Acids. — Collect some of the fatty acids, wash to remove
excess of sulphuric acid, and dissolve in ether.

a. Acid Reaction. — Add an ether solution of the fatty acid to neutral
litmus, or to faintly alkaline phenolphthalein. The former turns red, and
the red of the alkaline solution of the latter is discharged.

b. Acrolein Test. — Evaporate the ether from 2 c.c. of the solution, add
potassium bisulphate crystals to the acid in a test-tube, and raise to a high
heat over a Bunsen. No acrolein is given off. Repeat on neutral fat and
on glycerin. Both liberate the irritating fumes of acrolein.

1 8. Emulsification. — a. Shake up neutral olive oil and water, no
emulsion is formed and the oil quickly separates.

b. Add a couple of drops of fatty acid, a very good but temporary emul-
sion is now formed.

c. Use rancid fat, a temporary emulsion is formed.

d. Add a little soap to each of the above. A good permanent emulsion
is now formed, but best in c.

19. Lipoids. — a. Grind some pig's or calf's brain with ether in a
mortar3 place in a flask with sufficient ether to make a thin suspension of
the material and set aside until the undissolved material has sedimented
completely to the bottom. Decant the clear ether and add acetone until
the lecithins have been precipitated. Cholesterol will crystallize from the
filtrate on spontaneous evaporation of the latter. Sketch the cholesterol
crystals.

b. Show the presence of nitrogen in lecithin (see Exp. 2 a).

FATS 115

c. Try the acrolein test as in Exp. 17 b.

d. Fuse some lecithin in a metal crucible with a fusion mixture of 3
parts of caustic potash and i part of potassium nitrate. Dissolve in a
small volume of water, acidify slightly with nitric acid, add a fewr drops of
ammonium molybdate solution, and warm to 75° C. for a few minutes. A
yellow precipitate of ammonium phosphomolybdate indicates the presence
of phosphorus in the lecithin.

e. Try to saponify some cholesterol as in Exp. 16 c. As cholesterol is
not a fat, saponification does not take place.

20. The Salts. — Coagulate the protein in 10 grams of chopped meat or
25 c.c. of blood by boiling for a few minutes with 25 c.c. of water to which a
few drops of acetic acid have been added. Filter off the coagulated protein,
wash the precipitate on the paper with a very little hot water, and add the
washings to the original nitrate. The coagulum should filter off quickly
and the filtrate should be perfectly clear; otherwise repeat the experiment.
Make the following tests:

a. Chlorides. — Acidify a small portion of the filtrate with nitric acid
and add a few drops of silver nitrate solution. A white precipitate, which
dissolves on adding ammonia and reappears on acidification with nitric
acid, shows the presence of chlorides.

b. Sulphates. — Acidify a portion of the filtrate with hydrochloric acid
and add a few drops of barium chloride solution. A white precipitate of
barium sulphate indicates that sulphates are present. A much stronger
reaction can be obtained when the ash or alkali fusion of a tissue is tested,
the sulphur in the protein then having been oxidized to a sulphate.

c. Phosphates. — Acidify with nitric acid and then add a few drops of
ammonium molybdate solution. Warm in the water-bath at 75° C. for a
few minutes. A yellow precipitate of ammonium phosphomolybdate indi-
cates the presence of phosphate.

d. Calcium. — Add a few drops of ammonium oxalate solution to a por-
tion of the filtrate. A white precipitate of calcium oxalate forms. On
microscopic examination this is found to consist of characteristic minute
octahedrals.

e. Iron. — Acidify with hydrochloric acid and add a few drops of potas-
sium ferrocyanide. A Prussian blue color indicated the presence of iron.
Try the reaction on some blood which has been ashed in a crucible and
dissolved out in a little dilute hydrochloric acid. The iron is present in the
compound protein, hemoglobin, of the red corpuscles.

/. Magnesium. — Tease out some fibers of frog muscle in a few drops of
water on a microscope slide and invert a beaker containing a piece of filter-
paper moistened with ammonia over it. After a few minutes, examine
under the microscope. Characteristic star-shaped or fern-like crystals of
ammonium magnesium phosphate will be seen.

PLATE II

VARIETIES OF LEUCOCYTES

a. Polymorphonuclear Neutrophiles. — Note the varieties in size and shape
of granules, the regular staining of the nuclei, the light space around them,
their relatively central position in the cell.

b. Myelocytes. — Note the identity of granules with those just described; the
even, pale stain of nuclei, their position near the surface (edge) of the cell. The
two cells figured indicate the usual variations in size of the whole cell.

c. Small Lymphocytes. — In the cell at the left note the transparent proto-
plasm ; in the cell next to it note the very pale pink of protoplasm around the
nucleus which is deeply stained, especially at the periphery. The next cell
has an indented nucleus; its protoplasm relatively distinct. The cell on the
extreme right shows no protoplasm and is probably necrotic. In all note
absence of granules with this stain. With basic stains a blue network appears
in the protoplasm.

d. Large Lymphocytes. — Note the pale stain of nuclei and protoplasm,
regularity of outline; indented nucleus in one. Every intermediate stage
between these and the "small" lymphocytes occurs, and the distinction be-
tween them is arbitrary.

e. Eosinophile. — Note regular shape, loose connection of granules, their
copper color, their uniform and relatively large size, and spherical shape.

/. Eosinophilic Myelocyte. — Note similarity to the ordinary myelocytes b,
except as regards granules. Colors of granules may be, as in e, ordinary
eosinophile.

All the above were stained with the Ehrlich triacid stain, and drawn with
camera lucida. Oil immersion objective ^ and ocular No. iii. of Leitz.
(Cabot.)

116

KIRKES' PHYSIOLOGY

PLATE II

Polymorphonuclear

.•*>.

....

r

:— _ Myclory te.-

Snuill Lymphocytes

Eosinoplii'e

Varieties of Leucocytes

R. C. Cabot fee.

CHAPTER IV

THE BLOOD

THE blood is the fluid medium from which all the tissues of the body are
nourished. By means of the blood, materials absorbed from the alimentary
canal as well as oxygen taken from the air in the lungs are carried to the
tissues, while substances which result from the metabolism of the tissues are
carried to the excretory organs to be removed from the body. The blood
acts as a medium of exchange between the various tissues themselves. A
good example is found in the distribution by the blood of the products of
certain glandular activities, the internal secretions. The blood is an im-
portant factor in the regulation of the body temperature.

The blood is a somewhat viscid fluid, and in man and in all other
vertebrate animals, with the exception of the two lowest, is red in color.
The exact color of blood is variable; that taken from the systemic arteries,
from the left side of the heart and from the pulmonary veins is of a bright
scarlet hue; that obtained from the systemic veins, from the right side of
the heart, and from the pulmonary artery is of a much darker color, which
varies from bluish-red to reddish-black. At first sight the red color appears
to belong to the whole mass of blood, but on further examination this is
found not to be the case. In reality blood consists of an almost colorless
fluid, called plasma or liquor sanguinis, in which are suspended numerous
minute masses of protoplasm, called blood corpuscles. The corpuscles are
of the two varieties, the white ameboid corpuscles, or leucocytes, and the
red corpuscles, erythrocytes. The latter compose by far the larger mass of
blood-cells. They contain the red pigment, hemoglobin, to which the color
of the blood is due.

The plasma or fluid part of the blood is a remarkably complex chemical
mixture. It is kept in constant rapid circulation through the blood vessels
of the body and is, therefore, thoroughly mixed and homogeneous in
character.

Quantity of the Blood. — The quantity of blood in any animal under
normal conditions bears a fairly constant relation to the body weight. The
amount of blood in man averages T^- to y¥ of the body weight. In other
mammals the proportion of blood is also fairly constant, varying from
T2 to TO" °f the body weight. In many of the lower vertebrates, the fishes
for example, the relative quantity of blood is very much less.

An estimate of the quantity in man which corresponded very nearly
with this proportion has been more than once made by methods illustrated

117

Il8 THE BLOOD

by the following data: A criminal was weighed before and after decapita-
tion; the difference in the weight representing the quantity of blood which
escaped. The blood vessels of the head and trunk were then washed out
by the injection of water until the fluid which escaped had only a pale red
or straw color. This fluid was then also weighed, and the amount of blood
which it represented calculated by comparing the proportion of solid matter
contained in it with that of the first blood which escaped on decapitation.
Two experiments of this kind gave precisely similar results (Weber and
Lehmann).

This quantity of blood is distributed in the different parts of the body,
chiefly in the muscles, the liver, the heart, and larger blood vessels, as shown
by the following figures determined on the rabbit by Ranke (from Vierordt) :

Per cent.

Spleen 0.23

Brain and cord 1.24

Kidney i . 63

Skin 2.10

Abdominal viscera 6.30

Cartilage 8.24

Heart, lungs, and large blood vessels 22.76

Resting muscle 29.20

Liver 29-3°

It should be remembered, in connection with these estimations, that
the quantity of the blood must vary very considerably, even in the same
animal, with the amount of both the ingesta and egesta of the period im-
mediately preceding the experiment. It has been found, for example, that
the quantity of blood obtainable from the body of a fasting animal rarely
exceeds a half of that which is present soon after a full meal.

COAGULATION OF THE BLOOD.

The most characteristic property which the blood possesses is that of
clotting or coagulating. This phenomenon may be observed under the most
favorable conditions in blood which has been drawn into an open vessel. In
about two or three minutes, at the ordinary temperature of the air, the surface
of the fluid is seen to become semisolid or jelly-like, and this change takes
place, in a minute or two afterward, at the sides of the vessel in which it is
contained and then quickly extends throughout the entire mass. The time
which is occupied in these changes is about eight or nine minutes. The
solid mass is of exactly the same volume as the previously liquid blood, and
adheres so closely to the sides of the containing vessel that if the latter be
inverted none of its contents escape. The solid mass is the crassamentum
or clot. If the clot be watched for a few minutes, drops of a light, gtraw-
colored fluid, the serum, may be seen to make its appearance on the surface,

COAGULATION OF THE BLOOD 1 19

and, as it becomes greater and greater in amount, to form a complete super-
ficial stratum above the solid clot. At the same time the serum begins to
transude at the sides and at the under surface of the clot, which in the course
of an hour or two floats in the liquid. The appearance of the serum is due
to the fact that the clot contracts, thus squeezing the fluid out of its mass.
The first drops of serum appear on the surface about eleven or twelve min-
utes after the blood has been drawn; and the fluid continues to transude for
from thirty-six to forty-eight hours.

The clotting of blood is due to the development in the plasma of an in-
soluble substance called fibrin. This fibrin forms threads or strands through
the mass in every direction. The strands adhere to each other wherever
they come in contact, thus forming a very dense tangle and meshwork which
incloses within itself the blood-corpuscles. The clot when first formed,
therefore, includes the whole of the blood in an apparently solid mass, but
soon the fibrinous meshwork begins to contract and the serum is squeezed
out. When a large part of the serum has been squeezed out the clot is found
to be smaller, but firmer and harder, as it is now made up more largely of
fibrin and blood corpuscles. Thus in coagulation there is a rearrangement
of the constituents of the blood; liquid blood consisting of plasma and
blood corpuscles, and clotted blood of serum and clot. These relations are
roughly shown in the following diagram:

Liquid blood.

Plasma. Corpuscles.

Serum. Fibrin.

Clot.

Clotted blood.

The rapidity with which coagulation takes place varies greatly in different
animals and at different times in the same animal. Where coagulation is
very slow the red corpuscles, which are somewhat heavier than plasma,
often have time to settle considerably before the fibrin is formed. If the
blood is rapidly cooled to a temperature approaching o° C. then the clot is
very greatly delayed. Horse's blood is particularly favorable for demon-
strating this point. In it clotting occurs so slowly that very often the red
corpuscles will completely settle out, and when the blood is again warmed
and the clotting takes place there is a superficial stratum differing in appear-
ance from the rest of the clot, having a grayish-yellow color. This is known

120

THE BLOOD

as the buffy coat or crusta phlogistica. The buffy coat, produced in the man-
ner just described, commonly contracts more than the rest of the clot, on
account of the absence of colored corpuscles from its meshes. When the
clot is allowed to stand, the white corpuscles which have escaped the clot
by ameboid movement settle on its surface often in such numbers that they
form a distinct superficial layer, grayish-white in appearance.

That the clotting of blood is due to the gradual appearance in it of fibrin
may be easily demonstrated, For example, if recently drawn blood be
whipped with a bundle of twigs or wires, the fibrin may be withdrawn from
the blood before it can entangle the blood corpuscles within its meshes.
It adheres to the twigs in stringy threads relatively free from corpuscles.
The blood from which the fibrin has been withdrawn no longer exhibits the
power of spontaneous coagulability and it is now called defibrinated blood.
Although these facts have long been known, the closely associated problem
as to the exact manner in which fibrin is formed is by no means so simple.

FIG. 107. — Reticulum of Fibrin, from a Drop of Human Blood, after Treatment with

Rosanilin. (Ranvier.)

Fibrin is derived from the plasma. Pure plasma may be procured by
delaying coagulation in blood by keeping it at a temperature slightly above
freezing-point, until the colored corpuscles have subsided to the bottom of
the containing vessel. The blood of the horse is specially suited for the
purposes of this experiment. A portion of the colorless supernatant plasma,
if decanted into another vessel and exposed to the ordinary temperature of
the air, will coagulate, producing a clot similar in all respects to blood clot,
except that it is colorless from the absence of red corpuscles. If some of
the plasma be diluted with twice or three times its bulk of normal saline
solution (0.9 per cent.), coagulation is delayed, and the stages of the gradual
formation of fibrin in it may be conveniently watched. The viscidity which
precedes the complete coagulation may be actually seen to be due to the
formation of fibrils of fibrin — first of all at the edge of the fluid-containing

THEORIES OF COAGULATION 121

vessel, and then gradually extending throughout the mass. If a portion of
plasma, diluted or not, be whipped with a bundle of twigs the fibrin may
be obtained as a solid, stringy mass, just in the same way as from the entire
blood, and the resulting fluid no longer retains its power of spontaneous
coagulability.

Theories of Coagulation. — It is evident that the blood plasma contains
some substance or substances which take part in the formation of fibrin.
By numerous investigations it has been found that the direct antecedent of
the fibrin is the protein substance, fibrinogen. This fibrinogen exists in the
blood plasma at all times, but is somewhat increased under certain condi-
tions. The fibrinogen is reacted on by another substance known as thrombin
or by the historical term fibrin ferment. We shall not present the numerous
theories which have been held concerning blood coagulation, many of
which have been more or less disproven, but shall try to present the con-
Blood Tissue Cells

Plasma Blood Plates. Corpuscles.

Neutral Salts Fibrinogen Calcium Salts

(for dissolving
fibrinogen)

Fibrin-globulin

\

Prothrombin Thrombokinase

Thrombin

Fibrin
FIG. 1 08. — Marowitz' Schema of Coagulation.

densed statement of the present explanations of this intricate phenomenon.
One may start from the statement that the fibrinogen of the plasma when acted
upon by the thrombin, also of the plasma, produces an insoluble substance, fibrin.
The chief interest centers around the origin and character of the fibrinogen,
the origin and nature of the thrombin, and the conditions which influence its
activity.

The fibrinogen is present in blood plasma of the circulating blood of the
body at all times. It can be separated from plasma by various chemical
means, and when purified can be made to form fibrin under proper conditions.
All observers are agreed that this protein is the immediate precursor of the
insoluble fibrin. Its origin in the blood has been traced by Matthews with
some degree of certainty to the disintegration of the white blood corpuscles.

122 THE BLOOD

The thrombin is the substance which reacts on the fibrinogen in the
processes of fibrin formation. It does not exist in the living blood
vessels, or at least is present only in minute quantities, but makes its
appearance immediately the blood is drawn. Its origin is therefore of
peculiar interest.

Thrombin has not been chemically identified. But it is generally ad-
mitted that it is a calcium compound. At any rate, it is definitely proven
that calcium is a necessary element in the formation of the clot.

The substance thrombin, fibrin ferment, quickly appears in considerable
quantity when blood is drawn under ordinary conditions. The sources of
these substances and the part taken by each in the process of coagulation
are as follows (Marowitz): If blood be drawn, centrifugalized, and the
leucocytes and blood plates separated from the plasma and suspended in
water, their solution will cause the formation of fibrin from fibrinogen in
the presence of calcium. The leucocytes and platelets are, therefore, the
source of thrombogen. The thrombin can be isolated in a stable condition,
and when its solutions are added to fibrinogen solutions fibrin is formed.
By Marowitz' view the appearance of thrombin in the blood is due to the
interaction of at least three antecedent substances. These are, i, pro-
thrombin (thrombogen), 2, calcium, and 3, thrombokinase (cytozym). If
the blood is drawn from vessels with due precautions, i.e., not to allow it to
come in contact with the cut vessel or other tissue, clotting is very much
delayed. The plasma if separated by the centrifuge will remain unclotted
for a long time as shown by Howell for the terrapin's plasma. This plasma
will quickly clot at any time if a few drops of tissue extract in salt solution be
added. When blood is drawn over the lacerated tissue of a wound it clots
more quickly. These observations have led to the assumption of an acti-
vating substance or kinase to which the name thrombokinase has been given.
It is assumed to have its origin in tissue cells and in the cells of the blood,
especially the leucocytes.

If precautions are taken to draw the blood in such a manner as to re-
move the calcium from the plasma, no clot is formed. The calcium which
exists in solution in the plasma to the extent of 0.026 per cent, (measured
as calcium chloride) can be removed by precipitation with oxalate solution
or by the action of fluorides or citrates which bind the calcium so that it is
no longer available to the prothrombin. Such plasma contains fibrinogen,
prothrombin, and thrombokinase, and whenever calcium chloride is added
to excess, coagulation takes place.

L. J. Rettger has recently, 1909, made an exhaustive re-examination
of the conditions for the clotting of blood. He questions the interpretation
of the facts on the basis of which the assumption of a kinase is made.
He says : ' ' After such prolonged irrigation, to remove every trace of blood or
serum, bits of the organ or tissue were macerated in 0.9 per cent, solution

THEORIES OF COAGULATION 123

of sodium chloride, and portions of this macerated tissue were put into fi-
brinogen solutions. Of another part of the irrigated tissue filtered saline
extracts were made, and these were tested from time to time on fibrinogen
solutions. In not a single case in the repeated series of experiments was
there found any evidence of coagulation." "Terrapin's blood taken
carefully through an oiled cannula and put into a perfectly clean beaker will
remain fluid for days. The blood may be centrifuged, and the clear super-
natant plasma is then equally or more resistant to spontaneous clotting. If,
however, tissue extracts or pieces of tissue be added, the coagulation is pro-
nounced and immediate. The most apparent explanation is that of a
thrombin or coagulin or kinase present in the extract. But this blood or
plasma can be made to clot equally well and equally rapidly in ways which
preclude the presence of such a definite agent. If, for instance, dust par-
ticles, loose sweepings, or linty shreds be added, the coagulation is equally
prompt and in a number of experiments was more rapid than with tissue
extract." "The bird's blood or plasma clots with practically the same
rapidity and firmness if dust particles are generously added. Bits of down
or feathers introduced bring about a speedy clotting. Surely there can be
no question of a 'kinase' in these instances." "The existence of 'kinase'
or 'coagulins' in the various tissues is improbable. Using carefully pre-
pared fibrinogen solutions, extracts of tissues, irrigated to remove every
trace of thrombin-containing blood, cause no clotting. When the addition
of such extracts produces coagulation in bloods of bird or reptile, similar
results can be secured by the addition of substances, such as dust, lint,
shreds, etc., which preclude the presence of definite coagulating agents.
These results render very probable the assumption that in such plasmas all
the factors of coagulation are in reality present, and the addition of tissue
extract or other foreign substance brings into the mixture nothing that can
be regarded as a coagulin or as a kinase."

One may restate Morawitz' view in a word as follows: The coagulation
of the blood takes place because of the formation of fibrin from fibrinogen
by the action of thrombin. The fibrinogen is constantly present in the plasma.
The thrombin is formed by the interaction of three substances, prothrombin,
calcium, and thrombokinase. The prothrombin arises chiefly from the
disintegration of the blood platelets and leucocytes when the blood leaves the
blood vessels. The calcium is present in the blood plasma at all times.
The thrombokinase originates in tissue cells of the blood and of the organs of
the body in general.

Rettger's view is best given in his own words:

"On the basis of the work here presented it is not necessary to assume
the existence of a kinase in explaining the clotting of shed blood. The pro-
thrombin formed from the platelets and leucocytes by secretion or by proc-
esses of disintegration is activated to thrombin by the calcium salts present,

124 THE BLOOD

and the thrombin so formed combines in quantitative fashion with the
fibrinogen to form fibrin."

Conditions Affecting Coagulation. — From the preceding discussion
it is evident that the rapidity of the coagulation of the blood will be
influenced by anything that will influence the formation of the fibrin
factors or their interaction. The most important influences are the
following:

Temperature. — Cold retards coagulation. Gentle warmth, 40° C., has-
tens, but a temperature above 56° C. destroys clotting, since that temperature
heat-coagulates the fibrinogen.

Contact with Foreign Bodies. — Such contact hastens clotting. This is
due to the influence of such bodies in hastening the formation of fibrin
factors, especially the substances that arise from the disintegration of
leucocytes.

Condition of the Blood-vessel Walls. — Intravascular clotting often takes
place upon injury of the endothelial lining of the blood vessels, either from
the liberation of thrombokinase in quantity too great for elimination by the
healthy portion of the wall (Morawitz), or by the disturbance of the equi-
librium of the forces which prevent the interaction of the fibrin factors
present in the blood (Rettger). The healthy endothelium no doubt is an im-
portant factor in eliminating the small amounts of the fibrin factors that must
be constantly forming. The open wounds and lacerations of tissue that
accompany the loss of blood by accident are the very conditions most favor-
able to clotting, since large amounts of tissue extract are set free under
these conditions.

Neutral Salts. — The addition of neutral salts in the proportion of 2 or 3
per cent, and upward delay coagulation. When added in large proportions,
most of these saline substances prevent coagulation altogether. Coagulation,
however, ensues on dilution with water. The time during which salted blood
can be thus preserved in a liquid state, and coagulated by the addition of
water, is quite indefinite.

Oxalates and Fluorides. — These and other precipitants of calcium pre-
vent clotting by removing this substance.

Peptone. — The injection of commercial peptone (a mixture of proteoses
and peptones) in the blood vessels of an animal to the extent of o . 5 gram
of peptone per kilo weight of the body of the animal will deprive the blood
of the power of coagulation. If a smaller quantity be injected the coagula-
tion of the blood will be delayed. If peptone blood is drawn and centri-
fuged, the plasma obtained is called peptone plasma. Peptone plasma in
the blood vessels of the animal gradually regains the power to coagulate.
When blood is drawn into a physiological salt solution of proteose-peptone
clotting occurs.

MORPHOLOGY OF THE BLOOD 125

MORPHOLOGY OF THE BLOOD.

The corpuscles floating in the fluid plasma of the blood, when separated
by a centrifugal machine are found to make up 45 to 50 per cent, of the total
mass of the blood. These corpuscles, or formed elements, are of three
varieties, the red corpuscles or erythrocytes, the white corpuscles leucocytes,
and the blood platelets which have been called thrombocytes.

Red Corpuscles or Erythrocytes. — Human red blood corpuscles are
circular, biconcave discs with rounded edges, from 7/4 to 8// in diameter,
and about 2« in thickness. When viewed singly they appear of a pale
yellowish tinge; the deep red color which they give to the blood being ob-
servable in them only when they are seen en masse. They are composed
of a colorless, structureless, and transparent filmy framework or stroma,
infiltrated in all parts by the red coloring matter, the hemoglobin. The
stroma is tough and elastic, so that as the corpuscles circulate they admit
of elongation and other changes of form in adaption to the vessels, yet
recover their natural shape as soon as they escape from compression.

FIG. 109. FIG. no.

FIG. 109. — Red Corpuscles in Rouleaux. The rounded or uncolored corpuscles are
leucocytes.

FIG. no. — Corpuscles of the Frog. The central mass consists of nucleated colored
corpuscles. The other corpuscles are two varieties of the colorless forrn.

Number and Character of the Red Corpuscles. — The normal number of red
blood-cells in a cubic millimeter of human blood was estimated by Welcker,
in 1854, to be 5,000,000 in men and 4,500,000 in women. Numerous recent
observations, however, have shown that these estimates are a little low,
especially in men, and the average number has been placed by different
authorities at various points between 5,000,000 and 5,500,000. Still the
original numbers as given by Welcker are accepted at the present day as being
sufficiently accurate for ordinary purposes. It has been also shown that
there are many distinct physiological variations in the number, depending

126

THE BLOOD

on the time of day, digestion, sex, etc. The number of red cells usually
diminishes in the course of each day, while the leucocytes increase in number.
It has been suggested that this is due to the influence of digestion and
exercise.

It has generally been found that within half an hour or an hour after a
full meal the number of red cells begins to diminish, and that this keeps up

FIG. in. — The Illustration is Somewhat Altered from a Drawing by Gulliver, in the
Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in the
main Divisions of the Vertebrata. The fractions are those of an inch, and represent the
average diameter. In the case of the oval cells, only the long diameter is here given. It is
remarkable, that although the size of the red blood-cells varies so much in the different
classes of the vertebrate kingdom, that of the white corpuscles remains comparatively
uniform, and thus they are, in some animals, much greater, in others much less, than the
red corpuscles existing side by side with them.

for from two to four hours, when it is followed by a gradual rise to the normal.
The usual fall is 250,000 to 750,000 per cubic millimeter. These results
are most marked after a largely fluid meal, and are probably due to dilution
of the blood as a result of the absorption of fluids. In animals the number
of red cells is increased by fasting, but in man the results are variable, some

DEVELOPMENT OF THE RED BLOOD CORPUSCLES 127

authorities claiming an increase and others a decrease. In childhood there
is no difference between the sexes in the number of red cells per cubic milli-
meter, but after menstruation is established a relative anemia develops in
women. Welcker's original estimate placed the difference at 500,000 per
cubic millimeter, and these figures have been generally accepted, though
Leichtenstein asserts that the difference is 1,000,000.

Menstruation in healthy subjects has practically no effect, as not more
than 1 00-200 cubic centimeters of blood are lost normally in the course of
several days. Under such circumstances the normal diminution of red cells
per cubic millimeter is probably less than 150,000, though Sfameni has placed
the loss at about 225,000. In fact an increase has been claimed. The
leucocytes are slightly increased during menstruation. It is now the general
opinion that pregnancy has little or no effect on the number of red cells, and
that any anemia must be due to abnormal conditions. Post-partum anemia
should not last longer than two weeks.

The red corpuscles are not all alike. In almost every specimen of blood a
certain number of corpuscles smaller than the rest may be observed. They
are termed microcytes, or hematoblasts, and are probably immature
corpuscles.

A peculiar property of the red corpuscles, which is exaggerated in in-
flammatory blood, may be here again noticed, i. e., their great tendency to
adhere together in rolls or columns (rouleaux), like piles of coins. These
rolls quickly fasten together by their ends, and cluster; so that, when the
blood is spread out thinly on a glass, they form a kind of irregular network,
with crowds of corpuscles at the several points corresponding with the knots
of the net, figure 109. Hence the clot formed in such a thin layer of blood
looks mottled with blotches of pink upon a white ground.

The red corpuscles are constantly undergoing disintegration in different
parts of the circulatory system, particularly in the spleen. The liberated
hemoglobin contributes to the formation of the bile pigments in the liver.

Development of the Red Blood Corpuscles. — The first formed
blood corpuscles of the human embryo differ much in their general characters
from those which belong to the later periods of intra-uterine, and to all
periods of extra-uterine life. Their manner of origin is at first very simple.

Surrounding the early embryo is a circular area, called the vascular area,
in which the first rudiments of the blood vessels and blood corpuscles are
developed. Here the nucleated embryonal cells of the mesoblast, from
which the blood vessels and corpuscles are to be formed, send out processes
in various directions, and these, joining together, form an irregular mesh-
work. The nuclei increase in number, and collect chiefly in the larger masses
of protoplasm, but partly also in the processes. It appears that hemo-
globin then makes its appearance in certain of these nucleated embryonal
cells, which thus become the earliest red blood corpuscles. The proto-

128

THE BLOOD

plasm of the cells and their branched network in which these corpuscles
lie then become hollowed out into a system of canals enclosing fluid, in which
the red nucleated corpuscles float. The corpuscles at first are from about
IQ/J. to i6/z in diameter, mostly spherical, and with granular contents, and
a well-marked nucleus. Their nuclei, which are about 5^ in diameter,
are central, circular, very little prominent on the surfaces of the corpuscles,
and apparently slightly granular.

The corpuscles then strongly resemble the colorless corpuscles of the
fully developed blood but for their color. They are capable of ameboid
movement and multiply by division.

FIG. 112. — Part of the Network of Developing Blood Vessels in the Vascular Area of a
Guinea-pig, bl, Blood corpuscles becoming free in an enlarged and hollowed-out part of
the network; a, process of protoplasm. (E. A. Schafer.)

When, in the progress of embryonic development, the liver is formed,
the multiplication of blood-cells in the whole mass of blood ceases, and new
blood-cells are produced by this organ, and also by the spleen. These are
at first colorless and nucleated, but afterward acquire the ordinary blood
tinge, and resemble very much those of the first set. They also multiply by
division. The bone marrow also begins to form red corpuscles, though at
first in small amounts only. This function develops rapidly, however, so
that at birth the marrow represents the chief seat of production of the red
cells. Nevertheless, nucleated red cells are usually found at birth, sometimes
in considerable quantities in the liver and in the spleen. Non-nucleated
red cells begin to appear soon after the first month of fetal life, and gradually
increase so that at the fourth month they form one-fourth of the whole amount
of colored corpuscles. At the end of fetal life they almost completely re-
place the nucleated cells. In late fetal life the red cells are formed in almost
the same way as in extra-uterine life.

Various theories have prevailed as to the mode of origin of the non-

THE COLORLESS CORPUSCLES OR LEUCOCYTES 1 29

nucleated colored corpuscles. For a time it was thought that they were of
endoglobular origin, and merely fragments of some original cell, being pro-
duced by subdivision of the cell body itself. This theory easily accounted
for the absence of the nuclei, but it has not been supported by recent investi-
gations. At present it is the general belief that the non-nucleated cells, or

FIG. 113. FIG. 114.

FIG. 113. — Multiplication of the Nucleated Red Corpuscles. Marrow of young
kitten after bleeding, showing above karyokinetic division of erythroblast, and below the
formation of mature from immature erythrocytes. (Howell.)

FiG. 114. — Shows the Way in which the Nucleus Escapes from the Nucleated Red
Corpuscles, i, 2, 3, 4, represent different stages of the extrusion noticed upon the living
corpuscles, a, Specimen from the circulating blood of an adult cat, bled four times; b,
specimen from the circulating blood of a kitten forty days old, bled twice; c, specimens
from the blood of a fetal cat, 9 cm. long. Others from the marrow of an adult cat, two of
the figures showing the granules present in the corpuscles, which have been interpreted
erroneously as a sign of the disintegration of the nucleus. (Howell.)

erythrocytes, are derived from nucleated cells by a process of mitotic division,
and further that their nuclei gradually shrink or fade and are then extruded.
The use of some of the more recent stains seems to prove that there are traces
of nuclear material in the non-nucleated corpuscles.

After infancy and early childhood the origin of erythrocytes is practically
limited to the red marrow of the bones. The mother cells, or erythroblasts,

FIG. 115. — Colored Nucleated Corpuscles, from the Red Marrow of the Guinea-pig.

(E. A. Schafer.)

are constantly forming and setting free erythrocytes, the rate varying greatly
at different periods.

The Colorless Corpuscles or Leucocytes. — In human blood the
white corpuscles, leucocytes, are nearly spherical masses of granular proto-
plasm without cell wall. In all cases one or more nuclei exist in each
9

130 THE BLOOD

corpuscle. The corpuscles vary considerably in size, but average lo/u in
diameter.

The number of leucocytes in a cubic millimeter of blood is estimated
at 7,500 to 8,000. The proportion of white corpuscles to red, therefore, is
about one of the former to 700 of the latter. This proportion is not very
constant in health and great variations occur under the influence of disease,
especially in certain infectious diseases in which the number of white cor-
puscles is markedly increased.

After a full meal the white cells in a healthy adult are increased in number
about one-third, the increase beginning within an hour, attaining a maxi-
mum in three or four hours, and then gradually falling to normal. This
process is frequently modified by the character of the food, the greatest
increase occurring with an exclusively meat diet, while a purely vegetarian
diet has usually no effect. The increase is also more marked in children,
and especially in infants. The essential factor is probably the absorption
of albuminous matter in considerable quantities. This causes proliferation
of leucocytes in the adenoid tissue of the gastro-intestinal tract.

In pregnancy there is often a moderate increase in the number of white
cells during the later months. This does not begin until after the third
month, and is most marked and constant in primiparae. After parturition
the leucocytes gradually diminish under normal conditions, and usually
reach the normal within a fortnight. The essential factor is probably the
general stimulation in the maternal organism. It is well established that the
white cells are very numerous in the new-born, though different observers
have made very conflicting estimates. Still all agree that there is a very
rapid decrease in their numbers during the first few days, and that this is
followed by a less marked increase, which continues for many months.
According to Rieder, who is perhaps the most reliable, there are at birth
from 14,200 to 27,400 per cubic millimeter, and after the fourth day from
12,400 to 14,800.

Varieties of Leucocytes. — The colorless corpuscles present greater diver-
sities of form than the red ones, Plate II. They are usually classified ac-
cording to their reaction to staining agents or to the presence or absence of
granules in their cytoplasm. Kanthack and Hardy offer the following classi-
fication, based upon both phenomena:

Leucocytes.

A. Oxyphile (staining with acid dyes) . . . . \ *' Finely granular.

( 2. Coarsely granular eosmophile

B. Basophile (staining with basic dyes) ... i. Finely granular.

f i. Small lymphocyte.

C. Hyaline 4

( 2. Large myelocyte.

The finely granular oxyphile constitutes 75 per cent, of all leucocytes.
It has an average diameter of 10/1, and possesses phagocytic action to a

THE COLORLESS CORPUSCLES OR LEUCOCYTES 131

marked degree; that is, it possesses the power of ingesting foreign particles.
Its nucleus consists of several lobes united by threads of chromatin. This
cell \vas formerly known under the term neutrophile, because of its supposed
reaction to neutral dyes.

The coarsely granular form of eosinophile constitutes only 2 per cent, of
the leucocytes. It has a diameter of 12 jj. and a reniform nucleus.

The basophile cell is rarely found in normal blood. It may occur occa-
sionally during periods of digestion. It is a small, spherical cell, with an
irregular nucleus and a diameter of 7,«.

The small hyaline leucocyte is also called a lymphocyte, because of the
large numbers found in adenoid tissue, and is supposed to be an immature
form. The nucleus is proportionally large and is surrounded by but little

e'

•'•X f

*•»£

FIG. 116. — (a) Red blood corpuscle for comparison; (6) small hyaline cell or lym-
phocyte; (c) large hyaline cell or myelocyte; (d) fine granular oxyphile; (e) coarse granular
oxyphile or eosinophile; (/) basophile. (F. C. Busch.)

protoplasm in which no granules can be detected. The cell is about the
size of a red blood-cell and constitutes from 10 to 20 per cent, of all leucocytes.

The large hyaline or myelocyte varies in diameter from 8.5 to IO/JL. Its
nucleus is spherical or reniform, and is surrounded by more protoplasm than
in the case of the lymphocyte. It forms about 10 per cent, of the leucocytes.

Ameboid Movement of Leucocytes. — The remarkable property of the color-
less corpuscles of spontaneously changing their shape was first demonstrated
by Wharton Jones in the blood of the skate. If a drop of blood be examined
with a high power of the microscope, under conditions by which loss of moist-
ure is prevented, and at the same time the temperature is maintained at
about that of the body, 37° C., the colorless corpuscles will be observed
slowly to alter their shapes, and to send out processes at various parts of their

132

THE BLOOD

circumference. The ameboid movement which can be demonstrated in
human colorless blood corpuscles can be most conveniently studied in the
newt's blood. Processes are sent out from the corpuscle. These may be
withdrawn, but more often the protoplasm of the whole corpuscle flows
gradually forward to the position occupied by the process, thus the corpuscle
changes its position. The change of position of the corpuscle can also take
place by a flowing movement of the whole mass, and in this case the loco-
motion is comparatively rapid. The activity both in the processes of change

FIG. 117. — Human Colorless Blood Corpuscle, showing its successive changes of outline
within ten minutes when kept moist on a warm stage. (Schofield.)

of shape and also of change in position is much more marked in some cor-
puscles than in others. Klein states that in the newt's blood the changes
are especially noticeable in a variety of the colorless corpuscle, wrhich consists
of a mass of finely granular protoplasm with jagged outline and contains
three or four nuclei, or in large irregular masses of protoplasm containing
from five to twenty nuclei.

The property which the colorless corpuscles possess of passing through
the walls of the blood vessels will be described later on.

FIG. 118. — Blood Plates, showing chromatic centers regarded by some as nuclei, and ex-
hibiting ameboid movement. (Schafer^ from Kopsch.)

The Blood Plates or Thrombocytes. — A third variety of corpuscle
found in the blood is known as the blood plates. They are circular or elliptical
in shape, of nearly homogeneous structure, and vary in size from 0.5 to 5^.
Hence they are smaller than the red corpuscles. They vary in number from
5,000 to 45,000 per cubic millimeter and are preserved by drawing fresh
blood directly into Hayem's or other preserving fluid. Chemically, they

CHEMICAL COMPOSITION OF THE BLOOD 133

contain a nucleo-protein, and it is supposed that they take part in the phe-
nomenon of coagulation. According to Deetjen and others, ameboid move-
ment has been demonstrated in these bodies.

CHEMICAL COMPOSITION OF THE BLOOD.

In considering the chemical composition of the blood, it will be convenient
to take in order the composition of the various chief factors into which the
blood may be separated, viz., The Plasma; The Serum; The White Corpuscles;
The Red Corpuscles.

The Composition of the Plasma. — The plasma is the liquid part
of the blood in which the corpuscles float.

It contains the fibrin factors, inasmuch as when drawn from the blood
vessels it undergoes coagulation and separates into fibrin and serum. It
differs from the serum in containing fibrinogen, but in appearance and in
reaction it closely resembles that fluid. Its alkalinity, however, is greater
than that of the serum obtained from it. It may be freed from corpuscles
by the centrifugal machine or by the other means enumerated below.

The chief methods of obtaining plasma free from corpuscles are: i. By
cold. The temperature should be about o° C. and may be two or three degrees
higher, but not lower. 2. The addition of neutral salts, in certain proportion,
either as solids or in solution; e. g., of sodium sulphate, if solid i part to 12 parts
of blood; if a saturated solution i part to 6 parts of blood. Or magnesium
sulphate, saturated solution i part to 4 of blood. 3. By mixing frog's blood
with an equal part of a 5 per cent, solution of cane-sugar, and getting rid of the
corpuscles by filtration. 4. By the injection of commercial peptone into the
veins of certain mammals previous to bleeding them to death, allowing the
corpuscles to subside or by subjecting the blood to the action of a centrifugal
machine by the rapid rotation of which the whole of the solids are driven to the
outer end of the tubes in which the blood is placed.

PERCENTAGE COMPOSITION OF PLASMA.

Water 90.29

Solids—

1. Proteins —
Fibrinogen ^

Paraglobulin > 8 . 289

Serum albumin J

2. Extractives o. 566

3. Inorganic salts 0.850

9.71

100 .00

Water. — The water of the plasma varies in amount according to the
amount of food, drink, and exercise or other circumstances. It amounts
to about 90 per cent.

134 THE BLOOD

Proteins. — Fibrinogen is the substance in plasma which is converted into
fibrin on coagulation. It belongs to the class of proteins called globulins.
It is precipitated from plasma with serum globulin by saturation with MgSO4
and NaCl. It is soluble in dilute salt solutions, but is not soluble in water.
It can be distinguished from serum globulin by a number of special reactions:
i. Its coagulation temperature is lower, 55° to 56° C. 2. It is completely
precipitated by saturation with NaCl as well as with MgSO4. 3. It gives
rise to an insoluble protein, fibrin. It may be, however, that fibrinogen is
not a simple protein, but a mixture or loose chemical combination of two
or more proteins. Fibrinogen is present in plasma to the extent of 0.2 to
o . 5 per cent.

Serum globulin or paraglobulin is completely precipitated by MgSO4; in-
completely by NaCl, and coagulates at a temperature of 75° C. It is like-
wise soluble in dilute salt solutions, but insoluble in water. It is present in
plasma in from 3 . 5 to 4 per cent.

Serum albumin is the protein which predominates in human plasma.
It is readily obtained in crystalline form; is soluble in MgSO4 and NaCl
solutions, but insoluble in saturated ammonium sulphate solutions; and
coagulates in neutral or acid solutions at from 73° to 75° C.

Extractives. — The extractives are the nitrogen-containing substances,
such as urea, uric acid, creatin, creatinin, etc.; glycogen, dextrose, choles-
terin, etc., a total of 0.5 to 0.6 per cent. The dextrose content amounts
to from o.i to o . 15 per cent.

Ferments are also found in blood; first, a diastatic ferment converting
amyloids into sugars; second, a glycolytic ferment causing a disappearance
of sugar; third, a fat- splitting ferment, lipase; and fourth, fibrin ferment
(thrombin), or its precursor, prothrombin.

Inorganic Substances. — The blood plasma contains about 0.85 per cent,
of inorganic salts distributed as follows, the sodium chloride predominating:

Parts in 1000 of Plasma.

Chlorine 3-536

Sulphuric acid 0.129

Phosphoric acid 0.145

Potassium 0.314

Sodium 3-410

Phosphate of lime 0.298

Phosphate of magnesia 0.218

Oxygen 0.455

8-505

The Serum. — The serum is the liquid part of the blood or of the
plasma which remains after the fibrin has been formed and removed. It is
a transparent, yellowish, faintly alkaline fluid, with a specific gravity of
from 1025 to 1032. Serum may be obtained from blood corpuscles by allow-

THE COMPOSITION OF THE RED CORPUSCLES 135

ing blood to clot in large test-tubes or by subjecting test-tubes of whipped
blood to the action of a centrifugal machine for some time. Serum is chemi-
cally very much the same as plasma except that it has lost the fibrinogen in
the process of clotting and has gained the by-products of that process — throm-
bin, thrombokinase, and fibrin-globulin. The salts of serum are practically
those of plasma.

The Composition of the White Corpuscles. — The white corpuscles
are comparatively undifferentiated cellular elements, hence possess the
chemical composition of protoplasm. Lillienfeld has made an analysis
of the leucocytes of thymus gland from the calf, which contain 1 1 . 49 per
cent, of solids, as follows:

In 100 Parts of Dry Substance of Corpuscles of Calf.

Per cent.

Protein 1.76

Leuconuclein 68 . 78

Histon 8.76

Lecithin 7.51

Fat 4.02

Cholesterin 4-4°

Glycogen 0.80

96.03

The most noteworthy substance in this table is the nucleohiston content,
first isolated by Kossel and Lillienfeld. Beside the substances in the above
table, the white corpuscles contain salts of potassium, sodium, calcium, and
magnesium. The potassium phosphate is present in greatest amount.

The Composition of the Red Corpuscles. — Analysis of moist blood
corpuscles shows the following results:

Water 68.8 per cent.

Solids-
Organic 30. 388 \

Mineral 0.812 / 3

100. o

Of the solids the most important is the respiratory pigment, hemoglobin,
the substance to which the blood owes its color. It constitutes, as will be
seen from the appended table, more than 90 per cent, of the organic matter
of the corpuscles. Besides hemoglobin the corpuscles contain protein and
fatty matters, the former chiefly consisting of globulins, and the latter of cho-
lesterol and lecithin.

In 100 parts of organic matter are found:

Hemoglobin 90 . 54 per cent.

Proteins 8.67 per cent.

Fats 0.79 per cent.

136 THE BLOOD

Of the inorganic salts of the corpuscles, the iron omitted, there are present,
in 100 parts of corpuscles (Schmidt):

Potassium chloride 0.3679 per cent.

Potassium phosphate o . 2343 per cent.

Potassium sulphate 0.0132 per cent.

Sodium phosphate 0.0633 Per cent.

Calcium phosphate 0.0094 per cent.

Magnesium phosphate o .0060 per cent.

Soda 0.0341 per cent.

0.7282

Hemoglobin. — Of the substances in the erythrocytes, by far the most
important from every point of view is the pigment, hemoglobin. It composes
about 90 per cent, of the total solids of the corpuscles; therefore, between
14 and 15 per cent, of the blood itself. Hemoglobin is the most complex
compound in the body, having a molecule of the enormous molecular weight
of 16,669. Hemoglobin is intimately distributed throughout the stroma of
the corpuscle, and when dissolved out it can be crystallized.

Its percentage composition is €,53.85; H, 7.32; N, 16.17; O> 21.84; $,0.63
Fe o . 42. Jacquet gives the empirical formula for the hemoglobin of the dog,
C758H1205N195S3FeO218. The most interesting of the properties of hemo-
globin are its powers of crystallizing and its attraction for oxygen and other
gases under certain pressure relations.

Hemoglobin Crystals. — The hemoglobin (oxyhemoglobin) of the blood of
various animals possesses the powrer of crystallizing to very different ex-
tents. In some the formation of crystals is almost spontaneous, whereas
in others it takes place either with great difficulty or not at all. Among
the animals whose blood coloring- matter crystallizes most readily are the
guinea-pig, rat, squirrel, and dog; and in these cases to obtain crystals it
is generally sufficient to dilute a drop of recently drawn blood with water
and to expose it for a few minutes to the air. In many instances other means
must be adopted; e.g., the addition of alcohol, ether, or chloroform, rapid
freezing and then thawing, the application of an electric current, a tempera-
ture of 60° C., the addition of sodium sulphate, or the addition of decom-
posing serum of another animal.

The hemoglobin of human blood crystallizes with difficulty, as does also
that of the ox, the pig, the sheep, and the rabbit.

The forms of hemoglobin crystals, as will be seen from figures 119 and
120, differ greatly. Hemoglobin crystals are soluble in water. Both the
crystals themselves and also their solutions have the characteristic color of
arterial blood.

A dilute solution of oxyhemoglobin gives a characteristic appearance
with the spectroscope. Two absorption bands are seen between the solar

HEMOGLOBIN

137

lines D, which is the sodium band in the yellow, and E, see the frontispiece,
one in the yellow, with its middle line some little way to the right of D. This
band is very intense, but narrower than the other, which lies in the green
near to the left of E. Each band is darkest in the middle and fades away

FIG. 119. — Crystals of Oxyhemoglobin
— Prismatic, from Human Blood.

FIG. 120. — Oxyhemoglobin Crystals —
Tetrahedral, from Blood of the Guinea-pig.

at the sides. As the strength of the solution increases, the bands become
broader and deeper. Both the red and the blue ends of the spectrum be-
come encroached upon until the bands coalesce to form one very broad band
when only a slight amount of the green and part of the red remain unab-

FIG. 121. — Hexagonal Oxyhemoglobin Crystals, from Blood of Squirrel. On these
hexagonal plates prismatic crystals, grouped in a stellate manner, not unfrequently occur
(after Funke).

sorbed. Any further increase of strength leads to complete absorption of
the spectrum.

If crystals of hemoglobin are exposed to an atmosphere of oxygen they
take up oxgyen and form Oxyhemoglobin, each gram of the pigment fixing

138 THE BLOOD

a definite amount of oxygen, see chapter on Respiration. When subjected
to a mercurial air-pump the oxgyen is given off, and the crystals become
of a purple color. A solution of the oxyhemoglobin in the blood corpuscles
may be made to give up oxygen, and to change color in a similar manner.
One gram of oxyhemoglobin liberates 1.59 c.c. oxygen, or, according to Hiif-
ner's later determinations, i .34 c.c., see page 292.

This change may be also effected by passing through the solution of
blood or of oxyhemoglobin, hydrogen or nitrogen gas, or by the action of
reducing agents, of Stokes' s fluid* or ammonium sulphide are the most
convenient.

With the spectroscope, a solution of deoxidized or reduced hemoglobin
is found to give an entirely different appearance from that of oxidized hemo-
globin. Instead of the two bands at D and E, we find a single broader but
fainter band occupying a position midway between the two, and at the same
time less of the blue end of the spectrum is absorbed. Even in strong solu-
tions this latter appearance is found, thereby differing from the strong solu-
tion of oxidized hemoglobin which lets through only the red and orange
rays; accordingly, to the naked eye the one (reduced-hemoglobin solution)
appears purple, the other (oxyhemoglobin solution) red. The deoxidized
crystals or their solutions quickly absorb oxygen on exposure to the air,
becoming scarlet. If solutions of blood be taken instead of solutions of
hemoglobin, results similar to the whole of the foregoing can be obtained.

Venous blood never, except in the last stages of asphyxia, fails to show
the oxyhemoglobin bands, inasmuch as the greater part of the hemoglobin
even in venous blood exists in the more highly oxidized condition.

Action of Gases on Hemoglobin. — Carbonic-oxide gas passed through
a solution of hemoglobin causes it to assume a cherry-red color and to
present a slightly altered spectrum; two bands are still visible but are
slightly nearer the blue end than those of oxyhemoglobin, see Plate I. The
amount of carbonic oxide taken up is equal to the amount of the oxygen
displaced. Although the carbonic-oxide gas readily displaces oxygen, the
reverse is not the case, and upon this property depends the dangerous effect
of coal-gas poisioning. Coal gas contains much carbonic oxide, and, when
breathed, the gas combines with the hemoglobin of the blood and produces
a compound which cannot easily be reduced. This compound (carboxy-
hemoglobin) is not an oxygen carrier, and death may result from suffocation
due to the want of oxygen, notwithstanding the free entry of pure air into the
lungs. Crystals of carbonic-oxide hemoglobin closely resemble in form
those of oxyhemoglobin.

*Stokes's fluid consists of a solution of ferrous sulphate, to which ammonia has been
added and sufficient tartaric acid to prevent precipitation. Another reducing agent is a
solution of stannous chloride, treated in a way similar to the ferrous sulphate, and a third
reagent of like nature is an aqueous solution of yellow ammonium sulphide, NH4HS.

ESTIMATION OF HEMOGLOBIN 139

Nitric oxide produces a similar compound to the carbonic-oxide hemo-
globin, which is even less easily reduced.

Nitrous oxide reduces oxyhemoglobin, and therefore leaves the reduced
hemoglobin in a condition actively to take up oxygen.

Sulphuretted hydrogen, if passed through a solution of oxyhemoglobin,
reduces it and an additional band appears in the red. If the solution be
then shaken with air, the two bands of oxyhemoglobin replace that of reduced
hemoglobin, but the band in the red persists.

Methemoglobin. — If an aqueous solution of oxyhemoglobin is exposed
to the air for some time, its spectrum undergoes a change; the two d and

FIG. 122. — Fleischl's Hemoglobinometer.

e bands become faint and a new line in the red at C is developed. The
solution, too, becomes brown and acid in reaction, and is precipitable by
basic lead acetate. This change is due to the decomposition of oxyhemo-
globin, and to the production of methemoglobin. On adding ammonium
sulphide, reduced hemoglobin is produced, and on shaking this up with air,
oxyhemoglobin is again produced. Methemoglobin is probably a stage in
the deoxidation of oxyhemoglobin. It appears to contain less oxygen than
oxyhemoglobin, but more than reduced hemoglobin. Its oxygen is in more
stable combination, however, than is the case with the former compound.
Estimation of Hemoglobin. — The most exact method is by the esti-
mation of the amount of iron (dry hemoglobin containing 0.42 per cent,
of iron) in a given specimen of blood, but as this is a somewhat complicated
process, various methods have been proposed which, though not so exact,
have the advantage of simplicity. Of the several varieties of hemoglobinom-
eter, one of the best adapted to its purpose is that invented by Professor

140 THE BLOOD

Fleischl, of Vienna. In this instrument the amount of hemoglobin in a
solution of blood is estimated by comparing a stratum of diluted blood with
a standard solid substance of uniform tint similar spectroscopically to diluted
blood. The Fleischl instrument has been somewhat modified and made
more accurate by Miescher. The Fleischl-Miescher apparatus consists of a
stand with a metal plate having a circular opening and a plaster mirror below,
S, figure 122, which casts light through the opening. Beneath the plate is a
metal framework containing a colored glass wedge, and along the side of
the same is a scale graduated so as to indicate the percentage of hemoglobin
corresponding to the shades of the different parts of the wedge. This frame-
work can be moved by the wheel T which fits into a rack on its lower surface.
The scale can be read through a small opening M in the plate. Into the
large circular opening of the plate fits a cylindrical metal cell G with a glass
bottom and divided by a metal partition into two equal parts. One of these
halves lies over the wedge and is filled with distilled water. The other con-
tains the solution of blood in which the hemoglobin is to be estimated. The
apparatus is usually supplied with three cells. Of these, the first two are
used in estimating the hemoglobin according to Miescher' s modification
of Fleischl' s original method. This is the method now generally used.
These cells are furnished with a glass cover having a groove \vhich fits
upon the partition of the cell. Over this cover is placed a diaphragm
wTith a longitudinal slit, which only permits of the central part of each side
of the cell being seen. The third cell is for use when the original Fleischl
method is employed.

The patient's ear or finger is pricked, and the blood from the wound
sucked up into the graduated pipet until it reaches the mark J, f , or -f, a
i per cent, solution of sodium carbonate is then sucked in until the upper
mark is reached. The pipet is then well shaken in order to mix the blood
thoroughly. One-half of each of the two cells, which are, respectively, 12
and 15 millimeters high, is then filled with the mixture, the other half
being filled with water. An important point is that the liquids should com-
pletely fill the cells. The cover-glasses and diaphragms are then applied
and the cells are ready for examination. This must be done by artificial
light. Moreover, in order to have accurate results, light of the same inten-
sity should be always used. One of the cells is placed on the plate and the
wheel T turned until the colors of the two halves exactly correspond. When
this point is reached, the result is read off on the scale through the opening
M. This should be repeated several times with each of the cells, and the
average of the readings taken. The result obtained with the 1 2-millimeter
cell should be multiplied by f to bring it up to that of the larger. For example,
suppose the result of several readings to be:

With the large cell (15 mm.) 54 . oo

With the small cell (12 mm.) 42 .00

DERIVATIVES OF HEMOGLOBIN 141

If the readings obtained with the large cell are exactly correct, then the read-
ings with the smaller one should be 43.2, since 54 X | =43- 2- Or, if the
readings with the smaller cells are exact, the readings with the larger should
be 52 . 5, since 42 Xf = 52 . 5. Hence the mean of 54 and 52 . 5, namely 53 . 25,
should be taken as the correct figure. On looking at the corrected table of
hemoglobin values supplied with each instrument, we would find that this
number on the scale corresponds to a solution containing 400 milligrams
of hemoglobin per 1000 cubic centimeters of solution. But our original dilu-
tion was either i: 200, i: 300, or o: 400, according as our pipet had been
filled with blood up to the mark |, f , or J; so that in order to obtain the actual
percentage of hemoglobin in the blood under examination we should be
obliged to multiply our results by 200, 300, or 400. In the example we have
taken, the amount of hemoglobin would be, if our dilution was i : 200, 400 X
200=80,000 milligrams = 80 grams in 1,000 cubic centimeters =8 grams
in 100 cubic centimeters, or 8 per cent.

Another very simple method of approximately determining the hemo-
globin percentage is the hemoglobin scale devised by T. W. Talquist. This
consists of a series of shades of color corresponding to undiluted blood of
various hemoglobin values, ranging from 10 to 100 per cent, of an
arbitrary scale. This scale is included in a book, the remaining pages of
which consist of filter-paper, which is used for absorbing the specimen of
blood whose hemoglobin percentage is to be estimated. The blood-stained
filter-paper is compared with the hemoglobin scale by direct daylight until
a shade is found with which it corresponds. For approximate results this
method has proved very satisfactory.

Derivatives of Hemoglobin. — Hematin. — By the action of heat or
of acids or alkalies in the presence of oxygen, hemoglobin can be split up
into a substance called hematin, which contains all the iron of the hemo-
globin from which it was derived, and a protein residue, a histone, globin.
If there be no oxygen present, instead of hematin a body called hemochro-
mogen is produced, which, however, will speedily undergo oxidation into
hematin.

Hematin is a dark brownish or black non-crystallizable substance of
metallic luster. Its percentage composition is C, 64.30; H, 5.50; N, 9.06;
Fe, 8.82; O, 12.32; which gives the formula C68H70N8Fe2O10 (Hoppe-
Seyler). It is insoluble in water, alcohol, and ether; soluble in the caustic
alkalies; soluble with difficulty in hot alcohol to which is added sulphuric
acid. The iron may be removed from hematin by heating it with fuming
hydrochloric acid to 160° C., and a new body, hematoporphyrin, the so-called
iron-free hematin, is produced. Hematoporphyrin (C68H74N8O12, Hoppe-
Seyler) may also be obtained by adding blood to strong sulphuric acid, and
if necessary filtering the fluid through asbestos. It forms a fine crimson
solution, which has a distinct spectrum, viz., a dark band just beyond D,

142 THE BLOOD

and a second all but midway between D and E. It may be precipitated from
its acid solution by adding water or by neutralization, and when redissolved
in alkalies presents four bands, a pale band between C and D, a second
between D and E, nearer D, another nearer E, and a fourth occupying the
chief part of the space between b and F.

Hematin in Acid Solution. — If an excess of acetic acid is added to blood,
and the solution boiled, the color alters to brown from decomposition of
hemoglobin and the setting free of hematin; by shaking this solution with
ether, a solution of hematin in acid solution is obtained. The spectrum of
the ethereal solution shows no less than four absorption bands, viz., one in
the red between C and D, one faint and narrow close to D, and then two
broader bands, one between D and E, and another nearly midway between
b and F. The first band is by far the most distinct, and the acid aqueous
solution of hematin shows it plainly.

Hematin in Alkaline Solution. — If a caustic alkali is added to blood and
the solution is boiled, alkaline hematin is produced, and the solution becomes
olive-green in color. The absorption band of the new compound is in the
red, near to D, and the blue end of the spectrum is absorbed to a considerable

ife*.

FIG. 123. — Hematoidin Crystals. (Frey.) Fig. i23a. — Hemin Crystals. (Frey.)

extent. If a reducing agent be added, two bands resembling those of oxy-
hemoglobin, but nearer to the blue, appear; this is the spectrum of reduced
hematin, or hemochromogen. On violently shaking the reduced hematin
with air or oxygen the two bands are replaced by the single band of alkaline
hematin.

Hematoidin. — This substance is found in the form of yellowish crystals,
figure 123, in old blood extravasations and is derived from the hemoglobin.
Their crystalline form and the reaction they give with fuming nitric acid
seem to show them to be closely allied to bilirubin, the chief coloring matter
of the bile, and in composition they are probably either identical or isomeric
with it.

Hemin. — One of the most important derivatives of hematin is hemin.
It is usually called hydrochloride of hematin, but its exact chemical com-
position is uncertain. Its formula is said to be C32H30N4FeO3HCl, and it
contains 5.18 per cent, of chlorine, but by some it is looked upon as simply

VARIATIONS IN THE COMPOSITION OF HEALTHY BLOOD 143

crystallized hematin. Although difficult to obtain in bulk, a specimen may
be easily made for the microscope in the following way: A small drop of
dried blood is finely powdered with a few crystals of common salt on a glass
slide and spread out; a cover- glass is then placed upon it, and glacial acetic
acid added by means of a capillary pipet. The blood at once turns a brown-
ish color. The slide is then heated, and the acid mixture evaporated to
dryness at a high temperature. The excess of salt is washed away with
water from the dried residue, and the specimen may then be dried and
mounted. A large number of small, dark, reddish-black crystals of a rhom-
bic shape, sometimes arranged in bundles, will be seen if the slide be sub-
jected to microscopic examination, figure i23a.

The formation of these hemin crystals is of great interest and importance
from a medico-legal point of view, as it constitutes the most certain and
delicate test we have for the presence of blood (not of necessity the blood
of man) in a stain on clothes, etc. It exceeds in delicacy even the spectro-
scopic test. Compounds similar in composition to hemin, but containing
hydrobromic or hydriodic acid, instead of hydrochloric, may be also readily
obtained.

Hernog
on heatii
acidulatec

Globin

ig with /\ on heating with on treating with s
I alcohol / N. acidulated alcohol potassium ferri-
\/ ^v /\ cyanide, etc.
^ N. / \
/ X / \

Hemochromogen Hematin Globin

with strong / \ heat with
sulphuric and / \ glacial acetic
hydrobromic acids / \ acid and sodium
/ \chloride
/ *
Hematoporphyrin Hemin
(Iron-free hematin, (Hematin hydrochloride)
isomeric or identical
with bilirubin.)

on reduction, with Stoke's reagent, etc.

Scheme to Show the Relations of Hemoglobin .and its Derivatives.

Variations in the Composition of Healthy Blood. — The conditions
which appear most to influence the composition of the blood in health are
these: Diet, Exercise, Sex, Pregnancy, and Age.

Sex. — The blood of men differs from that of women, chiefly in being of
somewhat higher specific gravity, from its containing a relatively larger
quantity of red corpuscles.

Pregnancy. — The blood of pregnant women has rather lower than the
average specific gravity. The quantity of the colorless corpuscles is in-
creased in the later months, especially in primiparse; it is also claimed that
the fibrin is increased in amount.

Age. — The blood of the fetus is very rich in solid matter, and especially
in colored corpuscles; and this condition, gradually diminishing, continues

144 THE BLOOD

for some weeks after birth. The quantity of solid matter then falls during
childhood below the average, rises during adult life, and in old age falls again.

Diet. — Such differences in the composition of the blood as are due to the
temporary presence of various matters absorbed with the food and drink,
as well as the more lasting changes which must result from generous or poor
diet, respectively, need be here only referred to.

Effects of Bleeding. — The result of bleeding is to diminish the specific
gravity of the blood, and so quickly that in a single venesection the portion
of blood last drawn has often a less specific gravity than that of the blood that
flowed first. This is, of course, due to absorption of fluid from the tissues
of the body. The physiological import of this fact, namely, the instant
absorption of liquid from the tissues, is the same as that of the intense thirst
which is so common after either loss of blood or the abstraction from it of
watery fluid, as in cholera, diabetes, and the like.

For some little time after bleeding, the want of colored corpuscles is well
marked, but with this exception no considerable alteration seems to be
produced in the composition of the blood for more than a very short time;
the loss of the other constituents, including the colorless corpuscles, being
very quickly repaired.

Variations in Different Parts of the Body. — The composition of the blood,
as might be expected, is found to vary in different parts of the body. Thus
arterial blood differs from venous; and although its composition and general
characters are uniform throughout the whole course of the systemic arteries,
they are not so throughout the venous system, the blood contained in some
veins differing markedly from that in others.

Differences between Arterial and Venous Blood. — The differences between
arterial and venous blood are these:

Arterial blood is bright red, from the fact that almost all its hemoglobin
is combined with oxygen, oxyhemoglobin, while the purple tint of venous
blood is due to the deoxidation of a certain quantity of its oxyhemoglobin,
and its consequent reduction to the hemoglobin.

Arterial blood coagulates somewhat more quickly.

Arterial blood contains more oxygen than venous and less carbon
dioxide gas.

Some of the veins contain blood which differs from the ordinary standard
considerably. These are the Portal, the Hepatic, and the Splenic veins.

Portal Blood. — The blood which the portal vein conveys to the liver is
supplied from two chief sources; namely, from the gastric and mesenteric
veins, which contain the soluble elements of food absorbed from the stomach
and intestines during digestion, and from the splenic vein. It must, there-
fore, combine the qualities of the blood from each of these sources.

The blood in the gastric and mesenteric veins will vary much according
to the stage of digestion and the nature of the food taken, and can therefore

GLOBULOCIDAL AND OTHER PROPERTIES OF SERUM 145

be seldom exactly the same. Speaking generally and without considering
the sugar and other soluble matters which may have been absorbed from
the alimentary canal, this blood appears to be deficient in solid matters,
especially in colored corpuscles, owing to dilution by the quantity of water
absorbed, to contain an excess of protein matter, and to yield a less tenacious
kind of fibrin than that of blood generally.

The blood of the portal vein, combining the peculiarities of its two factors
the splenic and mesenteric venous blood, is usually of lower specific gravity
than blood generally, is more watery, contains fewer colored corpuscles,
more proteins, and yields a less firm clot than that yielded by other blood,
owing to the deficient tenacity of its fibrin.

Guarding (by ligature of the portal vein) against the possibility of an
error in the analysis from regurgitation of hepatic blood into the portal vein,
recent observers have determined that hepatic venous blood contains less
water, proteins, and salts than the blood of the portal veins; but that it yields
a much larger amount of extractive matter, in which is one constant element,
namely, grape-sugar, which is found whether saccharine or farinaceous
matter has been present in the food or not.

GLOBULOCIDAL AND OTHER PROPERTIES OF SERUM.

Cytolysis. — It has been known for some time that the sera of certain
animals when injected into the circulation of animals of another species will
cause destructive changes in the blood corpuscles, accompanied by symptoms
of poisoning, which may even end fatally. These results served to bring into
disrepute the use of foreign blood in transfusion, which has consequently
been practically abandoned. This discharge of the hemoglobin of the red
blood corpuscles and solution in the plasma (laking) is now included in the
general term Cytolysis, and more specifically known as Hemolysis. Agents
which produce such an effect are known as hemolytic or hemotoxic agents.
Sera of one species are not hemolytic for blood of all other species, but the
serum of one animal made be made to acquire such properties for the blood
of another.

This adaption is brought about in the following way: For instance,
the blood of the guinea-pig, which is not normally lytic for the red cells of the
rabbit, may be adapted to the latter by previously, at several successive
intervals (three to seven days) injecting into the abdominal cavity or sub-
cutaneous tissues of the guinea-pig small quantities of rabbit's blood. If
now a small quantity of serum be obtained from the guinea-pig by the usual
methods and mixed in a test-tube with some of the rabbit's blood diluted
with physiological salt solution, hemolysis occurs; that is, the coloring
matter of the rabbit's red blood-cells goes into solution and the cells appear
under the microscope as shadow corpuscles or ghosts, devoid of hemoglobin.

146 THE BLOOD

Such an artificially produced hemolytic serum is only lytic for the blood of
the animal species for which it has been adapted. It is true that it may also
show slightly lytic properties for closely allied species. It has therefore been
suggested as a possible valuable aid in determining relationships of various
animal species.

Concerning the nature of the lytic substance, it has been found that it
probably consists of two bodies acting conjointly, for if the serum be heated
to 56° C. for a short time, its lytic powers are lost, but may be restored by
adding a little serum of another animal of the same species which has not
been adapted, and whose serum is consequently not in itself lytic. Of these
two bodies, therefore, one is stable and is formed only in the adapted serum,
while the other is more unstable or labile (destroyed at 56° C.) and exists
normally in the blood plasma. The former is known as the immune body
and the latter as alexin. Lysis occurs only when both are present at the same
time, and not through the agency of one or the other singly.

This cytolytic adaptation has been extended to include other cells besides
the red blood corpuscles. Thus in a similar manner leucolytic, hepatolytic,
nephrolytic, and a number of other lytic sera have been developed.

It is further possible, under certain circumstances, that substances may
be developed in the tissues which are lytic for other tissue cells of the same
animal, autolytic substances. This may be an important physiological proc-
ess in the elimination of worn-out tissue cells, cellular elements in injury,
inflammation, etc.

Agglutinative Substances. — A further property of adapted sera is
that of agglutination. The adaptation is secured in the same way as in
the production of cytolysins. In fact, both cytolysis and agglutination may
occur at the same time. The normal blood serum of some animals may
be agglutinative for the blood-cells of some other species. In normal serum,
agglutinative and cytolytic properties may be present together or one only
may be normally present.

The activity of agglutinative substances is not destroyed at a tempera-
ture of 56° C. They do become inert, however, at 70° C., and, furthermore,
they cannot be restored by adding normal serum, as is the case with cytolysins.

Hemagglutinative substances are found in certain plant seeds; e.g., in
castor oil beans (Ricinus communis), in cotton seed, and in the common
legumes.

Precipitins. — Other forms of adaptive substances which may be found
in animal serum are those which, when mixed with the substances by means
of which adaptation has been secured, form a precipitate. By this means
blood of different species of animals may be detected even when in a dried
state. It has been suggested as a possible valuable aid in medico-legal
cases, since human blood in a dilution of i to 50,000 has been recognized
by this means.

NATURE OF THE ANTISUBSTANCES IN BLOOD 147

Opsonins. — Wright and Douglass have shown that there are certain
substances in the serum that affect bacteria in such a way that they are more
easily taken up and destroyed by leucocytes. The phagocytic power of the
leucocytes in destroying toxic bacteria is not made to increase by stimulative
substances, as Metchknikoff believed, but rather by those materials in the
serum diminishing the resisting power of the bacteria. These substances
are called by their discoverers opsonins. They found opsonin present in
normal serum, but also found that its quantity varies under certain conditions.
They suggested that the opsonins could be measured by determining the
phagocytic power. The ratio of the average number of bacteria taken up by
leucocytes in normal serum to the number taken up in the immune serum,
they called the opsonic index.

Antitoxins. — Certain kinds of bacteria, notably the diphtheria and
tetanus organisms, elaborate poisonous substances known as toxins. The
pathological conditions resulting from such infections are produced by the
poisons so formed. Behring first showed that immunity to diphtheria was
due to the presence in the blood plasma and blood serum of substances which
apparently combine with and so prevent the toxic action of the bacterial
products. This antitoxic power of the blood can be artificially developed by
injecting small doses of the toxins into an animal, usually a horse, at inter-
vals of some days. The protective power of the blood against the toxins can
thus be developed to a relatively enormous degree. The serum of an arti-
ficially immunized animal can be injected into other individuals of the same
or other species and an immunity will be conferred on the person or animal
so treated. Similarly, the antitoxic sera have a curative effect in infected
individuals if the disease is not too far advanced. Antitoxic sera are specific
for the particular toxin used for the immunization. Antitoxins can be
similarly prepared for the naturally occurring vegetable toxins, ricin and
abrin, for snake venoms, etc.

Anaphylaxis. — It has been found that if an animal, especially the
guinea pig, be injected with even the minutest quantity of protein material,
that after ten to fourteen days, the animal becomes susceptible to a sec-
ond injection of the same material if made intravascularly. Thus a guinea
pig may be sensitized with o.oooooi of a c.c. of blood serum; after two
weeks have elapsed, the introduction of a half c.c. of the same serum into
the circulation will in a few minutes lead to respiratory failure and death.
This phenomenon is relatively specific for foreign protein substances.
Guinea-pigs which have recovered from the second injection acquire a
temporary immunity against a third injection of the same protein. It has
been found that this peculiar susceptibility is transferred from the mother
guinea-pig to successive litters.

Nature of the Antisubstances in Blood. — The lecithins and fatty acids,
especially oleic acid, will in a measure replace a hemolytic complement.

148

THE BLOOD

The antitoxins and agglutinins in the blood seem either to be associated
with, or actually are a portion of, the para- or pseudoglobulin. During im-
munization, the pseudoglobulin of the blood may be twice the normal con-
tent; coincidently the per cent, of the serumalbumin will diminish. The
protein changes in the blood of horses and the antitoxic variations, how-
ever, are not parallel, and no quantitative relationship has been established.

PHYSICAL FACTORS OF BLOOD PLASMA OR SERUM.

Diffusion, Osmosis, Dialysis. — The term diffusion has long been ap-
plied to the regular mixing of the molecules of two gases when brought
into contact in a confined space, this interpenetration being due to the
to-and-fro movements of their molecules. More recently it has been
applied to the mixing of the molecules of two solutions when brought into
contact, as it has been found that they act in the same way and obey the
same laws as gases. If, however, the two solutions are separated by a
membrane, permeable to the solutions, diffusion will still occur. To this
form of diffusion the term osmosis has been applied in the case of water,
and dialysis in the case of diffusible substances. All bodies can be
divided into two groups, crystalloids and colloids. To the former group
belong bodies having a crystalline form, which readily go into solution
in water. All such bodies are diffusible (dialyzable), their power of
dialysis, however, varying considerably. To the second group belong
such bodies as have no crystalline form (amorphous). These are generally
bodies with a large molecule, which form colloidal suspensions in water and
are only slightly or not at all diffusible. An exception
to this second group is hemoglobin, which has a very
large molecule, but is crystalline and is diffusible. \ — T

The following may serve as simple illustrations:

Take a jar and divide it in two equal parts by an
animal membrane, M, figure 124, and place an equal
amount of distilled water in the two sides, A and B.

FIG. 124.

FIG. 125.

ISOTONIC SOLUTIONS 149

Now, since the molecules of water act like those of a gas and are con-
tinually moving to and fro, bombarding all the surfaces of their retainer,
the molecules of water in A and B will be continually striking all the surfaces
of A and B; but since the membrane is permeable to the water molecules,
there will be a continual interchange of molecules between A and B. If now,
in one side A we place a solution of sodium chloride, still keeping water
in B, the membrane being permeable to the sodium chloride, the first thing
we should notice would be an increase in the amount of water in A. For-
merly it would have been said that " the salt had attracted the water." Now
we should say that the salt had a certain osmotic pressure. The salt, how-
ever, being able to pass (dialyse) through the membrane,, will do so, and this
will continue until the strength of the two salt solutions, and therefore the
osmotic pressure on both sides, is equal.

Osmotic Pressure. — If now in A we place a solution of some soluble
colloidal substance to which the membrane is impermeable, or else replace
the membrane, M, we used in our former experiment by one which is not
permeable to the sodium chloride, and arrange our jar as in figure 125, so
as to be able to read off any increase of water which may pass into A, \ve
will notice that the amount of liquid in A will continue to increase up to a
certain point. Once that point is reached, there will be no further change,
since the substance in solution, in A, cannot pass through the membrane as
in the previous example. This pressure can be measured and expressed in
millimeters of mercury. It is constant for all solutions of this substance
that are of the same concentration when measured under like conditions of
temperature and pressure, and is called the osmotic pressure of this solution.

Of the numerous explanations regarding the nature of osmotic pressure
which have been more or less satisfactory, a simple one, and one that can
be easily understood, is as follows: In figure 125 one surface of the mem-
brane is being bombarded by the molecules of a non-diffusible substance
mixed with those of a diffusible one (water) ; while the other surface is being
bombarded entirely by water molecules. The former condition permits
only a fraction of the molecules to diffuse out, since fewer water molecules
get to the surface of the membrane; while the latter permits all of the
molecules which reach it to pass through.

Osmotic pressure can be estimated in several different ways in addition
to the above, viz., the determination of the freezing-point of the solution,
determination of the boiling-point, determination of the electrical conduc-
tivity. The results obtained with the various methods agree very closely.
The following solutions have the same osmotic pressure: Sodium chloride,
i . 64 per cent. ; potassium nitrate, i . 09 per cent. ; sugar 5 . 5 per cent.

Isotonic Solutions. — Solutions that have the same osmotic pressure
are called isotonic. The term isotonic is a relative one, implying a compari-
son with some other solution taken as a standard. In physiology it has been

150 THE BLOOD

customary to take blood plasma as a standard. A solution of o . 64 per cent,
sodium chloride is isotonic for the blood plasma of the frog, and a 0.9 per
cent, solution for that of man. Further, any solution which is of a lower
osmotic pressure than the standard solution is said to be hypoisotonic (Jiypo-
tonic] in relation to that solution. A solution of a higher osmotic pressure
is said to be hyperisotonic (hypertonic).

Water passes in the Direction of the Arrows.
Hypertonic saline solution (2 per cent.)

t

Blood-plasma

_U

Isotonic saline solution (o . 64 per cent.)

I.

Hypotonic saline solution (°-3 Per cent.)

If a hypotonic solution be mixed with blood, water from the hypotonic
solution passes through the cell membrane of the red corpuscles into the
stroma and causes it to swell. The hemoglobin at the same time passes
out and goes into solution in the diluted plasma. On the other hand, the
addition of a hypertonic solution to the plasma causes the red corpuscles
to lose their water and become crenated. The principles of osmosis have
been derived from the action of substances separated by dead animal or
plant membranes. It must be, however, remembered that in the applica-
tion of these principles to processes occurring in the living organism, the
cells, forming the various membanes, are an important modifying factor.
It is probable that physico-chemical processes, occurring in the protoplasm
of the cell, may change its permeability to the same substance at different
times.

THE CHARACTER AND COMPOSITION OF LYMPH.

The lymph is the fluid which immediately surrounds the tissue cells of
the living body. It fills up the spaces between the cells themselves and
between the cells and the blood vessels which ramify among the cell masses.
The lymph, therefore, is an intermediate fluid between blood plasma on the
one hand and the tissue cells on the other, receiving its ingredients by the
passage of fluid from the plasma through the walls of the finer blood vessels
in the one direction and by the discharge of the substances from the cells
themselves in the other.

The Chemical Composition of the Lymph.— Since the chief source
of the lymph is the blood plasma, one would naturally expect that its chemi-
cal composition would be very similar to that of plasma, which is in fact the
case. The variations that are noted in lymph taken from definite sources no
doubt have their, origin in the fact that the lymph passes through these

ANALYSIS OF LYMPH 151

organs slowly, and that ingredients peculiar to the necessities of the func-
tion and growth of the differentiated tissue of the organ are taken from the
lymph in special organs. Lymph obtained from a human lymphatic fistula
has been analyzed; the figures from Hammarsten are as follows, though
considerable variations appear in the analyses from other authorities:

ANALYSIS OF LYMPH.

Per cent.

Water 94 . 5 to 96 . 5

Solids 3.7 to 5.5

Proteins 3.4 to 4.1

Ethereal extract o . 06 to 0.13

Sugar o.i

Salts 0.8 to 0.9

Sodium chloride o. 55 to o. 58

Sodium carbonate o . 24

Disodic phosphate 0.028

The most notable fact to be derived from this composition table is the
low percentage of proteins present in the lymph.

The Formation of Lymph. — The manner in which the substances in
the lymph pass through the walls of the capillaries from the plasma is a
question which has been surrounded with considerable difficulty. It was
thought by Ludwig and many of his followers that the process involved
is merely one of filtration. Certainly the blood pressure in the capillaries
is in the main greater than that of the pressure of the lymph in the surround-
ing tissues, and this positive pressure will contribute so much to the direct
ingredients of the blood plasma through the capillary walls. It is true, as a
matter of experiment, that anything which contributes to an increase in
the capillary pressure is very apt to produce an edema of the corresponding
tissues. Since the colloidal materials represented by the protein are non-
diffusible, one would by this theory expect to find a diminished percentage
in the lymph, which is true, though not to the extent which the theory
demands.

Heidenhain was the first to question the adequacy of the blood pres-
sure and filtration hypothesis. He showed that many of the conditions
under which lymph formation takes place are not sufficient to produce nitra-
tions of the material found. He advanced the hypothesis that the living
endothelial lining of the blood vessels exerted a secretory activity in lymph
production. He discovered that various substances known as lymphagogues
when introduced into the circulatory system produce a remarkable increase
in the flow of lymph from the thoracic duct. Further, he noticed that the
concentration of the lymph was changed; i.e., increased. Heidenhain
thought that the lymphagogues acted directly on the capillary and endothelial

152 THE BLOOD

lining stimulating these cells to produce a greater quantity of lymph. He
divided such substances into two classes. The best known representatives
of the "first class" are such as proteoses and peptones, leech extract, ex-
tract of crustacean tissue, etc. The lymphagogues of the second class are
the neutral inorganic salts, sugars, and other crystalline substances. These
all cause a marked flow of lymph. The lymphagogues as a class cause fall
of blood pressure; for example, proteose-peptone infections. This fact
argues against their purely physical action. Many drugs act to increase
the flow of lymph in a way which cannot be presumed to be other than nor-
mal; i.e., they stimulate the physiological processes going on in the endo-
thelial cells. Such observations contribute strongly to the view advanced
by Heidenhain. Many investigations have been brought to the support of
the hypothesis that lymph formation is largely a process of secretion, yet
it seems at the present time that we cannot wholly deny that filtration and
osmosis play a part in the processes.

In following the action of peptones and proteoses, Pick and Spiro came
to the conclusion that it was not peptone, but some contaminating substance
which produced the characteristic action. This hypothetical substance
they called peptozyme. Underbill re-examined the influence of peptones,
using preparations made from plant proteins by hydration with enzymes,
heat, and acid, carrying the hydrolysis to a greater extent than did Pick and
Spiro. Underbill still obtained the great increase in the flow of lymph
together with the usual fall of blood pressure. Mendel published the
result of a demonstration of post-mortem lymph flow in which he showed
that "the lymph continued to flow for four hours without any extraordinary
mechanical assistance" after the death of the animal. This observation
would seem to give complete refutation of the filtration hypothesis. A
similar post-mortem salivary secretion has been observed, and in each case
the processes involved must be assumed to be physiological rather than
purely physical phenomena. Certainly the permeability or activity of the
endothelial lining of the blood vessels varies greatly at different times in
the life of an individual, and this variation in function is associated with the
marked change in the character and quantity of lymph produced.

LABORATORY EXPERIMENTS FOR THE EXAMINATION OF

THE BLOOD.

i. Microscopical Examination of the Blood. — Mount a drop of frog's
blood in o . 7 per cent, sodium chloride and examine with the low power of a
compound microscope. The red corpuscles will appear as oval nucleated
discs with a faint yellowish color, figure no. Here and there white granular
cells of irregular outline will be noted, the white corpuscles. Examine the
drop of blood with a high magnifying power and sketch the outline of the

ACTION OF FLUIDS ON THE RED CORPUSCLES 153

blood-cells. Select the white corpuscle which is most irregular in outline
and make a series of outline drawings once every minute to show its ame-
boid movements, figure 117.

Draw a drop of your own blood by puncturing the tip of the finger, under
sterile conditions, and mount in a drop of o . 9 per cent, physiological saline.
Examine with a high power, note the small biconcave red corpuscles which
appear faintly yellow in color and even adhere in rouleaux, figure 109. The
white corpuscles will appear as somewhat larger granular discs differing in
form and size. By mounting a drop of blood on a warm stage the ameboid
movements of the white corpuscles can be observed with comparative ease.

2. Action of Fluids on the Red Corpuscles.— Water.— When water is
added gradually to frog's blood, the oval disc-shaped corpuscles become
spherical and gradually discharge their hemoglobin, a pale, transparent
stroma being left behind. Human red blood-cells change from a discoidal

FIG. 126. FIG. 127. FIG. 128. FIG. 129.

•

FIG. 126. — Effect of Hypertonic Salt Solution on the Red Blood Corpuscles of Man.
FIG. 127. — Effect of Acetic Acid. FIG. 128. — Effect of Tannin. FIG. 129. — Effect
of Boric Acid.

to a spheroidal form and discharge their cell contents, becoming quite trans-
parent and all but invisible (ghost corpuscles).

Hypertonic Salt Solutions. — Mount a drop of human blood in 2 per cent,
sodium-chloride solution. The red blood-cells lose their disc shape and be-
come spherical with spinous projections or crenations, figure 126.

The original form of the red blood-cells can be restored by transferring
them to isotonic salt solution.

Dilute Acetic Acid. — This reagent causes the nucleus of the red blood-
cells in the frog to become more clearly defined; if the action is prolonged,
the nucleus becomes strongly granulated, and all the coloring matter seems
to be concentrated in it, the surrounding cell substance and outline of the
cell becoming almost invisible; after a time the cells lose their color altogether.
The cells in figure 127 represent the successive stages of the change. A
similar loss of color occurs in the red cells of human blood, which, from the
absence of nuclei, seem to disappear entirely.

Alkalies. — Alkalies cause the red blood corpuscles to absorb water and
finally to disintegrate.

Chloroform and Ether. — These reagents when added to the red blood-
cells of the frog cause them to part with their hemoglobin; the stroma of the

154 THE BLOOD

cells becomes gradually broken up. A similar effect is produced on the
human red blood-cell.

Tannin and Boric Acid. — When a 2 per cent, fresh solution of tannic acid
is applied to frog's blood it causes the appearance of a sharply denned little
knob, projecting from the free surface (Roberts' macula). The coloring
matter becomes at the same time concentrated in the nucleus, which grows
more distinct, figure 128. A somewhat similar effect is produced on the
human red blood corpuscle.

A 2 per cent, solution of boric acid applied to nucleated red blood-cells of
the frog will cause the concentration of all the coloring matter in the nucleus;
the colored body thus formed gradually quits its central position, and comes
to be partly, sometimes entirely, protruded from the surface of the now
colorless cell, figure 129. The result of this experiment led Briicke to dis-
tinguish the colored contents of the cell (zob'id) from its colorless stroma
(ecoid). When applied to the non- nucleated mammalian corpuscle its effect
merely resembles that of other dilute acids.

3. Phagocytosis in White Corpuscles. — Mix some very fine pigment
granules, bacterial emulsion, or charcoal with a few drops of frog's blood,
let stand for 10 or 20 minutes, then mount a drop on the glass slide or
make a smear and stain and examine under a high- magnifying microscope.
In a favorable field here and there will be found some white corpuscles
which have taken up the pigment. Colored corpuscles have been observed
with fragments of pigment embedded in their substance. White corpuscles
have also been seen in diseased states of the body to contain micro-organisms,
for example, bacilli and have the power of destroying these organisms, which
gives them the name phagocytes.

4. Enumeration of the Blood Corpuscles. — Several methods are
employed for counting the blood corpuscles, most of them depending upon

m

FIG. 130. — Thoma-Zeiss Hemacytometer, glass slide.

the same principle; i.e., the dilution of a minute volume of blood with a
given volume of a colorless solution similar in specific gravity to blood plasma,
so that the size and shape of the corpuscles are altered as little as possible.
A minute quantity of the well-mixed solution is then taken, examined under
the microscope, either in a flattened capillary tube (Malassez) or in a cell
(Hayem and Nache, Gowers) of known capacity, and the number of
corpuscles in a measured length of the tube or in a given area of the cell
is counted. The length of the tube and the area of the cell are ascertained
by means of a micrometer scale in the microscope ocular; or, in the case of
Gowers's modification, by the division of the cell area into squares of known

THE PERCENTAGE OF CORPUSCLES AND PLASMA

size. Having ascertained the number of corpuscles in the diluted blood, it
is easy to find out the number in a given volume of normal blood.

The hemacytometer, which is most used at the present time, is known as
the Thoma-Zeiss hemacytometer. It consists of a carefully graduated
pipet, in which the dilution of the blood is done; this is so formed that the
capillary stem has a capacity equaling one-hundredth
of the bulb above it. If the blood is drawn up in the
capillary tube to the line marked i, figure 131, the saline
solution may afterward be drawn up the stem to the line
101; in this way we have 101 parts of which the blood
forms i. As the content of the stem can be displaced
unmixed WTC shall have in the mixture the proper dilu-
tion. The blood and the saline solution are well mixed
by shaking the pipet, in the bulb of which is contained
a small glass bead for the purpose of aiding the mixing.
The other part of the instrument consists of a glass
slide, figure 130, upon which is mounted a covered disc,
m, accurately ruled so as to present one square milli-
meter divided into 400 squares of one-twentieth of a
millimeter each. The micrometer thus made is sur-
rounded by another annular cell, c, which has such a
height as to make the cell project exactly one-tenth
millimeter beyond m. If a drop of the diluted blood
be placed upon m, and c be covered with a perfectly flat
cover-glass, the volume of the diluted blood above each
of the squares of the micrometer, i.e., above each ffa,
will be :nnnr °f a cubic millimeter. An average of
ten or more squares is then taken, and this number multiplied by 4000 X
100 gives the number of corpuscles in a cubic millimeter of undiluted blood.
A separate pipet is used for making dilutions for counts of leucocytes. In
this, the dilution is made of one part of blood and ten parts of diluting fluid.
Acetic acid, o. 2 of one per cent., is usually employed for this purpose.

5. The Percentage of Corpuscles and Plasma in Human Blood.—
Fill the two graduated capillary tubes of a hematocrite with blood drawn
from the tip of your own finger, insert into the instrument, and centrifuge as
rapidly as possible. The experiment must be performed within the time
limit of clotting in order to be successful. The corpuscles will be thrown
down and the percentage of plasma and corpuscles can be read off directly.
Should one fail to fill the tube exactly full, then the percentage of plasma and
corpuscles can be calculated from the proportion which each bears to the
quantity in the tube.

6. Estimation of the Percentage of Hemoglobin. — The per cent, of
hemoglobin in a sample of blood can be obtained by the instrument known

Zeiss Hemacytome-
ter, pipet.

156 THE BLOOD

as Fleischl's hemometer, see figure 122. The principle of this instrument
rests on a comparison of the color of the sample of dilute blood with a stand-
ard glass wedge of uniform tint similar to that of blood. Fill one of the
chambers in the cells of the instrument half full with a 2 per cent, solution of
sodium carbonate. Now draw a drop of blood from the tip of a finger.
Touch the drop with the end of the standardized capillary tube, using care
to fill it accurately. Quickly wash this sample of blood out in the carbonate
solution in the cell and finish filling the cell. Put distilled water in the other
half of the cell, mount in the instrument, and examine in a dark room, using
candle-light. The glass wedge is graduated in percentage which can be
read off directly. This instrument is usually provided with several cells, in
which case as many samples may be taken and the average of the readings
used to determine the percentage.

Perhaps a more convenient and certainly a quicker method for deter-
mining the percentage of hemoglobin is Talquist's hemoglobinometer. By
this method a drop of blood is drawn directly on to absorbent-paper furnished
with the instrument, and the resulting stain is compared directly with a paper
color scale which is graduated in percentage. In this method the comparison
is made in ordinary daylight, and because of its rapidity it is very convenient
for clinical examinations.

7. Reaction of Blood Plasma. — Wet a piece of red litmus-paper in
saturated magnesium sulphate solution, then touch one end of the strip wdth
a drop of blood drawn from your finger under sterile conditions. After a.
few moments wash off the excess of corpuscles in neutral distilled water.
The blue at the point of contact with the blood indicates alkalinity.

8. The Specific Gravity of Blood. — From standard mixtures of
chloroform and benzol with specific gravity of i .050, i .060, and i .070 make
up a set of specific-gravity solutions of 1.050, 1.052, 1.054, etc., to 1.070,
These standards may be kept in stoppered 4-dram vials, or in test-tubes.
The specific gravity of blood is determined by inserting with a pipet a
drop of freshly drawn blood into the middle of one of the solutions, say
i .056. Since the blood does not mix with the chloroform and benzol, the
drop will rise or sink according to its relative specific gravity. By a few
trials one may quickly find a specific gravity in which the drop of blood
floats without rising or sinking. This represents the specific gravity of the
drop of blood.

This method permits rapid clinical application and has proven of con-
siderable interest in the hands of clinicians.

9. The Isotonicity of Blood. — The absorption or loss of water
by the corpuscles of blood in solutions of other concentrations than that of
blood plasma can be used as a means of determining the isotonicity of blood.
Make up a series of solutions of sodium chloride, varying by tenths, from
o . 5 to i . 2 per cent. Prepare a series of slides with vaselin rings and mount

COAGULATION OF BLOOD 157

drops of human blood in drops of saline of o . 6, 0.7, o . 8, o . 9, i , and i . i per
cent, examine every ten minutes under a high-power microscope. The
corpuscles of some of the slides will swell up and may disintegrate, others
will show crenation as in figure 126. In the isotonic solutions the corpuscles
wTill appear of their normal size and condition.

10. Coagulation of Blood. — a. Normal Clot. — Anesthetize a dog,
insert a cannula into the carotid or femoral artery, and draw samples of
blood into two or three clean, dry test-tubes. Draw one sample into a test-
tube that has had its sides oiled. Note the exact time at which the blood
was drawn into the test-tubes and set the test-tubes in a test-tube rack. Ex-
amine at intervals of 30 seconds by gently inclining the test tubes. Presently

FIG. 132. — Microscopic View of Clot Showing Fibrin Network.

it will be noted that the blood becomes more viscous and does not flow freely
up the sides of the test-tubes. Later the whole mass will become jelly-like
and will retain the form of the test-tube. Note the time of the first slight
change, and also when the clot becomes more perfect. The sample in the
oiled test-tube will be found to clot more slowly.

If the test-tubes of clotted blood are left standing for a day, the coagulum
will become similar in size and a transparent yellowish blood will make its
appearance on the surface or between the sides of the clot and the test-tube
wall. This fluid is the serum and it is squeezed out by the shrinking of
the fibrin which holds the corpuscles in its meshes.

b. Microscopic Examination of the Process of Clotting. — Take a drop of
fresh blood from the tip of your finger under sterile conditions and mount
on a microscopic slide in a few drops of salt solution, and examine immediately

158 THE BLOOD

under the high power. Small threads of fibrin will presently be seen to form
across the field, usually being most clearly obvious where fragments of
white corpuscles are noted, see figures 107 and 132. The threads of fibrin
become more apparent when stained with rosanilin.

c. Whipped Blood. — Draw a sample of blood into a glass tumbler,
enough to fill it one-half or two-thirds full. Immediately begin vigorously
stirring the blood with a bunch of stiff wires or a pencil, and keep it up until
the time of clotting has passed, 5 or 10 minutes. In this instance the wires
will break up and collect the fibrin as fast as it forms, and no firm mass will
be produced. The remaining fluid is called wpipped blood. The fibrin can
be removed from the wires and washed in tap water until all the adherent
red corpuscles are removed. This mass of fibrin is white, elastic, and com-
posed of a network of thread-like fibers. It is these fibers extending through
and through the mass of blood which makes it retain the form of the vessel
when undisturbed clotting occurs.

d. The Influence of Salt Solution on Blood Clotting. — Add 20 c.c. of satu-
rated magnesium sulphate, i per cent, sodium oxalate, and 2 . 5 per cent, of
sodium chloride in each of three beakers. Draw into each beaker 50 to
60 c.c. of blood and immediately mix thoroughly and let stand. The mag-
nesium and oxalate beakers will not coagulate even though they stand for
days, but the sodium-chloride blood will clot in a few mintues.

The magnesium-sulphate blood will coagulate if diluted with a sufficient
amount of distilled water or physiological saline solution. Make a series
of dilutions and note when coagulation takes place. The sodium-oxalate
blood will coagulate when a sufficient excess (i per cent.) of calcium chloride
is added to neutralize the excess of sodium oxalate. Demonstrate this on
a series of samples.

If a liter or so of magnesium or oxalate blood is secured and separated
by a centrifuge or by letting stand for a sufficient time, a sample of salted
plasma will be obtained. This sample wrill coagulate when it is treated as
just described for salted blood, showing that the antecedents of fibrin are
found in the plasma.

e. Action of Tissue Extracts on Coagulation. — Wash out the blood of
a small animal by circulating o . 9 per cent, saline through the arteries until
the outflowing fluid from the veins is clear. Take an organ, the liver for
example, grind it up in a sausage mill by running it through the mill two
or three times, then extract with 0.9 per cent, physiological saline. The
macerating mass should be shaken up at intervals, and may be kept from
spoiling by adding an excess of chloroform or by keeping on ice. A few
cubic centimeters of this fluid extract added to a sample of freshly drawn
blood will very greatly hasten the rapidity of coagulation. This tissue ex-
tract is called thrombokinase, as it is an activator which hastens the formation
of thrombin from thrombogen.

THE CHEMISTRY OF BLOOD PLASMA 159

11. The Chemistry of Blood Plasma (or Serum).— The blood
plasma contains all the chemical substances which are utilized by the tissues
in their nutrition or which are thro\vn off by the tissues as a result of their
activity. It is therefore a very complex mixture. The serum contains the
same substances in the same proportion, with the exception of the antecedents
of fibrin. It may, therefore, be used as a substitute for plasma in most
cases.

a. Proteins of Plasma. — There are three principal proteins in blood
plasma: serum- albumin, serum-globulin, and fibrinogen. These may be
isolated as follows: To a sample of blood plasma add an equal quantity of
sodium-chloride solution that has been saturated at 40° C. A white floccu--
lent precipitate of fibrinogen comes down. Filter off, and add to the filtrate
an equal volume of saturated ammonium sulphate. A second heavier pre-
cipitate of serum- globulin separates out. When this is separated, and crys-
tals of ammonium sulphate are added to the filtrate to complete saturation
at 40° C., a third precipitate of serum-albumin separates.

Each of these precipitates may be redissolved and purified by reprecipi-
tation and can be tested by the characteristic protein reactions, see page 107,
which they all give.

b. Sugars of Blood Plasma or Serum. — If a quantity of blood serum is
diluted with about 5 to 10 times its volume of water, and the proteins are
removed by slight acidulation with acetic acid and boiling and filtering, the
filtrate will contain reducing sugar and the various solids of blood plasma.
To a concentrated sample of the filtrate add Fehling's solution and boil.
A reddish precipitate indicates the presence of reducing sugar. If this ex-
periment is done quantitatively, about from o . i to o . 2 per cent, of sugar will
be found.

c. The Salts of Blood Plasma. — The salts of blood plasma are tested
best by evaporating some of the blood serum to dryness, and burning the
residue to oxidize the organic matter and dissolving the ash in water. Test
as follows: To a sample add i per cent, of silver nitrate; a white precipitate
soluble in an excess of ammonia, but not soluble in nitric acid, indicates
chlorides.

To a second sample add i per cent, barium chloride. If sulphates are
present there will be a white precipitate which settles out quickly.

Acidify a third sample with nitric acid and add ammonium molybdate
and heat. A yellow precipitate indicates the presence of phosphates.

To the fourth sample add an excess of strong ammonia and i per cent,
ammonium oxalate, heat. A white precipitate indicates the presence of
calcium.

12. Blood Corpuscles. — The characteristic substance in the composi-
tion of the corpuscles is the pigment known as hemoglobin, and this is the
only chemical factor that will be considered in these experiments.

l6o THE BLOOD

a. Hemoglobin Crystals. — Take a sample of dog's blood, or if a centri-
fuge is available separate and wash the sample of blood corpuscles, and
mix with about three volumes of saturated ether water, or if blood is used
dilute writh two or three volumes of water and add about 10 per cent, of pure
ether and shake thoroughly. Crystals of oxyhemoglobin will be formed, and
this can be mounted and examined with a microscope.

b. Spectrum of Hemoglobin and Us Compounds.

1. Oxyhemoglobin. — Dilute a sample of defibrinated blood with about
ten volumes of distilled water. From this stock solution make five solutions
all differing by 33 J per cent. Examine these with a direct- vision spectro-
scope. Make a drawing showing the absorption spectrum of each sample as
compared with the solar spectrum. Compare with the spectrum shown in
the frontispiece.

2. Hemoglobin. — The oxygen can be driven out from the hemoglobin
by adding to the above samples a few drops of ammonium sulphide and
gently warming. Re-examine with the direct-vision spectroscope and map
as before.

3. Carbon- monoxide Hemoglobin. — Pass a stream of ordinary illumi-
nating gas through the dilutions of hemoglobin. The carbon monoxide
of the gas will form a compound with the hemoglobin, which now turns a
bright scarlet color. When examined with the spectroscope, the absorp-
tion bands are found to be very similar to those of oxyhemoglobin. How-
ever, map the spectrum to the scale as usual. Add the reducing agent,
warm, and shake vigorously and re-examine. It is very difficult to break up
the combination of hemoglobin with carbon monoxide, hence the poisonous
action of this gas.

CHAPTER V.
THE CIRCULATION OF THE BLOOD

THE blood is contained in a system of closed vessels through which it is
kept in circulation during the life of the individual. The energy to keep up
this motion is supplied by the heart, which is a large muscular organ con-
sisting of four great divisions, the right and left auricles and right and left
ventricles. The right ventricle discharges its blood into the pulmonary

FIG. 133. — Diagram of the Circulation in an Animal with a Completely Separated
Right and Left Ventricle and a Double Circulation. (After Huxley.) Ad, Right auricle
receiving the superior and inferior venae cavse, Vcs and Vci; Dth, thoracic duct, the main
trunk of the lymphatic system; Ad, right auricle; Vd, right ventricle; Ap, pulmonary artery;
P, lung; Vp, pulmonary vein; As, left auricle; Vs, left ventricle; Ao, aorta; D, intestine;
L, liver; Vp, portal vein; Lv, hepatic vein.

artery, through which it passes to the lungs, returning through the pulmonary
veins to the left auricle, and into the ventricle. From the left ventricle
the blood is pumped into the great aorta, and through its branches distrib-
uted to the entire body. The terminal arteries are continuous with the
IT 161

1 62 THE CIRCULATION OF THE BLOOD

general capillaries of the body, and these in turn with the veins, which con-
duct the blood back to the right side of the heart again. It will be seen,
therefore, that the circulatory apparatus consists of two great divisions, the
pulmonary and the systemic circulation. This arrangement is illustrated
by the accompanying figure. A study of this figure will show that in certain
regions of the systemic circulation there are two capillary beds between the
main arteries and the main veins. This subordinate stream through the
liver is called the portal circulation, and the similar arrangement existing
in the kidney is called the renal circulation. This, in general, is the outline
of the course of the blood in its circulation.

To make a study of the various phenomena manifested in the physiology
of the circulatory apparatus, it is obvious that we have to do with certain
fundamental activities; first, the physiology of the pumping organ, the heart;
second, the behavior of the blood in the arteries, capillaries, and veins; third,
the co-ordination of these various divisions of the apparatus through the
nervous system. To understand this it will be necessary to have in mind in
detail the anatomical structure of the apparatus itself.

ANATOMICAL CONSIDERATIONS.

The Heart. — The heart is contained in the chest or thorax, and lies
between the right and left lungs, figure 143, enclosed in a membranous sac,
the pericardium. The pericardium is made up of two distinct parts, an
external fibrous membrane and an internal serous layer which not only
lines the fibrous sac, but also is reflected on to the heart, which it completely
invests. These form a closed sac, the cavity of which contains just enough
pericardial fluid to lubricate the two surfaces, and thus to enable them to glide
smoothly over each other during the movements of the heart. The vessels
passing in and out of the heart receive investments from this sac to a greater
or less degree.

The heart is situated in the chest behind the sternum and costal carti-
lages, being placed obliquely from right to left. It is of pyramidal shape,
with the apex pointing downward, outward, and toward the left, and the
base backward, inward, and toward the right. The heart is suspended in
the chest by the large vessels which proceed from its base, but, excepting
at the base, the organ itself hangs free within the sac of the pericardium.
The part which rests upon the diaphragm is flattened, and is known as the
diaphragmatic surface, while the free upper part is called the sternocostal
surface.

On examination of the external surface the division of the heart into parts
which correspond to the chambers inside of it may be traced. A deep trans-
verse groove, called the coronary sulcus, divides the auricles from the ventri-
cles; and the anterior longitudinal sulcus runs between the ventricles, both in

THE HEART

i63

front and in the back, separating the one from the other. The anterior groove
is nearer the left margin, and the posterior nearer the right, as the front
surface of the heart is made up chiefly of the right ventricle and the posterior
surface of the left ventricle. The coronary vessels which supply the tissue
of the heart with blood run in the furrows or sulci; also the nerves and lymph-
atics, which are embedded in more or less fatty material, are found in this
groove.

The Chambers of the Heart. — The interior of the heart is divided by a
longitudinal partition in such a manner as to form two chief chambers or
cavities, the right and the left. Each of these chambers is again subdivided
transversely into an upper and a lower portion, called, respectively, the auricle

FIG. 134. — Outline of Heart, Lungs, and Liver to Show their Relations to each other and to
the Chest Wall. (Heusman and Fisher's "Anatomical Outlines.")

and the ventricle, which freely communicate. The aperture of communica-
tion, however, is guarded by valves so disposed as to allow blood to pass
freely from the auricle into the ventricle, but not in the opposite direction.
There are thus four cavities in the heart, the auricle and ventricle of one side
being quite separate from those on the other, figure 135.

The right auricle, the right part of the base of the heart as viewed from
the front, is a thin-walled cavity of more or less quadrilateral shape, pro-
longed at one corner into a tongue-shaped portion, the right auricular appen-
dix, which slightly overlaps the exit of the aorta from the left ventricle.

The interior of the auricle is smooth, being lined with the general lining
membrane of the heart, the endocardium. The superior and inferior vena
caves open into the auricle. The opening of the inferior cava is protected

164

THE CIRCULATION OF THE BLOOD

and partly covered by a membrane called the Eustachian valve. In the
posterior wall of the auricle is a slight depression called the fossa ovalis,
which corresponds to an opening between the right and left auricles, exist-
ing in fetal life. In the appendix are closely set elevations of the muscular

FIG. 135. — The Right Auricle and Ventricle Opened and a Part of their Right and
Anterior Walls Removed so as to Show their Interior, i, Superior vena cava; 2, inferior
vena cava; 2', hepatic veins cut short; 3, right auricle; 3', placed in the fossa ovalis, below
which is the Eustachian valve; 3", is placed close to the aperture of the coronary vein;
f, f, placed in the auriculo-ventricular groove, where a narrow portion of the adjacent
walls of the auricle and ventricle has been preserved; 4, 4, cavity of the right ventricle,
the upper figure is immediately below the semilunar valves; 4', large columna carnea or
musculus papillaris; 5, 5', 5", tricuspid valve; 6, placed in the interior of the pulmonary
artery, a part of the anterior wall of that vessel having been removed and a narrow portion
of it preserved at its commencement where the semilunar valves are attached; 7, concavity
of the aortic arch, close to the cord of the ductus arteriosus; 8, ascending part or sinus of
the arch covered at its commencement by the auricular appendix and pulmonary artery; 9,
placed between the innominate and left carotid arteries; 10, appendix of the left auricle;
n, n, outside of the left ventricle the lower figure near the apex. (Allen Thomson.)

tissue, covered with endocardium, and on the anterior wall of the auricle are

similar elevations arranged parallel to one another, called musculi pectinati.

The right ventricle forms the right margin of the heart. It takes no

part in the formation of the apex. On section its cavity is similunar or

THE HEART 165

crescentic, figure 137. Into it are two openings, the venous orifice at the
base, and the arterial orifice of the pulmonary artery, also at the base but
more to the left. The part of the ventricle leading to the pulmonary artery
is called the conus arteriosus, both orifices are guarded by valves, the former
called the tricuspid and the latter the semilunar. In this ventricle are also
the projections of the muscular tissue called the trabeculce earned.

The left auricle is situated at the left and posterior part of the base of
the heart. The left auricle is only slightly thicker than the right and its
form and structure are the same as in the right. The left venous orifices are
oval and a little smaller than that on the right side of the heart. There is a
slight vestige on the septum of the foramen between the auricles.

FIG. 136. — Cross-section of a Completely Contracted Human Heart, at the Level of the
Lower and Middle Thirds. (According to Krehl.)

The left ventricle occupies the posterior and apical portion of the heart,
and is connected directly with the great aorta. It is separated from the
auricle by the bicuspid or mitral valve, and the opening into the great aorta
is guarded by the semilunar valves. The walls of the left ventricle are two
or three times as heavy as those of the right, and may be as much as half an
inch in total thickness.

The left ventricle is capable of containing 90 to 120 c.c. of blood. The
capacity of the auricles is considerably less after death owing to their con-
tracted condition. The whole heart is about 12 cm. long by 8 cm. at its
greatest width, and 6 cm. in thickness. The average weight in the adult is
about 300 grams.

1 66

THE CIRCULATION OF THE BLOOD

The walls of the heart are constructed almost entirely of layers of muscu-
lar fibers; but a ring of connective tissue, to which some of the muscular
fibers are attached, is inserted between each auricle and ventricle and forms
the boundary of the venous opening. Fibrous tissue also exists at the
origins of the pulmonary artery and aorta. The muscular fibers of each
auricle are in part continuous with those of the others and in part separate;
and the same holds true for the ventricles. The fibers of the auricles are,

FIG. 137. FIG. 138.

FIG. 137. — Cardiac Muscle Cells, Showing their Form, Branches, Nuclei, and Striae.
From the heart of a young rabbit. Magnified 425 diameters, a, Line of junction between
the cells (intercellular cement); b, c, branches of the cells. (Schafer.)

FIG. 138. — Cardiac Muscle Cells of the Left Ventricle of a Child at Birth (full term), to
show the form of the cells, their structural details, their relations to one another, and their
general agreement with those of cold-blooded vertebrates. A, Large cell with two nuclei;
this cell has nearly the proportions of those of the adult; B, group of cells in their natural
relation. At the right of the middle cell are two spaces or fissures, n, Nucleus. The
transverse striations cross the nuclei in all the cells, and each nucleus possesses several
nucleoli. (Gage.)

however, quite separate from those of the ventricles, the bond of connection
between them being the fibrous and the embryonic muscular tissue of the
auriculo-ventricular rings and the bundle of His in the septum.

The development of the heart shows that it is derived from an embryonic
tube, which in its growth becomes twisted upon itself and divided into the
two main divisions that we know in the adult. Anatomical dissections have
shown that the muscles of the ventricles form spiral sheaths extending from
the base of the two ventricles in spiral bands toward the apex. These bands
of muscle are wound about the surface of the ventricles in the right-to-left

THE VALVES OF THE HEART

i67

direction. At the apex they extend up into the deeper tissue. If the super-
ficial muscles are dissected off, there is left a great central core of muscle,
which is described by MacCallum as running more transversely around the

Fto. 139.

FIG. 140.

FIG. 139. — Diagram of the Course of the Superficial Muscle Layers Originating in the
Right and Left Coronary Sulci and in the Posterior Half of the Tendon of the Conus.
C, Anterior papillary muscle. (After MacCallum.)

FIG. 140. — Diagram of the Course of the Superficial Muscle Layers Originating in the
Anterior Half of the Tendon of the Conus. A, Posterior papillary muscle; B, papillary
muscle of the septum. (After MacCallum.)

FIG. 141.

FIG. 142.

FIG. 141. — Diagram of the Course of the Layer Superficial to the Deepest Layer of the
Muscle of the Left Ventricle, which is shown in outline. The deepest layer is also shown.
A, Posterior papillary muscle; B, papillary muscle of the septum. (After MacCallum.)

FIG. 142. — Diagram of a Layer still more Superficial to that Shown in Fig. 142, and
Ending in the Anterior Papillary Muscle. The deeper layers are represented in dotted
lines. A, Posterior papillary muscle; B, papillary muscle of septum; C, anterior papillary
muscle. (After MacCallum.)

wall of one ventricle, then through the septum and around the other in a
reverse scroll, figure 141.

The Valves of the Heart. — The valves of the heart are arranged so
that the blood can pass only in one direction. These are the tricuspid

1 68 THE CIRCULATION OF THE BLOOD

valve, between the right auricle and right ventricle, figure 135, and the semi-
lunar valve of the pulmonary artery, the mitral valve between the left auricle
and ventricle, and semilunar valve of the aorta. The bases of the tricuspid,
figure 152, and mitral valves are attached to the walls of the venous orifices
respectively. Their ventricular surfaces and borders are fastened by slender
tendinous fibers, the chorda tendinece, to the internal surface of the walls
of the ventricles at points which project into the ventricular cavity in the form
of bundles or columns, the musculi papillares.

The semilunar valves guard the orifices of the pulmonary artery and of
the aorta. They are nearly alike on both sides of the heart, but the aortic
valve is altogether thicker. Each valve consists of three parts which are
of similunar shape, the convex margin of each being attached to a fibrous
ring at the place of junction of the artery to the ventricle, and the concave
or nearly straight border being free, so as to form a little pouch like a pocket,
figure 151. In the center of each free edge of the valves which contains
a fine cord of fibrous tissue is a small fibrous nodule, the corpus Arantii of
the valves.

The Arteries. — The arterial system begins at the left ventricle in a
single large trunk, the aorta, which, almost immediately after its origin,
gives off in the thorax three large branches for the supply of the head, neck,
and upper extremities; it then traverses the thorax and abdomen, giving
off branches, some large and some small, for the supply of the various organs
and tissues it passes on its way. In the abdomen it divides into two chief
branches. The arterial branches, wherever given off, divide and subdivide
until the caliber of each subdivision becomes very minute. These smallest
arteries are called arterioles. These arterioles are continuous with the capil-
laries. Arteries frequently communicate or anastomose with other arteries.
The arterial branches are usually given off at an acute angle, and the areas
of the branches of an artery generally exceed that of the parent trunk, and,
as the distance from the origin is increased, the area of the combined branches
is increased also. As regards the arterial system of the lungs, the pulmonary
artery and its subdivisions, they are distributed in much the same manner
as the arteries belonging to the general systemic circulation.

The walls of the arteries are composed of three principal coats, the ex-
ernal, or tunica adventitia, the middle, or tunica media, and the internal, or
unica intima. The external coat, figures 143 and 144, a, the strongest and
toughest part of the wall of the artery, is formed of areolar tissue, with which
is mingled throughout a network of elastic fibers. The middle coat, figure
144, m, is composed of both muscular and elastic fibers with a certain pro-
portion or areolar tissue. In the larger arteries, its thickness is compara-
tively as well as absolutely much greater than in the small arteries, consti-
tuting, as it does, the greater part of the arterial wall. The muscular
fibers are unstriped, figure 145, and are arranged, for the most part, trans-

THE CAPILLARIES

169

versely to the long axis of the artery, figure 143, w, while the elastic element,
taking also a transverse direction, is disposed in the form of closely inter-
woven and branching fibers intersecting in all parts the layers of muscular
fiber. In arteries of various size there is a difference in the proportion of
the muscular and elastic element, elastic tissue preponderating in the largest
arteries and unstriped muscle in those of medium and small size. The
arteries are quite elastic in both large and small vessels. The internal coat
is formed by a layer of elastic tissue, called ihefenestrated membrane of Henle.
It is peculiar in its tendency to curl up when peeled off from the artery, and

FIG. 143.

FIG. 144.

FIG. 145-

FIG. 143. — Minute Artery Viewed in Longitudinal Section, e, Nucleated endothelial
membrane, with faint nuclei in lumen, looked at from above; i, thin elastic tunica intima;
m, muscular coat or tunica media; a, tunica adventitia. (Klein and Noble Smith.)

FIG. 144. — Transverse Section through a Large Branch of the Inferior Mesenteric
Artery of a Pig. e, Endothelial membrane; i, tunica elastica interna, no subendothelial
layer is seen; m, muscular tunica media, containing only a few wavy elastic fibers; e, c,
tunica elastica externa, dividing the media from the connective-tissue adventitia, a. Mag-
nification, 350 diameters. (Klein and Noble Smith.)

FIG. 145. — Muscular Fiber Cells from Human Arteries. Magnified 350 diameters.
a, Nucleus; B, a fiber cell treated with acetic acid. (Kolliker.)

in the perforated and streaked appearance which it presents under the micro-
scope. The inner surface of the artery is lined with a delicate layer of elon-
gated endothelial cells which make it smooth and polished and furnish a
nearly impermeable surface along which the blood may flow with the*
smallest possible amount of resistance from friction.

Nerves. — Most of the arteries are surrounded by a plexus of nerves or
nerve fibers, which twine around the vessel. The smaller arteries also have
a delicate network of similar nerve fibers many of which appear to end near
the nuclei of the transverse muscular fibers.

The Capillaries. — In all vascular textures, except some parts of the
corpora cavernosa of the penis, of the uterine placenta, and of the spleen,

i yo

THE CIRCULATION OF THE BLOOD

the transmission of the blood from the minute branches of the arteries to the
minute veins is effected through a network of capillaries. They may be
seen in all minutely injected preparations.

The point at which the arteries terminate and the capillaries commence
cannot be exactly denned, for the transmission is gradual. The capillaries
maintain essentially the same diameter throughout. The meshes of the

FIG. 146. — Vein and Capillaries. Silver-nitrate and hematoxylin stain, to show outlines
of endothelial cells and their nuclei. (Bailey.)

network that they compose are more uniform in shape and size than those
formed by the anastomoses of the minute arteries and veins.

The walls of the capillaries are composed of a single layer of elongated
or radiate, flattened and nucleated endothelial cells, so joined and dove-
tailed together as to form a continuous transparent membrane, figure 146.

FIG. 147. — Network of Capillary Vessels of the Air Cells of the Horse's Lung
^Magnified, a, a, Capillaries proceeding from b, b, terminal branches of the pulmonary
artery. (Frey.)

Outside these cells in the larger capillaries there is a structureless supporting
membrane on the inner surface of which they form a lining.

The diameter of the capillary vessels varies somewhat in the different
textures of the body, the most common size being about 1 2 micro millimeters,
"giro's" of an inch. Among the smallest may be mentioned those of the

THE CAPILLARIES

171

brain and of the follicles of the mucous membrane of the intestines; among
the largest, those of the skin and especially those of the medulla of the bones.

The form of the capillary network differs in the different organs of the
body, but is usually adjusted to the structural arrangement of the cells of
any given organ.

The capillary network is closest in the lungs and in the choroid coat of
the eye. In the human liver the interspaces are of the same size, or even

FIG. 148. — Capillaries of Striated Muscular Tissue. From a cat. Magnified 300 diam-
eters. A, Artery; V, vein. (Heitzmann.)

smaller than the capillary vessels themselves. In the human lung the spaces
are smaller than the vessels; in the human kidney and in the kidney of the
dog the diameter of the injected capillaries, compared with that of the inter-
spaces, is in the proportion of one to four, or one to three. The brain
receives a very large quantity of blood; but its capillaries are very minute
and are less numerous than in some other parts. In the mucous mem-

172 THE CIRCULATION OF THE BLOOD

branes, for example in the conjunctiva and in the cutis vera, the capillary
vessels are much larger than in the brain and the interspaces narrower,
namely, not more than three or four times wider than the vessels. In the
periosteum and in the external coat of arteries the meshes are much larger,
their width being about ten times that of the vessels. It may be held as a
general rule that the more active the functions of an organ are, the more
vascular it is.

The Veins. — The venous system begins in small vessels which are
slightly larger than the capillaries from which they spring. These vessels

FIG. 149. — Transverse Section through a Small Artery and Vein of the Mucous Mem-
brane of a Child's Epiglottis; the artery is thick- walled and the vein thin-walled. A,
Artery; the letter is placed in the lumen of the vessel, e, Endothelial cells with nuclei
clearly visible; these cells appear very thick from the contracted state of the vessel. Outside
it a double wavy line marks the elastic tunica intima. m, Tunica media consisting of
unstriped muscular fibers circularly arranged; their nuclei are well seen, a, Part of the
tunica adventitia, showing bundles of connective-tissue fiber in section, with the circular
nuclei of the connective-tissue corpuscles. This coat gradually merges into the surrounding
connective tissue. V, The lumen of the vein. The other letters indicate the same as in
the artery. The muscular coat of the vein, m, is seen to be much thinner than that of the
artery. X 350. (Klein and Noble Smith.)

are gathered up into larger and larger trunks until they terminate in the two
venae cavae and the coronary vein which enter the right auricle, and in four
pulmonary veins which enter the left auricle. The total capacity of the
veins diminishes as they approach the heart; but their capacity exceeds by
two or three times that of their corresponding arteries. The pulmonary
veins, however, are an exception to this rule. The veins are found after

THE VEINS

173

death more or less collapsed and often contain blood. They are usually
distributed in a superficial and a deep set which communicate frequently
in their course.

The coats of veins bear a general resemblance to those of arteries, figure
149. Thus, they possess outer, middle, and inner coats. The miter coat is
constructed of areolar tissue like that of the arteries, but is thicker. In some
veins it contains muscular cells arranged longitudinally. The middle coat
is considerably thinner than that of the arteries; it contains circular un-
striped muscular fibers mingled with a large proportion of yellow elastic and
white fibrous connective tissue. In the large veins near the heart the middle
coat is replaced for some distance from the heart by circularly arranged
striped muscular fibers continuous with those of the auricles. The internal
coat of veins consists of a fenestrated membrane lined bv endothelium. The

iv *•*

FIG. 150. — A, Vein with valves open. B, vein with valves closed; stream of blood passing
off by lateral channel. (Dalton.)

fenestrated membrane may be absent in the smaller veins. The veins are
supplied with valves in certain regions of the body, especially in the veins of
the arm and legs. The general construction of these valves is similar to
that of the semilunar valves of the aorta and pulmonary artery already
described. Their free margins are turned in the direction toward the heart,
so as to prevent any movement of blood backward. They are commonly
placed in pairs, at various distances in different veins. In the smaller veins
single valves are often met with, and three or four are sometimes placed
together or near one another in the larger veins, such as in the subclavians
at their junction with the jugular veins. During the period of their in-
action, when the venous blood is flowing in its proper direction, they lie by

174 THE CIRCULATION OF THE BLOOD

the sides of the walls of the veins; but when in action they come together
like valves of the arteries, figure 150. Their situation in the superficial
veins of the forearm is readily discovered by pressing along its surface, in a
direction opposite to the venous current, i.e., from the elbow toward the
wrist, when little swellings, figure 150, B, will appear in the position of each
pair of valves.

Lymphatic spaces are present in the coats of both arteries and veins;
but in the tunica adventitia or external coat of the large vessels they form
a distinct plexus of more or less tubular vessels. In smaller vessels they
appear as sinus spaces lined by endothelium. Sometimes, as in the arteries
of the omentum, mesentery, and membranes of the brain, the pulmonary,
hepatic, and splenic arteries, the spaces are continuous with vessels which
distinctly ensheath them, peri-vascular lymphatic sheaths. Lymph channels
are said to be present also in the tunica media.

THE ACTION OF THE HEART.

The heart's action in propelling the blood consists in the successive alter-
nate contraction, systole, and relaxation, diastole, of the muscular walls of
the auricles and the ventricles. This activity furnishes the power which
keeps the blood moving through the arteries, capillaries, and veins. The
heart in its activity is like a great force pump in that it injects a certain quan-
tity of blood at each contraction into the great arteries. Owing to the inter-
action between this heart-beat and the peripheral resistance to the flow of
blood, together with the elasticity of the vessels themselves, a high pressure
in the arteries is maintained all the time. The heart's contractions, then,
pumping against this high arterial tension, are sufficient to maintain a con-
stant flow of blood through the capillaries and, therefore, through the active
tissues.

The heart beats at an average rate of about 72 times per minute during
life. Each successive contraction really begins in the great veins, which
are muscular, and extends over the auricles and ventricles in regular sequence.
The contraction of each successive part is called its systole and the relaxation
its diastole. The diastole covers the period of active relaxation of the muscle
and the pause before beginning its next contraction. Each muscular cham-
ber of the heart may, therefore, be said to have its systole and diastole. The
whole series of events from the beginning of one contraction until the cor-
responding event in the next contraction is described as the cardiac cycle.

Action of the Auricles. — The description of the action of the heart
may be commenced at that period in each cycle in which the whole heart is
at rest. The heart is then in a passive state. The auricles are gradually
filling with the blood flowing into them from the veins, and a portion of this
blood is passing at once through the auricles into the ventricles, the opening

ACTION OF THE VENTRICLES 175

between the cavity of each auricle and that of its corresponding ventricle
being free during the pause of the entire heart. The auricles, however,
receiving more blood than at once passes through them to the ventricles,
become, near the end of the pause, passively distended. At this moment a
contraction wave begins on the bases of the venae cavae and, running down
from the walls of the veins, passes to the muscular walls of the auricles. The
contraction of the auricles, the right and left contracting at the same time,
forces the blood into the ventricles.

The contraction of the muscular walls of the great veins maintains a
condition of constriction of these veins during the time of the auricular con-
traction. This hinders the reflux of blood from the auricles into the veins
during the auricular systole. Any slight regurgitation from the right auricle
is limited by the valves at the junction of the subclavian and internal jugular
veins beyond which the blood cannot move backward, and by the coronary
vein which is supplied with a valve at its mouth. The force of the blood
propelled by the auricle into the ventricle at each auricular systole is trans-
mitted in all directions, but, being insufficient to open the semilunar valve,
it is expended in distending the walls of the ventricle.

Action of the Ventricles. — The dilatation of the ventricles which
occurs during the latter part of the diastole of the auricles, is completed by
the forcible injection of the contents of the latter. The ventricles, now dis-
tended with blood, immediately begin to contract. The tricuspid valve
is closed by the initial reflux of blood, or possibly by the currents of blood
formed by the sudden injection of the ventricles by the auricular contraction.
The ventricular systole follows the auricular systole so closely that it seems
continuous with it. As a result of the ventricular systole, sufficient pressure
is produced on its contents to overcome the pressure against the semilunar
valves of the aorta and the pulmonary artery, and the ventricles are thus
emptied completely. After the whole of the blood has been expelled from
the ventricles, the walls remain contracted for a brief period.

The form and position of the fleshy columns on the internal walls of the
ventricles no doubt help to produce the obliteration of the ventricular cavity
during contraction. The completeness of the closure may often be observed
on making a transverse section of a heart shortly after death in any case in
which rigor mortis is very marked, figure 136. In such a case only a central
fissure may be discernible to the eye in the place of the cavity of each ventricle.
The arrangement of. the muscles of the heart, as described on page 147, is
such as to expend the whole force of the contraction in diminishing the cavity
of the ventricle, or, in other words, in expelling its contents.

On the conclusion of the systole the ventricular diastole begins. The
muscular walls relax and, by virtue of their elasticity, a slight negative press-
ure is set up. This negative or suctional pressure on the left side of the
heart may be of importance in helping the pulmonary circulation. It is

i76

THE CIRCULATION OF THE BLOOD

somewhat inconstant in appearance, but has been found to be equal to as
much as 20 mm. of mercury, and is said to be quite independent of the
aspiratory power of the thorax itself, which will be described in a later
chapter. The ventricles now remain in a state of relaxation or rest until
the next systole begins.

The duration of the ventricular systole and the diastole has been variously
estimated. A computation of the time of these two phases, for man, in
figure 153, reproduced from Hiirthle, gives for the systole 0.38 of a second
and for the diastole 0.4 of a second, with a total of o. 78 of a second. This
is equivalent to a rate of 77 per minute. Variation in the time of the systole
and the diastole of the ventricle falls chiefly on the pause of the diastole.

The ventricles undergo little or no change of shape in the unopened chest.
At the moment in the systole when the ventricles begin to discharge their

Left anterior cusp of
pulmonary valve

Left posterior cusp of
pulmonary valve

Left posterior cusp of

aortic valve
Left coronary artery

Anterior cusp of
mitral valve

Posterior cusp of
mitral valve

Left ventricle

~~ Conus arteriosus

Right anterior cusp
of pulmonary valve

Right coronary
artery

Anterior cusp of
aortic valve

Right posterior cusp

of aortic valve
Anterior (infundibu-
lar) cusp of tricuspid

valve

Right (marginal)
cusp of tricuspid

valve

Posterior (septal)

cusp of tricuspid

valve

Right ventricle

FIG. 151. — The Bases of the Ventricles of the Heart, showing the auriculo- ventricular,
aortic, and pulmonary orifices and their valves. (Cunningham.)

contents into the aorta and pulmonary arteries, respectively, there is a sharp
decrease in size of the ventricles. This decrease takes place in all
dimensions.

Action of the Valves. — The Tricuspid Valve. — During the diastole
of both auricles and ventricles blood flows directly through the auricles into
the ventricles, the auricles during this period acting as continuations of the
large veins which empty into them. At the end of the period the ventricle
on each side has already been filled and distended by the pressure of blood
from the veins. The systole of the auricle completes this filling and slightly
overdistends the ventricle. When the force of the auricular contraction is

ACTION OF THE VALVES 177

spent, the ventricular walls rebound slightly toward their former position
and in so doing exert some pressure upon the ventricular side of the tricuspid
valve which floats the cusps upward toward the auricle. In this connection
another force comes into play, viz., vortex or back currents resulting from
the flow of the blood into the ventricle under the pressure of the auricular
systole. These currents aid in floating the valve cusps into apposition.
Thus the venous orifices of the ventricles are closed at the end of the auricular
systole; i.e., the end of the ventricular diastole. The ventricular systole
which follows simply serves to place the valves under greater tension thus
closing them still more firmly. It should be recollected that the diminution
in the breadth of the base of the heart in its transverse diameters during

FIG. 152. — The Tricuspid Valves of the Ox, Closed. Vertical section. (Krehl.)

the ventricular systole is especially marked in the neighborhood of the
venous orifices, and this aids in rendering the tricuspid valve competent to
close the openings by greatly diminishing the diameter. The cusps of the
valve meet not by their edges only, but by the opposed surfaces of their thin
outer borders. The margins of the valve are still more secured in apposition
with one another by the simultaneous contraction of the papillary muscles,
whose tendinous chords have a special mode of attachment for this very
object. They compensate for the shortening of the ventricular walls and
thus prevent the valve cusps from being everted into the auricle, an event
that does occur in certain valvular lesions.

The actions of the tricuspid and mitral valves on the right and left sides
of the heart are essentially the same.

The Semilunar Valve. — The commencement of the ventricular systole

178 THE CIRCULATION OF THE BLOOD

precedes the opening of the semilunar valve by a fraction of a second. The
intraventricular pressure increases with the progress of the systole until
there is a distinct increase over the arterial pressure, then the opening of the
valve takes place at once. The valve remains open as long as this difference
continues. When the diastole of the ventricle begins and the arterial blood
pressure exceeds the intraventricular pressure, there is an initial reflux of
blood toward the heart which closes the semilunar valve.

The dilatation of the arteries is peculiarly adapted to bring this about.
The lower borders of the semilunar valves are attached to the inner surface
of the tendinous ring which bounds the orifice of the artery. The tissue of
this ring is tough and inelastic and the valves are equally inextensible, being
formed mainly of tough fibrous tissue with strong interwoven cords. The
effect, therefore, of each propulsion of blood from the ventricle is to dilate
the wall of the first portion of the artery in the three pouches behind the
valve cusps while the free margins of the cusps are drawn inward toward
the center. This position of the valves and arterial walls is maintained
while the ventricle continues in contraction; but as soon as it relaxes, and
the dilated arterial walls can recoil by their elasticity, the blood is forced
backward toward the ventricles and onward in the course of the circulation.
Part of the blood thus forced back lies in the pouches (sinuses of Valsalva)
between the valve cusps and the arterial walls; and the cusps are pressed
together till their thin lunated margins meet in three lines radiating from
the center to the circumference of the artery, figure 151. The corpora
Arantii at the middle of the free margins insure a more effective closure.

The Sounds of the Heart. — When the ear is placed over the region
of the heart, two sounds may be heard at every beat. They follow in quick
succession and are succeeded by a pause or period of silence. The first
sound is dull and prolonged; its commencement coincides with the impulse
of the heart against the chest wall, and just precedes the pulse at the wrist.
The second sound is shorter and sharper, with a somewrhat flapping character.
The periods of time occupied, respectively, by the two sounds taken together
and by the pause between the second and the first are unequal. According
to Foster, the interval of time between the beginning of the first sound and
the second sound is o . 3 of a second, while between the second and the suc-
ceeding first it is nearly 0.5 of a second, see figures 153, 154, and 158. The
relative length of time occupied by each sound, as compared with the other,
may be best appreciated by considering the different forces concerned in
the production of the two sounds. In one case there is a strong, compara-
tively slow contraction of a large mass of muscular fibers, urging forward
a certain quantity of fluid against considerable resistance; while in the other
it is a strong but shorter and sharper recoil of the elastic coat of the large
arteries — shorter because there is no resistance to the flapping back of the
semilunar cusps as there was to their opening. The sounds may be ex-

THE SOUNDS OF THE HEART

179

pressed by the words lubb — dub. The beginning of the first sound corre-
sponds in time with the three coincident events, namely, the beginning of
the contraction of the ventricles, the closure of the tricuspid and mitral
valves, and the first part of the dilatation of the auricles. The sound con-
tinues through a somewhat longer interval than the second sound. The
second sound, in point of time, immediately follows the cessation of the

FIG. 153. — Simultaneous Tracings of the Cardiac Impact, or Cardiogram (lower), and
the Heart Tones (upper), of Man. The cross strokes at the beginning of the cardiac sound
tracing and on the cardiogram mark the synchronous events. (Hiirthle.)

ventricular contraction, and corresponds with the commencing dilatation of
the ventricles and the opening of the semilunar and mitral valves, figure 154.
The exact cause of the first sound of the heart is not absolutely known.
Two factors probably enter into it. First, the vibration of the semilunar and
mitral valves and of the chordae tendineae. Second, the vibration of the

FIG. 154. — Simultaneous Tracings of the Heart Tone and Pulse of the Carotid in the
Dog. A i and A2, First and second sounds; P, pulse; S, time in tenths and fiftieths of a
second. (Einthoven and Geluk.)

muscular mass of the ventricles themselves. The same mechanical condi-
tions produce equal tension on the ventricular muscle itself and, according
to the second view, this is sufficient to account for the first sound. Looking
upon the contraction of the heart as a simple contraction and not as a series
of contractions, or tetanus, it is at first sight difficult to see why there should
be any muscular sound when the heart contracts.

l8o THE CIRCULATION OF THE BLOOD

The cause of the second sound is more simple and definite than that of
the first. It is entirely due to the vibration consequent on the sudden closure
of the semilunar valves when they are pressed down across the orifices of
the aorta and pulmonary artery. The influence of these valves in producing
the sound was first demonstrated by Hope who experimented with the hearts
of calves. In these experiments two delicate curved needles were inserted,
one into the aorta and another into the pulmonary artery below the line of
attachment of the semilunar valves. After being carried upward about
half an inch the needles were brought out again through the coats of the
respective vessels, so that in each vessel one valve was held back against
the arterial walls. Upon applying the stethoscope to the vessels it was
found that after such an operation the second sound had ceased to be audible.

Tube to communicate
with the tambour

Tympanum Ivory Tape to attach

knob instrument to the chest

FIG. 155. — Cardiograph. (Sanderson's.)

Disease of these valves, when sufficient to interfere with their efficient action,
also demonstrates the same fact by modifying the second sound or destroying
its distinctness.

The Cardiac Impulse. — The heart may be felt to beat with a slight
shock or impulse against the walls of the chest at the level of the fifth inter-
costal space on the left side. Its extent and character vary in different
individuals, a factor of considerable clinical significance, and therefore es-
pecially discussed in works on clinical diagnosis. The cause of the cardiac
impulse has been variously described. It will be remembered that during
the period which precedes the ventricular systole the relaxed heart rests
quietly in the pericardial cavity and with its apex exerting no pressure
against the wall of the chest. When the ventricles contract, their walls
suddenly become firm and tense. Being firmly attached to the base the effect
of the movement is to press the hardened ventricle against the chest wall.
The discharge of the contents of the ventricle into the curved aorta intensi-

THE CARDIAC IMPULSE l8l

fies this pressure by its mechanical effect in tending to straighten the curve
of that vessel and thus holds the ventricle in firm contact with the chest.
It is this sudden pressure of the contracting heart against the chest wall that
is felt on the outside. The impact or shock is possibly more distinct because

Screw to adjust the lever

i

Writing lever Tambour Tube to the cardiograph

FIG. 156. — Marey's Tambour, to which the Movement of the Column of Air in the
Cardiograph is Conducted by a Tube, and from which it is Communicated by the Lever
to a Revolving Cylinder so that the tracing of the movement of the cardiac impulse is
obtained.

of the partial rotation of the whole heart toward the right and front along
its long axis. The movement of the chest wall produced by the ventricular
contraction against it may be registered by means of an instrument called
the cardiograph ; and the record or tracing, called a cardiogram, corresponds

FIG. 157. — Typical Cardiogram (upper trace) from the Dog. Taken simultaneously
with the aortic pressure (middle) and intraventricular pressure (lower) tracings. Time
in o. 01 of a second. (Hiirthle.)

almost exactly with a tracing obtained by an instrument applied over the
contracting ventricle itself.

The cardiograph, figure 156, consists of a cup-shaped metal box over
the open front of which is stretched an elastic india-rubber membrane upon

182

THE CIRCULATION OF THE BLOOD

which is fixed a small knob of hard wood or ivory. This knob, however,
may be attached, as in the figure, to the side of the box by means of a spring,
and may be made to act upon a metal disc attached to the elastic membrane.
The knob is for application to the chest wall over the place of the greatest
impulse of the heart. The box or tambour communicates by means of an
air-tight tube with the interior of a second or recording tambour supplied

with a long and light writing lever. The
shock of the heart's impulse being com-
municated to the ivory knob, and through
it to the first tambour, the effect is, of
course, at once transmitted by the column
of air in the elastic tube to the interior
of the second recording tambour, also
closed, and through the elastic and mov-
able disc of the latter to the writing lever
which is adjusted to a registering appa-
ratus. This latter generally consists of a
cylinder or drum covered with smoked
paper and revolving by clock-work with
a definite velocity. The point of the
lever writing upon the paper produces
a tracing of the heart's impulse, a
cardiogram.

Endocardiac Pressure.— The effect
of the muscular contractions and relaxa-
tions of the walls of the heart during its
systole and diastole is to produce varying
changes of pressure on its content of
blood. When this pressure is measured
by the proper instrument it is found that
the pressure in the left ventricle varies
between wide ranges. With the begin-
ning of the muscular contraction, the
pressure rises till it slightly exceeds that
of the pressure of the aorta, remains high
for a brief interval of time, then slowly

and quietly decreases to less than that of atmospheric pressure and remains
low until the beginning of the next systole. For the right ventricle the events
and variations are relatively the same.

In order to determine the endocardiac pressure communication must
be established with the cavities of the heart. This is accomplished by a
tube known as a sound, which is introduced into the left ventricle by passing
it down the common carotid artery or into the right auricle and ventricle

FIG. 158. — Double Cardiac Sound
for Simultaneous Registration of the
Blood Pressure in the Right Auricle
and Ventricle, or in the Aorta and
Left Ventricle. (Hurthle.)

ENDOCARDIAC PRESSURE

through the jugular vein. When such tubes are introduced and connected
with some form of pressure-recording apparatus, accurate tracings of the
variations in pressure during the heart-beat are obtained.

FIG. 159. — Simultaneous Registration of Curves of the Left Intraventricular Pressure
(lower), the Aortic Pressure (middle), and the Cardiac Impact (upper). Time, o.oi of a
second. (Hurthle.)

Systole,

Diastole/.

FIG. 160. — Schematic Cardiogram I, and Intraventricular Pressure Curves from the
Dog. The ventricular pressure curve of the descending type is represented by the dotted
line. Pressure in millimeters of mercury, time in tenths of a second. (Hurthle.)

Chauveau and Marey have been able to record and measure with much
accuracy the variations of the endocardiac pressure and the comparative
duration of the contractions of the auricles and ventricles. They placed

184 THE CIRCULATION OF THE BLOOD

three small india-rubber air-bags or sounds in the interior, respectively, of
the right auricle, the right ventricle, and in an intercostal space in front of
the heart of living animals — the horse. These bags were connected by
means of long narrow tubes with three levers arranged one over the other

FIG. 161. — Apparatus of MM. Chauveau and Marey for Estimating the Variations of Endo-
cardiac Pressure, and Production of the Impulse of the Heart.

in connection with a registering apparatus, figure 161. The synchronism
of the impulse with the contraction of the ventricles is also well shown by
means of the same apparatus, and the causes of the several vibrations of
which it is really composed have been demonstrated.

FIG. 162. — Tracings of i, Intra-auricular; 2, Intraventricular Pressures; and 3, of
the Cardiac Impulse of the Heart. To be read from left to right. Obtained by Chauveau
and Marey.

In the tracing, figure 162, the intervals between the vertical lines rep-
resent periods of a tenth of a second. The parts on which any given vertical
line falls represent simultaneous events. It will be seen that the contraction
of the auricle, indicated by the marked curve at A in the first tracing, causes
a slight increase of pressure in the ventricle which is shown at A ' in the second

ENDOCARDIAC PRESSURE 185

tracing, and produces also a slight impulse, which is indicated by A" in the
third tracing. The closure of the semilunar valves causes a momentarily
increased pressure in the ventricle at D', affects the pressure in the auricle D,
and is also shown in the tracing of the cardiac impulse D".

The large curve of the ventricular and the cardiac impulse tracings,
between A' and D', and A" and D", are caused by the ventricular contrac-
tion, while the smaller undulations, between B and C, B' and C', B" and C",
are caused by the vibrations consequent on the tightening and closure of
the tricuspid and mitral valves.

/TV*

FIG. 163. — Apparatus for Recording the Endocardiac Pressure. (Rolleston.)

It seems by no means certain that Marey's curves properly represent
the variations in intraventricular pressure. Objection has been taken to
his method of investigation: First, because his tambour arrangement does
not admit of both positive and negative pressure being simultaneously re-
corded; second, because the method is applicable only to large animals,
such as the horse; third, because the intraventricular changes of pressure
are communicated to the recording tambour by a long elastic column of air;
and fourth, because the tambour arrangement has a tendency to record
inertia vibrations. H. D. Rolleston, who has pointed out the above im-
perfections of Marey's method, has reinvestigated the subject with a more
suitable apparatus.

i86

THE CIRCULATION OF THE BLOOD

The method adopted by Rolleston is as follows:

A window is made in the chest of an anesthetized and curarized animal, and
an appropriately curved glass cannula introduced through an opening in the
auricular appendix. The cannula is then passed through the auriculo-ventric-
ular orifice without causing any appreciable regurgitation into the auricle,
or it may be introduced into the cavity of the right or left ventricle by an
opening made in the apex of the heart. In some experiments the trocar is
pushed through the chest wall into the ventricular cavity. His apparatus

FIG. 164. — Endocardiac Pressure Curve from the Left Ventricle of the Dog. The
thorax was opened and a cannula introduced through the apex of the ventricle; the abscissa
is the line of atmospheric pressure. G to D represents the ventricular contraction; from
D to the next rise at G represents the ventricular diastole. The notch, at the top of which
is F, is a post-ventricular rise in pressure from below that of the atmosphere and not a
presystolic or auricular rise in pressure.

is filled with a solution of leech extract in o . 7 5 per cent, saline solution, or with
a solution of sodium bicarbonate of specific gravity 1.083.

The animals employed were chiefly dogs. The movement of the column of
blood is communicated to the writing lever by means of a vulcanite piston
which moves with little friction in a brass tube connected with a glass cannula
by means of a short connecting tube.

When the lower part of the tube, A, is placed in communication with one
of the cavities of the heart, the movements of the piston are recorded by

FIG. 165. — Curve with a Dicrotic Summit from the Left Ventricle; the Abscissa Shows the

Atmospheric Pressure.

means of the lever, C. Attached to the lever is a section of a pulley, H, the
axis of which coincides with that of the steel ribbon, E; while, firmly fixed to
the piston, is the curved steel piston rod, /, from the top of which a strong
silk thread, /, passes downward into the groove on the pulley.

This thread, /, after being twisted several times around a small pin at the
side of the lever, enters the groove in the pulley from above downward, and

ENDOCARDIAC PRESSURE

i87

then passes to be fixed to the lower part of the curve on the piston rod as
shown in the smaller figure.

The movement of the lever, C, is controlled by the resistance to torsion of
the steel ribbon, E, to the middle of which one end of the lever is securely fixed
by a light screw clamp, F. At some distance from this clamp, the distance
varying with the degree of resistance which it is desired to give to the move-
ments of the lever, are two holders, G, G', which securely clamp the steel
ribbon.

As the torsion of a steel wire or strip follows Hooke's law, the torsion being
proportional to the twisting force, the movements of the lever point are pro-
portional to the force employed to twist the steel strip of ribbon — in other
words, to the pressures which act on the piston, B. To make it possible to
record satisfactorily the very varying ventricular and auricular pressures, the
resistance to torsion of a steel ribbon adapts itself very conveniently.

This resistance can be varied in two ways, ist, by using one or more pieces
of steel ribbon or by using strips of different thicknesses; or 2d, by varying
the distance between the holders, G, G', and the central part of the steel
ribbon to which the lever is attached.

FIG. 166. — Hiirthle's Spring Manometer. A, Viewed from the side; B, viewed from the top.

Rolleston's conclusions are: That there is no distinct and separate
auricular contraction marked in the pressure curves obtained from the right
or the left ventricle, the auricular and ventricular rises of pressure being
merged into one continuous rise. He concludes that the tricuspid and
mitral valves are closed before any great rise of pressure within the ventricle
above that which results from the auricular systole, a, figure 163. The
closure of the valve occurs probably in the lower third of the rise AB, figure
165, and does not produce any notch or wave. It is shown that the semilunar
valve opens at the point in the ventricular systole, situated at c, about or a
little above the junction of the middle and upper thirds of the ascending line
AB, and the closure about or a little before the shoulder, D. The figures

i88

THE CIRCULATION OF THE BLOOD

show, finally, that the minimum pressure in the ventricle may fall below
that of the atmosphere, but that the amount varies considerably.

On the whole, the most satisfactory recording instrument for the measure-
ment of endocardiac pressures is the membrane manometer devised by
Hiirthle. This instrument avoids mechanical errors in a most satisfactory
manner. By simultaneous tracings of the pressure in the ventricle and in
the aorta by Hiirthle's differential manometer, the exact moment of the

PAUSE

DIASTOLE

AURICLE

VENTRICLE

IMPULSE

FIG. 167. — Diagrammatic Representation of the Events of the Cardiac Cycle. For
events which occur in sequence, read in the direction of the curved arrow; for synchronous
events, read from the center to the periphery in any direction. (Coleman.)

opening and closing of the semilunar valve has been determined. By
similar methods we have been able to fix synchronism between other events
occuring during the beat. These we will summarize in the following section.
Cardiac Cycle. — The entire series of occurrences in a single heart-beat
is called the cardiac cycle. If the condition of the heart is considered at that
moment when its muscular walls are at rest it will be found that the tricuspid
and mitral valves are open, that the blood is flowing from the great veins
into the auricle and the ventricle, which form a continuous cavity, and

CARDIAC CYCLE 189

that the pressure is about that of the atmosphere, but slowly rising. Now a
wave of contraction begins on the great veins and extends toward the auri-
cles, which immediately contract and discharge their blood into the ventri-
cles, somewhat distending their walls. At this moment the ventricular
systole begins, the tricuspid and mitral valves are closed, the flow of blood
into the ventricles is checked, and the first heart sound is heard. The con-
traction of the ventricles produces a rapidly rising pressure on the enclosed
contents until the pressure exceeds that in the pulmonary artery (and aorta),
the semilunar valves open, and the blood is discharged into the arteries.
The ventricles ordinarily remain contracted for a brief moment after their
contents are emptied.

The ventricular diastole begins next and with the initial relaxation, and
the first slight fall of the intraventricular pressure below that of the aorta,
the semilunar valves close and the second sound is heard. The relaxation
rapidly proceeds and the intraventricular pressure drops to below atmos-
pheric pressure, the auriculo- ventricular valves fall open, the blood that has
been accumulating in the auricles flows into the ventricles and the whole
heart is in the state of pause described as the point of beginning.

The duration of the cardiac cycle varies with the heart rate. With a
rate of 75 per minute, the cardiac cycle will take o. 8 of a second. In round
numbers the systole of the auricle takes o . i of a second with a diastole of
0.7 of a second, o . 6 of which is in the pause or rest period. The ventricle
requires about o . 3 of a second for the systole, o . 5 of a second for the dias-
tole, with 0.2 to o . 3 of this for the pause. It is evident that the whole heart
is at rest at the same instant for from o . i to o . 2 of a second.

The relations of the cardiac sounds to the systole and the diastole have
been graphically recorded by Hiirthle, figure 153, and by Einthoven and
Geluk, figure 154. The former found that in a heart-beat lasting o. 76 of a
second the interval of time between the beginning of the first and second
sounds was o. 25 of a second, and that the sounds occur just at the begin-
ning of the ventricular systole and diastole, respectively.

During the cardiac cycle the ventricles are completely closed from the
moment of the beginning of the ventricular systole until the pressure amounts
to a little greater than the pressure in the corresponding arteries, which
takes about 0.2 of a second. From the opening of the semilunar valves
until the closure of those valves, about o . 15 of a second, the ventricular cavity
is in open communication with the arteries. There is, during the diastole,
a second moment of complete closure of the ventricles, from the time of the
closing of the semilunar valves until the ventricular pressure falls below the
auricular pressure which permits the tricuspid and mitral valves to open.

The Force of the Cardiac Action. — In estimating the amount of
work done by a machine it is usual to express it in terms of work units. A
convenient work unit for this purpose is the amount of energy required to

THE CIRCULATION OF THE BLOOD

lift a unit of weight, i.e., i gram or i kilogram, through a unit of height; i.e.,
i centimeter or i meter, the work required being i gramcentimeter for small
units, and i kilogrammeter for large units, respectively. The average work
done by the heart at each contraction can be readily computed by multi-
plying the weight of blood expelled by the ventricles by the height through
which it would have to be lifted to overcome the resistance to its discharge
from the cavities into the arteries.

The quantity of blood expelled and the pressure of the arteries can only
be estimated for man. But the computations from indirect observations
on other mammals indicate that the quantity of blood discharged from each
ventricle at a single contraction is from 80 to 100 c.c. The pressure of the
aorta, see page 208, is an average of, say, 150 mm. of mercury, or 200 cm. of
blood. The pressure in the pulmonary artery is much less, say, 30 mm. (20
to 40), of mercury or 40 cm. of blood. Collecting these facts, we have the
following computation:

Against

Work in

Blood
discharged.

pressure
column of

gramcenti-
meters.

blood.

The left ventricle

GO C C.

200 cm

18 ooo

The right ventricle

OO C.C.

40 cm.

•?.6oo

Total .

90 c.c.

240 cm.

21,600

This computation shows that each heart-beat expends 21,600 gramcenti-
meters (21.6 grammeters) of work. The amount of energy developed in the
contractions of the auricles may be ignored in this calculation, which is at
best only of relative value. Calculations based on the determinations of
Vierordt, also other earlier determinations, give much higher figures than
are presented here.

The Properties of the Heart Muscle. — It is evident that if we are
to arrive at any adequate explanation of the action of the heart, one of the
first questions that must be considered is, what are the fundamental
properties of heart muscle, as such?

It has already been shown, page 62, that the muscular fibers of the
heart differ in structure from skeletal muscle fibers on the one hand, and
from unstriped muscle on the other, occupying an intermediate position
between the two varieties. The heart muscle, however, possesses a property
which is not possessed by skeletal muscle, or by unstriped muscle to such a
degree, namely, the property of contracting rhythmically.

THE PROPERTIES OF THE HEART MUSCLE 1 91

Rhythmicity. — The property of rhythmic contraction is sho\vn by the
action of the heart within the body; its systole is followed by its diastole in
regular sequence throughout the life of the individual. The force and fre-

FIG. 168. FIG. 169.

FIG. 168. — The Heart of a Frog (Rana esculenta), from the Front. V, Ventricle; Ad,
right auricle; As, left auricle; B, bulbus arteriosus, dividing into right and left aortae.
(Ecker.)

FIG. 169. — The Heart of a Frog (Rana esculenta), from the Back. s. v.t Sinus venosus
opened; c. s. s., left vena cava superior; c. s. d., right vena cava superior; c. i., vena cava
inferior; v. p., vena pulmonales; A. d., right auricle; A. s. left auricle; A. p., opening of
communication between the right auricle and the sinus venosus. X 2^-3. (Ecker.)

quency of the systole may vary from time to time as occasion requires, but
there is no interruption to the action of the normal heart or any interference
with its rhythmical contractions. Further, in an animal rapidly bled to
death, the heart continues to beat for a time, varying in duration with the

FIG. 170. — Automatic Contractions of Sinus Muscle from the Terrapin's Heart in 0.7
per cent. Sodium Chloride. Time in minutes. (New figure by L. Frazier.)

kind of animal experimentally dealt with and depending on whether or not
there is entire absence of blood within the heart chambers. Furthermore,
if the heart of an animal be removed from the body, it still continues its

192

THE CIRCULATION OF THE BLOOD

alternate
that the

'

•-3 §

a!

systolic and diastolic movements for a varying time. Thus we see
power of rhythmic contraction depends neither upon connection
with the central nervous system nor yet upon the
stimulation produced by the presence of blood
within its chambers. Whether or not rhythmicity
is a property of heart muscle, as such, was con-
clusively settled by Gaskell and by numerous
later investigators by a very simple experimental
procedure. Gaskell cut thin strips of the apex
of the ventricle of the terrapin, which is free from
the nerve cells, at least nerve ganglia, and found
that they contracted rhythmically for hours.
This experiment has become a classic one for
the study of the cardiac muscular tissue. Strips
of cardiac muscle cut from the auricle and from
the contractile walls of the venae cavse, or sinus
venosus, of the terrapin also contract rhythmically.
If the strips of muscle are kept moist with the
same blood or serum, then the rhythm of the sinus
is greater than that of the auricle, and that of the
auricle greater than that of the ventricle, a differ-
ence that is based on a physiological differentia-
tion of the tissue. The sinus muscle is also more
delicately responsive to stimuli than is the ven-
tricular muscle; i.e., it is more irritable.

Porter has performed the more difficult exper-
iment of isolating a small disc of muscle from
the ventricle of the dog, leaving only the delicate
nutrient artery through which the muscle was fed
with defibrinated blood. This isolated small
piece of ventricle contracted vigorously for many
minutes. We may conclude, then, that the
mammalian heart muscle is also automatically
rhythmic.

Tonicity. — Cardiac muscle is characterized by
its maintaining a constant degree of partial con-
traction described as muscle tone, or tonicity.
This property is possessed by all parts of the
heart. In the auricle, however, and especially in
the muscular walls of the sinus and veins, there
is considerable variation in tonicity. Botazzi
showed that in the auricle of the toad the varia-
tions of tone were wave-like and periodic, even

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THE PROPERTIES OF THE HEART MUSCLE 193

though the auricle were contracting with its ordinary fundamental rhythm.
Howell has published numerous experiments showing tone waves in
auricular and sinus muscle of the terrapin, in which muscle there may

FIG. 172. — Automatic Contractions of a Strip of Ventricular Muscle from the Apex
of the Terrapin's Heart contracting in 0.7 per cent. Sodium Chloride; from + to + 0.03
per cent. Postassium Chloride is added to the Sodium Chloride. The rhythm is recovered
very slowly when the muscle is returned to o . 7 per cent, sodium chloride. Time in
minutes (upper) and seconds (lower stroke). (New figure by Watkins and Elliott.)

or may not be occurring at the same time the ordinary fundamental
rhythmic contractions, figure 170.

Irritability of Heart Muscle. — Mention was made above of the difference

FIG. 173. — Automatic Contractions of a Strip of Ventricular Muscle from the Apex of
the Terrapin's Heart, a, Contracting in 0.7 per cent, sodium chloride; b, when 0.03 per
cent, calcium chloride solution is added. Time in minutes. (Xew figure by L. Frazier.)

in irritability of heart muscle chosen from different parts of the heart. The
irritability of the muscle of each part also varies during the different stages
of the contraction. Experiment shows that the muscle is not irritable to a
13

194 THE CIRCULATION OF THE BLOOD

stimulus applied at any time from the beginning of the contraction until
the summit of the contraction is reached. This is called the refractory
period. From the summit, through the relaxation and succeeding pause,
the irritability rapidly increases until the beginning of the next contraction.
Considering the automatically contracting muscle, the point in which the
automatic contraction is released, i.e., begins, is the point of maximal irrita-
bility. It is the moment when the irritability is so great that the muscular
equilibrium is no longer stable, and the physiological contraction results.

The irritability of heart muscle is very sharply influenced by its condition
of nutrition, especially by the inorganic salts present in the blood and lymph,
see page 199. The salt content of the blood comprises about 0.7 per cent,
sodium chloride, 0.03 per cent, potassium chloride, and 0.025 to 0.03 per
cent, calcium (phosphate probably), as well as traces of other metal bases.

FIG. 174. — Refractory Period in the Ventricular Strip of the Terrapin.

The heart muscle has been shown by numerous investigators to be delicately
responsive to the proportions of these salts in the blood, or in any artificial
solution which may be substituted for blood. If the rhythm is to be taken
as an index of the irritability, then an increase of sodium and calcium salts
increases the irritability (rhythm), while the influence of an increase in potas-
sium is to depress the irritability.

Cardiac Contractions Always Maximal. — The heart muscle exhibits
another property which distinguishes it from ordinary skeletal muscle, viz.,
the way in which it reacts to stimuli. The latter, Chapter XIII, reacts
slightly to a stimulus little above the minimal, and with an increase of the
strength of the stimulus will give contractions of increasing amplitude until
the maximum contraction is reached. In the case of the heart-beats this is
not so, since the minimal stimulus which has any effect is followed by the maxi-
mum contraction; in other words, the weakest effectual stimulus brings out as
great a contraction as the strongest. If a contraction is induced earlier than

THEORIES OF THE HEART-BEAT 195

it would automatically occur, then the succeeding pause is longer; i.e., there is
a compensatory pause. Also the contraction induced is smaller and the one
following the compensatory pause is proportionately larger. This observa-
tion can easily be demonstrated on the heart strip, see figure 174, or on the
whole ventricle of the frog, which was originally used by Bowditch.

Nerve influence, nutrition, temperature, etc., will of course affect the
extent of the contractions, but under a given set of conditions it is held that
the contractions which occur are maximal for the particular state. This
is more readily understood when taken in connection with the fact that when
a contraction originates in a cardiac cell it is conducted throughout the extent
of all the cells of the muscular mass.

Theories of the Heart-beat. — The cause of the rhythmic power of
the heart as a whole has been the subject of much discussion and experimen-
tal observation. Two leading hypotheses have given inspiration to investi-
gators, and now one, now the other theory has attracted followers as new
facts have been discovered. The hypotheses that have been advanced to
explain the heart-beat are known as the neurogenic theory and the myogenic
theory, respectively.

The heart has long been known to have the power of rhythmic contrac-
tions after removal from the body and after all connection with the central
nervous system has been destroyed. The isolated heart, even of man, has
been made to contract with good rhythm when kept at the proper tempera-
ture and given the proper nutritive fluid.

The Neurogenic Theory. — The neurogenic theory attributes the remark-
able power of the heart to continue its contractions after removal from the
body, and presumably while in the body, to the presence of the local collec-
tions of nerve cells. The local nervous mechanism in the frog consists of
three chief groups of cells or ganglia.. The first group is situated in the
wall of the sinus venosus at the junction of the sinus with the right auricle,
RemaWs ganglia; the second group is placed near the junction between
the auricles and ventricles, Bidder's ganglia; and the third in the septum
between the auricles, von Bezold's ganglia. Small ganglia have been de-
scribed for the base of the ventricle, but no ganglia are present in the apical
part of the ventricles, though isolated cells have been found. The nerve
cells of which these ganglia are composed are generally unipolar, seldom
bipolar. Sometimes two cells are said to exist in the same envelope, con-
stituting the twin cells of Dogiel. The cells are large, and have very large
round nuclei and nucleoli, figure 175. As regards the automatic move-
ments of the heart when removed from the body, our knowledge has been
derived from the study of the hearts of the frog, tortoise, dog, cat, and rabbit.

If removed from the body entire, the frog's or terrapin's heart will con-
tinue to contract for many hours and even days, and the contraction has no
apparent difference from the contraction of the heart before removal; it

196

THE CIRCULATION OF THE BLOOD

will take place, as we have mentioned, without the presence of blood or
other fluid within its chambers. Not only is this the case, but the auricles
and ventricle may be cut off from the sinus, and both parts continue to pul-
sate; and, further, the auricles may be divided from the ventricle with the
same result. If the heart be divided lengthwise, its parts will continue to
pulsate rhythmically. The ventricle remains comparatively quiet, contrac-
tions occurring at longer intervals, if at all. However, the ventricle remains
irritable so long as bathed in blood, and will contract upon receiving a slight
stimulus; in fact, a single stimulus will often call forth a series of contractions
of the ventricle. The frog's ventricle, when its muscular and nervous con-

FIG. 175. — Isolated Nerve Cells from the Frog's Heart. 7, Usual form; II, twin cell; C,
capsule; N, nucleus; P, process. (From Ecker.)

nections with the auricle are physiologically severed, as by crushing, will
remain quiet when fed by its own blood, but contracts rhythmically when
fed with physiological salt solution.

It will be thus seen that the rhythmical movements appear to be more
marked in the parts supplied by the ganglia, that ventricular pieces con-
tract when still connected with the auricles, and that rhythmic contractions
of the ventricles do not readily occur in the ordinary condition when irri-
gated with blood. These are regarded as facts peculiarly in favor of the
neurogenic theory.

The Myogenic Theory. — In the myogenic theory the heart's rhythmical
contractions are explained as due to the inherent property of the cardiac
muscle itself. Most convincing facts in support of this theory have been
arrived at by a study of cardiac muscle, as such, and by studies on the whole
heart, particularly by Gaskell's method of blocking. The term blocking
is explained as follows: It will be remembered that under normal con-
ditions the wave of the contractions in the heart starts at the sinus and
travels down over the auricles to the ventricles, the irritability of the muscle
and its power of rhythmic contractions being greatest in the sinus, less in
the auricles, and least in the ventricles. By an arrangement of ligatures
or by a system of clamping one part of the heart may be more or less isolated

THEORIES OF THE HEART-BEAT IQ7

from any other portion. With such a clamp the contraction waves can be
more or less completely interrupted in their passage from the sinus end of
the heart past the clamp toward the ventricular end. If the clamp is com-
plete, so as to interrupt the physiological continuity between the parts, then
any contractions in the apical portion \vill be entirely independent of those
in the sino-auricular portion. If the blocking is partial only, then the ven-
tricular end of the heart always contracts in unison with the sino-auricular,
although its rate may be as i to i, i to 2, i to 3, etc. In other words, only
every second or every third sino-auricular contraction will be able to pass
the block.

The effects of blocking are due to the interruption of muscle continuity
rather than nerve continuity. This is beautifully demonstrated by an experi-
ment of zigzag cutting of the ventricle in the terrapin, since it cannot be
supposed that any nerves would pass through the ventricular mass by such
a zigzag course. In this experiment the contraction wave passes down
over the muscle and around the end of the cuts until it reaches the apex,
and the apex contracts in sequence with the auricle and base of the ventricle.
If the zigzag cuts are made almost complete so as to reduce to a minimum
the muscular tissue \vhich bridges from one cut to the next, then it happens
that occasional contractions will be unable to pass and the apex contracts
in the ratio of i to 2, or i to 3, etc., as described above. Thus, division of
the muscle has the same effect as partial clamping in the same position.

It was thought for a long time that in the mammal there was no mus-
cular continuity between the auricles and ventricles to conduct the contrac-
tion wave and that this was an insurmountable difficulty in the way of accept-
ing the myogenic theory of the heart beat. In 1893 Kent described a bundle
of muscle fibers arising in the wall of the right auricle and near the septum
and running down into and forming a muscular connection with the ventri-
cles. This bundle was also independently described by His, Jr., and gen-
erally bears his name. This band is called the atrioventricular bundle. The
bundle consists of a somewhat less differentiated type of cardiac fibers
imbedded in a syncytium and not only connects the auricle and ventricle, but
forms a network of strands among the proper fibers of the auricles and
ventricles. Miss De Witt has recently (1909) made an excellent model of
this system which is reproduced in figure 176.

The demonstration of the atrioventricular bundle has proven to be of
the strongest support to the myogenic theory. Erlanger has recently shown,
by an ingenious device for partially clamping this muscular band, that even
the mammalian ventricle exhibits the phenomenon of heart block. In his
experiments the ventricle contracts in unison with every auricular contrac-
tion, or only every second or every third, according to the degree of blocking.

It was shown long ago (by Merunowicz in 1875) that the isolated apex
of the ventricle of the frog remains quiet when filled with blood, but readily

THE CIRCULATION OF THE BLOOD

gives good rhythmic contractions in physiological saline and other artificial
solutions. The inactivity in blood is not necessarily, therefore, due to
nervous isolation from the ganglionated parts of the heart. Contractions
occur in the small bits of ventricular muscle as isolated by Gaskell, and
these may continue for hours. It is well known also that the embryonic
heart contracts rhythmically before nerve cells have reached the organ or
even before any blood is formed, as shown in the embryos of certain fishes.

The phenomena of heart block, the contractions of the ventricular apex
when physiologically isolated from the parts of the heart which contain the
ganglia, the behavior of isolated strips of the heart, especially of the ventricle
and the rhythm of the embryonic heart are all held to be in favor of the myo-
genic theory.

Automaticity of the Heart.— Whether one adopts the neurogenic
or myogenic theory of the heart's beat, he has still to explain the origin of
the heart's rhythm. In the former case one must look to the nervous
apparatus for the origin of the rhythm; in the latter case, the muscular ap-

FIG. 176. — Stereoscopic photograph of a model of the atrioventricular system in the
calf's heart. Viewed from behind. The auricular network or knoten is not shown.
Should be examined through a stereoscope. (Lydia M. DeWitt.)

paratus, a fact to which Brown-Sequard long ago called attention. In the
former view the problem is to explain not only the periodic origin of the
nerve discharges from local cardiac ganglia, but also to explain the orderly
discharge of nerve impulses which maintains the proper sequence between
sinus, auricle, and ventricle.

To perhaps the majority of physiologists the facts are best explained
by the myogenic theory. The origin of the rhythm is here supposed to be
due to the automatic property of the muscle itself. The sequence is ex-
plained on the observed facts, first, that muscular contraction in cardiac
muscle is conducted throughout the continuity of the mass, and second,

RELATION OF RHYTHM TO NUTRITION7 1 99

the most highly rhythmic part of the muscular tissue of the heart, the sinus,
sets the rhythm for the entire heart.

The function of the nervous system, by this view, is not to originate the
rhythm, but to regulate it, the detail of which
will be discussed below.

Relation of Rhythm to Nutrition. — The
whole heart, like the muscular parts of which

it is composed, responds delicately to its con- -| £

dition of nutrition. In the frog and the turtle
hearts the muscular fibers are brought in inti-
mate contact with the blood contained within
its cavities. In the mammalian heart, on the

other hand, a distinct system of vessels, the

^H^iBi^^^SI "G ~"~
coronary vessels and the vessels of Thebesius,

supply blood to the organ. If the heart is |t:

supplied with nutrient fluid similar to its
normal blood, and with proper aeration to
insure plenty of oxygen, it contracts with a
strong rhythm for many hours. This rhythm, •• -£-

however, responds quickly to changes in the
composition of the nutrient fluid. An abundant
supply of oxygen is absolutely necessary to the
maintenance of rhythm in the mammalian
heart, though the heart, especially a cold-
blooded heart, will contract for a time in an
atmosphere of hydrogen. No doubt the
organic constituents of blood are very essen-
tial to the prolonged maintenance of rhythm
in the heart, but the heart is not dependent on
these ingredients for its immediate reactions.
The inorganic salts seem to be peculiarly
closely related to the development and char-
acter of the cardiac rhythm, figures 172, 173,
and 174. Both the cold-blooded heart and

the mammalian heart respond very quickly to u

the influence of these salts. The details of

^^^35BBSH88E^5^^B — • _n

this influence have been discussed on page 193. mH ^ "

It is somewhat surprising, however, that the

highly organized mammalian heart will con-

tract rhythmically for hours on purely inor-

ganic nutrient fluid, provided only that the

oxygen be supplied in sufficient quantity and

under high enough tension. The isolated

It

•8*°

200 THE CIRCULATION OF THE BLOOD

mammalian heart also responds sharply to a change in the salt content of
the perfusion solution. For example, addition of potassium chloride to a
Locke solution slows or even suppresses the rate, as is shown in figure 177.

THE REGULATIVE INFLUENCE OF THE CENTRAL NERVOUS
SYSTEM ON THE HEART.

The heart is capable of automatic rhythmic movement, yet while in the
body its beats are under the constant control of the central nervous system.
The influence which is exerted by the central nervous system is of two kinds:
first, in the direction of slowing or inhibiting the beats, and second, in the
direction of accelerating or augmenting the beats. The influence of the
first kind is brought to bear upon the heart through the fibers of the pneu mo-
gastric or vagus nerves, and that of the second kind through the sympathetic
nerves.

The Inhibitory Nerves. — It has long been known, indeed since the
experiments of the Weber brothers in 1845, that stimulation of one or both

FIG. 178. — Effect on the Heart Rate and on the Arterial Blood Pressure of Stimulating
the Right Vagus of the Dog. Stimulus applied at the mark "on" and removed at "off."
Pressure in millimeters of mercury shown by the scale to the left. Time in seconds. (New
figure by Hill and Chilton.)

vagi produces slowing of the rhythm of the heart. It has since been shown,
in all of the higher vertebrate animals experimented with, that this is the
normal reaction to vagus stimulation. Moreover, a section of one vagus,
or at any rate of both vagi, produces acceleration of the pulse; and stimu-
lation of the distal or peripheral end of the divided nerve normally pro-
duces slowing or stopping of the heart's beats.

THE INHIBITORY NERVES 2OI

It appears that any kind of stimulus, either chemical, mechanical, elec-
trical, or thermal, produces the same effect, but that of these the most potent
is a rapidly interrupted induction current. A certain amount of confusion
has arisen as to the effects of vagus stimulation in consequence of the fact

FIG. 179. — Tracing Showing Action of the Vagus on the Heart of the Terrapin. Aur,
Auricular; vent, ventricular tracing. The part between words "on" and "off" indicates
a period of vagus stimulation. The part of tracing to the left shows the regular contractions
before stimulation. During stimulation, and for some time after, the beats of the auricle
and ventricle are arrested. After they commence again the auricle contracts weakly at
first, but soon acquire a much greater amplitude. The ventricular contractions that
follow the first weak auricular contractions are maximal in the terrapin, but not so in the
frog. See next figure. Time in seconds. New figure.

that fibers of the sympathetic nerve run within the trunk of the vagus nerves
of some animals.

The result of stimulation also depends, to some extent, upon the exact
position of the application of the stimulus. Speaking generally, however,

FIG. 180. — Tracing Showing Diminished Amplitude and Slowing of the Pulsations of
the Auricle and Ventricle of the frog without Complete Stoppage during Stimulation of the
Vagus. (After Gaskell.)

excitation of any part of the trunk of the vagus produces inhibition, the
stimulus being particularly potent if applied to the points where the nerves
enter the substance of the heart at the situation of the sinus ganglia. The
stimulus may be applied to either vagus with like effect.

2O2

THE CIRCULATION OF THE BLOOD

The effect of the stimulus of the vagus is twofold — to slow the rate, or
even to bring the heart to a complete standstill, and to produce a decrease
in the amplitude. The slowing does not take place until after the lapse of
a short latent period during which one or more contractions may occur.
The stoppage may be due either to prolongation of the diastole or to diminu-
tion of the systole. Vagus stimulation inhibits the spontaneous beats of
the heart only, it does not entirely suppress the irritability of the heart
muscle, since mechanical stimulation may bring out a beat during the pause
caused by vagus stimulation. The inhibition of the beats varies in duration
according to the strength of the stimulus and the animal stimulated. The
heart of the terrapin can be completely inhibited for hours with a strong
stimulus. The heart of a dog escapes from inhibition in a few seconds.
When the beats reappear, the few first are usually feeble, and may be auric-
ular only; after a time the contractions become more and more strong, and

FIG. 18 1. —Arterial Blood Pressure of the Dog, Showing the Effect on the Heart Rate
of Cutting both Vagus Nerves as marked. The scale to the left shows the pressure in
millimeters of mercury. Time in seconds. The momentary inhibition just before the
nerves were cut is probably due to mechanical stimulation of the nerves. (New figure by
Hill and Chilton.)

very soon exceed both in amplitude and frequency those which occurred
before the application of the stimulus. This phenomenon is shown in
figure 179, which illustrates the action of the vagus on the terrapin's heart.

The inhibitory fibers have their origin in nerve cells in the motor nucleus
of the vagus, and of the glosso-pharyngeal location in the floor of the fourth
ventricle. These cells have not been exactly identified, but the center is
called the cardio-inhibitory center. The center is a bilateral one and the
fibers from it pass into the great vagus trunk to be distributed to the heart
through superior and inferior cardiac branches which help to form the cardiac
plexus. Within the heart the inhibitory fibers form synapses with cells
whose axones reach the cardiac muscle cells. The cardiac-inhibitory center
is in constant tonic activity, and the tonic influence is eliminated when both
nerves are cut, figure 181.

THE INHIBITORY NERVES

203

The center is also influenced by afferent impulses which may reach it
from the heart itself, by the depressor nerve, or from other parts of the body.
These reflex stimulations of the heart through the vagus center are constantly
occurring during our daily life and are the most potent factors in co-ordi-
nations going on between the heart and the rest of the body.

Di-s

FIG. 182. — Diagrammatic Representation of the Origin and Course of the Cardiac
Nerves in the Dog. Di, D$, first to fifth dorsal spinal nerves. Inhibitory fibers in blue,
accelerators in red. (Modified from Moret.)

Rhythmical alterations of the heart rate occur in association with the
effects of the mechanical variations of pressure of the thorax on the heart
and blood vessels. Apparently the cardiac-inhibitory center is stimulated
during the fall of blood pressure. The activity of the center produces a
slower rate of the heart during expiration, shown in figure 243. This vari-
ation in heart rate disappears when the vagi are cut off from the center.

204 THE CIRCULATION OF THE BLOOD

The Accelerator Nerves. — The influence of the accelerator nerves
reaching the heart through the sympathetic, is the reverse of that of the
vagus. Stimulation of the sympathetic, even of one side, produces acceler-
ation of the rate of the heart-beats, and, according to certain observers, section
of the nerve produces slowing. The acceleration produced by stimulation
of the sympathetic fibers is accompanied by increased force, and so the action
of the nerve is more properly termed augmentor. The sympathetic differs
from the vagus in several particulars other than the augmentation which it
produces; first, the stimulus required to produce any effect must be more
powerful than in the case with the vagus stimulation; second, a longer time
elapses before the effect is manifest; and third, the augmentation is followed
by exhaustion, the beats being after a time feeble and less frequent. The
stimulation of the vago-sympathetic in the frog, which usually produces
inhibition, will occasionally produce acceleration, especially if the heart is
beating feebly at the time of the stimulation.

The fibers of the sympathetic system, which influence the heart-beat in
the frog, leave the spinal cord by the anterior root of the third spinal nerve.
They pass by the ramus communicans to the third sympathetic ganglion,
thence to the second ganglion, the annulus of Vieussens (around the sub-
clavian artery), through the first ganglion, and along the main trunk of
the sympathetic to near the exit of the vagus from the cranium. There
the two nerves join and run down to the heart within a common sheath,
forming the vago-sympathetic trunk.

In the dog the augmentor fibers leave the cord by the anterior roots of
the second and third dorsal nerves, and possibly also by the first, fourth,
and fifth dorsal nerves. They pass by the rami communicantes to the gang-
lion stellatum, or first thoracic ganglion around the annulus of Vieussens
to the inferior cervical ganglion of the sympathetic. Fibers from the annulus
or from the inferior cervical ganglion proceed to the heart, figure 182. The
course of the augmentor fibers in the spinal cord is not so well known except
that they originate in an augmentor center in the medulla. The circulation
of venous blood appears to stimulate the augmentor center, and of highly
oxygenated blood the inhibitory center.

The accelerator center, like the inhibitory, is in constant tonic activity;
and the cardiac acceleration on cutting the vagi, shown in figure 181, is in
part to be ascribed to this tone. When both nerves are stimulated together,
the resulting rate is the algebraic sum of the opposed influences, according
to Hunt. The accelerator center is influenced by afferent impulses arising
throughout the body, and these reflexes contribute to the general co-ordina-
tion of the chest with the activities of the body.

In addition to direct and reflex stimulation, impulses passing down from
the cerebrum may have a similar effect.

Other Influences which Affect the Heart. — A great variety of special

OTHER INFLUENCES WHICH AFFECT THE HEART 205

conditions influence the heart's action in the normal body, conditions that
are not discussed directly under any of the categories treated above. Of
these may be mentioned the coronary circulation, temperature, mechanical
tension, age.

The Coronary Circulation. — The contractions of the heart cannot long
be maintained without a due supply of blood or other nutrient fluid. The
nutrient fluid for the heart of man and the mammals is supplied from the
coronary arteries and the vessels of Thebesius. The coronary arteries arise
from the base of the aorta, where they receive the benefit of the highest arterial
pressure. The coronary arteries are terminal arteries; that is, they do not
permit the establishment of a collateral circulation when one of their branches
is blocked. If the block be complete, that portion of the heart wall supplied
by the branch dies. The immediate effect of the closure of a large' coronary
branch, in the dog, may be occasional and transient irregularity or arrest
of the ventricular contractions preceded by irregularities in the force of the
contractions and a diminution in the amount of work performed. The
force, rather than the rate, of the ventricular contractions is closely dependent
upon the blood supply to the coronary arteries. Porter and others have
shown that the pressure in the coronary vessels follows closely the pressure
in the aorta and that there is not, as formerly claimed, a closure of these
vessels by the pressure of the systole of the ventricle.

The vessels of Thebesius, which have been demonstrated to open both
into the auricular and ventricular cavities, must now be looked upon, ac-
cording to the investigations of Pratt, as an important source of cardiac
nutrition. Blood may pass through them by way of connecting branches
to the coronary arteries and veins. Pratt succeeded in maintaining cardiac
contractions for several hours when the only source of nutrition was from
these vessels. This source of nutrition may account for the survival of
hearts for years where pronounced arterio-sclerosis of the coronary arteries
exists.

Alteration of Temperature. — The effect of cold is to slow the rate of the
heart-beat, and if the heart of a frog be cooled down to o° C. it will stop
beating. It is said that the frog's heart may be frozen, and when thawed will
renew its spontaneous beats. The effect of heat is to quicken and shorten
the heart-beats, but at a moderate temperature, 20° C., the contractions are
increased in force.

The isolated mammalian heart is influenced by temperature variations
in much the same way as that of the frog. It will contract slowly in a low
temperature and rapidly in a temperature higher than that normal to the
body. The very rapid heart in some high fevers is in part due to the increase
in temperatures which affects the heart directly.

Mechanical Tension. — The mechanical factors produced by the heart-
beat are so prominent that it would be surprising indeed if there were no

206 THE CIRCULATION OF THE BLOOD

reaction of these mechanical conditions on the heart itself. The isolated
cardiac muscle responds very quickly to variations in tension. Beginning
with a low tension the activity of heart muscle is increased up to a certain
optimum tension, after which further increase is unfavorable to the develop-
ment of automatic rhythm. A quite strong stretching will paralyze the
muscle.

Tension on the whole heart influences its activity, not only through the
effects on the muscle, but indirectly through the nervous mechanism. High
tension, such as contracting against a high aortic pressure, stimulates sensory
nerves of the heart which, acting through the depressor nerve on the inhibi-
tory center, produce reflex slowing of the heart. It also produces reflex
vaso-dilatation. Both reflexes relieve the high tension on the heart. This
nerve reaction takes place with a tension which still mechanically stimulates
the cardiac- muscle substance, and the inhibitory effects must therefore over-
come the direct stimulating effect of the tension on the muscle fibers.

Age, Sex, etc. — The average heart rate for the normal adult man is 72
times a minute, but this rate will vary much in different individuals accord-
ing to the age, sex, size, and personal equation. The frequency of the heart's
action gradually diminishes from the commencement to near the end of life,
but is said to increase again somewhat in extreme old age, thus:

Before birth the average number of pulsations

per minute is 150

Just after birth 130 to 140

During the first year 1 1 5 to 130

During the second year 100 to 1 1 5

During the third year 90 to 100

About the seventh year 85 to 90

About the fourteenth year 80 to 85

In adult age 70 to 80

In old age 60 to 70

In decrepitude 65 to 75

The heart rate is greater in woman than in man. It is also greater in
small than in large individuals. The rate varies from the type in certain
individuals where no cause can be assigned other than personal equation.

Poisons and Other Chemical Substances. — A large number of chemical
substances have a distinct effect upon the cardiac contractions. Of these
the most important are atropine, muscarine, digitalis, barium, nicotine,
caffeine, etc.

Atropine produces considerable augmentation of the heart-rate, and
when acting upon the heart prevents inhibition by vagus stimulation. Its
effects are produced by poisoning the nerve endings of the vagus within
the heart. With these endings poisoned, stimuli arising in the inhibitory
center of the medulla (tonic activity), or artificially applied to the vagus,
cannot reach the heart muscle, and inhibition is impossible.

THE CIRCULATION THROUGH THE BLOOD VESSELS 2Oy

Muscarine, which is obtained from various species of poisonous fungi,
produces marked slowing of the heart-beats, and, in larger doses, stoppage
of the heart. It produces an effect similar to that of prolonged vagus stimu-
lation. The effect can be removed by the action of atropine, hence is
supposed to stimulate the nerve endings of the vagus.

Digitalis slows the heart by stimulating the vagi at their origin in the
inhibitory center in the medulla. The heart muscle itself is also rendered
more excitable.

Veratrine and aconitine have a somewhat similar effect.

Nicotine and caffeine are both very powerful cardiac stimulants. The
great injurious effects of nicotine on the heart are due to two causes, first,
to paralysis of the nervous mechanism and relative loss of control, second,
to the great direct stimulation of the cardiac muscle. The constant over-
use of tobacco, therefore, very sharply weakens the efficiency of the heart.
Caffeine does not lead to so great disturbance of the heart's nutrition as
does nicotine.

THE CIRCULATION THROUGH THE BLOOD VESSELS.

Blood Pressure. — The subject of blood pressure has been already
incidentally mentioned more than once in the preceding pages; the time has
now arrived for it to receive more detailed consideration.

That the blood exercises pressure upon the walls of the vessels containing
it is due to the following facts:

The heart at each contraction forcibly injects a considerable amount of
blood, 80 to 100 c.c., suddenly and quickly into the arteries.

The arteries are highly distensible and stretch to accommodate the extra
amount of blood forced into them. The arteries are already full of blood
at the commencement of the ventricular systole, since there is not sufficient
time between the heart-beats for the blood to pass into the veins.

There is a distinct resistance interposed to the passage of the blood from
the arteries into the veins by the enormous number of minute vessels, small
arteries (arterioles) and capillaries, into which the main artery has been
ultimately broken up. The sectional area of the capillaries is several hun-
dred times that of the aorta, and the friction generated by the passage of
the blood through these minute channels opposes a considerable hindrance
or resistance in its course. The resistance thus set up is called peripheral
resistance. The friction is greater in the arterioles, where the current is
comparatively rapid, than in the capillaries, where it is slow.

The interaction of these factors — heart-beat, elastic vessels, and periph-
eral resistance — is sufficient to maintain a continuous flow of blood through
the entire circulatory system. It is the interrelation of these factors which
maintains an even and steady flow through the capillaries and past the tissues,

208 THE CIRCULATION OF THE BLOOD

where it is desirable that the conditions of blood flow should be most con-
stant. In fact, we shall find that it is through the interaction of this same
group of factors, together with the possibility of variations through the regu-
lation of their nerve- motor mechanisms, that we have the great variations
and adjustments of blood pressure, speed of flow, volume of flow, and the
regulation of volume in particular parts of the body.

Arterial Blood Pressure. — That the blood exerts considerable pres-
sure upon the arterial walls in keeping them in a stretched or distended
condition may be readily shown by puncturing any artery; the blood is
instantly projected with great force through the opening, and the jet rises to
a considerable height, the exact level of which varies with the size of the artery
experimented upon. If a large artery be punctured the blood may be pro-
jected upward for several feet, whereas if it is a small artery the jet does not
rise so high. Another characteristic of the jet of blood from a cut artery,
particularly well marked if the vessel be a large one and near the heart, is the
intermittent character of the outflow. If the artery be cut across, the jet
issues with force, chiefly from the central end. If there is considerable
anastomosis of vessels in the neighborhood the jet from the peripheral end
may be as forcible and as intermittent as that from the central end. The
intermittent flow in the arteries which is due to the action of the heart, and
which represents the systolic and diastolic alterations of blood pressure,
may be felt if the finger be placed upon a sufficiently superficial artery. The
finger is apparently raised and lowered by the intermittent distention of the
vessel occurring at each heart-beat. This intermittent distention of the
artery is what is known as the Pulse, to the further consideration of which
we shall presently return, but we may say here that in the normal condition
the pulse is a characteristic of the arterial, and is absent from the venous, flow.

At the same time it must be recollected that in the veins also the blood
exercises a pressure on its containing vessel, though it is small when compared
with the arterial pressure. As might be expected, therefore, the blood is
not expelled with so much force if a vein be punctured or cut. The flow
from the cut vein is continuous and not intermittent, and the greater amount
of blood comes from the peripheral and not from the central end, as is the
case when an artery is severed.

Methods of Measuring Arterial Blood Pressure.— The pressure in
an artery may be measured by cutting the vessel and introducing into it a
glass tube which has a tall vertical limb. A column of blood will rise in the
tube at once to the height that can be supported by the pressure in that par-
ticular vessel. If the vessel be an artery, the blood will rise several feet,
according to the distance of the vessel from the heart, and when the pressure
has reached its highest point it will be seen to oscillate with the heart-beats.
This experiment shows that the pressure which the blood exerts upon the
walls of the containing artery equals the pressure of a column of blood of a

METHODS OF MEASURING ARTERIAL BLOOD PRESSURE 2OQ

certain height. In the case of the rabbit's carotid it is equal to 90 to 120 cm.
of blood, or rather more than the same height of water. In the case of the
vein, if a similar experiment be performed, blood will rise in the tube only
for 8 or 10 cm. or less.

The usual method of estimating the amount of blood pressure differs
somewhat from the foregoing simple experiment. Instead of a simple
straight tube of glass inserted into the vessel, a U-shaped tube containing
mercury, the mercurial manometer, is employed. The artery is connected

FIG. 183. — Diagram of Ludwig's Kymograph and Mercurial Manometer. A,
Revolving cylinder, worked by a clock-work arrangement contained in the box (5), the
speed being regulated by a fan above the box; cylinder supported by an upright (6), and
capable of being raised or lowered by a screw (a), by a handle attached to it; D, C, E,
represent a mercurial manometer, a somewhat different form of which is shown in the next
figure.

with the manometer by means of a small cannula which is inserted into the
vessel, an arrangement being made whereby the cannula, tubes, etc., are
filled with a saturated saline solution to prevent the clotting of blood when
it is allowed to pass from the artery into the apparatus. The loss of blood
is prevented during the preparation of the details of the experiment by a
clamp or bull-dog forceps. The free end of the U-tube of mercury contains
a very fine glass or metal rod with a bulb which floats upon the surface of the
mercury and oscillates with the oscillations of the mercury. As soon as
14

210 THE CIRCULATION OF THE BLOOD

there is free communication between the artery and the tube of mercury, the
blood rushes out and pushes before it the column of mercury. The mercury
will therefore rise in the free limb of the tube, and will continue to do so until
a point is reached which corresponds to the mean pressure of the blood
vessel used. The blood pressure is thus communicated to one limb of the
mercurial column; and the depth to which the latter sinks, added to the
height to which it rises in the other limb, the weight of the saline solution
being subtracted, will give the height of the mercurial column which the
blood pressure balances. For the estimation of the amount of blood pres-
sure at any given moment no further apparatus than this is necessary; but

FIG. 184. — Ludwig's Mercury Manometer. The manometer is shown in figure 183,
D, C, E. The mercury which partially fills the tube supports a float in the form of a piston,
nearly filling the tube;'a wire is fixed to the float, and the writing style or pen is guided by
passing through the brass cap of the manometer tube; the. pressure is communicated to
the mercury by means of a flexible metal tube filled with fluid.

for accurately noting the variations of pressure in the arterial system, as well
as its absolute amount, the instrument is usually combined with a recording
apparatus, called a kymograph, figure 183, and permanent records are made
of the observations.

The recording apparatus consists of a revolving cylinder, figure 183, A,
which is moved by clock-work, and the speed of which is capable of regula-
tion. The cylinder is covered with glazed paper, blackened in the flame
of a lamp, and the mercurial manometer is so fixed, figure 183, D, that its
float, provided with a style, writes on the cylinder as it revolves. There are
many ways in which the mercurial manometer may be varied; in figure 184
is seen a form which is known as Ludwig's. In order to obviate the necessity
of a large quantity of blood entering the tube of the apparatus, it is usual to

METHODS OF MEASURING ARTERIAL BLOOD PRESSURE

211

have some arrangement by means of which the mercury may be made to
rise in the tube of the manometer to the level corresponding to approxi-
mately the mean pressure of the artery experimented with, so that the writing
style simply records the variations of the blood pressure above and below

FIG. 185. — Arterial Cannula. T-form for convenience in washing out clots.

the mean pressure. This is done by causing the saline solution, generally
a saturated solution of sodium carbonate or of 10 per cent, magnesium sul-
phate, to fill the apparatus from a bottle suspended at a height about that
of the pressure to be measured, and capable of being raised or lowered as

bo

*»•< • 1 tvv * t * 1 1 1 1 1 1 * t 1 * t *•*•*-* * +*-*•* t t ft *•*-*-*

FIG. 186.— Tracing of Normal Arterial Pressure in the Dog, Obtained with the
Mercurial Manometer. The smaller undulations correspond with the heart-beats; the
larger curves with the respiratory movements. Pressure is in millimeters of mercury as
shown by the scale to the left. Time in seconds. (New figure by March and Nugent.)

required for the purpose. The cannula inserted and tied into the artery
may be of several different kinds. A glass T-tube with the end drawn out
and cut so that it is oblique, and provided with a slightly constricted neck
to prevent its coming out of the artery easily, is a very convenient form,

212 THE CIRCULATION OF THE BLOOD

figure 185. Of the two free ends of the T-cannula one is connected with
the manometer, the other with the pressure bottle. The peripheral end of the
cut artery is tied to obviate the escape of blood. By this means, the pressure
communicated to the column of mercury is the forward, and not the lateral,
pressure of blood, but there is very little difference.

As soon as the experiment is begun, the writing float is seen to oscillate
in a regular manner, and a curve of blood pressure is traced upon the smoked
paper by the style (or, if a continuous roll of unsmoked paper be used, the
trace is made by an inked pen) when a figure similar to figure 186 will be
obtained. This indicates two main variations of the blood pressure. The
smaller excursions of the lever correspond with the systole and diastole of ilie
heart, and the larger curves correspond with the respirations, being called
the respiratory undulations of blood pressure, to which attention will be directed

FIG. 187.— Tracing of Normal Arterial Pressure Taken from the Rabbit with a Hurthle
Manometer. The horizontal lines show zero pressure. Time in seconds. (Dreyer.)

in the next chapter. Of course, the undulations spoken of are seen only in
records of arterial blood pressure. They are more clearly marked in the ar-
teries nearer the heart than in those more remote. The amount of the
pressure in the smaller arteries as well as the indication of the systolic rise
of pressure is, comparatively speaking, small.

In order to record the details of the undulations of arterial pressure, it is
better for some purpose to use the Hurthle membrane manometer than the
mercurial manometer. Two views of this instrument are shown in figure 166.
The instrument consists of a hollow tube and cup covered with rubber sheet
against which a disc supported by a metal spring is adjusted. The appara-
tus is filled with fluid, the interior of which is connected with the artery by
means of a metal tube and cannula. The pressure transmitted to the appa-
ratus tends to stretch the rubber and bend the spring, and the movement thus
produced is communicated by means of a lever to a writing style and so to

PRESSURE MEASUREMENTS IN MAN 213

a recording apparatus. This instrument obviates the errors which might
be caused by the inertia of the mercury in the mercurial manometer; it also
shows in more detail the variations of the blood pressure in the vessel during
and after each individual beat of the heart.

As regards the actual amount of blood pressure, from observations which
have been made by means of the mercurial manometer, it has been found
that the pressure of blood in the carotid of a rabbit is capable of supporting
a column of 90 to 120 mm. of mercury; in the dog 100 to 175 mm.; in the horse
152 to 200 mm.; and in man the pressure is estimated to be about the same
as in the dog. To measure the absolute amount of this pressure in any
artery multiply the area of its transverse section by the height of the column
of mercury which is already known to be supported by the blood pressure
in any part of the arterial system. The weight of a column of mercury thus
found will represent the absolute pressure of the blood. Calculated in this
way, the blood pressure in the human aorta is equal to i .93 kilogrammeters;
that in the aorta of the horse being 5 . 2 kilogrammeters; and that in the radial
artery at the human wrist only o . 08 kilogrammeter. Supposing the muscu-
lar power of the right ventricle to be one-fourth that of the left, the blood
pressure in the pulmonary artery will be only 0.5 kilogrammeter. The
amounts above stated represent the arterial tension at the time of the
ventricular contraction.

The arterial pressure is greatest at the beginning of the aorta, and de-
creases toward the capillaries. It is greatest in the arteries at the period of
the ventricular systole and least during the diastole. The blood pressure
gradually lessens as we proceed from the arteries near the heart to those
more remote, and again from these to the capillaries, as it does also from
the capillaries along the veins to the right auricle.

Arterial Blood Pressure Measurements in Man. — A number of
instruments have been devised for estimating blood pressure in man for
clinical purposes. Some of these, though excellent in principle, are too com-
plicated for general use. The first simple and approximately accurate form
of apparatus was that devised by Riva-Rocci in 1896. This has been modi-
fied and improved in minor points since, but the principles of the original
instrument remain practically the same.

In brief, the apparatus, figure 188, consists of an elastic tube ending in a
rubber bag which can be adjusted about the arm or forearm, and a mercury
manometer connected with this tube and also with some form of air pump
used for inflating the tube about the arm and thus exerting pressure upon
its blood vessels. The elastic tube is covered by some inelastic tissue, usu-
ally a leather cuff, in order that the inflation of the bag may cause the full in-
crease of pressure to be exerted upon the encased arm. By inflating the bag
until the pulse at the wrist just disappears, and reading the height of the
column of mercury in the manometer, the maximum or systolic pressure is

214

THE CIRCULATION OF THE BLOOD

obtained in millimeters of mercury. If now the pressure on the arm is re-
duced until the widest oscillations of the mercury column are obtained, the
lowest position of the mercury meniscus represents the diastolic pressure.

The apparatus depends on the principle that an external pressure just
equal to the maximal pressure within an artery will hold the vessel in the
collapsed condition, a fact that has been proven for vessels that are exposed.
An external pressure that will just equal the minimal or diastolic pressure
will cause a complete collapse of a vessel during diastole and will allow a
complete expansion of an artery to its maximal limits during the systolic
period of pressure. In other words, the mercury of the manometer will
oscillate to its maximal. If the pressure is reduced to a still lower point, it

FIG. 188. — Riva-Rocci Apparatus (schematic) for Determining Blood Pressure in Man.

will not be sufficient to compress the artery completely, and the mercury
oscillations will again become smaller. In applying the instrument to the
brachial artery, one must, of course, deal with a vessel deeply buried in mus-
cular and other tissues. These latter tissues probably consume a certain
small percentage of the pressure, an error which may be ignored for all
comparative purposes.

Erlanger has perfected a form of sphygmomanometer which contains a
very ingenious and compactly arranged recording device, figure 189. This
instrument has a mercury manometer from which the pressures are read off
directly. On a side limb of the manometer there is a rubber bag enclosed
in a glass bell. The cavity of the bell outside of the rubber bag is connected

VENOUS BLOOD PRESSURE AND CAPILLARY PRESSURE

2I5

with a recording tambour, the entire apparatus being fully supplied with
the necessary valves and adjusting devices which make it mechanically very
perfect. The instrument is mounted on a stand with a small clock and
recording cylinder adapting it to convenient clinical use.

The brachial arterial pressure of man when taken by this form of appara-

FIG. 189. — Erlanger's Sphygmomanometer, Shown with the Rubber* Bag Attached to
the Arm. The picture is taken at the end of an experiment after the pressure in the instru-
ment is run up again to above the systolic pressure. The upper part of the cylinder shows
a sphygmogram taken with the instrument. (Experiment and photo by Hill and Watkins.)

tus has been found to vary greatly, but Erlanger gives no mm. of mercury
as the average of observations on young adults in the determination of the
systolic pressure; i.e., the maximal arterial pressure. He gives for the dias-
tolic pressure 40 to 45 mm. of mercury below the systolic pressure. Other
observers using the same method find a somewhat higher average pressure,
see figure 190, which represents a fair type of observation.

The Venous Blood Pressure and Capillary Pressure. — The blood
pressure in the veins is nowhere very great, but is greatest in the small veins,

21 6 THE CIRCULATION OF THE BLOOD

while in the large veins near the heart the pressure may become negative, or
in other words, when a vein is put in connection with a mercurial manom-
eter the mercury may fall in the arm farthest away from the vein and will
rise in the arm nearest the vein, the action being that of suction rather than
pressure. In the large veins of the neck the tendency to suck in air is es-
pecially marked, and is the cause of death in some accidents or operations in
that region. The amounfof pressure in the brachial vein is said to support
9 mm. of mercury, whereas the pressure in the veins of the neck may fall to
a negative pressure of from — 3 to — 8 mm.

The variations of venous pressure during systole and diastole of the
heart are very slight, and a distinct pulse is never seen in veins except under

FIG. 190. — Tracing taken with Erlanger's Sphygmomanometer. The figures indicate
pressure in millimeters of mercury. Systolic pressure 160; diastolic pressure, 120. (New
figure by Hill.)

extraordinary circumstances. In certain forms of cardiac valvular insuffi-
ciency there may be considerable regurgitation of the blood with a strong
venous pulse.

Careful observations upon the web of the frog's foot, the tongue and mesen-
tery of the frog, the tails of newts and small fishes, and upon the skin of the
finger behind the nail (von Kries) ; as well as estimations of the amount of
pressure required to empty the vessels of blood under various conditions,
all indicate that the capillary blood pressure is subject to very great varia-
tions. Apparently the variations follow the variations of pressure in the
arteries, though the measurements of the capillary pressure of the skin
in man indicate that it is occasionally markedly influenced by the venous
pressure variations (Hough). In the skin in man it is from 30 to 50 mm.
mercury.

The pulse in the arterioles, capillaries, and venules becomes more and
more evident as the extravascular pressure is increased. The pressure in
the web of the frog's foot has been found to be equal to about 14 to 20 mm. of
mercury; in other capillary regions the pressure is found to be equal to from
one-fifth to one-half of the ordinary arterial pressure.

GENERAL VARIATIONS IN BLOOD PRESSURE

217

General Variations in Blood Pressure.— The arterial blood pressure
may be made to vary by alterations in either of the chief factors upon which
the pressure in the vessels depends, but primarily by the cardiac contrac-
tions and the peripheral resistance. Thus, increase of blood pressure may
be brought about by either, i, a more frequent or more forcible action of
the heart, or, 2, by an increase of the peripheral resistance. On the other
hand, diminution of the blood pressure may be produced, either by a, a
diminished force or frequency of the contractions of the heart, or by b, a
diminished peripheral resistance. These different factors, however, al-
though varying constantly, are so combined that the general arterial pressure

FIG. 191. — Schema Showing the Relation between Blood Pressure, Velocity of Flow,
and Vascular Area, in the Arteries, Capillaries, and Veins. Ordinates represent height
of pressure and speed of flow. The abscissa, b-c, represents zero pressure and speed.
Space between lines a-b and d-e represents arterial system; between d-e and/-g, capillary
system, and between f-g and h-i, the venous system. Line A-B equals pressure; line C-D,
speed of flow; and line E-F, vascular area. (Modified from Gad.)

remains fairly constant. For example, the heart may, by increased force or
frequency of its contractions, distinctly increase the blood pressure, but this
increased action is almost certainly followed by diminished peripheral re-
sistance, and thus the two altered conditions may balance, with the result
of bringing back the blood pressure to what it was before the heart began
to beat more rapidly or more forcibly.

It will be clearly seen that the circulation of the blood within the blood
vessels must depend upon the diminution of the pressure from the heart
to the capillaries, and from the capillaries to the veins, the blood flowing in
the direction of least resistance. We shall presently see further that the
local flow also depends upon the relations between the heart's action and
the peripheral resistance both general and local.

2l8

THE CIRCULATION OF THE BLOOD

The Arterial Flow. — The character of the flow of blood through the
arterial system depends to a very considerable extent upon the structure
of the arterial walls, and particularly upon the elastic tissue which is so highly
developed in them.

The elastic tissue of the arteries, first of all, guards them from the sud-
denly exerted pressure to which they are subjected at each contraction of the
ventricles. In every such contraction, as is above seen, the contents of the

FIG. 192. — Cross Section of the Aorta to Show Elastic Tissue; e, elastic elements. (Bailey.)

ventricles are forced into the arteries more quickly than they are discharged
through the capillaries. The blood, therefore, being for an instant resisted
in its onward course, a part of the force with which it is impelled is directed
against the sides of the arteries; under this force their elastic walls dilate,
stretching enough to receive the blood, and becoming more tense and more
resisting as they stretch. Thus by yielding they break the shock of the
force impelling the blood. On the subsidence of the pressure, should the
ventricles cease contracting, the arteries are able by the same elasticity to
resume their former caliber.

The elastic tissue in the same way equalizes the current of blood by main-
taining pressure on it in the arteries during the period at which the ventri-

THE ARTERIAL FLOW IS RHYTHMIC 2 19

cles are at rest or are dilating. If the arteries were rigid tubes, the blood,
instead of flowing as it does in a constant stream, would be propelled through
the arterial system in a series of spurts corresponding in time to the ventric-
ular contractions and with intervals of almost complete rest during the in-
action of the ventricles. But in the actual condition of the vessels, the force
of the successive contractions of the ventricles is expended partly in the
direct propulsion of the blood and partly in the dilatation of the elastic ar-
teries; and in the intervals between the contractions of the ventricles, the
force of the recoil is employed in continuing the flow onward. Of course
the pressure exercised is equally diffused in every direction, and the blood
tends to move backward as well as onward. All movement backward,
however, is prevented by the closure of the semilunar valves, which takes
place at the very commencement of the recoil of the arterial walls.

The Arterial Flow is Rhythmic. — By the exercise of the elasticity
of the arteries, all the force of the ventricles is expended upon the circulation.
That part of the force which is used up or rendered potential in dilating the
arteries is restored or made active or kinetic when they recoil. There is no
loss of force, neither is there any gain; for the elastic walls of the artery can-
not originate any force for the propulsion of the blood; they only restore
that which they receive from the ventricles.

Since the ventricular discharge is intermittent, there will be intermittent
accessions of pressure, and therefore the flow of blood in the arteries will
be periodically accelerated. The volume of blood discharged from a cut
artery increases and decreases with the systole and diastole of the ventricles,
or with the systolic and diastolic pressures of the arteries themselves, see
page 215.

This equalizing influence of the resistance of the successive arterial
branches reacts so that at length the intermittent accelerations produced in
the arterial flow by the discharge of the heart cease to be observable, and
the jetting stream is converted into the continuous and even movement of
the blood which we see in the capillaries and veins. In the production of a
continuous stream of blood in the smaller arteries and capillaries, the re-
sistance which is offered to the blood stream in these vessels is a necessary
agent. Were there no greater obstacle to the escape of blood from the
larger arteries than exists to its entrance into them from the heart, the
stream would be intermittent, notwithstanding the elasticity of the walls of
the arteries.

The muscular element of the middle coat co-operates with the elastic in
adapting the caliber of the vessels to the quantity of blood which they con-
tain; for the amount of fluid in the blood vessels varies quite considerably
even from hour to hour, and can never be quite constant. Were the elastic
tissue only present, the pressure exercised by the walls of the containing
vessels on the contained blood would be sometimes very small and some-

220 THE CIRCULATION OF THE BLOOD

times inordinately great. The presence of a muscular element, however,
provides for a certain uniformity in the amount of pressure exercised: the
muscles are in constant action or tone, and it is by this adaptive, uniform,
gentle muscular contraction that the normal tone of the blood vessels is
maintained. Deficiency of this tone is the cause of the soft and yielding
arterial pulse, and the sluggish blood flow through the arterioles.

Incidentally it may be mentioned that the elastic and muscular contrac-
tion of an artery may also be regarded as fulfilling a natural purpose when,
the artery being cut, the sudden contraction at first limits, and then, in con-
junction with the coagulated fibrin, completely arrests, the flow of blood.
It is only in consequence of such contraction and coagulation that we are
free from danger through even very slight wounds; for it is only when the
artery is closed that the processes for the more permanent and secure pre-
vention of bleeding are established.

The Velocity of the Arterial Blood Flow.— The velocity of the blood
current at any given point in the various divisions of the circulatory system
is inversely proportional to the united sectional area at that point. If the
united sectional area of all the branches of a vessel were always the same
as the area of the vessel from which they arise, and if the aggregate sectional
area of the capillary vessels were equal to that of the aorta, the mean rapidity
of the blood's motion in the small arteries and in the capillaries would be the
same as in the aorta. If a similar correspondence of capacity existed in the
veins there would be an equal correspondence in the rapidity of the circula-
tion in them. But the volume of the arterial and venous systems may be
represented by two truncated cones with their apices directed toward the
heart; the area of their united bases, the sectional area of the capillaries,
being about eight hundred times as great as that of the truncated apex rep-
resenting the aorta. Thus the velocity of blood in the smallest arterioles
and the capillaries is about one-eight-hundredth of that in the aorta.

The velocity of the stream of blood is greatest in the neighborhood of
the heart. The rate of movement is greatest during the ventricular systole
and diminishes during the diastole. The rate of flow also decreases along
the arterial system, becoming least in the parts of the system most distant
from the heart. Chauveau has estimated the rapidity of the blood stream
in the carotid of the horse at over 20 inches per second during the heart's
systole, and nearly 6 inches during the diastole (520-150 mm.) see figure
191.

The Capillary Flow. — It is in the capillaries that the chief resistance
is offered to the progress of the blood; for in them the friction of the blood
is greatly increased by the enormous multiplication of the surface with which
it is brought in contact.

When the capillary circulation is examined in any transparent part of a
full-grown living animal by means of the microscope, figures 193, 194, the

THE CAPILLARY FLOW

221

blood is seen to flow with a constant equable motion; the red blood corpus-
cles moving along, mostly in single file, and bending in various ways to ac-
commodate themselves to the tortuous course of the capillary, but instantly
recovering their normal outline on reaching a wider vessel.

At the circumference of the stream and adhering to the walls of the larger
capillaries, but especially well marked in the small arteries and veins, there
is a layer of plasma which appears to be motionless. The existence of this
still layer, as it is termed, is inferred both from the general fact that such a
one exists in all fine tubes traversed by fluid, and from what can be seen in
watching the movements of the blood corpuscles. The red corpuscles occupy

FIG. 193. — Capillary Network from Human Pia Mater, Showing also an Arteriole in
"Optical Section"; and "a Small Vein. X 350. .4, Vein; B, arteriole; C, large capillary;
D, small capillaries. (Bailey.)

the middle of the stream and move with comparative rapidity; the color-
less corpuscles run much more slowly by the walls of the vessels; while next
to the wall there is a transparent space in which the fluid appears to be at
rest; for if any of the corpuscles happen to be forced within it, they move
more slowly than before, rolling lazily along the side of the vessel and often
adhering to its wall, figure 194. Part of this slow movement of the colorless
corpuscles and their occasional stoppage may be due to their having a ten-
dency to adhere to the walls of the vessels. Sometimes, indeed, when the
motion of the blood is not strong, many of the white corpuscles collect in
a capillary vessel, and for a time entirely prevent the passage of the red
corpuscles.

When the peripheral resistance is greatly diminished by the dilatation of
the small arteries and capillaries, so much blood passes on from the arteries

222

THE CIRCULATION OF THE BLOOD

into the capillaries at each stroke of the heart that there is not sufficient
remaining in the arteries to distend them. Thus, the intermittent current
of the ventricular systole is not always converted into a continuous stream
by the elasticity of the arteries before the capillaries are reached; and so
intermittency of the flow occurs both in capillaries
and veins and a venous pulse is produced. The
same phenomenon may occur when the arteries
become rigid from disease, and when the beat of the
heart is so slow or so feeble that the blood at each
cardiac systole has time to pass on to the capillaries
before the next stroke occurs; the amount of blood
sent at each stroke being insufficient properly to
distend the elastic arteries.

It was formerly supposed that the occurrence of
any transudation from the interior of the capillaries
into the midst of the surrounding tissues was con-
fined, in the absence of injury, strictly to the fluid
part of the blood; in other words, that, the corpuscles
could not escape from the circulating stream, unless
the wall of the containing blood vessel was ruptured.
It is true that the English physiologist Augustus
Waller affirmed in 1846 that he had seen blood
corpuscles, both red and white, pass bodily through
the wall of the capillary vessel in which they were
contained (thus confirming what had been stated a
short time previously by Addison). He said that
no opening could be seen before their escape and that none could be
observed afterward, so rapidly was the part healed. But these observations
did not attract much notice until the phenomenon of escape of the blood
corpuscles from the capillaries and minute veins, apart from mechanical
injury, was rediscovered by Cohnheim in 1867.

Cohnheim's experiment demonstrating the passage of the corpuscles
through the wall of the blood vessel is performed in the following manner:
A frog is curarized; that is to say, paralysis is produced by injecting under
the skin a minute quantity of the poison called curari. The abdomen
is then opened, a portion of the small intestine is drawn out, and its trans-
parent mesentery spread out under a microscope. After a variable time,
occupied by dilatation following contraction of the minute vessels and the
accompanying quickening of the blood stream, there ensues a retardation
of the current and the red and white blood corpuscles begin to make their
way through the capillaries and small veins.

The white corpuscles pass through the capillary wall chiefly by the
ameboid movement with which they are endowed. This migration

FIG. 194. — A Large
Capillaryfrom the Frog's
Mesentery Eight Hours
after Irritation had been
set up, Showing Emi-
gration of Leucocytes.
a, Cells in the act of
traversing the capillary
wall; b, some already
escaped. (Frey.)

THE VENOUS FLOW 223

occurs to a limited extent in health, but in inflammatory conditions is
much increased.

The process of diapedesis of the red corpuscles, which occurs under cir-
cumstances of impeded venous circulation, and consequently increased
blood pressure, resembles closely the migration of the leucocytes, with the
exception that they are squeezed through the wall of the vessel, and do not,
like the leucocytes, work their way through by ameboid movement.

Various explanations of these remarkable phenomena have been
suggested. Some believe that pseudo-stomata between contiguous
endothelial cells provide the means of escape for the blood corpuscles.
But the chief share in the process is probably due to mobility and con-
traction of the parts concerned, both of the corpuscles and of the capillary
wall itself.

The Speed of the Blood in the Capillaries. — The velocity of the
blood through the capillaries must, of necessity, be largely influenced by
that which occurs in the vessels on both sides of them, in the arteries and
the veins. Their intermediate position causes them to respond at once to any
alteration in the size or rate of the arterial or venous blood stream. Thus,
the apparent contraction of the capillaries, on the application of certain
irritating substances or during certain mental states, and their dilatation in
blushing may be referred primarily to the corresponding action of the small
arteries.

The Measurement of Velocity in the Capillaries. — The observation of
Hales, E. H. Weber, and Valentin agree very closely as to the rate of the
blood current in the capillaries of the frog. The mean of their estimates
gives the velocity of the systemic capillary circulation at about o . 5 mm. per
second. The velocity in the capillaries of warm-blooded animals is greater,
in the dog 0.5 to 0.75 mm. per second. This may seem inconsistent with
the facts, which show that the whole circulation is accomplished in about half
a minute. But the whole length of capillary vessels, through which any
given portion of blood has to pass, probably does not exceed o . 5 mm. There-
fore the time required for each quantity of blood to traverse its own appointed
portion of the general capillary system will scarcely amount to more than a
second. This comparatively slow velocity is evidently favorable to the
nutritive interchanges that go on through these thin-walled vessels between
the blood within the capillaries and the outside active tissues.

The Venous Flow. — The blood current in the veins is maintained,
a, primarily by the contractions of the left ventricle; but very effectual assist-
ance to the flow is afforded, b, by the action of the muscles capable of pressing
on the veins with valves, and, cy by the aspiration of the thorax and possibly,
d, by the aspiration of the heart itself.

The effect of muscular pressure upon the circulation may be thus ex-
plained: When pressure is applied to any part of vein, and the current of

224 THE CIRCULATION OF THE BLOOD

blood in it is obstructed, the portion behind the seat of pressure becomes
swollen and distended as far back as the next pair of valves, which are in
consequence closed. Thus, whatever force is exercised by the external
pressure of the muscles on the veins, is distributed partly in pressing the
blood onward in the proper course of the circulation, and partly in pressing
it backward and closing the valves behind.

The circulation might lose as much as it gains by such an action if it
were not for the numerous communications, or venous anastomoses; for
owing to these anastomoses the closing up of the venous channel by the
backward pressure is prevented from being any serious hindrance to the
circulation, since the blood which is arrested in its onward course by the
closed valves can at once pass through some anastomosing channel, and
proceed on its way by another vein. Thus the effect of muscular pressure
upon veins which have valves is turned almost entirely to the advantage
of the circulation; the pressure of the blood onward is all advantageous,
and the pressure of the blood backward is prevented from being a hindrance
by the closure of the valves and of the anastomoses of the veins.

The venous flow is also assisted by the aspiration of the thorax and to
some extent by that of the heart, since at some time during every cardiac
cycle the intra- auricular and intraventricular pressure falls below that of
the atmosphere. This activity will be considered more fully in the chapter
on Respiration. In this connection it may be said, however, that the pressure
in the great veins falls during inspiration and rises during expiration.

The Velocity in the Veins. — The velocity of the blood is greater
in the veins than in the capillaries, but less than in the arteries; this fact
depending upon the relative capacities of the arterial and venous systems.
If an accurate estimate of the proportionate areas of arteries and the veins
corresponding to them could be made, we might, from the velocity of the
arterial current, calculate that of the venous. The usual estimation is that
the capacity of the veins is about two or three times a* great as that of the
arteries, and that the velocity of the blood's motion is, therefore, about one-
half or one- third as great in the veins as in the arteries, i.e., 200 mm. a second.
The rate at which the blood moves in the smallest venules is only slightly
greater than that in the capillaries, but the speed of flow gradually increases
the nearer the vessel approaches to the heart. The sectional area of the
venous trunks, compared with that of the branches opening into them,
becomes gradually smaller as the trunks advance toward the heart,
figure 191.

The Velocity of the Circulation as a Whole. — It would appear that
a portion of blood can traverse the entire course of the circulation, in the
horse, in half a minute. Of course it would require longer to traverse
the vessels of the most distant part of the extremities than to go through
those of the neck, but taking an average length of the vessels to be traversed

THE VELOCITY OF THE CIRCULATION AS A WHOLE 225

it may be concluded that half a minute represents the average rate. Stewart
estimated that the circulation time in man is probably not less than twelve
nor more than fifteen seconds.

Satisfactory data for these estimates are afforded by the results of experi-
ments to ascertain the rapidity with which chemicals introduced into the
blood are transmitted from one part of the vascular system to another. The
time required for the passage of solutions of potassium ferrocyanide, mixed
with the blood, from one jugular vein, through the right side of the heart, the
pulmonary vessels, the left cavities of the heart, and the general circulation,
to the jugular vein of the opposite side, varies from twenty to thirty seconds
in the dog. The same substance is transmitted from the jugular vein to the
great saphenous vein in twenty seconds; from the jugular vein to the mes-
enteric artery in between fifteen and thirty seconds; to the facial artery,
in one experiment, in between ten and fifteen seconds; in another experi-
ment, in between twenty and twenty- five seconds; in its transit from the
jugular vein to the metatarsal artery, it occupies between twenty and
thirty seconds. The result is said to be nearly the same whatever the
rate of the heart's action. In more recent methods some innocuous dye
like methylene blue is used, since it permits the determination without
the loss of blood, the change in color being visible through the walls of the
blood vessels.

Stewart has made most accurate measurements of the circulation time
by the electrical- resistance method. Strong salt solutions injected into the
jugular vein on one side when they reach the other jugular (or any other
vessel) are instantly detected by a decrease in the electrical resistance through
the vessel when it is laid between the poles of the proper conductivity
apparatus.

In all these experiments it is assumed that the substance injected moves
with the blood and at the same rate, and does not move from one part of
the organs of circulation to another by diffusing itself through the blood or
tissues more quickly than the blood moves. The assumption may be ac-
cepted that the times above mentioned as occupied in the passage of the in-
jected substances are the times in which the portion of blood itself is carried
from one part to another of the vascular system.

Another mode of estimating the general velocity of the circulating blood
is by calculating it from the quantity of blood supposed to be contained in
the body and from the quantity which can pass through the heart in each
of its contractions. But the conclusions arrived at by this method are less
satisfactory. For the total quantity of blood and the capacity of the cavities
of the heart have as yet been only approximately ascertained. Still the most
careful of the estimates thus made accord very nearly with those already
mentioned; and it may be assumed that the blood may all pass through
the heart in about twenty-five seconds.
15

226 THE CIRCULATION OF THE BLOOD

THE PULSE.

The most characteristic feature of the arterial pressure and blood flow
is its intermittency, and this intermittent flow is seen or felt as waves of change
in diameter of the arteries, known as the Pulse.

The pulse is generally described as a wave-like expansion of the artery
produced by the injection of blood at each ventricular systole into the already
full aorta. The force of the left ventricle is expended in pressing the blood
forward and in dilating the aorta. With the injection of each new quantity
of blood into the aorta there is a wave of dilatation which passes on, expand-
ing the arteries as it goes, running as, it were, over the more slowly traveling
blood contained in them, and producing the pulse as it proceeds. A sharp
distinction must be made between the passage of the pulse wave along an
artery and the rate of flow of the blood in the vessel. The pulse produced by
any given beat of the heart is not felt at the same moment in all parts of the
body. Thus, it can be felt in the carotid a short time before it is perceptible
in the radial artery, and in this vessel before it occurs in the dorsal artery of
the foot. Careful measurements of the intervals between the time of the
pulse at the carotid and at the wrist shows that the delay in the beat is in
proportion to the distance of the artery from the heart. The difference in
time between the pulse of any two arteries probably never exceeds one-sixth to
one-eighth of a second. The rate at which the pulse travels in the arteries
is from five to ten meters per second.

The distention of each artery increases both its length and its diameter.
In their elongation the arteries change their form, the straight ones becoming
slightly curved, and those already curved becoming more so; but they re-
cover their previous form as well as their diameter when the ventricular
contraction ceases, and their elastic walls recoil. The increase of their
curves which accompanies the distention of arteries, and the succeeding
recoil, may be well seen in the prominent temporal artery of an old person.
In feeling the pulse, the finger cannot distinguish the sensation produced
by the dilatation from that produced by the elongation and curving. That
which it perceives most plainly, however, is the dilatation and return more
or less to the cylindrical form, of the artery which has been partially flattened
by the finger.

The Sphygmograph. — Much light has been thrown on what may
be called the form of the pulse wave by an instrument called the sphygmo-
graph, figures 195 and 196. The principle on which it acts will be seen
on reference to the figures.

A small button replaces the finger in the act of taking the pulse. This
button is made to rest lightly on the artery the pulsations of which it is de-
sired to investigate. The up-and-down movement of the button is com-
municated to the lever, to the hinder end of which is attached a light spring.

THE SPHYGMOGRAPH

227

The spring is adjusted to the proper tension to follow the movements of the
artery wall during the pulse wave. The sphygmograph is bound on the
wrist while taking a record.

It is evident that the beating of the pulse will cause an up-and-down

FIG. 195. — Diagram of the Lever of the Sphygmograph.

movement of the lever, the pen of which will write the effect on a smoked
card moved by the clock-work of the instrument.

Thus a tracing of the pulse is obtained, and in this way much more deli-
cate changes can be seen than can be felt by the mere application of the finger.

FIG. 196. — Dudgeon's Sphygmograph.

The principle of the sphygmometer of Roy and Adami is shown in the
diagram, figure 197.

The apparatus consists of a box, a, which is moulded to fit over the end of
the radius so as to bridge over the radial artery. Within this is a flexible bag,
b, filled with water, and connected by a T-lube with a rubber bag, h, and
mercurial manometer. The fluid in the box may be raised to any desired
pressure, and may then be shut off by tap, c. At the upper part of the box

228

THE CIRCULATION OF THE BLOOD

is a circular opening, and resting upon b is a flat button, d, which by means
of a short light rod, e, communicates the movement of b to the lever, /. At
the axis of rotation of this lever is a spiral watch-spring, g, which can be
tightened at will, so that the lever can be made to take a vertical position at
any desired hydrostatic pressure within the box. The movements of the lever
are recorded upon a piece of blackened glazed paper made to move in a vertical
direction past it. When in use, the box is fixed upon the wrist by an appro-
priate holder, and the pressure is raised to any desired height to which the
lever is adapted by tightening or slackening the spring; the tap, c, is then closed.
The pressure within the box acts in all directions, and is correctly indicated
by the manometer.

To manometer.

FIG. 197. — Diagrammatic Sectional Representation of the Sphygmometer. a, Box
by which the portion of the artery is covered; b, thin-walled india-rubber bag filled with
water, and communicating through tap, c, with the manometer and thick-walled rubber bag,
h; d, piston connected by rod, e, with recording lever,/; g, spiral spring, attached to axis of
lever, and by which the pressure in b, against the piston, d, is counterbalanced; k, skin and
subcutaneous tissue; m, end of radius seen in section; n, radial artery seen in section.
(Roy and Adami.)

Sphygmogram. — The tracing of the pulse obtained by the use of the
sphygmograph, called a sphymogram, differs somewhat according to the artery
from which it is taken, but its general characters are much the same in all
cases. It consists of a sudden upstroke, or anacrotic limb, figure 198, A,
which is somewhat higher and more abrupt in the pulse of the carotid and of
other arteries near the heart than in the radial and other arteries more re-
mote; and a gradual decline or catacrotic limb, B, less abrupt, and taking a
longer time than A. It is seldom, however, that the decline is an uninter-
rupted fall; it is usually marked about half-way by a distinct notch, C, called
the dicrotic notch, followed immediately by a second more or less marked
ascent of the lever called the dicrotic wave, D. Not infrequently there is

SPHYGMOGRAM 22Q

also at the beginning of the descent a slight wave previous to the dicrotic
notch ; this is called the pre-dicrotic wave, and in addition there may be one
or more slight waves after the dicrotic, called post-dicrotic, E. The inter-
ruptions in the downstroke are called the catacrotic waves to distniguish
them from an interruption in the upstroke, called the anacrotic wave, which
is sometimes met with.

The explanation of these tracings present some difficulties, not, how-
ever, as regards the two primary factors, viz., the upstroke and downstroke,

FIG. 198. — Diagram of Pulse Tracing. A, upstroke or anacrotic limb; R, downstroke or
katacrotic limb; C, pre-dicrotic wave; B, dicrotic; E, post-dicrotic wave.

because they are universally taken to mean the sudden injection of blood
into the already distended arteries, and the gradual recovery of the arteries
by their recoil. These points may be demonstrated on a system of elastic
tubes, with a pump to inject water at regular intervals, just as well as on the
radial artery, or on the arterial schema, a more complicated system of tubes
in which the heart, the arteries, the capillaries, and veins are represented.
If we place two or more sphygmographs upon such a system of tubes at in-
creasing distances from the pump, we may demonstrate, first, that the rise

FIG. 199. — Sphygmogram from the Radial Artery Taken with Marey's Sphygmograph.

(Langendorff.)

of the lever commences earliest in that nearest the pump, and, second, that
it is higher and more sudden. So in the arteries of the body the wave gradu-
ally gets less and less as we approach the periphery of the arterial system,
and it is lost in the capillaries.

The origin of the secondary waves is to some extent a matter of uncer-
tainty. The anacrotic wave occurs when the peripheral resistance is high;
that is, when, for some time during the systole, the flow from the aorta toward
the periphery is slower than the flow from the ventricle into the aorta. Thus

230

THE CIRCULATION OF THE BLOOD

it is seen in some cases of nephritis where the arteries are rigid and the periph-
eral resistance is high.

The dicrotic wave is the most important of the secondary waves, and
has been the subject of much discussion. It is constantly present in pulse
tracings, but varies in height. In point of time the dicrotic wave occurs
immediately after the closure of the aortic semilunar valves. In certain
conditions, generally of disease, it becomes so marked as to be quite plain
to the unaided finger. Such a pulse is called dicrotic. The generally ac-
cepted explanation of the cause of the dicrotic wave is that it represents a

B

FIG. 200. — A, Normal Pulse Tracing from Radial of Healthy Adult Obtained by the
Sphygmometer; B, from same artery, with the same extra-arterial pressure, taken during
acute nasal catarrh. 1-2 Anacrotic limb; 2-8 Catacrotic limb; 3 Predicrotic notch;
5 Dicrotic crest; 6 Postdicrotic notch; 7 Postcrotic crest.

rebound of the overdistended artery at the time of the closure of the aortic
valves. During systole, as the blood is forcibly injected into the aorta,
there is an overdistention of the artery. The systole suddenly ends, the
aorta by reason of its elasticity tends to recover itself, the blood is driven
back against the semilunar valves, closing them and at the same time giv-
ing rise to a wave, the dicrotic wave, which begins at the heart and travels
onward toward the periphery like the primary wave. According to Foster,
the conditions favoring the development of dicrotism are: i, a highly ex-
tensible and elastic arterial wall; 2, a comparatively low mean blood press-
ure, leaving the extensible reaction free scope to act; 3, a vigorous and rapid
stroke of the ventricle discharging into the aorta a considerable quantity
of blood. The other secondary waves are probably due to the oscillations

PERIPHERAL REGULATION OF THE FLOW OF BLOOD 231

in the elastic recoil of the arteries, though some of them at least may be
due to the inertia of the instruments used.

In the use of the sphygmograph care must be taken in the regulation of
the pressure of the spring. If the pressure be too great, the characters of
the pulse may be almost entirely obscured or the artery may be completely
obstructed and no tracing is obtained. On the other hand, if the pres-
sure is too slight, a very small part of the characters may be represented on
the tracing.

THE PERIPHERAL REGULATION OF THE FLOW OF BLOOD.

The flow of blood through the circulatory system depends on the inter-
action of several factors which have already been mentioned in another con-
nection: The rate and volume of the heart-beat, the elasticity of the blood
vessels, the resistance of the microscopic peripheral vessels, and the volume
of blood in the body. We have already learned, page 200, that both the
rate and volume of the contractions of the heart are under very minute
and intimate regulation and control through the cardiac nervous mechanism.
Also we have found that there is intimate co-ordination between the activity
of the heart and the activity of all other parts of the body, a co-ordination
secured through the nervous system. All regulation which affects the
heart must of necessity affect the general blood pressure and, therefore,
not directly any particular part.

The general elasticity of the blood vessels, and of the arteries in par-
ticular, which makes the general arterial pressure possible, is dependent
primarily on the presence of a large amount of elastic connective tissue in
the walls of the vessels. The elasticity of this tissue is a purely passive
property which can be utilized only by some positive source of energy, in
this instance the heart.

The Variations in Peripheral Resistance. — Certain arteries and
veins, especially the smallest ones, the arterioles and venules, are supplied
with muscular tissue in their walls. The activity of these muscles in the
vascular complex makes the peripheral regulation of the flow of blood
possible. This muscular tissue not only exhibits a passive elasticity
comparable to that of the yellow elastic connective tissue, but upon the
proper stimulation it actively contracts or relaxes, thus securing to the per-
ipheral resistance of the vessels an active adjustment to the ever-varying
dynamic conditions of the vascular apparatus.

The muscular tissue in the vessels increases relatively in amount as
the vessels become smaller. In the arterioles it is developed out of all
proportion to the other elements. In fact, in passing from the arterioles
to the capillary vessels, made up as we have seen of endothelial cells with a
supporting ground substance only, the last change on the side of the arteries,

232 THE CIRCULATION OF THE BLOOD

which occurs as the vessels become smaller, is the disappearance of
muscular fibers.

The office of the muscular coat is to adjust the size of the arterioles and,
therefore, the flow of the blood. It is to regulate the quantity of blood to be
received by each part or organ, and to adjust this quantity to the requirements
of each, according to various circumstances, but chiefly according to the de-
gree of activity which each organ at different times exhibits. The amount of
work done by each organ of the body constantly varies, and the variations
often quickly succeed each other, so that, as in the muscles for example,
within the same hour a part may be now very active and now quite inactive.
In all its active exercise of function, such an organ requires a larger supply of
blood than is sufficient for it during the times when it is comparatively
inactive.

It is evident that the heart cannot regulate the blood-supply to each part
of the body at different periods independently of the other parts. Neither
could this be regulated by any general and uniform contraction of the arteries.
But it may be regulated by the power which the arteries of each part have,
through their muscular tissue, of contracting or relaxing so as to diminish
or increase their size. In this way the supply of blood is varied according
to the requirements of the particular part of the body to which the vessels
are distributed. Thus, while the ventricles of the heart determine the total
quantity of blood to be sent onward at each contraction, and the force of
its propulsion, and while the large and merely elastic arteries distribute the
blood and equalize its stream, the smaller arteries by means of their muscu-
lar tissue regulate and determine the proportion of the whole quantity of
blood which shall be distributed to each particular organ.

The variation of the size of arterioles and, therefore, of the resistance
to the flow of the blood in them is secured by the contractions of the muscular
tissue, but the muscles are regulated in their contractions by the nervous
system. The muscular tissue in the blood vessels of the organs of the dif-
ferent parts of the body is also co-ordinated by the same regulative and con-
trolling influence of the nervous system.

The Discovery of the Vaso-motor Nerves. — More than half a cen-
tury ago (1851) it was shown by Claude Bernard that if the cervical sym-
pathetic nerve is divided, the blood vessels of the corresponding side of the
head and neck become dilated. This effect is best observed in the ear,
which if held up to the light is seen to become redder and the arteries to
become larger. The whole ear is distinctly warmer than the opposite one.
This effect is produced by removing the arteries from the tonic influence of
the central nervous system, which influence normally passes along the course
of the divided nerve.

If the peripheral end of the divided nerve be stimulated in its course
toward the organ, i.e., that farthest from the brain, the arteries which were

DISCOVERY OF THE VASO-MOTOR NERVES

233

before dilated return to their natural size, and the parts regain their former
condition. And, besides, if the stimulus is very strong or very long-continued,
the amount of normal constriction is passed and the vessels become much
more contracted than before. The natural condition, which is midway
between extreme contraction and extreme dilatation, is called the natural
tone of an artery. If this is not maintained, the vessel is said to have lost
tone, or, if it is exaggerated, the tone is said to be too great. The effects
described as having been produced by section of the cervical sympathetic
and by subsequent stimulation are not peculiar to that nerve and the vessels
to which it is distributed.

FIG. 201. — Small Artery and Vein of the Frog's Web. A, Under normal conditions;
B, upon stimulation of the sciatic nerve; Ar, artery; V, vein. In this experiment the vein
also showed well-marked vaso-constriction. (Greene.)

It has been found that for every part of the body there exists a nerve the
division of which produces the same effects, viz., dilatation of the vessels.
Such may be cited as the case with the sciatic, the splanchnic nerves, and
the nerves of the brachial plexus; when these are divided, dilatation of the
blood vessels in the parts supplied by them takes place. It appears,
therefore, that nerves exist which have a distinct control over the vascular
supply of every part of the body. These are called vaso-motor or vaso-
constrictor nerves. Bnt the arterioles are also under the influence of a
second set of nerves, also discovered by Claude Bernard, which produce
-exactly the opposite influence, i.e., dilatation. These nerves are called vaso-
dilator nerves.

234

THE CIRCULATION OF THE BLOOD

Mall has also shown that veins, at least the portal vein, possess a vaso-
motor nerve supply as well as arteries.

Vaso-constrictor Nerves. — The presence of vaso-constrictor nerves
can be shown in several different ways, of which the most convincing is that
of direct inspection. If a vascular membrane, like the web of the frog's
foot or the bat's wing, be adjusted on the stage of a microscope for direct

FIG. 202. — Arm Plethysmograph. Apparatus for measuring the change in volume in
the arm due to variation in the blood supply. The arm is enclosed in a glass cylinder
which is completely filled with fluid, the opening through which the arm is inserted being
closed by a rubber sleeve, A . The cavity of the glass cylinder communicates through the
tube, F, G, with the test-tube, M, which is supported in the jar, P. Any variation in
volume in the arm will cause water to flow out or into the test-tube, M , which is lowered
as the tube fills, and raised as it empties. The rise and fall of the test tube, M, is com-
municated over the pulley, L, to the writing pen, N, which records the movements on the
smoked cylinder. Kymograph not shown. (Mosso.)

inspection, and the smaller arterioles are under observation, then upon the
stimulation of the general nerve supplying the part these arterioles will
sharply decrease in size. In fact, the vaso-constriction is often so great as com-
pletely to occlude the vessel. Very soon after the stimulation the vessel
again dilates to its normal size.

The presence and course of the vaso-constrictor nerve supply to the
organs of the body have been demonstrated not by direct inspection, but
by the use of various forms of the plethysmograph. A plethysmograph is an

VASOCONSTRICTOR CENTER 235

instrument designed to measure the variations in the volume of an organ.
If the finger, the whole hand, the spleen, or the kidney be placed in such an
instrument and the proper steps be taken to record the volume changes, it
will be found that the volume of the enclosed organ is constantly changing
with every variation of the blood pressure. If the nerves to the organ are
stimulated by the usual rapidly interrupted induction current, for example
the splanchnics to the kidney, then there is a decrease in the volume of the
organ. This decrease takes place even when there is a simultaneous in-
crease of the arterial blood pressure, a result that can be explained only on
the assumption of vascular decrease in the organ. The decrease in the flow
of blood to the specific organ can be induced only by a great decrease in the
size of the arterioles produced by contractions of the circular muscles of
their walls.

FIG. 203. — Plethysmogram of the Hind Limb of a Cat, showing Vaso-constriction upon
Stimulating the Sciatic 64 times per second. To be read from right to left. (Bo\vditch
and Warren.)

Vaso-motor Tone. — Vaso-constrictor changes are constantly occur-
ring in the blood vessels of the organs of the body, a fact that has been
abundantly demonstrated by the plethysmographic experiments just men-
tioned. Direct inspection of the ear of an albino rabbit will show that the
arteries, and veins as well, are now full and large and red, and the interspaces
filled with blood, and now pale and constricted, and the interspaces relatively
bloodless. If the cervical sympathetic is cut as in Bernard's experiment,
then the ear vessels remain dilated, that is they lose their tone. This
shows that the condition is dependent primarily on the constant discharges
of nerve impulses from the nervous system. It is said that the vessels
regain their tone after a time when the nerves are cut. The regained power
may be ascribed to the muscle fibers themselves.

Vaso-constrictor Center. — When the tonic influence exerted by the
nerve fibers on the arterioles is traced back into the central nervous system,
it is found to be associated with the activity of certain groups of nerve cells,
or centers, which are called the I'aso-constrictor centers. This determination

236

THE CIRCULATION OF THE BLOOD

|Aur.

is made in part by the method of sectioning. A lesion of the cerebro-spinal
axis below the corpora quadrigemina is followed by partial or complete
general dilatation of the blood vessels and a great fall of blood pressure.
This is due to the isolation of the vaso-constrictor center, wrhich lies in the
floor of the fourth ventricle, a millimeter or two caudal to the corpora quad-
rigemina, and extends longitudinally over an area of
about three millimeters. Owsjannikow has shown
that the center is composed of two halves, each
half lying in the lateral column to the side of the
median line. This center is in constant action dur-
ing life, and its discharges are responsible for the
vascular tone described in the previous paragraph.
The vaso-constrictor center varies in its activity,
sometimes producing wave-like contractions with
relaxations of the arterial walls, producing varia-
tions in the blood pressure known as Traube-Hering
waves. These waves are more often observed in
mammalian blood-pressure experiments after pro-
longed operations, when the center may be supposed
to be itself in a weakened condition.

Secondary vaso-motor centers are present in the
spinal cord as proven by Goltz. Under normal con-
ditions they do not act independently of the medul-
lary center; but when the function of the latter has
been interrupted by section of the cord, then after a
few days the spinal cells below the section take on
central functions and bring about a re-establishment
of the lost vascular tone. If these centers be de-
stroyed by the destruction of the cord, then the tone
of the vessels immediately disappears, but is regained
after the lapse of a much longer time. This can be
ascribed to the presence of possible sympathetic
constrictor centers or more probably to a funda-
mental property of the muscles themselves. This
experiment wras carried out by Goltz and Oswald,
who found that after destruction of the lower part of
the spinal cord, the tone of the vessels of the hind
limbs, lost as a result of the operation, was later re-established.

Vaso-constrictor Reflexes. — Under normal conditions the medullary
center responds to afferent stimuli by vaso-motor reflexes. The secondary
vaso-motor centers in the spinal cord, when removed from the influence
of the bulbar center, can and do respond to afferent impulses by similar
vaso-motor action.

FIG. 204. — Diagram
Showing the Paths of the
Vaso-constrictor Fibers
along the Cervical Sym-
pathetic and the Ab-
dominal Splanchnic.
Aur. Artery of ear; G.
Cs, superior cervical
ganglion; An. V, an-
nulus of Vieussens; G.
St, stellate ganglion; D.
I, D.II, D.V, thoracic
spinal nerves; Abd. Spl,
abdominal splanchnic.
The arrows indicate the
direction of vaso-con-
strictor impulse.

VASO-CONSTRICTOR REFLEXES

237

The afferent impulses which excite reflex vaso-motor action may proceed
from the terminations of sensory nerves in general, or possibly from the
blood vessels themselves, and the constriction which follows generally occurs
in the area whence the impulses arise. Yet the reflex may appear elsewhere.
Impulses proceeding to the vaso-motor center from the cerebrum may cause
vaso-dilatation, as in blushing, or vaso-constriction, as in the pallor of fear
or of anger.

Afferent influence upon the vaso-motor centers is well shown by the
action of the depressor nerve, the existence of which was demonstrated by
Cyon and Ludwig. The depressor is a small afferent nerve which passes
up to the medulla from the heart, in which it takes its origin. It runs up-
ward in the sheath of the vagus or in the superior laryngeal branch of the

FIG. 205. — Blood-pressure Record (lower) and Respiratory Record (upper) Obtained
from a Dog upon Stimulating the Central End of the Divided Vagus, Both Vagi being Cut.
The marked fall in blood pressure is due to the effect of stimulating the depressor fibers
contained in the vagus trunk of the dog. (New figure by Dooley and Dandy.)

vagus or as an independent branch, as in the rabbit, communicating by
filaments with the inferior cervical ganglion as it proceeds from the heart.
If, in a rabbit, this nerve be divided and the central end stimulated during
a blood-pressure observation, a remarkable fall of blood pressure takes
place, figure 205.

The cause of the fall of blood pressure is found to proceed primarily
from the dilatation of the vascular district within the abdomen supplied by
the splanchnic nerves, in consequence of which the vessels hold a much
larger quantity of blood than usual. The engorgement of the splanchnic
area very greatly diminishes the amount of blood in the vessels elsewhere,
and so materially diminishes the blood pressure. The function of the de-
pressor nerve is that of conveying to the vaso-motor center afferent nerve
impulses from the heart, which produce an inhibition of the tonic activity

238 THE CIRCULATION OF THE BLOOD

of the vaso- motor center and, therefore, a diminution of the tension in the
blood vessels. This diminishes the overstrain on the heart in propelling
blood into the already too full or too tense arteries. It has been shown by
Porter and Beyer that the fall in blood pressure, following stimulation of the
depressor nerve, will still occur, even when the abdominal vaso-constriction
is kept constant by a simultaneous stimulation of the splanchnics. It is
therefore evident that the inhibitory effect of depressor- nerve stimulation is
a general one and not confined to the splanchnic area alone.

The action of the depressor nerve in causing an inhibition of the vaso-
motor center illustrates the more unusual effect of afferent impulses; that is,
inhibition of the vaso-constrictor tone. As a rule, the stimulation of the
central end of an afferent nerve, such as the sciatic or the internal saphenous,
produces the reverse, i.e., a pressor effect, and increases the tonic influence
of the center which by causing constriction of the arterioles raises the blood
pressure. Thus the reflex effects of stimulating an afferent nerve may be
either to constrict or to dilate the arteries. These reflexes may be general
enough to influence the general blood pressure or they may be limited to
definite local areas, but the local effects are the all-important ones, since
by these the local regulation of the blood flow is accomplished.

Traube-Hering Curves. — The vaso-motor center sends out rhythmical
impulses by which undulations of blood pressure of a large and sweeping
character are produced, quite independent of the so-called respiratory un-
dulations. The action of this center in producing such undulations is dem-
onstrated in the following observations. In an animal under the influence
of curari and with both vagi cut, and a record of whose blood pressure is
being taken, if artificial respiration be stopped, the blood pressure rises
sharply at first. After a time the rhythmical undulations shown in figure 206
occur. These variations are called Traube's or Traube-Hering curves.
There may be upward of ten of the respiratory undulations in one Traube-
Hering curve. They continue until the vaso-motor center is asphyxiated
and the heart exhausted, when the pressure falls. The undulations cannot
depend upon anything but the vaso-motor center, as the mechanical effects
of respiration have been eliminated by the curari and by the cessation of
artificial respiration, and the effect of the cardio-inhibitory center has been
removed by the division of the vagi. The rhythmic rise of blood pressure
is most likely due to a rhythmic constriction of the arterioles followed by a
rhythmic fall of pressure and relaxation, both being due to the action of the
vaso-motor center. The vaso-motor center, therefore, is capable of pro-
ducing rhythmical undulations of blood pressure.

Vaso -dilator Nerves. — Claude Bernard discovered (1856) that the
blood flow was increased through the salivary glands by stimulation of the
nerves (the chorda tympani for the submaxillary, and the tympanic branch
of the glossopharyngeal for the parotid), thus proving that the arteries have

VASODILATOR NERVES 239

not only vaso-constrictors, but also vaso-dilator nerves. Vaso-dilator nerves
have been described for most parts of the body. In general they are dis-
tributed in the same nerve trunks which bear the vaso-constrictors.

It is not supposed that the vaso-dilators produce widening of the
arterioles by stimulation to active muscular contraction; in fact, the circular

FIG. 206. — Traube-Hering's Curves. (To be read from left to right.) The curves
i, 2, 3, 4, and 5 are portions selected from one 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 is
omitted; the blood pressure rises in stages from i to 2, 3, and 4, but falls again in stage 5.
Curve i is taken from a period when artificial respiration was being kept up, but, the vagi
having been divided, the pulsations on the ascent and descent of the undulations do not
differ; when artificial respiration ceased, these undulations for a while disappeared, and the
blood pressure rose steadily while the heart-beats became slower. Soon, as at 2, new
undulations appeared; a little later, the blood pressure was still rising, the heart-beats still
slower, but the undulations still more obvious (3); still later (4), the pressure was still
higher, but the heart-beats were quicker, and the undulations flatter; the pressure then
began to fall rapidly (5), and continued to fall until some time after artificial respiration was
resumed. (M. Foster.)

arrangement of the muscle fibers would seem to exclude such a deduction. It
is probable that there is local inhibition of the tonic contraction of the mus-
cles, thus allowing the mechanical factor of the general blood pressure to
dilate the vessels. The vaso-dilator nerves are characterized by their re-
sponse to slowly developed stimuli, shown by Bowditch and Warren, and by
the retention of irritability after degeneration of the constrictors has taken
place, see figure 207.

240 THE CIRCULATION OF THE BLOOD

Vaso-dilator Centers. — No distinct medullary center has yet been shown
to regulate the vaso-dilator nerve activity. Such centers, if they exist,
should be influenced by isolating them from their efferent paths, on the one
hand, or by stimulation by afferent channels, on the other. The former
method of study has revealed nothing that can be compared to the tonic ac-
tivity of the constrictor center. Efferent dilator-nerve impulses can be re-
flexly produced by sensory stimulation. The isolated lumbar cord of a dog
is capable of reflex vaso-dilator activity, since stimulation of the skin of
the penis leads to reflex vaso-dilatation, indicating the presence of local vaso-
dilator centers in this portion of the spinal cord.

FIG. 207. — Plethysmogram of the Hind Limb of a Cat, Showing Vaso-dilatation upon
Stimulating the Sciatic Once per Second. To be read from right to left. (Bowditch and
Warren.)

Vaso-dilator Reflexes. — Perhaps the only unquestioned case of reflex
vaso-dilatation is that of the lumbar cord just mentioned. It is true that
many apparent reflexes can be noted, for example the increased flow of blood
in the salivary glands under gustatory reflexes, the blushing of the skin on ex-
posure to sudden warmth, or even the blushing of emotional origin, these On
first thought might be regarded as vaso-dilator reflexes. But each of these
instances can be just as readily explained as inhibitions of the vaso-constrictor
tonic activity. This double explanation can, as a matter of fact, be applied
to the action of the depressor nerve described above, page 237. On the
whole, however, while we cannot directly and unquestionably prove the fact,
yet it is probable that each of the above examples may be accepted as examples
of reflex vaso-dilatation by direct action on a vaso-dilator center or centers in
the cord.

The Relation of Vaso-constrictor and Vaso-dilator Activity.— The
distribution of two sets of regulative fibers for the muscular walls of the
blood vessels, when considered in connection with the other factors of the
vascular apparatus, gives a wonderfully complete mechanism for the co-ordi-
nation of the vascular supply with the activity of the different organs. Gen-
eral and broadly distributed activity of the constrictors produces increase of

VASO-CONSTRICTOR AND VASODILATOR NERVES 241

general blood pressure, of the dilators decrease of pressure, but local activity
of either set will produce a great reduction or increase of blood in the local
organ with little or no effect on the general pressure. When a vaso-dilatation
is produced locally in one organ and there is an accompanying vaso-constric-
tion in other regions, as usually happens, it is evident that the result may be
a flooding of the local region. This is exactly the thing that is accomplished
in the muscles in violent exercise, in the glands during secretion, in the stom-
ach during digestion. It is this mechanism that is utilized to throw a
large volume of blood to the skin when the temperature of the body is above
the average, or to blanch the skin when the temperature is low.

Normally, certain regions of the body are associated in that when vaso-
dilatation occurs in one region, vaso-constriction occurs in the other. This is
particularly true with the skin or surface of the body and the viscera or deeper
organs. The same relation is said to exist between some of the visceral
organs.

General Course of the Vaso-constrictor and Vaso-dilator Nerves. —
The cell bodies forming the medullary vaso-motor center give off axones,
axis-cylinder processes, some of which go to the nuclei of origin of certain
cranial nerves, while others pass down the cord to end at different levels
in contact with certain cells, probably small cells in the anterior horn and
lateral part of the gray matter. These cord cells constitute the spinal centers.
The neuraxones of the spinal cells leave the cord in certain spinal nerves in
the anterior roots, pass by the white rami to the sympathetic ganglionic
chain, where they end in physiological connection with the ganglionic cells.
Axones from these latter cells pass by an uninterrupted course to their termina-
tions on the blood vessel walls. The vaso-constrictor fibers leave the central
nervous axis by the ventral roots of all the dorsal nerves and the first two
lumbar roots, a comparatively restricted region. The vaso-dilators have
the same origin with two exceptions, viz., the vaso-dilators of the salivary
glands found in the seventh and ninth cranial nerves, and the nervi erigentes,
which arise in the roots of the second and third sacrals.

The nerves to the viscera pass direct to their blood vessels, but the vas-
cular nerves for the skin, muscles, limbs, etc., rejoin the main divisions of the
spinal nerves through the gray rami, see figures 417 and 418, and pass to the
blood vessels along with the general nerves of the organ or organs.

VASO-CONSTRICTOR AND VASO-DILATOR NERVES FOR
INDIVIDUAL ORGANS.

The particular paths for the vaso-motor nerves has been pretty definitely
established by numerous researches, especially by those of Langley and his
students.

The course of the vaso-constrictor and the vaso-dilator nerve fibers has
16

242 THE CIRCULATION OF THE BLOOD

been followed satisfactorily in many of the important parts of the body,
though the supply for some regions is yet obscure. This is particularly
true for the brain, where such supply is apparently absent. The two groups
of fibers run the same course, except in the cephalic and sacral regions already
mentioned. They may, therefore, be described together.

The Vascular Nerve Supply for the Head. — The vascular nerves
for the head, face, and mouth have their origin in the cord from the first to
the fifth dorsal spinal nerves. They pass through the white rami to sym-
pathetic ganglia, through the stellate ganglion, and up the cervical sympa-
thetic nerve to the superior cervical ganglion. From this ganglion they run
to their distribution, either along with the arteries, as with the salivary sup-
ply, or with the sensory nerves, as in the nerves to the mucous membrane
of the mouth, etc. The vascular nerves supplied to the base of the ear follow
the above course, but the nerves for the tip leave the stellate ganglion in the
ramus vertebralis, run to the third cervical nerve, and pass with its auricular
branch to the ear, a circuitous route determined by Fletcher.

The great exception to the above origin is with the vaso-dilator group.
Dilator fibers leave the base of the brain in the direct path of the seventh
cranial nerve to supply the submaxillary and sublingual glands, in the ninth
cranial nerve to the parotid gland, and in both these to the tongue.

The Vascular Regulation in the Brain. — The brain requires a large
and uniform supply of blood for the due performance of its functions. This
object is effected through the number and size of its arteries, the two internal
carotids and the two vertebrals. It is also desirable that the force with
which this blood is sent to the brain should be subject to less variation from
external circumstances than it is in other parts, an effect that is accomplished
by the free anastomoses of the large arteries in the circle of Willis. This
arrangement insures that the supply of blood will be uniform in both hemi-
spheres even though it may be limited through operation or accident to one
or more of the four principal arteries. Uniformity of supply is further
insured by the arrangement of the vessels in the pia mater. Previous to
their distribution to the substance of the brain the large arteries break up
and divide into innumerable minute branches. These capillaries after
frequent communication with one another enter the brain in a very uniform
and equable distribution. The arrangement of the veins within the cranium
is also peculiar. The large venous trunks or sinuses are formed so as to be
scarcely capable of change of size; and composed, as they are, of the tough
tissue of the dura mater, and in some instances bounded by the bony cranium,
they are not compressible by any force which the fullness of the arteries
might exercise through the substance of the brain. Nor do they admit of
distention when the flow of venous blood from the brain is obstructed.

The mechanical conditions in the brain and skull formerly appeared
enough to justify the opinion that the quantity of blood in the brain must

VASCULAR REGULATION IN THE BRAIN

243

be at all times the same. But it was found that in animals bled to death
without any aperture being made in the cranium, the brain became pale and
anemic like other parts. And in death from strangling or drowning, there
was congestion of the cerebral vessels; while in death by prussic acid, the
quantity of blood in the cavity of the cranium was determined by the position
in which the animal was placed after death, the cerebral vessels being con-
gested when the animal was suspended with its head downward, and com-
paratively empty when the animal was kept suspended by the ears. Thus,

FIG. 208. — Showing the Origin and Course of the Vascular Vaso-motor Xerves for the Head.

(Modified from Moret.)

although the total volume of the contents of the cranium is probably nearly
always the same, yet the quantity of blood in it is liable to variation, its in-
crease or diminution being accompanied by a simultaneous diminution or
increase in the quantity of the cerebro-spinal fluid. The cerebro-spinal
fluid being readily removed from one part of the brain and spinal cord to
another, and capable of being rapidly absorbed and as readily effused, would
serve as a kind of supplemental fluid to the other contents of the cranium
to keep it uniformly filled. Although the arrangement of the blood vessels
insures to the brain an amount of blood which is tolerably uniform, yet with

244 THE CIRCULATION OF THE BLOOD

every beat of the heart, and every act of respiration, and under many other
circumstances, the quantity of blood in the cavity of the cranium is con-
stantly varying. Roy and Sherrington are responsible for the view now
generally current that the brain, therefore, is largely if not entirely dependent
upon the general blood pressure for variations in the quantity of blood which
it receives. During a high blood pressure the amount of blood that flows
in a given unit of time is greater, and during low blood pressure less. Howell
has shown that in the decapitated dog's brain the flow of blood is directly
proportional to the difference in pressure.

Numerous attempts have been made to show vaso-motor mechanisms
for the cerebral arteries, but with generally unconvincing success. Huber
and others have shown nerve endings in such arteries by histological
methods. Bayless, Hill, and Gulland make the statement that "no
evidence has been found of the existence of cerebral vaso-motor nerves,
either by means of stimulation of the vaso-motor center or central end of
the spinal cord, after division of the cord in the upper dorsal region, or

I^IG. 209. — Vaso-dilatation in the Brain from Stimulation of the Cerebral Cortex
in the Presence of Complete Destruction of the Medulla in the Cat. The upper trace
is of the carotid pressure; the lower trace is of the brain oncometer. (Weber.)

by stimulation of the stellate ganglion, and that is to say the whole
sympathetic supply to the carotid and vertebral arteries." However,
Ernest Weber has recently (1909) reinvestigated the control of the blood
flow in the brain. He admits that the blood flow in the brain is sharply
dependent on the general blood pressure, but he presents convincing evi-
dence that both vaso-constrictors and vaso-dilators exist for the brain
vessels. The most striking facts are obtained upon stimulating general
sensory nerves, the central end of the sectioned cord, the cerebral cortex,
and the cervical sympathetic. The stimulation of the cervical sympathetic
calls forth vaso-dilatation in the brain even when the medulla is completely
destroyed. Weber, therefore, concludes that all these stimuli act reflexly.
through a special cerebral vascular center located at some as yet undeter-
mined point toward the cerebrum from the general medullary center. An
active cerebral vaso-dilatation may be accomplished through this center even
in the presence of an accompanying fall in general blood pressure. More
often the type of vascular reflex is that of dilatation followed by constriction
of the brain vessels. If there is an accompanying sharp rise in general

VASCULAR REGULATION IN THE BRAIN

245

blood pressure, then the reflex cerebral vascular dilatation is followed by
vaso-constriction which takes place while the general blood pressure is yet
high. Weber suggests that this local vaso-constrictor mechanism provides

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an apparatus for the regulation and control of the cerebral congestion
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the general medullary vaso-motor center.

246

THE CIRCULATION OF THE BLOOD

The question may be summarized by the statement that the regulation
of the flow of blood through the brain is accomplished by the interaction of
two factors: First, the indirect regulation of blood pressure through the
variations in the heart's activity, and through the general action of the
medullary vaso-motor apparatus producing vaso-constrictions or dilatations
in areas other than the brain. Second, the local and direct regulation of
the brain vessels through reflex action on a special local vascular center.

The Vascular Nerves for the Thoracic Viscera. — Numerous efforts
have been made to determine the vaso-motor nerve supply for the thoracic
organs, the heart and lungs. In the heart the observation is rendered com-
plex by the fact of the rhythmic contractions which produce mechanical
pressure on the coronary arteries. Martin, by direct observation through a
lens, and Porter, by measuring the outflow of the coronaries upon vagus
stimulation, came to exactly opposite views: the former that the vagus con-
tained vaso-dilators, the latter that it contained vaso-constrictors. Still
other experiments have been made to prove either constrictor or dilator
nerves for the coronary arteries, but the first is still undetermined.

The lesser circulation through the lungs has also proven a difficult situa-
tion to interpret as regards any nervous regulation of the pulmonary arteri-
oles. The evidence, while not conclusive, is that the vaso-constrictor supply
to the lungs is from the third to the fifth thoracic nerves, but that the vaso-
constriction produced is slight in comparison with regions of the systemic
circulation.

The Vascular Nerves for the Abdominal Viscera.— The vaso-con-
strictors and the vaso-dilators for the organs of the abdominal cavity have
a broad origin in the cord, from the first dorsal to the fourth lumbar in
the dog and cat. The nerves pass to the organs by the splanchnic nerves,
and by the solar, celiac, and mesenteric ganglia. The vascular nerves for
the different organs may be given in tabulated form:

Organ.

Vascular Nerves for the Abdominal Viscera.

Course to the organ.

/

Spinal origin of the vascu-
lar nerves.

5, 6, 7, 8, 9, 10, n, 12, 13 D, f Splanchnic nerves and

i L \ solar and celiac ganglia.

3, 4, 5, 6, 7, 8, 9, 10, n, 12, J Splanchnic nerves and

13 D, i L | solar and celiac ganglia.

J Splanchnic nerves and

3, 4, 5, 6, 7, 8, 9, 10, i iD . . | ^ and celiac gangUa>

-„.. , \ 4, 5, 6, 7, 8, 9, 10, n, 12, 13 J Splanchnic and celiac

• r ™ T \ ganglia.

( Inferior splanchnic and
inferior mesenteric
ganglia.

Stomach and in-
testine.

Spleen .........

Liver . .

Pelvic viscera . .

D, i, 2. 3, 4 L.
i, 2, 3, 4L

VASCULAR NERVES FOR THE EXTERNAL GENITAL ORGANS 247

The Vascular Nerves for the External Genital Organs. — The vaso-
dilators for these organs arise from the second and third sacral nerves and
pass to the organs by the nervi erigentes and the pelvic plexus. They form
the second great exception to the region of general outflow of vascular nerves.
The constrictors, on the other hand, arise in the spinal nerves from the last
dorsal and first four lumbar. They run the same course as given in the table
for the pelvic viscera.

The greatest variations in the quantity of blood contained at different
times in the external genital organs are found in certain structures which
contain what is known as erectile tissue. These organs, under ordinary cir-
cumstances, are soft and flaccid, but at certain times they receive an un-
usually large quantity of blood, become distended and swollen by it, and
pass into the state termed erection. Such structures are the corpora cavernosa
and corpus spongiosum of the penis of the male, and the clitoris in the female.
The nipple of the mammary gland in both sexes, and, according to some
authors, certain nasal membranes contain erectile tissue.

The corpus cavernosum of the penis, which is the best example of an
erectile structure, has an external fibrous membrane or sheath. From the
inner surface of the sheath numerous fine lamellae project into the cavity,
dividing it into small compartments, like cells when they are inflated. Within
these cells there is a plexus of veins upon which the erectile property of the
organ mainly depends. The plexus consists of short veins with very close
interfacings and anastomoses with very elastic walls admitting of great varia-
tions in size. They collapse in the passive state of the organ, but are capable
of an amount of dilatation which exceeds beyond comparison that of the
arteries and veins which convey the blood to and from them. The strong
fibrous tissue lying in the intervals of the venous plexuses, and the external
fibrous membrane or sheath with which it is connected, limit the distention
of the vessels and give to the organ its condition of tension and firmness.
The same general condition of vessels exists in the corpus spongiosum
urethrae, but the fibrous tissue around the urethra is much wreaker than
around the body of the penis, while around the glans there is none. The
venous blood is returned from the plexuses by comparatively small veins;
all of which are liable to the pressure of muscles where they leave the penis.
The muscles chiefly concerned in this action are the erector penis and
accelerator urinae. Erection results from the distention of the venous
plexuses by a sudden influx of blood resulting from the action of the nervous
vascular reflexes. It is facilitated by the special muscular mechanism
which prevents the outflow of blood.

The Vascular Nerves for the Trunk and Limbs. — The skin and
muscles of the trunk receive their cutaneous and motor nerves by a seg-
mental arrangement in which the innervation is by bands corresponding
with the segments of the cord and the spinal nerves. It is much the same

248

THE CIRCULATION OF THE BLOOD

with the vascular nerves; they are distributed to the skin and walls of the
trunk in the same segment in which they arise. Langley says that the suc-
cessive bands overlap somewhat.

In the fore legs or arms the vascular nerves arise from the first to the
fifth dorsal spinal nerves, run to the stellate ganglia, then by the gray rami
back through the ramus vertebralis to join those cervical nerves that enter
into the brachial plexus, figure 211.

FIG. 211. — Plan of Distribution of Vaso-constrictor Nerves for the Fore Limbs.
(Modified from Moret.)

The nerves for the blood vessels of the lower limbs arise from the tenth
dorsal to the second lumbar nerves. These pass to the ganglionic chain, and
gray rami are given off which join the lumbo- sacral plexus and run with the
divisions of that nerve complex to their distribution in the skin and muscles.
Vaso-constrictors and vaso-dilators have a common course to the lower limbs.

The Vaso-constrictor Nerves for the Veins. — Mall has proven that
vaso-constrictors are present for the portal vein. These fibers are present
in the splanchnic nerves. Other evidences have been observed which
render the view probable that vaso-motors for the veins in general exist.
Hough, for example, in an extended study of the capillary pressure found
many variations which were readily explained only on the assumption of
veno- motor activity, see figure 201.

LABORATORY EXPERIMENTS ON THE CIRCULATION 249

LABORATORY EXPERIMENTS ON THE CIRCULATION.

1. The Rate of the Human Heart-beat. — Determine the rate of
the heart-beat per minute by counting the radial pulse, using a watch for
the time. Make the determination after sitting quietly in a chair for five
minutes. Take the average of at least ten determinations for your own case.
Determine the heart-rate under the same conditions for as many different
persons as you can. Tabulate these determinations in a table which shows
age, sex, weight, and height of the different individuals, and compute a
general average for your entire set. Count the rate in children and in aged.

Note the effect on the averages obtained above after the person lies down
for five minutes, after standing quietly for the same time, and after five
minutes' brisk walk. Tabulate as directed.

Count the heart-rate immediately after two minutes' fast running, allow-
ing the person immediately to sit in a chair. Count the rate by two-minute
intervals until there is a complete return to the normal, as determined above.
Tabulate these results and compare the figures obtained from several dif-
ferent individuals.

Count your own heart-rate at one- hour intervals during one entire day,
giving special attention to the rate just before and just after meals, but in
every case make the count after sitting quietly for five minutes. A marked
diurnal variation will usually appear. Determine these rates on several indi-
viduals, and tabulate as before.

2. Human Cardiogram. — Apply a Burdon- Sanderson cardiograph
to the thorax over the point between the fifth and sixth ribs of the left side,
at which point the cardiac impulse is felt most distinctly. Connect the
cardiograph with a recording tambour, Marey's form, adjust the tension
of the cardiograph and the pressure of the air within the system, and take a
tracing of the movements of the lever of the recording tambour on the smoked
paper of the kymograph. The kymograph cylinder should travel at the rate
of about two to three centimeters per second. Take the time of the move-
ments of the kymograph by means of an electric magnet connected with an
electric clock beating seconds. After the record is secured the proper de-
scription should be written with a pencil on the smoked paper, and the paper
removed from the kymograph carefully and the whole record fixed in shellac.

When the record is dry, count the rate of the heart-beat from the record
and measure the time of the cardiac systole and diastole, and the time of
pause at the end of the diastole. If these facts are taken from records secured
under different conditions of exercise, etc., as outlined in the preceding ex-
periment, then they may be brought together in a table for convenience of
inspection. A comparison of such results will usually show that with the
higher heart-rates the decrease of the time of the cardiac cycle is at the ex-
pense of the time of the diastole; in other words, the time of the systole re-

250

THE CIRCULATION OF THE BLOOD

mains fairly constant, while the time of the diastole increases or decreases
with the rate, a fact to which Hiirthle has drawn attention, figure 157.

3. The Rate and Sequence of the Contractions of the Frog's Heart.
—Destroy the brain of the frog and open the thorax, but do not destroy
tLe pericardium. Count the rate of the heart per minute, then remove the
pericardium and make a second determination after the heart is exposed
to the air. The different parts of the heart when exposed are easily iden-
tified and the contractions which take place in definite sequence can be
determined without difficulty. Make this determination for the ventricle,
auricle, and sinus venosus by direct observation.

Prepare a cardiac lever as shown in figure 212, taking special care to ar-
range the foot so that it will not bind on the lever when in motion. Adjust

FIG. 212. — Heart Lever for Frog or Turtle Hearts.

the foot of the lever on the exposed ventricle and bring its point to write on
the smoked paper of a recording cylinder. This cylinder should travel at
the rate of about i cm. per second and its speed be determined by the writing
point of an electric magnet which is connected with the electric- clock circuit
marking seconds. Take care to adjust the time magnet in a vertical line
with the writing point of the heart lever, placing the heart lever about i cm.
above the magnet lever. The tracing of the ventricle's movement, or cardio-
gram, will show alternate contraction, relaxation, and pause of the ventricle.
It will also enable one to measure the exact proportion of the total time of the
cardiac cycle consumed by the systole and diastole, and also that portion of
the diastole in which the ventricle is wholly at rest.

After one has obtained the ventricular tracings and has learned the diffi-
culties of adjusting the apparatus, a second heart lever should be adjusted

THE FROG'S HEART 251

so that its foot rests upon the auricle, and the auricular movements there-
fore be traced on the smoked paper of the recording cylinder at the same
time as those of the ventricle. If some care is taken to adjust these two
writing points in a vertical line a splendid tracing showing synchronism
between auricle and ventricle is obtained. Measure the rate and the time

FIG. 213. — Cardiogram Showing Contractions of the Auricle, a, and Ventricle, v,
of a Frog. Time in seconds. The record shows the sequence of the auricle and ventricle.
(New figure by Dooley.)

of the different phases of the contraction of the auricle and ventricle and
tabulate them in the following form, always expressing fractions in the
decimal system:

Rate per Time of systole Timeof diastole Time of pause
minute in seconds in seconds in seconds

Auricle

Ventricle

4. The Contractions of the Excised Heart of the Frog.— Pith a

frog and expose the heart, as described in the preceding experiment. Re-
move it completely from the body by first cutting the arteries at their branch-
ing in front of the bulbus arteriosus, then carefully lifting up the parts of
the heart and cutting away the great veins where they enter the sinus. This
will remove the entire heart, including all its contractile parts. The frog's
heart, when thus removed and still wet with its own blood, will continue con-
tracting rhythmically and in its natural sequence for some hours. Place
such an isolated heart in a watch-glass and take a record of its contractions
by the apparatus described in the preceding experiment. (The same phe-
nomena may be studied on a heart isolated and mounted in a Williams'
apparatus.)

252 THE CIRCULATION OF THE BLOOD

Set this watch-glass on the metal warming-box supplied, and arrange
for the circulation of water of different temperatures through the box. Vary
the temperature of the box, and therefore of the heart placed upon it, by
allowing water of o° C., 10° C., 20° C., 30° C., 40° C., to flow through it. Or
place the heart in a watch-glass over a drinking glass of water of the proper
temperature. Record the contractions of the heart at each of these tempera-
tures on the recording drum as described in Experiment 3 above. The heart
being exposed will not take the same absolute temperature as the box, but
the relative temperature will be decreased or increased. Tabulate the rates
at these different temperatures by the plan previously described.

5. The Influence of Different Nutrient Fluids on the Excised
Heart. — Expose a frog's heart, as previously described, and insert a can-
nula into the ascending vena cava just where it enters the sinus. Ligate
the descending vena cava, introduce a cannula into one of the branches of
the aorta, and carefully separate the heart from the body without injuring its
cavities within the points of ligature. Or the ligatures may be laid and the
cannulae inserted without separating the heart from the body. Connect
the venous cannula with a Mariotte's bottle filled with physiological saline,
0.7 per cent, sodium chloride. Adjust the constant level tube for a pressure
of 6 cm. of fluid and allow the saline to flow through the heart. The arterial
cannula should be connected with a short rubber tube the mouth of which
allows the fluid to flow into a beaker or glass tumbler. The outlet of the
arterial tube should be about 2 cm. above the level of the heart so that the
heart must work against a slight pressure. The heart will continue its con-
tractions in good sequence and with a fairly rapid rate. Record the contrac-
tions on the smoked paper of the recording drum, together with a time trac-
ing in seconds, the drum traveling at the rate of about 2 to 5 mm. per second.

Use the tracing obtained under the influence of physiological saline solu-
tion as a normal and compare with it the rate and amplitude of the contrac-
tions when the heart is perfused with Ringer's solution; with Locke's solution;
with saline and potassium in the proportion found in Ringer's solution; with
saline and calcium in the proportion found in Ringer's solution; with milk
diluted 6 vols. with saline; with normal serum or blood; with blood or serum
diluted four times with saline. Tabulate the rates and amplitude of the
heart under these different influences by the method previously followed.

6. The Heart Volume. — Isolate a frog's heart by the method de-
scribed for irrigating it with fluid in the preceding experiment. Connect
it up in a Roy's tonometer, see figure 214, adjust the lever of the tonometer
for a tracing on the smoked paper of the recording cylinder. Use a time-
marker. This instrument records the change in volume with each heart
contraction. The influence of pressure, varied between 2 and 10 cm., and of
nutrient fluids on the heart volume may be determined.

7. The Isolated Heart of the Terrapin. — The heart of the terrapin,

AUTOMATIC CONTRACTIONS OF THE CARDIAC MUSCLE

253

being somewhat larger and somewhat more responsive than the heart of the
frog, may be substituted in the two immediately preceding experiments.
The facts obtained from it will be essentially the same as those obtained
from the frog's heart.

8. The Isolated Mammalian Heart. — The mammalian heart may
be isolated from the body and kept alive and contracting for many hours,
as has been demonstrated by

numerous recent observations. It
is only necessary to keep the tem-
perature approximately that of the
normal body and to irrigate the
heart through the coronary circu-
lation with blood, or diluted blood,
containing sufficient hemoglobin
to supply the heart with the
requisite amount of oxygen. Or
the heart may be kept alive on the
inorganic salt solutions, provided
these are supplied with oxygen
under considerable tension (Porter,
Howell). Even the human heart
has been isolated and kept con-
tracting for some hours in the FIG. 21 4.-Roy's Tonometer,
above manner (Kuliabko). The

method used is to insert a supply cannula into the aorta and irrigate the heart
through the coronary circulation, as described by Martin. Many interest-
ing experiments and demonstrations can be made on the mammalian heart,
but, as this experiment is usually a demonstration experiment, the detail
of procedure is left to be supplied by the demonstrator.

9. Automatic Contractions of the Cardiac Muscle. — Isolated por-
tions of the dog's ventricle have been kept in rhythmic contraction by Porter,
but the best laboratory material is supplied by the heart of the terrapin.
Cut a strip from the ventricle of the terrapin extending around its curved
apex, as shown by the dotted line in the accompanying figure, 215. Split
this strip longitudinally into two parts, each of which will then be about
3 to 5 mm. in diameter. Use care to cut smooth, straight strips. Tie a silk
thread around the extreme tips of each end of the strip, tying a loop of about
i cm. long at one end, and about 10 cm. long at the other. Suspend the strip
over a glass hook, figure 216, by the short loop, and connect it with a heart
lever by the long loop, as shown in the same figure. Use a tension of i
gram. Contractions of this strip as arranged will be recorded with a mag-
nification of about five and with the upstroke of the lever, which is convenient
for reading and interpretation. The strip may be kept moist with physio-

254

THE CIRCULATION OF THE BLOOD

logical saline in a specimen tube of about i by 3 inches in size, and the
arrangement of apparatus figured makes it possible easily and quickly to
change this solution for any other that may be desirable.

Contractions of the ventricular strip in saline usually begin in from 10 to
40 minutes after the preparation is made and go through a regular sequence
of slight increase in rate and amplitude for from 10 to 20 minutes, followed by
a very constant rate, but gradually decreasing amplitude for a period of from
2 to 3 hours, figure 171.

This preparation makes possible many instructive experiments tendino-
to show fundamental properties of cardiac muscle. The preparation con-
tains no nervous mechanism and its behavior may be safely attributed to
the muscle substance itself.

FIG. 215. — Heart of the Terrapin to Show the Method of Cutting the Apex Strip. V,
Ventricle; Au, auricles; Vc, venae cavae; Ao, aorta.

Try the following experiments: Submit the strip to saline solutions of
different temperatures, varying through steps of 5 degrees from o° C. to
40° C. Try the effect of the different ingredients in Ringer's solution; com-
bine potassium with saline, figure 172; calcium with saline, figure 173; and
potassium, calcium, and saline. Also try Locke's solution; solution of blood
diluted with saline; solution of milk with saline in the proportion of one
part milk to four of saline.

Cut and mount strips from the auricle and from the sinus, letting the
latter extend out on to the vena cava. In these last preparations care
must be taken to balance the lever, as a slight overtension paralyzes the
muscle. Immerse these strips in pure serum, compare their behavior with
that of the ventricle in pure serum. The sinus and usually the auricle
will be found rhythmic in serum, while the ventricle, if it contracts at all,
will contract with a very slow rhythm. Often there is a distinct progressive

INFLUENCE OF THE CARDIAC NERVES ON THE FROG'S HEART 255

decrease in the rhythm, the sinus having the same rhythm as the whole heart,
the auricle a considerably slower rhythm, and the ventricle with a very slow
rhythm or even quiet. The sinus preparation will show beside the funda-
mental rhythm a characteristic slow contraction and relaxation, which has
been described as tone, figure 170.

10. Influence of the Cardiac Nerves on the Frog's Heart.— Care-
fully pith a frog so as not to break the blood vessels at the base of the brain,
and thus permit the loss of the blood of the animal. Expose the heart as
previously described, make a cut through the manubrium, continue it
through the skin and muscles at the angle of the jaw, thus exposing the

FIG. 216. — Arrangement of Apparatus for Studying the Contractions of the Strip of the

Apex of the Ventricle.

vagus nerve. The vagus runs diagonally downward and backward along the
edge of a delicate muscle toward the heart. The glosso-pharyngeal is just
in. front of the vagus and the hypoglossal just behind it. The latter runs
parallel with the vagus near its origin, but lower down turns across the vagus
and runs to its distribution in the tongue muscles. These two nerves serve
to aid the student in the identification of the vagus, see figure 217. It is
usually better to cut the hypoglossal away, and also to cut the brachial and
the laryngeal nerves to prevent the stimulation of structures undesired.

Prepare an induction coil, see laboratory experiments on muscle. Use
platinum electrodes of the Harvard pattern, set the coil for a mild stimulus
when tested by the lips or the tongue, lift up the vagus gently and lay it on
the platinum tips of the electrodes, taking care that the electrodes do not
come in contact with the adjacent tissue. Arrange a signal magnet as
shown in the diagram, so that the signal magnet and the stimulating key of
the induction coil may be closed and opened at the same instant. When all

256

THE CIRCULATION OF THE BLOOD

is ready stimulate the vagus for five to ten seconds, recording the time with
the signal magnet and allowing the record to continue until the heart has
returned to its normal rate and amplitude. Most students fail in this ex-
periment by not allowing sufficient time in the record for a normal before
stimulation, and by not allowing sufficient time after stimulation for a return
to the normal. It will be better to take one good tracing, showing the facts
of the experiment, than several partial tracings, none of which are complete.
With these suggestions in mind, repeat the above experiment, using stimu-
lating currents of increasing intensity until complete cardiac inhibition is

FIG. 217. — Diagram Showing the Relations of the Vago-sym pathetic Nerve to the
Heart, in the Frog. Hy, Hypoglossal; Gl, glosso-pharyngeal; ~Lar, laryngeal; V, vago-
sympathetic; H, heart; L, lung.

produced. Perform experiments showing the influence of the time of the
stimulus on the inhibition; i.e., stimuli of i second, 2 seconds, 10 seconds,
and 30 seconds.

In the frog the vagus, or inhibitory, and sympathetic, or accelerator, fibers,
are found in one trunk, the vago-sympathetic, but the stimuli will usually
produce inhibitions and not acceleration. Occasionally with very weak
preparations direct acceleration may be produced. To get the pure inhibi-
tory or pure accelerator effects one must dissect back to the origin of the vagus
before it is joined by the sympathetic fibers; or to the sympathetic trunk
between the third spinal nerve and the point where it joins the vagus trunk.
In the study of the conditions in the above experiments one should note
the rate per minute and the amplitude in the normal, the period just before
stimulation, the rate and amplitude during the period of stimulation, and the
same at different times after the stimulation until constant results are ob-

ARTERIAL BLOOD PRESSURE IN A MAMMAL 257

tained. A tabulation of these results will usually enable one to judge the
influence of each of the various factors recommended in the experiment.

11. Influence of the Cardiac Nerves on the Terrapin's Heart. —
Instead of the frog one may use the terrapin in the above experiment.
In this animal the sympathetic can very readily be isolated, and accelerator
fibers have been described for it. In the experiments of the laboratory of
the author it has been very difficult to demonstrate very marked cases of
cardiac acceleration. The vagus produces inhibitions which differ from
the effects in the frog in that complete inhibitions of the ventricle are followed
by contractions that are apparently at once maximal, see figure 179. In
the frog the ventricular contractions when they reappear are at first slight,
but gradually increase in amplitude until they have their former value.

12. The Arterial Blood Pressure in a Mammal. — The arterial blood
pressure may be measured on the anesthetized cat, dog, or rabbit. Simple
blood pressure was originally measured by Hale's method of connecting
the artery with a vertical tube and allowing the blood to flow freely into
the tube until a column was raised to the height which balanced the pressure
in the vessel. This simple method is decidedly the best for the beginner,
since it does not nee ssitate the use of very complicated apparatus. At the
same time it gives practice in anesthesia and in operations under anesthetics,
and therefore serves as a good preparation for the more complicated ex-
periments which follow.

The necessary apparatus should be prepared first, as follows: A vertical
tube supported on a stand with a scale graduated in the metric system, as-
sorted cannulae of approximately the size of the carotid artery of the animal
to be operated on, linen- thread ligatures, dissecting set in good condition,
an animal-holder with strings or straps firmly to fasten the anesthetized
animal, a chloroform-ether mixture for dogs (or other anesthetic according
to the animal to be used). Four men should be assigned to perform this
experiment. While two are anesthetizing and preparing the animal, two
should arrange the apparatus as nearly ready for connecting with the
artery as possible. When all the apparatus is arranged and the animal
anesthetized, it should be tied firmly to the animal-holder. Let one experi-
menter attend strictly and at all times to anesthetizing the animal; recovery
from the anesthesia must not occur. Let the operator quickly expose about
3 cm. of the carotid artery by making an incision through the skin of the
neck 5 cm. long, and dissecting down between the muscles. Separate the
carotid from the adherent vagus nerve by tearing the connective tissue with
the scalpel handle, freeing the vessel from about 2 to 3 cm. of its length.
Lay two loose ligatures of linen thread around the vessel, place a small
bulldog forceps on the exposed artery nearest the heart, and ligate the end
nearest the head with one of the ligatures. Take up the intervening artery
with strong forceps and make a V-shaped cut near the ligature, pointing the
17

258 THE CIRCULATION OF THE BLOOD

cut toward the heart, and letting it extend about half-way across the artery.
Introduce a cannula through the opening toward the heart, and tie it firmly
with the second ligature. Connect the cannula with the rubber tubing to
the vertical glass tube.

When all is ready remove the bulldog forceps on the artery, following
which the blood will flow freely from the artery into the tube until the pressure
from the column of liquid is just equal to that inside the artery itself. If an
anti-coagulating fluid, 10 per cent, magnesium sulphate, is first introduced
into the vertical tube of fortunate height little blood will be lost and probably
clotting at the cannula will be delayed for some minutes. The mounting
of the blood into the empty tube makes, indeed, a more striking demon-
stration, but it has the disadvantage of quickly forming a clot which stops
the experiment itself.

An accurate measure of the height of the top of the column above the
level of the cannula at the artery represents the arterial blood pressure in
terms of blood, or of 10 per cent, magnesium sulphate. The specific gravity
of magnesium sulphate is i .030; of blood, 1.056; of mercury, 13.6. Record
the pressure you obtain in terms of blood and of mercury. Note also the
variations in pressure and account for the rhythm of each. There will be
a general variation of pressure, depending upon the degree of anesthesia.
If anesthesia is light and muscular movements happen, there will be an in-
crease in the blood pressure. If the anesthesia is heavy, then the blood pres-
sure falls. These points of variation should be marked and recorded at once
in note-books. Make full notes of all accessory facts which would aid you to
explain the variation in blood pressure, such as size of the animal, rate of
respiration, rate of heart-beat, the variations in anesthesia, the presence of the
reflexes, etc., etc.

Chloroform the animal to kill it, and note the change in blood pressure
during the process.

13. The Circulation Time. — The circulation time is most satisfactorily
determined in the laboratory by introducing a saline solution of methylene
blue into the jugular vein on one side. Note directly the time with a stop-
watch until the color appears in the jugular artery and the jugular vein of
the opposite side.

Anesthetize a cat or dog with a chloroform-ether mixture, tie it on the
animal-holder and, when the eye reflexes are lost, expose the jugular vein on
the right side, the carotid artery and the jugular vein on the left. Fill a
2-cm. hypodermic syringe with i per cent, methylene blue in physiological
saline, insert the needle into the right jugular vein, pointing it toward the
heart. Lift the left carotid artery and place under it a strip of moist white
paper 2 cm. wide; prepare the left jugular vein in the same way. Place the
animal so that these vessels are lighted to the best advantage. At a given
moment inject the contents of the hypodermic syringe, noting the time with a

THE ARTERIAL PULSE 259

stop-watch. Observe the color of the left carotid and the left jugular, respect-
ively, very carefully, and take the time when the first appearance of the
methylene blue is noted. The color will appear first in the artery, second
in the vein. The difference in time between the moment of injection and
the moment of color in the artery represents, with a slight correction, the
circulation time of the pulmonary or lesser circulation. The time from the
injection until the color in the jugular vein represents the total time of
circulation.

Stewart has made these determinations even more correctly by the elec-
trical-resistance method. He injected 10 per cent, salt solution and deter-
mined the variation in resistance by a galvanometer. If the galvanometer is
available, then check the above determinations by the electrical method,
arranging the apparatus under the direction of an instructor.

14. The Blood-pressure Model. — An artificial model of the circulatory
apparatus, which illustrates all mechanical parts involved, has been arranged
by Porter. Other forms, which show these as well, are usually available
or can be easily constructed. The model should have the following
possibilities: A pump, which permits of rhythmic action at a varying rate
and varying force; a resistance to the outflow liquid which can be increased
or decreased; and an elastic set of vessels into which the pump discharges.

If Porter's schema is used, determine the following points: The pressure
in terms of mercury in the arterial and venous limbs of the apparatus when
the pump makes a rate of 72 per minute; the influence on these two pressures
when the rate is increased, when it is decreased; the effect on these pressures
when the peripheral resistance is great, when it is low. If a sphygmograph
is available, take a tracing of the pulse in the elastic tube representing the
arterial side of the schema.

If an ordinary bulb syringe and simple apparatus is used, then deter-
mine the following: The character and rate of the outflow when water is
pumped into the rigid glass tube with no resistance to the outflow; wrhen a
glass tube of smaller caliber is connected with the end of the larger glass
tube so as to produce a high resistance to the outflow. Pump the water into
a rubber tube of smaller size and compare with the proceeding in which
there is no resistance to the outflow; also when a glass tube of small caliber
is introduced into the end in order to produce high resistance to the outflow.
Determine the amount of resistance necessary to produce a constant outflow
when the pump has a rate of 72 beats per minute. In this experiment what
effect is produced on the outflow if the rate of the pump is varied ? if the force
of the stroke is varied? if the elasticity of the rubber tube representing the
artery is varied ? If the resistance represented by the size of the glass tube
at the outflow is varied ?

15. The Arterial Pulse. — The form of the arterial pulse may be taken
by one of the various sphygmographs applied to the radial artery at the

260 THE CIRCULATION OF THE BLOOD

wrist or the common carotid in the neck. If the tambour method is used,
apply a sphygmograph tambour on the wrist with the central pressure over
the radial artery. Fasten it in place by the proper bands, adjusting the
tension by flexing the wrist. Connect the receiving tambour with a delicately
balanced, small-sized recording tambour, which should write its movements
on a cylinder revolving at the rate of i to 2 cm. per second.

A more convenient clinical instrument is the Dudgeon or the Jacquet
sphygmograph. These are to be applied at the wrist and give tracings
showing delicate variations in the form of the pulse wave with great magnifi-
cation and a considerable degree of accuracy. Make a comparison of the
form of the pulse wave from tracings taken from at least six different
individuals.

The syphygmogram from the carotid artery may best be taken by apply-
ing a tambour sphygmograph to the neck over the carotid and fastening it
in position, usually by a spring.

1 6. The Rate of Propagation of the Pulse Wave. — Apply tambour
sphygmographs to the carotid in the neck and to the radial at the wrist, and
make simultaneous record on a recording drum, adjusting the writing levers
of the two recording tambours in an exact vertical line. Let the recording
drum travel at the speed of 2 cm. or more per second, and record the speed
by a 50 double- vibration tuning-fork. The carotid pulse will be found to
precede the radial pulse by the fraction of a second. This short interval,
which can be determined in hundredths of a second by comparison with the
time tracing below, represents the time required for the pulse wave to
traverse the distance from the carotid to the radial. Measure the distance
on the individual used in the experiment and calculate the rate of propaga-
tion of the pulse wave in centimeters per second.

If the writing points of the recording levers in this experiment are made
of very delicate strips of note paper or of thin photographic film celluloid, so
as to offer little resistance to the surface of the drum, the detail of the pulse
wave at the two points will be accurately transcribed and may be compared.

17. The Capillary Circulation. — The capillary circulation is best
demonstrated in the laboratory by direct observation on the web of the frog's
foot by the use of the compound microscope. Give a 40-grm. frog a hypo-
dermic injection of o . 3 c.c. of ether under the skin of the back. Wet a piece
of cheesecloth the size of a handkerchief with tap water and wrap the etherized
frog so as to cover the entire body with the exception of the foot. When
the anesthesia has progressed so as to destroy voluntary movements, bind the
foot on an ordinary frog board and spread the web over the window in the
board. Choose an area of the skin which shows small arteries, capillaries,
and veins, and in which the blood is flowing freely and rapidly. Examine
with a low-power compound microscope. In a favorable field small arteries,
capillaries, and veins with blood flowing rapidly through them will be easily

BLOOD PRESSURE IN A MAMMAL AND ITS REGULATION 261

found. Choose one such field, cover with a piece of thin cover-glass, moisten-
ing with a drop of water if necessary, and examine with a high power. Note
in the small artery the pulsating current; the border of clear fluid along the
side of the main stream of blood; the slight pulsations; and the white cor-
puscles that will be found flowing along the borders of the current. In the
small veins there are usually no pulsations and the speed of the current is
somewhat less. In the capillaries a careful examination will reveal a deli-
cate wall, the individual corpuscles, and the fact that the red corpuscles are
actually larger than the diameter of the capillary at some points and must
be bent to pass through. Note that the capillaries form an intricate and
anastomosing network; that the current may occasionally reverse itself in
some of the anastomoses.

The anesthetizing effect of the dose of ether recommended will usually
continue about 15 to 20 minutes. If the observation is more prolonged, a
second dose of ether should be given. The capillaries in the tails of small
fish are often very readily observed, and these may be substituted for the
frog's web.

1 8. Capillary Blood Pressure. — Measure the capillary blood pres-
sure in your own finger by von Krie's method. This apparatus consists
of a small piece of glass an inch square, or less, which is placed across the
knuckle of the finger just back of the nail. A small weight pan is suspended
by a loop of thread over this glass plate so that weights put in the pan will
bring varying pressure on the plate above. Add weights to the pan until
an area of the skin, about 5 mm. in diameter, is blanched by the pressure.
Mark the outline of this bloodless area on the glass, take off the apparatus
and measure the exact area of glass so marked, weigh the entire apparatus
and compute the pressure per square centimeter for the area. This pres-
sure in terms of mercury represents the capillary blood pressure in the vessels
of the skin of the finger at that level. Vary the experiment by measuring
the pressure with the finger held at the level of the top of the head; with the
finger held as low as possible; held at the level of the heart. Tabulate the
measurements. The capillary blood pressure at the level of the heart is
usually from 40 to 50 mm. of mercury.

19. The Arterial Blood Pressure in a Mammal and Its Nervous
Regulation. — After the student has measured the arterial blood pres-
sure by Hale's method, described above, he is in a position to study the
variations and co-ordinations in the blood circulatory apparatus. The re-
cording apparatus consists of writing pens, seconds time marker, signal
marker, blood- pressure manometer preferably Ludwig's mercury manom-
eter, and a continuous paper kymograph preferably Ludwig's weight-
driven form for a continuous record of the arterial blood pressure. Connect
the cannula with the mercury manometer which is provided with a pressure
bottle. Use a cannula of the form shown in figure 185, connecting the side

262 THE CIRCULATION OF THE BLOOD

limb of the cannula with the mercury manometer, and the end limb with the
pressure bottle. When the apparatus is ready anesthetize a mammal (dog,
cat, or rabbit), and bind it down to the animal-holder. Let one operator
attend strictly and at all times to the anesthetic, for the animal must not under any
condition recover consciousness during the experiment.

Expose the carotid artery in the neck, as described in Experiment 1 2 above,
arrange it with ligatures for inserting the cannula, expose the vagus nerve
with the same care, and throw ligatures around it for convenience in lifting
it out of its bed. . Make in the carotid a V-shaped cut directed toward the
heart, insert and ligate the cannula as previously described. Before begin-
ning the experiment one should see that all the tubes are filled with the anti-
coagulating liquid and that the manometer is under pressure from 100 to
150 mm. mercury. When all is ready start the kymograph, ink the record-
ing pens, see that they are recording properly and that the adjustments are se-
cured, remove the bulldog forceps from the artery, and the pressure record
begins.

1. Take a tracing of the normal arterial pressure and heart rhythm with
the recording paper moving at the rate of o . 5 cm. per second.

2. Stimulate the vagus nerve with a mild-strength induction current.
If this stimulus is strong enough to produce change in blood pressure or in-
hibitions of the heart-rate, then allow sufficient time following the stimulus
for the blood pressure to return to the previous normal. Observing these
rules, vary the intensity of the stimulus from that which produces no ap-
parent effect to that which produces complete inhibition of the heart. Vary
the time of the stimulus from i to 10 seconds, using different strengths.

3. Allow the vagus to fall back in its warm bed and stimulate the skin
of the animal at some sensory surface, say the lips, the ear, or the foot. By
varying the intensity of the stimulus, a strength will be found which will
produce no reflexes of the voluntary muscles, but which will produce marked
effects on the heart rate and on the blood pressure. Expose the sciatic nerve,
or any other general nerve trunk, cut it, and stimulate the central end for
five seconds. With a proper strength of stimulus a greater effect is
produced on the heart and on the blood pressure than by stimulating a
small spot of skin.

4. Cut the right vagus nerve and mark the exact time on the tracing by
the signal marker. Do not disturb the animal or record until stable equi-
librium is again reached.

5. Now lift up the distal end of the divided right vagus, and stimulate
it with an electric current of the strength which previously just produced
inhibition. Repeat the experiment on the proximal end of the divided vagus.
The stimulation of the proximal end of the vagus produces no direct effect
on the heart rate when both vagi are cut (see 7 below), but does produce
profound changes on the blood pressure owing to vaso- motor effects.

ARTERIAL BLOOD PRESSURE IN MAN 263

6. After 10 to 15 seconds cut the left vagus, marking the time of cutting
with the same care on the tracing. As soon as the nerves are cut, the heart-
rate will be observed to increase sharply and the blood pressure to rise.
The respirations also change in rate and depth, a fact which can be noted by
its influence on the blood-pressure tracing.

7. Now lift up the distal end of the divided left vagus, and stimulate
it with an electric current of the strength which previously just produced
inhibition. Repeat the experiment on the proximal end of the divided vagus.
The stimulation of the proximal end of the vagus produces no direct effect
on the heart rate when both vagi are cut, but does produce profound
changes on the blood pressure owing to vaso-motor effects.

8. If the rabbit is used, stimulate the depressor nerve, which produces
marked fall in blood pressure from reflex effects.

9. Repeat the stimulation of the central end of the sciatic as described
in 3, now that the vagus nerves are cut. The stimulation of this nerve
no longer produces changes in the heart-rate, but the blood pressure
is influenced as before, showing that the vaso-motor centers are reflexly
stimulated.

10. When you have finished the outline of experiments, give an excess of
the anesthetic to kill the animal and continue the record until the animal is
dead. The blood pressure will fall rapidly, the heart-rate will become slower
but does not cease for a long time.

Should a clot form in the cannula, put a bulldog forceps on the artery,
disconnect the manometer tube, and wash the clot out by a stream of liquid
from the pressure bottle. Use care not to allow this fluid to enter the ex-
posed wound.

Represent the results of each individual experiment in the above series
in tabulated form which shall show: i, the blood pressure and heart-rate just
before each experiment; 2, during the experiment; and 3, at different times
after the experiment until the normal is reached. After the facts are taken
from the tracings and arranged in tabular form, make a study of these facts
and draw all the conclusions you can concerning the nervous regulations of
the heart and of the blood pressure. Make written report.

20. Arterial Blood Pressure in Man. — The arterial blood pressure
in man can be measured only indirectly by measuring the pressure which it
takes around the arm completely to close the artery. Some form of the
Riva-Rocci apparatus, preferably Erlanger's sphygmomanometer, should
be used. Adjust the rubber bag and leather sleeve of the Erlanger appara-
tus, figure 189, to an arm, and connect it to the sphygmomanometer, set the
valve, and quickly pump the pressure up to a point which occludes the pulse.
Adjust the writing point of the recording tambour to the smoked paper on
the cylinder, then lower the pressure by lo-mm. steps until the first pulse
appears. Now proceed with care, changing the pressure by 5-mm. steps

264 THE CIRCULATION OF THE BLOOD

until a record has been obtained which passes the maximal amplitude. Now
release the pressure from the arm.

The first point in the decreasing pressure at which the pulse tracing be-
gins to increase is known as the systolic pressure; the point in the pressure
which records the highest point in the amplitude of the pulse wave is known
as the diastolic pressure. The systolic pressure will vary from 120 to 150
mm. of mercury; the diastolic from 90 to 120 in different individuals of the
average physiology class, see figures 189 and 190.

FIG. 217 a. — Two pressure curves from the human forearm. The pressure scale is
given to the left. The new apparatus of Recklinghausen was used. The diastolic pres-
sure points (lower cross lines) and the systolic pressure points (upper cross lines) are
marked. The changes in the character of the pulse records here is abrupt and character-
istic. The brackets mark the zones of larger, L, and smaller, s, oscillations.

To the right is introduced a reconstruction tonogram built up from the measure-
ments of these curves. (Recklinghausen.)

21. The Vaso-motor Changes in the Finger, the Plethysmogram.—

Insert the finger in the Porter finger plethysmograph, fill the tube with
water, and connect it with a small-sized air tambour. The variations in
volume of the finger are slight, so that one must use a rather long, delicately
balanced recording lever. Take a tracing on a recording cylinder moving
at a slow speed, i mm. per second. The finger and its plethysmograph
should be supported by a swinging support so that no mechanical move-
ments will destroy the accuracy of the record. Observations through
several minutes will usually show variations in volume of the finger, which
will be rcorded by the tambour. Cold air in the face or cold water on the
hand will usually be marked by a decrease in volume indicating vaso-
constriction. Application of heat to other fingers of the same hand will lead
to increase in volume indicating vaso-dilatation.

22. The Vaso-motors of the Frog's Web. — Prepare a frog for ob-
servation of the circulation of the web under the microscope, as described
above; but give it just enough i per cent, curari to destroy voluntary
movements. Quickly dissect the sciatic nerve in the thigh, using extreme
care not to interfere with the circulation. Mount the preparation, pick out
an active field of capillaries, small arteries, and veins with the low power of

THE PLETHYSMOGRAM OF THE KIDNEY 265

the microscope, then adjust the high power to a field which shows one or
more small arteries. Make a drawing to record the diameter of these
arteries, using pigment cells for land- marks. Now quickly stimulate the
exposed sciatic nerve while keeping the selected artery under constant
observation. After a short stimulation the diameter of the vessels will be
seen to decrease considerably, sometimes to the point of complete occlusion.
When the stimulation ceases, the vessel will remain contracted for a few
seconds, then will slowly regain its usual caliber, figure 201. This is an
exceptionally good method for direct observation of the vaso-motor changes
in the smaller vessels.

23. The Pie thy smo gram of the Kidney. — Anesthetize a dog or cat, see Ex-
periments 1 2 and 1 9 above, and take blood-pressure tracings on the continuous-
paper kymograph. Now open the abdominal wall by an incision along the
median line, expose the left kidney and carefully dissect off its capsule, taking
care not to injure its artery and vein. Enclose the kidney in the renal onkom-
eter, fill the onkometer with oil, and connect it with a recording apparatus.
Brodie's bellows recorder is probably the best recording apparatus for this
purpose. Adjust the recording apparatus in the vertical line with the manom-
eter and signal pens.

Stimulation of the nerves which affect the general blood pressure through
the medium of the heart will be found to produce changes in the volume of
the kidney in the same direction as the blood-pressure change. On the
other hand, stimuli which give variations of the blood pressure without
direct change in the heart itself affect the volume of the kidney independent
of the blood pressure:

1. Dissect out and stimulate the splanchnic nerves just where they pass
through the pillars of the diaphragm. Stimulation of these nerves will
cause vaso-constriction in the kidney, which takes place without sharply
affecting the blood pressure.

2. Stimulate the depressor nerve or the central end of the divided vagus.
In this case the volume of the kidney will increase though the general blood
pressure decreases, showing that the fall of blood pressure is due to peripheral
vascular dilatation.

3. Stimulate the peripheral end of the divided vagus so as to slow or
even completely to stop the heart. The sharp fall in blood pressure is now
accompanied by decrease in the volume of the kidney, showing that the
kidney change is merely passively following that of the blood pressure.

CHAPTER VI
RESPIRATION

THE maintenance of animal life necessitates the continual absorption of
oxygen and the excretion of carbon dioxide by the living tissues. The blood
is the medium in all animals which possess a well- developed blood-vascular
system by which these gases are carried. Oxygen is absorbed by the blood
from without and conveyed to all parts of the organism; and carbon dioxide
which comes from the cells within is carried by the blood to the surfaces
from which it may escape from the body. The two processes — absorption
of oxygen and excretion of carbon dioxide — are complementary, and their
sum is termed the process of Respiration.

In all Vertebrata and in a large number of Invertebrata certain parts,
either lungs or gills, are especially constructed for bringing the blood into
proximity with the aerating medium (atmospheric air, or water containing
air in solution). In some of the lower Vertebrata (frogs and other naked
Amphibia) the skin is important as a respiratory organ, and is capable of
supplementing to some extent the functions of the proper breathing
apparatus.

A lung or a gill is constructed essentially of a fine transparent membrane,
one surface of which is exposed to the air or water, as the case may be, while
on the other surface is a network of blood vessels. The only separation be-
tween the blood and aerating medium is the thin wall of the blood vessels
and the thin membrane on which the vessels are distributed. The difference
between the simplest and the most complicated respiratory membrane is
one of degree only.

In the mammals and the higher vertebrates the respiratory membrane
is included within a respiratory cavity, the chest or thorax, which carries on
regular movements, the respiratory movements, to bring changes of air into
close contact with the respiratory surface.

The complexity of the respiratory membrane, the kind of aerating me-
dium, and the respiratory movements are not, however, the only conditions
which cause a difference in the respiratory capacity of different animals.
The quantity and composition of the blood, especially as regards the number
and size of the red corpuscles, and the vigor and efficiency of the circulatory
apparatus in driving the blood to and fro between the lungs and the active
tissues, these are conditions of equal, if not greater, importance.

It may be as well to state here that the lungs are only the medium for the
exchange, on the part of the blood, of carbon dioxide for oxygen. The

266

THE RESPIRATORY APPARATUS

267

living tissues are the seat of those combustion processes which consume
oxygen and produce carbon dioxide. These processes occur in all parts of
the body in the substance of the living active tissues, and are the true respira-
tory processes, sometimes called internal or tissue respiration.

THE RESPIRATORY APPARATUS.

The object of the respiratory movements being the interchange of gases
n the lungs, it is necessary that the atmospheric air shall pass into them
and that the changed air shall be ex-
pelled from them. The lungs are
contained in the chest or thorax, which
is a closed cavity having no communi-
cation with the outside except by
means of the respiratory passages.
The air enters these passages through
the nostrils or through the mouth,
thence it passes through the larynx
into the trachea or windpipe, which
about the middle of the chest divides
into two tubes, the bronchi, one to
each lung.

The Larynx. — The upper part of
the passage which leads exclusively
to the lung is formed by the thyroid,
cricoid, and arytenoid cartilages,
figure 218, and contains the vocal cords,
by the vibration of which the voice is
chiefly produced. These vocal cords
are ligamentous bands covered with
mucous membrane and attached to
certain cartilages which are capable of
movement by muscles. By their ap-
proximation the cords can entirely
close the entrance into the larynx; but
under ordinary conditions the entrance
of the larynx is formed by a more or

less triangular opening between them, FlG- 218.— Outline Showing the General

„ , Al . ,.7. T. . Form of the Larynx, Trachea, and Bronchi,

called the nma glottldis. Projecting as seen from Before, h, The great cornu

at an acute angle between the base of of the h>T°id bone; «, epiglottis; t, superior,

,, , ., i , . , .. andr, inferior cornu of the thvroid carti-

tne tongue and the larynx to which it iage; c, middle of the cricoid cartilage; tr,

is attached, is a leaf-shaped cartilage the trachea, showing sixteen cartilaginous

.,, ., , ., r r™ . rings; b, the right, and V, the left bronchus,

with its larger extremity free. This x i (Allen Thomson )

268

RESPIRATION

is. called the epiglottis. The whole of the larynx is lined by mucous mem-
brane, which, however, is extremely thin over the vocal cords. At its lower
extremity the larynx joins the trachea.

Taste buds have been found in the epithelium of the posterior surface of

the epiglottis, and in several other
situations in the laryngeal mucous
membrane.

The Trachea and Bronchi.—
The trachea extends from the
cricoid cartilage, which is on a
level with the fifth cervical vertebra,
to a point opposite the third dorsal
vertebra, where it divides into the
two bronchi, one for each lung,
figure 218. The trachea measures,
on an average, four or four and a
half inches, 12 to 14 cm., in length,
and from three-quarters of an inch
to an inch, 2 to 2.5 cm., in diameter,
and is essentially a tube of fibro-
elastic membrane within the layers
of which are enclosed a series of
cartilaginous rings, from sixteen to
twenty in number. These rings
extend only around the front and
sides of the trachea, about two-

Ii — -

FIG. 219. — Section of the Trachea, a,
Columnar ciliated epithelium; b, and c,
proper structure of the mucous membrane,
containing elastic fibers cut across trans-
versely; d, submucous tissue containing
mucous glands, e, separated from the hya-
line cartilage, g, by a fine fibrous tissue,/, h,
external investment of fine fibrous tissue.
(S. K. Alcock.)

thirds of its circumference, and
are deficient behind; the interval
between their posterior extremities
being bridged over by a continua-
tion of the fibrous membrane in
which they are enclosed, figure
219, h.

Immediately within this tube and

at the back is a layer of unstriped
muscular fibers. This muscular layer extends transversely between the
ends of the cartilaginous rings to \vhich it is attached, and also opposite the
intervals between them; its evident function being to diminish the caliber
of the trachea by approximating the ends of the cartilages. Outside there
are a few longitudinal bundles of muscular tissue, which, like the preceding,
are attached both to the fibrous and to the cartilaginous framework.

The mucous membrane, figures 219 and 220, consists largely of adenoid
tissue, separated from the stratified colummar epithelium, which lines it, by a

THE TRACHEA AND BRONCHI

269

homogeneous basement membrane. This is penetrated here and there by
channels which connect the adenoid tissue of the mucosa with the inter-
cellular substance of the epithelium. The stratified columnar epithelium
is formed of several layers, of which the most superficial layer is ciliated and

FIG. 220. — Ciliary Epithelium of the Human Trachea, a, Layer of longitudinally
arranged elastic fibers; b, basement membrane; c, deepest cells, circular in form; d, inter-
mediate elongated cells; e, outermost layer of cells fully developed and bearing cilia. X
350. (Kolliker.)

the cells often branched downward. Many of the superficial cells are of the
goblet variety. In the deeper part of the mucosa are many elastic fibers
between which lie connective-tissue corpuscles and capillary blood vessels.

Numerous mucous glands are situated on the exterior and in the substance
of the fibrous framework of the trachea, their ducts perforating the various

FIG. 221. — Transverse Section of a Bronchus, about £ inch in Diameter, e, Epithelium
(ciliated); immediately beneath it is the mucous membrane or internal fibrous layer, of
varying thickness; m, muscular layer; s, m, submucous tissue;/, fibrous tissue; c, cartilage
enclosed within the layers of fibrous tissue; g, mucous gland. (F. E. Schulze.)

structures which form the wall of the trachea, and opening through the
mucous membrane into the cavity of the trachea.

The two bronchi into which the trachea divides resemble the trachea
in structure, with the difference that in them there is a distinct layer of un-
striped muscle arranged circularly beneath the mucous membrane, forming

270 RESPIRATION

the muscularis mucoscc. On entering the substance of the lungs the carti-
laginous rings, although they still form only larger or smaller segments of
a circle, are no longer confined to the front and sides of the tubes, but are
distributed impartially to all parts of their circumference.

The bronchi divide and subdivide in the substance of the lungs into
smaller and smaller branches, which penetrate into every part of the organ
until at length they end in the smaller subdivisions of the lungs called
lobules.

All the larger branches have walls formed of tough membrane, contain-
ing portions of cartilaginous rings, by which they are held open, and un-
striped muscular fibers, as well as longitudinal bundles of elastic tissue.
They are lined by mucous membrane, the surface of which, like that of the
larynx and trachea, is covered with ciliated epithelium; but the several
layers become less and less distinct until the lining consists of a single layer
of more or less cubical cells covered with cilia, figure 221. The mucous
membrane is abundantly provided with mucous glands.

As the bronchi become smaller and smaller and their walls thinner, the
cartilaginous rings become fewer and more irregular, until in the smaller
bronchial tubes they are represented only by minute and scattered cartilag-
inous flakes. And when the bronchi by successive branches are reduced
to about TV of an inch, o . 6 mm., in diameter, they lose their cartilaginous ele-
ment altogether and their walls are formed only of a tough, fibrous, elastic
membrane with circular muscular fibers. They are still lined, however,
by a thin mucous membrane with ciliated epithelium, the length of the
cells bearing the cilia having become so far diminished that the cells are
almost cubical. In the smaller bronchi the circular muscular fibers are
relatively more abundant than in the larger bronchi and form a distinct
circular coat.

The Lungs and Pleurae. — The lungs occupy the greater portion of
the thorax. They are of a spongy elastic texture, and on section appear
to the naked eye as if they were in great part solid organs, except where
branches of the open bronchi or air-tubes may have been cut across and show-
on the surface of the section. In fact, however, the lungs are hollow organs
composed of a mass of air cavities all of which communicate finally with
the common air-tube, the trachea.

Each lung is enveloped by a serous membrane, the pleura, which ad-
heres closely to its surface and provides it with its smooth and slippery
covering. This same membrane lines the inner surface of the chest wall.
The continuity of this membrane, which forms a closed sac as in the case
of other serous membranes, will be best understood by reference to figure 222.
The appearance of a space, however, between the pleura which covers the
lung, visceral layer, and that which lines the inner surface of the chest, parietal
layer, is inserted in the drawing only for the sake of distinctness. These

THE FINER STRUCTURE OF THE LUNG 271

layers are, in health, everywhere in contact, one with the other; and between
them is only just as much fluid as will insure frictionless movement in their
expansion and contraction.

When considering the subject of normal respiration, one may discard
altogether the notion of the existence of any space or cavity between the
lungs and the wall of the chest. If, however, an opening be made so as to
permit air or fluid to enter the pleural sac, the lung in virtue of its elasticity
recoils, and a considerable space is left between it and the chest wall. In
other words, the natural elasticity of the lungs would cause them at all times
to contract away from the ribs were it not that the contraction is resisted by
atmospheric pressure which bears only on the inner surface of the air-tubes
and air-cells.

The pulmonary pleura consists of an outer or denser layer and an inner
looser tissue in which there is a lymph-canalicular system. Numerous

FIG. 222. — Transverse Section of the Chest.

lymphatics are to be met with, which form a dense plexus of vessels, many
of which contain valves. They are simple endothelial tubes, and take origin
in the lymph-canalicular system of the pleura proper. Scattered bundles
of unstriped muscular fiber occur in the pulmonary pleura. They are es-
pecialty strongly developed on the anterior and internal surfaces of the lungs,
the parts which move most freely in respiration. Their function is doubt-
less to aid in expiration.

The Finer Structure of the Lung. — Each lung is partially subdi-
vided into separate portions called lobes: the right lung into three lobes
and the left into two. Each of these lobes, again, is composed of a large num-
ber of minute parts, called lobules. Each pulmonary lobule may be con-
sidered to be a lung in miniature, consisting, as it does, of a branch of the
bronchial tube, of air-cells, blood vessels, nerves, and lymphatics, with a
small amount of areolar tissue.

272

RESPIRATION

On entering a lobule, the small bronchial tube, the structure of which
has just been described, a, figure 223, divides and subdivides; its walls at
the same time becoming thinner and thinner, until at length they are formed
only of a thin membrane of areolar and elastic tissue, lined by a layer of
squamous epithelium, no longer provided writh cilia. At the same time they
are altered in shape; each of the minute terminal branches widening out
funnel- wise, and its walls being pouched out irregularly into small saccular
dilatations, called air-cells, figure 223, b. Such a funnel-shaped terminal
branch of the bronchial tube, with its group of pouches or air-cells, has been
called an infundibulum, figures 223 and 224, and the irregular oblong space
in its center, with which the air-cells communicate, an intercellular passage.

FIG. 223.

FIG. 224.

FIG. 223. — Terminal Branch of a Bronchial Tube, with its Infundibula and Air-cells,
from the Margin of the Lung Injected with Quicksilver; Monkey, a, Terminal bronchial
twig; b, b, infundibula and air-cells. X 10. (F. E. Schulze.)

FIG. 224. — Two Small Infundibula, a, a, with air-cells, b, b, and the ultimate bronchial
tubes, c, c, with which the air-cells communicate. From a new-born child. (Kolliker.)

^ An inflated and dried turtle's lung illustrates the homologue of a lobule.
Such a preparation can be cut across to illustrate the intercellular passage,
the infundibulum, and the air-cells.

The air-cells, or air-vessels, are sometimes placed singly, like recesses
from the intercellular passage, but more often they are arranged in groups
or even rows, like minute sacculated tubes, so that a short series of vesicles
all communicating with one another open by a common orifice into the tube.
The vesicles are of various forms according to the mutual pressure to which
they are subject. Their walls are nearly in contact, and they vary from o . 3
to o . 5 mm. in diameter. Their walls are formed of fine membrane similar
to that of the intercellular passages and continuous with it. The membrane
is folded on itself so as to form a sharp-edged border at each circular orifice

THE FINER STRUCTURE OF THE LUNG

273

of communication between contiguous air-vesicles, or between the vesicles
and the bronchial passages. Numerous fibers of elastic tissue are spread
out in the walls between contiguous air-cells, and many of these are attached
to the outer surface of the wall of which each cell is composed, imparting to
it additional strength and the power of recoil after distention.

The air-cells are lined by a layer of epithelium, figure 225, the cells of
which are very thin and plate-like. The thin epithelial membrane is free on
one side, where it comes in contact \vith the air of the lungs, but on the other

FIG. 225. — From a Section of the Lung of a Cat, Stained with Silver Nitrate. A. D,
Alveolar duct or intercellular passage; S, alveolar septa, N, alveoli or air-cells, lined with
large, flat, nucleated cells, with some smaller polyhedral nucleated cells; M, unstriped
muscular fibers. Circular muscular fibers are seen surrounding the interior of the alveolar
duct, and at one part is seen a group of small polyhedral cells continued from the bronchus.
(Klein and Noble Smith.)

side a network of pulmonary capillaries is spread out so densely, figure 226,
that the interspaces or meshes are even narrower than the vessels. These
are on an average 3 «yo n of an inch, or 8 micromillimeters, in diameter. Be-
tween the atmospheric air-cells and the blood in these vessels, nothing in-
tervenes but the thin walls of the cells and capillaries. The exposure of the
blood to the air is the more complete because the wall between contiguous
air-cells, and often the spaces between the walls of the same, contain only
a single layer of capillaries both sides of which are at once exposed to the air.

The air-vesicles situated nearest to the center of the lung are smaller
and their networks of capillaries are closer than those nearer to the circum-
18

274 RESPIRATION

ference. The vesicles of adjacent lobules do not communicate. Those of
the same lobule or proceeding from the same intercellular passage com-
municate, as a general rule, only near angles of bifurcation, so that when any
bronchial tube is closed or obstructed the supply of air is lost for all the blood
vessels of that lobule and its branches.

Blood Supply. — The lungs receive blood from two sources: 0, the
pulmonary artery; b, the bronchial arteries. The former conveys venous
blood to the lungs for its oxidation, and this blood takes no share in the

FIG. 226. — Section of Injected Lung, Including Several Contiguous Alveoli. (F. E.
Schulze.) Highly magnified, a, a, Free edges of alveoli; c, c, partitions between neighbor-
ing alveoli, seen in section; b, small arterial branch giving off capillaries to the alveoli.
The looping of the vessels to either side of the partitions is well exhibited. Between the
capillaries is seen the homogeneous alveolar wall with nuclei of connective-tissue corpuscles
and elastic fibers.

nutrition of the deeper pulmonary tissues through which it passes. The
branches of the bronchial arteries are nutrient arteries which ramify in the
walls of the bronchi, in the walls of the larger pulmonary vessels, and in the
interlobular connective tissue, etc. The blood of the bronchial vessels is re-
turned chiefly through the bronchial, but partly through the pulmonary, veins.
Lymphatics. — The lymphatics are arranged in three sets: i. Ir-
regular lacunae in the walls of the alveoli or air-cells. The lymphatic vessels
which lead from these accompany the pulmonary vessels toward the root
of the lung. 2, Irregular anastomosing spaces in the walls of the bronchi.
3, Lymph spaces in the pulmonary pleura. The lymphatic vessels from all

THE MOVEMENTS OF THE RESPIRATORY MECHANISM 275

these irregular sinuses pass in toward the root of the lung to reach the bron-
chial glands.

Nerves. — The nerves of the lung are to be traced from the anterior
and posterior pulmonary plexuses, which are formed by branches of the
vagus and sympathetic. The nerves follow the course of the blood vessels
and bronchi, and many small ganglia are situated in the walls of the latter.

FIG. 227. — Capillary Network of the Pulmonary Blood Vessels in the Human Lung. X 60.

(Kolliker.)

THE MOVEMENTS OF THE RESPIRATORY MECHANISM.

Respiratory movement consists of the alternate expansion and contrac-
tion of the thorax, by means of which air is drawn into, or expelled from,
the lungs.

A movement of the side walls or floor of the chest to increase its diameter
or length will enlarge the capacity of the interior. By such an increase of
capacity there will be of course a diminution of the pressure of the air in the
lungs, and a fresh quantity of air will enter through the larynx and trachea
to equalize the pressure on the inside and outside of the chest. This move-
ment is called inspiration.

The movement which diminishes the capacity of the chest and increases
the pressure in the interior expels air until the pressure within and that with-
out the chest are again equal. This movement is called expiration. In both
cases the air passes through the trachea and larynx, whether in entering or
leaving the lungs, there being no other communication with the exterior of
the body. And the lung, for the same reason, remains closely in contact
with the walls and floor of the chest under all the circumstances described.
To speak of expansion of the chest is to speak also of expansion of the lung,
and vice versa.

276

RESPIRATION

Inspiration. — The enlargement of the chest during inspiration is due to
muscular action, which brings about an increase in the size of the chest cavity
through the contraction of the inspiratory muscles, the role played by the
lungs being a passive one. The chest cavity is increased in its three axes,
the vertical, lateral, and antero-posterior diameters. The muscles engaged
in ordinary inspiration are: the diaphragma, the intercostales externi, and
the scaleni and levatores costarum. During forced inspiration every
muscle is brought into play which by its contraction tends to elevate the ribs

and sternum or which wrill fix points against
which these muscles can act. This includes
almost every muscle of the trunk and neck.
Changes in the vertical diameter are due,
first, to the contraction of the diaphragm.
This muscle has the shape of a flattened
dome, its highest point being the central
tendon. While passive, its lower portions
are in apposition with the chest walls, figure
228, 7. On contraction, the dome is pulled
downward and the lower portion is pulled
away from the chest walls, the downward
displacement varying from 6 to 12 mm. in
normal respiration, and in forced respira-
tion may amount to as much as 45 mm.
The tendency of the diaphragm to pull the
lower ribs and lower part of the sternum

inward is counteracted by the outward pressure of the abdominal viscera,
and by the action of the quadrati lumbori, which by their attachment to
the last ribs fix these and, in case of deep inspiration, may even pull them
downward. The serrati postici inferiores also aid, being attached to the
four lower ribs.

Changes in the lateral and antero-posterior diameters are effected by the
raising of the ribs, which are attached very obliquely to the spine and sternum.
The elevation of the ribs takes place both in front and at the sides — the
hinder ends being prevented from performing any upward movement by
their pivot attachment to the spine. The movement of the front extremities
of the ribs is of necessity limited by an upward and forward movement of the
sternum to which they are attached, the movement being greater at the lower
end than at the upper end of the sternum.

The axes of rotation in these movements are two: one corresponding
with a line drawn through the two articulations which the rib forms with
the spine, a, b, figure 230, and the other with a line drawn from one of these
(head of rib) to the sternum, A B, figure 230; the motion of the rib around
the latter axis being somewhat after the fashion of raising the handle of a

FIG. 228. — Schematic Repre-
sentation of Diaphragm. In ex-
piration (/), quiet inspiration
(II), and deep inspiration (III).
(After Schaffer.)

INSPIRATION

277

bucket. The elevation of the ribs is accompanied by a slight opening out of
the angle which the bony part forms with its cartilage, and thus an additional
means is provided for increasing the antero-posterior diameter of the chest.
The movements of all the ribs except the twelfth consist of a rotation up-

Esophagus

Left subclavian artery
Left common carotid artery
Left superior intercostal vein
Left innominate vein

Parietal pleura
(cut edge)

Pericardium

Parietal pleura
(cut edge)

Aortic arch

Pulmonary artery
Bronchus

Pulmonary veins
Esophagus

Diaphragm

FIG. 229. — Thorax from the Left, Showing Left Pleural Sac, and the Diaphragm. The

lung is removed.

ward, forward, and outward. The twelfth presents only rotation down-
ward and backward.

The muscles involved in these movements of the ribs are the external
intercostals and the part of the internal intercostals situated between the
costal cartilages. Their action is to widen the intercostal spaces. The
scaleni fix the first and second ribs, thereby making a fixed point of action

278

RESPIRATION

for the other muscles involved. The serrati postici superiores assist the above
and also raise the third, fourth, and fifth ribs. The levatores costamm longi
and brevi elevate and evert all the ribs from the first to the tenth.

In extraordinary or forced inspiration, which may be due either to violent
exercise or to interference with the due entrance of air into the lungs, all the
above muscles act more strongly. The diaphragm descends lower, the
scaleni raise the first and second ribs instead of merely fixing them, as in
ordinary respiration, as do also the sterno-cleido-mastoids. These, together
with the sacro-spinales, which straighten the spine, increase the vertical
diameter. The trapezii and the rhomboidii assist in increasing the antero-

FIG. 230. — Diagram of Axes of Movement of Ribs.

posterior and lateral diameters by fixing the shoulders and thus giving a
fixed point for the action of the pectorales and latissimi dorsi.

The enlargement of the chest during inspiration presents peculiarities
in different persons. In children of both sexes the principal muscle in-
volved seems to be the diaphragm, and this type of breathing is known as
abdominal breathing. In men, the chest and sternum, together with the
front wall of the abdomen, are subject to a wide movement; this type of
breathing is called the inferior costal. In women, the movement appears
less extensive in the lower and more extensive in the upper part of the chest,
which is called the superior costal type. This has been shown to be due
rather to mode of dress than to a real difference in the sexes (Mosher).

Expiration. — Quiet expiration is a passive act due to the return of
the thorax and its contained lungs to their normal position when the mus-
cles involved in inspiration relax. This elastic recoil is sufficient in ordinary
quiet breathing to expel air from the lungs. In forced expiration, however,

RECORDING RESPIRATORY MOVEMENTS 279

which may occur to a slight degree in speaking, singing, etc., as well as in
the case of many involuntary and reflex acts, such as coughing, sneezing,
etc., other muscles are involved. Of these the principal are the abdominal
muscles, obliquus externus and internus, rectus abdominis, transversus ab-
do minis and pyramidalis. These act, first, by pressing the abdominal
viscera against the diaphragm and thereby forcing it up, their descent into
the pelvic cavity being prevented; second, by their attachments to the lower
ribs and cartilages, the muscles draw these downward and inward, thereby
lessening the size of the thoracic cavity; lastly, by their contraction, they
form a fixed point for the action of that part of the internal intercostals,
not involved in inspiration, to approximate the ribs.

When by the efforts of the expiratory muscles the chest has been squeezed
to less than its average diameters, it again, on relaxation of the muscles,
returns to the normal dimensions by virtue of its elasticity. The construc-
tion of the chest walls, therefore, admirably adapts them for recoiling against
and resisting as well undue contraction as undue dilatation.

Respiratory Movements of the Nostrils and of the Glottis. — During
the action of the inspiratory muscles which directly draw air into the chest,
those which guard the opening through which the air enters are also active.
In hurried breathing the dilatation of the nostrils is well seen, although
under ordinary conditions it may not be noticeable. The opening at the
upper part of the larynx, however, the rima glottidis, is dilated at each in-
spiration for the more ready passage of air, and becomes smaller at each
expiration; its condition, therefore, corresponds during respiration with
that of the walls of the chest. There is a further likeness between the two
acts in that, under ordinary circumstances, the dilatation of the rima glot-
tidis is a muscular act and its contraction chiefly an elastic recoil; although,
under various special conditions to be hereafter mentioned, there may be
considerable muscular contraction exercised.

Methods of Recording Respiratory Movements. — The movements of respira-
tion may be recorded graphically in several ways. The ordinary method is to
introduce a tube into the trachea of an animal, and to connect this tube by
some gutta-percha tubing with a T-piece, the side branch of which is connected
with a Marey's tambour, which may be made to write on a recording surface,
figure 173. If the tube attached to the free limb of the T-piece be partially
closed with a screw compress, the movements of inspiration and expiration are
larger than if it were open. The alteration of the pressure within the lungs on
inspiration and expiration is shown by the movement of the column of air in
the trachea and in its extension to the T-piece. By these means a record of the
respiratory movements may be obtained.

Various instruments have been devised for recording the movements of
the chest by application of apparatus to the exterior. Such is the stethometer
of Burdon- Sanderson, figure 233. This consists of a frame formed of two
parallel steel bars joined by a third at one end. At the free end of the bars
is attached a leather strap, by means of which the apparatus may be suspended

280

RESPIRATION

from the neck. Attached to the inner end of one bar is a tambour and ivory
button, to the end of the other an ivory button. The apparatus is suspended
with the transverse bar posteriorly, the button of the tambour is placed on the
part of the chest the movement of which it is desired to record, and the other but-
ton is made to press upon the corresponding side of the chest, so that the chest

FIG. 231. — Stethograph or Pneumograph. h, Tambour fixed at right angles to plate
of steel, /; c and d, arms by which instrument is attached to chest by belt, e. When the
chest expands, the arms are pulled asunder, which bends the steel plate, and the tambour is
affected by the pressure of &, which is attached to it on the one hand, and to the upright in
connection with horizontal screw, g. (Modified from Marey's instrument.)

is held as between a pair of calipers. The receiving tambour is connected
through a T-piece with a recording tambour of Marey's and with a bulb by
means of which air can be squeezed into the cavity of the typanum. When
adjusted the tube connected with the air ball is shut off by means of a screw
clamp. The movement of the chest is thus communicated to the recording
tambour.

FIG. 232. — Tracing of Thoracic Respiratory Movements obtained by means of
Marey's Pneumograph. (Foster.) A whole respiratory phase is comprised between a
and a; inspiration during which the lever descends, extending from a to b, and expiration
from b to a. The undulations at c are caused by the heart's beat.

A simpler form of this apparatus, called a pneumograph or stethograph,
consists of a thick india-rubber bag of elliptical shape about three inches long,
to one end of which a rigid gutta-percha tube is attached. This bag may be
fixed at any required place on the chest by means of a strap and buckle. By
means of the gutta-percha tube the variations of the pressure of air in the bag,.

RELATIVE TIME OF INSPIRATION AND EXPIRATION 281

produced by the movements of the chest, are communicated to a recording
tambour. This principle is applied in a modified form in Marey's pneumo-
graph, figure 231.

The variations of intrapleural pressure may be recorded by introducing a
cannula into the pleural or pericardial cavity. The cannula should be pre-
viously connected with a mercury or other form of manometer by tubing
filled with physiological saline.

Tambour.
Ivory button.

Tube to commu-
nicate with re-
cording tam-
bour.

Ball to fill appa- .
ratus -with air.

FIG. 233. — Stethometer. (Burdon-Sanderson.)

Finally, it has been found possible in various ways to record the diaphrag-
matic movements. This can be done by inserting a receiving tambour into
the abdomen below the diaphragm, by the insertion of needles into different
parts of the diaphragm and recording the movement of the free ends of needles
about the fulcrum formed where the chest wall is pierced, or by recording the
contraction of isolated strips of the diaphragm directly. These records all
give an accurate picture of the movements of the diaphragm.

The Relative Time of Inspiration and Expiration and the Respira-
tory Movement. — The acts of inspiration and expiration take up, under
ordinary circumstances, a nearly equal time. The time of inspiration,
however, especially in women and children, is a little shorter than that of
expiration, and there is commonly a very slight pause between the end of
expiration and the beginning of the next inspiration, see figure 232. The
ratio of the respiratory rhythm may be thus expressed:

Inspiration 6

Expiration 7 to 8

Pause Very slight

282

RESPIRATION

If the ear be placed in contact with the wall of the chest or be separated
from it only by a good conductor of sound or a stethoscope, a faint respiratory
murmur is heard during inspiration. This sound varies somewhat in dif-
ferent parts, being loudest or coarsest in the neighborhood of the trachea and
large bronchi (tracheal and bronchial breathing), and fading off into a faint
sighing as the ear is placed at a distance from these (vesicular breathing).
It is heard best in children. In them a faint murmur is heard in expiration
also. The cause of the vesicular murmur has received various explanations.
Most observers hold that the sound is produced in the glottis and larger

FIG. 234. — Tracing of the Normal Diaphragm Respirations of the Rabbit, a, With
quick movement of drum; b, with slow movement; /, inspiration; E, expiration. To be
read from left to right. (Marckwald.)

bronchial tubes, but that it is modified in its passage to the pulmonary
alveoli. In disease of the lungs the vesicular murmur undergoes various
modifications, for a description of which one must consult text-books on
physical diagnosis.

The Quantity of Air Breathed. — Tidal air is the quantity of air
which is habitually and almost uniformly changed in each act of breathing.
In a healthy adult man it is about 30 cubic inches, or about 500 c.c. or half
a liter. In college students the tidal air is somewhat less, varying from 300
to 400 c.c.

The complemental air is the quantity of air which can be drawn into the
lungs by the deepest inspiration over and above that which is in the lungs
at the end of an ordinary inspiration. Its amount varies, but may be reck-
oned as 100 cubic inches, or about 1,600 c.c.

QUANTITY OF AIR BREATHED

283

The reserve air is that which may be expelled by a forcible and deeper
expiration, after an ordinary expiration, such as that which expels the tidal
air. The reserve air amounts to from 1,200 to 1,500 c.c. This is also termed
the supplemental air.

The residual air is the quantity which still remains in the lungs after
the most violent expiratory effort. Its amount depends in great measure

FIG. 235.— Diagram of Hutchinson's Spirometer. (Landois.) .4, Graduated cylinder
serving as a receiver for the breath; it is supplied with a stopcock at the top for the ready
expulsion of air, and is balanced by weights passing over pulleys. B, Mouthpiece with
tube reaching nearly to the top of the graduated receiver (A} when the latter is sunk in the
reservoir ready for an experiment; there is a stopcock in this tube near the first angle, to
prevent regurgitation of air. C, Reservoir for the graduated receiver. In using the
spirometer the reservoir and graduated receiver are filled with water, or, to prevent the
absorption of carbon dioxide, with a saturated aqueous solution of common salt (NaCl).
When ready for an experiment, the stopcock at the top of the receiver is closed and that in
the tube of the mouthpiece opened, and the breath forced into the receiver. The receiver
rises as fast as the breath displaces the water. After the breath is forced into the receiver
the stopcock in the tube of the mouthpiece is closed, and the water outside and inside the
receiver brought to the same level, so that the air within the receiver shall be at the atmos-
pheric pressure. The amount of breath within the receiver is then read directly from the
scale attached to the receiver. For accurate measurement the breath should stand a few
minutes to acquire the temperature of the liquid over which it is collected; then the various
corrections for aqueous vapor tension, and the variations from the standard temperature
and pressure, should be made.

on the absolute size of the chest, but may be estimated at about 1,000 c.c.
to 1,200 c.c.

The total quantity of air which passes into and out of the lungs of an
adult, at rest, in 24 hours, is about 686,000 cubic inches. This quantity,
however, is largely increased by exertion; the average amount for a hard-
working laborer in the same time being 1,568,390 cubic inches.

The Respiratory Capacity. — The greatest respiratory capacity or vital

284 RESPIRATION

capacity of the chest is indicated by the quantity of air which a person can
expel from his lungs by a forcible expiration after the deepest possible in-
spiration. The vital capacity is the sum of the reserve, tidal, and comple-
mental airs. It expresses the power which a person has of breathing in the
emergencies of active exercise, violence, and disease. The average capacity
of an adult, at 15.4° C. (60° F.), is about 225 to 250 cubic inches, or 3,500
to 4,000 c.c.

The respiratory capacity or, as John Hutchinson called it, vital capacity, is
usually measured by a modified gasometer or spirometer, into which the experi-
menter breathes, making the most prolonged expiration possible after the
deepest possible inspiration. The quantity of air which is thus expelled from
the lungs is indicated by the height to which the air chamber of the spirometer
rises; and by means of a scale placed in connection with this, the number of
cubic inches or centimeters is read off.

In healthy men, the respiratory capacity varies chiefly with the stature,
weight, and age.

Circumstances Affecting the Amount of Respiratory Capacity. — For every
inch of height above the standard the respiratory capacity is increased, on an
average, by eight inches ; and for every inch below it is diminshed by the same
amount.

The influence of weight on the capacity of respiration is less manifest, and
considerably less than that of height. It is difficult to arrive at any definite
conclusions on this point, because the natural average weight of a healthy
man in relation to stature has not yet been determined.

By age, the capacity appears to be increased from about the fifteenth to the
thirty-fifth year, at the rate of five cubic inches per year; from thirty-five to
sixty-five it diminishes at the rate of about one and a half cubic inches per
year; so that the capacity of respiration of a man sixty years old would be
about thirty cubic inches less than that of a man forty years old, of the same
height and weight (John Hutchinson).

The number of respirations in a healthy adult person usually ranges from
14 to 1 8 per minute. It is greater in infancy and childhood. It varies
also much according to different circumstances, such as exercise or rest,
health or disease, etc. Variations in the number of respirations correspond
ordinarily with similar variations in the pulsations of the heart. In health
the proportion is about i to 4, or i to 5; and when the rapidity of the heart's
action is increased, that of the chest movement is commonly increased also,
but not in every case in equal proportion. It happens occasionally in disease,
especially of the lungs or air-passages, that the number of respiratory acts
increases in quicker proportion than the beats of the pulse; and, in other
affections, much more commonly, that the number of the pulses is greater
in proportion than that of the respirations.

The Force of Inspiratory and Expiratory Muscles. — The force
which the inspiratory muscles are capable of exerting on the chest is greatest

COMPOSITION OF THE ATMOSPHERE 285

in individuals of the height of from five feet seven inches to five feet eight
inches, and is equal to a column of three inches of mercury. Above this
height the force decreases as the stature increases; so that the average power
of men of six feet is measured by about two and a half inches of mercury.
The force manifested in the strongest expiratory acts is, on the average,
one-third greater than that exercised in inspiration. But this difference is
in a great measure due to the power exerted by the elastic reaction of the walls
of the chest; and it is also much influenced by the disproportionate strength
which the expiratory muscles attain from their being called into use for other
purposes than that of simple expiration. The force of the inspiratory act is,
therefore, better adapted than that of the expiratory for testing the muscular
strength of the body (John Hutchinson).

It has been shown that within the limits of ordinary tranquil respiration
the elastic resilience of the walls of the chest favors inspiration; and that it
is only in deep inspiration that the ribs and rib cartilages offer an opposing
force to their dilatation. In other words, the elastic resilience of the lungs,
at the end of an act of ordinary exhalation has drawn the chest walls within
the limits of their normal degree of expansion. Under all circumstances,
of course, the elastic tissue of the lungs opposes inspiration and favors
expiration.

It is possible that the contractile power which the bronchial tubes and
air- vesicles possess, by means of their muscular fibers may assist in expiration.
But it is more likely that its chief purpose is to regulate and adapt, in some
measure, the quantity of air admitted to the lungs, and to each part of them,
according to the supply of blood. The muscular tissue contracts upon and
gradually expels collections of mucus, which may have accumulated within
the tubes, and which cannot be ejected by forced expiratory efforts, owing
to collapse or other morbid condition of the portion of lung connected with
the obstructed tubes (Gairdner). Apart from any of the before-mentioned
functions, the presence of muscular fiber in the walls of a hollow viscus, such
as a lung, is only what might be expected from analogy with other organs.
Subject as the lungs are to such great variation in size, it might be antici-
pated that the elastic tissue, which enters so largely into their composition,
would be supplemented by the presence of much muscular fiber.

RESPIRATORY CHANGES IN THE AIR BREATHED.

Composition of the Atmosphere. — The atmosphere we breathe has,
in every situation in which it has been examined in its natural state, a nearly
uniform composition. It is a mixture of oxygen, nitrogen, carbon dioxide,
and watery vapor, with, commonly, traces of other gases, as argon, ammo-
nia, sulphureted hydrogen, etc. Of every 100 volumes of pure atmospheric
air, 79 volumes, on an average, consist of nitrogen and argon, the remaining

286 RESPIRATION

21 of oxygen. The proportion of carbon dioxide is extremely small; 10,000
volumes of atmospheric air contain only about 4 of that gas.

The quantity of watery vapor varies greatly according to the tempera-
ture and other circumstances, but the atmosphere is never without some.
In this country the average quantity of watery vapor in the atmosphere
varies greatly according to the re'gion. In some of our Western arid plains
in the dry season the air is almost free of moisture.

Character and Composition of Air which has been Breathed.—
The changes effected by respiration in the atmospheric air are: i, an increase
of temperature; 2, a diminution in the quantity of oxygen; 3, an increase in
the quantity of carbon dioxide; 4, a diminution of volume; 5, an increase in
the amount of watery vapor; 6, the addition of a minute amount of organic
matter and of free ammonia.

Temperature of the Expired Air. — Expired air, after its contact with the
Interior of the lungs, is hotter (at least in most climates) than the inspired air.
its temperature varies between 36° and 37.5° C. (97° and 99.5° F.), the
lower temperature being observed when the air has remained but a short
time in the lungs. Whatever may be the temperature of the air when in-
haled, it acquires nearly that of the blood before it is expelled from the chest.

The Oxygen of Expired Air. — Pettenkofer and Voit have found that the
mean consumption of oxygen during 24 hours by a man weighing 70 kilos
is about 700 grams or 490 liters. The quantity of oxygen absorbed increases
with muscular exercise, and falls during rest. In general terms the quantity
absorbed varies with the activity of the metabolic processes, following very
closely the variation of carbon dioxide under the conditions outlined below.

The Carbon Dioxide of Expired Air. — The percentage of carbon dioxide
is increased in expired air, but the total quantity of carbon dioxide exhaled
in a given time is subject to change from various circumstances. From
every volume of air inspired 4 to 5 per cent, of oxygen is abstracted; while
a rather smaller quantity, 4.38 per cent., of carbon dioxide is added in its
place. The expired air will contain, therefore, 438 volumes of carbon di-
oxide in 10,000. The total quantity of carbon dioxide exhaled into the air
breathed by a healthy adult, calculating that 15.4 c.c. of the 350 c.c. of the
average air exhaled at each expiration consists of carbon dioxide, and that
the rate of respiration per minute is on an average 16, would be about 400
liters in twenty-four hours. From actual experiment this amount seems
to be a trifle too great, since from the average of many investigations the
total amount of carbon dioxide excreted per day by the entire body has been
found to be about 400 liters, weighing 800 grams, and consisting of 218
grams of carbon, and 582 grams of oxygen. From the 218 grams of carbon
must be deducted about 10 grams excreted in other ways than by the lungs,
which leaves about 215 grams as the amount of carbon excreted by the aver-
age healthy man by respiration each day and night. These quantities

CHARACTER AND COMPOSITION OF AIR

must be considered approximate only, inasmuch as various circumstances,
even in health, influence the amount of carbon dioxide excreted, and, cor-
relatively, the amount of oxygen absorbed.

The total amount of carbon dioxide excreted is influenced sharply by a
number of factors : First, the depth and volume of respiratory movements. The
greater the volume of air breathed, the greater the total output of carbon
dioxide, though the percentage per unit of
expired air is decreased. This influence de-
pends upon the more efficient oxidative
processes in the presence of more thorough
ventilation of the lungs and blood. Second,
the carbon dioxide output varies with age.
It is greater with children and youth than
with the old. In extreme old age the total
output may not exceed that of the ten-year-
old child. Third, there is a diurnal variation
in carbon dioxide output. The respiratory
quotient, i.e., the ratio between carbon
dioxide eliminated and oxygen absorbed, is
greater during the day than during the
night. In the day, therefore, the carbon
dioxide exhaled in relation to the oxygen
absorbed is increased, and it is diminished
during the night. This is probably due to
the increased production of carbon dioxide
as a result of increased tissue activity during
the day, and, consequently, the breaking
down or katabolism of more substances.
Fourth, the character and quantity of the
food greatly influence the proportion of
carbon dioxide as indicated by the respira-
tory quotient. It is greater with carbohy-
drate foods. During fasting there is for the
first two or three days an increased carbon
dioxide output, but later this is decreased-
Fifth, the bodily exercise, in moderation,
increases the quantity of carbon dioxide ex-
pired by at least one-third more than it is
during rest. For about an hour after exercise the volume of the air expired
in the minute is increased nearly 2,000 c.c., or 118 cubic inches; and the
quantity of carbon dioxide about 125 c.c., or 7.8 cubic inches per minute.
Violent exercise, such as full labor or athletic competition, still further in-
creases the amount of the carbon dioxide exhaled. Sixth, the observations
made by Vierordt at various temperatures between 3.4°-23.8° C. (38° F.
and 75° F.) show, for warm-blooded animals, that within this range every
rise equal to 5.5° C. (10° F.) causes a diminution of about 33 c.c. (2 cubic
inches) in the quantity of carbon dioxide exhaled per minute.

The Volume of the Respired Air is Diminished. — When allowance has
been made for the expansion in heating, the volume of expired air is decreased,

FIG. 236. — Apparatus for Esti-
mating O2 and CO2 in Expired
Air. (Waller.)

288 RESPIRATION

the loss being due to the fact that a portion of the oxygen absorbed is not
returned in the form of carbon dioxide. Since the oxygen of a given volume
of carbon dioxide would have the same volume as the carbon dioxide itself
at a given temperature and pressure, a portion of the oxygen absorbed
must be used for other purposes than the formation of carbon dioxide.
In fact, some of it is used in the formation of urea, some in the formation
of water, etc. The volume of the carbon dioxide exhaled, divided by the
volume of the oxygen absorbed, gives what is known as the respiratory quo-
tient; thus

CO2 exhaled
O2 absorbed
Normally in man on a mixed diet the respiratory quotient is

4.0 to 4.5

= 0.8 to 0.9.

But it is subject to variation through several causes; for example, through
variation in the composition of the diet. On a pure carbohydrate diet the
respiratory quotient will rise above 0.9, i.e., to i.o, since carbohydrates
contain enough oxygen to oxidize the hydrogen in the molecule. On a diet
containing much fat the quotient is lowest, since relatively more oxygen is
needed completely to oxidize fat. The theoretical respiratory quotient for
fats is 0.7. The same is true, but to a less degree, in the case of proteins
which also require much oxygen for their complete oxidation. Muscular
exertion raises the respiratory quotient, because in its performance carbo-
hydrates are used up in relatively greater quantity.

The Watery Vapor in Respired Air. — The quantity of water vapor emitted
is, as a general rule, sufficient to saturate the expired air, or very nearly so.
Its absolute amount is, therefore, influenced by the following circumstances:
i. By the quantity of air respired; for the greater the volume of air, the
greater also will be the quantity of moisture exhaled; 2. by the quantity of
water vapor contained in the air previous to its being inspired; because the
greater the moisture inhaled, the less will be the amount to complete the
saturation of the air; 3. by the temperature of the expired air; for the higher
the temperature the greater will be the quantity of water vapor required to
saturate the air; 4. by the length of time which each volume of inspired air
is allowed to remain in the lungs; for although, during ordinary respiration,
the expired air is always saturated with water vapor, yet, when respiration is
performed very rapidly, the air has scarcely time to be raised to the highest
temperature or be fully charged with moisture ere it is expelled.

The quantity of water exhaled from the lungs in 24 hours ranges (accord-
ing to the various modifying circumstances already mentioned) from about
200 to 800 c.c., the ordinary quantity being about 400 to 500 c.c. Some of
this is probably formed by the chemical combination of oxygen with hydro-

RESPIRATORY CHANGES IN THE BLOOD 289

gen in the system; but the far larger proportion of it is water which has been
absorbed, as such, into the blood from the alimentary canal, and which is
exhaled from the surface of the air-passages and cells, as it is from the free
surfaces of all moist animal membranes, particularly at the high tempera-
ture of warm-blooded animals.

A small quantity of ammonia is added to the ordinary constituents of
expired air. It seems probable, however, both from the fact that this sub-
stance cannot be always detected and from its minute amount when present,
that the whole of it may be derived from decomposing particles of food left
in the mouth or the teeth, and that it is, therefore, only an accidental con-
stituent of expired air.

The Organic Matter in Expired Air. — It was formerly supposed that this
organic matter was injurious and gave rise to the unpleasant symptoms
which are experienced in badly ventilated rooms. But this has been strongly
questioned so that the matter cannot be considered settled at the present
time.

THE RESPIRATORY CHANGES IN THE BLOOD.

Pressure and Diffusion of the Air. — It must be remembered that
the tidal air in the lungs amounts only to from 300 to 500 c.c. at each in-
spiration. This amount at once mixes with the reserve and the residual
air already in the lungs. The mixture is facilitated by the air currents set
up in the deeper parts of the lungs by the sudden entrance of the tidal air;
but, after all is considered, it will be found that diffusion is the greatest factor
in producing a uniform mixture of the gases in the alveoli and in the air-cells
of the lungs. Just as a fresh supply of oxygen introduced within the door
of a closed room will quickly diffuse throughout the space of the entire room
so will the fresh tidal air diffuse into the space of the lungs. When the
tidal air is expired its average composition has been changed so it has only
about 16 per cent, of oxygen instead of the usual 20.96 per cent, of oxygen in
air. The oxygen content of the air still left in the lungs is probably some-
what less than the percentage in this expired air for the reason that the air
of the respiratory tree, the trachea, bronchi, and bronchioles, is never fully
mixed with the alveolar air.

The partial pressure of the oxygen of the air measured under standard
conditions is 159 mm. of mercury; that is, 20. 96 per cent, of 760 mm. of mer-
cury, the standard pressure of one atmosphere. The partial oxygen pressure
in expired air with 16 per cent, of oxygen is only 122 mm. of mercury. These
figures showT a diffusion pressure of at least 37 mm. of mercury to carry
oxygen into the deeper recesses of the lungs. The constant loss of oxygen
to the blood probably keeps the mean difference greater.

The Gases of the Blood. — Turning now to the consideration of the
gases of the blood in the lungs, a somewhat different picture presents itself.
19

290

RESPIRATION

The blood is a mass of corpuscles floating in the fluid plasma. An analysis
of the blood shows that it contains oxygen, carbon dioxide, and nitrogen, the
gases of the air. The usual method is completely to extract the blood gases
by an air-pump, figure 237, and determine the quantities in cubic centi-
meters per 100 c.c. of blood.

The Extraction of the Gases from the Blood. — As the ordinary air-pumps are
not sufficiently powerful for the purpose, the extraction of the gases from the
blood is accomplished by means of a mercurial air-pump, of which there are
many varieties, those of Ludwig, Alvergnidt, Geissler, and Sprengel being the

chief. The principle of action in all is much
the same. Ludwig's pump, which may be taken
as a type, is represented in figure 237. It con-
sists of two fixed glass globes, C and F, the
upper one communicating by means of the
stopcock, D, and a stout india-rubber tube with
another glass globe, L, which can be raised or
lowered by means of a pulley ; it also communi-
cates by means of a stopcock, B, and a bent
glass tube, A, with a gas receiver (not repre-
sented in the figure), A dipping into a bowl of
mercury, so that the gas may be received over
mercury. The lower globe, F, communicates
with C by means of the stopcock, E, with / in
which the blood is contained by the stopcock,
G, and with a movable glass globe, M, similar to
L, by means of the stopcock, H , and the stout
india-rubber tube, K.

In order to work the pump L and M are
filled with mercury, the blood from which the
gases are to be extracted is placed in the bulb /,
the stopcocks H , E, D, and B being open, and G
closed. M is raised by means of the pulley
until F is full of mercury, and the air is driven
out. E is then closed, and L is raised so that C
becomes full of mercury, and the air driven off.
B is then closed. On lowering L the mercury
runs into it from C, and a vacuum is established
in C. On opening E and lowering M, a vacuum

FIG. 237.— Ludwig's Gas-pump. is similarly established in F; if G be now opened,

the blood in I will begin ebullition, and the gases

will pass off into F and C, and on raising M and then L, the stopcock B being
opened, the gas is driven through A, and is received into the receiver over
mercury. By repeating the experiment several times the whole of the gases
of the specimen of blood is obtained, and may be estimated.

Pfluger's analysis of the arterial blood of the dog gave the following
volumes per cent.: oxygen 22.6, carbon dioxide 34.3, and nitrogen 1.8.
The analysis for the venous blood gives a very much lower oxygen and a
higher carbon dioxide per cent. The average oxygen content of venous

THE GASES OF THE BLOOD 29 1

blood is 10 to 12 per cent, and the carbon dioxide 45 per cent. The blood
in different veins of the body varies within wide limits as regards its gas
content.

Oxygen.

Carbon
dioxide.

Nitrogen.

zoo c.c. arterial blood 22.6 c.c. 34 c.c.

100 c.c. venous blood 12 . c.c. 45 c.c.

1.7 c.c.
1.7 c.c.

The large quantity of oxygen found in arterial and in venous blood is the
more striking when the facts of absorption of gases by liquids are reviewed.
A liquid such as water will, when exposed to a gas, take up the gas by absorp-
tion according to definite physical laws. Under constant temperature the
amount of gas absorbed, oxygen for example, varies directly as the pressure of
the gas, or partial pressure if the gas is in a mixture. The oxygen absorbed
by water from pure air as compared with expired air is in direct proportion
to the partial pressure of oxygen in the two airs, which is as 159 to 122.

The amount of gas absorbed for a unit of fluid under standard tempera-
ture and pressure (one atmosphere at o° C.), called its absorption coefficient,
is about the same for blood plasma as for water. Before one can determine
the actual amount of oxygen in the plasma, the tension or absorption
pressure must be determined.

The tension of the oxygen in arterial blood is found by an instrument
which enables one to measure the pressure at which oxygen is neither ab-
sorbed nor given off. The instrument commonly used is called an aerotonom-
eter. The principle of the instrument depends upon the fact that blood
exposed to mixtures of the gases in air tends to give up or absorb gases from
the air until complete equilibrium is established.

By this means observers have measured the tensions of the blood gases.
The results have been not very constant, but the oxygen tension has been
found to be from 4 (Strassburg) to 10 (Herter) per cent, of an atmosphere.
Many determinations have been given of both lower and higher percentages,
but, accepting the above limits for a working average, the oxygen tension
in arterial blood would be from 30.4 to 76 mm. of mercury.

Blood plasma exposed to an air with a partial pressure of 30 . 4 to 76 mm.
of mercury would absorb only from o. i to 0.3 (o. 26 c.c. Pfluger) of a cubic
centimeter of oxygen for 100 c.c. of blood. As a matter of fact, 100 c.c. of
whole blood contains from 20 to 22 . 6 c.c. of oxygen. It is evident that blood
cannot hold the oxygen in simple solution, but must retain it in chemical
combination. The red blood corpuscles have been shown to carry the
excess of oxygen by virtue of the special respiratory pigment, hemoglobin.

292

RESPIRATION

Combining Power of Hemoglobin with Oxygen. — One hundred
cubic centimeters of blood contain about 14 grams of hemoglobin, page 133.
Each gram of hemoglobin, when fully saturated with oxygen, according to
Hiifner's earlier determination, conbines with i .56 c.c. of oxygen. By later
work he gets the determination of i . 34 c.c. for hemoglobin of ox blood.

100
90

80
70
GO

50

40

30

'20

10

10

20

30

40

50

GO

90 100

FIG. 238. — Dissociation curves of oxyhemoglobin. The figures along the ordinates
represent percentages of saturation of hemoglobin by oxygen. The figures along the
abscissse represent mm. of oxygen pressure in mercury.

I. Bohr's dissociation curve of oxyhemoglobin dissolved in water.

II. Dissociation curve of oxyhemoglobin dissolved in Ringer's Solution. (After
Bancroft and Camis.)

This last figure indicates that the combining power of the hemoglobin is
dependent upon the iron in the molecules, in which one atom of iron combines
with one atom of oxygen. A number of investigators have examined the
conditions under which hemoglobin combines with oxygen — Hiifner, Bohr,
Lowy, and Bancroft and Camis. Hiifner, working with purified hemo-
globin in watery solution, found that when the oxygen tension in the air in
contact with the hemoglobin was increased above zero by graded stages,

COMBINING POWER OF HEMOGLOBIN WITH OXYGEN

293

the amount of oxygen that was combined was very great per unit of in-
creased pressure at the low pressures, but relatively less at the higher
pressures. Or, which amounts to the same, if hemoglobin saturated with
oxygen be subjected to decreasing oxygen pressure, it sets free the combined
oxygen, at first slowly, then more rapidly. By consulting the typical curve

too

80

70

60

50

30

20

10

/

10

20

30

FIG. 239. — Dissociation curves of oxy hemoglobin in: 1,0.7 Per cent, sodium chlor-
ide; II, in sodium bicarbonate, and III, in disodium phosphate. The figures along the
ordinates represent percentages of saturation of hemoglobin by oxygen. The figures
along the abscissae represent mm. of oxygen pressure in mercury. (Bancroft and Camis.)

showing this relation, it will be evident that the critical partial oxygen pres-
sures influencing this combination fall at about 30 to 35 mm. mercury of
oxygen tension and below. See figure 238.

A number of factors influence the dissociation of oxygen from hemoglobin
at a given oxygen tension. Of prime importance is the influence of the
presence of carbon dioxide gas as shown by Bohr and recently confirmed by
Bancroft and Camis. With an increase in the tension of carbon dioxide
there is a decrease in the fixation of oxygen.

294

RESPIRATION

TABLE SHOWING THE DISSOCIATION OF OXHEMOGLOBIN IN THE PRESENCE OF VARY-
ING TENSIONS OF CARBON DIOXIDE. (BANCROFT AND CAMIS.)

Tensions of oxygen in mm. mercury and the per cent, of saturation

Tension of car-

of the hemaglobin at each pressure

bon dioxide

10

IS

20

25

3°

35

40

45

50

60

70

80

100

5 mm. COz

28

35

47

58.S

70

81

89

93

95

96

98

99

99-5

10 mm. CO2

1 1

26

38.5

Si

63

74-5

83

88

9i -5

94-5

96.5

97-5 i 98.5

20 mm; CO2

o

10

25

49

53-8

65.5

74-5

80.5

84.5

90

93

95

97 -5

40 mm. CO2

o

0

i i

26

42 .5

56

65

72

77

83-5

88.5

93 \ 95 -5

80 mm. CO2

o

0

i

12. S

3i

45-5

56.5

64

69.5

77

83

87.5

92.5

The salts of the blood alsb influence the oxygen fixation by hemoglobin
under a given tension as indicated in the following table:

TABLE SHOWING THE INFLUENCE OF THE PRESENCE OF DIFFERENT SALTS ON

THE PERCENTAGE OF SATURATION OF HEMOGLOBIN UNDER A

CONSTANT OXYGEN TENSION OF 30 MM. MERCURY.

(BANCROFT AND CAMIS.)

1. Hemoglobin in water dissociation 60 per cent.

2. Hemoglobin in o . 7 per cent. NaCl dissociation. ... 75 per cent.

3. Hemoglobin in Ringer's solution dissociation 85 per cent.

4. Hemoglobin in NaHCO3 solution dissociation 89 per cent.

5. Hemoglobin in 0.9 per cent. KC1 dissociation 91 per cent.

6. Hemoglobin in Na2HPO4 solution dissociation. ... 93 per cent.

Bancroft and Camis find that the dissociation curve also varies in the
blood of different animals. Strassburg gives the oxygen tension of arterial
blood as 29.64 mm. of mercury, and for venous blood 22.04 mm- of mer-
cury. That is to say, during the brief interval in which the blood is in
the pulmonary capillaries the oxygen tension has increased by 7 . 6 mm.
of mercury, an increase of tension which would produce very little increase
in simple absorption of oxygen. Yet it is sufficient to cause fixation of
from four to five volumes per cent, of oxygen by the hemoglobin.

It is evident that there will be diffusion of oxygen from the high tension
toward the lower and in the direction indicated by the arrows in the table
above. As fast as the oxygen diffuses into the venous blood, thus tending to
raise the pressure of the gas in solution, it is taken up and fixed by the hemo-
globin. This process proceeds during the interval the blood is in the pul-
monary capillaries far enough to raise the oxygen tension from 22.04 mm-
of mercury to 29 . 64 mm. of mercury, and also far enough to permit of the
fixation of from four to five volumes per cent, of oxygen. The oxygen
diffusion pressures are indicated as follows:

ELIMINATION OF CARBON DIOXIDE 295

Oxygen pressure in the atmosphere 1 59 mm. of mercury

J

Oxygen pressure in the alveolar air 122 mm. of mercury

1

Oxygen pressure in the venous blood 22 .04 mm. of mercury

Liberation of Oxygen in the Tissue Capillaries.— When the arterial
blood reaches the capillaries of the tissues, then the situation which we have
just found holding good in the lungs is reversed. As rapidly as the oxygen
reaches the living protoplasm of the tissues it enters into fixed combination,
thus rendering it inert. The oxygen tension in the tissue cells will, there-
fore, be zero. Under these conditions the difference in pressure level be-
tween the oxygen tension in the blood and that in the tissues is sufficient to
cause a rapid diffusion of oxygen through the capillary walls with correspond-
ing liberation of the oxygen from the hemoglobin according to the laws of
combination given in the curves above. The total effect of this process is to
maintain a relatively high and constant diffusion pressure of the oxygen in
the blood. During the time the blood remains in the capillaries the total
oxygen tension will have been lowered from 29.64 to 22 .04 mm. of mercury,
yet this slight lowering of tension is sufficient to liberate from four to five
volumes per cent, of oxygen. This figure, of course, is comparative. In
many of the very active tissues, such as in muscle, a much larger per cent,
of oxygen will have been dissociated and the oxygen tension correspondingly
lowered so that the venous blood returning through such an active organ
may not have more than half the average amount of oxygen found in venous
blood.

Considering the pressure relations of oxygen from the time of its intro-
duction into the body with the fresh air to its fixation in the tissues we have
the following schema:

Oxygen pressure in the atmosphere 159 mm.

1

Oxygen pressure in the alveolar air 122 mm.

1

Oxygen pressure in the venous blood 22 .04 mm.

Tension of oxygen in the arterial blood 29 . 64 mm.

I

Tension of oxygen in the tissues o .00 mm.

Elimination of Carbon Dioxide by the Blood and the Respiratory
Apparatus. — The principles of absorption of gas by liquids discussed
in the preceding pages apply equally well for carbon dioxide with the excep-
tion that carbon dioxide is about three times as soluble in blood as is oxygen.
The carbon dioxide results from the oxidative processes going on in the tis-
sues, and this gas is present in large quantities in the tissues and their im-
mediately surrounding lymph. An analysis of the carbon-dioxide content
of venous blood reveals the presence of about 45 c.c. of the gas in 100 c.c. of

296 RESPIRATION

blood. This gas, like oxygen, is held in such large quantity by virtue of the
fact that it forms loose chemical combinations in the blood. Of the total
quantity not more than 5 per cent, is held in simple solution. From 10 to
15 per cent, of the total volume is found in firm combination in such forms
as carbonates, bicarbonates, etc. The remaining 85 and more volumes
per cent, is held in loose chemical combination, a combination which is broken
up under the same conditions of variation in carbon-dioxide tension as
were found to exist for oxygen in combination with hemoglobin. In the case
of carbon dioxide an analysis of plasma reveals the fact that the gas is in com-
bination with some compound of the plasma, probably a protein. In fact,
there is some evidence to show that carbon dioxide combines with the globu-
lin group. Carbon dioxide also forms loose chemical compounds with the
constituents of the red corpuscles, probably with the protein portion of the
hemoglobin molecule. The pressure relations of this gas as regards its
diffusion in the process of elimination are shown in the following table:

Carbon-dioxide tension in the tissues 58 mm. of mercury

!

Carbon-dioxide tension in the venous blood 4 5 mm. of mercury

'!

Carbon-dioxide tension in the alveolar air . . 23 to 38 mm. of mercury

1

Carbon-dioxide tension in the expired air. . . 5.8 mm. of mercury

Theories of Interchange of Gases in the Lungs and in the Tissues. —

The above discussion is on the basis of the mechanical interpretation of the
transfer of gases in the lungs and in the tissues. By this theory it is assumed
that the oxygen passes from the air in the lungs through the moist pulmonary
membrane of the alveoli through the capillary walls and into the blood
plasma, obeying the physical laws of gas diffusion. Likewise in the tissues
this theory presupposes that the difference in the mechanical tension in the
capillary blood plasma, the lymph, and the living tissue will lead to diffusion
of the oxygen in the direction of lowest pressure, i.e., toward the tissues.

Some facts have indicated that we cannot account for the transference
of oxygen by the purely mechanical theory. The idea has been advanced
that the living epithelial wall of the lung, as well as that of the capillaries,
exerts a distinct influence on the passage of oxygen of such nature that it
might be regarded as a secretion of this gas. This theory finds some addi-
tional support in the fact that in the air bladders of certain fishes a distinct
secretion of oxygen has been proven by Bohr.

THE NERVOUS REGULATION OF THE RESPIRATORY
APPARATUS.

Respiratory movement is essentially an involuntary act. Unless this
were the case, life would be in constant danger, and would cease on the

THE RESPIRATORY NERVE CENTER 297

loss of conciousness for a few moments, as in sleep. It is, however, of ad-
vantage to the body that co-ordination respiratory movements should be to
some extent under the control of the will. For, were it not so, it would be
impossible to perform those voluntary respiratory acts, such as speaking,
singing, and the like.

The Respiratory Nerve Center. — It has been known for centuries
that there exists a region of the central nervous system on the destruction of
which both respiration and life cease. Flourens, 1842, after many series
of experiments as to the exact position of what he called the "knot of life''
(naeud vital), placed it in the floor of the fourth ventricle, at the point of the V
in the gray matter at the lower end of the calamus scriptorius; a district of
considerable size, some 5 mm. in extent on each side of the middle line.
Observers subsequent to Flourens have attempted to show that the chief
respiratory center, on the one hand, is situated higher up in the nervous
system, in the floor of the third ventricle (Christiani), or in the corpora quad-
rigemina (Martin and Booker, Christiani, and Stanier), or lower down in
the spinal cord. The balance of experimental evidence, however, is to prove
that the sole centers for respiration are in a limited district in the medulla
oblongata in close connection with the vagus nucleus on each side, with
which they are probably identical. The destruction of this region stops
respiration. If the center be left in connection with the muscles of respira-
tion by their nerves, although the remainder of the central nervous system be
separated from it, respiration continues. It may be considered almost cer-
tain that the medullary center is the only true respiratory center. Langen-
dorff states that in newly born animals in which the medulla has been im-
mediately cut across at a level a few millimeters below the point of the
calamus scriptorius, respiration continues for some time, but this is ques-
tionable. Normal respiration does not occur after separation of the bulb
from the cord, and the so-called respiratory movements noticed by Langen-
dorff are merely tetanic contractions of the respiratory muscles in which often
enough other muscles take part.

The action of the medullary center is to send out impulses during in-
spiration, which cause contractions of the inspiratory muscles — a, of the
nostrils and jaws, through the facial and inferior division of the fifth nerves;
b, of the glottis, chiefly through the inferior laryngeal branches of the vagi; c
of the intercostal and other muscles which produce raising of the ribs, chiefly
through the intercostal nerves, and d, of the diaphragm, through the phrenic
nerves. If any one of these sets of nerves be divided, respiratory movements
of the corresponding muscles cease. Similarly it may be supposed that
the center sends out impulses to certain other muscles during expiration.

It has been suggested, however, that the center is double, that it is made
up of inspiratory cells which are constantly in action, and of an expiratory
group of cells which act less generally, inasmuch as ordinary tranquil ex-

298

RESPIRATION

piration is seldom more than an elastic recoil, and not a muscular act to
any marked degree.

The respiratory center is also bilateral, as has been proven by the method
of antero-posterior section of the medulla. The tracts from each half of the
center are separate and distinct. If the cervical cord be split into a right
and left half, and one side sectioned at the level of the second cervical ver-
tebra, then the respiratory movements of that side of the diaphragm cease
while on the opposide side they continue their rhythm.

Assuming this view of the quadruple nature of the respiratory centers
to be correct, there is some difference of opinion of the exact mode of action.
It is thought that the center may act automatically, but normally is influenced
by afferent impulses from the periphery, as well as by impulses passing
down from the cerebrum. The center is, in other words, both automatic and
reflex. It will be simplest to discuss its reflex function first.

Action of Afferent Stimuli on the Respiratory Rhythm. — Action
of the vagi. If both vagi be divided in the neck, the respirations become

BOTH VAGICUT

R. 120

"rrrrrrrrrrrrrrrrrr

FIG. 240. — The Effect on the Respiratory Rate of Cutting Both Vagi in the Dog.
The rate of 60 respirations per minute before the section of the nerves drops to 8 per
minute afterward. The arterial blood pressure is also shown, the pressure in mm. mer-
cury is shown in the scale to the left. Compare with figure 179.

much slower and deeper, figure 240. This may be the case, but to a less
marked degree, if one of the nerves is divided instead of both. If the cen-
tral end of the divided nerve be stimulated with a weak but properly adjusted
strength of interrupted current, the effect is that the respirations are quick-
ened, and if the stimuli are properly regulated the normal rhythm of respi-
ration may be resumed. If the stimuli be repeated with stronger currents,
the breathing is brought to a standstill, sometimes at the height of inspira-
tion, by tetanus of the diaphragm. Usually, however, stimulation of the
central end of the divided vagus produces still greater slowing than that
which follows the division, so that the respirations cease with the diaphragm
in a condition of complete relaxation, figures 205 and 241.

ACTION OF OTHER SENSORY NERVES 299

The action of the vagus may be to call forth either inspiration or expira-
tion— the impulses passing up the vagi being necessary to the production
of the normal respiratory rhythm. The fibers of the vagus are stimulated
under the following circumstances: those fibers which tend to inhibit expira-
tion and to stimulate inspiration are stimulated at their origin in the lung
when the lung is empty and in a condition of expiration. The fibers which
tend to inhibit inspiration and to promote expiration are stimulated when
the lung is fully expanded. The afferent impulses by this view are the
results of mechanical stimulation, and do not depend altogether upon the
chemical nature of the gases within the pulmonary alveoli.

on. of/

FIG. 241. — The Effect of Stimulating the Vagus on Respiratory Rate. The stimulus
was applied between the points "on" and "off." The inhibition lasts some seconds after
the stimulus is removed. Time in seconds. The intratracheal pressure is recorded.

The Respiratory Action of the Superior Laryngeal Nerves. — If the

superior laryngeal branch of the vagus be divided, which usually produces
no apparent effect, and the central end be stimulated, the effect is very con-
stant— respirations are slowed, but there is a tendency toward expiration,
as is shown by the contraction of the abdominal muscles. Thus, the vagus
contains fibers which stimulate inspiration and inhibit expiration, as well as
other fibers which have the reverse effect; while the superior laryngeal fibers
inhibit inspiration and stimulate expiration.

The superior laryngeal nerves are true expiratory nerves, and are nor-
mally set in action when the mucous membrane of the larynx is irritated.
They are not in constant action like the vagi.

Action of the Glosso-pharyngeal Nerves. — It has been ascertained,
by the researches of Marckwald, that while division of the glosso-pharyngeal
nerves produces no effect upon respiration, stimulation of them causes in-
hibition of inspiration for a short period. This action accounts for the very
necessary cessation of breathing during swallowing. The effect of the
stimulation is only temporary, and is followed by normal breathing
movements.

Action of Other Sensory Nerves. — The respiratory center is in-
fluenced strongly by afferent nerve impulses having their origin in general
sensory nerves, particularly the nerves of the skin. Cold water suddenly
dashed on the skin is followed by a deep inspiration. Stimulation of the
splanchnics or of the abdominal branches of the vagi produces expiration.
Stimulation of the isolated sciatic nerve of the dog or of the rabbit causes a

300 RESPIRATION

marked acceleration both of the rate and of the amplitude of the respiratory
movements, see figure 246. This acceleration is due to afferent impulses
which reach the respiratory center in the medulla over sensory paths, paths
which are not necessarily special respiratory afferent paths, but rather are
general afferent paths which affect the respiratory center through their
numerous collaterals in the brain stem.

It must be remembered that, although many sensory nerves may on
stimulation be made to produce an effect upon the respiratory center, yet
there is no evidence to show that any one of them, except the vagus, is con-
stantly in action. The vagi indeed are, as far as we know, the normal
regulators of respiratory movements, yet it is possible reflexly to influence
the respiratory rate and depth through impulses that may have their origin
in any sensory part of the body.

The respiratory center is also influenced by nerve activity of the cerebral
cortex, psychic activity. This is illustrated by the limited voluntary control
of the respiratory movements.

Automatic Action of the Respiratory Centers. — Although it has
been very definitely proved that the respiratory centers may be affected by
afferent stimuli, and particularly by those reaching them through the vagi,
there is reason for believing that the center is capable of sending out
efferent impulses to the respiratory muscles without the action of any afferent
stimuli. Thus, if the brain be removed above the bulb, respiration continues.
If the spinal cord be divided immediately below the bulb, the facial and
laryngeal respiratory movements continue, although no afferent impulses can
reach the center except through the cranial sensory nerves, and these indeed
may be divided without producing any effect, when the bulb and cord are
intact. As has been shown, too, respiration continues when the vagi are
divided. Isolation of the respiratory center from its sensory relations does
not destroy respiratory movements so long as the motor paths through the
phrenic nerves are intact. All of these experiments render it highly probable
that afferent impulses are not required in order that the respiratory centers
should send out efferent impulses to the respiratory muscles. The center,
then, is automatic.

Method of Automatic Stimulation of the Respiratory Center.— The
respiratory center is capable of working automatically apart from afferent
impulses, and this fact has been explained by the supposition that it is
stimulated to action by the condition of the blood circulating through it.
When the blood becomes more and more venous the action of the center
becomes more and more energetic, and if the air is prevented from entering
the chest, the respiration in a short time becomes very labored. If the
aeration of the blood is much interfered with, not only are the ordinary
respiratory muscles employed, but also those muscles of extraordinary in-
spiration and expiration which have been previously enumerated. Thus,

AUTOMATIC STIMULATION OF THE RESPIRATORY CENTER 301

as the blood becomes more and more venous, and by venous we mean that
the blood contains a relatively large amount of carbon dioxide and a dimin-
ished amount of oxygen, the action of the medullary center becomes more
and more profound. The question has been much debated as to what
quality of the venous blood it is which causes this increased activity; whether
it is its deficiency of oxygen or its excess of carbon dioxide. It has been
answered to some extent by experiments which offer no obstruction to the exit
of carbon dioxide, as when an animal is placed in an atmosphere of nitrogen.
Under these conditions dyspnea occurs, showing that blood which contains
a diminished amount of oxygen stimulates the cells of the respiratory center.
On the other hand, if the normal amount of oxygen is supplied while the
carbon dioxide of the blood is prevented from escaping and thus allowed to
accumulate in the blood, there is also a great increase in the respiratory
activity of the center; an excess of carbon dioxide in the blood, flowing
through the respiratory center, stimulates the cells to greater activity. It
is highly probable, therefore, that the respiratory centers may be stimulated
to action both by the absence of sufficient oxygen in the blood circulating
in it, and by the presence of an excess of carbon dioxide.

These facts are particularly well supported by the experiments of Zuntz
who varied the oxygen and the carbon-dioxide content of the air breathed,
and measured the volume breathed per minute. When the oxygen of the
air breathed was reduced by 10 to 50 per cent., the air breathed was increased
only slightly, 5 to 10 per cent. When the oxygen of the air was reduced
by 60 per cent., the volume of air breathed was increased 30 to 40 per cent.,
and even more. Other observations show us that the oxygen in the blood
in these experiments will fall in much less per cent, than the reduction in
the oxygen of the air would lead us to suspect.

When Zuntz kept the oxygen content of the air about constant, but in-
creased the carbon-dioxide content, then the amount of air breathed was
greatly increased. Air containing 18.4 per cent, of oxygen and 11.5 per cent,
of carbon dioxide increased the amount breathed per minute from 7 . 5 liters
to 32.5 liters. These experiments indicate that within the limits of its
normal variations in blood the carbon dioxide has a much greater influence
than oxygen on the irritability of the cells of the respiratory center.

But this is not all, since it has been observed by Marckwald that the
medullary center is capable of acting for some time in the absence of any
circulation and after excessive bleeding. The view taken by this author
with regard to the action of the center is as follows: The respiratory center
is set to act by the condition of its metabolism, much in the same way as
the heart is set to beat rhythmically. When anabolism is completed, katab-
olism or discharge occurs, and this alternate but crude and spasmodic
action will occur without a definite blood supply so long as the centers are
properly nourished and stimulated by their own intercellular fluid.

302 RESPIRATION

It is also apparent that the respiratory center is dependent on the
character of the blood supply, both as regards quantity or quality of the
blood. It has been shown that the presence in the blood of the products
of vigorous muscular metabolism will greatly increase the irritability of the
respiratory center, even if the blood itself be not particularly venous in
character as regards its gaseous content.

The Establishment of Respiratory Movements at Birth. — From
the preceding paragraph it appears that the regulation of the respiratory
movements is normally due to the automaticity of the respiratory center as
influenced, first, by the blood flowing through it and, second, by the afferent
nerve impulses which reach the center. The fetus in the womb is supplied
by arterial blood from the blood vessels of the mother. The fetus does not
ordinarily give respiratory movements before birth, but it may be made to
do so by experimental procedure. At birth the placental circulation is sud-
denly interrupted, and the blood rapidly increases in venosity until the skin,
lips, and mucous membranes are very cyanotic in appearance. It is at this
time that the respiratory center begins its rhythmic discharges, being aroused
by the direct stimulating effects of the great excess of carbon dioxide in the
strongly venous blood. It is more than possible that the irritability of the
center is also increased by the stimulation of the skin by the air, the contact
with clothing, and the hands of the nurse. We have already seen that
cutanous stimulation leads to increase in both respiratory rate and ampli-
tude even in the adult. The primary stimulus for the establishment of the
respiratory rhythm at birth, then, is the venosity of the blood, but this
cause is supported by the general reflexes which reach the respiratory
center.

Certain Special Types of Respiration. — Whatever the exact quality
of the venous blood which excites the respiratory center to produce normal
respirations, there can be no doubt that, as the blood becomes more and
more venous from obstruction to the entrance of air into the lungs or from
the blood not taking up from the air its usual supply of oxygen, the respi-
ratory center becomes either less or more active and excitable. Conditions
ensue which have received the names Apnea, diminished breathing; Hyper-
pnea, excessive breathing; Dyspnea, difficult breathing; and Asphyxia,
suffocation.

Apnea. — This is a condition of diminished respiratory movement. When
we take several deep inspirations in rapid succession by voluntary effort,
we find that we can do without breathing for a much longer time than usual;
in other words, several rapid respirations seem to inhibit for a time normal
respiratory movements. The reason for this partial cessation of respira-
tion, or apnea, is not that we overcharge our blood with oxygen, as was once
thought, for Hering has shown that animals in a condition of apnea may
have less oxygen in their blood than in a normal state, although the carbon

CERTAIN SPECIAL TYPES OF RESPIRATION 303

dioxide is less. It is probable that the cause of apnea is that by rapid in-
flations of the lungs impulses pass up by the vagi by means of which in-
spiration is after a while inhibited; or that by the repeated stimulation of
the center by vagus impulses which result in rapid respiratory movements,
anabolism is at last arrested. Apnea is with difficulty produced, if at all,
when the vagi are divided.

Asphyxia. — The condition of stress in the respiratory apparatus brought
about by insufficient respiratory activity leads to a condition of asphyxia.
Progressive asphyxiation may be brought on by anything which interferes
with the normal interchange of the respiratory gases of the blood.

Asphyxia may be produced by the prevention of the due entry of oxygen
into the blood, either by direct obstruction of the trachea or other part of the
respiratory passages, or by introducing instead of ordinary air a gas devoid
of oxygen, or by interference with the due interchange of gases between
the air and the blood.

The symptoms of asphyxia may be divided into three groups, which
correspond with the stages of the condition which are usually recognized;
these are: i, the stage of exaggerated breathing, hyperpnea; 2, the stage of
convulsions, dyspnea; 3, the stage of exhaustion, asphyxiation.

In the first stage the breathing becomes more rapid and at the same time
deeper than usual, the inspirations at first being especially exaggerated and
prolonged. This is soon followed by a similar increase in the expiratory
efforts being aided by the muscles of extraordinary expiration. This stage is
usually called hyperpnea. Hyperpnea soon passes into a condition of labored
breathing in which there is marked increase of the force of the expiratory
as well as of the inspiratory act, a condition described as dyspnea. All the
muscles capable of aiding either directly or indirectly in respiration
are ultimately brought into action. These respiratory convulsions are
followed by rather sudden onset of paralysis of the respiratory center and
death.

The conditions of the vascular system in asphyxia are: i, more or less
interference with the passage of the blood through the systemic and the pul-
monary blood vessels; 2, accumulation of blood in the right side of the heart
and in the systemic veins; 3, circulation of impure (non-aerated) blood in
all parts of the body, especially through the respiratory center.

Cheyne-Stokes' breathing is a rhythmical irregularity in respirations which
has been observed in various diseases. Respirations occur in groups. At
the beginning of each group the inspirations are very shallow, but each
successive breath is deeper than the preceding, until a climax is reached.
The inspirations then become less and less deep, until they cease altogether
for a time, after which the cycle is repeated. This phenomenon appears to be
due to the want of action of some of the usual cerebral influences w7hich pass
to, and regulate the discharges of, the respiratory center.

304 RESPIRATION

Effects of Vitiated Air. — Ventilation. — As the air expired from the
lungs contains a large proportion of carbon dioxide and a minute amount
of organic matter, it is obvious that if the same air be breathed again and
again, the proportion of carbon dioxide and organic matter in it will con-
stantly increase till it becomes unfit to breathe; long before this point is
reached, however, sensations of uneasiness occur, such as headache, languor,
and a sense of oppression. It is a remarkable fact, however, that the organ-
ism after a time adapts itself to a very vitiated atmosphere, and that a person
soon comes to breathe, without sensible inconvenience, an atmosphere which,
when he first enters it, feels intolerable. Such an adaptation, however, can
take place only at the expense of a depression of all the vital functions, which
must be injurious if long-continued or often repeated. This power of adapta-
tion is well illustrated by an experiment of Claude Bernard. If a sparrow
is placed under a bell-glass of such size that it will live for three hours, be
taken out at the end of the second hour (when it could have survived another
hour), and a fresh healthy sparrow introduced, the latter will die at once.

It must be evident that provision for a constant and plentiful supply of
fresh air, and the removal of that which is vitiated, are of greater importance
than the actual cubic space per person of occupants. Not less than 2,000
cubic feet per individual should be allowed in sleeping apartments (barracks,
hospitals, etc.), and with this allowance the air can be maintained at the
proper standard of purity only by such a system of ventilation as provides for
the supply of 1,500 to 2,000 cubic feet of fresh air per person per hour.

Effects of Breathing Gases Other than the Atmosphere. — Asphyxiation is
produced by the direct poisonous action of such gases as carbon monoxide,
which is contained to a considerable amount in common coal gas. The
fatal effects often produced by this gas (as accidents from burning charcoal
stoves in small, close rooms) are due to its entering into combinations with
the hemoglobin of the blood corpuscles and thus preventing the formation
of oxyhemoglobin because of the more stable carbon- monoxide hemoglobin.
The partial pressure of oxygen in the atmosphere may be considerably in-
creased without much effect in displacing the carbon monoxide, hence this
is rapidly fatal when breathed. Hydrogen may take the place of nitrogen
with no marked ill effect, if the oxygen is in the usual proportions. Sul-
phureted hydrogen destroys the hemoglobin of blood and thus produces oxygen
starvation. Nitrous oxide acts directly on the nervous system as a narcotic,
and may also form a compound with hemoglobin. Certain gases, such as
carbon dioxide in more than a certain proportion, sulphurous acid gases, am-
monia, and chlorine, produce spasmodic closure of the glottis and prevent
respiration.

Alteration in the Atmospheric Pressure. — Lower barometric pres-
sures than the normal occur in high altitudes, for example in mountain climb-
ing or in aerial navigation. The susceptibility to decrease in barometric

EFFECT OF RESPIRATION ON THE CIRCULATION 305

pressure varies in different individuals. At an altitude of about 10,000 feet
many persons experience mountain sickness, the symptoms of which are
nausea, dizziness, headache, and muscular weakness. At 15,000 feet the
pressure approaches the limit which the body can withstand, i.e., an oxygen
pressure of about 76 mm. Such pressures produce alternations in the re-
lations of the gases of the blood. The tension of the oxygen is no longer
sufficient, see figure 238, to allow the hemoglobin in the pulmonary capil-
laries to combine with its usual quota of oxygen, hence the tissues do not
receive their normal quantity. This condition is called anoxemia. The
factor of carbon dioxide elimination is also disturbed. It is observed that
the amount of carbon dioxide in the blood is diminished. Henderson has
recently given further evidence of the stimulative effects of carbon dioxide
in the body on certain functions of nervous and muscular mechanisms.
One may infer that the acapnia due to low pressures of the atmosphere may
contribute to the symptoms enumerated above, i.e., depression of muscular
tone, etc.

Men are often subjected to higher than normal barometric pressures in
caisson work, diving, etc.

Paul Bert has found in experimenting with animals that the oxygen pres-
sures may be gradually increased to a considerable extent without marked
effect, even to the extent of 8 or 10 atmospheres, but when the oxygen pres-
sure is increased up to 20 atmospheres the oxygen becomes poisonous and
the animals experimented upon died with severe tetanic convulsions. How-
ever, caisson workers often experience very severe symptoms, such as bleeding
from the nose, dyspnea, vascular inco-ordination, etc. These symptoms
are due not so much to the great increase in pressure as to the release from
the pressure. When the pressure is released too rapidly, the excess of gases
in the tissues and in the blood are set free more rapidly than they can be
thrown off by excretion processes. Gases, as such, gather in the blood
vessels and form embolisms which occlude the finer vessels. This, of course,
produces serious disturbances in the nutrition of the parts involved. If
these parts happen to be vital, death may result.

THE EFFECT OF RESPIRATION ON THE CIRCULATION.

As the heart, the aorta, and pulmonary vessels are situated in the air-
tight thorax, they are exposed to a certain alteration of pressure when the
capacity of the latter is varied during respiration. The disturbance of pres-
sure which occurs during inspiration causes, first, a decrease in the intra-
thoracic pressure, a decrease which affects all the organs of the thorax — the
lungs, the great blood-vessels, the heart. The expansion of the elastic lungs
counterbalances this change in pressure in part, but it never does so entirely,
since part of the pressure within the lungs is expended in overcoming their

306

RESPIRATION

elasticity. The amount thus used up increases as the lungs become more
and more stretched, so that the intrathoracic pressure during inspiration, as
far as the heart and great vessels are concerned, never quite equals the intra-
pulmonary pressure, and at the conclusion of inspiration is considerably
less than the atmospheric pressure. It has been ascertained that the amount
of the pressure used up in the way above described varies from 5 to 7 mm. of
mercury in ordinary inspiration, to 30 mm. of mercury at the end of a deep
inspiration. So it will be understood that the pressure to which the heart
and great vessels are subjected diminishes as inspiration progresses, and at

FIG. 242. — Diagram of an Apparatus Illustrating the Effect of Inspiration upon the
Heart and Great Vessels within the Thorax. I, The thorax at rest; II, during inspiration;
D represents the diaphragm when relaxed; D', when contracted (it must be remembered
that this position is a mere diagram), i. e., when the capacity of the thorax is enlarged; H,
the heart; V, the veins entering it, and A, the aorta; Rl, LI, the right and left lung; T, the
trachea; M, mercurial manometer in connection with pleura. The increase in the capacity
of the box representing the thorax is seen to dilate the heart as well as the lungs, and so to
pump in blood through V, whereas the valve prevents reflux through A. The position of
the mercury in M shows also the suction which is taking place. (Landois.)

its summit is less by from 7 to 30 mm. than the normal atmospheric pres-
sure, 760 mm. of mercury. It will be understood from the accompanying
diagram how an increase in the volume of the thorax will have the effect of
pumping blood into the heart from the veins. During inspiration the pres-
sure outside the heart and great vessels is diminished, and they, by virtue of
their elasticity, have therefore a tendency to expand and to diminish the intra-
vascular pressure. The diminution of pressure within the veins passing
to the right auricle and within the right auricle itself, will draw the blood
into the thorax, and so assist the circulation. This suction action of the
thorax is the cause of the slight negative pressure of the ventricles previously
described. The effect of more blood in the right auricle will, cateris paribus,
increase the amount passing through the right ventricle, and through the

EFFECT OF RESPIRATION ON THE CIRCULATION 307

*\

lungs into the left auricle and ventricle, and thus into the aorta. This all
tends to increase the blood pressure. The effect of the diminished pressure
upon the pulmonary vessels will also help toward the same end, an increased
flow through the lungs, so that, as far as the mechanical effects on the heart
and its veins are concerned, inspiration increases the blood pressure in the
arteries. The effect of inspiration upon the aorta and its branches within
the thorax would be, however, contrary; for as the external pressure is dimin-
ished, the vessels would tend to expand, and thus to diminish the tension of
the blood within them, but, inasmuch as the relative variation in pressure
on the large arteries is slight, the diminution of arterial tension caused by
this means will be insufficient to counteract the increase of blood pressure

FIG. 243. — Comparison of Blood-pressure Curve with Curve of Intrathoracic Pressure.
(To be read from left to right.) a is the curve of blood pressure with its respiratory
undulations, the slower beats on the descent being very marked; b is the curve of intra-
thoracic pressure obtained by connecting one limb of a manometer with the pleural cavity.
Inspiration begins at i and expiration at e. The intrathoracic 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. (M.
Foster.)

produced by the effect of inspiration upon the volume of discharge of the
veins of the chest, and the balance of the whole action would be in favor of
an increase of blood pressure during the inspiratory period. When a blood-
pressure tracing is taken at the same time that the respiratory movements
are being recorded, it will be found that, although, speaking generally, the
arterial tension is increased during inspiration, the maximum of arterial
tension does not correspond with the acme of inspiration, figure 243. In
fact, at the beginning of inspiration the pressure continues to fall for a brief
moment, then gradually rises until the end of inspiration, and continues to
do so for a moment after expiration has commenced. For explanation of
the influence of heart rate in this variation of blood pressure, associated
with the respiratory movement, see page 212.

In ordinary expiration all this would be reversed, but if the abdominal
muscles are violently contracted, as in extraordinary expiration, the same

308 RESPIRATION

relative effect would be produced as by inspiration. The immediate effect
during inspiration of the diminished intrathoracic pressure upon the pul-
monary vessels is to produce an initial dilatation of both artery and veins,
and this delays for a moment the passage of blood toward the left side of
the heart, resulting in an initial fall in the arterial pressure, but the fall of
blood pressure is immediately followed by a steady rise, since the flow is
increased by the initial dilatation of the vessels. The converse is the case
with expiration. As, however, the pulmonary veins are more easily di-
latable than the pulmonary artery, their greater distensibility increases the
flow of blood as inspiration proceeds, while during expiration, except at its
beginning, this property of theirs acts in the opposite direction, and diminishes
the flow. Thus, at the beginning of inspiration the diminution of blood
pressure, which commenced during expiration, is continued, but after a time
the diminution is succeeded by a steady rise. The reverse is the case with
expiration, i.e., there is at first a rise and then a fall of blood pressure.

As regards the effect of expiration, the capacity of the chest is diminished
and the intrathoracic pressure returns to the normal, which is still slightly
below the atmospheric pressure. The effect of this on the veins is to in-
crease their extravascular and so their intravascular pressure, and to di-
minish the flow of blood into the left side of the heart. This will, of course,
react to decrease the general blood pressure. Ordinary expiration does not
produce a distinct obstruction to the circulation, as even when the expiration
is at an end the intrathoracic pressure is less than the atmospheric pressure.
The effect of violent expiratory efforts, however, does have a distinct action
in obstructing the current of blood through the lungs, as seen in the con-
gestion in the exaggerated condition of straining, this condition being pro-
duced by pressure on the entire group of pulmonary vessels.

There are other mechanical factors, such, for example, as the effect of
the abdominal movements, both in inspiration and in expiration, upon the
arteries and veins within the abdomen and of the lower extremities. Also
the influence of the varying intrathoracic pressure upon the pulmonary
vessels, which ought to be taken into consideration. The effect of the
abdominal movements during inspiration is twofold. On the one hand,
blood is sent upward into the chest by compression of the vena cava inferior;
on the other hand, the passage of blood downward from the chest through
the abdominal aorta, and upward in the veins of the lower extremity, is to
a certain extent obstructed.

LABORATORY EXPERIMENTS IN RESPIRATION.

i. Respiratory Rate in Man. — Count your respirations for from
2 to 4 minutes while sitting quietly, and determine the average number per
minute. Repeat the counting after standing for 5 minutes, and after brisk

THE VOLUME OF AIR BREATHED BY MAN

3°9

exercise. These determinations involve the element of consciousness, under
which condition it is difficult for a person to breathe with his normal rate
and depth.

Make a series of determinations of respiratory rates of persons who are
sitting quietly but unconscious of your determinations. Count the rates
in a number of persons of different ages; where possible, take into considera-
tion height, weight, etc. Tabulate the results for a
comparison and for future reference.

2. The Character of Respiratory Movements
in Man. — A number of instruments have been de-
vised for measuring human respiratory movement,
many of which measure the change in diameter of
the chest in respiratory movement. Adjust one of
these, for example Burdon- Sanderson's stethograph,
to the thorax, and record the movement of the re-
ceiving tambour on a smoked-paper kymograph
which travels at the rate of i cm. per second. This
record, called a stethogram, will exhibit the respira-
tory rate, the relative time of the inspiratory and
expiratory phases, and the character of each.

3. The Actual Change of Diameter in the
Chest in Respiration. — Use a caliper provided for
the purpose and measure the dorso- ventral diameter
of the chest at a series of points along the sternum,
taking the reading at the height of the inspiratory
phase and of the expiratory phase in ordinary respi-
ration. Repeat the measurement in forced respira-
tion. Map the results on millimeter paper, as
indicated in figure 244.

Repeat these measurements in the transverse
diameter at the first, fifth, and tenth ribs.

Using the chest pantograph, figure 245, record

the outline of the chest at the level of the middle of the sternum during
expiration and at the end of inspiration.

4. The Volume of Air Breathed by Man.— Determine the average
volume of air breathed per respiration, using Hutchinson's spirometer, figure
235, set the instrument at the zero point, exhale into the instrument through
the tube, using all possible care to breathe with your normal rate and depth.
Better results will be obtained by taking the average from sets of ten consecu-
tive expirations into the instrument. From the average of the volume per
respiration, and the average number of respirations per minute, determined
in Experiment i, calculate the amount of air breathed per hour and
per day.

FIG. 244. — Change in
Diameter of the Body in
Respiration, Costal Type.
a, Outline of the body in
forced expiration. In the
heavy continuous line, b,
the outer margin indicates
the contour of the body in
ordinary inspiration and
the inner margin that of
ordinary expiration. c,
Contour of forced inspira-
tion. (After Hutchinson.)

3io

RESPIRATION

5. Vital Capacities. — Using the spirometer as in the preceding ex-
periment, set the instrument at zero and exhale into it:

a. Begin with the fullest possible inspiration and exhale the greatest
possible amount of air from the lungs. This is known as the vital capacity.

b. Beginning at the end of an ordinary expiration exhale into the instru-
ment the greatest possible amount. This is called the reserve air.

c. Following ordinary inspiration exhale into the instrument until you
reach the ordinary state of expiration. This involves the conscious fixing
of two points in the respiratory act, namely, the summit of inspiration and
of expiration, which are ordinarily automatically adjusted by the body. The
error of the determination is therefore great. It is better to make this meas-
urement in sets of ten, as in the preceding experiment, and take the average-

FIG. 245. — The Chest Pantograph for Recording the Outlines of the Chest. The
fixed point in the instrument is/; the points a, b, x, y, are movable joints; when point t
is made to trace the outline of the chest, point r will give a corresponding movement and
can be made to trace this movement on recording paper. (Hall.)

This reduces the error. This quantity of air is known as the tidal air. One
can measure the tidal air and the reserve air together, check them against
the sum of the two, as in a and b, separately.

d. The sum of the tidal and reserve air taken from the vital air will leave
the amount which one may inspire over and above that in the chest at the end
of ordinary inspiration. This is called complemental. The complemental
can be measured by inspiring the air from the spirometer, but this is not
good hygiene where large numbers are using the same instrument, unless
the instrument be thoroughly cleaned before the inspiration is taken.

6. The Respiratory Pressure in Man. — Measure the respiratory
pressure, the pressure of the air in the air-passages, by means of the mercury
manometer or by a graduated Marey's tambour. Connect the piece of
gas tubing with the proximal limb of the mercury manometer and provide
it with a glass mouthpiece. Insert this mouthpiece well back into the

CARBON DIOXIDE AND OXYGEN

311

cavity of the mouth, closing the lips firmly about it, leaving the pharyngeal
muscles relaxed. Note the variations in pressure at the height of ordinary
inspiration and expiration, with the nasal passages open. Repeat with
forced inspiration and expiration, close the nasal passages, and make the
maximal expiratory and inspiratory effort. The manometer may be ad-
justed to write on the smoked paper or one may read the variations directly
from the manometer schedule, in which case it facilitates the reading if one
clamps the rubber tube at the moment the reading is desired.

7. Demonstration of Carbon Dioxide in Expired Air. — Arrange
two flasks, as in figure 246, filling each one-third full of baryta-water or
lime-water. Close the lips around the mouthpiece of the apparatus and
inhale and exhale the air through it; close the nostrils if necessary. The

FIG. 246. — Apparatus for Demonstrating Excess of CO2 in Expired Air. Flasks filled with

lime-water.

inspired air will come through a, the expired air out through b. The baryta
water in b will quickly become clouded with a white precipitate of calcium
carbonate while that in a will remain clear or only very slightly clouded,
showing the excess of carbon dioxide in expired air.

8. Quantitative Determination of Carbon Dioxide and Oxygen in
Inspired Air and in Expired Air, by Hempel's Method. — Inspired Air. —
Fill a gas buret, see figure 236, with water and close the pinch-cock. Fill
it with air taken outside the laboratory. Measure the volume of gas con-
tained at the ordinary temperature and barometric pressure of the labora-
tory. Connect with a potash pipet, drive the air over into the bulb of the
pipet, shake it up until all the carbon dioxide is absorbed. Draw the air
back into the buret and measure. The amount of carbon dioxide in the
external air is usually so small that it is difficult to measure by this method.
Now connect the buret with a pipet containing pyrogallic acid, run the air
over into the pyrogallic-acid bulb and shake up thoroughly until no further
gas is absorbed, then remeasure the excess in the buret. The loss in volume
is due to the absorption of oxygen; the air remaining in the buret is nitrogen.
Compute in percentage the amounts of carbon dioxide, oxygen, and nitrogen
from the results of your test.

3I2

RESPIRATION

Expired Air. — Take a large sample of expired air by breathing through
a large tube into a gallon aspirator bottle. This is large enough to hold
six or eight expirations. Now fill the gas buret with a sample of this expired
air and analyze as before, first for carbon dioxide, then for oxygen; com-
pute the percentage of each gas, including nitrogen. The expired air will
usually be found to have lost from 4 to 5 per cent, of oxygen and have gained
a little more than that quantity of carbon dioxide.

From the percentages obtained in these experiments, and the volume of air
breathed per unit of time, computed in Experiment 4 above, determine the
amount of carbon dioxide exhaled per hour per kilogram of weight for your
own body. Compute also the amount of oxygen consumed.

FIG. 2460. — Arrangement of Tracheal Cannula and Marey's Tambour for Recording the
Chanoes in Intratracheal Pressure during Respiration. (Langendorff.)

9. The Rate and Character of the Respiratory Movements in the
Mammal. — a, The rate of respiration can be best determined by direct
count per minute, an effort being made to keep the animal under as nearly
normal conditions as possible; make the same determinations on a cat, a dog,
and a guinea-pig, b, The character of the respiratory movements can be
recorded by one of the various forms of stethograph adapted to the size of
the animal, or by the arrangement shown in figure 2460. It is necessary to
make the determination with the animal under the influence of an anesthetic.

10. The Determination of Carbon Dioxide Given Off in the Mam-
mal.— This determination can be made only by placing the animal in a res-
piratory calorimeter, and making the following measurements:

a. The amount of air which passes through the animal chamber, the
calorimeter.

b. The percentage of carbon dioxide in the air which is in the chamber.

c. The percentage of carbon dioxide in the air which leaves the chamber.
If the animal is small enough, for example the guinea-pig or a mouse,

THE NERVOUS MECHANISM OF RESPIRATORY MOVEMENT 313

the absorption tubes may be constructed of proper size to absorb all the
carbon dioxide passing through the chamber, and the total quantity for any
unit of time determined directly in grams. If now the animal is weighed
at the moment it is introduced into the cage, then the amount of carbon
dioxide per kilo weight can be quickly computed.

Calorimeters for larger animals require a larger volume of ventilation,
and the usual procedure is to measure the percentage in a sample as directed
above.

ii. The Nervous Mechanism of Respiratory Movement.

a. The Effect of Stimulating Cutaneous Nerves. — Use a small dog or a
cat for this experiment; anesthetize and introduce a tracheal tube with a

FIG. 2466. — Change in Respiration on Stimulating the Central End of the Sciatic
Nerve. The rate is sharply increased and the amplitude more than doubled. The
stimulation is between the points marked on and off, time in seconds. The inspiratory
movement following the stimulation was greater than the limit of the recording tambour.

side branch adapted for measuring the variations of pressure during respira-
tion. Connect the free limb of the tracheal tube with an ether apparatus
and adjust to secure constant anesthesia. Connect the side branch of the
tracheal tube with a Marey's recording tambour of medium size and supply
with a comparatively delicate membrane. The amplitude of the move-
ments of the tambour may be regulated by a screw compress on a connecting
tube. Arrange an induction coil with platinum electrodes in the usual
manner, figure 318, for stimulating, by means of the interrupted current.
Record the results of the experiment along with the variations of blood pres-
sure on a continuous-paper kymograph; the instrument should be supplied
with a time signal, a stimulating signal, etc.

Now stimulate the skin of the abdominal region, the groin, with a com-
paratively strong induction current, figure 2466. Dissect out the sciatic
nerve, cut it, stimulate the central end with a mild to medium strength of

314 RESPIRATION

current. The stimulus should be graduated carefully, for there is often such
a great increase in respiratory rate and volume that the animal may become
overanesthetized.

b. The effect of Stimulating the Vagus Nerve. — Isolate and stimulate
the vagus nerve with a medium strength of stimulus. The effect is usually
complete inhibition of respiratory movements. By means of graduated
stimuli one may demonstrate the accelerator effects from the stimulation
of the vagus. Stimulate also the superior laryngeal, and compare with the
effects of stimulating the whole vagus.

c. The Effect of Cutting the Vagus Nerves. — Isolate both vagus nerves
and section them as nearly at the same moment as possible. Be sure to
mark on the tracing the exact moment at which the nerves are cut. This
experiment should be performed with every accessory condition as constant
as possible, and the animal should not be disturbed for one or two minutes
so that the effects of the section will be recorded, figure 240. The result is
always a marked deepening and slowing of the respiratory movements.

d. The Effect of Stimulating the Central End of the Vagus. — Upon stimu-
lating the central end of the vagus after section, the respiration rate will be
inhibited as in b, showing that the vagus nerves carry afferent respiratory
fibers, figure 241.

e. The Effect of Stimulation of the Phrenic Nerves. — Isolate the right
phrenic nerve at its origin from the brachial plexus and stimulate it with a
medium strength of stimulus. Upon stimulating the nerve the diaphragm
will remain in contraction and the record will show that the thorax is in the
inspiratory phase.

Section this nerve and note the change in the character of respiratory
movements; make direct observations on the diaphragm, examining from
the abdominal side.

12. Demonstration of Apnea, Dyspnea, and Asphyxia. — Produce
deep anesthesia, then disconnect the ether bottle and connect the tracheal
tube with a hand bellows. Produce deep and forced artificial respiration
for twenty to thirty seconds. Stop the artificial respiration; the animal will
remain quiet without any effort at breathing. This is the condition of apnea.
Allow the animal to recover its normal respiration rate and again produce
deep anesthesia. Now clamp off the tracheal tube so that the animal can no
longer receive air and leave it so until death. As the blood becomes more
and more venous there will first be a marked increase in the respiration rate
and depth. This is known as hyperpnea. This stage is followed by one
of increasing respiratory amplitude in which the accessory respiratory mus-
cles not previously active are brought into forcible contractions, both inspira-
tory and expiratory phases are now forced, dyspnea. The movements con-
tinue to increase, and the muscles of the neck, larynx, mouth, and nostrils
now take part. There is a rather sudden decrease in the respiratory move-

RESPIRATORY INTERCHANGE, CALORIMETRY 315

ments, an extension of the limbs, and gasping movements of the mouth, after
which the animal remains quiet, death being produced by asphyxia.

13. Respiratory Interchange, Calorimetry. — The experiments are
conducted in such a manner that comparative analyses may be made
between the air inspired and that expired. Generally an animal is placed
in a chamber, called the respiratory chamber, which is then closed except
for two openings, one for the entrance of the inspired air, the other for the
escape of expired air. Some form of pump is used for renewing the air in the
chamber. Both the inspired and expired air is made to pass through reagents
which wrill absorb the contained carbon dioxide, such as baryta water or soda-
lime, and in turn through reagents which will absorb the watery vapor. When
the experiment is completed the differences between the two are determined.
The difference in oxygen has to be calculated, and is open to error. The
famous respiratory chamber of Pettenkofer is large enough to perform such
experiments on man, and is of very elaborate construction. But the most
perfect apparatus assembled for this purpose is the respiration calorimeter of
Atwater constructed for man, and the respiration apparatus of Armsby for
cattle.

CHAPTER VII
SECRETION IN GENERAL

ALL tissues of the body produce certain chemical changes as a result of
their protoplasmic activity. But in certain cells chemical elaborations have
come to be the chief function, the cells have been differentiated in that direc-
tion, and the name secreting tissue or gland tissue is applied. The end result
of metabolism in gland tissue is the extrusion on the free borders of the cells
of the products of their metabolism. The products are known as secretions
and the process itself is the act of secretion. Certain secretions which are
in the nature of waste products to the body as a whole, such as urine in the
kidney, are often called excretions, but the use of the term should not be allowed
to confuse the general similarity of this to other secretions as regards the
physiological changes involved in its production.

Most secretions accomplish some definite office in the economy of the
body. Those that are discharged on some free mucous surface, as the saliva,
gastric juice, tears, etc., are called external, or true secretions, or merely secre-
tions. Substances that are discharged back into the blood stream later to
influence the metabolism of tissues other than the ones which produced them
are called internal secretions.

Gland cells, like other tissues, draw their nourishment from the blood
and lymph. The product or secretion of gland cells may, in fact usually
does, contain some of the substances found in the blood, but there are also
present new materials elaborated by the cells, and even where the same sub-
stance exists both in the secretion and in the blood and lymph it can make
its appearance in the secretion only under the control of the protoplasm of
the gland cells. The saliva secreted by the salivary cells, for example, con-
sists of about 98 to 99 per cent, water containing in solution small quantities
of certain salts, also found in the lymph, and a small percentage of the en-
zyme, ptyalin. This enzyme is peculiar to the salivary secretion and is manu-
factured by the salivary-cell protoplasm. As is well known, it acts vigorously
in extreme dilution, hence the high per cent, of water in the secretion. The
passage of water from a solution as concentrated as blood plasma to a solu-
tion as dilute as saliva requires a high amount of osmotic energy, an amount
that can be supplied only from the chemical energy liberated by the cell in
its protoplasmic activity. After the removal of the special organ by which
each secretion is manufactured, the secretion is no longer formed. Cases
sometimes occur in which the secretion continues to be formed by the natural

SECRETING GLANDS 317

organ, but, not being able to escape toward the exterior, on account of some
obstruction, is reabsorbed and accumulates in the blood. It may be dis-
charged from the body in other ways; but these are not instances of true
vicarious secretions, and must not be so regarded.

Organs and Tissues of Secretion. — The principal secreting organs
are the following: i. The serous and synovial membranes; 2. the mucous
membranes with their special glands, e.g., the buccal, gastric, and intestinal
glands; 3. the salivary glands and pancreas; 4. the liver; 5. the mam-
mary glands; 6. the lachrymal glands; 7. the kidney and skin; 8. the
testes and ovaries, and 9. thyroid, supra-renal, etc.

The special structure and functions of the secreting organs will be given
in greater detail in the chapters which immediately follow. The general
types of structure and general conditions that influence the functions are
introduced at this point.

Structural Types of Secreting Organs. — Serous and Synovial Type.—
The serous membranes form closed sacs lining visceral cavities like the
abdominal, pericardial, or pleural cavities. The organs are, as it were,
pushed into this sac and carry before them an investment of membrane. The
serous membranes consist of a single layer of flattened polygonal cells
resting on a supporting membrane of connective tissue, supporting a rami-
fication of blood vessels, lymphatics, and nerves.

In some instances, i.e., synovial membranes, the secreting layer is in-
creased by finger-like elevations. This type of secreting organ produces
ordinarily only enough secretion to keep the surface moist.

The Mucous Type. — The mucous tracts, and different portions of each
of them, present certain structural peculiarities adapted to the functions
which each part has to discharge; yet in some essential characters the mucous
membrane is the same, from whatever part it is obtained. In all the princi-
pal and larger parts of the several tracts it presents an external layer of epithe-
lium, situated upon a basement membrane, and beneath this a stratum of
vascular tissue of variable thickness, containing lymphatic vessels and nerves.
The vascular stratum, together with the basement membrane and epithelium,
in certain cases is elevated into minute papillae and villi, in others depressed
into involutions in the form of glands. But in the imaginations of the secret-
ing membrane of gland cells, the supporting basement membrane and the net-
work of capillaries are still retained in their relative position. With increas-
ing complexity of involution the simple mucous membrane becomes packed
away in an apparently solid mass. The equivalent of a large amount of
secreting surface is thus condensed into a small space. In the process of in-
vagination some differentiation occurs in that certain of the gland cells be-
come conducting and have their secretory activity somewhat reduced.

Secreting Glands. — The secreting glands present, amid manifold
diversities of form and composition, a general plan of structure; but all are

SECRETION IN GENERAL

constructed with particular regard to the arrangement of the cells which has
just been described.

Secreting glands are classified according to certain structural types, as:
i. The simple tubular gland, A, figure 247, examples of which are furnished
by the follicles of Lieberkiihn, and the tubular peptic glands of the stomach.
They are simple tubes of mucous membrane, the walls of which are lined with

FIG. 247. — Plans of Extension of Secreting Membrane by Inversion or Recession in the
Forms of Cavities. A, Simple glands, viz., g, straight tube; h, sac; i, coiled tube. B,
Multilocular crypts; k, of tubular form; /, saccular. C, Racemose or saccular compound
gland; m, entire gland, showing branched duct and lobular structure; n, a lobule, detached
with o, branch of duct proceeding from it. D, Compound tubular gland. (Sharpey.)

secreting cells arranged as an epithelium. To the same class may be re-
ferred the elongated and tortuous sudoriferous glands.

2. The compound tubular glands, D, figure 247, form another division.
These consist of main gland tubes, which divide and subdivide. Each gland
may be made up of the subdivisions of one or more main tubes. The ulti-
mate subdivisions of the tubes are sometimes highly convoluted. They are

THE PROCESS OF SECRETION 319

formed of epithelium of various forms, supported by a basement membrane.
The larger tubes may have an outside coating of fibrous areolar or muscular
tissue. The salivary glands, pancreas, Brunner's glands, kidney, testes, with
the lachrymal and mammary glands, are examples of this type, but present
more or less marked variations among themselves.

3 . The racemose glands, in which a number of vesicles or acini are arranged
in groups of lobules, C, figure 247. The Meibomian follicles are examples
of this kind of gland. There seem to be glands of mixed character, com-
bining some of the characters of the tubular with others of the racemose type;
these are called tubulo-racemose or lubulo-acinous glands. The acini are
formed by a kind of fusion of the walls of several vesicles, which thus combine
to form one large cavity with recesses lined or filled with secreting cells. The
smallest branches of the gland-ducts sometimes open into the centers of these
cavities; sometimes the acini are clustered round the extremities or by the
sides of the ducts; but, whatever secondary arrangement there may be, all
have the same essential character of rounded groups of vesicles containing
gland cells, and opening by a common central cavity into minute ducts,
which in the large glands converge and unite to form larger and larger
branches, and at length one common trunk which opens on a free surface.

The Process of Secretion. — The process of secretion is dependent
upon the activity of the secreting cells. In the case of the water and salts the
physical processes of filtration and diffusion may play a part.

The chemical processes constitute the process of secretion properly so
called, as distinguished from mere transudation spoken of above. In the
process of secretion various materials which do not exist as such in the blood
are manufactured by the agency of the gland cells, using as a nutrient fluid
the blood or, to speak more accurately, the lymph which fills the interstices
of the gland textures.

Evidences in favor of this view are: i. That gland cells are constituents
of all glands, however diverse their outer forms and other characters, and
they are placed in all glands on the surfaces or in the cavity whence the secre-
tion is poured. 2. That certain materials of secretions are visible with the
microscope in the gland cells before they are discharged. Thus, granules
probably representing the precursors of the ferments of the pancreas may
be discerned in the cells of that gland. Granules of uric acid are found in
the cells of the kidneys of birds and fish, and fatty particles, like those of milk,
in the cells of the mammary gland.

Certain secreting cells, like the cells of the sebaceous glands, appear to
develop, grow, and attain their individual perfection by appropriating nutri-
ment from the fluid exuded by adjacent blood vessels and building it up so
that it shall form part of their own substance. In this perfected state the cells
subsist for some brief time and then appear to dissolve, wholly or in part, and
yield their contents to the peculiar material of the secretion. The changes

320 SECRETION IN GENERAL

which have been noticed from actual experiment in the cells of the salivary
glands, pancreas, and peptic glands will be described more fully in the
chapter on Digestion.

Discharge of secretions from the glands may either take place as soon as
formed, or the secretion may be long retained within the gland or its ducts.
The former is the case with the sweat glands. But the secretions of those
glands whose activity of function is periodical are usually retained in the cells
in an undeveloped form during the period of the gland's inaction.

When discharged into the ducts, the further course of secretions is affected:

(1) partly by the pressure from behind; the fresh quantities of secretion pro-
pelling those that were formed before. In the larger ducts, its propulsion is

(2) assisted by the contraction of the walls. All the larger ducts, such as
the ureter and common bile duct, possess in their coats plain muscular fibers;
they contract when irritated, and sometimes manifest peristaltic movements.
Rhythmic contractions in the pancreatic and bile ducts have been observed,
and also in the ureters and vasa deferentia. It is probable that the contrac-
tile power extends along the ducts to a considerable distance within the sub-
stance of the glands whose secretions can be rapidly expelled. Saliva and
milk, for instance, are sometimes ejected with much force.

Circumstances Influencing Secretion. — The principal conditions
which influence secretion are variations in the quantity of blood and varia-
tions in nerve impulses passing to the gland cells over secretory nerve fibers.

An increase in the quantity of blood traversing a gland, as in nearly all
the instances before quoted, coincides generally with an augmentation of its
secretion. Thus the mucous membrane of the stomach becomes florid when,
on the introduction of food, its glands begin to secrete. The mammary
gland becomes much more vascular during lactation. All circumstances
which give rise to an increase in the quantity of material secreted by an organ
produce, coincidently, an increased supply of blood. But we shall see that a
discharge of saliva may occur under extraordinary circumstances without in-
crease of blood supply, and so it may be inferred that this condition of in-
creased blood supply is not absolutely essential to the immediate formation
of secretion, but that it favors the prolonged activity of glands.

Influence of the Nervous System on Secretion. — The process of
secretion is largely regulated through the nervous system. The exact mode
in which the influence is exhibited must still be regarded as somewhat obscure.
In part it exerts its influence by increasing or diminishing the quantity of
blood supplied to the secreting gland, in virtue of the power which it exercises
over the contractility of the smaller blood vessels. It also has a more direct
influence, as is described at length in the case of the submaxillary gland, upon
the secreting cells themselves. This may be called trophic influence. Its
influence over secretion, as well as over other functions of the body, may be
excited by causes acting directly upon the nervous centers, upon the nerves

INFLUENCE OF THE NERVOUS SYSTEM ON SECRETION 32!

going to the secreting organ, or upon the nerves of other parts. In the latter
case a reflex action is produced : thus the impression produced upon the sen-
sory nerves by the contact of food in the mouth leads to afferent nerve im-
pulses to the secretory center in the central nervous system which is reflected
by the nerves supplying the salivary glands, and produces, through these, a
more abundant secretion of the saliva.

Through the nerves, various conditions of the brain also influence the
secretions. Thus, the thought of food may be sufficient to excite an abun-
dant flow of saliva. And, probably, it is the mental state which excites the
abundant secretion of urine in hysterical paroxysms, as well as the perspira-
tions, and occasionally diarrhea, which ensue under the influence of terror,
and the tears excited by sorrow or excess of joy. The quality of a secretion
may also be affected by mental conditions, as in the cases in which, through
grief or passion, the secretion of milk is altered, and is sometimes so changed
as to produce irritation in the alimentary canal of the child.

21

CHAPTER VIII
FOOD AND DIGESTION

THE term digestion includes those changes taking place in the body which
bring the materials of the food into such condition that they may be taken up
by the blood and lymphatic vessels and thus rendered available for the metab-
olism of the tissues. In the process the foods are rendered more soluble
and more diffusible. Certain bodies which are already soluble and diffusible
are converted into forms wrhich are more available for the tissues; as an ex-
ample, cane-sugar, although both soluble and diffusible, cannot be readily
used by the body until it is converted from a disaccharide to a monosaccha-
ride. In fact, few of the food materials are fit for immediate use when taken
into the body and are therefore practically useless until digested.

FOOD AND FOOD PRINCIPLES.

We have been accustomed to classify foods into certain main groups,
chiefly according to their chemical character, as follows:

Proteins. — Such as albumin, myosin, gluten, casein, etc.; gluco- protein,
nucleoprotein, etc.; gelatin, elastin, etc. These furnish nitrogen in avail-
able form.

Carbohydrates. — Such as starch, dextrose, cane-sugar, etc.

Fats. — Such as tristearin, tripalmitin, triolein.

Minerals. — The various salines found in animal and vegetable food.

Water.

The classes of foods just enumerated usually exist in mixtures rather than
in simple forms, as, for example, a beef roast contains a representative of each
of the five classes enumerated, though it is composed chiefly of water, pro-
teins, and fats. The human body is capable of using materials of a great
variety of forms, but most of these have the foods mixed in such a way as to give
representatives of each of the classes above in certain general proportions.

Nitrogenous Foods. — The Flesh of Animals, e.g., beef, veal, mutton,
pork, bacon, ham, chicken, eggs, milk, etc., are typical nitrogenous foods.

Of these, beef and eggs are richest in nitrogenous matters, containing
about 20 per cent. Mutton contains about 18 per cent., veal 16.5, and pork
10. Beef is firmer, more satisfying, and is supposed to be more strengthen-
ing than mutton, whereas the latter is more digestible. The flesh of young
animals, such as lamb and veal, is less digestible and less nutritious. Pork
contains a large amount of fat and is, therefore, comparatively indigestible.

322

NITROGENOUS FOODS

323

PERCENTAGE COMPOSITION AND FUEL VALUE PER POUND OF SOME COMMON
FOOD STUFFS. (ATWATER AND BRYANT.)

Water.
Per

Pro-
tein.
Per

Fat.
Per

Carbo-
hy-
drate.

Ash.
Per

Fuel
Value.
Per

cent.

cent.

Per

cent.

cent.

cent.

cent.

Meat (beef round)

7^ .6

22.6

2.8

i . ?

<C4O

Meat (pork loin)

552 . o

16.6

30 . i

i .0

1,^80

Fish (king salmon)

63.6

17.8

17.8

i . i

1, 080

Eees

77.7

13.4

10 . <

I . O

72O

Milk (cow's)

87 .0

? . T.

4 . o

^ • o

o . 7

^2 S

Milk (human)

89.7

2 . 0

3-i

6.0

0.2

Cheese (American)

31.6

28.8

35-9

°-3

3-4

2,055

Butter

I I . O

I . O

8s;. o

3 . o

3,6o <;

Bread (white)

•}-} 2

10 . Q

I . 7

m .6

I 0

,2 «; <;

Bread (corn)

38.9

7-9

4-7

46.3

2 . 2

,205

Rice . . . . .

12 . 1

8.0

o . 3

79.0

o .4

,6^O

Oatmeal

7 • ^

16.1

7 • 2

67.5

I . O

,860

Beans (dry) .

12 . 6

22.5

1.8

59-6

3-5

,605

Potatoes (white)

78.3

2 . 2

o . i

18.4

i .0

385

Potatoes (sweet)

69 .0

1.8

0.7

27.4

I . 2

57°

Fruit (strawberries)

90 .4

I .0

0.6

7 -4

0.6

180

Watermelon (edible portion) ....

92 .4

0.4

0 . 2

6.7

o-3

140

Meat contains: (i) Muscle proteins, chiefly myosin, blood proteins, colla-
gen (from the interstitial fibrous connective tissue), elastin (from the elastic
tissue), as well as traces of hemoglobin. (2) Fats, including the lipoids
lecithin and cholesterol. (3) Extractives, some of which are agreeable to
the palate and others weakly stimulating. These are divided into the
non-nitrogenous: glycogen, dextrose, lactic acid, inosit, etc., and into the
nitrogenous: consisting chiefly of creatin, and the purine bases. (4) Salts,
chiefly chlorides and phosphates of potassium, calcium, and magnesium.
(5) Water, the amount of which varies from 15 per cent, in dried bacon to
39 in pork, 51 to 53 in fat beef and mutton, and 72 per cent, in lean beef and
mutton.
TABLE OF PERCENTAGE COMPOSITION OF BEEF, MUTTON, PORK, AND VEAL.

(L/ETHEBY.)

Water.

Protein.

Fats.

Salts.

Beef — lean
Beef — -fat

72

ri

19-3

14.8

3-6

20 .8

5-i

4. 4

Mutton — lean

7 2

18.3

4Q

4 8

Mutton — -fat . . .

ZT.

12.4

11 . I

7 . C

Veal

6^

16.5

15.8

4 • 7

Pork — -fat

7Q

9.8

48 .0

2 . 1

324 FOOD AND DIGESTION

TABLE OF PERCENTAGE COMPOSITION OF POULTRY AND FISH. (LETHEBY.)

Water.

Protein.

Fats.

Salts.

Poultry
White fish .

74
78

210

18.1

3-8

2 . O

I . 2
I . O

Salmon

16 i

e cr

I d-

Eels (very rich in fat)
Oysters

75

7 c . 74.

9.9

11.72

13.8
2 .42

i-3

2.7'?

The flesh of nearly all animals has been occasionally eaten, and we may
presume that except for difference of flavor, etc., the average composition
is nearly the same in most cases.

Milk. — Milk is the entire food of young animals, and contains all the
elements of a typical diet. Albuminous substances are represented in the
form of caseinogen, and serum or lactalbumin; fats in thecream; carbohydrates
in the form of lactose or milk-sugar; salts, chiefly as calcium phosphate; and
water. From milk we obtain a number of food preparations, such as cheese
rich in protein and fat, butter and cream, buttermilk rich in proteins and
peculiarly well adapted for invalid diet, and whey which contains all the sugar
salts and the albumin.

TABLE OF COMPOSITION OF MILK, BUTTERMILK, CREAM, AND CHEESE.
(LETHEBY AND PAYEN.)

Nitrogen-
ous
matters.

Fats.

Lactose.

Salts.

Water

Milk (cow)
Buttermilk

4.1
4 • J

3-9

O . 7

5-2
6.4

0.8
0.8

86
88

Creciwi

4 • i

26.7

2.8

1.8

66

Cheese — ski wi

4.4. 8

6 i

4Q

A A

Cheese — cheddar

28 .4

•? i . i

4 • $

36

* i)

Eggs. — The yolk and albumin of eggs of oviparous animals bear the
same relation as food for the embryos that milk bears to the young of mam-
malia, and afford another example of the natural admixture of the various
alimentary principles. The proteins of eggs are ovalbumin and ovoglobulin
and the phosphoprotein, the vitellin of the yolk. In addition to the three
common fats there is a yellow fatty pigment, lutein (lipochrome), lecithin, and
cholesterol, a small quantity of dextrose, and inorganic salts, chiefly calcium,
potassium, sodium chlorides, and phosphates.

MINERAL OR INORGANIC FOODS 325

TABLE OF THE PERCENTAGE COMPOSITION OF FOWLS' EGGS.

Nitrogenous j Fats
substances. !

!

Salts.

Water

White

20 4

1.6

78

Yolk

1 6 . ^0.7

I . 7

52

Legumes are used by vegetarians as the principal source of the nitrogen of
the food. Those chiefly used are peas, beans, lentils, etc.; they contain a
nitrogenous substance called legumin, allied to albumin. Legumes contain
about 25 . 30 per cent, of this nitrogenous body and twice as much nitrogen
as wheat. Nuts also form a very nutritious article of diet.

Carbohydrate Foods. — Bread, made from ground grain obtained from the
various so-called cereals, viz., wheat, rye, maize, barley, rice, oats, etc., is
the direct form in which the carbohydrate is supplied in an ordinary diet.
It contains starch, dextrin, and a little sugar. It also contains gluten, com-
posed of vegetable proteins, and a small amount of fat.

TABLE OF PERCENTAGE COMPOSITION OF BREAD AND FLOUR.

Nitrogenous
matters.

Carbo-
hydrates.

Fats. Salts.

i

Water

Bread

8.1

1
|

1.6 2.3

7 7

Flour

10.8

70. 8q

2.0 1.7

I C

Various articles besides bread are made from flour, e. g., spaghetti, maca-
roni, etc. Dextrin and a small amount of dextrose are present in bread,
particularly in the crust.

Vegetables, especially potatoes. They contain starch and sugar. In
cabbage, turnips, etc., the salts of potassium are abundant.

Fruits contain sugar and organic acids, tartaric, malic, citric, and others.

Sugar, chiefly saccharose, used pure or in various sweetmeats.

Oils and Fats. — The substances supplying the oils and fats of the food
are chiefly butter, bacon and lard, suet (beef and mutton fat), and vegetable
oils. These contain the fats olein, stearin, and palmitin. Butter contains
some tributyrin, while vegetable oils, as a rule, contain no stearin.

Mineral or Inorganic Foods. — The salts of the food. Nearly all the
substances in the preceding classes contain a greater or less amount of the
salts required in food. Green vegetables and fruit contain certain salts,

326 FOOD AND DIGESTION

chiefly potassium. Sodium chloride is an essential food; it is contained in
nearly all solid foods, but so much is required that it has also to be taken as a
condiment. Potassium salts are found in muscle, nerve, and in meats
generally, and in potatoes and other vegetables. Calcium salts are contained
in eggs, blood of meat, wheat, and vegetables. Iron is contained in hemo-
globin, in milk, eggs, and vegetables.

Liquid Foods. — Water is essential to life, and from two to two and a
half pints a day must be consumed in addition to that taken mixed with solid
food. Of the non-alcoholic substances which may be added to it for flavoring
purposes, such as tea, coffee, cocoa, etc., the last can alone be considered to
have a certain food value, as it contains fats, albuminous material, and starch,
the other constituents of such substances being a volatile oil, an alkaloid
caffeine, and tannic acid. The food value of alcoholic beverages, which has
long been a subject of controversy, as now generally agreed is but slight.
Beer, wines, and spirits contain ethyl alcohol, the amount varying from i . 5
to 4 . 5 per cent, in beer to 40 to 80 per cent, in spirits.

The Effect of Cooking on Foods. — In general terms cooking may
be said to render food more easily digestible, both directly and indirectly,
through increased palatability. Subjecting food to high degrees of heat also
serves to kill parasites, such as trichinae and the various tapeworms, which
may be present and alive in raw meats. In the case of meats various methods
of cooking are employed. In roasting, the meat in bulk is subjected to a
high temperature in an oven for a short time, 250° C. for 15 minutes, followed
by a somewhat lower temperature, 175° C., until the cooking is completed.
This causes a coagulation of the outer layers of albumin so that the juices
of the meat are retained. In boiling, the meat is first immersed in boiling
water for a time and then the cooking continues at a lower temperature.
In a broth, the extractives may be obtained by heating the meat in water for
a long period. Such a broth contains the flavoring and the stimulating
extracts of the meat, but is of only slight nutritive value. A temperature
below the coagulation point, at 60° C., will extract more nutritive protein
substance. For small pieces of meat, broiling practically serves the same
purpose as does roasting for larger pieces. Frying, as usually employed,
is the least serviceable method of preparation, since the fat of other oily
material used so permeates the food as to render it difficult of penetration
by the digestive juices.

Cooking produces upon vegetables the necessary effect of rendering them
softer, so that they can be more readily broken up in the mouth. It also
causes the starch grains to swell up and burst, and so aids the digestive fluids
in penetrating into their substance. The albuminous matters are coagulated,
and the gummy, saccharine, and saline matters are removed. The con-
version of flour into dough is effected by mixing it with water, and adding a
little salt and a certain amount of yeast. Yeast consists of the cells of an

THE PROCESS OF DIGESTION 327

organized ferment (Torula cerevisia) ; this plant in its growth changes by
ferment action the sugar produced from the starch of the flour, and a quantity
of carbon dioxide and alcohol is formed; the gas together with the action of
heat during baking causes the dough to rise, and the gluten being coagulated,
the bread sets as a permanently vesiculated mass.

THE PROCESS OF DIGESTION.

The Enzymes. — The digestive process involves both mechanical and
chemical changes. The former are secured by the crushing and grinding
in the mouth, together with the mixing and kneading that come from the
peristalses of the stomach and intestine. The chemical changes are the
most important factors of the digestive process. The various secretions that
are poured into the mouth, stomach, and intestines all contain substances
which react on the foods to render the latter more soluble. The special
agency in each secretion is the presence of representatives of the chemical
groups known as enzymes. These enzymes, or unorganized ferments, are
the essential factors in the secretions which produce the chemical changes
in the foods. Their predominant action is one of hydrolytic cleavage; that
is, the substance acted upon takes up water and then splits into two different
substances, usually of the same class. The chemical nature of the en-
zymes is as yet undetermined because of the difficulty of getting absolutely
pure specimens. Their mode of action is at present regarded in the nature
of catalysis. That is to say, the enzymes by their presence facilitate reactions
that would otherwise take place but very slowly. Practically all are secreted
in the glands as zymogens, which bear the same relation to enzymes as
fibrinogen does to fibrin; they are transformed to enzymes by the proper
stimulus, but never exist as such in the glands.

Each enzyme has a special point of temperature at which it acts best, and
any change in the temperature retards its action; the action is suspended at
a definite point of low temperature, but the enzyme is not destroyed by cold.
The action is suspended at a somewhat higher temperature, and at a still
higher point the enzyme is destroyed. Some enzymes act only in an alka-
line medium, being destroyed in an acid medium, and vice versa. Others
act in either alkaline, or neutral, or acid media. Enzymes are hindered in
their action by the accumulation of the products of their activity. Most of
them cease acting altogether when these products reach a certain concen-
tration, but will begin acting again on the removal of these products or if
the mixture be simply diluted.

The quantity of the enzyme determines the rapidity of the action, but not
the amount; a small quantity will digest as much as a large quantity, but will
take longer. The enzymes are not used up in the course of their activity,
as far as can be seen, and do not seem to undergo any change in their
composition.

328 FOOD AND DIGESTION

Enzymes are more or less specific in their action. That is, each enzyme
is supposed to produce its change in only one particular substance, as in
starch, maltose, protein, fat, etc. An enzyme that can cause cleavage of the
starch molecule will not act on fat or protein or even on other members of
the starch group. This specific action is doubtless expressive of a definite
relation between the structure of the enzyme and the substance acted on.

An interesting fact as to enzyme action is its reversibility — a phenomenon
now well known and well established for carbohydrates and fats. Kastle
and Lowenhart have shown that lipase, which acts to split neutral fats into
fatty acid and glycerin, will also produce a synthesis, at least of butyric
acid and alcohol into ethylbutyrate. Taylor and Robertson in independent
papers have recently made the far-reaching discovery that the protein
molecule can be synthesized by the agency (apparent reversible action) of
enzymes.

Enzymes are classified either according to the chemical nature of their
action or according to the class of substances on \vhich they act; the former
classification is more logical, but the latter is more convenient and more
generally used.

TABLE OF DIGESTIVE ENZYMES.

Amylolytic.

Ptyalin of saliva, and amylopsin of pancreatic juice, change starch to mal-
tose. Maltase in the saliva, and pancreatic juice in the small intestine,
change maltose to dextrose. Lactase splits lactose to galactose and dextrose,
and invertase splits cane-sugar to levulose and dextrose in the small intestine.
Lipolytic.

Steapsin or lipase, found in the pancreatic juice, splits neutral fats into
glycerin and fatty acid.
Proteolytic.

Pepsin of the gastric secretion, and trypsin of the pancreatic secretion,
change proteins to proteoses and peptones, trypsin breaking the protein down
to simpler nitrogenous products. Erepsin of the intestine splits peptones to
simpler products.
Coagulating.

Rennin of the gastric juice coagulates milk.
Activating.

Enterokinase of the intestinal juice converts trypsinogen to trypsin.
(Thrombokinase of the blood is of this class.)

DIGESTION IN THE MOUTH.

The food is received into the mouth and is subjected to the action of the
teeth and tongue, being at the same time mixed with the first of the digestive
juices, the saliva. It is then swallowed, and, passing through the pharynx
and esophagus into the stomach, is subjected to the action of the gastric
juice, the second digestive juice. Thence it passes into the small intestines,
where it meets with the bile, the pancreatic juice, and the intestinal juices, all

HISTOLOGICAL STRUCTURE 329

of which exercise a digestive influence upon the portion of the food not already
digested and absorbed. In the large intestine some further digestion and
absorption take place, and the residue of undigested matter leaves the body
in the form of feces.

Mastication. — The act of mastication is performed by the biting and
grinding movement of the lower range of teeth against the upper. The
simultaneous movements of the tongue and cheeks assist by crushing the
softer portions of the food against the hard palate and gums, thus supple-
menting the action of the teeth, and by returning the morsels of food to the
action of the teeth as they are squeezed out from between them until they
have been sufficiently chewed.

The simple up-and-down or biting movements of the lower jaw are per-
formed by the temporal, masseter, and internal pterygoid muscles, the action
of which in closing the jaws alternates with that of the digastric and other
muscles passing from the os hyoides to the lower jaw, which open the jaws.
The grinding or side movements of the lower jaw are performed mainly by
the external pterygoid muscles, the muscle of one side acting alternately with
the other. When both external pterygoids act together, the lower jaw is
pulled directly forward, so that the lower incisor teeth are brought in front
of the level of the upper.

The act of mastication is voluntary. It will suffice here to state that the
afferent nerves chiefly concerned are the sensory branches of the fifth, ninth,
and tenth, and the efferent are the motor branches of the fifth and the twelfth
cerebral nerves.

The act of mastication is much assisted by the saliva, which is secreted by
the salivary glands in largely increased amount during the process. The
intimate incorporation of the saliva with the food is termed insalivation.

The Salivary Glands. — The glands which secrete the saliva in the
human subject are the salivary glands proper, the parotid, the submaxil-
lary, and the sublingual, and numerous smaller bodies of similar structure
and with separate ducts, which are scattered thickly beneath the mucous
membrane of the lips, cheeks, soft palate, and root of the tongue.

Histological Structure. — The salivary glands are compound tubular
or tubulo-racemose glands. They are made up of lobules. Each lobule con-
sists of the branchings of a division of the main duct of the gland, which
are generally more or less convoluted toward the extremities, that form the
alveoli, or proper secreting parts of the gland. The salivary secreting cells
are of cubical or columnar form and are arranged around a central canal.
The granular appearance frequently seen in the salivary cells is due to the
numerous zymogen granules which they contain.

During the rest period the cells are larger, highlyguamsme with obscured
nuclei and smaller lumen. During activity the cells becolar, ranller and
their contents more opaque.

330

FOOD AND DIGESTION

When the mucous type of gland is secreting, or on stimulation of the nerve,
mucinogen is converted into mucin, the cells swell up, appear more transparent
and stain deeply in logwood, figure 249. After stimulation, the cells become
smaller, more granular, and more easily stained, from having discharged their
contents, and the nuclei appear more distinct.

Nerves of large size are found in the salivary glands. They are princi-
pally contained in the connective tissue of the alveoli, and certain glands,
especially in the dog, are provided with ganglia. Some nerves have special

FIG. 248.

FIG. 249.

FIG. 248. — Section of the Submaxillary Gland of a Dog, Resting Stage. Most of the
alveolar cells are large and clear, being filled with the material for secretion (in this case,
mucigen), which obscures their protoplasm; some of the cells, however, are small and
protoplasmic, forming the crescents seen in most of the alveoli. (Ranvier.)

FIG. 249. — Section of a Similar Gland after a Period of Activity. The mucigen has
been discharged from the mucin-secreting cells, which consequently appear shrunken and
less clear. Both the cells and the alveoli are much smaller, and the protoplasm of the cells
is more apparent. The crescents of Gianuzzi are enlarged, c, Crescent cells; g, mucus-
secreting cells; /, lumen of alveolus. (Ranvier.)

endings in Pacinian corpuscles, some supply the blood vessels, and others
penetrate the basement membrane of the alveoli and end upon, but not in,
the salivary cells.

The blood vessels form a dense capillary network around the ducts of the
alveoli, being carried in by the fibrous trabeculae between the alveoli, in which
also the lymphatics begin by lacunar spaces.

The Nervous Mechanism of the Secretion of Saliva. — The secretion
of saliva is under the control of the nervous system. Under ordinary con-
ditions it is excited by the stimulation of the peripheral branches of two
nerves, the gustatory or lingual branch of the inferior maxillary division
of the fifth nerve, and of the glosso-pharyngeal, which are distributed to the
mucous membrane of the tongue and pharynx conjointly. The stimulation
occurs on the introduction of sapid substances into the mouth, and the
secretion is brought about in the following way: From the terminations of
the above-mentioned sensory nerves distributed in the mucous membrane

INFLUENCE OF NERVES ON THE SUBMAXILLARY GLAND 33!

an impression is conveyed upward (afferent) to the special nerve center
situated in the medulla oblongata which controls the process, and by it is
reflected to certain nerves supplied to the salivary glands, which will be pres-
ently indicated. In other words, the center, when stimulated to action by
the sensory impressions carried to it, sends out impulses along efferent or
secretory nerves supplied to the salivary glands. These cause the saliva to be
secreted by, and discharged from, the gland cells. Other stimuli, however,
besides that of the food, and other sensory nerves than those mentioned
may reflexly produce the same effects. For example, saliva may be caused
to flow by irritation of the mucous membrane of the mouth with mechanical,
chemical, electrical, or thermal stimuli, also by the irritation of the mucous
membrane of the stomach in some way, as in nausea which precedes vomit-
ing, when some of the peripheral fibers of the vagi are irritated. Stimulation
of the olfactory nerves by smell of food, of the optic nerves by the sight of it,
and of the auditory nerves by the sounds which are known by experience to
accompany the preparation of a meal may also stimulate the nerve center to
action In addition to these, as a secretion of saliva follows the movement
of the muscles of mastication, it may be assumed that this movement stimu-
lates the secreting nerve fibers of the gland, direct or reflexly. From the fact
that the flow of saliva may be increased or diminished by mental states, it
is evident that impressions from the cerebrum also are capable of stimulating
the center to action or of inhibiting its action.

Influence of Nerves on the Submaxillary Gland. — The submaxillary
gland has been the gland chiefly employed for the purpose of experimentally
demonstrating the influence of the nervous system upon the secretion of
saliva, because of the comparative facility with which the gland, with its blood
vessels and nerves, can be exposed to view in the dog, rabbit, and other
animals.

The chief nerves supplied to the gland are: (i) the chorda tympani, a
branch given off from the facial in the canal through which it passes in the
temporal bone; and (2) branches of the sympathetic nerve from the plexus
around the facial artery and its branches to the gland. The chorda, figure
250, passes downward and forward, under cover of the external ptery-
goid muscle, and joins the lingual or gustatory nerve, proceeds with it for a
short distance, and then passes along the submaxillary-gland duct,
giving branches to the submaxillary ganglion, and sending others to
terminate in the superficial muscles of the tongue. It consists of fine medul-
lated fibers which lose their medullae in the gland. If this nerve be exposed
and divided anywhere in its course from its exit from the skull to the gland no
immediate result will follow, nor will stimulation either of the lingual or of
the glosso-pharyngeal produce a flow of saliva. But if the peripheral end
of the divided nerve be stimulated, an abundant secretion of saliva ensues,
and the blood supply is enormously increased by dilatation of the arteries.

332

FOOD AND DIGESTION

The veins may even pulsate, and the blood contained within them is more
arterial than venous in character.

When, on the other hand, the stimulus is applied to the sympathetic fila-
ments (mere division producing no apparent effect), the arteries contract,
and the blood stream is in consequence much diminished; and only a sluggish
stream of dark blood escapes from the veins. The saliva, instead of being
abundant and watery, becomes scanty and tenacious. If both chorda tym-
pani and sympathetic branches be divided, the gland, released from nervous
control, may secrete continuously and abundantly (paralytic secretion).

.ortx

FIG. 250. — Showing the distribution of the divisions of the fifth, seventh, and ninth cranial.

(Sheldon.)

The abundant secretion of saliva which follows stimulation of the chorda
tympani is not merely the result of a filtration of fluid from the blood vessels,
in consequence of the largely increased circulation through them. This is
proved by the fact that, when the main duct is obstructed, the pressure within
may considerably exceed the blood pressure in the arteries, and also that, when
into the veins of the animal experimented upon some atropine has been previ-
ously injected, stimulation of the peripheral end of the divided chorda pro-
duces all the vascular effects as before, without any secretion of saliva accom-
panying them. Again, if an animal's head be cut off, and the chorda be
rapidly exposed and stimulated with an interrupted current, a secretion of

CHANGES IN THE GLAND CELLS 333

saliva ensues for a short time, although the blood supply is necessarily absent.
These experiments serve to prove that the chorda contains two sets of nerve
fibers: one set, v as o- dilator, which, when stimulated, act upon a local vaso-
motor center for regulating the blood supply, inhibiting its action, and
causing the vessels to dilate, and so producing an increased supply of blood
to the gland; while another set, which are paralyzed by injection of atropine,
directly stimulate the cells themselves to activity, whereby the cells secrete
and discharge the constituents of the saliva which they produce, the secretory
nerves. These latter fibers very possibly terminate on the salivary cells
themselves. If, on the other hand, the sympathetic fibers be divided, stimu-
lation of the tongue by sapid substances, or electrical stimulation of the trunk
of the lingual or of the glosso-pharyngeal, continues to produce a flow of
saliva. From these experiments it is evident that the chorda-tympani nerve
is the principal nerve through which efferent impulses proceed from the center
to excite the secretion of this gland.

The sympathetic nerve also contains two sets of fibers, vaso-constrictor
and secretory. But the flow of saliva upon stimulating the sympathetic is
scanty, and the saliva itself viscid. At the same time the vessels of the gland
are constricted. The secretory fibers may be paralyzed by the administra-
tion of atropine.

Nerves of the Parotid Gland. — The nerves which influence secretion
in the parotid gland are branches of the facial (lesser superficial petrosal)
and of the sympathetic. The former nerve, after passing through the otic
ganglion, joins the auriculo- temporal branch of the fifth cerebral nerve, and,
with it, is distributed to the gland. The nerves by which the stimulus ordi-
narily exciting secretion is conveyed to the medulla oblongata are, as in the
case of the submaxillary gland, the fifth and the glosso-pharyngeal. The
pneumogastric nerves convey a further stimulus to the secretion of saliva
when food has entered the stomach; the nerve center is the same as in the case
of the submaxillary gland.

Changes in the Gland Cells. — The method by which the salivary
cells produce the secretion of saliva appears to be divided into two stages,
which differ somewhat according to the class to which the gland belongs, viz.,
whether to (i) the true salivary or to (2) the mucous type. In the former
case it has been noticed, as already described, that during the rest which
follows an active secretion the lumen of the alveolus becomes smaller, the
gland cells larger and very granular. During secretion the alveoli and their
cells become smaller, and the granular appearance in the latter to a consider-
able extent disappears, and at the end of secretion the granules are confined
to the inner part of the cell nearest to the lumen, which is now quite distinct,
figure 251.

It is supposed from these appearances that the first stage in the act of
secretion consists in the protoplasm of the salivary cell taking up from the

334 FOOD AND DIGESTION

lymph certain materials from which it manufactures the elements of its own
secretion, and which are stored up in the form of granules in the cell during
rest; the second stage consists of the actual discharge of these granules, with
or without previous change. The granules are zymogen granules, and repre-
sent the chief substance of the salivary secretion, ptyalin. In the case of the
submaxillary gland of the dog, at any rate, the sympathetic nerve fibers ap-
pear to have to do with the first stage of the process, and when stimulated
the protoplasm is extremely active in manufacturing the granules, whereas
the chorda tympani is concerned in the production of the second act, the
actual discharge from the cells of the materials of secretion, together with a

FIG. 251. — Alveoli of True Salivary Gland. A, At rest; B, in the first stage of secretion;
C, after prolonged secretion. (Langley.)

considerable amount of fluid. The latter is an actual secretion by the
protoplasm, as it ceases to occur when atropine has been subcutaneously
injected.

In the mucus-secreting gland, the changes in the cells during secretion
have been already spoken of. They consist in the gradual production by the
protoplasm of the cell of a substance called mucigen, which is converted into
mucin, and discharged on secretion into the canal of the alveoli. The muci-
gen is, for the most part, collected into the inner part of the cells during rest,
pressing the nucleus and the small portion of the protoplasm which remains
against the limiting membrane of the alveoli.

The process of secretion in the salivary glands is identical with that of
glands in general. The cells which line the ultimate branches of the ducts
are the agents by which the special constituents of the saliva are formed. The
material which they have incorporated within themselves, which is doubtless
a product of the metabolism of the protoplasm of the cells, is given up again
almost at once in the form of a fluid, secretion, which escapes from the ducts
of the gland. The cells themselves undergo diminution in the mass of their
protoplasm, which is again renewed in the intervals of the active exercise of
the functions. The source whence the cells obtain the materials for the con-
struction of secretion is the blood plasma, which is filtered off from the circu-
lating blood into the interstices of the glands, as in all living tissues.

RATE OF SECRETION AND QUANTITY OF SALIVA 335

Saliva. — Saliva, as it commonly flows from the mouth, is the mixed
secretion of the salivary glands proper and of the glands of the buccal mucous
membrane and tongue. When obtained from parotid ducts, and free from
mucus, saliva is a transparent watery fluid, the specific gravity of which
varies from 1.004 to 1.008 and in which, when examined \vith the micro-
scope, are found floating a number of minute particles, derived from the
secreting ducts and vesicles of the glands. In the impure or mixed saliva
are found, besides these particles, numerous epithelial scales separated from
the surface of the mucous membrane of the mouth and tongue, and the so-
called salivary corpuscles, discharged probably from the mucous glands of the
mouth and the tonsils. These subside when the saliva is collected in a deep
vessel and left at rest. They form a white opaque sediment leaving the
supernatant fluid transparent and colorless, or with a pale bluish-gray tint.
Saliva also contains various kinds of micro-organisms (bacteria). The
saliva, when first secreted, appears to be always alkaline in reaction; the
alkalinity is about equal to o . 08 per cent, of sodium carbonate, and is due
to the presence of disodium phosphate, Na2HPO4.

The presence of potassium sulpho cyanide, KCNS, in saliva may be shown
by the blood-red coloration which the fluid gives with a solution of ferric
chloride, Fe2Cl6, and which is bleached on the addition of a solution of
mercuric chloride, HgCl2, but not by hydrochloric acid.

CHEMICAL COMPOSITION OF HUMAN SALIVA. (HAMMERBACHER.)

In 1,000 Parts.

Water 994 . 2

Solids 5.8

Mucus and epithelium 2.2

Soluble organic matter (ptyalin) 1.4

Potassium sulphocyanide o . 04

Salts 2.20

Saliva from the parotid is less viscid; less alkaline, the first few drops
discharged in secretion being even acid in reaction; clearer, although it may
become cloudy on standing from the precipitation of calcium carbonate by
the escape of carbon dioxide; and more watery than that from the submaxil-
lary. It has, moreover, a less powerful action on starch. Sublingual saliva
is the most viscid, and contains more solids than either of the other two, but
has little diastasic action.

Rate of Secretion and Quantity of Saliva. — The rate at which saliva
is secreted is subject to considerable variation. When the tongue and muscles
concerned in mastication are at rest, and the nerves of the mouth are subject
to no unusual stimulus, the quantity secreted is not more than sufficient with
the mucus to keep the mouth moist. During actual secretion the flow is
much accelerated.

336 FOOD AND DIGESTION

The quantity secreted in twenty-four hours varies greatly, but is at least
i liter.

Function of Saliva. — The purposes served by saliva are mechanical
and chemical.

Mechanical. — (i) It keeps the mouth in a due condition of moisture,
facilitating the movements of the tongue in speaking and in the mastication
of food. (2) It serves also in dissolving sapid substances, and renders them
capable of exciting the nerves of taste. (3) But the principal mechanical
purpose of the saliva is that, by mixing with the food during mastication, it

FIG. 252. — Showing the variation of the rate of secretion of saliva, second line from
the top, and variation of blood pressure, top line. At a, an injection of o . 2 mgr. pilocar-
pine. At b, 50 c.c. oxygenated blood was injected into the jugular vein. (Jonescu.)

makes a soft pulpy mass such as may be easily swallowed. To this purpose
the saliva is adapted both by quantity and quality. For, speaking generally,
the quantity secreted during feeding is in direct proportion to the dryness
and hardness of the food.

Chemical. — The chemical action which the saliva exerts upon the food in
the mouth is to convert the starchy materials which it contains into soluble
starch and then into sugar. This power the saliva owes to the enzyme
ptyalin. Certain investigators have of late asserted that saliva contains
another enzyme, known as maltase, which has the power of splitting the di-
saccharides into monosaccharides, or maltose into dextrose. The action of
this ferment is certainly very limited. The conversion of the starch under
the influence of the ferment into sugar takes place in several stages, and in
order to understand it a knowledge of the structure and composition of
starch granules is necessary. A starch granule consists of two parts: an en-

FUNCTION OF SALIVA 337

velope of cellulose, which does not give a blue color with iodine except on
addition of sulphuric acid, and of granulose, which is contained within, and
which gives a blue color with iodine alone. Briicke states that a third body
is contained in the granule, which gives a red color with iodine, viz., erythro-
granulose. The granulose swells up on boiling, bursts the envelope, and the
whole granule is more or less completely converted into a paste or gruel
which is called gelatinous starch.

When ptyalin acts upon boiled starch, it first changes the latter, by hydrol-
ysis, into soluble starch, or amidulin; this is more limpid and more like a true
solution, though it still gives the blue coloration on the addition of iodine.
This stage is very brief, only thirty seconds being sometimes required in labo-
ratory experiments to render a stiff starch paste completely fluid when a few
drops of saliva are added at body temperature. This rapidity of action is of
great importance, as under proper conditions of mastication practically all
the boiled starch of the food ought to enter the stomach as soluble starch.
When the starch has not been previously boiled, the envelope of cellulose
retards the action of the ptyalin to a very marked degree.

Starch.
Soluble starch.

Erythro-dextrin. Maltose and iso-maltose.

Achroo-dextrins. Maltose and iso-maltose.

The further stages of hydrolytic cleavage result in the formation of a
variable mixture of maltose and iso-maltose with a series of dextrins, but ap-
parently never result (in laboratory experiments) in the complete conversion
of the dextrins into sugars. Gradually, as the starch is converted, the blue
coloration with iodine is replaced by a purplish-red and finally by a red
color: the latter color is produced by ery thro- dextrin (so called from the
color). In the later stages no coloration is obtained with iodine, and for this
reason the dextrins formed are known as achroo-dextrins; there are probably
several of these, but they have not yet been sufficiently isolated. As sugar
appears very early in the process, even at the stage of erythro-dextrin, and
gradually increases in amount, it is generally concluded that maltose is
formed early in the decomposition of the starch molecule. The process is
usually represented schematically as above.

The sugars formed are maltose (C12H22On) and a closely allied sugar
known as iso-maltose. A small percentage of dextrose has been found by
some observers, and this is due to the action of maltase. Maltose is allied

FOOD AND DIGESTION

to saccharose or cane-sugar more nearly than to glucose; it is crystalline; its
solution has the property of polarizing light to the right to a greater degree
than solutions of glucose (3 to i); it is not so sweet, and reduces copper sul-
phate less easily. It can be converted into glucose by boiling with dilute
acids and by the action of the enzyme maltase present in saliva.

According to Brown and Heron, the reactions may be represented thus:
One molecule of gelatinous starch is converted by the action of an amylolytic

ferment into n molecules of soluble starch.

One molecule of soluble starch = (C12H20O10)10 -f-8H2O, which is further con-
verted by the ferment into

i. Erythro-dextrin, (C12H20O10)9 (giving red with iodine) +

Maltose (C12H22On).
then into 2. Erythro-dextrin (C12H20Oj0)8 (giving yellow with iodine)

+ Maltose 2 (C12H22On).

next into 3. Achroo-dextrin (C12H20O10)7 + Maltose 3 (C12H22On).
And so on; the resultant being:

Soluble starch (C12H20O10)10 + Water 8H2O = Maltose 8(C12H22OU) +
Achroo-dextrin (C12H20O10)2.

Many observers, however, believe that the maltose simultaneously pres-
ent with ery thro- dextrin is not actually split off from the starch molecule in
the formation of erythro-dextrin, but that it is the product of more advanced
hydrolysis in other starch molecules. They point out that in such a chemical
reaction of considerable time duration, it is improbable that all the starch
molecules are attacked at the same rate or are, at any given moment, equally
advanced in cleavage. Their theory is that there is a series of more and more
simple dextrins formed giving rise finally to the disaccharides.

The presence of sugar in such an experiment is at once discovered by the
application of Trommer's test, which consists in the addition of a drop or
two of a solution of copper sulphate, followed by a larger quantity of caustic
potash. When the liquid is boiled, an orange-red precipitate of copper sub-
oxide indicates the presence of sugar.

Influences which Affect the Action of Saliva on Starch. — Moderate
heat, about 37 . 8° to 40° C., is most favorable to the rapid cleavage of starch
by the ptyalin. Cold retards and o° C. suspends the action but does not de-
stroy the ferment. A temperature of 60° C. destroys the ptyalin.

Removal of the products of salivary digestion as they are formed facili-
tates the action of the enzyme, as an excess of these products is detrimental
to further action.

The reaction between starch and saliva takes place best in a neutral or
very faintly alkaline medium and is inhibited by strong alkalies and espe-
cially by acids even as weak as the acidity of the gastric juice. This last is
of particular importance since it raises the question as to how long the
ptyalin may act.

DEGLUTITION 339

The action of saliva on starch is not limited to the brief interval during
which food remains in the mouth, as is now well known, but may continue
for a time in the stomach.

Ptyalin is strictly an amylolytic ferment.

Starch appears to be the only principle of food with the exception of the
dextrins and glycogen, upon which the saliva acts chemically. The secretion
has no apparent influence on gum, cellulose, or on fat, and is equally destitute
of power over albuminous and gelatinous substances.

The salivary glands of children do not produce functionally active saliva
till the age of 4 to 6 months, and hence the bad effects of feeding them before
this age on starchy food, corn-flour, etc., which they are unable to render
soluble and capable of absorption.

Salivary Digestion in the Stomach. — Laboratory experiments have
demonstrated that while the addition of even o . 05 per cent, of hydrochloric
acid will inhibit the action of ptyalin on a solution of starch, if any proteins
be present in the solution much more acid must be added before the action
of the ptyalin is stopped. The explanation of the latter fact is that the acid
unites with the proteins in some chemical combination forming "combined
acid," which has little effect, comparatively, on ptyalin. This "combined
acid" gives a red color with litmus, but is distinguished from free acid by
giving a brownish instead of a bluish color with Congo red. When food enters
an empty stomach, as happens at the beginning of a meal the acid first com-
bines with the protein food stuffs and so does not at once affect the ptyalin.

A still more important fact in its bearing on this subject was recently
discovered by Cannon, who showed experimentally that starchy foods mixed
with weak alkali remain alkaline in the stomach for as much as an hour and
a half. Such foods when swallowed into the stomach are packed away in
that organ in a mass. The secretion of the acid gastric juice comes in con-
tact only with the outer surface of the mass, which is not materially disturbed
by the stomach peristalses. The center of the mass may, therefore, remain
alkaline until the outer layers are completely eroded away, and the ptyalin
may continue to act on starch during the whole time.

DEGLUTITION.

When properly masticated, the food is transmitted in successive portions
to the stomach by the act of deglutition or swallowing. The following account
of deglutition is based upon the researches of Kronecker and Meltzer, whose
experiments seem to modify in some details the earlier theory of Magendie:

The mouth is closed, and the food after thorough mixing with the saliva
is rolled into a bolus on the dorsum of the tongue. The tip of the tongue is
pressed upward and forward against the hard palate, thus shutting off the
anterior part of the mouth cavity. The mylo-hyoid muscles then suddenly

340 FOOD AND DIGESTION

contract, the bolus of food is put under great pressure and shot backward and
downward through the pharynx and into the esophagus and, if the food be
fluid enough, even to the cardiac orifice of the stomach. Coincidently with
the contraction of the mylo-hyoid muscles, the hyoglossi are thrown into
action, drawing the tongue backward and downward, not only increasing
the pressure upon the food, but forcing the epiglottis over the glottis, closing
the larynx.

It has been shown by the Roentgen-ray method that the character of the
food determines somewhat its passage through the esophagus. The dry
and semisolid foods are seized by the musculation of the esophagus and
passed down that organ by a peristaltic wave. The longitudinal muscles
contract, tending to enlarge the diameter of the esophagus in advance of the
food, while contractions of the circular muscles produce pressure on the
bolus just behind, thus forcing it along to the cardia. This wave reaching
the cardiac orifice about six seconds after the commencement of the act of
deglutition, forces the food into the stomach, the sphincter having previously
relaxed. The interval of time between the commencement of the act of
deglutition and the arrival of the more fluid food at the cardiac orifice of the
stomach may not be more than one-tenth second, though it remains at the
cardiac orifice without entering the stomach until the first parts of the act of
swallowing is reinforced by the subsequent contraction of the constrictors of
the pharynx and the passage of a peristaltic wave down the esophagus. In
some cases, however, the liquid food is not stopped at the cardiac orifice,
but is sent through the relaxed sphincter by the original force of the mylo-
hyoid contraction.

In man the esophagus was said to contract in three separate segments,
the first segment lying in the neck and being about six centimeters long, the
second being the next ten centimeters of the tube, and the third the re-
maining portion to the stomach. But the later Roentgen-ray observations
show no break in the continuous passage of the food, though the movement
of the food is slower in the lower segment of the esophagus.

The act of swallowing consists, then, of the contraction in sequence of
the mylo-hyoids, the constrictors of the pharynx, and of the esophagus. The
computed time of contraction is as follows:

Seconds.
Contraction of mylo-hyoids and constrictors of the pharynx ... 0.3

Contraction of the first part of the esophagus 0.9

Contraction of the second part of the esophagus 1.8

Contraction of the third part of the esophagus 3.0

6.0

If a second attempt at swallowing be made before the first has been com-
pleted (that is, before six seconds have elapsed), the remaining portion of the

DIGESTION IN THE STOMACH 341

first act is inhibited, and the contraction wave reaches the stomach six
seconds after the commencement of the second act.

During the act of deglutition the posterior nares are closed through the
action of the levator palati and tensor palati muscles, which raise the velum;
the palato-pharyngei, drawing the posterior pillars of the fauces together;
and the azygos uvulae, which raises the uvula — thus forming a complete cur-
tain. Otherwise the food would pass into the nose, as happens in the case
of cleft palate. At the same time the larynx is closed by the adductor
muscles of the vocal cords and the descent of the epiglottis, the larynx being
drawn upward as a whole through the action of the mylo-hyoid, genio-hyoid,
thyro-hyoid, and digastric muscles. The presence of the epiglottis is not
necessary for the completion of the act of deglutition.

Nervous Mechanism of Deglutition. — The sensory nerves engaged
in the reflex act of deglutition are branches of the fifth cerebral, supplying the
soft palate; the glosso-pharyngeal, supplying the tongue and pharynx; the
superior laryngeal branch of the vagus, supplying the epiglottis and the glottis.
The motor fibers concerned are branches of the fifth, supplying part of the
digastric and mylo-hyoid muscles and the muscles of mastication; the facial,
supplying the levator palati; the glosso-pharyngeal, supplying the muscles
of the pharynx; the vagus, supplying the muscles of the larynx through the
inferior laryngeal branch; and the hypoglossal, the muscles of the tongue.
The nerve center by which the muscles are harmonized in their action is
situated in the medulla oblongata. It cannot be definitely circumscribed,
but is in the general level of the vagus origin. The movements of the esoph-
agus are co-ordinated by the complex of sensory and motor fibers of the
fifth and the ninth to twelfth cranial nerves, which all take some part in this
complicated reflex.

Cannon has demonstrated that the smooth muscle of the lower end of
the esophagus and around the cardiac orifice is maintained in contraction
by a local reflex mechanism. This prevents regurgitation of the foods.
The local apparatus is brought into action by the stimulation of sensory cells
in the mucous membrane of this region of the stomach by the acid of the
gastric secretion. The reflex is assumed to be a local one taking place through
the intrinsic nervous mechanism. This acid closure of the cardiac is to be
compared with the similar mechanism for the pylorus, see page 354.

DIGESTION IN THE STOMACH.

The stomach of man and the carnivora is the dilated portion of the ali-
mentary canal following the esophagus. The esophagus enters the stomach
at the cardiac end and the pyloric end of the stomach is continuous with the
duodenal part of the intestine. It varies in shape and size according to its
state of distention. It is supplied with nerves from the vagus and from the
sympathetic and receives a special artery, the gastric artery.

342

FOOD AND DIGESTION

Structure of the Stomach. — The stomach is composed of four coats,
called, respectively, the external or peritoneal, the muscular, the submucous,

FIG. 253. — The Human Stomach and the Vagus Distribution. R. L., Recurrent
laryngeal; Ca2, inferior cervical cardiac branch; Ca^, Ca^, cardiac branches of vagus;
A. P. PL, P. P. PI., anterior and posterior. pulmonary plexuses; Oes. PL, esophageal plexus;
Cast. R. and!,., gastric branches of vagus, right and left; Coe, PL, coeliac plexus; Hep. pi.,
hepatic plexus.

and the mucous coat. Blood vessels, lymphatics, and nerves are distributed
in and between them.

STRUCTURE OF THE STOMACH

343

The muscular coat consists of three separate layers of fibers which, accord-
ing to their several directions, are named the longitudinal, circular, and
oblique. The longitudinal set are the most superficial and are continuous
with the longitudinal fibers of the esophagus and spread out in a diverging

manner over the cardiac end and sides of
the stomach to the pylorus. The circular
or transverse coat more or less completely
encircles all parts of the stomach; this
coat is thickest at the middle and in the
pyloric portion of the organ, and forms
the chief part of the thick ring of the
pylorus. The next and consequently
deepest coat, the oblique, is continuous
with the circular muscular fibers of the

FIG. 254.

FIG. 255.

FIG. 254. — From a Vertical Section through the Mucous Membrane of the Cardiac End
of Stomach. Two peptic glands are shown with a duct common to both, one gland only in
part, a, Duct with columnar epithelium becoming shorter as the cells are traced down-
ward; n, neck of gland tubes, with central and parietal or so-called peptic cells; h, fundus
with curved cecal extremity — the parietal cells are not so numerous here. X 400. (Klein
and Noble Smith.)

FIG. 255. — Cross-sections at Various Levels of Peptic Glands of Stomach. X 400.
M, Section through gastric pit near surface; M', section through gastric pit near bottom;
h, mouth of gland; k, neck; g, body near fundus; the chief cells are shaded lightly; b, parietal
cells. (Kolliker.)

esophagus at the cardiac orifice of the stomach. This coat is quite inter-
rupted and more or less incomplete. The muscular fibers of the stomach
and intestinal canal are unstriated.

344

FOOD AND DIGESTION

The mucous membrane of the stomach, which rests upon a layer of loose
cellular membrane, or submucous tissue, is smooth, soft and velvety. It is
of a pale pink color during life, and in the contracted state is thrown into
numerous longitudinal folds or rugae, which disappear when the organ is
distended. It is composed of a mass of short tubular secreting glands.

The Gastric Glands. — The glands of the mucous membrane of the
stomach are of two varieties, Cardiac and Pyloric.

FIG. 256.

FIG. 257.

FIG. 256. — Longitudinal Section of Fundus of Gland from Dog's Stomach, a,
Lumen of gland; b, intracellular canals in parietal cells; c, cut-off portion of parietal cell;
d, chief cells; e, intercellular canals leading from lumen of gland to canals in parietal cells.
(Bailey.)

FIG. 257. — Tubule of Pyloric Gland of Man. (Highly magnified.) Note the thin
basal layer of cytoplasm; the reticular cell body containing secretion; the subdivision of the
latter in some cells into proximal and distal masses. (Bailey.)

Cardiac glands are found throughout the whole of the cardiac end of the
stomach. They are arranged in groups of four or five, which are separated
by a fine connective tissue. Two or three tubes often open into one duct,
figure 254, which forms about a third of the whole length of the tube and
opens on the surface. The ducts and the free surface are lined with colum-
nar epithelium. The body of the gland is composed of granular secreting
cells, called chief cells or peptic cells. Between these cells and the membrana
propria of the tubes are large oval or spherical cells, granular in appearance
with clear oval nuclei; these cells are called oxyntic or parietal cells. They do
not form a continuous layer, figure 254. Intercellular tubules extending

THE GASTRIC GLANDS

345

from the duct of the gland between the chief cells and connecting with intra-
cellular secretory tubules in the parietal cells have been shown by the Golgi
method, figure 256.

As the pylorus is approached the gland ducts become longer and the
tube proper becomes shorter, and occasionally branched at the fundus.

The Pyloric Glands. — These glands have much longer ducts and larger
mouths than the peptic glands.

The parietal cells are absent in the pyloric glands. The pyloric glands
become larger as they approach the duodenum, also more convoluted and
more deeply situated. They are directly continuous with Brunner's glands
in the duodenum (Watney).

FIG. 258. — Scheme of Blood Vessels and Lymphatics of Stomach. X 70. a, Mucous
membrane; b, muscularis mucosse; c, submucosa; d, inner circular muscle layer; e, outer
longitudinal muscle layer; A, blood vessels; B, structure of coats; C, lymphatics. (Szymo-
nowicz, after Mall.)

Blood vessels and Lymphatics. — The blood vessels of the stomach first
break up in the submucous tissue and send branches upward between the
closely packed glandular tubes, which anastomose around them by a fine
capillary network with oblong meshes. Contiguous with this deeper plexus,
or prolonged upward from it, so to speak, is a more superficial network of
larger capillaries, which branch densely around the orifices of the tubes and
form the framework on which are molded the small elevated ridges of mucous

346 FOOD AND DIGESTION

membrane. From this superficial network the veins chiefly take their origin,
pass down between the tubes, with no very free connection with the deeper
intertubular capillary plexus, and open finally into the venous network in
the submucous tissue.

The lymphatic vessels surround the gland tubes with a network.
Toward the fundus of the peptic glands are masses of lymphoid tissue
which may appear as distinct follicles, somewhat like the solitary glands
of the small intestine.

Microscopic Changes in the Gastric Glands During Secretion.—
Langley has made a study of the histological changes in the glandular tissues
in the fresh state. He finds that during fasting or when the glands are at rest
the chief cells are granular throughout, being crowded with large highly re-
fractive granules. During activity these granules gradually disappear pro-
gressively from the base toward the border of the cell on the lumen of the tube.
They 'no doubt represent the zymogen substances from which the first dis-
charge of enzyme is derived during the activity of secretion. The parietal
cells are finely granular throughout, though they decrease in size during
activity, as in fact do the chief cells. Macallum by the use of microchemical
tests has shown the presence of a mineral acid, hydrochloric acid in the ducts
and intracellular canals of the parietal oxyntic cells. The pyloric cells do
not undergo such marked changes, and the mucous cells of the more super-
ficial layers of the mucosa cannot be said to show any special changes at the
time of digestional activity of the other layers. During periods of rest the
gastric cells increase in size and again become charged with granules as
before.

The Act of Secretion of Gastric Juice. — The gastric glands un-
dergo periods of rest and activity. The active secretion of normal gastric
juice takes place when food is introduced into the mouth, or in fact the
mere sight of appetizing food is followed by an abundant secretion of gastric
juice, as shown by Bidder and Schmidt on the dog with a gastric fistula. Such
observations strongly indicate that the act is a nervous phenomenon, at least
under nervous control.

Quite recently Pawlow has proved that secretory fibers are carried to
the gastric glands in the vagus trunk. His experiment consisted in estab-
lishing a gastric fistula, and some days later in dividing the esophagus
in the neck in such a manner that any food swallowed would be diverted
to the exterior through the cut end. A "fictitious meal " could then be given
to the animal, and the effect upon the stomach noted. As long as the vagi
were intact, certain foods (meats) caused a flow of gastric juice, though
none of the food reached the stomach. The secretion of gastric juice con-
tinued for hours with the production of a large quantity of secretion. When
the vagi had been cut, no secretion occurred. Moreover, 'he found that direct
stimulation of the vagus produced a flow of gastric juice.

THE GASTRIC JUICE

347

Khigine placed foods in an isolated gastric pouch prepared with care to
maintain the nervous relations intact, and it led to secretion of gastric juice
in the main part of the stomach. This is undoubtedly a nervous reflex effect.

Recently observations on a case of stricture of the human esophagus
which prevented food from reaching the stomach have shown that an
abundant flow of gastric juice takes place when food is taken into the mouth.

c.s

D.7

0.8

D.9

FIG. 259. — Very Diagrammatic Representation of the Nerves of the Alimentary
Canal. Oe to Ret, the various parts of the alimentary canal from esophagus to rectum;
L. V, left vagus, ending on front of stomach; rl, recurrent laryngeal nerve, supplying upper
part of esophagus; R. V, right vagus, joining left vagus in esophageal plexus; ce. pi.,
supplying the posterior part of stomach, and continues as R'V to join the solar plexus, here
represented by a single ganglion, and connected with the inferior mesenteric ganglion, m.
gl.; a, branches from the solar plexus to stomach and small intestine, and from the mesen-
teric ganglia to the large intestine; Spl. maj., large splanchnic nerve, arising from the
thoracic ganglia and rami communicantes; r. c., belonging to dorsal nerves from the 6th
to the pth (or loth); Spl. min., small splanchnic nerve similarly from the loth and nth
dorsal nerves. These both join the solar plexus, and thence make their way to the ali-
mentary canal; c. r., nerves from the ganglia, etc., belonging to nth and i2th dorsal and
ist and 2d lumbar nerves, proceeding to the inferior mesenteric ganglia (or plexus), m. gl.,
and thence by the hypogastric nerve, n. hyp., and the hypogastric nerve, n. hyp., and the
hypogastric plexus, pi. hyp., to the circular muscles of the rectum; /. r., nerves from the 2d
and 3d sacral nerves, S. 2, S. 3 (nervi erigentes) proceeding by the hypogastric plexus to the
longitudinal muscles of the rectum. (M. Foster.)

It seems conclusively established at the present time that the secretion of
gastric juice is a reflex act controlled by a definite nervous mechanism. This
reflex can be aroused by the sensory stimuli of taste, smell, and even sight.
It can also be initiated by stimuli arising in the stomach itself by the effects
of ingredients of the food or by the products of digestion. Indeed, it has
been shown that peptone is a very efficient stimulus for this stomach reflex.

Edkins, however, has recently shown that the contact of certain food

348

FOOD AND DIGESTION

products with the pyloric end of the stomach, where they are slightly ab-
sorbed, gives rise to some chemical substance — a gastric hormone or secre-
tagogue — which acts as a powerful stimulus to gastric secretion when it is
introduced into the circulation. Such food substances are dextrins, maltose
and dextrose, proteoses, and above all meat extract.

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FIG. 260. — Table to show the Secretion of Gastric Juice by the Dog. (Lliffine.)

The influence of the higher nerve centers on gastric digestion, as in the
case of emotions, is too well known to need more than a reference.

Immediately on the introduction of food or other stimulating substance,
the mucous membrane, which was previously quite pale, becomes slightly

THE ACID OF GASTRIC JUICE 349

turgid and reddened with the influx of a larger quantity of blood, and the gas-
tric glands commence actively to secrete. An acid fluid is poured out in
minute drops and the secretion may continue for hours.

The Gastric Juice. — The first analysis of gastric juice was made by
Prout on a small and impure specimen. Beaumont made an elaborate and
classic series of observations on the gastric secretion of Alexis St. Martin,
in whom there existed, as the result of a gunshot wound, an opening leading
directly into the stomach near the upper extremity of the great curvature
and three inches from the cardiac orifice. The introduction of any mechan-
ical irritant, such as the bulb of a thermometer, into the stomach through
this artificial opening excited the secretion of gastric fluid. This was drawn
off, and was often obtained to the extent of nearly an ounce.

The chemical composition of human gastric juice has been also investi-
gated by Schmidt. The fluid in this case also was obtained by means of an
accidental gastric fistula. The mucous membrane was excited to action by
the introduction of some hard matter, such as dry peas, and the secretion wras
removed by means of an elastic tube. The fluid obtained was found to be
acid, limpid, odorless, with a specific gravity of i . 002 to i . oio. It contained
a few cells and some fine granular matter. The analysis of the fluid obtained
in this way is given below. Essentially it is a weakly acid fluid containing
hydrochloric acid and two enzymes, pepsin and rennin, with possibly a third,
maltase. The gastric juice obtained from gastric fistulas of dogs and other
animals shows some difference in composition.

CHEMICAL COMPOSITION OF GASTRIC JUICE.

Dogs. Human.

Water 971 . 17 994-4

Solids 28.82 5. 60

Solids —

Ferment — pepsin T 7 • 5 3-I9

Hydrochloric acid (free) 2.7 0.2

Salts —

Calcium, sodium, and potassium chlorides; and

calcium, magnesium, and iron phosphates 8.57 2.19

The quantity of gastric juice secreted daily has been variously estimated;
but the average for a healthy adult may be assumed to range from 2,000 to
3,000 cubic centimeters in the twenty-four hours.

The Acid of Gastric Juice. — The acidity of the fluid is due to free
hydrochloric acid, although other acids, e.g., lactic, acetic, butyric, are not
infrequently to be found therein as products of gastric digestion or abnormal
fermentation. In healthy gastric juice the amount of free hydrochloric acid
is usually about o . 2 per cent. , but may be as much as o . 3 per cent. In patho-

35° FOOD AND DIGESTION

logical conditions it may be entirely absent, or may amount to 0.5 per cent.,
or even more.

Hydrochloric acid is the proper acid of healthy gastric juice, and various
tests have been used to prove this. The tests depend upon changes produced
in aniline colors by the action of hydrochloric acid even in minute traces,
whereas lactic and other organic acids have no such action.

An aqueous solution of oo-tropeolin, a bright yellow dye, is turned red on
the addition of a minute trace of hydrochloric acid, and aqueous solutions
of methyl violet and gentian violet are turned blue under the same circum-
stances. The lactic acid sometimes present in the contents of the stomach is
derived partly from the sarcolactic acid of muscle and partly from lactic-acid
fermentation of carbohydrates. Lactic acid (C3H6O3), if present, gives the
following test: A solution of 10 cubic centimeters of a 4 per cent, aqueous
solution of carbolic acid, 20 cubic centimeters of water, and one drop of ferric
chloride is made; forming a blue-colored mixture. A mere trace of free lactic
acid added to such a solution causes it to become yellow. Inasmuch as
mineral acids also discharge the color, the lactic acid is removed from the
gastric contents by shaking with ether and trying the test with the solution
of the residue after evaporation of the ether.

The protein matter in the food combines to some extent with the hydro-
chloric acid, which then is known as combined acid and does not redden litmus-
paper. As this combination is immediate, it follows that no free acid is found
in the gastric contents until the amount secreted is more than enough to satu-
rate the various albuminous affinities. It is partly for this reason that, as al-
ready mentioned, salivary digestion may continue in the stomach for some
time after the commencement of gastric digestion. According to Ehrlich, the
amount necessary to saturate the affinities of 100 grams of various articles
of diet is as follows:

Beef (boiled) 2.0 grams of pure HC1.

Mutton (boiled) 1.9 grams of pure HC1.

Veal (boiled) 2.2 grams of pure HC1.

Pork (boiled) 1.6 grams of pure HC1.

Ham (boiled) 1.8 grams of pure HC1.

Sweetbread (boiled) 0.9 gram of pure HC1.

Wheat bread 0.3 gram of pure HC1.

Rye bread 0.5 gram of pure HC1.

Swiss cheese 2.6 grams of pure HC1.

Milk (100 c.c.) o . 32-0 .42 gram of pure HC1.

The acid is chiefly found at the surface of the mucous membrane, but is
in all probability formed by the parietal cells of the cardiac glands, hence
called oxyntic, for no acid is formed by the pyloric glands in which this
variety of cell is absent. It seems established that the chlorides of the blood
are the source of the hydrochloric acid, for when these chloride salts are

ACTION OF PEPSIN AND HYDROCHLORIC ACID 351

reduced to the point at which they are tenaciously held the hydrochloric
acid is no longer secreted. One can only guess at the detail by which the
parietal cells secrete the acid.

The acid probably results (Maly) from a combination of common salt
with monosodic phosphate, NaH2PO4 +NaCl =Na2HPO4 +HC1; the di-
sodic phosphate is then reconverted by the action of carbonic acid and water,
Na2HPO4 +CO2 +H2O = NaH2PO4 +NaHCO3. All these salts are found
in the blood.

The Pepsin. — The pepsin of the gastric juice is derived from the ac-
tivity of the chief cells of the fundic glands. The zymogen pepsinogen,
which is its immediate precursor, is in all probability represented by the gran-
ules of the resting cells. The ferment pepsin does not exist as such in the
cells, for an extract of peptic glands in o . 2 per cent, soda solution kept at
40° C. retains for hours its power to digest protein when added to 0.2 per
cent, hydrochloric acid. If the extract be first treated with acid till it is
active, then neutralized and kept, it quickly loses its power to digest. The
enzyme is destroyed by the treatment, but the pro-enzyme is not so injured.

Digestive Action of Pepsin and Hydrochloric Acid. — The chief func-
tion of gastric juice is to alter the protein food stuffs so that they may be
readily absorbed. Less important functions are the antiseptic action of
the hydrochloric acid and the coagulation of milk. The chief digestive
power of the gastric juice depends on the pepsin and acid contained in it,
both of which are necessary for the process in the stomach.

This action on proteins may be shown by adding a little gastric juice
(natural or artificial) to some flakes of fibrin or to diluted egg albumin, and
keeping the mixture at a temperature of about 37 . 8° C. (100° F.). It is soon
found that the fibrin goes into solution and that the albumin cannot be pre-
cipitated on boiling. If the solution be neutralized with an alkali, a precipi-
tate of acid albumin is thrown down. After a while the acid albumin dis-
appears, so that no precipitate results on neutralization, and proper analysis
will show that all the fibrin or albumin has been converted into other protein
substances, viz., proteases and peptones. The process, as in the case of sali-
vary digestion, is never complete and the final result is always a mixture of
peptones with proteoses which cannot be further peptonized. The relative
proportions, of course, depend on the duration of the process. A side prod-
uct is found (as an insoluble residue) in artificial gastric digestion which
gives practically all the protein reactions and is soluble in dilute alkali,
though insoluble in water, sodium chloride, or dilute acid. This is known
as anti-albumid and may be changed into peptone by prolonged digestion; it
does not occur in physiological gastric digestion. The commonest proteose
is the one formed from albumin and is known as albumose, or by the more
general name proteose; this name is used in the subsequent descriptions of
the digestive processes.

352 FOOD AND DIGESTION

All classes of proteins are digested by gastric juice, leading to the produc-
tion of proteoses and peptones. The change is indicated best by the charac-
ters of the new protein formed. Peptones have certain characteristics which
distinguish them from other proteins. They are divisible; i.e., they possess
the property of passing through animal membranes. In their diffusibility
peptones differ remarkably from egg albumin, and on this diffusibility depends
one of their chief uses. Egg albumin as such, even in a state of solution,
would be of little service as food, inasmuch as its diffusibility renders difficult
its absorption or in the case of insoluble proteins effectually prevents absorp-
tion into the blood vessels of the digestive canal. When completely changed
by the action of the gastric juice into peptones, albuminous matters diffuse
readily, and can be then absorbed. Peptones, however, are not found in
the blood, even of the vessels immediately concerned in absorption from
the stomach and intestines. As will be shown, the proteins are broken
down into their simpler cleavage products in the intestine.

Products at Different Stages of Gastric Digestion. — The protein
is first changed into syntonin, or acid protein, by the combined action of the
pepsin and acid. Though the acid alone is capable of accomplishing this
step, the fact that it does not do so physiologically is proven by the great
length of time required in laboratory experiments for the change. The
acid is absolutely essential to the action of pepsin.

The next change is the conversion of the syntonin into proteoses which,
according to Neumeister, occurs in two successive stages. The first of these
stages is the conversion of syntonin into the primary proteoses; i. e., proto-
proteose and hetero-proteose. The second is the conversion of both proto-
proteose and hetero-proteose into the secondary proteoses; i.e., deutero-
proteose. The last change is the conversion of the deutero-proteose into the
end product peptone. This last change does not occur to any great extent
and the proteoses always predominate in the digesting mass. The action
of pepsin is one of hydrolysis and the products are hydrated forms of protein.
Schematically the changes in the proteins may be represented as follows:

Protein
Syntonin (acid protein).

Proto-proteose. Hetero-proteose.

Deutero-proteose. Deutero-proteose.

Peptone. Peptone.

Circumstances Influencing Gastric Digestion. — A temperature of
about 40° C. is most favorable to gastric digestion. The pepsin is destroyed

MOVEMENTS OF THE STOMACH 353

by a temperature of 55° (neutral) to 65° C. (acid solution) and its action is
retarded and suspended by low temperatures. It is inactive in neutral
or alkaline solution, for an acid medium is necessary. Hydrochloric is the
best acid for the purpose, but other mineral acids or the organic acids may
be substituted for the hydrochloric. Excess of peptone delays the action, and
the removal of the products of digestion facilitates the process.

Action of Rennin. — Milk is curdled by the action of gastric juice, the
casein being first precipitated, and then dissolved. The curdling is due to a
special ferment of the gastric juice, rennin, and is not due to the action of the
free acid alone. The effect of rennin, which is obtained commercially
from the fourth stomach of the calf, has long been known, as it is used ex-
tensively to cause precipitation of casein in cheese manufacture. The fer-
ment rennin is active in a neutral solution as well as in acid.

Time Occupied in Gastric Digestion. — Under ordinary conditions,
from three to four hours may be taken as the average time occupied by the
digestion of a meal in the stomach. But many circumstances will modify
the rate of gastric digestion. The chief are: The nature of the food taken
and its quantity (the stomach should be fairly filled, not distended) ; the time
that has elapsed since the last meal, which should be at least enough for the
stomach to be quite clear of food; the amount of exercise previous and
subsequent to a meal (gentle exercise being favorable, overexertion injurious,
to digestion); the state of mind; and the bodily health.

Summary of Changes in the Food in Gastric Digestion. — Briefly
summarizing the action of gastric juice, the facts appear as follows: Gastric
juice has a specific digestive action on protein foods of all kinds, converting
them into the more soluble proteases and peptones. The action is due to an
enzyme, pepsin, acting in and with an acid, hydrochloric acid. Digestion
takes place best at the temperature of the body, is destroyed by high heat
and suspended by cold, o° C. Putrefaction is prevented by gastric juice.
Milk is first coagulated by a special enzyme, rennin, and then digested as any
other protein. Gastric juice dissolves soluble substances like salts, saccha-
rides, etc. Fats and carbohydrates are not digested by gastric juice; in fact,
fats tend to hinder the action.

Pancreatic Digestion in the Stomach. — Boldyroff has recently shown
that after the ingestion of fats or fatty foods in sufficient amounts, that the
secretion of gastric juice is inhibited and that the presence of the pancreatic
and intestinal secretions can be demonstrated in the stomach contents. Under
these conditions, the pancreatic juice is present in amounts sufficient to have
a considerable proteolytic and fat-splitting action.

MOVEMENTS OF THE STOMACH.

Attention has been called to the fact that the stomach is a muscular sac
capable of holding quite a large mass of food. During a full meal as much

354 FOOD AND DIGESTION

as one to two liters or more of semisolid food is packed away in the organ in
a comparatively short space of time. The gastric juice is secreted by the
mucous membrane which surrounds the surface of the food mass. The result
is that the secretion begins to soften and digest the food over its surface, thus
tending to liquefy and erode away layer after layer of the food mass. The
picture is made clearer if one remembers that the food mass is retained al-
most wholly in the fundus of the stomach. The pyloric portion of the stom-
ach is quite strongly muscular and quite definitely marked off by the strong
transverse band at its union with the fundus.

Acid Closure of the Cardiac and Pyloric Orifices. — The gastric
juice is assisted in accomplishing digestion by the movements of the stomach
itself. When digestion is not going on, the stomach is uniformly contracted,
its orifices not more firmly than the rest of its walls; but, if examined shortly
after the introduction of food, it is found closely encircling its contents, and
its orifices are firmly closed like sphincters. The cardiac orifice, every time
food is swallowed, opens to admit its passage to the stomach, and immedi-
ately closes again. This closure of the cardiac orifice is accomplished by a
local reflex. The stimulus is the acid secretion covering the mucous mem-
brane in the immediate neighborhood.

The pyloric orifice, during the taking of food and the first part of gastric
digestion, is also so completely closed that little of the contents escape.
This valve, too, is automatically regulated, as demonstrated by Cannon.
The acid gastric content that escapes into the duodenum starts to flow down

the duodenum. This sets up a local reflex stimulus
that closes the pylorus until the bile and pancreatic
juice have neutralized or made the chyle alkaline.
The Peristalsis of the Stomach.— The char-
acter of stomach movements has been admirably
determined by recent observers using the Rontgen-
ray method. Thus Cannon, working with cats,
has shown that in from five to ten minutes after a
meal slight rings or constrictions occur in the py-
loric antrum and travel slowly toward the pyloric

valve in the form of a peristaltic wave. Successive

FIG. 261. — Diagram to waves begin a little further back toward the fundus
Show the Movement of Food each time and follow over the pyloric antrum with
in the Pylorus at Times when . , , .. , . . ,

the Pyloric Valve is Closed. clock-like regularity, in the cat one wave m ten

seconds, which requires in each case about twenty

seconds for its completion. In man they are doubtless slower. These
peristalses continue during the whole period of digestion for as much as
seven or even more hours.

These peristaltic contractions aid the gastric juice in carrying away the
softened layers of food by propelling it into the pylorus. There it is thoroughly

THE PERISTALSIS OF THE STOMACH

355

mixed with the gastric juice, forming the chyme. Figure 261 gives an idea of
the movement of the food in the antrum. The peristaltic contractions carry
it forward, but if the valve does not open to permit passage to the duodenum,
then the pressure will force the chyme back through the center toward the
fundus. After several minutes, i.e., when the secretion of alkaline bile and
pancreatic juice into the duodenum is well established, the pyloric sphincter

11A.M.

12M.

2RM.

5RM.

FIG. 262. — Outlines of the Roentgen-ray Shadows of the Stomach Content as Digestion

Progresses. (Cannon.)

\rill relax more often to allow fluid food to pass to the duodenum, but when
the more solid particles come up against the valve the sphincter promptly
contracts and remains so for some time. Toward the completion of digestion
even solid undigested particles are carried on into the intestine.

The movements of the stomach are under extraneous nervous regulation.
Cannon found that the peristalses were promptly inhibited in cats by ex-
citement. Stimulation of the vagi leads to contractions of the stomach

356

FOOD AND DIGESTION

while the splanchnics bring about relaxation or dilatation. It is also
demontrated that afferent vagus impulses influence the contractions in
the stomach.

It seems probable that automatic peristaltic contraction is inherent in the
muscular coat of the stomach, and that the central nervous system is only
employed to regulate it by impulses passing down by the vagi or splanchnic
nerves.

Vomiting. — The expulsion of the contents of the stomach in vomiting
is preceded by a deep inspiration with closure of the glottis, followed im-
mediately afterward by strong contractions of the muscles of the abdomen,
diaphragm, and stomach. The diaphragm forms an unyielding surface
against which the stomach can be pressed. In this way as well as by

its own contraction the diaphragm is
fixed, to use a technical phrase. At the
same time the cardiac sphincter muscle is
relaxed, and the orifice which it naturally
guards is actively dilated. The pylorus
is closed and, the stomach itself also con-
tracting, the action of the abdominal
muscles produces strong compression
which expels the contents of the organ
through the esophagus, pharynx, and
mouth. Reversed peristalic action of the
esophagus probably increases the effect.
It has been frequently stated that the
stomach itself is quite passive during
vomiting, and that the expulsion of its

contents is effected solely by the pressure exerted upon it when the capacity
of the abdomen is diminished by the contraction of the diaphragm. It is
true that facts are wanting to demonstrate with certainty the contraction
of the stomach in vomiting; but cases of fistulous opening into the organ
appear to support the belief that it does take place; and the analogy of the
case of the stomach with that of the other hollow viscera, as the rectum
and bladder, may also be cited in confirmation.

Vomiting is a reflex act. It can be excited by irritation of the lining of
the stomach, which is perhaps the normal stimulus. It is excited by stimula-
tion or irritation of other parts of the alimentary tube; i.e., the pharynx, the
uvula, the intestine, etc. Vomiting may occur from stimulation of sensory
nerves from many organs, e.g., kidney, testicle, etc., or by impulses arising
in the organs of special sense, the eye, olfactory membrane, etc. The sensory
impulses are co-ordinated by a nerve center located in the medulla. The
center may also be stimulated by impressions from the cerebrum and cere-
bellum or by changes arising in the center itself, the so-called central vomiting

FIG. 263. — Horizontal Section of a
Small Fragment of the Mucous Mem-
brane, including one entire crypt of
Lieberkiihn and parts of several others.

DIGESTION IN THE INTESTINES

357

occurring in disease of those parts. The efferent impulses are carried by the
phrenics and other spinal nerves and by the vagus.

DIGESTION IN THE INTESTINES.

The food that enters the small intestine has already been subjected to two
digestive enzymes. The ptyalin of the saliva and the pepsin of the gastric
juice together with the mechanical processes involved have reduced the food
to a pulpy mass, the chyme. This peptonized/00d contains most of the total
quantity of food eaten, little having been absorbed, as we shall see later, but
much of the starch has been changed to soluble maltose and dextrose and
the protein to albumoses and peptones. The discharge from the stomach
through the pyloric valve to the duodenum has been going on through three

FIG. 264. FIG. 265.

FIG. 264. — Piece of Small Intestine (previously distended and hardened by alcohol),
Laid open to Show the Normal Position of the Valvulae Conniventes.

FIG. 265. — Section of the Pancreas of a Dog During Digestion, a, Alveoli lined with
cells, the outer zone of which is well stained with hematoxylin; d, intermediary duct lined
with squamous epithelium. X 350. (Klein and Noble Smith.)

or four hours on an average for each full meal. This stream of food passing
down the small intestine, slowly because of the valvulae conniventes, meets
a number of secretions which contain enzymes which act on each of the three
great food principles, proteins, fats, and carbohydrates. These secretions
are the pancreatic fluid, the succus entericus, and the bile.

The Pancreas. — The pancreas is situated within the curve formed
by the duodenum, and its main duct opens into that part of the small intes-
tine through a duct common to it and to the liver and about two and a half
inches from the pylorus.

The pancreas bears some resemblance in structure to the salivary glands.
Its capsule and septa, as well as the blood vessels and lymphatics, are simi-

358

FOOD AND DIGESTION

larly distributed. It is, however, looser, the lobes and lobules being less
compactly arranged.

Heidenhain has observed that the alveolar cells in the pancreas of a fast-
ing dog consist of two zones, an inner or central zone which is finely granular,
and which stains feebly, and a smaller parietal zone of finely striated proto-
plasm which stains easily. The nucleus is partly in one, partly in the other
zone. During secretion it is found that the outer zone increases in size, and
the central granular zone diminishes, as in the case of the salivary glands.
The pancreatic cell itself becomes smaller from the discharge of the secretion.

FIG. 266. — Section of the Pancreas of Armadillo, Showing the Two Kinds of Gland-
structure. (V. D. Harris.)

During a period of rest the granular zone again increases in size and the
outlines of the cells become full and indistinct. The granules, as in the sali-
vary cells, are the material from which, under certain conditions, the fer-
ments of the gland are developed, and which are therefore a zymogen. In
addition to the ordinary alveoli of the pancreas there are distributed irregu-
larly in the gland other collections of cells of a different character, the islands
of Langerhans. These cells are considerably smaller, their protoplasm is
more granular and less easily stained with hematoxylin, and their nuclei are
small and stain deeply. The collections of cells vary in size and shape.
The islands of Langerhans' cells are not concerned with the production of
the pancreatic juice. The special form of nerve terminations, called
Pacinian corpuscles, are often found in the pancreas.

THEC PANREATIC JUICE

359

The secretion of the pancreas has been obtained for purposes of experi-
ment from the lower animals and from man in at least one case. A
pancreatic fistula is established in the dog by opening the abdomen and
exposing the duct of the gland which is then made to communicate with
the exterior. In Pawlow's method a circular bit of the intestinal mucous
membrane around the mouth of the duct in the intestine is brought to

FIG. 267. — Duct with Laterals to the Alveoli. Silver method of Golgi (E. Muller). A
Duct with branches; m, between the cells. B, Laterals more strongly magnified.

the surface and stitched into the wound. The secretion is then easily col-
lected into a vessel suspended under the opening.

The Pancreatic Juice. — Pancreatic juice is colorless, transparent,
slightly viscid, and alkaline in reaction. It varies in specific gravity from
i .010 to i .030, according as it is obtained from a permanent fistula — then
more watery, or from a newly opened duct. The solids vary in a temporary
fistula from 80 to 100 parts per thousand, and in a permanent one from 16 to
50 per thousand. It is characterized by having three distinct and important

36°

FOOD AND DIGESTION

enzymes known as trypsin, amylopsin, and steapsin, whose actions are, respect-
ively, proteolytic, amylolytic, and lipolytic (fat-splitting). Maltase, which
inverts the disaccharides, is also present, and a rennin is found in the pan-
creatic juice.

CHEMICAL COMPOSITION OF PANCREATIC JUICE. (C. SCHMIDT.)

Recent
fistula.

Perma-
nent
fistula.

I
Water 900 76

080 A. C

Solids 1 99.24
Organic substances j 90 . 44
Ash 8 80

IQ-5S

12.71

6 84

Sodium carbonate 0-58
Sodium chloride .. .. . 7-35

3-31
2 . c;o

Calcium, magnesium, and sodium phosphates .... 0.53

0.08

An extract of pancreas made from the gland which has been removed
from an animal killed during digestion possesses the active properties of
pancreatic secretion. It is made by first dehydrating in absolute alcohol
the gland which has been cut up into small pieces. After the entire removal
of the alcohol the gland is pulverized and extracted in strong glycerin.
The amount of the ferment greatly increases if the gland be exposed to the
air for three or four hours before placing in alcohol; indeed, a glycerin
extract made from the gland immediately upon the removal from the body
often appears to contain none of the ferments. The conversion of zymogen
in the gland into the ferment takes place only after the gland stands a while.
Dilute acid assists or accelerates the conversion, and if a recent pancreas be
rubbed up with dilute acid before dehydration, a glycerin extract made
afterward, even though the gland may have been only recently removed from
the body, is very active.

Nervous Regulation of the Secretion of the Pancreas. — Fibers from
the vagus and from the splanchnics are distributed to the pancreas. In
Pawlow's laboratory it has been found that stimulation of these nerves leads
to the increased secretion of the pancreas. Popielski, in studying the effects
of dilute hydrochloric acid solution in the duodenum, which resulted in a
marked increase of pancreatic secretion, explained the phenomenon as a
local nerve reflex.

Doubt has been cast on the whole question of nervous control by the
recent discovery of the fact that acid (0.4 per cent, hydrochloric acid) in the
duodenum results in the production of a chemical substance, secretin, by the

ACTION OF THE ENZYMES OF PANCREATIC JUICE

36i

duodenal mucous membrane. This secretin is absorbed into the circulation
and acts specifically on the pancreas to produce increased activity of the pan-
creatic cells. Acid extracts of the duodenal mucous membrane produce the
same effects on the pancreas, in fact this is the current method of stimulating
the flow of pancreatic juice at the present time, the secretion being collected
from a tube introduced into the duct.

1.

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3.

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6.

7.

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s'

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\

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32

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\

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U

j /
/ /

\
\

\

•; /
; /
/

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16

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FIG. 268. — Three Curves Showing the Secretion of Pancreatic Juice upon a Diet (i)
of 600 c.c. of milk; (2) of 250 gm. of bread; (3) of 100 gm. of meat. The divisions along
the abscissae represent hours after the beginning of the meal; the figures along the ordinates
represent the quantity of the secretion in cubic centimeters. (Walter.)

Under the normal stimulus of food, the flow of pancreatic juice is greatly
increased. The increase continues to a maximum in from two to three hours,
after which it gradually decreases through the period of digestion. Pawlow
has found a certain amount of adaptation not only of the quantity, but of
the enzyme composition of the pancreatic secretion to the kind and character
of the food (in dogs).

Action of the Enzymes of Pancreatic Juice. — The secretion of the

362 FOOD AND DIGESTION

pancreas accomplishes its digestive action by means of the enzymes given
above, viz., trypsin, amylopsin, steapsin, and maltase.

Trypsin. — Trypsin is a proteolytic enzyme. Strange to say, it does not
exist in the fresh pancreatic juice as such, but makes its appearance only
when there is an admixture with the succus entericus, the secretion of the
mucous membrane of the intestine. The succus entericus contains an ac-
tivating enzyme, enterokinase, which converts the inactive and stable trypsin-
ogen of the pancreatic juice into the active but less stable trypsin. This fact
is another of the wonderful series of contributions to the exact knowledge
of the subject of digestion made from Pawiow's laboratories.

Trypsin, like pepsin-hydrochloric acid, converts proteins into proteoses
and peptones. The change, however, does not stop here; the hydrolysis
with trypsin goes much further. While simple amino-acids, with the excep-
tion of traces of tyrosine, are not found in gastric digestions, these are rapidly
split off in the tryptic cleavage. Thus in tryptic digestion are formed : tyro-
sine, leucine, cystine, amino-valerianic acid, asparaginic acid, glutaminic
acid, histidine, lysine, and arginine. A portion of the protein, however,
is not completely broken down, the residue consisting of polypeptids
containing proline and phenyl-alanine combined with small amounts of
alanine, leucine, aspartic acid, and glutaminic acid. Glycocoll, when pres-
ent in the protein digested, is also combined in the resistant polypeptids.
Crystals of leucine and of tyrosine, especially, can be found in tryptic diges-
tion mixtures. The products formed from protein in tryptic digestion may
be given in the following graphic scheme:

Protein

I

Proteoses
Peptones

Polypeptids Amino-acids

Combinations of proline, phenyl- Tyrosine, tryptophane, cystine,

alanine and glycocoll, with rela- alanine, amino-valerianic acid,

tively small amounts of alanine, leucine, "aspartic acid, glutam-

leucine, asparaginic acid, and inic acid, histidine, lysine, argi-

glutaminic acid. nine.

>••*< The ferment trypsin acts best in an akaline medium, but will act also
in a neutral medium, or in the presence of a very small amount of combined
acid; it will not work in the presence of free acid. It therefore differs from
pepsin in being able to act without the aid of any other substance than water.
In the process of tryptic digestion, protein matter does not swell up at first,
but seems to be corroded at once.

TRYPSIN 363

Amylopsin.— Starch is converted by amylopsin into maltose by hydro-
lytic action similar to that of ptyalin, erythro-dextrin and one or more
achroo-dextrins being the intermediate products. The amylolytic enzyme
of the pancreatic juice, which cannot b2 distinguished from ptyalin, is called
amylopsin. The maltose thus formed is converted to dextrose by the maltase,
in which form it is ultimately absorbed.

Pancreatic juice, according to certain observers, possesses the property
of curdling milk. It contains a special ferment, rennin, for that purpose.
The ferment is distinct from trypsin, and will act in the presence of an acid
(W. Roberts). The milk-curdling ferment of the pancreas is, in some pan-
creatic extracts, said to be quite powerful, insomuch that i c.c. of a brine ex-
tract will coagulate 50 c.c. of milk in a minute or two.

Steapsin orLipase. — Oils and fats are emulsified and saponified by the pan-
creatic secretion. The terms emulsification and saponification may need a
little explanation. The former is used to signify an important mechanical
change in oils or fats, whereby they are made into an emulsion or, in other
words, are minutely subdivided into small particles. If a small drop of an
emulsion be looked at under the microscope it will be seen to be made up of
an immense number of minute rounded particles of oil or fat of varying
sizes. The more complete the emulsion the smaller are these particles. An
emulsion is formed at once if oil or fat, which when old is slightly acid from
the presence of free fatty acid, is mixed with an alkaline solution. Saponifi
cation signifies a distinct chemical change in the composition of oils and fats.
An oil or fat being made up chemically of glycerin, a triatomic alcohol, and
one or more fatty-acid radicles, when an alkali (potassium hydrate) is added
to it and heat is applied, two changes take place: first, the oil or fat is split up
into glycerin and its corresponding fatty acid; second, the fatty acid combines
with the alkali to form a soap which is chemically known as stearate, oleate,
or palmitate of potassium. Saponification thus means a chemical splitting
up of oils or fats into new compounds, and emulsification means merely a
mechanical splitting up into minute particles. The pancreatic juice has
been for many years credited with the possession of a special ferment,
which was called by Claude Bernard steapsin, and which is a lipase or
fat-splitting ferment. This ferment has not been isolated, but its pres-
ence may be demonstrated by adding portions of the fresh pancreas
to butter or other fat and maintaining the proper temperature. Its
action is made manifest by the liberation of butyric acid, which smells
like rancid butter.

The generally accepted theory is that only a small portion of the fat which
is eaten is thus changed into soap, and that the function of the saponified fat
is to assist in the emulsification of the major part, a process which is favorably
influenced by the bile. The proper emulsification of fat is a necessary pre-
liminary to its absorption, for when in disease the entrance of the pancreatic

364 FOOD AND DIGESTION

juice and of the bile to the intestine is interfered with, the feces contain a
great excess of fat.

Some recent experiments, however, tend to prove that the entire fat of the
food is changed in the intestine into fatty acids and glycerin; that the fatty
acids are entirely, or in part, changed to soaps ; and that these soaps, or mixture
of soaps and free fatty acids, are absorbed in solution. The chief facts favor-
ing this view are that: (i) The action of steapsin is sufficiently rapid to allow
the saponification of a full fatty meal within the ordinary period of digestion;
(2) histological examination has never shown that fat particles can pass into
a columnar cell, and none have ever been found in the broad striated border
of the cell; (3) the fat globules found in columnar cells after a fatty meal grow
steadily larger as the period of absorption progresses, indicating that they are
deposited from solution ; (4) the fatty acids are easily soluble in bile solutions,
and the solubility of the soaps is greatly increased by the presence of bile.
The fat constituents, according to this theory, are recombined in the columnar
cells to form neutral fats.

Conditions which Influence the Action of the Pancreatic Enzymes.

— The various pancreatic enzymes are influenced by heat, by the presence of
an excess of digestion products, etc., in the same way as ptyalin and pepsin.
Pancreatic enzymes act in a neutral, but best in an alkaline solution. The
trypsin, strange to say, is quickly destroyed by the alkaline solution (Bayliss
and Starling). The pancreatic juice offers the special case of a secretion of

FIG. 269. — The Liver from Below and Behind. L. S., Spigelian lobe; L. C., caudate
lobe;L. Q., quadrate lobe; R.L., right lobe;L.L., left lobe; g. bl., gall-bladder; v.c.i., inferior
vena cava; «./., umbilical fissure; /. d. v., fissure of the ductus venosus; p, portal fissure with
portal vein, hepatic artery, and bile-duct. (Wesley, from a His model.)

proenzyme which is stable in alkaline solution until acted on by enterokinase,
and the amount of kinase present will, therefore, markedly influence the
amount of digestion of protein per unit of time.

The Secretions of the Liver.— The liver, the largest gland in the body,
situated in the abdomen on the right side chiefly, is an extremely vascular
organ, and receives its supply of blood from two distant sources, viz., from

STRUCTURE OF THE LIVER

365

the portal vein and from the hepatic artery, while the blood is returned from
it into the vena cava inferior by the hepatic veins. Its secretion, the bile,
is conveyed from it by the hepatic duct, either directly into the intestine or,
when digestion is not going on, into the cystic duct, and thence into the gall-

FIG. 270. — Portion of a Lobule of Liver, a, Bile capillaries between liver cells, the network
in which is well seen; b, blood capillaries. X 350. (Klein and Noble Smith.)

bladder, where it accumulates until required. The portal vein, hepatic
artery, and hepatic duct branch together throughout the liver, while the
hepatic veins and their tributaries run by themselves. The interstices of the
vessels are filled by the liver cells.

FIG. 271. — Hepatic Cells and Bile Capillaries, from the Liver of a Child Three Months
Old. Both figures represent fragments of a section carried through the periphery of a
lobule. The red corpuscles of the blood are recognized by their circular contour; Tp
corresponds to an interlobular vein in immediate proximity with which are the epithelial
cells of the biliary ducts. (E. Hering.)

Structure of the Liver. — The liver is made up of small roundish or
oval portions called lobules, each of which is about ^V °f an mch (about
i mm.) in diameter, and includes the minute hepatic artery and hepatic
duct. The hepatic cells, which form the glandular or secreting part of the

;66

FOOD AND DIGESTION

liver, are of spheroidal form, somewhat polygonal from mutual pressure,
about 25 to sop in diameter, and possess one, sometimes two nuclei. The
cell substance contains a variable amount of glycogen and often some fatty
globules and possibly some granules of bile pigment.

The bile capillaries commence between the hepatic cells, and are bounded
by a delicate membranous wall of their own. They appear to be always
bounded by hepatic cells on all sides, and are thus separated from the nearest
blood capillary by at least the breadth of one cell, figures 271 and 272.

p x

FIG. 272. — Section of Liver. X 80. P, Portal vein; H, hepatic artery; B, bile-duct.

(Hendrickson.)

The gall-bladder, g. bl, figure 269, is a pyriform sac attached to the under
surface of the liver, and supported also by the peritoneum. The larger end,
or fundus, projects beyond the front margin of the liver, wrhile the smaller
end contracts into the cystic duct. It is a muscular walled reservoir covered
with a serous epithelium and lined by mucous membrane. The function
of the gall-bladder is to retain the bile during the interval of digestion.

The Bile. — The bile is a somewhat viscid fluid, of a yellow, reddish-
yellow, or green color, a strongly bitter taste, and, when fresh, with a scarcely

THE BILE 367

perceptible odor; it has a neutral or slightly alkaline reaction, and its specific
gravity is about 1.020. Its color and consistency vary much, quite inde-
pendent of disease; but, as a rule, bile becomes gradually more deeply colored
and thicker as it advances along its ducts, or when it remains long in the gall-
bladder where it becomes more viscid and ropy, darker, and more bitter.
This is on account of its greater degree of concentration, from resorption of
its water, and also from being mixed with mucus, lipoids, and phosphatid
proteins secreted by the lining membrane of the gall-bladder.

CHEMICAL COMPOSITION OF HUMAN BILE. (FRERICHS.)

Water 859.2

Solids — Bile salts 91 . 5

Fat 9.2

Cholesterol 2.6

Proteins and coloring matters 29.8

Salts 7.7

140.

Bile salts can be obtained as colorless, exceedingly deliquescent crystals,
soluble in wTater, alcohol, and alkaline solutions, giving to the watery solution
the taste and general characters of bile. They consist of sodium salts of gly-
cocholic and taurocholic acids; the formula of the former being C26H42NaNO6,
and of the latter C26H44NaNO7S.

The bile acids are easily decomposed by the action of dilute acids or alkalies
thus:

C26H43N06 + H20=C2H5N02+C24H4005
Glycocholic acid. Glycocoll. Cholic acid,
and C26H45NO7S + H2O =C2H7NO3S +C24H40O5
Taurocholic acid. Taurin. Cholic acid.

Glycocoll is amido-acetic acid, i.e., acetic acid C2H4O2, with one of the
atoms of H replaced by the radical amidogen NH2C2H,(NH,) O2, C2H5NO2.
Taurin likewise is amino-ethyl-sulphonic acid. Accordingly, it has the for-
mula CH2NH2CH2SO2OH. The proportion of these two salts in the bile of
different animals varies, e.g., in the ox bile the glycholate is in great excess,
whereas the bile of the dog, cat, bear, and other carnivora contains taurocho-
late alone. In human bile the glycocholate is in excess (4 . 8 to 1.5).

The yellow coloring matter of the bile of man and the carnivora is termed
bilirubin, C16H18N2O3, is crystallizable and insoluble in water, and soluble in
chloroform or carbon disulphide. A green coloring matter, biliverdin,
C16H18N2O4, which always exists in large amount in the bile of herbivora, is
formed from bilirubin on exposure to the air or by subjecting the bile to any

368

FOOD AND DIGESTION

FIG. 273. — Crystalline Scales of
Cholesterol.

other oxidizing agency, as by adding nitric acid. Biliverdin is soluble in
alcohol, glacial acetic acid, and strong sulphuric acid, but insoluble in water,
in chloroform, and ether. It is usually amorphous, but may sometimes
crystallize in green rhombic plates.

There is a close relationship between the coloring matters of the blood
and of the bile and, it may be added, between these and that of the urine,
urobilin, and of the feces, stercobilin. It is probable they are, all of them,

varieties of the same pigment, or derived from
the same source. Cholesterol C27H45OH,
and lecithin, C43H84NPO8 are constant con-
stituents of bile. Iron is found among the
salts of the ash.

The Role of Bile in Intestinal Digestion.
— Though it is not a true digestive fluid, in
that it has no ferment and digests nothing
itself, yet it must be regarded as an important
aid to digestion for the following reasons: (a)
Bile assists in emulsifying the fats of the food,
and thus renders them capable of passing into
the lacteals by absorption. For it has ap-
peared in some experiments in which the common bile-duct was tied that,
although the process of digestion in the stomach was unaffected, chyle
was no longer well formed. The contents of the lacteals consisted of clear,
colorless fluid, instead of being opaque and white, as they ordinarily are
after feeding. It is, however, the combined action of the bile with the
pancreatic juice to which the emulsification is due rather than to that of the
bile alone. The bile itself has a very feeble emulsifying power. If the
theory be accepted that fats are absorbed as fatty acids and soaps, in
solution, the action of the bile becomes very important because solutions of
bile salts have the power of dissolving the fatty acids. The moistening of
the mucous membrane of the intestines with bile, for this very reason,
facilitates absorption of fatty matters through it.

(b) The bile, like the gastric fluid, has a certain but not very considerable
antiseptic power, and may serve to prevent the decomposition of food during
the time of its sojourn in the intestines. Experiments show that the contents
of the intestines are much more fetid after the common bile-duct has been
tied than at other times. Moreover, it is found that the mixture of bile with
a fermenting fluid stops the process of fermentation.

Bile is also an excretive fluid carrying waste products thrown off by the
liver. The liver during fetal life is proportionately larger than it is after
birth, and the secretion of bile is active, although there is no food in the in-
testinal canal upon which it can exercise any digestive property. At birth,
the intestinal canal contains concentrated bile, mixed with intestinal secretion

MODE OF SECRETION AND DISCHARGE OF BILE

369

and this constitutes the meconium, or feces of the fetus. In the fetus, there-
fore, the main purpose of the secretion of bile must be directly excretive.
Probably all the residue of the bile secreted in fetal life is incorporated in
the meconium, and with it discharged.

Mode of Secretion and Discharge of Bile. — In considering the flow
of bile into the intestine, two factors are involved. These are the emptying
of the gall-bladder and an increased secretion by the hepatic cells.

The secretion oj bile can be studied by tying the common bile-duct of
a dog and then making a fistulous opening between the skin and the gall-
bladder; all the bile secreted is then discharged at the surface. In such
animals it has been found that the secretion of bile is continuous. With
the great discharge of bile into the intestine that occurs during the third
hour after a meal, there is an increased secretion of this fluid. This in-
creased secretion of bile can also be evoked by the introduction of o . 4 per
cent, hydrochloric acid into the duodenum, and occurs even after the di-
vision of all connections between the liver and the central nervous system.
There is evidence that the increased secretion of bile is brought about
through a mechanism identical with that for the secretion of pancreatic
juice, and that in each case one and the same substance — secretin — is
formed by the action of the cells of the mucous membrane and absorbed
into the blood stream and excites both the liver and pancreas to increased
activity.

FIG. 274. — Transverse Section through Four Crypts of Lieberkiihn, from the Large
Intestine of the Pig. They are lined by columnar epithelial cells, the nuclei being placed
in the outer part of the cells. The divisions between the cells are seen as lines radiating
from L, the lumen of the crypt; G, epithelial cells, which have become transformed into
goblet cells. X 350. (Klein and Noble Smith.)

The emptying of the gall-bladder has been investigated on dogs with a
Pawlow fistula. In this operation, the orifice of the duct, with the mucous
membrane around it, is cut out of the wall of the intestine and the latter
again closed. The excised portion with the opening of the bile duct is
stitched into the abdominal wound. The natural orifice of the duct is thus
made to open externally. The discharge of bile is found to begin almost im-
mediately after taking food; it attains its maximum during tbe third hour,
24

37°

FOOD AND DIGESTION

coincident with the pancreatic flow, and then rapidly diminishes. Dale has
shown that the muscular fibers of the wall of the gall-bladder are supplied
by nerves from both the vagus and the sympathetic. The former are motor,
while the latter convey inhibitory impulses. The contractions of the gall-
bladder are provoked reflexly on the passage of the acid chyme into the
intestine. The gall-bladder acts as a reservoir for the bile during the intervals

when digestion is not in progress. The
mechanism by which the bile passes into
the gall-bladder is simple. The orifice
through which the common bile-duct com-
municates with the duodenum is narrower
than the duct, and appears to be closed,
except wrhen there is sufficient pressure
behind to force the bile through it. The
pressure exercised upon the bile secreted
during the intervals between periods of
digestion appears insufficient to overcome
the force of the sphincter by which the orifice
of the duct is closed; and the bile in the
common duct traverses the cystic duct and
so passes into the gall-bladder. It is proba-
bly aided in this retrograde course by the
peristaltic action of the ducts.

The bile is discharged from the gall-
bladder and enters the duodenum on the
introduction of food into the small intestine.
It is pressed on by the contraction of the
coats of the gall-bladder and of the com-
mon bile-duct.

When the discharge of the bile into the
intestine is prevented by an obstruction of
some kind, as by a gall-stone blocking the

hepatic duct, it is reabsorbed in great excess into the blood, and, circu-
lating with it, gives rise to the well-known phenomena of jaundice. This
is explained by the fact that the pressure of secretion in the ducts,
although normally very low, not exceeding 15 millimeters of mercury
in the dog, is still higher than that of the portal veins. If the pressure
exceeds 15 mm. the secretion continues to be formed, but passes into the
blood vessels through the lymphatics.

The Intestinal Secretion, or Succus Entericus. — It is impossible to
isolate the secretion of the glands of Brunner or of the glands of Lieberkiihn,
but the total secretion of the intestinal mucosa can be secured by isolating a
loop of intestine by the operation known as the Thiry fistula. A few drops

FIG. 275.— Longitudinal Sec-
tion of Fundus of Crypt of Lieber-
kiihn. b, Goblet cell showing
mitosis; e, epithelial cell; k, cell of
Paneth; /, leukocyte in epithelium;
m, mitosis in epithelial cell. Sur-
rounding the crypt is seen the
stroma of the mucous membrane.
X 530. (Kolliker.)

DIGESTIVE CHANGES IN THE SMALL INTESTINE 371

of secretion, the succus entericus, can be obtained by this means. Intestinal
juice is a yellowish alkaline fluid with a specific gravity of i .on and contains
about 2 . 5 per cent, of solid matters.

Intestinal juice has only slight digestive action. It contains a weak pro-
teolytic enzyme and a weak amylolytic enzyme. Maltase is also present.
But the chief and most profound importance is given to the intestinal juice
by the discovery of the activating enzyme, enter okinase. This specific
activating enzyme for the trypsinogen of the pancreatic juice places the in-
testinal secretion in the rank of necessary secretion for efficient digestion.
Enterokinase can be prepared by extracting the superficial scrapings of
the intestinal mucous coat. The duodenal region is richest in enterokinase,
but the secretion of the lower intestinal lengths also contains the enzyme.

Extracts of the mucosa of the intestine have been found to contain an-
other substance which has the specific action of splitting peptones into
simpler polypeptids and amino-acids. This substance has been called
erepsin.

There are, therefore, three important new substances in the succus en-
tericus (or in the extract of the glands), secretin (page 360), erepsin, and
enterokinase, in addition to the proteolytic and diastatic enzymes.

Summary of the Digestive Changes in the Small Intestine. — The
thin chyme, which, during the whole period of gastric digestion, is being con-
stantly squeezed or strained through the pyloric orifice into the duodenum,
consists of albuminous matter that is breaking down, dissolving and half
dissolved; of fatty matter that is mechanically separated and melted, but
not dissolved at all; of starch in various stages of the process of con-
version into sugar, and as it becomes sugar dissolving in the fluids
with which it is mixed; and with these are mingled gastric juice and
fluid that has been swallowed, together with such portions of the food as
are not digestible.

The chyme in the duodenum is subjected to the influence of the bile and
pancreatic juice and also to that of the succus entericus. All these secretions
have a more or less alkaline reaction, and at once neutralize the acid of the
gastric chyme.

The special digestive changes in the small intestine are: (i) The fats are
changed by the bile and pancreatic juice in two ways: (a) They are
chemically decomposed by the alkaline secretions, and a soap and glycerin
are the result. (6) They are emulsified; i.e., their particles are minutely
subdivided and diffused, so that the mixture assumes the condition of a
milky fluid or emulsion. (2) The albuminous substances which have been
partly dissolved in the stomach are subjected chiefly to the action of the
pancreatic juice. The pepsin is rendered inert by the bile. The pancreatic
trypsin proceeds with the further conversion of the proteoses into peptones,
and, with the erepsin, of the peptones into leucin, tyrosin, and the other

372 FOOD AND DIGESTION

amino-acids. (3) The starchy portions of the food are now acted on briskly
by the pancreatic juice and the succus entericus, and are changed to maltose
and dextrose. (4) Salines are usually in a state of solution before they
reach the intestine.

Digestive Changes in the Large Intestine. — The changes which take
place in the chyme in the large intestine are probably only the continuation
of the same changes that occur in the course of the food's passage through
the upper part of the intestinal canal. No special enzymes have been clearly
shown for the mucous membrane of the large intestine. The enzymes of the
small intestine may continue their action here, being hindered only by the
acid developed from fermentation processes.

Action of Micro-organisms in the Intestines. — Certain changes take
place in the intestinal contents independent of, or at any rate supplemental
to, the action of the digestive ferments. These changes are brought about

,

00

V „

7

FIG. 276. — Types of Micro-organisms, a, Micrococci arranged singly; in twos,
diplococci — if all the micrococci at a were grouped together, they would be called staphylo-
cocci — and in fours, sarcinae; b, micrococci in chains, streptococci; c, and d, bacilli of
various kinds, one is represented with flagellum; e, various forms of spirilla;/, spores, either
free or in bacilli.

by the action of micro-organisms or bacteria. We have indicated elsewhere
that the digestive ferments are examples of unorganized ferments, so bacteria
are examples of organized ferments. Organized ferments, of which the yeast
plant may be taken as a typical example, consist of unicellular vegetable organ-
isms, which when introduced into a suitable medium grow with remarkable
rapidity. By their growth they produce new substances from those supplied to
them as food. Thus, for example, when the yeast cell is introduced into a solu-
tion of grape-sugar, it grows, and alcohol and carbon dioxide are produced.
The alcohol and carbon dioxide arise from the formation by the cell of some
chemical substances which are allied to the unorganized ferments and which
greatly increase in amount with the multiplication of the original cell. In
all such fermentative processes organisms analogous to the yeast cell are
present, and it is not strange that if the ferment cell is introduced into a
suitable medium it may by its rapid growth convert an unlimited amount of

ACTION OF MICRO-ORGANISMS IN THE INTESTINES 373

one substance into another. Speaking generally, a special variety of cell
is concerned with each ferment action, thus one variety has to do with
alcoholic, another with lactic, and another with acetous fermentation.

A considerable number of species of bacteria exist in the body during life
chiefly in connection with the mucous membranes, particularly of the digest-
ive tract. Many forms of bacteria have been isolated from the mouth, a few
varieties from the stomach, and a very large number from the intestines. It
is only in the last-named locality that their multiplication has much effect
from a physiological point of view. The normal (hydrochloric acid) acidity
of the stomach usually destroys all the micro-organisms taken in with the
food, but when the amount of this acid is deficient (and sometimes even
when it is normal) some of the spores may escape. On reaching the small
intestine these spores begin to develop in its alkaline medium, and may in-
crease to such an extent as to stop all intestinal digestion; the point where
this occurs varies from day to day. The large intestine always swarms
with micro-organisms, though they do not readily pass the ileocecal valve
into the small intestine. Some species of bacteria found in the intestine are
anaerobic; i.e., they do not develop in the presence of free oxygen.

The changes induced in the intestine by the activity of micro-organisms
are of two kinds, fermentation and putrefaction; the former of these results
in the breaking-down of carbohydrate matter, and the latter in the disintegra-
tion of protein matter. The process of fermentation is the less complex
and probably occurs normally in the small intestine. The lactic acid fermen-
tation is the most important, though the butyric acid fermentation is next;
under the influence of these bacteria the carbohydrates are butyrates
broken down into lactic and butyric acids, and perhaps into acetic
acid also. Carbonic acid gas may be formed at the same time and
cause flatulence. Cellulose and other insoluble carbohydrates are de-
composed, with the formation of marsh gas and hydrogen, which escape
by the rectum.

In putrefaction the process is somewhat similar to that in tryptic digestion,
the proteins being broken down into peptones, leucin, tyrosin, and a long row
of similar substances. It also results in the production of various gases, such
as carbon dioxide, sulphureted hydrogen, ammonia, hydrogen, and methane
(marsh gas), and of a high percentage of the volatile fatty acids, valerianic
and butyric. Of the aromatic substances the most important are some
phenol derivatives and indol and skatol, though their toxicity has been
greatly overestimated. Indol and skatol undergo oxidation in the liver after
absorption, forming indoxyl and skatoxyl. They are in part carried off in
the feces, but when the bowel is obstructed they are absorbed and eventually
appear in the urine, indoxyl and skatoxyl forming, respectively, indoxyl- and
skatoxyl-sulphuric acids and their salts. Tyrosin is broken down into para-
oxy-phenol-propionic acid, paracresol, and phenol; para-oxy-phenol- acetic

374

FOOD AND DIGESTION

acid is also formed. The phenols, after absorption, are in part con-
jugated with glycuronic acid which is formed by the incomplete oxida-
tion of dextrose and are eliminated into the urine. Experiments have
been performed to determine whether or not the intestinal bacteria are
necessary to normal digestion. The weight of evidence is in favor of the
view that they are not.

The Feces. — The contents of the large intestine, as they proceed toward
the rectum, become more and more solid, lose more liquid and nutrient
parts, and gradually acquire the odor and consistency characteristic of
feces. After a sojourn of uncertain duration in the sigmoid flexure of the
colon, or in the rectum, they are finally expelled by the act of defecation.
The average quantity of solid matter evacuated by the human adult in twenty-
four hours is about 200 to 250 grams, but the amount and character vary
exceedingly according to the food eaten. Vegetable foods contain much
indigestible matter, while meats and meat diets leave very little unabsorbed
material to be expelled in the feces.

TABLE OF COMPOSITION OF FECES.

The amount of water varies considerably, from 68 to 82 per cent, and
upward. The following table gives about an average composition:

Water ................................. ................ 733 .00

Solids, comprising:

a. Insoluble residues of the food, uncooked starch, cellulose,

woody fibers, cartilage, horny matter, mucin, seldom
muscular fibers and other proteins, fat, and cholesterin .

b. Certain substances resulting from decomposition of foods,

indol, skatol, fatty and other acids; calcium and mag-
nesium soaps ....................................

c. Special excretion, — excretin, excretoleic acid (Marcet),

and stercorin (Austin Flint) .......................

d. Salts — chiefly phosphate of magnesium and phosphate p 267.00

of calcium, with small quantities of iron, soda, lime, and
silica ............................................

e. Insoluble substances accidentally introduced with the

food .............................................

f. Mucus, epithelium, altered coloring matter of bile, fatty

acids, etc ........................................

g. Varying quantities of other constituents of bile and se-

cretions .......................................... J

1000 .00

Intestinal Gases. — Under ordinary circumstances, the alimentary
canal contains a considerable quantity of gases. The presence of gas in the
intestines is so constant and the amount in health so uniform that there can
be no doubt that its existence is a normal condition.

MOVEMENTS OF THE INTESTINES

375

The gas contained in the stomach and bowels is from air swallowed with
either food or saliva, gases developed by the decomposition of foods, or of the
secretions and excretions thrown into the intestines. The decomposition of

^,000000

FIG. 277. — Diagram Illustrating the Segmentation of the Food in the Small Intestine.

(Cannon.)

foods is the chief source. The following table, compiled by Brinton, is a col-
lection of analyses that have been made and is chiefly valuable as showing the
kinds of gases present.

GASES FOUND IN THE ALIMENTARY CANAL.

Composition by volume

Whence obtained

Oxygen < Nitrog.

Carbon
dioxide

Hydrogen Carbure
hydroge

t. Sulphuret.
n hydrogen

Stomach

i i

11 i i:

I
|

14

30
12

51
43
40

I
4 !

|

Small intestines

38 !

8 13
6 8
ii

1

1 Trace.

°- 5

Cecum

6

Colon
Rectum . .

35
46

.... 22

Expelled per anum

The amounts of the gases vary with the diet.

An analysis of the intestinal gases by Ruge in man is as follows:

Gases

Milk diet i Meat diet Vegetable diet

Carbon dioxide
Hydrogen

9 to i 6 1 8 to 13

A. T. to tj 4. ' O 7 to "?

21 to 34

I ^ to A.

Carbureted hydrogen.

O . Q I 2 6 to 3 7

A A tO <<

Nitrogen

36 to 38 ! 45 to 64

10 to 19

MOVEMENTS OF THE INTESTINES.

The muscular activity of the intestines accomplishes two important func-
tions; i.e., it thoroughly mixes the digesting food and secretions and it carries

FOOD AND DIGESTION

the content along the tract. Intestinal peristalses have been described for a
long time. These peristalses begin as contractions of the circular muscles,
producing ring-like constrictions that are propagated as waves over the intes-
tine from above downward. Such constrictions carry the intestinal contents
forward. The longitudinal muscles by their contraction produce pendular
motion of the intestine.

A most instructive contribution to the knowledge of intestinal movements
has been made by Cannon. He fed cats food mixed with 10 to 33 per cent, of
subnitrate of bismuth, and observed the shadows of the food when subjected
to the Roentgen rays. A length of food in the intestine was seen to be con-
stricted into a series of oval masses, figure 277. Each of these oval masses is
quickly constricted in the middle, and neighboring halves of adjacent masses
flow together. After this process is repeated a number of times a peristaltic
wave of the type previously described sweeps the whole content of the loop
down the intestinal tract.

Peristaltic contractions of the same general type as in the small intestine
also occur in the large intestine. Cannon has noted a variation here also.
The ascending and the transverse loops of the colon exhibit rhythmic anti-
peristalses which keep the content moving against the ileocecal valve for
several minutes at a time. From time to time strong general contractions,
in the cecum and ascending colon, force some of the food onward. When
material has accumulated in the transverse colon, deep successive tonic con-
strictions appear and force its contents into the descending colon. When
sufficient material has accumulated here, it is evacuated by strong peristalses
combined with compression by the contracting abdominal muscles.

Reverse peristalsis, antiperistalsis, does not commonly occur in the small
intestine, but large nutrient enemata introduced into the rectum and colon
may be forced by antiperistaltic waves in the large intestine to and through
the ileocecal valve into the small intestine. Here they are reacted on in the
same way as food which has been introduced in the normal way.

Influence of the Nervous System on Intestinal Peristalsis. — As in
the case of the esophagus and stomach, the peristaltic movements of the in-
testines may be directly set up in the muscular fibers by the presence of food
acting as the stimulus. Few or no movements occur when the intestines are
empty. The intestines are connected with the central nervous system both
by the vagi and by the splanchnic nerves, as well as by other branches of the
sympathetic which come to them from the celiac and other abdominal plex-
uses. The relations of these nerves respectively to the movements of the
intestine and the secretions are probably the same as in the case of the stom-
ach already considered.

The vagus fibers are described as the motor fibers for the intestine, while
the sympathetic are said to be at least in part inhibitory. Various states of
the central nervous system, such as fear, anger, etc., inhibit the intestinal

SALIVA AND SALIVARY DIGESTION 377

movements. The intestine carries out peristalses when isolated from the
body so that the central connections do not originate, but are only regulative.
The intestinal movements are essentially automatic, depending on the rhyth-
mic property of the muscle itself, but co-ordinated by the complex local
nervous mechanism.

The innervation of the large intestine is also double in character and
the relations are doubtless the same as in the small intestine.

Defecation. — The emptying of the rectum is essentially an involun-
tary act which has acquired a certain amount of voluntary regulation. The
act is accomplished wholly reflexly in dogs with isolated lumbar cord, in fact
has been observed when the lumbar spinal cord was removed. In the latter
case defecation occurs by automatic peristalsis of the rectum, while in the
former cases reflexes through the lumbar cord carry out the act. The
stimulus of the feces against the rectum and the internal sphincter initiate
the movement.

Normally in man the rectal stimulus gives rise to the consciousness of
the desire to defecate and to the initiation of efferent nerve impulses that may
increase the contraction of the external sphincter and inhibit the act tempo-
rarily. During defecation, however, the voluntary effort leads to relaxation
of the external sphincter, and the normal peristalsis of the rectum is sup-
ported by contractions of the abdominal musculature so as greatly to increase
the abdominal pressure, thus aiding the involuntary reflex.

LABORATORY EXPERIMENTS IN DIGESTION.
I. SALIVA AND SALIVARY DIGESTION.

1. Reflex Salivary Secretion. — Saliva, which is the mixed secretion
of the salivary and buccal glands, is produced more or less intermittently.
Examine, taste, or smell appetizing food, for example, an apple, the salivary
glands begin to discharge secretion which is poured into the mouth more
rapidly than under ordinary conditions. This increased activity is a reflex
secretion. It is brought about by the stimulation of sensory structures which
lead to afferent nerve impulses reacting on nerve centers in the medulla to
cause secretory nerve impulses to the glands. The stimulating effect of food
in the mouth causes the most rapid reflex secretion, which may last through
several minutes or even hours. Especially stimulating substances are,
beside food, such substances as tartaric acid, lemon juice, ether, alcohol, etc.,
in fact, anything that produces strong local irritation will lead to reflex
secretion.

2. The Secretory Nerves of the Salivary Glands of the Dog.— The
nervous mechanism for the salivary gland is well known, and the anatomical
relations are such as to make this gland a favorable one for studying the nerv-
ous mechanism of glands in general.

378 FOOD AND DIGESTION

Anesthetize a dog and bind it to a suitable holder. Expose the nerves to
the submaxillary gland as follows: cut through the skin of the lower jaw
along the inner border for about 3 inches. Isolate and double ligate the
jugular vein and any other veins in the field except the ones coming from the
submaxillary gland. Isolate and cut the digastric muscle, also the mylo-
hyoid, using pains not to injure the duct of the gland or its arteries. When
the muscles are laid back, the artery and accompanying sympathetic nerve
branches, the hypoglossal and the lingual nerves, the submaxillary duct and
the submaxillary gland, will all be exposed. Isolate and introduce a very
fine glass cannula into the submaxillary duct. A small nerve filament
branches from the lingual nerve and runs to the hilus of the gland, the chorda
tympani. Carefully expose the chorda, place a silk ligature under it for con-
venience in handling. Also expose the sympathetic filaments with the
artery.

Stimulate the chorda tympani with a mild induction current for a few-
minutes at a time at intervals, and note that the secretion which is absent or
forming slowly before stimulation now gathers quickly and leaves the end
of the cannula in a series of drops. Collect the saliva in a small beaker. One
can measure the rate of flow by collecting the saliva in a small graduated
cylinder or, by changing the beaker every ten minutes, making a record of
the quantity of secretion formed. Stimulate the sympathetic fibers, cutting
the hypoglossal nerve if necessary, and note that the secretion is very slightly
increased, but the increase lasts for only a few minutes. If the sympathetic
fibers are stimulated before the chorda, then the sympathetic secretion is
relatively less than if the order of stimulation is reversed.

During stimulation of the nerves, note the relative flow of blood through
the organ. During chorda stimulation the flow is increased; during sympa-
thetic stimulation it is decreased, as these nerves contain vaso-dilator and
vaso-constrictor fibers, respectively.

3. Microscopic Changes in the Gland Cells. — Make a histological
preparation (by any standard method of fixing and staining) of the submaxil-
lary gland of the cat, a, taken after a period of several hours' fasting when
the gland cells may be assumed to be at rest; and £, immediately after a period
of activity (from eating, or activity secured by the stimulation of the chorda
tympani) and note: a, The cells from the resting gland are relatively larger,
the nuclei are pushed back against the basement membrane, they have
sparsely sustaining protoplasm, and the cells are crowded with large gran-
ules, which in a fortunate preparation fill the entire cell. The outlines of the
cells are relatively indistinct and the lumen of the gland is small. 6, The
cells of the active gland are relatively small, the nuclei are centrally placed,
the protoplasm stains more definitely, the granules are usually present but
limited to the side of the cell next to the lumen, the outlines of the cells are
distinct, and the lumen is often quite large.

DIGESTIVE ACTION OF SALIVA ON STARCH 379

4. The Chemical Composition of Saliva. — Collect several cubic cen-
timeters of saliva as follows: Wash the mouth thoroughly with water, then
induce secretion of saliva by chewing a bit of paraffin or a piece of thoroughly
washed rubber. The inhalation of ether vapor will often facilitate the reflex
secretion. One should avoid strong acids to induce secretion unless their
presence is to be taken into consideration afterward. Make the following
tests:

Reaction. — A slip of neutral litmus-paper when introduced into freshly
collected saliva, or for convenience simply taken into the mouth during sali-
vary secretion, shows an alkaline reaction.

Mucin. — To 3 or 4 c.c. of saliva add 2 per cent, acetic acid drop by drop
until distinct acidity is obtained. On stirring the saliva with a glass rod a
sticky mucin makes its appearance.

Potassium Sulphocyanide. — To 2 c.c. of saliva in a test-tube add 2 or 3
drops of ferric chloride solution, slightly acidulated with hydrochloric acid,
a reddish-brown coloration indicates the presence of potassium sulpho-
cyanide. One should run a blank test on distilled water for comparison.

Chlorides. — Add silver nitrate to 2 c.c. of saliva after first removing
the proteins. A white, cloudy precipitate, which disappears on adding
ammonia and reappears on adding nitric acid, indicates the presence of
chlorides.

Proteins. — Remove the mucin from a sample of saliva, as above, and test
by the characteristic protein reactions. A faint trace of protein can usually
be demonstrated.

5. Digestive Action of Saliva on Starch. — Review the tests for starch,
dextrin, and dextrose, as preparation for an identification of these products
of salivary digestion. To 50 c.c. of i per cent, starch paste in the water-bath
at 40° C., add 5 c.c. of saliva, and mix thoroughly with a glass rod. Immedi-
ately begin two series of tests: a, for the presence of starch; b, for the presence
of reducing sugar. The tests for starch can be made by adding to 3 drops
of starch, on a porcelain plate, an equal quantity of dilute iodine in potassium
iodide solution. Use a glass rod. Make the tests every 2 minutes for 20
minutes. The tests for reducing sugar are best made by placing 2 c.c. of
Fehling's solution in each of a series of test-tubes and adding, at intervals
of 5 minutes, i c.c. portions of the digest from a dropping pipet and boil-
ing. If the tests are set away as fast as they are prepared, a reddish-yellow
cuprous oxide will settle out, and the series will give a rough comparison
as to the quantity of reducing sugar present.

In the first series the deep blue of the starch reaction quickly changes
to a reddish-blue, a red, a reddish-brown, until finally no change in color
other than that produced by the mixture of the iodine occurs, showing that
the starch has passed the second stage of erythro-dextrin in its disappearance.
The indication of reducing sugar in the second series shows that this erythro-

38o

FOOD AND DIGESTION

dextrin has been transformed into reducing sugar, and also that the amount
of sugar is greatly increased during the progress of the test.

6. The Influence of Temperature on Salivary Digestion. — Prepare
three test-tubes, a, b, c, containing 4 c.c. each of saliva. Boil a, place b in a
water-bath at 40° C., and place c in ice water. After c has been cooled down
to the temperature of the ice-bath, add to each 2 c.c. of i percent, starch solu-
tion and mix. At intervals of 2 to 5 minutes test these three samples for the
disappearance of starch and appearance of reducing sugar, as in Experi-
ment 5. No change will take place in a; b will be quickly digested, and the
digestion in c will be slight or suspended. Upon placing c in a warm bath
digestion will quickly occur.

7. Influence of Acids and Alkalies on Salivary Digestion. — To
each of 5 test-tubes, a, b, c, d, e, add five c.c. of saliva. Leave a for the normal ;
make b strongly alkaline; c exactly neutral; d acid to the extent of o. 2 to 0.3
per cent, hydrochloric acid; e strongly acid. Place all in the water-bath at
40° C. Add to each 2 c.c. of i per cent, starch paste and mix. Test for
starch and for reducing sugar at intervals of 20 minutes and compare, noting
the results in the following table:

A

B

C

D

E

Prepare and
set in
water-bath
40° C.

5 c.c. saliva

5 c.c. saliva
and
i c.c. strong
KOH

5 c.c. saliva
exactly
nevitralized

5 c.c. saliva
and
i c.c. 2 per
cent hydro-
chloric acid

5 c.c. saliva
and
i c.c. strong
hydrochlo-
ric acid

Then add. .

2 c.c. i per
cent, starch

2 c.c. i per
cent, starch

2 c.c. i per
cent, starch

2 c.c. i per
cent, starch

2 c.c. i per
cent, starch

Test for
starch and
sugar im-
mediately.

After 20
minutes.

After 40
minutes.

The results obtained in the Experiments 5, 6, and 7 show that starch is
converted into reducing sugar, and furthermore, that the conditions for its
conversion indicate that the change is accomplished by an amylolytic enzyme
which in this case is called ptyalin.

GASTRIC JUICE AND GASTRIC DIGESTION 381

8. The Action of Ptyalin is Favored by the Removal of the End
Products. — Place 50 c.c. of 2 per cent, starch paste in a dialyzing tube or
paper, suspend in a beaker of running water. Take 50 c.c. of the same
solution in a beaker, to each add 2 c.c. of saliva and mix thoroughly. Test
for the disappearance of starch at intervals of 20 minutes. The starch in
the dialyzing tube will disappear first because the reducing sugar passes out
through the dialyzer, while in the beaker it is retained and hinders the further
action of ptyalin.

II. GASTRIC JUICE AND GASTRIC DIGESTION.

9. The Secretion of Gastric Juice. — The conditions which influence
gastric secretion can be readily observed on the dog with a gastric fistula.
Take a dog which has had a gastric fistula (prepared some weeks before) and
which is in a condition of hunger, place him in a holder with a cup suspended

FIG. 278. — Operation on the Stomach to Form an Isolated Pouch with Nerves Intact.
S, Isolated sac; V, cavity of stomach; A, A, opening at the abdominal wall.

to collect the gastric juice, and exhibit before the dog some fresh meat or
other food which he enjoys, but do not allow him to eat it. After teasing the
animal for 5 or 10 minutes, an abundant flow of gastric juice will begin.
Pawlow calls this the psychic secretion.

If an esophageal fistula has also been performed the dog may be allowed
to eat the meat, of course swallowing it out of the esophageal fistula back into
the plate. In this experiment an abundant flow of gastric secretion takes
place and may continue for an hour or more.

If a gastric pouch has been performed by Pawlow's method, the animal
mav be allowed to eat the food, swallowing it into the stomach. In this case

382 FOOD AND DIGESTION

the reflex secretion just described takes place as usual, but is followed after
an hour or an hour and a half by a second increase in the quantity of secre-
tion. This second increase has been ascribed to the reflexes originating in
the stomach, possibly from the reflex stimulating action of the digestive prod-
ucts themselves.

10. Composition of Gastric Juice. — Test a sample of gastric juice
obtained from a gastric fistula, as follows:

Reaction. — Gastric juice is strongly acid. Test for free hydrochloric acid
as follows: Gastric juice turns congo-red to a blue color. Gastric juice plus
0.5 per cent, alcoholic solution of dimethyl-amido-azobenzol develops a
cherry-red color, a reaction that is given by free hydrochloric acid. Com-
bined hydrochloric acids and organic acids do not give the color. Giinz-
burg's reagent, consisting of 2 per cent, phloroglucin and i per cent, vanillin
in 80 per cent, alcohol, produces a rose-colored mirror on porcelain in the
presence of free hydrochloric acid. The test is very delicate.

Proteins. — The usual protein tests (page 107) can be applied to gastric
juice and show that it contains small quantities.

11. Artificial Gastric Juice. — The active principle, pepsin, of gastric
juice can be obtained by extracting the gastric mucous membrane of the
dog, pig, etc. Scrape off the mucous membrane, grind it to a fine pulp by
repeatedly running it through a sausage machine or by pounding in a mortar
with clean sand. The mucous membrane should be allowed to stand for
three or four hours before extraction, otherwise the zymogen, and not the
enzyme, will be obtained. Extract a portion of this gastric pulp in water and
filter. Or extract with glycerin for several weeks and filter. Either of these
extracts contains the enzyme. A solution of the glycerin extract in o . 2 per
cent, hydrochloric acid contains all the properties of gastric juice. This
solution is known as artificial gastric juice.

Commercial pepsin already prepared can be obtained on the market.
Artificial gastric juice is made from commercial pepsin by adding 3 to 5 grams
to a liter of o . 2 per cent, hydrochloric acid.

12. Digestive Action of Gastric Juice, or Artificial Gastric Juice.—
The digestive action of gastric juice is limited to proteins. Shreds of fibrin
which permit the gastric juice to come in intimate contact with all parts of
the material form the best protein for testing the action of this enzyme.
Prepare a series of test-tubes, a, b, c, d, each containing 5 c.c. of artificial
gastric juice. Add to a some shreds of fibrin; to b some boiled white of an
egg; to c some fibers of boiled meat; to d some fibers of raw meat; place in a
warm bath at 40° C. and examine at intervals of 20 minutes. Tabulate the
results by the plan indicated in Experiment 13, noting particularly the
rapidity with which the protein goes into solution.

13. Condition Affecting the Enzyme Action of Gastric Juice. — Pre-
pare a series of test-tubes containing 5 c.c. each of gastric juice, according

CLEAVAGE PRODUCTS OF GASTRIC DIGESTION

to the following table. Add a definite quantity of fibrin to each and note
the changes at intervals of 20 minutes.

B

5 c.c. gas- 5 c.c. neutral 5 c.c. alka- 5 c.c. boiled 5 c.c. gastric
Prepare. . . . trie juice at gastric juice line gastric gastric juice | juice at o° C.
40° C. at 40° C. juice at 4o°C. at 40° C.

Then add.

Fibrin

Fibrin

Fibrin

Fibrin

Fibrin

Note after
20 min-
utes.

After 40
minutes.

After 60
minutes.

14. Cleavage Products of Gastric Digestion. — Add 5 to 10 grams
of fibrin to 500 c.c. of artificial gastric juice in a flask and place in a water-
bath at 40° C. After one hour filter off 100 c.c. Exactly neutralize this
filtrate with i per cent, potassium hydrate. A precipitate makes its appear-
ance, and can be collected on the filter-paper, washed with distilled water,
and dissolved in i per cent, dilute hydrochloric acid, acid albumin. Test for
the protein reactions.

After twelve hours or more filter the remaining 400 c.c., exactly neutralize
to remove any traces of acid albumin, and filter. The filtrate contains pro-
teoses and peptones. Concentrate the filtrate over a water-bath to one-
fourth its volume, add an equal quantity of saturated ammonium sulphate
solution, a sticky precipitate of primary proteases separates out. Collect on
a filter-paper, wash with half- saturated ammonium sulphate, redissolve in
very dilute salt solution, and test for protein reactions. The primary pro-
teoses are precipitated by nitric acid.

To the filtrate from the half-saturated ammonium sulphate add crystals
of ammonium sulphate until complete saturation with the salt. Dentero-
albumoses separate out. Collect on a filter-paper, wash, dissolve, and test
for proteins. The secondary proteoses are not precipitated by nitric acid.

Finally the filtrate contains peptone. It can be isolated and tested by
concentrating over the water-bath, adding barium hydrate to slight excess
to remove the sulphate, filtering, and precipitating the excess of barium by

384 FOOD AND DIGESTION

exact neutralization with i per cent, sulphuric acid. Test for protein reac-
tions. Peptone gives a rose color in the biuret reaction. The xanthoproteic
reaction gives the color change, but not the usual precipitate. Peptone is re-
dissolved from its alcoholic precipitate without change. It is dialyzable.

15. Action of Rennin. — Add a solution of commercial rennin (jun-
ket powder), or of the extract of gastric mucous membrane of the fourth
stomach of the calf, to 5 c.c. of milk and let stand for a few minutes. Repeat
the test with artificial gastric juice. Also with neutral gastric juice. In each
case the milk will form a jelly-like clot, which is firmer in the test-tube con-
taining commercial rennin. In the test-tube containing artificial gastric
juice the milk is first coagulated, then slowly dissolved or digested. This
clotting is due to the special coagulating enzyme, rennin.

III. PANCREATIC JUICE AND PANCREATIC DIGESTION.

1 6. The Secretion of Pancreatic Juice. — If a dog containing a pan-
creatic fistula made by Pawlow's method is available, then try the experi-
ment of feeding the animal and noting the rate of secretion of pancreatic
juice through a period of two hours. When the gastric digestion has pro-
ceeded to the point where the acid chyme may be supposed to have entered
the duodenum, then a sharp increase in the flow of pancreatic juice takes
place. This increased activity will last through a period of two or three
hours or more. It is produced either by nerve reflexes (Pawlow) or by the
influence of the secretin produced by the intestinal mucous membrane when
stimulated by acid.

17. Influence of Secretin on the Rate of Secretion. — Make an ex-
tract of the intestinal mucous membrane, preferably from the duodenum,
by scraping off the membrane, grinding it to a pulp, and extracting it over a
water-bath in o . 2 per cent, hydrochloric acid, and filtering.

Anesthetize a large dog, open the abdomen, isolate the pancreatic duct,
introduce a cannula, and arrange for the collection of pancreatic juice. Intro-
duce a cannula into the saphenous vein and connect it with a buret containing
the extract of secretin already prepared. Inject 5-c.c. quantities of the
secretin solution into the vein at intervals of ten minutes. Measure the rate
of secretion of pancreatic juice by counting the drops per minute or, if the
secretion is rapid enough, by collecting it at intervals of five or ten minutes
and measuring it in a graduated pipet.

This method will often yield enough pancreatic juice in the course of a
couple of hours to make the pancreatic experiments which follow. Bayless
and Starling call it secretin juice.

1 8. Chemical Characters of Pancreatic Juice.— Test the reaction,
protein, salt, etc., content of the sample of pancreatic juice collected in the
last experiment.

CLEAVAGE PRODUCTS OF PANCREATIC DIGESTION 385

19. Artificial Pancreatic Juice. — Artificial pancreatic juice can be
prepared from the pancreas by grinding and macerating and extracting a
pancreas with water or glycerin, as described for the gastric glands in Experi-
ment ii above. Commerical preparations of pancreatic enzyme can be
obtained on the market. A solution of glycerin extract of pancreatic gland
or of commerical pancreatin in o. 2 per cent, sodium carbonate is known as
artificial pancreatic juice.

20. The Enzymes of Pancreatic Juice. — The pancreatic juice con-
tains enzymes which exert a digestive action on starches, fats, and proteins.
This fact can be tested as follows: a, to 5 c.c. of artificial pancreatic juice
add 2 c.c. of i per cent, starch paste, mix and set in the water-bath at 40° C.;

b, to i c.c. of pancreatic juice (artificial juice is not active), collected in Ex-
periment 17, add 0.5 c.c. of neutral olive oil, and place over a \vater-bath;

c, to 5 c.c. of artficial pancreatic juice add a few flocks of fibrin. Test the
digestive action on starch by the iodine test for the disappearance of starch,
or by the copper-reduction test for the presence of reducing sugar. Test the
fat by its reaction, noting that the neutral or slightly alkaline solution has
become acid, also by the fact that an emulsion has been formed. Note that
the protein has gone into solution.

The digestive action on starch is due to the enzyme amylopsin, or pan-
creatic diastase, as it is sometimes called. The fat-splitting effect is due to the
enzyme lipase, and the solution of the fibrin is accomplished by the proteolytic
enzyme, trypsin.

21. Conditions which Influence the Action of the Enzymes of
Pancreatic Juice. — To each of 5 test-tubes, a, b, c, d, e, add 5 c.c. of arti-
ficial pancreatic juice. Place a, b, c, d in the water-bath at 40° C., and e
into an ice-bath. Leave a normal, make b exactly neutral, add to c i c.c. of 2
per cent, hydrochloric acid, and boil d. Add to each tube 2 c.c. of i per cent,
starch paste. Follow the digestive changes by the tests previously outlined.
Tabulate according to the scheme on the following page:

Repeat this experiment with a second set of test-tubes containing fibrin.
Lipase is not very active in artificial pancreatic juice and may be omitted.
If pancreatic juice is available make a third set containing fat.

22. Cleavage Products of Pancreatic Digestion. — To 400 c.c. of arti-
ficial pancreatic juice add 25 grams of moist fibrin and place in a water-bath
at 40° C., add 2 c.c. of chloroform to prevent putrefactive changes. After three
or four hours filter off 100 c.c. and place the remainder on the water-bath for
one or two days. Test the filtrate for alkali albumin, albumoses, and
peptones by the method outlined in Experiment 14 above.

Filter the second portion and concentrate to a syrupy mass on the water-
bath. Crystals make their appearance. Pour off the fluid, wash the crystals
with cold water, and examine under the microscope for sheaves of tyrosin.
The filtrate contains leucin.
25

386

FOOD AND DIGESTION

A B

C

D

E

Take

5 c.c. pan-
creatic
juice 40° C.

Neutralize
5 c.c. pan-
creatic juice
40° C.

5 c.c. pancre-
atic juice and
i c.c. of 2 per
cent, hydro-
chloric acid

5 c.c. pan-
creatic
juice and
boil.

5 c.c. pan-
creatic
juice at o° C.

40° C.

2 C.C. Of

Then add.
starch

2 C.C. Of

starch

2 C.C. Of

starch

2 C.C. Of

starch

2 c.c. of
starch

Note after
20 min-
utes.

After 40
minutes.

After 60
minutes.

If the digestion had been allowed to proceed without the chloroform,
bacteria would have appeared in the solution, and protein cleavage products,
due to their action, would be found, notably indol, phenols, and volatile
fatty acids.

IV. BILE AND INTESTINAL JUICE.

23. Bile. — Secure bile from the gall-bladder of a pig or dog, or, if
it is possible, a sample of human bile. Test the reaction which, in fresh
bile, is neutral. Test for mucin, albumin, and for iron; hydrochloric acid
and ferrocyanide of potassium give a blue color when iron is present.

BileSalts. — Evaporate 10 c.c. of bile to complete dryness, mix with animal
charcoal, add 50 c.c. of absolute alcohol, filter; add an excess of ether to the
nitrate, which gives a white precipitate of bile salts. Crystals will form on
standing in a well-stoppered flask for a day or two.

Bile Acids. — A drop of syrup of cane-sugar in a test-tube of bile forms a
deep red-purple color at the line of separation from concentrated sulphuric
acid. Furfur aldehyde with cholalic acid gives the color.

Bile Pigments. — With i c.c. of bile in a test-tube strong nitroso-nitric
acid produces a play of colors beginning with green, blue, red, and yellow—
Gmelin's test.

Bile does not contain digestive enzymes, but the bile wets the mucous
surface of the intestine and facilitates the solution of fats and fatty acids.

INTESTINAL JUICE 387

24. Intestinal Juice. — The secretion of the mucous membrane of the
small intestine has been proven to have a weak digestive action on pro-
teins and perhaps on starches. It can be obtained from an intestinal fistula.
Its chief digestive importance consists in the presence of the activating
enzyme, enterokinase. Enterokinase can be prepared by extracting the
mucous membrane of the small intestine by the method outlined for making a
pancreatic extract.

To two test-tubes containing 5 c.c. of artificial pancreatic juice, or pref-
erably containing secretin pancreatic juice, add flocks of fibrin. Keep one
for the control, to the other add 2 c.c. of enterokinase solution. The test-
tube containing enterokinase will digest more rapidly and more effectively
than the other.

CHAPTER IX
ABSORPTION

ABSORPTION in its restricted use means the process by which the digested
foods pass through the walls of the alimentary canal and into the circulation.
In its more general meaning absorption is the process by which substances
pass from one part of the body to another by means other than the blood
and lymph vessels. Usually the absorption takes place from a free surface,
such as the alimentary canal, the skin, and the lungs.

The alimentary canal is lined throughout with a continuous layer of epi-
thelial tissue. This layer is only a single cell thick in most of its extent,
but nevertheless it effectively separates the food inside the canal from the
lymph in the tissue interspaces on the outside of the mucous membrane.
These spaces are separated from the blood in the adjacent blood vessels by a
second continuous layer, the endothelial walls of the capillaries. The food,
therefore, in its absorption, must pass through two layers of tissue to reach
the blood stream. But the submucous lymphatic spaces and vessels furnish
channels which may carry substances into the blood by way of the thoracic
duct. The mucous membrane is, therefore, the one strict barrier through
which the food must pass in the act of absorption.

The exact methods by which absorption takes place have long been a
subject of controversy and of research. But this problem is of such diffi-
culty that it is yet, in the main, unsolved. Known physical and chemical
laws were thought to explain the facts of absorption. Some of the known
physical factors concerned in absorption and elimination have already been
considered in a former chapter, osmosis and diffusion, Chapter IV. A third
factor, filtration, consists in the passage of a fluid under pressure through a
membrane. These factors undoubtedly play an important role in the pas-
sage of solutions through the alimentary mucous membrane and the walls of
the blood vessels. The part which the physical factors play is probably more
pronounced in the absorption of water and crystalloids. The nature of the
fluid within the digestive tract, and the movements of the walls of the stomach
and intestines by means of which the material to be absorbed is brought
into intimate contact with the absorbing membrane, are additional factors
which influence absorption.

But the mechanical and physical factors do not fully explain the observed
facts of absorption. It becomes more and more evident that there is an
unexplained factor bound up in the characteristics of the living protoplasm

ABSORPTION IN THE STOMACH 389

of the epithelial cells themselves. When isotonic blood serum is introduced
into the intestine the salts and water are at once absorbed, also the albumins,
but more slowly. In this experiment the osmotic conditions are in balance
and the pressure is greater on the side of the blood vessels, so that absorption
takes place with the actual expenditure of energy. The important fact
here is that the absorption through a living membrane is influenced by the
membrane in ways that we cannot yet explain. It is this factor which de-
termines the different rate of absorption and the so-called selective absorp-
tion in different regions of the alimentary canal.

As a rule, the current of absorption is from the stomach or intestine into
the blood; but the reversed action may occur, as, for example, when sulphate
of magnesium is taken into the alimentary canal. In this case there is a
rapid discharge of water from the blood vessels into the canal. The rapidity
with which matters may be absorbed and diffused through the textures of
the body has been found by experiment. It appears that lithium chloride
may be diffused into all the vascular textures of the body, and into some
of the non-vascular, as the cartilage of the hip-joint, as well as into the aque-
ous humor of the eye, in a quarter of an hour after being given by way of the
mouth and on an empty stomach. Lithium carbonate, when taken in five-
or ten-grain doses on an empty stomach, may be detected in the urine in
five or ten minutes; or, if the stomach be full at the time of taking the dose,
in twenty minutes.

Absorption in the Mouth. — The epithelial lining of the mouth is
of the thicker stratified type and the conditions are otherwise unfavorable
for absorption. Little, if any, absorption normally takes place in the mouth,
and the same is true for the esophagus.

Absorption in the Stomach. — The mucous and submucous coats of
the stomach, see figure 258, are well supplied with blood vessels and lym-
phatics. The mucous membrane is, however, so crowded with the peptic
glands that the relative amount of absorbing surface is small. It is limited
to the mucous membrane around the mouths of the glands.

Recent experiments have shown that though absorption does take place
in the stomach, it is not as active as was formerly supposed, even in the case
of water. Von Mering has found that water begins to pass from the stomach
into the intestine almost as soon as it is swallowed, and that very little of it
is absorbed from the stomach. Of 500 c.c. given by the mouth to a large
dog with a duodenal fistula, only 5 c.c. were absorbed in 25 minutes, the
rest having passed into the intestine. Peptones, sugars, and salts are ab-
sorbed in the stomach, but only to a limited extent. Peptones are not ab-
sorbed in appreciable amount unless present to as much as 5 per cent, or
more. Examination of the mucous membrane during the stage of active
digestion has revealed the presence of albumoses. Sugars, like peptones, are
absorbed by the stomach only to a slight extent in the weaker solutions,

390

ABSORPTION

but are readily absorbed when the more concentrated solutions are intro-
duced into the stomach, 5 per cent, and over (von Mehring). Fats are not
absorbed at all in the stomach. Even salts in the stomach are not readily
absorbed until the concentration is from three to four times that of the
blood. This fact is in direct opposition to the popular views on the subject.

While some absorption does take place in the stomach it is evidently not
of any great importance under normal conditions. The presence of alcohol
has been shown to increase the amount of absorption, and pepper, mustard,
and such drugs as produce mild local irritation accomplish the same result.

Absorption in the Intestines. — The products of digestion are all readily
absorbed in the small intestine, as is abundantly shown by experiments.

FIG. 279. — Scheme of Blood Vessels and Lymphatics of Human Small Intestine, a,
Central lacteal of villus; b, lacteal; c, stroma; d, muscularis mucosse; e, submucosa;/, plexus
of lymph vessels; g, circular muscle layer; h, plexus of lymph vessels; i, longitudinal
muscle layer; j, serous coat; k, vein; /, artery; m, base of villus; n, crypt; o, artery of villus;
p, vein of villus; q, epithelium. (Mall.)

Absorption from the small intestine has been studied in the human subject
in the case of a patient who had a fistulous opening in the lower part of the
ileum. For example, 85 per cent, of the protein of a test meal was absorbed
before the food reached the fistula. The food passes slowly down the length
of the small intestine, and the digestive changes produce a series of cleavages

ABSORPTION IN THE INTESTINES

391

which have known osmotic and diffusion properties. The question has been
to determine which of the cleavage products are most favorable for absorp-
tion and the details of the mechanism.

The mucous membrane of the small intestine possesses special structures
for absorption, the villi. Each villus projects as a finger-like process into
the lumen of the intestine. Its single-layered covering of epithelial cells
supported by a connective-tissue framework brings a relatively large extent

Lymphatics of head and
neck, right

Right internal jugular vein
Right subclavian vein

Lymphatics of right arm

Receptaculum chyli

Lymphatics of lower ex-
tremities

Lymphatics of head and
neck, left

Thoracic duct

Left subclavian vein

Thoracic duct

Lacteals

Lymphatics of lower ex-
tremities

FIG. 280. — Diagram of the Principal Groups of Lymphatic Vessels. (From Quain.)

of surface into contact with the digesting food, which is thus separated from
a loop of capillaries and lymphatic radicals.

The capillaries of the villus are connected with the veins which contribute
to the portal vein, hence carry blood to the liver. The lacteals of the villus
contribute to the mesenteric lacteal system, hence the chyle and lymph pass
through the mesenteric glands and the portal duct to the subclavian vein
in the neck. There are thus two routes by which absorbed foods may reach
the general circulation. These paths can be independently isolated; and a
study of the composition of their discharge during active absorption con-

392

ABSORPTION

tributes to our knowledge of the course taken by the different absorption
products.

Absorption of Proteins from the Intestines. — Protein is absorbed
chiefly in the small intestine, though just exactly how cannot at present be

FIG. 281.

FIG. 282.

FIG. 281. — Superficial Lymphatics of the Forearm and Palm of the Hand, 1. — 5, Two
small glands at the bend of the arm; 6, radial lymphatic vessels; 7, ulnar lymphatic vessels;
8, 8, palmar arch of lymphatics; 9, 9', outer and inner sets of vessels; fc, cephalic vein; d,
radial vein; e, median vein;/, ulnar vein. The lymphatics are represented as lying on the
deep fascia. (Mascagni.)

FIG. 282. — Lymphatic Vessels of the Head and Neck and the Upper Part of the Trunk.
(Mascagni.) £. — The chest and pericardium have been opened on the left side, and the
left mamma detached and thrown outward over the left arm, so as to expose a great part
of its deep surface. The principal lymphatic vessels and glands are shown on the side
of the head and face, and in the neck, axilla, and mediastinum. Between the left internal
jugular vein and the common carotid artery, the upper ascending part of the thoracic duct
marked i, and above this, and descending to 2, the arch and last part of the duct. The
termination of the upper lymphatics of the diaphragm in the mediastinal glands, as well as
the cardiac and the deep mammary lymphatics, is also shown.

ABSORPTION OF PROTEINS FROM THE INTESTINES

393

affirmed. In the preceding chapter the cleavage products of protein diges-
tion have been discussed. It was shown there that proteoses, peptones,
peptids, and the amino-acids are derived from the proteins as digestion
products. It has, in the past, been assumed that peptone represents the
form most freely absorbed. No peptone has, however, been isolated from
the blood or lymph on the vascular side of the epithelial membrane. The
present supposition is that the protein cleavage products are taken up by
the epithelium and synthesized into other and more complex forms before

FIG. 283. — A Small Portion of Medullary Substance from a Mesenteric Gland of the
Ox. d, d, Trabeculac; a, part of a cord of glandular substances from which all but a few of
the lymph corpuscles have been washed out to show its supporting meshwork of retiform
tissue and its capillary blood vessels (which have been injected and are dark in the figure) ;
6, 6, lymph sinus, of which the retiform tissue is represented only at c, c. X 300. (Kolliker.)

being discharged into the blood; or that they are resynthetized into the charac-
teristic tissue proteins after absorption. The digestion cleavages not so
utilized are desamidized by the liver, and the ammonia so formed subse-
quently converted into and eliminated as urea.

In animal foods, such as eggs, meat, etc., it is estimated that about 98
per cent, of the protein is absorbed; whereas in vegetable foods, where the pro-
tein is often protected from the action of the digestive enzymes, there may
be 10 to 15 per cent. loss. Analysis of the total lymph discharge of the
thoracic duct fails to show any increase of proteins during active digestion,
from which it is inferred that proteins pass by way of the liver.

The non-nitrogenous residue is oxidized or temporarily stored as glycogen.

From 12 to 15 per cent, of the protein remains in the food as it passes the

394 ABSORPTION

ileocecal valve. This amount, less the loss in the feces, is absorbed in the
large intestine.

Absorption of Carbohydrates by the Intestines.— Carbohydrates
are broken down to dextrose, levulose, etc., and are absorbed as such. Even
the soluble cane-sugar is split by the invertase of the intestine into the mono-
saccharides, dextrose and levulose. Starch is the source of most of the 500
grams of dextrose absorbed in an average diet per day. During the absorp-
tion of a carbohydrate meal the percentage of dextrose in the blood of the
portal vein is increased over the normal, which is o . i to 1.5 per cent. This
excess of dextrose passes through the liver and is temporarily stored in the

FIG. 284. — Section of the Villus of a Rat Killed during Fat Absorption, ep, Epithelium;
str, striated border; c, lymph cells; c', lymph cells in the epithelium; /, central lacteal con-
taining disintegrating lymph corpuscles. (E. A. Schafer.)

liver cells as glycogen. In the case of a fistula in the receptaculum chyii,
the chyle contained less than a half per cent, of the total dextrose absorbed.

Experiments on the rate of absorption of the different sugars seem to
indicate that their absorption does not follow known physical laws and that
we must assume an unknown chemical factor in the living protoplasm.

Dextroses are absorbed readily by the large intestine.

Fermentation processes from bacterial growth produce certain acids from
the carbohydrates, chiefly in the large intestine. These are readily absorbed.

Absorption of Fats by the Intestines. — Fats reach the absorbing
epithelium in two forms, as soluble glycerol and soaps and as finely emulsi-
fied fats. The first two are taken up by the epithelium readily enough,
but in the last the process of absorption is not so clear. It is comparatively

ABSORPTION OF MINERALS AND WATER IN THE INTESTINES 395

easy to demonstrate the presence of microscopic globules of fat, both in the
intercellular substance and in the epithelial cells themselves. But it has
been constantly noticed that there is a clear zone along the free borders of
the cells. Fat drops exist in the adjacent digesting mass, and in the deeper
parts of the cells, but not in this border zone. Since the demonstration of
the reversible action of lipase, the view has been strengthened that in the
very act of absorption the emulsified fats are decomposed and passed through
the cell border only to be resynthesized in the cell protoplasm. This is of
course against the strictly mechanical view. The decreasing efficiency of
fats when the bile, which wets the mucous
surface and dissolves the fatty acids, is
withheld from the intestine, also supports
this view. As absorption progresses the
size of the fat drops in the epithelial cells
increases, a fact that is readily explained
by supposing a continued synthesis and
accumulation of fat.

The fat drops are ultimately discharged
into the connective-tissue spaces and finally
pass into the lymph channels, the thoracic
duct, and into the blood of the subclavian
vein. This is the course taken by the
larger percentage of the fat. However,

some of the fat is absorbed into the capillaries of the villi and passes through
the liver. The presence of fat drops in the liver cells at certain times can
be ascribed to storage of this absorbed fat.

It is said that the more readily emulsified fats, those that melt readily at
the body temperature, are the more completely absorbed. The efficiency
of such absorption is as high as 96 to 98 per cent, for the oils, and decreases
sharply for such fats as the tallows.

The large intestine is capable of absorbing fats, though not so readily as
the small intestine.

Absorption of Minerals and Water in the Intestines. — The salts
common in the foods are most of them readily soluble, dissociate quite com-
pletely in the dilute solutions, and diffuse and dialyze readily. Of the salts
of the foods, the sodium and potassium cations and chlorine anion are the
most readily dissociated and are most diffusible, while the calcium and
magnesium cations and the sulphate anion are least diffusible. The sub-
stances pass through the intestinal epithelial cells and the intercellular sub-
stance; at least salts easily recognized by microchemical means have been
found in both localities during absorption. It seems probable that the forces
concerned are largely osmosis and diffusion.

Yet observers have not been able to show that the rate and character of

FIG. 285. — Mucous Membrane
of Frog's Intestine during Fat Ab-
sorption, ep, Epithelium; str,
striated border; C, lymph corpus-
cles; /, lacteal. (E. A. Schafer.)

396 ABSORPTION

the absorption of even the salines obey the known physical laws. In fact,
there is evidence that some of the salts, iron for example, are taken up as
organic compounds (hematogens of Bunge). The activity of the epithelial
cells is to be taken into account, even in the absorption of salts.

Water, which we have seen is not absorbed in the stomach, is readily
absorbed in the small intestine. Perhaps the bulk of water taken into
the system is absorbed in the upper part of the small intestine. In the large
intestine, too, it is absorbed with facility and in considerable quantities.
The content of the bowel is still quite fluid when it enters the ascending colon,
but the feces are quite firm on discharge from the rectum. There are many
analogies by which we may suppose a controlling influence of the epithelium
over the process of water absorption. Among the fishes there are species,
the salmon for example, in which the blood maintains a relatively constant
osmotic pressure, and therefore salt content. In the salmon this is about
the same as that of human blood. The blood is separated in the gills by
an extremely thin epithelium from the water in which the animals live, yet
these fishes go with impunity from sea- water, with two and a half times more
salt than the blood, to fresh water with practically no salt at all. The epi-
thelium of the gills permits the passage of oxygen, but it does not permit
the diffusion or dialysis of the salts or the wrater in either direction. It is
possible that there is a certain amount of resistance to the passage of water
through the walls of the stomach, wrhile the intestinal epithelium permits
water to pass readily.

The factors active in absorption are under searching investigation at the
present time, so that it is reasonable to hope that the near future will give
a more exact understanding of this intricate subject.

ABSORPTION FROM THE SKIN, THE LUNGS, ETC.

The dry corneous stratified epithelium covering the human body pos-
sesses great resistance to the absorption of most substances. The sebaceous
secretion keeps the surface slightly oily. Watery solutions do not readily
wet the surface and therefore do not penetrate. There is some absorption
of water on prolonged contact with the skin, but the amount is insignificant.
Medicated baths, especially hot baths, may be accompanied by some slight
absorption of the substances dissolved in the waters, though it must be con-
fessed that the primary good effects of such treatment come from other
sources.

On the other hand, oily substances come in more intimate contact with
the skin and penetrate deeper and more readily. Therefore, lotions con-
taining medicines are occasionally applied to the skin, and slow but gradual
absorption occurs. The volatile oils penetrate the skin readily.

The epithelial lining of the lungs seems peculiarly adapted to the quick

ABSORPTION FROM THE SKIN, THE LUNGS, ETC. 397

absorption of all gases except ammonia and volatile substances. This is
illustrated by the rapidity with which anesthesia may be accomplished by
breathing the vapors of ether or chloroform.

Solutions injected into or otherwise brought into contact with the sub-
dermal connective tissue, the surface of the body of a muscle, or intra-
muscularly, or within the peritoneal or thoracic cavities, very quickly pass
into the general circulation. They are practically injected into the lymph-
atic intercellular spaces in these instances and, of course, are very readily
carried through the lymphatic vessels, figures 280 and 282, to the thoracic
duct and into the blood. Readily diffusible substances, however, pass
directly through the blood capillary walls and do not necessarily follow the
longer lymph channel route. Comparing the rapidity of absorption in the
cases mentioned, that from the muscle is most rapid, a fact of medical im-
portance in the use of the hypodermic needle for the giving of medicines
in emergency.

CHAPTER X.
EXCRETION.

EVERY substance taken into the body, in whatever form, must, in the
end, be cast off again, no matter how great the change that may be wrought
during its sojourn. We have already found that in the lungs the expired
air, and in the intestine the feces, carry from the body waste matters of no
further use. We have now to find that the kidneys, separating the urine,
and the skin, separating the sweat and the sebum, are likewise channels by
which the body throws off water, salts, and broken-down organic matters
of no further use to the organism. Of these two organs, the skin and the
kidney, the latter is by far the more important in so far as the quantity and
complexity of its secretion is concerned.

STRUCTURE AND FUNCTION OF THE KIDNEYS.

General Structure. — The kidneys are twTo in number, and are situated
deeply in the lumbar region of the abdomen on either side of the spinal col-
umn behind the peritoneum. They correspond in position to the last two
dorsal and twro upper lumbar vertebrae, the right slightly below the left in
consequence of the position of the liver on the right side of the abdomen.
They are about 4 inches long, z\ inches broad, and ij inches thick. The
weight of each kidney is about 4^ ounces, 140 grams.

On dividing a kidney into two equal parts by a section carried through
its long convex border, figure 286, the main part of its substance is seen to
be composed of two chief portions called, respectively, cortical and medullary,
the latter being also sometimes called pyramidal, from the fact of its being
composed of about a dozen conical bundles of uriniferous tubules, each bun-
dle forming what is called a pyramid. The upper part of the ureter, or duct
of the organ, is dilated into the pelvis; and this, again, after separating into
two or three principal divisions, is finally subdivided into 8 to 12 smaller
portions, calyces, each of which receives the pointed extremity or papilla of
a pyramid. Sometimes, however, more than one papilla is received by a
calyx.

The kidney is a compound tubular gland. Both its cortical and its
medullary portions are composed essentially of numerous tubes, the tubuli
uriniferi, which begin at the opening on the Malpighian pyramid and, after
a devious course, end in the capsule of the glomerulus.

398

TUBULI URINIFERI

399

Tubuli Uriniferi. — The tubuli uriniferi, figure 287, are composed
of a nearly homogeneous membrane, and are lined internally by epithelium.
They vary considerably in size in different parts of their course, but are,
on an average, about 40/1 in diameter, and are found to be made up of several
distinct sections. The first section or part to be identified is the Mal-
pighian, or Bowman's capsule, figure 287. It is composed of a hyaline mem-
brana propria, thickened by a varying amount of fibrous tissue, and lined by

a b

FIG. 286. — Longitudinal Section of Kidney through Hilum. a, Cortical pyramid; b,
medullary ray; c, medulla; d, cortex; e, renal calyx;/, hilum; g, ureter; h, renal artery; i,
obliquely cut tubules of medulla; j and k, renal arches; /, column of Bertini; m, connective
tissue and fat surrounding renal vessels; n, medulla cut obliquely; o, papilla; p, medullary
pyramid. (Merkel-Henle.)

flattened nucleated epithelial plates. This capsule is the dilated extremity of
the uriniferous tubule which is invaginated to receive the glomerulus of con-
voluted capillary blood vessels. The invaginated portion of the tubule is of
particular importance since it is the membrane through which a large part
of the urine is secreted. The glomerulus is connected with an efferent and
an afferent blood-vessel. The Malpighian capsule is connected by a con-
stricted neck, figure 287, N, with the proximal convoluted tubule. This forms
several distinct curves and is lined with short columnar cells. The tube

4OO

EXCRETION

next passes almost vertically downward toward the medulla, forming the
spiral tubule, still within the cortex of the kidney, which is of much the same
diameter. The loop of Henle, L, in the medulla, is a very narrow tube lined
with flattened nucleated cells. Passing vertically upward from the loop of

LABYRINTH \MJ5DiRAY LABYR.

Pelvis

FIG. 287. — Scheme of Uriniferous Tubule and of the Blood Vessels of the Kidney,
Showing Their Relation to Each Other and to the Different Parts of the Kidney. G,
Glomerulus; BC, Bowman's capsule; N, neck, PC, proximal convoluted tubule; S, spiral
tubule; D, descending arm of Henle's loop; L, Henle's loop; A, ascending arm of Henle's
loop; IDC, distal convoluted tubule; AC, arched tubule; SC, straight collecting tubule;
ED, duct of Bellini; A, arcuate artery, and V, arcuate vein, giving off interlobular vessels
to cortex and vasa recta to medulla; a, afferent vessel of glomerulus; e, efferent vessel of
glomerulus; c, capillary network in cortical labyrinth; 5, stellate veins; vr, vasa recta and
capillary network of medulla. (Pearsol.)

Henle, the tubule varies somewhat in histological character, but the irregular
tubule and the distal convoluted tube, identical in all respects with the proxi-
mal convoluted tube, are to be noted. The proximal convoluted tubes
pass into the curved and straight collecting tubes, the latter running
vertically downward to the papillary layer, and, joining with other collecting

RENAL BLOOD SUPPLY

401

tubes, form larger ducts which finally open at the apex of the papilla. These
collecting tubes are lined with nucleated columnar or cubical cells.

Renal Blood Supply. — The renal artery divides into several branches
which pass in at the hilus of the kidney and are covered by a fine sheath
of areolar tissue derived from the capsule. They enter the substance of the
organ chiefly in the intervals between the papillae and at the junction between
the cortex and the boundary layer. The main branches then pass almost
horizontally, forming more or less complete arches and giving off branches

FIG. 288. — From a Vertical Section through the Kidney of a Dog, the Capsule of which
is Supposed to be on the Right, a, The capillaries of the Malpighian capsule, the glomerulus,
are arranged in lobules; n, neck of capsule; c, convoluted tubes cut in various directions; b,
irregular tubule; d, e, and /are straight tubes running toward capsules forming a so-called
medullary ray; d, collecting tube; e, spiral tube; /, narrow section of ascending limb.
X 380. '(Klein and Noble Smith.)

upward to the cortex and downward to the medulla. The former are for
the most part straight; they pass almost vertically to the surface of the kidney,
giving off laterally in all directions longer and shorter branches, which ulti-
mately supply the glomerulus. The small afferent artery, figures 287, a,
290, d, which enters the Malpighian capsule, breaks up in the interior into
a dense convoluted and looped capillary plexus, which is ultimately gathered
up again into several efferent vessels, comparable to minute veins, which
leave the capsule at one or more places near the point at which the afferent
artery enters it. On leaving, they do not immediately join other small
veins as might have been expected, but again break up into a second set
26

402

EXCRETION

of capillary vessels which form an interlacing network around the urinif-
erous tubules. This second capillary plexus terminates in small veins
which, by union with others, help to form the radicles of the renal vein.
These form venous arches corresponding to the arterial arches situated
between the medulla and cortex.

Thus, in the kidney, the blood entering by the renal artery traverses
two sets of capillaries before emerging by the renal vein, an arrangement
which may be compared to the portal system.

The tuft of vessels within the Malpighian capsule in the course of de-
velopment has been thrust into the dilated extremity of the urinary tubule,
which finally completely invests it. Thus within the Malpighian capsule

r

FIG. 289. — Transverse Section of a Renal Papilla, a, Large tubes or papillary ducts;
b, c, and d, smaller tubes of Henle; e, f, blood capillaries, distinguished by their flatter
epithelium. (Cadiat.)

there are two layers of squamous epithelium, a parietal layer lining the cap-
sule proper, and a visceral or reflected layer immediately covering the vas-
cular tuft, figure 290, and sometimes dipping down into its interstices. This
reflected layer of epithelium is readily seen in young subjects, but cannot
always be demonstrated in the adult, figures 290 and 291.

The vessels which enter the medullary layer break up into smaller arte-
rioles, which form a fine arterial meshwork around the tubes of the papillary
layer and end in a similar plexus from which the venous radicles arise. The
vessels do not form a double set of capillaries.

Besides the small afferent arteries of the Malpighian bodies there are,
of course, others which are distributed in the ordinary manner, for the nutri-
tion of the different parts of the organ; and there are numerous straight

RENAL NERVES

403

vessels, the vasa recta, in the pyramids between the tubes. Some of these
are branches of the vasa efferentia from Malpighian bodies, and therefore
comparable to the venous plexus around the tubules in the cortical portion,
while others arise directly as small branches of the renal arteries.

FIG. 290. — Malpighian Capsule and Tuft of Capillaries, Injected through the Renal
Artery with Colored Gelatin, a, Glomerular vessels; &, capsule; c, anterior capsule; d,
glomerular artery; e, efferent veins;/, epithelium of tubes. (Cadiat.)

FIG. 291. — Diagrams Illustrating Stages in the Development of the Malpighian Cap-
sule. In i and 2 the developing blood vessel is approaching the blind end of the capsule.
In 3 the tubule is beginning to invaginate and enclose the capillary. In 4 and 5 later
stages are shown. The cells forming the two layers of the capsule grow very thin. (Bailey.)

Renal Nerves. — Vaso-constrictor and vaso-dilator nerves are sup-
plied to the blood vessels of the kidney, but no clearly denned secretory
nerves have yet been demonstrated for the organ. The vascular nerves
arise out of the anterior spinal roots (Bradford), chiefly the eleventh to the

404 EXCRETION

thirteenth dorsal nerves. They reach the kidney by way of the splanchnic
nerves and the renal plexus to the renal artery along which they run into
the substance of the kidney. Berkely has demonstrated nerve plexuses
about the arterioles and around Bowman's capsule. Terminal knob-like
endings of nerve fibrils were shown. Some authors have claimed renal vaso-
constriction following vagus stimulation, but the fact seems not to be uni-
versally admitted.

The Ureters and Urinary Bladder. — The duct of each kidney, the
ureter, is a tube about the size of a goose-quill and from twelve to sixteen
inches in length. It is continuous above with the pelvis of the kidney, and
ends below by obliquely perforating the walls of the bladder and opening
on its internal surface. It has three principal coats, an outer fibrous, a
middle muscular, of which the fibers are unstriped and arranged in three
layers. The fibers of the central layer are circular, and those of the other
two layers longitudinal in direction. It has an internal mucous lining con-
tinuous with that of the pelvis of the kidney above and the lining of the
urinary bladder below. The urinary bladder, which forms a receptacle for
the temporary lodgment of the urine in the intervals of its expulsion from
the body, is more or less pyriform. Its widest part, which is situated
above and behind, is termed thefundus; and the narrow constricted portion
in front and below, by which it becomes continuous with the urethra, is
called its cervix or neck. It is constructed of four principal coats: serous,
muscular, areolar or submucous, and mucous. The fibers of the muscular
coat deserve special mention. They are unstriped, are arranged in three
principal layers, of which the external and internal have a general longitu-
dinal, and the middle layer a circular, direction. The latter are especially
developed around the cervix of the organ, and are described as forming a
sphincter vesicae. The mucous membrane is provided with mucous glands,
which are more numerous near the neck of the bladder.

The bladder is well provided with blood and lymph vessels and with
nerves. The latter are from the sacral plexus (spinal) and hypogastric
plexus (sympathetic). Ganglion cells are found, here and there, in the
course of the nerve fibers.

THE URINE.

Quantity and General Properties. — Healthy urine is a perfectly
transparent amber-colored liquid, with a peculiar but not disagreeable odor,
a bitterish salty taste, and a specific gravity of from i .020 to i .025. The
urine consists of water holding in solution certain organic and saline matters
as its ordinary constituents, and occasionally various other matters. Some
of the latter are indications of diseased states of the system and others are
derived from unusual articles of food or drugs taken into the stomach.

REACTION 405

The total quantity of urine passed in twenty-four hours is influenced
by numerous circumstances. In adults of average size and medium ac-
tivity the daily amount of urine may be given as from 1,200 c.c. to 1,500 c.c.
In Chittenden's recent observations on nine athletic students and on eight
soldiers the average daily output of urine through a period of about five
months was for the students 1,215 c.c. with average specific gravity of i .020,
and for the soldiers 1,042 c.c. with specific gravity of i .023.

GENERAL CHEMICAL COMPOSITION OF THE URINE.

Water 967

Solids:

Urea 14-230

Other nitrogenous crystalline bodies:

Uric acid, principally in the form of alkaline urates,

a trace only free

Kreatinin, xanthin, hypoxanthin

Hippuric acid

Mucus, pigments, and ferments

Salts :

Inorganic:

Principally sulphates, phosphates, and chlorides
of sodium and potassium, with phosphates
of magnesium and calcium, traces of silicates
Organic:

Lactates, oxalates, acetates, butyrates and for-
mates, which appear only occasionally. . . . J — 33

10.635

8.135

Sugar a trace sometimes.

Gases (nitrogen and carbon dioxide principally).

1,000

Reaction. — The normal reaction of the urine is slightly acid. This
acidity is due to carbon dioxide and to acid phosphate of sodium, and is less
marked soon after meals. After a time, varying in length according to the
temperature, the reaction becomes strongly alkaline from the change of
urea into ammonium carbonate, due to the presence of one or more specific
micro-organisms (micrococcus urece}. In the process of fermentation the
urea takes up two molecules of water, a strong ammoniacal and fetid odor
appears, and there are deposits of triple phosphates and alkaline urates.
This does not occur unless the urine is freely exposed to the air, or, at least,
until air has had access to it.

In most herbivorous animals the urine is alkaline and turbid. The
difference depends not on any peculiarity in the mode of secretion, but on
the difference in the food on which the two classes of animals subsist. For
when carnivorous animals, such as dogs, are restricted to a vegetable diet,
their urine becomes pale, turbid, and alkaline like that of herbivorous
animals, while the urine voided by the herbivora, e.g., rabbits, fed for some

406 EXCRETION

time exclusively upon animal substances, presents the acid reaction and
other qualities of the urine of carnivora, and its ordinary alkalinity is again
restored only on the substitution of a vegetable for the animal diet. Human
urine is not usually rendered alkaline by vegetable diet, but it becomes so
after the free use of alkaline medicines or of the alkaline salts with carbonic
or vegetable acids. These latter are changed into alkaline carbonates
previous to elimination by the kidneys.

Specific Gravity of Urine.— The average specific gravity of the human
urine is about i .020 to i .025. The relative quantity of water and of solid
constituents of which it is composed is materially influenced by the condition
and occupation of the body during the time at which it is secreted; by the
length of time which has elapsed since the last meal; by the amount of water
taken; and by several other less important circumstances. The morning
urine is the best adapted for analysis in health, since it represents the simple
secretion unmixed with the elements of food or drink. If it is not used the
whole of the urine passed during the period of twenty-four hours should be
taken. The specific gravity of the urine may thus, consistently with health,
range widely on both sides of the usual average. It may vary from 1.015
in the winter to 1.025 in the summer; but variations of diet and exercise,
and many other circumstances, may make even greater differences than
these. The variations may be extreme in disease, sometimes decreasing in
chronic nephritis to i . 004, and frequently increasing in diabetes, when the
urine is loaded with sugar, to i .050 or even to i .060.

AVERAGE DAILY QUANTITY OF THE CHIEF URINARY CONSTITUENTS (MODI-
FIED FROM PARKES.)

Per kilo of

Body weight.

Water

• • • 1,500

c.c.

23

. oooo

grams

Solids

72

.

grams

0

.8800

grams

Urea

33

. I 80

grams

0

. 5000

grams

Kreatinin

.QIO

grams

o

.0140

grams

Uric acid

•555

grams

0

.0084

grams

Hippuric acid

.400

grams

0

.0060

grams

Pigment and extractives

10

.000

grams

o

• 1510

grams

Sulphuric acid

... 2

.012

grams

0

.0480

grams

Phosphoric acid

3

. 164

grams

o

•0305

grams

Chlorine

7

.OOO

grams

0

. 1260

grams

Ammonia

.770

grams

Potassium

... 2

. 5OO

grams

Sodium

I I

.OQO

grams

Calcium

. 260

grams

Magnesium

.207

grams

Variations in the Constituents of Urine. — Most of the constituents
are, even in health, liable to variations from the proportions given in the
above table. The variations of the quantity of water in different seasons

THE NITROGENOUS SUBSTANCES IN URINE 407

and according to the quantity of drink and exercise have just been men-
tioned. The water of the urine is also liable to be influenced by the condi-
tion of the nervous system, being sometimes greatly increased, e.g., in hysteria
and in some other nervous affections, and at other times diminished. The
increase in water may be either attended with an augmented quantity of
solid matter in some diseases, as in ordinary diabetes, or may be nearly the
sole change, as in the affection termed diabetes insipidus. A febrile con-
dition almost always diminishes the quantity of water; and a like diminution
is caused by any affection which draws off
a large quantity of fluid from the body
through any other channel than that of the
kidneys, e.g., the bowels or the skin.

In disease or after the ingestion of special
foods, various abnormal substances occur in
urine, of which the following may be men-
tioned: Seralbumin, serum globulin,
enzymes (apparently some are present in
health also), proteoses, blood, sugar, bile
acids and pigments, casts, fats, various salts
taken as foods or as medicines, micro-organ- FIG. 292.— Crystals of Urea,
isms of various kinds.

The Nitrogenous Substances in Urine.— The nitrogenous waste prod-
ucts which are formed in the body in the metabolism of the protein foods
-are ultimately eliminated chiefly through the kidney, to some extent through
the bowel, and slightly through the skin. The total nitrogen in the urine
.and in the feces multiplied by the factor 6.25 is a measure of the nitrogenous
foods, i.e., proteins, metabolized by the body. The nitrogen excreted in the
urine is in the form of urea 87 . 5 per cent., ammonia 4.3 per cent., kreatinin
3 . 6 per cent., uric acid o . 8 per cent., and undetermined forms 3 . 73 per cent,
according to Folin. The total quantity of nitrogen eliminated in all these
forms per day is given as about 18 grams. In Chittenden's recent experi-
ments this quantity is reduced to as low as 6 grams or even less per day.

Urea. — Urea, CON2H4, is the principal solid constituent of the urine,
forming nearly one-half of the total quantity. It is also the most important
ingredient, since it is the chief form in which the waste nitrogen which is
derived from protein metabolism is excreted from the body.

Properties. — Urea, like other solid constituents of the urine, exists in a
state of solution. When in the solid state, it appears in the form of delicate
silvery acicular crystals, which, under the microscope, are seen as four-
sided prisms, figure 292. It readily combines with some acids, like a weak
base, and may thus be conveniently procured in the form of crystals of nitrate
or oxalate of urea, figures 293 and 294.

Urea is colorless when pure; when impure it may be yellow or brown.

408 EXCRETION

It is without odor and of a cooling niter-like taste. It has neither an acid
nor an alkaline reaction, and deliquesces in a moist and warm atmosphere.
At 15° C. it requires for its solution less than its own weight of water. It is
soluble in all proportions of boiling water, and requires five times its weight
of cold alcohol for its solution. It is insoluble in ether. At 120° C. it melts,
and at a still higher temperature decomposes.

Urea is decomposed by sodium hypochlorite or hypobromite or by nitrous
acid, with evolution of nitrogen. It forms compounds with acids, of which
the chief are urea hydrochloride, CON2H4.HCL; urea nitrate, CON2H4.-
HNO3; and urea phosphate, CON2H4.H3PO4. It forms compounds with

FIG. 293. — Crystals of Urea Nitrate. FIG. 294. — Crystals of Urea Oxalate.

metals such as HgO.CON2H4, (or with silver, CON2H2Ag2). Urea is iso-
meric with ammonium cyanate, NH4CNO, and was first prepared artificially
from that substance.

The Formation of Urea. — Proteins in the body have their nitrog-
enous moiety split off as ammonia, by what Folin considers essentially
a series of hydrolytic cleavages; this is then built up into urea, as described
more fully in the chapter on Metabolism. This last step is essentially a
synthetic process which, from the fact that ammonium carbonate introduced
into the blood is eliminated as urea, may be supposed to occur as follows:

NH2 NH2

/ /

CO -H20 =CO

\ \

ONH4 NH2

Ammonium Urea

Carbamate

Urea is present in varying amounts in all organs and fluids of the body, as
shown by the following determinations of Schoendorff on the dog:

Organ Perur«fa' °f

Blood 0.116

Muscle o . 080

Kidney 0.670

Liver 0.112

Heart 0.173

Brain 0.128

Spleen 0.122

URIC ACID 409

It has been proven that the kidney does not form urea; in fact the kid-
neys may be removed from the body, and urea will continue to accumulate
in the blood. Urea is formed chiefly in the liver, but may in part be con-
structed in other organs, as described more fully on page 408. It follows
that the kidney is only the channel for the elimination of this nitrogenous
compound.

Decomposition of the urea \vith development of ammonium carbonate
takes place from the action of bacteria (micrococcus ureae) when urine is
kept for some days after being voided, which explains the ammoniacal odor
then evolved. The urea is sometimes decomposed before it leaves the blad-
der, when the mucous membrane is diseased and the mucus secreted by it is
abundant; but decomposition does not occur unless atmospheric germs have
had access to the urine.

Quantity Excreted. — The quantity of urea excreted is, like that of the urine
itself, subject to considerable variation. For a healthy adult about 30 grams
per day may be taken as rather a high average. Its percentage in healthy
urine is from 2 to 2.5. Its amount is materially influenced by diet, being
greater on a diet of high protein content. The quantity of urea excreted
by children, relatively to their body weight, is much greater than by adults;
thus the quantity of urea excreted per kilogram of weight was found to be,
in a child, o . 8 gram; in an adult only o . 4 gram. Regarded in this way, too,
the excretion of carbonic acid gives similar results, the proportions in the
child and adult being as 82 to 34.

Uric Acid. — Uric acid, C5H4N4O3, see page 406, is present in the urine
of man and other animals. In birds and reptiles uric acid or its salts is the
chief form in which nitrogen is eliminated from the body.

Properties. — Uric acid is a colorless, crystalline compound of the purin
group, figure 295. It is odorless and tasteless. It is very slightly soluble in
water, quite insoluble in alcohol and ether, and freely soluble in solutions
of the alkaline carbonates and other salts.

A study of the elimination of nitrogen in birds, i.e., geese, has shown that
uric acid, like urea in mammals, is formed largely in the liver from antecedent
protein nitrogen. In man the elimination of uric acid (o . 3 to o . 7 gram per
diem) is more or less constant and characteristic for the individual; it in-
creases or decreases somewhat with the nucleoprotein and purin content
of the daily diet. This observation has led to the inference that uric-acid
nitrogen is derived from nuclear metabolism, page 94.

Other representatives of the purin group are adenin, guanin, xanthin,
hypoxanthin, etc. Chemically, caffeine from coffee is a trimethyl xanthin.

The most common form in which uric acid is deposited in urine is that
of a brownish or yellowish powdery substance, consisting of amorphus
ammonium or sodium urate. Urate sediments are commonly deposited on
cooling the urine; they are redissolved on warming it slightly. When de-

410 EXCRETION

posited in crystals, uric acid is most frequently obtained in rhombic or dia-
mond-shaped laminae, but other forms are not uncommon, figure 295.
When deposited from urine, the crystals are generally more or less deeply
colored, from being combined with the coloring principles of the urine.

Hippuric Acid.— This compound, C6H5.CO.NH.CH2COOH, has long
been known to exist in the urine of herbivorous animals in combination with
sodium. It also exists naturally in the urine of man, in a quantity equal to

FIG. 295. — Various Forms of Uric Acid Crystals. FIG. 296. — Crystals of Hippuric Acid.

or rather exceeding, that of the uric acid. The quantity excreted is increased
by a vegetable diet.

Hippuric acid appears to be formed in the body from benzoic acid. The
benzoic acid unites with glycocoll, and hippuric acid and water are formed
thus:

C6H5.COOH +CH2.NH2.COOH = C6H5.CO.NH.CH2.COOH + H2O.

Benzoic acid Glycin Hippuric acid

Hippuric acid is the first substance which was demonstrated to be synthet-
ized in the body.

Kreatinin. — This substance, which is the anhydride of kreatin, is pres-
ent in urine in a remarkably constant quantity, as shown recently by Folin's
analyses. Its daily excretion quantity is from i to 1.5 grams according to
the amount of active tissue in the individual. It is of especial importance
as a measure of the metabolism of muscle protoplasm.

Ammonia. — A considerable daily quantity of ammonia (about o . 7 gram)
in combination, as chloride, phosphate, or sulphate, is found in the normal
urine, showing that this is an important method of nitrogen elimination.

Pigments. — The pigments of the urine are the following: i. Urochrome,
a yellow coloring matter, giving no absorption band; of which but little is
known. Urine owes its yellow color mainly to the presence of this body.
2. Urobilin, an orange pigment, of which traces may be found in nearly all
urines, and which is especially abundant in the urines passed by febrile
patients. It is characterized by a well-marked spectroscopic absorption

SALINE MATTER

411

band at the junction of green and blue. Those who believe urobilin to
be identical with hydrobilirubin suppose that the bilirubin is reduced by
the putrefactive processes in the intestines, and is conveyed in its reduced
form by the blood stream to the kidneys. 3. Uroerythrin, occasionally
found.

Mucus. — Mucus sediment in the urine consists principally of mucin and
of the epithelial debris from the mucous surface of the urinary passages.
Particles of epithelium, in greater or less abundance, may be detected in most
samples of urine, figure 297. As urine cools, the mucus is sometimes seen
suspended in it as a delicate opaque cloud, but generally it falls. In inflam-
matory affections of the urinary passages, especially of the bladder, mucus
is secreted in large quantities.

FIG. 297.

FIG.

FIG. 297. — Urinary Deposit of Mucus, etc.

FIG. 298. — Urinary Sediment of Triple Phosphates (large prismatic crystals) and
Urate of Ammonium, from urine which had undergone alkaline fermentation.

Saline Matter. — Sulphuric acid, in the form of salts, is taken in very
small quantity with food. Sulphur is also a constituent part of the protein
molecule; hence its elimination, like that of nitrogen, gives a certain measure
of protein metabolism. It is excreted as inorganic sulphates of sodium and
potassium, and as ethereal sulphates, compounds of phenol, cresol, skatol,
i.e., cresol sulphuric acid (C7H7OSO2OH), etc.

The phosphoric acid in the urine is combined partly with the alkalies,
partly with the alkaline earths — about four or five times as much with the
former as with the latter. In blood, saliva, and other alkaline fluids of the
body phosphates exist in the form of alkaline, neutral, or acid salts. In the
urine they are acid salts, viz., the sodium, ammonium, calcium, and magne-
sium phosphates, the excess of acid being (Liebig) due to the appropriation
of the alkali with which the phosphoric acid in the blood is combined, by the
several new acids which are formed or discharged at the kidneys, namely the
uric, hippuric, and sulphuric acids.

412

EXCRETION

The phosphates are taken largely in both vegetable and animal food.
Some are excreted at once; others only after being transformed and incor-
porated with the tissues. Calcium and magnesium phosphates form the prin-
cipal earthy constituents of bone, and from the decomposition of the osseous
tissue the urine derives a quantity of this salt. The decomposition of other
tissues also furnishes large supplies of phosphorus to the urine, which phos-
phorus is supposed, like the sulphur, to be united with oxygen, and then
combined with bases. The quantity is, however, liable to considerable
variation. The earthy phosphates are more abundant after meals, wrhether
of animal or vegetable food, and are diminished after long fasting. The
alkaline phosphates are increased after animal food, diminished after vege-

FIG. 299. — Crystals of Cystin.

FIG. 300. — Crystals of Calcium Oxalate.

table food. Phosphorus uncombined with oxygen appears, like sulphur, to
be excreted in the urine. When the urine undergoes alkaline fermentation,
phosphates are deposited in the form of a urinary sediment, consisting chiefly
of ammonio-magnesium phosphate (triple phosphate), figure 298.

The chlorine of the urine occurs chiefly in combination with sodium.
Next to urea, sodium chloride is the most abundant solid constituent of the
urine. As the chlorides exist largely in food, and in most of the animal
fluids, their occurrence in the urine is easily understood.

Occasional Constituents of Urine. — Cystin, C3H7NSO2, figure 299,
is an occasional constituent of urine.

Another constituent of the urine is oxalic acid (about 0.02 gram per
diem), which is frequently deposited in combination with calcium, figure
300, as a urinary sediment. Pathologically, oxalic acid is found to be in-
creased in diabetes mellitus, in organic diseases of the liver, and in various
other conditions accompanied by derangement of the oxidation mechanism.

Dextrose and albumin are sometimes present in pathological urine, and are
of particular interest from the clinical point of view. See the subject
Internal Secretions of the Pancreas, page 459.

THE METHOD OF EXCRETION OF URINE 413

THE METHOD OF EXCRETION OF URINE.

The secretion of urine is an act the complexity of which can be profitably
discussed only after a clear understanding of three main factors which have
already been presented, viz., the chemical composition of the urine secreted,
the structure of the kidney tubule as a secreting organ, and, finally, the chem-
ical composition of the blood which supplies the materials to the kidney for
the formation of the urine. The substances found in the urine are, for the
most part, also to be found in the blood plasma. But the relative percent-
age composition is very different. The amount of urea in the blood is only a
fractional part as concentrated as in the urine, while albumins and sugars,
which are so plentiful in the blood, are normally present in the urine only
in traces. The presence of the glomerulus with its special vascular supply,
and the different loops of the tubule, with its gland-like epithelial wall,
would, a priori, lead one to suspect special functions for each.

Theories of the Secretion of Urine. — Bowman in 1842, wholly on
structural grounds, advanced a theory of urinary secretion. This theory was
given an experimental basis and elaborated by Heidenhain and generally
bears his name.

Heidenhain' s theory is stated as follows:

i. The secretion in the kidney depends upon the physiological activity of
special secreting cells which are of two kinds. 2. The first type of cell is
represented by the single layer of epithelium covering the glomerular capil-
laries. These cells secrete especially water and salts. 3. The second type of
cell is represented by the gland-like epithelial cells which form the convo-
luted tubules and the loop of Henle. These cells secrete the urea, uric acid,
and other specific constituents of the urine. 4. The activity of each kind of
cell is influenced by the chemical composition of the blood and by the flow
of blood through the kidney. 5. The relative secretory activity of the glomer-
ular cells and the tubule cells is sufficient to account for the variation in the
chemical composition of the urine.

Ludwigs theory, advanced in 1844, is a strictly mechanical theory of
urinary secretion based on experiments which he presented, i . He considered
the glomerulus and Bowman's capsule as a filtering apparatus in which
substances present in the blood are driven through the epithelium of the
capsule into the renal tubule by the positive pressure of the blood in the
glomerular capillaries. 2. This very dilute urine in the capsule is supposed
to be concentrated by the resorption of water as it flows down the tubule.
Ludwig originally considered this resorption of water an imbibition process
in which the greater saturation of salts in the blood caused water to be taken
up through the renal tubule walls, an osmotic process. At present most
observers who accept the view that filtration takes place at the glomerulus
explain the resorption of water down the tubules as an act of cellular
resorption or secretion.

414 EXCRETION

Experimental Observations. — There are numerous nerves to the
kidney, but no proven secretory influence has been shown. The variations
in the secretion of urine that follow nervous stimulation are quite satisfactorily
explained by the changes in the blood flow.

The kidney can be placed in an onkometer and its variation in volume
measured directly, figures 301 and 302. This volume measurement, when
taken with the arterial pressure, gives a very good index of the volume of
blood flowing through the kidney. Now when the kidney is inserted in an
onkometer and the urine collected from the ureter, it is found in general that

FIG. 301.— Diagram of Roy's Onkometer. a, Represents the kidney enclosed in a
metal box, which opens by hinge/; b, the renal vessels and ducts. Surrounding the kidney
are two chambers formed by membranes, the edges of which are firmly fixed by being
clamped between the outside and inside metal capsules (the latter not represented in the
figure), the two being firmly screwed together by screws at h, and on the opposite side.
The membranous chamber below is filled with a varying amount of warm oil, according
to the size of the kidney experimented with, through the opening then closed with the plug i.
After the kidney has been enclosed in the capsule, the membranous chamber above is filled
with warm oil through the tube e, which is then closed by a tap (not represented in the
diagram); the tube d communicates with a recording apparatus, and any alteration in the
volume of the kidney is communicated by the oil in the tube to the chamber d of the Onko-
graph, figure 302.

the greater the pressure and flow of blood the greater the secretion of urine,
as wrould follow if the glomerulus were a filtering mechanism. However, if
the renal vein is partially obstructed, even though the blood pressure be in-
creased, the amount of urine secreted is sharply decreased. If the vein is
completely occluded, the secretion of urine not only ceases for the time but
does not immediately begin again when the blood pressure and flow are re-
established. The closure of the vein for only one or two minutes is said to
stop the flow of urine for as much as forty-five minutes. This short inter-
ruption of the circulation is sufficient to bring about other changes in the

EXPERIMENTAL OBSERVATIONS 415

glomerular epithelium, for it now excretes albumin, which it did not previ-
ously let pass. Therefore, it is not pressure merely that favors the secretion,
there must also be an efficient flow of blood. The secretion is influenced
especially by the amount of blood flowing through the kidney in a given time.
In the frog the kidney has a double blood supply. The renal artery
supplies the glomeruli, while a branch of the renal-portal vein supplies the
tubules. Nussbaum ligated the renal artery in one kidney of the frog, while
leaving the circulation of the other kidney undisturbed. He found that the
operated kidney secreted little or no urine, but that it could be made to secrete
by injections of urea, but not by injections of albumin or sugar as in the nor-

FIG. 302. — Roy's Onkograph, or Apparatus for Recording Alterations in the Volume
of the Kidney, etc., as shown by the onkometer. a, Upright, supporting recording lever /,
which is raised or lowered by the needle b, which works through/, and which is attached
to the piston e, working in the chamber d, with which the tube from the onkometer com-
municates. The oil is prevented from being squeezed out as the piston descends, by a
membrane, which is clamped between the ring-shaped surfaces of the cylinder by the screw
* working upward; the tube h is for filling the instrument.

mal kidney. Ligation of the renal-portal vein, which supplies the tubules
in the frog, caused a decrease in the quantity of the secretion, whereas, ac-
cording to Ludwig's view, it ought to have increased the quantity, since
obviously resorption could not take place with any degree of efficiency. In
the main, the evidence is in favor of the view that even the glomerular epi-
thelium does not filter merely, but that it, as living protoplasm, regulates
and controls the quantity and kind of material passing through it.

Microchemical observations have been enlisted to demonstrate more fully,
if possible, the activity of the different parts of the epithelial tubule. Heiden-
hain, by injections of indigo- blue into the blood stream, followed by rapid
fixation of the kidney in alcohol at the proper stage of elimination, has
demonstrated crystals of the pigment in the renal epithelial cells and in the
lumen of the tubule. He concluded that these cells were actively eliminating
the pigment by a secretory process. This observation has been questioned.

416 EXCRETION

But Heidenhain's view is strengthened by Bowman's observation that in birds
crystals of uric acid are to be seen in the cells of the convoluted tubules, and
in the lumen adjacent.

Only traces of the sugars and proteins of the blood are found in normal
urine, but when either cane sugar, peptone, or egg albumin is introduced into
the blood it is rapidly eliminated by the kidney. Egg albumin is not essen-
tially different from the serum albumin of the blood, but the serum albumin
is not excreted. These are both non-dialyzable compounds. Sugar and
urea, both readily dialyzable, present the same comparison, i.e., urea is ex-
creted, while sugar is not. If, however, the percentage of sugar is high, o . 25
per cent, or more, it is then eliminated. The excretion of the highly diffusible
sodium chloride bears a similar quantitative relation to excretion. If present
in the blood in relatively low amounts it is not secreted, while if the concentra-
tion is slightly greater it may be quickly eliminated. Other inorganic salts

FIG. 303. — Curve Taken by Renal Onkometer Compared with that of an Ordinary Blood-
pressure Curve, a, Kidney curve; b, blood-pressure curve. (Roy.)

present only in traces, are meanwhile rapidly eliminated. Even the rapid
elimination of a slight excess of water in the blood can scarcely be explained
on purely physical grounds. To discharge the water across the glomerulus
from the blood to the urine requires an expenditure of osmotic pressure much
greater than that balanced by the blood pressure. That is, the epithelial cells
must do work, and the energy is dependent on metabolism in the cells.

It would seem, therefore, that the separation of urine in the kidney is a
secretory process dependent on the protoplasmic activity of the living renal
cells, that the apparent selective property of the cells is a manifestation of
such activity, and that even water is actively secreted.

Diuretics. — Certain substances increase the flow of urine and are
called diuretics. They act directly on the renal epithelium, for example
urea, or indirectly on the circulatory system to increase the flow of blood.
Digitalis is a wrell-known diuretic which increases the efficiency of the circula-
tion. It also stimulates the renal epithelium with the production of a marked
increase in the flow of urine. Caffeine diuresis can best be explained on an
assumed stimulating action of the renal epithelium. Urea introduced into
the blood produces a copious secretion of urine. Both urea and the saline

THE DISCHARGE OF THE URINE 417

diuretics induce a flow of urine out of all proportion to the osmotic changes
produced, and they may be regarded as direct stimulators of the renal
epithelium, a view supported by their stimulative action on other tissues.

THE DISCHARGE OF THE URINE.

As each portion of urine is secreted, it propels that which is already in the
uriniferous tubes onward into the pelvis of the kidney. Thence it passes
through the ureter into the bladder, from which at intervals it is discharged
to the exterior. The rate and mode of entrance of urine into the bladder
has been watched in cases of ectopia vesicae, i.e., cases in which fissures in
the anterior or lower part of "the walls of the abdomen and of the front wall
of the bladder expose to view the orifices of the ureters. The urine does not
enter the bladder at any regular rate, nor is there a synchronism in its move-
ment through the two ureters. Ordinarily two or three drops enter the
bladder every minute, each drop as it enters first raising up the little papilla
on which the ureter opens, and then passing through the orifice, which at
once again closes like a sphincter. Its flow is aided by the peristaltic con-
tractions of the ureters, and is increased in deep inspiration or by straining.
The urine collected in the bladder is prevented from regurgitation into the
ureters by the mode in which these pass through the walls of the bladder,
namely, by their lying a half to three-quarters of an inch between the muscu-
lar and mucous coats before they turn rather abruptly fonvard and open
through the latter into the interior of the bladder.

Micturition. — The contraction of the muscular walls of the bladder
may by itself expel the urine with little or no help from other muscles. The
vesicular pressure is increased in the voluntary act by the contraction of
the abdominal and other expiratory muscles which bear on the abdominal
viscera, thus aiding in the expulsion of the contents of the bladder. The
diaphragm is at the same time fixed in contraction and the sphincter of the
bladder relaxes. The pressure within the bladder under the combined con-
tractions of these expulsive muscles sometimes amounts to 8 to 10 cm. of
mercury. The act is completed by the accelerator urinae muscle, which, as
its name implies, quickens the stream and expels the last drop of urine from
the urethra. The act is under the regulative control of a nervous center in
the lumbar spinal cord, through which, as in the case of the similar center for
defecation, the various muscles concerned are coordinated in their action.
It is well known that the act may be reflexly induced, e.g., in children who
suffer from intestinal worms or other such irritation. Generally the afferent
impulses which set up the reflexes leading to the desire to micturate are ex-
cited by overdistention of the bladder, or sometimes by a few drops of urine
passing into the urethra. This impulse passes up to the lumbar center or
centers, and reflexly produces on the one hand inhibition of the sphincter

4i8

EXCRETION

and on the other contraction of the necessary muscles for the expulsion
of the contents of the bladder. In the voluntary act these motor centers
are stimulated to activity by impulses coming from the higher cerebral
centers.

THE STRUCTURE AND EXCRETORY FUNCTIONS OF THE SKIN.

The skin serves, i, as an external integument for the protection of the
deeper tissues, and 2, as a sensitive organ in the exercise of touch, a subject
to be considered in the chapter on the Special Senses. It is also, 3, an im-
portant secretory and excretory organ; and 4, an absorbing organ. 5, It
plays an important part in the regulation of the temperature of the body by

FIG. 304. — Vertical Section of the Epidermis of the Prepuce, a, Stratum corneum,
of very few layers, the stratum lucidum and stratum granulosum not being distinctly
represented; &, c, d, and e, the layers of the stratum Malpighii, a certain number of the cells
in layers, d; and e showing signs of segmentation; layer c consists chiefly of prickle or ridge
and furrow cells;/, basement membrane; g, cells in cutis vera. (Cadiat.)

controlling the loss of heat, i.e., a temperature-regulating function, discussed
in the chapter on Animal Heat.

Structure. — The skin consists principally of a vascular tissue named
the corium, derma, or cutis vera, and of an external covering of epithelium
termed the epidermis or cuticle. Within and beneath the corium are em-
bedded several organs with special functions, namely, sudoriferous glands,
sebaceous glands, and hair follicles; and on its surface are sensitive papilla.

STRUCTURE

419

The so-called appendages of the skin — the hair and nails — are modifications
of the epidermis.

The epidermis is composed of several strata of cells of various shapes and
sizes; it closely resembles in its structure the epithelium of the mucous mem-
brane that lines the mouth or covers the cornea. The following four layers
may be distinguished.

FIG. 305. — Vertical Section of Skin. A, Sebaceous gland opening into hair follicle;
B, muscular fibers; C, sudoriferous or sweat gland; D, subcutaneous fat; E, fundus of hair
follicle, with hair-papillae. (Klein.)

The stratum lucidum, a homogeneous membrane, consisting of squamous
cells closely arranged, in some of which a nucleus can be seen. Stratum
granulosum, consisting of one layer of flattened, fusiform, distinctly nucleated
cells. Stratum Malpighii or rete mucosum consists of many strata of cells.
The deepest cells, placed immediately above the cutis vera, are columnar
with oval nuclei, succeeded by a number of layers of more or less polyhedral
cells with spherical nuclei; the more superficial layers are considerably
flattened. The deeper surface of the rete mucosum is accurately adapted

420 EXCRETION

to the papillae of the true skin, being, as it were, molded on them. It
is very constant in thickness in all parts of the skin. The cells of the middle
layers of the stratum Malpighii are connected by processes, and thus form
prickle cells, figure 28. The pigment of the skin, in the deeper cells of the rete
mucosum, causes the various tints observed in different individuals and differ-
ent races. The epidermis maintains its thickness in spite of the constant wear
and tear to which it is subjected. The columnar cells of the deepest layer
of the rete mucosum elongate, multiply by division, the new cells produced
being pushed toward the free surface of the skin. There is thus a constant

production of fresh cells in the deeper
layers, and a constant throwing off of
old ones from the free surface. When
these two processes are accurately
balanced, the epidermis maintains its
thickness. When by intermittent
pressure a more active cell growth is
stimulated, the production of cells ex-
ceeds their waste and the epidermis
increases in thickness, as we see in
the horny hands of the laborer.

FIG. 3o6.-Terminal Tubules of The dermis> or cutis vera °r ^

Sudoriferous Glands, Cut in Various skin, is a dense and tough, but yielding

°he Skln °f thC Pig'S

D. rris.) and highly elastic structure support-

ing the epidermis. It is composed of

areolar connective tissue interwoven in all directions and forming numerous
spaces by its interlacements. These areolae in the deeper layers of the cutis
are usually filled with masses of fat cells, figure 305. Unstriped muscu-
lar fibers are also abundantly present, especially in the skin of animals which
erect the hairs with greater ease than is usually the case with man.

There is a rich network of blood vessels to the dermis. In the dermal
papillae and about the sweat glands there are special loops of capillaries.
Nerve fibers are also distributed to the papillae.

The special nerve terminations in the skin have been described on page 75.

Glands of the Skin. — The skin possesses glands of two kinds: Sudor-
iferous or sweat glands, and the sebaceous or oil glands.

A sudoriferous or sweat gland consists of a small lobular mass, formed
of a coil of a simple tubular gland, surrounded by blood vessels, and em-
bedded in the subcutaneous adipose tissue, figure 305, C. The duct as-
cends from this coiled mass for a short distance in a spiral manner through
the cutis and the epidermis, and then opens on the surface of the skin. In
the parts where the epidermis is thin, the ducts themselves are thinner
and more nearly straight in their course.

The duct is lined writh a layer of columnar epithelium continuous with

THE EXCRETORY FUNCTION OF THE SKIN

421

the epidermis. The coiled or secreting portion of the gland is lined with
at least two layers of short columnar cells with very distinct nuclei, figure 306.
The lumen is distinctly bounded by a special lining of cuticle.

The sudoriferous glands are abundantly distributed over the whole sur-
face of the body; but are especially numerous, as well as very large, in the
skin of the palm of the hand and of the sole of the foot. The glands by
which the peculiarly odorous matter of the axillae and groin is secreted form
a nearly complete layer under the cutis,
and are like the ordinary sudoriferous
glands, except in being larger and having
very short ducts.

The peculiar bitter yellow substance
secreted by the skin of the external
auditory passage is named cerumen, and
the glands themselves ceruminous glands;
but they do not much differ in structure
from the ordinary sudoriferous glands.

The sebaceous glands, figures 305
and 306, like sudoriferous glands, are
abundant in most parts of the surface of
the body, particularly in parts largely
supplied with hair, as the scalp and face.
They are thickly distributed about the
entrance of the various passages into the
body, as the anus, nose, lips, and ex-
ternal ear. They are entirely absent
from the palmar surface of the hand and
the plantar of the foot. They are
racemose glands composed of an aggre-
gate of small tubes or sacculi lined with columnar epithelium and filled
with an opaque white substance, like soft ointment, which consists of
broken-up epithelial cells which have undergone fatty degeneration. Mi-
nute capillary vessels overspread them; and their ducts open on either the
surface of the skin, close to the hair, or, which is more usual, directly into
the follicle of the hair. In the latter case, there are generally two or more
glands to each hair, figure 306.

The story of the structure and development of such epithelial structures
as the hair and nails is best left to the histologist, to whom the student is
referred.

The Excretory Function of the Skin. — The function of the skin which
is of special interest to this chapter is that of the secretion of the sweat. The
fluid secreted by the sweat glands is usually formed so gradually that the
watery portion of it escapes by evaporation as fast as it reaches the surface.

FIG. 307.— Sebaceous Gland from
Human Skin. (Klein and Noble
Smith.)

422 EXCRETION

But during strong exercise, exposure to great external warmth, in some
diseases, and when evaporation is prevented, the secretion becomes more
sensible and collects on the skin in the form of drops of fluid.

The perspiration, as the term is sometimes employed in physiology, in-
cludes all that portion of the secretions and exudations from the skin which
are thrown on the surface by the sweat glands. As a matter of fact, this is
mingled with various substances lying on the surface of the skin. The con-
tents of the sweat are, in part, matters capable of assuming the form of vapor,
such as carbonic acid and water, and in part other matters which are
deposited on the skin, and mixed with the sebaceous secretions.

The secretion of the sebaceous glands and hair follicles consists of cast-
off epithelium cells, with nuclei and granules, together with an oily material
and extractive matter. In certain parts, also, it is mixed with a peculiar
odorous principle, which contains caproic, butyric, and other fatty acids.
It is similar in composition to the unctuous coating, or vernix caseosa, which
is formed on the body of the fetus while in the uterus, and which contains
ordinary fat and cholesterol esters with fatty acids. This sebaceous secre-
tion serves the purpose of keeping the skin moist and supple, and, by its oily
nature, of both hindering the evaporation from the surface and guarding
the skin from the effects of the long-continued action of moisture. But
while it thus serves local purposes, its removal from the body entitles it to be
listed among the excretions of the skin.

CHEMICAL COMPOSITION OF SWEAT.

Water 995

Solids: 5

Organic acids (formic, acetic, butyric, pro-

pionic, caproic, caprylic) 0.9

Salts, chiefly sodium chloride 1.8

Neutral fats and cholesterol 0.7

Extractives (including urea), with epithelium i .6

The sweat is a colorless, slightly turbid fluid, alkaline, neutral or acid in
reaction, of a saltish taste, and peculiar characteristic odor.

Of the several substances it contains, however, only the carbon dioxide
and water need particular consideration.

. The quantity of water vapor excreted from the skin is, on an average,
between 750 and 1,000 c.c. daily. This subject has been very carefully
investigated by Lavoisier and Sequin. The latter chemist enclosed his
body in an air-tight bag provided with a mouthpiece. The bag was closed
by a strong band above, and the mouthpiece adjusted and gummed to the
skin around the mouth. He was weighed, then remained quiet for several

INFLUENCE OF THE NERVOUS SYSTEM ON SWEAT SECRETION 423

hours, after which time he was again weighed. The difference in the two
weights indicated the amount of loss by pulmonary exhalation. Having
taken off the air-tight dress, he was immediately weighed again, and a fourth
time after a certain interval. The difference between the two weights last
ascertained gave the amount of the cutaneous and pulmonary exhalation
together; by subtracting from this the loss by pulmonary exhalation alone,
while he was in the air-tight dress, he ascertained the amount of cutaneous
transpiration. The average loss by cutaneous and pulmonary exhalation in
a minute during a state of rest was eighteen grains — the minimum eleven
grains, the maximum thirty-two grains. Of the eighteen grains, eleven
passed off by the skin and seven by the lungs.

The quantity of watery vapor lost by transpiration is, of course, influenced
by all external circumstances which affect the exhalation from evaporating
surfaces, such as the temperature, the hygrometric state, and the stillness
of the atmosphere. But, of the variations to which it is subject under the
influence of these conditions, no calculation has been exactly -made.

The quantity of carbon dioxide exhaled by the skin on an average is
said to be about one two-hundredth of that eliminated by the pulmonary
respiration.

The cutaneous exhalation is most abundant in the lower classes of ani-
mals, more particularly the naked amphibia, as frogs and toads, whose skins
are thin and moist, and readily permit an interchange of gases between the
circulating blood and the surrounding atmosphere. Bischoff found that,
after the lungs of frogs had been tied and cut out, from 3 to 4 c.c. of carbon
dioxide gas was exhaled by the skin in eight hours. And this quantity
is very large, when it is remembered that a full-sized frog will generate only
about 10 c.c. of carbon dioxide by his lungs and skin together in six hours.

The importance of the respiratory function of the skin, which was once
thought to be proved by the speedy death of animals whose skins, after re-
moval of the hair, were covered with an impermeable varnish, has been shown
by further observations to have no foundation in fact. The immediate cause
of death in such cases is the interference with temperature regulation.

Influence of the Nervous System on Sweat Secretion. — The secre-
tion of sweat is closely connected with the quantity of blood flowing through
the cutaneous vessels. The quantity of sweat increases with vaso-dilatation
and diminishes with vaso-constriction. The sweat glands are also under the
control of efferent impulses passing to them from the special sweat centers
in the brain and spinal cord through special sweat nerves. Thus, if the
sciatic nerve be divided in a cat and the peripheral end be stimulated, beads of
sweat are seen to appear upon the pad of the corresponding foot. The sweat
appears even though at the same time the blood vessels are constricted, or
the blood flow entirely stopped by compression of the aorta, whereas if atropin
is injected previously to the stimulation, no sweat appears, although dila-

424 EXCRETION

tation of the vessels may be present. Secretion of sweat, too, may be brought
about reflexly.

The circulation of venous blood in the spinal bulb causes the sweating of
phthisis and of dyspnea generally, by stimulating the sweat center. If the
cat whose sciatic nerve is divided be rendered dyspneic, abundant sweat
occurs upon the foot of the uninjured, and none on the injured, side. The
effect of heat in producing sweating may be both local and general, and, again,
the various drugs which produce an increased secretion of sweat do not all
act in the same way; thus, there is reason for thinking that pilocarpine acts
upon the local apparatus, that strychnine and picrotoxin act upon the sweat
centers, and that nicotine acts both upon the central and upon the local
apparatus.

The special sweat nerves appear to issue from the spinal cord, in the
case of the hind limb of the cat, by the last two or three dorsal and first
two to four lumbar nerves, pass to the abdominal sympathetic, and from
thence to the sciatic nerve, the general course of the autonomic nerves
for this region. In the case of the fore limb, the nerves leave the cord
by the first to the sixth dorsal nerves, pass into the thoracic sympathetic,
and then join the brachial plexus, reaching the arm through the median and
ulnar nerves.

It will be as well to restate here the other functions which the skin sub-
serves. In addition to its excretory office, we have seen that it acts as a
channel for absorption. It is also concerned with the special senses, that of
touch and temperature, to the consideration of which as well as to its function
of regulating the temperature of the body we shall presently return. By its
general impermeability it prevents the loss of moisture of the body by direct
evaporation from the tissues. It should be recollected, however, that apart
from these special functions, by means of its toughness, flexibility, and elastic-
ity, the skin is eminently qualified to serve as the general integument of the
body, for defending the internal parts from external violence, while readily
yielding and adapting itself to their various movements and changes of
position.

LABORATORY EXPERIMENTS IN EXCRETION.
PHYSIOLOGICAL REACTIONS.

i. The Relation of Blood Flow through the Kidney to the Secre-
tion of Urine. — Properly to check this experiment one should make three
determinations: i, the general blood pressure; 2, the volume of the kid-
ney; 3, the amount of urine secreted. Anesthetize a dog and arrange the
apparatus for taking the blood pressure as directed in experiment 19. Pre-
pare a renal onkometer, see figures 301 and 302, and an onkograph for re-
cording the variations in the volume of the kidney. The renal onkometer

PHYSIOLOGICAL REACTIONS 425

consists of a double metal box to fit the form of a kidney. The inner halves
of this box should be covered so loosely with very thin sheet rubber that the
rubber can be fitted into the bottom of the cup without undue tension. The
rubber must be sealed to the outer edges of this inner cup with rubber cement
and allowed to dry. When it is completely dried the inner cup should be ad-
justed to the outer, and the spaces enclosed by the rubber sheet filled with
water. Or the onkometer may be closed with parchment and filled with oil
as described in experiment 23 on the Circulation. The half of the onkom-
eter that comes against the wall of the body cavity of the animal should be
completely closed with a stopper before the instrument is adjusted to the
kidney. Now adjust the onkometer to the kidney, taking care to place
the renal arteries, veins, and ureter in the tube in such a way as not to com-
press them. Fill the outer cup with water and connect this cavity by a
two-way cannula with the recording onkograph. In practice it is more
satisfactory if one introduces between the onkometer and onkograph an over-
flow bottle or bulb, adjusted to maintain the constant pressure on the kidney.
This direction varies from the usual one in that rubber sheeting instead of
parchment is used to cover the inner cup of the onkometer, a method that
permits the use of water instead of oil.

Isolate and insert a small cannula into the ureter. This cannula should
be clamped in a stand at a level as little above that of the kidney as possible.
The urine secreted may be collected in a 10 c.c. graduated cylinder and
measured at intervals of 5 or 10 minutes. Or, if the outflow is scanty, it may
be allowed to drop on a tambour recording apparatus, the rate of dropping
being indicative of the rapidity of secretion.

Determine the normal rate of secretion of a dog under constant anesthesia.
The anesthesia should be medium to light, but should be kept very uni-
form so as to maintain a strong blood pressure. Note the effect on secre-
tion and the corresponding effect on blood pressure and the kidney volume
produced by vagus inhibitions. Section the vagus nerves and produce in-
hibition by stimulating the peripheral end of the vagus. In this instance
there are no reflexes to complicate the experiment, so that the fall in blood
pressure is a direct cardiac effect. Stimulate the central end of the vagus
which produces a fall of blood pressure through the vaso-motor system.
There should be a normal period of at least ten minutes following each ex-
periment to allow the secretion of the kidney to return to the normal.

Expose the splanchnic nerves at the point where they pass beneath the
diaphragm into the abdominal cavity. Adjust a pair of shielded electrodes,
close the cavity, and, when the animal has returned to the normal uniform
rate of secretion and of blood pressure, stimulate the splanchnic nerves.
The splanchnics contain vaso-constrictor nerves for the kidney. The on-
kometer experiment should, therefore, demonstrate a sharp decrease in the
volume of the organ, while the blood pressure is only slightly changed. The

426 EXCRETION

rate of secretion should be followed for at least twenty minutes after stimula-
tion of the splanchnics. This test should be repeated two or three times.

In this connection demonstrate the influence of deep chloroform anesthe-
sia on urinary secretion. The chloroform should be pushed to the danger
limit and maintained there for a couple of minutes or more. Compare the
rapidity of the recovery of blood pressure with the recovery of the rate of
secretion.

2. Secretory Nerves for the Sweat Glands. — Langley has mapped
out the paths of the secretory nerves for the sweat glands. He has shown
that in the cat these fibers are distributed to the hind limb through the sciatic.
Anesthetize a half-grown cat, isolate the sciatic nerve, cut it and stimulate the
peripheral end with a medium to strong induction current. After a few
moments beads of perspiration will appear on the pads of the foot, which
should therefore be carefully examined before the experiment.

URINE ANALYSIS.

3. Daily Quantity. — Determine the total quantity, for 24 hours, of
urine secreted through a period of 3 or 4 days, beginning and ending the
period at a definite hour in the day, preferably on rising in the morning.
The daily secretion varies through wide extremes, depending upon the quan-
tity of liquid taken in the food, the daily exercise, the temperature, etc., etc.
In the analysis of urine it is always better to take a mixed 24-hour sample.

4. Specific Gravity. — Determine the specific gravity of 24-hour urine.
This is done by the instrument known as the urinometer which carries
a graduated scale at the neck. Care should be taken to float the urinom-
eter so that it does not come in contact with the measuring cylinder. The
scale should be read at the bottom of the meniscus.

5. Reaction. — Determine the reaction of perfectly fresh urine, using
litmus paper. The normal urine is slightly acid under ordinary conditions,
due to the presence of acid phosphates or perhaps in some cases to traces of
free organic acid.

After standing some time the reaction is usually alkaline, o\ving to fer-
mentation processes. The reaction may vary also according to the food,
vegetable foods tending to produce alkaline urine, while with animal foods
the reaction is acid.

6. The Total Quantity of Solids. — Determine the solids of urine
by evaporating 25 c.c. of a mixed sample of urine to dryness in a weighed
platinum or porcelain dish over a water bath. The residue should be dried
to constant weight in a drying oven at 105° C.

A useful rule for approximately estimating the total solids in any given
specimen of healthy urine is to multiply the last two figures representing the
specific gravity by 2 . 33. Thus, in urine of specific gravity 1025, 2.33X25 =

PHOSPHATES

427

58.25 grains of solids are contained in 1,000 grains of the urine. Or the
total solids are 5.825 per cent. In using this method it must be remem-
bered that the limits of error are much wider in diseased than in healthy
urine.

The solids of urine consist of inorganic salts of sodium, potassium, and
calcium, and of a long list of organic compounds, chiefly nitrogenous.

7. Chlorides. — Large quantities of sodium chloride are always present
in the normal urine. Add ammonia to 25 or 50 c.c. of albumin-free urine
and heat to precipitate earthy phosphates, filter. To a

sample of the nitrate add an excess of strong nitric acid
and a few drops of i per cent, silver nitrate. A white
flocculent precipitate of silver chloride comes down. This
precipitate is soluble in an excess of ammonia. Repre-
cipitate by adding nitric acid again. The test may be
made without removing the phosphates, though in this
case, upon adding ammonia, the disappearance of the
silver precipitate is complicated by the appearance of
insoluble phosphates.

The chlorides may be estimated quantitatively by
Yolhard's method, or some one of its modifications, which
depends upon the determination of the amount of chloride
precipitated by the silver. The student is referred to
chemical text-books for this and other quantitative
methods.

8. Sulphates. — Sulphates exist in the urine both in
inorganic and organic compounds, chiefly the former.
Add a few drops of hydrochloric acid to a sample of

urine in a test-tube, then a solution of barium chloride, the insoluble barium
sulphate settles out. If the test is made on the normal urine without the
addition of the acid, the inorganic sulphate will be precipitated, while the
ethereal or compound sulphate will remain in solution and can be filtered
off. This filtrate, when boiled with strong hydrochloric acid to 10 per cent,
over a water bath for a short time, will have the sulphates split off from the
organic radicle and may be precipitated by the addition of barium chloride
in hot solution.

9. Phosphates. — The phosphates of urine consist of the earthy and
alkaline salts, the latter predominating. Take a 50 c.c. sample of urine,
add strong ammonia, and heat. The phosphates of calcium and magnesium
separate out, as they are insoluble in alkaline solution. Filter.

To the filtrate add a solution of magnesium sulphate. This precipitates
the sodium and potassium phosphates as a triple phosphate of magnesium
which is insoluble. Test for phosphates in general are:

Add nitric acid to a sample of urine, warm gently, then add a few drops

FIG. 308.— The
Urinometer.

428

EXCRETION

of 10 per cent, ammonium molybdate; a yellow precipitate of ammonium
phospho-molybdate is formed. Or, add acetic acid, then a few drops of
uranium acetate; a bright yellow precipitate of uranium ammonium phos-
phate is formed. These two reactions are used as the basis for a quan-
titative determination of phosphorus.

10. The Preparation of Urea. — Take 100 c.c. of normal urine, evap-
orate to one-half its quantity, and precipitate the phosphates and sulphates
by adding a mixed solution of barium hydrate and nitrate. Filter, evaporate
the nitrate to dryness, take up in warm 95 per cent, alcohol, and*refilter.
Crystals of urea separate out when the alcohol is evaporated off.

FIG. 309. — Doremus' Ureometer.

Evaporate a large sample, 200 c.c., of urine to a syrupy mass, add nitric
acid. Crystals of urea nitrate are formed. Wash the crystals in dilute nitric
acid, then dissolve in water. The urea is set free by adding barium carbonate
until the carbon dioxide ceases to come off. Filter, evaporate over a water
bath to dryness, and dissolve the urea in 95 per cent, alcohol; decant, and
recrystallize by evaporating off the alcohol. (ij*

11. Urea Determination by Doremus' Ureometer. — Fill the ureom-
eter with hypobromite of sodium solution. Take a sample of urine in
the pipet which accompanies the instrument, drawing it exactly to the
mark. Insert the pipet past the bend of the ureometer and slowly and
carefully empty the urine so as not to lose any of the liberated nitrogen.
The instrument is graduated to read off the percentage of urea directly.

12. Uric Acid. — Concentrate over a water bath 500 c.c. of urine to
100 c.c. and boil with 10 c.c. or more of strong hydrochloric acid. Upon

ABNORMAL CONSTITUENTS OF URINE 429

cooling, crystals of uric acid are formed. Decant the supernatant liquid and
wash the crystals with a few cubic centimeters of 10 per cent, hydrochloric
acid. Dissolve the crystals and test.

The Murexide Test. — Add to 2 c.c. of uric acid solution in a test-tube an
equal quantity of nitric acid. Heat gently, a reddish ring forms at the point
of contact between the nitric acid and uric acid solution. Cool and add
ammonia carefully. The color ring deepens to a purple color. This test
succeeds well by evaporating a few drops of uric acid on a porcelain plate.
Add to the stain a drop of concentrated nitric acid and evaporate. Concen-
tric rings of reddish color will be formed. This color deepens to reddish -
purple when a drop of ammonia is added.

13. Creatinin. — Test 20 c.c. of urine in a beaker for creatinin by
adding a cubic centimeter of dilute solution of sodium nitroprusside and then
weak sodium hydrate. A ruby-red color, which quickly turns yellow, indi-
cates the presence of creatinin (Weyl's reaction). If the yellow solution
has an excess of acetic acid added and is then boiled, it turns first green and
later blue, forming ultimately a precipitate of Prussian blue. Urine mixed
with picric acid gives a red coloration when made alkaline with caustic
alkali solution.

14. Total Nitrogen in Urine. — Determine the total nitrogen in a sample
of urine by the Kjeldahl method. This method depends upon the con-
version of all the nitrogen to ammonia, the distillation of this ammonia
into a known quantity of sulphuric acid, and the final titration of the excess
of sulphuric acid when the distillation is complete. The computation is
made on the basis that i c.c. of a normal sulphuric acid is equivalent to
i c.c. normal sodium hydrate, and that in turn to i c.c. of ammonium
hydrate. The ammonia neutralizes a portion of the sulphuric acid in the
distillation. One c.c. of normal ammonium hydrate contains 0.014 gram
nitrogen, from which the total nitrogen in the sample used can be readily
computed.

15. Pigments of Urine. — The normal color of the urine is due to the
presence of a pigment, urobilin. Prepare urobilin by adding lead acetate
to a 200 c.c. sample of urine. A precipitate forms which carries down the
coloring mater. Filter. Add acid alcohol to the precipitate to extract the
coloring mater, refilter, which gives a deep yellow solution. Shake up with
a few cubic centimeters of chloroform which dissolves the pigment. Draw
off the chloroform solution and allow to evaporate. The residue is a brown-
ish mass of urobilin.

ABNORMAL CONSTITUENTS OF URINE.

Many abnormal constituents may appear in the urine under pathological
conditions, only two of which will be mentioned here.

1 6. Albumin in the Urine.— The detection of the presence of albumin,

430 EXCRETION

albuminuria, is of considerable clinical importance. The following are the
standard tests which present no special difficulty except when traces only
are present.

Heat Coagulation. — Take a half test-tube of urine, boil, and add a drop
of dilute acetic acid. A white coagulum indicates the presence of albumin.
A faint cloudy appearance indicates traces.

Nitric Acid Test. — To 5 c.c. of strong nitric acid in a conical test-tube
add 10 or 15 c.c. of urine, pouring it gently down the inclined side of the glass.
Allow the glass to stand for a few minutes, when a white coagulum appears
just above the line of contact of the acid with the urine. This test, known
as Heller's test, will usually indicate the presence of traces of albumin.

Picric Acid Test. — Add picric acid to a sample of urine. A whitish
precipitate of albumin will appear at the line of contact, as in the preceding
test.

Citric acid two parts and picric acid one part, when boiled with urine
will coagulate minute traces of the proteid.

17. Detection of Sugar in the Urine. — Trommels Test. — The pres-
ence of sugar in the urine can usually be detected by Trommer's test,
which depends upon the reduction of copper sulphate in the presence of
strong alkali. Boil fresh Fehling's solution and add to it a few drops of
urine. When sugar is present a reddish-yellow precipitate of copper oxide
comes out. The test should be set away for a few minutes when, if only
traces of the reduction are present, a reddish-brown stain will appear on
the bottom of the test-tube. Uric acid, if present in excess, may produce
a slight precipitation of the copper.

Fermentation Test. — If sugars are present in the urine, they can be de-
tected by adding yeast to a fermentation tube filled with urine, the liberation
of carbon dioxide indicating the presence of sugar. Cane sugar does not
support the growth of yeast, so it forms an exception by this test.

Phenyl-Hydrazin Test. — Phenyl-hydrazin forms crystals of phenyl-
glucosazone. To 10 c.c. of urine in a small beaker add o.i of a gram of
phenyl-hydrazin hydrochloride and a double quantity of sodium acetate.
Heat in the water bath for 20 minutes. Upon cooling a deposit of yellow
crystals of phenyl-glucosazone takes place, if glucose is present.

1 8. Quantitative Determination of Sugar in the Urine. — Fill a 10
c.c. graduated pipet with freshly prepared Fehling's solution. Take 10 c.c.
of urine, measured with a dropping-pipet into a small beaker, and boil.
While continuing to boil, add Fehling's solution slowly and cautiously so
long as the color is discharged. The amount of Fehling's required to reduce
the sugar is a measure of the quantity of reducing sugar present — i c.c. of
Fehling's being equivalent to 5 milligrams of dextrose.

For the presence of blood pigments and other abnormal constituents of
the urine, the student is referred to special handbooks on the subject.

CHAPTER XI
METABOLISM, NUTRITION, AND DIET.

THE term metabolism means, literally, an exchange of material. In its
broadest physiological sense it includes the study of the exchange of material
between the living tissues of the body and their surrounding media. This
includes the study of the income and outgo of material; the storing of energy-
yielding materials in the body; the transfer of this potential energy into kinetic
energy; and the nutritional processes within the various tissues. The build-
ing up of absorbed food material into the protoplasm of the cell or of simpler
compounds into more complex ones, which may be stored in the cell, is known
as anabolism, and the compounds themselves as anabolites. The breaking
down of these substances into simpler forms, whereby the potential energy
of the anabolites is transformed into kinetic energy, is known as katabolism,
and its products as katabolites.

In order to form an estimate of these processes going on in the body, the
amount and nature of the ingested material must be known, as well as the
amount of refuse or unused material that passes out of the alimentary canal
as feces, and the amount of excreted material from the various excretory
organs. It is also necessary to know the potential energy of the ingested
materials, and the possible potential energy must be checked against the ac-
tual energy liberated.

The food is intended to supply the place of the material which has been
utilized by the body, and, in a simpler form, eliminated in the excretions.
But in the choice of a diet this is not enough; the food should be sufficient
to supply such need without waste and without unduly increasing the output
of excreta, while at the same time the body should be maintained in health,
without increase or loss of weight. The food must also supply the energy
liberated without undue waste of the tissues themselves.

These requisites of a diet scale then allow for wide alterations in the
amount of different kinds of foods under different circumstances. Numer-
ous and most valuable experiments have been performed in recent years to
determine just what each article of the common food materials contributes to
the growth of the tissues and to the kinetic energy liberated by the tissues.
The potential energy of the food can also be checked against the kinetic
energy liberated. A single illustration of this class will serve. In an experi-
ment with mixed food lasting through four days, on a man with body weight
of 64 kilograms, and doing a minimum amount of work, Atwater made the
following determinations:

431

432 METABOLISM, NUTRITION, AND DIET

WEIGHT, COMPOSITION, AND HEAT OF COMBUSTION OP FOODS AND EXCRETA

PER DAY.

| ,

E

&

>> w

c

C

8j

•^ >>

£

d

"S

CO

*0 %

8

c
o

,Q

8

0 %

gv

1

1

1

ft

a1

•+j

W

I""

Food

Grms.

Grms.

Grms.

Grms.

Grms.

Grms.

Grms.

Grms.

Calor-
ies

Beef

IOO

6l.2

•? e . i

•? i

<: 62

20 o ?

2 90

227

Butter

25

2.6

•5

21 . I

.08

T5-77

2.50

194

Whole milk

850

726.8

32-3

45-1

39-9

5.10

67.74

9-94

768

Bread

300

123.9

22 .2

I 2 . O

139.2

3-90

82.53

12 .24

835

Shredded wheat

50

4.1

4.8

•7

39-7

.84

20 .46

2.87

204

biscuit.

Ginger snaps ....

50

3-3

2.8

3-6

39-2

• 5°

21.12

3-07

212

Sugar

20

20 o

8 4-?

I "'O

7 O

/ y

Total food per

!,395

921.9

97-7

85.6

278.0

16.04

236.09

34.82

2,5I9

day.

Average feces per

98.8

77-7

7-7

4.0

6-3

1.23

9.98

1.42

I 10

day.

Average urine per

1420 8

1363 . o

1 5 85

1 1 . 7O

2 08

I ? c

day.

Excretions — lungs

881 .0

221.?

2 3 Q 7

and skin.

Total excreta per ....

2322 .6

17.08

243

•27

4

.40

2,642

day.

i

I

|

Balance

I

— I . OA

7

T«

+ 30

4.2

1 2 3

Careful analyses of the excreta, many of which we have already had oc-
casion to call attention to, show that they are made up, besides water, chiefly
of the chemical elements carbon, hydrogen, oxygen, and nitrogen, but that
they also contain, to a less extent, sulphur, phosphorus, chlorine, potassium,
sodium, calcium, magnesium, iron, and certain other of the elements. Since
this is the case it must be evident that, to balance this waste, foods must be
supplied containing all these elements to a certain degree, and some of
them in large amount, viz., those which take a principal part in forming
the excreta.

The waste products of the body are eliminated through the lungs, the
skin, the alimentary canal, and the kidneys. In the lungs the chief waste
product is water and carbon dioxide gas. Some carbon dioxide gas and small
quantities of urea and salts are eliminated through the skin. From the
alimentary canal there are lost, through the feces, the indigestible and un-

METABOLISM, NUTRITION, AND DIET

433

absorbed substances from the food, together with products secreted into the
canal by the liver, pancreas, and mucous membrane. The secretion lost
daily by the kidney, aside from a large quantity of water, consists of nitrog-
enous waste products, chiefly urea., and inorganic solids, as were mentioned
in the chapter on Excretion.

The relations between the amounts of the chief elements contained in these
various excreta in twenty-four hours mav be thus summarized:

water. ! u. ±1.

JN. 1 U.

By the

lungs . 33° 248.8

6<\i . i ^

By the

skin 660 2 6

7 2

By the
By the

urine * , 7 o& 9-8 3.3
feces 120 20.0 3.0

15.8 1 1 . 1

3.0 i 12.0

Grams. . .

2,818

281 .2 6.3 18.8 i 681.45

From the water in this table should be subtracted the 296 grams of water
which are produced by the union of hydrogen and oxygen in the body during
the process of oxidation, and there should be added to the respective columns
the corresponding amounts of the constituent elements, i.e., 33 grams of
hydrogen and 262 grams of oxygen. There are 26 grams of salts eliminated
through the urine, and 6 by the feces; a total of 32 grams.

The quantity of carbon daily lost from the body amounts to about 281 . 2
grams and of nitrogen 18.8 grams, and if a man could be fed by these ele-
ments, as such, the problem would be a very simple one; a corresponding
weight of charcoal and, allowing for the oxygen in it, of atmospheric air
would be all that is necessary. But an animal can live upon these elements
only when they are arranged in a particular manner with others, in the form
of such food stuffs as we have already enumerated, page 322 et seq.; more-
over, the relative proportion of carbon to nitrogen in either of these com-
pounds alone is by no means the proportion required in the diet of man.
Thus, in protein, the proportion of carbon to nitrogen is only as 3.5 to i.
If, therefore, a man took into his body, as food, sufficient protein to supply
him with the needed amount of carbon, he would receive more than four times
as much nitrogen as is needed; and if he took only sufficient to supply him
with nitrogen, he would be starved for want of carbon. It is plain, therefore,
that he should take with the albuminous part of his food, which contains so
large an amount of nitrogen in proportion to the carbon he needs, substances
in which the nitrogen exists in relatively much smaller quantities than the
carbon.
28

434

METABOLISM, NUTRITION, AND DIET

It is, therefore, evident that the diet must consist of several compounds,
not of one alone.

Many valuable observations have been made with a view of ascertaining
the effect upon the metabolism of a variation in the amount and nature of
food. These are of great assistance in the consideration of dietetics.

METABOLISM OF PROTEINS.

Nitrogenous Equilibrium. — Experiments have been made, to a con-
siderable extent upon dogs, which demonstrate the necessity for protein
food. After a preliminary period without food, during which the output of
nitrogen as shown by the urea has diminished to a comparatively constant
amount, an animal is fed with a diet of lean meat which would suffice to pro-
duce the amount of urea, and so of flesh, which it has been losing during its
starvation period. The effect of this, however, is at once to send up the
amount of urea excreted to a point above that which had been lost previous
to the commencement of the flesh diet. Thus the output of nitrogen still
exceeds its income, and the weight of the animal continues slowly to dimin-
ish. It is only after a considerable increase of the flesh given in the food that
a point is reached where the income and the expenditure of nitrogen are equal,
and at which the animal is not using up quickly or slowly the nitrogen of its
own tissue, and is no longer losing flesh. This condition in which the nitro-
gen of the egesta equals the nitrogen of the ingesta is known as nitrogenous
equilibrium.

EXPERIMENT IN NITROGENOUS EQUILIBRIUM.

N N

Per cent.

S

S

E

•ays of experiment.

Intake. Output.

Differ-

Intake.

Output.

Grams. Grams.

ence.

Grams.

Grams.

T

i—< . .

1
90 . oo 89 . 81

— O . 2 I

6-12

131 .60 132 .75

+ 0.88

TT

I — 2

•2 ^ 80 36 1 6

-j- i oo

3-11

144.50 143 .13

-0.86

TTT

1—7 . .

I ^4 8 I I ^ 3 O2

— o ^ i

8-17

213.72 213.26

— 0 . 21

12.77

12.79

In the dog, according to Waller, nitrogenous equilibrium does not occur
until the amount of flesh of the food is over three times as great as would be
necessary to supply the nitrogen of the urine during a period of starvation.
Thus a dog excretes during a starvation period 0.50 gram of urea per kilo

THE ROLE OF PROTEINS IN METABOLISM 435

of body weight; in order to satisfy this waste it wrould be necessary to ad-
minister i . 50 grams per kilo of meat; this at once increases the urea excreted
to about 0.75 gram per kilo of body weight, and nitrogenous equilibrium
is not attained until over three times, viz., 3 grams per kilo of body weight,
of meat is given. Foster gives even a larger figure. The effect, therefore,
of protein food is largely to increase the excretion of urea.

Studies in nitrogenous equilibrium are based on the fact that when an
animal is given a diet with a constantly increasing amount of protein food
from day to day, after a fe\v days the total nitrogen found in the excreta
exactly balances that taken in the food. This condition of nitrogenous
equilibrium is established at different levels, varying sometimes according to
the individual and with the kind and quantity of other food principles taken
at the same time as the nitrogenous foods.

Chittenden's latest metabolism experiments have shown that with free
choice, but moderate use, of accessory articles of diet, the human body can
maintain itself in nitrogenous equilibrium for at least several months on an
average of 6 to 10 grams of nitrogen per day, the equivalent of 37.5 to 62.5
grams of dry protein.

The Role of Proteins in Metabolism. — The proteins of food are
described by Voit as having two relations to the protein metabolism, also to
outgoing urea. The first part of the protein of the food goes to maintain the
ordinary and quiet metabolism of the tissues, for which purpose it is actually
built up into the living protoplasmic molecule. The second part being
more directly oxidized causes a more rapid formation of urea, but never
becomes a part of the actual protoplasmic molecule. The former proteins
are called mot -photic or tissue proteins, the latter circulating or floating pro-
teins. Normally more protein is eaten than is needed to supply protein
to the protoplasm for growth, as has just been stated. Pfliiger takes the
view, however, that the tissues must have an excess of protein to destroy in
order to perform their metabolic processes normally. This use of the
proteins to form heat by their oxidation, and not to produce tissue, was
looked upon by the older physiologists as a wasteful use of good material,
and was called luxus consumption.

Folin has recently announced a theory of protein metabolism in which
he calls special attention to the relation of the nitrogenous excretion products
to the nitrogenous intake. He has presented evidence to show that the urea
contained in the urine varies almost directly writh the quantity of protein in
the food; that the ammonia also varies with the protein in the food; that the
uric acid decreases (and increases) with the protein in the food, but not in
direct ratio; while the creatinin excreted is "wholly independent of quan-
titative changes in the total amount of nitrogen eliminated."

436 METABOLISM, NUTRITION, AND DIET

TABLE SHOWING THE OUTPUT OF NITROGEN IN A NORMAL, HEALTHY INDIVID-
UAL ON A FOOD RICH IN NITROGEN, JULY 13™, AND POOR IN NITROGEN
JULY soTH (FOLIN).

July i3th. July 2oth.

Volume of urine . . .1,170 c.c. . 385 c.c.

Total nitrogen 1 6 . 08 grams 3 . 60 grams

Urea nitrogen 14 . 70 grams =87 . 5 per cent. 22.0 grams =61 . 7 per cent.

Ammonia nitrogen . 0.49 grams = 3.0 per cent, o .42 grams = n .3 per cent.

Uric-acid nitrogen . o . 18 grams = i . i per cent, o . 09 grams = 2.5 per cent.

Creatinin nitrogen . o . 58 grams = 3.6 per cent, o . 60 grams = 17.2 per cent.

Undetermined nitro- 0.8 5 grams = 4. 9 per cent. 0.2 7 grams = 7. 3 per cent,
gen.

Folin states this theory as follows: "It is clear that the metabolic proc-
esses resulting in the end products which tend to be constant in quantity
appear to be indispensable for the continuation of life; or, to be more defi-
nite, those metabolic processes probably constitute an essential part of the
activity which distinguishes living cells from dead ones. I would therefore
call the protein metabolism which tends to be constant, tissue metabolism,
or endogenous metabolism; the other, the variable protein metabolism, I
would call the exogenous or intermediate metabolism.

"The endogenous metabolism sets a limit to the lowest level of nitrogen
equilibrium attainable. Just where that level is fixed will depend on how
much, if any, urea is derived from the same katabolic processes that produce
the creatinin. If this can be determined, we shall have a formula expressing
more or less definitely the point of lowest attainable protein katabolism,
because at such a point the percentage composition of the urine should be
practically constant. The total nitrogen eliminated when this constant com-
position of the urine has been reached will indicate the lowest attainable
level of nitrogen equilibrium. "

The condition of nitrogenous equilibrium, therefore, is one which may
be maintained even if the amount of protein taken as diet far exceeds the
necessities of the economy, the urea being excreted in excessive amount; and
the wasteful use of protein food which is so common may not be attended
with harmful consequences, so long as the excreting organs are able to
eliminate nitrogen from the body.

It is only in cases of growth, by putting on of flesh, as in growing children,
that nitrogen is retained in the body in health, except to a very small amount.
According to calculations which have been made, it appears that the body
puts on 30 grams of flesh for every gram of nitrogen so retained.

Proteins as Fat- and as Glycogen-Formers. — Protein food is un-
doubtedly a source of energy in the body; and one can say that such protein
as is, according to Voit's view, metabolized without becoming part of the
tissue may be considered a source of energy. If this be true, one might ex-

THE EFFECT OF A GELATIN DIET 437

pect that proteins could be metabolized into other forms, such as carbo-
hydrates and fats. Bernard long ago stated that protein was a glycogen-
former; that abundant glycogen was stored in the liver when flesh diet was
fed, and argued that protein was the source of the glycogen. The careful
work of a number of investigators has not obtained sufficient evidence to
clear up this question absolutely, but the weight of evidence is in favor of the
view that in the body sugar can be formed from proteins. Lusk has recently
shown that some of the amino acids must have been converted into dextrose
after deamidization in the body. Whether or not protein can be metabolized
into fat, and stored as such, seems at present an open question, notwith-
standing the immense amount of work expended in trying to solve the
problem.

Cramer fed 450 grams of lean meat per day to a cat in a respiration
chamber for 8 days. The daily excretion of nitrogen was 13 grams, of
carbon 34.3 grams; calculating the amount of carbon in the food as 41.6
grams daily, this would leave 7 . 3 grams retained. This carbon might be
stored in the form of glycogen or as fat. Calculated as glycogen, it gives an
amount greater than an animal of that size could retain. Therefore, the
probabilities are that the carbon is deposited in the form of fat.

In the examination of the fat formed in the larvae of blow-flies developing
in a quantity of coagulated blood, Hoffmann found ten times more fat than
existed in the blood. These experiments point in the direction of fat
formation from protein.

The Effect of a Gelatin Diet. — The albuminoid eaten in greatest
quantity is gelatin. Though gelatin closely resembles the protein mole-
cule chemically, it cannot replace entirely the protein of the food. As was
stated in the chapter on the Chemistry of the Body, gelatin is deficient in
certain amino acids, notably tryptophane which is not present at all.
It is probable that because of the absence of this " building stone," the
body tissues cannot reform their characteristic proteins for which this
amino acid would be an essential constituent. In other words, nitrogenous
equilibrium cannot be maintained on a diet consisting of gelatin, carbo-
hydrates, and fats. Gelatin, then, is a substance whose food value in part
is comparable to that of carbohydrates and fats, as the following experiments
will prove: On a diet of 500 grams of meat, without any gelatin, the subject
lost nitrogen to the equivalent of 22 grams of protein, but wThen 200 grams
of gelatin were added the subject gained 54 grams. In another experiment,
when the diet consisted of 2,000 grams of meat without gelatin, the gain
was the equivalent of 30 grams of protein, but when 200 grams of gelatin
were added the gain became 376 grams. The lack of a mixed protein food
value is proven by still a third experiment in which the diet consisted at
first of 200 grams each of meat and of gelatin; here the gain was the equiva-
lent of 25 grams of protein, but, when the meat was omitted and the gelatin

43 8 METABOLISM, NUTRITION AND DIET

alone given, there was a loss of 118 grams. In these cases gelatin did not
take the place of protein in any sense, but rather saved it from oxidation as
a source of energy. The protein was so protected that, instead of being used
up, it helped to form tissue and increased the body weight. Gelatin, there-
fore, saved the protein material for constructive processes.

Murlin has investigated more exactly the substitution of gelatin for the
mixed proteins in the food. In a series of experiments on dogs, the nitrogen
output was first determined during fasting periods. Varying amounts
of gelatin containing from a fourth to two-thirds of this amount of nitrogen
were then fed, the remaining three-fourths to one-third of the fasting quantity
being supplied in meat or other proteins. The calorific requirement of
the animal was made up in each experiment with fats and carbohydrates.
Results show an equal sparing of body protein, whether one-fourth, one-
third, or one-half of the fasting nitrogen was fed in the form of gelatin,
the coincident sparing of protein by fats and carbohydrates being the same.
When the coincident sparing of protein by non-nitrogenous food was in-
creased by feeding a larger percentage of carbohydrates and less fat, the
fraction of the fasting nitrogen fed in the form of gelatin could be raised to
two-thirds, the other one-third being fed in meat. Nitrogenous equilibrium
was maintained on this diet for several days. The same result was obtained
on man. The evidence at hand indicates that other individual proteins,
in which certain amino acid constituents are deficient in quantity or which
are absent, like gelatin would not replace entirely the ordinary mixed
protein requirements.

The Formation of Urea. — The nitrogenous fraction of the protein mole-
cule is in the end converted largely into urea and is excreted from the body in
that form, as described in the chapter on Excretion. The method of forma-
tion of urea as well as the place where this occurs has given rise to great
controversy, while the intermediate products between proteins and urea
have not as yet been fully determined. We can state with certainty that
urea is not formed in the kidneys, since it is not only found in the blood of
the renal artery, but it accumulates in the blood if the kidneys are diseased
or removed and the separation of the urine is interfered with. Circulation
of blood through the kidney does not result in the formation of more urea
than is present in the blood to begin with.

There are a number of experiments that prove that urea is formed in the
liver. The power of the liver cells to form urea is shown by the increase of
urea in the blood leaving an isolated living liver through which an artificial
circulation is kept up. When ammonium carbamate and other ammonium
salts are added to the blood, the urea increases more rapidly and to a greater
extent. This change occurs even when the living hepatic tissue is chopped
up and simply mixed with the ammonium compounds in a beaker.

If blood from a well-fed animal be circulated through the isolated liver,

THE FORMATION OF UREA 439

there is a distinct increase in the amount of urea it contains. On the other
hand, if the blood be from a fasting animal there is little or no increase of
urea. Evidently, then, the blood from a well-fed animal contains something
which the liver cells are capable of transporting into urea. And, finally, if
the liver be removed and the animal kept alive, as has been done by Pawlow,
there is a marked diminution in the quantity of urea in the urine. The
power of the liver to form urea is thus demonstrated. The question which
now presents itself is, what is this antecedent substance or substances ?

It has already been indicated that urea follows closely the amount of
protein taken with the food, hence we must look directly to the nitrogenous
fraction of protein cleavage as the final source of urea. While the different
steps in the process of cleavage, probably hydrolytic (Folin), are yet very
obscure, still it is believed that ammonia is split off from the protein cleav-
age products and is then built up into urea by the liver. It is now believed
that ammonium carbamate is at least one true antecedent of urea.

In these experiments the liver is first shut out of the general circulation
by an Eck's fistula connecting the portal vein with the vena cava. This
operation cuts off the chief blood supply of the liver, viz., the portal blood,
but it leaves the small hepatic artery with its oxygen supply to the liver.
When animals survive this operation it is found that they can live only when
fed very carefully on a mixed diet from which proteins are almost entirely
eliminated, and that, if the food contain an excess of proteids, convulsions
ensue with fatal termination. Investigation of the composition of the urine
and of the blood, with the Eck's fistula, shows that the end product of pro-
tein metabolism is represented by ammonium carbonate carbamate and
that there is a considerable decrease in urea. If ammonium salts are in-
jected into the blood- of normal animals in a larger quantity than the liver
can dispose of, death ensues, following convulsions of the same nature as
those produced by an excess of protein food in the animals operated on.

Ammonium carbamate is shown to be, in part at least, the direct ante-
cedent of urea. The reaction by which the liver changes it to the inert
form of urea is as follows:

ONH4 NH2 NH2

/ / /

CO— H2O . CO H2O > CO

\ \ \

ONH4 ONH4 NH2

Ammonium carbonate. Ammonium carbamate. Urea.

The elimination of urea is increased very slightly by muscular activity.
But there is no direct relationship between the amount of work done and the
amount of nitrogen excreted as urea.

There is experimental evidence to show that while the liver produces the

44° METABOLISM, NUTRITION, AND DIET

major part of the urea eliminated, other organs or tissues are capable of
forming it to a limited degree.

Formation of Uric Acid. — The relation which uric acid and urea bear
to each other in different animals, as we have seen, is still obscure. The
fact that they exist together in the same urine makes it seem probable that
they have different origins. The entire replacement of one by the other, as
of urea by uric acid in the urine of birds, serpents, and many insects, shows
their close relationship. But although it is true that uric acid on oxidation
yields urea, this is not evidence that uric acid is an antecedent of urea in the
nitrogenous metabolism of the body. The chemical structure of the uric
acid shows it has a nucleus of purin, and therefore is a close relative of
adenin, guanin, hypoxanthin, xanthin, theobromin, caffein, etc. The nu-
cleins on cleavage yield members of this group, hence may be looked to as
the primary source of uric acid in man. Uric acid, according to Chittenden,
has a double origin — endogenous from nuclear metabolism, and exogenous
from metabolism of foods rich in nuclear and other purin compounds. In
man, at least, the uric acid is to be ascribed to these two sources.

Operative experiments on birds tend to show that the final step in uric-
acid formation takes place chiefly in the liver, for on the removal of this organ
ammonium compounds, i.e., lactates, accumulate in the blood.

Hippuric Acid, Creatinin, etc. — The hippuric acid found in the urine
is derived in part from aromatic constituents of vegetable diet which can be
transformed into benzoic acid in the body. It is derived in part also from
the phenyl propionic acid formed in the intestinal putrefaction of protein.
Hippuric acid is formed from the union of benzoic acid with glycocol
(C2H5NO2+C7H6O2=C9H9NO3+H2O): this union, in dogs, takes place
under experimental conditions in the kidneys themselves, but in other
animals the synthesis will occur after nephrectomy.

The source of the nitrogenous extractives of the urine is chiefly from the
metabolism of the nitrogenous foods and tissues, but we are unable to say
whether these nitrogenous bodies have merely resisted further decomposition
into urea, or whether they are the representatives of the decomposition of
special tissues, or of special forms of metabolism of the tissues. There is,
however, one exception, and that is in the case of creatinin. This represents
not only the creatinin which enters the body in ordinary flesh food, but is a
nitrogenous wraste which Folin regards as a measure of muscle metabolism.
The creatinin eliminated is almost a constant quantity in a given individual,
irrespective of the quantity of protein in the diet. Koch has shown some
relation of creatinin excretion to the amount of lecithin in the food.

THE METABOLISM OF FATS.

Fats, with carbohydrates, are the direct source of most of the energy
manifested by the body, a fact demonstrated by numerous observations.

SOURCE OF THE BODY FAT

441

The Energy Value of Fats in Metabolism. — Fats, in comparison
with other food principles, are of especial value as sources of energy. They
are completely oxidized in the body to carbon dioxide and water, and yield,
therefore, as much energy to the body as they yield upon oxidation outside
the body. The energy equivalent of i gram of fat is 9 . 3 large calories,
more than twice that of starch or of protein, which in the body yield only
4 . i calories each per gram.

A study of the elimination of nitrogen and of carbon during fasting shows
that the fats contribute to energy formation for many days. This is illus-
trated by the following computation by Voit:

METABOLISM IN A DOG DURING FASTING. (VoiT.)

Loss per kilogram of live weight.

Proteins
in grams

Fats
in grams

Total
weight

Second day
Fifth day . . .

2.21

i • 1 3

2 . 62

3 • 2 <

32.87
31.67

Eighth day

o . 06

7 . 2 <;

•JQ ^4.

The amount of fat metabolized is sharply influenced by the amount and kind
of other food. For example, if the amount of fat metabolized per day in
fasting is first determined, then a ration of protein given for a few days,
followed by a second fasting period, it will be found that the metabolism of
body fat is sharply increased in the second period, due to the stimulating
influence of the protein.

This is demonstrated by the following determination of Rubner:

Food of dog.
(Rubner.)

Nitrogen of
food.

Nitrogen
excreted.

Body fat
metabolized.

o

1
o .

4-^8

40 • 33

415 grams lean meat
o ...

14.11
o .

I3-72

2 80

25.44 average.

7O Q4.

760 grams lean meat

2 < . l6

2O . 6^

30.73 first two days.

The fat of the ordinary daily diet is absorbed into the blood and no doubt
contributes directly to oxidation processes. Just the steps in this oxidation
process cannot at present be given. If the fat food is insufficient, then the
body store is drawn upon; if in excess, then it is stored in the body.

Source of the Body Fat.— Excess of fat in the food can be stored as
fat in the body. This fact is demonstrated by Voit, Hoffmann, Rubner,

442

METABOLISM, NUTRITION, AND DIET

and others. Rubner states that 82 to 92 per cent, of the fat excess can be
stored. The fat stored is of the same kind given in the food, even though
the usual fat of the animal is different. The melting point of dog's
fat is about 20° C., but by feeding an excess of mutton fat the melting
point has been raised to 40° C. The subcutaneous fat of pigs subjected
to this experiment is more or less fluid according to the melting point of
the fat fed.

The body fat can also be derived from carbohydrate food, a fact which
the practices of the stock feeder and dairyman constantly verify. The ex-
periments will present the matter more vividly than pages of description.

GAIN IN FAT OF A PIG FED ON RICE. (MEISSL AND STROHMER.)

Pig weight.

Rice fed
daily.

Fat in
food.

Protein Protein
in food. gain.

Carbon
gain.

Net gain
in carbon.

140 kgm.

2 kgm.

5.3 gm. ; 104 gm.

38 gm.

289 gm.

269 gm.

It is obvious that the 5 . 3 grams of fat and the 66 grams of protein cannot
account for the carbon retained, and one must look to the carbohydrate as
the source of the fat.

Jordan placed a Jersey cow on a feed of hay and grain from which the
fat was extracted. The cow in 95 days assimilated 5 . 7 pounds of fat, in-
creased 47 pounds in weight, and produced 62.9 pounds of fat in the milk.
The nitrogen excreted was the equivalent of 33.3 pounds of protein. The
non-nitrogenous moiety of the protein, if its carbon had all gone into fat,
could not have produced over 17 pounds. Summarized, this experiment
shows conclusively that fat is synthesized from carbohydrate. It requires
about 2 . 7 grams of dextrose to form i gram of fat, and this condensation
takes place with the formation of carbon dioxide and water and the libera-
tion of about 15 per cent, of the available heat of oxidation.

Persistent excess of carbohydrate food produces an accumulation of fat,
which may not only be an inconvenience causing obesity, but may interfere
with the proper nutrition of muscles, produce a feebleness of the action of
the heart, and other troubles.

The formation of fat from protein is discussed on page 436.

Obesity is a condition of excessive storage of fats. In many of these
cases there is persistent storing of fat in the presence of a diet of low energy
value and when considerable physical labor is expended. It seems that
such persons must have a very economic protoplasmic metabolism, a bio-
logical factor that lacks sufficient explanation.

SOURCE OF GLYCOGEN 443

THE METABOLISM OF CARBOHYDRATES.

Energy Value. — The nutritive function of carbohydrates in the body
is to serve as a source of energy. They are oxidized, with the ultimate pro-
duction of carbon dioxide and water, and must liberate the same amount
of energy as when burned outside the body, i.e., 4.1 Calories per gram.
A given weight of dextrose, therefore, furnishes a little less than half the
energy of a corresponding weight of fat.

Carbohydrates are strictly energy-formers and may be regarded as the
immediate source of the energy of oxidations, while fats are reserves drawn
on only after the carbohydrates are used up. Dextrose is a constant constitu-
ent of the blood to the extent of about o.i to o . 15 per cent. When this per-
centage is increased above o. 25, the dextrose is either stored as glycogen, i.e.,
in the case of the portal blood during the absorption of a carbohydrate meal,
or eliminated by the kidney, i.e., as in diabetes.

The Formation of Glycogen — Glycogenesis. — The important fact
that the liver normally forms sugar, or a substance readily convertible
into it, was discovered by Claude Bernard in the following way: He fed a
dog for seven days with food containing a large quantity of sugar and starch;
and, as might be expected, found sugar in both the portal and hepatic blood.
But when the dog was fed with meat only, to his surprise, sugar wras still
found in the blood of the hepatic veins. Repeated experiments gave in-
variably the same result. No excess of sugar was found in the portal vein
under a meat diet, if care was taken to prevent reflux of blood from the he-
patic venous system. Bernard found sugar also in the substance of the liver.
It thus seemed to him certain that the liver formed sugar even when, from the
absence of saccharine and amyloid matters in the food, none could be brought
directly to it from the stomach or intestines.

Bernard subsequently found that a liver removed from the body, and
from which all sugar had been completely washed away by injecting a stream
of water through its blood vessels, contained sugar in abundance after the
lapse of a few hours. This post-mortem production of sugar was a fact
which could be explained only on the supposition that the liver contained a
substance readily convertible into sugar. This theory was proved correct
by the discovery of a substance in the liver allied to starch, termed glycogen.

Bernard's brilliant researches led him to announce the theory that the
carbohydrate which is periodically absorbed in large amount is stored in the
liver only to be reconverted to dextrose and discharged back into the blood
stream whenever the percentage falls below a certain level. He regarded the
liver as a storehouse which regulated the blood dextrose to a constant level.
This is the glycogenic function of the liver.

Source of Glycogen. — The greatest amount of glycogen is produced
by the liver upon a diet of starch or sugar, but a certain quantity is, or at

444 METABOLISM, NUTRITION, AND DIET

least may be, produced upon a protein diet. The glycogen, when stored in
the liver cells, may readily be demonstrated in sections of liver containing it
by its reaction (red or port- wine color) with iodine, and, moreover, when the
hardened sections are so treated that the glycogen is dissolved out, the proto-
plasm of the cell is so vacuolated as to appear little more than a framework.
There is no doubt that in the liver of a hibernating frog the amount of glyco-
gen stored up in the liver cells is very considerable.

AVERAGE AMOUNT OF GLYCOGEN IN THE LIVER OF DOGS UNDER VARIOUS.

DIETS. (PAVY.)

Diet. Amount of glycogen in the liver.

Flesh food 7.19 per cent.

Flesh food with sugar 14 • 5 per cent.

Vegetable diet, i.e., potatoes with bread or barley meal. 17 . 23 per cent.

The dependence of the formation of glycogen on the kind of food taken:
is also shown by the following results, obtained by the same experimenter:

AVERAGE QUANTITY OF GLYCOGEN FOUND IN THE LIVER OF RABBITS AFTER.
FASTING, AND AFTER A DIET OF STARCH AND SUGAR RESPECTIVELY.

After three days' fasting Practically absent.

After diet of starch and grape sugar 15-4 per cent.

After diet of cane sugar 16.9 per cent.

Glycogen is also formed from fats in diabetes, but there is no clear proof
that fats increase the amount of glycogen in the cells. Glycerol injected into
the alimentary canal may also increase the glycogen of the liver. Recent
observations indicate that glycogen may be formed in the turtle liver when
perfused with very dilute formaldehyde solutions. The diet most favor-
able to the production of a large amount of glycogen is a mixed diet con-
taining a large amount of carbohydrate, but with some protein.

Glycogen is stored in other organs of the body. Of these the muscles
are deserving of special mention. The amount of glycogen in the muscles,
of young animals is often considerable. The placenta is also a storehouse
of glycogen.

The Destination of Glycogen. — The chief theories concerning the
use of glycogen in the organism are advanced by Bernard and by Pavy..
The former considers glycogen as a reserve supply of carbohydrate. When-
ever the glycogen of the blood is reduced below the normal level, i.e., about
o.i to o . 1 5 per cent. , there is a conversion of glycogen into sugar. The sugar
enters the blood and passes to the tissues where its oxidation is a source of
energy. Pavy considers glycogen to be a stage in the synthesis of carbo-
hydrate into fat and protein. Bernard's theory is more generally accepted.
It explains more satisfactorily why the sugar content of the blood is so con-
stant. The conversion of glycogen to sugar takes place by the action of an

MINERAL MATTERS, WATER, ETC. 445

intracellular ferment in the glycogenic cells. Such an enzyme has been iso-
lated for the liver. It is this enzyme that converts the liver glycogen to dex-
trose after death, and which is destroyed by boiling in the usual process of
isolating glycogen from the liver or other tissues.

Glycosuria. — Sugar may be present to excess not only in the hepatic
veins, but in the systemic blood. When such is the case, the sugar is ex-
creted by the kidneys, and appears in variable quantities in the urine. This
condition is known as glycosuria.

Glycosuria may be experimentally produced by puncture of the medulla
oblongata in the region of the vaso-motor center, puncture diabetes. The
better fed the animal, the larger is the amount of sugar found in the urine
following this operation. In the case of a starving animal no sugar appears.
It is, therefore, highly probable that in puncture diabetes the sugar comes
from the hepatic glycogen, since in the one case glycogen is in excess, and in
the other it is almost absent. The nature of the change of nervous influence
is uncertain. This influence may be exercised in dilating the hepatic vessels,
or possibly may be exerted on the liver cells themselves.

Many other circumstances will cause glycosuria. It has been observed
after the administration of various drugs, e.g., strychnine; phloridzin, a glu-
coside, and its derivative phloretin, which is not a glucoside; morphine;
adrenalin; nitrite of amyl, etc.; after the injection of curari, poisoning with
carbon dioxide gas, the inhalation of ether, chloroform, etc., the injection of
oxygenated blood into the portal venous system. Glycosuria has been
observed in man after injuries to the head and in the course of various
diseases. In such cases the glycosuria appears to be due either to some ab-
normal activity of the liver cells themselves or to an interference with the
normal metabolism of the carbohydrate group. In this latter case it is pos-
sible that the usual complete oxidation of carbohydrate is interfered with.

The well-known disease, diabetes mellitus, in which a large quantity of
sugar is persistently excreted daily with the urine, has, doubtless, some close
relation to the normal functions of the pancreas. The nature of the relation-
ship has not yet been determined, though some recent experiments seem to
be pertinent, page 460.

Mineral Matters, Water, etc. — The chief mineral constituents of
the foods are sodium, potassium, calcium, magnesium, and iron, together
with chlorine, sulphur, and phosphorus. The inorganic substances are not
a source of heat. They may supply a certain amount of energy, as osmotic
energy, but this is of no significance as compared \vith their influence on the
metabolism of organic substances. An animal fed on a normal food de-
prived of the mineral constituents survives only a few weeks at most.

The amount of mineral matter in the tissues of the human body, exclusive
of the skeletal parts, is about one per cent. It is safe to say that this is
chiefly in complex organic combination in the body. The daily quantity

446

METABOLISM, NUTRITION, AND DIET

excreted is about twenty to thirty grams. This quantity enters the body in
the food, chiefly in combination with complex compounds. It is a question
as to what per cent, of organic salts, like the calcium, the phosphates, and
the iron, is available when taken into the body in inorganic form.

We have discussed in previous chapters the role of certain salts in their
influence on metabolism; for example, of sodium, potassium, calcium, iron,
etc. Foods like milk and eggs are especially rich in calcium and phosphorus
and are particularly desirable for young children, the former for its influence
on the growth of the skeleton, the latter for the same reason and as a stimu-
lator of growth of protoplasm in general. Lack of mineral constituents,
especially calcium compounds, in food shows its influence on metabolism
in the disease known as rickets.

Numerous investigations are in progress which may demonstrate more
fully the specific influence of phosphorus on animal nutrition and on
growth. Tunnicliff has demonstrated that an increase of the phosphorus

NUTRITION EXPERIMENT IN FIVE-MONTHS-OLD PIGS. (E. B. FORBES.)

Rations.

Per cent, gain

in live

weight in

60 days'

feeding.

Hominy ; blood flour ; bran extract. I 69.1

(Phosphorus mostly as phytin.)j
Hominy; blood flour; bone flour.! 61.0

(Phosphorus mostly as tricalcic

phosphate).
Hominy; blood flour. (Low phos- 41.6

phorus ration).

Per cent, gain in certain
tissues corresponding to
i per cent, gain in live
weight.

Psoas
muscle.

.81

.61

Ash of

humer-

us.

•59
.72

.08

Thick-
ness of
back fat.

.64
.82

i .04

content of the food of children, if given in complex organic form, increases
the efficiency of the metabolism of nitrogen by as much as 10 per cent.
If given to children as calcium phosphate it has no beneficial influence
in this regard. Forbes, in his experiments on the nutrition of pigs, shows
that the individuals fed with food to which phosphorus was added, as ground
fresh bone, grew larger and stronger skeletons, but that the presence of
organic phosphorous (phytin) led to the greatest general growth.

Per cent.

Animal.

Per cent.

. . . 0.036

Pork

o . 1 60

. . . o . 058

Milk

0.220

. . . o .089

Beef

0.285

. . . o . 140

Eggs

0-337

. . . 0 . 200

White cheese .

o-374

. . . o . 230

Mutton

0.425

EFFECTS OF DEPRIVATION OF FOOD 447

PERCENTAGE OF PHOSPHORIC ACID (P2O5) IN SOME FRESH FOODS. (QUOTED

FROM GlRARD, BY HuTCHINSON, IN "FOOD AND DIETETICS.")

Vegetable.

Carrot

Turnip

Cabbage

Potato

Chestnuts

Barley meal . . .

Salts in the body not only take part in the reactions themselves, but they
stimulate in other substances reactions that are of incalculable benefit to
the body.

The necessity for the taking of water in order to balance the daily ex-
cretion, is sufficiently obvious. Man will live only a few days if deprived of
water.

Effects of Deprivation of Food. — The animal body deprived of all
food dies from starvation in the course of a variable time. The length of
time that any given animal will live in such a condition depends upon many
circumstances, the chief of which are the nature and activity of the metab-
olism of its tissues.

The effect of starvation on the lower animals is, first of all, as might be
expected, a loss of weight. The loss is greatest at the beginning of the dep-
rivation period, but afterward decreases to a level from which it does not
vary much day by day until death ensues. Chossat found that the ultimate
proportional loss in different animals experimented on was almost exactly
the same, death occurring when the body had lost 40 per cent, of its original
weight. Different parts of the body lose weight in very different proportions.
The following most noteworthy losses are taken, in round numbers, from
the table given by Chossat:

Per cent. Per cent.

Fat 93 Liver 52

Blood 75 Muscles 43

Spleen 71 ; Nervous tissues 2

Pancreas 64

These figures are in practical agreement with those of later experimenters.
They show that the chief losses are sustained by the adipose tissue, the
muscles and glands. The nervous structures and the heart are maintained
at the expense of the other tissues and show but little change.

The effect of starvation on the temperature of the various animals ex-
perimented on by Chossat was very distinct. For some time the variation
in the daily temperature was more marked than its absolute and continuous

448

METABOLISM, NUTRITION, AND DIET

diminution, the daily fluctuation amounting to 3° C. instead of 0.5° to i° C.,
as in health. The temperature fell very rapidly a short time before death,
and death ensued when the loss had amounted to about 16 . 2° C. It has been
often said, and with truth, that death by starvation is really death from want
of heat. The effect of the application of external warmth to animals cold
and dying from starvation is more effectual in reviving them than the ad-
ministration of food.

The symptoms produced by starvation in the human subject are hunger,
accompanied, or it may be replaced, by pain, referred to the region of the

Ul

DAYS OF FASTING

FIG. 310. — The Elimination of Urea by Dogs during Fasting. (Voit.)
— — Following 2,500 grams of meat in the food.
- Following 1,500 grams of meat in the food.
- — Following minimal amount of protein in the food.

stomach; insatiable thirst; sleeplessness; general weakness, and emaciation.
The exhalations both from the lungs and from the skin are fetid, indicating
the tendency to decomposition which belongs to badly nourished tissues;
and death occurs often with symptoms of nervous disorder, delirium, or
convulsions. Death commonly occurs within from six to ten days after
total deprivation of food. This period may be considerably prolonged by

REQUISITES OF A NORMAL DIET 449

taking a very small quantity of food, or even by water alone. The cases
so frequently related of survival after many days or even some weeks of
abstinence have been due either to the last- mentioned circumstances, or to
other no less effectual conditions which prevented the loss of heat and
moisture.

During the starvation period the excretions diminish. The urea, as rep-
resenting the nitrogen, falls quickly in amount, reaches a minimum where it
remains constant for several days, then finally falls rapidly immediately
before death. The sulphates and phosphates undergo much the same type
of reduction. The carbon dioxide given out and the oxygen taken in di-
minish. The feces diminish as well as the bile. It is highly probable
that the greater part of the nitrogen represents the loss of weight of the
muscles.

In starvation, then, we see that the only income consists of water and
the inspired oxygen. The whole of the energy of the body given out in the
form of heat and mechanical labor is obtained at the expense of its own
tissues, there being as a result a constant drain of the nitrogen and carbon,
not to mention the other elements of which the tissues are composed. It is
obvious that such a condition cannot be endured for any length of time.

REQUISITES OF A NORMAL DIET.

It will be understood from the preceding discussion that it is necessary
that a normal diet should be made up of the various classes of foods in suffi-
cient quantity to supply the same amounts of carbon and nitrogen that are
gotten rid of by the excreta. No doubt these desiderata may be satisfied
by many combinations of foods, and it would be unreasonable to expect the
diet of every adult to be the same. The age, sex, strength, and circum-
stances surrounding each individual must ultimately determine what he
takes as food. A dinner of bread and cheese with an onion contains all the
requisites for a meal, but such diet would be suitable only for those possessing
strong digestive powers. It is a well-known fact that the diet of the con-
tinental nations differs from that of our own country, and that of cold from
that of hot climates, but the same principle underlies all, viz., the replace-
ment of the losses of the body in the most convenient and economical way
possible. Any one in active work requires more food than one at rest, and
growing children require more food in proportion to body weight than adult
men and women, but of a different variety.

The chief diet-scales which have been drawn up with the object of
supplying the proximate principles in the required proportions are given in
the table below:

29

45°

METABOLISM, NUTRITION, AND DIET

STANDARD DIETARIES.

Author.

Protein.

Fat.

Carbohy-
drate.

Calories.

Voit . .

118 grams

56 grams

500 grams

3 O 5 ^

Rubner
Moleschott
Munk

1 2 7 grams
130 grains
105 °Tams

52 grams
40 grams
56 grams

509 grams
5 50 grams
500 grams

3>°92
3,160
3 022

Wolff
Playfair
Atwater

1 2 5 grams
119 grams
125 grams

3 5 grams
5 i grams
125 grams

540 grams
53 1 grams
45° grams

3>°3°
3>I4°
3 ^20

Average

121 grams

59 grams

510 grams

2,1 -J C

The basis of computation for these diets is to supply the necessary protein
nitrogen first of all, and, second, to supply enough potential energy to balance
the energy expended per day.

The amount of the excreted carbon and nitrogen is not always the same.
It has been proven possible, for example, to subsist on 9 or 10 grams of nitro-
gen and 200 grams of carbon per diem, the ordinary diet for needle-women
in London, and the average of the cotton operatives in Lancashire during the
famine of 1862. The amount of these elements excreted falls to figures cor-
responding to such an income. Of course, upon such a diet the metabolism
is low, and persistent physical weakness must be the result, probably from
insufficient carbon. The 9 or 10 grams of nitrogen in such a semi-starvation
diet would be equivalent to 58 . 5 to 65 grams of protein, whereas the amount
of protein in some diets may be as high as 150 and more grams per day.
Chittenden's nutritional experiments, so often referred to in these pages,
have proven that adult men can subsist in nitrogenous equilibrium, and do
vigorous work and maintain good health, on a protein diet below that given
in the above example, i.e., on 6 to 10 grams of nitrogen. In such diets a
plentiful supply of carbohydrates is permitted, but the calorific value of the
diet is less than those in the table above.

Not only the proteins but also the fats may vary. The amount may be
as low as 35 grams and as high as 125 grams. The carbohydrates may vary
from 200 grams to 500 grams and upward. Sometimes, with a small pro-
portion of fats, the carbohydrates may be correspondingly increased to
make up the necessary carbon. A useful table, after Payen, will help to show
in what ways it is possible to obtain the requisite amount of nitrogen and
carbon from the most common food stuffs. In order to obtain the amount
of protein present from the proportion of nitrogen, multiply by 6. 25.

REQUISITES OF A NORMAL DIET

451

TABLE OF PERCENTAGES OF N AND C IN THE FOLLOWING SUBSTANCES.

Beef (without bone) .
Roast beef

EcrcrS

•3
3

N.

• 528
• 9

ii

I 7

c.

.76

. c

"feS*3 •

Cow's milk

o

.66

O

8

J

Cheese

2

to 7

•? c

. to

7 I

Beans
Lentils

4
•4

w /
•5
. i

o o

42

/

N.

C.

eal 1.95
L i.

44.
28.

oes 0.33

. 2 .

II .

Bread

Potat

Eels.

Mackerel 3-74

Sardines in oil 6 .

Butter o . 64

19.26

29.

83-

From these data, or from the composition of foods on page 323, it is pos-
sible to form various diet-scales which shall supply the needs of different
conditions of growth and decay of the body. Assuming that the average
amount of carbon and nitrogen required is about 300 grams and 20 grams,
respectively, this may be obtained as follows:

N. C.

340 grams (12 oz. or i Ib. avoirdupois) lean uncooked

meat.* 10 grams 37 grams

906 grams (32 oz. or 2 Ibs. avoirdupois) bread 9 grams 252 grams

19 grams 289 grams

But this diet is not the usual one; a certain proportion of the carbon is
usually supplied as butter, or bacon, and so if 90 grams of butter or bacon
be used it would supply about 72 grams of carbon, and the carbohydrate
would be diminished nearly one- third; but the nitrogen would also be di-
minished from 9 grams to 6 grams. It would be necessary to supply some
extra nitrogenous principle, which might be done by the addition of eggs,
milk, cheese, beans, or of any of the food-stuffs already enumerated at page
323 et seq., as supplying nitrogenous food chiefly. For example, 56 grams
(2 oz.) cheese contain, on an average, 3 grams of nitrogen and 20 grams of
carbon; or 28 grams cheese, containing 1.5 grams of nitrogen and about
10 grams carbon, together with 225 grams potatoes and 225 grams carrots,
supplying about i gram of nitrogen and 35 grams of carbon, may be added.
The diet would then read as follows :

N. C.

340 grams lean uncooked meat 10.0 grams 37 grams

600 grams bread 6.0 grams 1 68 grams

90 grams butter 0.5 grams 72 grams

28 grams cheese 1.5 grams 10 grams

225 grams potatoes 1 i.o grams 3 5 grams

225 grams carrots, j

19.0 grams

322 grams

The 30 grams of salts necessary to replenish the daily loss by excretion
in the urine are contained in the meat 16 grams, the bread 12 grams, and
vegetables about 4 grams.

* As meat loses 23 to 34 per cent, in cooking, the weight of cooked meat would be
proportionately less.

452 METABOLISM, NUTRITION, AND DIET

The fluid should consist of about 2,500 to 2,800 grams, and might be
given as water, with or without tea, coffee, or cacao, which are chiefly
stimulants.

The Energy Requirements of the Body. — The food must not only
make up for the substances eliminated from the body but must also supply
the potential energy of heat and motion set free in the living body. The
amount of heat is measured in terms of calories, or more often in large
Calories. The work energy may be expressed in gram-centimeters, or in
kilogrammeters. Since one calorie of heat is the equivalent of 42,670 gram-
centimeters of work, the two units may be computed interchangeably.

The source of the heat and work energy which is produced in the body is
from the metabolic changes of the tissues, the chief part of which is in the
nature of oxidation, since it may be supposed that the oxygen of the atmos-
phere taken into the system is ultimately combined with carbon and hydro-
gen. Any change, indeed, which occurs in the protoplasm of the tissues,
resulting in an exhibition of protoplasmic function, is attended by the evolu-
tion of heat and the formation of carbon dioxide and water. The more act-
ive the changes the greater is the amount of heat produced. In order that
the protoplasm may perform its functions, the waste of its own destructive
metabolism must be repaired by the due supply of food material to be built
up in some way into the protoplasmic molecule. In the tissues, as we have
several times remarked, two processes are continually going on: the building
up of the protoplasm from the food, anabolism, which is not accompanied
by the evolution of heat; and the oxidation of the protoplasmic materials,
katabolism, resulting in the production of energy, by which heat is set free.
Food is therefore necessary for the production of heat. It is not neccessary
to assume that the combustion processes, indeed, are as simple as the bare
statement of the fact might seem to indicate. But complicated as the vari-
ous stages may be, the ultimate result is as simple as in ordinary combustion
outside the body, and the products are the same.

This view, that the maintenance of the temperature of the living body
depends on continual chemical change, chiefly by oxidation of combustible
materials in the tissues or by the tissues, has long been established. The
quantity of carbon and hydrogen supplied as food, which, in a given time,
unites in the body with oxygen, is sufficient to account for the amount of heat
generated in the animal within the same period, page 454; an amount capable
of maintaining the temperature of the body at from 36.8° to 38.7° C., not-
withstanding a large loss by radiation and evaporation. This estimation
depends upon the chemical axiom that when a body undergoes a chemical
change the amount of energy set free is the same, supposing the resulting
products are the same, whether the change takes place suddenly or gradually.
If a certain number of grams of different substances are introduced as food,
and if they undergo complete oxidation, the amount of kinetic energy, as

THE ENERGY REQUIREMENTS OF THE BODY 453

shown in the amount of heat and mechanical work, is the same as would be
developed if the same bodies were completely oxidized outside the body.
If one gram of fat be taken into the body and is completely oxidized, result-
ing in the production of a definite amount of carbon dioxide and water, it
may be supposed to have produced the same amount of heat as it would have
produced outside the body. In the case of protein food it is a little different,
since it is never completely oxidized within the body, but may be supposed
to give rise to a definite amount of urea and other lower nitrogen compounds
not completely oxidized bodies. In this case the gram of protein may be
considered to liberate the same amount of heat as the protein would outside
the body minus the amount which would be obtained from the complete
oxidation of the resulting urea, etc.

The actual amount of heat produced per diem has been experimentally
ascertained in the case of man and animals by the aid of an apparatus, the
calorimeter. An animal is enclosed in a metal cage completely contained
in a second cage containing water. Air is let into and out of the inner box
by means of metal tubes so arranged that the inlet tubes maintain a con-
stant temperature and the outlet tubes pass through water between the two
chambers. The heat given out by the animal warms the water in the outside
box, and may be estimated by the rise- of its temperature, the amount of which
is known. At the same time the carbon dioxide output is measured.

The amount of heat evolved by the oxidation of various food stuffs has
been carefully measured by numerous observers; the figures calculated by
Rubner being perhaps most satisfactory, \vhich are:

HEAT VALUE TO THE BODY.

i gram carbohydrate 4.1 calories.

i gram fat 9.3 calories.

i gram protein 4.1 calories.

One gram of dry protein has a total heat value of 5 . 754 (Rubner), hence
it is obvious that protein is not completely oxidized by the body. Each
gram of protein yields at least one-third of a gram of urea, which has a heat
value of 2 . 5 calories per gram.

Atwater has checked the energy value of the foods actually consumed
against the actual liberation of heat and work energy of the human body.
He finds a wonderfully close agreement both for periods of rest and for periods
of work. Atwater's estimate for the energy needs of man are as follows:

Man without muscular work 2,700 calories.

Man with light muscular work 3,000 calories.

Man with moderate muscular work 3,5°° calories.

Man with severe muscular work 4,500 calories.

454 METABOLISM, NUTRITION, AND DIET

The daily output of energy for the adult man is as follows:

Kilogrammeters. Calories.

Work of heart per day

88 ooo

Work of respiratory muscle
Eight hours' active work

. . . . 14,000

21"? 344

Amount of heat produced in 24 hours

315,334 or
i 582 700 or

743
3 724.

1,898,034 or 4,467

This estimate is relatively high for ordinary activity as determined by
Atwater and others. It is indeed more energy than the standard diets in
the table given on page 450 will yield to the body. For example, Voit's
diet yields 3,055 calories, and the average of the table is only 3 . 125 calories.

THE INFLUENCE OF THE DUCTLESS GLANDS ON METABOLISM.

A further question to be considered is the relationship between the metab-
olism of the tissues and the products of the metabolism of other tissues.
The metabolism of one tissue may produce products, protein or otherwise,
which when taken up by the blood and carried to other tissues supply ex-
actly what is necessary for their complete anabolism.

The physiology of the internal secretions has revealed a number of such
influences that are best explained on the assumption of the presence of spe-
cial products.

The Thyroid and Accessary Thyroids. — These glands are situated in
the neck. The thyroid consists of two lobes, one on each side of the tra-
chea, extending upward to the thyroid cartilage, covering its inferior cornu
and part of its body; the lobes are connected across the middle line by a
middle bar or isthmus. The thyroid is covered by the muscles of the neck.
It is highly vascular, and varies in size in different individuals. The gland
is encased in a thin transparent layer of dense areolar tissue, free from fat,
containing elastic fibers. The gland vesicles are each lined with a single
layer of cubical cells and are filled with transparent nucleo-albuminous
colloid material.

The accessory thyroids possess the structure of the thyroid and apparently
perform the same function.

The colloid material which is formed within the thyroid and accessory
thyroid vesicles, and is believed to be their secretion, finally ruptures through
their walls into the lymph channels and thus gains entrance to the circulation.
The secretion of the thyroid falls into the class known as internal secretions,
and exerts an influence upon the metabolic processes of the body, probably
through its influence on the central nervous system. Complete extirpation
of the thyroid, at least in some animals, produces death, preceded by a group
of characteristic symptoms. In man and the monkey the symptoms after re-
moval come on slowly and resemble the disease known in man as myxedema.

THE THYROID AND ACCESSARY THYROIDS

455

This disease is known to be due to disease of the thyroid, whereby its func-
tion is interfered with. Moreover, if a piece of thyroid of sufficient size
be grafted into an animal from which the glands have been removed, and
the graft takes, the symptoms of thyroid removal are lessened in intensity
or disappear altogether. Thyroid feeding or the administration of thyroid
extracts relieves the symptoms of the disease myxedema.

FIG. 311. — Part of a Section of the Human Thyroid, a, Fibrous capsule; 6, thyroid
vesicles filled with, e, colloid substances; c, supporting fibrous tissue; d, short columnar cells
lining vesicles;/, arteries; g, veins filled with blood; h, lymphatic vessel filled with colloid
substance. (S. K. Alcock.)

The above facts show that the thyroid gland must perform some im-
portant function in the animal economy, and it is believed that this is accom-
plished by virtue of its internal secretion. The colloid material of the gland
has been submitted to much chemical study, and a substance called iodo-
thyrin has been isolated as its active principle. Baumann and Roos state
that iodothyrin exists in the gland in combination with protein bodies. lodo-
thyrin relieves the symptoms of thyroid removal much to the same extent
as thyroid feeding. It is a very resistant substance, and is not injured by the
action of the gastric juice or by boiling with 10 per cent, sulphuric acid for
a long time.

Total extirpation of the thyroids carries extirpation also of the para-
thyroids. The question is thus raised as to which part of this total appara-

456 METABOLISM, NUTRITION, AND DIET

tus is responsible for the derangement of functions noted. Only the symp-
toms safely ascribable to the thyroid proper have been presented above.

Accessory Thyroids.— Detached portions of thyroid tissue in the
neighborhood of the lateral lobes have the same structure as the thyroid
proper.

The Parathyroids. — There are smaller glandular structures associated
with the thyroids on each side known as the parathyroids. One is located
at the level of the lower border of the cricoid cartilage and in intimate rela-
tion to the posterior border of the lateral lobe of the thyroid. The other is
at the inferior border of the same lobe. In the dog there is an anterior para-
thyroid at the head of the thyroid and an external imbedded in the mass of
the thyroid. Extirpation of the parathyroids in the dog (Berkeley and Beebe)
leads to even a more profound disturbance of the metabolism resulting
in death. The usual symptoms are acute muscular weakness leading to
tetany followed by prolonged condition of increasing stupor and death.
Removal of the parathyroids in the dog leads to an increased excretion of
calcium and of ammonia and of other products indicative of disturbed met-
abolism. The derangement of calcium metabolism suggests the thought that
the symptoms might be relieved by supplying this substance. The matter is
presented in the following words of Berkeley and Beebe: '" Probably the
most striking argument in favor of Macallum's theory in respect to tetany
parathyreoprivus is that it may be relieved almost instantly by the intra-
venous injection of a soluble calcium salt. We have repeated the experi-
ment and find that intravenous injections of a soluble calcium salt will re-
lieve tetany almost instantly; intramuscular injections may be effective after
a period of thirty to forty-five minutes, and a similar period is required for
the beneficial effect after subcutaneous injection. The effect of the calcium
salt when given intravenously to an animal in advanced states of acute tetany
is one of the most striking in the range of physiological experimentation."

Nucleoproteins are richly present in the parathyroids and their extracts.
Injections of nucleoprotein preparations freshly prepared also relieve the
symptoms of acute tetany in dogs. The above authors close their discussion
with the statement: "In other words, we believe that the essential fact in the
production of symptoms following complete thyroparathyroidectomy is the
deranged metabolism giving rise to some active poison, and not the abnormal
excretion of calcium which we regard as an accompanying phenomena,
perhaps due in part to the starvation cachexia which ensues in most cases if
the animal is tided over the acute condition."

The Suprarenal Capsules or Adrenals. — These are two flattened,
more or less triangular or cocked-hat shaped glandular bodies, resting by
their lower border upon the upper border of the kidneys.

The gland tissue proper consists of an outside firmer cortical portion, and
an inside soft dark medullary portion, figure 312.

THE SUPRARENAL CAPSULES OR ADRENALS

457

The adrenals are very abundantly supplied with nerves, chkfly com-
posed of medullated fibers. These fibers are derived from the solar and
renal plexuses and the vagi, but the method of their termination is unknown.

A vast amount of information has been given concerning the function of
the suprarenal capsules within the last
few years by the researches of Schafer
and Oliver, Zyboulski, Abel, and others.
Brown-Sequard, it is true, showed by ex-
periment as early as 1856 that removal
of the suprarenals is followed by the
death of the animal, but his experiments
were repeated by others who did not
obtain the same results; and it was con-
cluded that the suprarenal capsules had
no function, or at least that their func-
tion was not known. Death was pre-
ceded in the case of Brown-Sequard's
animals by symptoms somewhat anal-
ogous to those of the disease of man
known as Addison's disease. The fail-
ures to produce symptoms after attempted
removal of the glands have probably re-
sulted from incomplete removal or the
presence of accessory bodies. Accessory
suprarenal capsules are commonly present
in some animals and are sometimes found
in man. Further, if one gland is removed,
the other hypertrophies. The experi-
ments of all recent observers confirm the
original experiments of Brown-Sequard.
The presence of the suprarenal capsules
is essential to life.

Schafer and Oliver found that injec-
tions of suprarenal extract produced
marked effects upon the muscular layer
of the arteries, the muscular tissue of the
heart, and the skeletal muscles. The
muscular layer of the arteries is markedly
contracted, causing vaso-constriction and
a rise of blood pressure. When the heart is freed from nervous control its
contractions are increased both in force and frequency, still further raising
blood pressure. If the vagi are undisturbed the heart beats more slowly,
showing an increase of vagus tone due to stimulation of the vagus center in

FIG. 312. — Vertical Section of
Adrenal. A, Capsule; B, cortex; C,
medulla; a, glomerular zone; &, fasci-
cular zone; c, reticular zone; v, vein
in medulla. (Merkel-Henle.)

458

METABOLISM, NUTRITION, AND DIET

the medulla. The contraction of the skeletal muscles in response to a single
stimulation is increased.

Very small doses of suprarenal extract are sufficient to produce marked
effects. Thus Schafer states that less than ^T^O" gram (¥^ grain) of the
desiccated gland is sufficient to produce an effect upon the heart and arteries
of an adult man.

It is a curious fact that only extracts of the medullary portion of the gland
are active. It has been further shown, by Christian! and others, that if only

FIG. 313. — Injection of Suprarenal Extract. Effect upon the heart, limb, spleen and
blood pressure, after section of cord and vagi. (Reduced to one-half.) (Schafer.)

small portions of the medulla remain, the animal operated upon survives;
while if all the medullary substance be removed, even though large portions
of the cortex remain, the animal invariably dies.

Abel has succeeded in separating the blood-pressure-raising constituent
of the gland extract, and calls it epinephrin, C10H13NO3 JH2O. Takamine
isolated an active principle to which he assigned the formula C9H13NO3,
and the name adrenalin. The hydrochloride salt is prepared commercially
and produces all the vascular effects assigned to the gland.

Destruction of the suprarenal capsules through disease in man results in
the production of a group of symptoms known as Addison's disease. The

THE INTERNAL SECRETION OF THE PANCREAS 459

administration of suprarenal extract to these cases sometimes results bene-
ficially, but not so uniformly as does thyroid feeding in myxedema.

Dreyer has given evidence that the products of this gland are discharged
into the blood of the adrenal vein in increased quantity on splanchnic
stimulation.

This gland furnishes, on the whole, very conclusive evidence of the pres-
ence of an internal secretion that is absolutely necessary to the normal
metabolism of other organs.

The Pituitary Body. — This body is a small reddish-gray mass, occupying
the sella turcica of the sphenoid bone.

It consists of two lobes, a small posterior one of nervous tissue, and an
anterior one resembling the thyroid in structure. The gland spaces of the
latter are oval, nearly round at the periphery, spherical toward the center
of the organ, and are filled with nucleated cells of various sizes and shapes
not unlike ganglion cells.

The function of the pituitary body has not yet been fully established.
It has been supposed that the pituitary body has a function associated with
that of the thyroid. On the other hand, tumors or other disease of the
pituitary body have been found after death in association with a disease
known as acromegaly, in which the bones and soft parts undergo great
hypertrophy.

Howell has found that extracts of the glandular lobe are inactive, but
that extracts of the infundibular lobe, when injected into the circulation,
produce marked rise of blood pressure, increase of vagus tonic inhibition,
and an augmentation of the heart's force.

The Internal Secretion of the Pancreas. — Minkowski and von
Mering have shown that total extirpation of the pancreas is followed in all
cases by the appearance of sugar in the urine in the course of a few hours.
The amount of sugar which appears is considerable, from 5 to 10 per cent.
This experimental disease is accompanied by an increase in the quantity of
urine and by abnormal thirst and appetite. It proves fatal in fifteen days or
less. These results are obtained only when the entire gland or more than
nine-tenths of it have been removed. If one-tenth or more of the gland be
left behind, sugar appears in the urine when carbohydrates are eaten, but not
otherwise. Nor is it necessary that the remaining portion of the gland be in
its normal situation. Successful grafts of pancreas under the skin of the
abdomen or elsewhere will prevent the appearance of sugar in the urine and
the other symptoms. If, however, the graft be subsequently removed, the
sugar in the urine and the other symptoms reappear, and the experimental
disease proceeds to a rapidly fatal issue. Opie and others have shown also
that in most cases of diabetes mellitus, there are pathological changes in the
islands of Langerhans.

The symptoms produced by total extirpation of the pancreas do not de-

460 METABOLISM, NUTRITION, AND DIET

pend upon the loss of the pancreatic juice proper to the organism. This
secretion may be diverted from the intestine through a pancreatic fistula
without the production of diabetes. Moreover, Hedon and Thiroloix have
rendered the acini of the gland functionally inactive, and ultimately de-
stroyed them, by the injection of paraffin or other substances into the duct
of Wirsung, without the supervention of diabetes.

These experiments have shown that the ordinary secreting cells degener-
ate and the islands of Langerhans increase in size, leading to the conclusion
that the islands are the structures that produce a special internal secretion
which influences or controls carbohydrate metabolism in the body. When
the dextrose cannot be readily burned in the body, the content of this sub-
stance in the blood is increased and this excess is eliminated by the kidneys.
Products of incomplete oxidation of the sugar are also thrown into the circu-
lation and eliminated into the urine. In diabetic cases oxybutyric acid,
aceto- acetic acid, acetone, etc., are found in the blood and urine. Neither
pancreatic nor muscle extracts have the power of burning sugar. Conheim,
however, showed that when extracts of the pancreas and of muscle were
brought together, the resulting mixture would destroy the dextrose added to
it. This interaction of pancreas and muscle, then, offers an explanation
of the perverted carbohydrate metabolism after removing or in pathological
conditions of the pancreas.

The Reproductive Glands. — The ovary and the testes are undoubt-
edly concerned with metabolism in the body. It has been shown repeatedly
that extracts of the testes when injected into the system lead to increased vigor
both of the muscular and of the nervous systems. Ergograms show an
increase in muscular power. Spermin isolated from the testes is claimed
by its discoverer to produce the beneficial effects described. The removal
of the testes in domestic animals is followed by an entire change in the
character of the development of the animal, especially in the so-called second-
ary sexual characters. Such animals show less vigor and less muscular power.

The removal of the ovaries in women, through surgical operation, has
resulted in very marked nervous symptoms. These symptoms are reduced
or entirely disappear on grafting a portion of the gland, and the disturbed
menstruation following ovariotomy becomes regular again. Experiments
by Loewy and Richter indicate that oxidations in the body are greatly in-
creased on feeding ovarian extract to ovariotomized animals.

There are other organs whose function is still obscure but in which
the indirect evidence points to an influence on metabolism at one stage or
another of the existence of the animal body. Enough has been given here
to show that the interrelation of the organs is extremely complex in so far as
the metabolism is concerned. It is not enough simply to know the foods and
their composition. The whole complex of intermediary metabolisms and
their influences must constantly be taken into consideration.

CHAPTER XII.
ANIMAL HEAT.

HEAT is produced by the metabolism of the tissues of the body. In man
and in such animals as are called warm-blooded, i.e., only mammals and
birds, there is an average body temperature which is maintained with only
slight variations in spite of changes in their environment. The possible
variations above and below this average are comparatively slight. The
average temperature in all mammals and birds is not the same, for, as we
shall see, the average temperature of man is 37° C. (98.6° F.), in some birds
it is as high as 44° C., while in the wolf it is said to be under 36° C.

The average temperature of the human body in those internal parts which
are most easily accessible, as the mouth and rectum, is from 36 , 9° to 37 . 4° C .
(98 . 5° to 99 . 5° F.). In different parts of the external surface of the human
body the temperature varies only to the extent of one or two degrees centi-
grade, when all are alike protected from cooling influences; and the differ-
ence which under these circumstances exists depends chiefly upon the
different degrees of blood supply. In the axilla and in the groin, the most
convenient situations, under ordinary circumstances, for examination by the
thermometer, the average temperature is 37° C. (98.6° F). In different
internal parts, the variation is one or two degrees; those parts and organs
being warmest which contain most blood, and in which there occurs the
greatest amount of chemical change, e.g., the muscles and the glands. The
temperature is highest when they are in a condition of activity. Those tis-
sues which subserve only a mechanical function and are the seat of least ac-
tive circulation and chemical change are the coolest. These differences of
temperature, however, are actually but slight, on account of the provisions
which exist for maintaining uniformity of temperature in different parts.

The average temperature of a healthy body varies somewhat according
to age, sex, time of day, climate, etc. The mean temperature is said to be
slightly higher, 0.5° C., in young children and in old persons than in adults.
It is perhaps very slightly higher in women than in men, in warm climates
than in cold, in winter than in summer. It varies slightly at different times
in the day, especially during sleep when metabolism is at a low ebb.

Diurnal Temperature Variations. — The discussion presented in this
paragraph is abstracted from an excellent paper on the subject by Professor
Gibson. "Certain features of daily rhythm are generally recognized,
such as the rise of temperature during the forenoon and afternoon, and

461

462 ANIMAL HEAT

the fall during the evening and early morning hours. A study of the
literature indicates considerable differences in the incidence of the maxi-
mum and minimum temperature, depending undoubtedly upon a variety
of causes. Despite differences as regards dietetic habits, work, age,
etc., the time of maximum temperature may be limited broadly between
4 and 8 P.M., and that of the minimum between 2 A.M. and 7 A. M., with an
average range of variation of over i° C. in rectal observations. While a
hot or cold climate may determine minimal variations in the peripheral tem-
perature of the body, the internal temperature, as measured in the rectum,
appears to suffer only very slight modifications from such causes. The rise
in temperature incidental to muscular exertion is transitory. The follow-
ing quotations serve to indicate prevalent views regarding the diurnal
rhythm. Pembrey writes: 'As regards the causes of the daily varia-
tion in temperature, muscular activity and food appear to be the most impor-
tant factors. In ordinary life man is most active and takes food during the
day, and is least active during the night. . . . We may conclude that the
daily variation in temperature is one of the features of a corresponding varia-
tion in the activity of the tissues of the body, as shown by the rate of the con-
traction of the heart, the frequency of respiration, the intake of oxygen, the
output of carbon dioxide, the discharge of urea, and the capacity for muscu-
lar work.' Jiirgensen's observations on fasting subjects in which a more
or less " normal" curve of temperature variations was maintained exclude
the diet factor from a preponderating role. In estimating the relative im-
portance of the bodily activities as distinguished from other environmental
conditions, studies on the influence of the inversion of the daily routine have
been made. Those of Benedict claim special interest, because the observa-
tions were practically continuous over long periods of time. Such an ar-
rangement was made possible by the use of a specially devised electric
resistance thermometer reading to 0.01° C., which can be inserted 10 cm.
to 15 cm. in the rectum and retained there without inconvenience during
both waking and sleeping hours. Two subjects were carefully observed by
Benedict: one a person usually working during the day, but made to work
at night and sleep during the day for a series of consecutive days; the other,
an individual long accustomed to night- work in the capacity of a night
watchman. From the results of these observations it has been assumed that
the general form of the night curve remains practically intact, even when
the daily routine is inverted, indicating a fixity of rhythm that is difficult to
explain. As Benedict says: 'Why the temperature of the human body
reaches a minimum at 2 A.M. to 6 A.M., independent of whether the subject is
sleeping soundly in the recumbent position or whether he is awake and
sitting, or even standing and walking, is a problem that calls for extended
research.' However, the transposition of the daily routine through a period
of practically half a day, experienced as the result of the time changes

VARIATION IN THE LOSS OF HEAT 463

during the trip from New Haven to Manila, produces a corresponding and
coincident shifting of the rhythmic temperature changes, so that the normal
character of the variations is always preserved."

Heat-producing Organs. — Heat is liberated in the body wherever
oxidative metabolism takes place. Of all the tissues of the body muscular
tissue is conspicuous for its mass and for its activity. It is evidently the great
heat-producing tissue. The manifestation of muscular energy is always ac-
companied by the evolution of heat and the production of carbon dioxide.
This production of carbon dioxide goes on while the muscles are in mechani-
cal rest, only in a less degree than that which is noticed during muscular
activity, and so it is certain that an active katabolism is going on in resting as
well as in contracting muscles. This katabolism is a source of much heat, and
so the total amount of heat produced in the muscular tissues per day must
be very great. It has been calculated that, even neglecting the heat produced
by the quiet katabolism of muscular tissue, the amount of heat generated by
muscular activity would supply the principal part of the total heat produced
within the body. The heart, as a special muscle, deserves particular mention
since it is in constant vigorous activity. All its energy is ultimately converted
into heat, accounting for about 5 per cent, of the total heat of the body. The
secreting glands, and principally the liver as being the largest and most ac-
tive, come next to the muscles and heart as heat-producing tissues. It has
been found by experiment that the blood leaving the glands is considerably
warmer than that entering them. The metabolism in the glands is very
active; and the more active the katabolism, the greater the heat produced.

It must be remembered, however, that although the organs mentioned are
the chief heat-producing parts of the body, all living tissues contribute their
quota, and this in direct proportion to their activity. The blood itself is also
the seat of katabolism and, therefore, of the production of heat; but the
share which it takes in this respect, apart from the tissues in which it circu-
lates, is very inconsiderable.

Regulation of the Temperature of the Human Body. — The average
temperature of the body is maintained under different conditions of external
circumstance by mechanisms which permit of (i) variation in the loss of heat,
and (2) variations in the production of heat. In healthy warm-blooded ani-
mals the loss and gain of heat are so nearly balanced one by the other that,
under all ordinary circumstances, a uniform temperature, within a degree or
two, is preserved.

Variation in the Loss of Heat. — The loss of heat from the human
body is principally regulated by the amount given off by radiation and con-
duction from its surface, by means of the constant evaporation of water from
the same part, heat being thus rendered latent, and to a much less degree by
loss from the air-passages. In each act of respiration, heat is lost to a greater
or less extent according to the temperature of the atmosphere; unless indeed

464 ANIMAL HEAT

the temperature of the surrounding air exceeds that of the blood. We must
remember, too, that all food and drink which enter the body at a lower tem-
perature abstract a small measure of heat; while the urine and feces which
leave the body at about its own temperature are also means by which a certain
small amount of heat is lost.

Heat Lost from the Surface of the Body. — By far the most impor-
tant loss of heat from the body, probably 90 per cent, and upward of the
whole amount, is that which takes place by radiation, conduction, and the
evaporation of moisture from the skin. The actual figures for ordinary
conditions are as follows: For every 100 calories of heat produced, 2.6 are
lost in heating the food and drink; 2.6 in heating the air inspired; 14.7 in
evaporation; and 80. i by radiation and conduction. During increased
activity of the body the proportion of heat lost by evaporation is greatly
increased. The means by which the skin is able to act as one of the most
important organs for regulating the temperature of the blood are, i, that
it offers a large surface for radiation, conduction, and evaporation; 2, that it
contains a large but adjustable amount of blood, and the quantity of blood
is greater under those circumstances which demand a loss of heat from the
body, and vice versa, which gives a means for varying the loss of heat by
radiation and conduction; 3, that it contains the sweat glands, which dis-
charge a quantity of moisture to be evaporated from its surface.

The circumstance which directly determines the quantity of blood in the
skin is that which governs the supply of blood to all the tissues and organs
of the body, namely, the power of the vaso- motor nerves to cause a greater
or less tension of the muscular element in the walls of the arteries, and, in
correspondence with this, a lessening or increase of the caliber of the vessel,
accompanied by a less or greater current of blood. A warm or hot atmos-
phere so acts on the sensory nerves of the skin as to lead to a reflex relaxa-
tion of the muscular fiber of the blood vessels; as a result, the skin becomes
full-blooded, relatively hot, and moist from sweating; and much heat is lost.
With a low temperature the blood vessels shrink, and with the consequently
diminished blood supply, the skin becomes pale, cold, and dry, an effect
produced through the vascular centers in the medulla and spinal cord.

The activity of the sweat glands of the skin is also regulated reflexly
through the sweat centers. The increased blood supply just described is
favorable to increased production of sweat by the sweat glands. Thus,
by means of the self-regulation the skin becomes the most important of the
means by which the temperature of the body is regulated.

The relative loss of heat by the means given, i.e., radiation, conduction,
and evaporation, will depend on two factors: first, the relative temperature
of the body to the surrounding air; and, second, the humidity of the air. If
the atmospheric temperature is the same as that of the body, of course there
will be no loss of heat by radiation and convection; if the air temperature is

HEAT LOST FROM THE SURFACE OF THE BODY. 465

higher, there will be an actual gain. When the humidity of the air is great,
there will be reduced evaporation of perspiration and consequent diminished
heat loss. If we assume a moisture-saturated air at the body temperature,
then heat loss becomes impossible and the temperature of the body will
rise. This is why a hot moist climate is so oppressive, while a hot but dry
atmosphere is readily borne by the human body. The amount of heat
required to evaporate i c.c. of water is 536 small calories, hence an increase
in the evaporation of perspiration readily compensates for a decrease in the
loss of heat by radiation and convection.

Many examples may be given of the power which the body possesses of
resisting the effects of a high temperature, in virtue of evaporation from the skin.
Blagden and others supported a temperature varying between 92° to 100° C.
(i98°-2 i2°F.) in dry air for several minutes; and in a subsequent experiment
he remained eight minutes in a temperature of 126.5° C- (260° F.). "The
workmen of Sir F. Chantrey were accustomed to enter a furnace, in which his
molds were dried, while the floor was red-hot, and a thermometer in the
air stood at 177 . 8° C. (3 50° F.), and Chabert, the fire king, was in the habit of
entering an oven the temperature of which was from 205°-3i5° C. (400°-
600° F.)." (Carpenter.)

But such heats are not tolerable when the air is moist as well as hot, so as
to prevent evaporation from the body. C. James states that in the vapor
baths of Nero he was almost suffocated in a temperature of 44.5° C. (112° F.),
while in the caves of Testaccio, in which the air is dry, he was but little incom-
moded by a temperature of 80° C. (176° F.). In the former, evaporation from
the skin was impossible ; in the latter it was abundant, and the layer of vapor
which would rise from all the surface of the body would, by its very slowly
conducting power, defend it for a time from the full action of the external heat.

Man is able by suitable clothing to increase or to diminish the amount of
heat lost by the skin. There are baths and other means which man and
animals instinctively adopt for lowering the temperature when necessary.

Although under any ordinary circumstances the external application of
cold only temporarily depresses the normal temperature to a slight extent, it
is otherwise in cases of high temperature in fever. In these cases a cool
bath may reduce the temperature several degrees, and the effect so pro-
duced lasts in some cases for many hours.

Extreme heat and cold produce effects too powerful, either in raising or
lowering the heat of the body, to be controlled by the proper regulating ap-
paratus. Walther found that rabbits and dogs kept exposed to a hot sun,
reached a temperature of 46° C. (114.8° F.), and then died. Cases of sun-
stroke furnish us with several examples in the case of man; for it would seem
that here death ensues chiefly or solely from elevation of the temperature.

The effect of mere loss of bodily temperature in man is less well known
than the effect of heat. From experiments by Walther it appears that rab-
bits can be cooled down to 8 . 9° C. (48° F.) before they die, if artificial respira-
tion be kept up. Cooled down to 17.8° C. (64° F.), they cannot recover
30

466 ANIMAL HEAT

unless both external warmth and artificial respiration be employed. Rabbits
not cooled below 25° C. (77° F.) recover by external warmth alone.

Loss of Heat from the Lungs. — The lungs and air-passages are very
inferior to the skin as a means for lowering the temperature. In giving
heat to the air breathed, the lungs stand next to the skin in importance. As
a regulating power, the inferiority is very marked. The air which is ex-
pelled from the lungs leaves the body at about the temperature of the blood,
and is always 'saturated with moisture. No inverse proportion, therefore,
exists, as in the case of the skin, between the loss of heat by radiation and
conduction, on the one hand, and by evaporation, on the other. The colder
the air and the drier, for example, the greater will be the loss in all ways.
Neither is the quantity of blood which is exposed to the cooling influence of
the air diminished or increased in the lungs, so far as is known, in accord-
ance with any need in relation to temperature. It is true that by varying the
number and depth of the respirations, the quantity of heat given off by the
lungs may be made to vary also for a few minutes. But the respiratory
passages, while they must be considered important means by which heat
is lost, are altogether subordinate, in the power of actively regulating the
temperature.

The loss of heat used to warm foods is an obvious method of expenditure
of heat which may be resorted to, especially in certain fevers. The loss of
heat by the excreta discharged from the body at a high temperature must be
of no use as a means of regulating the temperature, since the amount so lost
must be capable of little variation.

Variation in the Production of Heat. — It may seem to have been
assumed, in the foregoing pages, that the only regulating apparatus for tem-
perature required by the human body is one that shall, more or less, produce
a cooling effect; as if the amount of heat produced were always, therefore,
in excess of that which is required. Such an assumption would be incorrect.
The body has the power of regulating the production of heat, as well as its
loss.

The production of heat in the body is apparently different for each ani-
mal; i.e., the absolute amount of heat set free by different animals in a given
period varies. Each individual has his own coefficient of heat production.
From all that has been said on the subject it will be seen that the amount of
heat for all practical purposes depends upon the metabolism of the tissues of
the body; everything, therefore, which increases that metabolism will increase
the heat production; so, therefore, the absolute amount of heat produced by a
large animal, having a larger amount of tissues in which metabolism may
go on, will be, ceteris paribus, greater than that of a small animal. But the
activity of the tissue change in a small animal may be greater than in a large
one, as measured per kilo of body weight, and naturally no strict line can be
drawn between the two.

INFLUENCE OF NERVOUS SYSTEM ON HEAT PRODUCTION 467

HEAT PRODUCED PER KILO PER HOUR. (MuNK.)

Man i . o calories.

Dog (large) 1.7 calories.

Dog (small) 3.8 calories.

Guinea-pig 7.5 calories.

Rat 11.3 calories.

Mouse 19.0 calories.

Sparrow 35-5 calories.

The ingestion of foods increases the metabolism of the tissues. As one
would expect, the rate of heat production is found by experiment upon the
dog to be increased after a meal, reaching its height about six hours after a
meal.

It has also been experimentally ascertained that the rate of heat produc-
tion varies with the kind of food taken: for example, if sugar be added to the
meal of meat given to the dog, the height of maximum production is reached.
It is often said that the various nations have found by experience what food
is most suitable for the climate in which they live, and that such experience
can be trusted to regulate the quantity consumed. Although there have
been no very conclusive experiments to prove the view, yet it is a matter of
general observation that in northern climates and in colder seasons the quan-
tity of food taken is greater than in warmer climates or in warmer seasons.
Moreover, the kind of food is different. For example, persons living in the
colder climates require much fat in order to produce the requisite amount of
heat.

Influence of the Nervous System on Heat Production. — The influence
of the nervous system in modifying the production of heat must be very
important, as upon the nervous influence depends the amount of the metab-
olism of the tissues. The experiments and observations which best illus-
trate it are those showing, first, that, when the supply of nerves to a part is
cut off, the temperature of that part falls below its ordinary degree after a
time; and, second, that when there is severe injury to or removal of the
nervous centers the temperature of the body rapidly falls, even though arti-
ficial respiration be performed, the circulation maintained, and to all appear-
ance the ordinary conditions for chemical changes in the body be completely
maintained.

There is a heat-regulating nervous apparatus closely comparable to that
which regulates the secretion of saliva or of sweat, by means of which the pro-
duction of heat in the warm-blooded animals is increased or diminished, as
occasion requires. This apparatus probably consists of a center or centers
in the brain which may be reflexly stimulated, as, for example, by impulses
from the skin, and which act through special nerves supplied to the various
tissues. The evidence upon which the existence of this regulating appara-
tus is assumed is the marked effect in the increase of the oxygen consumed by

468 ANIMAL HEAT

a warm-blooded animal when exposed to cold, and the corresponding increase
in the output of carbon dioxide, indicating that there is an increase of the
metabolism and so an increased production of heat under such circumstances,
and not a mere diminution of the amount of heat lost by the skin, etc. A
cold-blooded animal reacts very differently to exposure to cold; instead of
increasing the metabolism as in the case of the warm-blooded animal, cold
diminishes the metabolism of its tissues. It is clear, therefore, that in warm-
blooded animals there is some apparatus not possessed by cold-blooded ani-
mals, which counteracts the effects of cold. In warm-blooded animals poi-
soned by curara, or in which section of the medulla has been done, it has been
found that this regulating apparatus is no longer in action, and under such
circumstances no difference appears to exist between such animals and those
which are naturally cold-blooded. Warmth increases their temperature,
and cold lowers it, and with this there is, of course, evidence of diminished
metabolism.

The explanation of these experiments is that in such animals the connec-
tion between the skin and the muscles through the nervous chain, such as
a thermotaxic nervous apparatus might be supposed to afford, is broken
either at the termination of the nerves in the muscles (curara) or at the sec-
tioned point of the bulb.

The position of these hypothetical centers is a matter of some difference
of opinion. It has been demonstrated that stimulation of certain parts of
the brain may, among other symptoms, produce increased metabolism of the
tissues with increased output of carbon dioxide and a raised temperature:
the parts of which this may be asserted are parts of the corpus striatum and
of the optic thalamus. The general thermogenic centers are probably closely
associated with the motor centers of the cord and brain stem. The thermo-
regulative centers are the nuclei in the corpus striatum and optic thalamus.
Assuming a constant or tonic activity of the thermogenic regulative centers,
it is easy to understand the fall of temperature on their destruction or on the
destruction of the nerve paths to the active tissues.

Experimental observations, such as have been made upon animals,
receive confirmation from the observations on patients who suffer from fever
or pyrexia; in them the temperature of the body may be raised several de-
grees, as we have already pointed out. This increase of temperature
might, of course, be due to diminished loss of heat from the skin, but this,
although a factor, is not the only cause. The amount of oxygen taken in
and the amount of carbon dioxide given out are both increased. With
this there must be increased metabolism of the tissues, and particularly of
the muscular tissues, since at the same time the amount of urea in the urine
is increased. Every one is familiar with the rapid wasting which is such a
characteristic of high fever; it indicates not only too rapid metabolism of
the body, but also insufficient time for the tissues to again build themselves

INFLUENCE OF NERVOUS SYSTEM ON HEAT PRODUCTION 469

up. In certain fevers, therefore, there may be supposed to be some inter-
ference with the ordinary cutaneous reflex channels by which the usual
temperature sensory stimuli in the skin are prevented from producing the
reflexes that result in diminished production of heat in the muscles and other
tissues. In consequence of this, and in spite of the condition of increased
heat of the body, both at the surface and in the deeper tissues, the production
of heat goes on at an abnormal rate. It is not certain whether the patho-
logical condition is one which stimulates the thermogenic center by means
of which the metabolism of the tissues is increased, or whether the normal
reflexes which ordinarily inhibit the activity of the center when the tempera-
ture rises fail to bring about their usual reactions. The first is the probable
explanation of the high fevers of certain toxemias.

Drugs may markedly interfere with the function of the thermogenic
mechanism. For example, in anesthesia for operative purposes the tem-
perature of the body falls below the normal unless heat loss is prevented.
If too great loss occurs so that the body temperature as measured in the
rectum (determined on cats) falls to 25° C., and lower, the heat regulating
mechanism ceases to be operative. It does not regain its function without
the aid of artificial heat. But recovery of the thermogenic function may
be accomplished by artificial aid even after the rectal temperature has fallen
to as low as 16° C. (Simpson and Herring).

CHAPTER XIII.
MUSCLE-NERVE PHYSIOLOGY.

The structure of muscle, of nerve, and of nerve relations to muscle are
all given in considerable detail in Chapter II, to which the reader is referred.

CHEMICAL COMPOSITION OF MUSCLE.

Muscle Plasma. — The principal substance which can be extracted
from muscle, when examined after death, is the protein body, myosin.
This body appears to bear somewhat the same relation to the living muscle
that fibrin does to the living blood, since the coagulation of muscle after
death is due to the formation of myosin. Thus, if coagulation be delayed
by removing the muscles immediately that an animal is killed, and rapidly
cooling them to a temperature below o° C. before the muscles themselves
lose their irritability, it is possible to express a viscid fluid of slightly alkaline
reaction, called muscle plasma (Kiihne). Muscle plasma, if exposed to
the ordinary temperature of the air, undergoes coagulation much in the same
way as does blood plasma under similar circumstances when separated
from the blood corpuscles at a low temperature. The appearances presented
by the fluid during the process are also very similar to the phenomena of
blood-clotting, viz., first of all an increased viscidity appears on the surface
of the fluid, and at the sides of the containing vessel, which gradually extends
throughout the entire mass, until a fine transparent clot is obtained. In the
course of some hours the clot begins to contract, and to squeeze out of its
meshes a fluid corresponding to blood serum. In the course of coagulation,
therefore, muscle plasma separates into muscle clot and muscle serum. The
muscle clot contains the substance myosin. It differs from fibrin in being
easily soluble in a 10 per cent, solution of sodium chloride. It is insoluble
in distilled water, and its solutions coagulate on application of heat; in short,
it is a globulin. During the process of clotting the reaction of the fluid
becomes distinctly acid.

The coagulation of muscle plasma can be prevented not only by cold,
but also, as Halliburton has shown, by the presence of neutral salts in certain
proportions; for example, of sodium chloride, magnesium sulphate, or sodium
sulphate. It will be remembered that this is also the case with blood plasma.
Dilution of the salted muscle plasma will produce slow coagulation.

It is highly probable that the formation of muscle clot is due to the
presence of a ferment, myosin ferment.

470

THE PROPERTIES OF LIVING MUSCLE 471

The relation between the proteins of living and dead muscle is represented
by Halliburton as follows:

Proteins of the living muscle.

Para-myosinogen. Myosinogen.

Soluble myosin.

Myosin.
(The protein of the muscle clot.)

About 75 per cent, of the total protein content of living muscle is myo-
sinogen and the remaining 25 per cent, is para-myosinogen. These proteins
may be separated by subjecting the muscle plasma to fractional coagulation.
The para-myosinogen coagulates at 47° C. and the myosinogen at 56° C.
Para-myosinogen is a globulin since it responds to the precipitation tests of
this group of proteins and is insoluble in water. Myosinogen, on the contrary,
is not a typical globulin since it is soluble in water, but is a pseudo- globulin.

Other Constituents of Muscle. — In addition to muscle ferments
already mentioned, muscle contains certain proteolytic enzymes, as do
other tissues, an amylolytic ferment, a maltase, and a lactic-acid forming
enzyme.

Certain acids are also present, particularly sarco-lactic acid.

Of carbohydrates, glycogen and dextrose are present. Glycogen is
present in considerable amount, especially in the muscles of wTell-nourished
animals.

Nitrogenous crystalline bodies, such as creatin, creatinin, xanthin, hypo-
xanthin, carnin, guanin, urea in very small amount, uric acid, and inosinic
and phospho-carnic acids, are all found on extracting dead muscle.

Chlorides and salts of potassium, calcium, magnesium, and iron are
present in muscle, the chief of which is potassium phosphate.

In extracts of muscles, especially of red muscles, there is a certain amount
of hemoglobin, and also of a pigment special to muscle, called by McMunn
myo-hematin, which has a spectrum quite distinct from hemoglobin, viz., a
narrow band just before D, two very narrow bands between D and E, and
two other faint bands, near E b, and between E and F close to F.

Fats occur in the connective tissue around and between the muscle
fibers, and lipoids and fat droplets also are present within the individual
muscle fibers.

THE PROPERTIES OF LIVING MUSCLE.

Elasticity. — Muscle has a certain amount of elasticity during rest.
It admits of being considerably stretched, but returns readily and completely

472 MUSCLE-NERVE PHYSIOLOGY

to its normal condition. In the living body the muscles are always stretched
somewhat beyond their natural length, they are always in a condition of
slight tension: an arrangement which enables the whole force of the con-
traction to be utilized in approximating the points of attachment. If the ex-
tensibility of a given muscle be measured by adding to it equal increments
of weight, it will be found that the extension or stretching is considerable at
first, but that the amount decreases with each additional weight. If the
figures obtained be plotted on co-ordinate paper, a curve approaching a parab-
ola is obtained, whereas a steel spring is perfectly elastic and gives a straight
line. When the weights are removed from a stretched muscle, one by one,
the muscle regains its original length, though slowly. Extreme fatigue
greatly decreases the elasticity, while an increase of temperature increases it.

Cardiac muscle and smooth muscle both manifest elasticity in the same
manner as skeletal muscle. In fact, the elasticity of the arterioles is chiefly
due to the smooth muscle in their walls, a fact that is of great importance in
the adaptability of the circulatory apparatus. The flexibility of the stom-
ach, the urinary bladder, etc., is traceable to the same property of their
muscular walls.

Contractility and Irritability of Muscle.— The property of muscular
tissue by which its peculiar functions are exercised is its contractility, which
is excited by all kinds of stimuli applied either directly to the muscles or in-
directly to them through the medium of their motor nerves. The property
of the muscle which enables it to respond to a stimulus is called its irritability.
This property, although commonly brought into action through the nervous
system, is inherent in the muscular tissue. This is proven: i. By the fact
that contractility is manifested in a muscle which is isolated from the influ-
ence of the nervous system by division of the nerves supplying it so long as
the natural tissue of the muscle is duly nourished. 2. It is manifested in a
portion of muscular fiber in which, under the microscope, no nerve fiber can
be traced. 3. Substances such as curara, which paralyze the nerve endings
in muscles, do not at all diminish the irritability of the muscle itself. 4.
When a muscle is fatigued, a local stimulation is followed by a contraction
of a small part of the fiber in the immediate vicinity, without any regard to
the distribution of nerve fibers.

Forms of Stimuli for Muscle or Nerve. — The power of contraction
in voluntary muscles is normally called forth in the body by nerve impulses
which reach the muscles over the motor nerves. But a muscle will respond
to stimuli of various kinds, and these stimuli may be applied directly to the
muscle or indirectly to the nerve supplying it. There are distinct advantages,
however, in applying the stimulus to the nerve, as it is more convenient as
well as more potent. The stimuli which will produce contraction in a
muscle are:

i. Mechanical Stimuli. — A blow, pinch, prick of the muscle or its nerve

APPARATUS USED TO PRODUCE MUSCLE CONTRACTION

473

will produce a contraction, repeated on the repetition of the stimulus. If
applied to the same point for a number of times such stimuli will soon destroy
the irritability of the preparation.

2. Thermal Stimuli. — If a needle or glass rod be heated and applied to a
muscle or its nerve, the muscle will contract. A temperature of over 45° C.
will cause the muscles of a frog to pass into a condition known as heat rigor.
The sudden change of temperature acts as a stimulus.

3. Chemical Stimuli. — A great variety of chemical substances will excite
the contraction of muscles, some substances being more potent in irritating
the muscle itself and other substances having more effect upon the nerve.
Of the former may be mentioned dilute acids, salts of certain metals, e.g.,
zinc, copper, and iron; to the latter belong strong glycerin, strong acids,
ammonia, bile salts in strong solution, etc.

4. Electrical Stimuli. — Any form of electrical current may be employed
to stimulate a muscle to contract, but either galvanism or the induced current
is usually chosen. For experimental purposes electrical stimuli are most
frequently used, as the strength of the stimulus may be conveniently regulated.
In order that a stimulus shall be effective, it must have a certain amount of
energy and the application to the muscle must have a certain abruptness.
For example, a comparatively weak galvanic current suffices to stimulate a
muscle to action when suddenly applied in full force. But if the electric
current be applied very gradually, a current many times stronger will fail to
arouse contraction of a muscle.

FIG. 314. — Diagram of a Daniell's Cell A, Dry Cell B.

f~ Necessary Apparatus used to Produce and Record a Muscle Contraction. —

Galvanic currents are usually obtained by the employment of a continuous-
current cell, such as that of Daniell, by which an electrical current which varies
but little in intensity is obtained. The cell (figure 3 14 A) consists of a positive
plate of well-amalgamated zinc immersed in a porous cell containing dilute
sulphuric acid; and this cell is again contained within a large copper vessel
(forming the negative plate) containing a saturated solution of copper sulphate.

474

MUSCLE-NERVE PHYSIOLOGY

The electrical current is made continuous by the use of the two fluids in the
following manner. The action of the dilute sulphuric acid upon the zinc plate
partly dissolves it and liberates hydrogen, and this gas passes through the
porous vessel and decomposes the copper sulphate into copper and sulphuric
acid. The former is deposited upon the copper plate, and the latter passes
through the porous vessel to renew the sulphuric acid which is being used up.
The copper-sulphate solution is renewed by crystals of the salt, which are
kept on a little shelf attached to the copper plate and slightly below the
level of the solution in the vessel. The current of electricity supplied by this
cell will continue without variation for a considerable time. Other cells,
such as the dry cell (which, however, is adapted to open-circuit work) may be
used in place of Daniell's. The way in which the apparatus is arranged is to
attach wires to the copper and zinc plates and to bring them to a key connect-

FIG. 315. — Du Bois Reymond's Key.

FIG. ^16. — Mercurv Kev.

ing the wires of the battery. One often employed' is Du Bois Reymond's,
figure 315. It consists of two pieces of brass about an inch long, in each of
which are two holes for wires and binding-screws to hold them tightly. These
pieces of brass are fixed upon a vulcanite plate to the under surface of which
is attached a screw clamp by which it can be secured to the table. The
interval between the pieces of brass can be bridged over by means of a third
thinner piece of similar metal fixed by a screw to one of the brass pieces, and
capable of movement by a handle at right angles so as to touch the other piece
of brass. If the wires from the battery are brought to the inner binding-
screws, and the bridge connects them, the current passes across it and back
to the battery. Wires are connected with the outer binding-screws, and the
other ends are joined together for about two inches, but, being covered
except at their points, are insulated ; the uncovered points are about an eighth
of an inch apart. These wires are the electrodes, and the electrical stimulus is
applied to the muscle through them, if they are placed behind its nerve.
When the connection between the two brass plates of the key is broken by
depressing the handle of the bridge, the key is then said to be opened.

APPARATUS USED TO PRODUCE MUSCLE CONTRACTION 475

An induced current is developed by means of an apparatus called an
induction coil, and the one most employed for physiological purposes is Du
Bois Reymond's, the one seen in figure 317.

Wires from a battery are brought to the two binding-screws, d' and d, a
key intervening. These binding-screws are the ends of a coil of coarse covered
wire, c, called the primary coil. The ends of a coil of finer covered wire, g, are
attached to two binding-screws to the left of the figure, one only of which is
visible. This is the secondary coil, and is capable of being moved nearer to
c along a groove and graduated scale. To the binding-screws to the left of g,
the wires or electrodes used to stimulate the muscle are attached. If the key
in the circuit of wires from the battery to the primary coil (primary circuit)
be closed, the current from the battery passes through the primary coil, and

FIG. 317. — Du Bois Reymond's Induction Coil.

across the key to the battery, and continues to pass as long as the key continues
closed. At the moment of closure of the key, at the exact instant of the com-
pletion of the primary circuit, an instantaneous current of electricity is in-
duced in the secondary coil, g, if it be sufficiently near and in line with the
primary coil ; and the nearer it is to c, the stronger is the current induced. The
current is only momentary in duration and does not continue during the whole
of the period while the primary circuit is complete. When, however, the
primary current is broken by opening the key, a second current, also momen-
tary, is induced in g. The former induced current is called the making, and
the latter the breaking shock; the former is in the opposite direction to, and
the latter in the same direction as, the primary current.

The induction coil may be used to produce a rapid series of shocks by means
of the accessory apparatus at the right of the figure, called the magnetic inter-
rupter. If the wires from a battery are connected with the two pillars by the
binding-screws, one below c and the other at a, the course of the current is
indicated by the arrows in figure 318. The current passes up the pillar from
e, and along the springs if the end of d' is close to the spring, then to the
primary coil c, and to wires covering two upright pillars of soft iron, 6, to the
pillar a, and out by the wires to the battery. In passing along the wire b the
soft iron is converted into a magnet, and so attracts the hammer, /, of the

476

MUSCLE-NERVE PHYSIOLOGY

spring, breaks the connection of the spring with df, and so cuts off the current
from the primary coil, and also from the electro-magnet. As the pillars, b,
are no longer magnetized the spring is released, and the current passes in the
first direction, and is in like manner interrupted. At each make and break of
the primary current, currents corresponding are induced in the secondary coil.
These currents are opposite in direction, but are not equal in intensity, the
break shock being greater. In order that the shocks should be nearly equal
at the make and break, a wire, figure 318, e, connects e and d', and the screw
d' is raised out of reach of the spring, and d is raised as in figure 318, so that
part of the current always passes through the primary coil and electro-magnet .
When the spring touches d the current in b is diminished, but never entirely
withdrawn, and the primary current is altered in intensity at each contact of
the spring with d, but never entirely broken.

FIG. 318. — Diagram of the Course of the Current in the Magnetic Interrupter of Du Bois
Reymond's Induction Coil. (Helmholz's modification.)

Preparation of a Muscle for Contraction under Stimuli. — The muscles of
the frog are most convenient for the purpose of recording contractions. The
frog is pithed; that is to say, its central nervous system is entirely destroyed
by the insertion of a stout needle into the spinal cord and the parts above it.
One of its lower extremities is used in the following manner: The large
trunk of the sciatic nerve is dissected out at the back of the thigh, and a pair of
electrodes is inserted behind it. The tendo achillis is divided from its attach-
ment to the os calcis and a ligature tightly tied around it. This is the tendon
of the gastrocnemius, which arises from above the condyles of the femur.
The femur is now fixed to a board covered with cork, and the ligature attached
to the tendon is tied to the upright of the muscle lever, figure 319, B. When
the muscle contracts the lever is raised. It is necessary to attach a small
weight to the lever. In this arrangement the muscle is in situ, and the nerve
is disturbed from its relations as little as possible.

The muscle may, however, be detached from the body with the lower end
of the femur from which it arises, and the nerve going to it may be taken away
with it. The femur should be divided at about the lower third and the bone
fixed in a firm clamp ; the nerve is placed upon two electrodes connected with
an induction apparatus, and the lower end of the muscle is connected by its
tendon with a lever which can write on a recording apparatus.

To prevent evaporation this so-called muscle-nerve preparation is placed
under a glass cover (moist chamber, figure 3 50) . The air in the moist chamber
is kept moist by means of water adherent to its sides.

CONDUCTIVITY IN MUSCLE 477

Recording the Effects of a Single Induction Shock. — With a muscle-nerve
preparation arranged in either of the above ways, on closing or opening the
key in the primary circuit we obtain and can record a contraction, and if we
use the clock-work apparatus revolving rapidly, a curve is traced such as is
shown in figure 320.

Another way of recording the contraction is by use of the pendulum myo-
graph, figure 352. Here the swing of the pendulum along a certain arc is
substituted for the clock-driven movements of the other apparatus. The
pendulum carries a smoked-glass plate upon which the writing lever of a

FIG. 319. — Arrangement of the Apparatus Necessary for Recording Muscle Contrac-
tions with a Revolving Cylinder Carrying Smoked Paper. A, Revolving cylinder; B, the
frog arranged upon a cork-covered board which is capable of being raised or lowered on the
upright, which also can be moved along a solid triangular bar of metal attached to the base
of the ^recording apparatus — the tendon of the gastrocnemius is attached to the writing
lever, properly weighted, by a ligature. The electrodes from the secondary coil pass to the
apparatus — being, for the sake of convenience, first of all brought to a key, D (Du Bois
Reymond's); C, the induction coil; F, the battery (in this figure a bichromate one); E,
the key (Morse's) in the primary circuit.

myograph is made to mark. The opening or breaking shock is sent into the
nerve-muscle preparation by the pendulum in its swing opening a key, figure
352, C, in the primary circuit. A muscle or its nerve is more irritable to an
opening shock than it is to a closing shock of the same strength, because the
duration of the former is shorter than that of the latter.

Conductivity in Muscle. — In an ameba or other simple undifferentiated
contractile protoplasmic unit a stimulus applied at any point is quickly
transmitted throughout the entire mass. Just so is it with differentiated

478 MUSCLE-NERVE PHYSIOLOGY

muscle. A stimulus applied at any point of a muscle will quickly be propa-
gated through the mass as far as there is protoplasmic continuity. In cardiac
muscle and in smooth muscle there is uninterrupted conduction from cell
to cell. But in voluntary muscle each fiber is physiologically isolated from
its neighbors. When a voluntary muscle fiber is stimulated either at the ex-
tremities or at its middle, the effect of the stimulus quickly passes through
the entire fiber, whether it arouses a distinct act of contraction or not.

The rate at which conduction takes place when a contraction accom-
panies it has been carefully measured by numerous observers. It varies
greatly in the different kinds of muscle, from two-tenths of a meter per second
in the rabbits' ureter (Engelmann) to ten meters per second in the voluntary
muscles of man.

SINGLE MUSCLE CONTRACTIONS.

Characteristics of a Single Contraction.— The Myogram.— The con-
traction of a muscle in response to a single effective stimulus of short dura-
tion is called a simple muscle contraction. A record of such a contraction
is called a myogram. The character of the myogram, and therefore the facts
revealed by it, are dependent on whether or not the record is made on a rapidly
moving recording surface. If the myogram is made on a recording surface
that is standing still, then it shows merely the extent of shortening of the

FIG. 320. — Record of a Simple Contraction of the Gastrocnemius of the Frog. Time
in o.oi second. Si, Moment of stimulation. Record taken on a rapid drum that was
provided with an automatic key.

muscle. The amount of shortening for a given muscle will depend on a series
of conditions, such as nutrition, load, temperature, etc., all of which will
be discussed presently.

When the record is made on a rapidly moving drum or on the pendulum
myograph, it is revealed that the simple contraction occupies a definite per-
iod of time with well-marked periods or phases. Although the stimulus may
be practically instantaneous, the contraction lasts a considerable fraction of a
second, in the frog's gastrocnemius about o. i of a second.

CHANGE IN SHAPE DURING MUSCULAR CONTRACTION

479

It will be observed that after the stimulus has been applied, as indicated
by the vertical line St, there is an interval before contraction commences.
This interval, termed the latent period, when measured by the number of vi-
brations of the tuning-fork directly beneath, is found to be about o.oi of a
second. The latent period is longer in some muscles than in others and
differs also according to the condition of the muscle and the kind of stimulus
employed. During the latent period there is no apparent change in the
muscle. The second part of the record shows the contraction phase proper.
The lever is raised by the sudden shortening of the muscle. The contrac-
tion is at first very rapid, but then progresses more slowly to its maximum.
It occupies on an average o . 04 of a second in the frog's gastrocnemius. The
third stage is the relaxation phase. After reaching its highest point, the lever
begins to descend, in consequence of the elongation of the muscle. At first
the fall is rapid, but it then becomes more gradual until the lever reaches the
abscissa or base line, when the muscle has attained its precontraction length.
The stage occupies o . 05 of a second. Usually after the contraction proper
is over the lever oscillates below and above the base line in a series of dimin-
ishing waves, the elastic rebound following movement of the simple contrac-
tion. These are, of course, wholly passive and would occur equally well if
we should lift the weight to the height of the contraction, then simply let it
fall while taking a record.

Change in Shape during Muscular Contraction. — There is a consider-
able difference of opinion as to the mode in which the transversely striated
muscular fibers contract. The most probable account is that the contraction

• FIG. 321. — The Microscopic Appearances During a Muscular Contraction in the
Individual Fibrillae, after Engelmann. i. A passive muscle fiber; c to d = doubly refractive
discs, with median disc a b in it; h and g are lateral discs;/ and e are secondary discs, only
slightly doubly refractive; figure on right same fiber in polarized light. The bright part
is doubly refracted, black ends not so. 2. Transition stage. 3. Stage of entire contrac-
tion. In each case the right-hand figure represents the effect of polarized light. (Landois,
after Engelmann.)

is effected by an approximation of the constituent parts of the fibrils, which,
at the instant of contraction, without any alteration in their general direction,
become closer, flatter, and wider, a condition which is rendered evident by
the approximation of the transverse striae seen on the surface of the fasciculus,
and by its increased breadth and thickness. The appearance of the zigzag

480

MUSCLE-NERVE PHYSIOLOGY

lines into which it was supposed the fibers are thrown in contraction is due
to the relaxation of a fiber which has been recently contracted and is not
at once stretched again by some antagonist fiber or whose extremities are

FIG. 322. — Reflecting Galvanometer. (Thomson.) A, The galvanometer, which
consists of two systems of small astatic needles suspended by a fine hair from a support, so
that each set of needles is within a coil of fine insulated copper wire; that forming the lower
coil is wound in an opposite direction to the upper. Attached to the upper set of needles
is a small mirror about ^ inch in diameter; the light from the lamp at B is thrown upon this
little mirror, and is reflected upon the scale on the other side of B, not shown in figure.
The coils u are arranged upon brass uprights, and their ends are carried to the binding-
screws. The whole apparatus is placed upon a vulcanite plate capable of being leveled
by the screw supports, and is covered by a brass-bound glass shade, /, the cover of which
is also of brass, and supports a brass rod, &, on which moves a weak curved magnet, m.
C is the shunt by means of which the amount of current sent into the galvanometer may
be regulated. When in use, the scale is placed about three feet from the galvanometer,
which is arranged east and west, the lamp is lighted, the mirror is made to swing, and the
light from the lamp is adjusted to fall upon it, and it is then regulated until the reflected
spot of light from it falls upon the zero of the scale. The wires from the non-polarizable
electrodes touching the muscle are attached to the outer binding-screws of the galvan-
ometer, a key intervening for short-circuiting; or if a portion only of the current is to pass into
the galvanometer the shunt should intervene as well with the appropriate plug in. When
a current passes into the galvanometer the needles and, with them, the mirror are turned
to the right or left according to the direction of the current. The amount of the deflection
of the needle is marked on the scale by the spot of light traveling along it.

kept close together by the contractions of other fibers. The contraction is
therefore a simple and, according to Edward Weber, a uniform, simultaneous,
and steady shortening of each fiber and its contents. What each fibril or

THE DEMONSTRATION OF MUSCLE CURRENTS 481

fiber loses in length, it gains in thickness. The contraction is a change of
form, not of size; it is, therefore, not attended with any diminution in bulk
from condensation of the tissue. This has been proved for entire muscles,
by making a mass of muscles, or many fibers together, contract in a vessel
full of water, with which a fine, perpendicular, graduated tube communi-
cates. Any diminution of the bulk of the contracting muscle would be
attended by a fall of fluid in the tube, but when the experiment is carefully
performed, the level of the'water in the tube remains the same, whether the
muscle be contracted or not.

In thus shortening, muscles appear to swell up, becoming rounder, more
prominent, harder, and apparently tougher. But this hardness of muscle in
the state of contraction is not due to increased firmness or condensation of the
muscular tissue, but to the increased tension to which the fibers, as well as
their tendons and other tissues, are subjected from the resistance ordinarily
opposed to their contraction. When no resistance is offered, as when a
muscle is cut off from its tendon, not only is no hardness perceived during
contraction, but the muscular tissue is even softer and more extensible than
in its ordinary uncontracted state. During contraction in each fiber it is
said that the anisotropous or doubly refractive elements become less refract-
ive and the singly refractive more so, figure 321.

Chemical Changes in Contracting Muscle. — i. The reaction of the
muscle, which is normally alkaline or neutral, becomes decidedly acid during
contraction, from the development of sarcolactic acid. 2. The muscle gives
out carbon dioxide gas and takes up oxygen. The amount of the carbon
dioxide given out does not appear to be entirely dependent upon the oxygen
taken in, and so doubtless in part arises from some other source. Muscle
contracts in an atmosphere of hydrogen, showing that oxygen is present in
fixed combination. A muscle, however, contracts for a longer time in an
atmosphere of oxygen. 3. Certain imperfectly understood chemical changes
occur, in all probability connected with i and 2, in which glycogen is con-
verted into dextrose and the latter oxidized.

Electrical Changes in Contracting Muscle. — Resting muscles un-
injured in the body have a uniform potential, i.e., are isoelectric. But when
removed from the body they are more or less injured and, therefore, show
differences of electrical potential between different points on the muscle,
called currents of injury or demarcation currents.

The Demonstration of Muscle Currents. — The demonstration of electrical
currents in muscle requires a galvanometer and non-polarizing electrodes. A
muscle prism is insulated, and a pair of non-polarizable electrodes connected
with a very delicate galvanometer, figure 322, are applied to various points
of the prism ; and by a deflection of the needle to a greater or less extent in one
direction or another, the strength and direction of the currents in the piece of
muscle can be determined. It is necessary to use non-polarizable and not
metallic electrodes in this experiment, as otherwise there is no certainty that

482 MUSCLE-NERVE PHYSIOLOGY

the whole of the current observed is communicated from the muscle itself
and not derived from the metallic electrodes and arising in consequence of the
action of the saline juices of the tissues upon them. The form of the non-
polarizable electrodes is a modification of Du Bois Reymond's apparatus,
figure 323, which consists of a somewhat flattened glass cylinder, a, drawn
abruptly to a point, and fitted to a socket capable of movement, and attached
to a stand, A, so that it can be raised or lowered as required. The lower por-
tion of the cylinder is filled with china clay moistened with saline solution,
part of which projects through its drawn-out point; the rest of the cylinder is
filled with a saturated solution of zinc sulphate into which dips a well-amal-

FIG. 323. — Diagram of Du Bois Reymond's Non-polarizable Electrodes, a, Glass
tube filled with a saturated solution of zinc sulphate, in the end, c, of which is china clay
drawn out to a point; in the solution a well-amalgamated zinc rod is immersed and con-
nected, by means of the wire which passes through a, with the galvanometer. The re-
mainder of the apparatus is simply for convenience of application. The muscle and the end
of the second electrode are to the right of the figure.

gamated piece of zinc connected by means of a wire with the galvanometer.
In this way the zinc sulphate forms a homogeneous and non-polarizable
conductor between the zinc and the china clay. A second electrode of the
same kind is, of course, necessary. Recently Porter has devised a boot-
shaped clay electrode that is burned, and hence has the immense advantage of
permanency.

Currents of Injury, or Demarcation Currents. — If a segment is cut
out of a living gastrocnemius, its cut ends present regions of maximal injury.
Such a preparation is called a muscle prism.

If the points on the surface of a muscle prism be connected with the gal-
vanometer by non-polorizable electrodes, it will be found that the currents
pass from point to point, as shown in the diagram, figure 324.

The strongest currents pass from the equator to a point representing the
middle of the cut ends; currents also pass from points nearer the equator to
those more remote, but not from points equally distant, which are isoelectric
points. The cut ends are always negative to the equator. The currents are

HEAT PRODUCED IN A SIMPLE CONTRACTION

483

in all probability due to chemical changes going on in the muscles at the in-
jured ends.

Action Currents. — When a muscle is made to contract the demar-
cation current undergoes a sharp decrease, as shown by the deflection of the
galvanometer needle, which swings back in the direction of equilibrium.
This deflection, originally called the current of negative variation, has been
shown to be due to the processes going on in the muscle during contraction,
and is therefore more properly called the action current. It occurs where no
previous demarcation current exists.

For the study of the action current the capillary electrometer is very con-
venient. The hearts of cold-blooded animals, because of their slow con-
traction, serve well for demonstration. The muscle contraction passes over

FIG. 324. — Diagram of the Currents in a Muscle Prism. (Du Bois Reymond.)

the ventricle in the form of a wave, the electric potential of the muscle chang-
ing as it becomes active or passive. For any two points on the heart muscle,
therefore, there will be two changes of potential, the active part first becom-
ing negative to the inactive, and then, as the wave passes down and the in-
active part becomes active, the current is reversed. This is known as a
diphasic current.

In certain fishes definite electrical organs exist, organs which are derived
from muscle-like tissues and which may be regarded morphologically as mus-
cles highly specialized for the production of energy in the form of electricity.

Heat Produced in a Simple Contraction. — Becquerel and Breschet
found, with the thermo-multiplier, about 0.5° C. of heat produced by each
forcible contraction of a man's biceps; and when the actions were long con-
tinued, the temperature of the muscle increased i° C. In the frog's muscle
a considerable number of contractions have been found to produce an ele-
vation of temperature equal on an average to less than o. 2° C., while a single
contraction produces, according to R. Heidenhain, from 0.001° to 0.005° C.
One gram of frog's muscle will produce in a single maximal contraction about
0.003 calorie or the equivalent of 128 gramcentimeters of work energy (since

484

MUSCLE-NERVE PHYSIOLOGY

i calorie = o . 4267 kilogrammeter of work) . The cause of the rise of tempera-
ture is the increased chemical activity at the time of contraction. As we
have already seen, in the chapter on Animal Heat, muscles have the power of
producing heat even when not contracting, i.e., changing shape.

The amount of heat energy developed during a single contraction will
vary sharply according to the tension under which the muscle contracts.
The heat production follows closely the energy of work produced, and
apparently obeys the same laws.

FIG. 325. — Figure for Work Energy, Showing Height of the Contraction of the Gastroc-
nemius of the Frog with Loads Increased by Ten Grams at a Time.

The Work Energy Liberated by a Simple Muscle Contraction.—

When a muscle contracts against a resistance and a load is moved, work
energy is liberated. In fact, the liberation of work energy and heat energy
are the specific functions of the muscles among the warm-blooded animals.
A frog's gastrocnemius weighing i gram and loaded with 50 grams will
contract from 0.5 to 0.6 cm.; i.e., will do 25 to 30 gramcentimeters of work
for each simple contraction. The amount of work done is intimately associ-

TABLE SHOWING THE RELATION BETWEEN LOAD AND WORK.

Load or tension. Height lifted.

Work done.

Grams. Centimeters.

Gramcentimeters.

o

I .2

0

40 0.8

32

80 0.5

40

120 0.4

48

1 60

O . 2

32

200

0. I

20 ,

240 o.o o

EFFECT OF THE STRENGTH OF STIMULUS 485

ated with the tension under which the muscle contracts. As the tension in-
creases from no load up to 100 or 150 grams (for a i-gram muscle), the work
increases. But as the tension continues to increase, the work falls off until
a point is reached at which the load is not lifted at all.

CONDITIONS WHICH AFFECT THE IRRITABILITY] OF

THE MUSCLE AND THE CHARACTER OF THE

CONTRACTION.

There are a number of conditions which influence both the irritability
of a muscle and the power and character of its contractions. Irritability
and contractility may vary independently, but as a rule any condition which
decreases one also decreases the other. The most important of these con-
ditions are: relation of the muscle to the central nervous system, condition
of nutrition, stimulus, temperature, fatigue, drugs, disease, etc.

Effect of the Strength of Stimulus. — A strength of current that is just
sufficient to give the contraction of a muscle is called a minimal stimulus.

FIG. 326. — Contraction of the Gastrocnemius Under the Influence of Variation of
Strength of Stimulus. The muscle was stimulated by Petzold's inductorium, graduated to
show units of current. The figures 6, 7, 8, 9, 10, etc., indicate relative strength of stimulus.

This is a comparatively weak induction current, one which can scarcely be
detected by the tip of the tongue. As the strength of the current is very
gradually increased, the height of the contraction curve increases until the
maximal stimulus is reached, which produces a contraction of an amplitude
beyond which no increase occurs even though the strength of the stimulus be
multiplied many fold. The range between the strengths of the minimal and
maximal stimuli is very restricted indeed. The absolute strength of a mini-

486 MUSCLE-NERVE PHYSIOLOGY

mal stimulus varies exceedingly for a given muscle, depending on its degree
of irritability. This narrow range between minimal and maximal stimuli
serves as a convenient means for detecting the variations in irritability. One
should count on a continued decrease in irritability in isolated muscles, hence
should choose a supramaximal stimulus for all such preparations when other
conditions surrounding the muscle are under investigation.

The Influence of Repeated Activity. — The irritability of muscle is
decreased by undue functional activity. The cause of the diminished ir-
ritability is twofold: when a muscle contracts, part of its substance is ex-
pended, part of its store of nutriment is exhausted, and it cannot contract so

FIG. 327. — Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers
printed on the figure indicate the contractions in the series which is recorded. (Lee.)

vigorously again until the loss is made up. To this extent fatigue has much
the same effect as cutting off or diminishing the blood supply. The other
cause for the diminution of irritability is the accumulation of poisonous prod-
ucts in the muscle, substances generated during contraction, probably sar-
colactic acid chiefly. In a living animal these poisonous products exert their
influence not only upon the muscle or muscles immediately concerned in
contraction, but upon the musculature of the body generally, and the effect
remains until they are eliminated from the body. Massage of the muscles
increases the passage of waste products into the general blood stream and the
rapidity of their elimination.

In the first few simple contractions, repeated in series, there is an increase
in the amplitude of the contractions resulting in the phenomenon known
as staircase contractions or "Treppe. " This stage is followed by a period
of sustained contractions, and this finally by a diminishing series of ampli-
tudes until the muscle fails to respond. After a few minutes' rest a muscle
will again give strong contractions, but only for a brief series.

If the time of the simple contractions is measured, it will be found, figure
327, that not only is the amplitude decreased, but the duration is greatly

THE INFLUENCE OF TEMPERATURE 487

increased as the contractions are repeated. The latent period changes very
little. The contraction phase is considerably prolonged, but the relaxation
phase is very greatly increased. As fatigue progresses, the total time of the
simple contraction may be two or three times longer than the normal. The
ability of the muscle to do work falls off rapidly, of course; and the greater
the load during the time fatigue is coming on, the more quickly complete
fatigue approaches.

The Influence of Temperature. — The irritability of muscle is in-
creased by raising its temperature slightly above that of the animal from
which it has been taken, while it is decreased by cooling. If, however, the
temperature be raised too high (40° C. for frog, 50° C. for mammal), the
muscle enters into a condition of heat rigor and its irritability is forever lost.

FIG. 328. — Contractions of the Gastrocnemius Muscle to Show the Influence of
Temperature on the Amplitude of the Contractions. At 40° C. the muscle has begun to
pass into rigor mortis, yet is able to give short contractions. The steps on the curve of rigor
at the right occur at temperatures of 41°, 42°, and 43° C.

After cooling, unless the cold be too severe and prolonged, the irritability re-
turns as the temperature is raised. A series of vertical records of simple con-
tractions beginning at room temperature and decreasing writh a contraction
at each fall of one degree reveals the fact that the amplitude falls off slowly
until a temperature of 12° to 10° C. is reached, then as gradually increases
until 4° to 2° C., after which the amplitude drops off sharply to about — 1° C.
However, this phenomenon is partly one of irritability, since a very strong
stimulus will produce a vigorous contraction until the muscle begins to
freeze. If at the freezing temperature the muscle be slowly and carefully
increased in temperature it will recover from the effects of the cooling with-
out apparent injury, and will give a reverse series to the one obtained by
decreasing the temperature. As the increase of temperature is continued
above room temperature the amplitude of the contractions very greatly
increases (also the elasticity), reaching a maximum in the frog's gastroc-
nemius at about 35° to 36° C. The amplitude sharply decreases above

488 MUSCLE-NERVE PHYSIOLOGY

35° C. up to 37° to 38° C., where heat rigor begins and the muscle per-
manently shortens. Heat rigor is usually complete at 40° to 41° C. A
muscle cannot recover its irritability after heat rigor has set in strongly.

If the time of the contraction is measured at different temperatures it will
be found to be greatly delayed at 2° to 4° C., and very much quicker than nor-
mal at 33° to 35° C. As in fatigue, the effect falls chiefly on the contraction
and relaxation phases and only slightly on the latent period. The latent
period is more sharply influenced by temperature than by fatigue.

FIG. 329. — Influence of Temperature on the Duration of the Contraction of the Frog's

Gastrocnemius.

Influence of Blood Supply. — In the normal human muscle there is a
delicately balanced vaso-motor mechanism by which the amount of blood
flowing through a muscle is immediately increased when the muscle is in con-
traction. This blood stream is of course carrying nutritive materials to the
muscle and taking away wastes. If the blood supply to a muscle is cut off,
then the muscle can only draw on its stored supply of potential energy, which
in active contraction is sooner or later exhausted. Under such conditions
the muscle increases in irritability for a few minutes and then gradually loses
both its irritability and its power to contract. Even mammalian muscles
have been kept alive and normal in their activity for several hours by irri-

EFFECT OF RATE OF STIMULATION 489

gating them with defibrinated and aerated blood (von Frey). Mammalian
muscles will remain irritable for 30 minutes, or longer if cooled, after being
shut off from their blood supply and isolated from the body, but both irrita-
bility and contractility soon disappear entirely.

Effect of Nerve Supply. — The voluntary or skeletal muscle normally
contracts in the body only when stimulated through its motor nerve. If the
motor nerve is severed, the muscle is cut off from its normal source of activity,
hence will undergo the changes resulting from disuse, which will be presently
discussed. Aside from this, it is held by most observers that there are dis-
tinct nutritive or trophic nerves which exercise a controlling influence over
the growth, development, and general nutritive processes going on in muscle.

When a motor nerve is cut, the muscle at first exhibits heightened irrita-
bility to all forms of stimuli. In a couple of weeks it decreases in its power
to respond to rapidly changing stimuli like induced currents. It responds
more readily to mechanical shocks and to galvanic currents for six or seven
weeks, then gradually loses the power of contracting through as many months.
The changes are due to protoplasmic degeneration. It is not clear in what
degree these changes are due to loss of trophic nerve influence, to inactivity,
and to changes in nutritive conditions. Since degeneration occurs when
the vascular supply is maintained, it would seem that the nutritive condition
must be chargeable to one or the other of the first two factors, probably to
both.

Use of muscle increases its power and also its irritability. A properly
regulated exercise is well known to contribute to the health and development
of muscles. In cases of paralysis, mechanical or electrical stimulation is
applied directly to the muscle in an effort to supply artificial exercise until the
nerves are regenerated and motor connections re-established. If such stim-
ulation is not applied, the muscle degenerates from disuse and loses its
irritability often before the nerves regenerate.

The Effect of Drugs. — Drugs affect the irritability of muscle, some
augmenting, others depressing it. Voluntary muscle, which does not ordina-
rily contract except when stimulated, can be made so irritable by certain
salts that it contracts automatically like heart muscle, and the converse.
Ether, chloroform, etc., anesthetize muscle just as they do nerve, suppressing
both irritability and contractility. Suprarenal extract increases the ampli-
tude of contraction, as do also caffeine, digitalis, nicotine, and others. Ver-
atrine is well known greatly to prolong the relaxation phase of the simple
contraction without materially affecting the contraction phase or the latent
period.

TETANIC AND VOLUNTARY MUSCULAR CONTRACTIONS.

Effect of Rate of Stimulation. — If we stimulate the muscle-nerve prep-
aration \vith two induction shocks, one immediately after the other, when the

49° MUSCLE-NERVE PHYSIOLOGY

point of stimulation of the second one corresponds to the crest of the con-
traction of the first, a second curve, figure 330, will occur, which will commence
near the highest point of the first and will rise nearly as much higher, so that
the sum of the height of the two curves almost exactly equals twice the height
of the first. This phenomenon is called summation. If a third and fourth
shock be passed, a similar effect will ensue, and curves one above the other
will be traced, the third being slightly lower than the second, and the fourth
than the third. If a continuous series of shocks occur, however, the lever
after a time ceases to rise any further, and the contraction, which has reached

FIG. 330. — Tracing of a Double Muscle Curve. To be read from left to rightv While
the muscle 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. (M.
Foster.)

its maximum, is maintained. The condition which ensues is called Tetanus.
A tetanus is really a summation of contractions, but unless the stimuli become
very rapid indeed, the muscle will still be in a condition of vibratory contrac-
tion and not of unvarying contraction.

If the shocks, however, be repeated at very short intervals, varying, in the
frog, from eighteen to thirty per second, the muscle contracts to its utmost
at once and continues at its maximum contraction for some time. The
lever rises almost perpendicularly and then describes a straight line, figure
331, c. The rate of stimulation required increases with the rapidity of the
simple contraction. If the stimuli are not so rapid the line of maximum con-
traction becomes wavy, indicating a tendency of the muscle to relax during
the intervals between the stimuli, figure 331, b. As the muscle becomes
fatigued, a less rapid rate of stimulation is required to produce a complete
tetanus, owing to the prolongation of the relaxation period in such a muscle.
The height of the contraction, however, is lessened. This condition of pro-
longed relaxation is known as contracture.

Co-ordinated Muscular Contractions. — In the human body the skel-
etal muscles contract only on stimulation through their motor nerves; i.e.,
under the influence of nerve impulses that have their origin in the central

CO-ORDINATED MUSCULAR CONTRACTIONS

491

nervous system. Such motor impulses may arise through reflexes, through
automatic activity of the nerve center, or by higher cerebral origin associated
with conscious psychic effort. In either case the apparatus consists of one
or more central neurones, an anterior-horn motor cell, and the muscle itself.
Conscious or voluntary effort may be taken as a type.

Simple contractions are possible to human muscles, but undoubtedly
tetanic contractions are the rule. If one holds the arm out at right angles to

FIG. 331. — a, Frog's gastrocnemius muscle stimulated with four induction shocks per
second, showing complete relaxation between stimuli; b, same muscle stimulated eight times
p^r second, showing partial relaxation between stimuli (incomplete tetanus); c, same
muscle stimulated twelve times per second, showing development of an almost complete
tetanus.

the trunk, the movement requires the continuous or tetanic contraction of the
deltoid and the series of extensor muscles. If the arm is retained in the
extended position long enough, extreme fatigue is felt and presently one can
no longer maintain the position. Yet, if the muscles involved are immediately
stimulated directly with an electric current, they contract, showing that such
exhaustion as exists is not wholly due to the muscle.

Mosso's ergograph was devised for the specific purpose of studying the
character of fatigue of voluntary effort. This apparatus is adapted to the

492 MUSCLE-NERVE PHYSIOLOGY

study of the fatigue of the flexors of the middle finger or, in the newer in-
strument devised by Storey, to the abductor of the index finger. Numerous
studies have shown, apparently, that the fatigue of voluntary effort involves,
first, the nervous apparatus and, later, the muscle; that the muscle still
retains a considerable reserve of energy when the apparatus as a whole is
exhausted.

Muscle in Rigor Mortis.— After the muscles of the dying body have
lost their irritability or capability of being excited to contraction by the ap-
plication of a stimulus, they spontaneously pass into a state of shortening
apparently identical in effect with that which ensues during life. It affects
all the muscles of the body, and, when external circumstances do not
prevent it, commonly fixes the limbs in that which is their natural posture of
equilibrium or rest. From the simultaneous contraction of all the muscles
of the trunk, a general stiffening of the body is produced, which constitutes
the rigor mortis or postmortem rigidity.

When this condition has set in, the muscle becomes acid in reaction (due to
development of sarcolactic acid), gives off carbonic acid in great excess,
diminishes in volume slightly, becomes shortened and opaque, its substance sets
in a firm coagulation. Rigor mortis comes on much more rapidly in death
after muscular activity, and is hastened by warmth.

The immediate cause of rigor mortis seems to be a chemical one, namely,
the coagulation of the muscle plasma. We may distinguish three main
stages: i, gradual coagulation; 2, contraction of the coagulated muscle
clot (myosin) and, 3, squeezing out of muscle serum. During the first stage,
restoration is possible, by the circulation of arterial blood through the muscles,
and even when the second stage has set in, vitality may be restored by dis-
solving the coagulum of the muscle by salt solution and by passing arterial
blood through the vessels. After the second stage is advanced, recovery is
impossible.

It has been noticed that the relaxation in muscles after rigor sometimes
occurs too quickly to be caused by putrefaction. The suggestion that in
such cases the relaxation is due to a ferment action is very plausible.
Subjecting fresh muscle to the action of heat (50° to 60° C.) or immersing
it in distilled water causes a similar coagulation to that of rigor mortis.
The former is known as heat rigor, and the latter as water rigor.

The muscles are not affected simultaneously by rigor mortis. It affects
the neck and lower jaw first; next, the upper extremities, extending from
above downward; and, lastly, reaches the lower limbs. In some rare in-
stances only it affects the lower extremities before or simultaneously with
the upper extremities. It usually ceases in the order in which it begins:
first at the head, then in the upper extremities, and lastly in the lower ex-
tremities. It never ordinarily commences earlier than ten minutes, and
never later than seven hours after death; and its duration is greater in pro-

MUSCLE IN RIGOR MORTIS 493

portion to the lateness of its accession. Heat is developed during the passage
of a muscular fiber into the condition of rigor mortis.

Since rigidity does not ensue until muscles have lost the capacity of being
excited by external stimuli, it follows that all circumstances which cause a
speedy exhaustion of muscular irritability induce an early occurrence of the
rigidity, while conditions by which the disappearance of the irritability is
delayed are succeeded by a tardy onset of the rigidity of rigor. This is the
explanation of its speedy occurrence, and equally speedy departure, in the
bodies of persons exhausted by chronic diseases; and its tardy onset and long
continuance after sudden death from acute diseases. In some cases of
sudden death from lightning, violent injuries, or paroxysms of passion, rigor
mortis has been said not to occur at all; but this is not alwavs the case. It

FIG. 332. — Curve of Shortening of the Gastrocnemius Muscle of the Frog, During Hea
Rigor. The numbers indicate degrees centigrade.

may, indeecf; be doubted whether there is really a complete absence of the
postmortem rigidity in any such cases; for the experiments of Brown-
Sequard make it probable that the rigidity may supervene immediately
after death, and then pass away with such rapidity as to be scarcely
observable.

The occurrence of rigor mortis is not prevented by the previous existence
of paralysis in a part, provided the paralysis has not been attended with very
imperfect nutrition of the muscular tissue.

The rigidity affects the involuntary as well as the voluntary muscles,
whether they be constructed of striped or unstriped fibers. The rigidity
of involuntary muscles with striped fibers is shown in the contraction of
the heart after death. The contraction of the muscles with unstriped fibers
is shown by an experiment of Valentin, who found that if a graduated tube
be connected with a portion of intestine taken from a recently killed animal,

494 MUSCLE-NERVE PHYSIOLOGY

and the intestine be tied at the opposite end, and filled with water, the water
will in a few hours rise to a considerable height in the tube, owing to the con-
traction of the intestinal walls. It is still better shown in the arteries, of
which all that have muscular coats contract after death, and thus present the
roundness and cord-like feel of the arteries of a limb lately removed or those
of a body recently dead. Subsequently they relax, as do all the other mus-
cles, and feel lax and flabby and lie as if flattened and with their walls
nearly in contact.

Muscular Metabolism During Contraction. — The question of the
metabolism of muscle both in a resting and in an active condition has for
many years occupied the attention of physiologists. It cannot be said even
now to be thoroughly understood. Most of the facts with reference to the
subject have been already mentioned. We may shortly recapitulate them
here: First, muscle during rest absorbs oxygen and gives out carbon
dioxide. This has been shown by an analysis of the gases of the blood going
to and leaving muscles. During activity, e.g., during tetanus, the same inter-
change of gases takes place, but the quantities of the oxygen absorbed and
of the carbon dioxide given up are increased, and the proportion between
them is altered thus:

Venous blood.

O2, less than in arterial
blood.

Co2, more than in arterial
blood

Of resting muscle 9 per cent.

Of active muscle .

12.26 per cent.

6.71 per cent.

10.79 per cent.

There is, then, a greater proportion of carbon dioxide produced in muscle
during activity than during rest.

During rigor mortis there is also an increased production of carbon
dioxide.

Second, muscle during rest produces nitrogenous crystallizable sub-
stances, such as creatin, from the metabolism which is constantly going on
in it during life; in addition there are formed, in all probability, sarcolactic
acid and other non-nitrogenous matters.

During activity the nitrogenous substances, such as creatin, undergo
very slight, if any, increase above the amount produced during rest — but
the sarcolactic acid is distinctly increased. The glycogen stored in the
muscle is gradually converted into dextrose and the latter oxidized to
furnish the energy developed in the contraction.

CONTRACTION IN INVOLUNTARY MUSCLE AND IN CILIA 495

During rigor mortis the sarcolactic acid is increased, and in addition
myosin is formed.

From these data it is assumed that the processes which take place in
resting and active muscles are somewhat different, at any rate in degree,
from actively contracting muscle. Also, there are obtained an increased
amount of heat and mechanical work; potential energy is converted into
kinetic energy.

THE TYPE OF CONTRACTION IN INVOLUNTARY
MUSCLE AND IN CILIA.

Cardiac Muscle. — Some detail concerning the action of cardiac muscle
has already been given in connection with the chapter on Circulation.
As compared with the activity of skeletal muscle, cardiac muscle differs most
strikingly in that it is automatic. A strip of heart muscle taken from any
part of the heart, under proper conditions, gives off a series of contrac-
tions, whether it receives any special stimulus or not, whereas we have just
found that skeletal muscle under similar conditions remains quiet unless
stimulated in some special way. The fibers of skeletal muscle are more or
less physiologically isolated from each other, and one fiber may contract with-
out involving contractions of the others. Cardiac muscle, on the other hand,
when stimulated at any point conducts the change produced throughout the
continuity of the mass. Cardiac muscle contractions are influenced by
tension, temperature, fatigue, etc., apparently, in the same way as skeletal
muscle.

When the contraction occurs it is always maximal. The actual am-
plitude of the contraction is dependent on the condition of nutrition of the
cardiac muscle. If the contractions are at a rapid rate they will be relatively
of less amplitude. If an extra contraction is induced in an automatic series,
so that the interval between two contractions is similar, then the amplitude
will be correspondingly reduced. Such an extra contraction is followed by
a delayed automatic contraction, the phenomenon of compensatory pause.
The contractions in cardiac muscle are simple contractions. In fact, it is said
to be impossible to produce a tetanus except in certain invertebrate hearts.
This possibility depends upon the fact that during the time of a single con-
traction there is a certain interval between the beginning and the crest of the
contraction, figure 174, in which the heart muscle is not irritable. This is
known as the refractory phase.

The duration of the contraction of heart muscle is much greater than
the contraction of skeletal muscle. The total time of a contraction in a frog's
gastrocnemius is o. i of a second, while the time of a contraction of the ven-
tricle in the same animal is at least o . 7 to o . 8 of a second. In the terrapin's
cardiac muscle the time of a contraction is over a second, but in the warm-

496

MUSCLE-NERVE PHYSIOLOGY

blooded cardiac muscle the time is shorter, perhaps from 0.4 to 0.5 of a
second for the human ventricular muscle.

Smooth Muscle. — The physiology of smooth muscle has been given
to some extent in previous chapters, particularly in connection with the move-
ments of the stomach and intestines. As compared with skeletal and cardiac
muscle it is a much more slowly acting contractile tissue. Isolated strips of
smooth muscle, as a rule, contract only when stimulated, though preparations

FIG. 333. — Contraction Area in Smooth Muscle. A, Showing the contraction nodes
of the fibers, the deep staining of the nodes, the condensation of surrounding connective
tissue; B, diagrammatic, showing the thickening of the longitudinal nbrillae. Intestine of
dog. (Caroline McGill.)

of certain tissues, like the stomach muscle of the frog, give off rhythmic
contractions occasionally. In this regard smooth muscle stands intermedi-
ate between skeletal and cardiac muscle; the former is normally never
automatic, the latter always.

Smooth muscle requires a different type of stimulus to produce contrac-
tion; the stimulus must be more prolonged and more intense. For example,
smooth muscle is not readily responsive to induction currents of short dura-
tion, but is readily stimulated by galvanic currents or induction currents of
longer duration. The stimulus must be applied through a longer interval
of time. Preparations of the stomach muscle can scarcely be made to

CHANGES DURING THE CONTRACTION OF SMOOTH MUSCLE 497

contract by a single induction current, no matter how intense. Such muscle
in the body is always associated with the local nervous apparatus which
plays an indeterminate part in its activity.

The ureters and gall-bladder are the parts most difficult to excite by
stimuli; they do not act at all till the stimulus has been long applied, and then
contract feebly and to a small extent. The contractions of the cecum and
stomach are quicker, and still quicker those of the iris and of the urinary
bladder. The contractions of the small and large intestines, of the vas
deferens, and of the pregnant uterus are yet more regular and more
sustained.

Changes During the Contraction of Smooth Muscle. — The dura-
tion as well as type of contraction in smooth muscle is very markedly differ-
ent from that of voluntary muscle. A contraction in smooth muscle is

FIG. 334. — Enlarged Detailed Drawing of the Nucleus of Smooth Muscle in the
Relaxed and in the Contracted State. Intestine of Necturus. Zeiss obj. 2, oc. 8.
(Caroline McGill.)

characterized by a very long latent period, a slowly developed contraction
phase, and an extremely delayed relaxation, figure 356, A. The amount and
duration of the contractions are dependent upon the strength and duration of
the stimulus, though the curve of contraction itself does not in other respects
differ sharply from the type of curve of the simple muscle contraction.

Owing to the apparently different structural type of smooth muscle, es-
pecial interest attaches to the changes which occur during its contraction.
Caroline McGill has recently re-examined the histological structure and in-
vestigated the function of this type of muscle, and we are able to present a
figure showing the changes. The longitudinal fibrillae, which are readily
stained with iron hematoxylin, show distinct shortening and thickening at the

498 MUSCLE-NERVE PHYSIOLOGY

nodes of contraction of the muscle, figure 333, B. The whole fiber is thick-
ened at the contraction nodes and stains very readily and usually uniformly.
However, by certain stains the fibrillae can be traced through the node. The
node is an apparent area of chemical differentiation. There is a marked con-
densation of the intermuscular fibrous tissue, which is doubtless purely a
passive phenomenon. The most striking change during contractions is
observed in the nucleus, figure 333, A, and figure 334. The nucleus during
rest is a long slender oval or spindle with a general chromatic network.
"During contraction, the smooth muscle nuclei shorten and thicken by an
active process. The chromatin collects, chiefly at the twro ends of the nu-
cleus, leaving a relatively clear area in the center."

Ciliary Motion. — Ciliary motion, which is closely allied to ameboid
and muscular motion, is alike independent of the will, of the direct influ-
ence of the nervous system, and of muscular contraction. It may continue
for several hours after death, or removal of the ciliated tissue, provided the
portion of tissue under examination be kept moist. Its independence of the
nervous system is shown also in its occurrence in the lowest invertebrate
animals which are apparently unprovided with anything analogous to a
nervous system, and in its persistence when the ciliated cells are completely
separated from each other by teasing out in serum or other physiological
solution. The vapor of chloroform arrests the motion; but it is renewed
on the discontinuance of the application of the anesthetic. The movement
ceases when the cilia are deprived of oxygen (although it may continue for
a time in the absence oifree oxygen), but is revived on the admission of this
gas. Carbon dioxide also stops the movement. The contact of various
substances, e.g., bile, strong acids, and alkalies, will stop the motion alto-
gether; but this depends chiefly on destruction of the delicate substance of
which the cilia are composed. Temperatures above 45° C. and below o° C.
stop the movement, whereas, moderate heat, and faintly alkaline solutions
are favorable to the action and revive the movement after temporary cessation.
The exact explanation of ciliary movement is not known. Whatever may
be the exact explanation, the movement must depend upon some changes
going on in the cells of which the cilia are a part and not on changes limited
to the cilia themselves, since, when the latter are cut off from the cell the
movement ceases, and when severed so that portions of the cilia are left
attached to the cell, the attached and not the severed portions continue the
movement. Ciliary contraction is to be regarded as a type of motor activity
carried out in a specialized form of motor apparatus. The changes going
on in the cell must be classed with similar changes in heart or skeletal
muscle. Ciliary tissue is like cardiac in at least two characteristics: the cells
are capable of conducting a stimulus from cell to cell, and ciliary activity
is automatic. As a special illustration of cilia-like action may be mentioned
the motion of spermatozoa, which are cells with a single cilium.

THE FUNCTION OF NERVE FIBER 499

THE FUNCTION OF NERVE FIBER.

The Nerve Impulse. — The motor nerve fibers of the muscle-nerve
preparation are of the medullated type described on page 66. But the es-
sential structure, possessed by all fibers, is the axis cylinder. The peculiar
function of the nerve fiber, i.e., of the axis cylinder, is its power to conduct
a physiological change along its extent, a phenomenon known as a nerve
impulse. A normal nerve impulse in a motor nerve has its origin in the
motor cell of the central nervous system of which the fiber is an outgrowth.
The manner in which such discharge from the cell takes place will be dis-
cussed later. But nerve impulses may be aroused by various artificial
means, they are influenced by certain conditions in the environment, and
possess certain other properties that may be discussed at this point.

Nerve Stimuli. — Nerve fibers like skeletal muscle require stimulation
before they can manifest any of their properties, since they have no powrer
of themselves of originating nerve impulses. The stimuli which are capable
of exciting nerves to action are, as in the case of muscle, very diverse. The
mechanical, chemical, thermal, and electrical stimuli which may be used
in the case of muscles are also, with certain differences in the methods em-
ployed, efficacious in stimulating the nerve. The chemical stimuli are chiefly
these: withdrawal of water as by drying; strong solutions of neutral salts of
potassium, sodium, etc.; free inorganic acids, except phosphoric; and some
organic acids. The electrical stimuli employed are the induction and con-
tinuous currents concerning which the observations in reference to muscular
irritability should be consulted. Galvanic currents stimulate nerves only at
the moment of turning on the current and of turning it off. Weaker electrical
stimuli will excite nerves than will excite muscles; the nerve impulse appears
to gain strength as it descends, and a weaker stimulus applied far from the
muscle will have the same effect as a slightly stronger one applied to the
nerve near the muscle.

Characteristics of the Nerve Impulse. — When a nerve impulse is
aroused in a motor nerve, as by stimulating a nerve in its course by an in-
duced current of medium strength, it is propagated along the axis cylinder
to the muscle where it arouses a contraction of the muscle fiber. In the con-
traction of the muscle we have indirect but conclusive evidence of the passage
of the nerve impulse, for it can be readily proven that the electrical current
does not escape to the muscle. In this instance it can be shown that there
is a nerve impulse passing from the point of stimulation in the direction away
from the muscle; i.e., the artificially aroused nerve impulse passes over the
entire extent of the fiber stimulated. In fact, a nerve impulse is known to
travel from its point of origin over the entire neurone affected. This anti-
dromal nerve impulse, of course, does not exist in the normal case, since the

500 MUSCLE-NERVE PHYSIOLOGY

normal nerve impulse arises in the nerve-cell body and passes out over fhe
fiber from its origin to its extremity.

The nerve impulse travels over the nerve fiber with a velocity that was
first determined by Helmholtz. He found that in the sciatic of the frog the
nerve impulse travels at the rate of twenty-seven meters per second. The
rate has been measured in a number of animals and varies between wide
limits. In human nerves the rate is variously given, but thirty meters per
second may be taken as a fair average.

The presence of the nerve impulse can be detected by the action current,
which exists in nerve as in muscle (see page 483 for methods of detecting
the action current).

Rheoscopic Frog. — The action current may be demonstrated by means of
the following experiment:

The muscle current produced by stimulating the nerve of one muscle-nerve
preparation may be used to stimulate the nerve of a second muscle-nerve
preparation. The hind leg of a frog with the nerve going to the gastrocnemius
cut long is placed upon a glass plate and arranged in such way that its nerve
touches in two places the gastrocnemius muscle, exposed but preserved in situ
in the opposite thigh of the frog. The electrodes from an induction coil are
placed behind the sciatic nerve of the second preparation, high up. On
stimulating it with a single induction shock, the muscles not only of the same
leg are found to undergo a twitch, but also those of the first preparation, al-
though this is not near the electrodes. The stimulation cannot be due to an
escape of the stimulating current into the first nerve, but is due to the action
current of the second muscle. This experiment is known under the name of
the rheoscopic frog.

When the nerve impulse is studied by means of the action current it is
found that a nerve impulse can be aroused by a weaker stimulus than is re-
quired to produce a minimal contraction of a muscle. The response of the
nerve to graduated strengths of the stimulus is increased very rapidly with
slight increase of strength of the stimulus, the augmentation extending
through a somewhat greater range than for muscle. If the stimulus is still
further increased there is only slight increase of the resulting nerve impulse.

Fatigue of Nerve Fiber. — Many efforts have been made to discover
evidences of fatigue of nerve fiber, with practically completely negative
results. A difficulty has been to secure means of measuring change in in-
tensity of the nerve impulse. The muscle quickly fatigues so that the
character of the muscle response cannot be taken when measured in the
ordinary way. An effective method used by Howell, Budgett, and Leonard
consists in cooling a segment of nerve to suspend its conductivity, during
stimulation of the free end, and periodically warming up the cooled segment
of nerve to test the strength of nerve impulse passing through it to the un-
fatigued muscle beyond. By this and other methods it has been found that

THE EFFECTS OF BATTERY CURRENTS ON NERVE FIBER 501

a motor nerve is not fatigued by at least ten hours' continuous stimulation
with induction currents.

One must hesitate to draw the conclusion, however, that the nerve fiber
conducts the nerve impulse without loss of energy. The fiber can be
anesthetized, it responds to temperature changes, and gives other evidences
of susceptibility to conditions which influence metabolism in other forms of
protoplasm. Perhaps the nerve fiber is capable of repairing its wastes as
rapidly as they occur.

The Effects of Battery Currents on Nerve Fiber.— Galvanic currents
influence nerves in ways that call for special discussion. A constant cur-
rent, say from a Daniell battery, can be introduced into the nerve of a muscle-
nerve preparation by means of a pair of non-polarizable electrodes, figure
323, and a convenient key arranged for turning the current on or off the
nerve. It will be found that with a current of moderate strength there will
be a contraction of the muscle, both at the closing and the opening of the key
(called, respectively, making and breaking contractions), but that during the
interval between these two events the muscle remains flaccid, provided the
battery current continues of constant intensity. If the current be a very
weak or a very strong one, the effect is not quite the same; one or the other
of the contractions may be absent. Which of these contractions is absent
depends upon another circumstance, viz., the direction of the current. The
direction of the current may be ascending or descending: if ascending, the
anode or positive pole is nearer the muscle than the cathode or negative pole,
and the current to return to the battery has to pass up the nerve; if descend-
ing, the position of the electrodes is reversed. It will be necessary before
considering this question further to return to the apparent want of effect of
the constant current during the interval between the make and the break
contraction. To all appearances no change is produced, but in reality a very
important alteration of the irritability and conductivity is brought about in
the nerve by the passage of this constant or polarizing current.

A second way of showing the effect of the polarizing current is by stimu-
lating the nerve by a pair of electrodes from an induction coil, while the polar-
izing current from the battery is flowing through the nerve. If the strength
of stimulus required in order that a minimum contraction be obtained by the
induction shock before the polarizing current is applied and the secondary
coil be removed slightly further from the primary, the induction current
cannot now produce a contraction. If, now, the polarizing current be sent in
a descending direction, that is to say, with the cathode nearest the muscle, and
the induction current which was before insufficient be applied between the
cathode and the muscle, it will now prove sufficient to cause a contraction.
This indicates that with a descending current the irritability of the nerve is
increased at the cathode. If, instead of applying the induction electrodes
below the polarizing electrodes, they are applied above them, the irritability of

502

MUSCLE-NERVE PHYSIOLOGY

the nerve is found to be decreased. If the polarizing current is reversed, i.e.,
made ascending, then the condition of irritability of the nerve is reversed.
Both methods show that the polarization consists in an increase in irritability
at the cathode, called catelectrotonus, and a decrease at the anode called
anelectrotonus. The total change is called by the term electrotonus. As there
is between the electrodes both an increase and a decrease of irritability on the
passage of a polarizing current, it is evident that there must be a neutral point
where there is neither increase nor decrease of irritability. The position of
this neutral point is found to vary with the intensity of the polarizing current;
when the current is weak the point is nearer the anode, when strong nearer the

FIG. 335. — Diagram Illustrating the Effects of Various Intensities of the Polarizing
Currents, n, n', Nerve; a, anode; k, cathode; the curves above indicate increase, and
those below decrease of irritability, and when the current is small the increase and decrease
are both small, with the neutral point near a, and so on as the current is increased in
strength.

cathode, figure 335. When a constant current passes into a nerve, therefore,
if a contraction result, it may be assumed that it is due to the increased irri-
tability produced in the neighborhood of the cathode, but the breaking con-
traction must be produced by a rise in irritability from a lowered state to the
normal in the neighborhood of the anode.

The contractions produced in the muscle of a muscle-nerve preparation
by a constant current have been arranged in a table which is known as
Pfluger's Law of Contractions. It is really only a statement as to when a
contraction may be expected:

Descending current Ascending current

Strength of current used

Make

Break

Make

Break

Very weak
Weak

Yes
Yes

No

No

No
Yes

No

No

Moderate
Strong

Yes

Yes •

Yes

No

Yes

No

Yes
Yes

EFFECT OF BATTERY CURRENTS ON DEEP-SEATED NERVES 503

During the passage of a constant current through a nerve and immediately
after its cessation, there is a change in the conductivity as well as of the irri-
tability of the nerve at the anode and cathode, respectively. During the pas-
sage of the current, the conductivity is increased at the cathode and decreased
at the anode. After the passage of the current, the effect is reversed. With
strong currents the area of decreased conductivity may be sufficient to act as a
block, preventing the passage of impulses over it.

The foregoing statements concerning the changes produced in a nerve
by the passage of a constant current may be briefly summarized as follows:

I. A nerve is more irritable to the closing of a constant current than it is to
the opening of a constant current.

II. During the passage of the current through the nerve, both its irritability
.and conductivity are increased at the cathode and decreased at the anode.

III. After the passage of the current, the irritability and conductivity are
tooth decreased at the cathode and increased at the anode.

The Effect of Battery Currents on Deep-seated Nerves. — The follow-
ing account is condensed from Lombard in "An American Text-book of
Physiology."

As an electric current cannot be applied to living human nerves directly,
it is applied to the skin along the course of the nerve. The current passes

Skin

FIG. 335 A.— Diagram of Skin and Subjacent Xerve. A, the positive electrode or
physical anode; B, the negative electrode or physical cathode. Signs, + physiological
anodes; signs — physiological cathodes. (After Waller.)

from the anode or positive pole through the skin, and spreads out in the
tissues much as the bristles of a brush; it then gradually concentrates and
leaves the skin at the cathode or negative pole.

In addition to the physical anode and cathode of the battery, there are
what are called physiological anodes and cathodes. There is a physiological
anode at every point where the current enters a nerve, and a physiological
cathode at every point where it leaves it.

Generally when the current is applied to nerves through the skin, only
part of it flows longitudinally along the nerves; most of it passes diagonally
.across them to the tissues below. Thus it happens that in that part of the
nerve beneath either the physical anode or cathode, groups of physiological
anodes and cathodes are found.

The contraction which occurs when the current is closed (closing con-
, traction) represents irritation at the physiological cathode, while the opening

5°4

MUSCLE-NERVE PHYSIOLOGY

contraction represents irritation at the physiological anode. Since there are
physiological anodes and cathodes beneath each electrode, one or more of
four conditions may arise:

1. Anodic closing contraction; i.e., the effect of the change developed at
the physiological cathode, beneath the physical anode (positive pole).

2. Anodic opening contraction, i.e., the effect of the change developed at
the physiological anode, beneath the physical anode (positive pole).

3. Cathodic closing contraction, i.e., the effect of the change developed
at the physiological cathode, beneath the physical cathode (negative pole).

4. Cathodic opening contraction, i.e., the effect of the change developed
at the physiological anode, beneath the physical cathode (negative pole).

The following abbreviations of these contractions are used: ACC, AOC,
KCC, KOC.

The closing contractions, KCC and ACC, are stronger than the opening
contractions, KOC and AOC. Of the closing contractions, KCC is stronger
than ACC. Of the opening contractions, AOC is stronger than KOC.
These facts are also shown in a table of the effects of gradually increasing the
strength of the current.

Weak currents. Medium currents. Strong currents.

KCC KCC KCC

— ACC ACC

- AOC AOC

KOC

Sometimes AOC is stronger than ACC.

r. nervi med. m. pron.
tereti.

m. palmaris longus

m. ulnaris int.

n. ulnaris

r. vol. prof. n. ulnar.

m. palmar brevis

m. abduc. dig. min. I

m. flex. dig. min. |

m. oppon. dig. min.

mm. lumbr. II.,III.,IV.

m. radial, intern,
m. fiex. dig. prof.

m. flex. dig. sublim.

m. flex. poll. long,
m. medianus

m. abduc. poll. brev.
m. oppon. poll,
m. flex. poll. brev.
m. adduc. poll,
m. luinbric. I.

FIG. 336. — Figure Showing Motor Points in the Forearm.

LOCOMOTION 505

In diseases which cause degeneration of the nerves going to a muscle,
stimulation causes results different from the above, and we get what is known
as the reaction of degeneration.

The intensity of the anodic or cathodic effects is increased by using small
electrodes, and decreased by electrodes of large surface. In fact in practice
it is usual to apply the indifferent electrode to an extended surface, thus re-
ducing its effect below the stimulating intensity. This gives only one active
stimulating electrode and is known as the method of unipolar stimulation.

SOME SPECIAL COORDINATED MOTOR ACTIVITIES.

I. LOCOMOTION.

The greater number of the more important muscular actions of the human
body, those, namely, which are arranged harmoniously so as to subserve
some definite purpose in the animal economy, are described in various parts
of this work in the sections which treat of the physiology of the processes by
which these muscular actions are resisted or carried out. There are, how-
ever, some very important and somewhat complicated muscular acts which
may be best described in this place.

Walking. — The coordinated movements of the body are carried out
by the skeletal muscles acting on the skeletal elements as a system of levers.
Even the bones of the skull are levers in so far as their relations to muscles
are concerned.

Examples of the Three Orders of Levers in the Human Body. — All levers
have been divided into three kinds, according to the relative position of the
power, the weight to be moved, and the axis of motion or fulcrum. In a lever of

If

\
_Q

FIG. 337-

the first kind the power is at one extremity of the lever, the weight at the
other, and the fulcrum between the two. If the initial letters only of the
power, weight, and fulcrum be used, the arrangement will stand thus: P. F. W.
A poker as ordinarily used, or the bar in figure 337, may be cited as an example
of this variety of lever; while, as an instance in which the bones of the human

MUSCLE-NERVE PHYSIOLOGY

skeleton are used as a lever of the same kind, may be mentioned the act of
raising the body from the stooping posture by means of the hamstring muscles
attached to the tuberosity of the ischium or of the triceps which extends the
forearm by action at the elbow, figure 337.

In a lever of the second kind, the arrangement is thus: P. W. F. ; and this
leverage is employed in the act of raising, the handles of a wheelbarrow, or in
stretching an elastic band, as in figure 338. In the human body the act of
opening the mouth by depressing the lower jaw is an example of the same kind

ELASTK

— the tension of the muscles which close the jaw representing the weight,
figure 338.

In a lever of the third kind the arrangement is F. P. W., and the act of
raising a pole, as in figure 339, is an example. In the human body there are
numerous examples of the employment of this kind of leverage. The act of
bending the forearm may be mentioned as an instance, figure 339. The act
of biting is another example.

At the ankle we have examples of all three kinds of lever, ist kind — Ex-
tending the foot. 3d kind — Flexing the foot. In both these cases the foot

FIG. 339.

represents the weight, the ankle joint the fulcrum, the power being the gas-
trocnemius muscles in the first case and the tibialis anticus in the second
case. 2nd kind — When the body is raised on tiptoe. Here the tip of the
toe is the fulcrum, the weight of the body acting at the ankle joint the
weight, and the gastrocnemius muscles the power.

In the human body, levers are most frequently used at a disadvantage as
regards power, the latter being sacrificed for the sake of a greater range of
motion. Thus in the diagrams of the first and third kinds it is evident that the
power is so close to the fulcrum that great force must be exercised in order to
produce motion. It is also evident, however, from the same diagrams, that

LOCOMOTION

507

by the closeness of the power to the fulcrum a great range of movement can
be obtained by means of a comparatively slight shortening of the muscular
fibers.

In the act of walking, almost every voluntary muscle in the body is brought
into play, either directly for purposes of progression, or indirectly for the
proper balancing of the head and trunk. The muscles of the arms are
least concerned; but even these are for the most part instinctively in action
to some extent.

Among the chief muscles engaged directly in the act of walking are those
of the calf, which, by pulling up the heel, pull up also the astragalus, and with
it, of course, the whole body, the weight of which is transmitted through the
tibia to this bone, figure 340. When starting to walk, say with the left leg,
this raising of the body is not entirely dependent on the muscles of the left

FIG. 340.

calf, but the trunk is thrown forward in such a way that it would fall prostrate
were it not that the right foot is brought forward and planted on the ground to
support it. Thus the muscles of the left calf are assisted in their action by
those muscles on the front of the trunk and legs which, by their contraction,
pull the body forward; and, of course, if the trunk form a slanting line, with
the inclination forward, it is plain that when the heel is raised by the calf
muscles, the whole body will be raised, and pushed obliquely forward and
upward. The successive acts in taking the first step in walking are repre-
sented in figure 340, i, 2, 3, etc.

Now it is evident that by the time the body has assumed the position No.
3, it is time that the right leg should be brought forward to support it and
prevent it from falling prostrate. This advance of the right leg is effected
partly by its mechanically swinging forward, pendulum-wise, and partly by
muscular action; the muscules used being — i, those on the front of the
thigh, which bend the thigh forward on the pelvis, especially the rectus
femoris, with the psoas and the iliacus; 2, the hamstring muscles, which
slightly bend the leg on the thigh; and, 3, the muscles on the front of the leg,
which raise the front of the foot and toes, and so prevent the latter in
swinging forward from striking the ground.

The second part of the act of walking, which has been just described, is
shown in the diagram, 4, figure 340.

508 MUSCLE-NERVE PHYSIOLOGY

When the right foot has reached the ground the action of the left leg has
not ceased. The calf muscles of the latter continue to act, and, by pulling up
the heel, throw the body still more forward over the right leg, now bearing
nearly the whole weight, until the time when the left leg should again swing
forward, and the left foot be planted on the ground to prevent the body
from falling prostrate. As at first, while the calf muscles of one leg and foot
are preparing, so to speak, to push the body forward and upward from
behind by raising the heel, the muscles on the front of the trunk and the
same leg (and of the other leg, except when it is swinging forward) are
helping the act by pulling the legs and trunk, so as to make them incline
forward, the rotation in the inclining occurring mainly at the ankle joint.
Two main kinds of leverage are, therefore, employed in the act of walking,
and if this idea be firmly grasped, the details will be understood with com-
parative ease. One kind of leverage employed in walking is essentially
the same writh that employed in pulling forward the pole, as in figure 339.
And the other, less exactly, is that employed in raising the handles of a
wheelbarrow. Now, supposing the lower end of the pole to be placed in
the barrow, we should have a very rough and inelegant, but not altogether
bad representation of the two main levers employed in the act of walk-
ing. The body is pulled forward by the muscles in front, much in the
same way that the pole might be by the force applied at p, while the raising
of the heel and pushing forward of the trunk by the calf muscles are roughly
represented on raising the handles of the barrow. The manner in which
these actions are performed alternately by each leg, so that one after the other
is swung forward to support the trunk, which is at the same time pushed
and pulled forward by the muscles of the other, may be gathered from the
previous description.

There is one more thing to be especially noticed in the act of walking.
Inasmuch as the body is being constantly supported and balanced on each
leg alternately, and therefore on only one at the same moment, it is evident
that there must be some provision made for throwing the center of gravity
over the line of support formed by the bones of each leg, as, in its turn, it
supports the \veight of the body. This may be done in various ways, and
the manner in which it is effected is one element in the differences which
exist in the walking of different people. Thus it may be done by an in-
stinctive slight rotation of the pelvis on the head of each femur in turn, in
such a manner that the center of gravity of the body shall fall over the foot
of this side. Thus when the body is pushed onward and upward by the
raising, say, of the right heel, as in figure 340, 3, the pelvis is instinctively
by various muscles made to rotate on the head of the left femur at the
acetabulum, to the left side, so that the weight may fall over the line of
support formed by the left leg at the time that the right leg is swinging
forward, and leaving all the work of support to fall on its fellow. Such a

LOCOMOTION 509

"rocking" movement of the trunk and pelvis, however, is accompanied
by a movement of the whole trunk and leg over the foot which is being
planted on the ground, figure 341, the action being accompanied with a
compensatory outward movement at the hip, more easily appreciated by
looking at the figure (in which this movement is shown exaggerated) than
from the description.

Thus the body in walking is continually rising and swaying alternately
from one side to the other, as its center of gravity has to be brought alternately
over one or the other leg; and the curvatures of the spine are altered in cor-

FIG. 341.

respondence with the varying position of the weight which it has to support.
The extent to which the body is raised or swayed differs much in different
people.

In walking, one foot or the other is always on the ground. The act of
leaping or jumping consists in so sudden a raising of the heels by the sharp
and strong contraction of the gastrocnemius muscles that the body is
jerked off the ground. At the same time the effect is much increased by
first bending the thighs on the pelvis, and the legs on the thighs, and then
suddenly straightening out the angles thus formed. The share which this
action has in producing the effect may be easily known by attempting to
leap in the upright posture, with the legs quite straight.

Running. — Running is performed by a series of rapid low jumps pro-
duced by each leg alternately; so that, during each complete muscular act
concerned, there is a moment when both feet are off the ground.

In all these cases, however, the description of the manner in which any
given effect is produced, can give but a very imperfect idea of the infinite

510 MUSCLE-NERVE PHYSIOLOGY

number of combined and harmoniously arranged muscular contractions
which are necessary for even the simplest acts of locomotion.

II. THE PRODUCTION OF THE VOICE.

Before commencing the consideration of the nervous system and the
special senses it will be convenient to consider first speech, the production of
the human voice, and the physiology of the larynx as a muscular apparatus.

The Larynx. — In nearly all air-breathing vertebrate animals there
are arrangements for the production of sound, or voice, in some parts of the
respiratory apparatus. In many animals, the sound admits of being variously
modified and altered during and after its production; and, in man, one such
modification occurring in obedience to dictates of the cerebrum, is speech.

It has been proven by observations on living subjects, by means of the
laryngoscope, as well as by experiments on the larynx taken from the dead
body, that the sound of the human voice is the result of the vibration of the
inferior laryngeal ligaments, or the true vocal cords which bound the glottis,
caused by currents of expired air impelled over their edges. If a free opening
exist in the trachea, the sound of the voice ceases, but it returns if the opening
is closed. An opening into the air-passages above the glottis, on the con-
trary, does not prevent the voice being produced. By forcing a current of
air through the larynx in the dead subject, clear vocal sounds are elicited,
though the epiglottis, the upper ligaments of the larynx or false vocal cords,
the ventricles between the upper ligaments and the inferior ligaments, and
the upper part of the arytenoid cartilages, be all removed. But the true
vocal cords must remain entire with their points of attachment, and be kept
tense and so approximated that the fissure of the glottis may be narrow.

The vocal ligaments or cords, therefore, are regarded as the proper organs
for the production of vocal sounds. The modifications of these sounds are
effected, as will be presently explained, by other parts, viz., by the tongue,
teeth, lips, etc. The structure of the vocal cords is adapted to enable them to
vibrate like tense membranes, for they are essentially composed of elastic
tissue; and they are so attached to the cartilaginous parts of the larynx that
their position and tension can be variously altered by the contraction of the
muscles which act on these parts.

Thus it will be seen that the larynx is the organ of voice. It may be said
to consist essentially of the two vocal cords and the various cartilaginous,
muscular, and other apparatus by means of which not only can the aperture
of the larynx (rima glottidis) be closed against the entrance and exit of air
to or from the lungs, but also by means of which the cords themselves can be
stretched or relaxed, brought together and separated in accordance with the
conditions that may be necessary for the air in passing over them to set them
vibrating to produce the various sounds. Their action in respiration has
been already referred to.

ANATOMY OF THE LARYNX

Anatomy of the Larynx. — The principal parts entering into the formation of
the larynx, figures 342 and 343, are — the thyroid cartilage ; the cricoid cartilage;
the two arytenoid cartilages; and the two true vocal cords. The epiglottis,
figure 343, has but little to do with the voice, and is chiefly useful in pro-
tecting the upper part of the larynx from the entrance of food and drink in

FIG. 342. — Cartilages of the Larynx Seen from the Front, i to 4, Thyroid cartilage; i,
vertical ridge or pomum Adami; 2, right ala; 3, superior, and 4, inferior cornu of the right
side; 5, 6, cricoid cartilage; 5, inside of the posterior part; 6, anterior narrow part of the
ring; 7, arytenoid cartilages. X f .

deglutition. The false vocal cords and the ventricle of the larynx, which is a
space between the false and the true cord of either side, need be only referred to.
Cartilages. — a, The thyroid cartilage, figure 342, i to 4, does not form a
complete ring around the larynx, but only covers the front portion, b, The
cricoid cartilage, figure 342, 5, 6, on the other hand, is a complete ring; the

Lig. Ary. epiglott.

Cart. Wrisbergii
Cart. Santorini

Cart, aryten
Troc. muscul

Lig. crico-aryten

Dig. cerato-crico. post, sup

Cornu. infer

Lig. carat-crico. post, inf,

Cart, tracheae.

Pars, membran.

FIG. 343. — The Larynx as Seen From Behind after Removal of the Muscles. The cartilages
and ligaments only remain. (Stoerk.)

back part of the ring being much broader than the front. On the top of this
broad portion of the cricoid are, c, the arytenoid cartilages, figure 342, 7, the
connection between the cricoid below and arytenoid cartilages above being a
joint with synovial membrane and ligaments, the latter permitting tolerably
free motion between them.

Joints and Ligaments. — The thyroid cartilage is also connected with the

512 MUSCLE-NERVE PHYSIOLOGY

cricoid, not only by ligaments, but also by joints with synovial membranes;
the lower cornua of the thyroid clasping the cricoid between them, yet not
so tightly but that the thyroid can revolve, within a certain range, around an
axis passing transversely through the two joints. The vocal cords are attached
behind to the front portion of the base of the arytenoid cartilages, and in
front to the re-entering angle at the back part of the thyroid; it is evident,
therefore, that all movements of either of these cartilages must produce an
effect on them of some kind or other. Inasmuch, too, as the arytenoid carti-
lages rest on the top of the back portion of the cricoid cartilage, and are
connected with it by capsular and other ligaments, all movements of the
cricoid cartilage must move the arytenoid cartilages, and also produce an
effect on the vocal cords.

a b

FIG. 344. — The Cartilages and Ligaments of the Larynx, Viewed from the Front, a,
Epiglottis; ft, hyoid bone; c, cartilage tritica; d, thyro-hyoid membrane; e, superior cornu of
thyroid cartilage; /, thyroid notch; g, pomum Adami; h, crico-thyroid membrane; i, inferior
cornu of thyroid cartilage;/, cricoid cartilage. (Cunningham.)

Intrinsic Muscles. — The intrinsic muscles of the larynx are so connected
with the laryngeal cartilages that by their contraction alterations in the condi-
tion of the vocal cords and glottis are produced. They are usually divided
into four classes according to their action, viz., into abductors, adductors,
sphincters and tensors. The abductors, the crico-arytenoidei, widen the
glottis by separating the cords; the adductors, consisting of the thyro-ary-
epiglottici, the arytenoideus posticus seu transversus, the thyro-arytenoidei
externi, the crico-arytenoidei laterals, and the thyro-arytenoidei interni, approxi-
mate the vocal cords, diminish the rima glottidis, and act generally as sphinc-
ters and supporters of the glottis. Finally, the tensors of the cords put the
cords on the stretch, with or without elongating them; the tensors are the
crico-thyroidei and the thyro-arytenoidei interni.

The attachments and the action of the muscles will be readily understood
from the following table. All the muscles are in pairs except the arytenoideus
posticus.

ANATOMY OF THE LARYNX

513

TABLE OF THE SEVERAL GROUPS OF THE INTRINSIC MUSCLES OF THE LARYNX AND

THEIR ATTACHMENTS.

Group Muscle

I.

Abductors.

II. and III.
Adductors

and
Sphincters.

Attachments

Action

Crico-aryt- This pair of muscles arises, on either side,
enoidei from the posterior surface of the cor-
postici. responding half of the cricoid cartilage.
From this depression their fibers con-
verge on either side upward and out-
ward to be inserted into the outer angle
of the base of the arytenoid cartilages
behind the cricoarvtenoidei laterales.

Draw inward and
backward the outer
angle of arytenoid
cartilages, and so
rotate outward the
processus vocalis and
widen the glottis.

In three
layers:

a. Outer
layer,
Thyro-
aryepi-
glottici.

A pair of muscles. Flat and narrow, Help to narrow or
which arise on either side from the pro- close the rima
cessus muscularis of the arytenoid car- glottidis.
tilage, then passing upward and inward
cross one another in the middle line to
be inserted into the upper half of the
lateral border of the opposite arytenoid
cartilage and the posterior border of the
cartilage of Santorini. The lower fibers
run forward and dowmvard to be in-
serted into the thyroid cartilage near
the commissure. The fibers attached
to the cartilage of Santorini are con-
tinued forward and upward into the
aryepiglottic fold.

b. Middle
layer.

i. Aryte-
noideus
posticus.

A single muscle. Half-quadrilateral,
attached to the borders of the arytenoid
cartilages, its fibers running horizontally
between the two.

ii. Thyro- A pair of muscles. Each of which con-
arytenoi- sists of three chief portions. The
d e i ex- lower and principal fibers arise from the
terni. lower half of the internal surface of the

thyroid cartilage, close to the angle, and
from the fibrous expansion of the crico-
thyroid ligament, and are inserted into
the lateral border of the arytenoid car-
tilage. The inner fibers to the lower
half of this border, and the outer fibers
into the upper half, some pass to the
cartilage of Wrisberg and the ary-
epiglottic fold.

Draws together the
arytenoid cartilages
and also depresses
them. When the
muscle is paralyzed,
the inter-cartilagin-
ous part of the cords
cannot come t o -
gether.

33

MUSCLE-NERVE PHYSIOLOGY

TABLE OF THE SEVERAL GROUPS OF THE INTRINSIC MUSCLES OF THE LARYNX AND
THEIR ATTACHMENTS. — Continued.

Group Muscle

IV.

Tensors.

Attachments

iii. Crico- A pair of muscles. They arise on either
arytenoi- side from the middle third of the upper
dei later- border of the cricoid cartilage and are
ales. inserted into the whole anterior margin

of the base of the arytenoid cartilage.

Some of their fibers join the thyroid-

aryepiglottici.

Action

Approximate the vocal
cords by drawing the
processus muscularis
of the arytenoid car-
tilages forward and
downward and so
rotate the processus
vocalis inward.

c. Inner- A pair of muscles. They arise on either Render the vocal cords

most layer, side, internally from the angle of the!
Thyro- thyroid cartilage, internal to the last

tense and rotate the
arytenoid cartilages

arytenoi- described muscle, b. iii., and, running and approximate the

dei in -I parallel to and in the substance of the
terni. vocal cords, are attached posteriorly to

the processus vocalis and to the outer
surface of the arytenoid cartilages.

Crico-thy-i A pair of fan-shaped muscles attached on

processus vocalis.

roidei.

Thyro-ary-
tenoidei
interni.

either side to the cricoid cartilage below;
from the mesial line in front for nearly
one-half of its lateral circumferencej
backward the fibers pass upward and
outward to be attached to the lower
border of the thyroid cartilage and to
the front border of its lower cornea.

The most posterior part is almost a dis-
tinct muscle and its fibers are all but
horizontal: sometimes this muscle is
described as consisting of two layers,
superficial with cortical fibers, deep
with oblique fibers, described under
Group III.

The thyroid cartilage
being fixed by its
extrinsic muscles, the
front of the cricoid
cartilage is drawn
upward, and its back,
with the arvtenoids
attached, is drawn
down. Hence the
vocal cords are elon-
gated antero-poste-
riorly and put upon
the stretch. Paral-
ysis of these muscles
causes an inability
to produce high
notes.

Nerve Supply. — The sensory filaments of the superior laryngeal branch of
the vagus supply the epithelial lining of the larynx, giving it that acute sensi-
bility by which the glottis is guarded against the ingress of foreign bodies,
or of irrespirable gases. The contact of these stimulates the nerve endings;
and the sensory nerve impulse conveyed to the medulla oblongata, whether
accompanied by sensation or not, arouses motor impulses through the fila-
ments of the recurrent or inferior laryngeal branch, which excite contraction of

ANATOMY OF THE LARYNX 515

the muscles that close the glottis. Both these branches of the vagi cooperate
also in the production and regulation of the voice. The inferior laryngeal
determines the degree of contraction of the muscles that vary the tension of
the vocal cords, and the superior laryngeal conveys to the brain the sensation
which indicates the state of contraction of these muscles. Both the branches
cooperate also in the actions of the larynx in the ordinary slight dilatation and
contraction of the glottis in the acts of expiration and inspiration, more
evidently in the acts of coughing and other forcible respiratory movements.

The Laryngoscope. — This is an instrument employed in investigating the
condition of the pharynx, larynx, and trachea. It consists of a large concave
mirror with perforated center and of a smaller mirror fixed in a long handle.
In use the patient is placed in a chair, a good light (argand burner, or lamp)
is arranged on one side of, and a little above his head. The operator fixes the

Lig. ary-epiglott.

Cart. Wrisbergii.
Cart. Santorini.

mm. Aryten. obliqu.

m. Crico-arytenoid. post.
Cornu inferior.
Lig. cerato-cric.

Pars. post, inf.membrani.
Pars, cartilag.

FIG. 345.— The Larynx as Seen from Behind. To show the intrinsic muscles posteriorly.

(Stoerk.)

concave mirror round his head in such a manner that he looks through the
central aperture with one eye. He then seats himself opposite the patient,
and so adjusts the position of the mirror, which is for this purpose provided
with a ball and socket joint, that a beam of light is reflected on the lips of the
patient.

The patient is now directed to throw his head slightly backward, and to
open his mouth ; the reflection from the mirror lights up the cavity of the mouth,
and by a little alteration of the distance between the operator and the patient
the point at which the greatest amount of light is reflected by the mirror — in
other words its focal length — is readily discovered. The small mirror fixed
in the handle is then warmed, either by holding it over the lamp, or by putting
it into a vessel of warm water; this is necessary to prevent the condensation of
breath upon its surface. The degree of heat is regulated by applying the back
of the mirror to the hand or cheek, when it should feel warm without being
painful.

After these preliminaries the patient is directed to put out his tongue,
which is held by the left hand of the operator gently but firmly against the

MUSCLE-NERVE PHYSIOLOGY

lower teeth by means of a handkerchief. The warm mirror is passed to the
back of the mouth, until it rests upon and slightly raises the base of the uvula,
and at the same time the light is directed upon it: an inverted image of the

FIG. 346. — The Parts of the Laryngoscope.

larynx and trachea will be seen in the mirror. If the dorsum of the tongue
be alone seen, the handle of the mirror must be slightly lowered until the
larynx conies into view ; care should be taken, however, not to move the mirror

FIG. 347. — To Show the Position of the Operator and Patient when Using the

Laryngoscope.

upon the uvula, as it excites retching. The observation should not be pro-
longed, but should rather be repeated at short intervals.

The structures seen will vary somewhat according to the condition of the
parts as to inspiration, expiration, phonation, etc. They are the following:

MOVEMENTS OF THE VOCAL CORDS 517

first, and apparently at the posterior part, the base of the tongue, immediately
below which is the accurate outline of the epiglottis, with its cushion or tubercle,
figure 348. Then are seen in the central line the true vocal cords, white and
shining in their normal condition. In the inverted image the cords are closer
together posteriorly. Between them is left an open slit, narrow while a high
note is being sounded, wide during a deep inspiration. On each side of the
true vocal cords, and on a higher level, are the false vocal cords. Still more
externally than the false vocal cords is the aryteno-epiglottidean fold, in which
are situated upon each side three small elevations; of these the most external
is the cartilage of Wrisberg, the intermediate is the cartilage of Santorini, while
in front and somewhat below the preceding is the summit of the arytenoid
cartilage seen only during deep inspiration. The rings of the trachea, and even
the bifurcation of the trachea itself, if the patient be directed to draw a deep
breath, may be occasionally seen.

Movements of the Vocal Cords. — The position of the vocal cords in ordi-
nary tranquil breathing is so adapted by the muscles that the opening of the
glottis is wide and triangular, figure 348, B, becoming a little wider at each
inspiration, and a little narrower at each expiration. On making a rapid
and deep inspiration the opening of the glottis is widely dilated, figure 348, C,
and somewhat lozenge-shaped.

In Vocalization. — At the moment of the emission of a note the opening is
narrowed, the margins of the arytenoid cartilages being brought into contact
and the edges of the vocal cords approximated and made parallel at the same
time that their tension is much increased. The higher the note produced, the
tenser do the cords. become, figure 348, A; and the range of a voice depends,
of course, in the main, on the extent to which the degree of tension of the
vocal cords can be thus altered. In the production of a high note the vocal
cords are brought well within sight, so as to be plainly visible with the help
of the laryngoscope. In the utterance of low tones, on the other hand, the
epiglottis is depressed and brought over the vocal cords, figure 349. The
epiglottis, by being somewhat pressed down so as to cover the superior cavity
of the larynx, serves to render the notes deeper in tone and at the same time
somewhat duller, just as covering the end of a short tube placed in front of
caoutchouc tongues lowers the tone. In no other respect does the epiglottis
appear to have any effect in modifying the vocal sounds.

The degree of approximation of the vocal cords also usually corresponds
with the height of the note produced; but probably not always, for the width
of the aperture has no essential influence on the pitch of the note, as long as
the vocal cords have the same tension; only with a wide aperture the tone is
more difficult to produce and is less perfect, the rushing of the air through the
aperture being heard at the same time.

No true vocal sound is produced at the posterior part of the aperture
of the glottis, the part of the aperture which is formed by the space between
the arytenoid cartilages. For if the arytenoid cartilages be approximated in
such a manner that their anterior processes touch each other, but yet leave an

MUSCLE-NERVE PHYSIOLOGY

opening behind them as well as in front, no second vocal tone is produced by
the passage of the air through the posterior opening, but merely a rustling
sound. The pitch of the note produced is the same whether the posterior
part of the glottis be open or not.

FIG. 348. — Three Laryngoscopic Views of the Superior Aperture of the Larynx and
Surrounding Parts. A, The glottis during the emission of a high note in singing; B, in
easy and quiet inhalation of air; C, in the state of the widest possible dilatation, as in
inhaling a very deep breath. The diagrams A', B', and C', show in horizontal sections of
the glottis the position of the vocal ligaments and arytenoid cartilages in the three several
states represented in the other figures. In all the figures, so far as marked, the letters
indicate the parts as follows, viz.: /, 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; in the margin of the aryteno-epiglottidean fold w, the swelling
of the membrane caused by the cartilages of Wrisberg; s, that of the cartilages of Santorini;
a, the tip or summit of the arytenoid cartilages; cv, the true vocal cords or lips of the rima
glottidis; cvs, the superior or false vocal cords; between them the ventricle of the larynx;
in C, tr is placed on the anterior wall of the receding trachea, and b indicates the com-
mencement of the two bronchi beyond the bifurcation which may be brought into view
in this state of extreme dilatation. (Quain, after Czermak.)

The Voice in Singing. — The laryngeal tones may be produced in three
different kinds of sequence. The first is the monotonous, in which the notes
have nearly all the same pitch as in ordinary speaking; the variety of the
sounds of speech being due to articulation in the mouth. In speaking, occa-
sional syllables receive a higher intonation for the sake of accent. The
second mode of sequence is the successive transition from high to low notes,

THE VOCAL RANGE OF THE VOICE 519

and vice versa, without intervals; such as is heard in the crying in children
and in the howling and whining of dogs. The third mode of sequence of the
vocal sounds is the musical, in which each sound has a determinate number
of vibrations, and the numbers of the vibrations in the successive sounds have
the same relative proportions that characterize the notes of the musical scale.
The different sounds made by the musical voice are characterized by the
three properties of tones in general, viz., the pitch, which is dependent on the
rate of vibration of the vocal cords; the loudness, which depends on the force of

FIG. 349. — View of the Upper Part of the Larynx as Seen by Means of the Laryngo-
scope during the utterance of a grave note, c, Epiglottis; s, tubercles of the cartilages of
Santorini; a, arytenoid cartilages; z, base of the tongue; ph, the posterior wall of the pharynx.
(Czermak.)

the vibration, and the quality or timber, which is dependent on the resonance
of the cavities of the respiratory apparatus, particularly of the mouth, phar-
ynx, and nasal cavities.

The Vocal Range of the Voice. — In different individuals this com-
prehends one, two, or three octaves. In singers, that is, in persons trained in
singing, it extends to three or more octaves. But the male and female voices
commence and end at different points of the musical scale. The lowest note
of the female voice is about an octave higher than the lowest of the male voice;
the highest note of the female voice about an octave higher than the highest of
the male. The entire scale of the average human voice includes, from the
lowest male note to the highest female, about three to three and a half octaves.
Some remarkable musical voices have had a range of three and a half octaves.
A principal difference between the male and female voice is, therefore, in their
pitch. But they are also distinguished by the quality of the tone. The voices
of men and of women differ among themselves, both in the general pitch and
in the quality. There are two kinds of male voices, technically called the bass
and tenor, and two of female voices, the contralto and soprano, all differing
from each other in general pitch. The bass voice reaches lower than the
tenor, and its strength lies in the low notes. The contralto voice is of lower
range than the soprano, and is strongest in the lower notes of the female voice.
The barytone and mezzo-soprano voices are intermediate in range; the bary-
tone being intermediate between bass and tenor, the mezzo-soprano between
the contralto and soprano. The difference in the pitch of the male and the
female voices depends primarily on the different size of the larynx and the

520 MUSCLE-NERVE PHYSIOLOGY

length of the vocal cords in the two sexes; their relative lengths in men and
women are as three to two.

The boy's larynx resembles the female larynx. His vocal cords before
puberty are not two- thirds the length of the adult cords; and the angle of the
thyroid cartilage is as little prominent as in the female larynx. Boy's voices
are alto and soprano, resembling in pitch those of women, but louder, and
differing somewhat from them in tone. But, after the larynx has undergone
the change produced during the period of development at puberty, the boy's
voice becomes bass or tenor. While the change of form is taking place the
voice becomes imperfect, frequently hoarse and crowing, and is unfitted for
singing until the readjustment of the larynx is complete and the muscles
which control the vocal cords are again coordinated. In eunuchs who have
been deprived of the testes before puberty, the voice does not undergo this
change. The voice of most old people is deficient in tone, unsteady, and
more restricted in extent. The first defect is owing to the ossification of the
cartilages of the larynx and the altered condition of the vocal cords; the want
of steadiness arises from the loss of nervous power and command over the
muscles, the result of which is here, as in other parts, a tremulous movement.
These two causes combined render the voices of old people void of tone, un-
steady, and weak.

Most persons have the power, if at all capable of singing, of modulating
their voices through a double series of notes of different character: namely,
the notes of the natural voice, or chest-notes, and the falsetto notes. The
natural voice, which alone has been hitherto considered, is fuller, and excites
a distinct sensation of much stronger vibration and resonance than the
falsetto voice, which has more of a flute-like character.

The Quality of the Voice. — The difference in quality of voices, seen
when two or more persons sound the same note, is due to differences in
resonance in the cavities of the mouth and larynx and also of the nose. The
shape of the roof of the mouth, the regularity of the teeth, and the size of the
tongue, and the size and clearness of the nasopharynx are all factors. The
size and shape of the larynx and mouth cavity which influence the voice
quality can be controlled to some extent during singing, and this is a special
point of training in voice culture.

Speech. — Besides the musical tones formed in the larynx a great number
of other sounds can be produced in the vocal tubes, between the glottis
and the external apertures of the air-passages, the combination of which
sounds into different groups to designate objects, properties, actions, etc.,
constitutes language. The languages do not employ all the sounds which
can be produced in this manner, the combination between certain sounds
being often difficult. Those sounds which are easy of combination enter, for
the most part, into the formation of the greater number of languages. Each
language contains a certain number of such sounds, but in no one are all

ARTICULATE SOUNDS 521

brought together. On the contrary, different languages are characterized by
the prevalence in them of certain classes of these sounds, while other sounds
are less frequent or altogether absent.

Articulate Sounds. — The sounds produced in speech, or the articu-
late sounds, are commonly divided into vowels and consonants: the distinc-
tion between which is that the sounds for the former are generated by the
larynx, while those for the latter are produced by interruption of the current
of air in some part of the air-passages above the larynx. The term consonant
has been given to these because several of them are not properly sounded, ex-
cept, consonantly with a vowel. Thus, if it be attempted to pronounce aloud
the consonants b, d, and g, or their modifications, p, t, k, the intonation fol-
lows them only in their combination with a vowel. To recognize the essential
properties of the articulate sounds, it is necessary first to examine them as they
are produced in whispering, and then investigate which of them can also be
uttered in a modified character conjoined with vocal tone. By this procedure
we find two series of sounds: in one the sounds are mute, and cannot be
uttered with a vocal tone; the sounds of the other series can be formed inde-
pendently of voice, but are also capable of being uttered in conjunction
with it.

All the vowels can be expressed in a whisper without vocal tone, that is,
mutely. These mute vowel sounds differ, however, in some measure, as to
their mode of production, from the consonants. All the mute consonants are
formed in the vocal tube above the glottis, or in the cavity of the mouth or
nose, by the mere rushing of the air between the surfaces differently modified
in disposition. But the sound of the vowels, even when mute, has its source
in the glottis, though its vocal cords are not thrown into the vibrations neces-
sary for the production of voice; and the sound seems to be produced by the
passage of the current of air between the relaxed vocal cords. The same
vowel sound can be produced in the larynx when the mouth is closed, the
nostrils being open, and the utterance of all vocal tone avoided. The sound,
when the mouth is open, is so modified by varied forms of the oral cavity as to
assume the characters of the vowels a, e, i, o, u, in all their modifications.

The cavity of the mouth assumes the same form for the articulation of
each of the mute vowels as for the corresponding vowel when vocalized; the
only difference in the two cases lies in the kind of sound emitted by the
larynx. It has been pointed out that the conditions necessary for changing
one and the same sound into the different vowels are differences in the size of
two parts — the oral canal and the oral opening; and the same is the case
with regard to the mute vowels. By oral canal is meant here the space
between the tongue and palate: for the pronunciation of certain vowels
both the opening of the mouth and the space just mentioned are widened;
for the pronunciation of other vowels both are contracted; and for others
one is wide, the other contracted. Admitting five degrees of size, both of

522 MUSCLE-NERVE PHYSIOLOGY

the opening of the mouth and of the space between the tongue and palate,
Kempelen thus states the dimensions of these parts for the following vowel
sounds:

Vowel. Sound. Size of oral opening. Size of oral canal.

a as in "far" 5 3

a as in "name" 4 2

e as in "theme" 3 i

o as in "go" 2 4

oo as in "cool" i 5

Another important distinction in articulate sounds is that the utterance of
some is only of momentary duration, taking place during a sudden change in
the conformation of the mouth, and being incapable of prolongation by a con-
tinued expiration. To this class belong b, p, d, and the hard g. In the
utterance of other consonants the sounds may be continuous; they may be
prolonged, ad libitum, as long as a particular disposition of the mouth and a
constant expiration are maintained. Among these consonants are h, m, n,
f, s, r, 1. Corresponding differences in respect to the time that may be oc-
cupied in their utterance exist in the vowel sounds, and principally constitute
the differences between long and short syllables. Thus the a as in far and
fate, the o as in go and fort, may be indefinitely prolonged; but the same
vowels (or more properly different vowels expressed by the same letters),
as in can and fact, in dog and gotten, cannot be prolonged.

All sounds of the first or explosive kind are insusceptible of combination
with vocal tone (intonation), and are absolutely mute; nearly all the con-
sonants of the second or continuous kind may be attended with intonation.

The tongue, which is usually credited with the power of speech, plays
only a subordinate, although very important, part. This is well shown by
cases in which nearly the whole organ has been removed on account of
disease. Patients who recover from this operation talk imperfectly, and
their voices are considerably modified; but the loss of speech is confined
to those letters in the pronunciation of which the tongue is particularly
concerned, namely, c, d, g, h, j, k, etc.

Stammering depends on a want of harmony between the action of the
muscles (chiefly abdominal) which expel air through the larynx, and that of
the muscles which guard the orifice (rima glottidis) by which it escapes, and
of those (of tongue, palate, etc.) which modulate the sound to the form of
speech. Over either of the groups of muscles, by itself, a stammerer may
have as much power as other persons, but he cannot harmoniously arrange
their conjoint actions.

LABORATORY EXPERIMENTS ON MUSCLE AND NERVES.

Physiological experiments on living muscle serve to demonstrate many
of the most fundamental particulars of the subject. The muscles, especially

THE IRRITABILITY OF NERVE 523

of cold-blooded animals, when isolated from the body retain their living
attributes for several hours under the ordinary conditions which can be
readily supplied in the laboratory. They, therefore, serve as specially
favorable experimental material.

The muscles of frogs, turtles, and other cold-blooded animals illustrate
practically all the facts which can be shown by the muscles of warm-blooded
animals and are therefore most advantageously used.

1. The Muscle-nerve Preparation. — The classical muscle-nerve prep-
aration is the gastrocnemius muscle and the sciatic nerve. Prepare it
as follows: Kill the frog by pithing. This is done by grasping the frog
firmly in one hand and writh the other making a cut with a blunt scalpel
through the cranium just over the medulla, turning the scalpel so as com-
pletely to destroy the medulla. Now take a slender knitting needle, quickly
run it up into the cranial cavity to destroy the brain, and down the spinal
canal to destroy the cord. After a brief spasmodic contraction of the muscles
of practically the entire body, the frog remains limp and motionless. In
making the muscle-nerve preparation it is better to isolate the tendon first,
then the nerve, and finally the femur. The nerve should be prepared as
long as possible and should not be allowed to come in contact with the skin.
If the preparation is to be used in a moist chamber, the skin should be entirely
removed; if it is to be used in the open air, the skin should be left on. Use
care not to stretch the nerve, and protect it from evaporation.

2. The Irritability of Nerve. j — Prepare a muscle nerve with its skin
on and do not cut away the foot. Mount it by inserting the femur in a
muscle clamp, letting the leg extend vertically upward, and the foot hang
over. The nerve should lie along the exposed moist femur, one end being
slightly free. Stimulate the nerve in the following ways:

a. Electrical Stimuli. — Apply the electrodes from the secondary coil of an
induction apparatus to the tip of the nerve. When an induction current of
sufficient strength is produced, the muscle to which the nerve is attached will
give contractions, thus moving the foot. Notice that contractions occur with
both make and break induction. Apply the electrodes from the two poles of
a dry battery. When the current of the battery is established a contraction
will occur, but does not continue during the time of the flow of the current.
When the current is stopped a second contraction occurs. The nerve is
irritable to both galvanic and faradic currents.

b. Mechanical Stimuli. — Pinch the nerve lightly with forceps, or give it
a sudden stroke with the scalpel handle. With each mechanical impact
there is a single contraction of the muscle.

c. Thermal Stimuli. — Touch the end of the nerve with a glass rod heated
in boiling water. At each time the nerve is brought in contact with the rod
there will be muscular contraction, as in the preceding cases. The experi-
ment succeeds better if the nerve comes in contact with the rod for several

524 MUSCLE-NERVE PHYSIOLOGY

millimeters of length. If the tip of the nerve has ceased to respond, then
snip it off with the scissors, and repeat the experiment on the fresh end.

d. Chemical Stimulation. — Many chemical substances when brought in
contact with living nerve fiber produce nerve impulses. Try crystals of
sodium chloride, magnesium sulphate, dilute ammonia, acetic acid, 10 per
cent, nitric acid, i per cent, mercuric chloride.

Tabulate your observations on all the forms of stimulation used above,
by the following outline:

Kind of stimulation. Effect produced.

3. Irritability of Muscle. — Repeat the experiments in number 2
above, applying the stimuli, electricity, etc., directly to the muscle substance,
choosing as far as possible portions of muscle which do not exhibit nerve
fiber. The muscle will usually respond by a contraction to each of the
above forms of stimulation.

These tests do not fully demonstrate the direct irritability of muscle sub-
stance, since in each case it is possible that nerves may have been stimulated.
The nerve influences over the muscle can be eliminated by the use of drugs, as
will be shown in the next experiment.

4. Independent Irritability of Muscle. — The influence of curara on
the muscle-nerve preparation is demonstrated as follows: Ligate one leg of
a frog near the thigh to stop the circulation on that side. Now inject
under the skin of the back three drops of i per cent, curara, allowing twenty
to thirty minutes for absorption. Make the following observations: Place
the animal on a glass plate with its back up and dissect out the sciatic nerve
in each leg. Use care not to injure in any wray the accompanying femoral
artery.

a. Stimulate the muscles of the ligatured leg, also the muscles of the cura-
rized leg, both will contract.

b. Stimulate the sciatic nerve of the ligated leg below the ligature where
it has not come in contact with the curara; also the sciatic of the opposite
side, which has come in contact with the curara. Stimulation of the first
nerve produces contraction of its muscle; of the second nerve does not pro-
duce contraction of its muscle.

From this experiment of Claude Bernard's it is evident that the curara does
not destroy the irritability of nerve fiber nor the irritability of the muscle
fiber, yet it does destroy the influence of the nerve over the muscle, probably

THE SIMPLE MUSCLE CONTRACTION

525

acting as a specific poison for the motor end-plates. If the motor end-plates
are destroyed, then forms of stimuli which produce contractions of the muscle
must act directly on muscle substance, proving that muscle substance, as such,
is irritable.

5. The Simple Muscle Contraction. — Striated muscle responds to
electrical stimuli even of almost instantaneous duration. The response
which the muscle gives to a single stimulus is called a simple muscle contrac-
tion, and is demonstrated as follows:

Make a muscle-nerve preparation with the tendon isolated and the skin
removed, and mount it in a moist chamber, figure 350. Connect the tendon

FIG. 350. — Moist Chamber.

with a recording lever by short copper-wire hooks. Lay the nerve across a
pair of platinum electrodes, shake a little water on the sides of the cover of
the moist chamber, and place it over the preparation so as to prevent drying
of the nerve and of the muscle. Arrange an induction coil with its keys,
battery, and electrodes connected as shown in the diagram, figure 351. Set
the secondary coil at a position which will give a strong contraction of the
muscle, and record this contraction on the smoked paper of an ordinary re-
cording cylinder. Whenever the induction shock is sent through the nerve
there will be a single contraction of the muscle. If this contraction is re-
corded on the drum standing still, then the record will be a vertical line, the
height of which can be measured. From it and the arms of the lever the
exact shortening of the muscle can be computed. Repeat the stimulus with
weaker and weaker currents, until no contraction is produced. As the
stimulus becomes weaker a point is reached at which the contractions rapidly
decrease in height and cease altogether. If, on the other hand, the stimulus
is stronger the contractions only slightly increase.

Arrange the apparatus so as to stimulate the muscle by an automatic key

MUSCLE-NERVE PHYSIOLOGY

attached to the recording drum. Adjust the apparatus and lever and revolve
the drum at a rapid rate, allowing the automatic key to be opened while the
drum is turning at a rapid speed. Or take a record on the pendulum myo-
graph, which is especially constructed for this experiment, figure 352. The
muscle contraction now is recorded as a wave which shows some consider-
able duration in time. Repeat the experiment, introducing a 100 double
vibration tuning fork to record the speed of the drum, and taking care to
mark the exact point on the record where the automatic key is opened. In
this record the muscle contraction shows three different periods or phases.
The first, a period of no activity, called the latent period, taking about o.oi

FIG. 351. — Arrangement of Apparatus in the Induction Coil, as Shown for Single

Inductions.

of a second; the second, the period of rapid shortening known as the con-
traction phase, taking about 0.04 of a second on the average; and the third,
a period of rapid relaxation or return to the normal, which takes about o . 05
of a second, see figure 353.

The time and character of the simple muscle contraction will be influ-
enced by: i, load or tension; 2, the exact temperature; 3, by the amount of
work it has previously done, or fatigue; 4, by the time since it was isolated
from the circulation. Perform a series of experiments varying these effects,
and record the results by the following outline:

Number of
the
Experiment.

Muscle
Used.

Temper-
ature.

Load.

Total Time of
Contraction,
in Seconds.

Latent
Period, in
Seconds.

Contraction
Period, in
Seconds.

Relaxation
Period, in
Seconds.

-

6. The Relation of the Contraction to the Strength of the Stimu-
lus.— Minimal and Maximal Stimuli. — Prepare a muscle nerve of the
frog and mount in the moist chamber and arrange for stimulating the muscle

MINIMAL AND MAXIMAL STIMULI

527

directly by means of the secondary current of the induction coil, with the ap-
paratus adjusted as in figure 351. Prepare a recording cylinder for making
vertical records of the contractions. Adjust the writing point of the muscle
lever to the drum and move the drum by hand i cm. after each succeeding
contraction. Set the secondary coil of the induction apparatus so that it will
be too weak to produce a stimulus. Now attempt to stimulate the muscle,
then move the induction coil toward the primary i cm. at a time and repeat
until the first slight contraction appears. Continue to slide the secondary coil
toward the primary, stimulate at each new position, moving the drum for-

FIG. 352. — Simple Form of Pendulum Myograph and Accessory Parts. A, Pivot upon
which pendulum swings; B, catch on lower end of myograph opening the key, C, in its
swing; D, a spring-catch which retains myograph, as indicated by dotted lines, and on
pressing down the handle of \vhich the pendulum swings along the arc to D on the left of
figure, and is caujjht by its spring.

ward for each stimulus as directed, until a series of contractions is obtained
through the range of variation of induction of which the apparatus is capa-
ble, usually twenty to thirty contractions.

A typical tracing, figure 326, shows that as the strength of the stimulus is
increased the amplitude of the contractions quickly mounts from the minimal
to a maximal, after which all further increase in the strength of the stimulus
produces contractions of practically the same height. The first perceptible
contraction is called the minimal contraction, the strength of the current
which produced it a minimal stimulus for that preparation. The contractions
of the greatest amount are called maximal contractions. The weakest

5*8

MUSCLE-NERVE PHYSIOLOGY

stimulus which produces a maximal contraction is called the maximal stimu-
lus, and all stronger stimuli supramaximal.

7. The Effect of Fatigue on the Amplitude of a Series of Simple
Muscle Contractions. — Prepare a gastrocnemius muscle for direct stimula-
tion and mount it in a moist chamber. Arrange the induction apparatus for
single stimuli. Adjust the recording lever of the muscle to a smoked-paper

FIG. 353. — Record of a Simple Contraction of the Gastrocnemius of the Frog. Time
in .01 of a second. St, Moment of stimulation. Record taken on a rapid drum that was
provided with an automatic key.

kymograph and set the speed of the kymograph to revolve at the rate of i mm.
per second. Now stimulate the muscle with the make induction (short-
circuiting the break) once every two seconds. The contractions will be re-
corded as vertical marks on the drum in regular order, at a distance of 2 mm.
apart, hence very slight changes in amplitude are readily detected. The
contractions gradually increase in height for the first ten or twenty, the phe-

FiG. 354. — The Type of Contractions given by the Gastrocnemius of the Frog to a
series of stimuli occurring at regular recurrent intervals. (Taskinen.)

nomenon of treppe, then run for from fifty to one hundred contractions of
practically uniform amplitude, after which there is a gradual but sharp
decrease known as fatigue. Repeat the experiment after ten minutes' rest.
The former variations occur now very rapidly, indicating that the fatigue
effects are only partially recovered from.

8. The Effect of Fatigue on the Time of the Simple Contraction.
Prepare a muscle nerve and mount it in the moist chamber, arrange for the

FATIGUE OF VOLUNTARY MUSCULAR CONTRACTION 529

record as directed under 5 above. Make a series of records of the simple
contraction when automatically stimulated, recording only every tenth or
twentieth contraction — the intermediate contractions should be shunted and
are used merely to produce fatigue. After a time the contractions will not
only diminish in amplitude, but there will be a gradual increase in the time
consumed by the contraction. This increase in time falls very slightly on
the latent period, is more pronounced in the contraction phase, but is very
marked in the relaxation phase, figure 355.

FIG. 355. — Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers
printed on the figure indicate the contraction in the series which is recorded. (Lee.)

9. Fatigue of Voluntary Muscular Contraction. — The human vol-
untary muscles are used to demonstrate this experiment. Use a Mosso's
ergograph, or any one of its numerous modifications. If the original form is
used, then the muscle should be loaded with about 3 kilos, and contractions
once a second recorded until the muscle can no longer lift the load. The load
may have to be adjusted to the individual, but should be chosen so that ex-
haustion will be obtained with about fifty contractions. This experiment
does not demonstrate complete exhaustion, but merely fatigue down to a
certain level. If an apparatus is previously arranged for direct stimulation
of the muscles by electric currents it will be found that the contractions of
the muscles still occur after the voluntary power is lost, showing that at least
a part of the phenomenon, possibly the chief part, is located in the nervous
tissue rather than in the muscle substance.

10. The Effect of Temperature on Muscle Contractions. — Pre-
pare a muscle nerve and mount it in Porter's latest form of temperature ap-
paratus. Adjust the levers for vertical records on the smoked paper of the
kymograph. Begin with a temperature of the tap water and gradually lower
the temperature of the preparation by adding small amounts of crushed ice
at first, later ice and some salt crystals, to the external chamber. Take care
to lower the external temperature very slowly and gradually — say about one

34

530 MUSCLE-NERVE PHYSIOLOGY

degree in two minutes. Stimulate the muscle with a supramaximal stimulus
twice in rapid succession, for i° C. of change. Record these contractions as
pairs of vertical marks on the drum i mm. apart, separating each pair by a
space of i cm. When o° C. is reached, or before if the muscle fails to con-
tract at a higher temperature, reverse the direction of the temperature change,
gradually but slowly increase it until the muscle goes into heat rigor, which
begins at from 38° to 40° C.

While the muscle is entering rigor, move the drum i cm. for each degree,
as before, so as to record the development of that process.

11. The Effect of Temperature on the Time of the Simple Con-
traction.— Repeat the preceding experiment, but record the contractions
by the method described in Experiment 5 above, recording a contraction for
every change of 5° C. Measure the time and amplitude of the different
contractions, and the phases of the simple contractions, and tabulate them
as shown in Experiment 5.

12. Effect of Load on the Height of the Contraction and on the
Work of Voluntary Muscle. — Make a muscle-nerve preparation and
arrange it for stimulation, as in Experiment 6 above. Set the induction coil
of the stimulating apparatus for an effective supramaximal stimulus. Re-
cord the contractions as a series of vertical lines on the kymograph, separated
by a distance of i cm. Begin with the load of the lever only for the first
contraction, then increase the load by steps of 20 grams each until the muscle
is no longer able to lift the weight used. Support the lever under a tension
of 20 grams. Use care that no mechanical changes of the apparatus are re-
corded on the smoked cylinder. Repeat the experiment on a fresh muscle,
but do not support the lever.

The amount of work done by the muscle at each contraction is the prod-
uct of the load in grams times the height in centimeters. The height of
the lift can be obtained in this experiment from the height of the record on
the drum and the length of the recording arm and power arm of the lever, in
which the length of the recording lever is to the length of the power lever
as the height of the record obtained is to the actual shortening of the muscle.
Compute the exact amount of work done by each contraction under varying
loads, and tabulate on coordinate paper. Compare the variation in work
done with the variation in amplitude of the contraction.

13. Tetanus. — A continued contraction of a voluntary muscle can
be shown to be a fusion of simple muscle contractions. This is called a teta-
nus. Prepare a muscle nerve in the moist chamber and arrange the induction
coil for stimulating with a series of rapidly repeated stimuli. The rate of the
stimulation is obtained from the tetanometer, a form of key for rapidly in-
terrupting the current, which should be connected with the primary coil in-
stead of the key, K, figure 351. Stimulate the muscle at a rate of 10 per
second, record the contractions on the drum moving at a speed of about

CARDIAC MUSCLE

S31

2 cm. per second. Use care not to overfatigue the muscle, i.e., stimulate
it only 2 or 3 seconds at a time. Repeat this test, increasing the rate of stimu-
lation each time by 5, that is, stimulate at 10, 15, 20, etc., per second. In the
first stimulus there will be a series of simple contractions with almost com-
plete intervening relaxations. As the rate is increased these relaxations be-
come less and less until presently a rate is found which produces continuous,
apparently uninterrupted contraction. This is a tetanus, the others are in-
complete tetani. The frog's gastrocnemius at a temperature of 20° C. is
tetanized with a stimulation of from 25 to 35 per second.

14. Cardiac Muscle. — Cardiac muscle differs from voluntary in that
the contractions occur rhythmically and automatically. This is shown by

FIG. 356. — Arrangement of Apparatus for Studying the Contractions of the Strip of the

Apex of the Ventricle.

the isolated frog's heart, which continues to contract when bathed with
blood or salt solution, often for hours. This isolated heart, however, has a
complicated local nervous mechanism. The apex of the ventricle of the
terrapin's heart is practically free from nerve ganglia and may be used to
demonstrate the characteristics of pure cardiac muscle. Cut a strip off the
apex of the terrapin's ventricle, as shown in figure 214, and mount it by
means of light silk-thread ligatures tied around the two ends of a strip and
attached to the apparatus, shown in figure 356. When such ventricular
strips are immersed in ordinary o . 7 per cent, sodium chloride they will begin
contractions in a few minutes, twenty minutes or so. The contractions will
be regular in rate and will continue through two or three hours, gradually
becoming smaller and smaller until the standstill is reached. If the strip is
immersed in its own serum it will give only occasional contractions, but it re-
mains irritable and capable of contracting at any moment. If changed to

53 2 MUSCLE-NERVE PHYSIOLOGY

salt solution, the salt solution apparently brings out the automatic rhythm
by an increase in its irritability. Portions of the auricle and of the sinus,
especially the latter, are more highly rhythmic than portions of the ventricle,
due to a specific difference in the muscle cells themselves and not to the
nervous mechanism.

Refer to the experiments on cardiac muscle at the end of the chapter on
Circulation.

15. Involuntary Muscle. — Strips of smooth or involuntary muscle,
cut from the stomach of a frog or terrapin or from the intestine of a frog,
may be used to show the physiology of this character of tissue. Mount a
strip in the moist chamber, or in the apparatus shown in figure 356, using

FIG. 356a. — Figure Showing the Type of Contraction of a Strip of Muscle from the
Stomach of a Frog. The muscle was stimulated with an interrupted current during the
time indicated by the signal tracing, immediately below the time tracing. Time in seconds.

*

care not to load it too heavily; the weight of the ordinary muscle lever may
produce too much tension. Stimulate the muscle for one or two seconds
with interrupted induction currents of moderate strength. Contractions will
follow, usually developing very, very slowly as compared writh striated
muscle, and lasting through many seconds, from thirty to one hundred
seconds. By using very strong inductions occasionally a contraction may
be secured with a single stimulus, but single-induction currents as a rule do
not produce effective stimuli for smooth muscle, which requires a more
slowly developed stimulus.

If the stomach muscle of the frog be used and it be handled with extreme
care, it may happen that automatic contractions will develop in the muscle
in the moist chamber. If so, these contractions will be found to be slow and
of varying amplitude. The terrapin's stomach muscle will ordinarily not
show automatic contractions, but by increasing the temperature to about

RATE OF THE NERVE IMPULSE 533

30° C. automatic contractions will sometimes occur in it. Smooth muscle
responds like voluntary muscle to variations in temperature, to fatigue,
strength of stimulus, etc., etc.

1 6. Ciliary Contractions. — Ciliated Epithelium. — Make a preparation
of ciliated epithelium by cutting out the esophagus of a terrapin or frog,
slitting it open longitudinally, and smoothing it out on a cork block. The
cilia of this membrane will drive in the direction down the esophagus. Test
the rate at which different loads are moved and measure the distance on the
preparation as follows: Cut pieces of clean white paper about 4 and 6 mm.
square. Select a favorable area on the ciliated surface as long as possible,
place the 4 mm. square paper at the beginning of the area, and measure the
time which it takes to travel the distance. Measure the speed in terms of
seconds per centimeter. Now replace the paper at the point of beginning
and load it with small weighed cubes of paraffin. The rate at which the
load is carried will slightly increase at first as the load is increased, but later
will sharply decrease. Elevate one end of the ciliated membrane and repeat
the experiment with different loads so that the cilia will now carry the load
uphill. Calculate the work done in terms of gramcentimeters of work per
square centimeter of ciliated surface acting on the load.

17. Rate of the Nerve Impulse. — Prepare a muscle-nerve with the
entire sciatic nerve. Sever the nerve where it leaves the cord, leaving it
attached to the fascia. Mount in a moist chamber using two electrodes.
Set one pair of electrodes on the nerve as near the muscle as possible, the
other at the extreme end of the sciatic. Take several pairs of simple muscle
contractions on the pendulum myograph stimulating, i, the long nerve, and,
2, the short nerve length. The difference in the time of the two latent
periods of each pair represents the time required for the nerve length between
the two pairs of electrodes. Compute the rate of the nerve impulse in meters
per second. Make a table of all the tests recorded and draw averages.

CHAPTER XIV.
THE NERVOUS SYSTEM.

THE nervous system consists of an extremely complex anatomical mass
of nerve cells and fibers. It is usually described as made up of two main
divisions, the cerebro-spinal system and the sympathetic. These two divi-
sions must be regarded as parts of one great whole, and in no sense coordinate.
The gross subdivision of the nervous system may be given as the following:
First, the cerebro-spinal axis, which consists of matter within the bony cra-
nium and spinal column, constituting the brain and cord. Second, smaller
masses for the most part in the abdominal and thoracic cavities, also in the
neck and head, and constituting the sympathetic ganglia. Third, the nerves
or bundles of nerve fibers which connect the central nerve axis with the per-
iphery and with the sympathetic ganglia. Fourth, there are special per-
ipheral organs in connection with the beginnings and endings of the nerve
fibers, the one for receiving nerve stimuli, the other for transmitting stimuli
to other tissues. These are properly parts of the nervous system. The
peripheral organs for receiving stimuli constitute the sense organs and will be
treated in a separate chapter.

I. FUNCTION OF THE NERVE CELL.

The Nerve Cell. — The nerve cell, the neurone, is considered the ana-
tomical and physiological unit of the nervous system. Waldeyer introduced
the term neurone to designate the nerve cell body and all its constituent proc-
esses. Much of the details of structure of types of neurones, both as to the
structure of the cell body and all its processes, have already been given in
Chapter II., see figures 83 to 106. It is sufficient to recall that the types of
nerve cells found in various parts of the nervous system vary extremely.
The peculiar feature, however, consists in the fact that the cell body has
one or more processes, branches, or arborizations, see figure 365. Some-
times these processes are short but complexly branched, sometimes they are
exceedingly long as compared with the extent of the cell body. The cell
processes may or may not be medullated. In medullated nerves the ad-
ventitious structures are subdivided into nodes, but the axis-cylinder process
is to be regarded as a continuation of the protoplasm of the cell body.

In recent years the structure of the cell body and its branches has been
very carefully investigated, with the result that we have learned that the
intimate structure is very complex. Networks of neurofibrillae have been

534

THE CHARACTERISTICS OF THE INDIVIDUAL NEURONE 535

described not only in the cell body, but extending throughout the course of
the processes and, in fact, from cell to cell. We are not in a position at the
present time fully to determine what bearing these neurofibrillae have on our
accepted theories of nerve function, other than that they are assumed to be
the conducting elements.

The Neurone Theory. — Our knowledge of the function of the ner-
vous system is best explained on the basis of the neurone theory, which con-
siders the neurone as a physiological unit. By this view each gross divi-
sion of the nervous system is supposed to consist of a large number of in-
dividual neurones,* each of which is a more or less complete morphological

FIG. 357. — Purkinje Cells from the Cerebellum of the Swallow. A, Taken in the morning;
B, taken in the evening. (Hodge.)

unit capable of carrying on certain functions of its own. Each of these
neurones maintains physiological continuity with its associates, presumably
by protoplasmic contact rather than by continuity; so that well-marked paths
of conduction are possible throughout the extent of the particular mass of
which the neurone is a part, and throughout the adjacent masses. By this
view, paths of conduction are made up of series or chains of individual neu-
rones which are in physiological continuity.

The Characteristics of the Individual Neurone.— The function of
the nerve cell may be discussed under two headings: The function of the
cell body, and the function of the cell processes.

* "According to the estimations of Meynert, the cortex of the cerebral hemisphere
alone contains twelve hundred millions of ganglion cells. Donaldson (The Growth of the
Brain, a Study of the Nervous System in Relation to Education, i2mo, London, 1897,
p. 159) states that for the total number of nerve cells in the central nervous system three
thousand millions is a moderate estimate." (Barker, the Nervous System and its Con-
stituent Neurones, p. 42, 1899.)

536

THE NERVOUS SYSTEM

The cell body of the neurone is the part that contains the nucleus and is
the center of those activities which influence the metabolism of the cell itself.
If the cell body be isolated from its processes, the processes will degenerate,
while the body continues to live. In other words, the cell body may be con-
sidered as the center of those trophic influences which regulate the nutrition

B

FIG. 358. — Spinal Ganglion Cells from the Cat. A, Normal taken before stim-
ulation; B, taken after five hours' stimulation. From the right and left, eight thoracic
ganglia. (Hodge.)

of the processes. Although the nerve cell as a whole is in many, perhaps in
most, cases a conducting organ, still those physiological processes which go on
in it produce marked changes in the protoplasm of the cell body. Hodge
has demonstrated that nerve cells which have been active for several hours,
in case of sparrows which have been flying about actively throughout the day,

INFLUENCE OF THE CELL BODY OVER ITS PROCESSES 537

or in bees after a day's work, show marked evidences of fatigue. These
evidences consist in the decrease in the size of the nucleus and the appearance
of vacuoles in its structure, also in the shrinking of the protoplasm of the cell,
which, in case of the cells of the spinal ganglia, draws away from its capsule.
If the cells are examined early in the morning the fatigue changes will not
be present, the cell having recuperated during the period of rest at night. It
has also been found that the Nissl granules which are present in the cell body
of resting cells decrease in number and show evidence of disintegration in
cells that have been stimulated for several hours.

The nerve processes or fibers are primarily conducting structures. But
their fibers are susceptible to artificial stimulation, as shown in the previous
chapter; that is, they are irritable. They are influenced by certain changes in
the environment, but they do not showr evidence of fatigue upon prolonged
functional activity.

Nutritive Influence of the Cell Body over its Processes — Wallerian
Degeneration. — The control of the cell body over the nutrition of the
cell processes is demonstrated by the changes which occur when these proc-
esses are severed from connection with the cell body. Under such conditions
the axis-cylinder process completely degenerates. Howell and Huber have
followed the degenerative changes in medullated nerve fibers. The medul-
lated fiber in the course of three or four days, in mammals, breaks up into
elliptical segments of myelin, containing small fragments of the axis-cylinder.
These changes in the cut-off section of nerve occur simultaneously through-
out its whole extent. In the course of a few weeks regenerative changes be-
gin, apparently under trophic influence of the nuclei of the primitive sheath.
These nuclei increase in number and form small masses of protoplasm which
ultimately produce a strand of embryonic protoplasm, which is described as
the "band fiber." If the ends of the sectioned nerve have originally been
brought together and sutured in place, then the axis-cylinder processes of the
portion of the nerve fiber still attached to the cell body will grow down into
the peripheral fibers, thus forming new axis-cylinder processes along the
course of the band fiber. If the stumps of the nerves are not so brought to-
gether, then apparently the band fiber again degenerates, especially in adult
tissues, though it has been claimed by Bethe and others that complete regen-
eration of the peripheral fiber will take place in very young animals. Even if
complete regeneration should take place in the peripheral fiber, unless con-
nection were established between it and the central end of the fiber it would
ultimately disintegrate and could only temporarily carry on any physiological
function.

The central end of the divided nerve, that is, the part maintaining con-
nection with the cell body, usually degenerates for a few nodes only, then re-
generation and growth of the original stump proceed. Instances are observed
in certain cases where the degeneration of the entire central fiber, includ-

538 THE NERVOUS SYSTEM

ing its cell body, takes place. This happens particularly in those relations
where the original neurone forms a link in a conducting path. Such a con-
ducting neurone would no longer perform its proper function so would
atrophy just as would a muscle fiber when cut off from its nervous relations.

In conclusion, one may infer that the cell body exercises a nutritive or
trophic control over the protoplasm of its branches, just as we have already
seen the neurone as a whole exercises trophic control over the nutritive
processes taking place in the tissue to which its branches are distributed, for
example, the voluntary muscles.

Specific Energy of the Nerve Impulses. — We have already discussed
the fact that a nerve fiber, also its cell body, is irritable to various forms of
mechanical, electrical, and other stimuli. In the complex of activity of the
nervous system it is found that whatever the form of the external stimulus
applied to a nerve, the resulting nerve impulse produces the same effects
in the central nervous system. The reaction in consciousness is constant
and unvarying and independent of the character of the external stimulus.
For example, if the temperature points on the skin be stimulated, as they
may, by a number of widely different types of external stimulus, the result-
ing sensation is the same; stimulation of a "heat point" by ice produces a
sensation of heat, not cold. This phenomenon has been called the specific
energy of the nerve impulse, and the term was first advanced by Johannes
Miiller. Different views are presented in explanation. But it seems ra-
tional to believe that the gist of the matter rests in two factors: i. The
highly differentiated sense organ is adapted especially to stimulation by a
particular stimulus, as the eye by light. 2. The central apparatus is de-
veloped in response to and especially adapted to receive the specific stimulus.
The interpretations that are made in consciousness in response to an inflow
of nerve impulses from the sense organ are more or less constant. When
the exceptional stimulus is applied to the special end organ it results in the
usual change in the sense organ, the resulting nerve impulses reach the usual
central area, and there is no physiological basis for other than the usual sen-
sations which development and experience have associated with activity in
the parts affected.

Transmission of Nerve Impulses through the Neurone.— The the-
ory has been advanced that in the nerve cell the primary function of some
processes is to carry nerve impulses toward the cell body, and of other proc-
esses to carry nerve impulses away from the cell body. At the present time
this view is advocated by perhaps the ablest living anatomists and neurolo-
gists. The dendrites conduct toward the cell body, and the axones away from
it. That is, the former are cellulipetal, the latter cellulifugal.

Impressions made upon the terminations or upon the trunk of an afferent
nerve may cause, a, pain or some other kind of general sensation; b, special
sensation; c, reflex action of some kind; or d, inhibition or restraint of action.

PHYSIOLOGICAL TYPES OF NEURONES 539

Similarly impressions made upon an efferent nerve may cause, a, contraction
of muscle (motor nerve); b, it may influence secretion (secretory nerve);
c, it may influence nutrition (trophic nerve) ; or d, it may inhibit, augment,
or stop any other efferent action.

By artificial stimulation nerve impulses can be made to pass in both di-
rections in all classes of nerve processes. That is to say, if a motor axone is
artificially stimulated in the middle of its course it will not only convey a nerve
impulse to its distribution, but also a nerve impulse will pass back over the fiber
to the cell body and out over the dendrites. Normally, in the complex of the
body, it is probable that such a neurone will be stimulated only at its points
of contact with other neurones chiefly through its dendrites, and especially
by means of the sensory cells. The dendrites therefore will receive the nerve
stimulus, carry it through the cell body to the axone and its distribution.
In such cells there is isolated, or uninterrupted, conduction throughout the
extent of the neurone. The nerve impulse is able to pass from a given
neurone to adjacent ones only at the termination of the axone or its branches,
and such terminations may be considered as special organs for the trans-
ference of the nerve impulses. This activity involves isolated conduction in
nerve fibers bound in a common nerve trunk. It has been supposed that the
myelin sheath of a medullated nerve acts as an insulator of the axis-cylinder,
but this can be only relatively true, for the reason that non-medullated nerves
do not possess the myelin sheath. In non-medullated nerves we must sup-
pose that the primitive sheath is sufficient to give insulated conduction, or
that it is an inherent property of the axis-cylinder itself to carry the nerve
impulse without transmission to adjacent fibers.

We have already, page 500, discussed the rate of transmission of the ne-rve
impulse in motor nerves which was given as from 27 to 30 meters per second.
In sensory nerves the rate is said to be somewhat higher; in human nerve
from 30 to 42 meters per second.

Physiological Types of Neurones.— Many classifications could be
made of nerve cells, based on the differences in their functional relations,
but attention will be called to only one. Neurones may be classified as
afferent or sensory, efferent or motor, and connecting or transmitting.

Under afferent neurones are classed all those neurones which transmit
the effects of external stimuli received through the sense organs, both general
and special sense organs. These neurones carry nerve impulses toward the
central nervous system, which may ultimately produce those changes in the
cerebral cortex which are associated with states of consciousness.

Under efferent neurones are included all those which transmit nerve im-
pulses from any part of the central nervous system to the muscles, that is,
motor nerves; or transmit nerve impulses to the glands, secretory nerves; or
that transmit nerve impulse, which inhibit peripheral action, inhibitory
nerves.

540 THE NERVOUS SYSTEM

Under central or transmitting neurones are included those units which
act as connecting links within the central organ, especially within coordi-
nate parts of the central nervous system, between the afferent and efferent
neurones.

Nerve Centers. — Whenever a number of neurones are gathered in

FIG. 359. — View of the Cerebro-spinal Axis of the Nervous System. The right half of
the cranium and trunk of the body has been removed by a vertical section; the mem-
branes of the brain and spinal cord have also been removed, and the roots and first part of
the fifth and ninth cranial, and of all spinal nerves of the right side, have been dissected
out and laid separately on the wall of the skull and on the several vertebrae opposite to the
place of their natural exit from the cranio-spinal cavity. (After Bourgery.)

STRUCTURE 541

one group to accomplish some specific function it is called a nerve center.
The term usually applies to the aggregation of cell bodies and their dendritic
processes in contradistinction to nerve trunks. There are aggregations
of nerve cells into different specific groups, to which we cannot in every
case ascribe a specific function. These groups are not called nerve centers,
but are described by the general anatomical term, ganglia. Such ganglia
are represented in the sympathetic chain, the spinal-root ganglia, the ganglia
of certain cranial nerves, etc. The nerve centers are found in the spinal cord,
the medulla, and the higher cranial groups. The medulla is particularly
rich in nerve centers. The cerebro-spinal axis is in fact an aggregation of
nerve centers of varying complexity in different parts.

It is by means of the nerve centers that the activities of the differentiated
parts of the human body are brought into intimate correlation. The nerve
centers exercise their influence through the power of inhibiting or decreasing
activity; or, on the other hand, of augmenting or increasing the activity in the
peripheral tissues or in other parts of the nervous system. For example, the
vagus center regulates the activity of. the heart muscle by its power to decrease
or inhibit cardiac contractions. This center, we have already found, is in
constant tonic activity; that is to say, in constant regulative control of the
heart. The cardiac augmentory center, on the other hand, produces just the
opposite effect, increasing the activity of the cardiac muscle. What is true
for the heart is likewise true in general for other tissues of the body. The
numerous nerve centers in the central nervous system are brought into cor-
relation through an exceedingly complex system of communicating fibers.
The cerebro-spinal axis may in fact be regarded as a segmental chain of nerve
centers, the complexity increasing from the cord toward the brain, and the
coordinating control culminating in the cerebral cortex.

II. THE STRUCTURE AND FUNCTION OF THE
SPINAL CORD.

STRUCTURE.

The spinal cord is a cylindrical column of nerve-substance connected
above with the brain through the medium of the bulb, and terminating below
in a slender filament of nerve substance, the filum terminate, which lies in the
midst of the roots of the many nerves forming the cauda equina.

General Features. — The cord is composed of nerve fibers and nerve
cells. The former are situated externally and constitute the chief portion
of the cord, while the latter occupy its central or axial portion and are so
disposed that on the surface of a transverse section of the cord two somewhat
crescentic grayish masses connected by a narrower portion or isthmus ap-
pear, figure 358. Passing through the center of the cord in a longitudinal
direction is a minute canal, the central canal, which is continued through

542

THE NERVOUS SYSTEM

the whole length of the cord, opening above into the space at the back of
the medulla oblongata and pons Varolii called the fourth ventricle. The
canal is lined by a layer of columnar ciliated epithelium.

The spinal cord consists of exactly symmetrical halves, separated an-
teriorly and posteriorly by vertical -fissures (the posterior fissure being deeper
but less wide and distinct than the anterior), and united in the middle by
nervous matter which forms the commissures. The central part, which
contains the central canal, is known as the gray commissure, and is bounded

15 15

i-i

FIG. 360. — Horizontal Section of the Cord and its Envelopes, at the Middle of a
Vertebral Body (Schematic), i, Spinal cord with 2, its anterior median fissure; 3, its
posterior median fissure; 4, anterior roots; 5, posterior roots; 6, pia mater (in red); 7,
ligamentum dentatum; 8, connecting fibers passing from the pia to dura mater; 9, visceral
layer, and 9', parietal layer of the arachnoid (in blue); 10, subarachnoid space; n, arach-
noid cavity; 12, dura mater (in yellow); 13, periosteum; 13', external periosteum; 14,
cellular tissue situated between the dura mater and the wrall of the vertebral canal; 15,
common posterior vertebral ligament; 16, intraspirial veins; 17, vertebra in section.
(Testut.)

by the anterior white commissure in front. Each half of the spinal cord is
marked on the sides (obscurely at the lower part, but distinctly above) by
two longitudinal furrows, which divide it into three portions, funiculi, or tracts
— an anterior, lateral, and posterior. From the groove between the anterior
and lateral funiculi spring the anterior roots of the spinal nerves; and just
in front of the groove between the lateral and posterior funiculi arise the
posterior roots of the same; a pair of roots on each side corresponding to
each segment of the cord.

ARRANGEMENT OF NERVE CELLS IN THE SPINAL CORD 543

The nerve tracts of the cord are made up of medullated nerve fibers of
different sizes, arranged longitudinally, and of a supporting material of
ordinary fibrous connective tissue and neuroglia, figure 105.

The general rule respecting the size of different segments of the cord
appears to be that each is in direct proportion in this respect to the size and
number of nerve roots given off from it, and has but little relation to the size
or number of those given off below it. Thus the cord is very large in the
middle and lower part of its cervical portion, whence arise the large nerve
roots for the formation of the brachial plexuses and the nerve supply of the
upper extremities; and again enlarges at the lowest part of its dorsal portion
and the upper part of its lumbar, at the origins of the large nerves which,
after forming the lumbar and sacral plexuses, are distributed to the lower
extremities. The chief cause of the greater size at these parts of the spinal
cord is increased in the quantity of the gray matter; for there seems reason
to believe that the white part of the cord becomes gradually and progressively
large from below upward, doubtless from the addition of a certain number
of ascending fibers from each pair of nerves.

From careful estimates of the number of nerve fibers in a transverse sec-
tion of the cord toward its upper end, and the number entering or issuing
from it by the anterior and posterior roots of each pair of nerves, it has been
shown that in the human spinal cord not more than half of the total number
of nerve fibers of all the spinal nerves are contained in a transverse section
near its upper end. It is obvious, therefore, that at least half of the nerve
fibers entering it must terminate somewhere within the cord itself.

The Arrangement of Nerve Cells in the Spinal Cord. — The gray mat-
ter of the spinal cord consists of numerous groups of nerve cells and of a
close meshwork of nerve fibers, most of which are very fine and delicate.
Medullated fibers mingled with the small gray fibers about the borders of the
gray substance. Mingled with it and supporting it is the meshwork of the
neuroglia.

The multipolar cells of the cord are either scattered singly or arranged in
groups or columns in bilateral symmetry. The following are to be distin-
guished, certain of the groups being more or less marked in all of the regions
of the cord, viz., a, those in the anterior columns; b, those in the lateral
columns; c, those in the posterior columns; and d, intrinsic cells distributed
throughout the gray matter.

The cells in the anterior columns are large and branching, and each gives
rise to an axis-cylinder process which passes out in the anterior nerve root.
These cells are everywhere conspicuous, but are particularly numerous
in the cervical and lumbar enlargements. In these districts they may be
divided into several groups; i. A group of large cells close to the tip of the
inner part of the anterior column, i, figure 362. This group is called the
antero-mesial group of motor cells. It forms a column the full length of the

544

THE NERVOUS SYSTEM

cord and is supposed to furnish motor innervation to the long muscles of the
trunk. 2. The antero-lateral group of cells, 2a, forms a column which has
its best development in the cervical and lumbo-sacral enlargements. It
probably furnishes motor fibers to the muscles of the limbs including those
of the shoulders and hips. 3. There are groups, 2b, 2c, the intermedio and
lateral groups, which form slender columns in the cord, through the entire
dorsal and the first two lumbar segments. The cells are small and closely
aggregated and characteristic in appearance. These nuclei reappear in the

FIG. 361. — From the Lower Lumbar Cord of Man, after a Preparation by Klonne and
Miiller stained by Weigert and Pal's method. A portion of the gray substance of the
anterior column with the adjoining portions of the lateral funiculus is represented, showing
anterior column cells and the fine medullated fibers which enter the gray substance from the
lateral funiculi and surround the nerve cells, which here are provided with fine pigmented
granules. High power. (Kolliker.)

upper cervical segments and in the sacral segments that give origin to the
nervi erigens. They are supposed to be the motor nuclei for the vaso-motor,
the pilo-motor, and the nerves of the swreat glands, i.e., the autonomic system.
4. The cells of the posterior vesicular column, or Clark's column, are in the
posterior portion of the gray matter of the cord. They form a conspicuous
column of cells, 3, 5, and 6 of figure 362, extending from the last cervical to the
second lumbar segments. These large cells contribute their axones to the
ascending cerebello-spinal (direct cerebellar) fasciculus which ascends to the
cerebellum and is believed to carry sensory impulses of prime importance in

ARRANGEMENT OF NERVE CELLS IN THE SPINAL CORD 545

the coordinations of muscular movements. The nerve relations and the
restricted location of the posterior vesicular column has also led to the sugges-
tion that its function has to do with the visceral afferent or sensory nerve
impulses. Sensory fibers from the posterior roots arborize around the cells
of the posterior vesicular column, i.e., the dorsal nucleus, see figure 363.
The dorsal nucleus is considerably broken up by the passage of bundles of
fibers through it, called the lateral reticular formation.

Besides these groups, which have their names largely on account of their
ocation, there are distributed throughout the gray matter a very large num-
ber of other cells, which are known as intrinsic cells. These are of two types,

FIG. 362. — Section of Spinal Cord, One Half of Which (Left) Shows the Tracts of the
White Matter, and the Other Half (Right) Shows the Position of the Nerve Cells in the
Gray Matter. 7, 10, 9, and 3 are tracts of descending degeneration; i, 2, 4, 6, and 8, of
ascending degeneration. Semidiagrammatic. See the text for a description of the groups
of nerve cells shown on the right. (After Sherrington.)

those restricted to connections wholly within the gray matter, and those that
send out axones which pass into the adjacent ground bundles of the same
or of the opposite side, and pass up and down the cord, to enter the gray
matter again. They connect by their end-brushes with cells at different
levels of the cord.

The functions of these connecting or intrinsic cells is to unite the pos-
terior and anterior regions of the cord, to serve as conductors between the
lateral halves, or to connect segments at different levels. They are also dis-
tributing fibers in that they bring a single or at least a small number of pos-
terior sensory neurones into connection with a relatively large number of
anterior or motor neurones.
35

546

THE NERVOUS SYSTEM

The Fasciculi or Tracts in the White Matter of the Spinal Cord.—

We have already shown that the white matter of the cord is divided on each
side into the anterior, lateral, and posterior funiculi. But evidence of various
kinds discussed below has shown the following main conducting channels or
tracts through the cord, see figures 363 and 364 for illustration.

Radix anterior
Fasciculus ccrcbrospinalis lateralis [pyramidalis lateralis] .

Anterior root fibre

Bundle to anterior funiculus from the formatio reticulari!

Fasciculus cerebrospinalis anterior

[pyramidalis anterior]

Bundle to anterior funiculus .-
from the formatio reticularis \

Substantia grisea.

Fasciculus

anterolateralis super-

ficialis [Gowersij and

(ascending) bundle from

anterior funiculus to the

formatio reticularis

Substantia alba

Bundle to lateral
funiculus from Deiters'
nucleus and from the
red nucleus .

Fasciculus cerebro

spinalis lateral!"

[pyramidalis lateral!

Nervus spinalis

Ganglion spinale
Cells of tho spinal ganglion
,. Fasciculus cerebellospinalis
f. Secondary reflex path

, Radix posterior

Collateral

to the posterior horn
Secondary path of
posterior funiculus
Descending posterior

root fibre
Primary reflex path

Ascending posterior
root fibre

>- Secondary reflex path

.Descending posterior
root fibre

Posterior root fibre

Sulcus medianus
posterior

- Posterior root fibre

FIG. 363. — Reconstruction of a Segment of the Spinal Cord Representing Both a Tran s-
verse and Longitudinal Section. (Held, from Spalteholz's Anatomy.)

Tracts of the Cord.

Funiculus posterior.

Fasciculus gracilis, tract of Goll (ascending).

Fasciculus cuneatus, tract of Burdach (ascending).

Comma, tract of Schultz (descending).
Funiculus lateralis.

Fasciculus cerebello- spinalis, direct cerebellar (ascending).

Fasciculus antero-lateralis super ficialis, tract of Gowers (ascending).

Fasciculus cerebro- spinalis lateralis, crossed pyramidal tract
(descending).

TRACTS OF DESCENDING DEGENERATION 547

Fasciculus lateralis proprius, lateral ground bundles (ascending

and descending).
Funiculus anterior.

Fasciculus cerebro-spinalis anterior, direct pyramidal tract (de-
scending).

Fasciculus anterior proprius, anterior ground bundles (ascending
and descending).

The methods for determining the tracts in the cord and the evidence on
basis of which function is ascribed are briefly the following:

The Embryological Method. — It has been found that, if the development
of the spinal cord be carefully observed at different stages, certain groups of
nerve fibers acquire their myelin sheath at earlier periods than others, and
that the different groups of fibers can therefore be traced in various directions.
This is known as the method of Flechsig.

Wallerian or Degeneration Method. — This method depends upon the fact
already presented that if a nerve fiber is separated from its nerve cell it
degenerates. It consists in tracing the course of tracts of degenerated fibers
which result from an injury, or lesions in any part of the central nervous
system. When fibers degenerate below a lesion the tract is said to be of
descending degeneration, and when the fibers degenerate in the opposite
direction the tract is one of ascending degeneration. By modern methods of
staining of the nervous tissue, it has proved comparatively easy to distinguish
degenerated parts in sections of the cord or of other portions of the central
nervous system. Degenerated fibers have a differential staining reaction
when the sections are treated by Marchi's method. Accidents resulting in
loss of function and in degeneration in the central nervous system in man
have given us much information as to its organization, but this has of late
years been supplemented and largely extended by the experiments on animals,
particularly upon monkeys. Considerable light has, by the method of
section and degeneration, been shed upon the path of conduction of impulses
to and from the various parts of the nervous system. Thus we not only
have embryological evidence mapping out different tracts, but also con-
firmatory pathological and experimental observations.

The tracts which have been made out are the following:

Tracts of Descending Degeneration.— The Lateral Pyramidal Tract.—
This tract is situated to the outer side of the posterior cornu of gray matter,
figure 360, 7. It originates in the cerebral cortex and extends throughout
the whole length of the spinal cord; at the lower part it extends to the margin
of the cord, but higher up it becomes displaced inward from this position by
the interpolation of another tract of fibers, the direct cerebellar tract. The
lateral pyramidal tract is large, and may touch the tip of the gray matter of
the posterior gray column, but it is separated from it elsewhere. It is oval

548 THE NERVOUS SYSTEM

in shape on cross-section, and diminishes in size from the cervical region
downward. The tract is particularly well marked out, both by the degener-
ation and by embryological methods. The fibers are supposed to pass off
as they descend, and to join the various local nervous mechanisms of nerve
cells and their branchings which are represented in the anterior columns of
the cord. The fibers of which this tract is composed are moderately large,
but are mixed with some that are smaller.

The Anterior Pyramidal Tract. — This tract is situated in the anterior
funiculus by the sides of the anterior fissure, figure 360, 10. It is smaller
than the lateral tract and is not present in all animals, though conspicuous
in the human cord and in that of the monkey. It can be traced upward to
the cerebral cortex, and downward as far as the mid or lower thoracic region,
where it ends.

Antero-lateral Descending Tract. — This is an extensive tract, elon-
gated but narrow, and reaching from the lateral pyramidal to the anterior
pyramidal tract. It is a mixed tract, since not all of its fibers degenerate
below the lesions.

Comma Tract. — This is a small tract of fibers in the posterior funiculus
which degenerates below the point of section of,, the cord. It consists of the
descending collaterals of the posterior ner^gitfcfts as they pass into the cord.

Tracts of Ascending Degeneration. — The fasciculus gracilis, tract of
Goll, and the fasciculus cuneatus, tract of Burdach. These tracts degenerate
upward on section of the cord, also on section of the posterior nerve roots,
figure 362, i. They exist throughout the whole of the cord and can be traced
into the bulb. They are sensory tracts, see page 561.

The Fasciculus Cerebello-spinalis, or Direct Cerebellar Tract. — This
tract is situated on the outer part of the cord between the lateral pyramidal
tract and the margin. It is found in the cervical, thoracic, and upper
lumbar regions of the cord, and increases in size from below upward. It
degenerates on injury or section of the cord itseli, but not on section of the
posterior nerve roots, since its fibers arise from the cells of the dorsal nucleus.
As the name implies, it is believed to pass up into the cerebellum, see
Page 572,

The Fasciculus Antero-lateralis, Tract of Gowers. — This tract lies
at the margin of the lateral funiculus of the cord and extends the full length,
see figure 364.

It will thus be seen that the three general divisions of the white matter
of the spinal cord — the anterior, the lateral, and posterior funiculi — are
subdivided into tracts in which the fibers degenerate upward, those in which
the fibers degenerate downward, and still others in which the fibers degener-
ate either way for only short distances when the cord is cut across. These
latter parts of the cord are composed of association fibers which connect
different levels of the cord. The association tracts form the antero-laterai

THE SPINAL NERVES

549

columns and the lateral limiting layer. The arrangement of these tracts is
shown well in figures 362 and 364.

The Spinal Nerves. — The spinal nerves consist of thirty-one pairs,
from the sides of the whole length of the cord, their number corresponding
with the intervertebral foramina through which they pass. Each nerve
arises by two roots, an anterior and a posterior, the latter being the larger.
The roots emerge through separate apertures of the sheath of dura mater
surrounding the cord; and directly after their emergence, where the roots lie
in the intervertebral foramen, a ganglion is found on the posterior root. The
anterior root lies in contact with the anterior surface of the ganglion, but none

Entering posterior
root

Lissauer's tract

ng anterior root

FIG. 364. — Diagrammatic Transverse Section of the Spinal Cord, Showing the Conduction
Paths and Groups of Cells. (Cunningham.)

of its fibers intermingle with those in the gangl'on, figure 361. But imme-
diately beyond the ganglion the two roots coalesce, and by the mingling of
their fibers form a mixed spinal nerve; the spinal nerve, after issuing from
the intervertebral canal, gives off anterior and posterior (or ventral and dorsal)
branches, each containing fibers from both the roots. A third or visceral
branch of the spinal nerve, ramus communicans, joins the sympathetic chain.
The anterior root of each spinal nerve arises by numerous separate and
converging bundles from the anterior columns of the cord; the posterior root
by more numerous parallel bundles, from the posterior column. The
anterior roots of each spinal nerve consist chiefly of efferent fibers; the pos-
terior exclusively of afferent fibers.

55°

THE NERVOUS SYSTEM

Course of the Fibers of the Spinal Nerve Roots. — The Anterior
Roots. — The anterior roots leave the cord in several bundles, which may be
called: i, Internal; 2, Middle; 3, External. All have their origin from the
groups of multipolar cells in the anterior columns. The internal fibers are
originated partly in the internal group of nerve cells of the anterior columns
of the same side; but a few fibers can be traced through the anterior com-
missure to cells of the anterior column of the opposite side.

The Posterior Roots. — The fibers of the posterior roots enter the spinal
cord to the inner or median side of the posterior column. The fibers, as

FIG. 365. — Section of the Spinal Cord, Showing the Grouping of Nerve Cells and the
Course of Nerve Fibers Entering in Posterior and Anterior Roots. Numerals 1-6 are
different types of the sensory fibers. Their collaterals, 7-12, connect with different regions
of the gray substance; 13 and 14, collaterals from descending tracts of the cord; r.a.,
anterior root; a, anterior motor cells; b, cells contributing fibers to the various tracts;
c, commissural cells; d, Golgi cells. (After Lenhossek.)

soon as they reach the cord, divide in a fork-like fashion, one branch pass-
ing down a short distance, about three centimeters, the other branch passing
up for a shorter or longer distance. This upper branch sometimes reaches
the whole extent of the cord, but generally it extends over only one or two
segments of the cord. The divisions of the posterior root fibers give off
in their course numerous collaterals, figure 368. The fibers of the posterior
roots are divided into two sets, an internal or median, an external or lateral
group. The lateral set consists mostly of small fibers which enter the
cord opposite the tip of the posterior horn. The fibers pass in part to the
marginal column of Lissauer, where they ascend and descend; in part they
penetrate the posterior column, and come in relation with its cells. From

THE FUNCTIONS OF THE CORD 551

the median set some fibers pass to Clarke's column, others pass by way
of the posterior commissure to the median cells of the other side. Others
pass through the gray matter to the anterior column cells of the same side,
figure 365. Besides this, they are connected through collaterals with the
intrinsic cells of the gray matter at different levels of the cord. One can
realize that each nerve root has, in this way, an effective grip upon a large
extent of the cord. This is seen well by studying figures 363 and 365.

The Peculiarities of Different Regions of the Spinal Cord.— The
outline of the gray matter and the relative proportion of the white matter
vary in different regions of the spinal cord, and it is, therefore, possible to
tell approximately from what region any given transverse section of the
spinal cord has been taken. The white matter increases in amount from
below upward. The amount of gray matter varies; it is greatest in the
cervical and lumbar enlargements, viz., at and about the 5th lumbar and the
6th cervical nerves, and least in the thoracic region. The greatest develop-
ment of gray matter corresponds with greatest number of nerve fibers pass-
ing from the cord.

In the cervical enlargement the gray matter occupies a large proportion of
the section, the gray commissure is short and thick, the anterior column is
blunt, while the posterior is somewhat tapering. The anterior and posterior
roots run some distance through the white matter before they reach the
periphery.

In the dorsal region the gray matter bears only a small proportion to the
white, and the posterior roots in particular run a long course through the
white matter before they leave the cord; the gray commissure is thinner and
narrower than in the cervical region.

In the lumbar enlargement the gray matter again bears a very large propor-
tion to the whole size of the transverse section, but its posterior columns are
shorter and blunter than they are in the cervical region. The gray commis-
sure is short and extremely narrow.

At the upper part of the conus medullaris, which is the portion of the cord
immediately below the lumbar enlargement, the gray substance occupies
nearly the whole of the transverse section, as it is invested only by a thin layer
of white substance. This thin layer is wanting in the neighborhood of the
posterior nerve roots. The gray commissure is relatively thick.

At the level of the fifth sacral vertebra the gray matter is again in excess, and
the central canal is enlarged, appearing T-shaped in section; while in the
upper portion of the filum terminate the gray is uniform in shape without any
central canal.

THE FUNCTIONS OF THE CORD.

The Reflex Arc and Reflex Action.— The spinal cord is morpho-
logically a segmental or metameric structure. This is shown both by its

552

THE NERVOUS SYSTEM

development and by its comparative anatomy. The pairs of nerves are
indicative of the component segments of the cord. The tracts of the cord are
in a sense connectives from segment to segment, connecting the cells of

FIG. 366. — Schematic Sketch of a Reflex Arc. A, With two neurones, an afferent and
an efferent; B, with three neurones, an afferent, efferent, and a connecting or intra-
central neurone.

both adjacent and of widely separated segments. The function of the cord

is comprised in the function of the segments and in the function of the tracts.

From a physiological point of view, it may almost be considered as an

axiom that before a nerve cell can send out a nerve impulse it must first

receive a stimulus of some kind.

mw.

P'iG. 367. — Showing the Arrange-
ment of a Simple Reflex Mechanism
Composed of a Motor and Sensory
Neurone, sg, Posterior spinal gan-
glion; s and sth, sensory root; m,
motor-nerve cell; mw, motor root.
(Kolliker.)

This stimulus usually consists of an afferent
impulse from the periphery. Its effect
upon the receiving cell may be insufficient
to cause any response, or the response may
be delayed for a long period and may in-
volve many complicated nervous activities
and even psychological processes. Where
the peripheral response is approximately
immediate, the reaction is known as a
reflex.

A reflex arc, reduced to its simplest
terms, consists of the following anatomical
elements: a, a sensory surface; ft, an affer-
ent neurone; c, an efferent neurone; d, a
muscle or gland. The simplest form of
reflex arc is schematically shown in figures
366 and 367.

The interlocking of fibers between
the termination of the afferent neurone
and the dendrite of the efferent neurone
shown in figure 366 is called a synapse.
The reflex arc is probably seldom as
simple as that shown in figure 367,
where only two neurones are involved.

THE REFLEX ARC AND REFLEX ACTION

553

More often, three or more neurones take part, as shown in figures 366 B,
and 368.

The neurone connecting the afferent neurone with the efferent neurone
belongs to the class of intracentral or connecting neurones. Since all parts
of the cord, in fact of the entire cerebro-spinal axis, are directly or indirectly
associated with one another by central neurones, figure 363, the possibility
of increasing the number of efferent limbs of the reflex arc can be readily
understood.

An involuntary physiological reaction in a tissue produced by efferent
nerve impulses which have been discharged from a nerve center under the
stimulus of a sensory or afferent nerve im-
pulse, is called a reflex act. Where the
nervous apparatus involved is of the type
represented in figures 366 and 367, the
activity is called a simple reflex. Most re-
flexes are more complex in character. The
afferent nerve impulse passes through more
than one simple channel in the cord, so that
in response to a sensory stimulus a series of
coordinated acts occurs in what may be
called a complex reflex.

The transmission of impulses within the
cord occurs over the pathways of least re-
sistance. Increasing a number of synapses,
or the number of neurone links in the chain
of conduction, increases the resistance so that

reflexes will occur most readily, other conditions being equal, where the small-
est number of neurones is involved, i.e., in the same segment of the cord in
which the sensory impulse enters, or in immediately adjacent segments. In
addition to the number of synapses in the reflex arc, certain strictly physio-
logical factors are of importance in determining reflex reaction; e.g., the in-
tensity of the exciting stimulus; the quality of the stimulus; the rapidity of
the recurrence of the stimulus; and the duration of its application. Thus,
a strong stimulus will bring about a reflex reaction sooner than a weak stimu-
lus of the same kind. A single weak stimulus which will cause no reflex may
do so if often enough arid rapidly enough repeated, the phenomenon of
summation of stimuli.

A reflex act once started may result in efferent impulses which continue
for some time after the exciting cause has been removed. The same phe-
nomenon is observed where groups of nerve cells are stimulated directly. It
has been found, by observing electrical changes in nerve fibers by means of
the capillary electrometer, that when their cells of origin are stimulated they
discharge impulses in a rhythmical manner.

FIG. 368. — Showing the Arrange-
ment of the reflex mechanism, with
a neurone intercalated between the
sensory and motor neurones.

554

THE NERVOUS SYSTEM

Usually, impulses are transmitted to a nerve cell only over its dendrite,
but it must be also assumed that such a conveyance of impulses may take

place over the collaterals of its axone near the
cell body, or the cell body may be stimulated
directly by the afferent neurone. The per-
ipheral fiber of the spinal ganglion cell.,
although it has the structure of an axone, may
be looked upon physiologically as a dendrite,
since homologues in lower vertebrates and
in man himself (nerve cells of the ganglion
of the cochlea of the auditory nerve) have
this structure, the nerve cell body being
situated near the sensory surface from which
impressions are received.

Irradiation of Impulses within the
Cord. — Taking as an example a frog whose
brain has been destroyed, a simple reflex may
be demonstrated by irritating the skin of one
foot with a weak stimulus. In response to
such a stimulus the foot is flexed upon the leg,
due to a contraction of the muscles of the
reflex arc corresponding to the sensory surface
irritated. If the strength or duration of the
stimulus be increased, other groups of muscles
are involved in the following order: i. Those
of the leg and thigh of the same side; 2,
homologous muscles of the opposite side; 3,
the arms of the same side and of the opposite
side.

The increasing complexity of the reflexes
aroused by stimulation of one and the same
sensory spot is not easy of explanation. We
know that there is almost an infinite number
of morphological paths in the cord, yet the
responses are orderly and observe a certain
sequence in their increasing complexity. The
reflexes have a mechanical definiteness which,
in a living structure, seems almost purposeful,
yet there is no conscious action in a frog
which has its brain destroyed.

The fact is that in the development of the

FIG. 369. — Scheme of Lower
Motor Neurone. The cell body,
protoplasmic processes, axone,
collaterals, and terminal arbor-
izations in muscle are all seen to
be parts of a single cell and
together constitute the neurone.
(Barker.) c, Cytoplasm of cell
body containing chromophilic
bodies, neurofibrils, and peri-
fibrillar substance; n, nucleus; n',
nucleolus; d, dendrites; ah, axone
hill free from chromophilic bodies;
ax, axone; sf, side fibril (col-
lateral); m, medullary sheath; nR,
node of Ranvier where side
branch is given off; si, neuri-
lemma and incisures of Schmidt;
m, striated muscle fiber; tel,
motor end plate.

nervous system certain physiological paths of slight resistance have been
established between the sensory areas and the muscles which move the parts

FUNCTIONS OF THE SPINAL NERVE ROOTS 555

for their protection. Apparently other physiological nerve pathways exist,
but it requires a stronger sensory stimulus to arouse nerve impulses along
these paths. In explanation we may suppose that the stronger afferent
impulses are sufficient to overcome the resistance of increasingly complex
paths, that they diffuse through greater and greater extents of the cord.
But we may repeat that in the normal state of the cord this diffusion is in an
orderly physiological sequence.

Orderly reflexes can be called forth only by stimulating sensory nerve
endings, the first of the essential structures of the reflex arc. If artificial
stimuli are applied to a nerve trunk, as the sciatic, unco-ordinated muscular
responses occur because the sensory stimuli are diffuse and general and are not
specific and local.

An involvement of multiple pathways may also be accomplished through
decreasing the resistance within the cord, as through the use of some drug
such as strychnine. In the strychninized frog a slight stimulus brings about
multiple and violent reflex spasms. These contractions have lost their order-
liness and are unco-ordinated. The entire musculature contracts. It is as
though the strychnine removed all differences in the facility with which
afferent stimuli spread through the cord, and that the resistance was re-
duced to the minimum. The strychnine effect is possibly due to a decrease
in the resistance at the synapses, and possibly also to an increase in the
irritability of the discharging nerve cells.

We must also suppose that the centers are particularly sensitive to certain
kinds of stimuli, sometimes producing very extensive and violent muscular
actions in response to a slight stimulus of a special kind. Such a condition
is illustrated in the violent and general muscular spasms occurring when a
small particle of food passes into the larynx, violent expiratory spasms
accompanied by contractions of other muscles taking place.

The time taken in a reflex action for the eye in man has been fpund to be
0.066 to 0.058 of a second, but this estimate includes the entire time from
the instant of stimulation to the beginning of the contraction of the muscle.

Functions of the Spinal Nerve Roots. — The anterior spinal nerve
roots are efferent in function and the posterior are afferent. The fact is
proved in various ways. Division of the anterior roots of one or more nerves
is followed by complete loss of motion in the parts supplied by the fibers of
such roots, but the sensation of the parts remains perfect. Division of the
posterior roots destroys the sensibility of the parts supplied by their fibers,
while the power of motion continues unimpaired. Moreover, stimulation of
the ends of the distal portions of the divided anterior roots of a nerve excites
muscular movements. There are sometimes slight evidences of sensory im-
pulses due to recurrent fibers that are distributed through the anterior root
to the spinal meninges. Stimulation of the proximal ends of the anterior
roots, which are still in connection with the cord, is followed by no appreciable

556 THE NERVOUS SYSTEM

effect. It must be remembered, however, that in the anterior or efferent
nerves other fibers besides motor are contained, e.g., vaso-motor, secretory,
heat fibers, and when the distal end of a divided nerve is stimulated, the
effects are exercised not only upon muscles, but upon glands, blood vessels,
etc. Stimulation of the distal portions of the divided posterior roots, on the
other hand, produces no muscular movements and no manifestations of
pain; for, as already stated, sensory nerves convey impressions only toward
the nerve centers. Stimulation of the proximal portions of these roots elicits
signs of intense pain. Muscular movements also ensue; but these are the
result of the reflex stimulation of the motor neurones of the anterior horn
of the cord or are movements in response to the afferent impulses passing
to higher centers from the roots stimulated.

Functions of the Ganglia on Posterior Roots. — The cells of the posterior
ganglia act as centers for the nutrition of the nerve fibers given off from them.
When these are cut, the parts of the nerves so severed degenerate, while the
parts which remain in connection with the cells of the ganglia do not. Thus
on section of the posterior nerve root beyond the ganglia the peripheral part
degenerates and the central does not, and on section of the root between
the ganglion and the cord the central part degenerates and the peripheral is
unaffected. The number of nerve cells in the spinal ganglia far exceeds
the number of nerve fibers in the corresponding root (Hardesty). The extra
cells, see figure 417, serve at least in part as association neurones connecting
the bipolar cells of the ganglion, cells of Dogiel, and to connect the ganglion
with the sympathetic system of nerves.

Spinal Reflexes in Man and Mammals. — Much of our knowledge of
the reflexes of the cord is derived from experiments on dogs, though paral-
ysis of the lower extremities in man, by accident or otherwise, has given con-
firmatory information. In man the spinal cord is so much under the control
of the higher nerve centers that its own individual functions in relation to re-
flex action are apt to be overlooked. But if the skin of the foot is stimulated,
in a man whose lumbar cord is completely separated by injury or disease, the
foot will be drawn away from the stimulus; or, if the stimulus be strong
enough, the entire leg wrill be moved. In both cases the movement may be
orderly and well co-ordinated, and shows that the sensory stimulus has pro-
duced a co-ordinated reflex through the lumbar cord. The injured person
feels no sensation of pain nor of action, and the phenomenon is independent
of the higher nerve regions. The stimulus that is supplied to man must be
carefully graded, since when too intense it calls forth muscular spasms or
convulsive action.

When the cord of mammals is first cut, the shock is very great, and the
lower or isolated portion of the cord remains for a time quite non-irritable.
The vaso-motor and thermogenic centers are cut off from the periphery so
that there is great vascular dilatation and marked fall of temperature, the

SPINAL REFLEXES IN MAN AND MAMMALS

557

effects of which are likely to lead to death unless the operated animal is
carefully attended. But these effects are slowly recovered from, and man,
as well as the lower mammals, soon regains the vascular tone. The general
tonus of the muscular system, which is lost at first, is also regained.

In this partially recovered condition man, and such animals as the cat, the
dog, and the monkey, perform certain of the lower functions with a re-
markable degree of perfection. Of course these functions are under constant
co-ordinative regulation and control in the normal animal, but experiments

B

FIG. 370. — Scheme of the Relation of the Posterior Root Fibers upon Entering the
Cord. A, The branch of the dorsal root fibers upon entering cord; B, terminal arborization
about cell bodies of the cord; DR, axones of the dorsal root; B, their ascending and descend-
ing branches; C, collaterals. (After Cajal.)

and observation have shown that much of such activity really is a primary
function of the cord. Of these activities the following may be especially
mentioned: Muscular tonus, general reflexes, the special reflexes of mic-
turition, defecation, erection and the sexual reflex, and parturition, some
of which will be briefly discussed.

The Center of the Tone of Muscles. — The tonic influence of the spinal cord
on the sphincter ani and sphincter urethrae will be presently mentioned. The
cord maintains these muscles in permanent tonic contraction. The condition
of the sphincters, however, is not altogether exceptional. Their contraction

558 THE NERVOUS SYSTEM

is the same in kind, though it exceeds in degree, that condition of the voluntary
muscles which has been called tone, a condition of slight contraction which
they always maintain during health. This tone of all the muscles of the
trunk and limbs depends on the spinal cord, just as does the contraction of
the sphincters. If an animal be killed by injury or removal of the brain,
the muscles retain their tenseness, but if the spinal cord be destroyed, all the
muscles become loose, flabby, and atonic, remaining so till rigor mortis
commences.

If an animal, such as the dog, be held off the ground in the erect position
assumed by the human body, when the trunk and hind limb muscles are not
in voluntary contraction the limbs will assume a normal pendular position.
In the pendular position the legs of a dog with cord severed hang more limp
and are more completely extended. The muscles of the former exhibit that
tone which keeps antagonistic muscles always slightly tense, the muscles of
the latter have lost the tenseness.

Whether or not muscular tone is maintained through the constant sub-
minimal action of sensory nerve impulses on the tonic centers of the cord, or
whether these centers are automatic in their action, is a question that can be
answered only by inference. The probability is that tone is a reflex activity,
though it may be contributed to by the normal healthy nutritional condition
of the muscles themselves — a condition which is itself dependent on the
trophic influence of the nerve cells of the cord and brain stem.

The Ano-spinal or Defecation Center. — The mode of action of the ano-
spinal center appears to be this: The mucous membrane of the rectum is
stimulated by the presence of feces or of gas in the large bowel. The stim-
ulus passes up by the afferent nerves of the hemorrhoidal and inferior mesen-
teric plexuses to the center situated in the lumbar enlargement of the cord,
and is reflected through the pudendal plexus to the anal sphincter, and to the
muscular tissue in the wall of the lower bowel. In this way there is produced
a relaxation of the first and a contraction of the second, and expulsion of the
contents of the bowel follows. The center in the spinal cord is partially
under the control of the will, so that its action may be either inhibited or
augmented. The action may be helped by the abdominal muscles, which
are voluntary muscles, but are also stimulated to contract by reflex action.

The Vesico-spinal or Micturition Center. — The vesico-spinal center acts
.in a very similar way to that of the ano- spinal. The center is also in the
lumbar enlargement of the cord. It is stimulated to action reflexly by the
presence of urine in the bladder. The action may be voluntary and is excited
by the sensation of distention of the bladder by the urine. The sensory fibers
concerned are the posterior roots of the lower sacral nerves. The action of
the spinal center is double, or it may be supposed that the center consists of
two parts, one of which is usually in action and maintains the tone of the
sphincter, and the other which causes contraction of the bladder and other

SPINAL REFLEXES IN MAN AND MAMMALS 559

muscles. When evacuation of the bladder occurs sensory impulses pass to
that part of the center which discharges impulses to the bladder and to cer-
tain accessory muscles which cause their contraction; and impulses pass to
that part of the center which inhibits the tonic action on the sphincter ure-
thras which procures its relaxation. The way having been opened by the
relaxation of the sphincter, the urine is expelled by the combined action of
the bladder and accessory muscles. The cerebrum may exert its influence
on the reflex not only by stimulating the center to action, but also by inhibit-
ing its action.

The Genito-spinal Center. — The presence of the genito-spinal center is
proven by the fact that dogs, and even man, are known to discharge semen
when the lumbar cord is severed and all voluntary motion and sensibility are
lost. The center situated in the lumbar enlargement of the spinal cord is
stimulated to action by sensory impressions from the glans penis. Efferent
impulses from the center excite the successive and co-ordinate contractions of
the muscular fibers of the vasa deferentia and vesiculae seminales and of the
accelerator urinae and other muscles of the urethra; and a forcible expulsion
of semen takes place, which, in cases of paraplegia, are not felt.

The Erectal Center. — This center is also situated in the lumbar region and
is a vascular center, already described in the chapter on Circulation. It
is reflexly excited to action by the sensory nerves of the penis, and also in the
normal animal by impulses passing down from the cerebrum. Efferent
impulses produce dilatation of the vessels of the penis.

The Parturition Center. — The center for the expulsion of the contents of
the uterus in parturition is situated in the lumbar spinal cord rather higher
up than the other centers already enumerated. The stimulation of the
uterus may, under certain conditions, excite the center to send out impulses
which produce a contraction of the uterine walls and expulsion of the con-
tents of the cavity. The center is independent of the will since delivery
takes place in paraplegic women, and also while a patient is under the influ-
ence of chloroform. Again, as in the cases of defecation and micturition, the
abdominal and thoracic muscles assist; their action being for the most part
reflex and involuntary.

Inhibition of Reflex Actions. — Movements such as are produced by stimu-
lating the skin of the lower extremities in the human subject, after division
or disorganization of a part of the spinal cord, do not always occur when the
cerebrum is active and the connection between the cord and the brain is in-
tact. The reflex which would occur in the animal with spinal cord only is
suppressed or inhibited in the normal animal through the regulative action of
the higher cerebral centers. When one is anxiously thinking, even slight
stimuli may produce involuntary and reflex movements. So, also, during
sleep, such reflex movements may be observed, when the skin is touched or
tickled; for example, when one touches the palm of the hand of a sleeping

560 THE NERVOUS SYSTEM

child, the impression on the skin of the palm producing a reflex movement of
the muscles which close the hand. But when the individual is awake no
such reflex is produced.

Further, many reflex actions are capable of being more or less controlled
or even altogether prevented by the will, of which the following may be
quoted as familiar examples:

When the foot is tickled we can, by an effort of will, prevent the reflex
action of jerking it awray. So, too, the involuntary closing of the eyes and
starting back, when a blow is aimed at the head, can be similarly restrained.
Darwin has mentioned an interesting example of the way in which such an
instinctive reflex act may override the strongest effort of the will. He placed
his face close against the glass of the cobra's cage in the Reptile House at
the Zoological Gardens, and, though of course thoroughly convinced of his
perfect security, could not by any effort of the will prevent himself from
starting back when the snake struck with fury at the glass.

It can be readily shown, by comparing a spinal frog and a normal unin-
jured frog, that stimuli which call forth definite reflexes in the one often pro-
duce no movement of the other.

Cutaneous and Muscle Reflexes as Diagnostic Signs.— In the hu-
man subject two classes of reflex actions dependent upon the spinal cord are
usually distinguished, the alterations of which, either of increase or of diminu-
tion, are indications of some abnormality, and are used as a means of diag-
nosis in nervous and other disorders. They are termed, respectively, cutane-
ous reflexes and muscle reflexes. Cutaneous reflexes are set up by a gentle
stimulus applied to the skin. The subjacent muscle or muscles contract in
response. Although these cutaneous reflex actions may be demonstrated
almost anywhere, yet certain of such actions as being most characteristic are
distinguished, e.g., plantar reflex, gluteal reflex, i.e., a contraction of the
gluteus maximus when the skin over it is stimulated; cremaster reflex, re-
traction of the testicle when the skin of the inside of the thigh is stimulated,
and the like. The ocular reflexes, too, are important. They are contraction
of the iris on exposure to light, and its dilatation on stimulating the skin of
the cervical region. All of these cutaneous reflexes are true reflex actions.
They differ in different individuals, and are more easily elicited in the young.

Muscle reflexes or tendon reflexes consist of a contraction of a muscle
under conditions of more or less tension, when its tendon is sharply tapped.
The so-called patellar- tendon reflex " knee-jerk" is the best known of this
variety of reflexes. If one knee be slightly flexed, as by crossing it over the
other, so that the quadriceps femoris is extended to a moderate degree, and
the tendon of the patella be tapped with the fingers, the muscle contracts and
the foot is jerked forward. Another variety of the same phenomenon is seen
if the foot is flexed so as to stretch the calf muscles, and the tendo Achillis is
tapped; the foot is extended by the contraction of the stretched muscles. It

CONDUCTION IN THE SPINAL CORD

appears, however, that the tendon reflexes are not exactly what their name
implies. The interval between the tap and the contraction is said to be too
short for the production of a true reflex action. It is suggested that the con-
traction is caused by local stimulation of the muscle, but that this would not
occur unless the muscle had previously been stimulated by the tension applied,
and placed in a condition of excessive irritability. It is probable that the
condition on which it depends is a reflex change
in the spinal irritability acting on the muscle or
exaggerated muscular tone, which is admitted
to be a reflex phenomenon in the spinal cord.

Conduction in the Spinal Cord. — With
the differentiation of the central nerve axis in
vertebrates the conduction in the spinal cord
becomes of increasing importance, reaching its
maximum in man. It is evident that the
cord is the path by which all nerve impulses
arising in the trunk or in the arms and legs
must reach the brain, or vice versa. Impulses
of peripheral origin can and do produce re-
flexes, but they can arouse sensations and be
perceived only after they have been conducted
to the cerebral cortex. Motor impulses arising
in the brain can reach the motor cells of the
anterior columns of the cord only through the
cord as a conducting path. The continuity of
the cord, therefore, while not necessary for the
execution of reflexes, is absolutely necessary
for the higher co-ordinations of the reflexes
and for the excitation and controlling influence
of the brain.

Illustrations of this are furnished by various
examples of paralysis, but by none better than
by the common paraplegia, or loss of sensation

and voluntary motion in the lowrer part of the body, in consequence of
destructive disease or injury of a section including the whole thickness of
the spinal cord. Such lesions destroy the communication between the brain
and all parts of the spinal cord below the seat of injury, and consequently
cut off from their connection with the brain the various organs supplied
with nerves issuing from those parts of the cord.

It is not probable that the conduction of motor and of sensory impulses is

effected under ordinary circumstances, to so great an extent as was formerly

supposed, through the gray substance of the cord, i.e., from cell to cell

through the short filaments lying wholly within the gray substance. But

36

FIG. 371. — Diagram to Show
the Manner in which the Fibers
of the Posterior Nerve Roots
Enter and Ascend the Posterior
Columns of the Cord. (Edinger.)

562 THE NERVOUS SYSTEM

cells with fibers running for short distances in the ground bundles are
numerous, and these short connectives are capable of conducting impulses
along the cord. All parts of the cord are not alike able to conduct all im-
pressions; and as there are separate nerve fibers for motor and for sensory
impressions, so in the cord separate and determinate tracts serve to conduct
always the same kind of impressions. The sensations of touch, and perhaps
of temperature and pain, do not appear to have such sharply limited tracts
as do the motor impulses.

Experimental and other observations point to the following conclusions
regarding the conduction of sensory and motor impressions through the
spinal cord. Many of these conclusions must, however, be received with
considerable reserve.

Sensory Impulses. — The sensory impressions of touch, pain, heat and
cold, and of the muscle sense are conducted to the spinal cord by the posterior
nerve roots. Certain sensory impressions are then carried directly into the
fasciculus gracilis on the same side, and thence up to the nucleus of this
column in the medulla. It is mainly the impulses of the muscle sense and
of the sense of touch that take this course through the cord, though the
sense of touch is not wholly interrupted upon injury to the posterior columns.
In lower animals it is scarcely interfered with at all. The posterior funiculi
unquestionably are the primary muscle sensory paths. Visceral sensations
are carried by the posterior root fibers to the cells of the column of Clarke
in the posterior horn, figure 363. From there the impulses pass to the direct
cerebellar tract on the same side, and thence up through the medulla to the
cerebellum, figure 388. The impressions of pain, and of heat and cold, are
conveyed to the nerve cells in the posterior cornua of the same side in part,
and in part to the nerve cells in the posterior cornu and median gray matter
of the apposite side. From this point, the impulses are taken up again by
intermediary neurones and conveyed through the anterior and lateral columns
of the cord to the brain in the ascending superficial antero-lateral tract, or
tract of Gowers. By reason of the great number of collaterals and the
interpolation in the course of the sensory path of many intermediary neu-
rones, it has been difficult to make out very sharply defined tracts in the
spinal cord for the conduction of the sensations of temperature, pain, and
touch. If one set of fibers is destroyed by disease, others seem able, through
the collaterals, to take up its functions. We can say that injury to the
lateral columns has resulted in loss of the sense of pain, heat, and cold, but
with only partial disturbance of touch sensations.

It is probable, also, that pain and temperature sensations cross over at
once to a considerable extent and pass up in the opposite side of the cord to
which they enter. Touch and the muscle sense impressions, especially the
latter, pass up largely upon the same side until they reach the medulla or
cerebellum.

MOTOR IMPULSES 563

Motor Impulses. — Motor impulses are conveyed downward from the
cerebral cortex of the brain along the pyramidal tracts, viz., the lateral
and the anterior, chiefly the former. In the lateral pyramidal tract the
impressions pass down chiefly on the side opposite to which they originate,
having crossed over in the decussation in the medulla. But some motor
impulses do not cross in the medulla, but descend in the anterior pyramidal
tract to lower levels of the cord, where they cross in the anterior commissure.
The motor fibers for the legs partially pass downward in the lateral columns
of the same side without decussation. This is also probably the case with
the bilateral muscles, i.e., muscles of the two sides that act together, such
as the intercostal muscles and other muscles of the trunk.

It is quite certain, as was just now pointed out, that the fibers of the an-
terior nerve roots are more numerous than the fibers proceeding downward
from the brain in the pyramidal tracts, the so-called pyramidal fibers. This
is because each pyramidal fiber is really a very long nerve process or axone,
and is supplied in its course with a large number of collaterals. These go off
at different points, and thus put it in relation with different groups of nerve
cells in the anterior columns at various levels. Each nerve fiber of the
pyramidal tract, by means of its collaterals, can control a number of nerve
cells, and can thus co-ordinate the action of impulses sent out through the
anterior roots to a number of groups of muscles. In other words, the gray
matter of the anterior columns contains an apparatus with various com-
plicated co-ordinating powers, which apparatus is under the regulative
control of the neurones whose cells of origin are in the cortex of the cerebrum.
This is the same apparatus that is also reflexly influenced by sensory im-
pressions passing to the cord from the periphery.

Division of a single anterior pyramid of the medulla at a point just above
the decussation is followed by paralysis of voluntary motions in the muscles of
the opposite side in all parts below. Disease or division of any part of the
cerebro-spinal axis below the seat of decussation of the pyramids is followed
by impairment or loss of voluntary motion on the same side of the body.
The paralysis is never quite complete, and the opposite side usually shows
some slight impairment of function of the muscle.

When one-half of the spinal cord is cut through in monkeys, the results
are as follows (Mott): Motor paralysis of the muscles of the same side
(never complete paralysis of the muscles used in bilateral associated action),
followed by gradual recovery of muscular movement, except of the finer
movements of the hand and foot; wasting and flabbiness of the muscles;
partial sensory paralysis of the same side (temperature, touch, pain, and
pressure) ; temporary vaso-motor paralysis on the same side. The tempera-
ture of the affected side is depressed i to 3° F.

564

THE NERVOUS SYSTEM

III. THE BRAIN.

General Arrangement of Parts of the Brain.— The great relative and
absolute size of the cerebral hemispheres in the adult man and in mammals
to a great extent mask the real arrangement of the several parts of the brain.
An examination of the accompanying diagram, figures 370, 371, reveals that
the parts of the brain are disposed in a linear series, as follows (from before
backward): Olfactory lobes, cerebral hemispheres, thalamencephalon
(thalami and third ventricle), the mid-brain (corpora quadrigemina and
crura cerebri, medulla oblongata, and cerebellum.

FIG. 372. — Diagrammatic Horizontal Section of the Vertebrate Brain. The figures
serve both for this and the next diagram. Mb, mid-brain; what lies in front of this is the
fore-, and what lies behind the hind-brain; Lt, lamina terminalis; Olf, olfactory lobes;
Hemp, hemispheres; Th. E, thalamencephalon; Pn, pineal gland; Py, pituitary body;
F. M., foramen of Munro; cs, corpus striatum; Th, optic thalamus, CC; crura cerebri; the
mass lying above the canal represents the corpora quadrigemina; Cb, cerebellum; I-IX, the
nine pairs of cranial nerves; i, olfactory ventricle; 2, lateral ventricle; 3, third ventricle; 4,
fourth ventricle; +, iter a tertio ad quartum ventriculum. (Huxley.)

The linear arrangement of parts actually occurs in an early stage of the
development of the human fetus, and it is permanent in some of the lower
vertebrata. In fishes the cerebral hemispheres are represented by a pair
of ganglia intervening between the olfactory and the optic lobes, and con-
siderably smaller than the latter, their adult development is fairly well repre-
sented by the figure 373. In Amphibia the cerebral lobes are further
developed, and are larger than any of the other ganglia.

GENERAL ARRANGEMENT OF PARTS OF THE BRAIN

565

In reptiles and birds the cerebral ganglia attain a still further development
and in Mammalia the cerebral hemispheres exceed in weight all the rest of the
brain. As we ascend the scale, the relative size of the cerebrum increases, till

FIG. 373. — Longitudinal and Vertical Diagrammatic Section of a Vertebrate Brain.
Letters as before. Lamina terminalis is represented by the strong black line joining Pn
and Py. (Huxley.)

FIG. 374. — Base of the Brain, i, Superior longitudinal fissure; 2, 2', 2", anterior
cerebral lobe; 3, fissure of Sylvius, between anterior and 4, 4', 4", middle cerebral lobe;
5, 5', posterior lobe; 6, medulla oblongata. The figure is in the right anterior pyramid; 7,
8, 9, 10, the cerebellum; +, the inferior vermiform process. The figures from 7. to IX.
are placed against the corresponding cerebral nerves; 777. is placed on the right crus cerebri.
VI. and F77. on the pons Varolii; X., the first cervical or suboccipital nerve. (Allen
Thomson.) X £.

in the higher apes and man the hemispheres, which commenced as two little
lateral buds from the anterior cerebral vesicle, having grown upward and
backward, completely covering in and hiding from view practically all the

566 THE NERVOUS SYSTEM

rest of the brain. At the same time the smooth surface of the cerebral
cortex of many lower mammalia, such as the rabbit, is replaced by the laby-
rinth of convolutions of the human brain.

When the cerebral hemispheres are removed, several large basal masses
of nerve substance are revealed: the optic thalami, the corpora quadrigemina,
and the cms cerebri. These structures, together with the pons and the me-
dulla, form a direct continuation forward of the spinal cord and sometimes
are designated under the general term of the brain stem.

FIG. 375. — Plan in Outline of the Brain as seen from the Right Side. X £. The parts
are represented as separated from one another somewhat more than natural, so as to show
their connections. A, Cerebrum; /, g, h, its anterior, middle, and posterior lobes; e,
fissure of Sylvius; B, cerebellum; C, pons Varolii; D, medulla oblongata; a, peduncles of the
cerebrum; b, c, d, superior, middle, and inferior peduncles of the cerebellum. (From
Quain.)

The human brain on superficial examination does not seem to follow the
general plan outlined above, but when the cerebral hemispheres and the
cerebellum are removed then it is found that what remains closely follows
the plan presented. This central axis is shown in part in figure 379.

The morphological parts of the brain usually given are:

The Brain or Encephalon.

I. The hind-brain or rhombencephalon.

1. Myelencephalon.

a. Bulb or medulla oblongata.

2. Metencephalon.

b. Pons Varolii.

c. Cerebellum.

ANATOMICAL STRUCTURE 567

II. Mid-brain or mesencephalon.

d. Corpora quadrigemina.

e. Crura cerebri.

III. Fore-brain, prosencephalon.

3. Thalamencephalon.

f. Optic thalami.

4. Telencephalon.

g. Corpora geniculata.
h. Corpora striata.

i. Cerebral hemispheres.

THE MEDULLA OBLONGATA AND PONS.
STRUCTURE.

Anatomical Structure. — The medulla oblongata is continuous with
the spinal cord at the upper end. It lies within the cranial cavity and forms
the first part of the brain stem. The medulla consists of masses of nerve
cells situated in the interior, but pretty generally distributed throughout
the mass. The cell-masses are subdivided by laminae of nerve fibers into
groups, or nuclei, which give origin to or form the terminations of the various
ranks of nerve fibers.

The nerve fibers are arranged partly in columns and partly in fasciculi
traversing the central cellular matter. The medulla oblongata is larger than
any part of the spinal cord. Its columns are pyriform, enlarging as they pro-
ceed toward the upper part of the brain, and are continuous with funiculi
of the spinal cord. Each half of the medulla, therefore, may be divided
into three columns or tracts of fibers, continuous with the three columns of
funiculi or of the spinal cord. The columns are more prominent than those
of the spinal cord, and are separated from each other by deeper grooves.
The anterior, continuous with the anterior columns of the cord, are called
the pyramids. The postero-median and external are represented at the
posterior or dorsal aspect of the cord as the fasciculus gracilis and the fascic-
ulus cuneatus. The posterior pyramids of the medulla, which include these
two columns of white matter, soon become much increased in width by the
addition of a new column of white matter outside the other two, which is
known as the fasciculus of Rolando. In the upper portion of the medulla the
fasciculi are replaced by the restiform bodies (the inferior peduncles of the
cerebellum). The lateral columns of the cord are scarcely represented as
such in the bulb.

It may be said then that the bulb at its commencement differs only slightly
in size from the cord, with which it is continuous. It soon becomes larger
both laterally and antero-posteriorly. It opens out on the dorsal surface into

568

THE NERVOUS SYSTEM

a space which is known as the fourth ventrical, and from being a cylinder
with a central canal it is flattened out on the dorsal surface by the gradual
approach of the central canal to that surface, where it is directly continuous
with the fourth ventricle.

On the anterior or ventral surface of the bulb it is found that the anterior
fissure is occupied at the most posterior part by fibers which are crossing
from one side to the other. This is known as the decussation of the pyramids.
It is formed of the lateral pyramidal fibers. The lateral pyramidal fibers of

FIG. 376.

FIG. 377-

FIG. 376. — Ventral or Anterior Surface of the Pons Varolii and Medulla Oblongata.
a, a, Anterior pyramids; b, their decussation; c, c, olivary bodies; d, d, restiform bodies; e,
arciform fibers;/, fibers passing from the anterior column of the cord to the cerebellum; g,
anterior column of the spinal cord; h} lateral column; p, pons Varolii; i, its upper fibers;
5, 5, roots of the fifth pair of nerves.

FIG. 377. — Dorsal or Posterior Surface of the Pons Varolii, Corpora Quadrigemina,
and Medulla Oblongata. The peduncles of the cerebellum are cut short at the side,
a, a, the upper pair of corpora quadrigemina; b, b, the lower;/,/, superior peduncles of the
cerebellum; c, eminence connected with the nucleus of the hypoglossal nerve; e, that of the
glosso-pharyngeal nerve; i, that of the vagus nerve; d, d, funiculus cuneatus; p, p, funiculus
gracilis; v, v, groove in the middle of the fourth ventricle, ending below in the calamus
scriptorius; 7, 7, roots of the auditory nerves.

either side after crossing the middle line become part of the pyramid of the
opposite side; the rest of the pyramid is made up of the fibers which in the
anterior column of the cord are known as the direct or anterior pyramidal
tract. The pyramidal fibers are those which degenerate after lesions of the
parts of the cerebrum known as the motor areas of the cortex. They are
the descending fibers of communication between the cerebral motor cells
of the cortex and the different segments of the spinal cord. The outer bor-
ders of the anterior pyramids of the bulb are marked by the exit from that
part of the nervous axis of the twelfth o hrypoglossal nerve. Still more later-

ANATOMICAL STRUCTURE

569

ally there is on either side a rounded elevation or column, the olivary body.
It begins at a level a little lower than the opening of the fourth ventricle. On
the dorsal side of the olivary body is the line of origin of the eleventh, tenth,
and ninth nerves, and from this to the posterior fissure is the region corre-
sponding to the lateral and posterior columns of the cord.

The changes in structure which are noticed in a series of sections of the
bulb from below upward may be summarized: In the dorsal or posterior re-
gion, the posterior columns are pushed more to each side by the large number
of sensory fibers ascending in the posterior funiculus and terminating in the

Optic chiasrna
Optic tract

Corpus geniculatum
extern urn

Corpus geniculatuin

internum

Locus perforatus

posticus

Middle peduncle
cft^e cerebellum

Restiform body

Oli

Pyramid

Anterior superficial,
arcnate fibi-es

Decussation of.
pyramids

Optic nerve

Infundibulum

•Tuber cinereum
orpora mamaaillaria
culo-motor nerve (III.)

Trochlear nerve (IV.)
winding round the crus
cerebri

Trigeminal nerve (V.)

Abducent nerve (VI.)
Facial nerve (VII.)
Auditory nerve (VIII.)

Vago-glossopharyngeal
nerve (IX. and X.)

Hypoglossal
nerve (XII.)

Spinal accessory
nerve (XI.)

First cervical nerve

FIG. 378. — Front View of the Medulla, Pons, and Mesencephalon of a Full-term Human

Fetus. (Cunningham.)

gracile and cuneate nuclei. The substance of Rolando is increased and be-
comes rounded, reaching almost to the surface of the bulb on each side, only
a small tract of longitudinal fibers of the root of the fifth nerve intervening.
There is a great increase of the reticular formation around the central canal.
Then at the ventral or anterior aspect the decussation of the pyramids begins.
By this crossing over of the fibers, the tip of the gray anterior cornu is cut off
from the rest of the gray matter. The central canal is pushed farther toward
the posterior surface, first of all by the decussation of the anterior pyramids
just mentioned, and later on, i.e., above, by another decussation of more
dorsal fibers. These fibers of the second decussation as they cross form a
median raphe and also help to break up the remaining gray matter into what
is called a reticular formation. These fibers arise from the nuclei of the funic-

57°

THE NERVOUS SYSTEM

TRACTS THROUGH THE MEDULLA

571

ulus gracilis and funiculus cuneatus of either side, and they are looked upon
as a sensory decussation.

The olivary bodies extend forward almost to the level of the pons. They
consist of both cells and fibers. The cellular matter consists of a plicated
thinnish layer of small nerve cells, folded upon itself in the form of a loop,
with the ends turned inward and slightly dorsal, figure 381, O. The gray
loop is filled with and covered by white fibers.

Internal to the olivary body on either side are two small masses of gray
matter, one more ventral to the other, called accessory olives, external and

't.C

n.c'

a.m.f.

FIG. 380. — Anterior or Dorsal Section of the Medulla Oblongata in the Region of
the Superior Pyramidal Decussation. a.m.f., Anterior median fissure; f,a., superficial
arciform fibers emerging from the fissure; py, pyramid; n.ar., nuclei of arciform fibers; /.a.,
deep arciform becoming superficial; o, lower end of olivary nucleus; n.L, nucleus lateralis;
f.r., formatio reticularis;/.a.2, arciform fibers proceeding from the formatio reticularis;
g., substantia gelatinosa of Rolando; a.V., ascending root of fifth nerve; n.c., nucleus
cuneatus; n.c.', external cuneate nucleus; n.g., nucleus gracilis; f.g., funiculus gracilis;
p.m.f., posterior median fissure; c.c., central canal surrounded by gray matter, in which
are n.XI., nucleus of the spinal accessory, and n.XII., nucleus of the hypoglossai; s.d.,
superior pyramidal decussation. (Modified from Schwalbe.)

internal, and on the surface of the anterior pyramid on either side a small
mass of gray matter, external arcuate nucleus; laterally another mass of the
same material, the representative of the lateral nucleus of the cord, is seen,
viz., the antero-lateral nucleus, which gives origin to the spinal accessory
nerve.

It will be necessary to follow as shortly as possible the fibers of the spinal
cord upward into the bulb and beyond.

Tracts Through the Medulla.— The crossed and direct pyramidal tracts
have already been described. Nothing definite is known of the antero-lateral
descending tracts. The direct cerebellar tracts pass laterally into the resti-

572 THE NERVOUS SYSTEM

form bodies and go to the cerebellum. The antero-lateral-ascending
tracts (Gowers) appear to have the same destination, but pass indirectly into
the cerebellum by way of the superior medullary velum; some of the fibers
probably pass upward to higher centers. The fibers of the tracts of Goll
and Burdach, of the cord, end in the nuclei of the funiculus gracilis and funic-
ulus cuneatus, respectively; at any rate, ascending degeneration of these
columns cannot be traced above these nuclei. The rest of the fibers of the
cord appear to end in the reticular formation of the bulb.

n.c.

***

FIG. 381. — Section of the Medulla Oblongata at about the Middle of the Olivary Body.
f.l.a., Anterior median fissure; n.ar., nucleus arciformis; p., pyramid; XII., bundle of
hypoglassal nerve emerging from the surface; at b, it is seen coursing between the pyramid
and the olivary nucleus, o.; f.a.e., external arciform fibers; «./., nucleus lateralis; a.,
arciform fibers passing toward restiform body, partly through the substantia gelatinosa,
g., partly superficial to the ascending root of the fifth nerve, a,V.; X., bundle of vagus root
emerging; _/>., formatio reticularis; c.r., corpus restiforme, beginning to be formed, chiefly
by arciform fibers, superficial and deep; n.c., nucleus cuneatus; n.g., nucleus gracilis; /,
attachment of the ligula;/.5., funiculus solitarius; n.X., Xn..', two parts of the vagus nucleus;
n. XII. , hypoglossal nucleus; n.t., nucleus of the funiculus teres; n.am., nucleus ambiguus;
r., raphe; A., continuation of the anterior column of cord; o',o", accessory olivary nucleus;
P.O., pedunculus olivae. (Modified from Schwalbe.)

Connections of the Bulb with the Cerebrum and Cerebellum. — The

pyramidal tracts connect the bulb with the cerebrum; and the direct cere-
bellar and the antero-lateral ascending tract, tract of Gowers, connect it with
the cerebellum. Other connections of the bulb with the cerebrum and with
the cerebellum are:

i. Fibers from the nucleus gracilis and nucleus cuneatus, which, as we
have said, are the endings of the fibers of the tracts of Goll and Burdach
of the cord, pass in sets in the following manner:

a. Internal arcuate fibers pass down and inward to the opposite side in
the reticular formation, composing in part the superior 01 sensory decussation,

FUNCTIONS OF THE MEDULLA 573

and in the inter-olivary region enter the mesial fillet, which passes upward
through the pons to end about the cells in the mid-brain and in the optic
thalami. These fibers are probably augmented by the addition of fibers
from the anterior columns of the cord, and by fibers arising from cells in the
sensory nuclei of the cranial nerves ending in the bulb.

b. External arcuate fibers, after decussating in the same way, pass out-
ward superficially over the anterior pyramid and olivary body, reaching the
restiform body and passing to the side of the cerebellum opposite to their
nuclei of origin. These fibers appear to be interrupted, at least in part, in
the external arcuate nuclei. They connect one side of the spinal cord with
the opposite side of the cerebellum through the gracile and cuneate nuclei.

c. Direct lateral fibers pass to the restiform body and so to the same side
of the cerebellum.

2. Fibers from the olivary body pass to the opposite side of the cerebellum
through the reticular formation and restiform body.

3. Fibers from the vestibular nucleus of the eighth or auditory nerve in
the floor of the fourth ventricle pass to the same side of the cerebellum.

FUNCTIONS OF THE MEDULLA.

The medulla is of great importance in the physiological economy of
the body. Its functions can be classified in three groups. First should be
given the function of conduction between the cord and the higher centers
of the brain. Second, the medulla is a center of numerous reflex activities,
especially those regulating the vital functions of the body, such as respiration,
circulation, and the like. A third function of centers in the medulla is that
of automatic activity.

The Medulla as a Conducting Path. — The medulla is the pathway
of all ascending and descending nerve impulses between the spinal cord and
most of the peripheral sensory and motor apparatus on the one hand, and the
cerebellum and the cerebral centers on the other. These conducting paths
are described in the tracts -that have already been discussed at some length.
They are represented graphically in the diagrams, figures 379, 382, and 388.

Reflex Centers of the Medulla. — The larger number of the cranial
nerves, as we shall presently see, take their origin from the medulla and
pons. Some of these nerves have both sensory an^ motor roots, while
others are either exclusively motor or sensory. A large percentage of the
afferent or sensory impulses that enter the medulla produce reflex effects
on the motor nuclei so richly represented in the medulla. The nuclei, or
centers, regulating some of the most important functions of the body are
among those in this group. When certain of these centers are interfered
with, death follows.

Life may continue when the spinal cord is cut away in successive portions

574

THE NERVOUS SYSTEM

from below upward as high as the point of origin of the phrenic nerves. In
amphibia, the brain has been all removed from above, and the cord removed
as far as the medulla oblongata from below; yet so long as the medulla oblon-
gata was left intact, respiration and life were maintained. But if the medulla
oblongata is wounded, particularly if it is wounded in its central part oppo-
site the origin of the vagi, the respiratory movements cease, and the animal

FIG. 382. — Diagram of Ascending Conduction Paths from the Cord through the Medulla
and the Thalamus to the Cerebral Cortex. (Cunningham.)

dies from asphyxiation. This effect ensues even when all parts of the
nervous system except the medulla oblongata are left intact.

Injury and disease in men are accompanied by the same nerve disturb-
ances as are exhibited by these experiments on animals. Numerous in-
stances are recorded in which injury to the medulla oblongata has produced
instantaneous death; and, indeed, it is through injury to it, or of the part of
the cord connecting it with the origin of the phrenic nerves, that death is
commonly produced in fractures attended by sudden displacement of the
upper cervical vertebrae.

REFLEX CENTERS OF THE MEDULLA 575

The majority of the medullary centers are reflex centers simply, and are
stimulated by afferent or by voluntary impulses. Some of them are auto-
matic centers and are capable of sending out efferent impulses without pre-
vious stimulation by afferent or by voluntary impulses. The automatic
centers are, however, normally influenced by reflex or by voluntary
impulses.

Some of these reflex centers which are bilateral are: i. Centers for the
movements of deglutition. The medulla oblongata contains in the motor
nuclei of the ninth and tenth nerves the centers whence are derived the motor
impulses enabling the muscles of the palate, pharynx, and esophagus to pro-
duce the successive co-ordinated and adapted movements necessary to the
act of deglutition, page 339. This is proved by the persistence of the act of
swallowing in some of the lower animals after destruction of the cerebral
hemispheres and cerebellum; its existence in anencephalous monsters; and
by the complete arrest of the power of swallowing when the medulla
oblongata is injured in experiments.

2. Centers for the combined muscular movements of sucking, the nerves
concerned being the facial for the lips and mouth, the hypoglossal for the
tongue, and the inferior maxillary division of the fifth for the muscles of the
jaw.

3. Centers for the secretion of saliva, which have been already mentioned,
page 330.

4. Centers for vomiting, page 356.

5. Centers for coughing, which is a reflex act quite independent of the
respiratory act.

6. Centers for the dilatation of the pupil, the fibers from which pass out
through the spinal cord in the two upper dorsal nerves into the cervical
sympathetic.

7. The respiratory center of the medulla has already been discussed as
regards its automatic action. It is only necessary to repeat here that
although it is automatic in its action, being capable of direct discharge of
respiratory impulses with no other stimulus than the condition of the blood
circulating within it, yet it is constantly reflexly influenced by afferent im-
pulses. The respiratory center has been proven to be bilateral. It also
consists of an inspiratory part and of an expiratory part. The center is
influenced by voluntary impulses, but one cannot voluntarily control this
center to the point of death. The vagus influence is probably the most
constant of those stimulating the respiratory center. But the respiratory
reflexes are going on constantly in response to afferent impulses flowing
into the medulla from numerous other sensory nerves over the entire body.

8. The Cardio-inhibitory Centers. — The medulla contains the centers
which maintain the proper rhythm of the heart, these centers acting through
the vagus fibers. These terminate in a local intrinsic mechanism which has

5/6 THE NERVOUS SYSTEM

been already discussed. It is claimed that the center can be stimulated
directly, as by the condition of the blood circulating within it. It is con-
stantly exerting a tonic influence over the heart, which is the chief reason for
considering it an automatic center. But the cardio-inhibitory center is
primarily a reflex center. Sensory or afferent impulses arriving over the
sensory paths in the vagus itself, by abdominal paths through the sympa-
thetic, and through cutaneous nerves, are constantly causing reflex discharges
of inhibitory impulses from this center.

9. Accelerator centers for the heart are present in the medulla. They
are reflexly stimulated by sensory impulses arising from the same general
source as in the preceding center.

10. Vaso-motor centers which control the unstriped muscle of the arteries,
are also situated in the medulla. The nerve cells constituting the center
are under the constant influence of nerve impulses flowing in from the sensory
and motor structures throughout the whole body. The reflexes produced by
the afferent impulses bring about the variations in vaso-motor tone that not
only regulate the general vascular responses of the body, but control and co-
ordinate the local changes in the size of the blood vessels.

11. Centers for the secretion of sweat exist in the medulla. The medul-
lary centers control the subsidiary spinal sweat centers. They may be
excited unequally so as to produce unilateral sweating.

The reflex medullary centers described above are comparable to the spinal
reflex centers previously described. If the medulla were completely isolated
from the higher cerebral centers, and the spinal cord removed with the ex-
ception of those paths which are necessary to maintain respiration, these
medullary reflex centers would be able to co-ordinate afferent impulses in the
same general way that isolated segments of the cord do. In the living body,
however, the medullary centers are under the influence of changes going on
in regions of the nervous system both above and below, changes which con-
stantly influence the details of the reactions. The activities are unconscious
reflexes in the same sense that the motor reflexes of the spinal cord are un-
conscious and machine-like. The main difference is one of complexity and
not of kind.

The Pons Varolii. — The pons Varolii is generally spoken of as a great
commissure of fibers; of fibers which connect the two halves of the cerebellum
and which connect the bulb and spinal cord with the cerebellum. It must not
be forgotten that the pons contains several smaller collections of nerve cells.
Sections reveal the following parts or structures, beginning with the anterior
or ventral surface.

i. Transverse or commissural fibers connect one side of the cerebellum
with the other through the middle peduncle. These fibers connect the cere-
bellar cortex with the cells of the pontine nuclei; some are afferent, some
efferent; some end in the gray matter of the pons on the same side near the

THE PONS VAROLII

577

ventral surface; others cross to the opposite side of the pons and then become
longitudinal, passing on to the tegmentum.

2. Fibers longitudinal in direction are arranged in larger or smaller bun-
dles and are separated by gray matter. Most of these fibers are pyramidal
fibers which pass down to the pyramids of the medulla.

3. The dorsal portion of the pons is made up to a considerable extent of
the reticular formation of the tegmental region together with one or two
distinct bundles of longitudinal fibers. The chief longitudinal bundle,
situated at the junction of the ventral two-thirds with the dorsal third, is the

FIG. 383. — Scheme to show the connections of the Posterior Longitudinal Bundle.
(Cunningham, modified from Held.)

fillet, including a, the larger mesial fillet, a sensory tract previously described
arising in the gracile and cuneate nuclei, and b, the lateral fillet, an auditory
tract, see figure 414. The second, the posterior longitudinal bundle, is situated
on each side of the mid-line, just internal to the mesial fillet. Some of the
connections of the posterior longitudinal bundle are shown in figure 383.

4. In the upper part of the pons there is a mass of gray matter containing
pigment, the locus ceruleus; and in the back part a second mass of gray matter,
the superior olive, which is connected with the auditory conduction path,
figure 414.
37

578

THE NERVOUS SYSTEM

IV. THE CEREBELLUM.

The cerebellum is a large division of the brain, located just beneath the
cerebrum and behind the medulla and pons. It is connected with the rest
of the brain by three peduncles on each side: the superior, the middle, and the
inferior peduncle, figure 384.

The cerebellum is composed of white and gray matter, the latter being
external as in the cerebrum, and, like it, infolded so that a larger area may be
contained in a given space. The convolutions of the gray matter, however,

FIG. 384. — Cerebellum in Section and Fourth Ventricle, with the Neighboring Parts.
I, Median groove of fourth ventricle, ending below in the calamus scriptorius, with the
longitudinal eminences formed by the fasciculi teretes, one on each side; 2, the same groove,
at the place where the white streaks of the auditory nerve emerge from it to cross the floor
of the ventricle; 3, inferior crus or peduncle of the cerebellum, formed by the restiform
body; 4, posterior pyramid; above this is the calamus scriptorius; 5, superior crus of
cerebellum, or processus e cerebello ad cerebrum (or ad testes); 6, 6, fillet to the side of the
crura cerebri; 7, 7, lateral grooves of the crura cerebri; 8, corpora quadrigemina. (From
Sappey, after Hirschfeld and Leveille.)

are arranged after a different pattern, as shown in figure 385. Besides the
gray substance on the surface, there is, near the center of the white substance
of each hemisphere, a small capsule of gray matter called the corpus dentatum,
figure 385, resembling very closely the corpus dentatum of the olivary body of
the medulla oblongata.

If a section be taken through the gray matter of the cerebellum, it will be
found to be composed of two layers, an outer, or molecular, and an inner, or
granular, layer. Each of these layers contains a large number of peculiar-
shaped nerve cells and very rich plexuses of nerve fibers. Recent studies
of the cortex of the cerebellum by modern methods have revealed a most
complex and beautiful arrangement of the parts.

THE GENERAL STRUCTURE OF THE CEREBELLUM 579

The General Structure of the Cerebellum. — The molecular layer
of the cerebellum contains several peculiar types of nerve cells, of which may
be specially mentioned Purkinje's cells and the basket cells. The cells of
Purkinje lie along the internal margin of the molecular layer, being, in fact,
practically at the boundary of the molecular and granular layers. They
measure 40 to 60 JJL in diameter, and have large, round nuclei. Each cell
gives off an enormous number of branching dendrites, which run up toward
the surface of the cerebellum in the shape of a bush.

The cells of Purkinje give off at their deeper surface an axone which
runs down into the white matter of the cerebellum. Recurrent collaterals
occur.

FIG. 385. — Outline Sketch of a Section of the Cerebellum, Showing the Corpus
Dentatum. The section has been carried through the left lateral part of the pons, so as to
divide the superior peduncle and pass nearly through the middle of the left cerebellar
hemisphere. The olivary body has also been divided longitudinally so as to expose in
section its corpus dentatum. cr, Crus cerebri;/, fillet; q, corpora quadrigemina; sp, superior
peduncle of the cerebellum, divided; mp, middle peduncle or lateral part of the pons Varolii,
with fibers passing from it into the white stem; av, continuation of the white stem radiating
toward the arbor vitae of the folia; 0, olivary body with its corpus dentatum; p, anterior
pyramid. (Allen Thomson.)

Lying in the molecular layer, somewhat external to the Purkinje cells,
are the cells of the type known as basket cells. These cells have a number of
dendrites; they also send out an axone which runs parallel to the surface of
the cortex and gives off numerous collaterals in its course that form baskets
around the cell bodies of the Purkinje cells, figure 386, ZK.

The granular layer contains a large number of very small granule-like
cells that Golgi was the first to show are really nerve cells. They are only
about 5 fj. in diameter, and they have a number of short dendrites which end in
clubbed extremities. They give off a very slender axis-cylinder process or
axone which runs up into the superficial part of the molecular layer and
there divides in a T-shaped fashion, the fibers run parallel to the surface
of the convolution and pass in between the branches of the cells of Purkinje.

The white substance of the cerebellum consists of nerve fibers, which are

58o

THE NERVOUS SYSTEM

of three kinds: i. Descending fibers, that are made up of the axis-cylinders
of the cells of Purkinje, carrying impulses down from the cerebellar cortex.
2. Ascending fibers, which pass into the granular layer, and there end in a
number of very short, finely divided brushes of fibers presenting a mossy
appearance, so that these are known as the mossy fibers. These connect
with the granular cells of this layer. 3. Ascending fibers, which pass up

FIG. 386. — Transverse Section Through a Cerebellar Folium (after Kolliker). Treated
by the Golgi method. P, Axone of cell of Purkinje; F, moss fibers; K and K', fibers from
white core of folium ending in molecular layer in connection with the dendrites of the cells
of Purkinje; M, simple cell of the molecular layer; GR, granule cell; CR1, axones of granule
cells in molecular layer cut transversely; M', basket cells; ZK, basket work around the cells
of Purkinje; GL, neuroglia cell; N, axone of an association cell.

through the granular into the molecular layer and there break up into a fine
network which interlaces with the dendritic branches of the cells of Purkinje.

Paths through the Cerebellar Cortex. — It will be seen that the ar-
rangements for the transmission and diffusion of nerve impulses and for the co-
operation of different cells are extremely complicated and delicate. It is not
possible to indicate absolutely by any schema the course of fibers and the
course of impulses through the cerebellum, but approximately it is some-
what like that in the accompanying figure 387.

Impulses pass up along the ascending fibers to the granular cells' by way of
the direct cerebellar, the fibers of the gracile and of the cuneatus, from the

FUNCTIONS OF THE CEREBELLUM

58:

restiform body, etc. These cells, being stimulated, send the impulses by their
axis- cylinders to the molecular layer, and through their T-shaped divisions to
the dendrites of the cells of Purkinje. Thence an impulse is sent out by the
axis-cylinder process of this cell. Other ascending impulses are brought up
by those fibers which pass directly to the molecular layer and send their ter-
minals winding around the dendrites of the cells of Purkinje. Prob-
ably impulses pass up also through the ascending fibers which affect the
basket cells, and, through them and their basket-like terminals, the cells of
Purkinje. Purkinje cells send cerebellar motor fibers to the nucleus dentatus

molecular
layer

** ^»^
granule

granule

FIG. 387. — A, Afferent fiber to basket (stellate) cell; B, neuraxone of Purkinje cell; C,
afferent fiber to Purkinje cell; D, afferent (mossy) fiber to granule cell.

cerebelli and through the superior peduncles to the red nucleus and the
thalamus, and to the ventro-lateral descending tract of the cord, to end
about the anterior horn cells.

Functions of the Cerebellum. — With the exception of its middle
lobe, the cerebellum is itself insensible to irritation and may be all cut away
without eliciting signs of pain (Longet). Its removal or disorganization by
disease is also generally unaccompanied by loss or disorder of sensibility;
animals from which it is removed can smell, see, hear, and feel pain, to all
appearances, as perfectly as before (Flourens; Magendie). It cannot, there-
fore, be regarded as a principal organ of sensation. Yet if any of its crura
be touched, pain is indicated; and, if the restiform tracts of the medulla
oblongata be stimulated, the most acute suffering appears to be produced.

These phenomena may properly be ascribed to the activity of the cerebral
cortex, since the number of collaterals on the fibers that pass to cerebellar
tracts is very great, and impulses arising from their stimulation may reach
the sensorium by paths other than through the cerebellum.

582

THE NERVOUS SYSTEM

The experiments of Longet and many others agree in supporting the view
that no stimulation of the cerebellar cortex leads to localized muscular con-
tractions. In other words, there is no localization in the cerebellar cortex as
in the cerebrum, the cerebellum apparently acting as a whole. If the cere-
bellum be removed, as was done by Flourens and numerous later physiologists,
a very profound disturbance in motor functions occurs. With the removal

Cranial Nerve
Vestibular)

FIG.

>. — Scheme of Principal Ascending Cerebro-spinal (black) and Cerebellar (red)
Conduction Paths. (Modified from Hardesty in Morris' Anatomy.)

of the superficial layers of the cerebellum, in pigeons particularly, there is
increasing feebleness and lack of harmony of the muscles concerned in lo-
comotion. When the entire organ is cut away in pigeons they lose the power
of walking, flying, and of standing in the usual erect way. Their power of
preserving equilibrium is lost, the most characteristic feature. Birds do not
remain in a state of stupor, but attempt to carry out the usual muscular activi-

FUNCTIONS OF THE CEREBELLUM 583

ties. If a pigeon is laid on its back it cannot recover its erect position, though
it make motions to do so. If set on its feet it will fall to one side or the other,
and is not able to hold its head in the customary position. The endeavors of
the animal to maintain its balance are insecure and uncertain, resembling
the lack of muscular control of a drunken man.

Such an animal does not lose the power of perceiving sensations, nor of
making voluntary efforts, as it will endeavor to avoid the blow that is
threatened.

The experiments afford the same results when repeated on all classes of
animals; and from them and the others before referred to, Flourens inferred
that the cerebellum belongs neither to the sensory nor the intellectual ap-
paratus; and that it is not the source of voluntary movements, although it be-
longs to the motor apparatus, but is the organ for the co-ordination of the
voluntary movements, or for the excitement of the combined action of muscles.

Such evidence as can be obtained from cases of diseases of this organ
confirms the view taken by Flourens; and, on the whole, it gains support from
comparative anatomy — animals whose natural movements require most
frequent and exact combinations of muscular contractions being those whose
cerebella are most developed in proportion to the spinal cord.

We must remember, too, that the cerebellum is connected with the pos-
terior columns of the cord through the cuneate and gracile nuclei as well as
with the direct cerebellar tract, all of which probably convey to the middle
lobe muscular sensations. It is also connected with the auditory nerves and
bulb by the internal and external arcuate fibers; and with the tegmentum
through the red nuclei. Its connection with the efferent tracts from the
different cerebral lobes through the pons is also highly important. Move-
ments of the eyes also occur on direct stimulation of the middle lobe. It
seems, therefore, to be connected in some way with all of the chief sensory
impulses which have to do with the maintenance of the equilibrium, and is
generally included in the nervous apparatus which is supposed to govern
this function of our bodies.

Foville supposed that the cerebellum is the organ of muscular sense, i.e.,
the organ by which the mind acquires that knowledge of the actual state
and position of the muscles which is essential to the exercise of the will upon
them; and it must be admitted that all the facts just referred to are as well
explained on this hypothesis as on that of the cerebellum being the organ for
combining movements. A harmonious combination of muscular actions
must depend as much on the capability of appreciating the condition of the
muscles with regard to their tension, and to the force with which they are
contracting, as on the power which any special nerve center may possess of
exciting them to contraction. And it is because the power of such harmonious
movement would be equally lost, whether the injury to the cerebellum involved
injury to the seat of muscular sense or to the center for combining muscular
actions, that experiments on the subject afford no proof in one direction more
than the other.

584 THE NERVOUS SYSTEM

Forced Movements. — The influence of each half of the cerebellum
is directed to muscles on the opposite side of the body; and it would appear
that, for the right ordering of movements, the action of its two halves must be
always mutually balanced and adjusted. For if one of its crura, or if the
pons on either side of the middle line, be divided, so as to cut off from the
medulla oblongata and spinal cord the influence of one of the hemispheres
of the cerebellum, strangely disordered movements ensue — forced movements.
The animals fall down on the side opposite to that on which the crus cerebelli
has been divided, and then roll over continuously and repeatedly; the rotation
being always round the long axis of their bodies, and generally from the side
on which the injury has been inflicted. The rotations sometimes take place
with much rapidity; as often, according to Magendie, as sixty times in a min-
ute, and may last for several days. Similar movements have been observed
in men; as by Serres in a man in whom there was apoplectic effusion in the
right crus cerebelli; and by Belhomme in a woman in whom an exostosis
pressed on the left crus. They may, perhaps, be explained by assuming that
the division or injury of the crus cerebelli produces paralysis or imperfect and
disorderly movements of the muscles of the opposite side of the body. Such
movements cease when the other crus cerebelli is divided; but probably only
because the paralysis of the body is thus made almost complete. Other
varieties of forced movements have been observed, especially those named
"circus movement," when the animal operated upon moves round and round
in a circle; and again those in which the animal turns over and over in a series
of somersaults. Nearly all these movements may also result on section of
one or other of the following parts: viz., medulla, pons, cerebellum, corpora
quadrigemina, corpora striata, optic thalami, and even, it is said, of the
cerebral hemispheres. But these structures are parts that involve tracts
used in the co-ordination of complex muscular movements.

THE MID-BRAIN.

The mid-brain includes the crura cerebri and the corpora quadrigemina.

The Peduncles of the Cerebrum, or Crus Cerebri. — The crura
diverge from the anterior edge of the pons Varolii and pass upward on either
side toward the cerebral hemispheres. At their anterior termination each
of them appears to have upon its dorsal surface, to the inner and outer sides,
respectively, two large masses of gray matter which have been already spoken
of, viz., the optic thalamus and the corpus striatum. The crus is made up
of two principal parts. The crusta or 'pes is in the ventral position, and the
tegmentum in the dorsal position. The two are separated by the substantia
nigra.

The pes consists of longitudinal fibers which pass anteriorly between the
optic thalamus and the posterior part (lenticular nucleus) of the corpus stria-

THE PEDUNCLES OF THE CEREBRUM 585

turn. In this situation the fibers form a compact mass. This constitutes
the internal capsule, and that portion of it which forms the angle at which
the fibers are bent is called the genuoi the capsule. The internal capsule
spreads out dorsally in the corona radiata. The fibers thus have the form
of a fan bent upon itself as they rise to pass into the cerebral hemisphere.
The fibers of the internal capsule are connected with different districts of the
cerebral cortex. Briefly the connections are, a, the fronto-pontine fibers are
in the anterior limb of the capsule; b, the pyramidal fibers in the genu and
the anterior part of the posterior limb; c, the temporo-pontine fibers in the

FIG. 389. — Diagram of the Motor Tract as Shown in a Diagrammatic Horizontal
Section through the Cerebral Hemispheres, Crura, Pons, and Medulla. Fr., Frontal lobe;
Oc., occipital lobe; AF., ascending frontal, AP., ascending parietal convolutions; PCF.,
pre-central fissure, in front of the ascending frontal convolution; FR., fissure of Rolando;
IFF., inter-parietal fissure, a section of crus is lettered on the left side; SN., substantia
nigra; Py., pyramidal motor fiber which on the right is shown as continuous lines con-
verging to pass through the posterior limb of 1C., internal capsule (the knee or elbow of
which is shown thus), upward into the hemisphere and downward through the pons to
cross the medulla in the anterior pyramids. (Gowers.)

posterior part of the posterior limb. Fibers connecting the optic thalami
and corpora striata with the cerebral cortex also run in the capsule. The
pes, internal capsule, and the corona radiata form the great sensory and motor
highway to and from the cerebral cortex.

The tegmentum is the continuation anteriorly of the reticular formation of
the medulla. It ends for the most part in the neighborhood of the optic
thalamus and in the parts beneath. The tegmentum of either side is sup-
posed to be concerned chiefly with afferent impulses. It is made up to a very
considerable extent of collections of gray matter, the most important of which
are the substantia nigra, separating the pes and tegmentum, and the nucleus
ruber, which is a rounded mass situated near the aqueduct of Sylvius. The

586 THE NERVOUS SYSTEM

latter serves as a way-station in the cerebello-cerebral conduction paths and
also has important connections with the spinal cord. The locus niger ex-
tends back as far as the posterior corpus quadrigeminum. Posteriorly, the
tegmentum is chiefly reticular in structure.

Corpora Quadrigemina. — There are two corpora quadrigemina on each
side, the superior and inferior. They form prominences on the dorsal
surface of the mid-brain, dorsal to the aqueduct of Sylvius. The inferior
corpora quadrigemina receive through the lateral fillet fibers from the
cochlear division of the eighth nerve, figure 414. They are closely associated
with the median corpora geniculata, and, like these, give origin to fibers
which continue the auditory conduction path upward to the auditory center.
The superior corpus quadrigeminum receives fibers from the optic nerve,
the mesial fillet, and also from the occipital cortex, as will be more fully de-
scribed later. It is closely associated with the external corpus geniculatum.
The corpora geniculata also form reflex centers for the eye muscles in the
reflexes that result in the adjustments of the eye to vision at different dis-
tances. The nervous connections of these nuclei are discussed in presenting
the optic tract and the auditory tracts.

V. THE FORE -BRAIN.

The fore-brain or prosencephalon consists of two divisons, the thalamen-
cephalon or thalami, and the telencephalon, or corpora geniculata, corpora
striata, and the cerebral hemispheres. These subordinate divisions will be
discussed in order.

The Thalami. — The optic thalami are oval in shape, and rest upon the
crura cerebri. They form part of the floor of the lateral ventricles and their
inner sides bound the third ventricle. They are connected by a transverse
tract, the middle commissure.

Each thalamus has several collections of gray matter, forming somewhat
indistinctly defined masses separated by white fibers. These masses of gray
matter are known as the nuclei of the thalamus, which are six in number.
They are called the anterior nucleus, the median nucleus, the lateral nucleus,
the ventral nucleus, the pulvinar, and the posterior nucleus. The corpora
geniculata are also closely associated with the optic thalamus. The anterior
nucleus is composed of large nerve cells which receive the terminations of
axones of cells of the corpora mammillaria at the base of the brain (bundle
of Vicq d'Azyr). There they meet the fibers of the fornix, which establish
a relation between this tubercle of the thalamus and the hippocampal con-
volutions. The median nucleus is connected by its axones with the cortex
of the island of Reil and the second and third frontal convolutions. The
lateral nucleus is quite large and lies against the internal capsule, into which
it sends fibers. It is connected with the central convolutions of the cortex.

CORPORA GENICULATA 587

The ventral nucleus lies beneath the preceding; it is relatively small. It is
connected with the cortex of the frontal lobe and with the operculum, the
central convolutions, and the supramarginal gyrus. The fifth nucleus,
known as the pulvinar, forms the posterior tip of the thalamus, and is con-
nected with the optic tract, see figure 406. The posterior nucleus, lying just
below the pulvinar, is a small mass and is connected with the cortex of the
interior parietal convolution. The cells of the thalamus are thus seen to be
connected with a large area of the cerebral cortex. The axones spread out
in a great fan in the corona radiata, the thalamus sending more fibers to the
cortex than are received from it.

The collections of nerve cells in the thalamus are shown by anatomical
investigations and by methods of physiological degeneration to be on the
pathway of ascending or afferent nerve tracts. Large masses of sensory
fibers pass through the thalami, the majority of which form synapses about
the nerve cells in the thalamus. Even in those cases where there is no dis-
tinct ending of the nerve fiber, collaterals are given off which establish physio-
logical connection with the nuclei.

The thalamus is thus closely connected with large areas of the cortex.
It must at least form an important relay station in all those activities which
involve the conscious perception of sensory stimuli wherever they may
arise. Flechsig even claims that in the thalamus there are definite points
of sensory localization corresponding to every sensory point in the periphery
of the body (including the special senses). The thalamus also receives
fibers from various parts of the cerebral cortex, thus establishing a double
relation with this region.

Owing to the difficulty of those operations which establish isolation of the
thalamus, it is not clear to what extent reflex actions may take place through
its nuclei. It is probable, however, that extensive co-ordinations of afferent
impulses may be mediated by the nuclei of the thalami. Such activities as
walking, riding, writing, speaking, etc., are possibly co-ordinated reflexes
through the thalami, perhaps with the assistance of the medulla in the case
of walking.

Corpora Geniculata. — The corpora geniculata form prominences on
each side of the peduncles of the cerebrum just ventral to the anterior corpora
quadrigemina. There are two on each side, the external or outer, and median
or inner. The external corpus geniculatum is at the side of the crus and
appears to be a swelling on the lateral division of the optic tract and actually
receives terminations of the optic fibers, thus constituting a way-station in
the optic conduction paths. Similarly the median appears to be the ter-
mination of the median division of the optic tract, from which it receives
some fibers, figure 406, but it is more intimately connected with the auditory
tracts, forming a way-station between the lateral fillet and the auditory cor-
tical center, figure 414.

5 88 THE NERVOUS SYSTEM

Corpora Striata. — The corpora striata are situated in front and to
the outside of the thalami, partly within and partly without the lateral
ventricles.

Each corpus striatum consists of two parts: An intraventricular portion,
the caudate nucleus, which is conical in shape, with the base of the cone for-
ward (this consists chiefly of gray matter), and an extraventricular portion,
the lenticular nucleus, separated from the other portion by the internal cap-
sule. The lenticular nucleus is shown in a horizontal section of the hemi-
sphere to consist of three parts, the two internal called globus pallidus major
and minor, and the outer called the putamen.

The cells of the corpora striata are somewhat evenly distributed, and not
grouped in nuclei. Their axones pass for the most part into the internal
capsule. It is doubtful if these ganglia have any direct anatomical relations
with the cortex of the brain, but they are intimately connected by fibers to and
from the thalami, and are connected with the substantia nigra (Flechsig).
These nuclei are developed from the walls of the embryonic brain tube and
are probably therefore homologous with the areas of the cortex. Their lesion
is said to be accompanied by disturbance in muscular co-ordination. Lesion
of the left lenticular nucleus is said to cause some disturbance in the power of
speech, though this has not been observed in the case of the right nucleus.
Lesions of the corpora striata produce disturbances in heat regulation,
causing a rise of body temperature, the rise amounting to as much as 2° or 3°
C. in the rabbit. The rise of temperature in man after lesion of the corpus
striatum on one side is said to be chiefly on the opposite side of the body
(Kaiser).

VI. THE CEREBRUM.

That portion of the brain which is concerned with all intellectual functions
is the cerebrum or, more strictly speaking, the cerebral cortex. The cerebral
cortex is the seat of those activities which we describe as intelligence —
including states of consciousness, acts of idea formation and volition, and
the phenomenon of memory.

The cerebrum includes the cerebral cortex, the mass of fibers connecting
it with lower portions of the brain, the basal nuclei represented by the
corpora striata, the thalami, etc. The structure and function of these
basal nuclei have already been given briefly, so we may turn our attention
now to the cerebral cortex.

Structure of the Cerebral Cortex. — The cerebral cortex forms a large
part of the mass of the cerebrum, in fact of the whole brain. Its superficial
appearance presents a series of ridges and folds, the gyri and sulci. For gen-
eral convenience anatomists have divided the cerebral cortex into five lobes:
the frontal, that portion in front of the fissure of Rolando extending down

STRUCTURE OF THE CEREBRAL CORTEX

to the Sylvian fissure ; the parietal, extending from the Sylvian fissure to the
parieto-occipital fissure, and bounded below by the Sylvian fissure; the
temporal lobe, just ventral to the parietal; the central lobe, or island of

asctanfUf.

FIG. 390. — Left Hemisphere, from Without. (After Eberstaller.)

FIG. 391. — The Cerebrum, from Above. (After Eberstaller.)

Reil; and the occipital lobe, which includes the posterior portion of the
cortex behind the parieto-occipital fissure. And, finally, the olfactory and
limbic lobes together make up the olfactory division of the brain. For the

590

THE NERVOUS SYSTEM

detailed arrangements of the cortical gyri and sulci the reader is referred to
figures 390, 392 and to text-books of anatomy.

In a transverse section of the cerebral cortex there is shown an external
gray layer chiefly composed of nerve cells and an internal white portion of
nerve fibers. The folding of the cortex into convolutions increases the total
mass of gray matter enormously.

The gray or cellular external part of the cerebral cortex has an average
thickness of about 3 mm.; being thin in the occipital and frontal region,
2mm., and thick in the precentral, 4 mm., and postcentral convolutions.

Several types of nerve cells have been described as present in the cortex,
the exact type and relative proportion varying somewhat in different regions.

Solo.

FIG. 392. — Right Hemisphere, from Within. (After Eberstaller.)

The typical characteristic cell, however, is the pyramidal cell. The py-
ramidal cell, as its name implies, has a pear-shaped cell body with numerous
protoplasmic processes. The apex of the cell is directed toward the surface
of the cortex, and supports numerous branches which extend out into the
adjacent territory, bringing it into contact with a relatively large number of
nerve cells. These processes are dendritic in character. The base of the
pyramidal cell always has a single axis-cylinder process which is directed
down into the white matter, and which in some cases ultimately finds its
course through the corona radiata into the pyramids below. The axis-
cylinder processes give off collaterals both in the immediate neighborhood
of the cell and somewhat deeper along its course.

In the superficial layer of the cortex there is a peculiar type of small cell,
first described by Cajal. Most of these cells are fusiform in shape, with the
long axis parallel to the surface of the convolution. They give off usually two
axones which run along parallel to the surface and send down numerous
fine collaterals at right angles. Another form of Cajal cell, triangular or

STRUCTURE OF THE CEREBRAL CORTEX

591

quadrangular in shape, is also seen. Both forms have, as a rule, more than
one axone. Their collaterals pass in a horizontal direction, forming a
fine band of fibers, known as tangential -fibers. A third type of cell is the
fusiform or polymorphous. Some of these are strictly fusiform in shape and
lie with their axes parallel to the surface of the convolution. They give off
protoplasmic processes which pass down toward the white matter, some of

FIG. 393.

FIG. 394.

FIG. 393. — Typical Pyramidal Cell from the Human Cortex, a, Cell body; b, main
dendrites with gemmules; c, lateral dendrites; d, axone and collaterals. Only a small
part of the axone is shown. (Bailey.)

FIG. 394. — Showing the Stages in the Development of a Pyramidal Cell. (Ramon y

Cajal.)

them turning to run in a horizontal direction. The fusiform and poly-
morphous cells are grouped in the same layer.

Besides these cells we find scattered through the cortex a considerable
number of the neuroglia cells. The character and position of these are
shown in figure 395.

The general arrangement of the layers of the cortex is described very dif-
ferently by the various authors. It is not uniform in the different parts of the
brain. The simplest and most representative type, however, of the arrange-

592

THE NERVOUS SYSTEM

ment is that in which the cortex is divided into four layers. The outermost,
or superficial, known as the molecular layer, contains relatively few cells.
It is composed of neuroglia tissue, embedded in which are a number of cells
of the Cajal types, which have just been described. There are also in this
layer many neuroglia cells. In the superficial part of the layer of some areas

FIG. 395. — The Principal Constituent Elements of the Gray Cortical Layer of the Anterior
Cerebrum. (After Ramon y Cajal.)

of the cortex are many tangential fibers. The second layer is composed of
small pyramidal cells. In parts of the brain there are here interposed
what are known as the vertical fusiform cells. The third layer is composed
of large pyramidal cells, in which, however, one also sees many small py-
ramidal cells. The fourth layer is composed of the fusiform and polymorphous
cells, beneath which is the white substance. This arrangement is shown

WEIGHT OF THE BRAIN AND CORD 593

in the accompanying figures, 395 and 397. The gray matter of the brain
contains, however, not only these layers and cells, but an infinitely rich
mass of fibers, which can be shown to have a certain definite arrangement.
Some of the fibers are vertical, passing directly up to the most superficial
layers of cells; others have a horizontal direction, dividing the gray matter
into different layers. These layers of fibers have received different names.
A typical arrangement is shown in figure 398. The most conspicuous
fibers are those of certain large triangular or pyramidal cells.

The efferent or axone fibers from the cerebral cortex may be divided into
three classes: i, the projection fibers, which descend through the corona

FIG. 396. — Scheme of Descending Conduction Pathways from the Cerebrum to Lower

Nerve Centers.

radiata and internal capsule, to end in lower centers; 2, the commissural
fibers, which cross to the opposite cerebral hemisphere, chiefly through the
corpus callosum; 3, the association fibers, which pass in bundles beneath
the cortex, to end in other regions of the same hemisphere.

It is by means of projection fibers and collaterals that associations are
made with nerve cells in the thalamus, tegmentum, and pons, and through
the latter region with tracts going to the cerebellum.

Weight of the Brain and Cord.— The brain of an adult man weighs from 48
to 50 oz., about 1,550 grams, or about 2 per cent, of the body weight. It
exceeds in absolute weight that of all the lower animals except the elephant
and whale. Its weight, relatively to that of the body, is exceeded only by that
of a few small birds, and some of the smaller monkeys.

In the new-born child the brain (weighing 10 to 14 oz.) is about 10 per
cent, of the total body weight. At the age of 7 years the weight of the
brain already averages 40 oz., and about 14 years the brain not infrequently
38

594

THE NERVOUS SYSTEM

n

IV

. .Tangential fibers (Vic
d'Azyr's ribbon)

.Striae of Bechterew

. Superradiary network (of
the second and third layers)

. . Striae of Baillarger

. . Intermediary network (of
the third and fourth layers)

. .Meynert's intracortical asso-
ciation fibers

. . Subcortical association fibers

FIG. 397. FIG. 398.

FIG. 397. — Schematic Diagram of the Different Layers of the Cerebral Cortex. (After
Ramon y Cajal.) I, II, III, and IV, Layers of cortical cells. M, Molecular layer; pPy,
layer of small pyramidal cells; gPy, layer of large pyramidal cells; Pm, layer of poly-
morphous cells.

FIG. 398. — Schematic Diagram Showing the Arrangement of the Nerve Fibers in the
Cerebral Cortex. The dotted lines separate the four cellular layers of Cajal. Sb, White
substance.

WEIGHT OF THE BRAIN AND CORD

595

reaches the weight of 48 oz. Beyond the age of forty years the weight slowly
but steadily declines at the rate of about i oz. in 10 years.

The average weight of the female brain is less than the male ; and this dif-
ference persists from birth throughout life. The difference amounts to about
5 oz. Thus the average weight of an adult woman's brain is about 44 oz.

The brains of idiots are generally much below the average, some weighing
less than 16 oz. Still the facts at present collected do not warrant more than
a very general statement, to which there are numerous exceptions, that the
brain weight corresponds to some extent with the degree of intelligence.

C.b

FIG. 399. — Brain of the Orang, § Natural Size, Showing the Arrangement of the
Convolutions. Sy, Fissure of Sylvius; R, fissure of Rolando; EP, external perpendicular
fissure; Olf, olfactory lobe; Cb, cerebellum; PV, pons Varolii; MO, medulla oblongata.
As contrasted with the human brain, the frontal lobe is short and small relatively, the fissure
of Sylvius is oblique, the temporo-sphenoidal lobe very prominent, and the external per-
pendicular fissure very well marked. (Gratiolet.)

There can be little doubt that the complexity and depth of the convolutions,
which indicate the area of the gray matter of the cortex, correspond with the
degree of intelligence.

The spinal cord of man weighs from i to ij oz. ; its weight relatively to the
brain is about 1:40 in the adult. As we descend the animal scale, this ratio
constantly increases till in the mouse it is 1:4. In cold-blooded animals
the relation is reversed, the spinal cord is the heavier. In the newt, i : 105;
and in the lamprey, i : 133.

The most distinctive points in the human brain, as contrasted with that of
apes, are: i. The much greater size and weight of the whole brain. The brain
of a full-grown gorilla weighs only about 15 oz. (450 grms.), which is less than
one-third of the weight of the human adult male brain, and barely exceeds
that of the human infant at birth. 2. The much greater complexity of the
convolutions, especially the existence in the human brain of tertiary convolu-
tions in the sides of the fissures. 3. The greater relative size and complexity
and the blunted quadrangular contour of the frontal lobes in man, which are
relatively broader, longer, and higher than in apes. In apes the frontal lobes
project keel-like (rostrum) between the olfactory bulbs. 4. The much greater

596 THE NERVOUS SYSTEM

prominence of the temporo-sphenoidal lobes in apes. 5. The fissure of Sylvius
is nearly horizontal in man, while in apes it slants considerably upward. 6.
The distinctness of the fissure of Rolando.

Most of the above points are shown in the accompanying figure of the brain
of the orang.

GENERAL FUNCTIONS OF THE CEREBRUM.

Evidence regarding the physiology of the cerebral hemispheres has
been obtained, as in the case of other parts of the nervous system, from the
study of anatomy, from pathology, and from experiments on the lower ani-
mals. The chief evidences regarding the functions of the cerebral hemi-
spheres derived from these various sources are briefly these: i. Any severe
injury of them, such as a general concussion, or sudden pressure as by apo-
plexy, may instantly deprive a man of all power of manifesting externally
any mental faculty. 2. In the same general proportion as the higher mental
faculties are developed in the vertebrates and especially in man at different
ages, as well as in different individuals, the greater is the development of
the cerebral hemispheres in comparison with the rest of the cerebro-spinal
system. 3. No other part of the nervous system bears a corresponding
proportion to the development of the mental faculties. 4. Congenital and
other morbid defects of the cerebral hemisphere are, in general, accompanied
by corresponding deficiency in the range or power of the intellectual faculties
and the higher instincts. 5. Removal of the cerebral hemispheres in the
lower animals produces effects corresponding with what might be antici-
pated from the foregoing facts.

Effects of the Removal of the Cerebrum. — The removal of the cere-
brum in the lower animals appears to reduce them to the condition of a
mechanism without spontaneity.

In the case of the frog, when the cerebral lobes have been removed, the ani-
mal appears similarly deprived of all power of spontaneous movement. But
it sits up in a natural attitude and breathes quietly. When pricked it jumps
away. When thrown into the water it swims. When placed upon a board
it remains motionless, although, if the board be gradually tilted over till the
frog is on the point of losing his balance, he will crawl up till he regains his
equilibrium and comes to be perched quite on the edge of the board.

If the frog be turned on his back, he regains his normal position. If his
back is stroked gently he will utter the usual croaking sound. These activi-
ties are carried on by the normal frog. There is one striking difference,
however, between the brainless frog and the normal: the former, if placed
in a position and left undisturbed, will remain without moving for an
indefinite time. It has apparently lost the power to initiate movements.
Presumably any memory impressions or effects of former experiences have
been lost. Even the more elemental stimuli, which come from tissue

EFFECTS OF THE REMOVAL OF THE CEREBRUM 597

hunger and thirst, apparently do not affect the brainless frog. In other
words, the operation has reduced the animal to the condition of an autom-
aton capable of carrying on complex activities, but only upon receiving
some definite stimulus. This condition contrasts sharply with that resulting
from the removal of the entire brain, leaving only the spinal cord. In this
spinal cord frog only the simpler reflex actions can take place. The frog
does not breathe. It lies flat on the table instead of sitting up. When
thrown into a vessel of water it sinks to the bottom. When its legs are
pinched it kicks out, but does not leap away as in the normal.

If the cerebrum of the frog be removed, taking special care not to interfere
with the optic nerves or the thalami, then it acts somewhat differently.
Whereas with the entire cerebrum removed it makes no effort to take food, in
this instance it is said to attempt to catch flies or other insects, and will show
other signs of spontaneous activity. It will avoid an object and shows signs of
responding to visual sensations, such as the attempt to feed just mentioned.

The cerebral lobes of the frog, however, -are very low in the scale of de-
velopment as compared \vith other vertebrates. The cortex is a simple
layer of rather small cells, and the total volume of the cortex as compared
with other portions of the brain is small.

The case of the pigeon, which represents a higher animal in the scale,
has been extensively studied by Flourens and others. They have shown
that when the cerebrum is carefully removed, leaving the basal nuclei un-
disturbed, and the animal has recovered from the immediate effects of the
shock, it is able to carry on many co-ordinate activities. In the first place it
can stand or perch without difficulty. If placed on its back it immediately
regains its equilibrium. If tossed in the air it flies until it comes in contact
with a firm support. If disturbed on its perch it will walk away, showing
the power to co-ordinate not only wing muscles, but the leg muscles. If left
undisturbed, such a pigeon will occasionally make motions, i.e., open its
eyes, move its head, preen its feathers, or even take a step or two. It
spends most of its time, however, sitting quietly as though asleep. If aroused,
the animal shows little or no signs of excitement or fright.

After several months such pigeons are usually said to increase the motions
of spontaneity or take short flights, avoiding obstacles in the way and alight-
ing definitely on the perch. They will pick around among food for definite
articles, apparently attempting to select the food. Early after the operation
the pigeon will pick at objects indiscriminately, but does not take food un-
less it is placed in the mouth.

Apparently the main effect produced here is to diminish the complexity
and efficiency of those activities which we call spontaneous. The surprising
thing is that there is as little disturbance among the motor functions as is
found.

In mammals it is difficult to remove the cerebral hemispheres, but in those

THE NERVOUS SYSTEM

animals in which the operation has been carried out, as for example in the
rabbit and rat, a result very similar to those observed in the case of the frog
and pigeon has been obtained. The animal is able to maintain its equi-
librium, to run or jump, and in fact successfully carry out the most compli-
cated co-ordinated movements, but it is unable to originate them without stimu-
lation. In the case of the dog, it has been found impossible to remove the
whole brain at one operation. However, Goltz has succeeded in removing
both the cerebral hemispheres of the dog by doing the operation in successive
stages and taking extraordinary precautions to protect his animal against the
great fall of temperature and the immediate shock of the operation. He
kept his dog alive for some eighteen months and secured a complete recovery
from the series of operations. Goltz' s dog was able to walk about, it re-
sponded to a bright light by closing its eyes, and could be aroused by a sharp,
loud sound. It spent its time lying down in the cage, sleeping rolled up dog-
fashion. When aroused by stimulation of the skin, it would move away
from the stimulating object and would sometimes growl and snap at the
object. If it snapped at the object it would do so without going toward it or
making the usual effort to seize the object which we are accustomed to expect
of a normal vicious dog. This dog did not spontaneously feed itself, but
had to have food placed in its mouth before it would swallow'. But the
animal finally learned to take food, as in the case of the pigeon. This
animal gave very definite responses to its condition of nourishment; it
slept quietly and was peaceful when fully fed, but was restless and irritable
when hungry.

Goltz' s dog showed complete absence of those activities which we would
call psychic. That is to say, it showed no memory signs, it was unable
to learn the signal for feeding, it did not manifest any fondness or signs of
pleasure at the presence of its caretaker. In short, there was a complete
loss of memory and intelligence, and the animal, although performing some
activities, was in fact reduced to a mere automaton. It would be difficult to
imagine a more crucial experiment to elucidate the function of the cerebral
cortex.

It is quite evident that the apparatus for carrying out co-ordinated move-
ments in these animals is not localized either in the cerebrum or in the spinal
cord. It must therefore be connected in some way with the parts of the
brain below the cerebrum and above the cord. There is no reason why such
an arrangement may not be supposed to exist in the human brain, although
we must look upon the cerebrum as the originator of voluntary movements.

LOCALIZATION OF THE MOTOR FUNCTION OF THE CEREBRAL

CORTEX.

The experiments upon the brains of various animals by means of electrical
stimulation have demonstrated that there are definite regions of the cerebral

MOTOR FUNCTION OF THE CEREBRAL CORTEX

599

cortex the stimulation of which produces definite movements of co-ordinated
groups of muscles of the opposite side of the body. Fritsch and Hitzig were
the first to show that the cerebral cortex responds to electrical irritation.
They employed a weak constant current in their experiments, applying a

FIG. 400.

FIG. 401.

FIGS. 400 and 401. — Brain of Dog, Viewed from Above and in Profile. F, Frontal
fissure sometimes termed crucial sulcus, corresponding to the fissure of Rolando in man;
S, fissure of Sylvius, around which the four longitudinal convolutions are concentrically
arranged; i, flexion of head on the neck, in the median line; 2, fle.xion of head on the neck,
with rotation toward the side of the stimulus; 3, 4, flexion and extension of anterior limb;
5, 6, flexion and extension of posterior limb; 7, 8, 9, contraction of orbicularis oculi and the
facial muscles in general. The unshaded part is that exposed by opening the skull.
(Dalton.)

pair of fine electrodes not more than one-twelfth inch apart to different parts
of the cerebral cortex. The results thus obtained have been confirmed and
extended by Ferrier and many others, stimulating chiefly with induction
currents.

6OO THE NERVOUS SYSTEM

The fundamental phenomena observed in all these cases may be thus
epitomized:

i. Excitation of the same spot on the cortex is always followed by the
same movement in the same animal. 2. The area of excitability for any
given movement is extremely small, and admits of very accurate definition.
3. In different animals excitations of anatomically corresponding spots pro-
duce contractions in similar or corresponding muscles.

The various definite movements resulting from the electric stimulation
of circumscribed areas of the cerebral cortex are enumerated in the descrip-
tion of the accompanying figures of the dog's and monkey's brains.

In the case of the dog the results obtained are summed up as follows by
Hitzig: i. One portion, anterior, of the convexity of the cerebrum is motor;
another portion, posterior, is non-motor. 2. Electric stimulation of the
motor portion produces co-ordinated muscular contraction on the opposite
side of the body. 3. With very weak currents, the contractions produced
are distinctly limited to particular groups of muscles; with stronger currents
the stimulus is communicated to other muscles of the same or neighboring
parts. 4. The portions of the brain intervening between these motor centers
are inexcitable.

Following strong stimulation of cortical motor centers other groups of
muscles than those innervated by the centers stimulated may also take part in
the contractions.

According to the further researches of Schafer and Horsley, electrical
stimulation of the marginal convolution internally at the parts corresponding
with the ascending frontal and parietal convolutions, from the front back-
ward, produces movements of the arm, of the trunk, and of the leg.

A good deal of doubt was thrown upon the experiments of Ferrier by
Goltz and other observers, from the results of excising the so-called motor
areas of the dog's brain. It was found that the part might be sliced away or
washed away with a stream of water, but that no permanent paralysis ensued.

More extensive observations, however, have, in the main, confirmed
Ferrier' s original statement, at any rate \vith regard to the monkey's brain.
Destruction of the motor areas for the arm produces some permanent paraly-
sis of the arm of the opposite side, and similarly of that for the leg, paralysis
of the opposite leg. If both areas are destroyed, permanent hemiplegia
ensues. Paralysis of so extensive and permanent a character does not, how-
ever, appear the rule when the brain of a dog is used instead of that of the
monkey. It is suggested that in the animal lower in the scale the functions
which in the monkey are discharged by the cortical centers may be subserved
to a greater extent by the basal ganglia.

Motor Areas of the Human Brain. — It is naturally of great impor-
tance to discover how far the results of experiments upon the dog and monkey
hold good with regard to the human brain. Evidence furnished by diseased

MOTOR AREAS OF THE HUMAN BRAIN 6oi

conditions is not wanting to support the general idea of the existence of cor-
tical motor centers in the human brain, figure 402.

So far, however, it has been possible to localize motor functions only
in the precentral convolutions and the walls of the adjacent sulci.

The relative position of the centers is probably much the same as in the
monkey's brain, those for the leg above, those of the arm, face, lips, and
tongue from above downward. Destruction of these parts causes paralysis,
corresponding to the district affected, and irritation causes contractions of
the muscles of the same part. Again, a number of cases are on record in

ANUS A VAGINA

OPENING VOCAL

OFJAW CORDS

MASTICATION

FIG. 402.— Scheme Showing the Motor Areas of the Brain. (Adapted from Griinbaum
and Sherrington by Cunningham.)

which aphasia, or the loss of power of expressing ideas in words, has been
associated with disease of the posterior part of the lower or third frontal con-
volution on the left side. This condition is usually associated with motor
paralysis on the right side of the body, right hemiplegia.

This district of the brain, particularly the convolutions bounding the
fissure of Rolando anteriorly, is now generally known as the motor area.
There is now no doubt whatever that this area gives origin to the nerve fibers
which proceed to the spinal cord, and are there represented as the pyramidal
tracts.

This is the reason that movements are produced on stimulation of the
white matter after the superficial gray matter of the animal's brain has been
sliced off.

These motor fibers are those which arise from the pyramidal cells of the
cortex. From the motor area of the cortex they converge to the internal cap-

602

THE NERVOUS SYSTEM

sules, and pass down to the crus. In the internal capsule the fibers which
pass to the pyramidal tracts of the spinal cord occupy that part known as
the knee (genu) and the anterior two-thirds of the posterior limbs of the cap-
sule, figure 404. In this district the fibers for the face, arm, and leg are in
this relation: those for the face and tongue are just at the knee, and below or
behind them come first the fibers for the arm and then those for the leg.

CALIOSUM

TEMPORO-PONTINE
TRACT

LOBt

FIG. 403. — Diagram of Certain Connections of the Frontal, Temporal, and Occipital
Lobes. Founded on the observations of Flechsig, Ferrier, and Turner. (Cunningham.)

The more accurately known arrangements of these fibers in the monkey's
brain, named in order, from above down, are those for the eye, head, tongue,
mouth, shoulder, elbow, digits, abdomen, hip, knee, digits. These fibers
come for the most part from the portion of the cortex in front of the fissure of
Rolando, chiefly from the precentral gyrus, hence called the Rolandic area.
Those fibers, passing between the occipital lobe and the thalamus and
superior corpora quadrigemina, are concerned with vision, and are called
fibers of the optic radiation. In like manner, from the inferior corpora
quadrigemina and the internal geniculate bodies, fibers which make up the
auditory radiation pass to the auditory center in the superior temporal gyrus.

THE BODY SENSORY OR SOMESTHETIC AREA

603

It has already been shown that the motor fibers of the internal capsule of
one side cross over to the opposite side in the decussation of the pyramids in
the medulla. This decussation is not quite complete, as some fibers pass
down on the same side in the direct pyramidal tract. A small portion of
these direct fibers end around the motor neurones of the same side, but the
great majority cross to the opposite side in the anterior commissure at some
lower lever of the cord. It follows that the motor areas of the cortex on one

FIG. 404. — Diagram to Show the Relative Positions of the Several Motor Tracts in
Their Course from the Cortex to the Crus. The section through the convolution is vertical;
that through the internal capsule, 1C, horizontal; that through the crus again vertical.
CN, caudate nucleus; O TH, optic thalamus; Z,2 andZ-3, middle and outer part of lenticular
nucleus; f, a, I, face, arm, and leg fibers. The words in italics indicate corresponding
cortical centers. (Gowers.)

side control the muscular movements of the opposite side of the body, but
also to a slight extent those of the same side. As a matter of fact, disease in
the region of the fissure of Rolando is usually accompanied by a disturbance
of the motor function on the opposite side of the body, although there is
some slight motor disturbance on the same side.

LOCALIZATION OF SENSORY FUNCTION IN THE CEREBRAL

CORTEX.

There is evidence that fibers from the nerves of special sense are specially
connected with definite and distinct parts of the cerebral cortex.

The fibers from the sensory nerves, we have found, are connected with
the cerebral cortex by chains of neurones. These sensory paths, although
complex, are definite and distinct. Their cortical connections have been
mapped out with considerable definiteness.

The Body Sensory or Somesthetic Area.— The motor function around
the pre-Rolandic region for a long time obscured the fact that this region,

604

THE NERVOUS SYSTEM

especially the post-central convolution, is intimately connected with the
perception of general body sensations. Physiological and pathological ob-
servations supported this view, and recently Flechsig has much strengthened
the view by his method of studying the progressive development of the brain.
In figure 405 we produce Flechsig' s diagram showing the body sensory
area, aptly designated by Barker the somesthetic area. The borders of the
area are more or less indefinite and less distinct than the main portion.
This is indicated in the figure by the lighter shading. Lesions of this area
in the cortex lead to loss of sensibility in definite regions of the opposite
side of the body.

Visual or Optic Center. — The termination of the optic nerve in each
eye, the retina, to the structure of which we shall return when treating of the
eye, is so arranged that when we look at an object with both eyes, symmetrical
parts of the retinae are used. For example, if we examine an object to the

AESTHETIC

FIG. 405. — Diagrams to Show Flechsig's Sensory and Association Areas on the Surface of the
Cerebral Hemisphere. (From Cunningham, after Flechsig.)

left of the center of vision, an image of that object is focused upon the right
half of both retinae, viz., upon the temporal side of the right retina, and upon
the nasal side of the left retina. The optic nerve fibers of these symmetrical
parts of the retinae are gathered together behind where the optic nerves de-
cussate, viz., in the optic chiasma. The fibers which come from the right
side of both eyes are contained in the optic tract of the same side, viz., the
right, those from the right eye being outside of the others. In the same way
the left optic tract contains internally fibers from the left side of the right eye
and externally those from the left side of the left eye. The optic tract thus
formed then passes backward and terminates in three distinct nuclei, viz.,
the pulvinar of the thalamus, the anterior corpus quadrigeminum, and the
lateral corpus geniculatum. These nuclei atrophy if the eyes are removed
from an adult animal; and if the eyes are removed from a newly-born
animal, they do not fully develop. Through the superior corpora quadri-
gemina the optic tract establishes synapses that bring it into relation with the

OLFACTORY CENTER IN THE CORTEX 605

nucleus of the third nerve, and which form the basis of the eye reflexes to
light stimulation.

It appears that some of the fibers of the optic tract pass directly into the
cerebral cortex without joining with the thalamus, corpus quadrigeminum,
or corpus geniculatum.

It was shown above that the fibers of the cerebral cortex, known as the
optic radiation, pass from the occipital region to the three nuclei about
which we are speaking, viz., into the pulvinar of the thalamus, the
anterior corpus quadrigeminum, and lateral corpus geniculatum, and
it is known that when the occipital cortex is removed, these three
atrophy. It has been further shown that in a newly-born animal the
removal of such a region is followed by imperfect development of the parts
in question.

If one optic nerve be divided, blindness of the corresponding eye results;
but if one optic tract be divided there is a half blindness in both eyes, wrhich is
called hemianopsia, or hemiopia, right or left, according as the right or left
field of vision is cut off. It is also evident that the occipital lobe, figures 403,
406, and particularly the cuneus, is concerned as a visual center. Not only
is the occipital lobe connected with the optic nerves, as we have seen, but
the removal of the right occipital lobe in an animal (monkey) is followed by
bilateral hemiopia of the right retinae. Rremoval of the left occipital lobe is
followed by left bilateral hemiopia. Removal of both occipital lobes is fol-
lowed by total blindness. Clinical observations give convincing proof that
in man also the occipital lobes are the cortical centers of vision and that
the same relations hold between the optic lobes and the retinal fields as in
the monkey.

Olfactory Center in the Cortex. — The olfactory nerve differs from
the other cranial nerves. In reality it is a representative of the olfactory lobes
of other animals, which are part of the cerebrum. The olfactory lobe origi-
nates as an offshoot from the cerebral vesicle, the front part of which is de-
veloped into the bulb of the olfactory nerve, while the back part forms its
peduncle. The nerve, the cavity of which in man is filled up in the fully de-
veloped condition with neurogliar substance, lies upon the cribriform plate
of the ethmoid bone, and is contained in a groove on the under surface of
the frontal lobe. On examination of the lobe it is found to be thus made up:
Beneath the neurogliar layer is a layer of longitudinal fibers and a few-
nerve cells, next to this is a layer of small cells, nuclear layer, fibers from the
layer of nerve fibers passing through it.

The nuclear layer is also separated into groups of cells by an interlacing
of the fibers. The next layer is thick and is composed of neuroglia and nerve
fibers, some of which are medullated, as well as of cells more or less pyramidal
in shape. Below this layer is the layer of olfactory glomeruli. These glomer-
uli are small synapses of olfactory fibers. The larger also includes small

6o6

THE NERVOUS SYSTEM

cells and granular matter. A further description of the anatomy of these
parts is given later, page 643.

Fibers of the olfactory nerve proper are found below this layer, and pass
through the cribriform plate to be distributed to the olfactory mucous mem-
brane. They arise from cells in the olfactory mucous membrane, and end in
the glomeruli. The peduncle of the nerve or the olfactory tract, as it is some-

FIG. 406. — Scheme of the Central Connections of the Optic Fibers. (Cunningham.)

times called, is made up of longitudinal fibers originating in the bulb, with
neuroglia and some nerve cells.

The fibers of the olfactory tract have been traced into the nucleus amyg-
dalae and its juncture with the hippocampal gyrus in the temporal lobe,
figure 392. The hippocampus must be in some way connected with smell,
since a lesion of it, leaving the olfactory tract uninjured, seriously interferes
with that sense.

Taste Center of the Cortex. — It is very uncertain where the taste center
is situated, if such exist. It has been placed in the anterior portion of the
inferior temporal convolution, not far from that of smell, figure 405.

Auditory Center in the Cortex. — This center has been localized in

ASSOCIATION CENTERS OF THE CEREBRAL CORTEX 607

the superior temporal convolution. Experiments have been made which
connect auditory impulses on either side with the inferior corpus quadri-
geminum and the median corpus geniculatum, for when the internal ear is
destroyed there results atrophy 01 these bodies as well as of the lateral fillet
of the opposite side. On the other hand, destruction of the part of the tem-
poral lobe above indicated is similarly followed by atrophy of the nuclei of
the same side. These nuclei bear much the same relation to the sense of
hearing as do the superior corpora quadrigemina and the lateral corpora
geniculata to the sense of sight, figures 406 and 414.

ASSOCIATION CENTERS OF THE CEREBRAL CORTEX.

The theory of localization of the function of different parts of the cerebral
cortex has received substantial support from the study of the motor and the
sensory areas in man and the mammals. But when the exploration of the
cortex is complete and the motor and sensory areas are bounded as definitely
as may be, there still remain great areas in which stimulation is apparently
non-effective so far as our present means of interpretation reveal. Trau-
matic and pathological lesions produce no sensory or motor disturbances.
The areas of this class which are most extensive, i.e., which cover the greatest
amount of cortex, are three in number — the frontal lobe, the parietal lobe,
and a large part of the temporal lobe below the superior temporal convolution.

Flechsig has made a study of the development of the human brain, paying
especial attention to the progressive development of the great tracts of fibers.
He has shown that the tracts appear in a certain order of sequence, also that
the myelinization takes place progressively.

These observations give justification to the assumption that effective
functionization is attained with the acquirement of the myelin sheath. He
showed a close correspondence in time between the development of the
tracts and the manifestation of functions known to involve the tracts in
question. The great somesthetic area and its tracts are first to develop;
then tracts to the occipital or visual center, to the auditory and other sensory
centers, and, finally, to those great areas whose functions remain obscure.

Basing his deductions on the facts of development, on the isolated cases of
lesion and disease, and on the careful comparative studies of the brains of
certain men of unusual intellectual powers, whose personal characteristics
and intellectual genius are known, Flechsig has advanced the hypothesis
that the areas of the cortex not concerned directly with motor or sensory
functions are association areas.

The Association Centers of Flechsig. — The great association centers
are the frontal, parietal, and temporal, figure 405. These regions of the
cortex are apparently not directly connected with tracts of the brain stem
and cord, but they are richly connected with the areas that do have connec-

608 THE NERVOUS SYSTEM

tion with the cord. Short association fibers connect neighboring convolu-
tions within the centers, fibers which are chiefly the axones of the poly-
morphous cells of the fourth layer of the cortex. Long association fibers
run from one center to another, such as the cingulum, superior and inferior
longitudinal fasciculi, etc. The longer connectives run from association
to association centers, and from association to sensory and motor centers.
Flechsig believes that the sensory centers are not connected directly with
each other, but only indirectly through the association areas.

Cases of injury and of disease of the human brain in the association areas
are not numerous, but such as there are tend to confirm Flechsig's hypothesis
that the function of these areas is that of the higher psychic activity.

FIG. 407. — The Association Fibers in the Centrum Ovale. A, Between adjacent con-
volutions; B, between frontal and occipital lobes; C, between frontal and temporal lobes,
the cingulum; D, between temporal and frontal lobes — lesion of this tract causes paraphasia;
E, between occipital and temporal lobes — lesion of this tract causes word-blindness; C.N,
caudate nucleus; O.T, optic thalamus.

The Anterior or Frontal Association Center. — The frontal area is
more closely connected with the motor areas and the centers for the somes-
thetic sense. With injury to this area the individual shows weakness in at-
tention, in reflection, and in control over the expressions of anger, self-appre-
ciation, and other activities that are expressive of personal volitions and
emotions.

The American crowbar case is a classical instance of lesion of the frontal
lobe. A young man of twenty-five had an iron bar, an inch and a quarter
in diameter and over three feet long, driven through his skull and brain
by the premature explosion of a blast of powder. He not only recovered,
but lived for twelve years afterward. At the post-mortem examination the
puncture was found to be through the prefrontal lobe, anterior to the coro-
nal suture.

This man was considered a most efficient workman and foreman before
the injury. After his recovery he was fitful, impatient of restraint, capri-

THE CRANIAL NERVES 609

cious, obstinate. He was most inconsiderate of his associates, profane and
passionate. From a shrewd business man he was changed to the intellectual
level of a child and was regarded by his associates as mentally unbalanced.

A summary of fifty cases of pathological lesions of the prefrontal areas of
the human brain is given by Williamson. The mental traits of thirty-two are
summarized in the following terms: "A condition of mental decadence; a
dull mental state; loss of power of attention; loss of memory; loss of spon-
taneity; the patient takes no heed of his surroundings; sleeping during the
greater part of the day, or remaining semi-comatose." Yet these patients
are able to walk about and execute well co-ordinated muscular activities of
all kinds that do not involve complex intellectual activity.

The Parietal Association Center. — Special mention is made of this
association area because there is increasing evidence that it is the parietal
region of the brain, rather than the frontal, as popularly believed, that is
most intimately concerned with the higher acts and powers of imagination,
idealization, and reasoning. It is the region through which the individual
maintains his interests and relations with the external world as against his
own body. The parietal association center is more closely related to the
visual, auditory, and speech centers of the cortex. The great musician
Bach had an exceptionally well developed parietal region.

On the Cortical Centers in General. — For purposes of clearness in
presentation, the cortical centers have been discussed one by one, but the
reader is guarded against the thought that their activities are in any sense
isolated. A motor area does not usually act in the absence of sensory or af-
ferent stimulation in the actual living body, whether it may do so on occa-
sion or not. Neither do sensory impressions arising in the peripheral sense
organ make their way over definite tracts to the brain and cortex and arouse
sensations alone. Sensations do not occur independent of motor activities
on the one hand, and of intellectual acts through the association centers on
the other.

The association centers are the highest co-ordinating regions of the nervous
system. They are to the sensory and motor centers what these latter are to
the reflex centers of the cord. The difference is one of degree and not of
kind. Further, the association centers are probably set into activity by the
complex of inflowing or afferent impulses in just the same sense that the
spinal reflex centers are set in activity by sensory or afferent stimuli; the
condition is, of course, a thousand times more complex.

THE CRANIAL NERVES.

The cranial nerves consist of twelve pairs; they appear to arise (super-
ficial origin) from the base of the brain in a bilateral series, which extends
from the under surface of the anterior part of the cerebrum to the lower end

39

6lO THE NERVOUS SYSTEM

of the medulla oblongata. Traced into the substance of the brain and
medulla, the roots of the nerves are found to take origin from various masses
of gray matter.

The roots of the first or olfactory and of the second or optic nerves are
discussed elsewhere. The third and fourth nerves arise from gray matter
beneath the corpora quadrigemina; and the roots of origin of the remainder
of the cranial nerves can be traced to gray matter in the floor of the fourth
ventricle, and in the more central part of the medulla, around its central
canal, as low down as the decussation of the pyramids.

According to their several functions the cranial nerves may be thus
arranged:

C Olfactory, optic, auditory, parts of

Nerves of special sense -j the facial, glosso-pharyngeal, and of

(__ the trigeminal.

-vr r ( The greater portion of the trigeminal,

Nerves of common sensation 4 .F, . . ,

( and part of the facial.

( The motor oculi, trochlearis, lesser di-
Nerves of motion -j vision of the tri-geminal, abducens,

(_ hypoglossal, and spinal accessory.
Mixed nerves... , Facial, glosso-pharyngeal, and vagus.

The physiology of the first, second, and eighth nerves will be considered
with the Organs of Special Sense, see also figure 416.

The Third Nerve or Motor Oculi. — Origin. — The third nerve arises in
three distinct bands of fibers from the gray nuclei surrounding the aqueduct
of Sylvius near the middle line, but ventral to the canal, figure 408. The
nucleus of origin consists of large multipolar ganglion cells, and extends to
the back part of the third ventricle as far as the level of the superior cor-
pora quadrigemina. The fibers pass from their origin partly through the
red nucleus to their superficial origin in front of the pons at the median side
of each crus. The third nerve does not decussate.

Function. — The third nerve supplies the levator palpebrae superioris mus-
cle, and all of the muscles of the eyeball, except the superior oblique, to
which the fourth nerve is distributed, and the rectus externus which re-
ceives the sixth nerve. Through the medium of the ophthalmic or lenticular
ganglion, of which it forms what is called the short root, it also supplies
motor filaments to the iris and ciliary muscle. The fibers which subserve
the three functions, accommodation, contraction of the pupil, and nerve-
supply to the external ocular muscles, arise from three distinct groups of
cells. Optic reflexes involving movements of the eyeballs are mediated
through fibers from cells of the superior corpora quadrigemina (which re-
ceive fibers from the optic nerve). These fibers from the corpora quadri-
gemina descend, chiefly through the posterior longitudinal bundle, figure

THE FOURTH NERVE, OR TROCHLEARIS

383, to the nuclei of the third, fourth, and sixth nerves, thus rendering
possible co-ordinated reflex movements of all the eye muscles.

When the third nerve is stimulated writhin the skull, all those muscles to
which it is distributed are contracted. When it is paralyzed or divided, the
following effects ensue: i. The upper eyelid can be no longer raised by the
levator palpebrae, but droops, ptosis, and remains gently closed over the eye,
under the unbalanced influence of the orbicularis palpebrarum, which is sup-
plied by the facial nerve. 2. The eye is turned outward and downward,
external strabismus, by the unbalanced action of the rectus externus and supe-
rior oblique, to which the sixth nerve is appropriated; and hence, from the

cq.s

c s

ILC

FIG. 408. — Section through Superior Corpus Quadrigeminum and Part of the Thal-
amus. s, Aqueduct of Sylvius; gr, gray matter of the aqueduct, c.q. s., superior corpus
quadrigeminum; /, stratum lemnisci; o, stratum opticum, c, stratum cinereum; Th, pulvinar
of optic thalamus; c.g.e, c.g.i, lateral and median corpora geniculata; br.s, br.i, superior and
inferior brachia-/, fillet; p.l, posterior longitudinal bundle; r, raphe; 777, third nerve, and
n.III, its nucleus; l.p.p, posterior perforated space; s.n, substantia nigra — above this is the
tegmentum with the circular area of the red nucleus; cr, crusta; 77, optic tract; M , medullary
center of hemisphere; n.c, nucleus caudatus; st, stria terminalis. (After Quain, from
Meynert.)

irregularity of the axes of the eyes, double sight, diplopia, is often experienced
when a single object is within view of both the eyes. 3. The eye cannot be
moved upward, downward, or inward. 4. The pupil becomes dilated,
mydriasis. 5. The eye cannot accommodate for short distances.

The Fourth Nerve, or Trochlearis. — Origin, — The fourth nerve
arises from a nucleus consisting of large multipolar ganglion cells situated
ventral to the aqueduct of Sylvius, and the inferior corpus quadrigeminum.
The fibers from both sides sweep dorsally around the central gray matter, and
reach the valve of Vieussens, where they decussate in the mid-line of the roof,
then pass forward along the lateral aspect of the crus. The nucleus of the
fourth nerve on either side is connected with those of the third and sixth
nerves and with the optic reflex center previously described.

6l2

THE NERVOUS SYSTEM

Functions. — The fourth nerve is exclusively motor, and supplies only the
trochlearis or superior oblique muscle of the eyeball.

The Fifth Nerve, or Trigeminal. — Origin. — The fifth or trigeminal
nerve resembles the spinal nerves in that it has two roots; namely, the larger
or sensory, in connection with which is the Gasserian ganglion, and the small
or motor root, which has no ganglion, and which passes under the ganglion
of the sensory root. The fibers of origin of the fifth nerve come from the
floor of the fourth ventricle. The motor root arises to the inside of the sen-

FIG. 409. — Fourth Ventricle with the Medulla Oblongata and the Corpora Quad-
rigemina. The Roman numbers indicate superficial origins of the cranial nerves, while the
other numbers indicate their deep origins, or the position of their central nuclei. 8, 8', 8",
Auditory nuclei nerves; t, funiculus teres; A, B, corpora quadrigemina; c.g, corpus genic-
ulatum; p.c. pedunculus cerebri; m.c.p, middle cerebellar peduncle; s.c.p, superior cere-
bellar peduncle; i.c.p, inferior cerebellar peduncle; l.c, locus ceruleus; e.t, eminentia teres;
a.c, ala cinerea; a.n, accessory nucleus; o, obex; c, clava; f.c, funiculus cuneatus; f.g, funicu-
lus gracilis.

sory about the middle of each lateral half of the fourth ventricle. The
sensory fibers, however, can be traced down in the medulla oblongata as far
as the upper part of the cord. The motor nucleus stretches forward as far
as the superior corpus quadrigeminum, giving rise to a bundle of long fibers
termed the descending root. The sensory nucleus receives a tract of sensory
fibers from the trigeminus extending as low as the second cervical nerve,
and this forms a tract at the tip of the posterior cornu, between it and the
restiform body. The cells of origin of the sensory tract are in the Gas-

THE FIFTH NERVE, OR TRIGEMINAL

6i3

serian ganglion. The nerve appears at the ventral surface of the pons
near its front edge, at some distance from the mid-line.

Motor Functions. — The first and second divisions of the nerve, which
arise wholly from the larger root, are purely sensory. The third division is
joined by the motor root of the nerve and is of course both motor and sensory.

Motor branches of the lesser or non-ganglionic portion of the fifth supply
the muscles of mastication, namely, the temporal, masseter, two pterygoid,
anterior part of the digastric and mylohyoid. Filaments are also said to
supply the tensor tympani and tensor palati (Kolliker). The motor func-

VM.

FIG. 410. — Section Across the Pons, About the Middle of the Fourth Ventricle, py,
Pyramidal bundles; po, transverse fibers passing pol, behind, and po2, in front of py; r,
raphe; o.s, superior olive; a.V, bundles of ascending root of V. nerve enclosed in a pro-
longation of the substance of Rolando; VI, the sixth nerve; nVI, its nucleus; VII, facial
nerve; VII. a, intermediate portion; nVII, its nucleus; 77/7, auditory nerve, nVIII,
lateral nucleus of the auditory. (After Quain.)

tion of these branches is proved by the violent contraction of all the muscles
of mastication in experimental irritation of the third or inferior maxillary
division of the fifth nerve; by paralysis of the same muscles when the nerve
is divided or disorganized; and by the retention of the power of these muscles
when the facial nerve is paralyzed. Whether the branch of the fifth nerve
which is supplied to the buccinator muscle is entirely sensory, or in part
motor also, must remain for the present doubtful. From the fact that this
muscle, besides its other functions, acts in concert or harmony with the
muscles of mastication in keeping the food between the teeth, it might be
supposed from analogy that it would have a motor branch from the same
nerve that supplies them. However, the so-called buccal branch of the fifth
is, in the main, sensory.

Sensory Functions. — All the anterior and antero-lateral parts of the face

614

THE NERVOUS SYSTEM

and head, with the exception of the skin of the parotid region, acquire com-
mon sensibility through branches of the ganglionic division of the fifth nerve.
The muscles of the face and lower jaw acquire muscular sensibility through
the filaments of the ganglionic portion of the fifth nerve distributed to them
with their proper motor nerves.

Through its ciliary branches and the branch which forms the long root
of the ciliary or ophthalmic ganglion, it exercises some influence on the

FIG. 411. — General Plan of the Branches of the Fifth. X ^. i, Lesser root of the
fifth; 2, greater root passing forward into the Gasserian ganglion; 3, placed on the bone
above the ophthalmic nerve, which is seen dividing into the supra-orbital, lachrymal, and
nasal branches, the latter connected with the ophthalmic ganglion; 4, placed on the bone
close to the foramen rotundum, marks the superior maxillary division, which is connected
below with the spheno-palatine ganglion, and passes forward to the infra-orbital foramen;
5, placed on the bone over the foramen ovale, marks the inferior maxillary nerve, giving
off the anterior auricular and muscular branches, and continued by the 'inferior dental
to the lower jaw, and by the gustatory to the tongue; a, the submaxillary gland, the sub-
maxillary ganglion placed above it in connection with the gustatory nerve; 6, the chorda
tympani; 7, the facial nerve issuing from the stylomastoid foramen. (Charles Bell.)

movements of the iris. When the trunk of the ophthalmic portion is divided,
the pupil becomes, according to Valentine, contracted in men and rabbits, and
dilated in cats and dogs, but in all cases becomes immovable even under all
the varieties of the stimulus of light. How the fifth nerve affects the iris is
unexplained; it has been suggested the influence of the fifth nerve on the
movements of the iris may be ascribed to the affection of vision in conse-
quence of the disturbed circulation or nutrition in the retina.

THE SEVENTH NERVE, OR FACIAL 615

Trophic Influence.— The morbid effects which division of the fifth nerve
produces in the organs of special sense make it probable that the fifth nerve
exercises some special or trophic influence on the nutrition of all these organs,
although the effects may in part be due to the loss of sensibility which is the
natural protective safeguard. Thus, after such division and within a period
varying from twenty-four hours to a week, the cornea begins to be opaque
and later it grows completely white. A low destructive inflammatory process
ensues in the conjunctiva, sclerotic coat, and in the interior parts of the eye.
The sense of smell may be at the same time lost or gravely impaired. Com-
monly, whenever the fifth nerve is paralyzed, the tongue loses the sense
of taste in its anterior and lateral parts, and according to Gowers in the
posterior part as well.

In Relation to Taste. — The tactile sensibility of the tongue is due to the lin-
gual branch of the fifth nerve, which supplies the anterior and lateral parts of
the tongue. The sense of taste in the lateral and anterior portions of the tongue
has recently been traced back to the pars intermedia and chorda tympani
of the seventh, figures 412 and 413. It forms also one chief sensory link
in the nervous circle for reflex action in the secretion of saliva. But, de-
ferring this question until the glosso-pharyngeal nerve is to be considered,
it may be observed that in some brief time after complete paralysis or division
of the fifth nerve, the power of all the organs of the special senses may be im-
paired. They may lose not merely their sensibility to common impressions,
for which they all depend directly on the fifth nerve, but also their sensibility
to the special stimuli to which they are adapted.

The Sixth Nerve, the Abducens. — Origin. — The sixth nerve arises
from a compact oval nucleus, situated somewhat deeply at the back part of
the pons near the middle of the floor of the fourth ventricle. The eminentia
teres marks its position. It contains moderately large cells with large nerve
axis-cylinder processes. It is connected, figure 375, with the nuclei of the
third, fourth, and seventh nerves, and with reflex centers of the optic tracts,
as previously mentioned. The root is thin, and passes ventrally and laterally
through the reticular formation, to the surface, which it reaches at the lower
edge of the pons, opposite the front end of the pyramid.

Functions. — The sixth nerve is exclusively motor, and supplies only the
rectus externus muscle of the eye. The muscle is paralyzed when the nerve
is divided. In all such cases of paralysis the eye squints inward and cannot
be moved outward.

The Seventh Nerve, or Facial. — Origin. — The facial or seventh pair of
nerves arises from the floor of the central part of the fourth ventricle, behind
and in line with the motor nucleus of the fifth, to the outside of and deeper
down than the nucleus of the sixth. The nucleus is narrower in front than
behind, and consists of large motor cells with well-marked axis-cylinder proc-
esses, which are gathered up at the dorsal surface of the nucleus to form a

6i6

THE NERVOUS SYSTEM

root. The root describes a loop around the nucleus of the sixth nerve,
running forward for some little distance dorsal to the nucleus, then descend-
ing vertically, passing to the outside of its own nucleus, between it and the
descending root of the fifth nerve. It emerges at the lower margin of the
pons, lateral to the sixth nerve, opposite the front edge of the groove between
the olivary and restiform bodies. The second or sensory root is smaller and
is called the pars intermedia, figure 412. It is the portion which is connected

V.G

I.C.

Sty. hy

FIG. 412. — The Seventh Nerve and Its Branches. VII, Facial nerve; P.I, pars
intermedia; VIII, auditory nerve; Aq.Fal, aqueduct of Fallopius; G.G, geniculate ganglion;
E.S.P, external superficial petrosal nerve; M.M, middle menmgeal artery; G.S.P, great
superficial petrosal nerve; G.P.D, great deep petrosal nerve; I.C, internal carotid artery;
Vid, Vidian nerve; M.G., Meckel's ganglion; Ty.Pl, tympanic plexus; S.D.P, small deep
petrosal nerve; G.Ph, Glosso-pharyngeal nerve; Ty, tympanic branch; S.S.P., small super-
ficial petrosal nerve; O.G., optic ganglion; Stap, nerve to stapedius; C.T, chorda tympani
nerve; Z,, lingual nerve; A.Va, communication with auricular branch of vagus; P. A,
posterior auricular nerve. Sty.hy, nerve to stylo-hyoid; Di, nerve to digastric (posterior
belly); T.F, temporal-facial division; C.F, cervico-facial division; T, temporal; M, malar;
I.O, infra-orbital; B, buccal, S.M, supra-mandibular; I.M, infra-mandibular branches.
(Cunningham.) ^ \{f. ^

with the chorda tympani and geniculate ganglion, figure 413. The pars
intermedia terminates within the brain in the fasciculus solitarius in com-
mon with the glosso-pharyngeal.

Functions. — The seventh nerve is the motor nerve of all the muscles of the
face, including the platysma, but not including the muscles of mastication.
It supplies the stapedius, the stylo-hyoid and the posterior part of the
digastric. Its branches also supply the rudimentary muscles of the external
ear.

Fibers from the chorda tympani are distributed to the submaxillary
gland and produce secretion when stimulated.

THE EIGHTH NERVE, OR AUDITORY 617

When the facial nerve is divided or in any other way paralyzed, the loss of
function in the muscles which it supplies interferes with the perfect exercise
of the organs of the special senses. Thus, in paralysis of the facial nerve the
orbicularis palpebrarum being powerless, the eye remains open through the
unbalanced action of the levator palpebra. The conjunctiva is thus contin-
ually exposed to the air and dust and is liable to repeated inflammation,
which may end in thickening and opacity of the cornea.

The sense of taste may be weakened or wholly lost in paralysis of the
facial nerve, which involves the chorda tympani. This result, which has
been observed in many instances of disease of the facial nerve in man, appears
explicable on the supposition that the chorda tympani is the nerve of taste

pars interned---^]

r. auric,

petros. 5 up. maj.

L motor "ZU.

FIG. 413.— Dissection of the Sensory and Motor Divisions of the P'acial in a 2o-cm. Embryo

' (Pig). (Streeter.)

to the anterior two-thirds of the tongue, its fibers being distributed with the
so-called gustatory or lingual branch of the fifth. Streeter has just published
a study of the development of the seventh and eighth nerves in which he
traces the chorda tympani through the pars intermedia, as shown in figure
413, thus settling this oft-disputed question.

The Eighth Nerve, or Auditory. — The eighth nerve consists of two
divisions, anatomically distinct and functionally independent. These are
the vestibular and the cochlear divisions of the auditory nerve.

The cochlear division arises in the spiral ganglion and passes to the
medulla to establish immediate connections with the ventral cochlear nucleus
and the tuberculum acusticum. The central relations of these nuclei are
established by the striae acusticae, the trapezoideus, and the lateral fillet with
the internal corpus geniculatum and the inferior corpus quadrigeminum of
the opposite side, as told by figure 414. These latter nuclei send tracts to
the auditory center in the superior temporal gyrus.

The vestibular division arises in the vestibular ganglion, which is entirely
distinct from the cochlear ganglion, and enters the medulla, passing to the
lateral or chief auditory nucleus. From this point the relations are not fully

6i8

THE NERVOUS SYSTEM

established, but apparently fibers pass to the nucleus fastigii of the opposite
side and to the vermis, where they are brought into relations with motor
descending paths.

Functions. — The cochlear branch is the auditory nerve proper, and the
vestibular is the nerve of equilibrium. The reader is referred to the chapter
on Hearing for the details of function.

CORPORA QUADRIGEMINA

FIG. 414. — The Nuclei of Origin and Central Connections of the Auditory and Vestibula

Nerve. (Cunningham.)

The Ninth Nerve, or Glosso-pharyngeal. — Origin. — The glosso-phar-
yngeal nerves, figure 378, IX, arise by nuclei intimately associated with
those of the vagus and spinal accessory nerves. The union of the nuclei is
indeed so intimate that it will be as well to consider the origins of the ninth,
tenth, and eleventh nerves together.

These three nerves emerge from the bulb and spinal cord in their numerical
order from above downward, the bulbar portion from the lateral aspect of
the bulb in a line between the olivary and restiform bodies; and the spinal

THE NINTH NERVE, OR GLOSSO-PHARYNGEAL 6lQ

portion from a line intermediate between the anterior and posterior nerve
roots as far down as the sixth or seventh cervical spinal nerves.

The combined glosso-pharyngeal-accessory-vagus nucleus appears to con-
sist of two parts, viz., one median or common origin, having conspicuous
nerve cells of moderate size, and three lateral origins, having but few cells of
small size. These are: i, the nucleus ambiguus, which lies on the lateral side
of the reticular formation and is the motor origin of the glosso-pharyngeal,
the vagus, and the spinal accessory; 2, the fasciculus solitarius, situated in
the bulb, ventral and a little lateral to the combined nucleus, is also called the
ascending root of the glosso-pharyngeal nerve or the respiratory bundle; and
3, the spinal portion, which takes origin from a group of cells lying in the ex-
treme lateral margin of the anterior cornu. This is the origin of the spinal
accessory; it corresponds to the antero-lateral nucleus of the bulb, and the
lateral part of the gray matter of the spinal cord.

The fibers of the spinal origin of the nerve pass from these cells through
the lateral column to the surface of the cord. The fibers from the median
part pass in a ventral and lateral direction through the reticular formation,
then ventral to or through the gelatinous substance and strand of fibers
connected with the fifth nerve, to the surface of the bulb.

The fibers from the nucleus ambiguus join the combined nerve, chiefly
the vagus and the glosso-pharyngeal.

The bundles of fibers of the fasciculus solitarius start in the lateral gray
matter of the cervical cord and higher in the reticular formation of the bulb,
run longitudinally forward, to pass into the roots of the ninth nerve. It is
composed of sensory fibers, chiefly of the glosso-pharyngeal, and of the
pars intermedia of the facial.

The glosso-pharyngeal nerve gives filaments through its tympanic branch
(Jacobson's nerve), to the fenestra ovalis and fenestra rotunda, and the Eu-
stachian tube; also to the carotid plexus, and through the petrosal nerve, to
the spheno-palatine ganglion. After communicating with the vagus and,
soon after it leaves the cranium, with the sympathetic, with the digastric
branch of the facial, and the accessory nerve, the glosso-pharyngeal divides
into the two principal divisions indicated by its name. These divisions
supply the mucous membrane of the posterior and lateral walls of the
upper part of the pharynx, the Eustachian tube, the arches of the palate,
the tonsils and their mucous membrane, and the tongue as far forward
as the foramen cecum in the middle line, and to near the tip at the sides and
inferior part.

Functions. — The glosso-pharyngeal nerve contains some motor fibers,
together with fibers of common sensation and the sense of taste.

Motor fibers are distributed to the palato-pharyngeus, the stylo-phar-
yngeus, palato-glossus, and constrictors of the pharynx.

Sensory fibers of touch and of common sensation are distributed to the

620 THE NERVOUS SYSTEM

pharynx, the tonsils, and posterior palate. Nerves of taste are supplied to
the taste buds on the posterior third of the tongue and to the fauces.

The Tenth Nerve, Vagus or Pneumogastric Nerve. — The origin of the
vagus nerve is, as we have just seen, situated in the lower half of the floor of
the fourth ventricle, figure 378. Its nucleus is said to represent the cells of
Clarke's column of the spinal cord. In origin it is closely connected with
the ninth, eleventh, and the twelfth. The combined glosso-pharyngeal-vago-
accessory nuclei lie outside of, close to, and parallel with the nucleus of the
twelfth. There are two main vagal nuclei, one motor, the other sensory.

Distribution. — It has, of all the nerves, the most varied distribution and
functions, either through its own filaments, or through those which, derived
from other nerves, are mingled in its branches. The vagus supplies sensory
branches, which accompany the sympathetic on the middle meningeal
artery, which supply the back part of the meatus and the adjoining part
of the external ear. It is connected with the petrous ganglion of the glosso-
pharyngeal, by means of fibers to its jugular ganglion, with the spinal acces-
sory, which supplies it with its motor fibers for the larger and upper portion
of the esophagus, and with its inhibitory fibers for the heart; also with the
twelfth; with the superior cervical ganglion of the sympathetic; and with the
cervical plexus. The parts supplied by the branches of the vagus are as
follows:

1. A large portion of the mucous membrane and some of the muscles
of the pharynx are supplied by its pharyngeal branches, through the phar-
yngeal plexus.

2. The mucous membrane of the under surface of the epiglottis, and of
the greater part of the larynx, and the crico-thyroid muscle, by the superior
laryngeal nerve.

3. The mucous membrane and muscular fibers of the trachea, the lower
part of the pharynx and larynx, and all the muscles of the larynx except the
crico-thyroid are supplied by the inferior laryngeal nerve. It also supplies
the first segment of the esophagus.

4. The mucous membrane and muscular coats of the esophagus receive
fibers from the esophageal branches.

5. The branches of the vagus form the supply of nerves to the heart and
the great arteries.

6. The lungs are supplied through the anterior and posterior pulmonary
plexuses.

7. The stomach, the intestines, the spleen, and the liver are supplied by
the gastric, splenic, and hepatic vagus branches.

Functions. — Throughout its whole course the vagus contains both sensory
and motor fibers. To summarize the many functions of this nerve, which
have been for the most part considered in the preceding chapters, it may be
said that it supplies, i, motor fibers to the pharynx and esophagus, to the

THE TENTH NERVE, VAGUS OR PNEUMOGASTRIC NERVE 621

\

Va.f

A.BR

FIG. 415.

FIG. 416.

FIG. 415. — The Distribution of the Tenth or Vagus Nerve. Va.R, Va.L., Right and
left vagi; r, ganglion of the root and connections with Sy., sympathetic, superior cervical
ganglion; g.Ph., glosso-pharyngeal; Ace., spinal accessory nerve; m, meningeal branch; Aur.
auricular branch; /, ganglion of the trunk and connections with Hy., hypoglossal nerve;
Ci, €2, loop between the first two cervical nerves — Sy., sympathetic, Ace., spinal accessory
nerve; Ph., pharyngeal branch; Ph.Pl., pharyngeal plexus; S.L., superior laryngeal nerve;
I.L., internal laryngeal branch; E.L., external laryngeal branch; I.C., internal, and E.G.,
external carotid arteries; Cai, superior cervical cardiac branch; Ca2, inferior cervical
cardiac branch; R.L., recurrent laryngeal nerve; Ca$, cardiac branches of recurrent laryn-
geal nerve; Ca^, thoracic cardiac branch (right vagus); A. P. PL, anterior, and P. P. PI.,
posterior pulmonary plexuses; Oes.Pl., esophageal plexus; Gast.R. and Gast.L., gastric
branches of vagus (right and left); Coe.PL, celiac plexus; Hep.Pl., hepatic plexus; PI.,
splenic plexus; Ren.PL, renal plexus. (Cunningham.)

FIG. 416. — The Constitution of the Cardiac Plexus. Sy., Cervical sympathetic cord;
C.i, superior, C.2, middle, and C.$, inferior cervical ganglia; Car.i, superior, Car. 2, middle,
and Car.3, inferior cervical cardiac sympathetic branches; Fa., vagus nerve; R.L., recurrent
laryngeal nerve; s, superior, and *,* inferior cervical cardiac branches of vagus; D.C.P.,
deep cardiac plexus; S.C.P., superficial cardiac plexus; A. P. P., anterior pulmonary
plexus; P.P.P., posterior pulmonary plexus; R.Car.P., right, and L.Car.P., left coronary
plexuses; Art.Pul., pulmonary artery. (Cunningham.)

622 THE NERVOUS SYSTEM

stomach and intestines, to the larnyx, trachea, bronchi, and lungs; 2, sensory
and, in part, 3, vaso-motor fibers to the same regions; 4, inhibitory fibers
to the heart; 5, inhibitory afferent fibers to the vaso-motor center.

Division of both vagi or of both their recurrent branches is often quickly
fatal in young animals; but in old animals the division of the recurrent nerve
is not generally fatal, and that of both the vagi, even, is not always fatal.

The Eleventh Nerve, or Spinal Accessory. — This nerve arises by two
nuclei, one the nucleus ambiguus from a center in the floor of the fourth
ventricle, partly but chiefly in the medulla and continuous with the glosso-
pharyngeal- vagus nucleus; the other, from the outer side of the anterior
cornu of the spinal cord as low down as the fifth or sixth cervical nerve. The
fibers from the two origins come together at the jugular foramen, but sepa-
rate again into two branches. The inner arises from the medulla and joins
the vagus, to which it supplies fibers, consisting of small medulla'ted nerve
fibers. The outer consists of large medullated fibers and supplies the tra-
pezius and sterno-mastoid muscles. The muscles of the larynx, all of which
are supplied, apparently, by branches of the vagus, are said to derive their
motor nerves from the accessory; and Vrolik makes the very significant
statement that in the chimpanzee the internal branch of the accessory does
not join the vagus at all, but goes direct to the larynx.

The Twelfth Nerve, or Hypoglossal.— Origin and Connections.— The
nerve arises from a large-celled and very long nucleus in the bulb, extending
from the floor of the fourth ventricle to the level of the olivary bodies close to
the mid-line and inside the nucleus ambiguus. Fibers from this nucleus run
from the ventral surface through the reticular formation in a series of
bundles passing between the olivary nucleus laterally and the pyramid and
accessory olive medially, to gain the ventral surface. The nerve emerges
from a groove between the pyramid and olivary body. The fibers of
origin are continuous with the anterior roots of the spinal nerves.

This nerve is the motor nerve to the muscles connected with the hyoid
bone, including those of the tongue. It supplies the sterno-hyoid, sterno-thy-
roid, and omo-hyoid through its descending branch, descendens hypoglossi;
the thyro-hyoid through a special branch; and the genio-hyoid, stylo-glossus,
hyo-glossus, and genio-hyoglossus and linguales through its lingual branches.

Functions. — The function of the hypoglossal is exclusively motor. In
cases of hemiplegia involving the functions of the hypoglossal nerve the
tongue when protruded deviates toward the paralyzed side, when withdrawn
it turns away from the paralyzed side. Occasionally it is not possible to
observe any deviation in the direction of the protruded tongue; probably
because the tongue is so compact and firm that the muscles on either side
can push it straight forward or turn it for some distance toward either side.
In hypoglossal paralysis from cerebral lesions or lesions of the peduncles the
paralysis is contralateral.

THE CIRCULATION DURING SLEEP 623

THE PHYSIOLOGY OF SLEEP.

All parts of the body which are the seat of active change require periods
of rest. The alternation of work and rest is a necessary condition of their
maintenance and of the healthy performance of their functions. These alter-
nating periods, however, differ much in duration in different cases; but, for
any individual instance, they preserve a general and rather close uniformity.
Thus, the periods of rest and work mentioned, in the case of the heart, oc-
cupy, each of them, about half a second; in the case of the ordinary respira-
tory muscles the periods are about four or five times as long. In many cases
(as of the voluntary muscles during violent exercise), while the periods during
active exertion alternate very frequently, yet the expenditure goes far ahead
of the repair, and, to compensate for this, an after-repose of some hours be-
comes necessary, the rhythm being less perfect as to time than in the case of
the muscles concerned in circulation and respiration.

Obviously, it would be impossible in the case of the brain, that there
should be short periods of activity and repose, or, in other words, of conscious-
ness and unconsciousness. The repose must occur at long intervals and must
be proportionately long. Hence the necessity for that condition which we
call Sleep; a condition which, seeming at first sight exceptional, is only an
unusually perfect example of what occurs, at varying intervals, in every
actively working portion of our bodies.

By exposing, at a circumscribed spot, the surface of the brain of a living
animal, and protecting the exposed part by a watch-glass, Durham was able
to proive that the brain becomes visibly paler, anemic, during sleep; and the
anema of the optic disc during sleep, observed by Hughlings Jackson, may
be taken as a strong confirmation, by analogy, of the same fact.

The Circulation During Sleep. — Blood is supplied to the brain in
four distinct but anastomosing arteries. This efficient anatomical arrange-
ment is obviously all the more important when it is remembered that the cir-
culation in the brain has only an inefficient local device for regulating the
blood-flow, and that the circulation of the brain is constantly influenced by
the variations in general blood pressure.

Howell and others have studied the circulation by the plethysmographic
method during sleep. The results show that with the loss of consciousness,
and immediately following, there is a sharp dilatation of the blood vessels of
the arm, probably chiefly of the skin, as shown by the increase in volume.
The vessels remain dilated until the individual begins to awaken, when there
is a rapid constriction with decrease of volume of the organ.

The dilatation of the general blood vessels draws off the supply of blood
from the brain, and the resulting partial anemia contributes to loss of con-
sciousness. The blood supply is ample for growth and repair and rest of the
nervous system. How efficient this rest period is for the rejuvenation of the

624 THE NERVOUS SYSTEM

nervous tissue is indicated even by the relatively gross means, figure 357,
shown in the histological preparations of nerve cells.

Somnambulism and Dreams. — What we term sleep occurs often in very
different degrees in different parts of the nervous system; and in reference to
some parts the expression cannot be used in the ordinary sense. For example,
during the most profound cerebral sleep the medulla is discharging rhythmic
nerve impulses to maintain respiratory movements.

The phenomena of dreams and somnambulism are examples of differing
degrees of sleep in different parts of the cerebro-spinal nervous system. In
the former case the cerebrum is still partially active; but the activity is no
longer corrected by the reception, on the part of the sleeping sensorium, of
impressions of objects belonging to the outer world. Neither can the cerebrum,
in this half-awake condition, act on the centers of reflex action of the volun-
tary muscles, so as to cause the latter to contract — a fact within the painful
experience of all who have suffered from nightmare.

In somnambulism the higher centers are capable of co-ordinating that train
of reflex nervous action which is necessary for progression, while the nerve
center of the muscular equilibrium sense (in the cerebellum?) is, presumably,
fully awake; but the sensorium is still asleep, and impressions made on it are
not sufficiently felt to rouse the cerebrum to a comparison of the difference be-
tween mere ideas or memories and sensations derived from external objects.

VII. THE SYMPATHETIC SYSTEM.

The fact has already been emphasized that the sympathetic system of
nerves is an organic and constituent part of the nervous system. This fact
should be constantly kept in view in the discussions that follow.

Organization and Distribution. — The sympathetic system consists
of those collections of nerve cells or ganglia lying outside of the brain and
cord (exclusive of the root ganglia), and the nerve tracts connecting them
with one another and with the cerebro-spinal axis. Its parts that should be
mentioned are: i. a double chain of ganglia and fibers, which extends
from the cranium to the pelvis, along each side of and in front of the vertebral
column, and from which branches are distributed both to the cerebro-spinal
system and to other parts of the sympathetic system. With these may be
included the small ganglia in connection with those branches of the fifth
cerebral nerve which are distributed in the neighborhood of the organs of
special sense, namely, the ophthalmic, otic, spheno-palatine, and submaxillary
ganglia. 2. Various ganglia and plexuses of nerve fibers which give off
direct branches to the thoracic and abdominal viscera, the chief of such
plexuses being the cardiac, solar, and hypogastric plexuses. In intimate
connection with these are many secondary plexuses, as the aortic, spermatic,
and renal. Fibers pass from the prevertebral chain of ganglia and from
the cerebro-spinal nerves to these plexuses. 3. Various ganglia and plexuses
in the substance of many of the viscera, as in the stomach, intestines, and

ORGANIZATION AND DISTRIBUTION

625

urinary bladder. These, which are for the most part microscopic, also
freely communicate with other parts of the system, as well as with the cerebro-
spinal axis.

The connections between these parts are as follows: i. The visceral
branches or white ram I, of certain spinal nerves, which pass into the ganglionic

GrayRamus
White Ramus

m Bathetic Ganglion.

Recurrent Branc

of Meninges

Sympathetic Gangl

White

Ramus
GrayRamus

FIG. 417. — Schematic Representation of the Relation of the Constituents of the Sympathetic
Chain and the Spinal Nerve. (Modified from Hardesty, in Morris' Anatomy.)

chain. 2. The gray rami consisting of bundles of fibers, usually non-medul-
lated, which pass from the chain ganglia back into the spinal or cranial nerves,
the fibers of which they accompany to the periphery. 3. From the ganglionic
chain the rami e/erentes pass into the collateral ganglia, and from these again
other branches pass off into the organs, to end in terminal ganglia or more
often in the tissue.
40

626 THE NERVOUS SYSTEM

The white rami are absent in all the spinal nerves in the regions above
the second (occasionally the first) thoracic nerve root, and below the second
lumbar nerve root, with the occasional exception of the roots of the third and
fourth lumbar nerves. This is a rather restricted field of origin for the pre-
ganglionic fibers which compose the white rami. The fibers enter the

FIG. 418. — Scheme of the Constitution and Connections of Gangliated Cord of the
Sympathetic. The gangliated cord is indicated on the right, with the arrangement of the
fibers arising from ganglion cells. On the left, the roots and trunks of the spinal nerves are
shown, with the arrangement of the white ramus communicans above and the gray ramus
below. The cells of origin in the ventral cord of the fibers constituting the white ramus are
not shown. (Cunningham.)

adjacent ganglia of the chain to end there or to pass to higher or lower levels
or to more peripheral ganglia.

A peculiarity in the structure of these white medullated visceral nerves is
the fineness of their fibers. They are a third or a fourth of the diameter of
ordinary medullated fibers, measuring i.S/j. to 2.7^ instead of 14/4 to iq/j..

FUNCTIONS 627

Such fibers are a peculiarity of the spinal nerve roots chiefly in the thoracic
region. But they are also found in the second and third sacral nerves, and
constitute there the nervi erigentes which pass directly to the hypogastric
plexus. From the hypogastric plexus branches pass upward into the inferior
mesenteric ganglia and downward to the bladder, rectum, and generative
organs. These nerves, called by Gaskell pelvic splanchnic nerves, differ from
the rami viscerales of the thoracic region only in not communicating with
the lateral ganglia. The branches which pass upward from the thoracic
region to the neck, he calls cervical splanchnics, and the splanchnics proper
abdominal splanchnics.

Functions. — The researches of Gaskell and of Langley have done
much to clear up the former confusion as to the distribution and functions
of the sympathetic nerves. The sympathetic nerve fibers are distributed to
smooth muscle, to gland cells, and to cardiac muscle. These are all organs
which carry on their activities either automatically or reflexly. There is no
voluntary control of the function of such organs.

The efferent sympathetic fibers supply the muscles of the vascular system,
to which they send the vaso-motor fibers, i.e., vaso- constrictor and cardiac
augmentor or accelerator; and vaso-inhibitory fibers, i.e., vaso-dilators.
They supply the muscles of the alimentary canal and of the urinogenital
system. The details of arrangement and functional control of these com-
plex systems have already been discussed in connection with the function of
the organ or part concerned. They supply the salivary, gastric, and pan-
creatic glands.

According to Gaskell the functions of the main sympathetic ganglia are
the following: i. The sympathetic ganglia are aggregates of large numbers
of multipolar cells around which the medullated fibers of the white rami form
synapses. The branches of the cells are of the non-medullated fiber type.
Thus a medullated conduction is converted in the ganglia into a non-medul-
lated path beyond the ganglia. 2. The ganglion cells exercise a nutritive
influence over the tissues to which their fibers are distributed. 3. The num-
ber of preganglionic fibers entering the ganglia is not so great as that leaving,
since the cells are multipolar (not shown in the schematic figure 417). This
serves to multiply the influence of a relatively simple efferent preganglionic
conduction path and to extend it over a larger area the parts of which are
usually acting co-ordinatively.

The sympathetic ganglia are not nerve centers in the usual sense. It is
better to regard them merely as distributing organs in which reflexes of cen-
tral origin and x comparatively simple type are distributed over relatively
large areas. These ganglia do not possess the power of reflex function. A
type of pseudo-reflex has been described depending on the law of neurone
reaction. But it is not supposed that such reflexes occur in the normal
animal.

628 THE NERVOUS SYSTEM

Afferent or sensory fibers of the ordinary spinal-root ganglion cells are
present in the sympathetic nerves of the splanchnic region, being distributed
merely to the visceral region. True afferent sympathetic fibers have been
demonstrated. These arise from cells located in the sympathetic ganglia,
and pass through the rami communicantes, to end by terminal arborizations
in the spinal ganglia, chiefly around cells of the Dogiel type. The number
and significance of these afferent neurones remain as yet uncertain.

CHAPTER XV.
THE SENSES.

THROUGH the medium of the nervous system man obtains a knowledge
of the existence both of the various parts of his body and of the external
world. This knowledge is based upon sensations resulting from the stimula-
tion of certain centers in the brain by nerve impulses conveyed to them by
afferent nerves. Under normal circumstances the following structures are
necessary for sensation: a, A peripheral organ for the reception of the im-
pression; by a nerve for conducting it; c, a nerve center for feeling or per-
ceiving it.

The senses may be conveniently classified according to the sensation which
is experienced. Each sense organ when stimulated is supposed to lead
to a sensation of distinctive character. Yet many of the sensations are
vaguely defined, such as thirst, fatigue, etc. Other sensations have 'a very
definite and readily identified quality such as sight, taste, etc. Sensations,
whether definite or vague, are referred by us to some source or origin either
in the body, i, the internal or so-called common sensations, or outside the
body, 2, the external or special senses. No sharp line can be drawn in
this classification.

Internal Senses. — Under this head fall all those senses which produce
sensations that are referred to an origin within the body, such as fatigue,
discomfort, faintness, satiety, nausea, together with hunger, thirst, the muscle
sense, and pain. In hunger and thirst there is a general bodily discomfort,
but in many persons also a distinct sensation referred to the stomach or to
the fauces. In this class must also be placed the various stimulations of
the mucous membrane of the bronchi, which give rise to coughing, and also the
sensations derived from various viscera. It is by means of the muscle sense
that we become aware of the condition of the muscles, and thus obtain the
information necessary for their adjustment to various purposes — standing,
walking, grasping, etc. This muscular sensibility is shown in our power to
estimate the differences between weights by the different muscular efforts
necessary to raise them. It must be carefully distinguished from the sense
of contact or pressure, of which the skin is the organ. When standing erect,
we can feel the ground contact, and there is a sense of pressure, due to our
feet being pressed against the ground by the weight of the body. Both
these are derived from the skin of the sole of the foot. If now we raise the
body on the toes, we are conscious, through the muscular sense, of a muscular

629

630 THE SENSES

effort made by the muscles of the calf. But the muscle sense will be dis-
cussed further, page 703.

It is manifestly impossible to draw a very clear line of demarcation
between some of these senses.

Special Senses. — The special senses include Touch, Temperature
(Heat and Cold), Taste, Smell, Hearing, Sight.

The most important distinction between common and special sensations
is that by the former we are made aware of certain conditions of various
parts of our bodies, while from the latter is gained a knowledge of the ex-
ternal world. This difference will be clear if we compare the sensations of
pain and touch, the former of which is a common, the latter a special, sensa-
tion. "If we place the edge of a sharp knife on the skin, we feel the edge
by means of our sense of touch; we perceive a sensation, and refer it to the
object which has caused it. But as soon as we cut the skin with the knife,
we feel pain, a feeling which we no longer refer to the cutting knife, but which
we feel within ourselves, and which communicates to us the fact of a change
of condition in our own body. By the sensation of pain we are neither able
to recognize the object which caused it nor its nature. "

It is important in studying the phenomena of sensation clearly to under-
stand that the sensorium, or seat of sensation, is in the brain, and not in the
particular organ through which the sensory impression is received. In com-
mon parlance we are said to see with the eye, hear with the ear, etc., but in
reality these organs are only adapted to receive stimuli which produce changes
that are, through their respective nerves, conducted to the sensorium, to give
rise to sensation.

Hence, if the optic nerve is severed, vision is no longer possible. Although
the image falls on the retina as before, the sensory impulse can no
longer be conveyed to the sensorium. When any given sensation is felt, all
that we can with certainty affirm is that some part of the brain is excited.
The exciting cause may be some object of the external world, producing an
objective sensation; or the condition of the sensorium may be due to some
excitement within the brain itself, in which case the sensation is termed sub-
jective. The mind habitually refers sensations to external causes; and hence,
whenever they are subjective we can hardly divest ourselves of the idea of an
external cause, and an illusion is the result.

Sensory Illusions. — Numberless examples of such illusions might
be quoted. As familiar cases may be mentioned humming and buzzing in
the ears caused by some irritation of the auditory nerve center. These
stimuli may even be interpreted as musical sounds, or voices, sometimes
termed auditory spectra. So-called optical illusions in which objects are
described as seen, although not present, may be caused by changes going
on in some part of the visual apparatus beyond the eye. Such illusions are
most strikingly exemplified in cases of delirium tremens or other forms of

THE SENSE OF TOUCH 631

delirium, and may take the form of animals such as cats, rats, or creeping
loathsome forms, etc.

One uniform internal cause, which may act on all the nerves of the senses
in the same manner, is capillary congestion. This one cause excites in the
retina, while the eyes are closed, the sensations of light and luminous flashes;
in the auditory nerve, the sensation of humming and ringing sounds; in the
olfactory nerve, the sense of odors; and the nerves of feeling, the sensation
of pain. In the same way a chemical substance introduced into the blood
may excite in the nerves of each sense peculiar symptoms: In the optic nerves,
the appearance of luminous sparks before the eyes; in the auditory nerves,
tinnitus aurium; and in the common sensory nerves, the sensations of creeping
over the surface. So, also, among external causes, the stimulus of electricity,
or the mechanical influence of a blow, concussion, or pressure, excites in the
eye the sensation of light and colors; in the ear, a sensation of a sound
or of ringing; and in the tongue, a saline or acid taste.

Sense Perceptions. — The habit of constantly referring our sensa-
tions to external causes leads us to interpret the various modifications which
external objects produce in our sensations, as properties of the external bodies
themselves. Thus we speak of certain substances as possessing a disa-
greeable taste and smell; whereas, the fact is their taste and smell are only
disagreeable to us. It is evident, however, that on this habit of referring our
sensations to causes outside ourselves, perception, depends the reality of
the external world to us; and more especially is this the case with the senses
of touch and sight. By the co-operation of these two senses, aided by the
others, we are enabled gradually to attain a knowledge of external objects
which daily experience confirms, until we come to place unbounded confi-
dence in what is termed the evidence of the senses.

We must draw a distinction between mere sensations, and the judgments
based, often unconsciously, upon them. Thus, in looking at a near object,
we unconsciously estimate its distance and say it seems to be ten or twelve
feet off. But the estimate of its distance is in reality a judgment based on
many things besides the appearance of the object itself; among which may
be mentioned the number of intervening objects, the number of steps which
from past experience we know we must take before we could touch it, and
many others.

I. THE SENSES OF TOUCH, TEMPERATURE, PAIN, AND
THE MUSCLE SENSE.

The Sense of Touch.— The sense of touch, like all the special senses,
possesses a special end-organ for the initiation of a nerve impulse through
contact with external objects. The sense organ of touch is not confined
to particular parts of the body of small extent, like the organ of sight, for
example, but is found in all parts of the skin and its inversions, the stomo-

632 THE SENSES

deum and proctodeum. The nerves of sensation are contained in the same
trunks with other sensory nerves. They are found in the posterior or sen-
sory roots of the spinal nerves and in the sensory divisions of the cranial
nerves, especially the fifth, seventh, ninth, and tenth.

All parts of the epidermis supplied with sensory nerves are thus, in some
degree, organs of touch, yet the sense is exercised in greatest perfection in
certain parts, the sensibility of which is extremely delicate, e.g., the skin of
the hands, the tongue, and the lips, which are provided with abundant touch
papillae. A peculiar and very acute sense of touch is exercised through the
medium of the nails and teeth, and, to a less extent, the hair may be consid-
ered an organ of touch, as in the case of the eyelashes.

FIG. 420. — Touch Corpuscle.

The sense of touch renders us conscious of the presence of a contact
stimulus, from the slightest to the most intense degree of its action. The
modifications of this sense often depend on the extent of the parts affected.
The sensation of pricking, for example, is produced when the sensitive fibers
are intensely affected in a small extent; the sensation of pressure indicates
a slighter affection of the parts over a greater extent and depth. It is by the
depth to which the parts are affected that the feeling of pressure is distin-
guished from that of mere contact.

In almost all parts of the body which have delicate tactile sensibility the
epidermis, immediately over the dermal papillae, is moderately thin. When
its thickness is much increased, as over the heel, the sense of touch is very
much dulled. On the other hand, when it is altogether removed, and the
cutis laid bare, the sensation of contact is replaced by one of pain. Further,
in all highly sensitive parts, the papillae are numerous and highly vascular,
and the sensory nerves are connected with special end-organs which have
been described on page 74 et seq.

ACUTENESS OF THE SENSE 633

The special endings of the nerves which have to do with touch may, how-
ever, be here again mentioned. They are of two kinds, viz.: i. Touch cor-
puscles, which are found chiefly in the hands and feet, particularly on the
palmar surface of the hands and fingers, but also on the under surface of the
forearm, on the nipple, eyelids, lips, and the genital organs. Touch corpus-
cles are situated in the cutis vera. 2. End bulbs are found in the conjunctiva
and other mucous membranes, the lips, genital organs, tongue, rectum, and
elsewhere, but not in the skin proper. As regards the Pacinian corpuscles
and similar end-organs, which are so widely distributed, and which may be in
some way connected with the sensation, when they are found in the skin they
are situated very deeply in the cutis vera or in the subcutaneous tissue.
They are extremely numerous on the nerves of the palmar surface of the
fingers. In addition to these special nerve endings, nerve fibers terminate
everywhere in the skin between the cells of the Malpighian stratum of the
epidermis.

The acuteness of the sense of touch depends very largely on the cutaneous
circulation, which is of course greatly influenced by external temperature.
Hence the numbness, familiar to everyone, produced by the application of
cold to the skin.

Acuteness of the Sense. — The perfection of the sense of touch on
different parts of the surface is proportioned to the minimal pressure required
to stimulate the point, i.e., the threshold stimulus. Or it can be measured
by the power which such parts possess of distinguishing and isolating the
sensations produced by two points placed close together. This latter is a
measure of the power of localization in a degree. This power depends, at
least in part, on the number of primitive nerve fibers; for the fewer the primi-
tive fibers which an organ receives, the more likely is it that several impres-
sions on different contiguous points will act on only one nervous fiber, and
hence be confounded, and perhaps produce but one sensation. Experiments
have been made to determine the tactile properties of different parts of the
skin, as measured by this power of distinguishing distances between points
of simultaneous contact. These consist in touching the skin with the points
of a pair of compasses sheathed with cork, and in ascertaining how close the
points of the compasses might be brought to each other and still be felt as
two bodies.

TABLE OF VARIATIONS IN THE TACTILE SENSIBILITY OF THE DIFFERENT PARTS

OF THE SKIN.

The measurement indicates the least distance at which the two blunted points
of a pair of compasses could be separately distinguished. (E. H. Weber.)

Tip of tongue i mm.

Palmar surface of third phalanx of forefinger 2 mm.

Palmar surface of second phalanges of fingers 4 mm.

Red surface of under-lip 4 mm.

634 THE SENSES

Tip of nose 6 mm.

Middle of dorsum of tongue 8 mm.

Palm of hand 10 mm.

Center of hard palate 12 mm.

Dorsal surface of first phalanges of fingers 14 mm.

Back of hand 25 mm.

Dorsum of foot near toes 37 mm.

Gluteal region 37 mm.

Sacral region 37 mm.

Upper and lower parts of forearm 37 mm.

Back of neck near occiput 50 mm.

Upper dorsal and mid-lumbar regions 50 mm.

Middle part of forearm 62 mm.

Middle of thigh 62 mm.

Mid-cervical region 62 mm.

Mid-dorsal region 62 mm.

In the case of the limbs, before the points are recognized as two, they
have to be further separated when the line joining them is in the long axis of
the limb than when in the transverse direction.

According to Weber the mind estimates the distance between two points
by the number of unexcited nerve endings which intervene between the two
points touched. It would appear that a certain number of intervening un-
excited nerve endings is necessary before two points touched can be recog-
nized as separate, and the greater this number the more clearly are the points
of contact distinguished as separate. The delicacy of the sense of touch may
be very much increased by practice. A familiar illustration occurs in the
case of the blind, who, by constant practice, can acquire the power of reading
raised letters the forms of which are almost, if not quite, undistinguishable by
the sense of touch to an ordinary person.

The different degrees of sensitiveness possessed by different parts may
give rise to errors of judgment in estimating the distance between two points
where the skin is touched. Thus, if blunted points of a pair of compasses
(maintained at a constant distance apart) be slowly drawn over the skin of
the cheek toward the lips, it is almost impossible to resist the conclusion that
the distance between the points is gradually increasing. When they reach
the lips they seem to be considerably farther apart than on the cheek. Thus,
too, our estimate of the size of a cavity in a tooth is usually exaggerated when
based upon sensations derived from the tongue alone. Another curious
illusion may here be mentioned. If we close the eyes, and place a small
marble or pea between the crossed fore and middle fingers, we seem to be
touching two marbles, figure 480. This illusion is due to an error of judg-
ment. The marble is touched by two surfaces which, under ordinary cir-
cumstances, could be touched only by two separate marbles, hence the mind,
taking no cognizance of the fact that the fingers are crossed, forms the con-
clusion that two sensations are due to two marbles.

SENSE OF TEMPERATURE

635

Sense of Temperature. — The whole surface of the body is more or
less sensitive to differences of temperature. The sensation of heat is distinct
from that of touch, hence it would seem reasonable to suppose that there are
special nerves and nerve endings for temperature. At any rate the power of
discriminating temperature may remain unimpaired when the sense of touch
is temporarily in abeyance. Thus if the ulnar nerve be compressed at the
elbow till the sense of touch is very much dulled in the fingers which it sup-
plies, the sense of temperature remains quite unaffected. And in certain
diseases of the cord the sense of touch may be impaired in a part, and tem-
perature remain undisturbed, or the converse.

The mapping of the surface of a part of the skin with reference to its
sensibility to temperature reveals the fact that there are definite heat and

FIG. 421. — Diagram of a Part of the Hand, Showing Distribution of Sense Spots; for
touch, A ; for heat, B\ and for cold, C. In A the skin is sensitive except at the parts marked
\vith black; in B and C, the intensity of the shading represents the relative sensitiveness.
(Goldscheider.)

cold spots. Furthermore, the areas do not coincide, leading us to conclude
that there are two distinct sense organs concerned, figure 421, B and C.

The sensations of heat and cold are often exceedingly fallacious, and in
many cases are no guide at all to the absolute temperature as indicated by
a thermometer. All that we can with safety infer from our sensations of
temperature is that a given object is warmer or cooler than the skin. Thus
the temperature of our skin is the standard; and as this varies from hour to
hour according to the activity of the cutaneous circulation, our estimate of
the absolute temperature of any body must necessarily vary too. If we put
the left hand into water at 5° C. (40° F.) and the right into water at 45° C.
(i 10° F.), and then immerse both in water at 27° C. (80° F.), it will feel warm
to the left hand, but cool to the right. Again, a piece of metal which has
really the same temperature as a given piece of wood will feel much colder,
since it conducts away the heat much more rapidly. For the same reason
air in motion feels very much cooler than air of the same temperature at rest.

In some cases we are able to form a fairly accurate estimate of absolute

636 THE SENSES

temperature. Thus, by plunging the elbow into a bath, a practised bath-
attendant can tell the temperature sometimes within half a degree centigrade.

The temperatures which can be readily discriminated are between 10° and
45° C. (50° and 115° F.); very low and very high temperatures alike produce
a burning sensation. A temperature appears higher according to the extent
of cutaneous surface exposed to it. Thus, water of a temperature which
can be readily borne by the hand is quite intolerable if the whole body be
immersed.

The delicacy of the sense of temperature coincides in the main with
that of touch, and appears to depend largely on the thickness of the skin;
hence, in the elbow, where the skin is thin, the sense of temperature is delicate,
though that of touch is not remarkably so. Weber has further ascertained
the following facts: two points so near together on the skin that they produce
but a single impression, at once give rise to two sensations, when one is hotter
than the other. Moreover, of two bodies of equal weight, that which is the
colder feels heavier than the other.

As every sensation is attended with a perception and leaves behind it an
idea in the mind which can be reproduced at will, we are enabled to compare
the idea of a past sensation with another sensation really present. Thus we
can compare the weight of one body with another which we had previously
felt, of which the idea is retained in our mind. Weber was indeed able to
distinguish in this manner between temperatures experienced one after
the other, better than between temperatures to which the two hands were
simultaneously subjected. This power of comparing present with past sensa-
tions diminishes, however, in proportion to the time which has elapsed between
them. After- sensations left by impressions on nerves of common sensibility
or touch are very vivid and durable. As long as the condition into which
the stimulus has thrown the organ endures, the sensation also remains,
though the exciting cause should have long ceased to act. Both painful and
pleasurable sensations afford many examples of this fact.

Sense of Pain. — As regards painful sensations, three views can be taken,
i, That it is a special sensation provided with a special conducting apparatus
in each part of the body; 2, that it is produced by an over-stimulation of the
special nerves concerned with touch or temperature, or of the other nerves
of special sense; or 3, that it is an over-stimulation of the nerves of common
sensation, which tell us of the condition of our bodies, both of the surface and
also of the internal organs. There seems to be much in favor of all of these
views. The weight of evidence is, however, rather against there being any
special pain sense with a special end-organ and fibers, though Barker in his
own arm experienced the presence of pain sensations while there was absence
of sensations of touch and temperature. It is, indeed, certain that, even if
any variety of pain be a special sensation, some kind of pain may be produced
by stimulation of the bare sensory nerves apart from any special form of

THE MUSCULAR SENSE 637

nerve termination. It is said that the main difference between the common
sensory apparatus which tells us of the condition of all parts of the body of
which thirst and hunger are but examples, and the special sense of touch and
temperature, is that the latter are provided with a special local apparatus.
By means of this apparatus we are able to localize the sensation. Such a
special apparatus is evidently not absolutely essential for the sensation of
pain, but this does not exclude the idea that pain may result from over-stimu-
lation of a nerve of special sense or of its termination.

The Muscular Sense. — The estimate of a weight is usually based on
two sensations: i, of pressure on the skin, and 2, the sense of muscular
resistance.

The estimate of weight derived from a combination of these two sensations
(as in lifting a weight) is more accurate than that derived from the former
alone (as when a weight is laid on the hand) ; thus Weber found that by the
former method he could generally distinguish 19 \ oz. from 20 oz., but not
19! oz. from 20, while by the latter he could at most distinguish only 14 \ oz.
from 15 oz. It is not the absolute, but the relative, amount of the difference
of weight which we have thus the faculty of perceiving.

It is not, however, certain, that our idea of the amount of muscular force
used is derived solely from the muscular sense. We have the power of esti-
mating very accurately beforehand, and of regulating, the amount of nervous
influence necessary for the production of a certain degree of movement.
When we lift a vessel, with the contents of which we are not acquainted,
the force we employ is determined by the idea we have conceived of its weight.
If it should happen to contain some very heavy substance, as quicksilver,
we shall probably fail in the attempt; the amount of muscular action, or
of nervous energy, which we had exerted being insufficient. It is possible
that in the same way the idea of weight and pressure in raising bodies, or in
resisting forces, may in part arise from a consciousness of the amount of
nervous energy transmitted from the brain rather than from a sensation
in the muscles themselves. The mental conviction of the inability longer to
support a weight must also be distinguished from the actual sensation of
fatigue in the muscles.

So, with regard to the ideas derived from sensations of touch combined
with movements, it is doubtful how far the consciousness of the extent of
muscular movement is obtained from sensations in the muscles themselves.
The sensation of movement attending the motions of the hand is very slight;
and persons who do not know that the action of particular muscles is neces-
sary for the production of given movements, do not suspect that the move-
ment of the fingers, for example, depends on an action in the forearm. The
mind has, nevertheless, a very definite knowledge of the changes of position
produced by movements; and it is on this that the ideas which it conceives of
the extension and form of a body are in great measure founded.

638 THE SENSES

There is no marked development of common sensibility to be made out
in muscles: they may be cut without the production of pain. On the other
hand, there is no doubt that afferent impulses must pass upward from muscles
and tendons acquainting the brain with their condition. This, then, must be
a special sense. It has been suggested that the minute end-bulbs of Golgi
found in tendons, and that the Pacinian corpuscles in the neighborhood of
joints, are the terminal organs of this special sense.

Judgment of the Form and Size of Bodies. — By the sense of touch the mind
is made acquainted with the size, form, and other external characters of
bodies. And in order that these characters may be easily ascertained, the
sense of touch is especially developed in those parts which can be readily
moved over the surface of bodies. Touch, in its more limited sense, or the
act of examining a body by the touch, consists merely in a voluntary employ-
ment of this sense combined with movement, and stands in the same relation
to the sense of touch, or common sensibility, generally, as the act of seeking,
following, or examining odors does to the sense of smell. The hand is the
best adapted for it, by reason of its peculiarities of structure — namely, its
capability of pronation and supination, which enables it, by the movement
of rotation, to examine the whole circumference of a body; the power it
possesses of opposing the thumb to the rest of the hand, and the relative
mobility of the fingers; and lastly from the abundance of the sensory terminal
organs which it possesses. In forming a conception of the figure and extent
of a surface, the mind multiplies the size of the hand or fingers used in the
inquiry by the number of times which it is contained in the surface traversed;
and, by repeating this process with regard to the different dimensions of a
solid body, acquires a notion of its cubical extent, but, of course, only an
imperfect notion, as other senses, e.g., the sight, are required to make it
complete.

It is impossible in this consideration to say how much of our knowledge
of the thing touched depends upon pressure and how much upon the mus-
cular sense.

II. TASTE AND SMELL.

The special sense organs for taste and smell are stimulated by chemical
substances, the former by chemicals in solution, the latter by volatile materials.
They are also closely associated in action and wye do not always differentiate
between the two.

THE SENSE OF TASTE.

The conditions for the perceptions of taste are: i, the presence of a sense
organ, a nerve, and a nerve center with special endowments; 2, the excitation
of the sense organ by the sapid matters, which for this purpose must be in a
state of solution; 3, a temperature of about 37° to 40° C. (98° to 100° F.).

THE NERVES AND ORGANS OF TASTE

639

The Nerves and Organs of Taste. — The principal organ of the sense
of taste is the tongue. But the soft palate and its arches, the uvula, tonsils,
and probably the upper part of the pharynx, are also endowed with taste.
These parts, together with the base and posterior parts of the tongue, are
supplied with branches of the glosso-pharyngeal nerve, and evidence has

FIG. 422. — Papillar Surface of the Tongue, with the Fauces and Tonsils, i, Circum-
vallate papillae, in front of 2, the foramen cecum; 3, fungiform papillae; 4, filiform and
conical papillae; 5, transverse and oblique rugae; 6, mucous glands at the base of the tongue
and in the fauces; 7, tonsils; 8, part of the epiglottis; 9, median glosso-epiglottidean fold
(frenum epiglottidis). (From Sappey.)

been already adduced that this is the principal nerve of the sense of taste.
The anterior parts of the tongue, especially the edges and tip, are innervated
by fibers from the lingual branch of the fifth, but which arise in the ganglion
of the pars intermedia and are distributed in the chorda tympani, figures 387
and 388.

640

THE SENSES

The mucous membrane in the regions just mentioned possesses special
epithelial structures called taste buds. The taste buds are very abundant
in the side walls of the circumvallate papillae. They are also present in the
fungiform papillae, in the foliate papillae, and in the mucous membrane.
The taste bud is located at the deeper part of the stratified epithelium, is
ovoid in shape, and its free end abuts on the surface or opens to the surface
by a short canal. It is composed of two kinds of modified epithelial cells —
the supporting cells, which are long, spindle-shaped cells that form a sheath
around the special gustatory cells; and the taste cells, which are neuro-epithe-
lial cells that are found in the center of the taste bud. They are very slender
cells that project on the surface by a delicate process. A bundle of nerve
fibrils enters the base of each taste bud and forms a net about the taste cells.

FIG. 423.

FIG. 424.

FIG. 423.— Taste Bud from Side Wall of Circumvallate Papillee. (Merkel-Henle.)
a, Taste pore; b, nerve fibers, some of which enter the taste bud, intrageminal fibers, while
others end freely in the surrounding epithelium, intergeminal fibers.

FIG. 424. — Vertical Section of a Circumvallate Papilla of the Calf, i and 3, Epithelial
layers covering it; 2, taste goblets; 4, and 4', duct of serous gland opening out into the pit
in which the papilla is situated; 5 and 6, nerves ramifying within the papilla. (Engelmann.)

The circumvallate, the fungiform, and the filiform papillae, shown in
figure 422, are special structures that facilitate the stimulation of the taste
buds by sapid substances. They are all formed by a projection of the
mucous membrane, and contain special branches of blood vessels and
nerves. In details of structure, however, they differ considerably one from
another.

Circumvallate Papillee. — These papillae, figure 424, eight or ten in number,
are situated in two V-shaped lines on the base of the tongue. They are
circular elevations from i to 2 mm. in diameter each, with a central depres-
sion, and surrounded by a circular fissure, at the outside of which is a slightly
elevated ring. Both the central elevation and the ring are formed of close
set simple papillae.

TASTE SENSATIONS 641

Fungiform Papilla. — The fungiform papillae are scattered chiefly over
the sides and tip, and sparingly over the middle of the dorsum, of the tongue;
the name is derived from their being usually narrower at the base than at
the summit. They also are supplied with loops of capillary blood vessels,
and nerve fibers.

Conical or Filiform Papilla. — These, which are the most abundant
papillae, are scattered over the whole surface of the tongue, but especially
over the middle of the dorsum. They vary in shape somewhat, but for the
most part are conical.

Taste Sensations. — The occurrence of two kinds of special sensi-
bility, i.e., touch and taste in the same part, makes it sometimes difficult to
determine whether the impression produced by a substance is perceived
through the ordinary tactile sensitive fibers, or through those of the sense of
taste. In many cases, indeed, it is probable that both sets of nerve fibers
are concerned, as when irritating acrid substances are introduced into the
mouth.

Many of the so-called tastes are due to the sapid substances being also
odorous, and exciting the simultaneous action of the sense of smell. This is
shown by the insipid taste of certain substances when their action on the
olfactory nerves is prevented by closing the nostrils. Many of the popular
drinks lose much of their apparent excellence if the nostrils are held close
while they are drunk.

When these accessory sensations are taken into account it is found that
the clearly defined tastes are reduced to four: sweet, bitter, acid, and salt.
These taste sensations are produced by the respective substances when in
solution. If dry salt or quinine is placed on the surface of the tongue, no
taste appears until solution takes place in the secretions of the tongue. A
piece of metal, as a silver coin, gives rise to a seemingly distinct taste sensa-
tion, called metallic, but it is probably not to be accepted as co-ordinate with
the others. The acid taste may be excited by electricity. If a piece of zinc
be placed beneath and a piece of copper above the tongue, and their ends
brought into contact, an acid taste (due to the feeble galvanic current) is
produced. The delicacy of the sense of taste is sufficient to discern one part
of sulphuric acid in 10,000 of water, or one part of quinine in 200,000 of
water. But it is far surpassed in acuteness by the sense of smell.

ACUTENESS OF THE SENSE OF TASTE. (HALL.)

The average of 10 individuals.

Sugar >i part to 520

Quinine i part to 444,000

Acetic acid i part to 5,640

Salt i part to 469

Exploration of the taste areas reveals the fact that regions of the tongue
and mouth are not equally sensitive to the sapid substances. Sweet tastes

41

642

THE SENSES

are especially developed at the tip and sides of the tongue, while bitter tastes
are almost absent in the front, but especially developed on the basal region,
and in the fauces and pharynx. Salts are more stimulating to the tip of the
tongue, and acids along the sides. Individual tests of the fungiform papillae
by Oehrwall showed that about half the papillae reacted to sweet, bitter, and
acid, but that certain ones reacted only to sweet, or to sweet and bitter, or
to acid and bitter. This suggests the specific nature of the taste sensations
and tends to prove that there may be a special organ for each kind of stimulus.
Experiments have also shown that it is possible to do away with the power
of tasting bitters and sweets while the taste for acids and salts remains.
This is done by chewing the leaves of an Indian plant, Gymnema sylvestre.
It has also been shown that the power of tasting sweet substances disappears
before that of tasting bitter. Other experiments have shown that the mech-
anisms for salt and acid tastes are distinct.

FIG. 425. — Localization of Taste. Bitter ; acid ....; salt, — . — . — ; sweet ; T,

tonsils; FC, foramen cecum; CF, circumvallate papillae; FP, fungiform papillae. (Hall.)

After-tastes and Contrasts. — Very distinct sensations of taste are
frequently left after the substances which excited them have ceased to act
on the nerve, as the after- taste of metallic bitter, which remains after breaking
the stimulating current. Such sensations often endure for a long time, and
modify the taste of other substances applied to the tongue. Thus, the taste
of sweet substances is intensified after the tasting of common salt. After
rinsing the mouth with water containing salt, it is said that sweet solutions
are perceived that are too dilute to be detected ordinarily. Many other
chemicals produce similar results. The application of a sapid substance,
acid for example, to one side of the tongue intensifies the sensation produced
by a sapid substance applied to the other side. There is a simultaneous con-

THE SENSE OF SMELL 643

trast which suggests that the same relation exists between tastes as between
colors, of which those that are opposed, i.e., complementary, render each
other more vivid, though no general principles governing this relation have
been discovered in the case of tastes. In the art of cooking, however, atten-
tion has at all times been paid to the consonance or harmony of flavors in
their combination or order of succession, just as in painting and music the
fundamental principles of harmony have been employed empirically while
the theoretical laws were unknown.

Frequent and continued repetitions of the same taste render the perception
of it less and less distinct, in the same way that a color becomes more and
more dull and indistinct the longer the eye is fixed upon it. There is fatigue
of the taste organ at some point.

THE SENSE OF SMELL.

The sensation of smell is produced by the action of odorous particles on a
special end-apparatus, which in turn causes nerve impulses that arouse
changes in a special area in the sensorium. The stimulating cause is the
direct action of chemical substances as in the sense of taste. In this case,

ir

FIG. 426.— Nerves of the Septum Nasi, Seen from the Right Side. X f .— /, The
olfactory bulb; i, the olfactory nerves passing through the foramina of the cribriform plate,
and descending to be distributed on the septum; 2, the internal or septal twig of the nasal
branch of the ophthalmic nerve; 3, naso-palatine nerves. (From Sappey, after Hirschfeld
and Leveille.)

however, the substances must reach the sensory membrane in a gaseous
state or in extremely fine division, so that it can quickly enter into solution
in the moisture on the sensitive mucous surface. The odorous particles are
carried to the membrane by inspiratory currents of air.

The Olfactory Apparatus.— The essential parts of the olfactory ap-
paratus are the nasal sensory or olfactory membrane to receive the special
stimuli, and the nervous apparatus to conduct the olfactory nerve-impulse to
the sensory area in the cortex cerebri for its perceotion.

644 THE SENSES

The nose is not entirely an organ for the seat of smell. In fact the nasal
cavities are divided into three districts called, respectively: Regio vestibularis
which is the entrance to the cavity. It is lined with a mucous membrane very
closely resembling the skin, and guarded by hairs and by sebaceous glands.
2, Regio respiratoria, which includes the lower and middle meatus of the
nose. It is covered with mucous membrane of stratified columnar ciliated
epithelium. The mucosa is thick and consists of fibrous connective tissue;
it contains a certain number of tubular mucous and serous glands. 3, Regio

FIG. 427. — Nerves of the Outer Walls of the Nasal Fossae, i, Network of the branches
of the olfactory nerve, descending upon the region of the superior and middle turbinated
bones; 2, external twig of the ethmoidal branch of the nasal nerves; 3, spheno-palatine
ganglion; 4, ramification of the anterior palatine nerves; 5, posterior, and 6, middle divisions
of the palatine nerves; 7, branch to the region of the inferior turbinated bone; 8, branch to
the region of the superior and middle turbinated bones; 9, naso-palatine branch to the
septum cut short. (From Sappey, after Hirschfeld and Leveille.)

olfactoria. This includes the anterior two-thirds of the superior meatus, the
middle meatus, and the upper half of the septum nasi, figures 427 and 428.
It is of a yellowish color. It consists of a thicker mucous membrane than
in 2, made up of loose, areolar connective tissue covered by epithelium of a
special variety, resting upon a basement membrane. The cells of the epithe-
lium are of two principal kinds: a, columnar epithelial cells whose function
is to support b, the bipolar olfactory cells. The epithelial cells are prismatic
in shape and have upon their surfaces facets into which the olfactory cells
fit themselves, figure 428, e. They are thus analogous to the cells of Miiller
of the retina. The olfactory cells have an oblong or fusiform shape, which
is mainly determined by the large nucleus. The thin protoplasmic body has
two processes, an external and an internal. The external is large and passes
up to the free surface, to end in a small bunch of fibrils that are not vibratile.
The internal process is very fine, often varicose, and passes through the

THE OLFACTORY APPARATUS

64S

cribriform plate to form a glomerular basket with the branches of the mitral
cells of the olfactory bulb.

The olfactory bulb must be studied in relation with the nerve fibers and
olfactory cells with which it is connected. These parts together form a sen-
sory end-organ which resembles in many respects the retina. The discovery
of its true structure has thrown a flood of light on
the architecture of the nerve centers as a whole.

The olfactory bulb is not a nerve, but a modi-
fication of the brain cortex. A transection shows
it to be made up of four layers: i. Peripheral
fibers. 2. Olfactory glomerules. 3. Layer of
mitral cells. 4. Layer of granular cells and deep
nerve fibers.

The first and external layer is composed of
the fine nerve fibrils of the olfactory nerves.
They pass through the cribriform plate of the
ethmoid, arising from the olfactory cells of which
they are processes.

The glomerular layer contains numbers of
small round bodies whose structure shows that
they are made up of the interlocking expansions
of the olfactory fibers, on the one hand, and of
the branches of the "mitral" cells, on the other.
These are mingled in a close network, but do not
anastomose. It was by the study of these bodies
in part that the fact of the non-continuity of the
neurones was demonstrated, figure 429. This
layer also contains small fusiform cells with
branching dendrites that extend outward to the
glomeruli. Each has an axis-cylinder process
which passes inward to join the fibers of the
internal olfactory nerves.

The layer of mitral cells contains large cells,
some of them triangular and some in the shape of a miter. They have
numerous dendrites, one of which passes into a glomerulus and then breaks
up in a fine arborization. An axis-cylinder process passes off from the
inner surface and is continued as an internal olfactory nerve fiber in the
olfactory tract.

The layer of granules and central fibers contains a large number of very
small nerve cells, which are peculiar in that they have no axis-cylinder,
Their dendrites extend chiefly into the layer of mitral cells. They resemble
the spongioblasts of the retina and probably have commissural functions.
This layer has also some small star-shaped cells whose dendrites end in the

FIG. 428. — Bipolar Olfac-
tory Cells from the Xasal
Fossae of the Rat (Full-term
Fetus). A, Epithelium of the
olfactory mucosa; e, epithelial
cells; /,/, nerve cells; i, nerve
fibers terminating freely on
the epithelial surface; h,
olfactory nerve fibers; g, sen-
sory nerve derived from the
trigeminus. (Cajal.)

646

THE SENSES

mitral-cell layer. Among these cells run numerous fibers, chiefly from the
mitral cells and the fusiform cells of the glomerular layer. The general
arrangement is shown in figure 429.

The Stimulation of the Olfactory Membrane.— The extent of the
nasal mucous surfaces, and of the frontal and antral sinuses connected with
them, might suggest that the sensory olfactory surface is widely distributed,
but such is not the case. Air impregnated with vapor of camphor has been
injected into the frontal sinus through a fistulous opening, and odorous sub-
stances have been injected into the antrum of Highmore; but in neither case

FIG. 429. — Principal Constituent Elements of the Olfactory Bulb of a Mammal. (Van

Gehuchten.)

was any odor perceived by the patient. All parts of the nasal cavities are
endowed writh cutaneous sensibility by the nasal branches of the first and
second divisions of the fifth nerve, hence the sensations of cold, heat, itching,
tickling, and pain, and the sensation of tension or pressure in the nostrils.
That these nerves cannot perform the functions of the olfactory nerves is
proved by cases in which the sense of smell is lost, while the mucous mem-
brane of the nose remains susceptible to the various modifications of the
sense of touch. But it is often difficult to distinguish the sensation of smell
from that of mere feeling, and to ascertain what belongs to each separately.
This is true particularly of the sensations excited by acrid vapors in the nose,

THE STIMULATION OF THE OLFACTORY MEMBRANE 647

as of ammonia, horse-radish, mustard, etc., and the difficulty is the greater
when it is remembered that these acrid vapors have nearly the same action
upon the mucous membrane of the eyelids.

The true olfactory membrane is limited to the small area on either side
of the superior meatus and supplied by the olfactory nerve. It is stimulated
by odorous substances when they penetrate the upper chamber of the nose.
Currents of air can be drawn over this membrane more certainly and effect-
ively by sniffing the air, as noticed in the acts of a dog following the trail.
The odorous particles must come into contact with the olfactory cells when
in solution in the moisture over the surface and produce the stimulus by chem-
ical change. Mere presence in solution is not always adequate to a stimula-
tion. It seems that movement over the surface is necessary, at least to effect-
ive stimulation. Haycraft has repeated some of the older experiments and
finds that eau de Cologne can be introduced into the nasal cavity in warm
saline solutions without producing a sensation of smell even when 10 per cent,
solutions are used. He also showed that Cologne, bergamot, etc., can be
slowly diffused into the nasal cavity without producing a stimulus. If,
while the vapor is thus in the nasal cavity, the nostril be closed and the
person goes into pure air and breathes, then an odorous sensation is at once
experienced. This shows that even odorous gases "must be moved over the
olfactory surface " in order to produce a stimulus.

The presence of bodies in quantities so minute as to be undiscernible
even by spectrum analysis, 0.00000003 °f a gram of musk, can be distinctly
smelt (Valentin). Opposed to the sensation of an agreeable odor is that of
a disagreeable or disgusting odor, which corresponds to the sensations of
pain, dazzling and disharmony of colors, and dissonance in the other senses.
The cause of this difference in the effect of different odors is unknown; but this
much is certain, that odors are pleasant or offensive in a relative sense only,
for many animals pass their existence in the midst of odors which to us are
highly disagreeable. A great difference in this respect is, indeed, observed
among men. Many odors, generally thought agreeable, are to some per-
sons intolerable; and different persons describe differently the sensations
that they severally derive from the same odorous substances. There seems
also to be in some persons an insensibility to certain odors, comparable with
that of the eye to certain colors; and among different persons, as great a
difference in the acuteness of the sense of smell as among others in the acute-
ness of sight. We have no exact proof that a relation of harmony exists
between odors as between colors and sounds, though it is probable that such
is the case, since it certainly is so with regard to the sense of taste. Such a
relation would account in some measure for the different degrees of perceptive
power in different persons; for as some have no ear for music, so others have
no clear appreciation of the relation of odors, and therefore little pleasure
in them.

648 THE SENSES

Most of the substances taken as foods into the mouth give off odorous
particles that stimulate the olfactory membrane. In fact, the chief elements
in food flavors are not tastes, but smells, or combinations of the two. This
is particularly true of meats. Meats are especially prized for their delicate
flavors, and cooking is performed to bring out these flavors. Yet meat has
little taste other than salt; the so-called tastes are due to odorous particles
entering the nostril and stimulating the olfactory membrane at the same
moment the taste buds of the mouth are stimulated.

Subjective sensations occur frequently in connection with the sense of
smell. Often a person smells something which is not present, and which
other persons cannot smell; this is very frequent with nervous persons, but
it occasionally happens to every one. In a man who was conscious of a bad
odor, the arachnoid was found after death to be beset with deposits of bone,
and a lesion in the middle of the cerebral hemispheres was also discovered.
Dubois was acquainted with a man who, ever after a fall from his horse,
which occurred several years before his death, believed that he smelt a bad
odor.

III. HEARING AND EQUILIBRATION.
THE ANATOMY OF THE EAR.

For descriptive purposes, the ear, or organ of hearing, is divided into
three parts, i, the external, 2, the middle, and 3, the internal ear. The first
two are only accessory structures to the third, which contains the essential
parts of the organ of hearing. The accompanying figure, 430, shows very
well the relation of these divisions to each other.

The External Ear. — The external ear consists of the pinna or auricle
and the external auditory canal or meatus.

The principal parts of the pinna, figure 430, are two prominent rims en-
closed one within the other, the helix and antihelix, and inclosing a central
hollow named the concha; in front of the concha, a prominence directed
backward, the tragus, and opposite to this one directed forward, the anti-
tragus. From the concha, the auditory canal passes inward and a little
forward to the membrana tympani, to which it thus serves to convey the
vibrations of the air. It consists of a fibro-cartilage tube lined by skin con-
tinuous with that of the pinna, and extending over the outer part of the mem-
brana tympani. Fine hairs and sebaceous glands are present toward the
outer part of the canal, while deeper in the canal are small glands, resembling
the sweat glands in structure, which secrete the cerumen.

Regarding the external ear, therefore, as a collector and conductor of
sonorous vibrations, all its inequalities, elevations, and depressions become
of evident importance; for those elevations and depressions upon which the
undulations fall will tend to intensify certain sound waves while not affecting

THE ANATOMY OF THE EAR

649

FIG. 430. — Diagrammatic View from Before of the Parts Composing the Organ of
Hearing of the Left Side. The temporal bone of the left side, with the accompanying
soft parts, has been detached from the head, and a section has been carried through it
transversely, so as to remove the front of the meatus externus, half the tympanic membrane,
the upper and anterior wall of the tympanum and Eustachian tube. The meatus internus
has also been opened, and the bony labyrinth exposed by the removal of the surrounding
parts of the petrous bone, i, The pinna and lobe; 2, 2', meatus externus; 2', membrana
tympani; 3, cavity of the tympanum; 3', its opening backward into the mastoid cells;
between 3 and 3', the chain of small bones; 4, Eustachian tube; 5, meatus internus, contain-
ing the facial (uppermost) and the auditory nerves; 6, placed on the vestibule of the laby-
rnth above, the fenestra ovalis; a, apex of the petrous bone; b, internal carotid artery; c,
siyloid process; d, facial nerve issuing from the stylo-mastoid foramen; e, mastoid process;
at squamous part of the bone covered by integument, etc. (Arnold.)

FIG. 431. — Tympanic Ossicles of Left Ear. A, Incus seen from the front; B, malleus,
viewed from behind; C, incus, and D, malleus, seen from inner aspect; E, stapes, i, Body
of incus, with articular surface for head of malleus; 2, processus longus; 3, processus
lenticularis; 4, articular surface for incus; 5, head, 6, neck; 7, processus brevis; 8, manu-
brium; 9, body; 10, short process; n, long process; 12, processus longus; 13, head, 14,
facet for incus; 15, manubrium; 1 6, head; 17, neck; 18, crus anterius; 19, crus posterius;
20, foot plate.

650

THE SENSES

others. It is thought that this forms at least an aid in determining the
direction whence a sound comes.

The Middle Ear or Tympanum. — The middle ear, or tympanum, 3,
figure 430, is separated by the membrana tympani from the external auditory
canal. It is a cavity in the temporal bone, opening through its anterior and
inner wall into the Eustachian tube.

The Eustachian canal establishes communication between the tym anic
cavity and pharynx, thus equalizing the air pressure on the sides of the
tympanic membrane, serving the same mechanical purpose as the vent-hole
in a snare or bass drum. The cavity of the tympanum communicates pos-
teriorly with air cavities, the mastoid cells, in the mastoid process of the tem-

Recessus epitympanic
Body of inc

Short process of inc
Ligament of inc

Chorda tympani nerve

Pyramid, with tendon

of stapedius muscle

issuing from it

Foot of stape

Superfoinigament of malleus

•Head of malleus

ior ligament of malleus
Handle of malleus

Tensor tympani muscle

Processus

cochleariformis
Osseous part of
Eustachian tube

FIG. 432. — Left Membrana Tympani and Chain of Tympanic Ossicles (Seen from Inner

Aspect). (Cunningham.)

poral bone; but its only opening to the external air is through the Eustachian
tube. The cavity of the tympanum is lined with mucous membrane, the
epithelium of which is ciliated and continuous with that of the pharynx. It
contains a chain of small bones, ossicula auditus, which extends from the
membrana tympani to the fenestra ovalis.

The Membrana Tympani. — The tympanic membrane is placed in a slant-
ing direction at the bottom of the external canal, its plane being at an angle
of about forty-five degrees with the lower wall of the canal. It is formed
chiefly of a tough and tense fibrous membrane, the edges of which are set
in a bony groove. Its outer surface is covered by a continuation of the
epithelial lining of the auditory canal, its inner surface with part of the
mucous membrane of the middle ear.

The Tympanic Ossicles. — The ear bones, or ossicles, are named the
malleus, incus, and stapes. The malleus is attached by a long slightly curved
process, called its handle, to the membrana tympani, the line of attachment

THE MIDDLE EAR OR TYMPANUM 651

being vertical, including the whole length of the handle, and extending from
the upper border to the center of the membrane. The head of the malleus
is irregularly rounded; its neck, or the line of boundary between it and the
handle, supports a short conical process which receives the insertion of the
tensor tympani muscle. The incus, shaped like a bicuspid molar tooth, is
articulated by its broader part to the malleus. Of its two fang-like processes,
one directed backward has a free end lodged in a depression in the mastoid
bone; the other, curved downward and more pointed, articulates by means
of a roundish tubercle with the stapes. The stapes is a little bone shaped
exactly like a stirrup, of which the base or bar fits into the f enestra ovalis.
The stapedius muscle is attached to the neck of the stapes.

The bones of the ear are covered with mucous membrane reflected over
them from the wall of the tympanum. They are movable both altogether
and one upon the other. The malleus moves and vibrates with every move-

FIG. 433. FIG. 434.

FIG. 433. — Right Bony Labyrinth, Viewed from the Outer Side. The specimen here
represented is prepared by separating piecemeal the looser substance of the petrous bone
from the dense walls which immediately enclose the labyrinth, i, The vestibule; 2,
fenestra ovalis; 3, superior semicircular canal; 4, horizontal or external canal; 5, posterior
canal; *, ampullae of the semicircular canals; 6, first turn of the cochlea; 7, second turn; 8,
apex; 9, fenestra rotunda. The smaller figure in outline below shows the natural size.
X 2.5. (Sommering.)

FIG. 434. — View of the Interior of the Left Labyrinth. The bony wall of the labyrinth
is removed superiorly and externally, i, Fovea hemielliptica; 2, fovea hemispherica; 3,
common opening of the superior and posterior semicircular canals; 4, opening of the
aqueduct of the vestibule; 5, the. superior, 6. the posterior, and 17, the external semicircular
canals; 8, spiral tube of the cochlea (scala tympani); 9, opening of the aqueduct of the
cochlea; 10, placed on the lamina spiralis in the scala vestibuli. X 2 .5. (Sommering.)

ment and vibration of the membrana tympani, and its movements are com-
municated through the incus to the stapes, and through the stapes to the
membrane closing the fenestra ovalis. The malleus, also, is movable in its
articulation with the incus. The membrana tympani which moves the long
process of the malleus is altered in its degree of tension by the degree of con-

652

THE SENSES

traction of the tensor tympani muscles. The stapes is movable on the proc-
ess of the incus, the contractions of the stapedius muscle draws it outward.
The axis round which the malleus and incus rotate is the line joining the
processus gracilis of the malleus and the posterior process of the incus.

The Internal Ear.— The internal ear, or labyrinth, constitutes the
proper organ of hearing. It contains special epithelial structures to which
are distributed the auditory nerves. The organ is located in a cavity in the

FIG. 435. — Membranous Labyrinth of a 30 mm. Human Fetus. A , Viewed from its Lateral
Aspect; B, viewed from the mesial aspect. (Streeter.)

petrous bone, called the osseus labyrinth. The auditory organ within is
called the membranous labyrinth. The membranous labyrinth contains a
fluid called endolymph; while outside it, between it and the osseous labyrinth,
is a fluid called perilymph. This is not a pure lymph, as it contains mucin.
The osseous labyrinth consists of three principal parts, namely the vesti-
bule, the cochlea, and the semicircular canals, containing the respective
divisions of the membranous labyrinth. The osseous labyrinth possesses
openings on its inner wall for the entrance of the divisions of the auditory
nerve from the cranial cavity, in its outer wrall the fenestra ovalis, 2, figure
433, an opening filled by the base of the stapes, and the fenestra rotunda.
The vestibule also presents an opening, the orifice of the aqueductus vestibuli.

THE COCHLEA AND THE ORGAN OF CORTI 653

The Membranous Labyrinth. — The membranous labyrinth cor-
responds generally with the form of the osseous labyrinth, so far as regards
the vestibule and semicircular canals, but is separated from the walls of these
parts by perilymph, except where the nerves enter into connection within it.
The labyrinth is a closed membrane containing endolymph.

The Utriculus and the Sacculus. — The vestibular portion of the inner ear
consists of membranous sacs, the upper, the utriculus, the lower called the
sacculus. The former is connected with the semicircular canals, the latter
with the cochlea by the cochlear canal. The utriculus and the sacculus have
on their floors each a special patch of sensory epithelium called the macula.
The fibers of the vestibular divisions of the auditory nerve end in the
maculae, figure 435. In the cavities of the sacculus and utriculus are small
masses of calcareous particles called otoliths.

The Semicircular Canals. — There are three semicircular canals for each
ear, one horizontal and two vertical ones placed almost at right angles to
each other. The three canals, therefore, occupy the three planes of space.
Each has a considerable enlargement or swelling, called an ampulla. The
epithelium of the ampulla is modified at the point of entrance of the nerve
into a thickened hillock called the crista acustica. This epithelium is com-
posed of rod cells or supporting cells which extend the full thickness of the
crista, and of hair cells, which occupy the
inner or free half of the crista. The hair
cells are the sensory cells. They have hair-
like processes which project from the free
ends of the cells out into the endolymph of
the cavity. Nerve fibrils run up into the
crista and apparently form terminal arboriza- Fic. 436— yiew of the Osseous
tions about the hair cells, or, according to Cochlea Divided through the
i , . ,, „ Middle, i. Central canal of the

some observers, end in the cells. modiolus; 2, lamina spiralis ossea;

The Cochlea and the Organ Of Corti. — 3> scala tympani; 4, scala vestibuli;
™, i i i • i , i ' i 5> porous substance of the modiolus

The membranous cochlea is located in the near one of the sections of the
spiral canal in the petrous bone, called the canalis spiralis modioli. x 5.
cochlear canal. It is attached to the wall

of the cavity between the fenestra ovalis and the fenestra rotunda, and to
the outer wall of the canal and the free border of the lamina spiralis almost,
but not quite, to its summit. A small cavity is thus left around the
upper end of the cochlea connecting the scala vestibuli above with the scala
tympani below. A cross-section through the cochlear canal shows the
relations of the cochlear canal which was named scala media by the earlier
anatomists. The free portion of the membranous wall above is called the
membrane of Reisner, while that below is called the basilar membrane. The
basilar membrane supports the special sensory apparatus for the reception
of stimuli of sound waves.

654 THE SENSES

Organ of Corti. — The basilar membrane supports cells of several types.
About midway between the outer edge of the lamina spiralis and the outer
wall of the cochlea are situated the rods of Corti. Viewed sideways, they are
seen to consist of an external and internal pillar, each rising from an ex-
panded foot or base on the basilar membrane, figure 438. They slant in-
ward toward each other, and each ends in a swelling termed the head, the
head of the inner pillar overlying that of the outer, figure 438. Each pair of
pillars forms, as it were, a pointed roof arching over a space, and by a suc-
cession of them a little tunnel is formed. It has been estimated that there

FIG. 437. — Semidiagrammatic Section of a Cochlear Whorl. (After Heitzmann.)

are about three thousand of these pairs of rods of Corti between the base of
the cochlea and its apex. They are found progressively to increase in length,
and become more oblique; in other words, the tunnel becomes wider, but
diminishes in height as we approach the apex of the cochlea.

Leaning against the rods of Corti and apparently supported by them
are sensory cells or hair cells. The hair cells are in two series, the inner and
the outer hair cells. The former consist of a single layer, the latter of three
or four layers, figure 438. There are two additional types of supporting cells,
the cells of Deiters and of Hensen. The whole structure when viewed from
above bears a remarkable resemblance to the keyboard of a piano.

The cochlear division of the auditory nerve enters the base of the modiolus
and sends a spiral whorl of fibers out under the spiral lamina. The gan-
glionic cells of the cochlear division of the auditory nerve are located in the
base of the lamina where they form the spiral ganglion. The nerve fibers

THE PHYSIOLOGY OF HEARING

655

from the ganglion cells pass out through small holes in the periphery of the
spiral plate of bone, to enter the organ of Corti. Here they form small
longitudinal bundles that quickly end about the hair cells.

THE PHYSIOLOGY OF HEARING.

All the acoustic contrivances of the organ of hearing are means for con-
ducting sound. Since all matter is capable of propagating sonorous vibra-
tions, the simplest conditions must be sufficient for mere hearing; since all
substances surrounding the auditory apparatus would stimulate it. The
complex development of the organ of hearing, therefore, must have for its

limb*

mcmbrana Uctoria,

outer hair-cells

nervejibrcs

inner rod vas basilar outer cells of Deiters
itpii-alc membrane rod

FIG. 438. — Semidiagrammatic Representation of the Organ of Corti and Adjacent
Structures. (Merkel-Henle.) a, Cells of Hensen; b, cells of Claudius; c, internal spiral
sulcus; x, Nuel's space. The nerve fibers (dendrites of cells of the spinal ganglion) are
seen passing to Cord's organ through openings (foramina nervosa) in the bony spiral
lamina. The black dots represent longitudinally running branches, one bundle lying to
the inner side of the inner pillar, a second just to the outer side of the inner pillar within
Corti's tunnel, the third beneath the outer hair cells.

object the more effective propagation of the sonorous vibrations and their
intensification by resonance; and, in fact, the whole of the acoustic apparatus
may be shown to have reference to these principles.

The external ear and the auditory passages influence the propagation of
sound to the tympanum by collecting from the atmosphere the sonorous
undulations that strike against the external ear and by transmitting them by
the air in the passage to the membrana tympani.

In animals living in the atmosphere, the sonorous vibrations are con-
veyed to the auditory epithelium through three different media in series;
namely, the air of the external ear and meatus, which sets in vibration the
tympanic membrane, the solid chain of auditory ossicles, and the fluid of the
labyrinth. Sonorous vibrations are imparted too imperfectly from air to

656 THE SENSES

the solid structures of the body as a whole for the propagation of sound to
the internal ear to be adequately effected by that means alone. In passing
from air directly into water, sonorous vibrations suffer also a considerable
diminution of their strength; but if a tense membrane exists between the
air and water, the sonorous vibrations are communicated from the former
to the latter medium with very great intensity. This fact, of which Miiller
gives experimental proof, furnished at once an explanation of the use of the
fenestra ovalis and of the membrane closing it. It is the means of com-
municating, in full intensity, the vibrations of the ear bones, or, in their
absence, of the air in the tympanum, to the fluid of the labyrinth. The
vibration of the fluid, the perilymph and endolymph, of the internal ear, sets
the basilar membrane in vibration and in consequence stimulates the sensory
apparatus resting upon it. This last is the essential stimulating act, while
all that precedes is more or less accessory or contributory to this act. Just
what the accessory apparatus contributes can be best understood by an ex-
amination of the stimulus and the sensation which results from its action.

Sound. — Any elastic body, e.g., air, a membrane, or a string, performing
a certain number of regular vibrations per second, gives rise to what is termed
a musical sound or tone. We must, however, distinguish between a musical
sound and a mere noise; the latter being due to irregular vibrations.

Musical sounds are distinguished from each other by three qualities:
i. Strength or intensity, which is due to the amplitude or length of the wave
of vibrations. 2. Rate, the number of vibrations in a second. 3. Quality,
or timbre, the peculiar property by which we distinguish the same note
sounded on two instruments, e.g., a piano and a flute. It has been proved
by Helmholtz to depend on the number of secondary tones, termed harmonics,
which are present with the predominating or fundamental tone; that is,
rhythmic vibrations are either simple in form, like the vibrations of a reed
or tuning-fork, or compound, like the vibrations of a violin or piano string.
If the string of a violin is plucked it not only vibrates as a whole, but in seg-
ments in the ratio of one, two, three, etc. The form of air wave that is pro-
duced by several such vibrating bodies is very complex indeed, as, for exam-
ple, when an orchestra is playing.

The compound wave can be analyzed into its constituent elements by a
system of resonators, on the principle of sympathetic vibration. If one
sounds a series of musical notes before such a system of resonators it will be
found that the tones and overtones are selected by the resonators and made
more prominent so that they can be identified.

The sensation of sound has in it certain elements that correspond closely
with the physical properties of sound, i.e., loudness, pitch, and quality.
Loudness is dependent merely on the intensity of the stimulation. A sound
wave of great energy, for example, produces a larger movement of the tym-
panic membrane, and it, through the chain of bones and the fluid of the

FUNCTIONS OF THE EXTERNAL AND MIDDLE EARS 657

internal ear, a larger swing of the basilar membrane, hence a more intense
stimulus of the organ of Corti.

Function of the External and Middle Ears. — It has already been
stated that the external ear collects the sound waves and conducts them
against the membrana tympani. This membrane vibrates as a whole to
the compound waves that impinge upon it, and thus serves for the trans-
mission of sound from the air to the chain of ossicles of the middle ear. It is
often compared to the membrane of a drum, but there are fundamental
differences.

When a drum is struck, a certain definite fundamental tone is elicited;
similarly a drum is thrown into vibration when certain tones are sounded in
its neighborhood, while it is quite unaffected by others. In other words, it
can take up and vibrate in response only to those tones whose vibrations

B

FIG. 439. — Showing .4 and B, Simple Pendular Vibrations, Separated by One Octave. C,
The form of the curve produced by the combination of A and 5.

nearly correspond in number with those of its own fundamental tone. The
tympanic membrane can take up an immense range of tones produced by
vibrations ranging from 30 to 4,000 or 5,000 per second. This would be
clearly impossible if it were an evenly stretched membrane. The fact is
that the membrana tympani is by no means evenly stretched, and this is due
partly to its slightly funnel-like form, and partly to its being connected with
the chain of auditory ossicles. Further, if the membrane were quite free in
its center, it would go on vibrating as a drum does some time after it is struck;
each sound would be prolonged, leading to considerable confusion. This
evil is obviated by the ear bones, which check the continuance of the vibra-
tions like the "dampers" in a piano.

The vibrations of the membrana tympani are transmitted by the chain
of ossicles to the fenestra ovalis and fluid of the labyrinth, their dispersion
in the tympanum being prevented by the difficulty of the transition of vibra-
tions from solid to gaseous bodies. The necessity of the presence of air on
the inner side of the membrana tympani, in order to enable it and the audi-
42

658

THE SENSES

tory ossicles to fulfil the objects just described, is obvious. Without this pro-
vision, neither would the vibrations of the membrane be free nor the chain
of bones isolated, so as to propagate the sonorous undulations with con-
centration of their intensity. But while the oscillations of the membrana
tympani are readily communicated to the air in the cavity of the tympanum,
those of the solid ossicles will not be conducted away by the air, but will
be propagated to the labyrinth without being dispersed in the tympanum.

The propagation of sound through the audi-
tory ossicles to the labyrinth must be effected by
oscillations of the bones as a whole.

The existence of the membrane over the
fenestra rotunda permits approximation and
removal of the stapes to and from the labyrinth.
When the membrane of the fenestra ovalis is
pressed toward the labyrinth by the stapes, the
membrane of the fenestra rotunda may, by the
pressure communicated through the fluid of the
labyrinth, be pressed toward the cavity of the
tympanum. The long process of the malleus
receives the undulations of the membrana tym-
pani, figure 440, a, a, and of the air in a direction
indicated by the arrows, nearly perpendicular to
itself. From the long process of the malleus they
the Action of the are propagated to its head, b; thence into the
»cus, c, the long process of which is parallel with
the long process of the malleus. From the long
process of the incus the undulations are communi-

cated to the stapes, d, which is united to the incus at right angles. The
several changes in the direction of the chain of bones have, however, no
influence in changing the character of the undulations, which remain the
same as in the meatus externus. From the long process of the malleus
the undulations are communicated by the stapes to the fenestra ovalis in a
perpendicular direction. Increasing tension of the membrana tympani
diminishes the facility of transmission of sonorous undulations from the
air to it. It has been inferred, therefore, that hearing is rendered less
acute by increasing the tension of the membrana tympani. This is
accomplished by the contractions of the tensor tympani muscle. The
exact influence of the stapedius muscle in the act of hearing is unknown.
It acts upon the stapes in such a manner as to make it rest obliquely
in the fenestra ovalis, depressing that side of the stapes on which it is
attached and elevating the other side to the same extent. It seems to
prevent too great a movement of the bone.

The pharyngeal orifice of the Eustachian tube is usually shut. During

FIG. 440. — Diagram to Il-
lustrate

the Internal Ear.

THE FUNCTION OF THE INTERNAL EAR 659

swallowing, however, it is opened; which may be shown as follows: If the
nose and mouth be closed and the cheeks blown out, a sense of pressure is
produced in both ears the moment we swallow. This is due, doubtless, to
the bulging out of the tympanic membrane by the compressed air, which at
that moment enters the Eustachian tube. The principal office of the Eusta-
chian tube has relation to the prevention of the effects of increased tension of
the membrana tympani. Its existence and openness will provide for the
maintenance of the equilibrium between the air within the tympanum and
the external air, so as to prevent the inordinate tension of the membrana
tympani which would be produced by too great or too little pressure on either
side. While discharging this office it serves as an outlet for mucus. If the
tube were permanently open, the sound of one's own voice would probably
be greatly intensified, a condition which would of course interfere with the
perception of other sounds. At any rate, it is certain that sonorous vibra-
tions can be propagated up the tube to the tympanum by means of a catheter
inserted into the pharyngeal orifice of the Eustachian tube.

The Function of the Internal Ear. — The fluids of the labyrinth re-
ceive the sonorous vibrations at the fenestra ovalis and, we must assume,
conduct the same throughout the cavity. In all forms of organs of hearing
even to the simplest, liquid is the medium through which the auditory sensory
epithelium is stimulated. We have already seen that in the mammalian ear
there is a special mechanical arrangement to intensify the vibrations of the
fluid in the cochlear canal.

The utriculus, sacculus, and semicircular canals are probably not con-
cerned with auditory function, but with the sense of equilibrium; hence they
will be discussed separately a little later.

The cochlea is the special organ of hearing. When it is set in vibration
the movement stimulates the sensory hair cells on the basement membrane,
producing a sensory impulse which is transmitted along the paths to the brain
and there produces an auditory sensation. If the stimulus results from a
disturbance of an explosive or non-harmonic nature, the sensation is inter-
preted as a noise. If the disturbance is rhythmic or harmonic and repeated
in sequence within certain limits of rate, then a tone is perceived.

The intensity of sound, the energy of the disturbance, affects the basilar
membrane by producing motion of varying amplitude. This stimulates the
hair cells with greater or less intensity, which can be detected by the sensorium
as loudness. Loudness of the sound sensation is interpreted as intensity of
sound wave.

The interpretation of pitch is accomplished by the ear through a wide
range of rates of vibration that produce sensations of tone. The average
person can perceive musical tones over a range of vibration of from sixty-four
double vibrations per second for the lower notes, to four thousand and ninety-
six for the higher notes. These limits may be extended to thirty per second

660 THE SENSES

and forty thousand per second, respectively, but only a small number of
tones can be perceived outside of the narrower limits given above. This
extraordinary range of tone is conceivable only on the supposition of local-
ization of the stimulus in some part of the organ. Most physiologists look
to the basilar membrane and the organ of Corti for the localization.

Suppose a simple tuning-fork to be vibrating with a frequency of sixty-
four per second, then these waves will be conducted through the auditory
apparatus until they fall on the basilar membrane, and will set it in vibration
at the same rate. The exact type of the vibration is at present a matter of
inference. The piano theory of Helmholtz gives probably the most satisfac-
tory explanation. It assumes that the basilar membrane vibrates as would
a number of strings set in its transverse dimension. In support of this as-
sumption it is asserted that the membrane is taut in the transverse and
loose in the longitudinal plane. Retzius has estimated that it contains
about 24,000 fibers, and that it measures in width at the base 0.135 mm.
and at the apex 0.234 mm. In the above illustration the vibration fre-
quency of sixty-four would supposedly set in sympathetic vibration that part
of the apex of the basilar membrane which vibrated in the same frequency,
and the sensory cells of the organ of Corti, located over the vibrating fiber,
would be stimulated accordingly. In the same way notes of medium and
of high frequency stimulate localized areas of sensory cells in the middle
and basal parts of the organ of Corti and produce sensations of correspond-
ing pitch.

This idea of localization of auditory sensory stimulation makes it easier
to understand the analysis by the ear of compound sonorous waves. Such
waves impinge on the membrana tympani and are transmitted through the
conducting media unanalyzed, and may be supposed to fall on the basilar
membrane as compound waves. The basilar fibers acting like so many
resonators, take up the constituent sonorous elements in sympathetic vibra-
tion. In short, the basilar membrane is an analyzer in which the compound
wave is reduced to its simple components, each of which stimulates its cor-
responding portion of the organ of Corti. The auditory nerve impulses are
conducted through the cochlear nerves to the sensorium where they produce
auditory sensations with the same definiteness of pattern as cutaneous or
optical stimuli produce sensations that correspond to the patterns of stimula-
tion. The audition is so definite that one can consciously pick out one or
the other of the constituent stimulating elements and follow and examine
the same to the exclusion of the others, as when one follows a single instru-
ment in an orchestra or a single voice in a group of chattering children.

Bernstein says of this wonderful organ:

"In the cochlea we have to do with a series of apparatus adapted for per-
forming sympathetic vibrations with wonderful exactness. We have here
before us a musical instrument which is designed not to create musical

AUDITORY JUDGMENTS 66 1

sounds, but to render them perceptible, and which is similar in construction
to artificial musical instruments, but which far surpasses them in the delicacy
as well as the simplicity of its execution. For, while in a piano every string
must have a separate hammer by means of which it is sounded, the ear pos-
sesses a single hammer of an ingenious form in its ear bones, which can make
every string of the organ of Corti sound separately."

Auditory Judgments. — Direction. — The power of perceiving the
direction of sounds is not a faculty of the sense of hearing itself, but is an act
of the mind judging by experience previously acquired. From the modifica-
tions which the sensation of sound undergoes according to the direction in
which the sound reaches us, the mind infers the position of the sounding
body. The only true guide for this inference is the more intense action of the
sound upon one than upon the other ear. But even here there is room for
much deception, by the influence of reflexion or resonance, and by the prop-
agation of sound from a distance, without loss of intensity, through curved
conducting tubes filled with air. By means of such tubes, or of solid con-
ductors, which convey the sonorous vibrations from their source to a distant
resonant body, sounds may be made to appear to orginate in a new situation.
The direction of sound may also be judged of by means of one ear only; the
position of the ear and head being varied, so that the sonorous undulations
at one moment fall upon the ear in a perpendicular direction, at another
moment obliquely. But when neither of these circumstances can guide us in
distinguishing the direction of sound, as when it falls equally upon both ears,
its source being, for example, either directly in front or behind us, it becomes
impossible to determine whence the sound comes.

Distance. — The judgment of the distance of the source of sounds is in-
ferred from their intensity. The sound is interpreted as coming from an
exterior sonorous body. When the intensity of the voice is modified in imita-
tion of the effect of distance, it excites the idea of its originating at a distance.
Ventriloquists take advantage of the difficulty with which the direction of
sound is recognized, and also the influence of the imagination over our judg-
ment, when they modulate the voices, and at the same time pretend, them-
selves, to hear sounds as coming from a certain direction.

Duration of the Auditory Stimulus. — By removing one or several teeth
from the toothed wheel of a vibrator, the fact has been demonstrated that in
the case of the auditory organ, as in that of the eye, the sensation continues
longer than the impression which causes it; for a removal of the tooth pro-
duced no interruption of the sound. The gradual cessation of the sensation
of sound renders it difficult to determine its exact duration beyond that of
the impression of the sonorous impulses.

Binaural Sensations. — Corresponding to the double vision of the same
object with the two eyes is the double hearing with the two ears; and analo-
gous to the double vision with one eye, dependent on unequal refraction, is

662 THE SENSES

the double hearing of a single sound with one ear, owing to the sound coming
to the ear through media of unequal conducting power. The first kind of
double hearing is very rare; instances of it, however, have been recorded.
The second kind, which depends on the unequal conducting power of two
media through which the same sound is transmitted to the ear, may easily
be experienced. If a small bell be sounded in water, while the ears are closed
by plugs, and a solid conductor be interposed between the water and one
ear, two sounds will be heard differing in intensity and tone, one being con-
veyed to the ear through the medium of the atmosphere, the other through
the conducting-rod.

Subjective Sensations. — Subjective sounds are the result of a state of irri-
tation or excitement of the auditory nerve produced by other causes than
sonorous impulses. A state of excitement of this nerve, however induced,
gives rise to the sensation of sound. Hence the ringing and buzzing in the
ears heard by persons of irritable and exhausted nervous system, and by
patients with cerebral disease, or disease of the auditory nerve itself; hence
also the noise in the ears heard for some time after a long journey in a rat-
tling, noisy vehicle. Ritter found that electric currents also excite sounds in
the ears. From the above truly subjective sound we must distinguish those
dependent, not on a state of the auditory nerve itself merely, but on sonorous
vibrations excited in the auditory apparatus. Such are the buzzing sounds
attendant on vascular congestion of the head and ear or on aneurysmal dilata-
tion of the vessels. Frequently even the simple pulsatory circulation of the
blood in the ear is heard. To the sounds of this class belong also the buzz
or hum, heard during the contraction of the palatine muscles in the act of
yawning, during the forcing of air into the tympanum so as to make tense the
membrana tympani.

Irritation or excitement of the auditory nerve is capable of giving rise to
movements in the body and to sensations in other organs of sense. In both
cases it is probable that the laws of reflex action, through the medium of the
brain, come into play. An intense and sudden noise excites in every person
closure of the eyelids, and in nervous individuals a start of the whole body
or an unpleasant sensation throughout the body like that produced by an
electric shock.

THE SENSE OF EQUILIBRIUM.

Although the utriculus, sacculus, and semicircular canals form the major
part of the labyrinth and are closely associated with the cochlea in develop-
ment, there is increasing evidence that these structures are not concerned
with hearing, but rather with a sense of equilibrium. This view has been
strengthened by recent investigations into the anatomical relations of the
different elements in the auditory nerve, figure 435.

THE SEMICIRCULAR CANALS 663

These structures have each a special modification of the sensory epithe-
lium which receives the vestibular branch of the eighth nerve. These
epithelial areas are differentiations of the embryonic ear pit, which is derived
from the epiblast. In fishes which have well-developed semicircular canals
and vestibule this sensory epithelium has a common origin from the em-
bryonic anlage which gives rise to the ear, the branchial sense organ, and
the lateral line organs, all of \vhich probably have static functions.

The Semicircular Canals. — The semicircular canals are connected
with the utriculus, are three in number on each side, and have been already
shown to lie in space practically at right angles to one another. Each is
filled with endolymph, and each has a special organ, the crista acustica,
wrhich receives a division of the vestibular branch of the eighth nerve.

The function of the semicircular canals is believed to be to give rise to
sensations by which we determine the motion of the body in space. It was
shown long ago that if one closes his eyes and turns rapidly around the vertical
axis, then suddenly stops and opens the eyes, surrounding objects seem to
be rotating around the same vertical axis. If the head be inclined so that
the face is in the horizontal plane and the rotation around the vertical axis
be repeated, then, upon suddenly raising the head into the ordinary position
and opening the eyes, objects seem to be moving about the head around the
norizontal axis. In both these cases the direction of the apparent motion
of objects depends upon the actual motion of the body that preceded it and
is in the opposite direction. In the first case the rotation is in the plane of
the horizontal semicircular canal. It is assumed here that, at the beginning of
such a movement, the endolymph, being fluid and inert, tends to remain still
for a moment and the canal to move over it so as to produce pressure in the
funnel of the ampulla. That is, it has the same effect as though the endo-
lymph moved in the canal. This relative motion bends the hairs of the hair
cells of the crista acustica, thus stimulating the hair cells and giving rise to
sensory nerve impulses. When the head suddenly stops rotating the situa-
tion is just reversed and there will be a second stimulation, but in the opposite
direction. When one considers the position of the three semicircular canals,
it will be seen that movement of the head in any direction will stimulate
one or more of the cristae, giving rise to either simple or complex sensory
impulses.

This theory is borne out by the effects of operation on the semicir-
cular canals. By the observations of Flourens, injury to the semicircular
canals causes disturbances in muscular co-ordination, especially in move-
ments that take place in the plane of the injured canal. If a horizontal canal
in a pigeon be sectioned, the animal supports its head in the vertical position,
very well, but is unable to co-ordinate its horizontal movements. It tends to
produce rotary motions around the vertical axis. If a vertical canal is sec-
tioned, the head falls to one or the other side according to the canal, and the

664 THE SENSES

animal shows instability of position in that plane. It has been shown that
stimulation of a sectioned canal produced reflex movements in that plane.

Muscular co-ordination is a complex phenomenon and involves the oper-
ation of numerous sensory impulses from other organs of the body, especially
from the eyes and general skin. Some confusion has arisen from the fact that
there are associated with the disturbance in the semicircular canals move-
ments of the eyes and head in higher animals, and of the eyes, head, and fins
in such animals as fishes — the so-called compensatory movements. Without
going into details, it is sufficient to state that the sense organs of the semi-
circular canals probably form only one of the series of sensory structures
concerned in the co-ordination of body movements.

The Utriculus and Sacculus. — The utriculus and sacculus each have
a sensory area, the maculae, over which there rests in the human ear
and in most animals small particles of calcareous matter, otoliths. These
otoliths, therefore, lie among the projecting hairs of the sensory cells. This
is characteristic of these sensory areas and differentiates them from the
arrangement present in the cristae. There would seem to be close agree-
ment in function between the maculae and cristae, and we naturally look to
the influence of the otoliths on the processes which result in the stimulation
of the maculae. Attempts have been made to remove the otoliths, with the
result that in such animals there is apparent inability to maintain a constant
position in space. The experiments have been performed which have sug-
gested the theory that the otoliths take an active part in stimulating the sen-
sory cells, probably by their mere pressure. If the head is inclined in one
or the other direction, the pressure of the otoliths will shift on the hair cells,
and that is sufficient to stimulate them. If this view is correct, then we may
regard these structures as static in function as compared with the semicircular
canals, which are dynamic. The anatomical separation of the nerves for the
cochlea from the division for the utriculus, sacculus, and semicircular canals
itself suggests isolation in function, figures 389 and 435. It is conceivable
that loud noises of an explosive nature may cause sufficient vibration of the
endolymph to affect the otoliths and thus stimulate the cristae. Yet, if such
stimulation takes place it is probably only of secondary importance.

IV. THE SENSE OF SIGHT.
THE EYE.

The eye, the organ of vision, is the most complex and most highly devel-
oped of the organs of special sense. It consists not only of a special sen-
sory epithelium, the retina, sensitive to light stimulation, but of a series of
special structures which intensify and localize the stimulus. There are
also accessory organs for the protection of the eye.

THE EYEBALL AND ITS PARTS

66s

The Eyelids and Lachrymal Apparatus. — The eyeball is kept moist
over its free surface and protected from external injury by the eyelids,
by the glands that secrete the lachrymal fluid to moisten the surface of the
cornea, and by the oil glands that secrete oil on the margins of the lids.

The conjunctiva, or lining membrane of the lids, which is reflected on to
the free surface of the eyeball, protects the eye from injury by its extraor-
dinary sensitiveness to irritation by dust or other external substance. Its
stimulation produces reflex secretion of the lachrymal fluid that flows over
the surface of the eye, and tends to wash away the stimulating substance.

FIG. 441. — Section of the Eyeball.

The Eyeball and its Parts.— The detail of the structure of the eye-
ball is too complex to be given here except in so far as seems necessary for a
clearer presentation of the physiological facts. A gross dissection reveals
the tough, white, outer coat, the sclera; the intermediate thin, vascular,
pigmented coat, the choroid; and the inner nervous coat, the retina.

The section also shows that the eyeball is specialized in structure in its
anterior region and that its contained cavity is divided into two parts, viz.,
the anterior and posterior chambers. The anterior chamber is filled with the
transparent aqueous fluid. This fluid is like lymph in its composition.
The posterior chamber between the lens and the retina is filled with the
clear jelly-like vitreous substance.

The Cornea. — The sclera is continuous with the cornea in front of the
eyeball, but the cornea is transparent and its radius of curvature is less than
that of the main portion of the eye. It is composed of stratified epithelial
cells, and is richly supplied with sensory nerves that form an intraepithelial

666

THE SENSES

plexus of delicate varicose fibrils. The cornea has no blood vessels, but
has a rich network of lymphatic spaces.

The Lens. — The lens is a special modification of epithelium composed
of highly refractive material, situated just behind the iris. It is enclosed
in a capsule and supported in its place by the suspensory ligament, which

FIG. 442. — Vertical Section of Rabbit's Cornea, a, Epithelium of cornea, showing the
different shapes of the cells at various depths from the free surface; b, portion of the proper
substance of the cornea. (Klein.)

is fused into the capsule around its equator. The lens is a biconvex struc-
ture composed of transparent fibers which are arranged in concentric
layers. Its posterior curvature is greater than the anterior, the radii being
6 and 10 mm. respectively.

FIG. 443.

FIG. 444.

FIG. 443. — Ciliary Processes, as Seen from Behind, i, Posterior surface of the iris,
with the sphincter muscle of the pupil; 2, anterior part of the choroid coat; 3, one of the
ciliary processes, of which about seventy are represented. X £.

FIG. 444. — Laminated Structure of the Crystalline Lens. The laminae are split up
after hardening in alcohol, i, The denser central part or nucleus; 2, the successive exter-
nal layers. X 4. (Arnold.)

The Ciliary Apparatus and the Iris.— These structures are a con-
tinuation and modification of the choroid coat in the anterior portion of the
eye. Around the circumference of the cornea the choroid coat is consider-
ably thickened and folded in the modification known as the ciliary apparatus.

THE CILIARY APPARATUS AND THE IRIS

667

A radial layer of muscle, figure 445, is knitted into the base of the cornea, on
the one hand, and extends back into the choroid, on the other. Thick bun-
dles of the circular fibers are also present in this mass of muscle. From the
ciliary processes, extending over the lens, is the iris. It is a sheet of connec-
tive tissue and muscle lined with epithelium and highly pigmented.

In the middle anterior portion is a round aperture, the pupil. The mus-
cle fibers are arranged circularly and radially and are of the unstriated
muscle type. Contractions of the circular muscles of the iris produce con-

anterior ciliary arteries and vein

greater arterial circle
angle of tbe IrU

canal of schlemm

ciliary muse!*

limbus cornese.

aaterior chamber

epithelium

anterior limiting (
membrane f

capsule ot leus

posterior limiting membrane

stroraa of iris
posterior surface of iris
spbiucter of. pupil

FIG. 445. — Meridional Section of a Portion of the Anterior Part of the Eyeball. (Toldt.)

striction of the pupil, while contractions of the radial fibers produce dilata-
tion. Both the ciliary apparatus and the iris are supplied with motor nerves.
Fibers of the third cranial nerve are distributed to the ciliary muscles,
apparently to both radial and circular muscles, and when these nerves are
stimulating the resulting contractions of the muscles tend to remove the ten-
sion from the capsule of the lens. These nerve fibers pass through the ciliary
ganglion where they form a synapsis with ganglionic cells. Motor fibers
from the third cranial nerve also supply the circular muscles of the iris, which
produce constriction of the pupil through the motor nerves by way of the

668

THE SENSES

cervical sympathetic and superior cervical ganglion, and the ophthalmic
branch of the fifth cranial nerve.

Structure of the Retina. — The retina occupies the deeper half of the
cup of the eyeball. It extends forward as far as the ora serrata, where its
complex structure changes the form to a simple epithelial layer, which lines
the anterior portion of the eyeball and the ciliary processes. In the centei
of the retina is a round yellowish spot having a minute depression in its
center, called the yellow spot of Sommering. The depression in its center is

Gangli-

onic

layer

Stratum
optfcum

Membrane limitans interim

FIG. 446. — Section of Human Retina. (Cunningham, modified from Schulze.)

thefovea central-is. About 2 . 5 mm. to the inner side of the yellow spot is the
point at which the optic nerve enters and spreads out its fibers into the retina.
The optic nerve arises from the base of the brain and passes forward
toward the orbit, being covered by the membranes which cover the brain.
The fibers of the optic nerve are exceedingly fine, and are surrounded by the
myelin sheath, but do not possess the ordinary external nerve sheath. As
they pass into the retina they lose their myelin sheaths and proceed as
axis-cylinders (the cells of origin of these fibers are in the retina). Neuroglia
supports the nerve fibers in the optic nerve trunk. In the center of the nerve
is a small artery, the arteria centralis retina. The number of fibers in the

STRUCTURE OF THE RETINA

669

optic nerve is said to be upward of 1,000,000. The fibers of the optic nerve
spread out over the inner surface of the retina as far as the ora serrata.

The retina itself consists of layers of nerve elements supported by deli-
cate connective tissue. The older descriptions recognize some eight or ten
layers in the retina. These appear in the ordinary microscopic preparations
and are shown in figure 446. But the newer investigations of Cajal, Golgi
Retzius, and others have shown that the retina is a much simpler structure
than heretofore described. The retina is formed of essentially three layers
of nerve cells. Naming from the center of the eye outward, they are: The

H

FIG. 447. — Transverse Section of a Mammalian Retina. A, Layer of rods and cones;
B, bodies of visual cells (external granular); C, external molecular layer; E, layer of bipolar
cells (internal granular); F, internal molecular layer; G, layer of ganglionic cells; H, layer
of optic-nerve fibers; a, rod; b, cone; c, body of the cone cell; d, body of the rod cell; e,
bipolar rod cells;/, bipolar cone cells; g, h, i, j, k, ganglionic cells ramifying in the various
strata of the internal molecular zone; r, inferior arborization of the bipolar rod cells, con-
necting with the ganglionic cells; r, inferior arborization of the bipolar cone cells; /, epithelial
or Miiller cells; x, point of contact between the rods and their bipolar cells; z, point of con-
tact between the cones and their bipolar cells; s, centrifugal nerve fiber. (Cajal.)

ganglionic layer; the layer of bipolar cells; and the layer of rods and cones,
figure 447. The cells of these layers have numerous fibrous processes which
interlock in such a way that they seem to form different areas when studied
in cross-section. If we recognize the strata of interlacing fibers, then the
following may be made out:

The layer of ganglion cells . .

The layer of bipolar cells . . .
The layer of visual cells

1. Ganglionic layer, with the fibers of the
optic nerve.

2. Internal molecular layer.

3. Internal granular layer.

4. The external molecular layer.

5. The external granular layer.

6. The layer of rods and cones.

670

THE SENSES

The Nerve Fiber and Nerve Cell Layers. — The inside of the retina i
formed of a layer of nerve fibers which have their origin in the adjacent largi
nerve cells and run toward the exit of the optic nerve. Externally the gan
glionic cells send up numerous processes, or dendrites, which interlace witl
the fibers of the bipolar cells of the second layer.

FIG. 448. — Perpendicular Section of the Retina of a Mammal. A, External grains o
bodies of rods; B, bodies of cones; a, horizontal external or small cell; b, horizontal interna
or large cell; c, horizontal internal cell with descending protoplasmic appendages; t
flattened arborization of one of the large cells; /, g, h, j, I, spongioblasts ramifying in th
various strata of the internal molecular zone; m, n, diffuse spongioblasts; o, ganglionic cell
i, external molecular zone; 2, internal molecular zone. (Cajal.)

The Middle Layer. — The middle layer consists of bipolar cells which sen(
one process toward the ganglionic layer to interlace with the dendrites of th
ganglionic cells, and one process externally. This process is often divide<
into many branches, which separate out into a horizontal brush, interlacinj

FIG. 449. — Distribution of the Rods and Cones. A, In the peripheral part of the retina
B, from the region of the macula lutea.

with the processes of the rods and cones. Special cells have been describee
for this layer of the retina, as, for example, the spongioblasts of Cajal.

The External Layer of Rods and Cones. — The rod cells are composed o
two parts quite different in structure, known as the outer and inner limbs

STRUCTURE OF THE RETINA

67i

The outer limb is a cylindrical rod about
30/4 long by 2^ in diameter. It is trans-
parent and composed of doubly refrac-
tive material. The inner limb of the
cell is about the same length as the outer,
is similar, and is longitudinally striated,
and contains a nucleus on its course,
figure 447, d.

The cone cells are also made up of
two limbs, the outer of which is conical
instead of cylindrical as in the case of
the rods. In other respects they are
similar to the rods in structure, with the
exception that the inner limb ends in a
brush of fibrils which interlace with the
bipolar cells of the middle layer. In
man and mammals the number of rod
cells is much greater than the cones,
but it is said that in birds cones predom-
inate. Even in man the center of the
fovea centralis is devoid of rods and con-
sists of cones only, figure 450.

All the elements of the retina are
sustained and isolated by large cells
lying vertically which are known as the
fibers of Muller. The nucleus of the
fiber of Muller is found at the level of
the layer of bipolar cells. The two ex-
tremities of the protoplasm or cell body
are condensed in two homogeneous
layers, known as the external and the
internal limiting layer. The external
limiting layer is placed just between the
two segments of the rod and cone cells,
forming a fenestrated membrane. The
internal limiting layer is situated upon
the internal surface of the retina.

At the ora serrata the highly special-
ized structure of the retina disappears.
The nerve fibers and ganglion cells dis-
appear, the connecting cells are fewer,
the cones more sparse, and the rods
shorten and disappear. The structure

10 9

FIG. 450. — Diagrammatic Section of
the Macula Lutea and Fovea Centralis,
2, Layer of nerve fibers; 3, layer of
multipolar cells; 4, internal molecular
layer, composed of intertwining arbor-
escent processes; 5, layer of bipolar
cells, or internal granular layer; 6,
external molecular layer, composed
of intertwining arborescent processes;
7, nuclei of epithelial cells, or external
granular layer; 8, frillwork formed
by processes from fibers of Muller,
often called the "external limiting
membrane"; 9, layer of rods and cones;
10, layer of pigment epithelium.

672

THE SENSES

is quickly reduced to that of a simple epithelial membrane known as the
pars ciliaris retinae.

At the pars ciliaris retinae, the retina is represented by a layer of columnar

FIG. 451. — Diagram of the Blood Vessels of the Human Retina. (Leber, after Jaeger.)
ans, vns, Superior nasal arterv and vein; ats, vts, superior temporal artery and vein; ani.
uni, inferior nasal artery and vein; ati, vti, inferior temporal artery and vein; am, vm,
macular artery and vein; ane, rme, median artery and vein.

cells, derived from the fusion of the nuclear layers which are in contact with
the pigment layers of the retina and continued over the ciliary processes.
Pigment Layer. — This layer, which was formerly considered part of the

FIG. 452. — Blood Vessels of the Macula Lutea. The part that is totally free from vessels is

the fovea centralis.

choroid, consists of cells which cover and entirely surround the outer limbs
of the rods and cones.

Blood Vessels of the Eyeball. — The eye is very richly supplied with blood
vessels. In addition to the conjunctival vessels, which are derived from the

REFRACTIVE MEDIA AND SURFACES 673

palpebral and lachrymal arteries, there are at least two other distinct sets
of vessels supplying the tunics of the eyeball: i. The vessels of the sclera,
choroid, and iris, and 2, the vessels of the retina. The first are the short and
long posterior ciliary arteries which pierce the sclerotic in the posterior half
of the eyeball, and the anterior ciliary which enter near the insertions of the
recti. These vessels anastomose and form a very rich choroidal plexus;
they also supply the iris and ciliary processes, forming a very highly vas-
cular circle round the outer margin of the iris and adjoining portion of
the sclerotic. The distinctness of these vessels from those of the conjunctiva
is well seen in the difference between the bright red of blood-shot eyes
(conjunctival congestion), and the pink zone surrounding the cornea which
indicates deep-seated ciliary congestion.

The central artery of the optic nerve enters the retina from the center of
the optic disc and sends out branches over the retinal cup lying in the nerve
fiber layer, figure 451. These blood vessels, however, are absent from the
fovea centralis and reduced in size in the macula lutea, figures 451 and 452.

THE OPTICAL APPARATUS.

The optical apparatus may be supposed, for the sake of description, to
consist of several parts: i, a system of transparent refracting surfaces and
media by means of which images of external objects are brought to a focus
upon the back of the eye; 2, a sensitive screen, the retina, which is a special-
ized sensory apparatus in connection with the terminations of the optic
nerve, and capable of being stimulated by luminous objects, and of sending
such impressions as to produce in the brain visual sensations. To these
main parts may be added, 3, an apparatus for focusing light from objects al
different distances from the eye; and 4, since both eyes are usually employed
in vision, an arrangement by means of which the eyes may be turned in the
same direction so that binocular vision is possible. The arrangement of
the optic nerve fibers, and of the continuation of these backward in the optic
chiasma, and thence to special districts of the brain have already been
discussed.

The eye may be compared to a photographic camera, in which the trans-
parent refracting media correspond to the photographic lens. In a camera
images of external objects are thrown upon a screen, the sensitive plate, at
the back of the camera box. In the eye, the camera proper is represented
by the eyeball with its choroidal pigment, the sensitive screen by the retina,
and the lens by the refracting media. In the case of the camera, the screen
is djusted to receive clear images of objects at different distances by a
mechanical apparatus for focusing. The corresponding adjustment in the
eye is accomplished by the accommodating mechanism.

Refractive Media and Surfaces. — At first sight it would seem as if
the refracting apparatus of the eye were very complicated, since it consists
43

674 THE SENSES

of so many parts. These parts are: the anterior surface of the cornea itself,
the posterior surface of the cornea, the aqueous humor, the anterior surface
of the lens, the substance of the lens itself (which is unequally refractive),
the posterior surface of the lens, and the vitreous humor. Thus there are
four surfaces, and at least, including the air, five media. For all practical
purposes, however, we may leave out of consideration all but three refracting
surfaces and their adjacent media. These are: the anterior surface of the
cornea, separating the air and the corneal substance; the anterior surface
of the lens, separating the aqueous humor and the lens substance; and the
posterior surface of the lens, separating the lens surface from the vitreous
humor.

Image Formation. — In the refraction through a simple transparent
spherical surface there are certain cardinal points to be considered. The
rays of light which fall perpendicularly on such a surface pass through with-
out refraction. All such rays cut the center of the radius of curvature of the

FIG. 453. — Diagram of a Simple Optical System. (Foster.) The curved surface, bd,
is supposed to separate a less refractive medium toward the left from a more refractive
medium toward the right.

lens, called the nodal point. A line that passes through the center of curva-
ture of a lens and thus pierces the nodal point is called the optical axis, and
the point on the surface pierced by the optical axis is the principal point.
In every optical system there are certain other cardinal facts to be considered.
All rays \vhich do not strike vertical to the curved surface are refracted
toward the optical axis. Rays which impinge upon the spherical surface of
a lens parallel to the optical axis will meet at a point upon the axis called the
posterior principal focus, figure 453, F. The posterior principal focus is
outside of the nodal point. Again, there is a point in the optical axis in front
of the surface, rays of light from which strike the surface so that they are
refracted in a line parallel with the axis, df"; such a point, F2, is called the
anterior principal focus.

In any given system the principal foci can be found by erecting verticals
at the nodal and principal points of the optical axis and laying off lengths
on each, a and b, proportional to the refractive indices of the media. A line

IMAGE FORMATION

675

drawn through a on the principal vertical and b on the nodal vertical will cut
the optical axis at the posterior principal focus, and vice versa.

If a luminous point outside the anterior principal focus is considered,
it is obvious that rays from it will be so refracted when they enter the convex
surface that they will become converging and will ultimately meet again in
a point or focus. Two such points form conjugate foci, figure 454. If the
anterior focus of a conjugate is moved away from the anterior principal focus,
then the posterior conjugate will move toward the posterior principal focus,
and the converse. If one conjugate is known, the other can be found as

FIG. 454. — Diagram to Show the Relations of Conjugate Foci, cd, Refracting surface;
AB and ba, conjugate foci; o, nodal point; F", posterior principal focus.

follows: From a point in the plane of the known conjugate, but outside the
principal axis, draw two rays, one perpendicular to the refracting surface
which will pass through the nodal point, the other parallel to the principal
axis. The latter will be refracted through the posterior principal focus and
when prolonged will meet the first ray in the plane of the second conjugate,
figure 454, a, This relationship between conjugate foci is played upon in the
focusing of a camera.

It is quite obvious that the eye, even considering only the three surfaces
above indicated, is a much more complicated optical apparatus than the one
described in the figure. It is, however, possible to reduce the refractive
surfaces and media to a simpler form when the refractive indices of the dif-
ferent media and the curvature of each surface are knowrn. All of these
data have been very carefully collected. They are as follows:

Index of refraction of aqueous and vitreous = J -3365

Index of refraction of the lens = 1.4371

Radius of curvature of cornea = 7.829 mm.

Radius of curvature of anterior surface of lens = 10.0

Radius of curvature of posterior surface of lens = 6.0

Distance between anterior surface of cornea and anterior sur-
face of lens = 3.6

Distance between anterior surface of cornea and posterior

surface of lens = 7.2 mm.

With these data it has been found comparatively easy by mathematical
calculation to reduce the different refractive surfaces of the different curva-

mm.
mm.

mm,

THE SENSES

tures into one mean curved surface of known curvature, and the different
refracting media into one mean medium the refractive power of which is
known.

The simplified or so-called schematic eye, formed upon this principle,
suggested by Listing as the reduced eye, has the following dimensions :

From the anterior surface of the cornea to the principal point = 2 . 3448 mm.

From the nodal point to the posterior surface of lens = o .4764 mm.

Posterior principal focus lies behind cornea =22. 8237 mm.

Anterior principal focus in front of cornea =12. 83 26 mm.

Radius of curvature of ideal surface = 5. 1248 mm.

In this reduced or simplified eye the principal posterior focus, about
23 mm. behind the spherical surface, would correspond to the position of
the retina behind the anterior surface of the cornea. The refracting surface
would be situated about midway between the posterior surface of the cornea
and the anterior surface of the lens.

The optical axis of the eye is a line drawn through the centers of curva-
ture of the cornea and lens, and when prolonged backward it cuts the retina
between the optic disc and fovea centralis. This differs somewhat from
the visual axis which passes through the nodal point of the reduced eye to

FIG. 455. — Diagram of the Method of the Formation of an Inverted Image Exactly Focused
upon the Retina. The dotted line is the ideal surface of curvature.

the fovea centralis, and forms an angle of five degrees with the optical axis.
The visual or optical angle is the angle included between the lines drawn
from the opposite borders of any object through the nodal point. It has
been shown by Helmholtz that the smallest angular distance between two
points which can be appreciated is fifty seconds, the size of the retinal image
being 3 . 65/1. This practically corresponds to the diameter of the cones at
the fovea centralis which is 3//, the distance between the centers of two
adjacent cones being 4^.

The image of an object formed upon the retina may be considered as a
series of points, from each of which a pencil of light diverges to the eye, and
this pencil has for its center or axis a ray which impinging upon the refract-

ACCOMMODATION 677

ive surface perpendicularly to the surface is not refracted, but passes through
the nodal point and is prolonged backward to the retina. The diverging
rays are also made to converge to a principal posterior focus behind the lens,
or the chief axis of the pencil of light proceeding from the point in question,
and this focus, if the image is to be clear, should fall on the retina.

Thus from each point of an object a corresponding image is formed on
the retina, so that an image of the distant object is produced. It is an inverted
image. Whether the image is blurred or not depends upon the refractive
power of the media and upon the distance of the anterior surface of the cor-

FIG. 456. — Diagram of the Course of a Ray of Light, to Show how a Blurred or
Indistinct Image is Formed if the Object be not Exactly Focused upon Retina. The
surface CC should be supposed to represent the ideal curvature. The nodal point should
be nearer the posterior surface of lens as in figure 455.

nea from the retina. If the refractive media are too powerful or the eye too
long, the image is formed in front of the retina, figure 456; if the reverse, the
image is formed behind the retina, and in both cases an indistinct and blurred
image is the result.

Accommodation. — The distinctness of the image formed upon the
retina is mainly dependent on the perfection with which the rays emitted
by each luminous point of the object are brought to a focus upon the retina.
If this focus occurs at a point either in front of or behind the retina, indis-
tinctness of vision ensues, in the way we have just described, with the pro-
duction of a halo. The focal distance, i.e., the distance of the point at which
the luminous rays are collected from a lens, besides being regulated
by the degree of convexity and density of the lens, varies with the distance
of the object from the lens, being greater as the distance is shorter, and vice
versa. In other words, the luminous points on the object and the focal points
on the retina are conjugate foci. Hence, since objects placed at various
distances from the eye can within certain limits be seen with almost equal
distinctness, there must be some provision by which the eye is enabled to
adapt itself, so that, at whatever distance the luminous object may be, the
focal point may always fall exactly upon the retina.

6; 8 THE SENSES

Accommodation is the act of adapting the eye to vision at different distances.
It is obvious that the effect might be produced in either of two ways, viz.,
i, by altering the convexity, and thus the refracting power, either of the cornea
or of the lens; or 2, by changing the position of the lens relative to the retina,
as in the focusing of a camera, so that whether the object be near or distant,
the focal points to which the rays are converged by the lens may always fall
exactly on the retina. The amount of either of these changes which is re-
quired in even the widest range of vision is extremely small, for from the re-
fractive powers of the media of the eye the
difference between the focal distances of the
images of an object at a distance and of one
at four inches is only about 3 . 5 mm. On
this calculation the change in the distance of
the retina from the lens required for vision at
all distances, supposing the cornea and lens
to remain the same, would not be more than

about 2.5 mm. Beer has shown that the
FIG. 457.— Diagram Showing . .

Three Reflections of a Candle, second method is indeed the type of accom-

i, From the anterior surface of modative apparatus in fishes. But in man

cornea; 2, from the anterior .

surface of lens; 3, from the and the higher animals accommodation occurs

posterior surface of lens. For by the first method, i.e.. by changing the con-
further explanation, see text. . ... .

The experiment is best per- vexity of the refracting surface.

formed by employing an in- The accommodation of the human eye for

strument invented by Helm- . . ./

holtz, termed a Phakoscope. objects at different distances is primarily due

to a varying shape of the lens, its front surface

becoming more or less convex, according as the distance of the object looked
at is near or far. The nearer the object, the more convex the front surface
of the lens, up to a certain limit, and vice versa; the back surface takes little
or no share in accommodation. The following simple experiment illustrates
this point: If a lighted candle be held a little to one side of a person's eye,
an observer looking at the eye from the other side sees three distinct images
of the flame, figure 457. The first and brightest is, i, a small erect image
formed by the anterior convex surface of the cornea; the second, 2, is also erect,
but larger and less distinct than the preceding, and is formed at the anterior
convex surface of the lens; the third, 3, is smaller, inverted, and indistinct;
it is formed at the posterior surface of the lens, which is concave forward, and
therefore, like all concave mirrors, gives an inverted image. If, now, the eye
under observation be made to look at a near object, the second image be-
comes smaller, clearer, and approaches the first. If the eye be now adjusted
for a far point, the second image enlarges again, becomes less distinct, and
recedes from the first. In both cases alike the first and third images remain
unaltered in size, distinctness, and relative position. This proves that during
accommodation for near objects the curvature of the cornea, and that of the

THE MECHANISM OF ACCOMMODATION

679

posterior surface of the lens, remain unaltered, while the anterior surface of
the lens becomes more convex and approaches the cornea.

The experiment, figure 458, is more striking when the two prisms of the
phakoscope which form two images of the candle are used. The pair of
images of the candle from the front surface of the lens not only approach
those from the cornea during accommodation, but also approach one another,
and become somewhat smaller, Sanson's images.

FIG. 459.

FIG. 458. — Diagram of Sanson's Images. A, When the eyes are focused for far
objects, and B, when they are focused for near objects. The figure to the right in A and
B is the inverted image from the posterior surface of the lens.

FIG. 459. — Phakoscope of Helmholtz. At B, B', are two prisms, by which the light
of a candle is concentrated on the eye of the person experimented with at C. A is the
aperture for the eye of the observer. The observer notices three double images, as in
figures 457 an(^ 45^, reflected from the eye under examination when the eye is fixed upon a
distant object; the position of the images having been noticed, the observed eye is then
focused on a near object, such as a reed pushed up by C; the images from the anterior
surface of the lens will be observed to move toward each other, in consequence of the lens
becoming more convex.

The Mechanism of Accommodation. — The mechanism of accommo-
dation depends primarily upon the inherent tendency of the lens to approxi-
mate the shape of a sphere. When the eye is at rest the intra-ocular tension
is such as to put stress on the suspensory ligament around its equator, which
compresses the elastic lens in its antero- posterior dimension. The elasticity
of the lens can make itself apparent when the tension of the suspensory liga-
ment is relaxed. This takes place completely after a division of the fibers
of the zonula. When we remove the lens from the eye of a young person,
we see it assume the spherical shape immediately upon the division of its

680 THE SENSES

connections. In life this slackening of the tension of the suspensory liga-
ment of the lens is brought about by the contractions of the fibers of the ciliary
body. This allows the anterior surface of the lens to become more convex,
by its own elastic powers, thus focusing entering rays of light from a near
object upon the retina, figure 460. It therefore appears that when the eye
is at rest it is focused for distant objects, in as much as the suspensory liga-
ment is taut and the anterior surface of the lens more flattened. The nor
mal eye is passive when in focus for distant objects. It is the active contrac-
tion of the muscles of accommodation that focuses for near objects. The
iris acts in co-ordination with the accommodative contractions of the ciliary
muscles. In viewing near objects the pupil contracts, and upon viewing
distant ones it dilates.

Range of Distinct Vision. — Near-point. — In every eye there is a limit to
the power of accommodation. If a book be brought nearer and nearer to the

FIG. 460. — Diagram Representing by Dotted Lines the Alteration in the Shape of the Lens
on Accommodation for Near Objects. (E. Landolt.)

eye, the type at last becomes indistinct, and cannot be brought into focus
by any effort of accommodation, however strong. This limit, which is
termed the near-point, can be determined by the experiment of Schemer.
Two small holes not more than 2 mm. apart are pricked in a card with a pin;
at any rate their distance from each other must not exceed the diameter of the
pupil. The card is held close in front of the eye, and a small needle viewed
through the pin-holes. At a moderate distance it can be clearly focused,
but when brought nearer, within a certain point, the image appears double
and more or less blurred. This point where the needle ceases to appear
single is the near-point of vision. Its distance from the eye can of course be
readily measured. It is usually about five or six inches, 12 to 15 cm. In the
accompanying figure, 461, the lens b represents the eye; e, /, the two pin-
holes in the card, nn the retina; a represents the position of the needle. When
the needle is at a moderate distance, the two pencils of light coming through

RANGE OF DISTINCT VISION

68l

e and / are focused at a single point on the ret!na nn. If the needle be brought
nearer than the near-point, the strongest effort of accommodation is not
sufficient to focus the two pencils, they meet at a point behind the retina.
The effect is the same as if the retina were shifted forward to mm. Two

FIG. 461. — Diagram of Experiment to Ascertain the Minimum Distance of Distinct Vision.

images, h, g, are formed, one from each hole. It is interesting to note that
when in this way two images are produced, the lower one, g, really appears in
the position Q, while the upper one appears in the position P. This may be
readily verified by covering the holes in succession.

FIG. 462. — Diagram of the Axes of Rotation of the Eye. The thin lines indicate axes of
rotation, the thick the position of muscular attachment.

During accommodation two other changes take place in the eyes. The
eyes converge by the action of the extra-ocular muscles, chiefly by the internal
and inferior recti or internal and superior recti. The pupils contract.

682 THE SENSES

Movements of the Eye. The eyeball possesses movement around three axes
indicated in figure 462, viz., an antero-posterior, a vertical, and a transverse,
passing through a center of rotation a little behind the centre of the optic axis.
The movements are accomplished by pairs of muscles.

Direction of Movement. By what muscles accomplished.

Inward Internal rectus.

Outward External rectus.

Upward { Superior rectus.

L Inferior oblique.

Downward.. ( Inf^or rectus.

1 Superior oblique.

Inward and upward . . { Jnrternal a*d superior rectus.

Inferior oblique.

Internal and inferior rectus.

Inward and downward <

[ bupenor oblique.

Outward and upward . . { External and superior rectus.

( Inferior oblique.

( External and inferior rectus.

Outward and downward

[ Superior oblique.

The contraction of all of the muscles during the act of accommodation,
viz., of the ciliary muscles, of the recti muscles, and of the sphincter pupillae,
is under the control of the fibers of the third nerve. But the superior oblique
may also be employed, in which case the fourth nerve is concerned.

Reflexes of the Pupil. — Contraction of the iris may occur under the
following circumstances: i. On exposure of the eye to a bright light. On
the local application of eserine (active principle of Calabar bean). 3. On the
administration internally of opium, aconite, and in the early stages of chloro-
form and alcohol poisoning. 4. On division of the cervical sympathetic or of
stimulation of the third nerve. Dilatation of the pupil occurs, i, in a dim
light; 2, when the eye is focused for distant objects; 3, on the local applica-
tion of atropine and its allied alkaloids; 4, on the internal administration of
atropine and its allies; 5, in the later stages of poisoning by chloroform,
opium, and other drugs; 6, on paralysis of the third nerve; 7, on stimulation
of the cervical sympathetic, or of its center in the floor of the front of the
aqueduct of Sylvius. The contraction of the pupil is under the control of
a center in the floor of the aqueduct beneath the anterior corpora quadril
gemina. This center is reflexly stimulated by a bright light, and the dilata-
tion when the center is not in action is due to the stimulation of the radia-
fibers of the iris by sympathetic nerves. In addition, it appears that both
contraction and dilatation may be produced by a local action of certain drugs
which is independent of, and probably often antagonistic to, the action of the
central apparatus of the third and sympathetic nerves.

The close co-ordination between the two eyes is nowhere better shown
than by the condition of the pupil. If one eye be shaded by the hand its

DEFECTS IN THE OPTICAL APPARATUS 683

pupil will of course dilate; the pupil of the other eye will also dilate, though
unshaded, due to crossed reflex action.

Defects in the Optical Apparatus. — Under this head we may con-
sider the defects known as: i, Spherical Aberration; 2, Chromatic Aberra-
tion; 3, Astigmatism; 4, Myopia; 5, Hypermetropia.

The normal or emmetropic eye is so perfect that parallel rays are brought
exactly to a focus on the retina without any effort of accommodation, figure
466. Hence all objects except near ones (in practice all objects at a distance
of twenty feet or more) are seen without any effort of accommodation; in
other words, the far-point of the normal eye at rest is at an infinite distance.
In viewing near objects we are conscious of the effort (the contraction of
the ciliary muscle) by which the anterior surface of the lens is rendered
more convex, and rays which would otherwise be focused behind the retina
are converged upon the retina.

Spherical Aberration — The rays in a cone of light from a point on an
object situated in the field of vision do not all meet in the same point in
the retina, owing to the greater refraction of the rays which pass through
the margin of a lens than those traversing its central portion. This defect
is spherical aberration. In the camera, telescope, microscope, and other
optical instruments it is remedied by the interposition of a screen with a
circular aperture in the path of the rays of light, cutting off all the marginal
rays and allowing the passage only of those near the center. Such cor-
rection is effected in the eye by the iris, which forms a diaphragm to cover the
circumference of the lens, and prevents the rays from passing through any
part of the lens but its center, which corresponds to the pupil. The iris is
pigmented to prevent the passage of rays of light through its substance.
The image of an object will be most defined and distinct when the pupil is
small, if the light is abundant; so that, while a sufficient number of rays are
admitted, the narrowness of the pupil may prevent the production of indis-
tinctness of the image by spherical aberration. But even the image formed
by the rays passing through the circumference of the lens, when the pupil is
much dilated, as in the dark, or in a feeble light, may, under certain circum-
stances, be well defined.

Distinctness of vision is further secured by the pigment of the outer sur-
face of the retina and of the posterior surface of the iris and the ciliary proc-
esses, which absorbs any rays of light that may be reflected within the eye,
and prevents their being thrown again upon the retina so as to interfere
with the images formed there. The pigment of the retina is especially im-
portant in this respect; for with the exception of its outer layer the retina is
very transparent; and if the surface behind it were not of a dark color, but
capable of reflecting the light, the luminous rays which had already acted
on the retina would be reflected again and would fall upon other parts of
the same membrane, producing indistinctness of the images.

684 THE SENSES

Chromatic Aberration. — In the passage of light through the periphery of
an ordinary convex lens decomposition of each ray into its elementary colored
parts commonly ensues, and a colored margin appears around the image,
owing to the unequal refraction which the elementary colors undergo. This
is termed chromatic aberration. It is corrected by the use of lenses constructed
of alternate layers of glass of different refractive indices so ground that they
produce chromatic dispersion in opposite directions and thus mutually cor-
rect any chromatic aberration which may have resulted. The human eye
has considerable chromatic aberration, as may readily be demonstrated,
Experiment 13, page 708.

An ordinary ray of white light in passing through a prism has its con-
stituent rays refracted in unequal degrees, and therefore appears as colored
bands fading off into each other, known as the spectrum. The colors of the
spectrum are arranged as follows: red, orange, yellow, green, blue, indigo,
violet; of these the red ray is the least, and the violet the most, refracted.
Hence, as Helmholtz has shown, the rays from a white point cannot be
accurately focused on the retina, for if we focus for the red rays, the violet
are out of focus, and vice versa; such objects, if not exactly focused, are often
seen surrounded by a pale yellowish or bluish fringe.

For similar reasons a red surface looks nearer than a blue one at an equal
distance, because, the red rays being less refrangible, a stronger effort of
accommodation is necessary to focus them, and the eye is adjusted as if for
a nearer object, and therefore the red surface appears nearer, Experiment 13.

Astigmatism. — This defect, which was first discovered by Airy, is due to
a greater curvature of the refractive surfaces of the eye in certain meridians
than in others. Thus vertical and horizontal lines crossing each other can-
not both be focused on one plane; one set stands out clearly, and the others
are blurred and indistinct. This defect, which is generally present in a slight
degree in all eyes, is usually seated in the cornea, but occasionally in the
lens as well.

The plane of greatest curvature in the cornea is usually in the vertical
meridian, a fact which doubtless comes from the pressure of the eyelids
during development. If one looks at figure 463, A or B, with one eye, the
three lines in the radii of the figure will be seen with unequal distinctness.
Certain sets will stand out sharp and black and others dim and with indistinct
outlines, and if the astigmatism is great enough the three lines may not be
distinguished. Figures C and D of this series enable one to detect minute
traces of astigmatism with great accuracy.

It is somewhat difficult to picture the rays from a luminous point in their
course through eyes which have this defect, but an examination of figure
464 will show their refraction. In this figure four rays coming from the
point L in the arrows are represented as striking on the refractive surface
of the eye at A , B, C, D, and being converged toward a focus. The rays A , C,

DEFECTS IN THE OPTICAL APPARATUS

685

separated by a vertical line on the refractive surface, are focused at/x, while
the lines A , B, separated by the horizontal distance on the refractive surface,
are brought to a focus at/2. The point L, therefore, has two apparent focal
points, one point composed of the rays that strike in a horizontal plane, /2, the
other of rays that strike in a vertical plane, /. If the retina of the eye be
placed at/j, it will see an image of a point with indistinct horizontal rays.

FIG. 463. — Astigmatic Charts.

If placed at the position /2 it will see a luminous point with indistinct rays in
the vertical plane. If the series of points in the arrow MN be considered,
it is evident that at the position/! the rays which fall in the vertical plane
will form distinct foci, while those that fall in the horizontal plane will form
overlapping diffuse images in that plane. Since they are overlapping, they
will not appear separate except at the ends of the image of the arrow, and the
arrow will therefore be seen distinctly. If the position /2 is considered
where the rays of the horizontal plane are focused, then it is evident that

FIG. 464. — The Unequal Refraction of Rays in an Astigmatic Eye. (John Green.)

the points in the arrow MN will present a series of rays or halos in the
vertical plane, thus rendering its outline very dim or indistinct. The con-
dition with the arrow OP is exactly the reverse. Hence, in the astigmatic
eye the images of the horizontal arrow MN will be distinct at the focus/!,
while the image of the vertical arrow OP will be distinct in the focus /2, and
the eye cannot see the two lines distinctly at the same time. This condition is
further illustrated in figure 465 which represents the type of image formed
at the position/! shown in figure 464.

Myopia. — This is that refractive condition of the eye in which parallel
rays are brought to focus in front of the retina, 4, figure 466. It is due

686 THE SENSES

either to an abnormal elongation of the eyeball antero-posteriorly or to an
increase in the convexity of the refracting surfaces, or to both of these con-
ditions. Parallel rays are focused in front of the retina, and, crossing,
form circles on the retina. Thus, the images of distant objects are blurred
and indistinct. The eye is, as it were, permanently adjusted for a near point.
Rays from a point near the eye are exactly focused on the retina. But those
which issue from any object beyond a slight distance, the myopic far-point,
which is less than twenty feet, cannot be distinctly focused. This defect
is corrected by concave glasses, which cause parallel rays entering the eye

FIG. 465. — Diagram of Character of Retinal Images in Astigmatism. (John Green.)

to diverge. Such glasses of course are needed only to give a clear vision of
distant objects. For near objects they are not required.

Hypermetropia. — This is that refractive condition of the eye in which
parallel rays are brought to a focus behind the retina, 3, figure 466. It is the
opposite of myopia, and is due either to an abnormal shortening of the eye-
ball antero-posteriorly or to a decrease in the convexity of the refracting
surfaces, or both. Parallel rays entering the eye at rest are focused behind
the retina. An effort of accommodation is therefore required to focus parallel
rays on the retina. When the rays are sharply divergent, as in viewing a very
near object, the accommodation is insufficient to focus them. Thus, both
near and distant objects require an effort of accommodation, and the eye
is under a constant strain which produces in the end various nervous, as
well as ocular, disorders. This defect is obviated by the use of convex
glasses, which render the pencils of light more convergent. Such glasses are
especially needed for near objects, as in reading, etc. They are also required
for distant vision to rest the eye by relieving the ciliary muscle from constant
work.

Presbyopia. — Presbyopia is a condition of diminished range of accom-
modation. It takes place writh considerable uniformity from youth to old
age. It is not a disease, but a physiological process which every eye under-
goes as its owner grows older. It is due to a gradual diminution of elasticity
of the lens by a short sclerosis from the center toward the periphery. It

VISUAL SENSATIONS, FROM EXCITATION OF THE RETINA 687

begins even in childhood, but advances so slowly that it is not until the age of
twenty-five or so that a distinct, though small, nucleus is present. With
advancing years the process goes on until finally the lens becomes inelastic
and is unable to assume a shape convex enough to focus rays from a near
object upon the retina, as in reading. The defect is remedied by the use of
convex lenses equivalent to the loss in accommodation.

FIG. 466. — Diagram Showing: i, Normal or emmetropic eye bringing parallel rays
exactly to a focus on the retina; 2, normal eye at rest, showing that light from a near point is
focused behind the retina, but by increasing the curvature of the anterior surface of the
lens (shown by dotted lines) the rays are focused on the retina; 3, hypermetropic eye. In
this case the axis of the eye is shorter and the lens normal (or the lens may be flatter than
normal and the eyeball normal); parallel rays are focused behind the retina; 4, myopic eye.
In this case the lens is too convex (or the axis of the eye is abnormally long); parallel rays
are focused in front of the retina.

Visual Sensations, from Excitation of the Retina. — Light is the
normal agent in the excitation of the retina. The only portion of the retina
capable of reacting to the stimulus is the rod and cone layer. The proofs of
this statement may be summed up thus: i. The point of entrance of the optic
nerve into the retina, where the rods and cones are absent, is insensitive to
light and is called the blind spot. The phenomenon itself is very readily

688 THE SENSES

demonstrated. If we close one eye, and direct the other upon a point at
such a distance to the side of any object that the image of the latter must
fall upon the retina at the point of entrance of the optic nerve, its image is
lost. If, for example, we close the left eye, and direct the axis of the right
eye steadily toward the circular spot in figure 467, while the page is held at
a distance of about six inches from the eye, both dot and cross are visible.
On gradually increasing the distance between the eye and the object, by
removing the book farther and farther from the face, keeping the right eye
steadily on the dot, it will be found that suddenly the cross disappears from
view, while on removing the book still farther it suddenly comes into view
again. The cause of this phenomenon is simply that the portion of retina
which is occupied by the entrance of the optic nerve is quite blind; and there-
fore that when it alone occupies the field of vision objects cease to be visible.

FiG. 467. — Diagram for Demonstrating the Blind Spot.

2. In the fovea centralis and macula lutea, which contain rods and cones but
no optic-nerve fibers, light produces the greatest effect. In the latter, cones
occur in large numbers, and in the former cones without rods are found,
whereas in the rest of the retina, which is not so sensitive to light, there are
fewer cones than rods. We may conclude, therefore, that cones are even
more important to vision than rods. 3. If a small lighted candle be moved
to and fro at the side of and close to one eye in a dark room while the eyes
look steadily forward into the darkness, a remarkable branching figure,
Purkinje's figures, is seen floating before the eye, consisting of dark lines on
a reddish ground. As the candle moves, the figure moves in the opposite
direction, and from its whole appearance there can be no doubt that it is a
reversed picture of the retinal vessels projected before the eye. The two
large branching arteries passing up and down from the optic disc are clearly
visible, together with their minutest branches. A little to one side of the disc,
in a part free from vessels, is seen the yellow spot in the form of a slight de-
pression. This remarkable appearance is due to shadows of the retinal
vessels cast by the candle. The branches of these vessels are chiefly dis-
tributed in the nerve fibers and ganglionic layers; and since the light of the
candle falls on the retinal vessels from in front, the shadow is cast behind
them, and hence those elements of the retina which perceive the shadows
must also lie behind the vessels. Here, then, we have a clear proof that the
light-perceiving elements of the retina are not the fibers of the optic nerve
forming the innermost layer of the retina, but the external layers of the retina,
the rods and cones.

When light falls on the rods and cones it produces changes which develop
nerve impulses that are transmitted by the chain of neurones extedngin

INTENSITY OF VISUAL SENSATIONS 689

through the retina, the optic nerve and chiasma, the geniculate bodies, etc.,
to the cerebral cortex of the occipital lobe, which is the sensorium for visual
sensations. We have already seen that the eye possesses a wonderful me-
chanical perfection for receiving and focusing light on definite parts of the
retina. A comparison of visual sensations shows that there are correspond-
ing qualities in the sensation, as, for example, its intensity, duration, localiza-
tion, complexity, etc.

Duration of Visual Sensations. — The duration of the sensation pro-
duced by a luminous impression on the retina is always greater than that
of the stimulus which produces it. However brief the luminous impression,
the effect on the retina always lasts for about one-twentieth of a second.
Thus, suppose an object in motion, say a horse, to be revealed on a dark
night by a flash of lightning, the image remaining on the retina during the
time of the flash. The object is really revealed for such an extremely short
period (a flash of lightning being almost instantaneous) that no appreciable
movement could have taken place in the period during which the stimulus
was produced on the retina of the observer. The horse would appear stand-
ing in the position of motion for about a twentieth of a second, though he
would not be seen to make any motions. And the same fact is proved in a
reverse way. The spokes of a rapidly revolving wheel are not seen as dis-
tinct objects, because at every point of the field of vision over which the re-
volving spokes pass, a given impression has not faded before another comes to
replace it. Thus every part of the interior of the wheel appears filled.

The duration of the after- sensation produced by an object is greater in a
ratio proportionate to the duration of the impression which caused it. Hence,
the image of a bright object, as of the light of a window, may be perceived
in the retina for a brief period, the positive after-image. If, however, the pri-
mary stimulation is sharp and intense there will follow presently an appear-
ance of the window in which all the contrasted lights are reversed, the
negative after image.

Intensity of Visual Sensations. — It is quite evident that the more
luminous a body the more intense is the stimulus it produces. But the in-
tensity of the sensation is not directly proportional to the intensity of the
luminosity of the object. It is necessary for light to have a certain intensity
before it can excite the retina, but it is impossible to fix an arbitrary limit
of the power of excitability. As in other sensations so also in visual sensa-
tions, a stimulus may be too feeble to produce a sensation. If it be increased
in amount sufficiently, it reaches a point that is intense enough to produce an
effect; this is a minimal or threshold stimulus. The amount of increase in
the stimulus that produces a perceptible change in the sensation is at first
very slight, but later quite great. It does not depend on the absolute change
of intensity of the stimulus, but is proportional to the intensity of the stimulus
already acting, Weber's law.

44

690

THE SENSES

This law, which is true only within certain limits, may be best under-
stood by an example. When the retina has been stimulated by the light of
one candle, the light of two candles will produce a difference in sensation
which can be easily and distinctly felt. If, however, the first stimulus is that
of an electric arc-light, the addition of the light of a candle will make no dif-
ference in the sensation. So, generally, for an additional stimulus to be felt,
it may be proportionately small if the original stimulus is small, and must
be greater if the original stimulus is great. The stimulus increases as the
numbers expressing its strength, while the sensation increases as the
logarithms.

Everyone is familiar with the fact that it is quite impossible to see the
fundus or back of another person's eye by simply looking into it. The interior
of the eye forms a perfectly black background to the pupil. The same re-

FIG. 468. — Diagram to Illustrate the Action of the Ophthalmoscope when a Plane
Concave Glass is Used, c, Observer's eye. The light reflected from any point, d, on
retina of a, would naturally be focused at e; if the lens b is used is would be focused at iy
in other words, at back of c. The image would be enlarged, as though of g, and would be
inverted. (After McGregor Robertson.)

mark applies to an ordinary photographic camera, and may be illustrated
by the difficulty we experience in seeing into a room from the street through
the window, unless the room be lighted from within. In the case of the
eye this fact is partly due to the feebleness of the light reflected from the
retina, most of it being absorbed by the retinal pigment. But the difficulty
is due more to the fact that every such ray is reflected back to the source of
light and cannot be seen by the unaided eye without intercepting the in-
cident light as well as the reflected rays from the retina. The difficulty is
surmounted by the use of the ophthalmoscope.

The ophthalmoscope, brought into use by Helmholtz, consists in its sim-
plest form of a concave mirror with a hole in it. The one described is one
of the less intricate of the modern instruments. It consists of, a, a slightly
concave mirror of metal or silvered glass perforated in the center, and fixed
into a handle; and b, a biconvex lens of 6 to 8 cm. focal length. Two methods
of examining the eye with this instrument are in common use — the direct
and the indirect: both methods of investigation should be employed. A
normal eye should be examined. A drop of a solution of atropine (two grains
to the ounce) or of homatropine hydrobromate should be dropped into the right
eye only about twenty minutes before the examination is commenced; the

THE OPTHALMOSCOPE

691

ciliary muscle is thereby paralyzed, the power of accommodation is abolished,
and the pupil is dilated. This will materially facilitate the examination;
but it is quite possible to observe all the details to be presently described with-
out the use of this drug. The room being now darkened, the observer seats

FIG. 469. — Diagram to Illustrate Action of Ophthalmoscope when a Biconvex Glass is
Used. The figure d on retina of a is under ordinary conditions focused at /and inverted.
If the lens b be placed between eyes, the image h is seen by the eye c as an enlarged image.
(After McGregor Robertson.)

himself in front of the person whose eye he is about to examine, placing himself

upon a somewhat higher level. A subdued but steady light is placed close to

the left ear of the patient in the examination of the right eye. Guiding the

mirror in his right hand, and looking through the central hole, the operator

directs a beam of light into the eye of the patient.

A red glare, called in practice the reflex, due to the

illumination of the retina, is seen. The patient is

then told to look at the little finger of the observer's

right hand as he holds the mirror; to effect this the

eye is rotated somewhat inward, and at the same

time the reflex changes from red to a lighter color,

owing to the reflection from the optic disc. The

observer now approximates the mirror, and with it

his eye to the eye of the patient, taking care to keep

the light fixed upon the pupil, so as not to lose the

reflex. At a certain distance, which varies with

the refractive power in different eyes, but is usually

an interval of about two or three inches between

the observed and the observing eye, the vessels of

the retina will become visible as lines running in

different directions. The smaller and brighter red

arteries can be distinguished from the larger and

darker colored veins. An examination of the

fundus of the eye reveals the optic disc and the

entrance of the blood vessels, the macula lutea,

and the fovea centralis. No blood vessels are seen

in the fovea. This constitutes the direct method

of examination, figure 468; by it the various details

of the fundus are seen as they really exist, and it is

this method which should be adopted for ordinary

use.

If the observer is ametropic, i.e., is myopic or
hypermetropic, he will be unable to employ the

direct method of examination until he has remedied his defective vision by
the use of proper glasses.

In the indirect method, figure 469, the patient is placed as before, and the
operator holds the mirror in his right hand at a distance of 30 to 40 cm. from

FIG. 470.— The Ophthal-
moscope. The small upper
mirror is for direct, the
larger for indirect, illumi-
nation.

692

THE SENSES

the patient's right eye. At the same time he rests his left little finger lightly'
upon the patient's right temple, and holding the lens between his thumb and
forefinger, two or three inches in front of the patient's eye, directs the light
through the lens into the eye. The red reflex, and subsequently the white one,
having been gained, the operator slowly moves his mirror, and with it his eye,
toward or away from the face of the patient, until the outline of one of the
retinal vessels becomes visible, when very slight movements on the part of the
operator will suffice to bring into view the details of the fundus above described,
but the image will be much smaller and inverted. The lens should be kept
at a fixed distance of two or three inches, the mirror being alone moved until
the disc becomes visible: should the image of the mirror obscure the disc,
the lens may be slightly tilted.

The Field of Vision. — The field of vision of an eye is that part of the
external world which can be seen by it when the eye is fixed. Under such
circumstances objects near the axis of vision stimulate points in the retina
near the fovea or on it, while objects at an angle of 60° to 90° from the axis

120

f,r,

150

255

270"

285"

FIG. 471. — Perimeter Chart, Showing Extent of Field of Vision for White Light and to the
Colors Red, Green, Yellow, and Blue. (Krapart.)

of vision stimulate regions of the opposite side of the retinal cup, i.e., the
retinal field is inverted.

The perimeter is an instrument for measuring the field of vision in terms
of angular measure. When a field is charted by means of the perimeter it
is revealed that objects can be seen further out in the field in some directions
than in others. For example, objects in the temporal field can be seen at
an angle of 90° to 100°, while on the nasal side they are seen only 60° to 70°.

VISUAL PURPLE 693

If the head is turned to the right or the left while keeping the eye fixed, it is
found that objects are seen at a greater angle. This shows that the limita-
tions are due to the facial boundaries of the eye preventing the light from
entering the eye and not from lack of sensitiveness of the retina. In fact,
the retina is sensitive to light out to the ora serrata.

Localization in the Retina. — Careful exploration of the retina with
the perimeter gives a measure not only of the extent of the visual field, but of
its acuteness and localization in different areas toward the periphery. Con-
sidering the minimal distance apart which two luminous points must be to
be distinguished as two, it is found that when the image falls on the fovea
the two points may be very near together, as little as one minute or even less.
Two stars can be seen only at a somewrhat greater angular distance, two to
three minutes. One minute angular measure covers an area on the retina of
a trifle over 4^. The diameter of the cones is about 2tu, so that the stimuli in
the fovea fall on at least two separate cones. The inference seems reason-
able that the retina in its most sensitive part can localize stimuli that fall on
adjacent cones.

The area of the fovea centralis is small, from 0.5 to 1.5 mm. Outside of
its area the acuteness of vision quickly falls off. The fact is roughly esti-
mated by fixing the vision on a letter in the printed line in the book before the
reader and then determining the number of letters to either side that can be
identified. The height of these letters is 1.5 mm.; by measuring the dis-
tance of the page from the eye one can quickly calculate the area of distinct
vision on the retina. Test types are printed on the basis of an angle of five
minutes.

In the outer limits of the retina the power of localizing stimuli is very
slight; in fact, in the extreme borders of the field it is difficult to determine
other than general form.

Visual Purple. — The method by which a ray of light is able to stimulate
the endings of the optic nerve in the retina is not yet understood. It is sup-
posed that the change effected by the agency of the light which falls upon the
retina is in fact a chemical alteration in the protoplasm, and that this change
initiates a nerve impulse that is transferred to the optic nerve endings. The
discovery of a certain temporary reddish-purple pigmentation of the outer
limbs of the retinal rods in certain animals, e.g., frogs, which had been
killed in the dark, forming the so-called rhodopsin or visual purple, appeared
likely to offer some explanation of the matter, especially as it was also found
that the pigmentation disappeared when the retina was exposed to light and
reappeared when the light was removed, and that it underwent distinct
changes of color when other than white light was used. It was also found
that if the operation were performed quickly enough and in the dark, the
image of an object, optogram, might be fixed in the pigment on the retina by
soaking the retina of an animal in alum solution.

694

THE SENSES

The visual purple cannot, however, be absolutely essential to the due pro-
duction of visual sensations, as it is absent from the retinal cones, and from
the macula lutea and fovea centralis of the human retina, and does not appear
to exist at all in the retinae of some animals, e.g., bat, dove, and hen, which
are, nevertheless, possessed of good vision.

However, the fact remains that light falling upon the retina bleaches the
visual purple, and this must be considered as one of its effects. It has been
found that certain pigments, also sensitive to light, are contained in the inner
segments of the cones. These colored bodies are said to be oil globules of

FIG. 472. — Sections of Frog's Retina Showing the Action of Light upon the Pigment
Cells and upon the Rods and Cones, (von Gendesen-Stort.) A, From a frog which had
been kept in the dark for some hours before death; B, from a frog which had been exposed
to light just before being killed. Three pigment cells are shown in each section. In A
the pigment is collected toward the nucleated part of the cell, in B it extends nearly to the
basis of the rods. In A the rods, outer segments, were colored red (the detached one
green); in B they had become bleached. In A the cones, which in the frog are much
smaller than the rods, are mostly elongated; in B they are all contracted.

various colors — red, green, and yellow — called chromophanes, and are found
only in the retinae of animals other than mammals. The rhodopsin at any
rate appears to be derived in some way from the retinal pigment, since the
color is not renewed after bleaching if the retina be detached from its pig-
ment layer. The second change produced by the action of light upon the
retina is the movement of the pigment cells. On the stimulation by light
the granules of pigment in the cells which overlie the outer part of the rod
and cone layer of the retina become diffused into the parts of the cells be-
tween the rods and cones, the melanin granules, as they are called, passing
down into the processes of the pigment cells. A movement of the cones and

EXTENT OF THE VISUAL FIELD FOR COLOR 695

possibly of the rods is also said to occur, as has been already incidentally
mentioned. Under the influence of the stimulus of light the outer parts of
the cones, which in an eye protected from light extend to the pigment layer,
are retracted. In is even thought by some that the contraction is under
the control of the nervous system. Finally, according to the careful re-
searches of Dewar and McKendrick, and of Holmgren, it appears that the
stimulus of light is able to produce an action current in the retina. Mc-
Kendrick believes that this is the electrical expression of those chemical
changes in the retina of which we have already spoken.

Color Sensations. — When a ray of sunlight enters the eye it produces a
sensation of white light. But if the ray first passes through a prism, then it
produces sensations corresponding to the colors of the spectrum. As is well
known, white light is produced by vibrations of the luminiferous ether through
a wide range of vibration rates. When a beam of white light is passed
through a dispersing prism those vibration rates of low frequency are re-
fracted less than those of higher frequency, giving rise to the spectrum.
Vibrations of the luminiferous ether of rates just outside of the spectral rates
exist, those which have a lower rate giving rise to heat rays, and those of
higher rate to the so-called actinic or chemical rays, because they exert a
powerful chemical action. Those spectral colors which stimulate the retina
to produce sensations of color presumably affect the retinal elements through
chemical changes which they produce there. But this matter will be
discussed under theories of color vision.

The examination of color sensations reveals certain correspondences be-
tween the physical color of the stimulus and the resulting color perception.
If a pure spectral color be allowed to fall on the retina, a corresponding simple
sensation is produced. If two colors fall on the same portion of the retina
at the same time, a sensation is produced that is different from that which
occurs when either color alone stimulates. The same fact holds true for
three colors or more. In fact, three spectral colors can be selected which
by proper combination can be used to produce sensations of all the colors of
the spectrum. Such colors are called the fundamental colors, and while
the choice is more or less arbitrary, red, green, and violet are the colors
usually considered.

Extent of the Visual Field for Color.— The retina is most sensitive
to color in the region of the macula lutea. If by means of the perimeter one
explores the retina to special red, for example, it is found that the color can
be identified only at a distance of from 30° to 50° from the macula; the
limits extending out somewhat farther on the nasal side of the retina; that
is, the part corresponding to the temporal visual field. In the same way yel-
low can be identified for from 40° to 70°, blue from 40° to 50°. The visual
field for green is quite restricted, usually extending only from 20° to 30°.
The extent of the color visual field varies greatly in different individuals.

696 THE SENSES

Complemental Colors, and After-images of Color. — Certain colors,
when allowed to stimulate the retina at the same time, tend to neutralize
each other. That is, they produce sensations approaching white, usually
some shade of gray, which will have a tinge of one or the other primary colors
according to the proportion of stimulation. These pairs of colors are called
complemental colors. Each spectral color has its complemental color, a fact
that is represented in figure 473. The complemental colors of greatest physi-
cal significance are red and green (greenish-blue), yellow and deep blue
(indigo blue), green (greenish-yellow), and violet.

FIG. 473. — Geometrical Color Table for Determining the Complemental Colors.

Positive after-images of color exist for a brief moment, but the greatest
significance attaches to the negative after-images. The negative after-images
of color following the stimulus of colored light upon the retina are not the
sensation of color produced by the color of an object, but are the opposite
or complemental color. The after-image of red is, therefore, green, and
that of green, red; that of violet, yellow, and of yellow, violet, etc. The
same relation holds with the other colors. A condition for the development
of a strong after-image is that the primary image shall have continued to a
certain degree of fatigue. The colors which reciprocally excite each other
in the retina are those placed at opposite points in the color table, figure 473.
The after-images of color are most intense in the axis of the visual field and
are not always present in the periphery of the retina, as can readily be seen
by examining the chart, figure 471.

Color sensations may also be produced by contrast. Thus, a very small
dull gray strip of paper, lying upon an extensive surface of any bright color,
does not appear gray, but has a faint tint of the color which is the comple-
ment of that of the surrounding surface. A strip of gray paper upon a green
field, for example, appears to have a tint of red, and when lying upon a red
surface, a greenish tint; it has an orange-colored tint upon a bright blue
surface, and a bluish tint upon an orange-colored surface; a yellowish color

THEORIES OF COLOR VISION 697

upon a bright violet, and a violet tint upon a bright yellow surface. The
color excited thus must arise as an opposite or antagonistic condition of the
retina, and the opposite conditions of which it thus becomes the subject,
would seem to balance each other by their reciprocal reaction. A necessary
condition for the production of the contrast colors is that the part of the
retina in which the new color is to be excited shall be in a state of compara-
tive repose; hence the small object itself must be gray. A second condition
is that the color of the surrounding surface shall be very bright.

Color-blindness. — Many persons are unable to distinguish one or
more of the fundamental colors, and therefore have different perceptions
of the color combination from that of the normal individual. It is said that
from 4 to 5 per cent, of men and about i per cent, of women are defective in
color vision. The defect is called color-blindness.

In very rare cases complete color-blindness exists. Such individuals
distinguish lights and shades only, that is, form. A more common defect,
however, is the absence of one or more of the fundamental color sensations,
the most common of all being the green-blind, or the red-green blind. The
red-green blind individual cannot distinguish red and green colored yarns
from each other or from shades of gray which reflect light with the same
intensity. When they are given the color test by the Holmgren yarns, they
indiscriminately mix the reds, greens, and grays. Cases have been described
in which the individual was red-blind alone, or green-blind alone. A less
common color defect is the inability to distinguish yellows and blues, yellow-
blue blindness.

Color-blindness may occasionally arise from disease or accident, but it
is usually congenital. The individual often does not discover his defect until
examined especially for his color vision. He may have learned to apply
the terms green and red to surrounding objects, such as the grass, bricks, etc.,
but he distinguishes these objects by slight differences in intensity of lumi-
nation, form, etc., and not by the sensations of color which the normal
individual experiences.

Theories of Color Vision. — We have no way of determining the
method by which the colors stimulate the retina other than our inferences
from indirect evidence. It is probable that the energy of light vibration
is transformed in the retinal structures into either physical or chemical
change, perhaps the latter. Those interested in the phenomena of color
vision generally accept one of two theories, or their modifications, in ex-
planation of the facts.

The Young-Helmholtz Theory of Color Vision. — This theory assumes
that there are three fundamental sensory elements in the retina which cor-
respond to and are stimulated primarily by the three primary colors — red,
green, and violet. The theory in its present form further assumes that each
color-perceiving element is slightly stimulated by others of the spectral rays,

698

THE SENSES

as shown in figure 474. When red rays fall upon the retina, they stimulate
the red-perceiving elements strongly and the green and violet very feebly.
The resulting sensation is that of red. So also is it with green and violet rays.
When the retina is stimulated by both red and green rays, the two correspond-

rv FlG' 474-— Diagram to Illustrate the Stimulating Effects of the Three Primary Colors
(Young-Helm hoi tz theory.) i is the red; 2, green, and 3, violet, primary color sensations.
1 he lettering indicates the colors of the spectrum. The diagram indicates by the height
of the curve to what extent the several primary sensations of color are excited bv vibrations
of different wave lengths. (Helmholtz.)

ing color-perceiving elements are strongly stimulated. The resulting color
perception, however, is a combination of the two sensations and corresponds
to some region of the spectrum between the red and green, according to the
relative intensity of the two stimuli. When all three color-perceiving ele-

B

FIG. 475. — Diagram to Illustrate the Reactions of the Three Photogenic Substances
according to Hering's Theory. (Foster.)

ments are stimulated at the same time, the. theory assumes that white light
will be perceived. In a similar manner all the various color sensations are
arrived at.

Hering's Theory of Color Vision. — This theory is based on the assump-

BINOCULAR VISION 699

tion that there are chemical substances in the retina, photogenic substances,
which are stimulated by the colors of the spectrum. It assumes three photo-
genic substances which are called the red-green, the yellow-blue, and the
white-black substances. By the theory, when the red-green substance is
stimulated by red or green light, respectively, the former produces destruc-
tive or katabolic changes, the latter constructive or anabolic changes, in the
substance. When red light falls upon the retina, it produces katabolism in
the red-green substance, which in turn develops a nerve impulse that arouses
the sensation of red. When green light, on the other hand, stimulates the
retina, it produces anabolism of the red-green substance and the sensation of
green. The same rule holds with the other two substances. It will be
noticed that this theory is based on the complemental colors.

When we apply the theories mentioned above to the phenomena of color-
contrast and color-blindness, we find that each is defective in some point.
By the Young-Helmholtz theory it is difficult to understand the perception
of the sensation black, for by the theory black could be perceived only as
the absence of all colors, and it is generally granted that there is a distinct
black sensation other than and different from mere darkness. This theory
explains more satisfactorily those cases of blindness to one color, as red-
blindness, for example. The Hering theory, on the other hand, gives us a
rational explanation for positive black sensation, and is particularly appli-
cable to the observed facts of color- contrast and negative color after-images.

Color after-images, as for instance the after-images of green following
stimulation by red light, are readily explained by Bering's theory, since the
strong katabolism in the red-green substance will be followed immediately
by anabolism to bring this substance up to its normal in the eye, thus pro-
ducing the after-image. This phenomenon can be explained by the Young-
Helmholtz theory only by assuming that following the stimulation by red
light and the consequent fatigue of red-perceiving elements there is sufficient
light entering the eye to stimulate the relatively sensitive green and violet
perceiving elements, thus producing an after-image. Strong after-images
are perceived in the dark room, so that the Hering theory is most applicable
in the explanation of these cases.

Binocular Vision. — When one looks at an object with a single eye,
the eye is so adjusted that the axis of vision is directed toward the object
investigated. This is called ocular fixation. The ocular fixation is accom-
plished by the co-ordinated contractions of the six ocular muscles. Its
purpose is to bring the image of the object examined in the external visual
field as nearly as possible upon the macula lutea. In binocular vision both
eyes are fixed on the same point in the visual field. A projection of the
visual axis of each eye will pierce the point of fixation in the external object.
It is evident that objects to either side of the point of fixation will give off
rays which will enter the eyes, stimulating fields in the retina on the opposite

yoo

THE SENSES

side of the visual axis. An examination of figure 476 will show that each
point in the visual field, A, B, C, Z), stimulates corresponding points,
a, b, c, d, af, bf, c', d', in the retinas of the two eyes, a, b, c, d, and
a' b', cf, d', are corresponding points in the two retinas. When a and a'
are stimulated at one and the same time, the resulting sensation is attributed
to one object in the visual field, A, and these are corresponding points. This
can be shown by pressing one eye out of its normal fixation so that the axes of

FIG. 476. — Diagram Showing the Symmetrical Correspondence of the Retinal Fields.
N, Nodal point; F, fovea centralis. The observer is supposed to be looking down upon the
optical apparatus from above. Note that the line CD, which is on the lower side of the
object, is the upper side of the image; and that the line BD, which is the right side of the
object, is the left side of the image, which brings it at the inner segment of the right retina
and the outer segment of the left retina.

the two eyes are not directed toward the same point. If one eye is pressed
lightly by the thumb while examining a given object, as soon as the pressure
is applied two objects will appear. This phenomenon is known as diplopia.
Diplopia is due to the fact that the images of visual objects do not fall on
corresponding points in the two retinae.

The parts of the retinae in the two eyes which thus correspond to each
other in the property of referring the images which affect them simulta-
neously to the same spot in the field of vision, are, in man, just those parts
which would correspond to each other if one retina were placed exactly in

BINOCULAR VISION

701

front of and over the other, as in figure 477. Thus, as we have noticed in
speaking of the distribution of the optic nerve fibers, the temporal portion
of one eye corresponds to or is identical with the nasal portion of the other
eye. The upper part of one retina is also identical with the upper part of
the other; and the lower parts of the two eyes are identical with each other.
The distribution of the optic nerve fibers corresponds with the distribution
of the identical points. The identical points on the upper and lower parts
of the retinae may also be shown by the following simple experiment.

FIG. 478.

FIG. 477. — Diagram to Show the Corresponding Parts of the Retinae.
FIG. 478. — Diagram to Show the Simultaneous Action of the Eyes in Viewing Objects
in Different Directions.

Pressure upon any part of the ball of the eye, so as to affect the retina,
produces a luminous circle, seen at the opposite side of the field of vision to
that on which the pressure is made. If, now, in a dark room, we press with
the finger at the upper part of one eye, and at the lower part of the other,
two luminous circles are seen, one above the other; so, also, two figures are
seen when pressure is made simultaneously on the outer or the inner sides
of both eyes. But if pressure be made with the fingers upon both eyes
simultaneously at their lower part, one luminous ring is seen at the middle
of the upper part of the field of vision. If the pressure be applied to
the upper part of both eyes, a single luminous circle is seen in the middle
of the field of vision below. So, also, if we press upon the outer side of one
eye and upon the inner side of the other eye, a single luminous spot is pro-
duced, and is apparent at the extreme right of the field of vision. The
hemispheres of the two retinae may, therefore, be regarded as lying one over
the other, as in C, figure 477. If the axes of the eyes, A and B, figure 478,
be so directed that they meet at a, an object at a will be seen singly, for
the point a of the one retina and a' of the other are identical. So, also, if
the object t3 be so situated that its image falls in both eyes at the same dis-
tance from the central point of the retina — namely, at b in the one eye

7O2 THE SENSES

and at b' in the other — /? will be seen single, for it affects identical parts of
the two retinae. The same will apply to the object 7-.

The reason why the impressions on the identical points of the two retinae
give rise to but one sensation, and the perception of but a single image,
must either lie in the structural organization and relations of the deeper
or cerebral portions of the visual apparatus, or it must be the result of a
mental operation; for in no other case is it the property of corresponding
nerves of the two sides of the body to refer their sensations to one spot.

Many attempts have been made to explain this remarkable relation be-
tween the eyes, by referring it to anatomical relation between the optic nerves.
The circumstance of the inner portion of the fibers of the two optic nerves
decussating at the commissure, and passing to the eye of the opposite side,
while the outer portion of the fibers continue their course to the eyes of the
same side, so that the left side of both retinae is formed from one root of the
nerves, and the right side from the other root, naturally led to an attempt
to explain the phenomenon by this distribution of the fibers of the nerves.
And this explanation is favored by cases in wrhich the entire half of one side
of the retina sometimes becomes insensible.

Visual Judgments. — Form and Solidity. — The estimation of the form
of bodies by sight is the result partly of the visual sensations and partly of the
association of ideas. The form of the image perceived by the retina depends
wholly on the outline of the part of the retina affected; the sensation alone is
adequate only to the distinction of superficial forms from each other which
lie in one plane, as of a square from a circle. But the idea of a solid body, as
a sphere, or a body of three or more surfaces, e.g., a cube, can be attained
only by the action of the mind in constructing it from the different superficial
images seen in different positions of the eye with regard to the object, and
(as shown by Wheatstone and illustrated in the stereoscope}, from two dif-
ferent perspective projections of the body being presented simultaneously to
the mind by the two eyes. Hence, when, in adult age, sight is suddenly
restored to persons blind from infancy, all objects in the field of vision appear
at first as if painted flat on one surface; and no idea of solidity is formed until
after long exercise of the sense of vision combined with that of touch. The
clearness with which an object is perceived, irrespective of accommodation,
would appear to depend largely on the definiteness of stimulation of the rods
and cones which its retinal image covers. Hence, the nearer an object is to
the eye, within the limits of vision, the more clearly are all its details seen.
Moreover, if we want carefully to examine any object, we always direct the
eyes straight toward it, so that its image shall fall on the yellow spot,
which has already been shown to be the area of the most acute vision.

In binocular vision the images of an object, while they fall in approxi-
mately corresponding points on the two retinae, are never absolutely the
same.

JUDGMENTS OF SIZE AND DISTANCE

7°3

When an object is placed so near the eyes that to view it the optic axes
must converge, a different perspective projection of it is seen by each eye,
these perspectives being more dissimilar as the convergence of the optic axes
becomes greater. Thus, if any figure of three dimensions, an outline cube,
for example, be held at a moderate distance before the eyes, and viewed with
each eye successively while the head is kept perfectly steady, A, figure 479,
will be the picture presented to the right eye, and B that seen by the left eye.
Wheatstone has shown that on this circumstance depends in a great measure
our conviction of the solidity of an object, or of its projection in relief. If
different perspective drawings of a solid body, one representing the image
seen by the right eye, the other that seen by the left, for example, the drawing
of a cube, A, B, figure 479, be presented to corresponding parts of the two
retinae, as may readily be done by means of the stereoscope, the mind will
perceive not merely a single representation of the object, but a body pro-
jecting in relief, the exact counterpart of that from which the drawings were
made.

Judgments of Size and Distance. — The estimation of the size of an object
and its distance away from the observer is based in part upon the visual
image and in part upon judgments due to past experience. The elements
are inseparable and mutually dependent. Thus, a lofty mountain many
miles away may subtend the same visual angle as a small hill near at hand .

FIG. 479. — Diagrams to Illustrate how a Judgment of a Figure of Three Dimensions is

Obtained.

While the size and shape of the two images may be identical, yet the image
of the hill near at hand is more distinct, its details are perceived, and its out-
lines are sharper than in the image of the mountain. If the atmosphere
be charged with moisture or with dust, the image of the mountain will be
still more indistinct and dim. From previous experiences we have learned
that the dimness and indistinctness of the one and the definiteness of the
other are associated with distance.

If two objects are very near at hand then there will be a difference in
the convergence of the two eyes in binocular vision. It is now well known
that the ocular muscles are possessed of a very delicate muscle sense. This
muscle sense leaves the impression which enables us to judge that the one
object is nearer and the other farther. In the common and familiar objects

7o4

THE SENSES

about us we have from long experience and intimate contact learned their
actual size and the character of the retinal image formed at definite but known
distances. When such an object forms an image of the common size and
usual distinctness on the retina, the judgment as to its distance is quickly
made.

In the case of unknown objects which are associated with known ob-
jects, the judgment of the size and distance of the latter is used in forming
a judgment of the size and distance of the former by comparison. Many
visual deceptions are based on these comparisons, a fact that is often taken
advantage of by photographers. It is also well known that people living in
a moist, hazy climate are utterly unable accurately to estimate distances
when suddenly transferred to a clear mountain climate.

LABORATORY DIRECTIONS FOR EXPERIMENTS ON THE
SENSE ORGANS.

i. Touch. — Use the small compasses with rounded tips provided for
the purpose, and determine the power of localization of the sense of touch
as follows: Have the person observed close his eyes, then touch different
parts of the skin, of the hand, arm, face, neck, etc., and let the observed one
announce the exact point touched.

The localization can also be determined by touching two points on the
skin with the points of the compasses separated by varying distances. Ex-
amine especially the skin on the forearm, on the back of the hand, on the

FIG. 480. — Aristotle's Experiment.

palm of the hand, the tips of the fingers, and at different points on the face,
including the lips and tip of the tongue. Touch these regions of the skin
with either one or with two points of the compasses, and allow the person
observed to announce results, drawing your conclusions according to the
principle of trial and error. Make a table showing the power of local dis-
crimination in the different regions.

SENSATIONS OF TASTE

705

2. Aristotle's Touch Experiment. — Roll the tips of the middle and
index fingers over a marble and note that the sensation from the two fingers
is interpreted as that of a single object. Now cross the fingers and repeat
the experiment. This time there is the sensation of touching two spheres.

3. Temperature Sensations. — It is a common experience that the
hand brought in the neighborhood of a warm or a cold object develops the
sensation of warmth or cold. Examine a given small area of the back of
the hand with the thermoesthesiometer. Certain points will give stronger
sensation of heat than others. Map these out carefully. Examine the same
area for the cold. A large number of cold spots will be found and they will
not coincide with the warm spots, figure 421.

The stimulation for the hot and cold spots does not depend upon the
absolute temperature, but on the relative temperature. Insert the hand in
water that feels lukewarm. Place the same hand in a cup of quite warm
water for a moment, then reinsert it in the lukewarm water. This will now
feel cold.

FIG. 481.— Localization of Taste. Bitter ; acid ; salt, — • ; sweet ; T,

tonsils; FC, foramen cecum; CF, circumvallate papilla; FP, fungiform papilla. (Hall.)

4. Sensations of Taste.— The distribution of taste organs in the
tongue is shown in figure 481. Examine your own tongue for organs of
sweet, acid, saline, and bitter, using solutions of i to 2 per cent, salt, 10 per
cent, sugar, 2 to 5 per cent, acid, 5 per cent, acetic acid, and o.i per cent,
quinine.

Wipe the tongue dry and apply the solution named from the tip of a glass
rod. The best form of rod is about 15 cm. long by o. 5 cm. in diameter, and
has one end drawn out to a slender pencil-shaped tip and of a size which
45

706 THE SENSES

will suspend a very small drop. Too large a drop diffuses over too great an
area of the tongue. Occasionally small crystals of sugar, salt, etc., give
more satisfactory results.

Perform the experiments on yourself before a mirror and map the re-
sults as shown in figure 481.

If the experiments are done with care certain papillae will be found which
give one or two of the taste sensations, but not all.

5. Sensations of Smell. — Quantitative experiments on the sense
of smell are difficult to determine. Inhale vapor of ammonia so dilute that
it can just be detected. Note that the sensation is strongest at the moment
of drawing the vapor into the nostril. Fill the nostrils with the diluted vapor
and close the external opening; the sensation quickly disappears. Keeping
the nostrils closed, walk into the open air, then inhale fresh air. At the
moment of the inhalation of fresh air the ammonia is again perceptible.
Repeat with bergamot, rose water, etc.

6. The Limits of the Sense of Hearing. — Use a set of tuning forks
for the purpose, and determine the lowest vibration per second which can be
perceived as sound. Determine the highest limits in the same way.

7. Acuteness of the Sense of Hearing. — Listen to the vibrations of
a tuning fork, or, better, to the ticking of a watch which is moved back and
forth from the ear. Measure the distance at which it can just be distin-
guished. This experiment should be performed with the person blindfolded,
and extraneous noise should, of course, be suppressed.

Refraction. — Light passes out from a luminous point in straight
lines so long as the line of propagation is in a medium of uniform density.
If the rays pass from a transparent medium of one density into a second
medium of different density, they will usually be turned out of their course, or
refracted. If the rays enter the second medium at right angles to its surface,
they will continue in straight lines, but if they enter at any other angle they
will be refracted. If the second medium is denser than the first, the rays will
be refracted toward the perpendicular; if it is less dense, away from the
perpendicular.

Use a Hall's refraction- measuring apparatus (constructed of a carpenter's
try square). Adjust it in a water-pan, and fill to the exact level with clear
water. Clamp a rule to the vertical limb of the apparatus at an angle with
the axial point of the instrument. Read the horizontal scale of the instru-
ment along the edge of the clamped rule. Remove the instrument from the
pan, using care not to disturb the adjustment of the ruler, and construct the
angle of refraction on co-ordinate paper. Determine the relation of the angle
of incidence and of refraction, and compute the refractive index of the water,
the air having a refractive index of one.

Repeat the determination using a block of glass. Construct a diagram.

9. To Determine the Refractive Power of a Convex Lens. — Use a

INVERTED IMAGE ON THE RETINA 707

meter stick which is provided with a movable diaphragm or screen, and a
holder for a lens. Measure the focal distance of lens number i as fur-
nished from the optical set. Put the lens in its holder and focus the image
of the sun or of an electric bulb on the screen, moving the screen back and
forth until the sharp focus is determined. If the lens is accurately ground,
the focus will be at a distance of one meter, which is the refractive power of
a one-diopter lens, by definition. In the same way determine the refractive
power of lenses numbers 2, 3, and 4.

Construct a diagram showing the path of the light in the formation of
the image in these cases.

If the measurement in the above case is made through two parallel open-
ings or diaphragms about 5 mm. in diameter each, and separated by 4 or
5 mm., the point of focus can be more accurately determined (see Scheiner's
Experiment, No. 14). Construct the mathematical figure showing the
course of both cones of rays in this test.

10. Determination of Near and Far Limits of Vision. — Support a
meter stick in a horizontal position at a comfortable level for the eye. Mount

FIG. 482. — Diagram of Experiment to Ascertain the Minimum Distance of Distinct Vision.

a needle in a cork and set it on the meter stick about 25 cm. in front of the
eye. Make two pin-holes in a card at a distance of about 2 mm. from each
other. Hold this card with the pin-holes close in front of the right eye, and
bring the eye up to the end of the meter stick; cover the other eye. Ob-
serve that when the needle is brought nearer and nearer to the eye, at a
certain distance it becomes double. Determine this distance very accurately.
It is the near-point of accommodation for the right eye. Make the same
determination for the left eye.

Hold the punctured card in front of the right eye, and move the needle
(it is better to use something larger) farther and farther away until it becomes
again double, if it does so. This is the far-point of accommodation. In
normal eyes infinity is the far limit. In practice an eye that has no far
limit under twenty feet is considered normal. This test should be made on
each eye.

ii. Inverted Image on the Retina.— Dissect off a segment of the
sclerotic of a fresh ox eye, or use a fresh eye from an albino rabbit. Make

708 THE SENSES

a tube of black paper of the size of the eye, and insert the eye in one end,
with the cornea directed into the tube. In the dark room examine the image
of the candle flame as formed on the retina of the eye in the tube. In a
favorable experiment, a clear inverted image of the candle can be seen on
the retina through the semi-transparent membranes of the eye. The same
experiment can be demonstrated with the camera, or with a small lens, using
a ground-glass plate to make the image more apparent.

12. Spherical Aberration. — In physical optics it is found that it is
difficult to grind lenses so that they will refract equally in the center or
optical axis and in the periphery. Unequal refraction of these two regions
is called spherical aberration. It is corrected in optics by diaphragms which
shut out the light, either from the borders of the lens or from its center.
The former method is used in the eye. To demonstrate spherical aberra-
tion, look at an object two meters from the eye, such as a part of the window.
Pass a card close in front of the eye until the light enters only at the
margin of the pupil, i.e., the borders of the lens. It will be found that
the object is no longer in focus and the outlines are dim and diffused.
Normal eyes are near-sighted for the rays that are refracted by the borders
of the lens.

13. Chromatic Aberration. — Look toward the borders between the
sash and the bright light of an open window, at a distance of twenty feet or
more. Use the right eye only. Bring a card across the pupil approaching
from the side of the light until the eye is almost covered with the card. The
window sash will seem to have a blue- violet fringe. If the card is brought
across from the opposite side, the sash will have a reddish-yellow fringe.

Make a cross of two strips of Bradley' s pure color paper, one red and
the other blue, on a black surface. When held at the proper distance
the red appears nearer than the blue. This phenomenon is brought out
more strongly by covering the colored papers with very thin white tissue
paper. The judgment of distance is based on the effort of accommoda-
tion which is greater for the red than for the blue and violet rays.

14. Schemer's Experiment. — Use two needles on corks, the method de-
scribed in Experiment i, placing one at a distance of 20 cm., and the other
about 60 cm. from the eye. Use only the right eye, look through two pin-
holes in a card at the far needle. The near needle will appear double,
but the images will be somewhat blurred. While looking at the far needle,
bring a cardboard across the right hole, note that the left image of the near
needle disappears, and vice versa. If one accommodates for the near
needle, the far needle appears double, and upon covering the right hole with
the card the right image of the far needle disappears. This is known as
Scheiner's Experiment. Construct a diagram to explain these phenomena.

15. Purkinje-Sanson's Images. — Examine the eye of another person
in a dark room as follows: With the observing eye focus for a far object,

ASTIGMATISM

709

let the observer hold a candle slightly to one side of the axis of vision and
about one foot from the eye. It the observer looks into the other eye from
the side opposite the candle, he will be able to see three reflected images,
figures 457 and 458. One, from the anterior surface of the cornea, is
bright and distinct, and of medium size and erect. In the middle of the
pupil there will be a second image, larger and quite dim. This is a reflec-
tion from the front of the lens. The third image, reflected from the posterior
surface of the lens, will seem to be farther back in the eye, quite small and
inverted. These images can all three be seen at once with careful adjust-
ment of the relative positions of the candle and the observer, with refer-
ence to the axis of vision of the eye observed.

If the observer protects his own eye from the direct light of the candle
by a blackened cardboard between his eye and the candle, and asks the
observed person to accommodate now for near objects, now for far, keeping

FIG. 483. — Disc of Concentric Lines for the Astigmatic^Test.

the axis of vision constant, he will be able to note that the middle image,
i.e., the one from the anterior surface of the lens, changes in size and in
relative position with reference to the other two, which are essentially con-
stant. With near accommodation this image becomes smaller and seems
to move toward the image from the cornea; with far accommodation it
becomes larger and appears to move to the image reflected from the posterior
surface of the lens. This shows that the act of accommodation consists in a
change in the convexity of the front of the lens.

1 6. The Phakoscope of Helniholtz. — This classical instrument was
invented by Helmholtz to demonstrate the act of accommodation, as out-
lined in the second paragraph of the preceding experiment. Repeat the
preceding experiment, using this instrument in a dark room.

17. Astigmatism. — Astigmatism is a term used to describe the con-
dition of unequal curvature of the refracting surfaces of the eye in the
different meridia. The cornea is the surface which usually shows the greatest

7IO THE SENSES

astigmatism. The defect is demonstrated by numerous forms of astigmatic
charts, the most serviceable of which are the barred-letter test type, the clock
dial, or the dials shown in figure 463 or 483. Hang an astigmatic dial at a
distance of six meters and test the right and left eyes separately, as follows:
When the vision is focused on the center of the dial, if the eye is normal,
the three bars in each radius of the clock dial will be seen with equal distinct-
ness and have sharp black lines. In an astigmatic eye one or more of these

FIG. 484. — Diagram for Demonstrating the Blind Spot.

radii will appear sharp and distinct, while the other will appear dim and
indistinct, the relative difference depending upon the degree of astigmatism.
Note the meridian of astigmatism in the right and left eyes separately. Use
the test set, and find the cylinder necessary to correct the astigmatism in
each eye and determine its meridian.

Astigmatism is commonly shown by the presence of radii when one looks
at the stars at night, or by the ragged outline of a pin-hole in a card, when
held at arm's length against a white sky. In extreme cases outlines like

FIG. 485. — The Blind Spot with the Eye 30 cm. from the Paper. The irregularity of
outline is due to the larger blood vessels.

the bars in the window sash or checks in clothing may be distorted, or some
of the lines may not even be seen.

1 8. The Blind Spot. — Look with the right eye at the spot in the ac-
companying figure at a distance of about 20 to 25 cm., covering the left eye.
Hold the spot in the line of direct vision and move the book to and from
the eye; in some cases it is necessary to rotate the book slightly. It will be
found that the cross to the right will, at a certain position, completely dis-

PURKINJE'S SHADOWS 711

appear. This happens when its image falls on the retina directly over the
entrance of the optic nerve, which has no visual cells, and is, therefore, the
blind spot. This area is large enough to cause a man completely to disappear
at a distance of about one hundred meters.

Place a sheet of white paper at a distance of 30 cm. in front of the eye,
holding the head in a fixed position against the special support furnished;
look with the right eye at the top of the cross made on the left of the sheet
of paper. Covering the sharpened portion of a lead pencil with white
paper, leaving the black tip exposed, move this pencil across the paper
from the visual center to the right. At a certain distance the black lead
will suddenly disappear. Mark this point. Continue to move the pencil
until the lead reappears. Mark this point. These two points represent
the limits of the blind spot in the horizontal plane, as magnified by the
conditions of the experiment. Mark the limits in the other meridians in
the same manner. Compute from the figures obtained the exact size of
the blind spot in your right eye, figure 485. Repeat on the left eye. Usually
these areas are not symmetrical. The computation may be based on the
following proportion: a, the diameter of the mapped blind spot is to the
distance of the map from the nodal point of the eye, b, as c, the distance
from the nodal point to the retina, which is i .5 cm., is to x, the diameter of
the actual blind spot in the retina, x varies from 1.5 to 3 or more mm.
a : b : : c : x.

19. Relations of the Size of the Retinal Image to Distance.— Com-
pute the size of the retinal images of familiar objects by the equation given
in the last experiment. Compute the size of the image formed on the retina
by a man six feet tall at a distance of 100 feet. Compute the size of the
image formed by a tower 125 feet tall at a distance of 575 feet.

20. Purkinje's Shadows.— Stand in front of a blackened wall in
the dark room. While looking toward the wall with the right eye accom-
modated for distant objects, move a lighted candle back and forth about
10 to 20 cm. to the right of the eye and a little below its level. Presently
many branching shadows will be seen as though they stood in space in front
of the individual. These are the shadows of the blood vessels cast upon the
retina. A careful examination will show that these shadows seem to con-
verge to a point to the right of the center of vision of the right eye. By
moving the candle up and down or from side to side, the shadows seem also to
move slightly. Many persons can readily see Purkinje's figures by looking
through the narrow spaces between the fingers of the hand moved close in
front of the eye, when the vision is directed toward a bright sky. One can
demonstrate by this means that the macula is free from blood vessels, since
the pattern of the blood vessels around the borders of the macula is very
readily determined. This is especially true if there is slight retinal
congestion.

712 THE SENSES

21. Duration of the Retinal Image. — When a beam of light falls
upon the retina for an instant it produces a stimulus which endures for a
time after the stimulus is removed. This interval can be measured by the
proper mechanical device. Place on the color wheel a disc, which has a
small segment cut out at one point on the periphery. Put a printed page
behind the segment with the observer standing in front. Rotate the segment
faster and faster until the printed page is seen continuously. At this point
the visual image made at one revolution of the disc lasts until the next im-
pression on the same spot. The speed of the revolution of the color wheel
can be measured by attaching an electric contact key and signal magnet to
the disc wheel and measuring the rate of interruptions against the known
vibrations of a tuning fork. The same phenomenon may be determined by
placing on the disc two complemental colors and judging the speed of
revolution required for complete fusion.

22. Limits of the Field of Vision. — The limits of the visual field are
determined by direct measurement with the perimeter. Set the person
whose retina is to be measured in a comfortable erect position, with one eye
at the center of the arc of the perimeter and the other covered by an eye-
shade. The observed eye must be fixed on the center of the field of vision,
and care must be used to prevent obstruction of the field. The examination
is made with greatest accuracy by bringing an object into the field of vision
from behind the person observed. When the individual examined first
detects the presence of the object, he announces it and the angle is read off
from the arc of the perimeter and recorded on the chart for the purpose.
These readings should be made in about twelve radii. They should be
made for each eye.

23. Limits for the Field of Vision for Color. — To measure the limits
of the field of vision for color one should proceed as in the preceding experi-
ment, except that small squares of colored papers are brought into the field
from the rear. The retina should be mapped for red, green, yellow, and
blue. Use Bradley' s pure color papers. Take four penholders and mount
on the end of one a centimeter square of red paper, on the others green,
yellow, and blue. To make a determination bring the color up from behind
and, as soon as it is certainly detected and announced, remove it from the
field of vision. Examine the eye for all four colors at one sitting, mixing
them indeterminately in the individual tests. Occasionally an eye will be
found which exhibits a well-marked restriction of the color field, though the
individual himself may not be completely color-blind.

24. Color-blindness. — Make an examination for color-blindness,
using Holmgren's colored yarns. Spread the yarns out on a table in the best
of light. Place the three confusion skeins in front of the individual to be ex-
amined and ask him to match them quickly from the skeins on the table,
paying no attention to lights and shades of the same color. A color-blind

VISUAL ACUITY 713

individual will confuse colored skeins, most usually the reds, greens, and
grays.

25. Color Mixing. — Use Bradley' s color wheel and test the effect of
simultaneous stimulation of the retina with two or more colors, by placing
on the wheel two or more colored discs, rotating the wheel at a speed
sufficient to cause complete fusion. The sensation produced by two colors
applied simultaneously will be entirely different from that produced by
either alone. Red and green (or greenish-blue), when mixed in the proper
proportion, produce a sensation of gray. The same effect may be had
from yellow and blue, orange and violet, or any of the complementary
colors chosen according to the geometrical color table, figure 473. By
mixing three colors, red, green, and violet, in the proper proportion one
can produce a sensation almost the same as that produced by white light.

26. Color After-images. — Color after-images can be demonstrated
by looking continuously at the center of one of the primary colors of Bradley' s
color charts against a white or gray wrall until there is apparent fatigue,
then suddenly removing the chart. An after-image of approximately the
complementary color will appear in the course of a few seconds. Occasion-
ally these images are very vivid. The experiments are brilliant if performed
in the dark room, using colored gelatin screens through which an intense
light shines. When the light is turned off, a brilliant after-image of the
complementary color appears.

27. Retinoscopy. — Use the ordinary small ophthalmoscope and ex-
amine the retina of the eye of a cat or rabbit. Dilate the pupil by the use of
atropine. Place the animal whose eye is to be examined on a support in
front of a bright but uniform light (an Argand burner). Reflect the light
from the mirror of the ophthalmoscope through the pupil into the retinal cup
of the animal. Usually the ophthalmoscope has to be focused for a cat's
retina. When a good light is secured, the retinal cup will appear as a bril-
liantly colored disc, with the branching blood vessels, and usually with
some brilliant bluish-green pigment in the lower portions of the retinal
disc.

After some practice on the cat or rabbit, the student should examine
the retina of one of his mates, preferably an eye that has an unusually wide
pupil. In some cases a light dosage of homatropine may be used on one eye.
This will dilate the pupil and the examination will be much easier.

Students are not recommended to use atropine unless under conditions
which permit the eye to rest for two or three days following.

28. Visual Acuity. — The visual acuity of the eye should be tested first
for the right eye, then for the left. Hang a test chart at a distance of twenty
feet, so that its disc is well illuminated, and allow the individual tested
to read off the letters on the chart, beginning with the larger ones at the top.
The letters on this chart are constructed on the basis of a visual angle of

714 THE SENSES

five degrees. When the letters marked lt twenty feet" or "six meters"
represent the limit of accurate identification, the visual acuity is said to
be i, or normal. If the line marked "thirty feet" is the limit, then the
acuity is one and a half; if "fifteen feet," then the visual acuity is three-
fourths, etc.

If the eyes tested are astigmatic, or have other optical defects, these
must first be corrected before testing for visual acuity.

29. The Test Set. — The student is recommended to close the experi-
ments on the eye by fitting glasses for himself and at least two others. He
should correct for the defects that have been revealed in the preceding experi-
ments, especially for astigmatism; myopia, or hypermetropia; and presby-
opia. Of course each eye must be tested and fitted separately.

CHAPTER XVI.

THE REPRODUCTIVE ORGANS.

THE REPRODUCTIVE ORGANS OF THE MALE.

THE male reproductive organs comprise the Testis, the Ductus Deferens,
the Vesicula Seminalis, the Prostate, and the Penis.

The Testis. — The testis consists of two parts, i, the testicle proper,
which is covered by the tunica albuginea and secretes the germinal cells,
and 2, the conducting tubules, which compose the epididymis and ductus
deferens.

The testicle is divided by connective- tissue septa into lobules, the tubuli
seminiferi. Each tubule is limited by a membrana propria on which rests
the germinal epithelium.

n •""'•" Piltfvf II !" •* J'M hi-1 /
I

FIG. 486. FIG. 487.

FIG. 486. — Plan of a Vertical Section of the Testicle, Showing the Arrangement of the
Ducts. The true length and diameter of the ducts have been disregarded, a, a, Tubuli
seminiferi coiled up in the separate lobes; b, tubuli recti; c, rete testis; d, ductuli efferentes
ending in the coni vasculosi; /, e, g, convoluted canal of the epididymis; h, vas deferens;/,
section of the back part of the tunica albuginea; i, i, fibrous processes running between the
lobes; s, mediastinum.

FIG. 487. — Vertical Section through the Wall of the Tubules of Epididymis. X 700.
(Kolliker.) b, Connective tissue and smooth muscle cells; e, basal layer of epithelial cells;
/, high columnar cells; p, pigment granules in columnar cells; c, cuticula; h, cilia.

On the approach of sexual maturity the process of spermatogenesis begins.
The germinal cells multiply rapidly, and, by a complex series of mitotic
divisions or stages, form ultimately the male reproductive cells, or sperm
cells.

715

7i6

THE REPRODUCTIVE ORGANS

The important stages in order are: archispermiocyte, spermatogonia,
primary and secondary spermatocytes, spermatids, and spermatozoa. The
spermatogonia stage is the stage of rapid multiplication; the spermatocyte,
that of maturation, comparable to the maturation stage of the ovum.

The sperm cells are the essential male reproductive cells. Each sperma-
tozoon consists of a minute oval head, a middle piece, and a tail. The head

spd

spc.t

spg.r

FIG. 488. — Later Stages in Spermatogenesis of the Bull, spg.r, Reserve spermato-
gonium; spg, spermatogonium; spc.g, spermatocyte in late synapsis stage; spc.i, spermacyte
in stage just preceding the maturation divisions; spd, spermatids in advanced stage of
histogenesis, with heads deeply embedded in Sertoli cell. Highly magnified. (After
Schoenfeld.)

is 4/* by 2 . 5/£. The middle piece and tail are about 50 to 6o/j. long. Sperm
cells possess the power of flagellate movement.

The Ductus Deferens. — This is the single duct proceeding from each
testicle to join its fellow at the base of the bladder. Each has an ampulla or
enlargement just before it unites with its fellow. The ductus deferens has
muscular walls and is lined with ciliated epithelial cells.

The Vesiculae Seminales. — The seminal vesicles have the appearance
of outgrowths from the base of the deferent ducts. Each deferent duct

THE VESICUL^E SEMINALES

717

c-

FIG. 489. — Section of a Tubule of the Testicle of a Rat, to Show the Formation of the
Spermatozoa, a, Spermatozoa; &, seminal cells; c, spermatoblasts, to which the sper-
matozoa are still adherent; d, membrana propria; e, nbro-plastic elements of the connective
tissue. (Cadiat.)

FIG. 490. — Dissection of the Base of the Bladder and Prostate Gland, Showing the
Vesiculae Seminales and Ductus Deferens. a, Lower surface of the bladder at the place
of reflection of the peritoneum; b, the part above covered by the peritoneum; i, left ductus
deferens, ending in e, the ejaculatory duct; the ductus deferens has been divided near i,
and all except the vesical portion has been taken away; s, left vesicula seminalis joining the
same duct; s,s, the right ductus deferens and right vesicula seminalis, which has been
unraveled; p, under side of the prostate gland; -m, part of the urethra; u, u, the ureters
(cut short), the right one turned aside. (Haller.)

718 THE REPRODUCTIVE ORGANS

just before it enters the prostate gland, through part of which it passes to
terminate in the urethra, gives off a side branch which bends back from it at
an acute angle. This branch, dilating, variously branching, and pursuing in
both itself and its branches a tortuous course, forms the vesicula seminalis.
Each vesicle is a single-branching, convoluted, and sacculated tube.

The microspic structure resembles closely that of the ductus deferens.
The Penis. — The penis is attached to the symphysis pubis by its root.
It is composed of three long, more or less cylindrical masses enclosed in

remarkably firm fibrous sheaths. Two, the
corpora cavernosa, are alike and are firmly
joined together. They receive below and be-
tween them the third part, or corpus spongi-
osum. The urethra passes through the corpus
spongiosum. The enlarged extremity, or glans
penis, is continuous with the corpus spongiosum.
Cowper's glands are at its base, and their ducts
open into the base of the urethra.

The Prostate Gland.— The prostate is
situated at the neck of the urinary bladder, and
encloses the base of the urethra. The prostate
is made up of small compound tubular glands
embedded in an abundance of muscular fibers
and connective tissue. The glandular sub-
stance consists of numerous small saccules,
opening into elongated ducts, which unite into
a smaller number of excretory ducts. The

™ni of the up?er part of. the rstate are

view, B, front view. small and hemispherical, in the middle and

lower parts the tubes are longer and more

convoluted. The ducts, twelve to twenty in number, open into the urethra.
They are lined by a layer of columnar cells, beneath which is a layer of
small polyhedral cells.

The muscular tissue of the prostate not only forms the chief part of the
stroma of the gland, but also forms a continuous layer inside the fibrous
sheath, as well as a layer surrounding the urethra continuous with the sphinc-
ter of the bladder.

The Seminal Fluid. — The sperm cells of the testes are joined on their
way to the exterior by the fluids secreted by the mucous lining of the various
tubules and glands. Of the fluids the chief ones are the secretions of the
seminal vesicles, of the prostate gland, and of Cowper's glands. The sperm
cells and the secretions together constitute the seminal fluid.

After the period of puberty the seminal fluid is secreted constantly but
slowly, except under sexual excitement. It is ordinarily received into the

THE REPRODUCTIVE ORGANS OF THE FEMALE

719

seminal vesicles, whence it is expelled at the time of coitus. In celibates the
seminal fluid may at times escape in small quantity into the urethra to be
washed away by the urine, or periodic reflex emissions may occur. The
seminal vesicles contribute a secretion, as well as a vesicle to receive the
sperm.

The secretion of the seminal vesicles and that of the prostate gland are
in some way concerned in maintaining the activity and prolonging the life of
the spermatozoa probably owing to the alkalinity of the secretions. These
cells remain alive in the fluid for as much as forty- eight hours after removal
from the body, and remain alive quite indefinitely in the vesicles in the body.
The secretions have been proven necessary to the life and function of the
spermatozoa by the results of operations in which the seminal vesicles and
the prostate were removed, whereby the animals became sterile.

THE REPRODUCTIVE ORGANS OF THE FEMALE.

The female genital organs consist of the Ovarium, the Tuba Uterina, the
Uterus, and the Vagina.

The Ovaries. — The ovaries are paired bodies, situated in the cavity of
the pelvis, and adherent to the posterior surface of the broad ligament. The

FIG. 4Q 2.— Diagrammatic View of the Uterus and Its Appendages, as Seen from
Behind. The uterus and upper part of the vagina have been laid open by removing the
posterior wall; the Fallopian tube, round ligament, and ovarian ligament' have been cut
short, and ^ the broad ligament removed on the left side. «, The upper part of the uterus;
c, the cervix opposite the os internum; the triangular shape of the uterine cavity is shown,
and the dilatation of the cervical cavity with the rugae termed arbor vitse; v, upper part of
the vagina; od, Fallopian tube or oviduct; the narrow communication of its cavity with that
of the cornu of the uterus on each side is seen; /, round ligament; lo, ligament of the ovary;
o, ovary; i, wide outer part of the right Fallopian tube; fi, its fimbriated extremity; po,
parovarium; h, one of the hydatids frequently found connected with the broad ligament
i (Allen Thomson.)

border of the ovary is called the hilum, and it is at this point that the blood
vessels and nerves enter it. Each ovary is about 4 cm. long, 2 cm. wide,
and i . 25 cm. thick. It is supported by the suspensory ligament.

720

THE REPRODUCTIVE ORGANS

The internal structure of the ovary consists of a peculiar soft fibrous
connective tissue, stroma, abundantly supplied with blood vessels. The
surface of the ovary is covered with cubical epithelium. Embedded in
the stroma in various stages of development are numerous minute follicles
or vesicles, the vesicular ovarian follicles, containing the ova, figure 494.
They are small and numerous near the surface of the ovary, either arranged
as a continuous layer, as in the cat or rabbit, or in groups, as in the human
ovary. Nearer the center are large and fully developed follicles.

Each follicle has an external membranous envelope, or tunica externa,
which is lined with a layer of nucleated cells, forming a kind of epithelium

FIG. 493. — Diagrammatic Section of the Ovary, Showing its Cortical or Ovigenous
Layer, Formed of Ovisacs in Various Stages of Evolution. (Duval.) A, A, A, Primordial
ovisacs; B, B, B, ovisacs further developed; C, ovisac approaching maturity; D, ripe ovisac
with its proligerous disc (DP) containing the ovum; MG, membrana granulosa; H, hilum
of ovary.

or internal coat and named the tunica interna. The cavity of the follicle
contains the ovule enclosed in a very delicate membrane. The large spher-
ical nucleus contains one or more nucleoli. The nucleus is known as the
germinal vesicle, and the nucleolus as the germinal spot.

The human ovum measures about 0.2 mm. in diameter. Its external
investment, or the zona pellucida, or vitelline membrane, is a transparent
membrane, about lo/z in thickness, which under the microscope appears
as a bright ring, figure 495. The ovum itself has the characteristic structure
of the typical cell, with the exception that its cytoplasm is filled with nu-
merous yolk granules. The larger granules or globules, which have the
aspect of fat-globules, are in greatest number at the periphery of the yolk.

The nucleolus, or germinal vesicle, is about o . 05 mm. in diameter. The
vesicle is of greatest relative size in the smallest ova.

The Graafian follicles are formed in the following manner: The em-
bryonic ovary is covered with short columnar cells, or the so-called germinal

THE OVARIES

721

epithelium. The cells of this layer undergo proliferation so as to form several
strata, and grow into the ovarian stroma as longer or shorter columns or
tubes. By degrees these tubes become cut off from the surface epithelium,
and form cell nests, small if near the surface, larger if in the depth of the
stroma. The nests increase in size from multiplication of their cells. Cer-
tain cells of the germinal epithelium enlarge and form ova; and the forma-
tion of ova takes place in the nests within the stroma. The small cells
of a nest surround the ova, and form their membrana granulosa, and the
stroma growing up separates the surrounded ova into so many Graafian
follicles.

Downgrowths of epithelium
•ininal epithelium

Ovum with its investing cells

Stratum granulosum

epithelial cells Ovarian strorna

Graah'an follicle

Ovum

Liquor folliculi
Discus proligerus

FIG. 494. — A, Diagrammatic Representation of the Manner in which the Vesicular
Ovarian Follicles Arise During the Development of the Ovary. B, Diagram Illustrating
the Structure of a Ripe Vesicular Ovarian Follicle. (Cunningham.)

The smallest follicles are formed at the surface, and make up the cortical
layer. It is said by some that the superficial follicles as they ripen become
more deeply placed in the ovarian stroma; and, again, that as they increase
in size they make their way toward the surface.

When the vesicular ovarian follicles mature, they form little prominences
on the exterior of the ovary covered only by a thin layer of condensed fibrous
tissue and epithelium. From the earliest infancy, and through the whole
fruitful period of life, there appears to be a constant formation, development,
and maturation of ovarian vesicles, with their contained ova. Until the
period of puberty, however, the process is comparatively inactive. But,
coincident with the other changes which occur in the body at the time of
puberty, the ovaries enlarge and become very vascular, the formation of
ovarian vesicles is more abundant, the size and degree of development
attained by them are greater, and the ova are capable of being fertilized.
46

722

THE REPRODUCTIVE ORGANS

The Uterine Tubes or Oviducts.— The uterine tubes are about 10
cm. in length and extend between the ovaries and the upper angles of the
uterus. At the point of attachment to the uterus each tube is very narrow;
but in its course to the ovary it increases to about 3 mm. in thickness. At
its distal extremity, which is free and floating, it bears a number of fimbricr,
one of which is longer than the rest and is attached to the ovary. The canal

FIG. 495.— Diagrammatic Representation of a Human Ovum and Its Coverings.
(Cunningham.)

The corona radiata, which completely surrounds the ovum, is represented only in the
lower part of the figure.

1, Corona radiata; $; vitellus or yolk;

2, granular layer; 6, germinal vesicle (nucleus) ;

3, vitelline membrane; 7, germinal spot (nucleolus);

4, zona pellucida (oolemma) ; 8, nuclear membrane.

of the tube is narrow, especially at its point of entrance into the uterus. Its
other extremity is wider and opens into the cavity of the abdomen by the
fimbriae. The uterine tube is invested with peritoneum, and its canal is
lined with ciliated epithelium.

The Uterus. — The uterus, u, c, figure 492, is a somewhat pyriform
organ, and is about 7 . 5 cm. in length, 5 cm. in breadth at its upper part
or fundus, but at the neck or cervix only about i . 25 cm. The part be-
tween the fundus and neck is termed the body of the uterus; it is about
2 . 5 cm. in thickness.

The uterus is constructed of three principal layers, or coats: serous,
fibrous and muscular, and mucous. The serous coat, which has the same
general structure as the peritoneum, covers the organ except the front surface
of the neck. The middle coat is a thick mass of unstriped muscle. The
muscle fibers become enormously developed during pregnancy. The arteries

OVULATION AND MENSTRUATION 723

and veins are found in large numbers in the outer part so as to form almost a
special vascular coat. The mucous membrane of the uterus is composed of
columnar ciliated epithelium, which extends also to the interior of the
tubular glands, of which the mucous membrane is largely made up. In the
cervix of the uterus the mucous membrane is arranged in permanent longi-
tudinal folds, plica palmatT. The glands of this part branch repeatedly,
and extend deeply into the substance of the cervix. The body has numerous
simpler tubular glands. The glands are also lined with ciliated epithelium.
They secrete a thick glairy mucus, resembling white of egg.

The Vagina. — The vagina is a membranous canal 8 to 10 cm. long,
extending obliquely downward and forward from the neck of the uterus,
which it embraces, to the external organ of generation. It is lined with
mucous membrane, covered with stratified squamous epithelium, which in
the ordinary contracted state of the canal is thrown into transverse folds.
External to the mucous membrane, the walls of the vagina are constructed
of unstriped muscle and fibrous tissue, within which in the submucosa,
especially around the lower part of the tube, is a layer of erectile tissue. The
lower extremity of the vagina is embraced by an orbicular muscle, the
sphincter vagina. The external organs of generation are the clitoris, the
labia internet, or nymphce; and, the labia externa or pudenda, formed of the
external integument, and lined internally by mucous membrane. Numerous
mucous follicles are scattered beneath the mucous membrane of the external
organs of generation; and two larger lobulated glands, the glands of Bar-
tholin, analogous to Cowper's glands in the male, are located at the sides
of the lower part of the vagina. The ducts of these glands are about 12 mm.
long and open immediately external to the hymen at the mid- point of the
lateral wall of the vaginal orifice.

Ovulation and Menstruation.— In the process of development in the
ovary, the individual vesicular ovarian follicle increases in size and gradually
approaches the surface of the ovary. When fully ripe or mature, it forms a
little projection on the exterior. Coincident with the increase in size, which
is caused by the augmentation of its liquid contents, the external envelop
of the distended vesicle becomes very thin and eventually bursts. The ovum
and fluid contents of the vesicle escape on the exterior of the ovary, whence
they pass into the uterine tube.

In man and mammals ovulation apparently occurs only at certain periods.
These periods seem to precede or occur during the changes in the woman
that constitute the phenomenon of menstruation, or, in the lower mammals,
of heat.

That ovulation and discharge occur periodically, and only during the
phenomenon of heat, in the lower mammalia, is made probable by the facts
that, in all instances in which ovarian vesicles have been found presenting
the appearance of recent rupture, the animals were at the time or had recently

724

THE REPRODUCTIVE ORGANS

been in heat. There are few authentic and detailed accounts of ovarian
vesicles being found ruptured in the intervals of heat; and females do not ad-
mit the males, and never become impregnated, except at those periods. Al-
though conception is not confined to the periods of menstruation, yet it is
more likely to occur about a menstrual epoch than at other times.

The exact relation between the discharge of ova and menstruation is not
very clear. It was formerly believed that menstruation was the result of
a congestion of the uterus arising in association with the enlargement and
rupture of a vesicular ovarian follicle; but though a vesicular ovarian

FIG. 496.

FIG. 497.

FIG. 498.

FIG. 496. — Diagram of Uterus just Before Menstruation. The shaded portion

represents the thickened mucous membrane.
FIG. 497. — Diagram of Uterus when Menstruation has just Ceased, Showing the

Cavity of the Uterus Deprived of Mucous Membrane.

FIG. 498. — Diagram of Uterus a Week After the Menstrual Flux has Ceased. The
shaded portion represents renewed mucous membrane. (J. Williams.)

follicle is, as a rule, ruptured at each menstrual epoch, yet instances are
recorded in which menstruation has occurred where no ovarian follicle can
have been ruptured, and cases where ova have been discharged in amenor-
rheic women. It must therefore be admitted that menstruation is not de-
pendent on the maturation and discharge of ova.

Observations made after death, and facts obtained by clinical investiga-
tion, support the view that rupture of a vesicular ovarian follicle does not
happen on the same day of the monthly period in all women. In the minor-
ity of cases it may occur toward the close or soon after the cessation of a

SOURCE AND CHARACTER OF MENSTRUAL CHANGES 725

flow. On the other hand, in almost all subjects examined after death, of
which there is record, rupture of the follicle appears to have taken place
before the commencement of the menstrual flow.

However, the presence of the ovaries seems necessary for the performance
of the menstrual function; for women do not menstruate when both ovaries
have been removed by operation. See page 46 for a discussion of the
functional effects of removal of the ovary.

Source and Character of Menstrual Changes. — The menstrual periods
usually occur at intervals of a lunar month, the duration of each being from
three to six days. In some women the intervals are so short as three weeks
or even less; while in others they are longer than a month. The periodical
return is usually attended by pains in the loins, a sense of fatigue in the lower
limbs, and other symptoms, which vary extremely in different individuals.

The menstrual discharge is a thin sanguineous fluid, and consists of blood,
epithelium, and mucus from the uterus and vagina. The menstrual flow
is preceded by a general engorgement of all the pelvic organs with blood.
The cervix and vagina become darker in color and softer in texture, and
the quantity of mucus secreted by the glands of the cervix and body is in-
creased. The uterine mucous membrane is swollen and the glands are
enlarged. The discharge of blood, the source of which is the mucous
membrane of the body of the uterus, is probably associated with uterine
contractions. There is great difference of opinion as to whether or not
any of the uterine mucous membrane is normally shed during the process
of menstruation. John Williams believes that the wrhole of the mucous
membranes of the body of the uterus is thrown off at each monthly period,
forming a true decidua menstrualis, figure 496, while Moricke and others
believe that the mucous membrane remains intact. Leopold believes
that red blood corpuscles escape from the congested capillaries and under-
mine the superficial epithelium, and that in this way the superficial layer of
the mucous membrane is eroded and subsequently regenerated. There
is a period of regeneration followed by a period of rest before the next
repetition. Minot distributes the variations in time as follows:

Tumefaction '. 5 days

Menstrual discharge 4 days

Restoration of mucosa 7 days

Period of rest 12 days

The menstrual period is often accompanied by profound disturbances in
other parts of the body, especially of the vascular and of the nervous systems,
and of the nutritive processes.

Corpus Luteum. — Immediately before, as well as subsequent to, the rupture
of an ovarian follicle and the escape of its ovum, changes ensue in the interior
of the follicle, which result in the production of a yellowish mass, termed a
corpus luteum.

726 THE REPRODUCTIVE ORGANS

When fully formed, the corpus luteum of mammals is a roundish solid
body, of a yellowish or orange color, and composed of a number of lobules,
which surround, sometimes a small cavity, but more frequently a small
stelliform mass of substance, from which delicate processes pass as septa
between the several lobules. The processes gradually change till they
nearly fill the cavity of the follicle, and even protrude from the orifice in
the external covering of the ovary. Subsequently this orifice closes, but the
fleshy growth within still increases during the earlier period of pregnancy,
the color of the substance gradually changing to yellow, and its consistency
becoming firmer. After the orifice of the follicle has closed, the growth
of the yellow substance continues during the first half of pregnancy, till
the cavity is reduced to a comparatively small size or is obliterated; in the
latter case, merely a white stelliform cicatrix remains in the center of the
corpus luteum.

The first changes of the internal coat of the ovarian follicle in the proc-
ess of formation of a corpus luteum seem to occur in every case in which an
ovum escapes. If the ovum is impregnated, the growth of the yellow sub-
stance continues during nearly the whole period of gestation and forms the
large corpus luteum commonly described as a characteristic mark of
impregnation.

The significance of the corpus luteum is found in the belief that it is the
portion of the ovary especially concerned in the production of an internal
secretion that affects the uterus, especially stimulating it at and before the
menstrual period.

Menstrual Life. — The occurrence of a menstrual discharge is one of
the most prominent indications of the commencement of puberty in the fe-
male sex; though its absence even for several years is not necessarily at-
tended with arrest of the other characters of this period of life or incapability
of impregnation. The average time of its first appearance in females of
this country and others of about the same latitude is from fourteen to fifteen:
but it is much influenced by the kind of life to which girls are subjected,
being accelerated by habits of luxury and indolence, and retarded by con-
trary conditions. Its appearance may be slightly earlier in persons dwelling
in warm climates than in those inhabiting colder latitudes. The menstrual
functions continue through the whole fruitful period of a woman's life, and
usually cease between the forty-fifth and fiftieth years, which time is known
as the climacteric. Menstruation does not usually occur in pregnant women.

CHAPTER XVII.
DEVELOPMENT.

Changes Which Occur in the Ovum Prior to Impregnation. — The

ovum when ripe and detached from the ovary is a single cell enclosed within
the zona pellucida, and containing the germinal vesicle and germinal spot.
The ovum undergoes a series of changes preparatory to fertilization, known
as maturation, the general effect of which is to reduce the chromatin in antici-

FIG. 499. — The Maturation of the Ovum; Extrusion of the "Polar Bodies." (Dia-
grammatic.) A, An ovum at the commencement of the process; B, after the formation of
the spindle. The chromosomes are gathered at the equator of the spindle. C, One apex
of the spindle has projected into a bud on the surface, and half of the divided dyads have
passed to each pole; D, the separation of the first polar body; E, the commencement of the
second polar body; F, the completion of the second polar body. (Cunningham.)

pation of the added chromatin from the sperm nucleus. The primary change
observed in the ovum consists in the migration of the germinal vesicle or nu-
cleus to the surface, and the disappearance of its nuclear membrane, with a
consequent indistinctness of its outline. Its protoplasm becomes to a con-
siderable extent confounded with the yolk substance, and its germinal spot

727

728

DEVELOPMENT

FIG. 500. — Conversion of the
Morula to the Blastula. For-
mation of Blastodermic Vesicle and
Membrane. A, Appearance of
segmentation cavity and attach-
ment of inner cell mass to ectoderm
at upper pole of ovum; B1, exten-
sion and flattening of inner cell
mass as it occurs in rabbits and
some other mammals; B2, exten-
sion of entoderm as it occurs in
insectivora, monkeys, apes, and
man; C, completion of bilaminar
blastodermic vesicle; BC, blasto-
dermic cavity; EC, ectoderm; EE,
embryonic ectoderm; EN, ento-
derm; 7, inner cell mass; SC, seg-
mentation cavity; ZP, zona pellu-
cida. (Cunningham.)

disappears. The next step in the process is
the appearance in the yolk of two centro-
somes in a clear space near the poles of the
elongated vesicle, and the formation of a
nuclear spindle, with the aster at either end
lying near the surface of the yolk. The
nucleus now divides into two parts, and that
nearer the surface is extruded from the ovum
enveloped in a very small amount of proto-
plasm. This forms the first polar body.
The nucleus again divides by mitosis, one-
half of the chromatin is extruded from the
ovum, forming a second polar cell; the chro-
matin that remains behind constitutes the
female pronucleus. The centrosome has dis-
appeared and the ovum undergoes no
further changes unless fertilized by the
sperm.

Changes Following Impregnation.—
The process of impregnation of the ovum
has been observed most accurately in the
lower types. The process is as follows:
The head of a single spermatozoon joins
with an elevation of the yolk substance, the
tail remaining motionless and then disap-
pearing. The head enveloped in the proto-
plasm then sinks into the yolk and becomes
a nucleus, from which the yolk substance is
arranged in radiating lines. This is the
male pronucleus. The middle piece of the
sperm is believed to furnish a new centro-
some to the ovum. The centrosome now
divides and moves to either side the two
pronuclei, a segmentation spindle is formed,
and the egg undergoes its first segmentation.

The process of segmentation begins
almost immediately in each half of the
yolk, and cuts it also in two. The
process is repeated until at last by con-
tinued cleavages the whole yolk is changed
into a mulberry-like mass, still enclosed
by the zona pellucida, figure 500. Fertili-
zation probably takes place in the Fallopian

CHANGES FOLLOWING IMPREGNATION

729

tubes, and segmentation of the fertilized ovum occurs on its passage to
the uterus.

The passage of the ovum from the ovary to the uterus occupies probably
eight or ten days in the human.

The peripheral cells, which are formed first, arrange themselves at the sur-
face of the yolk into membrane, the ectoderm. The deeper cells of the in-
terior pass gradually toward the surface, thus increasing the thickness of the
membrane already formed by a second, or entoderm, layer of cells, while the
central part of the yolk, the blastoderm cavity, remains filled only with a clear
fluid. By this means the yolk is shortly converted into a kind of secondary
vesicle, the walls of which are composed externally of the original vitelline
membrane, and within by the newly formed cellular layer, the blastoderm or
germinal membrane, as it is called.

FIG. 501. — Section of the Lining Membrane of a Human Uterus at the Period of
Commencing Pregnancy, Showing the Arrangement and Other Peculiarities of the Glands,
d, d, d, with Their Orifices, a, a, a, on the Internal Surface of the Organ. Twice the
natural size.

Important changes occur in the structure of the mucous membrane of
the uterus. The epithelium and subepithelial connective tissue, together
with the tubular glands, increase rapidly, and there is a greatly increased
vascularity of the whole mucous membrane, while a substance composed
chiefly of nucleated cells fills up the interf ollicular spaces in which the blood
vessels are contained. The effect of these changes is an increased thickness,
softness, and vascularity of the mucous membrane, the superficial part of
which itself forms the membrana decidua.

The object of this increased development is the production of nutritive
materials for the ovum; for the cavity of the uterus shortly becomes filled
with secreted fluid, consisting almost entirely of nucleated cells in which the
chorion villi are embedded.

When the ovum first enters the uterus it becomes embedded in the structure
of the decidua, which is yet quite soft, and in which soon afterward three
portions are distinguishable. These have been named the decidua vera, the
decidua basalis, and the decidua capsularis.

In connection with these villous processes of the chorion there are de-

73°

DEVELOPMENT

veloped depressions or crypts in the decidua vera, which correspond in shape
to the villi they are to lodge; and thus the chorionic villi become more or less
embedded in the maternal structures. These uterine crypts, it is important
to note, are not, as was once supposed, merely the open mouths of the
uterine follicles.

The Placenta. — During these changes the deeper part of the mucous
membrane of the uterus, at and near the region where the placenta is placed,
becomes hollowed out by sinuses, or cavernous spaces, which communicate
on the one hand with arteries and on the other with veins of the uterus. Into

Decidua basalis
Unchanged layer Maternal vessel

Primitive streak
Mesoderm

Placental villus

Ectoderm

Stratum spongiosnm
Stratum compactunix^

Placental villus

Villus

Cavity of
blastoderm

Cavity which
becomes coelom

Mesoderm

Decidua vera-/

Entoderm
Decidua vera

FIG. 502. — Diagram of the Early Stage of Human Embryo in Relation to the Uterus.

(Cunningham.)

these sinuses the villi of the chorion protrude, pushing the thin walls of the
sinuses before them, and so come into intimate relation with the blood con-
tained in them. There is no direct communication between the blood vessels of
the mother and those of the fetus; but the layer or layers of membrane inter-
vening between the blood of the one and of the other offer no obstacle to a
free interchange of matters between them by diffusion and osmosis. Thus
the villi of the chorion, containing fetal blood, are bathed or soaked in mater-
nal blood contained in the uterine sinuses.

The placenta, therefore, of the human subject is composed of a fetal
part and a maternal part — the term placenta properly including all that
entanglement of fetal villi and maternal sinuses, by means of which the

CIRCULATION OF BLOOD IN THE FETUS

731

blood of the fetus is enriched and purified after the fashion necessary for the
proper growth and development of those parts which it is designed to nourish.
The whole of this structure is not, as might be imagined, thrown off
immediately after birth. The greater part, indeed, comes away at that time,
as the after-birth; and the separation of this portion takes place by a rending
or crushing through of that part at which its cohesion is least strong, namely,
where it is most burrowed and undermined by the cavernous spaces before
referred to. In this way it is cast off with the fetal membrane. The remain-

FIG. 503. — Diagrammatic View of a Vertical Transverse Section of the Uterus at the
Seventh or Eighth Week of Pregnancy, c, c, c', Cavity of uterus, which becomes the
cavity of the decidua, opening at c, c, the cornua, into the Fallopian tubes, and at c' into the
cavity of the cervix, which is closed by a plug of mucus; dv, decidua vera; dr, decidua
reflexa, with the sparser villi embedded in its substance; ds, decidua serotina, involving
the more developed chorionic villi of the commencing placenta. The fetus is seen lying
in the amniotic sac. The umbilical cord and its vessels pass up from the umbilicus to
the distribution of the blood vessels in the villi of the chorion- and the pedicle of the
yolk-sac the cavity between the amnion and chorion. (Allen Thomson.)

ing portion is either gradually absorbed, or thrown off in the uterine dis-
charges which occur at this period. A new mucous membrane is of course
gradually developed.

Circulation of Blood in the Fetus. — The circulation of blood in the
fetus differs considerably from that of the adult.

Returning from the placenta by the umbilical vein the blood is first con-
veyed to the under surface of the liver, where the stream is divided — a part of

732 DEVELOPMENT

the blood passing straight on to the inferior vena cava through a venous canal
called the ductus venosus, while the remainder passes into the portal vein and
reaches the inferior vena cava only after circulating through the liver. It is
carried by the vena cava to the right auricle of the heart, into which cavity
the blood is also pouring that has circulated in the head and neck and arms,

FIG. 504. — Diagram of the Fetal Circulation.

and has been brought to the auricle by the superior vena cava. It might be
naturally expected that the two streams of blood would be mingled in the
right auricle, but such is the case only to a slight extent. The blood from the
superior vena cava — the less pure fluid of the two — passes almost exclusively
into the right ventricle, through the auriculo- ventricular opening, just as it
does in the adult. The blood of the inferior vena cava is directed by a fold

CIRCULATION OF BLOOD IN THE FETUS

733

of the lining membrane of the heart, called the Eustachian valve, through the
foramen ovale into the left auricle and into the left ventricle, and out of this
into the aorta, and thence to all the body, but chiefly to the head and neck.
The blood of the right ventricle is sent out in small amount through the pul-
monary artery to the lungs, and thence to the left auricle, as in the adult,
but the greater part by far passes through a canal, the ductus arteriosus,
leading from the pulmonary artery into the aorta just below the origin of the
three great vessels which supply the upper parts of the body, and is distributed

FIG. 505. — Dissection of the Lower Half of the Female Mamma During the Period of
Lactation. §. — In the left-hand side of the dissected part the glandular lobes are exposed
and partially unravelled, and on the right-hand side the glandular substance has been
removed to show the reticular loculi of the connective tissue in which the glandular lobules
are placed, i, Upper part of the mammilla or nipple; 2, areola; 3, subcutaneous masses
of fat; 4, reticular loculi of the connective tissue which support the glandular substance
and contain the fatty masses; 5, one of three lactiferous ducts shown passing toward the
mammilla, where they open; 6, one of the sinus lactei or reservoirs; 7, some of the glandular
lobules which have been unravelled; 7', others massed together. (Luschka.)

to the trunk and lower parts of the body. A large portion passes out by
way of the two umbilical arteries to the placenta. From the placenta it is
returned by the umbilical vein to the under surface of the liver, from which
the description started.

After birth the foramen ovale, the ductus arteriosus, and ductus venosus
all close, and the umbilical vessels are tied off, so that the two streams of
blood which arrive at the right auricle by the superior and inferior vena cava,
respectively, thenceforth mingle in this cavity of the heart, and pass into the
right ventricle, by way of the pulmonary artery to the lungs, and through

734 DEVELOPMENT

these, after aeration, to the left auricle and ventricle, to be distributed over
the body.

Parturition. — With the implantation of the embryo and the develop-
ment of the placenta, the uterus grows rapidly until the end of pregnancy.
The muscles of its walls increase enormously in volume, apparently by
an increase, in the size of the fibers, and the whole structure may become
thirty or forty times its size in the resting period. Many changes take
place also in other parts of the body, changes which are dependent on the
presence of the fetus. Full-term pregnancy occurs when the uterus is
isolated from the nervous system, hence it has been inferred that there is
some sort of special secretion, possibly of the embryo itself, that makes its
way into the blood and influences the organs of the mother.

FIG. 506. FIG. 507.

FIG. 506. — Section of Mammary Gland of Bitch, Showing Acini, Lined with Fpithelial

Cells of a Polyhedral or Short Columnar Form. X 200. (V. D. Harris.)
FIG. 507. — Globules and Molecules of Cow's Milk. X 400.

At the end of the period of pregnancy the strong uterine walls begin
periodic contractions which ultimately result in the delivery of the fetus.
These contractions are at first weak and at long intervals, but later become
very strong and follow each other in rapid succession. The uterine con-
tractions are supported by reflex contractions of the abdominal and thoracic
muscles. After the fetus is delivered the uterine contractions become
milder, but still continue until the placenta is finally expelled.

The initiation of the contractions of the uterus at delivery probably de-
pends on the chemical stimulation of some substance or substances produced
in the uterus itself or in the fetus; substances that react on the nervous mech-
anism and on the uterine muscles themselves. This view cannot be said to
be proven, but it is supported by certain observed facts and experiments.

Lactation. — There is a marked development of the mammary glands,
especially in the later part of the period of gestation. Upon delivery of the
fetus the gland enlarges very sharply and an abundant secretion is formed.

THE COMPOSITION OF MILK 735

Tne secretion of the first few days is called the colostrum. It contains a
larger per cent, of solids, has the large granular colostral corpuscles, is more
alkaline than ordinary milk, and has a specific gravity of 1040 to 1046.

The mammary glands have been isolated from the nervous system to
determine whether or not the association in time between their changes and
the changes in the uterus were of a nervous nature. The isolated mammas
develop and begin lactation at parturition as in the normal. It would seem
that here, too, there is some special form of stimulation through the medium
of the blood. Yet one must not draw the conclusion that the nervous system
exerts no influence on the mammary gland. Stimulation of the nerves to the
gland produces vascular changes that increase or decrease the quantity of
secretion. Many observations have been noted in women, which show that
the secretion of milk is sharply influenced by, or even completely suppressed
by, nervous states.

The Composition of Milk. — Milk has a specific gravity of 1028 to
1034. Its fat is held in emulsion. Under the microscope, it is found that
the milk globules vary in size, the majority being from 2 to 3/z in diameter.
The old view that they have an investing membrane of albuminous material
is now generally discarded.

COMPOSITION OF COLOSTRUM (PFEIFFER).

Proteins 5-71

Fat 2 . 04

Sugar 3.74

Salts 0.28

Water 88.23

100 .00

SALTS IN WOMAN'S MILK (ROTCH).

Calcium phosphate 23-87

Calcium silicate 1.27

Calcium sulphate 2.25

Calcium carbonate 2.85

Magnesium carbonate 3-77

Potassium carbonate 23.47

Potassium sulphate 8.33

Potassium chloride I2-05

Sodium chloride » . . . 21.77

Iron oxide and alumina ° • 3 7

100.00

In addition to the oil or butter fat, milk contains certain proteins, milk-
sugar, and several salts. Its percentage composition is given in the tables
appended.

736

DEVELOPMENT

CHEMICAL COMPOSITION OF MILK.

(AFTER FOSTER, HARRINGTON, et al.}
Human. Cow. Mare. Bitch.

Water

87.30

87

OO

76

Solids

12 . 7O

I ?

IO

24

Fats

4 . OO

4 . o

2 . O

IO . O

Proteins

I . ZO

40

2 C

I O . O

Sugar

7 . OO

4 • 3

^ • o

•J . C

Salts..

O . 2O

0.7

0. «

0. <

FAHRENHEIT
and
CENTIGRADE
SCALES.

MEASUR

FRENCH INI

LENGTH.

1 metre }
10 decimetres | = 39.37 English
100 centimetres f inches.

EMENTS.

CO ENGLISH.

A grain equals about 1.16 gram.,
a Troy oz. about 31 gram.,
a Ib. Avoirdupois about ^ Kilogrm.,
and 1 cwt. about 50 Kilogrms.

F.
500°
401
392
383
374
356
347
338
329
320
311
302
284
275
266
248
239
230
212
203
194
176
167
140
122
113
105
104
100

C.

260°
205
200
195

1,000 millimetres j (or 1 yd. and 3^ in.)

CAPACITY.

1,000 cubic decimetres 1 = 1 cubic
1 .000,000 cubic centimetres j metre.

190
180
175
170
165
160
155
150
140
135
130
120
115
110
100
95
90
80
75
60
50
45
40.54
40
37.8

1 decimetre )
10 centimetres V = 3.937 inches
100 millimetres ) (or nearly 4 inches.)

1 cubic decimetre )
or V = 1 litre.
1,000 cubic centimetres )

OR
ONE LITRE = 1 pt. 15 oz. 1 dr. 40.
(For simplicity, Litre is used to signify
1 cubic decimetre, a little less than 1
English quart.)
Decilitre (100 c.c.) = 3^ oz.
Centilitre (10 c.c.) = 2f dr.
Millilitre (1 c.c.) = 17 m.
Decalitre = 2£ gal.
Hectolitre = 22 gals.
Kilolitre (cubic metre) = 27^ bushels.
A cubic inch = 16.38 c.c. ; a cubic foot
= 28.315 cubic dec., and a gallon =
4.54 litres.

1 centimetre 1 = .3937 or about
10 millimetres f (nearly g inch.)
1 millimetre = nearly & inch.

OR,
ONE METRE = 39.37079 inches.
(It is the ten-millionth part of a quarter
of the meridian of the earth.)
1 Decimetre = 4 in.
1 Centimetre — T45 in.
1 Millimetre = <ftin.
Decametre = "62.80 feet.
Hectometre — 109.36 yds.
Kilometre = 0.62 miles.
One inch = 2.539 Centimetres.
One foot = 3.047 Decimetres.

One mile =1.60 Kilometre.
The cubic centimetre (15.432 grains— 1
gramme) is a standard at 4° C., the
grain at 16°. 66 C.

CONVERSION SCALE.

To convert GRAMMES to OUNCES avoir-
dupois, multiply by 20 and divide by 567.
To convert KILOGRAMMES to POUNDS,
multiply by 1,000 and divide by 454.
To convert LITRES to GALLONS, mul-
tiply by 22 and divide by 100.
To convert LITRES to PINTS, multiply
by 88 and divide by 50.
To convert MILLIMETRES to INCHES,
multiply by 10 and divide by 254.
To convert METRES to YARDS, multi-
ply by 70 and divide by 64.

98.5
95
86
77
68
50
41
32
23
14
+ 5
- 4
-13
-22
- 40
-76

36.9

30
25
20
10
5
0
- 5
- 10
-15

WEIGHT.

(One gramme is the weight of a cubic
centimetre of water at 4° C. at Paris).
1 gramme ]
10 decigrammes ! = 15.432349 grs.
100 centigrammes ( (or nearly 15^).
1,000 milligrammes J

SURFACE MEASURE.

1 square metre = about 1550 sq. inches.
Or 10.000 sq. centimetres, or 10.75 sq. ft.
1 sq. inch — about 6 4 sq. centimetres.

- 20
-25
-30
-40
-60

1 decigramme )
10 centigrammes V = rather more
100 milligrammes ) than 1^£ grain.

1 centigramme ) = rather more
10 decigrammes i than ^ grain.

1 sq. foot = " 930 "

1 deg.F. = .54°C.
1.8 " = 1°C.
3.6 " = 2°C.
4.5 " •-= 2.5°C.
5.4 " - 3°C.

ENERGY MEASURE.

1 kilogrammetre=about7.24ft. pounds.
1 foot pound = " .1381 kgm.
1 foot ton = ' 310 kgm.

1 milligramme = rather more
than 3$,y grain.
OR

1 Decigramme = 2 dr. 34 gr.
1 Hectogrm. = ^ oz. (Avoir.)
1 Kilogrm. = 2 Ib. 3 oz. 2 dr. (Avoir.)

HEAT EQUIVALENT.

1 kilocalorie = 424 kilogrammetres.

To convert de-
grees F. into de-
grees C., subtract
32, and multiply
by|.

ENGLISH

Apothecaries Weight.

7000 grains = 1 Ib.
Or
437.5 grains = 1 oz.

MEASURES.

Avoirdupois Weight.

16 drams = 1 oz.
16 oz. = 1 Ib.
28 Ibs. =.- 1 quarter.
4 quarters = 1 cwt.
20 cwt. = 1 ton.

To convert de-
grees C. into de-
grees F., multiply
by §, and add 32°.

Measure of 1 decimetre, or 10 centimetres, or 100 millimetres.

Illllllll

! | 1

1 2
The micron (symbol.

34567891
u.) is the unit of microscopic measurement = Tata mm. = 2B&ra inch.

47

737

INDEX.

ABDOMINAL viscera, vascular nerves

for, 246

Abducens nerve, 615
Absorption, 388

conditions for, 389

methods of, 388, 391

places for, 389, 397

rapidity of, 389, 397

through the intestines, 390
the lungs, 396
the mouth, 389
the skin, 396
the stomach, 389

Accelerator centers for heart, 204, 567
Accessory olives, 571

thyroids, 454, 456
Accommodation of vision, 677, 679
Achromatic layer, 18

spindle, 20
Achromatin, 19
Achroodextrin, 337
Acid albumin, 112, 383
Acromegaly, 458
Activating ferments, 328
Adamkiewicz reaction, 107
Addison's disease, 457, 458
Adenoid tissue, 36
Adipose tissue, 38, 39
Adrenalin, 458
Adrenals, 456
After-birth, 731

-images, 689, 696, 713

-sensations, 636
Agglutinative substances, 146
Air cells, 272

changes in, during respiration,
286

composition of, 286

diffusion of, 289

pressure of, 289, 310

quantity breathed, 282, 309

volume breathed, 309

Albumin, acid, 112

alkali, 112

egg, 105

properties of, no

serum, 88

Albuminate, acid, 112
Albuminoids, 89
Albumins, 88

reactions of, no
Alcohol as a food, 326
Alkali metaprotein, 112
Ameba, 3

Ameboid movement, 3, 131
Amino-acids, 84, 91
Amitosis, 10, 20
Ammonia, effect of breathing, 304

in the urine, 410
Ammonium carbamate, 439
Amylolytic ferments, 328
Amylopsin, 328, 360, 363
Anabolism, 6, 431
Anabolites, 431
Anacrotic limb, 228

wave, 229
Anaphase, 2 1
Anaphylaxis, 147
Anelectrotonus, 502
Animal heat, 461
Animals differentiated from plants,

1 1

Anode, 501, 504
Ano-spinal center, 558
Anterior association center, 608
Antiperistalsis, 376
Antisubstances in blood, 147
Antitoxins, 147
Apnea, 302, 314
Arborization, intefepithelial, 74
Archispermiocyte, 715
Archoplasm, 19
Areolar tissue, 35
Aristotle's experiment, 704, 705

739

740

INDEX

Arterial flow, 218, 219
rhythmic, 219
velocity of, 220

pulse, 259

blood-pressure and nervous

regulation in, 261, 263
Arteries, 168

blood-pressure in, 213

nerves of, 169
Arterioles, 168
Articulate sounds, 520
Asphyxia, 303, 315
Assimilation, 6

Association centers of brain, 607
Aster, 20

Astigmatism, 684, 709
Atmosphere, composition of, 285
Atmospheric pressure, 304
Attraction sphere, 19
Auditory center, 606

judgments, 66 1

nerve, 617

Auricles, action of, 174
Autolytic substances, 146
Axis cylinder, 67
Axone, 65

BACTERIA in digestive tract, 373
Basement membrane, 23, 317
Basket cells, 579
Basophile, 131
Bezold's ganglia, 195
Bidder's ganglia, 195
Bile, 366, 386

acids, 367, 386

capillaries, 366

coloring matter of, 367

chemical composition of, 367

discharge of, 369

functions of, 368

mode of discharge of, 369

mode of secretion of, 369

pigments of, 386

salts, 367, 386
Bilirubin, 367
Biliverdin, 367
Binaural sensations^, 66 1
Binocular vision, 699
Bioplasm, 2
Biuret reaction, 108
Bladder, urinary, 404
Blastema, 2

Blastoderm, 14
Blind spot, 687, 710
Blood, 117

antisubstances in, 147
arterial flow, 218
buffy coat, 120
capillary flow, 220
carbon dioxide of, 295
chemical composition of, 133
circulation of, 161, 207
experiments on, 249
in fetus, 731
coagulation of, 118, 157
calcium in, 124
conditions affecting, 124
fibrin in, 119
theories of, 121
corpuscles of, 117

chemical composition of, 159
colorless, 129

ameboid movement of,

131, 223
chemical composition

of, J35

number of, 130
phagocytosis, 154
varieties of, 130

enumeration of, 154

percentage of, 155

red, 125

action of reagents on, 153
characters of, 125
chemical composition

of, i35

development of, 127
number of, 125
origin of, 129
varieties of, 129
defibrination of, 120
differences between arterial and

venous, 144
elimination of carbon dioxide by,

295

examination of, 152
ferments in, 134
flow, arterial, 218
capillary, 220
regulation of, 231
velocity of, 224

in arteries, 220
in capillaries, 223
in veins, 224

INDEX

74i

Blood flow, venous, 223
gases of, 289
hemoglobin, 136
isotonicity of, 156
laboratory experiments on, 152
laking of, 145
microscopical examination of,

J52

morphology of, 125
oxygen of, 292
plasma, 117

chemistry of, 159

composition of, 133

percentage of, 155

physical factors of, 148

reaction of, 156
plates, 132
portal, 144
pressure, 207

arterial, 208, 257, 261, 263

capillary, 216, 261

in man, 213

model, 259

respiratory undulations of,
212

variations in, 217

venous, 215

production of heat by the, 463
quantity of, 117

influence on secretion, 320
respiratory changes in, 289
serum, 118

chemistry of, 159

composition of, 135

globulicidal properties of,

145

specific gravity of, 156

uses of, 117

variations in composition of, 143

velocity of flow, 224

venous flow, 223

whipped, 158
Blushing, 237
Body, chemical composition of, 79

energy requirements of, 452

experiments on the chemistry of,

I05
Bone, 42

blood-vessels of, 43
canaliculi of, 44
cells, 45
compact, 50

Bone, development of, 46

growth of, 51

Haversian canals of, 44

lacunae of, 44, 45

lamellae of, 44, 45

marrow, 42

microscopic structure of, 44

ossification in cartilage, 47
in membrane, 46

periosteum of, 43
Bowman's sarcous elements, 61

theory of urinary secretion, 413
Brain, 564, 566

after-, 566

arrangement of different parts,

564

association centers of, 607

distinctive characters of human,
566, 574

fore-, 567, 586

gray matter in, 588

hind-, 566

mid-, 567, 584

motor areas of, 598, 600
of human, 600
tracts in, 603

Rolandic area of, 602

sensory areas of, 603

stem, 566

vascular nerve-supply of, 242

weight of, 593
Bread, composition of, 325
Bronchi, 268
Buffy coat, 120
Bulb, the, 567, and see Medulla

centers in, 573

connections with cerebrum and
cerebellum, 572

functions of, 573
Bundle of Vicq d'Azyr, 586
Burdach, tract of, 548

CAJAL, cells of, 592
Calcification, 47, 50
Calcium salts in the body, 103

in coagulation of the blood,

122

tests for, 115
Calorimeter, 315, 453
Calorimetry, 315
Canaliculi, 44
Cane sugar, 100

742

INDEX

Capillaries, 169

blood-pressure in, 215

structure of, 170
Capillary circulation, 260

flow, 220

velocity of, 223
Carbohydrates, 98, 113

absorption of, by intestines, 394

as foods, 322, 325

chemical reactions of, 113

metabolism of, 443
Carbon, amount excreted, 433

dioxide, determination of, 311,

312
elimination of, 286, 287, 295,

423

in proteins, 106
monoxide, effect of breathing,

3°4

hemoglobin, 160
Carbonates, 104
Carboxyhemoglobin, 138
Cardiac action, force of, 189

contractions, automatic, 253
experiments on, 250
maximal, 194
cycle, 174, 188
impulse, 180
muscle, 62, 495, 531
action of, 495

compared with other

muscles, 496, 531
automatic contractions of,

253

development of, 65
properties of, 190
refractory phase, 495
nerves, 255
orifice, 354

Cardio-accelerator centers, 204, 543
Cardiogram, 181, 249, 250
Cardiograph, 181

Cardio-inhibitory centers, 202, 575
Cartilage, 39

development of, 41
elastic, 41

embryonic spongy bone, 48
hyaline, 40
temporary, 40
vascularization of, 48
white fibro-, 41
Catabolism, 6, 431

Catabolites, 43 1
Catacrotic limb, 228

wave, 229

Catelectrotonus, 502
Cathode, 502, 503
Caudate nucleus, 588
Cell, i, 8, 18, 19

body, 1 8

connection, modes of, 22

difference between plant and
animal, 1 1

differentiation, 14, 18

division of, 10, 19

functions of, u, 14

growth, 7, 10

multiplication, 19

nucleus of, 9, 18

reticulum of, 8

structure of, 8, 18
Cells, decay and death of, 23

derived elements of, 23

modes of connection, 22

origin of, 22

shapes of, 22

types of, 22
Cellulose, 13, 103
Center for muscle tone, 557
Centers, motor, 598, 60 1

sensory, 603

spinal, 558
Centrosome, 19

Cerebellar cortex, paths through, 580
Cerebellum, 578

connection with bulb, 572

functions of, 581

general structure of, 579
Cerebral cortex, fibers from, 591

structure of, 588
Cerebrum, 588

arrangement of parts, 588

connection with bulb, 572

effects of removal of, 596

functions of, 596

motor areas of cortex, 598, 60 1

peduncles of, 584

sensory areas of, 603

weight of, 593
Cerumen, 421
Ceruminous glands, 421
Chemical composition of the body, 79
of tissue, 90, 91

elments in the body, 79

INDEX

743

Chemical structure of proteins, 80
Chemistry of the body, experiments

on, 105
Chest, changes in diameter of, during

respiration, 309
Cheyne-Stokes breathing, 303
Chlorides in the body, 103

in the urine, 412

tests for, 115

Chlorine, effect of breathing, 304
Chlorophyll, 12
Cholesterol, 98
Chorda tympani, 331, 378
Chordae tendineae, 168
Chromatic aberration, 684, 708
Chromatin, 19
Chromophanes, 694
Chromophiles, 73
Chromoplasm, 18
Chromoproteids, 92
Chromosome, 20
Chyme, 355
Cilia, 31
Ciliary apparatus, 666

contraction, 498, 533

epithelium, 533

motion, 498
Circulation, coronary, 205

atmospheric pressure on, 304

during sleep, 623

effect of respiration on, 305

in brain, 242

in erectile structures, 247

laboratory experiments, on, 249

local peculiarities of, 241

of blood, 161

regulation of flow, 231

time of, 258

through blood-vessels, 207

velocity of, 224

vegetable, 4
Coagulated proteids, 96
Coagulating ferments, 328
Coagulation of blood, 118, 157

calcium salts in, 122

conditions affecting, 124, 158

theories of, 121
Cochlea, 653
Cohnheim's areas, 62
Cold, influence of extreme, 467
Collagen, 90, no
Collaterals, 69

Colloids, 148

Color, after-images, 689, 696, 713
-blindness, 697, 712
complemental, 696
extent of visual field for, 695
Hering's theory of, 698
limits of field of vision for, 712
-mixing, 713
sensations of, 695, 696
Young's and Helmholtz's theory

of, 697

Colorless corpuscles, 129
Colostrum, 735
Comma tract, 548
Common sensations, 629
Compact bone formation, 50
Complemental air, 282, 310
Compound proteids, 92
Conductivity of muscle, 477
Conjugated proteins, 87
Conjunctiva, 664
Connective tissues, 32
adenoid, 36
adipose, 38
areolar, 35, 37
cells of, 32
development of, 37
fibrous, 37
gelatinous, 35
general structure of, 32
intercellular substance of, 33
lymphoid, 36
retiform, 36
varieties of, 33
white fibrous, 34, 37
yellow elastic, 34, 37
Consonants, 521
Contractility of muscle, 724
Contraction phase of muscle, 479
Contracture, 490
Convoluted tubule, 398
Cooking, effects of, 326
Cornea, 665
Corona radiata, 585
Coronary circulation, 205
Corpora cavernosa, 247
geniculata, 586, 587
quadrigemina, 584, 586
striata, 588
Corpus Arantii, 168
dentatum, 578
luteum, 725

744

INDEX

Corpus spongiosum, 247
Corpuscles, blood, 117, 159

Malpighian, 399

of Bowman, 399

of Golgi, 77

of Krause, 76

of Meissner, 75

of Pacini, 75, 358
Coughing, center for, 575
Cranial nerves, 608
Crassamentum, 1 1 8
Creatinin, 410, 429, 440
Crura cerebri, 584
Crus cerebri, 584
Crusta, 584

petrosa, 53

phlogistica, 120
Crystalloids, 148
Crystals protein, 105
Cutis vera, 420

anserina, 58
Cystin in urine, 4 1 2
Cytolysis, 145
Cytoplasm, 18

DEATH, 7
Decay, 7
Decidua basalis, 729

capsularis, 729

menstrualis, 725

vera, 729

Decussation of the pyramids, 568
Defecation, 377

center for, 558
Degeneration in spinal cord, 547, 548

reaction of, 505

Wallerian, 537, 547
Deglutition, 339

center for, 342, 575

nervous mechanism of, 341

time occupied in, 340
Demarcation currents, 481, 482
Dendrites, 65
Dental papilla, 56
Dentine, 53
Depressor nerve, 237
Dermis, 420
Development, 727
Dextrin, 101

tests for, 113
Dextrose, 99

tests for, 113

Diabetes mellitus, 445

Dialysis, 148

Diapedesis, 223

Diaphragm in respiration, 256, 276,
277

Diaster, 20

Diastole of heart, 174, 175

Dicrotic notch, 228
pulse, 230
wave, 228, 250

Diet, normal, requisites of, 431, 449
tables, 450

Diffusion, 148

Digestion, 322, 327

enzymes in, 327, 328
experiments in, 377
in intestines, 357, 371, 372
in mouth, 328, 379, 380
in stomach, 339, 341, 353

Digestive ferments, 328

Diphasic current, 483

Diplopia, 6 1 1, 700

Disassimilation, 6

Distance, estimation of, 703

Diuretics, action of, 416

Dogiel's cells, 195

Dreams, 624

Du Bois-Reymond's induction coil,

475

key, 474

Ductless glands, influence on metabo-
lism, 454

Ductus arteriosus, 733
deferens, 716
venosus, 732
Dyspnea, 303, 314

EAR, cochlea of, 653

external, 648

function of, 657

internal, 652

function of, 659

membranous labyrinth, 653

middle, 650

function of, 657

organ of Corti, 653

ossicles of, 650

tympanum, 650
Eck's fistula, 439
Edestin, 105
Egg albumin, 105
Eggs, composition of, 324, 325

INDEX

745

Eighth nerve, 617

Elastic vessels, 207

Elasticity of muscle, 471

Elastin, 90, in

Electrodes, 474

Electrotonus, 502

Elements, chemical, in body, 79

Eleventh nerve, 622

Embryonic spongy bone cartilage, 48

Emission of semen center, 558

Emulsification, 114, 363, 368

Enamel, 54

cap, 57

germ, 56

organ, 56

papilla, 56
End-brushes, 70

-bulbs, 76

-plates, 63

Endocardiac pressure, 182
Endocardium, 163
Endomysium, 60
Endoneurium, 69
Endothelium, 25
Energy, income and output of, 453

requirements for body, 452
Enterokinase, 328, 371, 387
Enzymes, 327

action of, on pancreatic juice,

361, 385

activating, 328

amylolytic, 328

classification of, 327

coagulating, 328

digestive, 328

lipolytic, 328

proteolytic, 328
Eosinophile, 116, 131
Epiblast, 14
Epidermis, 418
Epiglottis, 268
Epinephrin, 458
Epineurium, 69
Epithelial tissues, 23
Epithelium, 23

ciliated, 30, 32, 533

classification of, 24

columnar, 25, 26, 29

cubical, 24

functions of, 25, 32

glandular, 30

simple, 24, 25

Epithelium, situations of, 24, 31

specialized, 30

squamous, 24, 28

stratified, 24, 28

transitional, 29
Equilibrium, sense of, 662
Erectile tissue, 247
Erection center, 559
Erepsin, 328, 371
Ergograph, 491
Erythroblasts, 129
Erythrocytes, 125
Erythrodextrin, 337 •
Eustachian tube, -650, 658

valve, 164, 733
Excreta, analysis of, 432, 433

channels of elimination of, 433

quantity of, 432
Excretion, 316, 398, 424

during starvation, 449

from skin, 421

laboratory experiments in, 424
Expiration, forced, 278

muscles of force of, 284

quiet, 278

relative time of, 281
Expired air, carbon dioxide of, 286,

3". 312

changes in, 285

oxygen of, 286
External genitals, vascular nerves

for, 247
Eye, 664

anatomy of, 665

astigmatism, 684, 709

chromatic aberration of, 684, 708

image formation, 674

movements of, 682

muscles concerned in, 682

optical apparatus, 673
axis, 676

refractive surfaces and media, 673

schematic, 676

spherical aberration of, 672, 683
Eyeball, 665

blood-vessels of, 672

ciliary apparatus, 666

cornea, 665

iris, 666

lens, 666

retina, 668
Eyelids, 665

746

INDEX

FACIAL nerve, 615

function of, 616
paralysis of, 617
relation to taste, 617
secretory, 616
Fallopian tubes, 686
Falsetto voice, 520
Far-point, 707
Fasciculus antero-lateralis, 548

cerebello-spinalis, 548

cuneatus, 546, 567

gracilis, 567

of Rolando, 567

solitarius, 619 •
Fasting, 447, 448

metabolism during, 441
Fatigue, effect on muscular contrac-
tion, 528, 529
Fats, 96, 1 14

absorption of, by intestines, 394

as food, 322, 325

chemical reactions of, 114

digestion of, 363, 364

emulsification of, 114, 363, 368

energy value of, 441

metabolism of, 440

saponification of, 114, 363

source of, in body, 441
Fatty acids, tests for, 114
Feces, 374

composition of, 374

excretion by, 433
Fermentation in intestine, 373

in the blood, 134

unorganized, 327, and see En-
zymes

Fetus, circulation of blood in, 731
Fibers of Remak, 67
Fibrin, 96

ferment, 121
Fibrinogen, 121, 134
Fictitious feeding, 346
Fifth nerve, 612
Fillet, 577
Filtration, 388

Finger, vasomotor changes in, 264
Fish, composition of, 324
Fission, 7
Food, and digestion, 322

effects of deprivation of, 447

mastication of, 329

-principles, 322

Food, salts of, 325
Foods, 322

carbohydrates, 322, 325

classification of, 322

effect of cooking, 326

fats, 322, 325

heat production from, 453, 467

income and output of energy, 43 2

inorganic, 322, 325

liquid, 326

mineral, 322, 325

nitrogenous, 322

percentage composition of, 323

proteins, 322

salts, 325

water, 322

Forced movements, 584
Fore-brain, 567, 586
Form, estimation of, 702
Fossa ovalis, 164
Fourth nerve, 6 1 1
Fovea centralis, 668
Frontal association center, 608

GALACTOSE, 100

Gall-bladder, 366

Galvanic currents, 473

Ganglia, 541

spinal, functions of, 556

Gases in alimentary canal, 375

Gastric digestion, 344, 381

changes in food in, 353
circumstances influencing,

352

cleavage products of, 383
products of, 352
time of, 353
juice, 346, 381
acid of, 349
action on milk, 353

on proteins, 352
artificial, 382
chemical composition of, 349,

.382.
digestive action of, 382

enzyme action of, 382
fictitious meals, action on,

346

hydrochloric acid in, 350
pepsin in, 351
psychic secretion of, 381
quantity of, 349

INDEX

747

Gastric juice, secretion of, 346, 381

secretion, changes in glands dur-
ing, 346

nervous mechanism of, 347
Gelatin, 1 1 1

effect of diet of, 437
Gelatinous tissue, 35
Gemmation, 7
Genito-spinal center, 559
Germinal epithelium, 721

matter, 9

spot, 720

vesicle, 720
Giant cells, 42
Glands, cardiac, 344

ceruminous, 421

gastric, 344

mammary, 734

pyloric, 345

reproductive, relation to metabo-
lism, 460

salivary, 329

sebaceous, 421

secreting, 317

sudoriferous, 420

types of, 317
Globulin, serum, 89
Globulins, 86

properties of, no

reactions of, 89
Globus pallidus, 588
Glomerulus, 401
Glosso-pharyngeal nerve, 618

in respiration, 299
Glottis, respiratory movements of,

279

Glucose, 99
Glutelins, 86
Glycocoll, 367
Glycogen, 102, 443

destination of, 444

formation of, 443

relation to metabolism, 443

sources of, 443, 444

tests for, 113
Glycogenesis, 443
Glycoproteins, 95, in
Glycosuria, 445
Goblet cells, 27
Golgi, corpuscles of, 77
Goll, tract of, 546
Gowers' tract, 548

Graafian follicles, 720
Granulose, 101

HAVERSIAN canals, 44
Head, vascular nerve supply of, 242
Hearing, acuteness of, 706
limits of, 706
physiology of, 655
Heart, 162

action of, 174
anatomy of, 162
automaticity of, 198
-beat, 180, 207

rate of, 249, 250

sequence, 250

theories of, 195
-block, 196
capacity of, 165
chambers of, 163
character of contraction, 190, 194
coronary circulation of, 205
cycle of, 174, 1 88
depressor nerve of, 237
development of, 166
endocardiac pressure, 182
excised, experiments on, 250, 251
force of action, 189
frequency of action, 174, 206
ganglia of, 195
impulse of, 180

influence of accelerator nerve on,
204, 576

of coronary circulation on,
205

of drugs on, 206

of inhibitory nerves on, 200,
576

of mechanical tension on,
205

of nervous system on, 200

of nutrient fluids on, 252

of sympathetic system on,
232

of temperature on, 205

of vagus on, 200
irritability of, 193
isolated, 252, 253
metabolism of, 199
methods of investigating beat,

249
muscle, 62, 531

properties of, 190

748

INDEX

Heart, nerves of, 200

production of heat by, 463
regulation of force and frequency

of contraction, 200
relation of rhythm to nutrition,

199

rhythmic contraction of , 191, 199
size of, 165
sounds of, 178

causes of, 179
structure of, 165
tonicity of, 192
valves of, 167

action of, 176
volume of, 252
weight of, 165
work per diem, 454
Heat, animal, 461

dissipation of, 464
from lungs, 466
from skin, 464
influence of extreme, 465

of nervous system on pro-
duction of, 467

produced in muscular contrac-
tion, 483

-producing tissues, 461, 463
production of body-, 452,461,466
regulation of body-, 463, 467

centers for, 468
-rigor, 473, 492
variations in loss of, 463

in production of, 466
Heidenhain's experiments on urine

secretion, 413
Heller's ring test, 108
Hemacytometer, 155
Hematin, 141, 142
Hematoblasts, 127
Hematoidin, 142
Hematoporphyrin, 141
Hemianopsia, 605
Hemin, 142
Hemiopia, 605
Hemochromogen, 141
Hemoglobin, 95, 136, 160, 294
action on gases, 138
combining power with oxygen,

292

derivatives of, 141, 160
estimation of , 139, 155
reduced, 138

Hemoglobinometer, 139, 156
Hemolysis, 145
Hemometer, 156
Henle's membrane, 169

loop, 400

Hepatolytic sera, 146
Hind-brain, 566
Hippuric acid, 410

formation of, 410, 440
Histones, 91
Hyaline cartilage, 39

cells, 131

leucocytes, 131
Hyaloplasm, 8, 18
Hydrochloric acid, 350, 351
combined, 350
digestive action of, 351
test for free, 350
Hydrogen, amount excreted, 433

effect of breathing, 304

in proteins, 106
Hyperisotonic solutions, 150
Hypermetropia, 686
Hyperpnea, 303, 314
Hypertonic solutions, 150
Hypoblast, 14
Hypoglossal nerve, 622
Hypoisotonic solutions, 150
Hypotonic solutions, 150

INCOME of energy, 453

Indol, 386

Induced currents, 475

Induction coil, 475

Infundibulum, 272

Inhibition, function of nerve centers

in. 559
Inogen, 495
Inorganic foods, 325

substances, 103
Insalivation, 329
Inspiration, 276

forced, 276

muscles of, 276
force of, 282

quiet, 276

relative time of, 281
Inspired air, 286, 311
Intercellular substance, 22, 33
Interepithelial arborizations, 74
Internal capsule, 585

secretions, 316, 454, 459

INDEX

749

Internal senses, 629
Intestinal digestion, 357
role of bile, 368

gases, 374

juices, 370, 386

secretion, 370

functions of, 371
Intestines, absorption in, 390

action of microorganisms in, 372

defecation, 377

digestion in, 357

feces in, 374

fermentation in, 373

gases in, 375

large, summary of digestive
changes in, 371

movements of, 375

influence of nervous system
on, 376

putrefaction in, 373

small, summary of digestive
changes in, 371

vascular nerves for, 246
Intonation, 522
Inulin, 102
Invertase, 328
Involuntary muscle, 532
Iodine, 104
lodothyrin, 455
Iris, 666

contraction of, 682
Iron, 104

tests for, 115
Irritability, 5

of heart-muscle, 193

of muscle", 472, 524
Islands of Langerhans, 358
Isotonic solutions, 149
Isotonicity of blood, 156
Ivory, 53

JUDGMENT of form and size of bodies,

638

of form and solidity, 702
of size and distance, 703

Jumping, 509

KARYOKINESIS, 10, 20
Karyolymph, 18
Karyoplasm, 18
Karyosomes, 19
Keratin, 89, no

Kidneys, 398

action of diuretics on, 416
blood supply of, 401
effect of blood pressure on, 424
factors affecting secretion from,

4i3

function of, 398

glomeruli of, 401

Malpighian bodies of, 399

nerves of, 403, 414

structure of, 398

tubuli uriniferi of, 399

vasa efferentia of, 403
recta of, 403

vascular nerves of, 246

volume of, 414
Krause, corpuscles of, 76

membrane of, 61

Kronecker-Meltzer theory of deglu-
tition, 339
Kymograph, 209

LABYRINTH, 653

Lachrymal apparatus, 665

Lactalbumin, 88

Lactase, 328

Lactation, 734

Lacteals, 391

Lactic acid, test for, 350

Lactose, 101

Lacunae, 45

Laky blood, 145

Langerhans, islands of, 358

Large intestine, summary of digestive

changes in, 372
Laryngoscope, 515
Larynx, 267, 510
Latent period of muscle, 479, 526
Leaping, 509
Lecithins, 97
Lecithoproteins, 95
Legumes, composition of, 325
Lens of eye, 666
Lenticular nucleus, 588
Leucocytes, 125, 129
Leucolytic sera, 146
Levers, action of, in the body, 505
Levulose, 100
Lichenin, 102

Liebermann's reaction, 107
Life, phenomena of, i
Limbs, vascular nerves for, 247

750

INDEX

Linin, 19
Lipase, 328, 363
Lipoids, tests for, 114
Lipolytic ferments, 328
Liquid foods, 326
Liquor sanguinis, 117
Liver, 364

glycogenic function of, 443

secretions of, 364

structure of, 365

urea formation in, 438

vascular nerves for, 246
Lobules, 270

Localization, cerebral, 598, 603
Locomotion, 505
Locus ceruleus, 577
Ludwig's theory of urine secretion,

Lungs, 270

absorption from, 396

blood supply of, 274

excretion by, 433

interchange of gases in, 296

loss of heat from, 466

lymphatics of, 274

nerves of, 275

structure of, 271
Luxus consumption, 435
Lymph, 150

chemical composition of, 150

flow, 152

formation of, 151
Lymphagogues, 151
Lymphatic sheaths, perivascular, 1 74

spaces, in blood-vessels, 174
Lymphocyte, 116, 131
Lymphoid tissue, 36
Lytic substances, 146

MAGNESIUM salts in the body, 103
Malpighian bodies, 399
Maltase, 328, 336, 360
Maltose, 100, 338
Mammary glands, 734
Manometer, 187, 209
Marrow, bone, 42
Mastication, 329

muscles of, 329

nervous mechanism of, 329
Maximal stimulus, 485
Meat, composition of, 323
Meconium, 369

Medulla oblongata, 567, 570, and see

Bulb

as a conducting path, 573
functions of, 573
reflex centers of, 573
section of, 565
Medullary sheath, 66
Medullated fibers, 66
Meissner's corpuscles, 75
Melanins, 96
Membrana decidua, 729

propria, 23

tympani, 650

Membranous labyrinth, 653
Menstrual discharge, 725

life, 726

Menstruation, 723
Mesoblast, 14
Mesothelium, 24
Metabolism, 6, 430

constructive, 6

destructive, 6

during fasting, 441

endogenous, 436

exogenous, 436

influence of ductless glands on,

454
reproductive glands on, 460

intermediate, 436

nutrition and diet, 43 1

tissue, 436
Metaphase, 20
Metaplasm, 18
Metaproteins, 95, 112
Methemoglobin, 139
Microcytes, 127

Micro-organisms, action of, in intes-
tines, 372
Microsomes, 8
Micturition, 417

center for, 558
Mid-brain, 567, 584
Milk, composition of, 324, 735
Millon's reaction, 107
Mineral foods, 325, 445

absorption of, in intestines, 395

acids, precipitation with, 108
Minimal stimulus, 485
Mitosis, 10, 20
Molisch reaction, 108
Monaster, 10, 20
Mossy fibers, 580

INDEX

751

Motor activities, coordinated, 505

areas of cortex, 598, 601
of human brain, 600

end-plates, 63

impressions, 563

-oculi nerve, 610

tracts in human brain, 603
Mouth, absorption, in, 389

digestion in, 328

in speech, 521
Movement, ameboid, 3

gliding, 4

streaming, 4
Movements, circus, 584

forced, 584
Mucigen, 334
Mucines, 95, 334
Mucoids, 95, in
Mucous membranes, 3 1 7
Mucus in urine, 411
Murexide test, 428
Muscle, blood supply of, 63

cardiac, 62, 495, 531

chemical changes of, 481

chemical composition of, 470, 471

clot, 470

coagulation of, 470

conditions affecting irritability
of, 485

conductivity of, 477

contractility of, 472

contraction of, 473, 497, 525

contracture, 490

currents, demonstration of, 481

development of, 59, 64

effect of blood supply on, 488
of drugs on, 489
of nerve supply, 489
of single induction shocks

on, 477

of temperature on, 487
of use on, 488

elasticity of, 471

electrical phenomena of, 481

end-plates, 63

experiments in, 522

ferments, 471

heart, 62, 495, 531

in rigor mortis, 492

involuntary, 58, 496, 532

compared with skeletal and
cardiac, 496

Muscle, irritability of, 472, 524
-nerve preparation, 476, 523
nerve supply of, 63
non-striated, 58
plain, 58
plasma, 470
plates, 74
properties of, 471
record of contraction of, 473
serum, 470
skeletal, 60
stimuli, 472, 526
striated, 60
tetanus, 490
-tone, center of, 557
voluntary, 60

Muscular action as heat producer, 463
activity, 4

center for tone of, 557
contraction, 473, 495

action currents, 483
apparatus for producing and

recording, 473
contraction, changes in shape

shape during, 479
characteristi s of single, 478
chemical changes during,

481

conditions affecting charac-
ter of, 485
co-ordinated, 490
differences between volun-
tary and involuntary, 496
effect of blood supply on,

488

of drugs on, 489
of fatigue on, 528
of load on, 530
of nerve supply on, 489
of rate of stimulation

on, 489
of repeated activity on,

486
of strength of stimulus

on, 485, 526
of temperature on, 487,

529. 53°
of use on, 488
electrical changes during,

481

energy liberated during, 484
heat produced during, 483

752 INDEX

Muscular contraction, latent period Nerve fibers, 65, 66, 74

of, 479, 526 effect of battery current o

metabolism during, 494 501, 503

preparation for, 476 fatigue of, 500

record of, 473 functions of, 499

recording, 477 medullated, 66

refractory phase of, 495 non-medullated, 67

response to stimuli in volun- impulses, 499

tary and involuntary, 466 cellulifugal, 538

simple, 478, 525 cellulipetal, 538

single twitch, 478 character of, 499

summation of contractions, rate of, 533

490 specific energy of, 538

tetanic, 489, 530 transmission through

voluntary, 489 neurone, 538

co-ordination, 490, 664 velocity of, 500

energy, 484 stimuli, 472, 499, 523

tissue, 58 terminations, 74

Muscularis mucosae, 270 tissue, 65

Musculi papillares, 168 trunks, 69

pectinati, 164 Nerves, cardiac, 255

Mydriasis, 611 cranial, 609

Myelin sheath, 66 functions of, 610

Myelocyte, 106, 131 depressor, 237

Myeloplaxes, 42 effect of currents on human, 50

Myogram, 478 503

Myograph, pendulum, 478, 527 experiments on, 522

Myohematin, 471 irritability of, 523

Myopia, 685 spinal, 549

Myosin, 471 vasomotor, 232, 233, 238

ferment, 470 Nervous system, 534

Myosinogen, 471, 495 functions of, 534

Myxedema, 454 influence on secretion, 32

423

NASAL region, smell, 644 sympathetic, 624

Near-point, 680, 707 tissues, 65, 67

Nephrolytic sera, 146 axones of, 65, 538

Nerve cells, 72, 534 dendrites of, 65, 538

arrangement of, in spinal ganglia of, 540

cord, 543 neuroglia of, 65, 78

body, 72 Pacinian corpuscles, 75

characteristic of individual, Neuraxone, 65

535 Neurilemma, 66

functions of, 534, 535 Neuroglia, 65, 78

neurone theory, 535 Neurone, 65, 534

nutritive influence of, 537 theory, 535

transmission of impulses types of, 539

through, 538 varieties, 539

centers, 540 Neutrophile, 116, 131

functions of, 541 Ninth nerve, 618

collaterals, 69 Nitrogen in proteins, 106

end-brushes, 70 Nitrogenous bodies, 79

INDEX

753

Nitrogenous equilibrium, 434

foods, 322

output, 436

substances, 79

Nitrous oxide, effect of breathing, 304
Nodes of Ranvier, 66
Nceud vital, 297
Nostrils, respiratory movements of,

279

Nuclear matrix, 18
Nuclei of optic thalamus, 586
Nucleic acid, 92
Nucleins, 92
Nucleoli, 19
Nucleoplasm, 18
Nucleoproteins, 92
Nucleus, 9, 1 8

ambiguus, 619

ruber, 585

structure of, 18

OBESITY, 442
Ocular fixation, 699
Odontoblasts, 53, 56
Oils, as food, 325
Olfactory apparatus, 643

bulb, 645

center, 605

glomeruli, 605

membrane, 646

nerve, 605

tract, 606

Olivary bodies, 569, 571
Olive, accessory, 571

superior, 577
Onkograph, 415
Onkometer, 414
Ophtha1moscope, 690
Opsonins, 147
Optic center, 604

nerve, 668

thalami, 586
Optical apparatus, 673
defects in, 683
Organ of Corti, 653
Organized ferments, 372
Osmosis, 148
Osmotic pressure, 149
Osseous labyrinth, 650
Ossicles of ear, 615
Ossification, 46

center of, 47
48

Ossification in cartilage, 47, 51

in membrane, 46, 51
Osteoblasts, 47
Osteoclasts, 49
Osteogenetic fibers, 47
Output of energy, 454
Ovaries, 719

relation to metabolism, 460
Oviducts, 722
Ovulation, 723
Ovum, 720, 722

changes in, following impregna-
tion, 728

prior to impregnation, 727
Oxalic acid in urine, 412
Oxygen, amount excreted, 433

in expired air, 286

in tissues, 295

determination of, in air, 311
Oxyphile, 130

PACINIAN corpuscles, 75, 358
Pain, sense of, 636
Pancreas, 357

enzymes of, 360
extirpation of, 459
extract of, 360
internal secretion of, 459
islands of Langerhans in, 358
secretion of, 359
structure of, 357
Pancreatic digestion, 353, 384

cleavage products of, 385
fistula, 359
juice, 359, 384

artificial, 385

chemical characters of, 384

composition of, 360
conditions influencing action

of, 364
enzymes of, 360, 385

action of, 361, 364,

385
secretion of, 384

action of nerves on,
action of secretin

360, 384

Papillae of skin, 419
of tongue, 640

Paralytic secretion of saliva, 330
Parathyroid glands, 456
Parietal association center, 608

60

754

INDEX

Parotid gland, 329

nerves of, 333
Parturition, 734

center, 559

Peduncles of cerebrum, 584
Pelvic viscera, vascular nerves for,

246

Penis, 718
Pepsin, 328

action of, 351

in gastric juice, 351
Pepsinogen, 351
Peptone plasma, 124
Peptones, 96, 112, 351

characteristics of, 352
Perforating fibers of Sharpey, 46
Pericardium, 162
Perichondrium, 39, 47
Perimysium, 60
Perineurium, 69
Periosteum, 43

Peripheral resistance, 207, 231
Peristalsis, intestinal, 376

of stomach, 354

reversed, 376

Perivascular lymphatic sheaths, 174
Perspiration, 422
Pes, 584

Pfliiger's law of contractions, 502
Phagocytes, 154
Phagocytosis, 154
Phakoscope of Helmholtz, 709
Phenomena of life, i
Phenomenon of treppe, 528
Phosphates, 103
Phosphoproteins, 95
Phosphoric acid in urine, 411
Phosphorus in foods, 447

in proteins, 106

Phrenic nerve, influence on respira-
tion, 314
Physiological material, source of, 16

utilization of, 16
Physiology, i
Pigment cells, 33
Pigments, bile, 386
Pituitary body, 459
Placenta, 730

Plants differentiated from animals, 1 1
Plasma, 117, 133

chemistry of, 159

composition of, 133

Plasma, percentage of, in blood, 155

reaction of, 156
Plasmosomes, 19
Plethysmogram, 234, 265
Pleurae, 270
Pneumogastric nerve, 620, and see

Vagus

Pneumograph, 280
Pons, 567

Varolii, 576
Postdicrotic wave, 229
Posterior longitudinal bundle, 577

pyramids, 567

roots of spinal nerves, 550, 555
Potassium salts in the body, 103
Poultry, composition of, 324
Precipitins, 146
Predicrotic wave, 229
Presbyopia, 686
• Pressor nerves, 238
Pressure, endocardiac, 182
Prickle cells, 22, 28
Prolamins, 89
Proliferation, 47
Pronucleus, female, 728

male, 728
Prophase, 20
Prostate gland, 718
Protamines, 91
Proteins, 80

absorption of, from intestines,

392

action of trypsin on, 362
as fat formers, 436
as glycogen formers, 436
carbon in, 106
chemical structure of, 80
circulating, 435
classification of, 86
coagulated, 96
color reactions of, 107
composition of, 106
compound, 92
conjugated, 87
crystals, 105

decomposition products, 362
derived, 87, 112
digestion of, 350
floating, 435
hydrogen in, 106
metabolism of, 434, 435
morphotic, 435

INDEX

755

Proteins, nitrogen in, 106

phosphorus in, 106

precipitation, reactions of, 108

preparation of, 105

properties of, 85

reactions of, 107

simple, 86, 87

sulphur in, 106

tissue, 435

wheat, 83

Proteolytic ferments, 328
Proteoses, 96, 112, 351
Prothrombin, 121
Protoplasm, i, 2

chemistry of, 3

definition of, 2

effect of stimuli on, 5

growth of, 7

irritability of, 5

movement of, 3

physiological characteristics of, 3

properties of, 2

reproduction of, 7

structure of, 8
Ptosis, 611
Ptyalin, 328, 336

action of, 328, 336, 380
Pulse, 226

arterial, 259

dicrotic, 230

variations in rate of, 206

-wave, rate of propagation of, 260
Pulvinar, 587
Pupil, 666

contraction of, 682

dilatation of, 682
center for, -575

reflexes, 682
Purines, 94
Purkinje's cells, 579

figures, 688

shadows, 711

Purkinje-Sanson's images, 708
Putamen, 588

Putrefaction in intestines, 373
Pyloric orifice, 354
Pyramids, 567

decussation of, 568
Pyrimidines, 93

RACEMOSE glands, 319
Ranvier, nodes of, 66

Reaction of degeneration, 505
Red corpuscles, 125

action of reagents on, 153
chemical composition of , 135
development of, 127
origin of, 128
varieties of, 129
nucleus, 586
Reflex action, 551

time of, 556
arc, 551

centers in medulla, 573
Reflexes, complex, 553
cutaneous, 560
inhibition of, 559
morbid, 559
muscle, 560
simple, 553

special centers for, 557
spinal, 556
tendon, 560
Refraction, 706
Refractory period, 194

phase, 495

Relaxation phase of muscle, 479
Remak's fibers, 67

ganglia, 195
Rennin, 328, 360

action of, 353, 363, 384
Reproductive organs, 715
of female, 719
of male, 715
Reserve air, 283, 310
Residual air, 283
Respiration, 266

changes in diameter of chest,

during, 309

Respiration, effect of altitude on, 304
of, on circulation, 305
of various gases on, 304
of vitiated air on, 304
expiration, 278
influence of cutaneous nerves on,

313

of general sensory nerves on,

299. 3*3

of glosso-pharyngeal on, 299

of phrenic on, 314

of superior laryngeal on, 299

of vagus on, 298, 314
inspiration, 276
internal, 267

756

INDEX

Respiration, laboratory experiments

in, 308

mechanism of, 275
nervous apparatus of, 296, 313
rhythm of, 280
special types of, 302
tissue, 267

volume of air breathed, 309
Respirations, number of, 284, 308
Respiratory apparatus, 267

elimination of carbon diox-
ide by, 295

nervous regulation of, 296
capacity, 283, 310

circumstances affecting, 284
center, 297, 575

automatic action of, 300
stimulation of, 300
changes in air breathed, 285
in the blood, 289
in the tissues, 295
interchange, 315
movements, 275

character of, 309
establishment of, at birth,

302

nervous mechanism of, 313
of nostrils and glottis, 279
rate and character of, 312
recording of, 279, 309
relative time of, 281
murmur, 282
muscles, force of, 284
pressure, 289, 310
quotient, 288
rate, 284, 308
rhythm, 281

action of stimuli on, 298
terms for quantity of air

breathed, 282
Rete mucosum, 419
Reticular formation in medulla, 569
Reticulum, 8, 18
Retiform tissue, 36
Retina, 668

cones of, 670

inverted image on, 707

layers of, 669

localization in, 693

movement of pigment cells,

694
rods of, 670

Retinal image, duration of, 712

relation of size to distance,

712

Retinoscopy, 713
Rheoscopic frog, 500
Rhodopsin, 693
Rhythmical contractility, 191
Rhythmicity of arterial flow, 2 1 9
Ribs, movement of, in respiration,

277
Rigor mortis, 492

cause of, 492

heat, 493

order of occurrence, 493

water, 492
Rima glottidis, 267
Rolandic area, 602
Running, 509

SACCHAROSE, 100
Sacculus, 653, 664
Saliva, 335

action of, on starch, 337, 338, 379
chemical composition of, 335, 379
function of, 336
properties of, 336
ptyalin in, 328, 336, 337
quantity of, 335
secretion of, center for, 330
mechanism of, 330
rate of, 335
Salivary digestion in stomach, 339

influence of acids and alka-
lies on, 380

of temperature on, 380
glands, 329

changes in, during secretion,

333, 378
nerves of, 377
structure of, 329
secretion, 333

reflex, 377

Salts, absorption of, by intestines, 395
as foods, 325
bile, 367, 386
in the body, 103

tests for, 115
Sanson's images, 679
Saponification, 114, 363
Sarcode, 2
Sarcolemma, 61
Sarcoplasm, 62

INDEX

757

Sarcostyles, 61

Sarcous elements of Bowman, 61
Schemer's experiment, 708
Schwann, sheath of, 66
Sebaceous glands, 421
Secretin, 360, 371

influence on pancreatic secretion,

36°, 384
Secreting glands, 317

production of heat by, 463
types of, 317

organs, types of, 317
Secretin, 316

circumstances influencing, 320

discharge of, 320

external, 316

internal, 316, 454, 459

organs and tissues of, 317

process of, 319

psychic, 381

true, 316

Segmentation, 728
Semicircular canals, 653, 663
Semilunar valves, 168
action of, 177
Seminal fluid, 718
Sensations, binaural, 66 1

common, 629

objective, 630

of color, 695

special, 630

subjective, 630
Sense, hearing, 648

muscular, 629, 637

of equilibrium, 662

of pain, 636

of sight, 664

of smell, 643

of taste, 638

of temperature, 635

of touch, 63 1

organs, directions for experi-
ments on, 704

perceptions, 631
Senses, the, 629

internal, 629

special, 630
Sensorium, 630
Sensory areas of brain, 603

illusions, 630

impressions, 562
Serous membranes, 317

Serum, 118, 134

agglutinative substances, 146

albumin, 106

blood, 118, 134

chemistry of, 159

composition of, 135

globulicidal action of, 145

globulin, 89

hemolytic action of, 145

precipitins of, 146
Seventh nerve, 615
Sharpey's fibers, 46
Sight, 664
Silicon, 104
Sixth nerve, 615
Size, estimation of, 703
Skein, 20
Skin, absorption from, 396

amount of carbon dioxide ex-
haled by, 422

excretion by, 433

excretory functions of, 418, 421

exhalation from, 422

functions of, 418, 423

glands of, 420

loss of heat from, 464

papillae of, 419

respiratory functions of, 423

structure of, 418
Sleep, 623
Small intestine, digestion in, 371

mucosa of, 391

villi of, 391
Smell, center for, 605

sensation of, 706

sense of, 643
Soaps, 98

Sodium salts in the body, 103
Solidity, judgment of, 702
Solubility, 114

Somesthetic area of brain, 603
Somnambulism, 624
Sound, 656
Sounds, articulate, 518, 520

localization of, 660

of the heart, 178

pitch of, 659
Special centers in bulb, 573

sensations, 630
Speech, 510, 520

action of tongue in, 521

mouth in, 521

758

INDEX

Spermatids, 715
Spermatocytes, 715
Spermatogonia, 715
Spermatozoa, 715, 716, 719
Spermin, 460

Spherical aberration, 683, 707
Sphygmogram, 228
Sphygmograph, 226
Sphygmomanometer, 216
Sphygmometer, 227
Spinal accessory nerve, 622
bulb, 567
centers, 557, 558
cord, 541

antero-lateral ascending

tract, 548

descending tract, 548
arrangement of nerve cells

in, 543
ascending degeneration of,

548

comma tract of, 548
conduction in, 561
course of motor impulses in,

563
of sensory impulses in,

562

crossed pyramidal tract, 547
descending degeneration of,

547

direct cerebellar tract, 548
pyramidal tract, 547,

548

fasciculi of, 546
functions of, 541, 545, 551
Gowers' tract, 548
hemisection of, 564
intrinsic cells in, 545
irradiation of impulses in,

554

peculiarities of different re-
gions, 551

reflex action in, 551, 557
reticular formation, 545
tracts of, 546
weight of, 593

nerve-roots, functions of, 555

nerves, 549

anterior roots, 550, 555
course of fibers, 550
posterior roots, 550, 555

reflexes, 556

Spirem, 20

Spleen, vascular nerves for, 246

Spongioplasm, 8, 18

Staircase contractions, 486

Stammering, 522

Starch, 101

action of amylopsin on, 363

of ptyalin on, 337, 338, 379

chemical reactions of, 113

hydrolysis of, 113
Starvation, 447

death from, 447

effect on body temperature, 448

symptoms of, 448
Steapsin, 328, 360, 363
Stercobilin, 368
Stereoscope, 702
Stethograph, 280
Stethometer, 279
Stimuli, forms of, 472

maximal, 485, 526

minimal, 485, 526
Stokes' fluid, 138
Stomach, 341

absorption from, 389

action of pylorus, 354

blood-vessels of, 345

changes in glands during secre-
tion, 346

digestion in, 339, 341, 353

gases in, 375

glands of, 344

lymphatics of, 345

movements of, 353

nerves of, 342

nervous control of movements
of, 354

peristalsis of, 354

secretion in, 346

structure of, 342

vascular nerves for, 246
Stomata, 25
Strabismus, 61 1
Stratum granulosum, 419

lucidum, 419

Malpighii, 419
Striated muscle, 60

development of, 64
Submaxillary gland, action of atro-

pine on, 33 i

paralytic secretion of, 332
secretion of, 333

INDEX

759

Substantia nigra, 584, 585
Succus entericus, 370
Sucking, center for, 575
Sudoriferous glands, 420
Sugar, test for, in urine, 430
Sulphates, 104
Sulphur in proteins, 106
Sulphureted hydrogen, effect of

breathing, 304
Sulphuric acid in urine, 411
Sulphurous acid, effect of breathing,

3°4
Summation, 490

of stimuli, 553

Superior laryngeal nerve in respira-
tion, 299

Supplemental air, 283
Suprarenal capsules, 456

active principle of, 457
functions of, 457
internal secretion, 459
nerves of, 457

relation to Addison's dis-
ease, 457, 458
extract, 457
Swallowing, 339
Sweat, 422

centers, 576

chemical composition of, 422

glands, 420

influence of nervous system on

secretion of, 423, 426
Sympathetic ganglia, functions and

structure, 624, 627
nervous system, 624
functions, 627

organization and distribu-
tion, 624
Synapse, 552

Synovial membranes, 317
Systole of heart, 174, 175

TACTILE corpuscles, 75, 633
of Meissner, 75

menisques, 77
Taste, 638

after-, 642

buds, 639

center, 606

influence of fifth nerve on, 615

seat of, 638, 641

sensation of. 705

Taste, varieties of, 641
Taurin, 367
Teeth, 51

dentine of, 53
development of, 56
enamel of, 54
ivory of, 53
permanent, 52
structure of, 52
temporary, 51
Tegmentum, 577, 584
Telophase, 21
Temperature, body, 461

dissipation of, 464
influence of extreme heat

and cold on, 465
regulation of, 463
sense of, 635, 705
variations in, 461
influence of, on muscular con-
traction, 487, 529
Tenth nerve, 620
. Testes, 715

relation to metabolism, 460
Tetanometer, 530
Tetanus, 490, 530
Thermogenic centers, 468
Third nerve, 610
Thoracic viscera, vascular nerves for,

246

Thorax, respiratory changes in diam-
eter, 309
Thrombin, 121
Thrombocytes, 132
Thrombogen, 123
Thrombokinase, 122, 158
Thyroid gland, 454

accessory, 454, 456
functions of, 454
Tidal air, 282, 310
Tissues, connective, 32
elementary, 23
epithelial, 23

interchange of gases in, 296
muscular, 58
nervous, 65
Tone, of artery, 233

of muscle, 192, 557,
Tongue, 639

action of, in speech, 521
papillae of, 640
Tonicity of heart muscle, 192

760

INDEX

Tooth-pulp, 52
Touch corpuscles, 633

sense of, 631, 704

acuteness of, 633
Trabeculae carneae, 165
Trachea, 268
Tract of Burdach, 546

of Goll, 546

of Cowers, 548
Traube-Hering curves, 238
Treppe, phenomenon of, 528
Tricuspid valve, action of, 176
Trigeminus nerve, 612

functions of, 613
Tri-olein, 97
Tri-palmitin, 97
Tri-stearin, 97
Trochlearis nerve, 6 1 1
Trommer's test, 430
Trunk, vascular nerves for, 247
Trypsin, 328, 360

action of, 362
Tubular glands, 318
Tubuli seminiferi, 679

uriniferi, 398
Twelfth nerve, 622
Tympanum, 650

UNORGANIZED ferments, 327, and see

Enzymes

Unstriped muscle, 58
Urea, 407

amount in tissues of body,
408

antecedents of, 438

determination of, 428

formation of, 408, 438

preparation of, 428

properties of, 407

quantity excreted, 409
Ureters, 404
Uric acid, 409, 428

condition of, in urine, 409

formation of, 440

properties of, 409

tests for, 429
Urinary bladder, 404
Urine, 404

abnormal constituents of, 429

albumin in, 412, 429

ammonia in, 410

analysis of, 426

Urine, average daily quantity of con-
stituents, 406

chlorides in, 412, 427

creatinin in, 410, 429

cystin in, 412

dextrose in, 412, 430

discharge of, 417

diuretics, action of, 416

excretion by, 433

of, experiments on, 414

factors affecting secretion of, 413

nitration theory of secretion, 413

general properties of, 404

hippuric acid in, 410, 440

method of excretion of, 413

mucus in, 411

nitrogenous substances in, 407

occasional constituents of, 412

oxalic acid in, 412

phosphates in, 411, 427

pigments in, 410, 429

quantity of, 405, 426

reaction of, 405, 426

relation of blood pressure to
secretion of, 424

saline matter in, 411

secretion of, theories of, 413

solids of, 426

specific gravity of, 406, 426

sugar in, 430

sulphates in, 411, 427

urea in, 407, 428

uric acid in, 409, 428

variations in quantity of con-
stituents, 406
in specific gravity, 406
Uriniferous tubules, 398
Urobilin, 368, 410, 428
Urochrome, 410
Uroerythrin, 411
Uterine tubes, 722
Uterus, 722
Utriculus, 653, 664

VAGINA, 723
Vagus nerve, 620

effects of section, 622
functions of, 620
relation to deglutition, 341
to gastric secretion, 347
to heart's action, 198
to respiration, 299, 314

INDEX

Valves of heart, 167

action of, 176

of veins, 173
Vascularization, 48
Vasoconstrictor activity, 240

center, 235

nerves, 234, 241, 248

reflexes, 236
Vasodilator activity, 240

center, 240

nerves, 233, 238

reflexes, 240
Vasomotor centers, 576

changes, 264

nerves, 232, 242

tone, 235
Veins, 172

blood pressure in, 215

structure of, 172

valves of, 173

vasoconstrictor nerves in, 248
Venous flow, 223

velocity of, 224
Ventilation, 304

Ventricles of heart, action of, 175
Vesico-spinal center, 558
Vesiculae seminales, 716
Vesicular breathing, 282
Vicq d'Azyr, bundle of, 586
Villi, 391

Visceral sensations, 562
Vision, accommodation of, 677,
679

binocular, 699

field of, 692

limits of, 695, 707, 712

localization of, 693

mechanism of accommodation,
679

range of distinct, 680
Visual acuity, 713

center, 604

judgments, 702

purple, 693

Visual sensations, 687

after-images, 689
intensity of, 689
sense, 664
Vital capacity, 283, 310

phenomena, i
Vitiated air, effects of, 304
Vocal cords, 267, 510

movements of, 517
Voice, 510

difference between male and

female, 519, 520
in singing and speaking, 518
production of, 510
quality of, 520
vocal range of, 519
Vomiting, 356

action of abdominal muscles, 356
of diaphragm, 356
of pylorus, 356
center for, 356
nervous mechanism of, 357
Vowels, 521

WALKING, 505

Wallerian degeneration, 537, 547

Water, 104

absorption of, in intestines, 395
amount excreted, 422, 433
in expired air, 288
in the body, 104
as food, 326
rigor, 492

Weyl's reaction, 429
White fibrous tissue, 34

development of, 37
Wreath, 20

XANTHO-PROTEIC reaction, 107

YELLOW elastic tissue, 34

development of, 37

ZYMOGENS, 327

>

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