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TEXT-BOOK OF HUMAN PHYSIOLOGY.

BRUBAKER.

TEXT-BOOK

OF

HUMAN PHYSIOLOGY.

ALBERT P. BRUBAKER, A.M., M.D.,

PROFESSOR OF PHYSIOLOGY AND HYGIENE IN THE JEFFERSON MEDICAL COLLEGE; PROFESSOR

OF PHYSIOLOGY IN THE PENNSYLVANIA COLLEGE OF DENTAL SURGERY;

LECTURER ON PHYSIOLOGY AND HYGIENE IN THE DREXEL •

INSTITUTE OF ART, SCIENCE, AND INDUSTRY.

•SJHttb ColoreB plates an6 354 miustcattons.

'O^'^.C^ ^^

PHILADELPHIA:

P. BLAKISTON'S SON & CO.,

I0I2 WALNUT STREET.
1904.

Copyright, 1904, by P. Blakiston's Son & Co.

PKE5S or WM. r. rr.LL coMPANr

PHILADCLPHIA

TO

HENRY C. CHAPMAN, M.D.,

PROFESSOR OF INSTITUTES OF MEDICINE AND MEDICAL JURISPRUDENCE IN
THE JEFFERSON MEDICAL COLLEGE,

IN GRATEFUL RECOGNITION OF THE MANY KINDNESSES RECEIVED FROM

HIM, DURING A PERIOD OF TWENTY-FIVE YEARS, THIS

VOLUME IS RESPECTFULLY DEDICATED BY

THE AUTHOR.

PREFACE.

The object in view in ihc preparation of this volume was the
selection and presentation of the more important facts of physiology,
in a form which it is believed will be helpful to students and to
practitioners of medicine. Inasmuch as the majority of students in
a medical college are preparing for the practical duties of professional
life, such facts have been selected as will not only elucidate the
normal functions of the tissues and organs of the body, but which
will be of assistance in understanding their abnormal manifestations
as they present themselves in hospital and private work. Both in
the selection of facts and in the method of presentation the author
has been guided by an experience gained during twenty years of
active teaching.

The description of physiologic apparatus and the methods of
investigation, other than those having a clinical interest, have been
largely excluded from the text, for the reason that both are more
appropriately considered in works devoted to laboratory methods
and laboratory instruction, and for the further reason that the student
receives this information while engaged in the practical study of
physiology in the laboratory, now an established feature in the
curriculum of the majority of medical colleges. For those who have
not had laboratory opportunities a brief account of some essential
forms of apparatus and the purposes for which they are intended
will be found in an appendix.

I wish to acknowledge my indebtedness to Professor Colin C.
Stewart for many valuable suggestions in the preparation of different
sections of the volume; to Dr. Carl Weiland for assistance in the
chapter on vision; to Dr. Joseph P. Bolton for excellent suggestions
on questions relating to physiologic chemistry.

TABLE OF CONTENTS.

CHAPTER I. PACE

Introduction, 17

CHAPTER II.
Chemic Composition of the Human Body, 24

CHAPTER III.
Physiology of the Cell,. 41

CHAPTER IV.
Histology of the Epitheli.a.l .a.nd Connective Tissues, 47

CHAPTER V
The Phy'siology of the Skeleton 58

CHAPTER VI.
GENER.A.L Physiology of Muscle-tissue, 63

CHAPTER VIE
The GENER.A.L Physiology of Nerve-tissue, 103

CHAPTER VIII.
Foods, 133

CHAPTER IX.
Digestion, 151

CHAPTER X.
Absorption, 213

CHAPTER XI.
The Blood, 229

CHAPTER XII
The Circul.\tiqn of the Blood, 263

CHAPTER XIII.
Respir.\tion, 335

CHAPTER XIV
Animal Heat, 3S5

CHAPTER XV.
Secretion, 395

X TABLE OF CONTENTS.

CHAPTER XVI. PAGE

Excretion', 420

CHAPTER XVH.
The Cextral Organs of the Nerve System and their Nerves, 440

CHAPTER XVIII.

The Medulla Oblongata; the Isthmus of the Encephalon; the Basal

Gangli.a, 467

CHAPTER XIX
The Cerebrum. 486

CHAPTER XX.
The Cerebellum, 514

CHAPTER XXI.
The Crani.al N'erves, 522

CHAPTER XXII.
The Sympathetic N'erve System, 561

CHAPTER XXIII.
Phonation; Articulate Speech, 572

CHAPTER XXIV.
The Special Senses, 585

CHAPTER XXV.
The Sense of Sight, 598

CHAPTER XXVI.
The Sense of Hearing, 637

CHAPTER XXVII
Reproduction, 650

APPENDIX.
Physiologic Apparatus, 671

Index, 693

TEXT-BOOK OF PHYSIOLOGY.

CHAPTER I.
INTRODUCTION.

An animal organism in the living condition exhibits a series of
phenomena which relate to growth, movement, mentahty, and re-
production. During the period preceding birth, as well as during
the period included between birth and adult hfe, the individual
grows in size and complexity from the introduction and assimilation
of material from without. Throughout its hfe the animal exhibits
a series of movements, in virtue of which it not only changes the
relation of one part of its body to another, but also changes its posi-
tion relatively to its environment. If, in the execution of these
movements, the parts are directed to the overcoming of opposing
forces, such as gravity, friction, cohesion, elasticity, etc., the animal
may be said to be doing w^ork. The result of normal growth is the
attainment of a physical development that will enable the animal,
and, more especially, man, to perform the work necessitated by the
nature of its environment and the character of its organization. In
man, and probably in lower animals as well, mentahty manifests
itself as intellect, feehng, and volition. At a definite period in the
life of the animal it reproduces itself, in consequence of which the
species to which it belongs is perpetuated.

The study of the phenomena of growth, movement, mentahty,
and reproduction constitutes the science of animal physiology.
But as these general activities are the resultant of and dependent
on the special activities of the individual structures of which an
animal body is composed, physiology in its more restricted and
generally accepted sense is the science which investigates the actions
or functions of the individual organs and tissues of the body and
the physical and chemic conditions which underlie and determine
them.

This may naturally be divided into:
I. Special physiology, the object of which is a study of the ntal
phenomena or functions exhibited by the organs of any individual
animal.

17

i8 TEXT-BOOK OF PHYSIOLOGY.

2. Comparalive physiology, the object of which is a comparison of
the vital phenomena or functions exhibited by the organs of
two or more animals of different species, with a view to un-
folding their points of resemblance or dissimilarity.

Human physiology is that department of physiologic science
which has for its object the study of the functions of the organs of
the human body in a state of health.

Inasmuch as the study of function, or physiology, is associated
with and dependent on a knowledge of structure, or anatomy, it is
essential that the student should have a general acquaintance not
only with the structure of man, but w^ith that of typical forms of
lower animal life as well.

If the body of any animal be dissected, it will be found to be
composed of a number of well-defined structures, such as heart,
lungs, stomach, brain, eye, etc., to which the term organ was originally
applied, for the reason that they were supposed to be instruments
capable of performing some important act or function in the general
activities of the body. Though the term organ is usually employed
to designate the larger and more famihar structures just mentioned,
it is equally apphcable to a large number of other structures which,
though possibly less obvious, are equally important in maintaining
the life of the individual — e. g., bones, muscles, nerves, skin, teeth,
glands, blood-vessels, etc. Indeed, any complexly organized struc-
ture capable of performing some function may be described as an
organ. A description of the various organs which make up the body
of an animal, their external form, their internal arrangement, their
relations to one another, constitutes the science of animal anatomy.

This may naturally be divided into:

1. Special anatomy, the object of which is the investigation of the

construction, form, and arrangement of the organs of any
individual animal.

2. Comparative anatomy, the object of which is a comparison of the

organs of two or more animals of different species, with a view
to determining their points of resemblance or dissimilarity.
If the organs, however, arc subjected to a further analysis, they
can be resolved into simple structures, apparently homogeneous, to
which the name tissue has been given — e. g., epithelial, connective,
muscle, and nerve tissue. When the tissues are subjected to a
microscopic analysis, it is found that they are not homogeneous
in structure, but composed of still simpler elements, termed cells
and fibers. The investigation of the internal structure of the organs,
the physical properties and structure of the tissues, as well as the
structure of their component elements, the cells and fibers, con-
stitutes a department of anatomic science known as histology,

INTRODUCTION. 19

or as it is prosecuted largely with the microscope, microscopic
anatomy.

Human anatomy is that department of anatomic- science which
has for its object the investigation of the construction of the human
bodv.

GENERAL STRUCTURE OF THE ANIMAL BODY.

The body of every animal, from fish to man, may be divided
into —

1. An axial portion, consisting of the head, neck, and trunk; and —

2. An appendicular portion, consisting of the anterior and posterior

limbs or extremities.

The axial portion of all mammals, to which class man zoologi-
cally belongs, as well as of all birds, reptiles, amphibians, and fish,
is characterized by the presence of a bony, segmented axis, which
extends in a longitudinal direction from before backward, and which '
is known as the vertebral column or backbone. In virtue of the
existence of this column all the classes of animals just mentioned
form one great division of the animal kingdom, tJie Vertehrata.

Each segment, or vertebra, of this axis consists of —

1. A soHd portion, known as the body or centrum, and

2. A bony arch arising from the dorsal aspect and surmounted by

a spine-like process.

At the anterior extremity of the body of the animal the vertebrae
are variously modified and expanded, and, with the addition of new
elements, form the skull; at the posterior extremity they rapidly
diminish in size, and terminate in man in a short, tail-like process.
In many animals, however, the vertebral column extends for a
considerable distance beyond the trunk into the tail. The vertebral
column may be regarded as the foundation element in the plan of
organization of all the higher animals and the center around which
the rest of the body is developed and arranged with a certain degree
of conformity. In all vertebrate animals the bodies of the segments
of the vertebral column form a partition which serves to divide
the trunk of the body into two cavities — viz., the dorsal and the
ventral. (See -Fig. i.)

The dorsal cavity is found not only in the trunk, but also in
the head. Its walls are formed partly by the arches which arise
from the posterior or dorsal surface of the vertebrae and partly by
the bones of the skull. If a longitudinal section be made through
the center of the vertebral column, and including the head, the
dorsal cavity will be observed running through its entire extent.
Though for the most part it is quite narrow, at the anterior ex-

TEXT-BOOK OF PHYSIOLOGY.

tremity it is enlarged and forms

Fig I. — Diagrammatic Longitud-
inal Section of the Body.
V, V. Bodies of the vertebrae
which divide the body into the
dorsal and ventral cavities, a, a' .
The dorsal cavity. C, p'. The
abdominal and thoracic divisions
of the ventral cavity, separated
from each other by a trans-
verse muscular partition, the
diaphragm d. B. The brain.
Sp. C. The spinal cord. e. The
esophagus. S. The stomach,
from which continues the intes-
tine to the opening at the poste-
rior portion of the body. /. The
liver, p. The pancreas, k. The
kidney, o. The bladder. /'. The
lungs, h. The heart.

the cavity of the skull. This cavity
is lined by a membranous canal,
the neural canal, in which are con-
tained the brain and the neural or
spinal cord. Through openings in
the sides of the dorsal cavity nerves
pass out which connect the brain
and spinal cord with all the struc-
tures of the body.

The ventral cavity is confined
mainly to the trunk of the body.
Its walls are formed by muscles
and skin, strengthened in most
animals by bony arches, the ribs.
Within the ventral cavity is con-
tained a musculo-membranous tube
or canal known as the alimentary
or food canal, which begins at the
mouth on the ventral side of the
head, and, after passing through
the neck and trunk, terminates at
the posterior extremity of the trunk
at the anus. It may be divided
into mouth, pharynx, esophagus,
stomach, small and large intestines.

In all mammals the ventral
cavity is divided by a musculo-^
membranous partition into two
smaller cavities, the thorax and
abdomen. The former contains the
lungs, heart and its great blood-
vessels, and the anterior part of
the alimentary canal, the gullet or
esophagus; the latter contains the
continuation of the ahmentary
canal — that is, the stomach and
intestines — and the glands in con-
nection with it, the liver and pan-
creas. In the posterior portion of
the abdominal cavity are found the
kidneys, ureters, and bladder, and
in the female the organs of repro-
duction. The thoracic and ab-
dominal cavities are each lined by
a thin serous membrane, known,

INTRODUCTION. 2r

respectively, as the pleural and peritoneal membranes, which, in
addition, are reflected over the surfaces of the organs contained
within them. The alimentary canal and the various cavities con-
nected with it are lined throughout by a mucous membrane.

The surface of the body is covered by the skin. This is com-
posed of an inner portion, the derma, and an outer portion, the epi-
dermis. The former consists of fibers, blood-vessels, nerves, etc. ; the
latter of layers of scales or cells. Embedded within the skin are
numbers of glands, which exude, in the different classes of animals,
sweat, oily matter, etc. Projecting from the surface of the skin are
hairs, bristles, feathers, claws. Beneath the skin are found muscles,
bones, blood-vessels, nerves, etc.

The appendicular portion of the body consists of two pairs
of symmetric limbs, which project from the sides of the trunk, and
which bear a determinate relation to the vertebral column. They con-
sist fundamentally of bones, surrounded by muscles, blood-vessels,
nerves and lymphatics. The limbs, though having a common plan
of organization, are modified in form and adapted for prehension
and locomotion in accordance with the needs of the animal.

Anatomic Systems. — All the organs of the body which have
certain pecuHarities of structure in common are classified by anato-
mists into systems — e. g., the bones, collectively, constitute the bony
or osseous system; the muscles, the nerves, the skin, constitute,
respectively, the muscle, the nerve, and the tegumentary systems.

Physiologic Apparatus. — More important from a physiologic
point of view than a classification of organs based on similarities of
structure is the natural association of two or more organs acting
together for the accomplishment of some definite object, and to
which the term physiologic apparatus has been apphed. While in
the community of organs which together constitute the animal body
each one performs some definite function, and the harmonious co-
operation of all is necessary to the life of the individual, everywhere
it is found that two or more organs, though performing totally dis-
tinct functions, are cooperating for the accomplishment of some
larger or compound function in which their individual functions are
blended — e. g., the mouth, stomach, and intestines, with the glands
connected with them, constitute the digestive apparatus, the object
or function of which is the complete digestion of the food. The
capillary blood-vessels and lymphatic vessels of the body, and espe-
cially those in relation to the villi of the small intestine, constitute
the absorptive apparatus, the function of which is the introduction
of new material into the blood. The heart and blood-vessels con-
stitute the circulatory apparatus, the function of which is the dis-
tribution of blood to all portions of the body. The lungs and trachea,

22 TEXT-BOOK OF PHYSIOLOGY.

together with the diaphragm and the walls of the chest, constitute
the respiratory apparatus, the function of w^hich is the introduction
of oxygen into the blood and the elimination from it of carbon dioxid
and other injurious products. The kidneys, the ureters, and the
bladder constitute the urinary apparatus. The skin, with its sweat-
glands, constitutes the perspiratory apparatus, the functions of both
being the excretion of waste products from the body. The liver,
the pancreas, the mammary glands, as well as other glands, each
form a secretory apparatus which elaborates some specific material
necessary to the nutrition of the individual. The functions of these
different physiologic apparatus — e. g., digestion, absorption of food,
elaboration of blood, circulation of blood, respiration, production
of heat, secretion, and excretion — are classified as nutritive junctions,
and have for their final object the preservation of the individual.

The nerves and muscles constitute the nervo-muscular apparatus,
the function of which is the production of motion. The eye, the
ear, the nose, the tongue, and the skin, with their related structures,
constitute, respectively, the visual, auditory, olfactory, gustatory, and
tactile apparatus, the function of which, as a whole, is the reception
of impressions and the transmission of nerve impulses to the brain,
where they give rise to visual, auditory, olfactory, gustatory, and
tactile sensations.

The brain, in association with the sense organs, forms an appa-
ratus related to mental processes. The larynx and its accessory
organs — the lungs, trachea, respiratory muscles, the mouth and
resonant cavities of the face — form the vocal and articulating appa-
ratus, by means of which voice and articulate speech are produced.
The functions exhibited by the apparatus just mentioned — viz.,
motion, sensation, language, mental and moral manifestations — are
classified as functions of relation, as they serve to bring the individual
into conscious relationship with the external world.

The ovaries and the testes are the essential reproductive organs,
the former producing the germ-cell, the latter the sperm element.
Together with their related structures, — the fallopian tubes, uterus,
and vagina in the female, and the urogenital canal in the male, —
they constitute the reproductive apparatus characteristic of the two
sexes. Their cooperation results in the union of the germ-cell and
sperm element and the consequent development of a new being.
The function of reproduction serves to perpetuate the species to
which the individual belongs.

The animal body is therefore not a homogeneous organism, but
one composed of a large number of widely dissimilar but related
organs. As all vertebrate animals have the same general plan of
organization, there is a marked similarity both in form and struc-
ture among corresponding parts of different animals. Hence it is

INTRODUCTION. . 23

that in the study of human anatomy a knowledge of the form, con-
struction, and arrangement of the organs in different types of animal
life is essential to its correct interpretation ; it follows also that in the
investigation and comprehension of the complex problems of human
physiology a knowledge of the junctions of the organs as they manifest
themselves in the different types of animal life is indispensable.
As many of the functions of the human body are not only com])lex,
but the organs exhibiting them are practically inaccessible to in-
vestigation, we must supplement our knowledge and judge of their
functions by analogy, by attributing to them, within certain hmits,
the functions revealed by experimentation upon the corresponding
organs of lower animals. This experimental knowledge, corrected
by a study of the chnical phenomena of disease and the results of
post-mortem investigations, forms the basis of modern human physi-
ology.

CHAPTER 11.

CHEMIC COMPOSITION OF THE HUMAN BODY.

Since it has been demonstrated that every exhibition of functional
activity is associated with changes of structure, it has been apparent
that a knowledge of the chemic composition of the body, not only
when in a state of rest, but to a far greater degree when in a state
of activity, is necessary to a correct understanding of the intimate
nature of physiologic processes. Though the analysis of the dead
body is comparatively easy, the determination of the successive
changes in composition of the hving body is attended with many
difficulties. The living material, the bioplasm, is not only complex
and unstable in composition, but extremely sensitive to all physical
and chemic influences. The methods, therefore, which are employed
for analysis destroy its composition and vitality, and the products
which are obtained are peculiar to dead rather than to living material.

Chemic analysis, therefore, may be directed —

1. To the determination of the composition of the dead body.

2. To the determination of the successive changes in composition

which the hving bioplasm undergoes during functional activity.
. A chemic analysis of the dead body, with a view to disclosing
the substances of which it is composed, their properties, their intimate
structure, their relationship to one another, constitutes what might
be termed chemic anatomy. An investigation of the living ma-
terial and of the successive changes it undergoes in the performance
of its functions constitutes what has been termed chemic physi-
ology or physiologic chemistry.

By chemic analysis the animal body can be reduced to a number
of liquid and solid compounds which belong to both the inorganic
and organic worlds. These compounds, resulting from a proximate
analysis, have been termed proximate principles. Tha^ they may
merit this term, however, they must be obtained in the form under
which they exist in the living condition. The organic compounds
consist of representatives of the carbohydrate, fatty, and proteid
groups of organic bodies; the inorganic compounds consist of water,
various acids, and inorganic salts.

The compounds or proximate principles thus obtained can be
further resolved by an ultimate analysis into a small number of
chemic elements which are identical with elements found in many
other organic as well as inorganic compounds. The different chemic

24

CHEMIC COMPOSITION OF THE HUMAN BODY. 25

elements which are thus obtained, and the percentages in which they
exist in the body, are as follows — viz., oxygen, 72 per cent.; hydrogen,
9.10; nitrogen, 2.5; carbon, 13.50; phosphorus, 1.15; calcium, 1.30;
sulphur, 0.147; sodium, o.io; potassium, 0.026; chlorin, 0.085;
fluorin, iron, silicon, magnesium, in small and variable amounts.

THE CARBOHYDRATES.

The carbohydrates constitute a group of organic bodies, con-
sisting mainly of starches and sugars, having their origin for the
most part in the vegetable world. In many respects they are closely
related, and by appropriate means are readily converted into one
another. In composition they consist of the elements carbon,
hydrogen, and oxygen. As their name implies, the hydrogen and
oxygen are present in the majority of these compounds in the pro-
portion to form water, or as 2 : i. The molecule of the carbo-
hydrates just mentioned consists of either six atoms of carbon or a
multiple of six; in the latter case the quantity of hydrogen and
oxygen taken up by the carbon is increased, though the ratio remains
unchanged.

The carbohydrates may be divided into three groups — viz.: (i)
amylases, including starch, dextrin, glycogen, and cellulose; (2)
dextroses, including dextrose, levulose, galactose; (3) saccharoses,
including saccharose, lactose, and maltose. According to the number
of carbon atoms entering into the second group (six), they are fre-
quently termed monosaccharids; those of the third group, disaccharids
— twice six; those of the first group, polysaccharids — multiples of six.

Though but few of the members of the carbohydrate group are
constituents of the human body, yet on account of their importance
as foods, and their relation to one another, a few of their chemic
features will be stated in this connection.

I. AMYLOSES, (CeHio05)n.

Starch is widely distributed in the vegetable world, being abundant
in the seeds of the cereals, leguminous plants, and in the tubers
and roots of many vegetables. It occurs in the form of microscopic
granules, which vary in size, shape, and appearance, according to
the plant from which they are obtained. Each granule presents
a nucleus, or hilum, around which is arranged a series of eccentric
rings, alternately hght and dark. The granule consists of an envelope
and stroma of cellulose, containing in its meshes the true starch
material — graniilose. Starch is insoluble in cold water and alcohol.
When heated with water up to 70° C, the granules swell, rupture,
and Hberate the granulose, which forms an apparent solution; if
present in sufficient quantity, it forms a gelatinous mass termed

26 TEXT-BOOK OF PHYSIOLOGY.

starch paste. On the addition of iodin, starch strikes a characteristic
deep bhie color; the compound formed — iodid of starch — is weak,
the color disappearing on heating, but reappearing on cooling.

Boihng starch with dilute sulphuric acid (twenty-five per cent.)
converts it into dextrose. In the presence of vegetable diastase or
animal ferments, starch is converted into maltose and dextrose, two
forms of sugar.

Dextrin is a substance formed as an intermediate product in
the transformation of starch into sugar. There are at least two
principal varieties — erythrodextrin, which strikes a red color with
iodin, and achroodextrin, which is without color when treated with
this reagent. In the pure state dextrin is a yellow-white powder,
soluble in water. In the presence of vegetable ferments erythro-
dextrin is converted into maltose.

Glycogen is a constituent of the animal liver, and, to a slight
extent, of muscles and of tissues generally. In the tissues of the
embryo it is especially abundant. When obtained in a pure state
it is an amorphous, white powder. It is soluble in water, forming
an opalescent solution. With iodin it strikes a port-wine color. In
some respects it resembles starch, in others dextrin. Like vegetable
starch, glycogen or animal starch can be converted by dilute acids
and ferments into sugar (dextrose).

Cellulose is the basic material of the more or less solid framework
of plants. It is soluble in ammoniacal solution of cupric oxid, from
which it can be precipitated by acids. It is an amorphous powder;
dilute acids can convert it into dextrose.

2. DEXTROSES, CeHijOe-

Dextrose, glucose, or grape-sugar is found in grapes, most
sweet fruits, and honey, and as a normal constituent of liver, blood,
muscles, and other animal tissues. In the disease diabetes mellitus
it is found also in the urine.

When obtained from any source, it is soluble in water and in hot
alcohol, from which it crystalhzes in six-sided tables or prisms. As
usually met with, it is in the form of irregular, warty masses. It is
sweet to the taste. When examined with the polariscope, dextrose
turns the plane of polarized hght to the right. It is therefore termed
dextro-rotatory. It has for a long time been known that when sugar,
cupric hydroxid, and an alkali — e. g. , sodium or potassium — are
present in solution, the sugar will abstract from the cupric hydroxid
a portion of its oxygen, thus reducing it to a lower stage of oxidation
giving rise to cuprous oxid. Sugar has a similar action on both
silver and bismuth. On this property of sugar a standard solution
of cupric hydroxid was suggested by Fehhng which may be employed
for both qualitative and quantitative tests for the presence of sugar
in solution.

CHEMIC COMPOSITION OF THE HUMAN BODY. 27

FeJiling's Test Solution. — This is a solution of cupric hydroxid
made alkaline by an excess of sodium or potassium hydroxid with
the addition of sodium and potassium tartrate. It is made by
dissolving cupric sulphate 34.64 grams, potassium hydroxid 125
grams, sodium and potassium tartrate 173 grams, in distilled water
sufficient to make one liter.

The reaction is expressed by the following ecjuation:

CuSO^ + 2KOH = Cu(OH), + KoSO^.

The object of the sodium and potassium tartrate is to hold the
cupric hydroxid in solution.

For quahtative analysis it is only necessary to boil a few cubic
centimeters of this solution in a test-tube; then add the suspected
solution and again heat to the boihng-point. If sugar be present,
the cupric hydroxid is reduced to the condition of a cuprous oxid,
W'hich shows itself as a red or orange-yellow precipitate. The color
of the precipitate depends on the relative excess of either copper or
sugar, being red with the former, orange or yellow with the latter.
The dehcacy of this test is shown by the fact that a few minims of
this solution will detect in i c.c. of water the ^ oi ?i milligram of
sugar.

For quantitative analysis, 10 c.c. of Fehling's solution, diluted
with 40 c.c. of water, are heated in a porcelain capsule, to which
the suspected solution is cautiously added from a buret until the blue
color entirely disappears. The strength of this solution is such that
I c.c. is decolorized by 5 milligrams of sugar (dextrose), from which
the percentage of sugar in any solution can be determined.

All the sugars, with the exception of chemically pure saccharose,
may be tested for with this solution.

The Fermentation Test. — All the sugars with the exception of
lactose undergo reduction to simpler compounds, mainly alcohol and
carbon dioxid, under the action of the yeast plant, Saccliaroinyces
cerrcisice. The change with dextrose is expressed in the following
equation :

CgHijOg = aCjHsO + 2CO.,.
Dextrose = Alcohol -i- Carbon Dioxid.

About 95 per cent, of the dextrose is so changed, the remaining
5 per cent, yielding secondary products — succinic acid, glycerin, etc.
As a means of testing any solution for the presence of sugar this
method may be adopted. It is generally very satisfactory. From
the quantity of carbon dioxid and alcohol thus produced the quantity
of sugar in the solution may be determined.

Levulose, or fruit-sugar, is found in association with dextrose
as a constituent of many fruits. It is sweeter than dextrose and
more soluble in both water and dilute alcohol. From alcoholic

28 TEXT-BOOK OF PHYSIOLOGY.

solutions it crystallizes in fine, silky needles, though it usually occurs
in the form of a syrup.

Levulose is distinguished from dextrose by its property of turning
the plane of polarized light to the left ; the extent to which it does so,
however, varies with the temperature and concentration of the
solution.

Under the influence of the yeast plant it slowly undergoes fer-
mentation, yielding the same products as dextrose. It also has a
reducing action on cupric hydroxid.

Galactose is obtained by boiling milk-sugar (lactose) with dilute
sulphuric acid. In many chemic relations it resembles dextrose.
It is less soluble in water, however, crystallizes more easily, and has
a greater dextro-rotatory power. It also undergoes fermentation
with the yeast plant.

3. SACCHAROSES, CijHj^On.

Saccharose, or cane-sugar, is widely distributed throughout
the vegetable world, but is especially abundant in sugar-cane, sor-
ghum cane, sugar-beet, Indian corn, etc. It crystallizes in large
monoclinic prisms. It is soluble in water and in dilute alcohol.
Saccharose has no reducing power on cupric hydroxid, and hence its
presence can not be detected by Fehhng's solution. It is dextro-
rotatory. Boiled with dilute mineral, as well as with organic acids,
saccharose combines with water and undergoes a change in virtue of
which it rotates the plane of polarized light to the left, and hence the
product was termed invert sugar. This latter has been shown to be a
mixture of equal quantities of levulose and dextrose. This inversion
of saccharose through hydration and decomposition is expressed in
the following equation :

C12H22O11 4- HjO = CeHijOg -I- CeHjjOe
Saccharose -f Water = Levulose 4- Dextrose

Invert Sugar.

Saccharose is not directly fermentable by yeast, but through the
specific action of a ferment, invertin or invertase, secreted by the
yeast plant, or the inverting ferment of the small intestine, it under-
goes inversion, as previously stated, after which it is readily fermented,
yielding alcohol and carbon dioxid.

Lactose is the form of sugar found exclusively in the milk of the
mammalia, from which it can be obtained in the form of hard,
white, rhombic prisms united with one molecule of water. It is
soluble in water, insoluble in alcohol and ether. It is dextro-rotatory.
It reduces cupric hydroxid, but to a less extent than dextrose. Dilute
acids decompose it into equal quantities of dextrose and galactose.
Lactose is not fermentable with yeast, but in the presence of the

CHEMIC COMPOSITION OF THE HUMAN BODY. 29

lactic acid bacillus it is decomposed into lactic acid, and finally into
butyric acid, as expressed in the following equation:

CijH^On + H3O = 4C3He03

Lactose + \\ atcr = Lactic Acid.

2C3H6O3 = C.HsO, + 2CO2 + 2H2
Lactic Acid = Butyric Acid -r Carbon + Free

Dioxid Hydrogen.

Maltose is a transformation product of starch, and arises when-
ever the latter is acted on by malt extract or the diastatic ferments
in saliva and pancreatic juice. The change is expressed by the fol-
lowing equation:

2C6H10O5 + H,0 = C,2H,,Oii
Starch. Water. Maltose.

Maltose crystalHzes in the form of white needles, which are
soluble in water and in dilute alcohol. It is dextro-rotatory. In
the presence of ferments and dilute acids maltose undergoes hydra-
tion and decomposition, giving rise to two molecules of dextrose.
It has a reducing action on cupric hydroxid. Fermentation is readily
caused by yeast, but whether directly or indirectly by inversion is
somewhat uncertain.

Osazones. — All the sugars which possess the power of reducing
cupric hydroxid are capable of combining with phenyl-hydrazin,
with the formation of compounds termed osazones. The osazones
so formed are crystalline in structure, but have different melting-
points, varying degrees of solubihty and optic properties, all of
which serve to detect the various sugars and to distinguish one from
the other. Of the different osazones, phenyl-glucosazone is the
most characteristic, and occurs in the form of long, yellow needles.
It may be obtained from dextrose by the following method: To 50
c.c. of a dextrose solution add 2 gm. of phenyl-hydrazin and 2 gm.
of sodium acetate, and boil for an hour. On coohng, the osazone
crystalhzes in the form of long, yellow needles.

THE FATS.

The fats constitute a group of organic bodies found in the tissues
of both vegetables and animals. In the vegetable world they are
largely found in fruits, seeds, and nuts, where they probably originate
from a transformation of the carbohydrates. In the animal body
the fats are found largely in the subcutaneous tissue, in the marrow
of bones, in and around various internal organs and in milk. In
these situations fat is contained in small, round or polygon-shaped
vesicles, which are united by areolar tissue and surrounded by blood-
vessels. At the temperature of the body the fat is liquid, but aftei
death it soon solidifies from the loss of heat.

30 TEXT-BOOK OF PHYSIOLOGY.

The fats are compounds consisting of carbon, hydrogen, and
oxygen, of which the first is the chief ingredient, forming by weight
about 75 per cent., while the last is present only in small quantity.
The fat found in animals is a mixture, in varying proportions
in different animals, of three neutral fats — stearin, palmitin, and
olein. Each fat is a derivative of glycerin and the particular acid
indicated by its name — e. g., stearic acid, in the case of stearin, etc.
The reaction which takes place in the combination of glycerin and
the acid is expressed in the following equation:

CaHsCHO), + (HC,8H,502)3 = C,U,(C,,U,,0,), + 3H2O.
Glycerin. Stearic Acid. Stearin. Water.

Hence, strictly speaking, the fats are compound ethers, in which
the hydrogen of the organic acid is replaced by the trivalent radicle,
tritenyl, C3H5.

Stearin, C3H-('CjgH3502)3, is the chief constituent of the more
solid fats. It is soHd at ordinary temperatures, melting at 55° C,
then solidifying again as the temperature rises, until at 71° C. it melts
permanently. It crystallizes in square tables.

Palmitin, CJi-(C^^lls^02)s, is a semifluid fat, soHd at 45° C.
and melting at 62° C. It crystalhzes in fine needles, and is soluble
in ether.

Olein, C3H5('CjgH3302)3, is a colorless, transparent fluid, liquid at
ordinary temperatures, only solidifying at 0° C. It possesses marked
solvent powers, and holds stearin and palmitin in solution at the
temperature of the body.

Saponification. — When subjected to the action of superheated
steam, a neutral fat is saponified — /. e., decomposed into glycerin and
the particular acid indicated by the name of the fat used: e. g., stearic,
palmitic, or oleic. The reaction is expressed as follows:

C3H5(C,8H3302)3 + SH^O = C3H5(HO)3 + 3(C,8H3402)

Olein. Water. Glycerin. Oleic Acid.

The fatty acids thus obtained are characterized by certain chemic
features, as follows:

Stearic acid is a firm, white solid, fusible at 69° C. It is soluble
in ether and alcohol, but not in water.

Palmitic acid occurs in the form of white, glistening scales or
needles, melting at 62° C.

Oleic acid is a clear, colorless liquid, tasteless and odorless when
pure. It crystallizes in white needles at 0° C.

If this saponification takes place in the presence of an alkaH, —
e. g., potassium hydroxid or sodium hydroxid, — the acid produced
combines at once with the alkali to form a salt known as a soap, while
the glycerin remains in solution. The reaction is as follows:

3KHO + (C,8H3,02)3 = 3(KC,8H330j) + C3H5(HO)3
Potassium. Oleic Acid Potassium Oleate. Glycerin.

CHEMIC COMPOSITION OF THE HUMAN BODY. 31

All soaps are, therefore, salts formed by the union of alkalies and
fatty acids. The sodium soaps are generally hard, while the potas-
sium soaps are soft. Those made with stearin and palmitin are harder
than those made with olein. If the soap is composed of lead, zinc,
copper, etc., it is insoluble in water.

Emulsification. — When a neutral oil is vigorously shaken with
water or other fluid, it is broken up into minute globules that are
more or less permanently suspended; the permanency depending
on the nature of the hquid. The most permanent emulsions are
those made with soap solutions. The process of emulsification and
the part played by soap can be readily observed by placing on a
few cubic centimeters of a solution of sodium carbonate (0.25 per
cent.) a small quantity of a perfectly neutral oil to which has been
added 2 or 3 per cent, of a fatty acid. The combination of the acid
and the alkali at once forms a soap. The energy set free by this
combination rapidly divides up the oil into extremely minute globules.
A spontaneous emulsion is thus formed.

In addition to the ordinary fats, there are present in different
tissues several compounds which, though usually regarded as fats,
nevertheless differ materially from them in composition, containing,
as they do, both nitrogen and phosphorus. These nitrogenized or
phosphorized fats are as follows:

Lecithin, C^^HgpN.POg, is found in blood, lymph, red and
white corpuscles, nerve tissue, yolk of eggs, etc. ' When pure, it
presents itself generally under the form of a white, crystalline powder,
though sometimes as a white, waxy mass. Lecithin is easily decom-
posed, yielding, with various reagents, glycero-phosphoric acid, cholin
and stearic acid.

Protagon, C^ggHg^gX-POgg, is found most abundantly in the
brain tissue, especially in the white portion. It crystalhzes from
warm alcohohc solutions, on coohng, in the form of white needleSj
generally arranged in groups. It melts at 200° C, and forms a
syrupy liquid.

Cerebrin, C1-H33N.O3, is found largely in the brain, in nerves,
and in pus-corpuscles. It is a soft, white, amorphous powder, in-
soluble in water, but swelling up like starch in boiling water. When
boiled with dilute acids, it is decomposed, yielding a fermentable
dextro-rotatory sugar, identical with galactose. Cerebrin may,
therefore, be regarded as a glucosid.

THE PROTEIDS.

The proteids constitute a group of organic bodies which are
found in both vegetable and animal tissues. Though present in
all animal tissues, they are especially abundant in muscles and

32 TEXT-BOOK OF PHYSIOLOGY.

bones, where they constitute 20 per cent, and 30 per cent, respectively.
Though genetically related, and possessing many features in common,
the different members of the proteid group are distinguished by
characteristic physical and chemic properties which serve not only
for their identification, but for their classification into more or less
well-defined groups as follows:

1. NATIVE PROTEIDS.

The members of this group are soluble in water, in dilute saline
solutions, and in saturated solutions of sodium chlorid and mag-
nesium sulphate. They are coagulated by heat, and when dried
form an amber-colored mass.

(a) Serum-albumin is found in blood, lymph, chyle, tissue
fluids, and milk. It is obtained readily by precipitation from
blood-serum, after the other proteids have been removed, on
the addition of ammonium sulphate. When freed from saline
constituents, it presents itself as a pale, amorphous substance,
soluble in water and in strong nitric acid. It is coagulated
at a temperature of 73° C, as well as by various acids — e. g.,
citric, picric, nitric, etc. It has a rotatory power of — 62.6°.

(b) Egg-albumin. — Though not a constituent of the human
body, egg-albumin resembles the foregoing in many respects.
When obtained in the solid form from the white of the egg,
it is a yellow mass without taste or odor. Though similar
to serum- albumin, it differs from it in being precipitated by
ether, in coagulating at 54° C, and in having a lower rotatory
power, —35.5°.

2. GLOBULINS.

The members of this group are insoluble in water and in saturated
solutions of sodium chlorid and magnesium sulphate and ammonium
sulphate. They are soluble, however, in dilute saline solutions —
e. g., sodium chlorid (i per cent.), potassium chlorid, ammonium
chlorid, etc. They are coagulated by heat.

(a) Serum-globulin or Paraglobulin. — This proteid, as its name

implies, is found in blood-serum, though it is present in other
animal fluids. When precipitated by magnesium sulphate
or carbon dioxid, it presents itself as a flocculent substance,
insoluble in water, soluble in dilute acids and alkahes, and
coagulating at 75° C.

(b) Fibrinogen. — This proteid is found in blood-plasma in asso-

ciation with serum-globuHn and serum-albumin. It is also
present in lymph-tissue fluids and in pathologic transudates.
It can be obtained from blood-plasma which has been pre-
viously treated with magnesium sulphate on the addition of

CHEMIC COMPOSITION OF THE HUMAN BODY. 33

a saturated solution of sodium chlorid. It is soluble in
dilute acids and alkalits, and coagulates at 56° C.

(c) Myosinogen. — This proteid is a constituent of the protoplasm

of the muscle-fibers. During the living condition it is liquid,
but after death it readily undergoes decomposition into an
insoluble portion known as myosin and a soluble albumin.
It is soluble in dilute hydrochloric acid and dilute alkalies.
It coagulates at 56° C.

(d) Globin. — This is a product of the spontaneous decomposition

of the coloring-matter of the blood, — hemoglobin, — and arises
when the latter is exposed to the air.

(e) Crystallin or Globulin. — This is obtained by passing a stream

of CO2 through a watery extract of the crystalline lens.

3. DERIVED ALBUMINS OR ALBUMINATES.

The proteids of this group are derived from both native albumins
and globuhns by the gradual action of dilute acids and alkalies, and
may be regarded as compounds of a proteid with an acid or an
alkali.

(a) Acid-albumin. — This is formed when a native albumin is
digested with dilute hydrochloric acid (0.2 per cent.) or dilute
sulphuric acid for some minutes. It is precipitated by neu-
tralization with sodium hydroxid (o.i per cent, solution).
After the precipitate is washed, it is found to be insoluble
in distilled water and in neutral saline solutions. In acid
solutions it is not coagulated by heat.

(b) Alkali-albumin. — This is formed when a native albumin is

treated with a dilute alkali — e. g., o.i per cent, of sodium
hydroxid — for five or ten minutes. On careful neutralization
with dilute hydrochloric acid, it is precipitated. It is also
insoluble in distilled water and in saline solutions; it is not
coagulable by heat.

(c) Caseinogen. — This is the principal proteid of milk, in which

it exists in association with an alkali, and hence was formerly
regarded as a native alkali-albumin. It is precipitated by
acetic acid and by magnesium sulphate. It is coagulated by
rennet — that is, separated into an insoluble proteid, casein or
tyrein, and a soluble albumin. Calcium phosphate seems to
be the natural alkali necessary to this process, for if it be
removed by dialysis, or precipitated by the addition of
potassium oxalate, coagulation does not take place.

4. COAGULATED PROTEIDS.

Although these proteids are not found as constituents of the
animal organism, they possess much interest on account of their
3

34 TEXT-BOOK OF PHYSIOLOGY.

relation to prepared foods and to the digestive process. They are
produced when solutions of egg-albumin, serum-albumin, or globuhns
are subjected to a temperature of ioo° C. or to the prolonged action
of alcohol. They are insoluble in water, in dilute acids, and in
neutral sahne solutions. In this same group may be included also
those coagulated proteids which are produced by the action of animal
ferments on soluble proteids — e. g., fibrin, myosin, casein.

Fibrin. — Fibrin is derived from a soluble proteid — fibrinogen —
by the action of a special ferment. It is not present under
normal circumstances in the circulating blood, but makes its
appearance after the blood is withdrawn from the vessels
and at the time of coagulation. It can also be obtained by
whipping the blood with a bundle of twigs, on which it accu-
mulates. When freed from blood by washing under water,
it is seen to consist of bundles of white elastic fibers or threads.
It is insoluble in water, in alcohol, and ether. In dilute acids
it swells, becomes transparent, and finally is converted into
acid-albumin. In dilute alkalies a similar change takes place,
but the resulting product is an alkali-albumin. Fibrin pos-
sesses the property of decomposing hydrogen dioxid, H2O2
— i. e., liberating oxygen, which accumulates in the form of
bubbles on the fibrin. On incineration fibrin yields an ash
which contains calcium phosphate and magnesium phosphate.

5. PROTEOSES AND PEPTONES.

During the progress of the digestive process, as it takes place in
the stomach and intestines, there is produced by the action of the
gastric and pancreatic juices, out of the proteids of the food, a series
of new proteids, known as proteoses and peptones. The chemic
properties of these substances will be considered in connection with
the process of digestion.

6. ALBUMINOIDS.

The albuminoids constitute a group of substances similar to the
proteids in many respects, though dift'ering from them in others.
When obtained from the tissues, in which they form an organic
basis, they are found to be amorphous, colloid, and when decom-
posed yield products similar to those of the true proteids. The
principal members of this group are as follows:

(a) Mucin. — This is the viscid, tenacious constituent of mucus
secreted by the epithelial cells of mucous membranes. It is
also present in the intercellular substance of the connective
tissue. It is readily [precipitated by acetic acid.

(b) Collagen, Ossein. — These are two closely allied, if not identical,

substances, found respectively in the white fibrous connec-

CHEMIC COMPOSITION OF THE HUMAN BODY. 35

tivc tissue and in bone. When the tendons of muscles, the
hgamcnts, or decalcified bone are boiled for several hours,
the collagen and ossein are converted into soluble gelatin,
which, when the solution cools, becomes solid.

(c) Chondrigen.^This is supposed to be the organic basis of
the more permanent cartilages. When they are boiled, they
yield a substance which gelatinizes on cooling, and to which
the name chondrin has been given.

((/) Elastin is the name given to the substance composing the
fibers of the yellow, elastic connective tissue.

(e) Keratin is the substance found in all horny and epidermic
tissues, such as hairs, nails, scales, etc. It differs from most
proteids in containing a high percentage of sulphur.

(/) Nuclein. — This is an amorphous substance obtained from the
nuclei of both animal and vegetable cells. The chief con-
stituent appears to be nucleic acid. Chemic analysis shows
that nuclein contains not less than three per cent, of phos-
phorus. On boiling with strong alkalies, nuclein is partially
decomposed, yielding a proteid resembling globulin and phos-
phoric acid. A nucleo-proteid is a compound of nuclein and
a proteid.
The average percentage composition of several proteids is shown
in the following analyses:

c. H. X. o. s.

Egg-albumin, 52.9 7.2 15.6 23.9 0.4 (Wiirtz).

Serum-albumin, 53.0 6.8 16.0 22.29 i-77 (Hammersten).

Casein, ^^.^ 7.07 15.91 22.03 0.82 (Chittenden and Painter).

Myosin, 52-82 7. 11 16.77 21.90 1.27 (Chittenden and Cummins).

The molecular composition of the proteids is not definitely known,
and the formulae which have been suggested are therefore only
approximative. Leow assigns to albumin the formula C^^^iu^is"
O22S, while Schiitzenberger raises the numbers to Cj^oHjgjNgjO-jSg,
either of which shows that the proteid molecule is extremely complex.
As a class, the proteids are characterized by the following properties :

1. Indiffusibility. — None of the proteids normally assumes the

crystalline form, and hence they are not capable of dift'using
through parchment or an animal membrane. Peptone, a product
of the digestion of proteids, is an exception as regards its diffu-
sibility. As met with in the body, all proteids are amorphous,
but vary in consistence from the liquid to the solid state. The
colloid character of the proteids permits of their separation and
purification from crystalloid diffusible compounds by the process
of dialysis.

2. Solubility. — Some of the proteids are soluble in water, others in

solutions of the neutral salts of varying degrees of concentration.

36 TEXT-BOOK OF PHYSIOLOGY.

in strong acids and alkalies. All are insoluble in alcohol and
ether.

3. Coagulability. — Under the influence of heat and various acids

and animal ferments, the proteids readily pass from the soluble
liquid state to the insoluble sohd state, attended by a permanent
alteration in their chemic composition. To this change the
term coagulation has been given. The various proteids not
only coagulate at different temperatures, but with different
chemic reagents — distinctive features which permit not only of
their detection, but separation. Proteids are capable of pre-
cipitation without losing their solubility by ammonium sulphate,
sodium chlorid, and magnesium sulphate.

4. Fermentability. — In the presence of specific microorganisms —

bacteria — the proteids, owing to their complexity and instabihty,
are prone to undergo disintegration and reduction to simpler
compounds. This decomposition or putrefaction occurs most
readily when the conditions most favorable to the growth of
bacteria are present — viz., a temperature varying from 25° C.
to 40° C, moisture, and oxygen. The intermediate as well as
the terminal products of the decomposition of the proteids are
numerous, and vary with the composition of the proteid and
the specific physiologic action of the bacteria. Among the
intermediate products is a series of alkaloid bodies, some of
which possess marked toxic properties, known as ptomains or
toxins. The toxic symptoms which frequently follow the inges-
tion of foods in various stages of putrefaction are to be attributed
to these compounds. The terminal products are represented
by hydrogen sulphid, ammonia, carbon dioxid, fats, phosphates,
nitrates, etc.
Color Tests for Proteids. — When proteids are present in solu-
tion, they may be detected by the following color reactions — viz. :

1. Xanthoproteic. The solution is boiled with nitric acid for several

minutes, when the proteid assumes a light yellow color. After
the solution has cooled, the addition of ammonia changes the
color to an orange or amber-red.

2. The rose-red reaction. The solution is boiled with acid nitrate

of mercury (Millon's reagent) for a few minutes, when the
coagulated proteid turns a purple-red color.

3. The blue- violet reaction. A few drops of copper sulphate solution

arc first added to the proteid solution, and then an excess of
sodium hydroxid. A blue- violet color is produced, which deepens
somewhat on heating, but no further change ensues.

CHEMIC COMPOSITION OF THE HUMAN BODY. 37

INORGANIC CONSTITUENTS.

The inorganic compounds and mineral constilucnls obtained
from the soHds and fluids of the body are very numerous, and, in
some instances, quite abundant. Though many of the compounds
thus obtained are undoubtedly derivatives of the tissues and necessary
to their physical and physiologic activity, others, in all probability,
are decomposition products, or transitory constituents introduced
with the food. Of the inorganic compounds, the following are the
most important:

WATER.

Water is the most important of the inorganic constituents, as it
is indispensable to hfe. It is present in all the tissues and fluids
without exception, varying from 99 per cent, in the sahva to 80
per cent, in the blood, 75 per cent, in the muscles to 2 per cent, in
the enamel of the teeth. The total quantity contained in a body
weighing 75 kilograms (165 pounds) is 52.5 kilograms (115 pounds).
Much of the water exists in a free condition, and forms the chief part
of the fluids, giving to them their characteristic degree of fluidity.
Possessing the capability of holding in solution a large number of
inorganic as well as some organic compounds, and being at the same
time diffusible, it renders an interchange of materials between all
portions of the body possible. It aids in the absorption of new
material into the blood and tissues, and at the same time it transfers
waste products from the tissues to the blood, from which they are
finally ehminated, along with the water in which they are dissolved.
A portion of the water is chemically combined with other tissue con-
stituents and gives to the tissues their characteristic physical properties.
The consistency, elasticity, and pliability are, to a large extent, con-
ditioned by the amount of water they contain. The total quantity
of water ehminated by the kidneys, lungs, and skin amounts to about
3 kilograms {6\ pounds).

CALCIUM COMPOUNDS.

Calcium phosphate, Ca3(POj2, has a very extensive distribu-
tion throughout the body. It exists largely in the bones, teeth, and
to a slight extent in cartilage, blood, and other tissues. Milk con-
tains 0.27 per cent. The soKdity of the bones and teeth is almost
entirely due to the presence of this salt, and is, therefore, to be
regarded as necessary to their structure. It enters into chemic union
with the organic matter, as shown by the fact that it can not be
separated from it except by chemic means, such as hydrochloric
acid. Though insoluble in water, it is held in solution in the blood
and milk by the proteid constituents, and in the urine bv the acid

38 TEXT-BOOK OF PHYSIOLOGY.

phosphate of soda. The total quantity of calcium phosphate which
enters into the formation of the body has been estimated at 2.5
kilograms. The amount ehminated daily from the body has been
estimated at 0.4 gm., a fact which indicates that nutritive changes
do not take place with much rapidity in those tissues in which it is
contained.

Calcium carbonate, CaCOg, is present in practically the same
situations in the body as the phosphate, and plays essentially the
same role. It is, however, found in the crystalline form, aggregated
in small masses in the internal ear, forming the otoliths, or ear stones.
Though insoluble, it is held in solution by the carbonic acid diffused
through the fluids.

Calcium fluorid, CaF2, is found in bones and teeth.

SODIUM COMPOUNDS.

Sodium chlorid, NaCl, is present in all the tissues and fluids
of the body, but especially in the blood, 0.6 per cent., lymph, 0.5,
and pancreatic juice, 0.25 per cent. The entire quantity in the body
has been estimated at about 200 gm. Sodium chlorid is of much
importance in the body, as it determines and regulates to a large
extent the phenomena of diffusion which are there constantly taking
place. This is illustrated by the fact that a solution of albumin
placed in the rectum without the addition of this salt will not be
absorbed. When the salt is added, absorption takes place. The
ingested water is absorbed into the blood largely in consequence of
the percentage of this salt which it contains. The normal percentage
of sodium chlorid in the blood-plasma assists in maintaining the shape
and structure of the red blood-corpuscles by determining the amount
of water entering into their composition. The same is true of other
tissue elements.

Sodium chlorid also influences the general nutritive process, in-
creasing the disintegration of the proteids, as shown by the increased
amount of urea excreted. During its existence in the body it under-
goes chemic transformations or decompositions, yielding its chlorid
to form the potassium chlorid of the blood-corpuscles and muscles
and to form the hydrochloric acid of the gastric juice.

Sodium phosphate, XajHPO^, is found in all solids and fluids
of the body, to which, with but few exceptions, it imparts an alkahne
reaction. This is especially true of blood, lymph, and tissue fluids
generally. It is essential to physiologic action that all tissue elements
should be bathed by an alkahne medium.

Sodium carbonate, Na2C03, is generally found in association
with the preceding salt. As it is an alkahne compound, it also
assists in giving to the blood and lymph their characteristic alkalinity.
In carnivorous animals the sodium phosphate is the more abundant,

CHEMIC COMPOSITION OF THE HUMAN BODY. 39

while in the herbivorous animals the sodium carbonate is the more
abundant.

Sodium sulphate, Xa,SO^, is present in many of the tissues and
fluids, especially in the urine. Though introduced in the food, it is
also, in all probability, formed in the body from the decomposition
and oxid*ation of the proteids.

POTASSroM COMPOUNDS.

Potassium chlorid, KCl, is met with in association with sodium
chlorid in almost all situations in the body. It preponderates, how-
ever, in the tissue elements, especially in the muscle tissue, nerve
tissue, and red corpuscles. The plasma with which these structures
are bathed contains but a very small amount of this salt, but, as
previously stated, a relatively large cjuantity of sodium chlorid.
Though introduced to some extent in the food, it is very likely that
it is also formed through the decomposition of the sodium chlorid.

Potassium phosphate, K,HPO^, is found in association with
sodium phosphate in all the fluids and sohds. As it has similar
chemic properties, its functions are practically the same.

Potassium carbonate, K,C03, is generally found with the pre-
ceding salt.

MAGNESroM COMPOUNDS.

Magnesium phosphate, MggfPO^),, is found in all tissues, in
association with calcium phosphate, though in much smaller quantity.

Magnesium carbonate, ^NlgCOg, occurs only in traces in the
blood.

Both of these compounds have functions similar to the calcium
compounds, and exist, in all probabiHty, under similar conditions.

IRON COMPOUNDS.

Iron is a constituent of the coloring-matter of the blood. Traces,
however, are also found in lymph, bile, gastric juice, and in the
pigment of the eyes, skin, and hair. The amount of iron contained
in a body weighing 75 kilograms is about 3 gm. It exists under
various forms — e. g., ferric oxid, and in combination with organic
compounds.

Chemic analysis thus shows that the chemic elements into which
the compounds may be resolved by an ultimate analysis do not exist
in the body in a free state, but only in combination, and in char-
acteristic proportions, to form compounds whose properties are the
resultant of those of the elements. Of the four principal elements
which make up 97 per cent, of the body, O, H, N are extremely
mobile, elastic, and possessed of great atomic heat. C, H, N are
distinguished for the narrow range of their affinities, and for their

40 TEXT-BOOK OF PHYSIOLOGY.

chemic inertia. C possesses the great atomic cohesion. O is noted
for the number and intensity of its combinations.

As the properties of the compounds formed by the union of
elements must be the resultants of the properties of the elements
themselves, it follows that the ternary compounds, starches, sugars,
and fats must possess more or less inertia, and at the same time
instabihty; while in the more complex proteids, in which sulphur
and phosphorus are frequently combined with the four principal
elements, molecular instabihty attains its maximum. As all the
foregoing compounds possess in varying degrees the properties of
inertia and instability, it follows that living matter must possess
corresponding properties, and the capability of undergoing unceas-
ingly a series of chemic changes, both of composition and decom-
position, in response to the chemic and physical influences by which
it is surrounded, and which underlie all the phenomena of life.

PRINCIPLES OF DISSIMILATION.

In addition to the previously mentioned compounds, — viz.,
carbohydrates, fats, proteids, and inorganic salts, — there is obtained
by chemic analysis from the tissues and fluids of the body:

1. A number of organic acids, such as acetic, lactic, oxalic, butyric,

propionic, etc., in combination with alkaline and earthy bases.

2. Organic compounds, such as alcohol, glycerin, cholesterin.

3. Pigments, such as those found in bile and urine.

4. Crystallizable nitrogenized bodies, such as urea, uric acid, xanthin,

hippuric acid, creatin, creatinin, etc.
While some few of these compounds may possibly be regarded as
necessary to the physiologic integrity of the tissues and fluids, the
majority of them are to be regarded as products of dissimilation of
the tissues and foods in consequence of functional activity, and
represent stages in their reduction to simpler forms previous to being
eliminated from the bodv.

CHAPTER III.
PHYSIOLOGY OF THE CELL.

A microscopic analysis of the tissues sliows that they can be
resolved into simpler elements, termed cells, which may, therefore,
be regarded as the primary units of structure. Though cells vary
considerably in shape, size, and chemic composition in the different
tissues of the adult body, they are, nevertheless, descendants from
typical cells, known as embryonic or undifferentiated cells, examples
of which are the leukocytes of the blood and lymph and the first
offspring of the fertilized ovum. Ascending the hne of embryonic
development, it will be found that every organized body originates
in a single cell — the ovum. As the cell is the elementary unit of all
tissues, the function of each tissue must be referred to the function
of the cell. Hence the cell may be defined as the primary anatomic
and physiologic unit of the organic world, to which every exhibition
of life, whether normal or abnormal, is to be referred.

Structure of Cells. — Though cells vary in shape and size and
internal structure in different portions of the body, a typical cell may
be said to consist mainly of a gelatinous substance forming the body
of the cell, termed protoplasm or bioplasm, in which is embedded a
smaller spheric body, the nucleus. The shape of the adult cell varies
according to the tissue in which it is found; when young and free
to move in a fluid medium, the cell assumes a spheric form, but when
subjected to pressure, may become cylindric, fusiform, polygonal,
or stellate. Cells vary in size within wide limits, ranging from -3 yVo
of an inch, the diameter of a red blood-corpuscle, to ^-ki) of an inch,
the diameter of the large cells in the gray matter of the spinal cord.
(See Fig. 2.)

The cell protoplasm consists of a soft, semifluid, gelatinous
material, varying somewhat in appearance in different tissues.
Though frequently homogeneous, it often exhibits a finely granular
appearance under medium powers of the microscope. Young cells
consist almost entirely of clear protoplasm. Mature cells contain,
according to the tissue in which they are found, material of an en-
tirely different character — e. g., smafl globules of fat, granules of
glycogen, mucigen, pigments, digestive ferments, etc. Under high
powers of the microscope the cell protoplasm is found to be pervaded
by a network of fibers, termed spongioplasm, in the meshes of which
is contained a clearer and more fluent substance, the hyaloplasm.

41

42

TEXT-BOOK OF PHYSIOLOGY.

The relative amount of these two constituents varies in different
cells, the proportion of hyaloplasm being usually greater in young
cells. The arrangement of the fibers forming the spongioplasm also
varies, the fibers having sometimes a radial direction, in others a
concentric disposition, but most frequently being distributed evenly
in all directions. In many cells the outer portion of the cell proto-
plasm undergoes chemic changes and is transformed into a thin,
transparent, homogeneous membrane, — the cell membrane, — which
completely incloses the cell substance. The cell membrane is
permeable to water and watery solutions of various inorganic and
organic substances. It is, however, not an essential part of the cell.

The nucleus is a small vesicular body embedded in the proto-
plasm near the center of the cell. In the resting condition of the cell

Nuclear membrane.

Linin.

Nuclear fluid (matrix). .

Nucleolus. • 4

, Chromatin-cords
(nuclear network).

Nodal enlargements
of the chromatin.

■ ■ Cell membrane.
-- Exoplasm.

~" Microsomes.

— Centrosoma.

- - Spongioplasm.
-- Hyaloplasm.

__ Foreign inclosures.

Fig. 2. — Diagram of a Cell. Microsomes and spongioplasm are only partly drawn.

it consists of a distinct membrane, composed of amphipyrenin, in-
closing the nuclear contents. The latter consists of a homogeneous
amorphous substance, — the nuclear matrix, — in which is embedded
the nuclear network. It can often be seen that a portion of one
side of the nucleus, called the pole, is free from this network. The
main cords of the network are arranged as V-shaped loops about it.
These main cords send out secondary branches or twigs, which,
uniting with one another, complete the network. The nuclear cords
arc composed of granules of chromatin, — so called because of its
affinity for certain staining materials, — held together by an achromatin
substance known as linin. Besides the nuclear network, there are
embedded in the nuclear matrix one or more small bodies composed

PHYSIOLOGY OF THE CELL. 43

of pyrenin, known as nucleoli. At the pole of the nucleus, either
within or just without in the protoplasm, is a small body, the centro-
some, or pole corpuscle.

Chemic Composition of the CeU. — The composition of living
protoplasm is difficult of determination, for the reason that all chemic
and physical methods employed for its analysis destroy its vitahty,
and the products obtained are pecuhar to dead rather than to living
matter. Moreover, as protoplasm is the seat of constructive and
destructive processes, it is not easy to determine whether the products
of analysis are crude food constituents or cleavage or disintegration
products. Nevertheless, chemic investigations have shown that even
in the living condition protoplasm is a highly complex compound—
the resultant of the intimate union of many different substances.
About 75 per cent, of protoplasm consists of water and 25 per cent,
of sohds, of which the more important compounds are various
nucleo-proteids (characterized by their large percentage of phos-
phorus), globulins, traces of lecithin, cholesterin, and frequently fat
and carbohydrates. Inorganic salts, especially the potassium,
sodium, and calcium chlorids and phosphates, are almost invariable
and essential constituents.

MANIFESTATIONS OF CELL LIFE.

Growth, Nutrition. — All cells exhibit the three fundamental
properties of life — viz., growth, nutrition, reproduction. All cells
when newly reproduced are extremely small, but by the absorption
of nutritive material from their surrounding medium, they gradually
grow until they attain their mature size. This is accomplished by
the power which living material possesses of transforming, vitalizing,
and organizing crude nutritive material, through a series of upward
changes, into material similar to itself. To all these changes the
term assimilation, or anaholism, has been given. Some of the
absorbed material, in all probability, never becomes an integral part
of the living bioplasm, but undergoes disruption and oxidation,
giving rise at once to heat and force. Coincident with the assimila-
tive processes, a series of disintegrative processes is constantly taking
place, whereby the living material is reduced, through a series of
downward chemic changes, to simpler compounds, such as water,
carbon dioxid, urea, etc. To all these downward changes the term
dissimilation, or katabolism, has been given. As a result, also, of
these various changes, the protoplasm gives rise to the production
of material of an entirely different character, such as globules of fat,
granules of glycogen, mucigen, digestive ferments, etc. The sum
total of all changes which go on in the cell, both assimilative and
dissimilative, are embraced under the general term nutrition, or

44 TEXT-BOOK OF PHYSIOLOGY.

metabolism. Every cell presents in its nutritive activities an epitome
of the nutritive activities of the body as a whole.

Physiologic Properties of Protoplasm. — All Hving protoplasm
possesses properties which serve to distinguish and characterize it —
viz., irritability, conductivity, and motility.

Irritability, or the power of reacting in a definite manner to some
form of external excitation, whether mechanic, chemic, or electric,
is a fundamental property of all living protoplasm. The character
and extent of the reaction will vary, and will depend both on the
nature of the protoplasm and the character and strength of the
stimulus. If the protoplasm be muscle, the response ^^dll be a con-
traction; if it be gland, the response will be secretion; if it be nerve,
the response will be a sensation or some other form of nerve activity.

Conductivity, or the power of transmitting molecular disturbances
arising at one point to all portions of the irritable material, is also
a characteristic feature of all protoplasm. This power, however, is
best developed in that form of protoplasm found in nerves, which
serves to transmit, with extreme rapidity, molecular disturbances
arising at the peripher}' to the brain, as well as in the reverse direction.
Muscle protoplasm also possesses the same power in a high degree.

Motility, or the power of executing apparently spontaneous
movements, is exhibited by many forms of cell protoplasm. In
addition to the molecular movements which take place in certain
cells, other forms of movement are exhibited, more or less constantly,
by many cells in the animal body — e. g., the wa^^ng of ciha, the
ameboid movements and migrations of white blood-corpuscles, the
acti^^ties of spermatozooids, the projection of pseudopodia, etc.
These movements, arising without any recognizable cause, are fre-
quently spoken of as spontaneous. Strictly speaking, however, all
protoplasmic movement is the resultant of natural causes, the true
nature of which is beyond the reach of present methods of investi-
gation.

Reproduction. — Cells reproduce themselves in the higher ani-
mals in two ways — by direct division and by indirect di\dsion, or
kar}'okinesis. In the former the nucleus becomes constricted, and
divides without any special grouping of the nuclear elements. It is
probable that this occurs only in disintegrating cells, and never in
a physiologic multiplication. In division by karj'okinesis (Fig. 3)
there is a progressive rearranging and definite grouping of the nucleus,
the result of which changes is the division of the centrosoma, the
chromatin, and the rest of the nucleus into two equal portions, which
form the nuclei. Following the division of the nuclei, the proto-
plasm divides. The process may be divided into three phases:
I. Prophase. — The centrosoma, at first small and lying within the
nucleus, increases in size and moves into the protoplasm, where

PHYSIOLOGY OF THE CELL.

45

it lies near the nucleus, surrounded by a clear zone, from \vhich
delicate threads radiate through an area known as the attraction
sphere. The nucleus enlarges and becomes richer in chromatin.
The lateral twigs of the chromatin cords are drawn in, while
the main cords become much contorted. These cords have a
general direction transverse to the long axis of the cell, and
parallel to the plane of future cleavage. They are seen as
V-shaped segments or loops, chromosomes, having their closed,
ends directecl toward a common center, the polar -field, while
the other ends interdigitate on the opposite side of the nucleus

Close Skein
(viewed from
the side).
Polar field.

Loose Skein (viewed
from above — /. e., from

the pole). Mother Stars (viewed from the side).

<'tS»

Polar
radia-
tion.

~ Spindle.

Mother Star (viewed
from above).

Daughter Star.

W'mi,.

Beginning Completed

Division of the Protoplasm.

Fig. 3. — Karyokinetic Figures Observed in the Epithelium of the Oral
Cavity of a S.\lamander. The picture in the upper right-hand corner is from
a section through a dividing egg of Siredon pisciformis. Neither the centrosomes
nor the first stages of the development of the spindle can be seen by this mag-
nification. X 560.

— the anti-pole. The polar field corresponds to the area occu-
pied by the centrosoma. This arrangement is known as the
close skein; but as the process goes on, the chromosomes become
thicker, shorter and less contorted, producing a much looser
arrangement, known as the loose skein. During the formation
of the loose skein, the centrosoma divides into two portions,
which move apart to positions at the opposite ends of the long
axis of the nucleus. At the same time delicate achromatin
fibers make their appearance, arranged in the form of a double

46 TEXT-BOOK OF PHYSIOLOGY.

cone, the apices of which correspond in position to the centro-
soma. This is known as the nuclear spindle. During the
prophase the nuclear membrane and the nucleoH disappear.

2 The Metaphase. — The two centrosomes are at opposite ends of
the long axis of the nucleus, each surrounded by an attraction
sphere, now called the polar radiation. The chromosomes
become yet shorter and thicker, and move toward the equator
of the nucleus, where they he with their closed ends toward the
axis, presenting the appearance, when seen from the poles, of
a star, — the so-called mother star, or monaster. While moving
toward the equator of the nucleus, and often earher, each
chromosome undergoes longitudinal cleavage, the sister loops
remaining together for a time. Upon the completion of the
monaster, one loop of each pair passes to each pole of the nucleus,
guided, and perhaps drawn by the threads of the nuclear spindle.
The separation of the sister segments begins at their apices,
and as the open ends are drawn apart they remain connected
by delicate achromatin filaments drawn out from the chromo-
somes. This separation of the daughter chromosomes, and
their movement toward the daughter centrosomes, is called
metakinesis. As they approach their destination, we have the
appearance of two stars in the nucleus — the daughter stars, or
diasters.

3. Anaphase. — The daughter stars undergo, in reverse order, much
the same changes that the mother star passed through. The
chromosomes become much convoluted, and perhaps united to
one another, the lateral twigs appear, and the chromatin resumes
the appearance of the resting nucleus. The nuclear spindle,
with most of the polar radiation, disappears, and the nucleoli
and the nuclear membrane reappear, thus forming two complete
daughter nuclei. Meanwhile the protoplasm becomes con-
stricted midway between the young nuclei. This constriction
gradually deepens until the original cell is divided, with the
formation of two complete cells.

CHAPTER IV.

HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE

TISSUES.

I. EPITHELIAL TISSUE.

The epithelial tissue consists of one or more layers of cells
resting on a homogeneousi membrane, the other side of which is
abundantly supplied with blood-vessels and nerves. The form
of the epithelial cell varies in different situations, and may be
flattened, cuboid, spheroid, or columnar. (See Figs. 4, 5, and 6.)
The form of the cell in all instances is related to some specific
function. When arranged in layers or strata, the cells are cemented
together by an intercellular substance.

Fig. 4. — Epithelial Cells of Rabbit, Isolated. X 560. i. Squamous cells
(mucous membrane of mouth). 2. Columnar cells (corneal epithelium). 3.
Columnar cells, with cuticular border, s (intestinal epithelium). 4. Ciliated cells;
h, cilia (bronchial epithelium).

The epithelial tissue forms a continuous covering for the surfaces
of the body. The external investment (the skin) and the internal
investment (the mucous membrane, which Hnes the entire alimentary
canal and its associated body cavities) are both formed, in all situa-
tions, by the homogeneous basement membrane, covered with one
or more layers of cells. All materials, therefore, whether nutritive,
secretor}-, or cxcretor}-, must pass through epithelial cells before they
can enter into the formation of the tissues or be eliminated from them.
The nutrition of the epithelial tissue is maintained by the nutritive
material derived from the blood diffusing itself into and through
the basement membrane. Chemically, the epithelial cells of the
epidermis — hair, nails, etc. — are composed of an albuminoid material

47

48

TEXT-BOOK OF PHYSIOLOGY.

(keratin), a small quantity of water, and inorganic salts. In other
situations, especially on the mucous membranes, the cells consist
largely of mucin, in association with other albuminoids. The con-
sistency of epithelium varies in accordance with external influences,
such as the presence or absence of moisture, pressure, friction, etc.
This is well seen in the skin of the palms of the hands and the soles
of the feet — situations where it acquires its greatest density. In the
ahmentary canal, in the lungs, and in other cavities, where the reverse
conditions prevail, the epithelium is extremely soft. Epithelial
tissues also possess varying degrees of cohesion and elasticity —
physical properties which enable them to resist considerable pressure
and distention without having their physiologic integrity destroyed.
Inasmuch as these tissues are poor conductors of heat, they assist in

preventing too rapid radiation
"'~"~— -«^_^^ of heat from the body, and

^'"er":;^-'^!;^ cooperate with other mechan-

.«*:: ::-^- isms in maintaining the normal

3 —

vm'i^'i

,.)' */
'i\('

Fig. 5. — Stratified Squamous Epi-
thelium (Larynx of Man).
X 240. I. Columnar cells. 2.
Prickle-cells. 3. Squamous cells.

Fig. 6. — Stratified Ciliated Epi-
thelium. X 560. From the res-
piratory nasal mucous membrane
of man. i. Oval cells. 2. Spindle-
shaped cells. 3. Columnar cells.

temperature. The physiologic activity of all epithelial tissue depends
on a due supply of nutritive material derived from the blood, which
not only maintains its nutrition, but affords those materials out of
which are formed the secretions of the glands, whether of the skin or
mucous membrane.

Functions of Epithelial Tissue. — In succeeding chapters the
form, chemic composition, and functions of epithelial cells will be
considered in connection with the functions of the organs of which
they constitute a part. In this connection it may be stated in a
general way that the functions of the epithehal tissues are:
I. To serve on the surface of the body as a protective covering to the
underlying structures which collectively form the true skin, thus

THE CONNECTIVE TISSUES. 49

protecting them from the injurious influences of moisture, air,
dust, microorganisms, etc., which would otherwise impair their
vitaHty. Wherever continuous pressure is appHed to the skin,
as on the palms of the hands and soles of the feet, the epithelium
increases in thickness and density, and thus prevents undue
pressure on the nerves of the true skin. The density of the
epidermis enables it to resist, within limits, the injurious influence
of acids, alkalies, and poisons.

2. To promote absorption. Inasmuch as the skin and mucous mem-

branes cover the surfaces of the body, it is obvious that all
nutritive material entering the body must first traverse the epi-
thehal tissue. Owing to their density, however, the epithehal
cells covering the skin play but a feeble role as absorbing agents
in man and the higher animals. The epithelium of the mucous
membrane of the alimentary canal, particularly that of the small
intestine, is especially adapted, from its situation, consistency,
and properties, to play the chief role in the absorption of new
materials into the blood. The epithehum hning the air-vesicles
of the lungs is engaged in promoting the absorption of oxygen
and the exhalation of carbon dioxid.

3. To form secretions and excretions. Each secretory gland con-

nected with the surfaces of the body is Hned by epithehal cells,
which are actively concerned in the formation of the secretion
peculiar to the gland. Each secretory organ is similarly provided
with epithehal cells, which are engaged either in the production
of the constituents of the excretion or in their removal from the
blood.

2. THE CONNECTIVE TISSUES.

The connective tissues, in their collective capacity, constitute
a framework which pervades the body in all directions, and, as the
name implies, serve as a bond of connection between the individual
parts, at the same time affording a basis of support for the muscle,
nerve, and gland tissues. The connective-tissue group includes a
number of varieties, among which may be mentioned the areolar,
adipose, retiform, white fibrous, yellow elastic, cartilaginous and
osseous. Notwithstanding their apparent diversity, they possess
many points of similarity. They have a common origin, developing
from the same embryonic material; they have much the same struc-
ture, passing imperceptibly into one another, and perform practically
the same functions.

Areolar Tissue. — This variety is found widely distributed
throughout the body. It serves to unite the skin and mucous mem-
brane to the structures on which they rest; to form sheaths for the
support of blood-vessels, nerves, and lymphatics; to unite into com-
4

so

TEXT-BOOK OF PHYSIOLOGY.

pact masses the muscular tissue of the body, etc. Examined with
the naked eye, it presents the appearance of being composed of
bundles of fine fibers interlacing in every direction. In the embryonic
state the elements of this form of connective tissue are united by a
ground substance, gelatinous in character. In the adult state this
substance shrinks and largely disappears, leaving intercommunicating
spaces of varying size and shape, from which the tissue takes its
name. When subjected to the action of various reagents, and
examined microscopically, the bundles can be shown to consist of
extremely delicate, colorless, transparent, wavy fibers, which are
cemented together by a ground substance composed largely of mucin.
Other fibers are also observed, which are distinguished by a straight
course, a sharp, well-defined outline, a tendency to branch and unite
with adjoining fibers, and to curl up at their extremities when torn.
From their color and elasticity they are known as yellow elastic fibers.

Distributed throughout the
meshes of the areolar tissue
are found flattened, irregularly
branched, or stellate corpuscles,
connective -tissue corpuscles,
plasma cells, and granule cells.

'CPq-

super-
posed
layers

Fig. 7. — Adipose Tissue.

Fig. 8. — Fat-Cells from the Axilla
OF Man. I. The equator of the
cell in focus. 2. The objective
somewhat elevated. 3, 4. Forms
changed by pressure, p. Traces
of protoplasm in the vicinity of
the flat nucleus k.

Adipose Tissue. — This tissue, which exists very generally
throughout the body, though found most abundantly beneath the
skin, around the kidneys, and in the bones, is practically but a
modification of areolar tissue. In these situations it presents itself
in small masses or lobules of varying size and shape, surrounded
and penetrated by the fibers of connective tissue. (See Fig. 7.)
Microscopic examination shows that these masses consist of small
vesicles or cells, round, elliptical, or polyhedral in shape, depending
somewhat on pressure. (See Fig. 8.) Each vesicle consists of a thin,

THE CONNECTIVE TISSUES.

51

colorless, protoplasmic membrane, thickened at one point, in which a
nucleus can usually be detected. This membrane incloses a globule of
fat, which during hfe is in the liquid state. It is composed of olein,
stearin, and palmitin. The origin of the fat is to be referred to a
retrograde change in the protoplasmic material of the connective-tissue
cells. When this protoplasm becomes rich in carbon and hydrogen,
it is speedily converted into fat, which makes its appearance in the
form of minute droj)s in different portions of the cell. As the drops
accumulate, at the expense of the cell protoplasm, they gradually
coalesce, until there remains but a thin stratum of the protoplasm,
which forms the wall of the vesicle. Adipose tissue may, therefore,
be regarded as areolar tissue, in which, and at the expense of some
of its elements, fat is stored for the future needs of the organism.
A diminution of food, especially of fat and carbohydrates, is promptly
followed by an absorption of fat by
the blood-vessels and by its transfer-
ence to the tissues, where it is either
utilized for tissue construction or for
oxidation purposes. In the situations
in which adipose tissue is found it
seems, by its chemic and physical
properties, to assist in the prevention
of a too rapid radiation of heat from
the body, to give form and roundness,
and to diminish angularities, etc.

Retiform and adenoid tissue are
also modifications of areolar tissue.
The meshes of the former contain but
little ground substance, its place being
taken by fluids; the meshes of the
latter contain large numbers of lymph
corpuscles.

Fibrous Tissue. — This variety of connective tissue is widely
distributed throughout the body. It constitutes almost entirely the
ligaments around the joints, the tendons of the muscles, the mem-
branes covering organs such as the heart, liver, nervous system,
bones, etc. All fibrous tissue, wherever found, can be resolved into
elementary bundles, which on microscopic examination are seen to
consist of delicate, wavy, transparent, homogeneous fibers, which
pursue an independent course, neither branching nor uniting with
adjoining fibers. (See Fig. 9.) A small amount of ground substance
serves to hold them together. Fibrous tissue is tough and inexten-
sible, and in consequence is admirably adapted to fulfil various
mechanical functions in the body. It is, however, quite pliant, bend-
ing easily in all directions. When boiled, fibrous tissue yields gelatin,
a derivative of collagen.

Fig. 9. — Connective - Tissue
Bundles of Various
Thicknesses of the In-
termuscular Connective
Tissue of Man. X 240.

52

TEXT-BOOK OF PHYSIOLOGY.

Elastic Tissue. — The fibers of elastic tissue are usually associated
in varying proportions with the white fibrous tissue; but in some
structures — as the ligamentum nuchae, the ligamenta subflava, the
middle coat of the larger blood-vessels — the elastic fibers are almost
the only elements present, and give to these structures a distinctly
yellow appearance. The fibers throughout their course give off
many branches, which unite with adjoining branches to form a more
or less close network. As the name implies, these fibers are highly
elastic, and are capable of being extended as much as 60 per cent,
before breaking. (See Fig. 10.)

Cartilaginous Tissue.— This form of connective tissue differs
from the preceding varieties chiefly in its density. As a rule, it is

^f^l^ - / /

;/rH^^n^'

Fig. 10. — Elastic Fibers. X 560. A. Fine elastic fibers, /, from intermuscular
connective tissue of man; h, connective-tissue bundles swelled by treatment vi^ith
acetic acid. B. Very thick elastic fibers, /, from ligamentum nuchae of ox; h,
connective-tissue bundles. C. From a cross-section of the ligamentum nuchae of
ox; /, elastic fibers; h, connective-tissue bundles.

firm in consistency, though somewhat elastic. It is opaque, bluish-
white in color, though in thin sections translucent. All cartilaginous
tissues consist of connective-tissue cells embedded in a sohd ground
substance. According to the amount and texture of the ground
substance, three principal varieties may be distinguished:
I . Hyaline cartilage, in which the cells, relatively few in number, are
embedded in an abundant quantity of ground substance (Fig. 11).
The body of the cells is in many instances distinctly marked off
from the surrounding substance by concentric hnes or fibers,
which form a capsule for the cell. Repeated division of the cell
substance takes place, until the whole capsule is completely

THE CONNECTIVE TISSUES. 53

occupied by daughter cells. The ground substance is pervaded
by minute channels, which communicate on one hand with the
spaces around the cells, and on the other with lymph-spaces in
the connective tissue surrounciing the cartilage. By means of
these channels, nutritive fluid can permeate the entire structure.
Hyaline cartilage is found on the ends of the long bones, where
it enters into the formation of the joints; between the ribs and
sternum, forming the costal cartilage, as well as in the nose and
larynx.
White fibro-cariilage, the ground substance of which is pervaded
by white fibers, arranged in bundles or layers, between which

, ^

Fig. II. — Hyaline Cartilage. X 240. A. Surface view of the ensiform process
of frog, fresh; p, protoplasm of cartilage-cell, which entirely fills the lacuna; k,
nucleus; g, hyaline matrix. B. Portion of cross-section of human rib-cartilage
several days after death; examined in water: the protoplasm, s, of the cartilage-
cells has withdrawn from the walls of the lacunae, h; the nuclei are invisible.
I. Two cells within one capsule, k; x, a developing partition. 2. Five cartilage-
cells within one capsule; the lowest cell has fallen out, and here only the empty
space is seen. 3. Capsule cut obliquely, and apparently thicker on one side.
4. Capsule not cut, but showing the cell within, g. Hyaline matrix transformed
into rigid fibers, /.

are scattered the usual encapsulated cells. (See Fig. 12.) White
fibro-cartilage is tough, resistant, but flexible, and is found in
joints where strength and fixedness are required. Hence it is
present between the vertebrae, forming the intervertebral discs,
between the condyle of the lower jaw and the glenoid fossa, in
the knee-joint, around the margins of the joint cavities, etc. In
these situations it assists in maintaining the apposition of the
bones, in giving a certain degree of mobility to the joints, and in
diminishing the effects of shock and pressure imparted to the
bones.

54

TEXT-BOOK OF PHYSIOLOGY.

\

C

'I,

■J

Yellow fibro-cariilage, the ground substance of which is pervaded
by opaque, yellow elastic fibers, which form, by the interlacing

of their branches, a complicated
^ network, in the meshes of which

are to be found the usual cor-
puscles. (See Fig. 13.) As
these fibers are elastic, they
impart to the cartilage a very
considerable degree of elas-
ticity. Yellow fibro-cartilage
is well adapted, therefore, for
entering into the formation of
the external ear, epiglottis.
Eustachian tube, etc.- — struc-
tures which require for their
functional activity a certain
degree of flexibihty and elas-
ticity.

Osseous Tissue. — Osseous tis-
sue, as distinguished from bone, is
a member of the connective-tissue
group, the ground substance of
which is permeated with insoluble lime salts, of which the phosphate
and carbonate are the most abundant. Immersed in dilute solutions
of hydrochloric acid, they can be converted into soluble salts and dis-

%'il M

Ijf

Fig.

12. — From a Horizontal Sec-
tion OF THE Intervertebral
Disc of Man. g. Fibrillar con-
nective tissue, z. Cartilage-cell
(nucleus invisible), k. Capsule
surrounded by calcareous gran-
ules. X 240.

Fig. 13.- — Elastic Cartilage. X 240. i. Portion of section of vocal process (ante-
rior angle) of arytenoid cartilage of a woman thirty years old; the elastic substance
in the form of granules. 2 and 3. Portions of sections of epiglottis of a woman
sixty years old; a fine network of elastic fibers in 2, a coarser network in 3. z.
Cartilage-cell, nucleus not visible; k, capsule.

solved out. The osseous matrix left behind is soft and phable.
When boiled, it yields gelatin.

A thin, transverse section of a decalcified bone, when examined
microscopically, reveals a number of small, round, or oval openings,

THE CONNECTIVE TISSUES.

55

which represent transverse sections of canals which run through the
bone, for the most part in a longitucHnal cUrection, though frecjuently
anastomosing with one another. These so-called Haversian canals
in the living state contain blood-vessels and lymphatics. (See
Fig. I4-)

Around each Haversian canal is a series of concentric laminae,
composed of white fibers. Between every two laminae are found small
cavities (lacunar), from which radiate in all directions small canals
(canaliculi), which communicate freely with one another. The
Haversian canals, with their associated lacunae and canaliculi,
form a system of intercommunicating passages, which circulate
lymph destined for the nourishment of bone. Each lacuna
contains the bone corpuscle, which bears a close resemblance to the

Periosteum.

Outer ground lamella;.

Haversian canals.

Haversian lamella;.

Interstitial lamellae.
Inner ground lamella;.

Marrow.

Fig. 14. — From a Cross-section of a Metacarp of Man. X 50. The Haversian
canals contain a little marrow (fat-cells). Resorption line at h.

usual branched connective-tissue corpuscle, and whose function
appears to be the maintenance of the nutrition of the bone.

The surface of every bone in the living state is invested with a
fibrous membrane, the periosteum, except where it is covered wdth
cartilage. The inner surface of this membrane is loose in texture,
and supports a fine plexus of capillary blood-vessels and numerous
protoplasmic cells — the osteoblasts. As this layer is directly con-
cerned in the formation of bone, it is spoken of as the osteogenetic
layer.

A section of a bone shows that it is composed of two kinds of
tissue — compact and cancellated. The compact is dense, resembhng
ivory, and is found on the outer portion of the bone; the cancellated
is spongy, and appears to be made up of thin, bony plates, which
intersect one another in all directions, and is found in greatest abun-

56 TEXT-BOOK OF PHYSIOLOGY.

dance in the interior of the bones. The shaft of a long bone is hollow.
This central cavity, which extends from one end of the bone to the
other, as well as the interstices of the cancellated tissue, is filled in the
living state with marrow. The marrow or medulla is composed of a
connective-tissue framework supporting blood-vessels. In its meshes
are to be found characteristic bone cells or osteoblasts, the function
of which is supposed to be the formation of bone. In the long bones
the marrow is yellow, from the presence in the connective-tissue
corpuscle of ,fat globules, which arise through the transformation of
the cell protoplasm. In the cancellated tissue, near the extremities
of the long bones, this fatty transformation does not take place to the
same extent, and the marrow appears red. The cells of the red
marrow are beheved to give birth indirectly to the red blood-cor-
puscles.

Physical and Physiologic Properties of Connective Tissues.
— Among the physical properties may be mentioned consistency,
cohesion, and elasticity. Their consistency varies from the semi-
liquid to the soKd state, and depends on the quantity of water which
enters into their composition. Their cohesion, except in the softer
varieties, is \Qry considerable, and offers great resistance to traction,
pressure, torsion, etc. In all the movements of the body, in the con-
traction of muscles, in the performance of work, the consistence and
cohesion of these tissues play most important roles. Wherever the
various forms of connective tissue are found, their chemic com-
position and structure are in relation to their functions. If traction
be the preponderating force, the structure becomes fibrous, as in
ligaments and tendons, and the cohesion greatest in the longitudinal
direction. If pressure be exerted in all directions, as upon mem-
branes, the fibers interlace and offer a uniform resistance. When
pressure is exerted in a definite direction, as on the extremities of the
long bones, the tissue becomes expanded and cancellated. The
lamellae of the cancellated tissue arrange themselves in curves which
correspond to the direction of the greatest pressure or traction. Ex-
tensibihty is not a characteristic feature, except in those forms con-
taining an abundance of yellow elastic fibers. The elasticity is an
essential factor in many physiologic actions. It not only opposes and
Hmits forces of traction, pressure, torsion, etc., but on their cessation
returns the tissues or organs to their original condition. Elasticity
thus assists in maintaining the natural form and position of the organs
by counterbalancing and opposing temporarily acting forces.

The Skeleton. — The connective tissues in their entirety con-
stitute a framework which presents itself under two aspects: (i)
As a solid, bony skeleton, situated in the trunk and limbs, affording
attachment for muscles and viscera; (2) as a fine, fibrous skeleton,
found everywhere throughout the body, connecting the various

THE CONNECTIVE TISSUES. 57

viscera and affording support for the epithelial, muscle, and nerve
tissues.

THE ANIMAL BODY AS A MACHINE FOR DOING

WORK.

The animal body is characterized by the power of executing a
great variety of movements, all of which have reference to a change
of relation of one part of the body to another, or to a change of posi-
tion relatively to the environment, as in the various acts of locomotion.
Since in the execution of these movements the different parts are
of necessity applied or directed to the overcoming of opposing
forces in the environment, the animal is said to be doing work. In
the conception of the animal body as a machine for the accomphsh-
ment of work the skeleton, the muscle and nerve tissues constitute the
three primary mechanisms, all of which bear certain definite relations
one to another.

CHAPTER V.

THE PHYSIOJ.OGY OF THE SKELETON.

The Skeleton is the passive framework of the body, the axial
portion of which (the vertebral column, head, ribs, and sternum)
imparts more or less fixity and rigidity, while the appendicular por-
tions (the bones of the arms and legs) impart extreme mobihty. The
bones of the arms and legs more especially may be looked upon as
constituting a system of levers, the fulcra of which, the points of
rest around which they move, lie in the joints.

That a lever may be effective as an instrument for the accom-
plishment of work, it must not only be capable of moving around its
fulcrum, but it must at the same time be acted on by two opposing
forces, one passive, the other active. In the movement of the bony
levers of the animal body, the passive forces are largely those con-
nected with the en\dronment, e. g., gravity, cohesion, friction, elas-
ticity, etc. The active forces by which these latter are opposed and
overcome through the intermediation of the bony levers are found in
the muscles attached to them. For the execution of all these move-
ments, it is essential that the relation of the various portions of the
bony skeleton to one another shall be such as to permit of movement
while yet retaining close apposition. This is accomplished by the
mechanical conditions which have been evolved at the points of union
of bones, and which are technically known as articulations or joints.
A consideration of the body movements involves an account of
(i) the static conditions, or those states of equilibrium in which the
body is at rest— e. g., standing, sitting; (2) the dynamic conditions,
or those states of activity characterized by movement — e. g., walking,
running, etc. In this connection, however, only those physical and
physiologic pecuHarities of the skeleton, especially in its relation to
joints, will be referred to, which underhe and determine both the
static and dynamic states of the body.

Structure of Joints. — The structures entering into the formation
of joints are:

I, Bones, the articulating surfaces of which are often more or less
expanded, especially in the case of long bones, and at the same
time variously modilied and adapted to one another in accordance
with the character and extent of the movements which there
take place.

58

THE PHYSIOLOGY OF THE SKELETON. 59

2. Hyaline cartilage, which is closely applied to the articulating end

of each bone. The smoothness of this form of cartilage facili-
tates the movements of the opposing surfaces, while its elasticity
diminishes the force of shocks and jars imparted to the bones
during various muscular acts. In a number of joints, plates
or discs of white fibro-carlilage are inserted between the surfaces
of the bones.

3. A synovial membrane, which is attached to the edge of the hyaline

cartilage, entirely inclosing the cavity of the joint. This mem-
brane is composed largely of connective tissue, the inner surface
of which is lined by endothehal cells, which secrete a clear,
colorless, viscid fluid — the synovia. This fluid not only fifls up
the joint-cavity, but, flowing over the articulating surfaces,
diminishes or prevents friction.

4. Ligaments, — tough, inelastic bands, composed of white fibrous

tissue, — which pass from bone to bone in various directions on
the different aspects of the joint. As white fibrous tissue is in-
extensible but pHant, hgaments assist in keeping the bones in
apposition, and prevent displacement while yet permitting of
free and easy movements.
Classification of Joints. — All joints may be divided, according

to the extent and kind of movements permitted by them, into (i)

diarthroses; (2) amphiarthroses; (3) synarthroses.

I. Diarthroses. — In this division of the joints are included all those
which permit of free movement. In the majority of instances
the articulating surfaces are mutually adapted to each other.
If the articulating surface of one bone is convex, the opposing
but corresponding surface is concave. Each surface, therefore,
represents a section of a sphere or a cylinder, which latter arises
by rotation of a line around an axis in space. According to the
number of axes around which the movements take place all
diarthrodial joints may be divided into:

I. Uniaxial Joints. — In this group the convex articulating surface is
a segment of a cylinder or cone, to which the opposing surface
more or less completely corresponds. In such a joint the single
axis of rotation, though nearly, is not exactly at right angles
to the long axis of the bone, and hence the movements — flexion
and extension — which take place are not confined to one plane.
Joints of this character — e. g., the elbow, knee, ankle, the pha-
langeal joints of the fingers and toes — are, therefore, termed
ginglymi, or hinge-joints. Owing to the obliquity of their
articulating surfaces, the elbow and ankle are cochleoid or screw-
ginglymi. Inasmuch as the axes of these joints on the opposite
sides of the body are not coincident, the right elbow and left
ankle are right-handed screws; the left elbow and right ankle.

6o TEXT-BOOK OF PHYSIOLOGY.

left-handed screws. In the knee-joint the form and arrangement
of the articulating surfaces are such as to produce that modifica-
tion of a simple hinge known as a spiral hinge, or helicoid. As
the articulating surfaces of the condyles of the femur increase in
convexity from before backward, and as the inner condyle is
longer than the outer, and, therefore, represents a spiral surface,
the line of translation or the movement of the leg is also a spiral
movement. During flexion of the leg there is a simultaneous
inward rotation around a vertical axis passing through the outer
condyle of the femur; during extension a reverse movement takes
place. Moreover, the slightly concave articulating surfaces of
the tibia do not revolve around a single fixed transverse axis, as
in the elbow-joint, for during flexion they slide backward, during
extension forward, around a shifting axis, which varies in posi-
tion with the point of contact.

In some few instances the axis of rotation of the articulating
surface is parallel with rather than transverse to the long axis of
the bone, and as the movement then takes place around a more
or less conic surface, the joint is termed a trochoid or pulley — e. g.,
the odonto-atlantal and the radio-ulnar. In the former the collar
formed by the atlas and its transverse ligament rotates around
the vertical odontoid process of the axis. In the latter the head
of the radius revolves around its own long axis upon the ulna,
giving rise to the movements of pronation and supination of the
hand. The axis around which these two movements take place
is continued through the head of the radius to the styloid process
of the ulna.

2. Biaxial Joints. — In this group the articulating surfaces are un-

equally curved, though intersecting each other. When the sur-
faces lie in the same direction, the joint is termed an ovoid joint
— e. g., the radio-carpal and the atlanto-occipital. As the axes
of these surfaces are vertical to each other, the movements per-
mitted by the former joint are flexion, extension, adduction, and
abduction, combined with a slight amount of circumduction;
the latter joint permits of flexion and extension of the head, with
inclination to either side. When the surfaces do not take the
same direction, the joint, from its resemblance to the surfaces of
a saddle, is termed a saddle- joint — e. g., the trapezio-metacarpal.
The movements permitted by this joint are also flexion, exten-
sion, adduction, abduction, and circumduction.

3. Polyaxial Joints. — In this group the convex articulating surface

is a segment of a sphere, which is received by a socket formed
by the opposing articulating surface. In such a joint, termed an
enarthrodial or ball-and-socket joint, — e. g., the shoulder-joint,
hip-joint, — the distal bone revolves around an indefinite number

THE PHYSIOLOGY OF THE SKELETON. 6i

of axes, all of which intersect one another at the center of rotation.
For simplicity, however, the movement may be described as
taking place around axes in the three ordinal planes — viz., a
transverse, a sagittal, and a vertical axis. The movements around
the transverse axis are termed flexion and extension; around the
sagittal axis, adduction and abduction; around the vertical
axis, rotation. When the bone revolves around the surface of an
imaginary cone, the apex of which is the center of rotation and
the base the curve described by the hand, the movement is
termed circumduction.

2. Amphiarthroses. — In this division are included all those joints

which permit of but slight movement — e. g., the intervertebral,
the interpubic, and the sacro-ihac joints. The surfaces of the
opposing bones are united and held in position largely by the
intervention of a firm, elastic disc of fibro-cartilage. Each joint
is also strengthened by hgaments.

3. Synarthroses. — In this division are included all those joints in

which the opposing surfaces of the bones are immovably united,
and hence do not permit of any movement — e. g., the joints
between the bones of the skull.

The Vertebral Column. — In all static and dynamic states of the
body the vertebral column plays a most essential role. Situated fli
the middle of the back of the trunk, it forms the foundation of the
entire skeleton. It is composed of a series of superimposed bones,
termed vertebrce, which increase in size from above downward as
far as the brim of the pelvic cavity. Superiorly, it supports the skull;
laterally, it affords attachment for the ribs, which in turn giipport the
weight of the upper extremities; below, it rests upon the pelvic bones,
which transmit the weight of the body to the inferior extremities.
The bodies of the vertebrae are united one to another by tough elastic
discs of fibro-cartilage, which, collectively, constitute about one-
quarter of the length of the vertebral column. The vertebrae are held
together by ligaments situated on the anterior and posterior surfaces
of their bodies, and by short, elastic ligaments between the neural
arches and processes. These structures combine to render the
vertebral column elastic and flexible, and enable it to resist and
diminish the force of shocks communicated to it.

The amphiarthrodial character of the intervertebral joints endows
the entire column with certain forms of movement which are neces-
sary to the performance of many body activities. While the range
of movement between any two vertebras is slight, the sum total of
movement of the entire series of vertebras is considerable. In different
regions of the column the character, as well as the range of move-
ment, varies in accordance with the form of the ^•ertebras and the
inchnation of their articular processes. In the cervical and lumbar

62 TEXT-BOOK OF PHYSIOLOGY.

regions extension and flexion are freely permitted, though the former
is greater in the cervical, the latter in the lumbar region, especially
between the fourth and fifth vertebrae. Lateral flexion takes place
in all portions of the column, but is particularly marked in the cer-
vical region. A rotatory movement of the column as a whole takes
place through an angle of about twenty-eight degrees. This is most
evident in the lower cervical and dorsal regions.

The skeleton may, therefore, be regarded as a highly developed
framework, which determines not only the form of the body, and
affords support and protection to the various softer organs and
tissues, but also, through the mobility of its joints, permits of a great
variety of comphcated movements.

CHAPTER VI.
GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

The muscle-tissue, which closely invests the bones of the body
and which is familiar to all as the flesh of animals, is the immediate
cause of the active movements of the body. This tissue is grouped
in masses of varying size and shape, which are technically known as
muscles. The majority of the muscles of the body are connected
with the bones of the skeleton in such a manner that, by an alteration
in their form, they can change not only the position of the bones with
reference to one another, but can also change the individual's relation
to surrounding objects. They are, therefore, the active organs of
both motion and locomotion, in contradistinction to the bones and
joints, which are but passive agents in the performance of the corre-
sponding movements. In addition to the muscle masses which are
attached to the skeleton, there are also other collections of muscle-
tissue surrounding cavities such as the stomach, intestine, blood-
vessels, etc., which impart to their walls motility, and so influence the
passage of material through them.

Muscles produce movement of the structures to which they are
attached by the property with which they are endowed of changing
their shape, shortening or contracting under the influence of a stim-
ulus transmitted to them from the nervous system. Muscles are
divided into:

1. Voluntary muscles, comprising those the activity of which is

called forth by an act or effort of volition.

2. Involuntary muscles, comprising those the activity of which is

entirely independent of the volition.
The voluntary muscles are also known from their attachment to
the skeleton as skeletal, and from their microscopic appearance as
striped or striated muscles. Though for the most part these muscles
are red, there are certain muscles in man and other animals which
are pale in color. The involuntary muscles, from their relation to the
viscera of the body, are known also as visceral, and from their micro-
scopic appearance as plain, smooth, or non-striated muscles.

THE VOLUNTARY OR SKELETAL MUSCLE.

All skeletal muscles consist of a central fleshy portion, the body
or belly, provided at cither extremitv with a tendon in the form of a

63'

64

TEXT-BOOK OF PHYSIOLOGY.

7

cord or membrane. The body is the active, contractile region, the
source of the movement ; the tendon is the inactive region, the passive
transmitter of the movement to the bones.

A skeletal muscle is a complex organ consisting of a framework of
connective tissue, supporting muscle-fibers, blood-vessels, nerves, and
lymphatics. The general body of the muscle is covered by a dense
layer of connective tissue, the epi-mysium, which blends with and
partly forms the tendon. From the under surface of this covering,
septa of connective tissue pass inward, dividing and grouping the

fibers into larger and smaller
bundles, termed fasciculi. The
fasciculi, invested by a special
sheath, the peri-mysium, are
prismatic in shape and on
cross-section present an ir-
regular outhne. The muscle-
fibers composing the fasciculi
are separated one from an-
other and supported by a very
delicate connective tissue, the
endo-mysium. The connec-
tive tissue thus surrounding
and penetrating the muscle
binds the fibers into a dis-
tinct organ and affords sup-
port to all remaining struc-
tures (Fig. 15).

Histology of the Skeletal
Muscle-fiber. — The muscle-
fibers for the most part are
arranged parallel one to an-
other and in a direction cor-
responding to the long axis of
the muscle. They vary in
length from 30 to 40 milh-
meters and in breadth from
20 to 30 micromilhmeters. There are exceptional fibers, however,
which have a much greater length. As the fibers have but a limited
length in the vast majority of muscles, each end, more or less pointed
or beveled, is united to adjoining fibers by cement. In this way a
muscle is increased in length.

When examined with the microscope, the muscle-fiber is seen to be
cyhndric or prismatic in shape and to consist of a thin transparent
membrane, the sarcolemma, in which is contained the true muscle
or sarcous substance. The sarcolemma is elastic and adapts itself

^.

vr

v:'-

W

Fig. 15. — From a Cross-section of the
Adductor Muscle of a Rabbit. P.
Peri-mysium, containing two blood-ves-
sels, at g; m, muscle-fibers; many are
shrunken and between them the endo-
mysium, p, can be seen; at x the sec-
tion of muscle-fiber has fallen out.
X 60.

GENERAL PHYSIOLOGY OF MUSCLE TISSUE.

6S

Fig. 1 6. — Muscle-fiber of a Rabbit.
a. Dark band. b. Light band.
c. Intermediate line. n. Nucleus.

to all changes of form the sarcous substance undergoes. Beneath
the sarcolemma there are several nuclei surrounded by granular
material. Each fiber also presents a series of transverse bands
alternately dim and bright which
give to it a striated appearance.
If the bright bands are examined
with high magnifying powers, each
one is seen to be crossed by a fine
dark hne which at the time of its
discovery was regarded as the
optic expression of a membrane
attached laterally to the sarco-
lemma. It has since been re-
solved into a row of granules
(Fig. i6).

The muscle-fiber also presents
a longitudinal striation which in-
dicates that it is composed of
finei; elements placed side by side,

termed fibrillae. The fibrillas extend throughout the entire length
of the fiber, though they are not of uniform thickness (Fig. 17). That

portion of the fibril corresponding
in position to the dim band is
thick, prismatic, or rod-hke in
shape, and termed a sarcostyle;
that portion corresponding in po-
sition to the bright band is ex-
tremely thin and narrow and pre-
sents at its middle a slight enlarge-
ment or granule. The fibrillae are
embedded in a clear transparent
fluid which, from its supposed
nutritive character, is termed sar-
coplasm. The diminution in cah-
ber of the fibrillae at different
levels permits of the accumulation
and storage of a larger amount
of nutritive material than could
otherwise be the case. It is for
this reason that the fiber at these
points presents a brighter appear-
ance.

When the muscle-fiber is ex-
amined under crossed Nichol prisms, the dim band appears bright
and the bright band appears dim against a dark background, indi-

FlG.

17. — A. Diagram of arrangement
of the contractile substance ac-
cording to the view of Rollett; the
granular figures represent the con-
tractile elements, the intervening
light areas the sarcoplasm. B.
Small muscle-fiber of man; the
corresponding parts in the two
figures are indicated; /, i, I, respec-
tively the transverse, the interme-
diate, and lateral discs, n. Muscle
nuclei. — (Piersol.)

66

TEXT-BOOK OF PHYSIOLOGY.

LYMPH SPACE

MUSCLE
FIBER

CAPILLARY BLOOD
VESSEL

eating that the former is doubly refracting or anisotropic, the latter
singly refracting or isotropic.

The Blood-supply. — Muscles in the physiologic condition re-
quire for the maintenance of their activity a large amount of nutritive
material. This is obtained from the blood furnished by the blood-
\-essels. The vascular supply to the muscles is very great and the
disposition of the capillary vessels w^ith reference to the muscle-
fiber is very characteristic. The arterial vessels, after entering the
muscle, are supported by the peri-mysium; in this situation they give
off short, transverse branches, which immediately break up into a
capillary network of rectangular shape within which the muscle-
fibers are contained. The muscle-fiber, in intimate relation with
the capillary, is bathed with lymph derived from it. Its contractile

substance, however, is separ-
ated from the lymph by its
own investing membrane,
through which all interchange
of nutritive and waste mate-
rials must take place. The
relation of the capillary vessel
to the muscle-fiber is shown
in Fig. 1 8.

The nutritive material
passes through the capillary
wall into the lymph-space,
then through the sarcolemma
into the interior of the fiber,
where it comes into relation
with the living muscle mate-
rial. The waste products aris-
ing in the muscle as a result
of nutritive changes pass in
the reverse direction into the
blood,- by which they are car-
ried away to ehminating or-
gans. Lymphatics are present in muscle, but confined to the con-
nective tissue, in the spaces of which they take their origin.*

The Nerve-supply. — The nerves which carry the stimuH to a
muscle enter near its geometric center. Many of the fibers pass
directly to the muscle-fibers with which they are connected; others
are distributed to blood-vessels. Every muscle-fiber is supplied
with a special nerve-fiber except in those instances where the nerve-
trunks entering a muscle do not contain as many fibers as the muscle.
In such cases the nerve-fibers divide near their termination until the
number of branches equals the number of muscle-fibers. The

Fig. iS.

-Relation of the Blood-vessel
TO THE Muscle-fiber.

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 67

individual muscle-fiber is penetrated near its center by the nerve
where it terminates; the ends being practically free from nerve in-
tlucnce. The stimulus that comes to the muscle-fiber acts primarily
upon its center, the effect of which then travels in both directions
to the ends. The manner in which the ncrvc-fibcrs terminate in
muscle will be more fully described in connection with the histology
of the nerve tissue.

CHEMIC COMPOSITION OF MUSCLE.

The chcmic composition of living muscle is but imperfectly under-
stood owing to the fact that shortly after death some of its constituents
undergo a spontaneous coagulation and for the reason that the
methods employed for analysis also tend to alter its composition.
To human muscle, the following average percentage composition has
been given :

Water, 73.5

Proteids, including those of sarcolemma, connective-
tissue, pigments, 18.02

Gelatin, 1.99

Fat, 2.27

Extractives, 0.22

Inorganic salts, 3-i2. (Halliburton.)

(The composition of muscles of different animals, consumed as
foods, will be found in the chapter on Foods.)

When fresh muscle is freed from fat and connective tissue, frozen,
rubbed up in a mortar, and expressed through hnen, a shghtly yellow
syrupy alkaline or neutral hquid is obtained which has been termed
muscle-plasma. This fluid at normal temperatures coagulates
spontaneously, the phenomena resembling in many respects those
observed in the coagulation of blood-plasma. The coagulum subse-
quently contracts and squeezes out an acid muscle-serum. The
coagulated proteid is known as myosin and belongs to the class of
globuhns. Inasmuch as it is not present in living muscle and only
makes its appearance under conditions not strictly physiologic, it is
regarded as a derivative of a pre-existing proteid w^hich has been
termed myosinogen. According to Halliburton, the proteids of living
muscle are four in number, distinguished by their varying solubilities
in different salts and by the varying temperatures at which they
coagulate. From muscle-plasma may then be obtained: (i) Para-
myosinogen and (2) myosinogen, the former coagulating at 47° C, the
latter at 56° C. It is myosinogen which is converted into myosin
under the influence of some special ferment, though both enter into
the formation of the muscle-clot. From the muscle-serum may also
be obtained at 68° C. a globulin body termed myoglobuhn and a
small quantity of myoalbumin. Among the proteids may be men-

68 TEXT-BOOK OF PHYSIOLOGY.

tioned hemoglobin, which gives the color to the muscles. Spectro-
scopic investigation reveals the presence of a special pigment, myo-
hematin, which is supposed to have a respiratory function, inasmuch
as its absorption bands change by oxidation and reduction.

Among the extractives containing nitrogen may be mentioned
creatin, creatinin, xanthin, carnin, urea, uric acid, carnic acid, etc.
Among the extractives free of nitrogen, glycogen, dextrose, inosite,
lactic acid, fat, are the most important. Inorganic salts are relatively
abundant, of which potassium is the most abundant among the bases,
and phosphoric acid among the acids.

THE PHYSICAL AND PHYSIOLOGIC PROPERTIES OF MUSCLE-
TISSUE.

Consistency. — The consistency of muscle-tissue during hfe
varies considerably in accordance with different states of the muscle.
In a state of tension it is hard and resistant ; in the absence of tension
it is soft and fluctuating to the sense of touch. Tension alone gives
rise to hardness.

Cohesion. — The cohesion of a muscle is largely dependent on the
quantity of connective tissue it contains. A band of fresh human
muscle one square centimeter in cross-section was able to resist a
weight of 14 kilograms without rupture (McAhster). Cohesion
resists the forces of traction and pressure.

Elasticity. — Muscle, in common with many other organic as
well as inorganic substances, is capable of being extended beyond the
normal length through the action of external forces and of resuming
the normal length when these forces cease to act. All such bodies
are said to be elastic; and the greater the variations between the
natural and acquired lengths, the greater is their elasticity said to be.
Muscle therefore possesses extensibihty and elasticity.* If the
muscle of a frog, preferably the sartorius, the fibers of which are
arranged in a practically parallel manner, be fastened at one ex-
tremity by a clamp, and then extended by a series of successive
weights which differ by a common increment, it will be found that
the extensibility of muscle does not follow the law of elasticity as
determined for inorganic bodies; i. e., directly proportional to the
weight and to the length of the body extended; but that while in-
creasing in length with each successive weight, the increase is always
in a diminishing ratio. Thus, for example, as shown in Fig. 19:
The extension produced by 5 grams is 5 millimeters, that produced
by 10 grams is only 4 millimeters more, and so on with additional

* By this latter term is here meant the power by virtue of which the muscle
returns to its original length, and is used synonymously with perfect retractibility.

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

69

Fig. 19. — Extension Curve
OF Muscle. — {Gad.)

weights until the increase in passing from 25 to 30 grams is only i
millimeter. The extensibiHty is thus shown to be proportionately
greater with small than with larger weights. It is, however, actually
greater with the larger weights. The ex-
tention curve A B formed by joining the
ends of the muscle approximates that of a
parabola. The muscle in returning to its
original length also shows a variation from
the behavior of inorganic bodies. With
the successive removal of the weights, the
elasticity of the muscle asserts itself with
gradually increasing energy until its nor-
mal length is nearly, if not entirely, re-
gained (Fig. 20). Though it is usually
stated that the elasticity of muscle is in-
complete, it must be borne in mind that
the experiments have usually been made
on muscles removed from the body, de-
prived of blood and nerve influences,
and hence under abnormal conditions.
It is highly probable that in the living
body muscles possess perfect elasticity
which enables them to completely return
to their normal length after extension. The extension and elastic
recoil of muscle depends on the maintenance of physiologic condi-
tions. If the nutrition is impaired, by fatigue, deficient blood-sup-
ply, or any pathologic condition, the elasticity is at once impaired.

Tonicity. — This is a property pos-
sessed by all muscles in the body in con-
sequence of being stretched to a shght
extent beyond their normal length. This
may be due to the action of antagonistic
muscles or to their mode of growth, the
muscles growing somewhat more slowly
than the bones to which they are at-
tached. That muscles are so stretched
is shown by the shortening which at once
takes place when their tendons are di-
vided. This muscle tonus or tension is
closely connected with the elasticity and
plays an important role in muscle contraction; being always on the
stretch, the muscle loses no time in acquiring that degree of tension
necessary to immediate action on the bone to which it is attached.
The working power of a muscle is also increased by the presence,
within limits, of some resistance to the act of contraction. Accord-

. 20. — Curve of Elas-
ticity Produced by
Continuous Extension
AND Recoil of a Frog's
Muscle. 0 x. Abscissa
before; x', after extension.

70 TEXT-BOOK OF PHYSIOLOGY.

ing to Marey, the amount of work is considerably increased when
the muscle energy is transmitted by an elastic body to the mass to be
moved, while at the same time the shock of the contraction is less-
ened. The position of a passive limb is the resultant also of the
elastic tension of antagonistic groups of muscles.

Another explanation for the tonicity of muscle is found in the fact
that the skeletal muscles of the body receive continuously nerve
impulses from the thermogenic centers. The chief function of the
tonicity would thus be the production of heat, other functions which
the tone subserves being merely secondary.

Irritability, Contractility. — These are terms employed to de-
note that property of muscle-tissue in virtue of which it responds by a
change of form, becoming shorter and thicker on the application of
any external agent which acts as a stimulus. On the withdrawal
of the stimulus the muscle again undergoes a change of form,
becoming longer and narrower, and returns to its original con-
dition. All muscles which possess this capability are irritable and
contractile; and all agents which excite the muscle to action are
stimuli. The rapid change of form which a highly irritable muscle
undergoes in response to the action of a stimulus of short duration is
usually termed a twitch or pulsation. With appropriate apparatus
it can be shown that the muscle at the time of the twitch becomes
warmer and exhibits electric phenomena. The muscle is therefore
an apparatus for the conversion of potential into kinetic energy:
viz., heat, electricity, and mechanic motion.

Though usually associated with the activity of the nervous system,
and to some extent dependent on it, irritability is nevertheless an
independent endowment of the muscle and persists for a longer
or shorter period, as shown by many experiments, after all nerve
connections have been destroyed. Among the proofs which may be
presented in support of this view is the following: The introduction
of the drug curara into the body of an animal produces in a short
time complete paralysis. Experiment has shown that curara sus-
pends the conductivity of the intramuscular terminations of the
nerve-fiber and thus separates the muscle entirely from the nerve.
Though the animal is incapable of executing a single movement, its
muscles respond promptly on the apphcation of a stimulus. More-
over, portions of muscles exhibit irritabihty in which there is no trace
of nerve structure. This is the case with the ends of the sartorius
muscle of the frog and the anterior end of the retractor muscle of
the eyeball of the cat. These and other facts demonstrate the in-
dependence of muscle irritability.

In the living body irritability and nutritive activity, with which
it is closely associated, are maintained by a due supply of oxygen,
of nutritive material, the removal of waste products, and a nor-

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 71

mal temperature. The muscles of the cold-blooded animals, and
especially the frog, retain their irritability for a much longer period
than the muscles of the warm-blooded animals. This is the case also
with the individual muscles after removal from the body of the animal.
The reason for this is found in all probability in the difference in the
rate of their nutritive activities and in the cjuantity of nutritive mate-
rial stored up in their cells. The duration of the irritability of isolated
muscles can be considerably prolonged by keeping them moist.

Muscle Stimuli. — Though consisting of a highly irritable tissue,
muscles do not possess spontaneity of action. They require for the
manifestation of their characteristic activity the application of a
stimulus. In the living body all contractions, at least of the skeletal
muscles, occurring under normal or physiologic conditions are caused
by the action of "nerve impulses" transmitted by the nerves from the
central nervous system to the muscles. The nerve impulse is the
normal or physiologic stimulus. After removal from the body and
freed from nerve connections muscles can be excited to action by
various agents — e. g., mechanic, chemic, thermic, electric. These
are artificial or non-physiologic stimuli.

1. Mechanic Stimuli. — Cutting, pinching, sharply tapping the muscle

will cause it to contract, providing the stimulus has sufficient
intensity. With each stimulation a short, l^eeting contraction
ensues. If repeated with sufficient rapidity, a series of con-
tinuous but irregular pulsations are produced.

2. Chemic Stimuli. — Various chemic substances in solution will

excite single or continuous pulsations if the strength of the solu-
tion is not such as to destroy at once the irritability. They owe
their efficiency as stimuli to the rapidity with which they alter
the composition of the muscle-substance. Among these may be
mentioned solutions of potassium and sodium, weak solutions of
the mineral and organic acids, ammonium vapor, distilled water,
glycerin, and sugar.

3. Thermic Stimuli. — The application of a heated object, such as a

hot wire, causes the muscle to rapidly contract.

4. Electric Stimuli. — The most efficient stimulus and the one least

injurious to the tissue is the electric current. Either the con-
stant or the induced current may be used.*
The Constant Current. — If the ends of the wires in connection with
an electric cell be provided with non-polarizable electrodes and the

* Since the study of the physiologic properties of both muscle-tissue and nerve-
tissue involves the employment of electricity as a stimulus, is becomes necessary for
the student to familiarize himself with certain forms of apparatus by which it is gen-
erated, controlled, and applied. For the purpose of not interrupting the continuity
of the text this information is embodied in an appendix. The facts therein contained
should be mastered by the student.

72 TEXT-BOOK OF PHYSIOLOGY.

latter placed on opposite ends of a freshly prepared sartorius muscle
of a frog which has been previously curarized, it will be found on
closing or making the circuit that the muscle will exhibit a short quick
pulsation. During the actual passage of the current, especially if
it is weak, there may be no apparent change in the muscle. If the
current is strong, the muscle may, on the contrary, remain in a state
of continuous contraction. With the opening or breaking of the
current the muscle at once relaxes, or perhaps again contracts and
then relaxes. The extent of the contraction depends mainly on the
strength of the current, being greater with strong, less with weak
currents. When the current is sufficiently strong to elicit both
making and breaking contractions, it is found that the contraction
occurring on the make or closure of the circuit is always greater
than that occurring on the break or opening of the circuit. More-
over, it has been shown in many ways that the contraction occur-
ring on the closure of the circuit has its origin at the point where
the current is leaving the muscle — i. e., in the immediate neighbor-
hood of the negative pole or cathode — and propagates itself to the
opposite extremity; while the contraction occurring on the opening
of the circuit has its origin at the point where the current is entering
the muscle, i. e., in the neighborhood of the positive pole or anode.

The Induced Current. — If the primary spiral of the inductorium
be connected with an electric cell and the secondary spiral be con-
nected with a muscle, it wall be found that the current induced in the
secondary circuit, both on the make and break of the primary, will
also cause the muscle to sharply and rapidly pulsate if the two spirals
are sufficiently near each other. Observation, however, makes it
evident that the pulsation occurring with the break of the primary
circuit is more energetic than that occurring with the make, a result
the opposite of that obtained with the constant current. This is
not due to any difference in the electricity, however, but to pecuHarities
in the construction of the inductorium. When the primary circuit
is interrupted with sufficient frequency, as it can be by throwing into
the circuit Neef's hammer or some other form of interrupter, the con-
tractions excited by the induced currents may be made to succeed one
another so rapidly that they become fused together, producing a
spasm or tetanus of the muscle. The rapidity with which the induced
current appears and disappears, its brief duration, the ease with which
its strength can be regulated, combine to render it a most efficient
stimulus for either muscle or nerve.

Conductivity. — All muscle protoplasm possesses conductivity.
The change excited in a muscle-fiber by the arrival of a nerve impulse
is at once conducted with great rapidity in opposite directions to
the end of the fiber; the advance of the excitation process is im-
mediately succeeded by the contraction process, the change of form

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 73

which constitutes the contraction. With the disappearance of the
former, the latter also disappears and the muscle resumes its pre-
vious passive condition. There is no evidence, however, that the
excitation process travels transversely, — that is, into adjoining fibers,
— being prevented from doing so by the presence of the hmiting
membranes, the sarcolemmata. The fact that each muscle-fiber
receives its own, or at least a branch of a nerve-fiber, and hence its
own nerve impulse or stimulus, would also indicate that the excitation
process can not be conducted longitudinally into adjoining fibers,
or at least with sufiicient rapidity for the purposes of ordinary muscle
actions. Nevertheless if a long muscle, such as the sartorius, from a
curarized frog be stimulated at one end with an induced electric cur-
rent, the excitation and the contraction processes will be conducted
with extreme rapidity to the opposite end of the muscle. The rapidity
of conduction in human muscles has been estimated at from 10 to 13
meters per second, and in frog's muscle at from 3 to 4.5 meters per
second. The contraction process, the thickening of the muscle, is
termed the contraction wave. As it is the result of the excitation
process and immediately succeeds it, its rate of conduction must be
the same as that given above. With appropriate apparatus the
duration of the wave at any given point has been shown to be, in the
frog's muscle, one-tenth of a second and its length three-tenths of a
meter.

PHENOMENA ATTENDING A MUSCLE CONTRACTION.
PHYSICAL PHENOMENA.

The most obvious change in a muscle during the contraction is
that relating to its form. The muscle not only becomes shorter, but
at the same time thicker. The extent to which it may shorten when
unopposed may amount to 30 per cent, or more of its original length.
The increase in thickness practically compensates for the diminution
in length, for there is no observable diminution in volume. The
change in form of the entire muscle results from a corresponding
change of form of its individual fibers as determined by microscopic
examination, eaCh of which becomes shorter and thicker. The
successive changes in both the muscle and the individual fibers are
represented in Fig. 21.

When the contraction begins, the dim band increases and the
bright band diminishes in width. This Engelmann attributes to
the passage of fluid material from the bright into the dim band. At
the time of relaxation there is a return of this material and the bands
assume their original shape and volume. As the contraction wave
reaches its maximum the optic properties of the bright and dim bands
change. The former now becomes darker and less transparent

74

TEXT-BOOK OF PHYSIOLOGY.

until at the crest of the wave it assumes the appearance of a distinct
dark band; the latter now becomes clear and bright in comparison.
This change in the appearance of the fiber is due to an increase in
refrangibility of the bright and a decrease in the refrangibility of the
dim band coincident with the passage of the fluid from the former
into the latter. There is at the height of the contraction a complete
reversal in the positions of the striations. At a certain stage between
the beginning and the crest of the wave the striee almost entirely dis-
appear, giving to the fiber an appearance of homogeneity. There is,
however, no change in refractive power as shown by the polarizing
apparatus. When the contraction wave has reached the stage of
greatest intensity, there is a reversal of the above phenomena as the
fiber returns to its former condition, that of relaxation.

Fig. 21. — Showing the Changes in a Muscle and Muscle-fiber during Con-
traction.

Elasticity. — During the contraction of a muscle there is a greater
or less alteration in its elasticity, as shown by the fact that it is ex-
tended to a greater degree by the same weight in the active than in
the passive condition. The degree to w^hich the extensibihty is in-
creased and the elasticity decreased is dependent on the amount of
the resisting force. These facts, as determined experimentally, are
represented in Fig. 22. Let A B and A b represent the length of the
normal unweighted muscle, passive and active states respectively; the
line B B', the extension curve of the passive muscle produced by
successive weights, 5, 10, 15, 20, 25, 30 grams, differing by a com-
mon increment; the Hne b B', the extension curve of the active con-
tracted muscle when weighted with the same weights; A' B' the length
of the muscle when the weight is sufficiently great to prevent shorten-
ing. It will be observed from these facts that while the muscle is
extended in both the passive and active states by corresponding

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

75

weights, the extension during the latter is progressively greater, until
with a given weight the length of the muscle is the same. Under
such circumstances, there being no shortening of the muscle, the
energy of its contraction manifests itself physically merely as tension.
In the successive actions of the muscle represented in the same figure
there is to be observed also a combination of a change of length and

A

A

N

0 5

lO"

s

1

5 2

0 z

5 3

0

,

K

R

Fig. 22. — ExTENSiox Curves: B B', of the resting; b B', of the contracting muscle.

a change of tension, the ratio of the one to the other being deter-
mined by the amount of the supported weights. When the weight
is shght in amount, the shortening of the muscle reaches a maximum
and the tension a minimum; when the weight is large in amount, the
reverse conditions obtain.

THE CONTRACTION PROCESS. METHODS OF INVESTIGATION.

The contraction of a muscle as it takes place in the hving body and
under normal physiologic conditions is a complex act, persisting for
a variable length of time in accordance with the number of stimuU
transmitted to it in a given unit of time, and as determined experi-
mentally is the resultant of the fusion of a greater or less number of
separate and individual contractions or pulsations. To this enduring
contraction the term tetanus has been given. With the aid of ap-
propriate apparatus it has become possible to obtain and record
single muscle contractions, to analyze and decompose them into their
constituent elements, or to combine them in such a manner as to pro-
duce practically a normal physiologic tetanus. As in the experi-
mental study of the phenomena of a muscle contraction it frequently
becomes necessary to remove the muscle from the body of the animal,
the muscles of warm-blooded animals are not well adapted for this
purpose, owing to the rapid akeration in composition they undergo,

76

TEXT-BOOK OF PHYSIOLOGY.

with a consequent loss of irritability, when deprived of their normal
blood-supply. The excised muscles of cold-blooded animals, par-
ticularly of the frog, — in which, owing to the relatively slow rate of
the nutritive activities, the irritability and contractility endure for a
long period of time, even though deprived of blood, — are particularly
valuable for experimental studies. The muscles generally employed
are the gastrocnemius, the sartorius, and the hyoglossus. If kept
at a normal temperature and moistened with 0.6 per cent, solution of
sodium chlorid, such a muscle will contract for a long period of time
on the application of any form of stimulus, but especially the electric.
Graphic Record of a Muscle Contraction. — Inasmuch as the
changes in the form of a muscle during a single contraction take place
with extreme rapidity, their succession, peculiarities, and time re-

FiG. 23. — Myograph. K. Recording cylinder. M. Moist chamber. L. Record-
ing lever. W. Weight. I. Induction coil.

lations cannot be determined with any degree of accuracy by the
unaided eye. This difficulty can largely be overcome by the employ-
ment of the graphic method, the principle of which consists in record-
ing the movements by means of a pen on some appropriate moving
and receiving surface. To accomphsh this object the muscle is at-
tached at one extremity by a clamp to a firm support, and at the other
extremity to a weighted lever, which is, however, sufficiently light to
enable it to take up, reproduce, and magnify its movements. The
end of the lever provided with a pen is applied to a smooth surface,
such as glazed paper on a cyhnder or plate, and covered with lamp-
black. If the surface is stationary, the contraction is recorded as a
vertical line; if it is placed in movement at a uniform rate by clock-

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

77

work, the contraction is recorded in the form of a curve, the width of
the arms of which will depend on the rate of movement. The time
relations of the phases of the contraction can be obtained by placing
beneath the lever a pen attached to an electro-magnet thrown into
action by a turning-fork vibrating in hundredths of a second. In
order to determine the rapidity with which the contraction follows
the stimulation, it is essential that the moment of the latter be also
recorded. This is accomplished by an automatic key, the opening
or closing of which develops the stimulus which excites the muscle.
A combination of these different apphances constitutes a myograph
and the curve of contraction a myogram. (See Fig. 23.)

The Isotonic Myogram. — With the object of obtaining a curve
of successive changes in the length of a muscle during a single con-
traction and at the same time avoiding changes in tension, the weight

Fig. 24. — The Isotonic Myogram.

attached to the lever should be apphed close to its axis, a mechanic
condition which practically maintains a uniform tension throughout
the contraction. To this method the term "isotonic" has been given
and the curve so obtained an isotonic myogram.*

The Character of an Isotonic Myogram. — With the muscle
arranged as previously described and stimulated directly with a single
induction shock, the contraction will be recorded in the form of a
curve similar to that represented in Fig. 24, in which the hne t t repre-
sents the abscissa of time; a, the moment of stimulation; and bed,
the degree of shortening at each successive moment. The undulating
Hne shows the time relations, the distance from crest to crest represent-

* In the ordinary method of recording a muscular movement, i. e., with the weight
attached to the lever immediately beneath the muscle and known as the "loaded
method," a certain momentum is imparted to the weight, which continues after the
muscle has ceased to act, both when shortening and relaxing, and so imparts to the re-
cording lever additional movements which vitiate the true character of the curve.

78 TEXT-BOOK OF PHYSIOLOGY.

ing hundreths of a second. The curve may be divided into three
portions :

1. A short but measurable portion between the point of stimulation

and the first evidence of the shortening, a b, known as the
"latent period." The duration of this period for the skeletal
muscle of the frog was originally determined to be o.oi second,
but with the employment of more accurate apparatus it has been
reduced to 0.0025 to 0.004 second. During this period it is
supposed that certain chemic changes are taking place prepara-
tory' to the exhibition of the movement. The duration of the
latent period is influenced by a variety of conditions, e. g., tem-
perature, fatigue, strength of stimulus, etc.

2. An ascending portion, b c, the contraction or period of increasing

energy. The contraction as shown by the character of the curve
begins slowly, then proceeds rapidly, and again slowly as the
shortening reaches its maximum. The contraction may be said
to end when the tangent to the curve becomes parallel with the
abscissa.

3. A descending portion, c d, the relaxation or period of decreasing

energy. The relaxation as shown by the character of the curve
begins slowly, then proceeds rapidly, and again slowly as the
muscle attains its original length. The termination of the re-
laxation is at the point where the curve cuts the abscissa. The
curve beyond this point may be complicated by the presence of
one or more residual or after- vibrations, which are probably due
to the inertia of the lever as well as to changes in the muscle
elasticity.
The duration of the period of shortening is about 0.04 second, and
of the period of relaxation 0.05 second. A single pulsation of the
isolated muscle of the frog therefore occupies, from the moment of
stimulation to termination, the tenth of a second. Muscles of many
other animals have a contraction period the duration of which varies
considerably from this. Thus, in man the time of a single contrac-
tion is one-twentieth of a second, in some insects one three-hundreth
of a second, and in the turtle one second. Pale muscles have a shorter
period than the red.

Influences Modifying the Contraction Process. — The con-
traction process in its entirety as well as in its individual parts is
considerably modified by external conditions, among which may be
mentioned the following:

I. Stimulus. As the contraction is the response of the muscle to
a stimulus, the vigor of the former is proportional, within limits,
to the strength of the latter. Thus, with single induction shocks
the height of the contraction or the degree of shortening increases
as the strength of the stimulus increases from a minimum to a

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

79

maximum value (Fig. 25). The rate at which the muscle is
stimulated with a given stimulus will also influence the character
of the contraction process. If the intervals between the successive
stimulations be such as permit the muscle to recover from the
effects of the contraction, it may contract as many as a thousand
times without showing any particular variation from the normal
form. In the earher period of stimulation there is apparently
a decrease in the irritability and consequently in the energy of
the contraction for a short time. This is followed by an in-
crease in the irritability, as shown by a gradual increase in the
height of the curve until a certain maximum is reached and
maintained (Fig. 26). These so-called staircase contractions have
been observed in the muscles of both cold-blooded and warm-
blooded animals. In time, however, as the muscle becomes
fatigued the eft'ects of repeated contractions manifest themselves
in a lengthening of the latent period, a diminution in the
rapidity and extent of the contraction, and an increase in the

Fig. 25. — Shouting the Ef-
fects OF IXCREASIN'G

Strength of Stimulus.

Fig.

26. — Showing Staircase Con-
tractions.

time of relaxation. If the intervals between successive stimu-
lations be not sufficient for the muscle to recover itself, the same
phenomena arise, though more quickly.
2. Temperature. The temperature at which all phases of the con-
traction process, as represented by the myogram, attain their
physiologic maximum value is about 30° C. If the temperature
of the muscle falls to 20° C. there is a corresponding decline in
activity, as shown by an increase of the latent period, a decrease
in the height of curve, — /'. e., in the shortening of the muscle, —
an increase both in the contraction and relaxation periods. As
the temperature approaches 0° C. the height of the curve again
suddenly increases, indicating, for some unknown reason, an
increase in the irritability. This is, however, scarcely a physio-
logic condition. At a temperature of 40° C. to 50° C. the muscle
suddenly contracts and passes into the condition of heat rigor.
The proteid constituents of the muscle are coagulated and the
irritability destroyed (Fig. 27).

8o

TEXT-BOOK OF PHYSIOLOGY.

The Load. The extent to which a muscle is loaded or weighted
will not only determine the height of the contraction, but also the
time relations of all its phases. This is apparent from an ex-
amination of Fig. 28, in which it is shown that with an increase
in load there is a decrease in the height of the contraction, an
increase in the latent period, and a general decrease in the dura-
tion of both the periods of rising and falling energy.

J.

C

S

^

Cr=5= -^ — —

=

\y , -' ^ -^ ^ v^--^^^N^x.^\.^\^ 1

Fig. 27. — Single Contractions of the Gastrocnemius at Different Tempera-
tures. Time Tracing, 200 per Second. — {Brodie.)

4. Muscle Fatigue. Prolonged or excessive activity of our own
muscles is accompanied by a feehng of stiffness or soreness and
lassitude. There is at the same time a diminution in the rate and
vigor of the contractions and the power of doing work. To this
condition the term fatigue has been given. The cause of the
fatigue is attributed to a diminution in the amount of the energy-
holding compounds as well as to the production and accumulation

Fig. 28. — Contractions of a Gastrocnemius with Different Loads. — (Brodie.)

of waste products resulting from activity. Among the waste
products phosphoric acid, potassium phosphate, lactic acid, and
carbon dioxid are the most important. The more rapidly they
are removed, the sooner is a fatigued muscle restored to its normal
condition. It is highly probable that the nerve-centers are more
easily fatigued than the muscles. The condition of fatigue with

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 8i

its attendant phenomena is shown by an excised frog muscle
when stimulated for a long period of time by induction shocks
at intervals of one second. In a variable period of time the
muscle shows an increase in the duration of the latent period,
a diminution of the height of the contraction, in the power of
doing work, and an increase in the time required for relaxation.
If the stimulation continues, the contractions gradually decline
as the muscle becomes exhausted. (See Fig. 29.)

Fig. 29. — Fatigue Curves. Every Twentieth Contraction Recorded.

5. Nutrition. — The irritabihty of a muscle which conditions the con-
traction process is dependent on the maintenance of its nutrition ;
hence a continuous and sufficient supply of nutritive material
and a rapid removal of waste products are essential conditions
for the exhibition of normal contractions. A diminution of
blood-supply or an accumulation of waste products sooner or
later impairs the irritabihty and diminishes the vigor and extent
of the contraction. Various drugs — e. g., veratrin, barium, etc.
— introduced into the circulation and finding their way into the
muscle modify the contraction process, as shown by a ver\' great
increase in the duration of the relaxation period.
The Isometric Myogram. — With the object of obtaining a

curve of the increase and de-
crease in the tension of a muscle

during a single contraction, with

the exclusion as far as possible

of a change in length, the muscle

may be made to contract against a

strong spring or similar resistance

sufficient to practically though

not absolutely prevent shorten-
ing. To this method the term

isometric has been given, and the

curve so obtained an isometric

myogram or a tonogram. The

recording portion of the lever is prolonged some distance so that the
6

Fig. 30. — a. Diagram of Isotonic; b,
OF Isometric Muscle Curves.

82 TEXT-BOOK OF PHYSIOLOGY.

very slight upward movement at its axis, close to which the muscle
is attached, will be considerably magnified. That the ordinate value
of an isometric curve may be known, the apparatus must be graduated
by subjecting the spring to a series of weights playing over a pulley
supported by the muscle clamp.

The curve of the variation in tension obtained by the isometric
method is shown in Fig. 30, b, in which the two curves are con-
trasted. The form of the curve indicates that the muscle attains its
maximum of tension more rapidly than its maximum of shortening ;
that the tension endures for a certain period of time unchanged; that
the fall in tension takes place more rapidly than the muscle relaxes.

The Work Accomplished by a Muscle during the Time of a
Single Contraction. — By work is meant the overcoming of opposing
forces. In the physiologic activities of the body the muscles at each
contraction not only overcome the resistances of antagonistic muscles,
the weight of the limbs, the friction of joints, etc., but in addition
overcome various external resistances connected with the environ-
ment— e. g., gravity, cohesion, friction, elasticity, etc. The muscles
may therefore be regarded as machines for the accompUshment of
work. Experimentally the work done by an isolated muscle may be
calculated by multiplying the weight by the height through which it
is lifted. In the following table it will be observed that the extent
to which a muscle will shorten in response to a maximal stimulus
is greatest when it is unweighted ; but as weights differing by a com-
mon increment are added, the height of the contraction diminishes
until with a given weight it is nil. The work done is shown in the
followino; table:

Weight.

Height.

Work Done.

0 grams

14

mm.

0

gram-

-millimeters

50 "

9

450

*'

100 "

7

700

'^

150 "

5

750

200 "

2

400

'^

250 "

0

0

'*

From the preceding figures it is evident that the mechanical work of
a muscle increases with increasing weights up to a certain maximum,
and then dechnes to zero. Equally when the muscle contracts to its
maximum without being weighted, and when it does not contract at
all from being overweighted, no work is done. Between these two
extremes the muscle performs varying amounts of work.

The maximum amount of force which a muscle puts forth during a
contraction is naturally measured by the amount of work done; but
as this varies with the degree to which the muscle is weighted, another
measure has been adopted, to which the term absolute muscle force
or static force has been given. The absolute force is measured by

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 83

the weight which is sufficient to prevent the muscle from shortening.
This is best determined by the method of after-loading in which the
muscle is not extended by the weight previous to the contraction.
It has been found that the absolute force of a muscle is directly de-
pendent on the number and not the length of the fibers it contains
and proportional to the physiologic transverse section of the muscle.
The transverse section of a muscle is obtained by dividing the volume
1058 (obtained by dividing its weight by the specific weight of mus-
cle-tissue) by the average length of the fibers.

For purposes of comparison it is customary to refer the absolute
force to units of diameter — viz., one square centimeter. Rosenthal
estimates the force for the square centimeter of the muscle of the frog
at from 2 to 8 kilograms; for the muscles of man at 6 to 8 kilograms;
Koster at about ten kilograms for the muscles of the leg and 7 or 8
kilograms for the muscles of the arm.

Action of Successive Stimuli. — If a series of successive stimuli
be appHed to a-muscle, the effect will vary according to the rapidity
with which they follow one another. As previously stated, if the

Fig. 31. — Summation Curve. Fig. 32. — Summation Curve.

interval preceding each stimulus be sufficiently long to enable the
muscle to recover from the effects of the previous contraction, there
will be no effect for a long time except a slight increase, in the early
period, of the irritability as shown by the increased height of the
curve or shortening of the muscle. If, however, a second stimulus
be apphed to a muscle during the period of relaxation, a second con-
traction immediately follows which is added to or superposed on the
first; the effect produced will be greater than that produced by either
stimulus separately.

A third stimulus apphed during the relaxation of the second con-
traction produces a third contraction which adds itself to the second,
and so on (Fig. 31). The increment of increase in the extent of the
successive contractions gradually diminishes, however, until the muscle
reaches a maximum of contraction. The superposition of the second
contraction on the first, the third on the second, and so on, is termed
summation of effects. Experiment has shown that the greatest effect
of a second stimulus — that is, the highest contraction — is produced

84 TEXT-BOOK OF PHYSIOLOGY.

when the stimulus is appMed during the last third of the period of
rising energy, when the sum of the two contractions is almost twice as
great as the first contraction (Fig. 32). The effects following both
maximal and submaximal stim.uli indicate that the muscle cannot
attain its maximum of shortening except through a summation of
several stimuli. If a second maximal stimulus enter a muscle dur-
ing the latent period following the first, the effect produced will be
no greater than that produced by a single stimulus. The muscle
during this period is said to be refractory or non-responsive to a
second stimulus. If, however, the stimuli are submaximal they add
themselves together, and though the effect is but a single contrac-
tion, it is larger than either would have produced separately. This
is termed the summation of stimuli.

Still further, if a series of subminimal stimuh, each of which is
alone insufficient to produce a contraction of the muscle, be apphed
in rapid succession, a contraction frequently results. This is termed
the summation of subminimal stimuli.

Tetanus. — When a muscle is stimulated by a series of induction
shocks at the rate of four or six per second, it undergoes a corre-
sponding number of contractions of about equal extent. If the rate
of stimulation is increased up to the point when the interval before
each stimulus is less than the duration of the entire contraction pro-
cess, the muscle does not have time to completely relax between each
successive stimulus, and hence remains in a more or less contracted
state, during which it exhibits a series of alternate partial contrac-
tions and relaxations. To this condition of muscle activity the term
incomplete tetanus or clonus is apphed. A graphic record of an in-
complete tetanus is given in Fig. 33.

In such a tracing it is observed that the second stimulation, oc-
curring before the muscle had time to relax, gave rise to a second
contraction, which was superposed on the first; the same result fol-
lowed the third stimulus, the fourth, the fifth, and so on. Owing
largely to this summation of the contractions there is a gradual rise
in the height of the contraction curve. This condition of the muscle,
viz., continued contraction, combined with diminished power of
relaxation, is termed contracture. The tracing also shows that as
the stimulus continues, the base hne, that connecting the lowest
points of the contractions, gradually rises and takes the form of a
curve which increases in height with the stimulation. The apex
line, that connecting the highest points of the contractions, also rises
at the same time, indicating a continuous increase in the height of
the contractions. The duration of incomplete tetanus depends on
a variety of circumstances, e. g., character of muscle, rate and strength
of stimulation, etc., but mainly on the rapidity with which the muscle
becomes fatigued. With the oncoming of fatigue the muscle begins

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 85

to relax, and ultimately returns to its normal condition, notwith-
standing the continued stimulation. If the stimulation be with-
drawn, the muscle does not at once return to its original length but
remains more or less contracted for a variable time. This contrac-
tion after stimulation is known as the contraction-remainder.

If the stimulation be still further increased in frequency, the
individual contractions become fused together and the curve described
by the lever becomes a continuous line. (See Fig. 33.) Notwith-
standing the fact that the individual contractions are no longer visible,
it can be shown by other methods that the muscle is undergoing a
series of slight alternate contractions and relaxations or vibrations
at least. After a varying length of time the muscle becomes fatigued,
relaxes, and returns to its natural condition even though the stimu-
lation continues. The number of stimuli per second necessary to
develop tetanus will depend under normal circumstances on the

Fig. 33. — Curves Showing the Analysis of Tetanus of a Frog's Muscle (Gas-
trocnemius). The numbers under the curves indicate the number of shocks per
second apphed to the muscle. There is almost complete tetanus with twenty-
five per second, and it is a little lower than the previous one because the muscle
was slightly fatigued. — {Stirling.)

period of duration of the individual contractions. The longer this
period, the less the number of stimuli required, and the reverse.
Hence the number of stimuli will vary for different classes of animals
and for different muscles in the same animal, f. ^., 2 or 3 for the
muscles of the tortoise, 10 for the muscles of the rabbit, 15 to 20 for
the frog, 70 to 80 for birds, 330 to 340 for insects.

Voluntary Tetanus. — The voluntary contractions as they occur
in the living body are to be regarded as states of tetanus more or less
complete; for the simplest voluntary contraction, however rapidly
it takes place, has always a longer duration than a single con-
traction caused by a single induction shock. As tetanus experi-
mentally produced is the result of a certain number of successive
stimulations per second, it is assumed that a voluntary tetanus is the
result of the transmission to the muscles of a certain number of nerve

86 TEXT-BOOK OF PHYSIOLOGY.

stimuli per second. In other words, the voluntary tetanus is also the
result of a discontinuous stimulation. The number of stimuli trans-
mitted to a muscle has been estimated by the employment of the
graphic method to vary from 8 to 13 per second, 10 being about the
average. Unless the contraction process of human muscle differs
from that of frogs, it is difficult, however, to see how 10 stimulations
per second can give rise to even an incomplete tetanic contraction.

Muscle Sound. — Providing a muscle be kept in a state of tension
during its contraction, the intermittent variations in tension cause
the muscle to emit an audible sound. This so-called muscle-sound or
tone is an evidence that the stimulation of the muscle is not continu-
ous, but discontinuous. If the muscle is tetanized by induction
shocks, the pitch of the tone will correspond with the number of
stimuli. A voluntary contraction is attended by a tone having a
vibration frequency of about 36 to 40 per second, which is regarded
as the first overtone of the muscle tone, which would have a vibration
frequency in consequence of from 18 to 20 per second. This was
formerly regarded as an indication of the rate of stimulation of volun-
tary contraction. This view, however, is no longer sustained.

CHEMIC PHENOMENA.

The chemic changes which underlie the transformation of energy
in the living muscle even when in a state of rest are active and com-
plex, though but little is known as to their exact character. As shown
by an analysis of the blood flowing to and from the resting muscle,
it has, while flowing through the capillaries, lost oxygen and gained
carbon dioxid. The amount of oxygen absorbed by the muscle
(9 per cent.) is greater than the amount of carbon dioxid (6.7 per
cent.) given off. Notwithstanding the relation of the oxygen ab-
sorbed to the carbon dioxid produced, there is no parallelism between
these two processes, as the carbon dioxid will be given off in the
absence of oxygen or in an atmosphere of nitrogen.

In the active or contracting muscle all the chemic changes are
increased, as shown both by an increased absorption of oxygen and
an increased production of carbon dioxid, though the ratio existing
between them differs considerably from that of the resting muscle.
Thus, according to Ludwig, an active muscle absorbs 12.26 per
cent, of oxygen and gives off 10.8 per cent, carbon dioxid. During
the activity of a muscle its tissue changes from a neutral to an acid
reaction, from the development of sarcolactic acid and possibly
phosphoric acid. The degree of the acidity depends to some extent
on the duration of the contraction periods. Chemic analysis of a
tetanized muscle shows that it contains less glycogen than a resting
muscle, and that it contains a larger amount of water. Coincident

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 87

with muscular contraction, tiic blood- vessels become widely dilated,
leading to a large increase in the blood-supply and a rapid removal
of the ])roducls of decomposition.

Rigor Mortis.^ — A short time after death the muscles pass into a
condition of extreme rigidity or contraction which lasts from one to
live days. In this state they offer great resistance to extension.
Their tonicity disappears, their cohesion diminishes, and their irri-
tability ceases. The time of the appearance of this postmortem
rigidity varies from a quarter of an hour to seven hours. Its onset
and duration are influenced by the condition of the muscle irrita-
bihty at the time of death. When the irritability is impaired from
any cause, such as chronic disease or defective blood-supply, the
rigidity appears promptly but is of short duration. After death from
acute diseases it is apt to be delayed, but will continue for a longer
period. The rigidity first appears in the muscles of the lower jaw
and neck; next in the muscles of the abdomen and upper extremities;
finally in the trunk and lower extremities. It disappears in prac-
tically the same order. Chemic changes of a marked character
accompany this process. The muscle becomes acid in reaction from
the development of sarcolactic acid and there is a large increase in
the amount of carbon dioxid given off. The immediate cause of the
rigidity appears to be coagulation of the myosinogen within the sarco-
lemma with the formation of an insoluble proteid, myosin. In the
early stages of the coagulation restitution is possible by the circula-
tion of arterial blood through the vessels. The final disappearance
of this postmortem rigidity is due to the action of acids which render
the myosin soluble, and possibly to the action of various micro-
organisms which give rise to putrefactive changes.

Source of the Muscle Energy .^ — Notwithstanding many in-
vestigations, the nature of the materials which are the immediate
source of the muscle energy is not known. The absence of any notice-
able increase in the quantity of urea or other nitrogen-holding com-
pounds excreted renders it probable that the energy does not come
from the metabolism of proteid materials. The marked production
of carbon dioxid and sarcolactic acid points to the decomposition of
some unstable compound, of a carbohydrate character, rich in carbon
and oxygen. It has been suggested that glycogen furnishes the
energy, inasmuch as this substance, generally present in muscle, dis-
appears during activity. A muscle which has been tetanized contains
less glycogen than the corresponding muscle at rest. A muscle which
has been separated from the nervous system by division of its nerves
and thus prevented from contracting accumulates glycogen. Bunge
is of the opinion that though the carbohydrates are the main, they are
not the only sources of muscle energy. If there is a deficiency or
absence of carbohydrate food, the muscle will utilize fat and pro-

88 TEXT-BOOK OF PHYSIOLOGY.

teid, for experiment has shown that the available glycogen is entirely-
consumed the second or third day. The mechanism by which the
energy is liberated, whether by decomposition or direct oxidation, is
unknown. The fact that muscle will contract in an atmosphere
free of oxygen, that no free oxygen can be obtained from muscle,
w^ould support the idea that the mechanism is one of decomposition.
Hermann suggests that the energy of a contraction is liberated by
the splitting and subsequent re-formation of a complex body belonging
neither to the carbohydrates nor fats, but to the proteids— to this hypo-
thetic body the term inogen is given. This complex molecule, the
product of the nutritive activity of the muscle-cell in undergoing
decomposition, would yield carbon dioxid, sarcolactic acid, and a
proteid residue resembling myosin. On the cessation of the con-
traction the muscle-cell recombines the proteid residue with oxygen,
carbohydrates, and fats, and again forms the energy-holding com-
pound, inogen. The phenomena of rigor mortis support this view.
At the moment of this contraction the muscle gives off CO2 in large
amount, develops sarcolactic acid and myosin. There is thus a close
analogy between the two processes; in other words, a contraction is a
partial death of the muscle. If this view is correct, then the oxygen
is required mainly for heat production through oxidation processes.

THERMIC PHENOMENA.

The potential energy Hberated during a contraction is transformed
into kinetic energy — viz., heat and mechanic motion. Though heat
production is taking place even during the passive condition, prob-
ably through oxidation processes, it is largely increased by muscle
activity. The skeletal muscle of the frog, the gastrocnemius, shows
after tetanization an increase in temperature from 0.14° C. to 0.18°
C, and after a single contraction from 0.001° C. to 0.005° C. The
amount of heat thus produced will vary with a variety of conditions,
as strength of stimulus, tension, work done, etc.

Stimulus. — It has been experimentally determined that an in-
crease in the strength of the stimulus from a minimal to a maximal
value increases the amount of heat hberated. This is the direct result
of increased chemic change naturally following increased stimulation.

Tension. — The greater the tension of a muscle, the greater, other
conditions being the same, is the amount of heat liberated. If the
muscle is securely fastened at both extremities so that shortening is
practically impossible during the stimulation, the maximum of heat
production is reached. In the tetanic state the great increase in tem-
perature is due to the tension of antagonistic and strongly contracted
muscles. In both instances, mechanic motion being prevented, the
liberated energy is transformed into heat.

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 89

Mechanic Work. — If the muscle is permitted to shorten and
raise a weight, some of the energy Hberated takes the form of mechanic
motion. If the weight is removed at the height of the contraction,
external work is accomplished. The greater the weight raised,
within hmits, the greater is the percentage of energy which takes the
direction of mechanic motion. In accordance with the law of the
conservation of energy, the heat produced, stated in calories, plus
the energy required in the raising of the weight, expressed in kilogram-
meters of work, must equal the potential energy transformed.

A muscle during a tetanic contraction of short duration accom-
plishes more work than during a single contraction; the weight in
each case being the same. In the former condition the height of
contraction through summation, and hence the work done, is greater
than in the latter. The work done by a short tetanic contraction may
be two or three times that of a single contraction, but after the
muscle reaches its maximum degree of shortening and then con-
tinues in a state of tetanus, no further work is done. Internal
work is done, however, as shown by an increase in the temperature.

When a weight which is lifted by a muscle during a single con-
traction is allowed to act on the muscle during the relaxation, no
external work is accomplished. All the energy set free manifests
itself as heat. Internal work is done, as shown by the fact that the
muscle becomes fatigued.

ELECTRIC PHENOMENA.

Electric Currents from Injured Muscles. — The energy hber-
ated during a muscle contraction is not only transformed into
heat and mechanic motion, but to soine extent also into electric
energy. The presence of points of different potential on the
surface of the muscle, the necessary condition for the development
of electric currents, is tested by means of non-polarizable elec-
trodes connected by wires with a sensitive galvanometer or capil-
lary electrometer. When such electrodes are brought in contact
with a muscle properly prepared, there is at once developed and con-
ducted to the galvanometer an electric current the intensity and direc-
tion of which are indicated by the deflection of the galvanometer needle.
The existence of this current is most conveniently demonstrated with
single muscles the fibers of which are parallel — e. g., the sartorius, or
the semimembranosus of the frog. If the tendinous ends of either of
these muscles be removed by a section made at right angles to the long
axis, a muscle prism is obtained which presents a natural longitudi-
nal surface and two artificial transverse surfaces. A line drawn around
the surface of such a muscle prism at a point midway between the
two transverse sections constitutes the equator.

po

TEXT-BOOK OF PHYSIOLOGY.

When the natural longitudinal and artificial transverse surfaces are
connected with the wires of a galvanometer the terminals of which are
provided with non-polarizable electrodes, an electric current is at once
developed. In all instances the current, as shown by the deflection
of the needle, originates at the transverse surface, passes through
the muscle to the longitudinal surface, thence through the galvan-
ometer to the transverse surface. The longitudinal surface is, there-
fore, electropositive, the transverse surface electronegative. The
two points exhibiting the greatest difference of potential, and

hence the most powerful current, lie
in the equator and in the center of the
transverse surface. Currents of grad-
ually diminishing intensity are ob-
tained when the electrode placed on
the longitudinal surface is removed
toward either end. Feeble currents
are developed when two points situ-
ated at unequal distances, either on
corresponding or opposite sides of the
ecjuator, are connected; in either case
the current flows from the point lying
nearest the equator to the point farth-
est from it. Similar currents are ob-
tained when two points on the cross-
section situated at unequal distances
from the central axis are connected, in
which case the direction of the current
will be from the point lying nearest
the periphery toward the center. On
the contrary, no current is developed
when two points on the longitudinal
surface equally distant from the equa-
tor, or two points on the transverse
surface equally distant from the cen-
tral axis, are connected. Such points
are said to be isoelectric. These facts
are shown in Fig. 34. The natural -ends of the muscle, enclosed by
sarcolemma and tendon, do not exhibit, if carefully preserved from
injury, the negativity characteristic of the artificial transverse ends.
Similar electric conditions are exhibited by the muscles of man
and other mammals, by the muscles of birds, reptiles, amphibia, etc.
The currents developed by connecting the equator on the longitu-
dinal surface with the axis of the transverse surface have an electromo-
tive force in the frog muscle of from 0.037 to 0.075 o^ ^ Daniell cell.
The electric currents in the muscle are intimately associated with

Fig. 34. — Diagram to Illustrate
THE Current in Muscle.
The arrowheads indicate the
direction; the thickness of the
Unes indicates the strength of
the currents.

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

91

the chemic changes underlying its nutrition, and hence their intensity
rises and falls with all the conditions Avhich maintain or impair mus-
cle nutrition and irritability. The currents observed in the injured
muscle during the inactive state have been termed currents oj rest.
du Bois-Reymond regarded them as preexistent, intimately connected
with the Kving condition of the muscle, and essential to the performance
of its functions, and to be explained by the view that the entire muscle
is composed of molecules each of which exhibits the same difference
of potential on its longitudinal and transverse surfaces as the muscle
prism itself. Hermann denies the existence of currents in normal
resting muscle and attributes them to injuries of the surface, due to
methods of preparation, in consequence of which the tissue dies and
becomes electronegative to the uninjured area, which remains electro-
positive. These currents Hermann terms "demarcation currents."

Negative Variation of the Muscle Current. — If a muscle
exhibiting a current of injury be excited to activity by tetanizing in-
duced currents apphed to

the opposite end of the ..^r-^

muscle, it will be ob-
served that as the con-
traction wave passes over
the muscle there is a
movement of the galvan-
ometer needle toward the
zero point, indicating a
diminution of the poten-
tial on the longitudinal
surface. To this dimi-
nution in the strength of
the current the term
negative variation was
given. On the withdrawal of the stimulus the needle again
returns in a short time to its former position. The diminution
of potential on the longitudinal surface of the muscle is now
attributed to the passage of the excitation and contraction pro-
cesses, to a temporary disintegration of the muscle substance (Fig.
35). With their disappearance and the subsequent restoration of
the nutrition of the muscle, the former electric condition returns.

The primary deflection of the galvanometer needle is due to the
demarcation current which arises as a result of the difference in
electric potential produced by the destructive chemic changes taking
place at the cut end of the muscle. The negative variation is caused
by the fact that the activity of the muscle, \^^th its attendant chemic
changes, will always be greater in the uninjured equatorial region,
and hence will always tend to counterbalance the original source of
difference in electric potential.

Fig. 35. — The Negath^e Variation of the De-
marcation Current. A. The contraction
wave, which as it passes beneath the electrode
at B causes a diminution of potential.

92

TEXT-BOOK OF PHYSIOLOGY.

Electric Currents from Non-injured Muscles. — Though per-
fectly normal resting muscle, according to Hermann, is isoelectric,
nevertheless electric currents are developed during activity to which
he has given the term action currents, and which are attributed to
the propagation of the contraction wave.

Action Currents. — When two isoelectric points on the longitu-
dinal surface of a muscle are connected with a galvanometer and a
single stimulus apphed directly to one extremity, it can be shown
that as the contraction wave passes beneath A, Fig. 36, the muscle-
tissue at that point becomes electronegative toward B and a cur-
rent at once passes through the galvanometer from B to A, as
shown by the deflection of the needle toward A. As the con-
traction wave passes beneath B it in turn becomes electronegative,

Fig. 36.

-The Condition Leading to the Development of the First Action
Current.

and a temporary condition of equal potential is established when the
needle returns to the zero point. In a very short time the nutrition of
A is restored and becomes electropositive toward B, when a current
will pass through the galvanometer in the opposite direction from
A to B, as shown by the movement of the needle toward B, Fig. 37.
As the contraction wave passes beyond B its nutrition is restored and
becomes of equal potential with A. The term phasic is applied to
these currents. The first current flows in the muscle in the direction
of progress of the contraction wave — first phase; the second current
flows in the reverse direction — second phase; the current is therefore
diphasic. When a muscle is tetanized, there is but a single current
observed, which, however, endures so long as the tetanic contrac-

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

9.3

tion is maintained. To this current the term decremential is given.
When a muscle is excited to action by the nerve impulse which en-
ters at its center, two contraction waves are developed, one in each
half of the muscle, and hence there are two sets of diphasic action
currents.

The presence of action currents in the muscle of the Hving body
during a single contraction was demonstrated by Hermann in the mus-
cles of the forearm. The arrangement of the experiment was, briefly,
as follows : The forearm was surrounded by two twine electrodes sat-
urated with zinc solution, one being placed at the physiologic middle
— the nervous equator — the other at the wrist. Both electrodes were
then connected with the galvanometer. When the brachial plexus was
stimulated in the axillary space, the deflections of the galvanometer

Fig 37. — The Condition Leading to the Development of the Second Action

Current.

needle, when analyzed with the repeating rheotome, indicated phasic
currents with a single contraction. In the first phase — atterminal —
the wrist became positive and the current passed in the muscle toward
its termination; and in the second — abterminal — it became negative
and the current now passed in the reverse direction. The action
currents which are observed in the frog's muscle were thus shown
to be present in the living human muscle, with this difference, how-
ever: that the second phase, — abterminal, — instead of being weaker
in man, is equally strong with the atterminal. This experiment also
revealed the fact that the rapidity of propagation of the excitation
wave was much greater in man, amounting to about twelve meters
per second. Hermann therefore denies the preexistence of electric
currents and regards them as due to locaHzed temporary disintegra-

94 TEXT-BOOK OF PHYSIOLOGY.

tion of the muscle in consequence of activity, as they disappear on
the restoration of the muscle to its normal condition.

Work Done Daily. — The muscle system in its entirety is to be
regarded as a machine for the transformation of potential into kinetic
energy, and in so doing accomplishes work. Through the inter-
mediations of the bones of the skeleton which play the part of levers
the indi^ddual not only changes his position in space, but overcomes
to some extent the resistances offered by the environrrient. The
employment of artificial levers, tools, as distinguished from natural
levers, bones, materially adds to the effectiveness of the muscle
machine. The amount of work which a man of average physical
development weighing 72 kilos can perform in eight hours has been
variously estimated. It will naturally vary according to the character
of the occupation. If the work done be calculated from the number
of kilograms raised one meter, the average laboring-man performs
about 300,000 kilogrammeters.

SPECIAL ACTION OF MUSCLE GROUPS.

The individual muscles of the axial and appendicular portions of
the body are named with reference to their shape, action, structure,
etc.; e. g., deltoid, flexor, penniform, etc. In different localities a
group of muscles having a common function is named in accordance
with the kind of motion it produces or to which it gives rise: e. g.,
groups of muscles which alternately diminish or increase the angular
distance between two bones are known respectively as flexors and
extensors; such muscle groups are usually found in association
with ginglymus joints. Muscles which rotate the bone to which
they are attached around its own axis without producing any great
change of position are known as rotators, and are found in association
with enarthrodial or ball-and-socket joints. Muscles which impart
an angular movement to the extremities to and from the median line
of the body are termed adductors and abductors respectively.

In addition to the actions of individual groups of muscles in pro-
ducing special movements, in some regions of the body, several
groups of muscles are coordinated for the accomplishment of certain
definite functions; e. g., the functions of respiration, mastication, etc.
The coordination of axial and appendicular muscles enables the
individual to assume certain postures, such as standing, sitting, and
lying; to engage in various acts of locomotion, as walking, running,
dancing, swimming.

Levers. — The function or special mode of action of individual
muscles can be understood only when the bones with which they are
connected are regarded as levers whose fulcra or fixed points lie in
the joints where the movement takes place, and the muscles as sources

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

95

of power for imparting movement to the levers with the object of
overcoming resistance.

In mechanics levers of three kinds or orders are recognized
according to the relative positions of the fulcrum or axis of motion,
the apphed power, and the weight to be moved. (See Fig. 38.)

In levers of the first order the fulcrum, F, lies between the weight
or resistance, W, and the power or moving force, P. The distance
P F is known as the power arm and the dis-
tance W F as the weight arm. As examples «

of this form of lever found in the human ^ ^ ±, .

body may be mentioned : W a P \ ''

1. The elevation of the trunk from the F • |

flexed position. The axis of move- /\ w p^^^

ment, the fulcrum, lies in the hip-joint; ^ I v

the weight, that of the trunk, acting as ^ p — ^(3)

if concentrated at the center of gravity, j,^^ 38.— the Three Or-
which lies close to the tenth dorsal ver- ders of Levers.

tebra ; the power, the muscles attached

to the tuberosity of the ischium. The opposite movement is
equally one of the first order, but the relative positions of P and
W are reversed.

2. The head in its movement backward and forward on the atlas.
In levers of the second order the weight lies between the power

and the fulcrum. As illustration of this form of lever may be men-
tioned:

1 . The depression of the lower jaw, in which movement the fulcrum is

the temporomaxillary articulation; the resistance, the tension
of the elevator muscles; the power, the contraction of the de-
pressor muscles.

2. The raising of the body on the toes, in which movement the ful-

crum is the toes, the weight that of the body acting through the
ankle, the power the gastrocnemius muscle applied to the heel
bone.
In levers of the third order the power is applied at a point lying

between the fulcrum and the weight. As examples of this form of

lever may be mentioned:

1. The flexion of the forearm, in which the fulcrum is the elbow-

joint, the power the biceps and brachialis anticus muscles ap-
phed at their points of insertion, the weight that of the forearm
and hand.

2. The extension of the leg on the thigh.

When levers are employed in mechanic operations, the object
aimed at is the overcoming of a great resistance by the appHcation of
a small force acting through a great distance, so as to obtain mechanic
advantage. In the mechanism of the human bodv the reverse gener-

96 TEXT-BOOK OF PHYSIOLOGY.

ally obtains, viz., the overcoming of a small resistance by the appli-
cation of a large force acting through a short distance. As a result
there is a gain in the extent and rapidity of the movement of the
lever. The power, however, owing to its point of application, acts
at a great mechanic disadvantage in many instances, especially in
levers of the third order.

Postures. — Owing to its system of joints, levers, and muscles the
human body can assume a series of positions of equilibrium, such as
standing and sitting, to which the term posture has been given. In
order that the body may remain in a state of stable equilibrium in
any posture, it is essential that the vertical line passing through its
center of gravity shall fall within the base of support.

Standing is that position of equilibrium in which a line drawn
through the center of gravity of the entire body falls within the base
of support. This position is maintained largely by the mechanical
conditions of the joints, apparently for the purpose of reducing to a
minimum muscular action, so that it can be prolonged for some time
without giving rise to fatigue. In the military position, which may
be assumed as the normal position, all the joints must be in such a
condition of extension and fixation that the body will represent a
rigid column resting on the astragalus and supported by the arch of
the foot. This is accomplished :

1. By balancing the head on the apex of the vertebral column. This

is done by the action of the muscles on the back of the neck.
The muscular effort is, however, very slight, as the center of
gravity of the head lies but a short distance in front of the
articulation.

2. By making the vertebral column erect and rigid. This is brought

about by the action of the common extensor muscles of the trunk.
In this condition the center of gravity lies just in front of the
tenth dorsal vertebra. The head, trunk, and upper extremities
are now supported by the hip- joints; and in order that this sup-
port may give to the body a certain degree of stable equilibrium,
independent of muscular action, the line of gravity falls behind the
line uniting the center of rotation of the two joints. In conse-
quence the body would fall backward were it not prevented by
the tension of the iliofemoral ligament and the fascia lata.
The line of gravity, continued downward, passes through the knee-
joint posterior to the axis of rotation, and hence the body would now
fall backward were it not prevented by the tension of the lateral
ligaments and the contraction of the quadriceps femoris muscle.
Though the body is supported by the astragalus, the line of grav-
ity does not pass through the line uniting the two joints, for in so
doing constant muscular effort would be required to maintain stable
equilibrium; passing a short distance in advance of this hne, there

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 97

would be a tendency of the body to fall forward, which is prevented
by the extensor muscles of the foot. When the body is in the erect
or military position, the center of gravity lies between the sacrum
and last lumbar vertebra. Standing is thus an act of balancing, and
requires not only the static conditions of joints, but the dynamic
conditions of various groups of muscles, and hence is not a position
of absolute ease and cannot be maintained for any length of time
without experiencing discomfort and fatigue. Sitting erect is an
attitude of equilibrium in which the body is balanced on the tubera
ischii, when the head and trunk together form a rigid column.

Locomotion is the act of transferring the body as a whole through
space, and is accomplished by the combined action of its own muscles.
The acts involved consist of walking, running, jumping, etc.

Walking is a comphcated act involving almost all the voluntary
muscles of the body either for purposes of progression or for bal-
ancing the head and trunk, and may be defined as a progression in
a forward horizontal direction due to the alternate action of both
legs. In walking one leg becomes for the time being the active or
supporting leg, carrying the trunk and head; the other the passive
but progressing leg, to become in turn the active leg when the foot
touches the ground. Each leg is therefore alternately in an active
and passive state.

Running is distinguished from walking by the fact that at a given
moment both feet are off the ground and the bodv is raised in the air.

THE VISCERAL MUSCLE.

The visceral muscle, as the name imphes, is found in the walls
of hollow viscera, where it is arranged in the form of a membrane
or sheet. It is present in the walls of the alimentary canal, blood-
vessels, respiratory tract, ureter, bladder, vas deferens, uterus,
fallopian tubes, iris, etc. In some situations it is especially thick
and well developed — e. g., uterus and pyloric end of the stomach; in
others it is thin and slightly developed.

The Histology of the Visceral Muscle-fiber. — When examined
with the microscope, the muscle sheet is seen to be composed of
fibers, narrow, elongated, and fusiform in shape. As a rule, they
are extremely small, measuring only from 40 to 250 micromilhmeters
in length and from 4 to 8 micromilhmeters in breadth. The center
of each fiber presents a narrow, elongated nucleus. The muscle -
protoplasm which makes up the body of the fiber appears to be
enclosed by a delicate elastic membrane resembhng in some respects
the sarcolemma of the skeletal muscle. In some animals the visceral
fiber presents a longitudinal striation suggesting the existence of
fibrillae surrounded by sarcoplasm (Fig. 39). The fibers are united

08

TEXT-BOOK OF PHYSIOLOGY.

longitudinally and transversely by a cement material. The muscle
is increased in thickness by the superposition of successive layers.
At varying intervals the fibers are grouped into bundles or fasciculi
by septa of connective tissue (Fig. 40). Blood-vessels ramify in the
connective tissue and furnish the necessary nutritive material.

The visceral muscle receives stimuli from the spinal cord, not
directly, however, as in the case of the skeletal muscle, but indirectly

Fig. 39. — Two Smooth Muscle-fibers from Small Intestine of Frog. X 240.
Isolated with 35 per cent, potash-lye. The nuclei have lost their characteristic
form through the action of the lye. — (Siohr.)

through the intermediation of ganglion cells, which may be located
at some distance from the muscle or near the walls of the viscera.
Non-medullated fibers from the ganglion pass directly into the
muscle, where they frequently unite to form a general plexus. From
this plexus fine branches take their origin and ultimately become
physiologically associated with the muscle-fiber.

Physiologic Properties. — The visceral muscles which have
been subjected to experiment are mainly those of the stomach, in-
testine, bladder, ureter, and iris. From the results of the experiments

which have been published, it is
evident that all visceral muscles
possess elasticity, tonicity, irrita-
bility, and conductivity.

The elasticity of the bladder
muscle of the cat was strikingly
shown in the experiments pub-
hshed by Dr. Colin C. Stewart.
When this muscle was weighted
with weights differing by a com-
mon increment, it was extended
on the addition of each weight,
though to a progressively less extent. On the removal of the weights
the muscle eventually returned to its former length. The records of
the extension were similar to, if not identical with, those of the skele-
tal muscle.

Tonicity is a property common to all visceral muscles. Each
muscle is continuously in a state of contraction intermediate between
that of complete contraction and that of relaxation. In how far this
is due to local and inherent causes or to stimuli reflected from the

Connective-tissue
septum.

Nucleus.

Smooth muscle-fiber
in tr.msverse section.

Fig. 40. — Section of the Circular
Layer of the Mu.scular Coat of
THE Human Intestine. — (S/olir.)

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE.

99

nervous system as a result of ])eripherally acting causes is not in
individual instances readily determinable. From time to time the
tonicity varies, increasing and decreasing in response to these various
stimuli and in accordance with the functional activities of the organs
in which the muscle is found.

The irritability manifests itself by a change of form, and doubt-
less by the liberation of heat on the application of any form of stimulus
— mechanic, chemic, thermic, electric.

The conductivity is less marked in the visceral than in the skeletal
muscle, and, contrary to what is observed in the latter, the conduction
extends laterally as well as longitudinally from fiber to fiber. This
is shown by stimulation of the exposed intestine. Shortly after the
stimulus is applied the muscle contracts longitudinally — i. e., in a
direction at right angles to the long axis of the intestine, partially
obliterating its lumen. From this point the conduction process indi-
cated by the contraction wave passes in opposite directions for some
distance along the canal. As to whether this is accomplished by
protoplasmic processes extending from fiber to fiber, or whether the
uniting membrane differs in conducting power from the sarcolemma,
is as yet a matter of doubt. From the fact that the upper two-thirds
of the ureter, though free of nerve-cells, exhibits lateral conduction,
it is evident that it may take place independent of the nervous sy,stem.

The Contraction of the Visceral Muscle. — The general character
of the contraction may be witnessed on opening the abdomen of a
recently killed animal, especially the rabbit. Shortly after exposure
to the air the walls of the intestine begin to contract in a most vig-
orous manner. The contraction wave beginning at various points
is propagated in both directions, running along the intestinal wall
for a variable distance. A succession of similar waves may be ob-
served for some minutes. To the alternate contraction and relaxa-
tion of the muscle-fibers, which are circularly arranged, the term
peristalsis is usually given. The excised stomach of a dog kept
under suitable conditions will exhibit similar movements. The
same holds true of the bladder muscle of the cat, the muscle of the
ureter, etc. Careful observation shows a certain periodicity in the
movements. Inasmuch as the cause is not apparent, these contrac-
tions arc termed spontaneous or automatic.

Graphic Record of the Contraction. — For experimental pur-
poses narrow transverse sections of the stomach of the frog or the
entire bladder muscle of the cat, excised or in situ, according to the
method of Dr. Colin C. Stewart, may be employed. If kept moist,
they will retain their irritability for some hours. The changes of
form may be recorded with the usual muscle lever. When thus pre-
pared, the muscle may exhibit for several hours a series of pulsa-
tions, rhythmic in character. With spontaneously acting mammalian

lOO

TEXT-BOOK OF PHYSIOLOGY,

muscle the contraction and relaxation periods are of equal duration.
With the amphibian muscle they are of unequal duration, as a rule.
In both classes of animals the character of the record, a succession
of large and small contractions, would indicate that the general
rhythmic movement is compounded of two or three secondary
rhythms which differ in rate and character. A single pulsation may
be recorded by stimulating the bladder muscle with the induced or the
make and break of the constant current. A curve of such a contrac-
tion is shown in Fig. 41. The contraction takes place more rapidly
than the relaxation; the two phases occupying five and thirty-five
seconds respectively. The latent period covered 0.25 second. With
other muscles the time relations are slightly different. Tetanization
of the bladder muscle of the cat occurred when
the stimuH succeeded each other with a certain
rapidity; the interval between stimuH approxi-
mating a period somewhat less than two sec-
onds. This muscle responds to variations in
temperature, to strength of stimulus, to the
load, in a manner similar to, if not identical
with, the skeletal muscle .
I \^^^ The Function of the Visceral Muscle. —
-* In a general way it may be said that the vis-
ceral muscle determines and regulates the pas-
sage through the viscus or organ of the material
contained within it. The food in the stomach
and intestines is subjected to a churning pro-
cess by the muscles, in consequence of which
the digestive fluids are more thoroughly incor-
porated and their characteristic action in-
creased. At the same time the food is carried
through the canal, the absorption of the nutri-
tive material promoted, and the indigestible
residue removed from the body. The blood
is delivered in larger or smaller volumes ac-
cording to the needs of the tissues through a relaxation or contrac-
tion of the muscle-fibers of the blood-vessels. The urine is forced
through the ureter and from the bladder by the contraction of their
respective muscles. The mode of action of the individual muscles
will be described in successive chapters.

Ciliary Movement. — The free surface of the epithehum cover-
ing the mucous membrane in certain regions of the body is charac-
terized by the presence of dehcate filamentous processes termed
ciha. (See Fig. 42.) Ciliated epithehum is found in man and
mammals generally, in the nose, Eustachian tube, larynx, with the
exception of the vocal membranes, trachea and bronchial tubes as

iriMiniiifriiirmiiiinMiiifiirrmr.rf

Fig. 41. — The Curve
OF Contraction
or THE Bladder
Muscle at Body-
tesiperature lnt
Response to a
Single Induction
Current. The

TlilE IS indicated
IN SECONDS .

{Stewart.)

GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. loi

far as the pulmonary lobules, Fallopian lubes, uterus, and epididymis.
The lumen of the central canal of the spinal cord and the cavities of
the brain are lined, especially in childhood, by cells provided w^ith
similar cilia. Ciliated epithelium is also found in all classes of ani-
mals, and especially in the invertebrates.

The cilia found in the human body vary in length from 0.003 ^'^'^•
to 0.005 ^^^T^- They are apparently structureless and colorless, and
appear to have their origin in and to be a prolongation of a trans-
parent material on the outer surface of the cell material. The
number of cilia present on the surface of any individual cell varies
approximately from five to twenty-five. When ciliated epithelial cells,
freshly removed from the mucous membrane and moistened with
normal saline, are examined with the microscope, it will be found
that the ciHa are in continuous and rapid vibratile movement, so
much so that the individual cihum cannot be distinguished. In
time, however, their vitahty declines and the rapidity of movement
diminishes. When the movement of the individual cilium falls to
about eight or ten per second, its character
can be readilv determined. It will then be Sl/^,.
seen that the' movement is, as a rule, alter- ^ F^'^ip'/f^i*
nately a backward and a forward one, the J

cilium lowering and then raising itself, the ^ '-

latter taking place more quickly and ener- [
getically than the former. As the cilium
raises itself it becomes somewhat flexed in
a direction corresponding to that of the

general movement. The movement, how- yig. 42. Ciliated Epi-

ever, varies in character in different situa- thelium.

tions and in different animals. The cause

of the movements and the mechanism of their coordination are
unknown. They are, as far as known, independent of the nervous
system. The force of ciliary motion is very great. A load of twenty
grams can be supported and carried forward by the cilia on the
mucous membrane of the mouth and esophagus of the frog. The
activity of the ciha is associated with the nutrition of the cell of
which they are a part and rises and falls with it. Experimentally
it has been found that the rate and energy of the movement are
greatest at a temperature of about 35° to 40° C, especially if they
are bathed with normal saline, rendered slightly alkahne. Low
temperatures, acids, alkahes, carbon dioxid, etc., retard the move-
ment.

The function of the ciha, though not always apparent, is asso-
ciated with the function of the passages in which they are found. As
the surfaces of these passages are swept by a current of considerable
power, it is probable that they assist in the passage of the materials

I02 TEXT-BOOK OF PHYSIOLOGY.

which ordinarily traverse them. Mucus and particles of dust are
carried upward through the air-passages; the ovarian cell is carried
from the ovary toward the uterus; the spermatozoa, as well as the
fluid in which they are contained, are carried forward through the
epididymis ducts.

CHAPTER VII.
THE GENERAL PHYSIOLOGY OF NERVE-TISSUE.

The nerve-tissue, which unites and coordinates the various
organs and tissues of the body and brings the individual into relation-
ship with the external world, is arranged in two systems, termed
the encephalospinal or cerebrospinal and the sym pathetic.

The encephalospinal system consists of:

1. The brain and spinal cord, contained within the cavities of the

cranium and the spinal column respectively, and

2. The cranial and spinal nerves.

The sympathetic system consists of:

1 . A double chain of ganglia situated on each side of the spinal column

and extending from the base of the skull to the tip of the coccyx.

2. Various collections of ganglia situated in the head, face, thorax,

abdomen, and pelvis. All these ganglia are united by an elab-
orate system of intercommunicating nerves, many of which are
connected with the cerebrospinal system.

HISTOLOGY OF NERVE-TISSUE.

The Neuron. — The nerve-tissue has been resolved by the in-
vestigations of modern histologists into a single morphologic unit, to
which the term neuron has been apphed. The entire nervous system
has been shown to be but an aggregate of an infinite number of
neurons, each of which is histologically distinct and independent.
Though having a common origin, as shown by embryologic investi-
gations, they have acquired a variety of forms in different parts of the
nervous system in the course of development. The old conception
that the nervous system consisted of two distinct histologic elements,
nerve-cells and nerve-fibers, which differed not only in their mode of
origin, but also in their properties, their relation to each other, and
their functions, has been entirely' disproved.

The neuron, or neurologic unit, is histologically a nerve-cell, the
surface of which presents a greater or less number of processes in
varying degrees of differentiation. As represented in figure 43, A, the
neuron may be said to consist of: (i) The nerve-cell, neurocyte, or
corpus; (2) the axon, or nerve process; (3) the end-tufts, or terminal
branches. Though these three main histologic features are every-
where recognizable, they exhibit a variety of secondary features in

103

104

TEXT-BOOK OF PHYSIOLOGY.

different situations in accordance with peculiarities of function.
Though the nerve-cell and the nerve-fiber are but part of the same
neuron, it is convenient at present to describe them separately.

The Nerve-cell. — The nerve-cell, or body of the neuron, presents
a variety of shapes and sizes in different portions of the nervous
system. Originally ovoid in shape, it has acquired, in course of de-
velopment, pecuharities of form which are described as pyramidal,
stellate, pear-shaped, spindle-shaped, etc. The size of the cell
varies considerably, the smallest having a diameter of not more than

Each cell

300

^ (J- of an inch, the largest not more than ^^ of an inch.

.. Neurilemma.

_. Nerve-cell.

Terminal
branches.

Fig. 43. — A. Efferent neuron. B. Afferent neuron.

consists of granular, striated protoplasm, containing a distinct ves-
icular nucleus and a well-defined nucleolus. A cell membrane has
not been observed. From the surface of the adult cell portions of
the protoplasm are projected in various directions, wliich portions,
rapidly dividing and subdividing, form a series of branches, termed
dendrites or dendrons. In some situations the ultimate branches of
the dendrites present short lateral processes, known as lateral buds,
or gemmules, which impart to the branches a feathery appearance.
This characteristic is common to the cells of the cortex of the cere-
brum and of the cerebellum. The ultimate branches of the den-

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 105

drites, though forming an intricate feltwork, never anastomose with
one another nor unite with dendrites of adjoining cells. According
to the number of axons, nerve-cells are classified as monaxonic,
diaxonic, polyaxonic. Most of the cells of the nervous system of the
higher vertebrates are monaxonic. In the gangha of the posterior
or dorsal roots of the spinal and cranial nerves, however, they are
diaxonic. In this situation the axons, emerging from opposite poles
of the cell, either remain separate and pursue opposite directions, or
unite to form a common stem, which subsequently divides into two
branches, which then pursue opposite directions. (See Fig. 43, B.)
The nerve-cell maintains its own nutrition, and presides over that of
the dendrites and the axon as well. If the latter be separated in any
part of its course from the cell, it speedily degenerates and dies.

The axon, or nerve process, arises from a cone-shaped projection
from the surface of the cell, and is the first outgrowth from its pro-
toplasm. At a short distance from its origin it becomes markedly
differentiated from the dendrites which subsequently develop. It
is characterized by a sharp, regular outline, a uniform diameter, and
a hyahne appearance. In structure, the axon appears to consist of
fine fibrilliE embedded in a clear, protoplasmic substance. Shafer
advocates the view that the fibrillae are exceedingly fine tubes filled
with fluid. The axon varies in length from a few millimeters to one
meter. In the former instance the axon, at a short distance from its
origin, divides into a number of branches, which form an intricate
feltwork in the neighborhood of the cell. In the latter instance
the axon continues for an indefinite distance as an individual struc-
ture. In its course, howTver, especially in the central nervous system,
it gives off a number of collateral branches, which possess all its his-
tologic features. The long axons serve to bring the body of the cell
into direct relation with peripheral organs, or with more or less re-
mote portions of the nervous system, thus constituting association or
commissural fibers.

The more or less elongated axon becomes invested, as a rule, at a
short distance from the cell with nucleated oblong cells, which subse-
quently become modified and constitute the medullary or myehn
sheath. This is invested by a thin, cellular membrane — the neu-
rilemma. These three structures thus constitute what is known as a
medullated nerve-fiber. In the central nervous system the outer
sheath is frequently absent. In the sympathetic system the myelin
is also frequently absent, though the axon is inclosed by the neuri-
lemma, thus constituting a non-medullated nerve-fiber.

The end-tufts or terminal organs are formed by the splitting of the
axon into a number of filaments, which remain independent of one
another and are free from the medullary investment. The histologic
pecuharitics of the terminal organs vary in different situations, and in

ir6 TEXT-BOOK OF PHYSIOLOGY.

many instances are quite complex and characteriscic. In peripheral
organs, as muscles, glands, blood-vessels, skin, mucous membrane,
the tufts are in direct histologic and physiologic connection with their
cellular elements. In the central nervous system the tufts are in more
or less intimate relation with the dendrites of adjacent neurons.

Nerve-fibers. — The axons with their secondary investments
together constitute the nerve-fibers, and according as they possess or
do not possess the medullary sheath, they may be divided into two
groups — viz., meduUated and non-medullated fibers.

Medullated Nerve-fibers. — These consist for the most part of
three distinct structures:

1. An external investing sheath, tubular in shape, termed the neuri-

lemma.

2. An intermediate semifluid substance — the medulla or m3'elin.

3. An internal dark thread — the axis-cylinder.

The neurilemma is a thin, transparent, homogeneous membrane
closely adherent to the medulla. Owing to its colorless appearance,
it can be seen only with difficulty in fresh tissue. When treated
with various reagents, it becomes distinct. Physically, it is quite
resistant and elastic. Its function is doubtless that of a protecti\-e
agent to the structures within.

The meduUa, myelin, or white substance of Schwann completeh'
fills the neurilemma and closely invests the axis-cylinder or axon. In
fresh tissue the medulla is clear, homogeneous, semifluid, and highly
refracting. In composition it is oleaginous. When the nerve is
treated with various reagents which alter its composition, the medulla
becomes opaque and imparts a white, glistening appearance. The
function of the medulla is quite unknown.

At interv'als of about seventy-five times its diameter the medul-
lated nerv'e-fiber undergoes a remarkable diminution in size, due to
an interruption of the medullary substance, so that the neurilemma
lies directly on the axis-cylinder. These constrictions, or nodes of
Ranvier, taking their name from their discoverer, occur at regular
intervals along the course of the nerve, separating it into a series of
segments. The portion between the nodes is termed the internodal
segment. It has been suggested that in consequence of the absence
of the myelin at these nodes, a free exchange of nutritive material
and decomposition products can take place between the axis-cylinder
and the surrounding plasma. •

The axis-cylinder, or axon, the direct outgrowth of the nerve-cell,
is the most essential element of the nerve-fiber, as it alone is uni-
formly continuous throughout. In the natural condition it is trans-
parent and invisible; but when treated with proper reagents, it
presents itself as a pale, granular, flattened band, more or less solid
and .somewhat elastic. It is albuminous in composition. With

GENERAL PHYSIOLOGY OF NERVE-TISSUE.

107

high magnilicalion the axis presents a longitudinal striation, indicating
a fibrillar structure. The fibrillae appear to be embedded in an
intervening semifluid substance, the neuroplasm.

Non-medullated Nerve-fibers. — These consist, for the most
part, only of the axis-cylinder, though in some portions of the nervous
system a neurilemma is also present. Though much less abundant
than the former variety, they are distributed largely throughout the
nervous system, but are particularly abundant in the sympathetic.
Owing to the absence of a medulla, they present a rather pale or
grayish appearance.

Structure of Nerve-trunks. — After their emergence from the
brain and spinal cord, the nerve-fibers become bound together, by

Fig. 44. — Transverse Section of a Nerve (Median), ep. Epineurium. pe.
Perineurium, ed. Endoneurium.

connective tissue, into the form of continuous bundles, which connect
the brain and cord with all the remaining structures of the body.
The bundles are technically known as nerve-lrnnks or nerves. Each
nerve is invested by a thick layer of lamellated connective tissue,
known as the epineurium. A transverse section of a nerve shows
(see Fig. 44) that it is made up of a number of small bundles of
fibers, each of which possesses a separate investment of connective
tissue — the perineurium. Within this membrane the nerve-fibers are
supported by a fine stroma — the endoneurium. After pursuing a
longer or shorter course, the nerve-trunk gives off branches, which
interlace ver)' freely with neighboring branches, forming plexuses,
the fibers of which are distributed to associated organs and regions

io8 TEXT-BOOK OF PHYSIOLOGY.

of the body. From their origin to their termination, however, nerve-
fibers retain their individuahty, and never become blended witli
adjoining fibers.

As nerves pass from their origin to their peripheral terminations,
they give off a number of branches, each of which becomes invested
with a lamellated sheath — an offshoot from that investing the parent
trunk. This division of nerve-bundles and sheath continues through-
out all the branchings down to the ultimate nerve-fibers, each of
which is surrounded by a sheath of its own, consisting of a single
layer of endothelial cells. This delicate transparent membrane, the
sheath of Henle, is separated from the nerve-fiber by a considerable
space, in which is contained lymph destined for the nutrition of the
fiber. Near their ultimate terminations the nerve-fibers themselves
undergo division, so that a single fiber may give origin to a number
of branches, each of which contains a portion of ihi parent axis-
cylinder and myelin.

Blood-supply. — Nerves being parts of living cells require for
the maintenance of their nutrition a certain amount of blood. This
is furnished by the blood-vessels ramifying in and supported by the
connective-tissue framework. Here as elsewhere there is a constant
exchange, through the capillary wall and the neurilemma, of nutritive
material to the nerve proper and of waste materials to the blood.

The Chemic Composition and Metabolism. — Chemic analysis
of nerve-tissue has shown the presence of water, proteids (two glob-
ulins and a nucleo-proteid), neurokeratin and nuclein, two phos-
phorized bodies (protagon and lecithin), several cerebrosides (nitro-
gen-holding bodies of a glucoside character, as shown by their yielding
the reducing carbohydrate galactose), inorganic salts, and a series of
nitrogen-holding bodies such as creatin, xanthin, urea, leucin, etc. As
to the metabolism that is taking place in nerve-cells and fibers,
practically nothing definite is known. That such changes, how-
ever, are taking place would be indicated first by the blood-supply,
and second by the fact that withdrawal of the blood-supply is followed
by a loss of irritability. The metabolism of the central nervous
system is more active and extensive. In this situation any withdrawal
of blood from compression or occlusion of blood-vessels is followed
by impairment of nutrition and loss of function.

The Relation of the Nerves to the Central Nervous System. —
The nerve-trunks in connection with the spinal cord, thirty-one pairs
in number, pass through the intervertebral foramina. Near the outer
limits of the foramina each nerve-trunk divides into two branches,
generally termed roots, one of which, curving shghtly forward and
upward, enters the spinal cord on its anterior or ventral surface, while
the other, curving backward and upward, enters on the posterior
or dorsal surface. The former is termed the anterior or ventral

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 109

root; the latter, the posterior or dorsal root. Each dorsal root
presents near its union with the ventral root a small ovoid grayish
enlargement known as a ganglion. Both roots previous to entering
the cord subdivide into from four to six fasciculi.

A microscopic examination of a cross-section of the spinal cord
shows that the fibers of the ventral roots can be traced directly into
the body of the nerve-cells in the anterior horns of the gray matter.
The fibers of the dorsal roots arc not so easily traced, for they diverge
in several directions shortly after entering the cord. In their course
they give off collateral branches which, in common with the main
fiber, end in tufts which become associated with nerve-cells in both
the anterior and posterior horns of the gray matter.

Of the nerves in connection with the base of the brain, some
present a similar ganglionic enlargement, and therefore may be re-
garded as dorsal nerves, while others may be regarded as ventral
nerves. Their relations within the medulla oblongata are similar
to those within the spinal cord.

Efferent and Afferent Nerves.^ — Nerves are channels of com-
munication between the brain and spinal cord, on the one hand, and
the muscles, glands, blood-vessels, skin, mucous membrane, viscera,
etc., on the other. Some of the nerve-fibers serve for the transmission
of nerve energy from the brain and spinal cord to certain peripheral
organs, and so increase or retard their activities; others serve for the
transmission of nerve energy from certain peripheral organs to the
brain and spinal cord which gives rise to sensation or other modes of
nerve activity- The former are termed efferent or centrifugal, the
latter afferent or centripetal nerves. Experimentally it has been de-
termined that the anterior or ventral roots contain all the efferent
fibers, the posterior or dorsal roots all the afferent fibers.

THE PERIPHERAL ENDINGS OF NERVES.

The efferent nerves as they approach their ultimate terminations
lose both the neurilemma and myelin sheath. The axon or axis-
cyHnder then divides into a number of branches which become
directly and intimately associated with tissue-cells. The particular
mode of termination varies in different situations. These terminations
are generally spoken of as end-organs, terminal organs, or end-tufts.

In the skeletal muscle the nerve-fiber loses both neurilemma and
myelin sheath at the point where it comes in contact with the muscle-
fiber. After penetrating the sarcolemma, the axon or axis-cylinder
divides into a number of small branches which appear to be embedded
in a relatively large mass of sarcoplasm and nuclei, the whole form-
ing the so-called "motor plate." Each muscle-fiber possesses one
such plate or end-organ in mammalia, several in the frog.

no TEXT-BOOK OF PHYSIOLOGY.

In the visceral muscle the terminal nerve-fibers derived from
sympathetic or peripheral neurons are primarily non-medullated.
The axons divide and subdivide and form plexuses which surround
the muscle-cell bundles. Fine fibers from the plexuses are given off

Nerve-fiber
bundle.

Fig. 45. — Motor Nerve-endings of Intercostal Muscle-fibers of a Rabbit.

X 150.

which ultimately come into relation with each individual cell, on the
surface of which they terminate in the form of one or more granular
masses.

In the glands, taking as an illustration the parotid and mammary
glands, the nerve-fibers, also derived from sympathetic or peripheral

neurons, pass into the body of
the gland and ultimately reach
the acini, on the outer surface of
which they ramify and form a
plexus. From this plexus fine
fibers penetrate the acinus wall
and end on the gland-cell. The
fibers present a varicose appear-
ance (Fig. 46).

The afferent nerves as they
approach their ultimate termina-
tions undergo similar changes.
The end-tufts become associated, in some situations, with speciahzed
end-organs which are extremely complex; e. g., the retina in the eye,
the organ of Corti in the ear, the taste-beakers in the tongue, the
olfactory cells in the nose.

Fig. 46. — Terminations of Nerve-
fibers IN THE Gland-cells. A.
Cell of the fjarotid gland of a rabbit.
B. Cells of the mammary gland
of a cat in gestation. — (Doyen and
Moral)

GENERAL PHYSIOLOGY OF NERVE-TISSUE.

In the skin and mucous membranes the mode of termination
varies considerably. The following are some of the principal modes:

1. Free endings in the epithelium.

2. Tactile cells of Merkel.

3. Tactile corpuscles in the papilke of the true skin.

4. Pacinian corpuscles found attached to the nerves of the hand and

feet, to the intercostal nerves, and to nerves in other situations.

5. End-bulbs of Krause in the conjunctiva, clitoris, penis, etc.

(A consideration of these end-organs will be found in the chapters
devoted to the organs of which they form a part.)

In the skeletal muscles afferent fibers become associated with small
spindle-shaped structures known as muscle-spindles or neuromuscle
end-organs. These spindles vary in length from i mm. to 4 mm.
They consist of a capsule of fibrous tissue containing from five to
twenty muscle-fibers. After penetrating the several layers of the
capsule, the nerve-fibers lose the neurilemma and myehn sheaths.
The axons or axis-cyhnders then divide into several long narrow
branches which wind themselves in a spiral manner around the con-
tained muscle-liber and terminate in small oval-shaped discs. Similar
endings have been observed in the tendons of muscles.

Development and Nutrition of Nerves. — The efferent nerve-
fibers, which constitute some
of the cranial nerves and all
the ventral roots of the spinal
nerves, have their origin in
cells located in the gray matter
beneath the aqueduct of Syl-
vius, beneath the floor of the
fourth ventricle, and in the
anterior horns of the gray mat-
ter of the spinal cord. These
cells are the modified descend-
ants of independent, oval,
pear-shaped cells — the neuro-
blasts— which migrate from
the medullary tube. As they
approach the surface of the
cord their axons are directed
toward the ventral surface,
which eventually they pierce.
Emerging from the cord, the

axons continue to grow, and become invested with the myelin sheath
and neurilemma, thus constituting the ventral roots.

The afferent nerve-fibers, which constitute some of the cranial
nerves and all the dorsal roots of the spinal nerves, develop outside

Posterior

Ga/tfflion/

Fig.

rderuir

47. — Diagram Showing the Mode of
CjRiGiN or THE Ventral and Dorsal
Roots.

112 TEXT-BOOK OF PHYSIOLOGY.

of the central nervous system and only subsequently become con-
nected with it. (See Fig. 47.) At the time of the closure of the
medullary tube a band or ridge of epithehal tissue develops near the
dorsal surface, which, becoming segmented, moves outward and forms
the rudimentary spinal gangUa. The cells in this situation develop
two axons, one from each end of the cell, which pass in opposite
directions, one toward the spinal cord, the other toward the per-
iphery. In the adult condition the tAvo axons shift their position,
unite, and form a T-shaped process, after which a division into tAvo
branches again takes place. In the gangha of all the sensori-craniai
and sensori-spinal nerves the cells have this histologic peculiarity.

The efferent fibers are therefore to be regarded as outgrowths
from the nerve-cells in the ventral horns of the gray matter, and serve
to bring the cells into anatomic and physiologic relationship directly
with the skeletal muscles and indirectly, through the intermediation
of gangha (see sympathetic nervous system), with visceral muscles
and glands.

The afferent fibers are to be regarded as outgrowths from the
cells of the dorsal nerve ganglia, and serve to bring the skin, mucous
membrane, and certain visceral structures into relation with special-
ized centers in the central nervous system.

Nerve Degeneration. — If any one of the cranial or spinal nerves
be divided in any portion of its course, the part in connection with
the periphery in a short time exhibits certain structural changes, to
which the term degeneration is apphed. The portion in connection
with the brain or cord retains its normal condition. The degenerative
process begins simultaneously throughout the entire course of the
nerve, and consists in a disintegration and reduction of the medulla
and axis-cyhnder into nuclei, drops of myehn, and fat, which in time
disappear through absorption, leaving the neurilemma intact. Coin-
cident with these structural changes there is a progressive alteration
and diminution in the excitabihty of the nerve. Inasmuch as the
central portion of the nerve, which retains its connection with the
nerve-cell, remains histologically normal, it has been assumed that
the nerve-cells exert over the entire course of the nerve-fibers a
nutritive or a trophic influence. This idea has been greatly strength-
ened since the discovery that the axis-cyhnder, or the axon, has its
origin in and is a direct outgrowth of the cell. When separated
from the parent cell, the fiber appears to be incapable in itself of
maintaining its nutrition.

The relation of the nerve-cells to the nerve-fibcrs, in reference to
their nutrition, is demonstrated by the results which follow section
of the ventral and dorsal roots of the spinal nerves. If the anterior
root alone be divided, the degenerative process is confined to the
peripheral portion, the central portion remaining normal. If the

GENERAL PHYSIOLOGY OF NERVE-TISSUE.

113

posterior root be divided on the peripheral side of the gungHon,''de-
generation takes place only in the peripheral portion of the nerve.
(See Fig. 48.) If the root be divided between the ganghon and the
cord, degeneration takes place only in the central portion of the root.
From these facts it is evident that the trophic centers for the ventral
and dorsal roots lie in the spinal cord and spinal nerve gangha,
respectively, or, in other words, in the cells of which they are an
integral part. The structural changes which nerves undergo after
separation from their centers are degenerative in character, and the

Fig. 48. — Degeneration of Spinal Nerves and Nerve-roots after Section.
A. Section of nerve-trunk beyond the ganglion. B. Section of anterior root.
C. Section of posterior root. D. Excision of ganglion, a. Aiiicri^r root. p.
Posterior root. g. Ganglion. — (Dalton.)

process is usually spoken of, after its discoverer, as the Wallerian
degeneration.

When the degeneration of the efferent nerves is completed, the
structures to which they are distributed, especially the muscles, un-
dergo an atrophic or fatty degeneration, with a change or loss of their
irritabihty. This is, apparently, not to be attributed merely to in-
activity, but rather to a loss of nerve influences, inasmuch as inactivity
merely leads to atrophy and not to degeneration.

CLASSIFICATION OF NERVES.

The efferent nerves may be classified, in accordance with the
characteristic form of activity to which they give rise, into several
groups, as follows :

1. Muscle or motor nerves, those which convey nerve energy or nerve

impulses to muscles and excite them to activity.

2. Gland or secretory nerves, those which convey nerve impulses to

glands, and cause the formation and discharge of the secretion
peculiar to the gland.

3. Vascular or vaso-motor nerves, those which convey nerve impulses

to blood-vessels, and cause, either by stimulation or inhibition of

114 TEXT-BOOK OF PHYSIOLOGY.

the mechanism of their walls, a contraction (vaso-constrictors)
or dilatation (vaso-dilators) of the vessel.

4. Inhibitory nerves, those conveying nerve impulses that cause a

slowing or complete cessation of the rhythmic action of organs.

5. Accelerator nerves, those conveying impulses that cause an increase

in the rhythmic action of certain organs.
The efferent nerves have been somewhat differently classified by
Gaskell as follows:

1. Nerves to skeletal muscles.

2. Nerves to vascular muscles.

(a) Vaso-motor, i. e., vaso-constrictors; accelerators and aug-
mentors of the heart.

(b) Vaso-inhibitory, i. e., vaso-dilators; and inhibitors of the
heart.

3. Nerves of the visceral muscles.

{a) Viscero-motor.
(b) Viscero-inhibitory.

4. Nerves to glands.

The afferent nerves may also be classified, in accordance with
the character of the sensations . or other modes of nerve activity to
which they give rise, into several groups, as follows :

1. Sensorifacient nerves, those conveying nerve impulses that give

rise in the brain to conscious sensations. They may be sub-
divided into —

(a) Nerves of special sense — e. g., olfactory, optic, auditory, gusta-
- tory, tactile, thermal, pain, pressure, muscle — giving rise to

correspondingly named sensations.

(b) Nerves of general sense — e. g., the visceral afferent nerves —

those which give rise normally to vague and scarcely percept-
ible sensations, such as the general sensations of well-being
or discomfort, hunger, thirst, fatigue, sex, want of air, etc.

2. Reflex nerves, those which convey nerve impulses to the nerve-

centers and cause a discharge and transmission of nerve impulses
outward through efferent nerves to muscles, glands, or blood-
vessels, and thus influence their activity. It is quite probable
that one and the same nerve may subserve both sense and
reflex action, owing to the collateral branches which are given
off from the posterior roots as they ascend the posterior column
of the cord.

3. Inhibitor nerves, those which are capable reflexly of retarding or

inhibiting the activity of either nerve-centers or peripheral
organs.

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 115

PHYSIOLOGIC PROPERTIES OF NERVES.

Nerve Irritability or Excitability and Conductivity. — These
terms are employed to express that condition of a nerve which enables
it to develop and to conduct nerve impulses from the center to the
periphery, from the periphery to the center, in response to the action
of stimuH. A nerve is said to be excitable or irritable so long as it
possesses these capabilities or properties. For the manifestation of
these properties the nerve must retain a state of physical and chemic
integrity; it must undergo no change in structure or chemic composi-
tion. The irritability of an efferent nerve is demonstrated by the
contraction of a muscle, by the secretion of a gland, or by a change
in the caliber of a blood-vessel, whenever a corresponding nerve is
stimulated. The irritability of an afferent nerve is demonstrated by
the production of a sensation or a reflex action whenever it is stimu-
lated. The irritability of nerves continues for a certain period of
time after separation from the nerve-centers and even after the death
of the animal, the time varying in different classes of animals. In
the warm-blooded animals, in which the nutritive changes take place
with great rapidity, the irritability soon disappears — a result due to
disintegrative changes in the nerve, caused by the withdrawal of the
blood-supply and other non-physiologic conditions. In cold-blooded
animals, on the contrary, in which the nutritive changes take place
relatively slowly, the irritability lasts, under favorable conditions, for
a considerable time. Other tissues besides nerves possess irritabihty,
that is, the property of responding to the action of stimuli — e. g.,
glands and muscles, which respond by the production of a secretion
or a contraction.

Independence of Tissue Irritability. — The irritabihty of nerves
is distinct and independent of the irritability of muscles and glands,
as shown by the fact that it persists in each a variable length of time
after their histologic connections have been impaired or destroyed by
the introduction of various chemic agents into the circulation. Curara,
for example, induces a state of complete paralysis by modifying or
depressing the conductivity of the end-organs of the nerves just where
they come in contact with the muscles, without impairing the irrita-
bility of either nerve-trunks or muscles. Atropin induces complete
suspension of glandular activity by impairing the terminal organs of
the secretory nerves just where they come into relation wdth the
gland-cells, without destroying the irritabihty of either gland-cell or
nerve.

Nerve-fibers Stimuli. — Nerves do not possess the power of
spontaneously generating and propagating nerve impulses ; they can
be aroused to activity only by the action of an external stimulus. In
the physiologic condition the stimuli capable of throwing the nerve

ii6 TEXT-BOOK OF PHYSIOLOGY.

into an active condition act for the most part on either the central or
peripheral end of the nerve. In the case of motor nerves the stimulus
to the excitation, originating in some molecular disturbance in the
nerve-cells, acts upon the nerve-fibers in connection with them. In
the case of sensor}' or afferent nerves the stimuli act upon the peculiar
end-organs with which the sensory nerves are in connection, which in
turn excite the nerve-fibers. Experimentally, it can be demonstrated
that nerv^es can be excited by a sufficiently powerful stimulus applied
in any part of their extent.

Nerves respond to stimulation according to their habitual func-
tion; thus, stimulation of a sensor}^ nerve, if sufficiently strong, re-
sults in the sensation of pain; of the optic nerve, in the sensation of
light; of a motor nerve, in contraction of the muscle to which it is
distributed; of a secretory nerve, in the activity of the related gland,
etc. It is, therefore, evident that peculiarity of nerve function de-
pends neither upon any special construction or activity of the nerve
itself nor upon the nature of the stimulus, but entirely upon the pecu-
liarities of its central and peripheral end-organs.

Ner\'e stimuli may be divided into — ■

1. General stimuli, comprising those agents which are capable of

exciting a nerve in any part of its course.

2. Special stimuli, comprising those agents which act upon nerves

only through the intermediation of the end-organs.

The end-organs are specialized highly irritable structures placed
between the nerve-fibers and the surface. They are especially
adapted for the reception of special stimuli and for the liberation of
energy, which in turn excites the nerve-fiber to activity.

General stimuli:

1 . Mechanic : Sharp taps, sudden pressure, cutting, etc.

2. Thermic: Sudden apphcation of heated object.

3. Chemic: Contact of various substances which alter their chemic

composition quickly, e. g., strong acids or alkalies, sol. sodium
chlorid 15 per cent., sugar, urea, etc.

4. Electric: Either the constant or induced current.
Special stimuli:

For afferent nerves —

1. Light or ethereal vibrations acting upon the end-organs of the

optic nervT in the retina.

2. Sound or atmospheric undulations acting upon the end-organs of

the auditor}'' nerve.

3. Heat or vibrations of the air acting upon the end-organs in the skin.

4. Chemic agencies acting upon the end-organs of the olfactory and

gustator}' nerves.
For efferent nerves —

A molecular disturbance in the central nerve-cells from which
they arise, the nature of .which is unknown.

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 117

Nature of the Nerve Impulse. — As to the nature of the nerve
impulse generated by any of the foregoing stimuli, either general or
special, but httle is known. It has been supposed to partake of the
nature of a molecular disturbance, a combination of physical and
chemic processes attended by the liberation of energy, which propa-
gates itself from molecule to molecule. The passage of the nerve
impulse is accompanied by changes of electric tension, the extent of
which is an indication of the intensity of the molecular disturbance.
Judging from the deflections of the galvanometer needle it is probable
that when the nerve irhpulse makes its appearance at any given point
it is at first feeble, but soon reaches a maximum development, after
which it speedily declines and disappears. It may, therefore, be
graphically represented as a wave-Hke movement with a definite
length and time duration. Under strictly physiologic conditions the
nerve impulse passes in one direction only; in efferent nerves from
the center to the periphery, in afferent nerves from the periphery to
the center. Experimentally, however, it can be demonstrated that
when a nerve impulse is aroused in the course of a nerve by an ade-
quate stimulus it travels equally well in both directions from the point
of stimulation. When once started, the impulse is confined to the
single fiber and does not diffuse itself to fibers adjacent to it in the
same nerve-trunk.

Rapidity of Conduction of the Nerve Impulse. — The passage
of a nerve impulse, either from the brain to the periphery or in the
reverse direction, requires an appreciable period of time. The
velocity with which the impulse travels in human sensory nerves has
been estimated at about 50 meters a second, and for motor nerves at
from 28 to 2^ meters a second. The rate of movement is, however,
somewhat modified by temperature, cold lessening and heat increas-
ing the rapidity; it is also modified by electric conditions, by the
action of drugs, the strength of the stimulus, etc. The rate of trans-
mission through the spinal cord is considerably slower than in nerves,
the average velocity for voluntary motor impulses being only 1 1 meters
a second, for sensory impulses 12 meters, and for tactile impulses 40
meters a second.

Nerve Fatigue. — Inasmuch as nerves are parts of living cells,
the seat of nutritive changes, it might be supposed that the passage
of nerve impulses would be attended by the disruption of energy-
holding compounds, the production of waste products, the liberation
of heat, and in time by the phenomena of fatigue. Though it is
probable that changes of this character occur, yet no rehable
experimental data have been obtained which afford a clue as to the
nature or extent of any such changes. Stimulation of motor nerves
with the induced electric current for four hours appears to be without
influence either on the intensity of the nerve impulse or the rate of its
conduction.

ii8

TEXT-BOOK OF PHYSIOLOGY.

Identity of Efferent and Afferent Nerves and Nerve Impulses.

— Notwithstanding the classification of nerve-fibers based on differ-
ences of physiologic actions, there are no characters, either histologic
or chemic, which serve to distinguish them from one another. More-
over, as the nerve impulse is conducted through a nerve-fiber equally
well in both directions, as determined by experiments, it is probable
that it does not differ in character in the two classes of nerves. That
the efferent fibers conduct the nerve impulses from the nerve-centers
to the peripher}^, and the afferent nerves from the periphery to the
centers, is because of the fact that they receive their stimulus physio-
logically only in the centers or at the periphery. The fundamental
reason for difference of effects produced by stimulation of different
nerves is the character of the organ to which the nerve impulse is
conducted. A nerve is merely the transmitter
of the nerve impulse, which if conducted to a
muscle excites contraction; to a gland, secretion;
to a blood-vessel, variation in caliber; to special
areas in the brain, sensations of light, sound,
pain, etc.

Electric Excitation of Nerves. — For the
purpose of studying the physiologic activities of
nerves it has been found convenient to employ
the nerve-muscle preparation (the gastrocnemius
muscle and sciatic nerve) and to use as a stimulus
the induced electric current. (See Fig. 49.)
When kept moist, this preparation is extremely
sensitive to either the galvanic or the induced
current.

Though the development and conduction of a
nerve impulse may be demonstrated by the de-
flection of the galvanometer needle or the move-
ment of the mercury in the capillary electrometer,
it is more conveniently demonstrated by the con-
traction of a muscle, the vigor of which, within limits, may be taken
as a measure of the intensity of the impulse. The preparation
should be enclosed in a moist chamber and the nerve connected
with the inductorium through the intervention of non-polarizable
electrodes. The muscle may be attached to the muscle-lever and
its contractions recorded.

A single shock of an induced current develops, it is believed,
a single nerv^e impulse followed by a single muscle contraction. A
minimal contraction following a minimal electric stimulus presupposes
the development of a nerve impulse of low intensity. Within certain
limits a maximal contraction following a maximal electric stimulus
presupposes the development of a nerve impulse of high intensity.

Fig. 49. — Nerve-
muscle Prep-
aration OF A
Frog. F. Fe-
mur. S. Sciatic
nerve. I. Ten-
do Achillis.

GENERAL PHYSIOLOGY OF NERVE-TISSUE.

119

Intermediate contractions indicate nerve impulses of corresponding
intensity.

Tetanization of a muscle indicates that the nerve impulses arrive
at the muscle with a frequency so great that the muscle does not
succeed in relaxing from the effect of one stimulus before the next
arrives. Incomplete as well as complete tetanus may be developed
by gradually increasing the frequency of the stimulus. The character
of the contraction caused by indirect stimulation — /. e., though the
nerve — does not differ in any essential respect from that due to direct
stimulation.

ELECTRIC PHENOMENA OF NERVES.

-It was discovered
be obtained from

Electric Currents from Injured Nerves.-

by du Bois-Reymond that electric currents can
nerves as well as from muscles, and
that the electric properties of the
former correspond in most respects to
those of the latter. The laws govern-
ing the development and mode of
action of the currents derived from
muscles are equally apphcable to the
currents derived from nerves.

A nerve-cylinder obtained by mak-
ing two transverse sections of any
given nerve presents, as in the case of
muscles, a natural and two artificial
transverse surfaces. A line drawn
around the cyhnder at a point lying
midway between the two end surfaces
constitutes the equator. From such a
cyhnder strong currents are obtained
when the natural longitudinal surface
and the transverse surface are con-
nected with the electrodes of the gal-
vanometer circuit. The strength of
the current thus obtained will diminish
or increase according as the electrode
on the longitudinal surface is removed
from or brought near to the equator.
If two symmetric points on the longi-
tudinal surface equidistant from the
equator are united, no current is obtainable. When asymmetric
points on the longitudinal surface are connected, weak currents are
obtained, in which case the point lying nearer the equator becomes
positive to the point more distant, which becomes negative. From

Fig. 50. — Diagram to Illus-
trate THE Currents in
Ner\es. The arrowheads
indicate the direction; the
thickness of the lines indicates
the strength of the currents.

I20 TEXT-BOOK OF PHYSIOLOGY.

these facts it is evident that all points on the longitudinal surface, are
electrically positive to the transverse surface and that the point of
greatest positive tension is situated near the equator (Fig. 50).

The electromotive force of the nerve-current varies in strength
with the length and thickness of the nerve. The strongest current
obtained from the nerve of the frog is equal to the 0.002 of a Daniell
cell; that obtained from the nerve of the rabbit, 0.026 of a Daniell.
The existence of the nerve, its strength, duration, etc., depend largely
on the maintenance of physiologic conditions. Ail influences w^hich
impair the nutrition of the nerve diminish the current. With the
death of the nerve all electric phenomena disappear.

Negative Variation of the Nerve Current. — During the pas-
sage of the nerve impulse the resting nerve current, or the demarca-
tion current, diminishes more or less completely in intensity, undergoes
a negative variation, as shown by the return of the galvanometer
needle, due to a change in its electromotive condition or to a diminu-
tion of the difference in potential between the positive longitudinal
and negative transverse sections. This negative variation of the de-
marcation current is observed equally well from either the central or
peripheral end of the nerve. If the two ends of the nerve are con-
nected with' galvanometers and the nerve stimulated in the middle,
the demarcation currents simultaneously undergo a negative variation.
This may be taken as a proof that the excitation process propagates
itself equally well in both directions. The negative variation is inti-
mately connected with changes in the molecular condition of the nerve
and is not due to any extraneous electric or other influence. And
du Bois-Reymond was also enabled to obtain a negative variation of
the current in the nerves of a Hving frog which were yet in connection
with the spinal cord. In this experiment the sciatic nerve was divided
at the knee and freed from its connections up to the spinal column ; the
transverse and longitudinal surfaces were then placed in connection
with the electrodes of the galvanometer wires and the current per-
mitted to influence the needle. The animal was then subjected to
the action of strychnin. Upon the appearance of the muscle
spasms the needle was observed to swing backward toward the zero
point to the extent of from i to 4 degrees, and upon the cessation of
the spasms to return to its previous position. In an experiment of
this nature it is obvious that the negative variation was the result of a
physiologic stimulation of the nerve arising within the spinal cord.

The question also here arises as to whether the negative variation
is due to a steady, continuous decrease of the natural current, or
whether it is due to successive and rapidly following variations in its
intensity, similar to that observed in muscles. Though this cannot
be demonstrated with the physiologic rheoscope, as was the case with
the muscle, there can be no doubt, both from experimentation and

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 121

analogy, that the latter supposition is the correct one. It has been
■ shown that when non-polarizable electrodes connected with Siemen's
telephone are placed in connection with the longitudinal and trans-
verse sections of a nerve, low, sonorous vibrations are perceived
during tetanic stimulation, — a proof that the active state of the nerve
is connected with the production of discontinuous electric currents.
The oscillations of the mercurial column of the capillary electrom-
eter also reveal similar electric changes. It was also demonstrated
by Bernstein with a specially devised apparatus, the repeating rheo-
tome, that the negative variation is composed of a large number of
single variations which succeed each other in rapid succession and
summarize themselves in their effect on the needle.

Electric Currents from Uninjured Nerves. — The pre-existence
of electric currents in living and wholly uninjured nerves while at
rest has also been denied by Hermann, who regards all portions of
the nerve as isoelectric, any difference of potential being the result of
some injury to its surface.

Action Currents. — For reasons to be stated below, it is very diffi-
cult to determine the presence of diphasic action currents during the
passage of an excitatory impulse through the nerve-fiber. The so-
called negative variation of the resting nerve current,— the demarca-
tion current, — which is occasioned by tetanic stimulation, Hermann
regards as the expression of an action current which flows in the nerve
in a direction opposite to the demarcation current. The origin of this
action current is to be sought for in the continuous negativity of that
portion of the longitudinal surface of the nerve in contact with the
diverting electrode, while the dying substance of the transverse surface
takes no part in the excitation. This tetanic action current, or nega-
tive variation, was discovered by du Bois-Reymond, and Bernstein
later succeeded in obtaining this action current during the passage
of a single excitation process. That the return of the galvanometer
needle toward the zero point is not due to an annulment of the demar-
cation current itself, but to the appearance of an action current, is
shown by the fact that if the former be compensated by a battery
current until the needle rests on the zero point the appearance of the
latter current wnll cause the needle to swing in a direction the opposite
of that caused by the demarcation current. The negative variation
and action current may therefore be regarded as one and the same
thing. It is the expression of the change the nerve is undergoing
during the passage of the nerve impulse. The rapidity with which
the negative variation or action current travels, the variation in its
intensity from moment to moment, the time required for it to pass
a given point, would express the change in the nerve to which the
term nerve impulse is given. From experiments made with the
differential rheotome, Bernstein calculated that the speed of the

122 TEXT-BOOK OF PHYSIOLOGY.

negative variation is about 28 meters a second; that it is at first
feeble, soon rises to a maximum, and then dechnes; that it requires
0.0006 to 0.0008 of a second to pass a given point. From these data
it is evident that the negative variation or action current has a space
value of about 18 mm. Transferring these statements to the nerve
impulse, it may be said that it is a molecular disturbance, traveling
at the rate of about 28 meters a second, is wave-like in character, 18
millimeters in length, and occupies 0.0006 to 0.0008 of a second in
passing any given point.

Absence of Diphasic Action Currents. — When any two points on
the longitudinal surface which do not exhibit a current are connected
with the galvanometer and a single wave of excitation passes beneath
the electrodes, it might be expected that, as in the case of the muscle,
a diphasic action current would be observed, from the fact that the
portions of the nerve beneath the electrodes become alternately neg-
ative with reference to all the rest of the nerve. This, however, is
not the case, the absence of the two opposing phases of the action
current being explained on the supposition that the negativity of the
two led-off points is of equal amount, and that, owing to the great
rapidity with which the excitation wave travels, the two phases fall
together too closely in time to alternately influence the galvanometer
needle. During stimulation of the nerve, when two currentless or iso-
electric points are connected, there is also an absence of the action
current, as was observed first by du Bois-Reymond, and which is to
be explained on similar grounds. It is true that an apparent action
current is sometimes seen when the stimulating current is very power-
ful or the seat of stimulation too near the diverting electrodes. This,
however, must be attributed to an electrotonic state of the nerve.

The Effects of a Galvanic Current on a Nerve. — When a con-
stant galvanic current of medium strength is made to pass through a
portion of a nerve, several distinct effects are produced :

1. The development of a nerve impulse at the moment the current
enters and at the moment the current leaves the nerve, i. e., at the
moment the circuit is made and at the moment it is broken. The
development of the nerve impulse is made evident by the contraction
of the muscle if the nerve-muscle preparation be used. If the current
be either very weak, or very strong, the muscle contraction may not
always take place.

2. The development of electric currents on each side of the positive
pole or anode, and the negative pole or cathode (see Fig. 51), which
can be led off by means of wires into a galvanometer circuit from
either the artificial transverse and longitudinal surfaces, or from any
two points on the longitudinal surface as shown by the deflection
of the galvanometer needle. The direction of these electric cur-
rents in the nerve coincides with that of the galvanic or "polarizing

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 123

current." The "natural nerve currents," the currents of injury or
demarcation currents, as they arc variously termed, are at the same
time increased and decreased at opposite extremities of the nerve
according to the direction of the polarizing current.

To this changed condition of the electromotive forces in a nerve
the term electrotonus was given (du Bois-Reymond). The currents
themselves are known as electrotonic currents; from their relation
to the anode and cathode, they are termed anelectrotonic and cat-
electrotonic currents. The condition of the nerve around the poles
both in the intra-polar and extra-polar regions is known as an-
electrotonus and catclcctrotonus.

The electrotonic currents vary considerably in strength and ex-
tent, according to the intensity of the polarizing current, increasing
steadily with the intensity of the latter up to the point at which the
polarizing current begins to destroy the physical and chemic integrity
of the nerve. The electrotonic currents are strongest in the imme-
diate neighborhood of the electrodes, but gradually diminish in strength

J

] POLARIZING \
♦ "^ CURRENT 3

+1 — ^ i-

GALVANOMETER

anelectrotonic katelectroton ic

currents currents

Fig. 51. — Electrotonic Currents.

as the distance between the polarized and led-off portions is increased.
The distance to which the electrotonic currents extend along the nerve
will depend very largely upon the strength of the polarizing current,
though it is conditioned by the physical state of the nerve ; for if it be
ligated or injured beyond the polarized portion, the electrotonic cur-
rents are abolished. The electrotonic currents have no necessary
connection with the natural nerve currents, nor are they to be regarded
as branchings of the galvanic current. They are in all probability of
artificial origin, due to an inner positive and negative polarization of
the nerve which extends for a variable distance on each side of the
poles, and due to the action of the polarizing or the galvanic current.
3. An alteration in the excitability and conductivity of the nerve
in the neighborhood of the poles, whereby the results of nerve stimu-
lation— that is, muscle contraction, sensation, and inhibition — are
increased or decreased according to the strength and direction of the
current. To this condition the term electrotonus was also given
(Pfliiger). This word has thus been employed to express two distinct

124

TEXT-BOOK OF PHYSIOLOGY.

series of effects exhibited by a nerve through a portion of which a con-
stant galvanic current is passing. It appears desirable, for the sake of
clearness, to limit the term electrotonus to the electric or electrotonic
currents which can be led off from either extremity of the nerve, and
to apply to the modifications of irritability which accompany electro-
tonus the expression, electrotonic alteration of excitability and con-
ductivity.

During the passage of the current the excitability of the intra-
polar as well as the extra-polar regions undergoes a change which,
as shown on examination, is found to be diminished in the neigh-
borhood of the anode or positive pole and increased in the neigh-
borhood of the cathode or negative pole. These alterations in the
excitability are most marked in the immediate vicinity of the elec-
trodes, though they extend for some distance into both the extra-
polar and intra-polar regions, though with gradually diminishing
intensity, until they finally disappear. Between the electrodes there

K f

Fig. 52. — Scheme of the Electrotonic Excitability.

is 'a point where the excitability is unchanged and known as the
neutral or indifferent point (Fig. 52). The extent to which the ex-
citability is modified as well as the position of the neutral point will
depend largely on the strength of the polarizing or galvanic current.
The electrotonic alterations of excitability and conductivity can
be experimentally demonstrated on the muscle-nerve preparation in
the following manner:

I. With a descending current of medium strength. Previous to the
closure of the polarizing current, the nerve is stimulated first
in the extra-polar anodic region and the extra-polar cathodic
region with an induction shock of medium intensity and the
height of the contraction recorded. On repeating the stimulation
after closure of the polarizing current the contraction resulting
from stimulation of the anodic region will be enfeebled or may be
entirely wanting, while the contraction from stimulation of the
cathodic region will be decidedly increased. (See Fig. 53.)

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 125

With an ascending current of the same strength. After prehmi-
nary testing of the excitabihty and the subsequent closure of
the polarizing current, it will be found that stimulation of the
extrapolar anodic region will provoke a much less energetic

^m^aa

ANODE

\ REGION OF
^INCREASED EXCITABILITY

i^

KATHODE

SECONDARY COH

Fig. 53. — Diagram Showing the Region of Increased Excitability Caused by
THE Passage of a Galvanic Current, Stimulation of which Gives Rise
to Increased Contraction.

contraction or perhaps none at all. Stimulation of the extra-
cathodic region, though of increased excitability, as shown by
the previous experiment, may also fail to provoke a contraction,
owing to the diminished conductivity of the region in the neighbor-

REGION OF
DECREASED EXCITABILITY

Fig. 54. — Diagram Showing the Region of Decreased Excitability Caused
BY THE Passage of a Galvanic Current, Stimulation of which Gives
Rise to Decreased Contraction.

hood of the anode. The impulse on reaching this region is
blocked in its passage. A similar if not more marked decrease

126

TEXT-BOOK OF PHYSIOLOGY.

in the conductivity may be developed in the region of the cathode
if the current strength be very great. (See Fig. 54.)

The Law of Contraction; Polar Stimulation. — It was stated
in a previous paragraph that when a galvanic current of medium
strength is made to enter a nerve, and when it is withdrawn from the
nerve, there is a contraction of its related muscle. These are generally
known as the make and break effects. During the actual passage
of the current no effect is observed so long as its strength remains
uniform. Any sudden variation in the strength of the current at
once arouses the nerve to activity, as shown by a muscle contraction.

The muscle response to the make and break of the constant current
is more or less variable unless the direction of the current as well as
its strength be taken into consideration. If the current is made to
flow from the central toward the peripheral end of the nerve it is
termed a direct, descending, or centrifugal current; if it is made to
flow in the reverse direction, it is termed an indirect, ascending, or
centripetal current. The strength of the current is determined and
regulated by means of a rheocord.

The make and break of currents of different but known strengths
and directions give rise to contractions which occur with more or less
regularity. The order in which they occur under these varying
conditions of experimentation has been determined and tabulated
as follows by Pfliiger, and is termed the law of contraction:

Current Intensity.

Ascending Current.

Descending Current.

Make.

Break.

Alake.

Break.

Weak,

Contraction.
Contraction.
Rest.

Rest.

Contraction.

Contraction.

Contraction.
Contraction.
Contraction.

Rest.

Medium,

Strong, _ _ _

Contraction.
Rest or weak

contraction.

The results as above tabulated are sometimes complicated on the
opening of the circuit by a series of irregular pulsations of the muscle,
an apparent tetanus, and long known as the opening tetanus of
Ritter, which is attributed to rapid changes in the irritability of the
nerve, in the region of the anode. A similar tetanic contraction of the
muscle is sometimes observed on the closure of the circuit due to
continued excitation in the region of the cathode. This is known
as the closing tetanus of Wundt. All the phenomena of the law of
contraction were explained by Pfliiger on the assumption that the
current stimulates the nerve only at the one electrode, at the cathode
on closing, and at the anode on opening; or, in o-ther words, by the
appearance of catelectrotonus or by the disappearance of anelectro-
tonus, both conditions being attended by a rise of excitability — not,
however, by the opposite changes. It is further assumed that the

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 127

appearance of calelectrotonus is more effective as a stimulus than the
disappearance of anelectrotonus. For these reasons the term polar
stinmlaiion is generally employed in discussing the make and break
effects of the galvanic current. The law of contraction may then be
explained as follows: Very feeble currents, either ascending or de-
scending, produce contraction only upon the closure of the circuit, the
sudden increase 0} the excitahilily in the catelecirotonic area being
alone sufficient to generate an impulse. The contraction which
follows the closing of the weak ascending current depends upon the
fact that the decrease of excitabihty and conductivity at the anode is
insufficient to interfere with the conduction of the cathodal stimulus.
Medium currents, either ascending or descending, produce contrac-
tion both on closing and opening the circuit. The appearance of
catelectrotonus and the disappearance of anelectrotonus are both
sufficiently powerful to generate an impulse without, however, seri-
ously impairing the conductivity of the nerve.

Very strong currents produce contraction only upon the opening
of the ascending and closure of the descending currents, or upon the
passage of the excitabihty in the former from the marked anelectro-
tonic decrease to the normal condition, and in the latter from the nor-
mal to that of catelectrotonic increase. The absence of contraction
upon the closure of the ascending current is dependent upon the
blocking of the cathodal stimulus by the decrease of the excitabihty
and conductivity at the anode. With the opening of the descending
current the disappearance of anelectrotonus should also be followed
by contraction, which would indeed be the case if the stimulus so
generated was not blocked by the decrease of the conductivity at the
cathode.

The order in which the contractions occur may be tabulated as
follows :

With Ascending Current. With Descending Current.

Weak, I. K. C. C* __ K. C. C.

Medium, 2. K. C. C. A. O. Cf K. C. C. A. O. C.

Strong, 3. .. A. O. C. K. C. C. A. O. C.(?)

Polar Stimulation of Human Nerves. — The preceding state-
ments as to changes in the excitability caused by the passage of a
constant current, as well as to the law of contraction, are based en-
tirely on experiments made with the isolated nerve of the frog. It
is probable, however, that the same phenomena would have been
observed had the nerve of a mammal been used and its excitabihty
been maintained.

If the electrodes connected with the wires of a sufficiently strong
galvanic batter}^ be applied to the skin over the course of a superficially

* K. C. C, cathodal closing contraction, f A. O. C, anodal opening contraction.

128 TEXT-BOOK OF PHYSIOLOGY.

lying nen'e, e. g., the brachial, it will be found that there occurs on
the closure of the circuit an increase in the excitability in the extra-
polar anelectrotonic region and a decrease in the excitability in the
extra-polar catelectrotonic region, as shown by stimulating the nerve
in the extra-polar regions with the induced current — results which are
n apparent contradiction to those obtained with the isolated nerve.
This want of accordance in the results of the two classes of experi-
ments arises from a failure to recognize the fact that the physiologic
anode and cathode do not coincide with the physical anode and
cathode.

It has been experimentally demonstrated that owing to the large
amount of readily conducting tissue by which the nerve is surrounded,
the current density, though great immediately under the electrode,
quickly decreases at a short distance from it, so that for the nerve it
becomes almost nil. The current, therefore, shortly after entering,
again leaves the nerve at various points which become physiologic
cathodes. Stimulation of this physiologic cathode with the induced
current gives rise, therefore, to the phenomenon of increased excita-
bility in the region of the anode. If, however, the galvanic and
stimulating current be combined in one circuit and both be applied
to the same tract of nerve, results will be obtained which harmonize
with those obtained with the frog's nerve.

The changes in the excitability of a nerve of a living man and the
contractions which follow the closing and opening of the constant
current have been thoroughly studied by Waller and de Watte ville.
These observers employed a method similar to that of Erb, conjoin-
ing in one circuit the testing and polarizing currents. By the graphic
method they recorded first the contraction produced by an induc-
tion shock alone; and, secondly, the contraction produced by the
same stimulus under the influence of the polarizing current. As a
result of many experiments, they also demonstrated an increase of
the excitability in the polar region when it is cathodic, and a decrease
when it is anodic. Following the suggestion of Helmholtz, that the
current density quickly decreases with the distance from the elec-
trodes, they recognize, at the point of entrance and exit of the current
from the nerve, two regions — a polar, having the same sign as the
electrode, and a peripolar, having the opposite sign (Figs. 55 and 56).
The peripolar regions also experience similar alterations of excita-
bility, though less in degree, according as they are cathodic or anodic.

As it is impossible to confine the current to the trunk of the nerve
when surrounded by living tissues, as is easily the case when experi-
menting with the frog's nerves, it is incorrect to speak of either
ascending or descending currents. Waller,* who has thoroughly

*" Human Physiology," p. 363, 1891.

GENERAL PHYSIOLOGY OF NERVE-TISSUE.

129

studied the elcctrotonic effects of the galvanic current from this point
of view, sums up his conchisions in the following words: "We must
apply one electrode only to the nerve and attend to its effects alone,
completing the circuit through a second electrode, which is appHcd
according to convenience to some other part of the body.

"Confining our attention to the first electrode, let us see what
will happen according as it is anode or cathode of a galvanic current
(Figs. 55 and 56). If this electrode be the anode of a current, the
latter enters the nerve by a series of points and leaves it by a second
series of points; the former, or proximal series of points, collectively
constitutes the polar zone or region; the latter, or distal series of
points, collectively constitutes the peripolar zone or region. In such
case the polar region is the seat of entrance of current into the nerve —
i. €., is anodic; the peripolar region is the seat of exit of current from
the nerve — i. e., is cathodic. If, on the contrar}^ the electrode under
observation be the cathode of a current, the latter enters the nerve

Fig. 55. — Anode of Battery. Polar
region of nerve is anodic. Peri-
polar region of nerve is cathodic.

Fig. 56. — Cathode of Battery. Polar
region of nerve is cathodic. Peri-
polar region of ner\'e is anodic.

by a series of points which collectively constitute a 'peripolar' region,
and it leaves the nerve by a series of points which collectively con-
stitute a 'polar' region. The current, at its entrance into the body,
diffuses widely, and at its exit it concentrates; its 'density' is greatest
close to the electrode, and, the greater the distance of any point from
the electrode, the less the current density at that point; hence it is
obvious that the current density is greater in the polar than in the
peripolar region. These conditions having been recognized, we may
apply to them the principles learned by study of frogs' nerves under
simpler conditions. Seeing that, with either pole of the battery,
whether anode or cathode, the nerve has in each case points of en-
trance (constituting a collective anode) and points of exit to the cur-
rent (constituting a collective cathode), and admitting as proved that
make excitation is cathodic, break excitation anodic, we may, with a
sufficiently strong current, expect to obtain a contraction at make
and at break with either anode or cathode apphed to the nerve; and
9

I30

TEXT-BOOK OF PHYSIOLOGY.

we do so, in fact. When the cathode is apphed, and the current is
made and broken, we obtain a cathodic make contraction and a cathodic
break contraction; when the anode is applied, and the current is made
and broken, we obtain an anodic make contraction and an anodic
break contraciio?i. These four contractions are, however, of very
different strengths; the cathodic make contraction is by far the
strongest; the cathodic break contraction is by far the weakest; the
cathodic make contraction is stronger than the anodic make con-
traction; the anodic break contraction is stronger than the cathodic
break contraction. Or, otherwise regarded, if, instead of comparing
the contractions obtained with a sufficiently strong current, we ob-
serve the order of their appearance with currents gradually increased

M. biceps brachii.

M. brach. anticus

medianus

pronator teres.
M. flex, digitor. commun. profund.

M. flex, carpi radialis.

M. fl^. digitor. sublim.

M. flex. dig. subl. (dig. ind. et min.)
^M. Hex. poU.longus.
^. med

N. ulnaris.

M. flexor carpi ulnaris.

N. ulnaris.

Fig. 57. — Motor Points of the Median and Ulnar Nerves, with the Muscles

Supplied by Them.

from weak to strong, we shall find that the cathodic make contraction
appears first, that the cathodic break contraction appears last, and
the formula of contraction for man reads as follows :

"Weak current, K. C. C.

Medium current, K. C. C. A. C. C. A. O. C.

Strong current, K. C. C. A. C. C. A. O. C.

K. O. C.

The constant or the galvanic current is frequently used for thera-
peutic and diagnostic purposes. In accordance with the statements
above quoted, one electrode should be apphed to the part to be in-
vestigated, the other to some indifferent region. The electrode con-

GENERAL PHYSIOLOGY OF NERVE-TISSUE. 131

veying the current to or from this part should be of a size sufficient
to locahze the current and to increase its density. It was discovered
by Duchenne that there arc certain points all over the body stimula-
tion of which is more quickly followed by muscle contraction than
others. It was subsequently discovered by Remak that these points
coincide with the entrance of the nerve into the muscle. It is to
these motor points that the one electrode should be applied. The
position of some of these points on the forearm is shown in Fig.

57-

Reactions of Degeneration. — In consequence of the degen-
eration and changes in irritability which occur in nerves and muscles
when separated, either experimentally or as the result of disease, the
response of these structures to the induced and the make and break
of the constant current differs from that observed in the physiologic
condition. The facts observed under the application of these two
forms of electricity are of importance in the diagnosis and thera-
peutics of the precedent lesions. The principal difference of behavior
is observed in the muscles, which exhibit diminished or abolished
excitability to the induced current, while at the same time manifesting
an increased excitability to the constant current ; so much so is this the
case that a closing contraction is just as likely to occur at the positive
as at the negative pole. This pecuHarity of the muscle response is
termed the reaction of degeneration. The synchronous diminished
excitability of the nerves is the same for either current. The term
"partial reaction of degeneration" is used when there is a normal
reaction of the nerves, with the degenerative reaction of the muscles.
This condition is observed in progressive muscular atrophy.

Reflex Action. — Inasmuch as many of the muscle movements of
the body, as well as the formation and discharge of secretions from
glands, variations in the caliber of blood-vessels, inhibition and
acceleration in the activity of various organs, are the result of stimu-
lations of the terminal organs of afferent nerves, they are termed, for
convenience, reflex actions, and, as they take place for the most part
through the spinal cord and medulla oblongata and independently
of the brain or of voHtional influences, they are also termed involun-
tary actions. As many of the processes to be described in succeeding
chapters are of this character, requiring for their performance the
cooperation of several organs and tissues associated through the
intermediation of the nervous system, it seems advisable to consider
briefly, in this connection, the parts involved in a reflex action, as
well as their mode of action. As shown in Fig. 58, the necessary
structures are as follows :

1. A sentient surface, skin, mucous membrane, sense-organ, etc.

2. An afferent nerve- fiber and celk

3. An emissive cell, from which arises —

132

TEXT-BOOK OF PHYSIOLOGY.

4. An efferent nerve, distributed to a responsive organ, as

5. Muscle, gland, blood-vessel, etc.

Such a combination of structures constitutes a reflex mechanism
or arc, the nerve portion of which is composed of but two neurons —
an afferent and an efferent. An arc of this simpHcity would of neces-
sity subserve but a simple movement. The majority of reflex activ-
ities, however, are extremely complex, and involve the cooperation
and coordination of a number of structures frequently situated at
distances more or less remote from one another. This imphes that
a number of neurons are associated in function. The afferent
neurons are brought into relation with the dendrites of the efferent
neurons by the end-tufts of the collateral branches, which may extend

for some distance up
A and down the cord be-

j-y ef/i /^^^$C]?N /C""^ fo^^ passing into the

various segments.

For the excitation of
a reflex action it is es-
sential that the stimulus
applied to the sentient
surface be of an inten-
sity sulScient to develop
in the terminals of the
afferent nerve a series of
nerve impulses, which,
traveling inward, will be
distributed to and re-
ceived by the dendrites
of the emissive or motor cell. With the reception of these impulses
there is apparently a disturbance of the equihbrium of its molecules,
a hberation of energy, and, in consequence, a transmission outward
of impulses through the efferent nerve to muscle, gland, or blood-
vessel, separately or collectively, with the production of muscular
contraction, glandular secretion, vascular cHlatation or contraction,
etc. The reflex actions take place, for the most part, through the
spinal cord and medulla oblongata, which, in virtue of their contained
centers, coordinate the various organs and tissues concerned in the
performance of the organic functions. The movements of mastica-
tion; the secretion of sahva; the muscular, glandular, and vascular
phenomena of gastric and intestinal digestion; the vascular and
respiratory movements; the mechanism of micturition, etc., are illus-
trations of reflex activity.

. 58. — Diagram Showing Structures Con-
nected WITH Reflex Actions. A. Trans-
verse section of spinal cord with centers in the
anterior horn of the gray matter for muscles,
m, glands,^, and blood-vessels, b. ef.n. Efferent
nerves which convey nerve impulses to these
organs, s. Sensory surface, af.71. Afferent

.nerve conveying nerve impulses to the centers
in the spinal cord.

CHAPTER VIII.
FOODS.

The functional activity of every organ and tissue of the body is
accompanied by a more or less active disintegration of the living
material, the bioplasm, of which it is composed. The complex and
highly unstable molecules of this living material are continually
undergoing disruption and falling into less complex and more stable
compounds; these, through oxidative processes, are eventually re-
duced through a series of descending chemic stages to a small number
of simpler compounds which, being of no further value to the organ-
ism, are ehminated by the various ehminating or excretor)^ organs,
the lungs, skin, kidney, liver. Among these excreted compounds the
more important are urea, uric acid, and carbon dioxid. Many other
compounds, organic as well as inorganic, are also eliminated from
the body in the various excretions, though they are present in but
small amounts. Coincident with this disintegration of Hving material
there is a transformation of its potential into kinetic energy, which
manifests itself for the most part as heat and mechanic motion.

In order that the organs and tissues may continue in the per-
formance of their functions, it is essential that they be supphed with
nutritive materials similar to those which enter into their own com-
position: \'iz., proteids, fat, carbohydrates, water, and inorganic
salts. These compounds, though originally derived from the food,
are immediately derived from the blood as it flows through the capil-
lar}' blood-vessels. The blood is therefore to be regarded as a reser-
voir of nutritive material in a condition to be absorbed and trans-
formed into utihzable and living material. Inasmuch as the mate-
rials lost to the body daily, through disintegration and oxidation,
though considerable, are supphed by the blood, it is evident that this
fluid would diminish rapidly in volume, with a corresponding decline
in functional activity, were it not restored by the introduction into
the body of new material in the food. With the diminution of the
volume of the blood and an insufficient supply to the tissues, there
arise the sensations of hunger and thirst, which lead to the consump-
tion of food and the subsequent restoration of the physiologic condi-
tion of the tissues. These two sensations are also partially dependent
on the empty condition of the stomach and the dn-mess of the mucous
membrane of the mouth and throat.

^33

134 TEXT-BOOK OF PHYSIOLOGY.

The foods which are consumed daily in response to the sensations
of hunger and thirst are complex in composition and contain, though
in varying amounts, proteids, fats, carbohydrates, water, and inor-
ganic salts, which, in contradistinction to foods, are termed food
principles or nutritive principles. In these compounds is also to be
found the potential energy necessary to maintain the dynamic equi-
librium of the body and which will become manifest as heat and
mechanic motion in the transformations of the material underlying
the nutritive processes.

The animal body may be therefore regarded as a machine capable
each day of performing a certain amount of work by the expendi-
ture of a definite amount of energy. In the performance of its work,
whether it be the raising of weights against gravity, the overcoming
of friction, cohesion, or elasticity, the machine suffers disintegration
and loses a portion of its available energy. Unlike other machines,
however, it possesses the power, within limits, of self-renewal, self-
adjustment, when supphed with foods in proper quantity and quality.

QUANTITIES OF FOOD PRINCIPLES REQUIRED DAILY.

In order that the body may continue in the performance of its
work and yet retain a given weight, it is essential that the loss to the
body daily shall be exactly compensated by the introduction and
assimilation of a corresponding amount of food principles. If this
condition is realized, the body neither gains nor loses, but remains in
a condition of nutritive equilibrium. The determination of the exact
quantities of the different food principles required daily and their
ratio one to another is made from an examination of the quantity and
composition of the daily excretions. Since the proteids disintegrated
are represented in the excretions by urea and similar nitrogen-holding
compounds and the fats and carbohydrates by carbon dioxid, it
becomes possible to determine from them the quantities required to
restore equilibrium under any given condition. But as the activity
of the nutritive changes will vary in accordance with climatic condi-
tions, work done, etc., and as the excreted products will vary in the
same ratio, it is obvious that the required amounts of food will vary
in accordance with these varying conditions, if equilibrium is to be
maintained.

Various estimates have been made by different investigators as
to the amounts of the excreted products and the food principles re-
quired daily, which, though differing to some extent, have, neverthe-
less, an average nutritive and energy-producing value. The follow-
ing table shows the diet scale of Vierordt and the excretions to which
it would give rise. As the income and outgo practically balance,
there would be no change in the weight.

FOODS.

135

COMPARISON OF THE INCOME AND OUTGO.

Income.

Proteid,

Fat,

Carbohydrates, _.

Salts,

Water, 2818

Oxygen,

Gkams.

120

Ounces.

4-25

90
330

3-17
11.64

32
2818

756

I-I3
99-30
26.66

4146

146.13

Outgo.

Water,

Urea,

Feces, dry,

Salts,

Carbon dioxid,

Water formed in body.

Grams. Ounces.

2818

40

38

32

922

296

99-3°

1.40

1.60

1-13

32-37

10.33

4146

146.15

Other estimates as to the amounts of the organic food principles
required daily are as follows :

Ranke. Voit. Moleschott. Atwater. Hultgren.

Grams. Grams. Grams. Grams. Grams.

Proteid, 100 118 130 125 134

Fat, 100 56 84 125 79

^ Starch, 250 500 550 400 522

In arranging tables showing the relation between the income and
the outgo, it is generally customary to state merely the amounts by
weight of the nitrogen and carbon each contains. This method
furnishes sufficiently accurate information regarding the metabolism
of the body, for the reason that the nitrogen represents the proteid,
and the carbon, with the exception of that contained in the proteid,
the fat and carbohydrates which have undergone disintegration or
metabolism.

The following balance table, as given by Ranke, shows the rela-
tion of the nitrogen to the carbon in the average mixed diet and in the
excretions of a man weighing 70 kilograms, in a condition of nutritive
equilibrium :

Income.

Grams.

N.

C.

Proteid, . _

100
100
250

15-5

53.0

Fat, . - -

79.0
93 -o

Carbohydrates,

iS-5

225.0

Outgo.

Grams.

N.

C.

Urea,

31-5 I
0.5 J

14.4
I.I

Uric acid, _ __ _ ___

6.16

Feces,

10.84

CO2,

208.00

^S-^

225.00

136 TEXT-BOOK OF PHYSIOLOGY.

From the above it will be observed that the daily discharge for
each kilogram of body- weight is 0.21 gram nitrogen and 3.03 grams
of carbon; the relation of the two being j^ = 14.5. On a diet in
which there is an excess of either proteid or carbohydrates this ratio
necessarily changes.

CLASSIFICATION OF FOOD PRINCIPLES.

Though the food principles are grouped as proteids, fats, carbo-
hydrates, etc., the members of each group differ somewhat in chemic
composition, digestibility, and nutritive value. These groups are as
follows:

I. Proteids.

Principle. Where found.

Myosin, Flesh of animals.

Albumin, vitellin, White of egg, yolk of egg.

Caseinogen, Milk.

Serum-albumin, fibrin, Blood contained in meat.

Glutin, Grain of wheat and other cereals.

Vegetable albumin, Soft-growing vegetables.

Legumin, Peas, beans, lentils, etc.

2. Fats.

Animal fats, In adipose tissue of animals.

Vegetable oils, In seeds, grains, nuts, fruits, and other

vegetable tissues.

3. Carbohydrates.

Dextrose or grape-sugar, )-. , .

Levulose or fruit-sugar, / ^" ^^^"^•

Lactose or milk-sugar, Milk.

Saccharose or cane-sugar, Sugar-cane, beet roots.

Maltose, Malt and malted foods.

Starch ' ^^^^^1^, tuberous roots, and legumin-

, I ^^^ plants.
Glycogen, Liver, muscles.

4. Inorganic.

Water, .

Sodium and potassium chlorid, ) , 1 n • i 1 ,11

Sodium, potassium, and calcium ' ^"^ ^^''^^ ^^^ ^^™^^ ^"^ vegetable

phosphates and carbonates, I 00 s.

Iron, /

5. Vegetable Acids.

Citric, tartaric acetic, malic, In fruit and vegetables.

6. Accessory Foods.
Coffee, Tea, Cocoa, Alcohol.

FOODS. 137

Disposition of Food. — The proteid principles of the food, after
undergoing digestion and conversion into peptones, are absorbed
into the blood. During the act of absorption they are transformed
into the form of proteids characteristic of blood. After being dis-
tributed by the blood-stream to the tissues, they are brought into
relation with the Uving cells. The disposition made of the proteid
material by the bioplasm of the cell has not been definitely deter-
mined. According to Voit, of the proteid thus brought into contact
with the Hving tissues, only a small percentage is utiHzed and assimi-
lated for tissue repair. This he terms tissue or organ proteid. The
remaining large percentage circulating in the interstices of the tissues,
though not forming an integral part of them, is acted on directly by
them, merely in \Tirtue of contact — split up, oxidized, and reduced to
simpler compounds. This he terms circulating proteid.

According to Pi^iiger and others, this view is not tenable. Pfliiger
asserts that, as material changes or metabolism can only take place
within hving cells, all the proteid must first be assimilated and organ-
ized by the cells before it can undergo metaboHc changes. Metab-
ohsm by contact action is denied, and the division of proteids into
organ and circulating proteid is not justifiable.

In the process of metabolism the proteid suffers disintegration, giv-
ing rise through oxidation to some carbon-holding compound, possibly
fat, and to some nitrogen-holding compounds, which eventually give
rise to urea. The intermediate stages, though not definitely known, are
possibly represented by glycin, creatin, ammonium carbamate, etc.
The disintegration of the proteids is attended by the disengagement of
heat, thus contributing to the general store of the energy of the body.

The jat principles, after digestion, are absorbed by the lymphatic
vessels and discharged by the thoracic duct into the blood, from which
they rapidly disappear. Though it is possible that a portion of the
fat enters directly into the formation of the living material, it is gener-
ally beheved that it is at once oxidized and reduced to carbon dioxid
and water with the liberation of energy. The natural supposition
that a portion of the ingested fat was directly stored up in the cells of
the areolar connective tissue, thus giving rise to adipose tissue, has
been a subject of much controversy, though modern experimentation
renders this very probable. The body-fat, under physiologic con-
ditions, is also a product of the metabohc activity of connective-tissue
cells and is a derivative of both proteids and carbohydrates.

The carbohydrate principles, after digestion, are absorbed into
the blood as dextrose. This compound is then stored up in the Hver
and muscles as glycogen. The intermediate stages which glycogen
passes through before it is reduced to carbon dioxid and water are
only imperfectly known. Though a large part of the carbohydrate
material is at once oxidized, it is now well established that another

138 TEXT-BOOK OF PHYSIOLOGY.

portion contributes to the formation of, if it is not directly converted
into, fat. As the carbohydrates form a large portion of the food, they
contribute materially to the production of energy.

The inorgajiic principles, though not playing apparently as active
a part in the metabohsm of the body as the organic, are nevertheless
essential to its physiologic activity.

Water is promptly absorbed after ingestion and becomes a part
of the circulating fluids — blood and lymph. In the digestive appa-
ratus it favors the occurrence of those chemic changes in the food
necessary for their absorption, it promotes absorption of the food,
holds various constituents of the blood and other fluids in solution,
hastens the general metabohsm of the body, holds in solution various
products of metabohc activity, and, leaving the body through the
excretory organs, promotes their elimination.

Sodium chlorid is absorbed into the blood and, unless taken in
excess, is utilized in replacing that which is lost to the organism daily.
The exact role which sodium chlorid plays in the nutritive process
is unknown ; but, as it is present as a necessary constituent in all the
fluids and sohds of the body, and as it is instinctively employed as
a condiment, it may be assumed to have a more or less important
function.

When taken as a condiment, it imparts sapidity to the food and
excites the flow of the digestive fluids; it ukimately furnishes the
chlorin for the hydrochloric acid of the gastric juice. Judging from
the impairment of the nutrition as observed in animals after depriva-
tion of salt for a long period of time, it favorably influences the growth
and functional activity of all tissues.

It is well known that herbivorous animals, races of men as well as
individuals who Hve largely on vegetable foods, require a larger addi-
tional amount of sodium chlorid than carnivorous animals, or human
beings who live largely on animal foods, even though the two classes
of foods contain relatively the same amounts. The explanation is
that the vegetable foods contain potassium salts which, meeting in
the blood with sodium chlorid, undergo decomposition into potassium
chlorid and sodium carbonate or phosphate, ah of which, when in
excess, are at once ehminated by the kidneys. The blood, therefore,
becomes poorer in sodium chlorid, one of its necessary constituents.

Potassium phosphate and carbonate are also essential to the
normal composition of the soHds and fluids. They impart a certain
degree of alkahnity to the blood and lymph, one of the conditions
necessary to the hfe and activity of the tissue-cells bathed by them.
When administered in small doses, they increase the force of the
heart, raise the arterial pressure, and increase the activity of the
circulation.

Calcium phosphate and carbonate are partly utilized in maintain-

FOODS. 139

ing the solidity of the bones and teeth, replacing the amount metab-
olized daily. Inasmuch as the metaboHsm of these two tissues is
slight, there is not much need in the adult for lime as an article of
food. In young animals lime is essential to the solidification and
development of bone. When deprived of it, the skeleton undergoes
a defective development similar to the pathologic condition known
as rickets. Lime is present in milk to the extent of 0.15 per cent., as
well as in eggs and peas in relatively large quantities.

Iron is contained in both animal and vegetable foods, not, how-
ever, in the form of inorganic iron, nor in the form of an organic salt,
but as a compound with nuclein, thus forming an integral part of the
proteid molecule. After absorption the iron is utihzed in the forma-
tion of the coloring-matter of the blood-corpuscles — hemoglobin.
The organic compounds of iron and the nucleins have been termed
hematogens. The amount of iron ingested has been estimated at
from 10 to 90 milligrams, the larger part of which is ehminated in
the feces. The relatively small part eliminated by the kidneys and
liver is usually taken as the amount metabohzed, though it is probable
that this is not wholly true, as there is evidence that iron can be re-
tained in the body and utilized again in the formation of new hemo-
globin. Contrary to what might be expected, milk contains but a
very small quantity of iron, not more than 3 or 4 milHgrams in 1000
grams (human milk) — an amount insulficient for the development of
the necessary hemoglobin. This is compensated for, however, by
the accumulation of iron in the liver during intrauterine life. Ac-
cording to Bunge, the liver of a newly born rabbit contains as much
as 18.2 milligrams per 100 grams of body- weight, while at the end
of twenty-four days it only contains 3.2 milHgrams per 100 grams of
body-weight.

Vegetable acids increase the secretions of the alimentary canal, and
are apt, in large amounts, to produce flatulence and diarrhea. After
entering into combination with bases to form salts, they stimulate the
action of the kidneys and promote a greater elimination of all the
urinary constituents. In some unknown way they influence nutrition;
when deprived of these acids, the individual becomes scorbutic.

The accessory foods, — coffee, tea, and cocoa, — when taken in
moderation have a stimulating influence on the nervous system, as
shown by the removal of both mental and physical fatigue, by an
increased capacity for sustained mental work, by the persistent wake-
fulness among those unaccustomed to their use. Coffee more especially
increases the frequency and force of the heart-beat, raises the arterial
pressure, and hastens the general blood-flow. It has no influence
either in the way of increasing or decreasing proteid metabolism.

Tea frequently acts as an astringent on the ahmentary canal on
account of the tannin which passes into the water when the infusion

I40 TEXT-BOOK OF PHYSIOLOGY.

is made. Inasmuch as tannin also coagulates peptones, the excessive
use of tea as a beverage is apt to derange the digestive organs and
the general process of digestion.

Cocoa is more nutritive than either coffee or tea, on account of the
large amount of fat and proteid it contains. It is, hov^^ever, less
stimulating.

The active principles in coffee, tea, and cocoa, and to which their
effects are to be attributed, are cajfein, thein, and theohromin respec-
tively. These alkaloids are chemically closely related one to the
other and to the compound xanthin. They are present in the coffee
seeds, the tea leaves, and the cocoa bean to the extent of 1.7 per cent.,
1.4 per cent., and 1.6 per cent, respectively. When prepared as a
beverage, however, there is three times as much caffein in coffee
as thein in tea.

Alcohol when taken in small quantities stimulates the digestive
glands to increased activity and thus promotes digestive power. Its
absorption into the blood is followed by increased action of the heart,
dilatation of the cutaneous blood-vessels, a sensation of warmth,
and an excitation of the brain. In large quantities it acts as a paralyz-
ant, depressing more especially the vaso-constrictor nerve-centers and
certain areas of the brain, as shown by an impairment in the power of
sustained attention, clearness of judgment, and muscle coordination.

Alcohol is undoubtedly oxidized in the body, as only about 2
per cent, can be obtained from the urine and expired air. It thus
contributes to the store of the body-energy. As to whether for this
reason it can be regarded as a food, — that is, whether it can be sub-
stituted in part at least for fat or carbohydrate material without im-
pairing the proteid metabohsm, — is at present a subject of experimen-
tation and discussion. According to some investigators, alcohol does
not retard proteid metabohsm, for when it is introduced into the body
in amounts equivalent to the carbohydrates withdrawn from the food
there is at once a rise in the amount of nitrogen excreted. Hence it
cannot be regarded as a food. According to other investigators,
alcohol retards or protects proteid metabohsm just as effectually as
an equivalent amount of starch or sugar. Many more experiments
are required to decide this question. When taken habitually in large
quantities, alcohol deranges the activities of the digestive organs,
lowers the body-temperature, impairs muscle power, lessens the
resistance to depressing external conditions, diminishes the capacity
for sustained mental work, and leads to the development of structural
changes in the connective tissues of the brain, spinal cord, and other
organs. In zymotic diseases and in cases of depression of the vital
powers it is most useful as a restorative agent.

FOODS. 141

THE ENERGY OR HEAT VALUE OF FOOD PRINCIPLES.

The food consumed not only restores the material metabolized
and discharged from the body, but also the energy which has
been expended as heat and mechanic motion. The food principles
are products of the constructive processes taking place in the vege-
table world during the period of growth and activity. At the time
of their formation there is an absorption and storing of the sun's
energy which then exists in a potential condition. During the metab-
oHsm of the animal body these compounds are reduced through
oxidation to relatively simple bodies, such as carbon dioxid, water,
urea, etc., with the hberation of their contained energy. All of the
energy of the body, whatever its manifestations may be, can be traced
to chemic changes going on in the tissues, and more particularly to
those changes involved in the oxidation of the food principles.

The amount of heat or energy wdiich any given food principle will
yield can be determined by burning a definite amount {e. g., 1 gram)
to carbon dioxid and water and ascertaining the extent to which the
heat thus liberated will raise the temperature of a given amount of
water {e. g., 1 kilogram). The amount of heat may be expressed in
gram or kilogram degrees or calories, a gram calorie or kilogram
calorie being the amount of heat required to raise the temperature of
a gram or a kilogram (1000 grams) of water 1° C. The apparatus
employed for this purpose is termed a calorimeter, and consists
essentially of a closed chamber in which the oxidation takes place,
surrounded by a water jacket, the rise in temperature of the water
indicating the amount of heat produced.

The results obtained by investigators employing different calorim-
eters and different food principles of the same group vary, though
within certain limits: e. g., 1 gram casein yields 5.867 kilogram cal-
ories; I gram of lean beef, 5.656 calories; i gram of fat yields 9.353,
9.423, 9.686 calories; i gram of carbohydrate, 4.182, 4.479, etc.,
calories. These numbers represent the physical heat values of these
food principles.

In the human body as determined by calorimetric methods the
oxidation of the food principles yields practically the same amount
of heat they yield when oxidized outside the body, with the excep-
tion of the proteids, which are oxidized only to the stage of urea. As
this compound is capable of further reduction in the calorimeter to
carbon dioxid and water with the hberation of heat, the quantity of
heat it contains must therefore be deducted from the calorimetric
heat value of the proteid. According to Rubner, i gram urea will
yield 2.523 kilogram calories. As the urea which results from the
oxidation of i gram of proteid is about ^ of a gram, the amount of
heat to be deducted from the heat value of the proteid is ^ of 2.523, or
841 calories. It has also been shown that some of the ingested

142 TEXT-BOOK OF PHYSIOLOGY.

proteid escapes in the feces^ the heat value of which must also be
determined and deducted. This having been done, the physiologic
heat value becomes 4.124 calories.

The following estimates give approximately the number of kilo-
gram calories produced when the food is burned to carbon dioxid,
water, and urea in the body :

I gram proteid yields, 4.124 calories

I " fat " _ 9.353

I " carbohydrate yields 4. 116 "

The total number of kilogram calories or kilogram degrees of
heat yielded by any of the previously given diet scales can be readily
determined by multiplying the quantities of food principles con-
sumed by the above-mentioned factors. The diet scale of Vierordt,
for example, yields the following:

120 grams of proteid yields, 494.88 calories.

90 " fat " 841.77 "

330 " starch " 1358.28 "

2694.93

The total calories obtained from other diet scales would be as
follows: Ranke, 2335; Voit, 3387; Moleschott, 2984; Atwater, 3331;
Hultgren, 3436.

Starvation. — The relation of the different food principles to the
general nutritive process becomes more apparent from an examination
of the excretions from the body during the process of starvation com-
bined with an examination of the organs and tissues after death.
If an animal be deprived entirely of food, a dechne in body-weight
at once sets in, which continues until about 40 per cent, of the weight
has been lost, when death generally ensues. This results from the
fact that the active tissue cells consume, for the purpose of maintain-
ing the normal temperature of the body, not only their own reserve
food material, but that of the less active or storage tissues as well;
and, in consequence, there is a progressive diminution in weight.

The phenomena which characterize this non-physiologic con-
dition are as follows: hunger, intense thirst, gastric and intestinal
uneasiness and pain, diminished pulse-rate and respiration, muscular
weakness and emaciation, a lessening in the amount of urine and its
constituents, diminished exhalation of carbon dioxid, an exhalation
of a fetid odor from the body, vertigo, stupor, delirium, at times con-
vulsions, a sudden fall in body-temperature, and finally death. The
duration of life after complete deprivation of food varies from eight to
thirteen days or more, though this period can be prolonged if the ani-
mal be supplied with water, this being more essential under the cir-
cumstances than the organic materials which can be supplied by the
organism itself. The duration of the starvation period will vary in
accordance with the previous condition of the animal and the amount

FOODS.

143

of reserved food the body contains. The excretion of urea declines
very rapidly during the first two days — a fact which has been attrib-
uted to a rapid consumption of the surplus proteid food. After
this period, when the tissues begin to metabohze their own proteid,
the excretion remains fairly constant until toward the close, when the
amount eliminated falls very rapidly. As proteids contain about 16
per cent, of nitrogen, i part of nitrogen equals 6.25 parts of proteid.
Hence, for every i gram of nitrogen or 2.14 grams urea excreted,
it may be assumed that 6.25 grams of proteid or, according to Voit, 30
grams of flesh have been metabolized. The daily excretion of urea,
therefore, indicates the extent of the proteid metaboHsm. It has
been observed also that there is a steady diminution in the excretion of
carbon dioxid, though this is greatest in the last few days. As fat
contains about 76 per cent, of carbon, i part of carbon equals 1.31
parts of fat. Hence, for every i gram of carbon or 3.66 grams carbon
dioxid excreted it may be assumed that 1.31 grams of fat have been
metabolized. The daily excretion of carbon, therefore, indicates the
extent of fat metabohsm. The carbohydrates are here left out of
consideration, as they constitute only about i per cent, of the body-
weight. It must be borne in mind, however, that in the metabolism
of proteid a certain quantity of fat is produced which also undergoes
oxidation. The amount of the carbon or the fat that the proteid
would give rise to, as previously determined, must therefore be sub-
tracted from that eliminated by the lungs, etc., in order to determine
the amount of body-fat metabolized. Observations of human beings
in the fasting condition show that for a period of ten days there is a
daily excretion of about 21 grams of urea, equivalent to about 70
grams of proteid. This amount, however, may be reduced to from
50 to 60 per cent, if the individual has a surplus of body-fat. Human
beings under similar circumstances may lose during the first few days
200 grams of fat daily.

The following table shows the excretion of nitrogen and
carbon and the calculated amounts of proteid and fat metabolized
from an experiment made by Ranke on himself during a fast of
twenty- four hours, beginning twenty- four hours after the last meal:

Disintegration of Tissue.
(Calculated.)

Expenditure.

Nitrogen.

Carbon.

Urea, 17 gm., \

Uric acid, 0.2 gm., j

Parhnn HinviH

Nitrogen.

Carbon.

Proteid, 50 gm.,

Fat, 1Q0.6 gm..

7.8
0.0

7.8

26.5

7.2
0.0

3-4
180.6

184.0

7.2

184.0

144

TEXT-BOOK OF PHYSIOLOGY.

Coincidently with these losses to the body there is also a gradual
loss of inorganic salts, and toward the termination of the period a
sudden fall in temperature of several degrees centigrade, in conse-
quence of rhe final consumption of all available food, when death
ensues, in all probabihty, from a cessation in the action of the heart.

Postmortem Appearances. — It has been experimentally determined
that animals die when the body- weight has dechned to about 40 per
cent. Postmortem examination shows that the loss of material,
though very generally distributed throughout the body, is greatest
in organs and tissues least essential to life.

The results of an analysis of the organs and tissues of a cat after
a thirteen-day period of starvation, during which the animal lost
1017 grams in weight, are given in the following table, based on data
furnished by Voit :

Organ.

Adipose tissue, _.

Spleen,

Liver,

Testes,

Muscles,

Blood,

Kidneys,

Skin and hair,..

Lungs,

Intestines,

Pancreas,

Bones,

Heart,

Nervous system.

^ I Actual Loss

Percentage.] qj. Tissue.

Grams.

97

267

67

6

54

49

40

I

31

429

27

37

26

7

21

89

18

3

18

21

17

I

14

55

3

0

3

I

It will be observed from this table that the adipose tissue suffers
the greatest loss, the entire amount disappearing with the exception
of a sm.all portion in the posterior part of the orbital cavity and
around the kidneys. The muscles, though only losing 31 per cent,
of their weight, yet furnish 429 grams of presumably proteid material,
for nutritive purposes. The heart and nervous system experience
but sHght loss.

Mixed Diet. — The chemic composition of the tissues, taken in
connection with their metabohsm during starvation, implies that no
one article of food is sufficient for tissue repair and heat production;
but that all classes of foods — in other words, a mixed diet — are
essential to the maintenance of a normal nutrition. Experimental
investigation has also conclusively estabhshed this fact. Moreover,
the amounts of nitrogen and carbon eliminated daily, and the ratio

FOODS. 145

existing between them, indicate the amounts of proteid, fat, and
carbohydrate whicli are required to cover the loss.

Metabolism on a Purely Proteid Diet. — Notwithstanding
the chemic composition of the proteids and the possibihty of their
giving rise to both fat and a carbohydrate during their metabohsm,
it has been found extremely dil!icult to maintain the normal nutrition
for any length of time on a pure proteid or fat-free flesh diet. This,
however, has been accomplished with dogs. It was found, however,
that, in order to maintain the equilibrium, it was necessary to increase
the proteids from two to three times the usual amount. Thus, a dog
weighing 30 to 35 kilograms requii-ed from 1500 to 1800 grams of
flesh daily in order to get the requisite amount of carbon to prevent
consumption of its own adipose tissue. Under similar circumstances,
a human being weighing 70 kilograms would require more than 2000
grams of lean beef — an amount which, from the nature of the digestive
apparatus, it would be practically impossible to digest and assimilate
for any length of time. Even the shght habitual excess beyond the
amount normally required is imperfectly assimilated and gives rise
to the production of nitrogen-holding compounds which, on account
of the difflculty with which they are eliminated by the kidneys, ac-
cumulate within the body and develop the gouty diathesis, with all
its protean manifestations.

Metabolism on a Fat and Carbohydrate Diet. — As nitrogen
is an indispensable constituent of the tissues, it is evident that neither
fat nor carbohydrates can maintain nutritive equilibrium except for
very short periods. On such a diet the tissues consume their
own proteids, as shown by the continuous excretion of urea, though
the amount is less than during starvation. An excess of fat retards
the metabolism of proteids. The same holds true for the carbohy-
drates.

Thus, in any well-arranged dietary there should be a combina-
tion of proteids, fats, and carbohydrates in amounts sufficient to
maintain nutritive equilibrium; in other words, to repair the loss of
tissue and to furnish the requisite amount of heat in accordance with
work done, as well as with climatic and seasonal variations.

COMPOSITION OF FOODS.

The food principles essential to the maintenance of the nutrition
of the body are contained in varj-ing proportions in compound sub-
stances termed foods; e. g., meat, milk, wheat, potatoes, etc. Their
nutritive value depends partly on the amounts of their contained
food principles and partly on their digestibility. The dietary of
civihzed man embraces foods derived from both the animal and
vegetable worlds.

146

TEXT-BOOK OF PHYSIOLOGY.

Composition of Animal Foods. — The following table shows the
average percentage composition of various kinds of meats, cow's
milk, and eggs:

In 100 Parts.

Beef. Veal.

Water, 76.25

Proteid, 20.24

Fat, j 1.68

Carbohydrates, j 0.50

Salts, t 1.38

77.82

19.86

0.82

0.80

0.70

Mut-
ton.

75-59
17. II

5-47
0.60
1.23

Pork. I Fowl.

72.57

19-31

5.82

0.60

1.70

70.80

22.70

4.10

1.20

1.20

Fish.

79-3°

18.30

0.70

0.90

0.80

Cow's
Milk.

86.87
4-75
3-50
4.00
0.17

Eggs.

73-67
12.55
12. II

0-55
1-13

Meats. — It will be observed from these analyses that the meats
contain from 18 to 20 per cent, of a proteid which belongs in virtue
of its chemic relations to the group of globuhns. In the living con-
dition this body, known as myosinogen, is in a semi-fluid condition,
but shortly after death undergoes coagulation, giving rise to solid
myosin and a soluble albumin. There are also present in meat small
percentages of other forms of proteid; e. g., myoalbumin, myoglob-
ulin, paramyosinogen, etc. After being subjected to the cooking
process, meats contain the albuminoid body gelatin, a product of the
transformation of the proteids of the connective tissue.

The percentage of fat, contained within the meat substance,
is very small except in mutton and pork, where it rises to 5.4 per cent,
and 5.8 per cent, respectively. The fat-globules in these meats are
packed closely between the muscle-fibers, and prevent the easy
entrance of the digestive fluids, and hence they are more difficult of
digestion than beef.

The carbohydrates vary from 0.5 to i per cent., and are represented
by glycogen. The principal inorganic salts are potassium phosphate
and sodium chlorid.

Cooking, when properly done, not only makes the meat more
palatable and appetizing from the development of agreeable flavors,
but converts the connective tissue, which, in old animals especially,
is tough and resisting, into gelatin, thus rendering it more easy of
mastication and digestion. At the same time parasitic organisms,
such as the embryonic forms of tenia or tapeworm, trichina
spiralis, as well as bacterial growths, which frequently infest the
bodies of animals, are destroyed and made harmless.

Milk is the natural food of the young of all mammals, and is
usually regarded as typical on account of the ratio existing among
its nutritive principles. The analysis given above is that of cow's
milk. Examined microscopically, milk is seen to consist of a clear
fluid, the milk plasma, holding in suspension an enormous number of
small, highly refractive oil globules, which measure on the average

FOODS.

147

about Jo ^(717 of an inch in diameter. Each globule is supposed by
some observers to be surrounded l:)y a thin albuminous envelope,
which eniblcs it to maintain the discrete form. Others deny the
existence of such a membrane. The chief proteid constituent of
milk, caseinogen, is held in solution by the presence of phosphate of
lime. On the addition of acetic acid or sodium chlorid up to the
point of saturation the caseinogen is precipitated as such and may be
collected by appropriate chemic methods. When taken into the
stomach, caseinogen is coagulated; that is, it is separated into casein
or tyrein and a small quantity of a new soluble proteid. This change
is brought about by the presence in the gastric juice of a special
ferment known as rennin or pexin.

The fat of milk is more or less solid at ordinary temperatures.
It is a combination of olein, palmitin, and stearin, with a small quan-
tity of butyrin and caproin. When milk is allowed to stand for some
time, the fat-globules rise to the surface and form a thick layer known
as cream. When subjected to the churning process, the fat-globules
run together and form a coherent mass — butter.

Lactose is the particular form of sugar found in milk. In the
presence of Bacillus acidi lactici, the lactose is decomposed into
lactic acid and carbon dioxid, the former of which not only imparts
a sour taste to the milk, but causes a precipitation of the caseinogen.
The chief salt found in milk is phosphate of lime, and this is the
chief source of this agent in the formation of bones.

Eggs are also to be regarded as complete natural foods, inasmuch
as they contain all the necessary food principles. The analysis
given in the above table represents the composition of the entire egg.
The white of the egg contains 12 per cent, of proteid and 2 per cent,
of fat. The yolk, however, contains 15 per cent, of proteid and 30
per cent, of fat.

Composition of Cereal Foods. — The average composition of
the principal cereals is shown in the following table :

In 100 Parts.

Water,

Proteid,

Fat,

Carbohydrate,

Cellulose,

Salts,

Wheat.
13-56

Rye.

Barley.

Oats.

Corn.

1
Rice.

12.65

13-77

12.37

13.10

13.12

12.35

12-55

II. 14

10.41

9-85

7.88

1-75

1.97

2.16

5-23

4-57

-0.85

67.Q0

67-95

64-93

57-78

68.42

76.55

2.63

3.00

5-31

II. 19

2.50

0-55

1.81

1.88

2.69

3.02

1-56

1.05

Buck-
wheat.

12.62

10.02

2.24

64-43
8.67
2.02

That the cereals are most important and useful articles of diet is
evident from their composition, consisting, as they do, of proteids
and carbohydrates in large proportion. Owing to the cellulose or

148

TEXT-BOOK OF PHYSIOLOGY.

woody fiber which envelops and penetrates tlie grain, they are some-
what difi&cuh of digestion. A section of a grain of wheat shows the
external cellulose envelope, the husk, beneath which is a layfer of large
cells containing the chief proteid^the gluten. The interior of the
grain consists of small cavities, the walls of which are formed of cellu-
lose and which contain the granules of starch, fat, small quantities of
proteid, and inorganic salts. All other cereals have a similar structure.

In the preparation of white flour from wheat it is customary to
remove the husk, a process which involves the removal also of a por-
tion, if not aU, of the gluten cells, so that such flour contains less nitrog-
enized material than the original grain. It is possible, however, in
the mining of wheat, to remove only the husk and retain the gluten in
the flour, as in the preparation of whole wheat flour.

Bread is an artificially prepared food made either of wheat or
rye. Owing to the fact that the proteids of the other cereals do not
possess the same adhesive properties when kneaded with water, they
can not be used for bread-making purposes. In the making of bread,
the flour is kneaded with water until a glutinous mass — dough — is
formed. During this process, salt, sugar, and yeast are added. It
is then placed in a temperature of about ioo° F. In the presence of
heat and moisture the natural ferment of the flour — diastase — con-
verts a portion of the starch into sugar, which in turn is split up into
carbon dioxid and alcohol by the yeast plant. The bubbles of
carbon dioxid, becoming entangled in the dough, cause it to swell
or rise and subsequently give the porous or spongy character to the
bread. When baked at a temperature of 400° F., the alcohol is
driven off; yeast cells and other organisms are destroyed; the starch,
particularly that on the surface, is dextrinized. Thus prepared,
white bread consists of water, 32 per cent.; proteid, 8.8 per cent.;
fat, 1 .7 per cent. ; carbohydrate, 56.3 per cent. ; salts, 0.9 per cent. The
principal salts are potassium and magnesium phosphate. Whole
wheat bread consists of water, 40 per cent.; proteid, 12.2 per cent.;
fat, 1.2 per cent.; carbohydrate, 43.5 percent.; salts, 1.3 percent.;
cellulose, 1.8 per cent.

Composition of Vegetable Foods. — The average composition
of some of the principal vegetables is shown in the following table :

In 100 Parts.

Water,

Proteid,

Fat,

Carbohydrates, 53-67

Cellulose,

Salts,

Pota-

Tur-

Toma-

Aspa-

Beans.

13-74

Peas.

toes.

Beets.

nips.
89.42

toes.
96.30

ragus.

14.99

75-47

82.20

93-75

23.21

22.85

1-95

1.80

1-35

0.90

1.79

2.14

1.79

0.15

0.30

0.18

0.50

0.25

53-67

52.36

20.69

13.00

7-36

2.80

2.63

3-69

5-43

0.76

_-

0.94

--

1.04

3-55

2.58

0.98

1.60

0-75

0.40

0.54

Cab-
bage.

89.97
1.89
0.20
4.87
1.84
1.23

FOODS.

149

The vegetable foods, as a class, vary considerably in nutritive
value and digestibility, the latter depending on the amount of cellu-
lose they contain. A section of a vegetable shows not only the pres-
ence of an external cellulose envelope, but also an inner framework
which penetrates its substance in all directions. The nutritive
principles are contained in small cavities, the walls of which are
formed by the framework. Nearly all vegetables require cooking
before being eaten. When subjected to heat and moisture, not only
is the texture of the vegetable softened and disintegrated, but the
starch grains are hydrated and partially prepared for conversion
into dextrin and sugar. At the same time various savory substances
are set free, which make the food more palatable.

Beans and peas contain large quantities of a proteid, legumin,
and starch, and hence are especially valuable as nutritive foods.
The presence of the cellulose envelope, especially in ripe beans and
peas, combined with rather a dense texture, renders them somewhat
difficult of digestion. Potatoes, though largely employed as food,
are extremely poor in proteids, 2 per cent., and carbohydrates, 20 per
cent. When sufficiently cooked they are easily digested, owing to
the small amount of cellulose they contain.

Green vegetables, — e. g., lettuce, spinach, tomatoes, asparagus,
onions, etc., though containing food principles in small amounts,
are, nevertheless, valuable adjuncts to the dietary, for the reason
that they contain inorganic as well as organic salts, which appear
to be necessary to the maintenance of the normal nutrition. The
want of green vegetables has been supposed to be the cause of
scurvy.

Ripe fruits, grapes, cherries, apples, pears, peaches, strawberries,
lemons, oranges, etc., though consumed largely, possess but little
nutritive value. They consist largely of water, 75 to 85 per cent.,
proteids a trace, sugar from 5 to 13 per cent., organic acids (citric,
maHc, tartaric), pectosc, and various inorganic salts.

Relative Value of Animal and Vegetable Foods. — Though
both animal and vegetable foods contain the different classes of food
principles, it is not a matter of entire indifference as to which are
consumed. It has been found by experiment that animal proteids
are more easily and completely digested and absorbed than vegetable
proteids; that cellulose is not only highly indigestible, but by its pres-
ence in large quantities retards the digestive process and impairs the
activity of the entire digestive mechanism, though in moderate quan-
tity it undoubtedly aids digestion indirectly by mechanically pro-
moting peristalsis. The following table shows the relative diges-
tibility of the two classes of foods:

15°

TEXT-BOOK OF PHYSIOLOGY.

Weight of Food.

Vegetable.

Animal.

Digested.

Undigested.

Digested.

Undigested.

Of loo parts of solids,

Of loo parts of proteid,

Of loo parts of fats or carbo-
hydrates,

75-5
46.6

90-3

24-5
53-4

9-7

89.9
81.2

96.9

II. I
18.8

3-1

Construction of Dietaries. — Inasmuch as neither animal nor
vegetable foods contain the food principles in proper quantities and
proportions, the instinctive choice of mankind has led to a com-
bination of the two classes of foods. From the analyses tabulated
above it becomes comparatively easy to construct a suitable dietary,
composed of different articles of food, in which the food principles
shall bear the proper ratio one to the other — a ratio based on the total
quantity of nitrogen (15 to 20 grams) and carbon (225 to 300 grams)
eliminated from the body daily.

It is only necessary, therefore, to combine two or more foods,
the composition of which is known, in quantities sufficient to furnish
the requisite amount of nitrogen and carbon, or their equivalents in
proteid, fat, and carbohydrates. As illustrations of such combina-
tions the following examples are given:

Food Principles.
Proteid, loo gm.

!Fat, 100 gm.
Carbohydrates, 250 gm.

Foods.

Meat, 250 gm..

Bread, 400 gm..

Fat, 100 gm..

Sugar, 70 gm..

8.8 oz.

14.2 oz.

3-5 oz.

2.5 oz.

N.
15

gm

Foods.

Meat, 225

Bread, 450 gm

Fats, 113 gm

Potatoes, 450 gm

Milk, 225 gm

Eggs, 113 gm

Cheese, 56 gm

15

N. C.

i lb 7.5 gm. 34 gm.

I lb. 5.5 gm. 117 gm.

■J lb. --- 84 gm.

I lb. 1.3 gm. 45 gm.

^ pint 1.7 gm. 20 gm,

\ lb. 2.0 gm. 15 gm.

I lb. _3^ gm. ^o gm.

21.0 335

(Waller.)

DAILY RATION OF THE UNITED STATES SOLDIER.

Fresh beef, 20 oz.

or pork, 12 oz.

or bacon, 12 oz.

Flour, 18 oz.

or soft bread, 18 oz.

or hard bread, 16 oz.

Potatoes, 16 oz.

or potatoes 11 5 and tomatoes 45 16 oz.

Beans or peas, 2.4 oz

Rice or hominy, 1.6 oz.

Coffee, 1.6 oz.

Sugar, 2.00 oz.

Vinegar, 0.32 gill

Salt, 0.60 gill

225

CHAPTER IX.
DIGESTION.

Foods are heterogeneous compounds consisting of organic and
inorganic nutritive principles associated with a varying amount of
non-nutritive material, such as the dense parts of the connective
tissue of the animal foods and the woody fiber or cellulose of the
vegetable foods. Before the nutritive principles can be utiHzed they
must be dissociated from the non-nutritive material. Even when
consumed in the free state, the food principles are seldom in a condi-
tion to be absorbed into the blood and assimilated by the tissues.
When foods are consumed in their natural state or after they have
been subjected to the cooking process, they are subjected while in
the food canal to the solvent action of various fluids by which they
are disintegrated and reduced to the hquid condition. The nutri-
tive principles freed from their combinations are changed in chemic
composition and transformed into substances capable of absorption.
To all the physical and chemic changes which foods undergo in the
food canal the term digestion has been given.

The digestive apparatus comprises the entire alimentary or food
canal and its various appendages: the teeth, the tongue, the mouth,
the gastric and intestinal glands, the pancreas, and the Hver (Fig. 59).

The canal itself is a musculo-membranous tube about thirty-two
feet in length, and extends from the mouth to the anus. It may be
subdivided into several distinct portions, as mouth, pharynx, esoph-
agus, stomach, small and large intestines. The mouth is provided
(i) with teeth, by which the food is divided, (2) with the tongue,
and (3) with glands, by which a solvent fluid, the saHva, is secreted.
The glands, though situated for the most part outside the mouth, are
connected with it by means of ducts. Posteriorly the mouth opens
into the pharynx or throat, a somewhat pyramidal-shaped structure
about five inches in length, which in turn is followed by the esoph-
agus or gullet, a tube about nine inches in length. As the esophagus
passes through the diaphragm it expands into the stomach, a curved
pyriform organ, which serves as a reservoir for the reception and
retention of the food for a varying length of time. The small intes-
tine is that portion of the alimentary canal extending from the end
of the stomach to the beginning of the large intestine; owing to its
length, about twenty-two feet, it presents a very convoluted appear-
ance in the abdominal cavity. Embedded in its walls are the intes-
tinal glands which open on its surface and secrete the intestinal

151

152

TEXT-BOOK OF PHYSIOLOGY.

fluid. In the upper portion of the small intestine, within five inches
of the stomach, there are generally two orifices, the terminations of
the ducts of the liver and pancreas, organs which secrete the bile
and pancreatic juice respectively. The large intestine is from five
to six feet in length and extends from the end of the small intestine
to the anus. Its walls contain a large number of glands.

^

/c^

{ Alose.

LJ'U'M-- Salivary Gfand

Sa//i/iSry _ _ .
G/snds

^

_J \Pharynx

Windpipe-.

-/--

^-^

Liver- - ■

■--jiflfll/IMmmi

ijL

^■Ajiullel-

9

Y""^"^

Cy/orus

Stomachii

Duodenum ■''

Small Intesline)

Vermiform /ippendoc -

Fig. 59. — Diagram of the Alimentary Canal.

The general process of digestion is largely accomplished by the
chemic action of the digestive fluids: the sahva, the gastric, intestinal,
and pancreatic juices, and the bile. Though taking place through-
out a large portion of the food canal, the process may be subdivided
into several stages: viz., mouth digestion, gastric digestion, and in-
testinal digestion.

DIGESTION. 153

As a result of the action of these fluids the nutritive principles are
prepared for absorption into the blood; the non-nutritive principles,
along with certain waste products, pass into the large intestine to be
finally extruded from the body.

MOUTH DIGESTION.

The digestion of the food as it takes place in the mouth comprises
a series of physical and chemic changes, the result of the action of
the teeth, the tongue, and the saliva. The mechanic division of the
food and the incorporation of the saliva with it are termed respec-
tively mastication and insalivation.

MASTICATION.

Mastication is the mechanic division of the food, and is accom-
plished by the teeth and the movements of the lower jaw under the
influence of muscle contractions. Complete mechanic disintegration
of the food is essential to its subsequent solution and chemic trans-
formation; for when finely divided it presents a larger surface to the
action of the digestive fluids and thus enables them to exert their
respective actions more effectively and in a shorter period of time.

The Teeth. — In man passing from childhood to adult hfe two
sets of teeth make their appearance. The first set constitute the
temporary, deciduous, or milk teeth; the second set constitute the
permanent teeth, which should last with proper care through life or
to an advanced age.

The temporary teeth, twenty in number, ten in each jaw, though
smaller than the permanent teeth, have the same general conforma-
tion. They are divided into four incisors, two cuspids or canines,
and four molars for each jaw.

The permanent teeth, thirty-two in number, sixteen in each jaw,
are divided into four incisors, two cuspids or canines, four bicuspids
or premolars, and six molars for each jaw.

Each tooth may be said to consist of three portions: (i) the
crown, or that portion which projects above the gums; (2) the root
or fang, that portion embedded in the alveolar socket; (3) the con-
stricted portion or neck, which is surrounded by the free margin of
the gum. The teeth are firmly secured in their sockets by a fibrous
membrane, the peridental membrane, which is attached, on the one
hand, to the alveolar process, and, on the other, to the cementum.

A vertical section of a tooth shows that it consists of three distinct
sohd structures, the enamel, the dentine, and the cementum, which
have the anatomic relationship as represented in Fig. 60. In the
center of the dentine there is a cavity the general shape of which varies
in different teeth, and which is occupied during the hving condition by
the tooth pulp.

Microscopic examination of the tooth reveals the presence of

154

TEXT-BOOK OF PHYSIOLOGY.

>&•'

PC—!

irregular stellate spaces, the interglobular spaces, between the dentine
and the cementum, which are occupied by connective-tissue cells.
Clefts of varying size are also observed at the junction of the dentine
and the enamel, and which extend for some distance into the latter.
The enamel is composed of dense hard cyhnders which, on account
of their small size and close relationship, appear to be hexagonal in
shape. These cylinders are held together by cement substance. The
free border of the enamel is covered, in early hfe at least, by a thin

membrane known as the cuticle or
membrane of Nasmyth.

The dentine is somewhat less dense
than the enamel. It is composed of
connective-tissue fibers embedded in
a ground-substance, both of which
have undergone calcification in the
course of development. The dentine
is penetrated by a series of fine canals,
the dentine canals or tubules, which
begin by open mouths on the pulp
side. From this point the tubules
pass outward to the cementum and
enamel, where their terminal branches
communicate with and terminate in
the interglobular spaces and clefts.
In their course the tubules give off a
series of branches which communicate
freely with one another. The dentine
bordering the tubule is somewhat
more dense than the intertubular por-
tion and constitutes what is known
as the dentinal sheath or Neumann's
sheath.

The cementum resembles bone be-
cause it contains both lacunae and
canahculi, though it is, as a rule,
devoid of Haversian canals.
The pulp consists of a framework of connective tissue which
affords support to blood-vessels and nerves, both of which enter the
pulp chamber through a small foramen at the apex of the root. The
outer surface of the pulp is covered with a layer of large spheric
cells, the odontoblasts. Each ceh presents on its inner surface short
processes which pass into the pulp; on its outer surface it presents a
long process which enters a dentine tubule and extends as far as its
ultimate terminations. Collectively these processes are known as
the dentine fibers. Inasmuch as the fibers do not completely occupy

Fig. 6o. — Vertical Section of
Tooth in Jaw. E. Enamel.
D. Dentine. P. M. Periodontal
membrane. P. C. Pulp cavity.
C. Cement. B. Bone of lower
jaw. V. Vein. a. Artery. N .
Nerve.

DIGESTION. 155

the lumen of the tubule, it is probable that there is a free circulation
of lymph from the pulp chamber through the dentine tubules into the
enamel clefts, into the interglobular spaces, and possibly into the
lacume of the cementum.

The peridcnlal membrane is composed of connective-tissue fibers
abundantly supplied with blood-vessels and nerves.

Movements of the Lower Jaw. — The lower jaw is capable of a
downward and upward, an antero-posterior, and a lateral move-
ment, all dependent on the peculiar construction of the —

Tem poro-maxillary Articidaiion. — This articulation is formed by
the anterior portion of the glenoid cavity, the eminentia articularis,
and the condyle of the inferior maxilla, all of which are united by
means of ligaments. Situated between the glenoid cavity and the
condyle is a plate of fibro-cartilage oval in shape and biconcave.
This cartilage divides the joint into two cavities, — one above, the
other below, — each of which is provided with a synovial membrane.
The function of the cartilage is to present constantly an articulating
surface to the condyle in the various movements of the lower jaw,
which it is enabled to do by virtue of its mobility.

In the downward movement of the lower jaw each condyle ghdes
forward, carrying with it the interarticular fibro-cartilage the upper
concave surface of which is applied to the convex surface of the
eminentia articularis. In the upward m.ovement of the jaw both the
condyles and the cartilages pass backward and resume their normal
position. The movements of depression and elevation are made
possible by the transverse direction of the condyle. In the carnivor-
ous animals, whose food requires considerable cutting, these move-
ments are especially well developed. In the antero-posterior move-
ment the jaw moves in a horizontal direction and the condyles and
the articular cartilages ghde forward and backward in the glenoid
fossse. In the rodent animals the long axis of the condyle runs
in the antero-posterior direction, which allows of a considerable
ghding movement. When the jaw performs a lateral movement, the
condyle and cartilage of one side remain in their normal position,
while the opposite condyle and cartilage glide forward in the glenoid
fossa, directing the symphysis of the jaw to the opposite side of the
median line. The lateral movements are well exhibited by the
herbivorous animals, in which they are quite extensive, and made
possible by the small size of the condyle and the large extent of
articulating surface. In man the structure of the joint is such as to
admit of all these possibilities, and the lower jaw acquires in conse-
quence great freedom of movement.

The Functions of the Muscles of Mastication. — The move-
ments of the lower jaw are caused by the action of numerous
muscles, which, having a fixed point of origin, are attached to various

156 TEXT-BOOK OF PHYSIOLOGY.

points on its surface. The muscles concerned in the movements
of mastication are presented in the following table :

Anterior belly of digastric • ^ j^^ ^^e lower jaw and open

Mylohyoid r the mouth.

Geniohyoid J

Temporal . , ^ ) Elevate the lower jaw and close

Interna portion of masseter the mouth.

Internal pter>'goid J

E.xternal pters'goids ] Draw the lower jaw forward and

External portion of masseter r cause the lower teeth to project

Anterior fibers of temporal j beyond the upper.

Posterior fibers of temporal '\

Internal portion of masseter ' Draw the lower jaw back to its

Digastric, mylohyoid, and genio- ( normal position.

hyoid J

Internal pters'goids \ Contracting alternately, draw the

External pter^'goids j jaw to the opposite side.
Pter^'goids, external and internal \ produce grinding movements of

J^^POial r the lower jaw.

!Masseter J ^

The action of the depressor muscles becomes apparent when their
points of origin and insertion are considered. The anterior belly
of the digastric, the mylohyoid, the geniohyoid muscles, agree in
ha\dng a similarity of origin — the hyoid bone— and a common area
of insertion, the anterior portion of the inferior maxillary. Their
anatomic relation is such that their combined action will depress the
lower jaw and open the mouth.

The elevator muscles arise from various points on the side of
the head, and are inserted into the coronoid process, ramus, and
internal surface of the angle of the lower jaw. When the mouth
has been opened, the simultaneous contraction of these muscles
elevates the jaw and closes the mouth with considerable force. The
power of these muscles is very great, and depends on the shortness
and thickness of the muscle-bundles.

The action of the rotator muscles, those which give rise to the
lateral movements of the jaw, depends in hke manner on their origin
and insertion. Arising from the superior maxillary and sphenoid
bones, they are inserted into the neck of the condyle and angle of
the lower jaw respectively. When they contract, the condyle on the
corresponding side is drawn forward, while the opposite condyle
remains stationar}^ As a result, the symphysis of the jaw is directed
to the opposite side. The grinding movements of the jaw are pro-
duced by the coordinated action of all the groups of muscles acting
more or less successively.

For the proper mastication of the food it is essential that it be
kept between the opposing surfaces of the teeth. This is accom-
plished by the contraction of the orbicularis oris and buccinator
muscles from without and the tongue muscles from within.

DIGESTION.

157

Nerve Mechanism of Mastication. — The movements of masti-
cation, though originating in efforts of the will and under its control,
are for the most part of an automatic or reiiex character; for when
once initiated by a voluntary effort they continue for an indefmite
period — so long, in fact, as the impressions which the food makes
upon the afferent nerves are received by the nerve-centers which
regulate and control them. That the masticatory movements are of
this reflex nature is shown by the fact that they will be maintained
even though the voluntary effort which called them forth has sub-
sided and the attention has been directed to some entirely different
subject. It would appear that all that is necessary under such con-
ditions is the exciting action of the food upon the periphery of the
afferent nerves distributed to the tongue and mouth.

The nerves involved in this reflex are shown in the following table :

Afferent or Excitor Nerves.

1 . Lingual branch of fifth nerve.

2. Glossopharyngeal.

Efferent or Motor Nerves.

1. Inferior maxillary division of fifth

nerve.

2. Hypoglossal or sublingual.

3. Facial or portio dura.

The nerve-center coordinating the movements of mastication is
situated in the medulla oblongata. The afferent or excitor nerves
which receive the impressions of the food are distributed largely to
the mucous membrane of the tongue. When these impressions are
received by the center in the medulla oblongata, it discharges nerve
impulses, which, passing outward through motor nerves, excite con-
traction in the masticatory muscles. The motor nerves innervating
the muscles are: (i) The small root of the fifth nerve, which, after
emerging from the cavity of the cranium through the foramen ovale,
joins the inferior maxillary division of the large sensory root. It
then is distributed to the masseter, temporal, internal, and external
pterygoids, anterior belly of the digastric, and mylohyoid muscles,
and controls their movements. (2) The hypoglossal nerve, which,
after emerging through the anterior condyloid foramen, passes down-
ward and forward to be distributed to the extrinsic and intrinsic
muscles of the tongue. (3) The facial or portio dura, which, after
emerging from the stylomastoid foramen, is distributed to the mus-
cles of the face. Irritation of any one of these nerves produces con-
vulsive movements in the muscles to which it is distributed, while
their division is followed by paralysis of these muscles. The medulla
not only generates the impulses which are directly responsible for
the movements of mastication, but also coordinates them in such a
manner that the movements of mastication may be directed toward
the accompHshment of a definite purpose.

158

TEXT-BOOK OF PHYSIOLOGY.

INSALIVATION.

Insalivation is the incorporation of the saKva with the food, and
takes place for the most part during mastication. The sahva ordi-
narily present in the mouth is a complex fluid composed of the various
secretions of the parotid, submaxillary, and subhngual glands and
the muciparous follicles of the mouth, which collectively constitute
the salivary apparatus (Fig. 6i).

The parotid gland is situated in front of and partly below the

external ear, where it is
held in position by the
fascia and skin. From the
anterior border of the gland
there emerges a duct (Sten-
sen's), which, after crossing
the masseter muscle to its
anterior border, turns in-
ward, pierces the buccin-
ator, and opens on the sur-
face of the cheek opposite
the second upper molar
tooth.

The submaxillary
gland is situated below the
jaw in the anterior part of
the submaxillary triangle.
From the gland there
emerges a duct (Wharton's)
which opens into the mouth
by a minute orifice on the
surface of a papilla by the
side of the tongue.

The sublingual gland
is situated just beneath the
mucous membrane in the
anterior part of the mouth,
where it forms a projection
between the gums and tongue. The posterior part of the gland
gives origin to a duct (the duct of Rivinus, described also by Bartho-
hnj which opens into the mouth with or very near to the duct of
Wharton. The anterior part of the gland gives origin to a varying
number of ducts (Walthers) which open separately along the edge of
the sublingual plica of the mucous membrane.

Histologic Structure of the Salivary Glands. — In their ulti-
mate structure the salivary glands bear a close resemblance to one

Fig.

6i. — Salivary Glands, i, 2. Parotid.
3. Duct of Steno. 4. Submaxillary. 5.
Sublingual. 6. Mylohyoid muscle. 7.
Lingual branch of the fifth nerve. 8. Duct
of Wharton. 9. Digastric muscle. 10.
Sternomastoid muscle. 11. External jugu-
lar vein. 12. Facial vein. 13. Temporal
vein. 14, 15. Internal jugular vein. 16.
Branch of the cervical plexus. 17. Sub-
lingual nerve. — {Le Bon.)

DIGESTION.

159

another. They are compound tubulo-alvcolar glands composed of
small irregularly shaped lobules united by areolar tissue and con-
nected by branches of the saUvary ducts. Each lobule is made up of
a number of small alveoH or acini more or less tubular in shape which
are the terminal expansions of the smallest ducts. (See Fig. 62.)
The wall of the acinus is formed by a reticulated basement mem-
brane, surrounded externally by blood-vessels, the spaces between
which constitute lymph-spaces or channels. The inner surface of
the acinus membrane supports a single layer of irregular spheric
or polygonic epithelial cells. The cells do not entirely fill up the
cavity of the acinus, but leave an intercellular space, the lumen,
which constitutes the beginning of the duct for the transmission of
the secretion to the mouth. From
each acinus there passes a narrow
intercalary duct lined by a layer of
flattened cells. The common ex-
cretory duct — formed by the union
of the intralobular and interlobular
ducts — consists also of a basement
membrane, lined, however, by tall
columnar epithelial cells. The sali-
vary glands are abundantly supplied
with blood-vessels and nerves which
are closely related to their activity.

Based partly on the character
of their secretions and partly on
the microscopic appearance of their
secreting cells, the salivar}' glands
have been divided by Heidenhain
into two classes: viz., serous or al-
buminous, and mucous glands. To
the first class belong the parotid, a
portion of the submaxillary, and a portion of the glands of the
tongue. To the second class belong a portion of the submaxillary
gland, the sublingual, a portion of the glands of the tongue, the glands
of the cheeks, hps, palate, and pharynx. It is possible that a single
alveolus of any gland may contain both albuminous and mucous
cells.

In the serous glands the cells are more or less spheric in shape,
nucleated, and almost completely filled with dark granular material
(Fig. 63). In the mucous glands the cells are large, clear in appear-
ance, and loaded with a highly refracting material resembhng mucin
(Fig. 64). Between the basement membrane and the clear cells are
to be found in the acini of the submaxillary glands small crescentic
shaped cells filled with granular material which stains deeply with vari-

— — -^- Acini.

Fig. 62. — .-M^Ht-ME OF THE Human
Submaxillary Gland.

i6o

TEXT-BOOK OF PHYSIOLOGY

ous coloring-matters. These are known as the demilunes of Heiden-
hain. At one time it was supposed that they were young cells des-
tined to take the place of the clear cells which were believed to be
exhausted and to have undergone disintegration. At the present time
they are regarded as albuminous or serous cells which exhibit changes
similar to the cells of the parotid gland.

The glands embedded in the mucous membrane covering the
tongue, hps, cheek, palate, and pharynx are for the most part hned
with epithelial cells which contain a highly refracting matter similar
to, if not identical with, that found in the cells of the submaxillary
and subhngual glands.

Nerve-supply. — Experimental research has demonstrated that
each salivary gland receives nerve-fibers which influence the pro-
duction of the secretion (secretory nerves) and fibers which dilate or
constrict the blood-vessels (vaso-dilator and vaso- constrictor nerves).

Fig. 63. — Section of Human Paro
TiD Gland Including Several
Acini, d. Cut intralobular duct.
— (Piersol.)

Fig. 64. — Section of Human Sub-
lingual Gland. Among the
clear cells lining the mucous
acini are nests (g, g) of granular
elements which constitute the
demilunes of Heidenhain.

The secretory fibers penetrate the basement membrane and finally
terminate between and on the surface of the secretory cells. The
vaso-motor fibers terminate between and on the muscle-cells in the
walls of the blood-vessels. The nerve-fibers in direct relation with
the cells and blood-vessels of the parotid gland are derived from the
otic ganglion. The cells of this ganghon are, however, invested by
the terminal branches of other nerve-fibers (preganglionic) derived
from the medulla oblongata. The relation of these preganghonic
fibers to the blood-vessels and cells is shown by the increase in
secretion and a change in the cahber of the vessels when they are
subjected to electric stimulation. The nerve-fibers which are in
direct relation with the vessels and cells of the submaxillary and
subhngual glands are derived from the submaxillary, the sublingual,
and the superior cervical ganglia. These local ganglion cells are
also closely invested by the terminal branches or arborizations of the

DIGESTION. i6i

fibers of nerves (preganglionic fibers) coming direct from the medulla
oblongata and spinal cord.

The Parotid Saliva. — The parotid saliva, as it flows from the
orifice of Stensen's duct, is clear, hmpid, free from viscidity, dis-
tinctly alkahne in reaction, with a specific gravity of 1.003. Chemic
analysis shows that it consists of water, a small quantity of proteid
matter, a trace of a sulphocyanogen compound, and inorganic salts.
The secretion is increased during mastication, and especially on the
side engaged in mastication. Dry food causes a larger flow than
moist food. The situation of the orifice of the parotid duct is such
that as the secretion is poured into the mouth it is at once incorporated
with the food by the movements of the lower jaw, and thus fulfils the
physical function of softening and moistening it.

The Submaxillary Saliva. — The submaxillary saliva is clear,
slightly viscid, alkaline in reaction, and has a specific gravity of
1.002. It consists of water, proteid matter (mucin), and inorganic
salts.

The Sublingual Saliva. — The subhngual saliva is clear, extremely
viscid, and strongly alkaline in reaction. It consists of water, proteid
matter (chiefly mucin), and inorganic salts.

The small racemose glands embedded in the mucous membrane
on the inner surface of the cheeks and lips, on the hard and soft
palate, on the tongue and pharynx, secrete a fluid which is grayish
in color, extremely viscid and ropy. It contains a large amount of
mucin.

Mixed Saliva. — The saliva of the mouth is a complex fluid com-
posed of the secretions of all the salivary glands. As obtained from
the mouth it is frothy, colorless, slightly turbid, and somewhat viscid.
The specific gravity is low, ranging from 1.003 to 1.006. The re-
action is usually distinctly alkaline. It may, however, be neutral
or even acid in reaction if there is any fermentation of food particles
in the mouth or as a result of disorders of the alimentary canal.
When examined with the microscope, the saliva is seen to contain
epithelial cells, salivary corpuscles resembling leukocytes, particles
of food, various microorganisms, and especially Leptothrix huccalis.

The chemic composition of the saliva is shown in the following
table :

COMPOSITION OF HUMAN SALIVA.

Water, 995-i6 994.20

Epithelium, 1.62 2.20

Soluble organic matter, 1.34 1.40

Potassium sulphocyanid, o.c6 0.04

Inorganic salts, 1.82 2.20

1000.00 1000.04

(Jacubowitsch.) (Hammerbacher.)

i62 TEXT-BOOK OF PHYSIOLOGY.

Water constitutes the main ingredient, amounting to 99.5 per cent.
The soluble organic matter is proteid in character and is a mixture
of mucin, globulin, and serum-albumin. The potassium sulpho-
cyanid is mainly derived from the parotid gland. Its presence can be
demonstrated by the addition of a few minims of a dilute solution of
slightly acidulated ferric chlorid, when a characteristic red color is
developed. The inorganic constituents comprise the sodium, calcium
and. magnesium phosphates, sodium carbonate, sodium and potas-
sium chlorids.

Quantity of Saliva. — The estimation of the total quantity of
mixed saliva secreted in twenty-four hours is exceedingly difficult, and
the results obtained must be only approximative. It is, of course,
subject to considerable variation, depending upon habit, the nature of
the food, etc. The experiments of Professor Dalton and the results
obtained by him are eminently trustworthy, and in all probability
represent as nearly as possible the exact amount secreted. He found
that without any artificial stimulus he was enabled to collect from
the mouth about 36 grams (540 grains) of saliva per hour, but that
upon the introduction of any stimulating substance into the mouth the
quantity could be greatly increased. During mastication the saliva
was poured out in greater abundance, the amount depending upon
the relative dryness of the food. He found that wheaten bread ab-
sorbed 55 per cent, of its weight, and fresh cooked meat 48 per cent.
If, therefore, the average quantity of bread and meat required daily
by a man of ordinary physical development and activity be assumed
to be 540 grams (19 oz.) of the former and 450 grams (16 oz.) of the
latter, these two substances would absorb respectively 297 grams
(4573.8 grains) and 216 grams (3326.4 grains), making a total of 513
grams (7900 grains). If, therefore, the amount secreted and mixed
with the iood during an estimated two hours of mastication be
added to the amount secreted during the remaining twenty-two
hours, supposing that it continues at the rate of 36 grams per hour,
we have a total amount of 513 -f 792 grams, or 1305 grams (19,780
grains), or about 2.8 pounds.

Histologic Changes in the Salivary Glands during Secretion,
— During and after secretion very remarkable changes take place in
the cells lining the acini, which are in some way connected with the
production of the essential constituents of the salivary fluids. In the
case of the parotid gland, which may be regarded as the type of a
serous or albuminous gland, the following changes have been observed
by Langley (Fig. 65). During the period of rest and just previous to
secretoiy activity, the epithehal cells are enlarged and swollen, and
encroach on the lumen of the acinus. The protoplasm of the cells
is so completely filled with dark fine granules as not only to obscure
the nucleus, but to almost obliterate the line of union of the cells.

DIGESTION.

163

As soon as secretion becomes active, however, the granules begin to
disappear from the outer region of the cell and move toward the inner
border and into the lumen of the acinus. From these observations
it might be inferred that during rest the protoplasm of the cells gives
rise to granular material, and that during and after secretory activity

Fig. 65. — Cells of the Alveoli of a Serous or Watery Salivary Gland. A.
After rest. B. After a short period of acti\-ity. C. After a prolonged period of
activity. — (Yeo's " Text-Book of Physiology.")

there is an absorption of new material from the lymph and a recon-
struction of the granular material.

In the submaxillary gland, a portion of which may be taken
as a type of a mucous gland, similar changes have been observed
(Fig. 66). During rest the epithelial cells are large, clear in appear-
ance, highly refractive, and loaded with small globules resembling
mucin. The nucleus, surrounded by a small quantity of proto-
plasm, lies near the margin of
the cell. That the granules
are not protoplasmic in char-
acter is shown by the fact
that they do not stain on the
addition of carmine. When
treated with water or dilute
acids, the globules swell up,
coalesce, and form a uniform
mass. The chemic relations
of this substance indicate that
it is the precursor of mucin
— namely, mucigen. During
secretory activity the cells dis-
charge these mucigen granules into the lumen of the acinus, where
they are transformed into mucin. Though the appearance of the
gland-cell appears to indicate it, there is no evidence for the view
that the cell itself undergoes disintegration in the process.

The Physiologic Actions of Saliva. — The constant presence of
salivary glands in the different classes of animals and the large amount

Fig. 66. — The Appearance Presented by
THE Cells of the Submaxillary
Gland of the Dog after Prolonged
Secretion.

i64 TEXT-BOOK OF PHYSIOLOGY.

of secretion they pour daily into the ahmentary canal point to the
conclusion that this mixed fluid plays an important role in the general
digestive process. Experiment has demonstrated that it has a two-
fold action, physical and chemical.

Physically, saliva softens and moistens the food, unites its par-
ticles into a consistent mass by means of its contained mucin, and
thus facilitates swallowing.

Chemically it converts starch into sugar. This action is more
marked with boiled than with raw starch, a fact which depends
on the physical structure of the starch grain. In the natural con-
dition each starch grain consists of a cellulose envelope or stroma
in the meshes of which is contained the true starch material, the
granulose. When boiled for some minutes, the starch grain absorbs
water, the granulose swells and ruptures the cellulose envelope, after
which it passes into an imperfect opalescent solution more or less
viscid, depending on the relative amounts of water and starch. This
is the change largely brought about by the process of cooking. If
a portion of this hydrated starch be kept in the mouth for a few
minutes it will be converted into sugar, a fact made evident by the
sense of taste.

The chemic action of saliva in converting starch into sugar, as
well as the intermediate stages, can be experimentally shown in the
following manner: To 5 volumes of a thin starch solution in a test-
tube add two volumes of filtered saliva. Place the mixture in a
water-bath at a temperature of 35° C. In a few minutes the starch
passes into a soluble condition and the fluid becomes clear and trans-
parent. On testing the solution from time to time with iodin the
characteristic blue reaction will be found to gradually disappear, the
color passing from blue to violet, to red, to yellow. If now the solu-
tion be boiled with a solution of cupric hydroxid (Fehling's solution)
a copious red or yellow precipitate of cuprous oxid is formed, which
indicates the presence of sugar. The polariscope shows that this
sugar is maltose, C^^H^^O^^. During the conversion of the starch
intermediate substances are formed to which the term dextrin is
applied. After the starch has been rendered soluble it undergoes
a cleavage into maltose and a dextrin, which, as it gives rise to a
red color with iodin, is termed erythrodextrin. At a later stage this
erythrodextrin also undergoes a cleavage into maltose and a second
variety of dextrin, which, as it does not give rise to any color with
iodin, is termed achroodextrin. It is claimed by some investigators
that this form can also in time be transformed into sugar. It is
possible that a small quantity of dextrose is also formed.

The successive stages of the conversion of starch into sugar may
be represented by the following schema :

DIGESTION. 165

T^ ^, , ^ . f Achroodextrin.

Starch . Soluble Starch == ( Erythrodextrm | Maltose.

*• Maltose.

This change consists in the assumption by the starch of a molecule
of water, and for this reason the process is termed hydrolysis. The
nature of the chemic change is shown in the following formula:

3(CeH,o05) + H2O = CnHjjOn + CeHioO^

Starch + Water = Maltrose + Dextrin.

The amylolytic or starch-changing action of saliva depends on
the presence of an unorganized ferment or enzyme known as ptyalin.
This enzyme is present in the secretion of each of the salivary
glands. The chemic character of ptyalin is unknown, though there
are reasons for beheving that it partakes of the nature of a proteid.
It is a product in all probabihty of the katabolic activity of the secre-
tory cells. According to Latimer and Warren, ptyalin is a deriva-
tive of the zymogen, ptyalogen. This latter compound has been
shown to be present in the glands of the dog, cat, and sheep.
Ptyalin effects the transformation of starch merely by its presence,
and undergoes no perceptible consumption in the process. The
activity of this enzyme is very great, and unless interfered with by an
excess of sugar and dextrin, it acts practically indefinitely.

The activity of ptyalin is modified by various external conditions,
among which may be mentioned the chemic reaction of the medium
in which it is placed. It is most active when the medium is moder-
ately alkahne. Its activity is arrested either by strong alkahes or
acids, though the presence of a small percentage of an acid does not
appear to have any effect in either hastening or retarding the process.
This fact has a bearing upon the question as to whether the action of
the saliva is interfered with in the stomach by the presence of the
gastric juice. At present it is a disputed matter, but the weight of
authority is in favor of the view that the transforming action may
continue for almost half an hour during the early stages of gastric
digestion. The temperature also influences the rapidity with which
the transformation of the starch is effected. At a temperature of
95° to 106° F. the pt3^alin acts most energetically, while its activity
is entirely arrested by reducing the temperature to the freezing-point
or raising it to the boiling-point.

The Nerve Mechanism of Secretion. — The secretion of the
sahva is a complex act and involves the cooperation of gland-cells,
blood-vessels, and nerves. During the intervals of mastication the
glands are practically at rest as far as the discharge of saliva is con-
cerned. The cells, however, are actively engaged in absorbing from
the surrounding lymph-spaces materials derived from the blood
from which they construct their characteristic contents. The blood-

i66 TEXT-BOOK OF PHYSIOLOGY.

vessels possess that degree of dilatation necessary for nutritive pur-
poses.

With the beginning of mastication the blood-vessels suddenly
dilate, the blood-supply is increased, and the gland-cells begin to dis-
charge water, inorganic salts, and their organic constituents into the
lumen of the acinus. This continues until mastication ceases, when
all the structures return to their former condition of relative inactivity.
The entire process is reflex in character and takes place through the
medulla oblongata. It requires the usual mechanism necessary for
all reflex acts — viz., a sentient surface, afferent nerves, emissive
cells, efferent nerves, and the responsive organs.

With the introduction of food into the mouth impressions are
made on the terminal branches of the afferent nerves distributed in
the mucous membrane. Nerve impulses developed by the mechanic
and chemic action of the food are then transmitted to the medulla
oblongata and received by emissive cells. These in turn discharge
nerve impulses which are transmitted through efferent nerves to the
structures, producing the vascular and secretory effects already stated.

The nerves and nerve-centers which constitute the reflex mechan-
ism for the secretion of saliva are shown in the following table:

Afferent Nerves. Nerve-centers. Efferent Nerves.

1. Lingual branch of fifth Medulla oblongata. Chorda tympani for the submax-

nerve. illary and sublingual glands,

auriculotemporal branch of the
fifth nerve for the parotid
gland.

2. Glossopharyngeal. Sympathetic nerve.

That the secretion of the saliva is regulated by the above mechan-
ism, and that the lingual branches of the fifth nerves and the
glossopharyngeal are the afferent nerves, can be demonstrated by
exposing the glands and their nerve connections and subjecting them
to experiment. Under such circumstances, if a cannula be placed
in the duct of the submaxillary gland, and the lingual nerve stimu-
lated by an induced electric current of moderate strength, a copious
flow of saliva at once takes place. If now the glossopharyngeal nerve
be stimulated in a similar manner, the effect on the secretion wifl be the
same. Division of these two nerves in an animal, in such a way as to
prevent the nerve impulses from reaching the medulla oblongata, is
followed by a marked diminution in the amount of saliva secreted.
The reflex centers, however, may receive impulses and be excited to
activity by impulses coming through other nerves — e. g., the pneumo-
gastric, when the mucous membrane of the stomach is stimulated;
the sciatic, when after division its central end is stimulated; through
nerve-fibers that originate higher up in the brain and are stimulated
bv ideas and emotions.

DIGESTION. 167

Whenever these centers are stimulated, either by nerve impulses
coming through afferent nerves, from the periphery or from the
brain, impulses are generated which pass outward through efferent
nerves — the chorda tympani nerve to the submaxillary and sublingual
glands, and the auriculo-temporal nerve to the parotid gland.

The chorda tympani nerve is a branch of the facial, the trunk of
which it leaves in the aqueduct of Fallopius. It then crosses the
tympanic cavity, emerges through the glaserian fissure, and joins
the lingual branch of the inferior maxillary division of the fifth

S^bNerne

^m

^,*.^^*^-

Ner^e

::::^^^

OfioOdnqlion // 1

4\

Jecottaens

Alen/e

iC\"'"

v^^^^ Chorda .
~\,/^ Tympani
■i^:^^^-. Nerve

\^

J"

I-

....Sub Maxillary
Ganglion

^

:^^^ ' GlossQ
^ Pharyngeal

\ Sub Maxillary Oland

Superior..
Oartgl'o^ \ V

Fig. 67. — Scheme of the Nerves Involved in the Secretion of Saliva.

nerve. After passing forward as far as the sublingual gland, nearly
all of the original fibers leave the lingual nerve by four or five strands
to become connected by terminal branches with nerve-ganglion cells in
relation with the submaxillary and sublingual glands. (See Fig. 67.)
The nerve-fibers which conduct nerve impulses outward from
the medulla to the parotid gland are believed to pass through the
glossopharyngeal nerve, through the tympanic branch or nerve of
Jacobson, to the otic ganglion, with which they become connected.

1 68 TEXT-BOOK OF PHYSIOLOGY.

From this ganglion new nerve-fibers arise, the terminal branches of
which become connected with the secretory cells of the gland.

The effects on the secretion and flow of saliva from the submaxil-
lary gland which follow division and stimulation of the chorda tym-
pani nerve are shown in the following way : a cannula is inserted into
Wharton's duct and the rate of flow estimated; the nerve is then
divided, after which the flow ceases. The peripheral end of the
nerve is then stimulated with the induced electric current, when a
copious secretion of a thin saliva takes place, accompanied by a
marked dilatation of the blood-vessels of the gland. The quantity of
blood passing through the vessels is so great as to give to the venous
blood an arterial hue and to the small veins a distinct pulsation. It
would appear from these effects that the chorda contains two sets of
fibers, one of which inhibits the action of a local vaso-motor mechan-
ism permitting the blood-vessels to dilate (vaso-dilator fibers), the
other of which stimulates the secretory cells to activity, either directly
or through the intermediation of local ganglia. That local ganglia
are involved is shown by the effects which follow the injection
of nicotin into the circulation. After a sufficient dose — lo milli-
grams for the cat — stimulation of the chorda has no effect. Stimu-
lation of the nerve-plexus beyond the ganglion, however, is at once
followed by vascular dilatation and secretion.

It might be inferred that the increase in the flow of saliva is due
to filtration, the result of the increased blood-supply to the gland, and
not to the influence of any true secretory fibers stimulating the
activities of the secretory cells. That this is not the case, however,
can be demonstrated in several ways: First, the pressure in the duct
of the submaxillary gland, as shown by the mercurial manometer,
rises, when the gland is secreting, considerably above the pressure in
the carotid artery, which could not be the case if it were due to a mere
filtration ; for if pressure alone were the cause, the flow of saliva would
cease as soon as the pressure in the tube equaled the pressure in the
blood-vessels. Second, even in the absence of blood the gland can
be made to yield a secretion, as shown by stimulating the nerve in a
recently killed animal. Third, after the injection of atropin into the
circulation the secretion is abolished, but the local vasomotor mechan-
ism is unimpaired, for stimulation of the nerve, as in the previous
instance, gives rise to a dilatation of the vessels and an increased
blood-supply. There is thus abundant proof that the chorda tym-
pani contains two sets of fibers — one regulating the blood-supply to
the gland, the other stimulating the secretory cells.

The influence of the auriculo-temporal branch of the fifth nerve
upon the parotid gland is similar to the action of the chorda tympani
on the submaxillary gland. The active fibers of this nerve are prob-
ably derived from the ninth nerve or glossophaiyngeal. If the nerve

DIGESTION. 169

be stimulated by the induced electric current, there follows a dilata-
tion of the blood-vessels and an abundant discharge of a thin saliva,
rich in water and salts, but containing a small amount of organic
matter. Division of the nerve, extirpation of the otic ganglion,
division of Jacobson's nerve, is followed by a loss of reflex secretion.
Stimulation of Jacobson's nerve, as shown by Heidenhain, gives rise
to the secretion.

The sympathetic fibers which influence the salivary secretion
emerge from the spinal cord mainly through the second, third, and
fourth thoracic nerves. After passing into the sympathetic chain
they ascend to the superior cervical ganglion, w^ith the cells of which
they become connected through the intermediation of fine terminal
branches. From this point non-medullated nerve-fibers follow the
branches of the external carotid artery to the different glands. There
is no evidence that these fibers have any connection, anatomic or
physiologic, with local ganglia at or near the submaxillary or sub-
lingual glands. If the sympathetic nerve in the neck, especially in
the dog, be divided and the peripheral end stimulated with the in-
duced electric current, there is at once a contraction of the smaller
blood-vessels of the gland and a diminution of the blood-supply, a
result showing the presence of vaso-constrictor fibers. Nevertheless
both the submaxillary and sublingual glands pour out a saliva which
is dijQFerent from that poured out when the chorda tympani is stimu-
lated. The quantity is less, it is more viscid, richer in organic matter,
of a higher specific gravity, and more active in the transformation of
starch into sugar. Stimulation of the fibers passing to the parotid
gland is followed by contraction of the vessels and an abolition of the
secretion; but at the same time there is an increased activity of the
secretory cells, for subsequent stimulation of the auriculo-temporal
nerve not only causes an increase in the amount of water and in-
organic salts, but an increase also in the amount of organic matter
far beyond that produced when the auriculo-temporal has alone been
stimulated. Histologic examination shows that the small ducts of
the gland are filled with thick organic matter after stimulation of
the cervical sympathetic.

DEGLUTITION.

Deglutition is that part of the digestive process which is concerned
in the transference of the food from the mouth through the pharynx
and esophagus into the stomach. This is an extremely complex act
and involves the action of a large number of structures, all of which
are made to act in proper sequence under the coordinating influence
of the nervous system. The deglutitory canal consists of the mouth,
pharynx, and esophagus, each of which presents certain anatomic
features on which its physiologic action depends.

lyo

TEXT-BOOK OF PHYSIOLOGY.

The cavity of the mouth communicates posteriorly with the
pharynx by a narrow orifice, the isthmus of the fauces. This orifice
is bounded above by the soft palate, laterally by the anterior and
posterior half arches, and below by the tongue.

The pharynx is an oval-shaped cavity extending from the base of
the skull to the lower border of the cricoid cartilage, a distance of

a^6

Fig. 68. — Vertical Section of the Nasal Fossa and Mouth, i. Left nares.
2. Lateral cartilage of the nose. 3. Portion of the internal alar cartilage form-
ing the skeleton of the lower part. 4. Superior meatus. 5. Middle meatus.
6. Inferior meatus. 7. Sphenoidal sinuses. 8. External boundary of the pos-
terior nares. 9. Internal elliptical opening of the Eustachian tube. 10. Soft
palate. 11. Vestibule of the mouth. 12. Vault of palate. 13. Genioglossus
muscle. 14. Geniohyoid muscle. 15. Cut margin of the mylohyoid muscle.
16. Anterior pillar of the palate (anterior half-arch), presenting a triangular figure
with the base inferiorly, covering partly the tonsil. 17. Posterior pillar (poste-
rior half-arch) of the palate. 18. Tonsil. 19. Follicular (mucous) glands at the
base of the tongue. 20. Cavity of the larynx. 21. Ventricle of the larynx.
22. Epiglottis. 23. Cut OS hyoides. 24. Cut thyroid cartilage. 25. Thyro-
hyoid membrane. 26. Section of posterior portion of the cricoid cartilage.
27. Section of the anterior portion of the same cartilage. 28. Crico-thyroid
membrane.

about 12 centimeters. (See Fig. 68.) Its walls are formed mainly by
three pairs of muscles — the superior, middle, and inferior constrictors
— each consisting of red, striated muscle-fibers, and hence capable
of rapid and energetic contractions. Superiorly the pharynx is
attached to and supported by the basilar process of the occipital

DIGESTION. 171

bone; infcriorly it becomes continuous with the esophagus. The
anterior wall of the pharynx is imperfect and presents openings which
communicate with the nasal chambers, the mouth, and the larynx.
The lateral wall on either side presents the opening of the Eustachian
tube which leads directly into the cavity of the middle ear. The
interior of the pharynx is hned by mucous membrane. The pharynx
is partially separated from the mouth by the velum pendulum palati,
a muscular structure attached above to the hard palate; its lower
edge or border is directed downward and backward and presents in
the middle line a conical process, the uvula. On either side the palate
presents two curved arches, the anterior and posterior, formed re-
spectively by the palato-glossei and palato-pharyngei muscles. The
laryngeal orifice or glottis is placed just beneath the base of the
tongue. It is triangular in shape, wide in front, narrow behind, and
directed downward and backward. It is bounded above by a thin
plate of cartilage, the epiglottis, placed just behind the tongue and so
arranged that it can easily be depressed and elevated.

The esophagus, the continuation of the deglutitory canal, extends
downward from the lower border of the cricoid cartilage for a dis-
tance of from 22 to 25 centimeters, to a point opposite the ninth
thoracic vertebra, where it expands into the stomach. Its walls are
composed of an internal or mucous and an external or muscular coat,
united by areolar tissue. The muscular coat consists of an external
layer of longitudinal libers arranged in three bands and of an internal
layer composed of libers arranged circularly in the upper part and
obhquely in the lower part of the esophagus. In the upper third
the fibers are striated ; in the middle third they are a mixture of both
striated and non-striated; in the lower third they are entirely non-
striated.

The deglutitive act may be for convenience divided into three
stages, viz. :

1. The passage of the food from the mouth into the pharynx.

2. The passage of the food through the pharynx into the esophagus.

3. The passage of the food through the esophagus into the stomach.

In the first stage the bolus of food is placed on the superior surface
of the tongue. The mouth is then closed and respiration is momen-
tarily suspended. The tip of the tongue is placed against the pos-
terior surfaces of the teeth. The tongue, because of its intrinsic
musculature, then arches from before backward against the roof of
the mouth and pushes the bolus of food through the isthmus of the
fauces into the pharynx. This completes tht first stage. It is a
voluntary effort and accomplished partly by the tongue, though,
as shown by Meltzer, mainly by the mylohyoid muscles.

The second and third stages, or the passage of the food through
the pharynx and esophagus into the stomach, have been attributed

172 TEXT-BOOK OF PHYSIOLOGY.

until quite recently entirely to peristaltic movements of their muscu-
lature. It has been stated that with the passage of the food through
the isthmus of the fauces the posterior wall of the pharynx advances
and seizes the food, and in consequence of a rapid peristaltic move-
ment running through its constrictor muscles from above downward
is transferred to the esophagus; that with the entrance of the food
into the esophagus a similar peristalsis, varying in rapidity in different
sections in consequence of a change in the character of its muscula-
ture, gradually transfers the food into the stomach. There can be
but shght doubt that by this method the bolus of food, especially if
it is of firm consistence and of a size sufficient to distend the esoph-
agus, is transferred into the stomach, but that it is the exceptional
rather than the usual method has been demonstrated by Kronecker,
Falk, and Meltzer.

In 1880 the first of these experimenters made the observation that
the sensation in the stomach following the swallowing of a mouthful
of cold water occurred too quickly to be explained by the prevalent
behef that its transference was caused by ordinary peristalsis, the rate
of progression of which was known to be slow. Falk then discovered
the fact, by introducing through the mouth into the pharynx a tube
connected externally with a water manometer, that during the act of
swallowing there is a sudden rise of pressure equal to about twenty
centimeters of water.

These experiments demonstrated that at the beginning of degluti-
tion there is a sudden rise of pressure, the result of a quickly acting
force resident in the mouth or pharynx, in consequence of which the
food is rapidly thrown down into the stomach, peristalsis playing no
part in the process. The proof, however, of these statements was
furnished by Meltzer. This observer introduced into the pharynx
and esophagus rubber tubes, the ends of which were provided with
thin-walled rubber balloons which could be distended with air.
The outer ends of the tubes were connected with Marey's recording
tambours. Any compression of the balloon would be followed by
the passage of the air into the tambour and an elevation of the lever.
With one balloon in the pharynx and the other in the esophagus at
varying depths, and the recording levers of the tambours applied
against the surface of a revolving cylinder, it became possible, with
the addition of a chronogram, to obtain a graphic representation of
the time relations of simultaneous and successive compressions of
the two balloons.

It was found as the result of many experiments that no matter
how deep the position of the esophageal balloon, it was compressed
simultaneously with the pharyngeal balloon, as shown by the rise of
the levers on swallowing a mouthful of water. The interval of time
between the rise of the two levers did not amount to more than the

DIGESTION.

173

tenth of a second. The inference was that the water was projected
or shot down the pharynx and esophagus in this period of time, and
in its passage compressed both balloons practically at the same in-
stant. The same was found to be true when small masses of more
consistent food were swallowed.

The curves of the entire deglutitive act recorded by the two levers
are, however, different in form. (See Fig. 69.) The pharyngeal curve,
I, presents two crests, the first. A, being due to the compression caused
by the passage of the bolus, the second, B, due to the compression
exerted by the contraction of the phar}'ngeal muscles. The inter\'al
of time between these two crests amounts to not more than 0.3
second. In the esophageal curve, 3, the elevation, C, corresponds
to the elevation, A, and is likewise due to the compression exerted

Fig. 69. — Tracing of the Act of Deglutition, i. A indicates the compression of
the elastic bag caused by the bolus projected by the contraction of the mylohyoid
muscles. B. Contraction of the pharynx. 2. Line marking seconds. 3. Trac-
ing of the bag in the esophagus 12 cm. from the teeth. C. Compression of the
bag by the bolus corresponding to A. D. Compression by the residues of the
bolus carried on by the contraction of the phar}'nx, B. E. Contraction of the
esophagus.

by the bolus. The interval of time between the beginning of the
first and second curves was not more than o.i second, regardless of
the depth to which the esophageal balloon was plunged. At a later
period a second rise of the lever was recorded ; the time of its appear-
ance, height, duration, etc., were found to increase with the depth of
the balloon.

These facts demonstrate that deglutition consists of two phases:
(i) a rapid rise of pressure in the pharynx, as a result of which the
bolus is suddenly shot down to the stomach; (2) a peristaltic con-
traction of the musculature of the canal, which, acting as a supple-
mentary force, carries onward any particles of food in the canal and
forces the bolus through the closed sphincter at the end of the esoph-
agus.

174

TEXT-BOOK OF PHYSIOLOGY.

The immediate cause of the sudden rise of pressure was shown by
Meltzer to be the contraction of the mylohyoid muscles. When
the nerves going to these muscles were divided in a dog, deglutition
was practically abolished. These muscles are probably assisted in
their action by the contraction of the hyoglossus muscles as well as
the tongue itself.

It was also demonstrated in these experiments that the contrac-
tion of the esophagus did not partake of the character of ordinary
peristalsis. It was found that the esophagus contracted in three
distinct segments, corresponding in all probability to the difference
in the character of their muscular fibers. The first segment, about
six centimeters in length, was found to begin to contract about 1.2

seconds after the beginning of
the first curve and lasting 2
seconds; the second segment,
about twelve centimeters in
length, beginning to contract
about 1.8 seconds or 3 seconds
after the beginning of the first
section, and lasting for from
5 to 7 seconds; the third seg-
ment, six centimeters in length,
contracting from 6 to 7 sec-
onds. The beginning and the
end of the contraction for each
segment occurred simultane-
ously throughout its entire ex-
tent. If, however, a series of
deglutitory acts follow each
other in quick succession,
there is an inhibition of the
peristaltic contractions until
after the final swallow.

Closure of the Posterior
Nares and Larynx. — Not-
withstanding the rise of pressure in the pharynx during the act of
swallowing, it is seldom under normal circumstances that any por-
tion of the bolus ever finds its way either into the larynx or nasal
chambers, for the reason that the openings of these cavities are fully
closed by appropriate means.

At the moment the food passes into the pharynx the posterior
nasal openings are closed against the entrance of the food by a septum
formed by the pendulous veil of the palate and the posterior half
arches. The palate is drawn upward and backward until it meets
the posterior wall of the pharynx, and at the same time is made tense.

Fig. 70. — Diagram showing the Manner
OF Closure of the Posterior Nares
AND Larynx during Deglutition.

DIGESTION. 175

by the action of the levator palati and tensor palati muscles respec-
tively (Fig. 70). This septum is completed by the advance toward
the middle line of the posterior half arches caused by the contrac-
tion of the muscles which compose them — the palato-pharyngei.
When these structures are impaired in their functional activity,
as in diphtheritic paralysis and ulcerations, there is not infre-
quently a regurgitation of food, especially liquids, into the nose.
The lar}-nx is equally protected against the entrance of food during
deglutition under normal circumstances. That this accident occa-
sionally happens, giving rise to severe spasmodic coughing, and even
in extreme cases to suffocation, is abundantly shown by the records
of clinical medicine. Usually it does not occur, for in addition to
other methods there is a complete suspension of the act of inspiration
by which particles of food might be drawn into the larynx. At the
same time the larynx is drawn well up under the base of the tongue
and closed by the descent of the epiglottis. The glottis itself is also
closed by the constrictor muscles which surround it.

Nerve Mechanism of Deglutition. — Deglutition is almost ex-
clusively a retiex act throughout its entire extent, and requires for
its inauguration merely a stimulus to some portion of the mucous
membrane of the deglutitory canal. The first stage is primarily
voluntary, but from inattention to the process may become second-
arily reflex. The origin and course of the afferent nerves, stimu-
lation of which excite reflexly the movements of the pharj'nx and
esophagus, however, are practically unknown. In the rabbit deg-
lutition can be excited by stimulating the anterior central part of
the soft palate. In man it has not yet been possible to locate an
area stimulation of which will give rise to a reflex deglutitory act.
Though electric stimulation of the superior laryngeal nerve will cause
reflex deglutitory movements, it is obvious that the terminals of this
nerve can not be the source of the natural afferent impulses. Stimu-
lation of the glossophar}'ngeal nerve causes an inhibition of the
movements.

The center from which emanate ner\-e impulses which excite the
various muscles to action has been located experimentally in the
medulla oblongata just above the alae cinereae. The efferent nerves
comprise branches of the facial, hypoglossal, motor filaments of the
third division of the fifth nerve, motor filaments of the glossopharyn-
geal and vagus derived in all probability from the spinal accessory.
Inasmuch as the different mechanisms act not only in a coordinate
but sequential manner, it is possible that the deglutition center is not
a single circumscribed collection of cells, but a series of centers corre-
sponding to the origin of the eft'erent nerves, the activities of which
are coordinated by some single true deglutition center.

176 TEXT-BOOK OF PHYSIOLOGY.

GASTRIC DIGESTION.

After the food has passed through the esophagus it is received by
the stomach, where it is retained for a variable length of time, during
which important changes are induced in its physical and chemic com-
position. The disintegration of the food inaugurated by mastication
and insalivation is still further carried on in the stomach by the sol-
vent action of the acid fluid there present, until the entire mass is
reduced to a hquid or semi-liquid condition.

The stomach is a dilated and highly specialized portion of the
alimentary canal intervening between the esophagus and small intes-
tine. When moderately distended with food, it is somewhat conical
or pyriform in shape and slightly curved on itself. It is situated
obliquely and in some individuals almost vertically in the upper part
of the abdominal cavity, extending from the left hypochondrium to
the right of the epigastrium. The dimensions and capacity of the
stomach undergo considerable periodic variation according to the
extent to which it is distended by food. In the average condition it
measures in its long diameter from 25 to 35 centimeters, in its vertical
diameter at the cardia 1 5 centimeters, in its antero-posterior diameter
from II to 12 centimeters. The capacity of the stomach varies from
1500 to 1700 c.c. In the empty condition its walls are collapsed and
partly in contact, and the entire organ is drawn up into the upper
part of the abdominal cavity. The opening through which the
food passes into the stomach is known as the esophageal orifice or
the cardia. The opening through which it passes into the intestine
is known as the pylorus, the pyloric or gastro-duodenal orifice.
Between these two orifices the stomach along its upper border pre-
sents a curve and along its lower border a much larger curve, known
as the lesser and greater curvatures respectively. The left end of the
stomach is termed the fundus or cardiac end; the right, the pyloric
end. Passing from the fundus toward the pylorus, the stomach
gradually narrows, and at a point situated about 5 cm. from the pyloric
opening it frequently presents a constriction which divides the general
cavity into two portions: viz., the fundus and the antrum of the
pylorus.

The walls of the stomach are formed by four distinct coats united
by areolar tissue and named, from without inward, as the serous,
muscle-, submucous, and mucous.

The external or serous coat is thin and transparent and formed by a
reduplication of the general peritoneal membrane.

The middle or muscle-coat consists of three layers of non-striated
muscle-fibers, named from their direction the longitudinal, circular,
and oblique (Fig. 71). The longitudinal fibers are most abundant
along the lesser curvature and are a continuation of those of the

DIGESTION.

1/7

esophagus; over the remainder of the stomach they are thinly scat-
tered, but toward the pyloric orifice they are more numerous and
form a tolerably thick layer which becomes continuous with the
fibers of the small intestine.' The circular fibers form a complete
layer encircling the entire organ, with the exception, perhaps, of a
portion of the fundus. The fibers of this coat cross the longitudinal
fibers at right angles. At the junction of the fundus with the pyloric
antrum the circular fibers are arranged in a well-defined bundle
termed the sphincter aniri pylorici. In the pyloric region the circular
fibers are more closely arranged, forming thick annular rings. At
the pyloric opening the circular fibers are again crowded together and

Fig. 71. — Fibers Seen WITH THE Stomach Everted. 1,1. Esophagus. 2. Circular
fibers at the esophageal opening. 3, 3. Circular fibers at the lesser curvature.
4, 4. Circular fibers at the pylorus. 5, 5, 6, 7, 8. Oblique fibers. 9, 10. Fibers
of this layer covering the greater pouch. 11. Portion of the stomach from which
these fibers have been removed to show the subjacent circular fibers. — (Sappey.)

form a distinct muscle band, — the sphincter pylori, — which projects
for some distance into the interior of the stomach. It has been stated
by Riidinger that the inner fibers of the longitudinal coat become con-
nected with this circular band and constitute a distinct muscle, the
dilatator pylori. The obhque fibers are most distinct over the cardiac
portion of the stomach, but extend from left to right as far as the
junction of the middle and last thirds of the stomach. They are
continuations of the circular fibers of the esophagus.

The submucous coat consists of loose areolar tissue carrjdng
blood-vessels, nerves, and lymphatics. It serves to unite the muscle

178

TEXT-BOOK OF PHYSIOLOGY.

Epithelium. -

Tunica
propria.

't^f^,.r^f?t,r

'%

-^^-

to the mucous coat. Its inner surface bears a thin layer of muscular
tissue, the muscularis mucosa, which supports the mucous membrane.
The internal or mucous coat is loosely attached to the muscular
coat. In the empty and contracted state of the stomach it is thrown
into longitudinal folds or rugae, which are, however, obhterated when
the organ is distended with food. The mucous membrane in adult
life is smooth and velvety in appearance, gray in color, and covered
with a layer of mucus. Its average thickness is about one milHmeter.

The surface of the mem-
brane is covered with a
layer of columnar epi-
thehal cells, each of
which possesses a nu-
cleus and nucleolus. At
the pylorus there is a
circular involution of
the mucous membrane
which is known as the
pyloric valve. This is
strengthened by fibrous
tissue and embraced by
the sphincter muscle pre-
viously described.

Gastric Glands. —
The surface of the mu-
cous membrane when
examined with a low
magnifying power pre-
sents throughout in-
numerable depressions
polygonal in shape and
separated by slightly
elevated ridges. At the
bottom of these spaces
are to be seen small
orifices, which are the
mouths of the glands embedded in the mucous membrane. A
vertical section of the gastric walls (Fig. 72) shows not only the
position and appearance of the glands, but the relation of the
various tissues which enter into the formation of these walls. An
examination of the mucous membrane in different regions of the
stomach reveals two distinct types of glands, cardiac or fundic,
and pyloric, which differ not only in histologic structure, but also
in function. Both types extend through the entire thickness of the
mucosa.

M uscu-
laris.

Muscularis
mucosje.

Submucosa.

Inner cir-
cular layer
of muscle.

Outer longi-
tudinal layer
of muscle.

Serosa.

Fig. 72.

Transverse Section of the Wall of a
Human Stomach. X i5- The tunica propria
contains glands standing so close together that
its tissue is visible only at the base of the glands
toward the muscularis mucosae.

DIGESTION.

179

The cardiac, jundic, or peptic glands, are formed by an involu-
tion of the basement membrane of the mucosa and lined by epithehal
cells. Each gland may be said to consist of a short duct, or neck,
and a body or fundus (Fig. 73). The latter portion is wavy or
tortuous and frequently subdivided into as many as 8 to 10 distinct

and separate tubules. The duct
is lined by columnar epithelial
cells similar to those covering
the surface of the mucosa. The
lumen of the fundus is bordered
Lv'i^jg. by epithelial cells, cuboid in

shape, and consisting of a gran-
ular protoplasm containing a
distinct spherical nucleus. These
cells are generally spoken of as
the chief or central cells. In
addition to the chief cells, the
fundus contains a second variety
of cell, which is of a larger size,

Fig. 73. — Peptic Gland from
Stomach of Dog. a. Wide
mouth and duct which receive
the terminal divisions of the
gland, b, c. Neck and fun-
dus of the tubes, e. Central
or chief cells, d. Parietal or
acid cells. — (After Piersol.)

, ^If-j, Secretory
capillaries.

Fig. 74. — Section of Fundus Gland
of Mouse. Left upper half drawn
after an alcohol preparation, right
upper half after a Golgi prepara-
tion. The entire lower portion is a
diagrammatic combination of both
prepa ratio ns . — (Stohr . )

of a triangular or oval shape, and consisting of a finely granular pro-
toplasm. From this situation just beneath the gland wall they have
been termed parietal or border cells. Each parietal cell appears to
be surrounded and penetrated by a system of passages which open
into the lumen of the gland by means of a delicate cleft or canaliculus

iSo

TEXT-BOOK OF PHYSIOLOGY.

(Fig. 74). Glands with these histologic features are most abundant
in the middle zone of the stomach. Toward the extreme left end
of the fundus the glands are largely, if not entirely, devoid of pari-
etal cells.

The pyloric glands are also formed by an involution of the

mucous membrane and lined by epi-
thelial cells (Fig. 75). The ducts
are much longer than the ducts of
the fundic glands. At its extremity
each duct becomes branched, giving
rise to a number, from 2 to 16, of
short tubes, each of which has a large
lumen and communicates with the
duct by a narrow short neck. The
ducts are lined throughout by colum-
nar epithelium. According to Mall,
the total number of openings on the
surface of the mucous membrane of
the dog's stomach is somewhat over
1,000,000, and the total number of
blind tubes opposite the muscularis
mucosa exceeds 16,500,000. Accord-
ing to Sappey, the surface of the
mucous membrane of the human
stomach presents over 5,000,000 ori-
fices of gastric glands.
Blood-vessels, Nerves, and Lymphatics. — The blood-vessels
of the stomach after entering the mucosa break up into a number of
branches which are distributed to the muscular and mucous coats.
The branches to the latter soon form a capillary network with oblong
meshes which not only surround the tubules but form a network just
beneath the surface of the mucosa. Veins gradually arise from the
capillaries which empty into the larger veins of the mucosa. The
glands are also supported by processes of smooth muscle-fibers
passing up from the muscularis mucosa.

The nerve- fibers distributed to the stomach are derived from the
vagus and the sympathetic branches of the solar plexus. After
piercing the serous coat the fibers form or unite with a plexus of
fibers situated between the circular and longitudinal layers of the
muscle- coat. At the nodal points of this plexus large nerve-gang-
lion cells are to be found, the whole forming the mechanism known
as Auerbach's plexus. A similar plexus of cells and fibers in more
or less intimate anatomic connection with the foregoing is found
between the muscle and submucous coats, and is known as Meiss-
ner's plexus. From this plexus fine nerve filaments are distributed

Fig. 75. — Section of Pyloric
Glands from Human Stom-
ach, a. Mouth of gland
leading into long, wide duct
(b), into which open the ter-
minal divisions, c. Connec-
tive tissue of the mucosa. —
{After Pier sol.)

DIGESTION. i8i

to muscle- fibers, blood-vessels, and glands. In the latter structure
terminal arborizations have been detected in close contact with the
secreting cells themselves.

The lymphatics, which are quite numerous, originate in the
meshes of the mucosa. The larger trunks enter lymph-glands lying
along the greater and lesser curvatures of the stomach.

Gastric Fistulas. — The general process of digestion, as it takes
place in the stomach, has been studied in human beings and animals
with a fistula in the walls of the stomach and abdomen, the result
either of accident or of necessary surgical or experimental procedures.

The earliest observations on gastric digestion were made by Dr.
Beaumont on Alexis St. Martin, who, as the result of a gunshot
wound, was left with a permanent fistulous opening into the fundus
of the stomach. This opening two years after the accident was about
two and a half inches in circumference and usually closed from within
by a fold of mucous membrane which prevented the escape of the food.
This valve could be readily displaced by the finger and the interior
of the stomach exposed to view. After the complete recovery of St.
Martin, Dr. Beaumont during the years between 1825 and 183 1 at
intervals made numerous experiments on the nature of gastric diges-
tion. As the result of an admirable series of investigations it was
estabhshed that the digestion of the food is largely a chemic act, due
to the presence of an acid fluid secreted by the mucous membrane;
that this fluid is secreted most abundantly after the introduction of
food into the stomach; that different articles of food possess varying
degrees of digestibihty; that the duration of digestion varies according
to the nature of the food, exercise, mental states, etc., and that the
process is aided by continuous movements of the muscular walls.

Since Dr. Beaumont's time the estabUshing of a gastric fistula in
human beings has been necessitated by pathologic conditions of the
esophagus, x^fter recovery these cases offered fair facilities for the
study of the process when the food was introduced through the
opening. Similar fistute have been established in both carnivorous
and herbivorous animals with a view of studying the process as it
takes place in them. The results obtained in these instances in many
respects corroborate those obtained by Dr. Beaumont, though many
new facts, unobserved by him, have been brought to hght.

Gastric Juice. — -The gastric juice obtained from the human
stomach free from mucus and other impurities is a clear, colorless
fluid with a constant acid reaction, a slightly saline and acid taste,
and a specific gravity varying from 1.002 to 1.005. The juice ob-
tained from the dog's stomach possesses essentially the same char-
acteristics, though its acidity as well as its specific gravity are slightly
greater. When kept from atmospheric influences, it resists putre-
factive change for a long period of time, undergoes no apparent

i82 TEXT-BOOK OF PHYSIOLOGY.

change in composition, and loses none of its digestive power. It
will also prevent and even arrest putrefactive change in organic
matter. The chemic composition of the gastric juice has never
been satisfactority determined, owing to the fact that the secretion
as obtained from fistulous openings has not been absolutely normal.
The following analyses represent the composition of a sample
obtained by Schmidt from the stomach of a woman who had a fistula,
but who was nevertheless in good health; also the composition of the
juice from a dog:

COMPOSITION OF GASTRIC JUICE.

Human. Dog.

Water, 994.40 973.06

Organic matter, 3.19 i7-i3

Hydrochloric acid, 0.20? 3.34

Calcium chlorid, 0.06 0.26

Sodium chlorid, 1.46 2.50

Potassium chlorid, 0.55 1.12

Calcium phosphate ] 1.73

Magnesium " > 0.12 0.23

Ferric " j 0.08

Ammonium chlorid, 0.47

The organic matter present in gastric juice is a mixture of mucin
and a proteid, products of the metabohc activity of the epithehal
cells on the surface of the mucous membrane and of the chief or
central cells of the gastric glands respectively. Associated with the
proteid material are two ferment or enzyme bodies, termed pepsin
and rennin. As is the case with other enzymes, their true chemic
nature is practically unknown.

Pepsin, though present in gastric juice, is not present as such in
the chief cells of the glands, but is derived from a zymogen, pro-
pepsin or pepsinogen, when the latter is treated with hydrochloric
acid. This antecedent compound is related to the granules ob-
served in and produced by the cell protoplasm during the period
of rest. Though pepsin is largely produced by the central cells of
the fundic glands, it is also produced, though in less amount, by
the cells of the pyloric glands. Pepsin is the chief proteolytic agent
of the gastric juice and exerts its influence most energetically in the
presence of hydrochloric acid and at a temperature of about 40° C.
Other acids— g. g., phosphoric, nitric, lactic, etc. — are also capable
of exciting it to activity, though with less intensity.

Rennin or pexin is present in the gastric juice not only of man and
all the mammaha, but also of birds and even fish. In its origin from a
zymogen substance, in its relation to an acid medium and an optimum
temperature, it bears a close resemblance to pepsin. Its specific
action is the curdling of milk, a condition due to the coagulation of
caseinogen.

DIGESTION. 183

Hydrochloric acid is the agent which gives lo the gastric juice its
normal acidity. Though the juice frequently contains lactic, acetic,
and even phosphoric acids, it is generally believed that they are the
result of fermentation changes occurring in the food, the result of
bacterial action. The percentage of hydrochloric acid has been the
subject of much discussion. The analysis of human gastric juice
made by Schmidt shows a percentage of 0.02, while that of the dog
is 0.34. It is probable, however, that the low percentage of HCl in
human gastric juice was due to the admixture with saliva. At
present it is believed from analyses made for chnical purposes that
the acid is present to the extent of at least 0.2 per cent. This degree
of acidity is not constant during the entire process of digestion. In
the earlier as well as in the later stages it is much less.

The immediate origin of the hydrochloric acid is difficult of ex-
planation. That it is derived, however, primarily from the chlorids
of the food and secondarily from the blood-plasma has been estab-
lished by direct experiment. If all the chlorids be removed from
the food and all chlorids be withdrawn from the animal tissue by the
administration of various diuretics, — c. g., potassium nitrate, — there
will be a total disappearance of hydrochloric acid from the stomach.
On the addition of sodium or potassium chlorids to the food, there is
at once a reappearance of the acid.

As to the nature of the process by which the acid is formed, noth-
ing definite is known. Various theories of a chemic and physical
character have been offered, all of which are more or less unsatis-
factory. As no hydrochloric acid is found either in the blood or
lymph, the most plausible view as to its origin is that which regards
it as one of the products of the metabolism of the gland-cells, and
more particularly of the parietal or border cells, and which for this
reason have been termed acid-producing or oxyntic cells. From the
chlorids furnished by the blood the chlorin is derived, which, uniting
with hydrogen, forms the HCl. The base set free returns to the blood,
which in part accounts for its increased alkalinity during digestion
as well as the diminished acidity of the urine. The acid thus formed
passes through the canaliculi, which penetrate and surround the cells,
into the lumen of the gland.

Hydrochloric acid exerts its influence in a variety of ways. It is the
main agent in the derivation of pepsin and rennin or pexin from their
antecedent zymogen compounds, pepsinogen and pexinogen (Warren) ;
it imparts activity to these ferments; it prevents and even arrests fer-
mentative and putrefactive changes in the food -by destroying micro-
organisms; it softens connective tissue, it dissolves proteids and acid-
ifies the proteids, thus making possible the subsec^uent action of pepsin.

The inorganic salts of the gastric juice are probably only inci-
dental and play no part in the digestive process.

i84 TEXT-BOOK OF PHYSIOLOGY.

Mode of Secretion. — The observations of Dr. Beaumont and
the experiments of many physiologists have made it certain that the
secretion of the gastric juice is intermittent and not continuous, that
it is only on the introduction and digestion of the food that the normal
amount is poured out. During the intervals of digestive activity the
stomach is practically free from all traces of the juice. The mucous
membrane is pale and covered with a layer of mucus having an alka-
line or neutral reaction. The introduction, however, of small por-
tions of food or irritation with a glass rod causes a change in the
appearance of the mucous membrane. At the points of irritation
the membrane becomes red and vascular and in a few minutes small
drops of the secretion make their appearance; these coalesce and
run down the sides of the stomach. The chemic reaction then
changes from alkalinity to acidity.

Though the secretion of the gastric juice can be excited by these
artificial means, the amount secreted, owing to the local character of
the stimulation, is but shght compared with the quantity secreted
when the natural stimulus — well-masticated food saturated with
alkahne saliva — passes into the stomach. Under such circum-
stances, the stimulus being general, the blood-vessels dilate, the
mucous membrane becomes uniformly red, and in a short time the
secretion makes its appearance.

From experimental investigations there is reason to beheve that
the physical contact of the food with the mucous membrane is not
sufficient to maintain a continuous secretion, and that other factors
must.be invoked. For it is not until digestion is well under way that
the juice is secreted in normal and necessary quantity. Attempts
have been made to determine the relative degree of influence of
different articles of food on the rate of secretion. Of all substances
capable of increasing the flow none are so efficient as peptones, their
introduction into the stomach being followed by a copious secretion.
For this reason it has been asserted that after the primary physical
stimulation of the food there is a secondary chemic stimulation by
peptones, the result of the digestive process. As to whether they are
absorbed by the mucous membrane and directly stimulate the gland-
cells, or whether they act as chemic stimuli to afferent nerves in the
mucosa, nothing definite can be stated.

Histologic Changes in the Gastric Cells during Secretion. —
During the periods of rest and secretory activity the cells of the
gastric glands undergo changes in histologic structure which are
believed to be connected with the production of the ferments and
acid. In the resting period the protoplasm of the chief or central
cells of the fundus glands becomes crowded with large and well-
defined granules, which during the period of secretory activity largely
disappear, so much so, that only the luminal border of the cell is

DIGESTION.

i8S

occupied by them, the outer border being clear and hyahne in appear-
ance. The parietal cells during rest are large and finely granular,
but after secretion they are smaller in size though still granular.
(See Fig. 76, A and B.)

The cells of the pyloric glands, though containing granules, do not
show any marked difference between the resting and active condition.
According to some observers, they contain pepsinogen; according to
others, mucin. The epithelial cells fining the ducts of the pylorus
and fundus glands, if not identical with the epithelial cells on the sur-
face of the mucous membrane, pass by transitional forms into them.
Among these cells are found many goblet cells which secrete a portion

Fig. 76. — Sections of Deep Ends of Fundus Glands of the Cat in Different
Secretive Phases. X 1000. — (Bensley.) A. From a fasting stomach. The
chief cells are tilled with large zymogen granules; nuclei near the outer ends of
cells. Gentian-\4olet preparation, b b b. Border cells. B. Six hours after an
abundant meal of raw flesh. The chief cells exhibit two zones, the inner occupied
by large zymogen granules, the outer by a deeply staining, obscurely fibrillar
element, prozymogen; the nuclei he at the junction of the two zones, bb b. Border
cells, pr. Prozymogen. c. Mucin-secreting cell, similar to those found in the
neck of the gland. Gentian-violet preparation.

of the mucus found in the stomach and gastric juice. In the period
of rest the protoplasm of the epithelial cells absorbs and assimilates
from the surrounding lymph-spaces material which eventually makes
its reappearance as a product of metabolism in the form of granules
and hydrochloric acid. With the onset of digestive activity there is a
dilatation of the blood-vessels, an increase in the blood-supply, a
stimulation through the nerve-supply of the cells, and an output of a
fluid to which the name gastric juice is given.

Influence of the Nervous System. — The secretion of gastric
juice is largely a reflex act and under the control and influence of the

i86 TEXT-BOOK OF PHYSIOLOGY.

central nervous system. Though the mechanism involved is ob-
scure, it has frequently been observed that the sight of food or the
chewing of food without its passage into the stomach is attended by a
dilatation of the blood-vessels and a copious flow of gastric juice
within a few minutes, showing the cooperation of vaso-motor and
secretory nerve influences, a result similar to that which occurs when
the food comes into contact with the mucous membrane itself. It
was also observed by Dr. Beaumont that mental emotions, such as
fear and anger, will arrest the normal secretion.

Many attempts have been made with varying degrees of success
to determine the paths of the efferent impulses to the glands. As the
vagus is the only cranial nerve connecting the stomach with the
central nervous system, it has been the subject of much experimenta-
tion. The results obtained, however, have not been uniform. The
recent investigations of Pawlow are most reliable. He found that
division of both vagi was followed by a loss of reflex action. Stimu-
lation of the peripheral ends with induction shocks, one per second,
after a latent period of about seven minutes, caused a flow of gastric
juice.

Physiologic Action of Gastric Juice. — In the study of the
physiology of gastric digestion as it takes place under normal con-
ditions it is important to bear in mind that the foods introduced into
the stomach are heterogeneous compounds consisting of both nutritive
and non nutritive materials, and that before the former can be digested
and utilized for nutritive purposes they must be freed from their
combinations with the latter. This is accomplished by the solvent
action of the gastric juice, which in virtue of the chemic activity of its
constituents on proteids, gradually disintegrates the food and reduces
it to the liquid or semi-liquid condition.

The nature of this change and the respective influence which the
acid and pepsin exert can be studied with almost any form of proteid.
The most suitable form, however, is coagulated fibrin obtained from
blood by whipping and thoroughly freed from blood by washing
under a stream of water. The chemic features of proteids, as well as
the typical forms contained in the different articles of food, have
been considered in connection with the chemic composition of the body
and the composition of foods (see pages 31 and 136). For purposes of
experimentation artificial gastric juice may be employed. This is as
effective as the normal secretion and in no essential respect differs
from it. A glycerin extract of the mucous membrane acidulated
with 0.2 per cent, hydrochloric acid is probably the best.

If small pieces of fibrin be suspended in clear gastric juice and
kept at a temperature of 104° F. (40° C.) for an hour or two, they will
be dissolved and will entirely disappear, giving rise to a slightly
opalescent mixture. In the early stages of the process the fibrin be-

DIGESTION. 187

comes swollen and transparent and partly dissolved. If at this time
the solution be carefully neutralized, the dissolved portion can be
regained in the form of acid-albumin or syntonin — a fact which in-
dicates that the first effect of the gastric juice is the acidification of the
proteids. This having been accomplished, the pepsin becomes opera-
tive, and in a varying length of time transforms the acid-albumin into
a new form of proteid, termed peptone, of which, as indicated by
chemic tests, there are probably two forms — antipeptone and hemi-
peptone. This form of proteid differs from all other forms of proteid
in being soluble in both acids and alkahes and non-coagulable by
heat. In the transformation of acid-albumin into peptones it is
possible to isolate by the addition of ammonium sulphate inter-
mediate bodies to which the term alhumoses or proteoses has been
given, and which differ somewhat in their solubility. The albumoses
are termed, in the order in which they make their appearance,
primary and secondary. Inasmuch as two forms of peptone can be
isolated after complete digestion of any given proteid, it is assumed
from this and other facts that their appearance has been preceded by
two forms of albumose. This supposed change is represented by
the following scheme:

Albumin
Acid-albumin

Proto-albumose = ( t, ^ ) = Hetero-albumose

\ Proteoses '

Deutero-albumose \ -r, . ) = Deutero-albumose

V Proteoses '

i 1

Peptone (Ampho-peptones) Peptone.

From the fact that one form of peptone, under the influence of the
pancreatic ferment trypsin, can be decomposed into leucin, tyrosin,
aspartic acid, etc., it is beheved that all the simple proteids contain
two distinct groups or radicles, termed hemi and anti groups, and
that it is this fact which determines the line of cleavage and the char-
acteristics of the cleavage products. The two forms of peptone,
hemipeptone and antipeptone, are frequently included under the term
ampho-peptones.

Nearly all forms of proteid are in a similar manner transformed
into peptones by gastric juice. Beyond this stage, however, there
does not seem to be any further change, peptones apparently being
the final products of gastric digestion. The intimate nature of this
change is practically unknown, but there are reasons for thinking
that it is a process of hydration, attended by cleavage, with increasing
solubihty of the resulting products.

i88 TEXT-BOOK OF PHYSIOLOGY.

Characters of Peptones. — The peptones resulting from the diges-
tion of different proteids, though resembhng each other in many re-
spects, yet possess different chemic characteristics, as shown by their
reaction to various chemic reagents. Though having some resem-
blance to the proteids from which they are derived, they are to be
distinguished from them by the following general characteristics :

1. They are not coagulable either by heat or by nitric acid.

2. They are soluble in water, either hot or cold, and in acid and

alkaline solutions.

3. They are diffusible, passing through animal membranes with

great rapidity. It has been demonstrated that peptones diffuse
about twelve times as rapidly as the proteids from which they
are derived.
Neither on fat nor starch has gastric juice any appreciable effect,
and when these substances are introduced into the stomach they
pass into the intestine unchanged. Notwithstanding the fact that
dilute solutions of hydrochloric acid (0.3 per cent.) will promptly
invert cane-sugar into dextrose and levulose, and that gastric juice
will accomplish the same result in test-tubes, there is no strong
evidence for the belief that the inversion of cane-sugar takes place to
any marked extent in the stomach under normal conditions. The
starch, however, which has been subjected to the action of the saliva
still continues to be converted into maltose during the first fifteen to
thirty minutes or possibly longer. Even though gastric juice is being
secreted and though hydrochloric acid solutions with a strength of
0.3 per cent, will arrest the action of ptyalin, starch digestion con-
tinues for the reason that the acid combines with the proteids and
is thus rendered inoperative. After the above-mentioned period,
free acid makes its appearance when salivary digestion ceases.

Action of Gastric Juice on Foods. — The action of gastric
juice on proteids affords a key to its influence in the reduction of
foods to the liquid or semi-liquid condition. It is evident that it will
be most active in the digestion of food consisting largely of proteid
materials, such as meat, eggs, milk, etc. Meat is disintegrated first
by the conversion of the proteids of the connective tissue, which have
been more or less gelatinized by cooking, into peptones. The
sarcolemma of the muscle-fibers which have been thus separated
is in a similar manner attacked and converted into peptones. The
true muscle or sarcous substance, consisting largely of myosin, un-
dergoes a corresponding change. If the quantity of meat be not too
large and the gastric juice be secreted in proper amount, it is possible
that all the meat will be digested in the stomach. It is quite probable,
however, that this is not the case and that a portion of the semi-
digested meat passes into the intestine, where its final solution is
effected.

DIGESTION. 189

The white of egg, especially when shghtly boiled, is much more
readily digested than when raw or firmly coagulated by prolonged
boiling. In either condition, however, the connective tissue is dis-
solved and peptonized, after which the native albumin undergoes the
same change. The yolk of the egg consists largely of fat held in sus-
pension by a proteid substance, vitellin, which is also capable of
transformation into peptone.

Adipose tissue is similarly reduced. The proteids of the con-
nective tissue and of the fat vesicles are dissolved and peptonized
and the fat-drops set free. Milk undergoes a pecuHar change in
composition before its proteid constituents can be transformed into
peptones. The caseinogen in the presence of calcium salts is always
in the soluble state. When acted on by the gastric juice, the case-
inogen undergoes coagulation which consists in the formation of a
sohd compound, casein, and a soluble albumin. This change is due
to the presence and activity of the ferment rennin. The necessity
. for this change, however, is not apparent. The coagulated casein
presents itself in the form of a flocculent curd, which is finer in human
than in cow's milk, and hence more easily digestible. The casein
is acidified by the hydrochloric acid and tlien converted into peptone.

Vegetables, though consisting of a woody or cellulose framework,
undergo a partial disintegration in the stomach. When boiled and
physically disintegrated by the teeth, the gastric juice is enabled to
penetrate the framework and dissolve and peptonize the various
proteid constituents. As a general rule, the vegetable proteids are
more difficult of digestion than the animal proteids.

Duration of Gastric Digestion. — The length of time the food
remains in the stomach and the relative digestibihty of dift'erent
articles of food were carefully studied by Dr. Beaumont on St. Martin,
and though the results obtained by him may not be absolutely correct,
viewed in the hght of recent knowledge of the digestive process, yet
in the main they have been corroborated in various ways. As a
result of many observations Dr. Beaumont came to the conclusion
that the average length of time an ordinary meal consisting of meat,
bread, potatoes, etc., remained in the stomach undergoing digestion
was about three and a half hours, the duration of the process, how-
ever, being increased when an excessive quantity of food was taken or
the quantity and quality of the gastric juice impaired by abnormal
conditions of the system. As soon as the food is liquefied by the
gastric juice that portion not absorbed by the gastric vessels passes
into the intestines, this continuing for two to three hours until the
stomach is completely emptied. The relative digestibihty of the dif-
ferent foods was also made the subject of many experiments by Dr,
Beaumont. After repeating and verifying his observations made
under varying conditions, he summed up his results in a table, of

IQO

TEXT-BOOK OF PHYSIOLOGY.

which the following is an abstract, in which the mode of preparation
and the time required for the digestion of different foods are exhibited :

TABLE SHOWING DIGESTIBILITY OF VARIOUS ARTICLES OF FOOD.

Hours. Minutes.

Eggs, whipped, i 20

" soft boiled, 3

" hard boiled, 3 30

Oysters, raw, 2 55

" stewed, 3 30

Lamb, broiled, 2 30

Veal, broiled, 4

Pork, roasted, 5 15

Beefsteak, broiled, 3

Turkey, roasted, 2 25

Chicken, boiled, 4

" fricasseed, 2 45

Duck, roasted, 4

Soup, barley, boiled, i 30

" bean, " 3

" chicken, " 3

" mutton, " 3 30

Liver, beef, broiled, 2

Sausage, " 3 20

Green corn, boiled, 3 45

Beans, " 2 30

Potatoes, roasted, 2 30

" boiled, 3 30

Cabbage, " 4 3°

Turnips, " 3 30

Beets, " 3 45

Parsnips, " 2 30

Movements of the Stomach. — During the period of gastric
digestion the muscle walls of the stomach become the seat of a
series of movements, peristaltic in character, which not only incor-
porate the gastric juice with the food, but also serve to eject the
liquefied portions of the food into the small intestine.

The movements of the human stomach as described by Beau-
mont, as well as the movements of the dog's stomach as stated by
different observers, are not in agreement in all respects, and are,
moreover, open to question for the reason that they were not ob-
served under strictly physiologic conditions. The more recent in-
vestigations of Cannon have thrown new light on this subject. By
means of the Rontgen rays he has been enabled to study the move-
ments in the living animal and under normal conditions. The
animal (the cat) was fed with bread and milk, to which was added
subnitrate of bismuth. This substance, being opaque, rendered the
movements of the stomach walls visible on the fluorescent screen.
With paper placed over the screen it was possible to sketch the
changes in shape that the stomach undergoes at different periods of
the digestive act. Some of these changes are represenetd in Fig.

DIGESTION.

191

77. The anatomic features of the cat stomach of interest in this

connection are represented in Fig. 78.

These investigations show that different portions of the stomach

walls exhibit ditTerent forms of activity, which for convenience of

description are separately described
by Cannon as follows:

I. The Movements oj the Pyloric
Part. — Within live minutes. after a
cat has finished a meal of bread
there is visible near the duodenal
end of the antrum a slight annular
contraction which moves peristaltic-
ally to the pylorus; this is followed
by several waves recurring at regu-
lar intervals. Two or three min-
utes after the first movement is seen,
very slight constrictions appear near
the middle of the stomach, and,
pressing deeper into the greater
curvature, course slowly toward the
pyloric end. As new regions enter

Left

Fig. 77. — Shadow Sketches
OF THE Outlines of
THE Stomach of a Cat
Immediately after a
Meal (ii.o), and at
Various Intervals
Afterward (at 12.0, at
2.0, 3.30, 4.30).— (ir. B.
Cannon.)

Post

Fig. 78. — The cardiac portion is all that
part to the left, as the stomach lies in the
body, of WX. The cardia is at C. The
pylorus is at P, and the pyloric portion
is the part between P and II'A'. This
has two divisions: the antrum, between
P and YZ, and the pre-antral part, be-
tween WX and YZ. The lesser curva-
ture is on the top of the outline between
C and P, and the greater curvature be-
tween the same points along the lower
border. — (Amer. Jour, of Physiology.)

into constriction, the fibers just previously contracted become relaxed,
so that there is a true moving wave, with a trough between two crests.
When a wave swings round the bend in the pyloric part, the indenta-
tion made by it deepens; and as digestion goes on the antrum

192 TEXT-BOOK OF PHYSIOLOGY.

elongates and the constrictions running over it grow stronger, but, until
the stomach is nearly empty, they do not entirely divide the cavity.
After the antrum has lengthened, a wave takes about thirty-six sec-
onds to move from the middle of the stomach to the pylorus. At all
periods of digestion the waves recur at intervals of almost exactly ten
seconds. It results from this rhythm that when one wave is just
beginning several others are already running in order before it.
Between the rings of constriction the stomach is bulged out, as shown
in the various outlines in Fig. 77.

Movements of the Pyloric Sphincter.- — During the first ten or
fifteen minutes after the first constriction of the antrum the pylorus
is tightly closed. After this period it opens at irregular intervals to
permit the passage of liquefied food which is ejected by peristaltic
weaves for a distance of two or three centimeters into the duodenum.
The frequency with which the pylorus opens depends apparently on
the degree to which the food is softened. When the food is hard,
the pylorus closes more tightly and remains closed a longer period
than when it is soft.

The Activity of the Cardiac Portion. — As digestion proceeds, the
pre-antral part of the stomach elongates and assumes the shape of
a tube, which becomes the seat also of peristaltic constriction waves.
As a result, some of the food is gradually forced into the antrum to
succeed that which has been prepared and ejected into the duodenum.
As the pre-antral tube is emptied of its contents the longitudinal and
circular fibers of the fundus steadily contract and gradually force
its contents into the tubular portion. This continues until the fundus
is completely emptied. The changes in shape which the cardiac
portion undergoes during digestion are represented in Fig. 77. The
fundus acts as a reservoir for the food and forces out its contents a
little at a time as the antral mechanism is ready to receive them.
Since peristaltic movements are absent from the cardiac portion the
food is not mixed with gastric juice, and therefore salivary digestion
can continue for a considerable period. There is no evidence of a
circulation of food in the stomach as usually described. On the
contrary, the movement through the pre-antral tube and antrum is
in general a progressive though an oscillating one. As the con-
striction waves rapidly pass over the food it is advanced toward the
pyloric opening, but as this is closed the food is forced backward
through the advancing constricted ring for a variable distance.

The effect of the constriction waves is to mix the food with the
gastric juice, triturate and soften it. So soon as this is effected, the
pylorus relaxes, when the advancing constriction wave expels it into
the intestine. With its expulsion room is afforded for an additional
quantity of food, and hence there is a general advance of the food
mass toward the pylorus.

DIGESTION.

193

Though these observations were made on the cat, evidence is
accumulating which goes to show that in human beings the walls
of the stomach exhibit constriction waves which are similar in all
respects to those above described.

The Nerve Mechanism of the Stomach. — The movements
of the stomach are to some extent independent of the nervous system,
though they are coordinated and regulated by it. The isolated
stomach of the dog and of other animals as well, if kept warm and
moist, will exliibit rhythmic peristaltic movements for a period var}--
ing from an hour to an hour and a half. Though nerve-cells and
fibers are present in the walls of the stomach, between the layers of
muscle-libers, it is not beheved that they are the immediate sources
of the stimulus to the contraction. The stimulus lies within the
muscle substance itself, and is therefore myogenic. When once
initiated, the contraction process propagates itself from fiber to
fiber. The stomach, however, receives nerve impulses from the
central nervous system by way of the vagi and the splanchnic nerves,
which determine the movements in accordance with the needs of
digestion. Experimentally it has been shown that the vagus is the
augmentor, the splanchnic the inhibitor, nerve of the stomach move-
ments. Experimentally it has been shown that stimulation of the
peripheral end of the divided vagus augments the vigor of the peris-
talsis of the pyloric region and at the same time increases the con-
traction of the sphincter pylori muscle. Stimulation of the peripheral
end of the divided splanchnic is followed by inhibition of the peris-
talsis and a loss of tone.

INTESTINAL DIGESTION.

The physical and chemic changes which the alimentary principles
undergo in the small intestine, and which collectively constitute in-
testinal digestion, are probably more important and complex than
those taking place in the stomach, for the food is, in this situation,
subjected to the solvent action of the pancreatic and intestinal juices,
as well as to the action of the bile, each of which exerts a transforming
influence on one or more substances and still further prepares them
for absorption into the blood.

To rightly appreciate the physiologic actions of the digestiAc
juices poured into the intestine the nature of the partially digested
food as it comes from the stomach must be kept in mind. This
consists of water, inorganic salts, acidified proteids, hemipeptones
and antipeptones, starch, maltose, liquefied fat, saccharose, lactose,
cellulose, and the indigestible portion of meats, cereals, and fruits.
Collectively they are known as chyme. As this acidified mass passes
through the duodenum its contained acids excite a reflex secretion
13

194 TEXT-BOOK OF PHYSIOLOGY.

and discharge of the intestinal fluids: e. g., pancreatic juice, bile,
and intestinal juice. Inasmuch as these fluids are alkaline in re-
action they exert a neutralizing and precipitating influence on vari-
ous constituents of the chyme. As soon as this has taken place,
gastric digestion ceases and those chemic changes are inaugurated
which eventuate in the transformation of all the remaining undigested
nutritive materials into absorbable and assimilable compounds which
cohectively constitute intestinal digestion.

THE SMALL INTESTINE.

The small intestine, in which this stage of digestion takes
place, is a convoluted tube, measuring about seven meters in length
and 3.5 cm. in diameter, and extending from the pyloric orifice of
the stomach to the beginning of the large intestine.

The intestine consists of four coats: viz., serous, muscular, sub-
mucous, and mucous.

The serous coat is the most external and is formed by a reflection
of the general peritoneal membrane.

The muscle coat, situated just beneath the former, surrounds
the entire intestine. It is composed of , non-striated fibers which are
more abundant and better developed in the upper than in the lower
portions of the intestine. The muscle coat consists of two layers
of fibers: (i) an external or longitudinal, and (2) an internal or
circular layer. The longitudinal fibers are most marked at that
border of the intestine free from peritoneal attachment, though they
form a thin layer all over the intestine. The circular fibers are much
more numerous, and completely encircle the intestine throughout
its entire extent.

The submucous coat consists of areolar tissue and serves to unite
the muscular with the mucous coat. A thin layer of muscle-fibers,
the muscularis mucosa, is placed on its inner surface.

The mucous coat is soft and velvety in appearance and covered
by a single layer of columnar epithelium. Its entire surface is covered
with small conical projections termed vilh. Throughout its entire
extent, with the exception of the lower portion of the ileum, the
mucous membrane presents a series of transverse folds — the valvulae
conniventes, or valves of Kirkring. These folds vary from one-
fourth to half an inch in width and extend one-half to two-thirds of
the distance around the interior of the bowel. Each valve consists
of two layers of the mucous membrane permanently united by fibrous
tissue. It is believed that the valves retard to some extent the pas-
sage of the food through the intestine and present a greater surface
for absorption.

Blood-vessels, Nerves, and Lymphatics. — The blood-vessels.

DIGESTION. 195

of the small intestine, which are very numerous, are derived mainly
from the superior mesenteric artery. After penetrating the intestinal
walls the smaller vessels ramify in the submucous coat and send
branches to the muscle and mucous coats, supplying all their struc-
tures with blood. After circulating through the capillary vessels the
blood is returned by small veins, which subsequently unite to form
the superior mesenteric vein, which, uniting with the splenic and gas-
tric veins, forms the portal vein. The nerves are derived from the
lower part of the solar plexus. The branches follow the blood-vessels
and become associated with two plexuses, one (Auerbach's) lying
between the muscle coats, the other (Mcissner's) lying in the sub-
mucous coat. The lymphatics, which originate in the mucous and
muscle coats, are very abundant. They unite to form those vessels
seen in the mesenter}- and empty into the thoracic duct.

Intestinal Glands. — The gland apparatus of the intestine by
which the intestinal juice is secreted consists of the duodenal (Brun-
ner's) and the intestinal (Lieberkiihn's) glands.

The duodenal glands are situated beneath the mucous membrane
and open by a short wide duct on its free surface. They are racemose
glands lined by nucleated epithelium. The secretion of these glands
is clear, shghtly viscid, and alkaline. Its chemic composition and
function are unknown.

The intestinal glands or follicles are distributed throughout the
entire mucous membrane in enormous numbers. They are formed
mainly by an inversion of the mucous membrane and hence open on
its free surface. Each tubule consists of a thin basement membrane
lined by a layer of spheric epithelial cells, some of which undergo
distention by mucin and become converted into mucous or goblet
cells. The epithelial secreting cells consist of granular protoplasm
containing a well-defined nucleus. The intestinal follicles constitute
the apparatus which secretes the chief portion of the intestinal juice.

Intestinal Juice.- — Owing to its admixture with other secretions
and to the profound disturbance of the digestive function, caused by
the establishment of intestinal fistulae, this fluid has rarely been ob-
tained in a state of purity or in quantities suflicient for accurate
analyses or for experimental purposes. Its physiologic properties
and functions are therefore imperfectly known. Various attempts
have been made by physiologists, by the employment of different
methods, to obtain this secretion. The method usually employed
is that of Thiry and Vella. This consists in dividing the intestine at
two places, about eight or ten inches apart, restoring the continuity
of the intestine, and then uniting the two ends of the resected portion
to the edges of two openings in the abdominal walls. The resected
portion, being supphed with blood-vessels and nerves, maintains its
nutrition and secretes a miore or less normal juice.

196

TEXT-BOOK OF PHYSIOLOGY.

When obtained from a dog under these circumstances the intes-
tinal juice is watery in consistence, slightly opalescent, light yellow in
color, alkaline in reaction, with a specific gravity of i.oio. Chemic
analysis reveals the presence of proteids, mucin, and sodium car-
bonate.

The intestinal juice obtained by Tubbey and Manning from a
small portion of the human intestine (ileum) was opalescent, occa-
sionally brownish in color, alkaline, and had a specific gravity of 1.006.
On the addition of hydrochloric acid, carbonic acid was given off,
showing the presence of carbonates. It contained proteids and

mucms.

PANCREAS.

The pancreas is a long flattened gland, situated deep in the
abdominal cavity, lying just behind the stomach. It measures from
six to eight inches in length, two and a half in breadth, and one in
thickness. It is usually divided into a head, body, and tail. The
head is directed to the right side and is embraced by the curved
portion of the duodenum; the tail is directed to the left side and
extends as far as the spleen (Fig. 81). The pancreas communicates

Pancreatic ducts. Common bile-duct

Tail.

Fig. 81. — Pancreas and Duodenum Removed from the Body and Seen from
Behind. The Gland is Cut to Show the Ducts. — {Landois and Stirling.)

with the intestine by means of a duct. This duct commences at the
tail and runs transversely through the body of the gland. As it
approaches the head of the gland it gradually increases in size until
it measures about one-tenth of an inch in diameter. It then curves
downward and forward and opens into the duodenum. In its course
through the gland it receives branches which enter it nearly at right
angles. The pancreas is richly supplied with blood-vessels and
nerves, the latter coming from the solar plexus.

Histologic Structure. — In its structure the pancreas resembles
the sahvary glands. It consists of a connective-tissue framework

DIGESTION.

197

which divides the gland tissue into lobules. Each lobule is com-
posed of a number of acini or alveoli, more or less elongated or
tubular in shape. Each acinus gives origin to a small duct which,
uniting with adjoining ducts, forms the lobular duct, which becomes
tributary to the main duct. The acinus is lined by a layer of cylin-
dric epithelial cells characterized by a difference in structure be-
tween the central and peripheral ends (Fig. 82). The central end,
that bordering the lumen of the acinus, is dark in appearance and
tilled with dark granules, while the peripheral end is clear and homo-
geneous. The relative depth of these two zones varies according to
the functional activity of the gland. During the intervals of digestion
the granular layer is very deep and occupies almost the entire cell;
after active digestion the granular layer is very narrow, while the

Fig. 82. — Section of Human Pan-
creas, INCLUDING Several Acini
and Two Ducts. The Cells
Present a Central Granular
AND A Peripheral Clear Zone.
— (Piersol.)

Fig. 83. — Section of Human Pan-
creas showing, a, a, Islands

OF LaNGERHANS, .AND b THE

Usual Acini. — (Piersol).

clear zone is largely increased in depth. The blood-vessels of the
pancreas are arranged around the acini in a manner similar to that
observed in the salivary glands. The ultimate terminations of the
nerves in the epithelium are probably by means of the usual end-tufts.

The Islands of Langerhans. — Throughout the body of the pan-
creas and especially in the outer extremity there are found between
and among the acini collections of globular cells arranged in the
form of rods or columns, separated from the acini and from one
another by layers of connective tissue in which ramify large tortuous
capillar)' blood-vessels. These columnar bodies, seen in cross-
section in Fig. ^T^, have been named, after their discoverer, the
islands of Langerhans.

Embryologic investigations have shown that these cells are

198 TEXT-BOOK OF PHYSIOLOGY.

outgrowths from the primitive acini, to which they remain attached
for some time by means of a foot-stalk. This subsequently becomes
constricted by the connective tissue and the cells become completely
detached. The cells then assume the columnar arrangement, after
which vascularization takes place.

From thie fact that complete extirpation of the pancreas as well as
its various diseases is followed by serious disturbances of the carbohy-
drate metabolism it has been suggested that the islands of Langerhans
have a function separate and distinct from that of the glandular portion
of the pancreas ; that they secrete a specific material which partakes of
the nature of an internal secretion which is absorbed by the blood
circulating around them and carried to different tissues. The effect
on the metabolism of the body which follows extirpation of the pan-
creas will be referred to in a subsequent chapter.

Pancreatic Juice. — The pancreatic juice may be obtained by
introducing a silver cannula, through an opening in the abdominal
wall, into the duct, and securing it by a ligature. In a short time
the juice flows from the distal end of the cannula, when it can
be collected. According to Bernard, normal juice can only be ob-
tained during the first twenty-four hours. The juice obtained from
a temporary fistula is clear, slightly opalescent, viscid, of a decidedly
alkaline reaction, and has a specific gravity in the dog of 1.040.
When cooled to 0° C, it assumes a gelatinous consistence. At 100° C.
it completely coagulates. When obtained from a permanent fistula,
the juice is watery and the solid constituents are very much diminished
in amount.

The chemic composition of the pancreatic juice of the dog as deter-
mined by Schmidt is as follows: water, 900.76; organic matter, 90.44;
inorganic salts, 8.80. Of the inorganic salts, sodium carbonate is
probably the most essential, as it is this salt which gives to the juice
its alkaline reaction.

Mode of Secretion. — The secretion of the juice is, in the rabbit
and dog at least, almost continuous during a period of twenty-four
hours after a single average meal, though the rate of flow varies con-
siderably during this period. As soon as food enters the stomach
the flow of the pancreatic juice begins and steadily increases in
amount until about the third hour, when it reaches its maximum;
after this period the flow diminishes until the sixth hour, when it
again increases for about an hour. It then gradually diminishes
until it ceases entirely. During the period of secretory activity the
gland becomes red and vascular from a dilatation of the blood-vessels.

The discharge of the juice associated with the introduction of
food into the stomach is brought about in all probability through
the agency of the nervous system, though the exact mechanism is
imperfectly understood. It is probable that impressions made on

DIGESTION.

199

the terminal filaments of the pncumogastric nerve ascend to the
medulla, whence impulses pass outward through vaso-motor and
secretory nerves to the blood-vessels and secreting cells of the glands.
Stimulation of the peripheral end of the divided vagus gives rise to
increased secretion. Inasmuch as various agents, such as mineral
and organic acids, placed on the duodenal mucous membrane excite
the flow, it is cpiite probable that the passage of the acid contents of
the stomach through the duodenum also acts as a powerful stimulus
to the secretion and discharge of the juice. According to Bayliss
and Starling, the secretory activity of the pancreas is initiated and
maintained by the action of a specific substance to which they have
given the term secretin. This substance is developed in the duo-
denal glands in consequence of the action of the acids in the chyme
and then carried by the blood-stream to the pancreas. The total
amount of pancreatic juice secreted in twenty-four hours has been
only approximately determined; the estimates based upon the amount
obtained from dogs vary from 175 to 800 grams.

Histologic Changes in the Cells during Secretory Activity. —
Reference has already been made to the fact that the cells lining the
acini consist of two
zones: an outer one,
clear and homogene-
ous; and an inner
one, dark and granu-
lar. The position of
the nucleus of the cell
varies, being at one
time in the outer, at
another time in the
inner, zone. If the
pancreas be examined
microscopically dur-
ing the intervals of
digestion, it will be
observed that the
inner zone is broad,
highly granular, oc-
cupying nearly the
entire cell, while the
outer zone is narrow

and clear. If, however, the gland be examined shortly after a
period of active secretion, the reverse conditions will be observed;
that is, the inner zone will be narrow, containing relatively few
granules, while the outer zone will be clear and wide. This
change in the cell has been witnessed in the pancreas of the living

Fig. 84. — One Saccule of the Pancreas of the
Rabbit in Different States of Activity. A.
After a period of rest, in which case the outlines
of the cells are indistinct and the inner zone —
/. e., the part of the cells (a) next the lumen (c) —
is broad and filled with fine granules. B. After
the gland has poured out its secretion, when the
cell outhnes {d) are clearer, the granular zone (a)
is smaller, and the clear outer zone is wider.- —
{Yeo's "Text-book of Physiology," after Kuhne
and Lea.)

200 TEXT-BOOK OF PHYSIOLOGY.

animal — rabbit — by Kiihne and Lea. They observed that as soon
as digestion set in, the granules of the broad inner zone began to
pass toward the lumen of the acinus and to gradually disappear as
the secretion was poured out, while the outer zone increased in
width until almost the entire cell became clear and homogeneous.
(See Fig. 84.) After secretion ceased the granules again made their
appearance, the result, in all probability, of metabohc activity.

Physiologic Action of Pancreatic Juice. — Experimental in-
vestigations have demonstrated the fact that pancreatic juice is the
most complex in its physiologic action of all the digestive fluids. In
virtue of its contained enzymes, pancreatic juice acts :

1. On starch. When normal pancreatic juice or a glycerin
extract of the gland is added to a solution of hydrated starch, the
latter is speedily transformed into maltose, passing through the inter-
mediate stage of dextrin. The process is in all respects similar to
that observed in the digestion of starch by saHva. Pancreatic juice,
however, is more energetic in this respect than sahva. The enzyme
which effects this change is termed amylofsin. When the starch
which escapes salivary digestion passes into the small intestine and
mingles with pancreatic juice, it is very promptly converted into
maltose by the action or in the presence of this enzyme.

2. On proteid. When proteid bodies are subjected to the action
of pancreatic juice, they are transformed into peptones which do not
differ in essential respects from those formed by gastric juice. The
intermediate stages, however, are believed to be somewhat different.
The enzyme which effects this change is termed trypsin.

When fibrin, for example, is added to trypsin in a solution rendered
alkaHne by sodium carbonate, it does not swell up and become trans-
lucent, as it does when treated with hydrochloric acid and pepsin.
On the contrary, it becomes corroded on the surface, fragile, and in a
short time vmdergoes solution. The first product is a compound
termed alkah-albumin. After solution has taken place, various chemic
changes are initiated which eventuate in the production of peptone and
certain nitrogenized bodies, leucin, tyrosin, aspartic acid, etc. The
intermediate stages in this process have not been satisfactorily deter-
mined. At no time during artificial pancreatic digestion is there any
evidence of the presence of the primary proteoses (proto-albumose
and hetero-albumose). The secondary proteoses (deutero-albumose)
are usually present. It will be recalled that when the amphopeptone
of peptic digestion is subjected to the action of trypsin a portion of it,
approximately one-half, is decomposed into leucin and tyrosin, while
the remaining half retains its peptone characteristics. This latter
portion is termed antipeptone; the former portion is termed hemi-
peptone, though it has never yet been isolated and is therefore only
a hypothetic compound.

DIGESTION. 201

Inasmuch as during pancreatic digestion antipeptone is present
as well as leucin and tyrosin, it is believed by some investigators that
both antipeptone and hemipeptone are formed from the deutero-
albumose, the latter speedily undergoing decomposition. This view
is illustrated in the following scheme :

Proteid
Alkali-albumin
Deutero-proteose or deutero-albumose

Anti-peptone Hemipeptone

Leucin Tyrosin Aspartic acid, etc.

When the proteids which have escaped digestion in the stomach
pass into the small intestine and mingle with the pancreatic juice,
they are doubtless digested in the course of the intestinal canal,
passing through the stages just described. As leucin and tyrosin are
found in the intestine during digestion, it is probable that a portion
of the peptone undergoes decomposition into these bodies; but as
to the extent to which this takes place or in how far it is a necessary
process under normal conditions, nothing definite can be said. It is
probable that it takes place when there is an excess of proteid food
or when for any reason digestion is prolonged or absorption is delayed.

3. On fat. If pancreatic juice be added to a perfectly neutral
fat — olein, palmitin, or stearin — and kept at a temperature of about
100° F. (38° C), it will at the end of an hour or two be partially de-
composed into glycerin and the particular fatty acid indicated by
the name of the fat used — e. g., oleic, palmitic, stearic. The oil will
then exhibit an acid reaction. The reaction is represented in the
following formula :

C3H5(C,8H330,)3 + 3H20 = (C,sH3,0,)3 + CsHsCHO),
Triolein. Water. Oleic Acid. Glycerin.

If to this acidified oil there be added an alkah, e. g., potassium or
sodium carbonate, the latter will at once combine with the fatty acid
to form a salt known as a soap. The reaction is expressed in the
following equation :

Sodium Carbonate. Oleic Acid. Sodium Oleate. Carbonic Acid.

NajCOj -i- C,8H3402 = NajOCisHajOa 4- HoCOj

Coincident with the formation of the soap the remaining neutral oil
undergoes division into drops of microscopic size, which float in the
soap solution, forming what has been termed an emulsion, which is
white and creamy in appearance. The action of the pancreatic juice

202 TEXT-BOOK OF PHYSIOLOGY.

may then be said to consist in the cleavage of the neutral fats into
fatty acids and glycerin, after which the formation of the soap and
the division of the fat takes place spontaneously. The enzyme
which produces the cleavage of the neutral fats has been termed
steapsin. The extent to which the cleavage of the fat takes place in
the intestine has not been definitely determined. There are some
who think the amount is relatively small, while others consider that
it is large, practically all of the fat undergoing this decomposition,
with the formation of soap and glycerin prior to their absorption.

According to Pawlow, the relative amounts of the pancreatic
enzymes produced are conditioned by the character and amounts
of the food principles consumed. Thus, if chyme contains an ex-
cess of either starch, proteid, or fat, there is a corresponding increase
in the amount of either amylopsin, trypsin, or steapsin produced.
The pancreas apparently adapts its activities to the character of
the food. Though it is probable that each enzyme is a derivative
of a special zymogen, it is only positively known that this is the case
with trypsin. This enzyme is a derivative of the zymogen, trypsin-
ogen. The pancreatic juice at the moment of its discharge into
the intestine does not contain trypsin but trypsinogen. The trans-
formation of the latter into the former is accomphshed, according
to Pawlow, by a special ferment secreted by the epithelium of the
small intestine and termed enterokinase.

The rapidity with which pancreatic juice in the presence of bile
and hydrochloric acid (under conditions such as are present in the
duodenum) can develop sufficient fatty acid to form an emulsion was
determxined by Rachford to be two minutes. The activity of steapsin
is thus shown to be very great.

Physiologic Action of the Intestinal Juice. ^ — The part played
by the intestinal juice in the digestive process is yet a subject of dis-
cussion, as the results obtained by different observers are in some
respects contradictory, due to the fact that animals, including hpman
beings, have been the subjects of experimentation. Notwithstanding
the actions of saliva, gastric and pancreatic juice, there yet remain
in the food saccharose, maltose, and lactose, three forms of sugar
which are believed by most observers to be non-assimilable and
therefore require some change before they can be absorbed and
assimilated. An extract of the intestinal mucous membrane or the
intestinal juice of a dog, added to a solution of saccharose, will in a
very short time convert it into dextrose and levulose, which together
constitute invert sugar. The enzyme by which this inversion is
produced, though nothing definite is known as to its nature, has been
termed inverlin. Tubbey and Manning state that the human intes-
tinal juice as obtained by them has the same action. In the case
of intestinal fistulae reported by Busch, which were supposed to be

DIGESTION. 203

located in the upper third of the intestine, it was found that when
saccharose was introduced into the lower opening, it was not inverted
but appeared in the feces unchanged.

Maltose is also rapidly transformed into dextrose. Lactose
appears to be unaffected by the pure juice. As it is non-assimilable
it has been supposed to undergo conversion into dextrose while pass-
ing through the epithelial cells of the intestinal mucosa.

Intestinal juice also has a slight diastatic action on starch.

THE LIVER.

The liver is a highly vascular conglomerate gland situated in
the right hypochondriac region and connected with the intestine by
a duct.

Inasmuch as the liver performs several functions related to both
secretion and excretion, a consideration of its structure and its vari-
ous functions will be deferred to a subsequent chapter. In this
connection the bile, its physical properties and chemic composition
in relation to the digestive process, will only be considered.

The bile is a product of the secretory activity of the liver cells.
As it is poured into the intestine in man and most mammals at
a point corresponding to the orifice of the pancreatic duct, and most
abundantly at the time the food is passing through the duodenum,
it is usually regarded as a digestive fluid possessing an influence
favorable if not necessarv^ to the completion of the general digestive
process.

Anatomic Relations of the Biliary Passages. — After its forma-
tion by the liver cells the bile is conveyed from the liver by the bile
capillaries, which uniting finally form the main hepatic duct. This
duct emerges from the liver at the transverse fissure. At a distance
of about 5 centimeters it is joined by the cystic duct, the distal ex-
tremity of which expands into a pear-shaped reservoir, the gall-
bladder, in which the bile is temporarily stored (Fig. 85). The duct
formed by the union of the hepatic and cystic ducts, the common
bile-duct, passes downward and forward for a distance of about 7
centimeters, pierces the walls of the intestine and passes obhquely
through its coats for about a centimeter and opens on the surface of
a papilla in conjunction with the pancreatic duct. Near its termina-
tion it presents a sphincter- like constriction. The walls of the biliary
passages are composed of a mucous membrane internally, a fibrous
and muscular coat externally. Small racemose glands are embedded
in the mucous membrane of the main ducts.

Physical Properties and Chemic Composition of Bile. — The
bile obtained directly from the liver through a fistulous opening in
the hepatic duct is always thin and watery, while that obtained from

204

TEXT-BOOK OF PHYSIOLOGY.

the gall-bladder ^s more or less viscid from admixture with mucin,
the degree of this viscidity depending on the length of time it remains
in this reservoir. The specific gravity of human bile varies within
normal limits from i.oio to 1.020. The reaction is invariably alka-
line in the human subject when first discharged from the liver, but
may become neutral in the gall-bladder. The alkalinity depends
on the presence of sodium carbonate and sodium phosphate. When
fresh, it is inodorous; but it readily undergoes putrefactive changes,
and soon becomes offensive. Its taste is decidedly bitter. When

•20 12 19

21 22

Fig. 85. — Gall-bladder, Hepatic, Cystic, and Common Ducts, i, 2, 3. Duode-
num. 4, 4, 5, 6, 7, 7. 8. Pancreas and pancreatic ducts. 9, 10, 11, 12, 13. Liver.
14. Gall-bladder. 15. Hepatic duct. 16. Cystic duct. 17. Common duct. 18.
Portal vein. ig. Branch from the cehac a.xis. 20. Hepatic artery. 21. Coro-
nary artery of the stomach. 22. Cardiac portion of the stomach. 23. Splenic
artery. 24. Spleen. 25. Left kidney. 26. Right kidney. 27. Superior mesen-
teric artery and vein. 28. Inferior vena cava. — {Sappey')

shaken with water, it becomes frothy — a condition which lasts for
some time and which is due to the presence of mucin.

The color of bile obtained from the hepatic duct is variable,
usually a shade between a greenish-yellow and a brownish-red. In
different animals the color varies. In the herbivorous animals it is
usually green; in the carnivorous animals it is orange or brown. In
man it is green or a golden yellow. The colors are due to the pres-
ence of pigments. Microscopic examination does not show the
presence of structural elements.

DIGESTION. 205

Human bile obtained from an accidental biliary listula was shown
by Jacobson to contain the following ingredients, viz. :

COMPOSITION OF HUMAN BILE.

Water. 977-40

Sodium glycocholate, 9.94

Cholesterin, 0.54

Free fat, o.io

Sodium palmitate and stearate, 1.36

Lecithin, 0.04

Other organic matters, 2.26

Sodium chlorid, 5.45

Potassium chlorid, 0.28

Sodium phosphate, 1.33

Calcium phosphate, 0.37

Sodium carbonate, 0.93

1000.00

In this analysis the soHd ingredients constitute 22.5 parts per 1000,
of which two-thirds are organic and one-third inorganic. The
amount of soHds varies according to the animal from which the bile
is obtained.

Sodium Glycocholate and Taurocholate. — Of the various in-
gredients of the bile none are more important than these two salts,
usually known as the bile salts. The sodium glycocholate is found
most abundantly in the bile of herbivora, the sodium taurocholate
in the bile of the carnivora. These salts are compounds of sodium
and glycocholic and taurocholic acids. When separated from the
sodium, the acids will crystallize in the form of fine acicular needles.
Under the influence of hydrating agents, such as dilute acids and
alkalies, both acids will undergo cleavage into their respective com-
ponents— e. g., glycocoll and cholalic acid, taurine and cholalic acid.
Glycocoll and taurine are crystallizable nitrogenized compounds
known chemically as amido-acetic and amido-isothionic acids re-
spectively. The bile salts are produced in the liver by a true act
of secretion, as they are not found in any of the tissues and fluids of
the body. After being discharged into the intestine they undergo
chemic changes, after which they can no longer be recognized. In
all probability they are reabsorbed into the blood and play some
ulterior part in the nutrition of the body.

Cholesterin. — Cholesterin is a constant ingredient of bile, though
it is not confined to this fluid, as its presence has been determined in
the cr}^stalline lens, blood-corpuscles, nerve-tissue, and various patho-
logic fluids. It is an organic non-nitrogenized substance resembling
the fats in some particulars, but differing from them in not being
capable of saponification with alkalies. It presents itself in the form
of thin transparent rectangular crystals, insoluble in water but soluble

2o6 TEXT-BOOK OF PHYSIOLOGY.

in ether and boiling alcohol (Fig. 86). It is held in solution in bile by
the bile salts. If they are deficient in amount, the cholesterin may
pass out of solution, collect around some foreign matter, and form
a gall-stone. Cholesterin is a product of the metabolism largely of
nerve-tissue, from which it is absorbed by
the blood, carried to the liver, and excreted.
In the intestine it is converted into stercorin
and discharged from the body in the feces.

Bilirubin, Biliverdin. — These two pig-
ments impart to the bile its red and green
colors respectively. Bihrubin is present in
the bile of human beings and the carnivora,
^'"chv7t?.1-(W»^ biliverdin in the bile of the herbivora. As
and Stirling.) the former pigment readily undergoes oxi-

dation in the gall-bladder, giving rise to the
latter pigment, almost any specimen of bile may present any shade of
color between red and green. Bilirubin is regarded as a derivative
of hematin, one of the cleavage products of hemoglobin, the coloring-
matter of the blood. In the liver the hematin combines with water,
loses its iron, and is changed to bilirubin. By continuous oxidation
there are formed biliverdin, bilicyanin, and choletelin. After their
discharge into the intestine the bile pigments are finally reduced to
hydrobihrubin, which becomes one of the constituents of the feces.
An oxidation of the bihrubin can be produced by nitroso-nitric acid.
If this agent is added to a thin layer of bile on a porcelain surface,
a series of colors will rapidly succeed one another, commencing with
green and passing to blue, orange, purple, and yellow. This is the
basis of the well-known test for bile pigments suggested by Gmehn.

Lecithin is one of the products of the metaboHsm of nerve-tissue.
It is removed from the blood by the liver cells and thus becomes one
of the constituents of the bile, in which it is held in solution by the
bile salts.

Mode of Secretion of Bile. — The manner in which the bile
flows from the liver into the main hepatic ducts, the variations in the
rate of its discharge into the intestine, as well as the total quantity
secreted daily, have been approximately determined by fistulous
openings either in the hepatic ducts or in the gall-bladder. Although
the liver presents some physiologic peculiarities, there is no reason
to beheve that the conditions of secretion therein are different from
those in any other secretory organ, or that any other structure than
the cell is engaged in this process. As shown by chemic analysis,
the bile consists of compounds, some of which, like the bile salts,
are formed in the liver cells out of material furnished by the blood,
by a true act of secretion, while others, such as cholesterin and lecithin,
principles of waste, are merely excreted from the blood to be finally

DIGESTION. 207

eliminated from the body. The bile is thus a compound of both
secretory and excretory principles.

The flow of bile from the liver is continuous but subject to con-
siderable variation during the twenty-four hours. The introduction
of food into the stomach at once causes a slight increase in the flow,
but it is not until about two hours later that the amount secreted
reaches its maximum; after this period it gradually decreases up to
the eighth hour, but never entirely ceases. During the intervals of
digestion though a small quantity passes into the intestine, the main
portion is diverted into the gall-bladder, where it is retained until
required for digestive purposes. When acidulated food passes over
the surface of the duodenum there is excited, through reflex action,
a contraction of the muscular walls of the gall-bladder and ducts and
a gush of bile into the intestine, the discharge continuing intermit-
tently until digestion ceases and the intestine is emptied of its con-
tents.

The total quantity of bile secreted daily has been estimated to be
from 500 to 800 grams.

Physiologic Action of Bile. — Notwithstanding our knowledge
of the complex composition of bile, the quantity discharged daily, and
the time and place of its discharge, its exact relation to the digestive
process has not been fully determined. No specific action can be
attributed to it. It has but a shght, if any, diastatic action on starch.
It is without influence on proteids. By virtue of the bile salts it con-
tains, it hastens the action of pancreatic juice in splitting neutral oils
into fatty acids and glycerin, and in this way aids in their digestion.
The bile salts also dissolve insoluble soaps, which may be formed
during digestion.

Bile favors the digestion of fat. If it be excluded from the intes-
tine there is found in the feces from 22 to 58 per cent, of the ingested
fats. At the same time the chyle, instead of presenting the usual
white creamy appearance, is thin and slightly yellow. The manner
in which the bile promotes fat digestion is yet a subject of investiga-
tion. If all the fat is converted into fatty acid and glycerin, with the
formation of soaps, as seems probable, the action of the bile becomes
more apparent from the fact, already stated, that it dissolves and
holds in solution the soaps so formed which would be necessary to
their absorption by the epithelial cells. As an aid to digestion the
bile has been regarded as important, for the reason that its entrance
into the intestine is attended by a neutralization and precipitation of
the proteids which have not been fully digested and are yet in the
stage of acid-albumin. In this way gastric digestion is arrested and
the foods are prepared for intestinal digestion.

Though bile possesses no antiseptic properties outside the body,
itself undergoing putrefactive changes very rapidly, it has been

2o8 TEXT-BOOK OF PHYSIOLOGY.

believed that in the intestine it in some way prevents or retards putre-
factive changes in the food. There can be no doubt that if the bile
be prevented from entering the intestine there is an increase in the
formation of gases and other products which impart to the feces
certain characteristics which are indicative of putrefaction. As to
the manner in which bile retards this process nothing definite can be
stated.

Bile has been supposed to be a stimulant to the peristaltic move-
ments of the intestine, inasmuch as these movements diminish when
bile is diverted from the intestine.

Though no definite nor specific action on any of the different
classes of food principles can be attributed to the bile, there is abun-
dant evidence to show that its presence in the ahmentary canal during
digestion is essential to the maintenance of the nutrition of the body.
That the bile as a whole, or at least part of its constituents, favorably
influences digestion and general nutrition is evident from the
phenomena which follow its total exclusion from the intestine, as
when the common bile-duct is Hgated and a fistula of the gall-bladder
is established. The following phenomena were observed in a young
dog so prepared by Professor FHnt. During the first five days
succeeding the operation the abdomen was tumid and there was
some rumbhng in the bowels. Though the animal ate every day, the
discharge of fecal matter became infrequent, the matter passed being
grayish in color and highly offensive. After two weeks the alvine
discharges took place three and four times daily. For four days the
weight remained normal; afterward it began to diminish, and from
this time the animal continued to lose strength and weight until its
death, thirty-eight days after the operation. Ten days after the oper-
ation the appetite, which had been very good, increased, but did
not become ravenous until a few days before death. The animal
usually ate from a pound to a pound and a half of beef-heart daily,
always refusing fat. There was an absence at all times of jaundice,
fetor of the breath, and falling of the hair. Postmortem examination
showed that the bile-duct was obliterated, and there was no evidence
that any bile could have passed into the intestine. The results of this
and similar cases go to show that that portion of the bile which is
secretory in character is essential to digestion and the nutrition of
the body — that, though large quantities of food are consumed, pro-
gressive diminution of weight takes place until nearly 40 per cent, of
the body is consumed. In some instances the breath becomes fetid
and there is a falling of the hair, showing some profound disturbance
of the general nutritive process.

Intestinal Peristalsis. — During digestion the walls of the in-
testine exhibit a scries of contractions which, beginning at the pylorus,
run along the canal to its termination in the large intestine. These

DIGESTION. 209

contractions, known as the vermicular or peristaltic, are extremely
slow, creeping along the canal in a progressive manner from above
downward. The peristalsis is produced by the contraction of both
the circular and longitudinal muscle-fibers. By the contraction
of the former the caliber of the canal is constricted behind a portion
of the food, and as the wave of constriction advances it carries the
food with it. At the same time, the longitudinal fibers contracting,
the segment of the canal is shortened and drawn up over the ad-
vancing portion of the food. The result of these movements is to
push the food through the canal, to turn it over and to incorporate
the digestive fluids with it.

Though the general movement of the intestinal contents is gradu-
ally downward, Cannon has shown that the result of the peristaltic
movements is to divide the mass into segments, and that the mere
presence of a segment in the lumen of the intestine seems to excite the
overlying circular fibers to activity in such a way that each segment is
again divided. The lower half of each segment then unites with the
upper half of the segment below, to commingle with it and to expose
new surfaces of the food mass to contact with the actively absorbing
mucosa. A continual repetition of this process results in a thorough
mixing of the food with the digestive juices and materially aids the
process of absorption.

Influence of the Nervous System. — The peristaltic movements
of the small intestine, though independent of the central nervous
system, are nevertheless at times largely influenced by it. Stimu-
lation of the vagus nerve generally increases the vigor of the contrac-
tion; stimulation of splanchnic nerves inhibits or diminishes the
contraction. These nerve pathways serve to transmit to the intestinal
walls nerve impulses, which increase or diminish the force and extent
of their contractions.

An excised portion of intestine (removed from the body) will
exhibit rhythmic movements for some time. Stimulation either by
electric or chemic agencies will also develop contractions which will
be propagated in the usual direction. As to the manner in which
the contraction wave is propagated to adjoining fibers, practically
nothing is known. It may be connected with the nerve-fiber plexuses
(Meissner's and Auerbach's) in the walls of the intestine.

The Large Intestine. — The large intestine is that portion of the
alimentary canal situated between the termination of the ileum and
the anus. It varies in length from four and a half to five feet, in
diameter from one and a half to two and a half inches. It is divided
into the cecum, the colon (subdivided into an ascending, transverse,
and descending portion, including the sigmoid flexure), and the
rectum.

The cecum is situated in the right iliac fossa. It is that dilated
14

2ro TEXT-BOOK OF PHYSIOLOGY.

portion of the large intestine below the orifice of the small intestine.
The posterior and inner wall presents a small opening which leads
into a narrow round process about four inches in length — the vermi-
form appendix. The opening of the small intestine into the cecum is
narrow and elongated and bordered by two folds of mucous mem-
brane strengthened by fibrous and muscle-tissue. These folds
constitute the so-called ileo-cecal valve. When the cecum is dis-
tended the margins of these folds are approximated and effectually
prevent the return of material into the small intestine.

The colon ascends to the under surface of the liver, where it bends
at a right angle, crosses the abdominal cavity to the spleen, bends
again, and descends to the left ihac fossa. At this point it turns upon
itself to form the sigmoid flexure. The rectum is a dilated pouch,
situated within the true pelvis. It measures from 15 to 18 centi-
meters in length. Within an inch of its termination at the anus it
presents a constriction formed by a circular band of muscle-fibers
— the internal sphincter.

The walls of the large intestine consist of three coats: viz., serous,
muscular, and mucous.

The serous is a reflection of the general peritoneal membrane.

The muscular is composed of both longitudinal and circular
libers. The longitudinal fibers are collected into three narrow
bands which are situated at points equidistant from one another.
At the rectum they spread out so as to completely surround it. As
the longitudinal bands are shorter than the intestine itself, its surface
becomes sacculated, each sac being partially separated from adjoining
sacs by narrow constrictions. The circular fibers are arranged in
the form of a thin layer over the entire intestine. Between the sac-
cuh, however, they are more closely arranged. In the rectum they
are well developed, and at a point an inch above the anus they
form, as stated above, the internal sphincter.

The mucous membrane of the large intestine possesses neither
villi nor valvulae conniventes. It contains a large number of tubules
consisting of a basement membrane hned by columnar epithelium.
They resemble the foUicles of Lieberkiihn. The secretion of these
glands is thick and viscid and contains a large quantity of mucin.

Contents of the Large Intestine. — As a result of the actions
of sahva, of gastric, intestinal, and pancreatic juice, and of the bile,
the food is disintegrated and liquefied. The nutritive principles,
proteid, starches, sugars, and fats, undergo chemic changes and are
transformed into peptones, dextrose, soap and glycerin, fatty acids,
under which forms they are absorbed. After the absorption of these
nutritive substances the residue of the food, comprising the indigestible
and undigested matter, passes out of the small intestine into the large
intestine and forms a portion of its contents. This residue consists

DIGESTION. 211

of the hard parts of the cereals, vegetable seeds, cellulose, etc., the
quantity and variety of which depend on the nature of the food.
These substances, passing into the large intestine along with the
excrementitious matters of the bile, become incorporated with the
mucous secretions and assist in the formation of the feces. Under
the influence of a peristaltic movement similar to that witnessed in
the small intestine, all this excrementitious matter is deprived by
absorption of the excess of contained water and is gradually car-
ried downward to the sigmoid flexure, where it accumulates prior to
its extrusion from the body.

Intestinal Fermentation. — Owing to the favorable conditions
in the intestine for fermentative and putrefactive processes — e. g.,
heat, moisture, oxygen, and the presence of various microorganisms
— the food, when consumed in excessive quantity or when acted on
by defective secretions, undergoes a series of decomposition changes
which are attended by the production of gases and various chemic
compounds. Dextrose and maltose are partially reduced to lactic
acid; this to butyric acid, carbon dioxid, and hydrogen. Fats are
reduced to glycerol and fatty acids; the glycerol, according to the
organisms present, yields succinic acid, carbon dioxid, and hydrogen.
The proteids under the prolonged action of the pancreatic juice are
decomposed, with the production of leucin and tyrosin. These
crystalUne compounds are in turn reduced to simpler forms. The
former yields valerianic acid, ammonia, and carbon dioxid; the
latter gives rise to indol, which is the antecedent of indican, found in
the urine. Skatol, another derivative of the proteid molecule, due
to bacterial action, gives the characteristic odor to the feces.

Feces. — The feces consist of water, mucin, the indigestible resi-
due of the food, decomposition products, and inorganic salts. The
consistency of the fecal matter varies from fluid to semi-fluid, depend-
ing largely on the length of time it remains in the intestine and the
extent to which absorption of its watery portion has taken place. The
odor is due to the presence of sulphuretted hydrogen and skatol.
The color is due partly to the altered coloring-matter of the bile, hydro-
hilirubin or stercohilin, and partly to the character of the food. The
total quantity discharged daily varies from four to six ounces.

Defecation. — Defecation is the final act of the digestive process
and consists in the expulsion of the indigestible residue of the food
from the intestine. This act usually takes place in the human being
but once in twenty-four hours, as the diet contains but a minimum
quantity of indigestible matter. Previous to their expulsion the feces
which have accumulated in the sigmoid flexure must pass downward
into the rectum. In so doing they develop the sensation which leads
to the act of defecation. The descent of the feces is accompHshed by
the peristaltic contraction of the intestinal wafl. Coincident with the

212 TEXT-BOOK OF PHYSIOLOGY.

passage of the feces into the rectum there is a relaxation of the sphinc-
ter muscles and a contraction of the longitudinal and circular mus-
cular fibers, in consequence of which the feces are expelled. These
complex muscular actions are also aided by the voluntary contrac-
tions of the diaphragm and abdominal muscles.

Nerve Mechanism of Defecation. — The act of defecation is
primarily reflex, though somewhat influenced by voluntary efforts.
Under normal conditions the sphincter muscles governing the anal
orifice are firmly contracted, thus preventing the escape of gases or
semi-sohd matter. This tonic contraction is maintained by a nerve-
center located in the lumbar region of the spinal cord. This center
can be inhibited and the sphincter muscle relaxed, either reflexly, by
impressions made on the mucous membrane of the rectum, or directly,
by volitional impulses from the brain. When the desire to evacuate
the bowels is experienced, the impressions made by the feces on the
afferent nerves of the rectal mucous membrane develop nerve im-
pulses, which are transmitted to the rectal center and to the brain.
If the act of defecation is to take place, the inhibitory effect of the
rectal impulses is strengthened by volitional impulses descending
the cord, followed by a relaxation of the sphincter. At the same time
motor impulses are transmitted to the rectal and abdominal muscles,
which, cooperating, expel the rectal contents. If the act is to be
suppressed, the controlling influence of the rectal or sphincter center
is strengthened and the reflex mechanism for a while held in abey-
ance. The exact course of the afferent and efferent nerves concerned
in this reflex is yet a subject of investigation.

CHAPTER X.
ABSORPTION.

Absorption is the process by which nutritive material is trans-
ferred from the tissues, from the serous cavities, and from the mucous
surfaces of the body, into the blood. The most important of these
surfaces, especially in its relation to the formation of blood, is the
mucous surface of the alimentary canal, for it is from this organ that
the new materials are derived which maintain the quantity and
quality of the blood. The absorption of material from the inter-
stices of the tissues and from the serous cavities may be regarded as
an act of resorption, or a return to the blood of liquid nutritive material
which has escaped through the walls of the capillary blood-vessels
for purposes of nutrition, and which, if not returned, would lead to
an accumulation and the development of edematous conditions.

The anatomic mechanisms involved in the absorptive process
are, primarily, the tissue or lymph-spaces, the lymph- and blood-
capillaries; secondarily, the lymph-vessels and the veins.

Tissue or Lymph-spaces; Lymph-capillaries. — Everywhere
throughout the body, in the connective-tissue system and in the inter-
stices of the several structures of which an organ is composed, are
found spaces or clefts of irregular shape and size, determined largely
by the structure of the organ in which they are found, which have
been termed tissue oV lymph-spaces, from the fact that they contain
a clear fluid, lymph. These spaces are devoid for the most part of
any endothehal lining, but as they communicate more or less freely
one with another, there is a circulation of lymph through them and
around the islets of tissue (Fig. 87). In addition to the connective-
tissue lymph-spaces, different observers have described special spaces
or clefts in organs such as the kidney, Hver, spleen, testicle, and in
all secreting glands between their basement membrane and the sur-
rounding blood-vessels, all of which contain a greater or less quan-
tity of lymph. Within the brain, spinal cord, bone, and other tissues
it has been shown that the smallest blood-vessels and capillaries are
bounded and limited by a cyhndrical sheath containing lymph, which
is known as a perivascular lymph-space. A similar sheath surrounds
the smallest nerve-bundles and fibers, enclosing a perineural lymph-
space. The large serous cavities of the body, pleural, peritoneal,
pericardial, etc., are also to be regarded as lymph-spaces. The sur-
faces of these cavities, however, are covered with a layer of endo-

213

214

TEXT-BOOK OF PHYSIOLOGY.

thelial cells with sinuous margins. At intervals between these cells
are to be found small free openings which have received the name
of stomata.

The lymph-capillaries in which the lymph-vessels proper
take their origin are arranged in the form of plexuses of quite irreg-
ular shape. In most situations they are intimately interwoven
with the blood-vessels, from which they can be readily distinguished
by their larger caliber and irregular expansions. The wall of the
lymph-capillary is formed by a single layer of endothelial cells
with characteristic sinuous outlines. These capillaries anastomose

very freely one with an-
other and communicate,
on the one hand, with
the lymph-spaces and
on the other with the
lymph - vessels proper.
As the shape, size, etc.,
of both lymph - spaces
and capillaries are de-
termined largely by the
nature of the tissue in
which they are found, it
is not always possible to
separate one from the
other. Their function,
however, may be re-
garded as similar: viz.,
the reception and collec-
tion of the lymph which
has transuded through
the walls of the blood-
vessels and its transmis-
sion onward into the
regular lymph- vessels.
The blood-capilla-
ries not only permit of a transudation of the liquid nutritive material
from the blood through their delicate walls, but are also engaged, if
not in the reabsorption of a portion of this transudate, at least in the
absorption of waste products resulting from tissue metabolism.

Lymph-vessels. — The lymph-vessels constitute a system of
minute, delicate, transparent vessels found in nearly all the organs
and tissues of the body, and take their origin from the lymph-
capillaries and spaces above described. From their origin they
gradually converge toward the trunk of the body, and finally empty
into the thoracic duct. In their course they anastomose very

Fig. 87. — Origin of Lymphatics from the Cen-
tral Tendon of the Diaphragm Stained
with Nitrate of Silver, s. The lymph-
spaces and lymph-canals, communicating at x
with the lymphatics, a. Origin of the lym-
phatics by the confluence of several juice
canals. B. Capillary blood-vessel. — {Landois
and Stirling.)

ABSORPTION.

2'5

freely with adjoining vessels. The diameter of a lymph-vessel
varies from i to 2 mm. After the lymphatics have emerged from
the lymph-capillaries they acquire three distinct coats, each of which
possesses definite histologic features.

The internal coat is composed of a delicate lamina of longitudinally
disposed elastic fibers covered with a layer of flattened nucleated
endothelial cells with wavy outlines.

The middle coat consists of white fibrous tissue arranged longi-

FiG. 88. — Lymph-\ EssELs AND Lymph-glands of the Head and Neck. — {From
Gould's Dictionary.)

tudinally and of non-striated muscle and elastic fibers arranged
transversely.

The external coat consists of practically the same structures, though
the muscle-fibers are longitudinally disposed.

The lymphatics are provided with valves which are so numerous
and located at such short intervals as to give the vessels a beaded
appearance. These valves are arranged in pairs and consist of two
semilunar folds with their concavities directed toward the larger
vessels. They are formed by a reduplication of the lining membrane,

2l6

TEXT-BOOK OF PHYSIOLOGY.

which is strengthened by fibrous tissue derived from the middle

coat.

Lymph-glands. — In their course toward the thoracic duct the

lymph-vessels pass through a num-
ber of small lenticular bodies
termed lymph-glands. These are
exceedingly abundant in some situ-
ations, as the cervical, axillary, and
inguinal regions, and the abdominal
cavity. As the lymph-vessels ap-
proach a gland they divide into a
number of branches before entering
it, known as the ailerent vessels.
From the opposite side of the gland
the lymphatics again emerge as
efferent vessels to unite to form
larger trunks. A section of a gland
shows that it consists of an outer
dense cortical and an inner soft
pulpy medullary portion. Each
gland is covered externally by a
dense membrane of fibrous tissue
containing in its meshes non-stri-
ated muscle-fibers. From the inner
surface of this membrane there pass
inward septa of connective tissue
which, as they converge toward the
center of the gland, divide the outer
zone of the gland into small conical
compartments or alveoli. When the
septa reach the medullary portion,
they subdivide and form bands or
cords which interlace in every direc-
tion and constitute a loose mesh-
work the spaces of which communi-
cate with one another and with the
alveoli (Fig. 90). Within the meshes
of this framework the proper gland
substance is contained. In the cor-
tical compartments it is moulded
into pear-shaped masses; in the
medullary meshwork it assumes

the form of rounded cords which are connected with one another.

In both regions, however, it is separated from the septa by a space

termed a lymph sinus, through which the lymph flows as it passes

.:^

%K

Fig.

. — Lymph-vessei.s
Arm. — {Deaver.)

ABSORPTION.

217

through the gland. The lymph sinus is crossed by a network of
retiform connective tissue which offers considerable resistance to
the passage of the lymph. The gland substance consists also of a
framework of retiform connective tissue in the meshes of which large
numbers of lymph-corpuscles are contained. The gland substance
is separated from the lymph sinus by a dense layer of a reticulum,
which, however, does not prevent lymph and even corpuscles from
passing through it into the lymph sinus.

The lymph-glands are abundantly suppHed with blood-vessels.
The arteries enter the gland at the hilum, penetrate into the medullary
substance, and terminate in a fine capillary plexus which is supported
bv the connective tissue. The veins arising from this plexus leave
the gland also at the hilum.

Fio. Qo. — Diagrammatic Section of a Lymph-gland, a. /., Afferent, e. I., efferent
lymphatics. C. Cortical substance. M. Reticular cords of medulla. /. s. L3'mph
sinus, c. Capsule, with trabecule, /r. — {Landois and Stirling.)

The lymph-vessels which enter a gland first ramify in the in-
vesting membrane and then open directly into the lymph sinus.
The vessels which leave the gland are also in communication with
the sinus. After the lymphatics enter the gland they lose their
external and middle coats, retaining only the internal or endothehal
coat, which lines the inner surface of the lymph sinus. The current
of lymph, therefore, is from the afferent vessels through the lymph
sinus into the eft'erent vessels. In addition to this primary current,
there is a secondary current flowing from the capillar}^ blood-vessels
outward and into the sinus, which carries with it large numbers of
lymph-corpuscles. It is quite probable that the movement of the

2i8 TEXT-BOOK OF PHYSIOLOGY.

lymph through this compHcated system of passages is aided by'jithe
contraction of the muscle-fibers in the capsule of the gland.

The lymph- corpuscles or lymphocytes originate for the most part
in the gland substance of the cortical alveoli. In this situation there

Fig. 91. — Diagram showing the Course of the Main Trunks of the Absorbent
System. The lymphatics of lower extremities (D) meet the lacteals of intestines
(LAC) at the receptaculum chyli (RC), where the thoracic duct begins. The
superficial vessels are shown in the diagram on the right arm and leg (S), and
the deeper ones on the arm to the left (D). The glands are here and there shown
in groups. The small right duct opens into the veins on the right side. The
thoracic duct opens into the union of the great veins of the left side of the neck
(T). — {Yeo's "Text-book of Physiology.")

are groups of cells, so-called germ centers, which divide very rapidly
by mitosis and give rise constantly to groups of young cells v^hich
soon find their way into the lymph stream.

The Thoracic Duct. — The thoracic duct is the ereneral trunk of

ABSORPTION. 219

the lymph system, into which the vessels of the lower extremities,
of the abdominal organs, of the trunk, of the left arm, and of the left
side of the head empty their contents. It is about twenty inches in
length and an eighth of an inch in diameter. It extends upward
from the third lumbar vertebra along the vertebral column to the
seventh cervical vertebra, where it empties into the venous system
at the junction 0} the internal jugular and subclavian veins on the left
side. The thoracic duct wall has the same general structure as the
wall of the lymph-vessel: viz., an internal or endothelial; a middle
elastic and muscular; an external or fibrous. It is also provided
with numerous valves.

The lymph-vessels of the right side of the head, of the right arm,
and a portion of the right side of the trunk terminate in the right
thoracic duct, which is about 25 to 30 mm. in length and which emp-
ties into the venous system at the junction of the internal jugular and
subclavian veins on the right side. The general arrangement of the
lymphatic system is diagrammatically shown in Fig. 91.

LYMPH.

Properties of Lymph. — The lymph obtained from the thoracic
duct during the intervals of digestion or from one of the large trunks
of the leg is a clear, colorless or slightly opalescent fluid having an
alkaline reaction and a specific gravity of 1.020 to 1.040. Examined
microscopically it is seen to hold in suspension a large number of
corpuscles similar to those seen in the lymphatic glands and to the
white corpuscles of the blood. Their number has been estimated
at about 8200 per cubic millimeter, though this count will vary within
wide limits according as the lymph examined has passed through
a large or small number of glands. The lymph corpuscle consists of a
small cjuantity of protoplasm in which is embedded a distinct nucleus.
Some of these lymphocytes contain distinct granules, more or less
refractive, which impart to the corpuscle a distinctly granular ap-
pearance. When withdrawn from the vessels lymph undergoes a
spontaneous coagulation, though the coagulum is never as firm as
that observed in the coagulation of the blood. The cause of the
coagulation is the appearance of fibrin. After a variable length of
time the coagulum separates into a liquid and a solid portion, the
serum and the clot.

Chemic Composition. — Although the lymph obtained from the
tissue spaces, from the lymph-vessels, as well as from the so-called
serous cavities has the same general chemic characteristics, there is rea-
son for the view that it varies in its ultimate composition according
as it is derived from one region of the body or from another. The
needs of any individual tissue as well as the character of its metabolic

220 TEXT-BOOK OF PHYSIOLOGY.

products will in all probability not only change its normal composi-
tion, but also the relative amounts of its normal constituents.

Chemic analysis has shown that the lymph from the thoracic duct
contains from 3.4 to 4.1 per cent, of proteids (serum-albumin, fibrin-
ogen), 0.046 to 0.13 per cent, of substances soluble in ether (probably
fat), 0.1 per cent, of sugar, and from 0.8 to 0.9 per cent, of inorganic
salts, of which sodium chlorid (0.55 per cent.) and sodium carbonate
(0.24 per cent.) are the most abundant (Munk). There are usually
in most specimens small quantities of potassium, calcium, and mag-
nesium salts. Fibrinogen is seldom present beyond o.i per cent.,
which will account for the feeble and slow coagulation. Lymph
contains both free oxygen and carbon dioxid. Of the former, how-
ever, there is but a small percentage; of the latter, about 45 vols, per
cent., partially in the free state and partially combined with sodium.
Urea is also present in very small amounts. This analysis indicates
that lymph resembles blood-plasma in the character of its constitu-
ents, though their relative quantities vary considerably. With the
exception that it contains no red corpuscles, lymph may be regarded
as a diluted blood.

Production of Lymph. — Though blood is the common reser-
voir of nutritive material, the latter is not available for nutritive
purposes as long as it is confined within the blood-vessels. The
capillary wall, thin as it is, and composed of but a single layer of
endothelial cells, would be sufficient to prevent its utilization by the
tissues, if it were not permeable to the liquid portion of the blood.
As this is the case, however, it is found that as the blood flows
through the capillary vessels a portion of the blood-plasma passes
through the capillary wall and is received into the tissue spaces,
where it comes into intimate contact with the tissue-cells.

The forces concerned in the passage of the constituents of the
blood-plasma across the capillary wall have been the subject of much
investigation. According to some investigators, diffusion and filtra-
tion are sufficient to account for all the phenomena. It is assumed
that the capillary wall, being an animal membrane, is freely per-
meable to water and crystalloid bodies generally; less so, however,
to colloid bodies, such as the proteids of the blood-plasma; moreover,
that the physiologic conditions of the capillary walls are such as to
permit of a diffusion from the blood to the tissues and the reverse,
according to laws similar at least to those determining the passage
of substances through animal membranes as determined experiment-
ally. The force giving rise to filtration is the difference between the
pressure exerted by the blood within the capillary vessels and the
pressure exerted by the fluid in the tissue spaces, any increase or de-
crease of this pressure being attended by an Increase or decrease in
the production of lymph. Thus compression of the veins of a part

ABSORPTION. 221

which interferes with the outtlow of blood from the capillaries, or a
dilatation of the arterioles which increases the inflow of blood, will
increase both the capillar}' pressure and the production of lymph.
The reverse conditions will, of course, diminish lymph production.
Hemorrhages which lower the general blood-pressure may so lower
the capillary pressure as not only to stop the flow to the tissues, but
give rise to a diffusion current from the tissues into the blood.

The quantitative composition of the lymph compared with that
of the blood indicates that it is produced by diffusion and filtration.
In the lymph the concentration of the inorganic salts is practically
the same as in the blood ; the concentration of the proteids, however,
is somewhat less. These facts are in accordance with what is known
regarding the diffusibility of both crystalloids and colloids through
animal membranes.

According to other investigators, the production of lymph is not
so much due to intracapillary pressure as it is to the speciahzed
activities of the endothelial cells, activities which indicate that lymph
is a secretion the composition of which varies in different situations
in virtue of a difference in the molecular structure of the endothelial
cells. As is the case with many of the secreting cells of the body,
the injection of various substances into the blood apparently increases
the activity of the endothehal cells, as shown by an increased lymph
production without any appreciable increase of intracapillary pressure.
Thus it has been shown that after the injection into the blood of
sugar, sodium chlorid, sodium sulphate, urea, etc., there is an increase
in the flow of lymph from the thoracic duct. The lymph, however,
under these circumstances is richer in water than normally. As the
blood at the same time increases its percentage of water, it is
assumed that the water is extracted from the tissues, by reason of an
increased percentage of salts in the tissue spaces due to increased
activity of the endothelial cells. A higher percentage of salts in the
lymph than in the blood is difiicult to account for on the diffusion-
filtration theon,'. The injection of peptones, albumin, the extract
of the muscles of the leech, crab, mussel, etc., is also followed by an
increase in the amount of lymph discharged from the thoracic duct;
but in this instance the lymph possesses a higher degree of concen-
tration, being richer not only in inorganic but also organic constit-
uents. The cause of this increase in both the quantity and quahty
of the lymph is believed to be an increased activity in the secreting
power of the endothelial cells. It is possible that all these facts may
be otherwise interpreted; the subject is yet a matter of investigation.

Functions of Lymph. — The lymph, from its situation, its rela-
tion to the tissues, and its composition, must be regarded as the source
of the nutritive material from which the tissues derive those sub-
stances necessary for their growth and repair, as well as for the

222 TEXT-BOOK OF PHYSIOLOGY.

storage and liberation of energy. It may also be regarded as a
reservoir for the reception of all those compounds which arise from
tissue metabolism prior to their removal by the blood-vessels and
lymphatics.

Absorption of Lymph. — The production of lymph is apparently
a continuous process, and as a result there is more lymph passing
through the capillary vessels than is necessary for the immediate needs
of the tissues. Should this accumulate, there would arise the con-
dition of edema and an interference with the functional activity of
the tissues. As soon as a certain pressure arises in the tissue spaces
there is a movement of the lymph into the lymph- capillaries and
vessels toward the termination of the thoracic duct, where the pres-
sure is relatively low. In consequence of this difference in pressure
the lymph is withdrawn from the tissues.

It is quite possible under even normal conditions of pressure in
the tissue spaces that some of the more diffusible constituents of the
lymph should be absorbed by the capillary blood-vessels. As to
whether the relatively feebly diffusible colloids should be so resorbed
is as yet a matter of investigation.

ABSORPTION OF FOODS.

The most important of the absorbing surfaces, especially in its
relation to the absorption of new material, is the mucous membrane
of the alimentary canal, and more particularly that portion lining the
small intestine, provided as it is with specialized absorbing structures
— the villi. Though certain substances can be absorbed from the
mouth, it is not probable that any food is so absorbed. From the
changes which the food principles undergo in the stomach it might
naturally be inferred that their absorption would promptly follow.
Experimental researches have demonstrated, however, that this takes
place, if 'at all, but to a slight extent. If, however, solutions of inor-
ganic salts, sugars, and peptones possessing a concentration of at
least 5 per cent. — a degree of concentration seldom realized under
normal conditions — are introduced into the stomach, their absorption
will be effected, the rate of absorption following in a general way the
increase, within limits, in concentration. Water is practically not
absorbed from the stomach. The absorption of the products of
digestion — i. e., dextrose, levulose, peptones, soaps, glycerin, fatty
acids, salts, along with water, in which for the most part they are
held in solution — is therefore limited very largely to the small intes-
tine, and is accomplished by the villous processes projecting from the
surface of the mucous membrane.

Structure of the Villi. — The villi are small filiform or conical
processes, from 0.5 to i mm. in length, and from 0.2 to 0.5 mm. in

ABSORPTION.

223

breadth, covering the surface of the mucous membrane from the
])yloric orifice to the upper surface of the ilco-cecal valve. Each
villus consists of a basement membrane (see Fig. 92) supporting tall
columnar epithelial cells. Each cell is composed of granular bio-
plasm containing a distinct nucleus. At its free extremity a narrow

-s^-if 1 I' i}\

Fig. q2. — Longitudinal Sec-
tion OF A \'lLLfS FROM IN-
TESTINE OF THE Dog, Highly
Magnified. a. Columnar
epithelium containing goblet-
cells {h) and migratory leuko-
cytes (/;). c. Basement mem-
brane, d. Plate-like connec-
tive-tissue elements of core.
€, e. Blood-vessels. /. Ab-
sorbent radical or lacteal. —
{PJersol.)

Fig. 93. — Section of Injected Small
Intestine of Cat. a, b. Mucosa.
g. Villi, i. Their absorbent vessels.
h. Simple follicles, c. Aluscularis mu-
cosae, j. Submucosa. g, e' . Circular
and longitudinal layers of muscle.
/. Fibrous coat. All the dark lines
represent blood-vessels filled with the
injection mass. — (Piersol.)

border of the cell presents a striated appearance, as if it were com-
posed of small rods embedded in some cement substance. Goblet
or mucin-holding cells are also to be found among the columnar
cells. The body of the villus, that portion within the basement
membrane, consists of a reticulated connective tissue supporting

224

TEXT-BOOK OF PHYSIOLOGY.

arteries, capillaries, veins, and lymphoid corpuscles. In the center
of the villus there is usually a single though at times a double club-
shaped lymph-capillary, the walls of which are composed of epithe-
lioid cells with sinuous margins. This capillary probably begins by a
blind extremity and opens at the base of the villus into the subjacent
lymph-vessels. The communicating orifice is guarded by a valve.
It is also surrounded by a layer of non-striated muscle-fibers, arranged
longitudinally, derived from the muscularis mucosae and attached to
the apex of the body of the villus.

The arteries which penetrate the vilH are derived from those of the

submucous coat of the intes-
tine, which are the ultimate
branches of the intestinal artery,
and serve the purpose of deHv-
ering nutritive material to the
capillary plexus (Fig. 93).
While passing through the lat-
ter a portion of the blood-
plasma transudes through the
capillary walls into the spaces
of the reticulated tissue, consti-
tuting lymph. At the same
time products of tissue metab-
ohsm pass through the capil-
lary walls into the blood. The
blood then passes into the ven-
ules, which, leaving the villus
at its base, unite with the veins
of the submucous coat to form
the intestinal veins. These
finally unite with the gastric and
splenic veins to form the portal
vein, which enters the liver at
the transverse fissure (Fig. 94).
The excess of lymph within the
villus passes into the club-
shaped lymph-capillary, to be
finally carried by the lymph-
atics of the mesentery into the thoracic duct. During the intervals
of digestion and in the absence of food from the intestine there is,
of course, no absorption of food nor the removal from the villus of
anything but the excess of lymph and metabohc products.

Function of the Villi.— The vilh, and especially the epithehal
cells covering them, are the essential agents in the absorption of the
products of digestion. It is by the activity of these cells that the

Fig. 94. — Diagram of the Portal
Vein {pv) arising in the Alimen-
tary Tract and Spleen {s), and
Carrying the Blood from These
Organs to the Liver. — ( Yeo's
^'Text-hook of Physiology.")

ABSORPTION. 225

new materials arc taken out of the alimentary canal and transferred
into the lymph-spaces, in the body of the villi, from which they are
subsequently removed by the blood-vessels and lymphatics. As to
the mechanism by which the epithelial cells accomplish this result,
nothing definite can be asserted. Inasmuch as the absorption of
food does not take place in accordance with the laws of osmosis as at
present understood, it has been suggested that the cells possess a
"selective action" dependent on their organization and living con-
dition, an action which is to a great extent conditioned and hmited
by the degree of diffusibility of the substances to be absorbed.

Absorption oj Water and Inorganic Salts. — Water and inorganic
salts after their absorption from the intestine and transference into
the lymph-spaces of the villi pass through the walls of the capillary
blood-vessels and are carried by the way of the portal vein into the
liver. Unless water be present in excessive amounts, there is no
appreciable absorpion of water by the lymphatics.

Absorption oj Sugar. — As previously stated, all the carbohydrates,
with the exception possibly of lactose, are transformed by the diges-
tive fluids into either dextrose or levulose, under which forms they
are absorbed by the epithelial cells. It is possible, however, that
soluble dextrin may also be absorbed. Whatever the form under
which the carbohydrates are absorbed, they never leave the epithe-
lial cells except as dextrose and levulose. Direct experimentation
has shown that the sugars are taken up by the capillary blood-vessels
and carried direct to the liver. Analysis of the blood of the portal
vein after the ingestion of large quantities of sugar may reveal an
increase of 0.25 per cent.; while after the injection of sugar into the
intestine the percentage may rise as high as 0.4. As chemic analysis
of lymph obtained from the thoracic duct shows no increase in the
percentage of sugar beyond that normally present (o.i per cent.), it
is assumed that sugar is not removed from the villi by the lymphatics.

Absorption of Proteids. — Since most of the proteidsare transformed
through hydration and cleavage by the action of the gastric and pan-
creatic enzymes into peptones, there is reason to beheve that this
change is necessary to their complete and rapid absorption. Never-
theless it has been shown by the results of experimentation that
unchanged native proteids, such as egg-albumin, and partially
digested proteids, such as acid and alkali albumin, albumoses, may
likewise be absorbed from the small intestine, though in far less
amounts. It has also been demonstrated that native proteids can
be absorbed from the large intestine. Inasmuch as chemic analysis
has failed to detect more than a trace of either peptone or native pro-
teid in the portal blood or in the lymph of the thoracic duct, it must
be assumed that the epithelium after absorbing must also synthetize
them into some form of coagulable proteid (serum-albumin) which is
IS

226 TEXT-BOOK OF PHYSIOLOGY.

readily assimilable by tlie blood. That such a reconversion is neces-
sary would appear from the fact that the introduction of peptones
even in small amounts into the blood is followed by their elimination
unchanged in the urine. When injected into the blood in large
amounts, they act as toxic agents, giving rise to a fall of blood-pres-
sure, a diminished coagulability of the blood, coma, and death.

After passing through the epithelium into the spaces of the villi
they are removed by the blood-vessels and carried direct to the liver.
Even though there is no appreciable increase in the amount of pro-
teid in the portal blood during digestion, there is every reason to
think that this is the route by which it reaches the general circulation.
Ligation of the thoracic duct does not interfere with proteid absorp-
tion nor with the normal elimination of urea nor with the weight of
the animal.

Absorption of Fat. — As previously stated, there are two views as
to the changes which fats undergo during digestion. According as
the one or the other is accepted will depend the view as to the nature
of the absorptive process. If it be assumed that the final stage in
the digestion of fat is a purely physical one, the production of an
emulsion in which the fats present themselves as fine granules, it is
difficult to give any satisfactory explanation of the mechanism by
which the epithelial cells take them up. Various theories have been
advanced to explain the process, but none are free from serious ob-
jections. This view of fat absorption has largely been based on the
observation that during digestion fatty granules can be seen in all
portions of the cell apparently passing toward the interior of the
villus. If, on the contrary, it be admitted that the final stage in the
digestion of fats is the formation of soaps and glycerin, both of which
are soluble, their absorption can more readily be accounted for.
According to this view, the soaps and glycerin are again synthetized
by a process the reverse of that which is produced by the pancreatic
enzyme, with the appearance of minute granules of fat. That this
is the more probable view as to the mechanism of fat absorption is
evident from the fact that when animals are fed with alkaline soaps
and glycerin, or with fatty acids alone, globules of fat are found in
the epithelial cells and in the interior of the villus.

With the passage of the fat-granules into the interior of the villus
they at once enter the lymph-radicle and become constituents of
the lymph-stream, to which they impart a white, milky appearance.
If the abdomen of an animal in full digestion be opened, the lymph-
vessels of the mesentery present themselves as distinct white threads.
An examination of the fluid they contain, known as chyle, shows the
presence of fat-granules of microscopic size. With the passage of
the chyle into the thoracic duct it also presents the same milky ap-
pearance. For this reason the lymphatics of the mesentery were

ABSORPTION. 227

erroneously termed laclcals. The chyle as obtained from these
lymph- vessels possesses the same qualitative though not quantitative
composition as lymj)h, the difference being mainly in the large excess
of fat in the former. Indeed, chyle may be regarded as lymph plus
fat.

Routes for the Absorbed Food. — Physiologic experiments have
demonstrated that the agents concerned in the removal of the products
of digestion after their absorption from the interior of the villus are:

1. The blood-vessels of the gastro-intestinal tract, which unite to

form the portal vein.

2. The lymph- vessels of the small intestine, which converge to empty

into the thoracic duct.

The products of digestion find their way into the general circu-
lation by these two routes, as follows:

The water, inorganic salts, proteids, and sugar after entering the
blood-vessels of the villus are carried by the blood directly into the
liver by the portal vein; after circulating through the capillaries of
the Hver and being influenced by the Hver cells, they are discharged
by the hepatic veins into the ascending vena cava.

The fats after entering the lymph-radicle of the villus are
carried by the lymph-stream into the thoracic duct, by which they are
poured into the blood at the junction of the left subclavian and in-
ternal jugular veins.

Forces Aiding the Movement of Lymph and Chyle. — The
force which primarily determines the movement of the lymph has its
origin in the beginnings of the lymph-vessels, the lymph-spaces,
and depends on a difference in pressure here and at the termination
of the thoracic duct. The rise of pressure in the lymph-spaces is
due to the continual production of lymph, either by filtration or
secretory activity of the capillary walls. As soon as the pressure
rises above that in the thoracic duct a forward movement of lymph
takes place. Other things being equal, the rate of movement will be
proportional to the difference of pressure. The first movement of
the chyle, its passage from the lymph-capillary in the villus into
the subjacent lymph- vessel, has been attributed to a shortening
of the villus and a compression of the capillary by the contraction of
the non-striated muscle-fibers by which it is surrounded. With
the entrance of the chyle into the subjacent lymph-vessel there is
a distention of the vessel and a rise in pressure. When the muscle-
fibers relax, regurgitation is prevented by the closure of the valves at
the base of the villus. The elastic tissue of the lymph-vessel now re-
coils and forces the chyle toward the thoracic duct. After the empty-
ing of the lymph-capillary the conditions as far as pressure is con-
cerned are favorable to the absorption of new material. The

228 TEXT-BOOK OF PHYSIOLOGY.

rhythmic contractions of the intestinal wall undoubtedly aid in the
movement of lymph and chyle.

It is quite possible that the walls of the general lymphatic system
aid the forward movement of lymph by more or less rhythmic con-
tractions of their contained muscle-fibers.

Inasmuch as the lymph-vessels lie in situations in which they
are subject to compression by muscles during contraction, it is prob-
able that the fluid in the vessels will be forced onward toward the
thoracic duct at each compression, a backward movement being
prevented by the closure of the valves which are everywhere present
in the vessels. Experimental observations have demonstrated the
truth of this supposition. Alternate contraction and relaxation of
the muscles of the leg will, in an animal at least, increase considerably
the flow as well as the production of lymph from the thoracic duct.
Massage has a similar influence. The respiratory movements also
aid the flow of both lymph and chyle from the thoracic duct and
larger lymph- vessels into the venous blood. During inspiration the
negative pressure of the thorax is increased, the increase being pro-
portional to the extent of the inspiration. The positive pressure of
the air within the lungs on the thoracic structures, venae cavse, thoracic
duct, etc., being at the same time diminished, there is an expansion of
and a fall of pressure in the thoracic duct and venae cavae. As the
lymph in the abdominal portion of the thoracic duct is subjected to
the higher intra-abdominal pressure, its contents are forced ener-
getically toward the end of the thoracic duct. During expiration
the reverse conditions obtain. As the negative pressure diminishes
and the positive intrapulmonary pressure increases the upper part of
the thoracic duct is compressed and the lymph is forced into the
subclavian vein at its junction with the internal jugular. Regurgita-
tion here is prevented by a closure of the valves.

CHAPTER XI.
THE BLOOD.

The blood is a highly complex nutritive fluid, the presence and
proper circulation of which in the living organism are essential to the
maintenance and activity of all physiologic processes. The escape
of the blood from the vessels, especially in the higher animals, is
followed by a loss of the physiologic properties of all the tissues
within a short period of time. The immediate dependence of the
functional activities of the tissues and organs on the presence of the
blood can be demonstrated by the following experiment : If the nozzle
of a syringe, adapted to the size of the animal, be introduced through
the jugular vein into the right side of the heart and the blood be sud-
denly withdrawn, there is an immediate cessation in the activity of
all the organs; the return of the blood to the vessels within a limited
period of time is promptly followed by a renewal of their activity.

Though contained within a practically closed system of vessels,
the blood is brought into intimate relation with all the tissue elements
through the intermediation of the capillaries. As the blood flows
through these delicate vessels, portions of its soluble nutritive con-
stituents, including oxygen, are given up to the tissues, by which they
are utiHzed for growth, repair, and functional activity. At the same
time the tissues yield up to the blood a series of decomposition prod-
ucts, resulting from their activity, which vary in quantity and quality
according as the blood traverses the muscles, nerves, glands, or
other tissues.

The blood may be regarded, therefore, as a reservoir of nutritive
materials prepared by the digestive apparatus and absorbed from
the food canal; of oxygen, absorbed from the respiratory surface of
the lungs; of decomposition products, produced by and absorbed
from the tissues. Though the blood varies in composition in different
])arts of the body in consequence of the introduction of both nutritive
material and decomposition products, it nevertheless presents certain
average physical, morphologic, and chemic properties which dis-
tinguish it as an individual tissue.

Constituents of Blood. — A microscopic examination of the blood
as it flows through the capillary vessels of the web of the frog or the
mesentery of the rabbit shows that it is not a homogeneous fluid, but
that it consists of two distinct portions: viz., (i) a clear, transparent,
slightly yellow fluid, the plasma or liquor sanguinis; (2) small par-

229

230 TEXT-BOOK OF PHYSIOLOGY.

tides termed corpuscles floating in it, of which there are two varieties,
the red and white, including among the latter two smaller bodies, the
blood-plates and elementary granules. The different constituents
can be roughly separated by appropriate means when the blood is
withdrawn from the body. If the blood of the horse is allowed to
flow directly into a tall cylindric glass vessel, surrounded by ice, it
separates in the course of a few hours into three distinct layers in
accordance with their specific gravities. The lower layer is dark red
and consists of the red corpuscles ; the middle layer is grayish in color
and consists of the white corpuscles; the upper layer is clear, and
transparent and consists of the plasma. The red corpuscles occupy
almost one-half, the white one-fortieth, the plasma a trifle more than
one-half of the height of the entire blood-column, which indicates
approximately the different volumes of each. The same result can
be obtained with human blood by the use of the centrifuge or hema-
tocrit.

PHYSICAL PROPERTIES OF BLOOD.

1. Color. — Within the blood-vessels two kinds of blood are dis-
tinguished— the arterial, the color of which is a bright scarlet, and
the venous, the color of which is a dark bluish-red or purple. The
cause of the color as well as the difference in color is the presence in the
red corpuscles of a coloring-mater, hemoglobin, in different degrees of
combination with oxygen. The intensity of the color in either kind
of blood is dependent on the thickness of the blood-stream, for in the
finest capillaries, as seen under the microscope, there is an almost
total absence of color. As the arterial blood passes into and through
the systemic capillaries, the hemoglobin yields up a portion of its
oxygen to the tissues and changes in color, though the change is
not appreciable by the eye. On passing into the veins, however,
the blood-stream soon presents its characteristic dark bluish color,
which deepens as it approaches the lungs. On passing into and
through the capiflary vessels of the lungs the hemoglobin absorbs a
new volume of oxygen, changes in color, and on emerging from the
lungs the blood presents its characteristic scarlet color.

2. Opacity. — Owing to the fact that the corpuscles have a re-
fracting power different from the plasma, the blood, even in thin
layers, is opaque. The repeated refractions and reflections which
light undergoes in passing through plasma and corpuscles is attended
by such a dissipation that it is impossible to see printed matter through
it. That the opacity is due to the shape of the corpuscles rather than
to their contained coloring-matter is evident from the fact that when
the hemoglobin is caused to separate from the corpuscles by the
addition of chemic reagents, the blood, though it deepens in color,
becomes at once transparent.

THK BLOOD. 231

3. Odor. — When freshly drawn the blood possesses a peculiar
characlerislic odor which has been attributed to the presence of a
volatile fatty acid in combination with an alkaline base. The in-
tensity of the odor may be increased by the addition of concentrated
suli)huric acid, by means of which the volatile acid is set free.

4. Specific Gravity. — The specific gravity of blood lies within
the limits of 1.051 and 1.059, averaging in man 1.056 and in woman
1 .053. Normally, variations from these values are only temporary and
are connected with variations in physiologic processes. The specific
gravity is diminished by the ingestion of licjuids and abstinence from
soHd food. It is increased by abstinence from liquids, by the inges-
tion of dry food, and by the elimination of large quantities of water
by the lungs, skin, and kidneys.

5. Alkalinity. — The reaction of the blood is alkaline from the
presence of the disodium phosphate (Na^HPO^) and the sodium car-
bonate, Na.,C03. The alkahnity can be readily shown by allowing
the blood to remain for a few seconds on slightly reddened glazed
litmus paper. On washing off the blood a distinct blue color pre-
sents itself against a red or violet background. The alkahnity varies
within narrow limits in consec^uence of variations in physiologic
processes. It is increased in the early stages of digestion and de-
creased after the absorption of the hydrochloric acid and the pep-
tones, and decreased after muscular exercise in consequence of the
increased production and absorption of acids. According to v. Jaksch,
the alkahnity corresponds to from 260 to 300 milhgrams of sodium
hydrate, NaOH, for every 100 c.c. of blood; according to Lowy,
from 300 to 325 milligrams. The hitherto unavoidable error in these
estimates is about 30 milligrams.

6. Temperature. — The terriperature varies from 36.78° C.
(98.2° F.) in the superior vena cava to 39.7° C. (103.4° F.) in the
hepatic vein, the mean being about 38° C. (100° F.).

Coagulation of the Blood. — Within a few minutes after the
blood is withdrawn from the vessels of a living animal it begins to
lose its fluidity, becomes somewhat viscid, and if left undisturbed
passes rapidly into a semi-sohd or jelly-like state. To this change
in the physical condition of the blood the term coagulation has been
apphed. The blood, during the progress of coagulation, not only
assumes the shape of the vessel in which it is contained, but becomes
so firmly adherent to its walls that it may be inverted without the
coagulum becoming dislodged. If a portion of such a jelly-like mass
be examined microscopically, it will be found to be penetrated in all
directions by a felt-work of extremely fine dehcate fibrils, which,
having made their appearance before the corpuscles had time to
settle to the bottom of the fluid, have entangled them in the meshes

232

TEXT-BOOK OF PHYSIOLOGY.

so that the entire mass retains its characteristic color. These fibrils
are collectively known as fibrin (Fig. 95).

If the coagulated blood be allowed to remain undisturbed, a
clear, transparent, sHghtly yellowish fluid makes its appearance on
the surface of the mass, which as it accumulates forms a layer of
varying degrees of thickness. Within a few hours the blood-mass
detaches itself from the sides of the vessel in consequence of the re-
traction of the fibrils, while at the same time the clear fluid increases
in amount and accumulates along the sides and bottom of the vessel.
The shrinkage in the volume of the red coagulum and the increase
of the volume of the clear fluid which is expressed from its meshes
continue for a period varying from ten to fifteen hours, according
to certain external conditions. The blood has now become separated
into two distinct portions: viz., a solid contracted red mass, termed
clot, and a clear fluid, termed serum. The clot consists of the fibrin
containing in its meshes the red and white corpuscles; the serum

Fig. 95. — Diagram to Illustrate the Process of Coagulation, i. Fresh blood,
plasma, and corpuscles. 2. Coagulating blood (birth of fibrin). 3. Coagulated
blood (clot and serum). — {Waller.)

consists of all the constituents of the plasma except the antecedents
of the fibrin. The stages of coagulation are shown in Fig. 95.

If the blood coagulates slowly the red corpuscles, owing to their
greater specific gravity, subside to the bottom of the blood-mass,
giving to it a deeper color; the white corpuscles, owing to their lesser
specific gravity, remain near the surface of the clot and give to it a
more or less whitish appearance, producing the so-called hujjy coat.
In certain inflammatory conditions the coagulating power of the blood
is much diminished, and the corpuscles, having time to subside, a well-
developed buffy coat is formed which at one time had much interest
for pathologists. As the contraction of the fibrin takes place more
actively in the center, there being here less resistance than at the
sides of the coagulum, the upper surface usually becomes depressed
or cupped.

Coagulation of Plasma. — Clear plasma may be obtained by
means of the centrifuge from blood to which suflicient magnesium
sulphate has been added to prevent coagulation, or from horse's

THE BLOOD. 233

blood wliich has been allowed to flow into a tall vessel surrounded by
a cooling mixture so as to prevent coagulation and thus permit the
red corpuscles to subside. If such plasma be subjected to room-tem-
perature, it very shortly undergoes coagulation, exhibiting practically
I he same phenomena as blood itself. After a variable length of time
it also separates into a soft, colorless coagulum or clot consisting of
llbrin, and a clear fluid, the serum. The presence of the red cor-
puscles is therefore not essential to the process of coagulation.

Rapidity of Coagulation. — The rapidity with which the blood
coagulates varies in dift'erent classes of animals under the same con-
ditions: e. g., the blood of the pigeon coagulates immediately; that of
the dog, in from one to three minutes; that of the horse, in from five
to thirteen minutes; that of man, in from four to seven minutes.
The time, however, can be lengthened or shortened by either chang-
ing the external conditions or by altering temporarily the normal
composition of the blood.

Coagulation is retarded or prevented by the following agents,
viz.: (i) A low temperature, especially that of melting ice. (2) The
addition of magnesium sulphate (i volume of a 25 per cent, solution
I0 3 volumes of blood); of sodium sulphate (i volume of a saturated
solution to 7 volumes of blood). (3) The addition of potassium
oxalate (i volumes of a i per cent, solution to 3 volumes of blood).
(4) The injection into the blood of commercial peptone. (5) The
mouth secretion of the leech.

Coagulation is hastened by the following agents, viz.: (i) A
gradually increasing temperature from 38° C. to 50° C. (2) The
addition of water in not too large amounts. (3) The presence of
foreign bodies. (4) Agitation of the blood — e. g., stirring.

Fibrin and Defibrinated Blood. — If freshly drawn blood is
stirred with a bundle of twigs or glass rods for a feAv minutes, the
fibrin collects on them in the form of thick bundles or strands; after
washing it with water the entangled corpuscles are removed, when
the fibrin assumes its natural white appearance. The strands can
be resolved into a large number of delicate fibers which possess ex-
tensibihty and retractibility, and are therefore elastic. The chemic
features of fibrin have already been considered (see page 34). The
remaining fluid, similar in its physical appearance to the blood, is
termed defibrinated blood. When such blood is allowed to remain
at rest for a few days, the remaining red corpuscles gradually sink
to the bottom of the fluid, above which will be found the clear serum.

COMPOSITION OF PLASMA AND SERUM.

Plasma. — The plasma obtained by any of the methods previously
described is a clear, colorless, transparent, slightly viscid fluid, with

234, TEXT-BOOK OF PHYSIOLOGY.

a specific gravity of 1.026 to 1.029. ^^ is composed largely of water
holding in solution proteids, sugar, fatty matter, inorganic salts, urea,
cholesterin, lecithin, etc. In composition it is. quite complex, con-
taining as it does not only the nutritive materials derived from the
digestion of the food, but also the substances resulting from the
disintegration of the tissues consequent on their functional activity.

Serum. — The serum is the clear, transparent, shghtly yellow
fluid expressed from the coagulated blood during the contraction of
the fibrin. It consists practically of the ingredients of the plasma,
with the exception of those substances which entered into the for-
mation of fibrin. The average composition of plasma is shown in
the following table:

COMPOSITION OF PLASMA.

Water, 90.00

f Serum-albumin, 4.50

Proteids -^ Paraglobulin, 3.40

( Fibrinogen, 0.30

Fatty matters, 0.25

Sugar, o.io

Extractives, 0.60

Inorganic salts, 0.85

100.00

Serum-albumin. — Of the proteid constituents of the blood,
serum-albumin is the most abundant, existing to the extent of from
4 to 5 per cent. From its similarity to egg-albumin it is regarded as
holding an important position as a nutritive agent, for it is out of this
common proteid that in all probability each individual tissue elabor-
ates the special proteid characteristic of it, since during starvation
the albumin steadily diminishes in amount. As it passes through
the walls of the capillary vessels it is found in the lymph, pericardial
fluid, and similar secretions in various parts of the body, as well as in
various pathologic transudates. It is also present in serum. While
circulating in the lymph-spaces the serum-albumin is utilized in
replacing the proteids which have undergone disintegration during
tissue metabolism. Its supply in the blood is maintained by the
absorption of peptones which are formed from the proteids of the food
and which during the time of absorption are changed in some unknown
way into serum-albumin. It is readily obtained from plasma or
serum by saturating either of these fluids with magnesium sulphate,
when all the proteids except serum-albumin are precipitated. After
their removal the remaining fluid is subjected to a temperature of
from 70° to 75° C, when the serum-albumin is precipitated in a
coagulable form, after which it can be removed and its chemic
features determined.

Paraglobulin. — This proteid, though present in plasma, is best

THE BLOOD. 235

obtained from serum when this fluid is saturated with magnesium
sulphate. As the line of saturation is approached the fluid becomes
turbid, and after a few minutes a fine white precipitate occurs. It
can then be collected on a filter, dried, and its chemic properties
determined. In its reactions it resembles the various members of the
globulin class. The amount varies from 2 to 4 per cent, in the blood
of man. As to the physiologic importance or antecedents of para-
globulin nothing is definitely known. Its constant presence in the
blood would indicate that it plays an equally important, though
perhaps dift'crcnt, part with serum-albumin in the nutrition of the
body.

Fibrinogen. — This proteid can be obtained from plasma, lymph,
pericardial, and peritoneal fluids, as well as from hydrocele fluid.
It is, however, not to be obtained from serum, as it is removed from
the blood during the formation of solid fibrin. It is normally present
in the blood in very small quantity, amounting to not more than 22
to T,T, parts per thousand. Fibrinogen may be obtained from plasma
which has been prevented from coagulating, by the addition of mag-
nesium sulphate in certain quantities or by the addition of a satu-
rated solution of sodium chlorid. In a few minutes a flaky precipitate
occurs. By repeated washing and precipitation with sodium chlorid
solutions of varving strength the fibrinogen mav be obtained in a
pure state. The history of fibrinogen is unknown. Beyond the fact
that it contributes to the formation of fibrin there is no positive
knowledge either as to its origin, its nutritive value, or its final dis-
position in the blood under normal conditions.

Fat. — The plasma as well as the serum contains a very small
quantity of fat in the form of microscopic globules. Though the
percentage is normally not above 0.25, yet just after a meal rich in
fatty matter the amount may be so great as to give to the blood
a milky or opalescent appearance. Within a few hours, however,
this excess of fat disappears from the blood, though its immediate
disposition is unknown. Soaps or alkaline salts of the fatty acids,
though formed during the digestion of fats, are not present in the
blood. Lecithin and cholesterin are present in very small quantities.

Sugar. — Sugar is present in the blood in the form of dextrose,
and is now regarded as a normal constituent. The amount is
about I part per thousand, though it may be present to the extent
of 3 parts per thousand. Beyond this, the excess soon appears in
the urine.

Extractives. — The blood contains a series of nitrogenized
bodies, such as urea, uric acid, creatin, creatinin, xanthin, etc., which
result from the katabolic changes in nerve- and muscle-tissues as
well as from subsequent chemic combinations and decompositions.
Though constantly absorbed from the tissues, they seldom accumu-

236

TEXT-BOOK OF PHYSIOLOGY.

late beyond a small amount, since they are constantly being elimi-
nated from the blood by the various excretory organs.

Inorganic Salts. — The inorganic salts of the plasma are chiefly
sodium and potassium chlorids, sulphates, and phosphates, together
with calcium and magnesium phosphates. Of the salts, sodium
chlorid is the most abundant, amounting to 5.5 parts per thousand.
Some of the salts are alkaline and impart to the blood its alkalinity.
Calcium phosphate is present in small quantity — 2 parts per 1000.
This salt is wanting in serum for the reason that it became a constitu-
ent of fibrin at the time of coagulation. In other respects serum
differs but slightly from plasma in the proportions of its saline con-
stituents.

HISTOLOGY OF THE RED CORPUSCLES OR ERYTHROCYTES.

The histologic features of the red corpuscles are readily observed
in a drop of freshly drawn blood when examined microscopically.
The field of the microscope will be seen to be crowded with red cor-
puscles floating in a clear transparent fluid — the plasma. Here and

there will also be seen a
white corpuscle, round or
irregular in shape, and
granular in appearance.
Within a short time a
characteristic phenomenon
takes place: viz., the ar-
ranging of the corpuscles
in the form of columns of
varying length, resembling
rolls of coins. These rolls
interlace with each other at
all angles and form a net-
work in the meshes of
which lie individual red
and white corpuscles. (See
Fig. 96.) The cause of
this tendency of the cor-
puscles to adhere to one
another is not definitely
known. Since it does not
take place in circulating blood, and since it is to a great extent
prevented by defibrinating the blood, it has been supposed to be
dependent on the formation of some adhesive substance connected
with the formation of fibrin.

Color. — When viewed by transmitted light, a single corpuscle
is slightly yellow or greenish in color; but when a number are grouped

Fig. 96. — Corpuscles trom Human Sub-
ject. A few colorless corpuscles are
seen among the colored discs, many of
which are arranged in rouleaux. —
(Funke.)

THE BLOOD. 237

together, the color deepens and the corpuscles appear red. In either
case the color is due to the presence in the corpuscle of a specific
coloring-matter, hemoglobin.

Shape. — The red corpuscle is a circular, flattened disk with
rounded edges. Each surface is perfectly smooth and presents a
shallow depression in its center, so that it is also biconcave. A
longitudinal section of a corpuscle would present, when viewed
edgewise, an outline similar to that of Fig. 97. This difference in
the thickness of the peripheral and central portions of the corpuscle
gives rise to differences in optical
appearances when examined micro- r7" — ^c;~^-9-^^ — ,^^^^,

scopically. At a certain distance of aL [ Jb

the object-glass the corpuscle pre- i\^ ^^^^ — \ — -~-.,,^^^ yi

scnts in its peripheral portion a " "ci

bright rim, and in its central por- ^'^'^- 97--Ideal Transverse Sec-

. ^ , ' rr 1 -L • • TiON OF A Human Red CorpTjS-

tion a dark spot. If the objective cle. (Magnified 5000 times.)

be brought nearer and the center a, b. Diameter, c, d. Thickness.

accurately focused, the reverse ap-
pearance obtains; the central portion becomes bright and the periph-
eral portion dark. The cause of this difference in optical appear-
ance is the unequal distribution of the transmitted Hght in conse-
quence of the shape of the corpuscle.

Size. — The diameter of a typical well-developed red corpuscle
under normal conditions is 0.0075 mm.; its greatest thickness is
0.0019 rnm. Though this may be assumed as the average diameter,
there is a small percentage of distinctly smaller and a small per-
centage of distinctly larger corpuscles. The following table shows
the results of measurement made by different observers:

Xormal Limits. Average Diameter.

Welcker, diameter 0.0045-0.0095 0.0070

Hayem, " 0.0060-0.0688 0.0075

Gram, " 0.0067-0.0093 0.007S

Melassez, " 0.0076

0.00747
(3 2'oo inch)

Structure. — The red corpuscle of man as well as all other mam-
mals possesses neither a nucleus nor a limiting membrane, but appears
to consist of a homogeneous substance more or less semisolid in con-
sistence. Under the influence of certain reagents the corpuscle
separates into two distinct portions: viz., a colorless protoplasmic
stroma and a coloring-matter which diffuses into the surrounding
hquid. The presence of the former can be demonstrated by the
addition of iodin, which imparts to it a faint yellow color. The
stroma is elastic, and determines not only the shape of the corpuscle
but gives to it the properties of extensibility and retractibility.

TEXT-BOOK OF PHYSIOLOGY.

Number of Red Corpuscles. — In any given specimen of blood
the corpuscles are so numerous and the spaces between them so
small that it seems almost impossible to determine their number.
This, however, has been accomplished for a cubic millimeter of
blood by various observers employing different methods with compara-
tively uniform results. The average normal number of corpuscles in
one cubic millimeter of blood is, for men, 5,000,000; and for women,
4,500,000. This value, however, will vary within slight limits, with
variations in the activity of physiologic processes and to a large extent
at times in pathologic states of the blood or body. The number is
increased in the cutaneous veins by all influences which cause a
diminution in the quantity of water in the blood — e. g., copious
sweating, acute watery diarrhea, fasting, abstinence from liquids;
the number is diminished by influences which dilute the blood — e. g.,
the ingestion of liquids, the absorption of fluids from the tissue spaces,
etc. But it is well to remember that these influences which produce
changes in the number of corpuscles per cubic milhmeter do not
necessarily produce corresponding changes in the total number of
red corpuscles in the body. In women lactation, menstruation, and
the act of parturition diminish the number. High altitudes appar-
ently increase the number of corpuscles, as shown by their increase in
the blood of the peripheral vessels. Whether this is an indication
that there is a corresponding increase of the total number in the
general volume of the blood is uncertain. The following table will
show the increase in the count per cubic millimeter at different
altitudes:

Place.

Height above Sea-level.

Red Cells.

Author.

Christiana,

0 meter
148 meters

314 "
414

425 "
700 "

1800 "

4392

4,974,000
5,225,000
5,322,000
5,752,000
5,748,000
5,900,000
7,000,000
8,000,000

Laache.

Gottingen,

Schaper.
Reinert.

Steirlin.

Tiibigen,

Auerbach,

Koppe.

Egger.

Viault.

(Koppe.)

Reibaldsgriin,

Arosa,

The Cordilleras,

Moro cocha.

This increase in the number of corpuscles takes place, according
to Viault's observations, within two or three weeks, and is apparently
not connected with either diet or mode of life, but rather with dimin-
ished atmospheric, if not oxygen, pressure. On returning to sea-
level there is a gradual reduction, without any apparent destruction
of the corpuscles, to their normal number. The reason for these
variations is not clear.

The method of counting corpuscles introduced by Vierordt and

THE BLOOD.

239

Welckcr has been modified by different observers, and especially by
Thoma and Zeiss. On account of the great number of corpuscles
in I cubic millimeter of blood, it becomes necessary for purposes of
enumeration that the blood be diluted a definite number of times and
that the diluted mixture be placed in a counting chamber possessing
a definite capacity. By means of the pipette or melangeur of Potain
and the counting chamber of Thoma both these objects are attained.

The pipette consists of a capillary tube (Fig. 98) p^

provided with an enlargement containing a freely mov-
able small glass ball, a. One end of the tube is pointed,
while to the other end is attached a rubber tube for the
purpose of facilitating the introduction of the blood
and the diluting fluid. The capillary tube, which is
accurately calibrated, carries marks, ^, i, loi, which
signify that if the tube be filled with blood up to the
mark i and the diluting fluid be sucked into the
tube up to the mark loi, the blood wull be diluted
100 times. If the blood be sucked up to the mark
\ and the diluting fluid to loi, then the blood will
be diluted 200 times. In using the pipette the point
is introduced iiito a drop of blood derived from a
small wound in the skin of the lobe of the ear or
finger and sucked into the tube by introducing the
rubber tube into the mouth. The tube is then
quickly inserted into a solution, similar in specific
gravity to the plasma, which will preserve the shape
and size of the corpuscles, such as Gowers's sodium
sulphate solution, sp. gr. 1.025, or a 3 per cent,
sodium chlorid solution,* and the fluid sucked into
the tube up to the mark loi. On shaking the
pipette for a few minutes, the admixture will take
place, aided by the movements of the glass ball.

Fig. 99 shows both a section view, A, and a
surface view, C, of the counting chamber. This con-
sists of an oblong glass plate on which are cemented
two small pieces of glass, one of which has in the
center a circular opening in which is placed the other, a circular disc or

* Various solutions have been devised for diluting blood, any one of which may
be employed, e. g.:

Hayem's Fluid: Toisson's Fluid:

Hydrarg. bichlor., 0.5 gm. Aqua; destillat., 160.00 parts.

Sodium sulphate, 5.0 " Glycerinae, 30.00 "

Sodium chlorid, 2.0 " Sodium sulphate, __ 8.00 "

Aqua; destillat., 200.0 " Sodium chlorid, i.oo "

Methyl-violet, 0.025 part.

Gowers's Fluid:

Sodium sulphate, gr. 104

.\cid. acetic, ^]

Aquas dest., q. s. ad 3iv.

Fig. 98. — Melan-
geur OR Pipette.
— {Landois and
Stirling.)

240

TEXT-BOOK OF PHYSIOLOGY.

stage. Their relation is such that a narrow groove or moat separates the
one from the other, the floor of which is formed by the glass plate. The
surface of the circular stage is exactly o.i mm. lower than that of the
cover-glass, a. On the surface of the glass stage a series of small squares
is engraved, each one of which has a side length of ^V ^^^^- ^-nd an area
of 4^ square mm., B. To facilitate counting, a group of i6 squares is

surroimded by a heav}'-
a b dark line. This group is

separated from adjoining
groups, also enclosed by
dark lines, by an inter-
mediate Kght line, which
serves as a guide in pass-
ing from one group to
another. When a cover-
glass is accurately applied
to the glass, b, each one
of the small squares will
have a cubic capacity of
4^_X O.I, or :n)Vo cubic
milhmeter, and every four
such squares will have
therefore a capacity of
ToV^ cubic miUimeter.

Before placing the di-
luted blood on the cotmt-
ing stage, the fluid in the
tube of the pipette should
be blown out and dis-
carded, as it contains no
portion of the blood. A
few drops are then placed
on the glass stage and
covered with the cover-
glass. After a few min-
utes the corpuscles settle
over the ruled spaces and
are ready for counting.
The number of corpuscles
in a horizontal series of 4
squares is then counted; this number is then multipUed by 1000 in order
to get the number in i cubic millimeter of the diluted blood, and this
product by 100 or 200 according to the extent of the dilution: e. g., four
squares contain 50 corpuscles; multiphed by 1000 and then by 100 =
5,000,000. The accuracy of the counting is proportional to the number
of squares counted. If 200 squares are counted and the average taken,
the probable limit of error will not be more than 2 per cent.

Effects of Reagents on the Red Corpuscles. — Within the
blood-vessels the composition of the plasma is such that both the

Fig. 99. — Apparatus of Thoma and Zeiss
FOR Counting the Corpuscles. A. In
section. C. Surface view without cover-
glass. B. Microscopic appearance with the
blood-corpuscles. — {Landois and Stirling)

THE BLOOD. 241

form and composition of the corpuscles are maintained under normal
physiologic conditions. This fluid, therefore, is preservative of the
structure and function of the corpuscle. When examined micro-
scopically with a view of determining their histologic features, the
plasma must be diluted, and in consequence they rapidly undergo
physical and chemic changes from the absorption or loss of water.
To prevent these effects the corpuscles must be immersed in a fluid
containing a percentage of salts approximating that of the plasma.
Under such circumstances they will neither absorb nor give up
water. Such a fluid is found in the physiologic salt solution, which
contains 0.64 per cent, sodium chlorid. This fluid maintains the
chemic equilibrium of the corpuscles, and is therefore said to be
isotonic to the corpuscle.

If distilled water be added to the drop of blood, the corpuscle
absorbs it, swells up, and assumes a more or less spherical form,
sometimes cup-shaped. The hemoglobin dissolves out and the
stroma becomes almost invisible. Its presence can be detected by
the addition of iodin. The addition of salt solutions, — e. g., sodium
chlorid, sodium sulphate, ammonium chlorid, etc., — which increase
the density of the plasma, cause a shrinkage of the corpuscles so that
they assume a crenated or notched appearance. Dilute solutions of
acetic acid, of alkalies, especially potassium and sodium hydrate,
cause the corpuscles to swell, to lose their color, dissolve, and en-
tirely disappear. Many other agencies of a physical and chemic
nature, such as heat 60° C, electricity, bile salts, the vapor of
chloroform, ether, ammonium sulphocyanid, etc., also destroy the
integrity of the corpuscles, and cause the hemoglobin to separate
from the stroma and diffuse into the plasma without itself under-
going any appreciable change in composition. The blood at the same
time will become transparent and change to a dark red color, to
which the term "lake color" has been given.

The Corpuscles of Other Vertebrated Animals. — In all mam-
mals, with the exception of the camel, llama, and dromedary, the
red corpuscles present the same shape and structure as the corpuscles
of man, and may be described as circular, flattened, biconcave disks.
In the animals excepted the corpuscles are oval. The size, however,
varies in different animals from 0.0092 mm. (2T4 5" inch) in the ele-
phant to 0.0023 n^ni. (Y2"i2T inch) in the musk-deer, while in most
animals the average lies between 0.0084 mm. and 0.0050 mm. Inas-
much as the question may arise as to whether the corpuscles of any
given specimen of blood are those of a human being or of some other
mammal, a knowledge of the size of the corpuscles becomes a matter
of medicolegal as well as of physiologic interest. Though the
differences in size are slight, yet it is possible for skilled microscopists,
when examining fresh blood, to make a diagnosis between the cor-
16

242

TEXT-BOOK OF PHYSIOLOGY.

puscles of man and those of the domesticated animals, with the ex-
ception, perhaps, of the guinea-pig. The diagnosis of the corpuscles
of dried blood which have been altered by the action of various ex-
ternal agents, even though capable of a certain degree of restoration,
is most difficult, and should not be attempted in criminal cases with-
out large experience in microscopy, in measurements and methods
of preparation of all kinds of blood-corpuscles, and a proper per-
ception of corpuscular forms and sizes. In the following table the
average results of the measurements of the corpuscles in different
classes of animals are given (abstracted from Formad's compilation) :

Gulliver.

WORMLEY.

C. Schmidt.
Mallinin.

French Medico-
legal Soc.
Welcker.

FORMAD.

Inch.

Mm.

Inch.

Mm.

Inch. Mm.

Inch.

Mm.

Inch.

Mm.

Man,

Guinea-pig, .

Dog,

Rabbit,

Ox

Pig,

Horse

Cat,

Sheep,

Goat

1.3200
1.3538
I-3S32
1.3607
1.4267
1.4230
1.4600
1.4404
1.5300
1.6366

0.0079
0.0071
0.0071
0.0070
0.0060
0.0060
0.0057
0.0058
0.0048
0.0040

3250
3223
3561
3653
4219
4268
4243
4372
4912
6189

0.0078
0.0079
0.0071
0.0070
0.0060
0.0059
0.0059
0.0058
0.0031
0.0041

3300

3300*

3636

3968

4354

4098

4464

4545

5649

6369

0.0077
0.0077
0.0070
0.0064
0.0058
0.0062
0.0057
0.0056
0.0045
0.0040

3257

32i3t

3485

3653

4545

4098

4545

3922

5076

5525

0.0078
0.0079
0.0073
0.0069
0.0056
0.0062
0.0056
0.0065
0.0059
0.0046

1.3200
1.3400
1-3580
1.3662
1.4200
1.4250
1. 43 10

1.5000
1. 6100

0.0079
0 0075
0.0071
0.0069
0.0060
0.0060
0.0059

0.0051
0.0042

In birds, reptiles, and amphibians the corpuscles are larger
than in mammals, are oval in shape, and
nucleated. (See Fig. 100.) As the scale of
animal life is descended the corpuscles in-
crease in size, until in the proteus and am-
phiuma the long diameter attains an average
length of 0.058 mm. and 0.077 nmi- respec-
tively. In fish the corpuscles are smaller, oval,
and nucleated, with the exception of the lam-
prey eels, in which they are circular, biconcave,
and nucleated, though the nucleus is gener-
ally concealed in the peripheral portion of
the corpuscle. As they are almost twice the
size of the human red corpuscles, they can,
notwithstanding the similarity of shape, be
readily distinguished from them.
Function of the Red Corpuscles. — The red corpuscles, in
virtue of the capacity of their contained hemoglobin for oxygen
absorption, may be regarded as carriers of oxygen from the lungs to
the tissues, and therefore important factors in the general respiratory

Fig. 100. — Amphibian
Colored Blood-
corpuscles. I. On
the flat; 2, on edge.
— {Landois and Stir-
ling.)

* Masson.

t Woodward.

THE BLOOD. 243

process. The size as well as the number of the corpuscles in different
classes of animals appears to be directly related to the activity of the
respiratory process. In those animals in which the corpuscles are
small and numerous and the total superficial area large, respiration
is active, the quantity of oxygen absorbed is large, and the energy
evolved through oxidation great. In those animals, on the contrary,
in which the corpuscles are large and relatively few in number, the
reverse conditions obtain. This is in accordance with the fact that
the superficial area of any given volume of substance is increased in
proportion to the extent to which it is subdivided.

The superficial area of a single human red corpuscle has been
estimated at 0.000128 sq. mm. If the number of corpuscles in i
cubic millimeter of blood averages 5,000,000, the superficial area
would amount to 640 square millimeters ; and if the amount of blood
in the body of a man weighing 75 kilos is taken as one-thirteenth of
this weight, — that is, 5769 grams (5463 c.c), — the total area of the
corpuscular surface will amount to 3496 square meters.

Life-history of Red Corpuscles. — In the performance of their
functions the red corpuscles undergo more or less disintegration and
final destruction; but as the average number is maintained under
normal physiologic conditions, there must be a constant renewal from
day to day. The evidence of destruction of red corpuscles is fur-
nished by the presence in the blood in various situations of the body
of a pigment containing iron and the presence of pigments in the bile
and urine, all of which are believed to be derivatives of effete hemo-
globin. The blood-pigment (hematin), which contains the iron of
the hemoglobin, is found in the capillaries of the fiver, in the cells of
the splenic pulp, and in the marrow of the bones. Whether the
presence of the pigment in these organs is a proof that the corpuscles
are destroyed here, or whether they are to be regarded merely as
agents concerned in the further reduction and elimination of the
hematin, is uncertain. The genetic relationship between bile-pig-
ment and hemoglobin is shown by the fact that any artificial destruc-
tion of hemoglobin or its injection into the blood is attended by an
increase in the quantity of bile-pigment eliminated. It appears also
from chemic considerations that the hemoglobin will undergo cleavage
into a globuhn body and hematin, which by the loss of its iron is readily
converted into the bile-pigment, bifirubin. The amount of this latter
pigment may therefore be taken as an index of the extent of corpus-
cular destruction.

This gradual decay of corpuscles as well as the losses occasioned
by hemorrhages necessitate a continuous formation of new cor-
puscles, so that the normal number may be maintained. The rapidity
with which corpuscles may be renewed, in the woman at least, is
shown by a computation of Mr. Charles L. Mix. A woman loses

244 TEXT-BOOK OF PHYSIOLOGY.

during a menstrual period 150 c.c. of blood. At the end of twenty-
eight or thirty days this volume is restored, so that in one day 5 c.c,
or 5000 c.mm., of blood must be formed, or 208 c.mm. per hour and
3^ c.mm. per minute. That is, during a certain number of years
15,750,000 corpuscles must be formed every minute, and this inde-
pendent of the daily loss due to functional activity.

At the present time there is a general agreement among histolo-
gists that in adult life the red corpuscles are derived from embryonic
forms, the so-called erythroblasts, which are found chiefly in the
marrow of the long bones.* In this situation both arterial and venous
capiharies are relatively large and the blood is separated from the
surrounding marrow by extremely thin walls. In the passages of this
capillary network the erythroblasts make their appearance most
probably by a transformation of preexisting marrow cells. At first
they are large, -homogeneous, colorless, perhaps shghtly tinged with
hemoglobin and distinctly nucleated. They increase in number by
karyokinesis and at the same time increase in their hemoglobin con-
tent. The nucleus is finally extruded, carrying with it a portion of
the perinuclear cytoplasm, after which the remainder of the cor-
puscle assumes the shape and size of the adult corpuscle and is carried
out into the general circulation. After severe hemorrhage the forma-
tive processes in the marrow may become so active that erythroblasts
make their appearance in the blood-stream before the extrusion of
the nucleus has taken place.

CHEMIC COMPOSITION OF RED CORPUSCLES.

Hemoglobin. — The red corpuscle consists of a stroma and a
coloring-matter, hemoglobin. In the normal condition the latter is
amorphous and in some unknown way combined with the former
and not merely diffused in its meshes. The amount of hemoglobin
per corpuscle is estimated at 90 per cent., so that the corpuscle may
be conceived of as a mass of hemoglobin supported and enclosed by a
protoplasmic stroma.

If blood which has been rendered laky, .by water or any other
of the known agencies, be allowed to slowly evaporate, the dissolved
hemoglobin undergoes crystallization. The rapidity with which the
crystals form varies in the blood of different animals under similar
conditions. According to the ease with which crystalhzation takes
place, Preyer has classified various animals as follows: (i) Very
difficult — calf, pigeon, pig, frog; (2) difficult — man, monkey, rab-

* For an admirable resume of the various views regarding the origin and formation
of red corpuscles see the paper of Mr. Charles L. Mix, Boston Med. and Surg. Journal,
1892, Nos. II and 12; also paper by Prof. W. H. Howell, Journal of Morphology,
vol. IV, 1892.

THE BLOOD.

245

bit, sheep; (3) easy — cat, dog, mouse, horse; (4) very easy — guinea-
pig, rat.

The hemoglobin crystals vary in shape according to the blood
from which they are obtained (Fig. loi). Those obtained from the
guinea-pig are tetrahedral; those
from man and most mammals
are prismatic rhombs; those
from the squirrel are in the form
of hexagonal plates. Notwith-
standing these slight differences,
all forms belong to the same
crystal system, with the excep-
tion of those from the squirrel.

A simple but very effective
method of obtaining blood-crys-
tals suggested by Reichert is to
lake defibrinated blood, espe-
cially that of the dog, rat, guinea-
pig, and horse, with acetic or
ethyUc ether and then add a
solution, I to 5 per cent., of
ammonium oxalate. A drop of
this mixture placed under the
microscope will show crystal for-
mation in a very few minutes.

Chemic Composition of
Hemoglobin. — By appropriate
methods hemoglobin can be ob-
tained in a practically pure form,
and when subjected to a tem-
perature of 100° C. its water of
crystallization is driven off, after
which it can be analyzed. In

the subjoined table the results of several analyses are given for 100
parts of hemoglobin.

Fig. ioi. — Crystallized Hemoglobin.
a, b. Crystals from venous blood of
man. c. From blood of cat. d. Of
Guinea-pig. e. Of marmot. /. Of
squirrel. — (Gautier).

C,
O,

H,

N,
S.
F,

Dog.

Horse.

Dog.

GOINEA-PIG.

53-91

22.62

6.62

15.98

51-15

23-43

6.76

17.94

53-85
21.84

7-32
16.17

54-12

20.68

7-36

16.78

0.54

0-39

0-39

0.58

0.33
Jaquet.

0.33
Zinoffsky.

0-43

0.48

Hoppe-

Seyler.

246 TEXT-BOOK OF PHYSIOLOGY.

The elementary composition of hemoglobin is thus seen to vary
slightly in different animals, suggesting that there may be different
kinds of hemoglobin. The rational molecular formula is not known.
On the assumption that each molecule contains one atom of iron,
Preyer suggested the following empirical formula: CeooHgeoNjs^Oj^g-
SgFe, with a molecular weight of 13,332; Jaquet has suggested a
different formula : viz., C758Hj203Ni95O2i8S3Fe, with a molecular weight
of 16.669. It is very evident from this that the molecule is of enor-
mous size and exceedingly complex.

Quantity of Hemoglobin. — The quantity of hemoglobin in blood
as determined by chemic, chromometric, and spectro-photometric
methods amounts to about 14 per cent, in man and 13 per cent, in
woman. Of the chemic methods, that based on the amount of iron
is the most familiar. Chemic analysis has shown that hemoglobin
contains 0.43 per cent, and blood 0.056 per cent, of iron; with these
two factors the quantity of hemoglobin can be determined by the
following formula: x = ~^^- = 13.33 per cent. The total
quantity of hemoglobin in the blood, assuming the latter to be about
5769 grams (one-thirteenth of the body-weight, 75 kilos) will therefore
amount to 769 grams; e. g., x = ^^^^ i^J^^^ ^ 7^9- ^^^ ^^^^^ amount
of iron in the blood is obtained by the following formula: viz., x =
576921^6 _ ^23 grams.

Under normal physiologic conditions the percentage of hemo-
globin undergoes but slight variation. In pathologic states there is
frequently a great diminution in the amount, especially in chlorosis,
splenic leukemia, and pernicious anemia, diseases in which it dimin-
ishes to 2 1 per cent, in many instances. For the determination of
these variations in the hemoglobin for clinical purposes two chromo-
metric methods are at present largely employed, that of Gowers and
v. Fleischl. All chromometric methods are based on the principle
that if two equally thick and equally well-illuminated solutions pre-
sent the same intensity of color, their richness in coloring-matter is
the same. There are two methods by which this can be done: (i) By
diluting the blood to be examined with water until the shade of color
corresponds to that of a solution of hemoglobin of known strength
(Gowers). (2) Diluting a given quantity of blood with a given
quantity of water and then finding an identical color which repre-
sents a previously determined quantity of hemoglobin (v. Fleischl).

Gowers' hemoglobinometer consists (Fig. 102) of two glass tubes
of exactly the same size. One, A, contains glycerin jelly colored
with picro-carmine the shade of which corresponds to that of normal
blood diluted 100 times, 20 c.mm. in 2000 c.mm. of water repre-
senting a I per cent, solution. The other tube, B, is ascendingly
graduated with 120 divisions, each one of which corresponds to 20

THE BLOOD.

247

c.mm. With a graduated pipette 20 cubic millimeters of blood are
accurately measured and blown into the bottom of the tube B, in
which a few drops of distilled water have been placed so as to prevent
coagulation. Water is then added drop by drop until the color of
the diluted blood is exactly that of the standard. The division of
the scale reached by the dilution will represent the relative per-
centage of hemoglobin. If this tint is not obtained until the dilu-
tion reaches 100 divisions, the quantity of hemoglobin is normal.
If more water must be added, it is in excess; if less, it is diminished.
If, for example, the 20 cubic miUimeters of blood from an anemic
patient gave the standard tint at 60 divisions, the blood contained
but 60 per cent, of the normal amount of hemoglobin.

Fig. 102. — GowERS' Hemoglobinometer. A. Pipette bottle for distilled water.
B. Capillary pipette. C. Graduated tube. D. Tube with standard dilution.
F. Lancet for pricking the finger. — (Landois and Stirling.)

Von Fleischl's hemometer consists of a metallic cell divided into
two compartments, a and a', by a vertical partition (Fig. 103). In
the former a definite cjuantity of blood is placed and diluted with a
known quantity of water. Beneath the compartment a' is placed
a glass wedge stained with the golden purple of Cassius or simi-
lar pigment, the color of which passes from a deep red at one end to
clear glass at the other (Fig. 104). To the side of this wedge is
placed a scale ranging from o to 120. By means of the screw,
R T, the glass wedge is moved until the color of the glass and
diluted blood is identical. The illumination of the blood and glass
wedge is accompanied by lamplight reflected from the white reflect-
ing surface beneath. The depth of color of the glass opposite 100 on

248 TEXT-BOOK OF PHYSIOLOGY.

the scale corresponds to that of normal blood. If, therefore, the
colors are identical at 75 divisions, the blood contains but 75 per
cent, of hemoglobin.

Ver}' frequently the diminution of corpuscles and hemoglobin

Fig. 103. — Von Fleischl's Hemometer. K. Red colored wedge of glass moved
by R. G. Mixing vessel with two compartments, a and a'. M. Table with
hole to read off the percentage of hemoglobin on the scale P. T. To move K.
S. Mirror of plaster-of-Paris.

proceeds along parallel lines, in which case the amount of hemoglobin
per corpuscle is supposed to be normal and the color-index = i.
If the hemoglobin diminution is greater than the corpuscles, as is
the case in many pathologic conditions, the color-index is less than
unity. If the percentage of corpuscles is determined by the method

of counting to be 80 per cent.
(4,000,000 per cubic milh-
meter) and the percentage of
hemoglobin 60, the color-
index is obtained by dividing
the latter by the former; e. g.,
f^ = 0.75. In other words,
each corpuscle has but 0.75
per cent, of the normal
amount of hemoglobin.
Absorption Spectra. — Both oxyhemoglobin and reduced hemo-
globin, Hke other soluble pigments, have an absorbing influence on
certain waves of light, and hence give rise to absorption bands which

Fig. 104. — Tinted Glass Wedge of the
VON Fleischl Hemometer. — (Da
Costa's Hematology)

THE BLOOD.

249

can be studied with the spectroscope, and which are so character-
istic as to serve for their identification.

In principle a spectroscope consists of a prism which decomposes
the light from a narrow slit into a band of all the spectral colors.
A form of spectroscope in common use is that shown in Fig. 105.
It consists of a tube, B, which has at one end a slit that can be
narrowed or widened by means of a screw. The light, having
passed through it, falls on an achromatic convex lens (called the
coUimator) at the opposite end of the tube which renders the diver-
gent rays of light parallel. These parallel rays subsequently fall
on the prism, by which they are dispersed and directed into the

Fig. 105. — The Spectroscope. A. Telescope. B. Tube for the admission of
light and carr\'ing the collimator. C. Tube containing a scale, the image of
which when illuminated is reflected above the spectrum. D. The fluid exam-
ined.— {Landois and Stirling.)

tube. A, w^hich is nothing more than a small telescope. On looking
into it at the ocular end the spectral colors are seen If the light
has been derived from the sun, the spectrum will present vertical dark
hnes, the so-called Fraunhofer's hnes. They are given from A to F
in Fig. 106. If a colored medium be held in front of the slit so that
the Hght has to pass through it first, certain dark bands wiU appear
in the spectrum, owing to the absorption of certain rays.

Dilute solutions of arterial blood show two absorption bands
between the Fraunhofer Hnes, D and E, in the green and vellow

250

TEXT-BOOK OF PHYSIOLOGY.

portion of the spectrum. (See Fig. 106.) The band nearest D
frequently designated as alpha is dark in the center and sharply-
defined. The band which Hes toward E is broader and less sharply
defined.

As the amount of light absorbed varies with the concentration of
the solution as well as its thickness, and gives rise to absorption bands
of different widths and intensities, it becomes necessary, in order to
obtain the characteristic bands, to employ only dilute solutions.

The absorption spectra, as seen with different strengths of solu-
tion one centimeter thick, are shown grapically in Fig. 107. It will be
observed that solutions varying in strength from o.i per cent, to 0.6
per cent, give rise to the two characteristic bands, but with gradually

Red. Orange. Yellow.

Green.

Cyan Blue.

Reduced
Hemoglobin

Fig. 106. — Spectra of Hemoglobin and Some of its Compounds. — (Landois and

Stirling.)

increasing breadths. With a percentage greater than 0.65 per cent,
the hght between D and E, the yellow-green, becomes extinguished
and the two bands fuse together, forming a single band overlapping
slightly the hues D and E. At the same time there is a progressive
darkening of the violet end of the spectrum. At 0.85 per cent., all
the Hght is absorbed with the exception of a small amount of the red.
Solutions less than o.oi per cent, to 0.003 V^^ cent, show but a single
absorption band — that nearest D.

A solution of venous blood or of reduced hemoglobin shows but a
single absorption band (see Fig. 106), frequently designated as
gamma, broader and less marked between the hnes D and E, but
extending slightly beyond D. Fig. 108 shows in the same graphic

THE BLOOD.

251

manner the increasing breadth of the absorption band with increas-
ing strengths of solution, as well as the simultaneous absorption of
light at both the red and violet ends of the spectrum.

Compounds of Hemoglobin. — The coloring-matter of the
blood is characterized by the property of combining with and of
again yielding up oxygen. The union is a chemic one, taking place
under certain pressure conditions. It therefore may exist in two
states of oxidation, distinguished by a difference in color and their
absorption spectra. If hemoglobin either in blood or in solution
be shaken with air, it at once combines with oxygen and is con-
verted into oxyhemoglobin, which imparts to the blood or solution a
bright red or scarlet color. If the blood or solution be now deprived

Fig. 107. — Graphic Representation
OF THE Absorption of Light in
A Spectrum by Solutions of
Oxyhemoglobin of Different
Strengths. The shading indi-
cates the amount of absorption of
the spectrum, and the numbers at
the side the strength of the solu-
tion.

Fig. 108. — Graphic Representation
OF the Absorption of Light
in a Spectrum by Solutions
OF Hemoglobin of Different
Strengths. The shading indi-
cates the amount of absorption of
the spectrum, and the numbers at
the side the strength of the solu-
tion.

of oxygen, the oxyhemoglobin is converted into reduced hemoglobin,
which imparts to the blood or solution a dark bluish or purple color.
The quantity of oxygen absorbed by i gram of hemoglobin is
estimated at 1.56 c.c. measured at 0° C. and 760 mm. of mercury.
The compound formed by the union of oxygen and hemoglobin is a
very feeble one; for when the pressure is lowered the union becomes
less stable, and as the zero point is approached, as in the Torricelhan
vacuum, a rapid dissociation of the oxygen takes place. This, how-
ever, is not due entirely to a fall of pressure but partly to the dis-
sociating force of heat, which increases in power as the pressure falls.
The same dissociation of oxygen can be brought about by passing
through blood indifferent gases, such as hydrogen, nitrogen, carbon

252 TEXT-BOOK OF PHYSIOLOGY.

dioxid, which lower oxygen pressure, or by the addition of reducing
agents, such as ammonium sulphid or Stokes' fluid.

These experimental determinations of the relation of oxygen to
hemoglobin partly explain the oxidation and deoxidation of the
hemoglobin in the lungs and tissues. As the blood passes through
the lungs and is subjected to the oxygen pressure there, the hemoglo-
bin combines with a definite quantity of oxygen, and on emerging
from the lungs exhibits a bright red or scarlet color; as the blood
passes through the systemic capillaries where the oxygen pressure
in the surrounding tissues is low, the oxyhemoglobin yields up a por-
tion of its oxygen, becoming deoxidized or reduced, and the blood
on emerging from the tissues exhibits a dark bluish color. The portion
of oxygen given up to the tissues is termed respiratory oxygen. In
loo parts of arterial blood the coloring-matter presents itself almost
exclusively in the form of oxyhemoglobin. In passing through the
capillaries about 5 per cent, only gives up its oxygen and becomes
reduced, so that both kinds are present in venous blood. In asphyx-
iated blood only reduced hemoglobin is present. It is this capa-
bihty of combining with and of again yielding up oxygen, that
enables hemoglobin to become the carrier of oxygen from the lungs
to the tissues.

Carbon Monoxid Hemoglobin. — Carbon monoxid is a con-
stituent of both coal-gas and water-gas. From either source it is
likely to accumulate in the air, and if inspired for any length of time
produces a series of effects which may eventuate in death. If blood
be brought into contact with this gas, it assumes a bright cherry-red
color, which is quite persistent and due to the displacement of the
loosely combined oxygen and the union of the carbon monoxid with
the hemoglobin. The compound thus formed is very stable and resists
the action of various reducing agents. The passage of air or of some
neutral gas through the blood for a long period of time will gradually
displace the carbon monoxid and enable the hemoglobin to again
absorb oxygen. It is for this reason that partial poisoning with the
gas is not fatal. It is to its power of displacing oxygen and form-
ing a stable compound with hemoglobin and thus interfering with
its respiratory function that carbon monoxid owes its poisonous
properties. Examined spectroscopically, solutions of carbon mon-
oxid hemoglobin exhibit two absorption bands closely resembling
in position and extent those of oxyhemoglobin; but careful examina-
tion shows that they are slightly nearer the violet end of the spectrum
and closer together. (See Fig. 106.) A useful test for CO blood
is the addition of caustic soda, which produces a cinnabar red pre-
cipitate.

Methemoglobin. — This is a pigment, closely related to oxy-
hembglobin, found in the blood after the administration of various

THE BLOOD. 253

drugs, in cysts and in the urine in hematuria and hemoglobinuria.
It is also produced when a solution of hemoglobin is exposed to the
air and becomes acid in reaction and brown in color. The spectrum
shows two absorption bands similar to oxyhemoglobin, but in addition
a new and r^uite distinct band near the hne C, in the red. If the
acid solution be rendered alkaline by the addition of ammonia, this
band disappears and another makes its appearance near the hne D.
The addition of ammonium sulphid develops reduced hemoglobin,
which, on the absorption of oxygen, produces again oxyhemoglobin,
as shown by the spectroscope.

Hematin. — Boihng hemoglobin or adding to it acids or alka-
lies decomposes it and develops one or more proteid bodies to
which the general term globulin has been given, and an iron-holding
pigment termed hematin. This is regarded as an oxidation product
of hemoglobin and constitutes about 4 per cent, of its composition.
When obtained in a pure state, it is a non-crystalhzable blue-black
powder with a metalhc luster. According as it is treated with acids or
alkahes, two forms of hematin can be obtained (acid and alkahne),
each of which has special properties, giving rise to different absorp-
tion bands.

Hemochromogen. — This pigment is derived from hemoglobin,
of which it constitutes about 96 per cent., during decomposition in
the absence of oxygen. In solution it produces a purple color, but
soon absorbs oxygen and is converted into hematin.

Hemin. — This pigment is a derivative of hematin, presenting
itself in the form of microscopic rhombic plates or rods (Teichmann's
cr)'stals), which are so characteristic as to serve as tests for blood-
stains in medico-legal inquiries. These cr\-stals are readily obtained
by adding to a small quantity of dried blood on a glass shde a few
drops of glacial acetic acid and a cr}'stal of sodium chlorid; after
heating gently for a few minutes over a spirit lamp and then allowing
the mixture to cool, cr}'stanization of the hemin soon takes place.

Hematoidin. — This term has been apphed to a pigment which
occurs in the form of yellow cr}'stals in old blood-clots or in blood
which has been extravasated into the tissues. In its chemic com-
position and in its reactions it closely resembles bilirubin, the pigment
of the bile, exhibiting the same characteristic play of colors on the
addition of nitric acid.

The Stroma. — The stroma of the red corpuscles obtained by the
methods which dissolve out the hemoglobin has been shown by
analysis to consist of from 60 to 70 per cent, of water and 40 to 30
per cent, of solid material, containing a proteid resembling cell-
globulin, lecithin, cholesterin, and inorganic salts, among which
potassium phosphate is especially abundant.

254 TEXT-BOOK OF PHYSIOLOGY.

HISTOLOGY OF THE WHITE CORPUSCLES OR LEUKOCYTES.

The histologic features of the white corpuscles can readily be
observed under the same conditions as in the case of the red corpuscles.
Within the smaller blood-vessels they are seen adhering to the walls
of the vessel ; in a drop of freshly drawn blood they are found in the
spaces between the rouleaux of red corpuscles. (See Fig. 96, p. 236.)

Shape and Size. — In the resting condition, whether seen in the
vessel or on the stage of the microscope, the white corpuscle, as its
name implies, is grayish in color, round or globular in form, though
often presenting a more or less irregular surface. Its diameter varies
from 0.0004 to 0.0013 mm., though the average is about o.ooii mm.
or about -2^^~o inch.

Structure. — A typical white corpuscle consists of a ground-
substance uniformly transparent and apparently homogeneous, in
which are embedded a number of granules of varying size, some of
which are very fine, while others are larger. By various reagents it
has been demonstrated that the granules are fatty, proteid, and
carbohydrate (glycogen) in character. In the fresh cells the ex-
istence of a nucleus is difficult of detection, though its presence can
be demonstrated by the addition of acetic acid, which renders the
perinuclear cytoplasm more transparent and makes the nucleus
conspicuous and sharply defined. From its structure it is apparent
that the white corpuscle belongs to the group of undifferentiated
tissues and resembles the cells of the embryo in its earliest stages as
well as the unicellular organism, the amceba.

Number of White Corpuscles. — The number of white cor-
puscles per cubic millimeter of blood is much less than the number
of red corpuscles, the ratio being in the neighborhood of i white to
700 red. This ratio, however, varies within wide limits in different
portions of the body and under normal variations in physiologic
conditions. In the blood of the splenic artery there is but i white
to 2260 red, while in the splenic vein there is i white to every 60 red;
or about thirty-eight times as many as in the artery. In the portal
vein there is i white to 740 red, while in the hepatic vein there is i
white to 170 red.

The total number of white corpuscles per cubic milhmeter has
been estimated at from 5000 to 10,000, though the average is about
7500. The number, however, is influenced by a variety of physio-
logic conditions. The ingestion of food rich in proteid material
raises the count from 30 to 40 per cent., as compared with the
count before the meal. Fasting for a few days always lowers the
count, and in a case of total abstinence of food for a week, reported
by Luciani, the count fell to 861 per cubic millimeter, after which
it rose to 1530, where it practically remained for the succeeding three

THE BLOOD.

255

Fig.

109.- — HxjMAN Leukocytes show-
ing Ameboid Movements.

weeks of the fasting period. In the new-born the number is greater
than in adults — 17,000 to 20,000 per cubic miUimeter. Cabot states
that 30,000 is never a high count after a meal in infants under two
years. In the later months of
pregnancy, especially in primi-
parae, the number increases to
16,000 to 18,000. jMany patho-
logic conditions of the body also
influence the count very con-
siderably.

The method for counting the
white corpuscles is similar to that
used in counting the red. The
given volume of blood should,
however, be diluted with 10 vol-
umes of a one-third of one per
cent, solution of acetic acid,
which renders the red corpuscles
invisible and thus facihtates the
counting of the white. The pip-
ette should have a larger bore

than that used for the red, and a greater number of squares in the
counting chamber should be counted, so as to diminish the percent-
age of error.

Physiologic Properties. — The white corpuscles possess the

characteristic property of
exhibiting movements simi-
lar to those observed in the
amoeba, and are therefore
termed ameboid. These
movements consist in alter-
nate protrusions and re-
tractions of portions of the
cell body, as a result of
which they exhibit a great
variety of forms. (See Fig.
109.) The protruded pro-
cess can also attach itself
to some point of the sur-
face on which it rests, and
then draw the body of the
corpuscle after it. By a
repetition of this process
the corpuscle can slowly
creep about and change its position in space. In virtue of these

Fig. no. — Small Vessel of a Frog's Mesen-
tery showing Diapedesis. w, w. Vas-
cular walls, a, a. Poiseuille's space, r,
r. Red corpuscles. /, /. Colorless cor-
puscles adhering to the wall, and, c, c, in
various stages of extrusion. /, /. Ex-
truded corpuscles. — {Landois and Stirling.)

256 TEXT-BOOK OF PHYSIOLOGY.

ameboid movements the corpuscle can appropriate small particles
of pigment, such as indigo or carmine, and after a short time
ehminate them from various parts of the surface. It is also capable
of thrusting a process into and through the wall of the capillary
vessel, after which the remainder of the corpuscle follows (Fig.
no). This continues until the corpuscle is outside the vessel and in
the lymph-space, where it resumes its original shape and movement.
This process is best observed in inflammatory conditions, when the
blood has come to rest and the vessels are occluded with both red and
white corpuscles. To this passage of the white blood-corpuscles
through the capillary wall the term diapedesis is given. The move-
ments of the white corpuscles are increased by a rise in temperature
up to 40° C, beyond which they cease, owing to the coagulation of
the cell-substance. A low temperature also arrests the movements.
Induced electric currents also cause contraction and death of the cell.
Moisture and oxygen are necessary to their activity. From their
similarity to lower organisms the white corpuscles may be regarded
as independent organisms living in the animal fluids, just as the
amoeba lives in its natural liquid medium.

Classification. — With the aid of the tricolor staining fluid of
Ehrlich four distinct forms of white corpuscles or leukocytes can be
demonstrated to be present in the blood, viz.:

1. Small lymphocytes, so called from their resemblance to the cor-

puscles of the lymph-glands, consisting of a small dark nucleus
surrounded by a very thin layer of cytoplasm.

2. Large mononuclear lymphocytes, which represent the preceding type

at a later stage of development and in the possession of a large
amount of perinuclear cytoplasm more or less hyaline and devoid
of granules. The nucleus is often deeply notched, resembling a
horseshoe in shape. This cell is capable of executing ameboid
movements.

3. Polymorphonuclear leukocytes or neutrophiles, which represent

the adult condition of the cell. The nucleus is irregular and
assumes a variety of shapes in different cells, a feature which
has suggested the name given to the cell. The perinuclear cyto-
plasm contains a number of granules which are made evident
when stained with the neutral mixture of Ehrlich. These
cells exhibit active ameboid movements. They make up about
60 to 70 per cent, of the whole number of the white blood-cells.

4. Eosinophile cells, the granules of which stain most readily with

acid stains like eosin. The granules are spheric and larger
than in the previous cell. The nucleus is pale and irregular
in shape. The eosinophile cell is regarded as the old or "over-
ripe" cell and is the most actively ameboid of all the cells. It
is present to the extent of from ^ to 4 per cent.

{Triacid Stain.")

I, 2, 3, 4. Small Lymphocytes.

Contrast the faintly colored protoplasm of these cells in the triple stained specimen
with their intensely basic protoplasm in the film stained with eosin and methylene-
blue, 17 and 18. The cell body of i is invisible. Note the kidney-shaped nucleus
in 4.

5, 6. Large Lymphocytes.

With tliis stain the nucleus reacts more strongly than the protoplasm; with eosin
and methylene-blue (19, 20), on the contrary, the protoplasm is so deeply stained
that the nucleus appears pale by contrast. This peculiarity is also observed in
the smaller forms of lymphocytes.

7, 8. Transitional Forms.

Note the moderately basic and indented nucleus, and the almost hyahne non-
granular protoplasm. Compare 8 with the myelocyte, 7, Plate I, these cells
differing chiefly in that the myelocyte contains neutrophile granules.

9, 10, II. Polynuclear Neutrophiles.

These cells are characterized by a polymorphous or polynuclear nucleus, sur-
rounded by a cell body filled with fine neutrophile granules. In 11 the nuclear
structure is obviously separated into four parts; in 9 it is moderately, and in 10
markedly, polymorphous.

12, 13. Eosinophiles.

The nuclei are not unlike those of the polynuclear neutrophile, except that they
are somewhat less convoluted, and poorer in chromatin, staining less intensely.
The protoplasm is filled with coarse eosinophile granules, the characteristics of
which are clearly illustrated by 13, a "fractured" eosinophile.

14. Eosinophilic Myelocyte.
Compare with 15.

15, 16. Myelocytes. {Neutrophilic.)

These cells are morphologically similar to 14, except that they contain neutrophile
instead of eosinophile granules. Note that the granules of the myelocyte are
identical with those of the polynuclear neutrophile. A dwarf form of myelocyte
is represented by 16.

{Eosin and Methylene-blue.)

17, 18. Small Lymphocytes.

Note the narrow rim of pseudo-granular basic protoplasm surrounding the nucleus,
and the pale appearance of the latter.

19, 20. Large Lymphocytes.

Budding of the basic zone of protoplasm is represented by 20. Both of these
cells belong to the same type as 5 and 6.

21, 22. Large Mononuclear Leukocytes.

Compared with 19 and 20, these cells have a decidedly less basic protoplasm, but
a somewhat more basic nucleus. In the triple stained film these differences can-
not be detected, so that they must be classed as large lymphocytes.

23. Transitional Form.

The distinction between this cell and 24 is not marked; the nucleus of the latter
simply being somewhat more basic and convoluted.

24, 25, 26, 27. Polynuclear Neutrophiles.

With this stain these cells show a feebly acid protoplasm, and lack granules.
Note that the more twisted the nucleus the deeper it is stained. Compare with
9, 10, and II.
28, 29. Eosinophiles.

Compare with 12 and 13.

30. Eosinophilic Myelocyte.
Compare with 14.

31. Basophile. {Finely granular.)

This cell is characterized by the presence of exceedingly fine (5-granules, staining
the pure color of the basic dye. The nucleus is markedly convoluted and deficient
in chromatin. The cell here shown was found in normal blood.

32. 33, 34, 35, 36. Mast Cells.

The granules take a modified basic color, as shown by their royal-purple tint in
this illustration. Note their unusually large size and ovoid shape in 35, their
peculiar distribution in 35 and 36, and their irregularity in size in 32 and 36.
With the triacid mixture these granules, as well as those of the finely granular
basophile, 31, remain unstained, showing as dull-white stippled areas in the cell
body. The nuclear chromatin of the mast cell is so delicate and so feebly stained
that it is barely visible. These cells were found in the blood of a case of spleno-
medullary leukemia.

PLATE I.

/TX

O O ( . j t

The Leukocytes.

(1-16, Triacid Stain; 17-36, £oiJ« ani Methylene-blue.)

(E. F. Faber, /fc.)

(From DaCosla's ''Clinical Hematology.")

THE BLOOD. 257

Origin of White Corpuscles. — The white corpuscles which are
present in the blood are beheved to be derived from the lymphocytes
or lymph-corpuscles which find their way into the blood at the points
where the lymph-ducts discharge their lymph: viz., at the junc-
tions of the internal jugular and subclavian veins. Along the course
of the lymph-vessels are to be found, in different regions of the
body, numerous lymph-glands the meshes of w^hich are filled with
small, colorless, nucleated cells, which arise by self-division and rep-
resent the early stages in the development of lymphocytes. Similar
corpuscles are found in the mucous membranes, skin, spleen, and the
fluids of the tissues. As the lymph flows through the glands these cells
are washed out and carried direct to the blood. In their passage they
grow in size by increasing the amount of their cytoplasm and even-
tually become normal adult leukocytes. After an unknown period
of life they undergo dissolution and disappear.

Chemic Composition. — The chemic composition of the white
corpuscles has been inferred from an analysis of pus-corpuscles,
with which they are practically indentical, and of lymph-corpuscles
from the lymph-glands. Of the corpuscle about 90 per cent, is
water and the remainder solid matter consisting mainly of proteids,
of which nuclein, nucleo-albumin, and cell globulin are the most
abundant. The two former are characterized by the presence of a
considerable quantity of phosphorus, amounting to as much as 10
per cent. Lecithin, fat, glycogen, and earthy and alkahne phos-
phates are also present.

Functions. — The functions of the white corpuscles are but im-
perfectly known, and at present no positive statements can be made.
It has been suggested that wherever found in the body, whether in
blood or tissues, they are engaged in the removal of more or less in-
soluble particles of disintegrated tissues, in attacking and destroying
more or less effectively various forms of invading bacteria and thus
protecting the body against their deleterious activity. This they do
by surrounding, enveloping, and incorporating either the tissue par-
ticle or bacterium and digesting it. On account of this swallowing
action these cells were termed by Metchnikoff phagocytes and the
process phagocytosis. He regards them as the general scavengers of
the body. It has been suggested that they are also engaged in
the absorption of fat from the lymphoid tissue of the intestine. In
their dissolution they contribute to the blood-plasma certain proteid
materials which assist under favorable circumstances in the coagu-
lation of the blood.

HISTOLOGY OF THE BLOOD-PLATES.

The blood-plates or plaques are small histologic elements circu-
lating in the blood-plasma. They were discovered by Hayem, who
17

2S8 TEXT-BOOK OF PHYSIOLOGY.

applied to them the term hematoblasts, on the supposition that they
were the early stages in the development of the red corpuscles. This
is now known to be erroneous. On account of their specific, distinct
characters, and their constant presence in the blood of living animals
(guinea-pig and bat), they are now regarded as normal constituents
of the blood and designated as the third corpuscle. When blood is
freshly drawn from the body, the plaques rapidly undergo disintegra-
tion and disappear; but by treating the blood with osmic acid, the
form and structure of the plaque may be retained.

The blood-plaque may be defined as a colorless, grayish- white,
homogeneous or finely granular protoplasmic disk, varying in diam-
eter from 1.5 to 3.5 micro-millimeters. The edges are rounded and
well defined, but it is not certain whether they are only flattened or
are slightly biconcave. There is, however, no nucleus. The ratio of
the plaques to the red corpuscles is i to 18 or 20, and the total number
per cubic millimeter has been estimated to be 250,000 to 300,000.

When blood is shed they tend to adhere to each other and form
irregular masses known as Schultze's granular masses. If threads
are suspended in blood, the plaques accumulate in enormous numbers
upon them and appear to form a center from which fibrin filaments
radiate as coagulation proceeds. The white thrombi which form in
blood-vessels in consequence of diseased states — e. g., endocarditis,
atheromatous ulceration, etc. — are composed very largely of blood-
plaques and fibrin threads. The function of the blood-plaques is
unknown, but it has been surmised that in some way they are, like
the leukocytes, concerned in the coagulation of the blood. When-
ever they are diminished in number, as in purpura and hemophilia,
coagulation tends to take place very slowly.

The blood-plaques can be seen with high powers of the micro-
scope in the blood-vessels of the omentum of the guinea-pig and rat,
especially when the blood-stream begins to slow. They are also
readily seen in the blood-vessels of subcutaneous connective tissue
of various animals, and especially in that of the new-born rat. A
small quantity of this tissue moistened with normal saline and exam-
ined microscopically with suitable powers will show large numbers
of plaques within the blood-vessels.

THE TOTAL QUANTITY OF THE BLOOD; ITS GENERAL COMPOSITION.

The determination of the total quantity of the blood in an animal
is best made by the chromometric method, somewhat modified at
present, of Welcker. This consists, first, in bleeding an animal,
collecting all the blood it yields, and weighing it; second, in washing
out the vessels with a normal saline solution until the fluid comes
from the veins clear and free from blood; third, in mincing the tissues

THE BLOOD. 259

of the body, after removal of the contents of the alimentary canal,
soaking them in water for twenty-four hours, and then expressing
them. All the washings are collected and weighed. A given
volume of the normal defibrinated blood, treated with carbon
monoxid so as to give it uniform color, is then diluted with water
until its tint is identical with that of the washings similarly treated
with carbon monoxid. From the quantity of water necessary to
dilute the blood the quantity of blood in the washings is readily
determined. The animal having been previously weighed and the
weight of the contents of the alimentary canal deducted, the ratio
of the total weight of the blood to the weight of the body at once
becomes apparent. By this method it has been shown that the ratio
of blood to body- weight in a human adult is i : 13; in an infant,
I : 19; in a dog, i : 13; in a cat, i : 21. Thus an adult man of 75
kilos weight would have 5769 grams of blood.

The amount of blood in the different organs has been determined
by ligating the blood-vessels in the living animal, removing the organ,
and after allowing the blood to escape subjecting the tissues to the
chromometric methods described above. According to Ranke, the
volume of the blood is distributed as follows: Heart, lungs, arteries,
and veins, ^; Hver, I; muscles, \; other organs, ^.

General Composition. — The results of the analyses of the blood
will varv' with the animal and the methods employed. The following
table, taken from Gad, shows the average composition, expressed in
whole numbers, of horse's blood. In essential respects the ratio of
the constituents in human blood would not be materially different.

One thousand parts of blood contain :

(Water, 200 200
THemoglobin, 116
Solids, 128 -< Other organic matter, 10

(Salts, 2

fWater, 604 604

Fibrin, 7

Albumin, 52

Fat, I

Other organic matter, 3

Potassium and sodium salts, 4

Calcium and magnesium salts, i

Plasma, 672

'-Solids, 68

CHEMISTRY OF COAGULATION.

The changes which eventuate in the formation of fibrin, and
hence all the subsequent phenomena of coagulation, are chemic in
character; but as these changes take place in organic compounds the
composition of which is but imperfectly known, the intimate nature
of the process is quite obscure. All the theories which have been
advanced in explanation, though approximating the truth, are more
or less incomplete and in some respects contradictory. Since the

26o TEXT-BOOK OF PHYSIOLOGY.

coagulation is coincident with the appearance of the fibrin, the ante-
cedents of this substance, the physical and chemic conditions which
condition its development, and the succession of chemic changes in-
volved must be determined, before any consistent theory can be
established.

Extra-vascular Coagulation. — At present it is generally be-
lieved that the immediate factors concerned in extra-vascular coagu-
lation are fibrinogen, a calcium salt, and a ferment-body. As to the
manner in which these three bodies react one with another there is a
diversity of opinion. At least five different theories are current at
the present time, all of which have some features in common, though
presenting points of difference.

Alexander Schmidt long contended that fibrin was the result of
a union of fibrinogen and paraglobulin ; that the union was brought
about by a ferment-body; that the presence of the neutral salts of the
plasma was necessary to the activity of the ferment. Previous to his
death in 1893 Schmidt modified his view as follows: The insoluble
fibrin is developed out of a soluble fibrin derived from paraglobuhn,
which in turn is a product of general cell disintegration; the conver-
sion of the fibrinogen into fibrin is due to the activity of a ferment,
thrombin, a derivative of pro-thrombin, a product of the disintegra-
tion of leukocytes, lymph-cells, etc. ; that the production of thrombin
is conditioned by the presence of the neutral salts of the plasma in
normal percentages ; that no one of these salts, calcium included, acts
in a specific manner; finally, that fibrin is not a compound of a pro-
teid and calcium.

Hammersten, as a result of many years of investigation, beheves
that paraglobuhn is not necessary to the process, fibrinogen alone
being transformed into fibrin under the influence of the ferment, in the
presence of a neutral salt, especially calcium, which acts specifically
in a manner different from the sodium salts. Inasmuch as the quan-
tity of fibrin produced is always less than the quantity of fibrinogen
previously present, Hammersten concludes that the latter substance,
under the influence of the ferment, undergoes a cleavage into two
unequal portions, one of which remains in solution, the other sohdify-
ing as fibrin. While admitting that the calcium salts act specifically,
he believes that they are concerned rather with the production of the
ferment than the fibrin, for if the ferment is present in sufficient
quantity coagulation takes place in a typical manner even in the total
absence of calcium.

Arthus and Pages conclude that for the transformation of fibrin-
ogen into fibrin the calcium salts are absolutely essential and act in a
specific manner; that the ferment causes a cleavage of fibrinogen into
two substances, one of which remains in solution, the other com-
bines with calcium to form fibrin. They offer in support of this

THE BLOOD. 261

view the fact that if a i per cent, solution of potassium oxalate be
added to blood in quantity sufficient to precipitate the calcium, coagu-
lation will not take place; but if calcium is restored coagulation
proceeds in the usual manner. They transfer the sphere of influence
of calcium to the formation of the fibrin rather than to the formation
of the ferment.

Pekelharing's researches led him to the conclusion that there
arises from the disintegration of the leukocytes a nucleo-proteid,
pro-thrombin, which combining with the calcium salt forms the
ferment thrombin. This compound then transfers the calcium to
the fibrinogen, which in turn becomes fibrin; the latter is therefore
a proteid-calcium compound.

Lihenfeld asserts that fibrin formation is a cleavage process by
which fibrinogen is separated into two bodies, one an albumose which
remains in solution, the other a proteid to which he has given the
name thrombosin. This cleavage is attributed to the action of the
usual ferment, a product of the disintegration of leukocytes. Throm-
bosin combines, according to Lilienfeld, with calcium to form fibrin.

In a critical examination of these different theories Hammersten
denies that fibrin is a compound of a proteid and calcium ; for chemic
analysis of both fibrinogen and fibrin shows that the former contains
as much calcium as the latter, and that therefore the view of coagu-
lation according to v^hich fibrinogen unites v^ith calcium to form
fibrin is without foundation. On the contrary, he maintains that the
specific influence of the calcium is directed toward the production of
the ferment, for if this be present in sufficient quantity coagulation
takes place in a typical manner, no matter vv^hether the blood has
been decalcified by potassium oxalate or not.

Intra-vascular Coagulation. — So long as the relations of the
blood and the vascular system remain physiologic no coagulation
occurs in the vessels. The reason assigned for this is that the fer-
ment, though continually being produced, is as rapidly being de-
stroyed, and hence never accumulates in amount sufficient to develop
fibrin. This view is supported by the fact that if a solution of cell-
protoplasm, leukocytes, lymph-corpuscles, etc., presumably contain-
ing a large amount of the ferment, be injected into the blood-vessels,
extensive intra-vascular coagulation promptly follows. It is also
believed that the lining of the blood-vessel in some unknown way
restrains the coagulation process even though the circulation has
come to rest.

Under pathologic conditions of the circulatory apparatus, espe-
cially of the internal lining, intra-vascular coagulation frequently
arises, though the process can not be considered as identical with
extra-vascular coagulation. Many pathologists assert that in its
origin, mode of formation, and structure the intra-vascular coagulum

262 TEXT-BOOK OF PHYSIOLOGY.

or thrombus is not a true coagulum as ordinarily understood, but
rather a conglutination of blood-elements. Whenever the integrity
of the internal wall of the vessel is impaired by disease or by the in-
troduction of foreign bodies, there is primarily a deposition and
accumulation of blood-plaques at the injured area or on the foreign
body which constitutes to a large extent the mass of the thrombus
which at once forms. The thrombi which form on the surface of
atheromatous ulcers, on the valves of the heart, and in the veins in
consequence of diseased states, on threads or needles passed through
the vessels, at the orifices of torn blood-vessels, consist largely of
blood-plaques. A thrombus so formed may contain a number of
delicate fibrin threads, which, however, present a different appear-
ance from the fibrin of the extra- vascular clot. In the thrombi which
form around foreign bodies there is always a larger quantity of fibrin
than in those originating from causes wholly within the vessel.

CHAPTER XII.
THE CIRCULATION OF THE BLOOD.

Each organ and tissue of the body is the seat of a more or less
active metabohsm, the maintenance of which is essential to its physio-
logic activity. This metabohsm is characterized by the assimilation
of food materials and the production of waste products ; that it may
be maintained it is imperative that there shall be a continuous supply
of the former and a continuous removal of the latter. Both condi-
tions are subserved by the blood. In order, however, that this fluid
may fulfil these functions it must be kept in continuous movement,
must flow into and out of the tissues in volumes varying with their
activity, under a given pressure and with a certain velocity.

The apparatus by which these results are attained is termed
the circulatory apparatus. This consists of a central organ,
the heart; a series of branching diverging tubes, the arteries; a net-
work of minute passageways with extremely delicate walls, the capil-
laries; a series of converging tubes, the veins. These structures are
so arranged as to form a closed system of vessels within which the
blood is kept in continuous movement mainly by the pressure pro-
duced by the pumping action of the heart, though aided by other
forces. (See Fig. III.)

In this system a particle of blood which passes any given point
will eventually return to the same point, no matter how intricate or
tortuous the route may be through which it in the mean while travels ;
for this reason the blood is said to move in a circle, and the movement
itself is termed the circulation.

In order to understand the reasons for the movement of the blood
in one direction only, as well as for many other phenomena connected
with the circulation, a knowledge of the structure of the heart and
its internal mechanism is of primary importance.

THE PHYSIOLOGIC ANATOMY OF THE HEART.

The heart is a cone or pyramid shaped hollow muscular organ
situated in the thorax just behind the sternum. The base is directed
upward and to the right side ; the apex downward and to the left side,
extending as far as the space between the cartilages of the fifth and
sixth ribs. In this situation the heart is enclosed and suspended
in a fibroserous sac, the pericardium, attached to the great vessels at
its base.

263

264

TEXT-BOOK OF PHYSIOLOGY.

The heart is a double organ, consisting of a right and a left half,

separated by a vertical septum. The
general cavity of each side is partially
subdivided by a transverse constriction
into two smaller cavities, an upper and
a lower, known respectively as the
auricle and the ventricle. The heart
may therefore be said to consist of
four cavities, the walls of which are
composed of muscle-tissue. Of these
four cavities, the right auricle and the
right ventricle constitute the venous
heart; the left auricle and the left
ventricle, the arterial heart.

The right auricle is quadrangular
in shape and presents on its posterior
aspect two large openings, the termi-
nations of the two final trunks of the
venous system, the superior and in-
ferior vena cavce (Fig. 112). Below,
the auricle communicates with the ven-
tricle by a large opening which, from
its position, is termed the auriculo-
ventricular opening. The walls of the
auricle are extremely thin, not meas-
uring more than two millimeters in
thickness.

The right ventricle, as shown on
cross-section, is crescentic in shape
owing to the projection of the ven-
tricular septum. It presents at its
upper left angle a cone-shaped pro-
longation, the conus arteriosus. From
this prolongation, and continuous with
it, arises the pulmonary artery. The
wall of the ventricle measures in the
middle about four millimeters in thick-
ness. The inner surfaces of the ven-
tricle show: (i) a comphcated system
of muscle ridges and bands, the col-
umncB carnece (fleshy columns), and
(2) a set of muscle projections, the
musculi papular es (papillary muscles),
which arise by a broad base from the
walls of the ventricle and project upward toward the auriculo-

FiG. III. — Diagram of Circula-
tion. I. Heart. 2. Lungs.
3. Head and upper extremi-
ties. 4. Spleen. 5. Intestine.
6. Kidney. 7. Lower e.xtremi-
ties. 8. Liver. — (Dallon.)

THE CIRCULATION OF THE BLOOD.

265

ventricular opening. From the apex of each papillary muscle there
are given off fine tendinous cords, the chordcB iendincce, which become
attached above to the auriculo-ventricular valve.

Fig. 112. — 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. -\ — \-. Placed
in the auriculo-ventricular groove, where a narrow portion of the adjacent walls
of the auricle and ventricle has been preser\'ed. 4, 4. Cavity of the right ventri-
cle; 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 cov-
ered 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. 11, 11. The outside of the left ventricle, the lower figure near
the apex. — {Allen Thomson.)

The left auricle, similar in general shape to the right, presents
posteriorly four openings, the terminations of the four final trunks
of the venous system of the lungs, the pulmonary veins. Below is

266

TEXT-BOOK OF PHYSIOLOGY.

Fig. 113. — The Left Auricle and Ventricle Opened and a Part of Their
Anterior and Left Walls Removed. J. — The pulmonary artery has been
divided at its commencement; the opening into the left ventricle is carried a short
distance into the aorta between two of the segments of the semilunar valves;
and the left part of the auricle with its appendix has been removed. The right
auricle is out of view. i. The two right pulmonary veins cut short; their open-
ings are seen within the auricle, i'. Placed within the cavity of the auricle on
the left side of the septum and on the part which forms the remains of the valve
of the foramen ovale, of which the crescentic fold is seen toward the left hand
of i'. 2. A narrow portion of the wall of the auricle and ventricle preserved
round the auriculo-ventricular orifice. 3, 3'. The cut surface of the walls of the
ventricle, seen to become very much thinner toward 3", at the apex. 4. A small
part of the anterior wall of the left ventricle which has been preserved with the
principal anterior columna carnea or musculus papillaris attached to it. 5, 5.
Musculi papillares. 5'. The left side of the septum, between the two ventricles,
within the cavity of the left ventricle. 6, 6'. The mitral valve. 7. Placed in
the interior of the aorta, near its commencement and above the three segments of
its semilunar valve which are hanging loosely together. 7'. The exterior of the
great aortic sinus. 8. The root of the pulmonary artery and its semilunar valves.
8'. The separated portion of the pulmonary artery remaining attached to the
aorta by 9, the cord of the ductus arteriosus. 10. The arteries rising from the
summit of the aortic arch. — (Allen Thomson.)

THE CIRCULATION OF THE BLOOD.

267

placed the corresponding auriculo-ventricular opening. The wall
of the auricle measures about 3 mm. in thickness. The left ventricle
(Fig. 113) is conic in shape from above downward and oval or cir-
cular in shape on cross-section. At its upper right angle it presents
a circular orifice, the margins of which give attachment to the walls
of the aorta, the main arterial trunk of the systemic circulation. The
inner surfaces of the ventricle show a similar though better devel-
oped system of columnae carneae, muscuh papillares, chordae tendinese,
etc. The wall of the left ventricle measures about 11.5 mm. in thick-
ness in the middle.

The Endocardium. — The cavities of both the right and left sides
of the heart are lined by a thin firm connective-tissue membrane,
closely adherent to the muscle-
tissue, termed the endocar-
dium. It also contains elastic
fibers and smooth muscle-
fibers. Its entire surface is
covered over with a layer of
polygonal endothelial cells.
This membrane serves to re-
sist undue distention of the
heart during contraction and
to prevent separation of the
muscle-fibers. The endocar-
dium is continuous with the
hning membrane of the blood-
vessels.

The Cardio - pulmonary
Vessels. — Though the two
sides of the heart are separ-
ated from each other by a
vertical septum, they are ana-
tomically and physiologically
connected by the intermedia-
tion of the pulmonary system
of vessels: viz., the pulmonary
artery, capillaries, and veins
(Fig. 114).

The pulmonary artery arises from the conus arteriosus of the right
ventricle. After a short upward course it divides into a right and a
left branch, which enter corresponding lungs. The vessel at once
divides and subdivides into a number of branches, which, after fol-
lowing the bronchial tubes to their termination, give origin to capil-
laries that surround the air-cells of the pulmonary lobules.

The capillaries in this situation are extremely abundant and well

Fig. 114. — Diagram of the Heart and
Pulmonary Circulation in Mamma-
lians, a. Right auricle, b. Right ven-
tricle, c. Pulmonary artery, d. Lungs.
e. Pulmonary vein. /. Left auricle, g.
Left ventricle, h. Aorta, i. Vena cava.
—{Dalto)i.)

268

TEXT-BOOK OF PHYSIOLOGY

developed. They lie close to the inner surfaces of the air-cells. The
blood is thus brought into intimate relationship with the pulmonary
air, and the exchange of gases — the excretion of carbon dioxid and
the absorption of oxygen — for which the cardio-pulmonary vessels
exist, is readily accomphshed.

The pulmonary veins which return the blood to the heart are
formed by the convergence and union of the small veins which emerge

from the capillary sys-
tem. The final trunks
thus formed, the four
pulmonary veins , — two
from each lung, — enter
the posterior wall of the
left auricle.

The Course of the
Blood through the
Heart. — There is thus
estabhshed a pathway
between the venae cavas
on the right side and the
aorta on the left side, by
way of the right side of
the heart, the cardio-
pulmonary vessels, and
the left side of the heart.
The venous blood
flowing toward the heart
is emptied by the supe-
rior and inferior vense
cava into the right auri-
cle, from which it passes
through the auriculo-
ventricular opening into
the right ventricle (Fig.
115); thence into and
through the pulmonary
artery and its branches
to the pulmonary capil-
laries, where it is arteriahzed by the exchange of gases — the giving
up of a portion of carbon dioxid to the lungs and the absorption
of oxygen — and changed in color from bluish-red to scarlet. The
arteriahzed blood, flowing toward the heart, is emptied by the pul-
monary veins into the left auricle, from which it passes through the
auriculo-ventricular opening into the left ventricle; thence into the
aorta and its branches to the systemic capillaries, where it is

Fig. 115. — Diagram or Course of Blood through
THE Heart, i, 2. Superior and inferior venae
cavee. 3. Right auricle. 4. Right ventricle.
5, 5, 5. Pulmonary artery and branches. 6, 6.
Pulmonary veins. 7. Left auricle. 8. Left
ventricle. 9. Aorta. 10. Innominate artery.
II. Left carotid artery. 12. Left subclavian
artery. — {After Moral and Doyon.)

THE CIRCULATION OF THE BLOOD. 269

de-arterialized by a second but opposite exchange of gases — the
giving up of a portion of its oxygen to the tissues and the absorption
of carbon dioxid from the tissues — and changed in color from scarlet
to bluish-red. The venous blood is again returned by the systemic
veins to the venae cavas. Though the blood is thus described as
flowing first through the right side and then through the left side, it
must be kept in mind that the two sides fill synchronously; that
while the blood is flowing into the right side from the venas cavae,
it is also flowing from the pulmonary veins into the left side in equal
quantities and velocities.

Though there is but one set of capillaries, as a rule, between
arteries and veins, there is an exception in the case of the arteries and
veins of the abdominal viscera. Thus the veins emerging from the
capillaries of the stomach, intestines, pancreas, and spleen, instead
of passing directly to the inferior vena cava, unite to form a large
vein — the portal vein — which enters the liver. In this organ the
portal vein divides to form a second capillary system which is in
close relation to the liver cells and from which arise the veins which
unite to form the hepatic veins. These latter vessels empty into the
inferior vena cava just below the diaphragm.

From the foregoing facts physiologists frequently divide the
general circulation into:

1. The pulmonary circulation, which includes the course of the blood

from the right side of the heart through the lungs, to the left
side of the heart.

2. The systemic circulation, which includes the course of the blood

from the left side of the heart through the aorta and its branches,
through the capillaries and veins to the right side of the heart.

3. The portal circulation, which includes the course of the blood from

the capillaries of the stomach, intestines, pancreas, and spleen
through the portal vein to the liver.

Orifices and Valves. — The movement of the blood along the
path of the circle above outlined is accomphshed by the alternate
contraction and relaxation of the muscle walls of the heart. That
the movement may be a progressive one, that there shall be no
regurgitation during the relaxation, it is essential that some of the
orifices of the heart be closed. This is accomphshed by the heart
valves.

The right auriculo-ventricular opening is surrounded and strength-
ened by a ring of fibrous tissue to which is attached a membrane par-
tially subdivided into three portions or cusps, which during the period
of relaxation are directed into the ventricle (Fig. 116); during the
period of contraction they are raised and placed in complete apposi-
tion, when they act as a valve preventing a backward flow into the
auricle (Fig. 117). In the former position the valve is open; in the

270

TEXT-BOOK OF PHYSIOLOGY.

Fig. 116. — Right Cavities of the Heart.
Atiriculo-ventricular valves open, arte-
rial valves closed. — (DaUon.)

latter, shut. For these reasons this structure is known as the tri-
cuspid valve. This valve is
formed of fibrous tissue de-
rived from the fibrous ring,
some muscle-fibers, covered
over by a redupHcation of
the endocardium. To the
under surface and to the
edges of this valve the ten-
dinous cords of the papillary
muscles are firmly and intri-
cately attached. These cords
are just sufficiently long to
permit closure of the valve
and to prevent their being
floated into the auricle.

The orifice of the pul-
monary artery is also sur-
rounded by a ring of fibrous
tissue to which are attached
three semilunar or pocket-
shaped membranes, the
semilunar valves. Each valve is formed by a reduphcation of the
endocardium strengthened by fibrous tissue. In the center of the
free edge of the valve there
is a small nodule of fibro-
cartilage* (the corpus Aur-
antius). The outer edge
of the valve is strengthened
by a delicate fibrous band.
A similar band strengthens
the convex attached por-
tion of the valve just where
it is joined to the fibrous
ring. A third set of fibers
pass toward the nodule, in-
terlacing in all directions.
Two narrow crescentic-
shaped areas (the [lunulae)
near the free edge are de-
void of these fibers. Dur-
ing the period of relaxation
of the heart the edges of
the valves are in close
apposition and prevent a

Fig. 117. — Right Cavities of the Heart.
Auriculo-ventricular valves closed, semi-
lunar valves open. — (Dalton.)

THE CIRCULATION OF THE BLOOD.

271

Fig. 118. — Valves of the Heart, i
auriculo-ventricular orifice, closed
tricuspid valve. 2. Fibrinous ring,
auriculo-ventricular orifice, closed
mitral valve. 4. Fibrinous ring. 5
orifice and valves. 6. Pulmonic

. Right
by the
3. Left
by the
, Aortic
orifice

and valves. 7, 8, 9.
(Bonamy and Beau.)

Muscular fibers. —

return of the blood into the ventricle (Fig. ii6); during the con-
traction they are directed into the artery (Fig. 117). In the former
position they are shut; in the latter, they are open.

The left auriculo-ventricular opening is provided with a similar
though better developed fi-
brous ring and membran-
ous valve. It is, however,
subdivided into but two
portions or cusps, and is
therefore termed the bi-
cuspid valve, or, from its
fancied resemblance to a
bishop's mitre, the mitral
valve. The general ar-
rangement, connections,
and mode of action of this
valve are similar in all re-
spects to those of the tricus-
pid valve. The orifice of
the aorta is also surrounded
by a ring of fibrous tissue
to which are attached three
semilunar or pocket-shaped
valves (Fig. 113), which in

their arrangement, connections, and mode of action are similar in all
respects to those at the orifice of the pulmonary artery. The anatomic
relations of the cardiac orifices one to the other and the appearance
presented by the valves when closed are repre-
sented in Fig. 119.

The Heart Muscle-fibers and Their Ar-
rangement.— The muscle-fibers of the heart,
though transversely striated and nucleated,
differ in shape and arrangement from those
found in any other situation. The individual
fiber is short and broad and usually divided at
one or both ends. By this means the fibers are
united not only longitudinally, but laterally.
(See Fig. 119.) The fibers are devoid of a
sarcolemma and united one to the other by a
cement material. The entire musculature is
permeated and supported by connective tissue
which is so arranged as to group the fibers in
bundles or fasciculi of varying size.
The arrangement of the muscle bundles is quite comphcated and
in accordance with the functions of the individual portions of the

Fig. 119. — Muscle-
fibers FROM THE
Heart of a Mam-
mal. — (Landois
and Stirling.)

272

TEXT-BOOK OF PHYSIOLOGY.

heart. In the auricles the bundles are arranged in two sets : an outer
transverse set, which pass from auricle to auricle, and an inner longi-
tudinal set, which pass over the auricles to be attached anteriorly
and posteriorly to the connective tissue of the auriculo-ventricular
groove. The longitudinal fibers of each auricle are practically in-
dependent of each other. Circularly arranged fibers are present near
the terminations of the venae cavae and pulmonary veins.

In the ventricles the muscle-bundles are also arranged in two

sets, a superficial longi-
tudinal and a deep
transverse, though their
arrangement is some-
what more complicated
than that observed in
the auricles. In a gen-
eral way it may be said
that the superficial lon-
gitudinal fibers on both
the anterior and poste-
rior surfaces from their
origin in the connective
tissue of the auriculo-
ventricular groove pass
obliquely downward and
forward from right to
left toward the apex,
where they turn back-
ward and inward in a
vortex, after which they
ascend to terminate in
the wall of the septum,
the columnae carneae
and musculi papillares.
Longitudinal fibers are
also found on the inner
surface. The transverse
fibers are very abundant
and surround each ven-
tricle separately. Between the superficial longitudinal and deep
transverse fibers there are several layers of fibers which possess
varying degrees of obliquity. The general arrangement of the fibers
is such as to ensure a complete and simultaneous discharge of blood
from both auricles and ventricles (Fig. 120).

Fig.

120. — Muscle-fibers of the Ventricles.
I. Superficial fibers, common to both ventri-
cles. 2. Fibers of the left ventricle. 3. Deep
fibers, passing upward toward the base of the
heart. 4. Fibers penetrating the left ventricle.
— {Sappey, after Bonamy and Beau.)

THE CIRCULATION OF THE BLOOD. 273

THE MECHANICS OF THE HEART.

The immediate cause of the movement of the blood through the
vessels is the contraction and relaxation of the muscle -walls of the
heart, and more particularly of the walls of the ventricles, each of
which plays alternately the part of a force-pump, and to a slight
extent of a suction-pump. The motive power is furnished by the
heart itself, by the transformation of potential energy, stored up
during the period of rest, into kinetic energy — i. e., heat and mechanic
motion.

The contraction of any part of the heart is termed the systole;
the relaxation, the diastole. As each side of the heart has two cavities
the walls of which contract and relax in succession, it is customary to
speak of an auricular systole and diastole, and a ventricular systole
and diastole. As the two sides of the heart are in the same anatomic
relation to each other, they contract and relax in the same periods
of time.

The movements of the heart, as well as many phenomena con-
nected with the flow of blood through its cavities, have been deter-
mined by observation of, and experiment on, the exposed heart of a
mammal, — e. g., dog, cat, rabbit, — supplemented and corrected by
experiments on the heart in its normal relations. Valuable informa-
tion as to the heart-beat and the influences which modify it has been
obtained from experiments made on the isolated heart of the turtle,
frog, and allied animals.

If the thorax of a dog completely anesthetized is opened and
artificial respiration estabhshed, the heart will be observed in active
movement inside the pericardium. If this sac is divided and turned
aside, the heart will be fully exposed to view. At the normal rate
of movement characteristic of the dog it will be almost impossible
to determine either the succession of events or their duration. But
by observing the heart under different conditions at different rates of
movement and with instrumental aids physiologists have succeeded
not only in analyzing the movements, but in describing their sequence
and in estimating their time duration.

Thus it has been determined that the heart presents two distinct
movements which alternate with each other in quick succession. One
is the movement of contraction, or the systole, by which the blood
contained within its cavities is ejected into the arteries — pulmonary
artery and aorta; the other is the movement of relaxation, or the
diastole, followed by a pause during which the cavities again fill up
with blood from the venae cavae and pulmonary veins.

Sequence of Events. — It has been ascertained that though occur-
ring with extreme rapidity neither the contraction nor the relaxation
of either the auricle or the ventricle is a simultaneous process;

2 74 TEXT-BOOK OF PHYSIOLOGY.

that the contraction process passes over the heart in the form of
a wave; that it begins, indeed, at the terminations of the great
veins, then passes to and over the auricles, thence to and over the
ventricles from base to apex with great rapidity, but occupying in
these different regions unequal periods of time; that the relaxation
immediately succeeds the contraction, in the same order, and that at
the close of the ventricular relaxation there is a period during which
the whole heart is in repose, passively filling with blood.

Changes in Position and Form. — In passing from the diastoHc
to the completed systolic condition the exposed heart undergoes
changes both of position and form as the contraction rises to its
maximum. This having been attained, the heart undergoes reverse
changes until the original diastolic condition is regained. Thus
at the time of the ventricular systole the apex is tilted upward, the
entire heart is twisted on its axis from left to right and forced down-
ward by the expansion and elongation of the pulmonary artery and
aorta. At the time of the diastole, the reverse movements take place.

It is probable, however, that these movements are not permitted to
the same extent in the unopened chest, for the following reasons:
the heart is enclosed in the pericardium, is supported posteriorly by
the expanded lungs, and both posteriorly and inferiorly by the
diaphragm, all of which cooperate in keeping the heart, and more
particularly the right ventricle, in close contact with the chest-wall
and limiting its movements By means of needles inserted into the
apex of the heart, through the chest-walls, it has been shown by their
slight movement that the apex is practically a fixed point.

In the diastolic condition the shape of the heart near the base is
elliptic on cross-section, the long diameter extending from side to side.
In the completed systolic condition the shape of the same cross-section
is that of a circle. In passing from the diastolic to the systolic con-
dition the transverse diameter diminishes while the antero-posterior
diameter increases, while the whole heart becomes somewhat more
conic in shape. It is questionable if the vertical diameter per-
ceptibly shortens. During the systole the heart hardens, increases in
convexity, and is more forcibly pressed against the chest-wall. As
this takes place suddenly, it gives rise to a marked vibration of the
chest-wall, known as the cardiac impulse. This is principally ob-
served in the space between the fourth and fifth ribs, between the
left edge of the sternum and a line drawn vertically through the nipple.
The cardiac impulse is synchronous with the cardiac systole.

The Cardiac Cycle. — The entire period of the heart's pulsation
may be divided into three phases, viz. :

1. The auricular contraction.

2. The ventricular contraction.

3. The pause or period of repose, during which both auricles and

ventricles are at rest.

THE CIRCULATION OF THE BLOOD.

275

These three phases collectively constitute a cardiac cycle or a
cardiac revolution. The duration of a cycle, as well as the duration
of each of its three phases, varies in different animals in accordance
with the number of cycles which recur in a unit of time. In human
beings in adult life there are about 72 cycles to the minute; the average
duration therefore is 0.83 second. From this it follows that the time
occupied by any one of the three phases must be extremely short and
difi&cult of determination. From observations made on human
beings and from experiments on animals the following estimates
have been made and accepted as approximately correct:

1. The auricular systole, 0.16 second.

2. The ventricular systole, 0.32 second.

3. The period of rest for both auricles and ventricles, 0.32 second.
The relations of these three phases to one another may be illustrated

by the following diagram (Fig. 121), in which the space 1-2 is the
duration of a cardiac cycle di-
vided into eight equal spaces,
each of which represents one-
tenth of a second. The hne A
represents the auricular, the hne
V the ventricular phase. The
rise in the line A represents the
contraction; the fall and subse-
quent continuation, the relaxa-
tion and pause. The rise in the
line V and its continuation rep-
resent the contraction; the fall
and subsequent continuation, the
relaxation and the pause. From
this it is apparent that the auric-
ular contraction or systole has a

brief duration, 0.16 second, while the relaxation or diastole has a
long duration, 0.64 second; that the ventricular contraction immedi-
ately following the auricular has a duration of 0.32 second, while the
relaxation and diastole have a duration of 0.48 second; that the pause
of the entire heart, that is, the period between the termination of the
ventricular systole and the beginning of the next auricular systole, is
only 0.32 second.

The frequency of the heart-beat varies with a variety of con-
ditions: e. g., age, sex, posture, exercise, etc.

Age. — The most important normal condition which modifies the
activity of the heart is age. Thus :

Before birth, the number of beats a minute averages 140

During the first year it diminishes to 128

During the third year it diminishes to 95

From the eighth to the fourteenth year it averages 84

In adult life it averages J. 72

Fig. 121. — The Phases of the Heart's
Pulsation.

276 TEXTBOOK OF PHYSIOLOGY.

Sex. — The heart-beat is more rapid in females than in males.
Thus while the average beat in males is 72, in females it is usually
8 or 10 beats more.

Posture. — Independent of muscle efforts the rate of the beat is
influenced by posture. It has been found that when the body is
changed from the lying to the sitting and to the standing position,
the heart will vary as follows — from 66 to 71 to 81 on the average.

Exercise and digestion also temporarily increase the number of
beats.

The Action of the Valves. — As previously stated, the forward
movement of the blood is permitted and regurgitation prevented by
the alternate action of the auriculo-ventricular and the semilunar
valves. As a point of departure for a consideration of the action of
the valves and their relation to the systole and diastole of the heart,
the close of the ventricular systole may be conveniently selected.

At this moment, if the blood is not to be returned to the ventricles,
the semilunar valves must be instantly and completely closed. This
is accomplished in the following manner: During the outflow of blood
from the ventricles the valves are pushed outward toward the walls
of the vessels, though not coming into contact with them; for behind
them are the pouches of Valsalva, containing blood, continuous with
and under the same pressure as that in the vessels themselves. With
the cessation of the outflow and the beginning of the relaxation the
pressure of the blood behind the valves suddenly forces them inward
until their free edges, including the lunulae, come into complete appo-
sition. By this means the orifices of the pulmonary artery and aorta
are securely closed and a return flow prevented. Reversal of the
valves is prevented by their mode of attachment to the fibrous rings
of the orifices.

During the ventricular systole the relaxed auricles have been
filling with blood. With the ventricular relaxation this volume, or
its equivalent, flows readily into the empty and easily distensible
ventricles, its place being taken by an additional volume of blood
flowing from the venas cavae and pulmonary veins. Whether the
ventricles exert a suction power at the moment of their relaxation is
an undecided question. A steady stream of blood into the auricles
and ventricles continues throughout the entire period of rest until
both cavities are filled. The tricuspid and bicuspid valves which
hang down into the ventricular cavities are now floated up by cur-
rents of blood welling up behind them until they are nearly closed.
The auricles now contract, forcing their contained volumes, or at
least the larger portions of them, into the ventricles, which become
fully distended.

With the cessation of the auricular systole the ventricular systole
begins. If the blood is not to be returned to the auricles at this

THE CIRCULATION OF THE BLOOD. 277

moment, the tricuspid and mitral valves must be suddenly and com-
pletely closed. This is readily accomplished by reason of the position
of the valves, which have been floated up and placed almost in apposi-
tion by the blood itself. With the beginning of the ventricular pressure
the blood is forced upward against the valves until their free edges
are brought together and the orifices closed. Reversal of these
valves is prevented by the contraction and shortening of the papil-
lary muscles, which in consequence exert a traction on their under
surfaces. The blood now confined in the ventricle between the
closed auriculo-ventricular and semilunar valves is subjected to
pressure from all sides. As the pressure rises proportionately to the
vigor of the contraction, there comes a moment when the intra-
ventricular pressure exceeds that in the aorta and pulmonary artery.
Immediately the semilunar valves of both vessels are thrown open and
the blood discharged. Both contraction and outflow continue until
the ventricles are practically empty, after which ventricular relaxa-
tion sets in, attended by a rapid fall of pressure. Under the influence
of the positive pressure of the blood in the sinuses of Valsalva the
semilunar valves are again closed, the column of blood supported,
and regurgitation is prevented. With the accumulation of blood in
the auricles the cardiac cycle is completed.

Relative Functions of Auricles and Ventricles. — Though
both auricles and ventricles are essential to the continuous movement
of blood, they possess unequal values in this respect. The passage
of the blood through the pulmonary and systemic vessels is accom-
pUshed by the driving power of the right and left ventricles respec-
tively, aided, however, by minor extra-cardiac forces. They may
be regarded therefore as force-pumps.

If the heart consisted of ventricles only, the flow of blood from
the venae cavae and pulmonary veins would be temporarily arrested
during their systole and their subsequent refifling delayed. This is
obviated, however, by the addition of the auricles; for during the
ventricular systole the blood continues to flow into the auricles, in
which it is temporarily stored until the ventricular relaxation sets in.
With this event the accumulated blood passes into the ventricles, which
are thus practically filled before the auricular systole occurs by which
the filling is completed. By this means there is no delay in the filling
of the ventricles, and hence their effective working as force-pumps
is more readily secured. The auricles may therefore be regarded
as feed-pumps. For this reason it is probable, notwithstanding the
contraction of the circular muscle-fibers at the terminations of the
venous system, the flow of blood into the auricles is never entirely
arrested. Regurgitation in these vessels does not occur for the reason
that the pressure in the auricles is not higher than, if as high as, in
the great veins.

278

TEXT-BOOK OF PHYSIOLOGY.

max valve

to manometer

Synchronism of the Two Sides of the Heart. — If the balance
of the circulation is to be maintained, the two sides of the heart must
act synchronously. That they do so can be shown by attaching
levers to their walls and thus recording their activities. The syn-
chronism is so perfect that until recently it was generally believed to
be dependent on nerve connections ; but Porter has shown that if the
ventricles are cut away from the auricles, in which the nerve mechan-
ism seemed to He, the synchronism of the former is not interfered
with; that the apical halves of the ventricles will beat synchronously
if perfused with blood through an artery; that a very small bridge of
muscle-tissue will carry the wave of excitation from one part to neigh-
boring parts of the ventricle. It is therefore probable that the syn-
chronism is accomphshed through muscle connections only. The
left ventricle, in keeping with the greater work it has to do, has a
greater development than the right, and therefore contracts more
energetically. The ratio between the energy of the left and right
sides is approximately 3 to i.

Intra-cardiac Pressure. — It has been stated that during the

pause of the heart when its cavities are
filling with blood the semilunar valves
are kept closed by the pressure of the
blood in the pulmonary artery and
aorta, a pressure due to the resistance,
as will be explained later, offered to
the flow of the blood mainly by the
smaller arteries and capillaries; that
they are opened only when the press-
ure of the blood within the ventricle
exceeds that in the arteries. It be-
comes, therefore, a matter of impor-
tance to determine the extent of this
pressure as well as its variations dur-
ing the course of a cardiac cycle.
This can be done by inserting a long
catheter into either the right or left
ventricle, through the jugular vein or
the carotid artery respectively, and
connecting its free extremity with a
mercurial manometer. By the inter-
position of a double valve such as represented in Fig. 122, it
becomes possible, according to the direction the blood is permitted
to flow, to obtain either the maximal or the minimal pressure that
occurs in the heart during a series of cycles. Thus Goltz found in
the left ventricle of the dog a maximal pressure of 114 to 135 mm.;
in the right ventricle, a pressure of 35 to 62 mm. Minimal pres-

mm valve

Fig

to heart

122. — V. Frank's Valve.
This is placed in the course of
the tube between heart and
manometer, so that the latter
may be used as a maximum,
minimum, or ordinary man-
ometer according to the tap
which is left open. — {Starling.)

THE CIRCULATION OF THE BLOOD. 279

sures of — 23 to — 52 mm. for ihc left ventricle have also been
obtained.

The maximal pressure in the ventricles during the systole, though
always higher than that in the arteries, is not a fixed or an invariable
pressure, as it rises and falls with the latter from moment to moment.
Within hmits the cardiac power, and therefore the intra-cardiac
pressure, is capable of considerable increase. The function of the
heart is to drive the blood through the vessels with a given velocity.
This is only possible by first overcoming the resistance to the flow
offered by the vessels, as indicated by the arterial pressure. As this
is a variable factor, rising and falHng very considerably at times, the
heart must meet and exceed each rise, if the circulation is to be main-
tained. The power put forth by the heart is proportional to the
work it has to perform. If the arterial pressure continues higher
than the average for any length of time, the heart meets the condition
by an hypertrophy of its walls.

The Intra-ventricular Pressure Curve. — An accurate interpre-
tation of the play of the heart mechanism necessitates the obtaining of
a graphic record of the course of the intra-ventricular pressure, its varia-
tions and time relations. With such a record may be compared the
records of the pressures in the vence cavse, on the one hand, and in the
aorta, on the other hand, and their relations one to another accurately
defined.

The intra-ventricular pressure has been obtained by specially de-
vised manometers or tonometers or tonographs, as they are variously
termed, the construction of which is such as to enable them to respond
instantly to the very rapid variations of the pressure which occur
during the brief cardiac cycle. One of the best is that of Hiirthle.
This consists of a small metalhc tambour 5 or 6 millimeters in diam-
eter, covered by a thin rubber membrane. A small button resting
on the membrane plays against an elastic steel spring, by the tension
of which the pressure of the blood is counterbalanced. The move-
ments of the membrane are taken up, magnified, and recorded by a
suitable lever. A long cannula is inserted into the right ventricle
through the jugular vein or into the left ventricle through the carotid
artery. Both cannula and tambour are filled with an alkaline solu-
tion to prevent coagulation of the blood, and then joined air-tight.
The pressure of the blood in the ventricle is thus transmitted by a
liquid column to the tambour and to its attached lever. With such
a manometer a curve is registered similar to that shown in Fig. 123.
To obtain the absolute value of this curve in millimeters of mercury
it is necessary to previously graduate the instrument. An examination
of the curve shows that previous to the ventricular contraction there
is a very shght rise of pressure above that of the atmosphere, repre-
sented bv the fine a — b. This mav be due to the inflow of blood

28o

TEXT-BOOK OF PHYSIOLOGY.

from the auricle during the diastole. At o the pressure suddenly
rises, passes quickly to its maximum value, (2), which is maintained
mth sKght variations for some time, and then suddenly (3) begins
to fall, and, rapidly reaches the hne of atmospheric pressure, or even
passes below it, becoming negative in fact for a short period. The
curve may also be taken as a record of the ventricular contraction,
for there are reasons to beheve that the two closely coincide through-
out their entire course. A characteristic feature of this curve is the
more or less horizontal portion comprised between the points 2 and 3,
marked by several elevations and depressions, which has been termed
the systolic plateau.

With other forms of elastic manometers, especially those in which
the transmission of the intra- ventricular pressure is effected by air
or by a combination of air and liquid, this portion of the curve is

represented by a single peak, which
is taken as an indication that the
maximum pressure once reached is
not maintained, but immediately
begins to fall to its original level,
notwithstanding the continued con-
traction of the ventricle. Those
who adhere to this view attribute
the plateau to the closure of the
orifice of the catheter by the con-
tracting and approximating walls
of the ventricle. There are reasons
for believing, however, that the
former curve is the more correct
representation of the course of the
intra-ventricular pressure. Bayliss
and StarHng photographed on a
moving surface the oscillations of a fluid, a solution of sodium sul-
phate, in a capillary glass tube one end of which was closed, the
other end placed in connection with an intracardiac catheter, the
oscillations representing the variations in pressure. The photogram
thus obtained resembles the curve obtained by Hiirthle's membrane
manometer.

The Relation of the Intra-ventricular Pressure Curve to the
Intra-cardiac Mechanisms. — By itself the curve of the intra-
ventricular pressure affords no indication as to events occurring
within the heart: i. e., as to the times during the systole, of the
closure of the auriculo-ventricular valves and the opening of the
semilunar valves, or the times during the diastole, of the closure of the
semilunar valves and the opening of the auriculo-ventricular valves.
By registering the curve of pressure in the aorta simultaneously

Fig

123. — V. Curve of the pressure
in the ventricle of the dog. — •
(Hiirthle.) A. Curve of the pres-
sure in the aorta. The curves
were taken simultaneously. s.
Tuning-fork vibrations, loo per
second.

THE CIRCULATION OF THE BLOOD. 281

with the pressure in the left ventricle (Fig. 123), and by coniparing
these with the curve of the successive differences of pressure in these
two cavities as determined by the "differential manometer," it be-
comes possible to mark on the ventricular pressure curve the points
at which the foregoing events lake place.

During the systohc plateau the blood is passing from the ventricle
into the aorta. Independent of the slight elevations and depressions
there is an absolute fall of pressure between the beginning and the
end of the plateau. There is also a corresponding fall in the aortic
pressure, corresponding to these two points. The curve of the dif-
ference of pressure shows, however, that the ventricular pressure is
slightly higher than the aortic. This fall in both ventricular and
aortic pressures is due to the escape of blood from the arterial
into and through the capillary system. At 3, however, whether
completely emptied or not, the ventricle suddenly relaxes, and its
pressure soon falls below that in the aorta. As soon as this takes
place the semilunar valves must close, if regurgitation into the ven-
tricular cavity is to be prevented. A comparison of the aortic pres-
sure curve shows a slight notch, the "dicrotic notch," just preceding
a shght elevation, the "dicrotic" wave. This notch is taken as the
moment when the semilunar valves close. The corresponding point
on the ventricular pressure curve has been placed just where the
ordinate 4 cuts the descending portion. As yet, however, the pressure
is higher in the ventricle than in the auricle, and so continues until
near the hne of atmospheric pressure. At this point the pressure in
the auricle, due to the accumulation of blood during the ventricular
systole, now forces open the mitral valve and the blood flows into the
ventricle. The opening of the mitral valve occurs about the point
where the ordinate 5 cuts the curve.

The ventricular pressure curve affords but shght, if any, indication
of the auricular systole. It apparently does not give rise to any
noticeable increase in the ventricular pressure. The slight rise in
the pressure curve, which just precedes the abrupt rise due to the
ventricular systole, may be taken as an indication of an increasing
pressure due to the inflow of blood from the auricle. As soon as
the pressure in the ventricle exceeds that in the auricle the mitral
valve closes. This is marked on the curve where the ordinate cuts
it, at o. Coincident with this, the ventricular systole begins, and as
the blood is contained within a closed cavity the pressure abruptly
rises. A comparison of the aortic curve shows that for a short time
during the ventricular systole, the pressure is falling, but at one point
it turns at a sharp angle and rapidly rises. This is an indication that
the semilunar valves are suddenly thrown open and the blood begins
to pass into the aorta. This event occurs at a moment marked on
the ventricular curve by the ordinate i. Beyond this point the pres-

282 TEXT-BOOK OF PHYSIOLOGY.

sure continues to rise, for the aortic pressure must not only be ex-
ceeded, but a certain velocity must be imparted to the blood. Between
the ordinates i and 4, the semilunar valves remain open and the
blood passes into the aorta.

In accordance with the foregoing the ventricular systole may be
subdivided into two periods :

1. The period of rising tension, from the beginning of the systole to

the opening of the semilunar valves, occupying from 0.02 to
0.04 second.

2. The period of ejection, from the opening of the semilunar valves

to the end of the systole, occupying about 0.2 second.
The ventricular diastole may also be divided into two periods :

1. The period of falling tension or relaxation, from the end of the

systole to the time of lowest pressure in the ventricle, occupying
about 0.05 second.

2. The period of fihing, from the opening of the mitral valve to the

beginning of the systole.

Negative Pressure. — As shown by the ventricular pressure curve
there is a moment when the pressure falls below atmospheric pres-
sure, becoming negative to it. The extent to which this takes place,
its duration and frequency, have never been satisfactorily determined.
The cause of the negative pressure, its influence on the opening of
the auriculo-ventricular valves, and on the entrance of blood into the
ventricles are equally unknown. The most probable cause is an
expansion of the base of the ventricles due to the enlargement of the
aorta and pulmonary artery. That it is not due to the expansion
of the thorax is evident from the fact that it is occurs when the thorax
is open and the heart exposed.

Heart-sounds.^ — Two sounds accompany each pulsation of the
heart, both of which may be heard by applying the ear or the stetho-
scope to the chest- walls, especially over the region of the heart. One
of these sounds is low in pitch, dull and prolonged; the other is high
in pitch, clear and short. These sounds can be approximately repro-
duced by pronouncing the syhables lubb-dupp, lubb-dupp. The
long dull sound occurs with the systole, the first phase of a new cardiac
cycle, and is therefore termed the first sound; the short clear sound
occurs at the beginning of the diastole, with the second phase of the
cardiac cycle, and is therefore termed the second sound. The first
sound is the systolic, the second the diastolic, sound. With the ear
it can readily be determined that there is a brief pause between the
first and second sounds, and a longer pause between the second and the
first sounds. The duration of the first sound is almost equal to the
duration of the systole — viz., 0.3 second; the duration of the second
sound is not more than o.i second. The systohc sound is heard
most distinctly over the body of the heart; the diastohc sound is

THE CIRCULATION OF THE BLOOD. 283

heard most distinctly in the neighborhood of the third rib to the right
of the sternum.

The causes of the heart-sounds have enhsted the attention of
cHnicians and physiologists for years, and many factors have been
assigned for their production. At present it is generally believed
that the first sound is the product of at least two, possibly three,
factors: viz., the contraction of the muscular walls of the ventricles,
the simultaneous closure and subsequent vibration of the tricuspid
and mitral valves, and the sudden increase of pressure of the apex of
the heart against the chest-wall.

That the contraction of the ventricular muscle gives rise to a
sound is certain from the fact that it is perceptible in an excised heart
when the cavities are free from blood and when the valves are pre-
vented from closing. The explanation of this sound is extremely
difficult, as the contraction, though pro-
longed, is not of the nature of a tetanus
and therefore not characterized by rapid
variations of tension. The apex element
may be eliminated by placing the individual
in the recumbent position.

The second sound is the product of the
simultaneous closure and subsequent vibra-
tion of the aortic and pulmonary valves
which occurs at the beginning of the ven-
tricular diastole as the blood surges back Fig. 124.— Scheme of a
, , , , , . ,° Cardiac Cycle. The

agamst the closed valves. ihis has been inner circle shows what

definitely proved by the fact that the sound events occur in the

disappears when the valves are destroved Jl^^^^' f^,^ ^^^ °^^^^'

111 11111- 1 1 • '1 ^^^ relation of the

or held back by hooks mtroduced mto the sounds and silences to

aorta and pulmonary artery. It is also these events,

possible that the vibration of the column of

blood produces an additional tone which adds itself to that produced
by the valves.

The relation of the sounds to the systole and diastole of the heart
is represented in Figs. 124 and 121.

The Blood-supply to the Heart. — The nutrition of the heart,
its contractiHty, the force and frequency of the beat, are dependent
on and maintained by the introduction of arterialized blood into and
the removal of waste products from its tissue. This is accomplished
by the coronary arteries, on the one hand, and the coronary veins, on
the other. The arteries, two in number, the right and left, arise from
the aorta in the pouches of Valsalva just above the right and left
semilunar valves. Turning in opposite directions, they ultimately
anastomose, forming a circle around the base of the ventricles.
From both the risrht and left arterv branches are s;iven off which run

284 TEXT-BOOK OF PHYSIOLOGY.

over the walls of both auricles and ventricles, the most important
of which in man are the anterior and posterior interventricular.
These main vessels lie in grooves on the surface of the heart beneath
the visceral pericardium, surrounded by connective tissue and fat.
Small branches penetrate the heart-muscle in which they break up
into capillaries. From the capillary areas small veins arise which,
passing backward, converge to form the coronary veins. These
follow the course of the arteries and finally terminate in the coronary
sinus, located in the auriculo- ventricular groove on the posterior
surface of the heart. This sinus opens into the right auricle between
the opening of the inferior vena cava and the auriculo- ventricular
opening. Its orifice is guarded by a valve, which is usually single,
though sometimes double.

While by far the larger portion of the blood is returned by the
coronary veins, it is also certain that some of it is returned by small
veins which open into little pits or depressions on the inner surface of
the heart-walls, known as the foramina Thebesii. It has been lately
shown by Pratt that these foramina are present not only in the auricular
wall, as generally stated, but in the walls of all the cavities. These
foramina communicate through a capillary plexus with both arteries
and veins, and by special large passages with the veins alone.

During the systole the intra-mural vessels are compressed and the
blood driven out of the capillaries into the veins ; during the diastole,
the vessels again dilate and permit the blood to re-enter freely from
the arteries. The greater the force and frequency of the beat, the
greater the volume of blood passing through the coronary system.

The period of time in the cardiac cycle during which the coronary
arteries are filled with blood, whether during the systole or the dias-
tole, has been a subject of much discussion. At present, however,
as the result of many experiments it is generally believed that they
are filled at the time of the systole. A comparison of the tracings of
the pulse-wave taken simultaneously in the carotid and coronary
arteries shows that the pressure rises and falls simultaneously in both
vessels; that there is a complete agreement between the two trac-
ings, and as a corollary both vessels are filled during the systole.
But because of the pressure which the heart muscle must exert upon
the smaller arteries and veins within its own substance during systole,
it is probable that there is a freer circulation in the coronary vessels
during the period of diastolic repose.

In mammals the nutrition of the heart-muscle, its irritability and
contractility, depend on the blood-supply derived from the coronary
vessels. This is shown by the effects which follow its withdrawal.
Ligation of both coronary arteries in the dog is followed by a diminu-
tion in the force and frequency of the heart-beat, and in a few minutes
by complete cessation. Ligation of even a single branch of a coro-

THE CIRCULATION OF THE BLOOD. 285

nary artery, provided it supply a sufficiently large territory, — e. g.,
the arteria circumflexa, — is sufficient to cause arrest in at least 80
per cent, of animals (Porter). With the ligation of this vessel there
occurs a gradual diminution in the force and frequency of the systole,
As the power of coordinate contraction ceases the heart-muscle
frequently exhibits a series of independent contraction of individual
fibers and cells known as fibrillary contraction. All the results which
follow ligation are to be attributed in the light of experiment to the
sudden anemia which • is thus estabhshed. The removal of the
ligature and the return of the blood will restore the nutrition and re-
establish coordinate contractions. The excised heart of the mammal
mav be again made to beat by passing w^arm defibrinated blood
through the coronary vessels under a suitable pressure.

In frogs and allied animals the heart is nourished by blood flow-
ing, during the diastole, from the interior of the heart into a system
of irregular channels which penetrate the walls in all directions.
With the systole the blood is returned to the cavities. The excised
heart of the mammal — e. g., the cat — may be partially nourished in
a similar manner through the foramina Thebesii. If the warm
defibrinated blood of the same animal be introduced into the ventricle
under a pressure of about 75 mm. of blood, the heart will recommence
and continue to beat for a period varying from one to several hours.
The Causation of the Heart-beat. — The beat of the heart, its
frequency and regularity, its continuance from the early stages of
fetal development till death, has long been an interesting subject
for physiologic investigation. Though related to the functional
activities of the body at large, the activity of the heart is in a sense
independent of them, for it will continue for a variable length of time
after they have ceased. The heart of the frog and the turtle wall
continue to beat under appropriate conditions for some hours after
separation of all its anatomic connections and removal from the body.
The heart of the dog or cat will, however, beat but for a few minutes.
The human heart would in all probability act in the same w^ay.

The reason for the longer continuance of the beat of the excised
heart of the cold-blooded animal beyond that of the w^arm-blooded
animal lies probably in the difference in the rate of their respective
metabolisms. There is reason to believe that each cell of the heart-
muscle, in common with other tissue-cells, during life stores up and
holds in reserve a larger quantity of nutritive material than is necessary
for its immediate needs. When separated from the general blood-
supply, the cells at once begin to utilize this reserved material. With
its exhaustion the irritability declines and in a short time disappears.
As the metabolism is far more rapid in the warm-blooded than in the
cold-blooded animal, it is probable that the reserved nutritive material
is utihzed much more quickly in the former than in the latter. So

286 TEXT-BOOK OF PHYSIOLOGY.

long as it lasts in either class, the irritabihty and contractility persist.
The passage of defibrinated blood through the vessels of the excised
heart of the dog may maintain the duration of the irritability for a
period of from one to six hours.

Whatever the immediate or exciting cause of the heart contraction
may be, the fundamental condition for its manifestation is the main-
tenance of the irritability. So long as this persists at the normal
level the heart-muscle will contract in response to the appropriate
stimulus.

Nature of the Stimulus. — As the heart continues to beat after
removal from the body, it is evident that the stimulus does not origi-
nate in the central nerve system but in the heart itself. Two views
have been held as to its origin and nature:

1. That it originates in the nerve-cells found in various parts of the

heart-muscle; that it is a nerve impulse rhythmically and auto-
matically discharged by these cells and transmitted by their
axons to the heart-muscle cells.

2. That it originates in the muscle-cells themselves; that it is chemic in

character and due to a reaction between the inorganic salts in the
muscle cells and those in the lymph by which they are surrounded.

According to the first view the stimulus is neurogenic, according
to the second view myogenic, in origin.

The presence of nerve-cells; their relation to the muscle-cells; the
pronounced rhythmic activity of the sinus and auricles in which the
nerve-cells are abundant ; the feeble activity of the apex, in which they
are wanting,— these and other facts lend support to the view that the
stimulus originates in the nerve-cells. To them have been attributed
the power of automatic activity.

The fact, however, that portions of the heart-muscle in which
nerve-cells have not yet been shown to exist can be made to exhibit
rhythmic contractions for even a long period of time shows that
the stimulus does not necessarily originate in nerve-cells. Porter
has conclusively shown that the apex of the dog's heart, which is
generally believed to be totally devoid of nerve-cells, can be made to
beat for hours by feeding it through its nutrient artery with warm defi-
brinated blood. Unless it be assumed that the heart-muscle contracts
automatically, without cause, it is evident there must be present in the
blood some agent or agents which by individual or collective action
act as a stimulus to the muscle-cell. Attempts have been made to
isolate these agents, to determine not only their individual, but also
their cooperative action, when combined in proportions approximat-
ing those in which they exist in the blood. The agents known to be
directly concerned in exciting and sustaining the heart-beat are sodium
chlorid, calcium phosphate or chlorid, and potassium chlorid. Rin-
ger's combination of these salts is made by saturating a 0.65 per cent.

THE CIRCULATION OF THE BLOOD. 287

solution of sodium chloric! with calcium phosphate, and then adding
to each 100 c.c, 2 c.c. of a i per cent, solution of potassium chlorid.
A frog's heart immersed in this solution will continue to beat for
several hours. A combination of the chlorids of sodium, calcium,
and potassium is equally efficient in maintaining the heart-beat.

The collective as well as the individual actions of these salts have
been strikingly brought out by the experiments of Professors Howell
and Green, from whose papers the following statements are derived.
In these experiments strips from the terminations of the venae cavae
and from the ventricle of the terrapin's heart were employed. The
proportion of these salts most favorable to the contraction of the
venae cavas strips is the following: viz., sodium chlorid, 0.7 per cent.;
calcium chlorid, 0.026 per cent.; potassium chlorid, 0.03 per cent.;
for the contraction of the ventricular strips a larger percentage of the
calcium is required: viz., 0.04 to 0.05. From this fact it is inferred
that the venae cavas region is more sensitive to the action of the com-
bined salts than the ventricle. With the latter strength of the solu-
tion, the ventricular strips may contract for several days. In the
first proportion as well as in serum the ventricular strips do not con-
tract, but are kept in good condition for contraction for several days.
An increase in the quantity of the calcium chlorid sufficient to raise
the percentage to 0.04 or 0.05 will after a brief latent period give rise
to rapid and energetic contractions.

The action of the individual salts is also best shown with ven-
tricular strips. In a 0.7 per cent, sodium chlorid solution the strip
beats rhythmically and energetically, but for a short period and
with gradually diminishing force, until it entirely ceases. A reason
assigned for this is the removal of other salts necessary to the excita-
tion of the contraction. In a calcium chlorid solution 0.7 per cent. —
/. e., isotonic with the sodium chlorid — the heart strip is thrown into
strong tone, but does not rhythmically contract. If, however, the
strip is placed in normal sahne, and calcium chlorid added in amounts
equal to that present in the blood, it will after a very short latent
period begin to contract rapidly and energetically and for a longer
time than when in sodium chlorid solution alone. The contractions
not infrequently occur before relaxation is completed, so that the
strip passes into the condition of contracture.

In potassium chlorid solutions isotonic — o.g per cent.- — with
sodium chlorid solution the heart strip also fails to contract. This
is the case also when the potassium is added to the sodium chlorid
in amount practically equal to that found in the blood. With the
foregoing combination of inorganic salts it is beheved that the sodium
chlorid maintains the osmotic pressure between the heart tissues and
the surrounding fluid; that the calcium salt prevents the washing out
of the calcium salts, and at the same time acts as a stimulus to the

288

TEXT-BOOK OF PHYSIOLOGY.

heart-cells; that the potassium chlorid acts antagonistically to the
calcium. From these facts it may be inferred that the stimulus is
chemic in character and, though continuously acting, calls forth but
periodic contractions.

PROPERTIES OF THE HEART-MUSCLE.

1. Irritability. — The heart-muscle in common with other muscles

possesses irritability in virtue of which it responds by a change
of form to the action of a stimulus. Whatever the stimulus,
here, as elsewhere, there is a conversion of potential into kinetic
energy — heat and mechanic motion. The normal physiologic
stimulus is at present undetermined. In common -vN'ith other
forms of muscle tissue, the heart may be made to contract by
artificial stimuli — e. g., mechanic, thermic, chemic, and electric.
The irritabihty depends on the nutrition, and so long as this is
maintained the muscle will respond by a contraction to any stim-
ulus. The irritability is most marked in the neighborhood of the
venae cavae terminations. It is least marked in the ventricles.

2. Conductivity.^ — The heart-muscle possesses conductivity. The

excitation process and the subsequent contraction wave, both of
which take their rise under physiologic conditions near the venae
cavae terminations, are conducted over the auricles, thence to the
ventricles from base to apex. The propagation of both processes
is accomplished by muscle-tissue alone, independently of the
nerve systems. The conductivity, however, is not equally well
developed in every part of the heart. This is especially true of

the tissue at the auriculo-ventricular
junction. At this point the contrac-
tion wave is delayed for an appreci-
able period, a condition due to the
embryonic character of the muscle-
tissue. In the frog's heart the excita-
tion process begins in the sinus ven-
osus, from which it passes to the
auricles, thence to the ventricles. The
excitation process as well as the con-
traction wave is delayed both at the
sinu-auricular and auriculo-ventricular junctions. In Fig. 125,
which is a graphic record of the heart-beat, the two elevations
of the lever on the up-stroke, a and b, represent the contraction
of the sinus and the auricle respectively, while the two depres-
sions c and d indicate the delay in the transmission of the con-
traction wave at the two junctions. There is here an anatomic
obstacle to the conduction of the contraction. This may be
artificially increased by compressing the heart between the

Fig. 125. — Record of the
Contraction of the
Frog's Heart.

THE CIRCULATION OF THE BLOOD.

289

auricles and ventricles with a clamp. By carefully regulating the
pressure it is possible to so block the wave that three or four
auricular contractions may occur before a single ventricular
contraction (Fig. 126).
Rhythmicity. — The beat of the heart is a uniform movement,
occurring at regular intervals. Each phase of each beat occupies a
regular measure of time. The beat is therefore rhythmic in char-
acter. The heart-muscle as a whole varies in rhythmic power in
its different parts. It is best developed in the frog and tortoise,
in the sinus venosus, less so in the auricles, least in the ventricles.
This may be shown by division of the tissue between sinus and
auricles in situ. At once the auriculo-ventricular portion ceases
to beat, while the sinus continues contracting as usual. In a
short time the auricles and ventricles begin to beat, though less
rapidly than formerly. Separation of the auricle from the ven-
tricle is again followed by rest. In due time the auricle begins

Aun

Fig. 126.-

Vent.

-Record of the Auricular and Ventricular Contractions before

AND APTER the CLOSURE OF THE ClAMP AT a.

to beat, while the ventricle remains quiescent. If the ventricle
be now stimulated in a rhythmic manner, it may resume rhythmic
activity. These facts are taken as an indication that the rhythmic
power is developed in unequal degree in the three parts of the
heart.

Automaticity. — The heart-muscle continuing to contract rhythmi-
cally, even after removal from the body and without the aid of
any external stimulus is said to be automatic in action. This,
however, does not exclude the action of an internal stimulus.

Tonicity. — The heart-muscle, hke the vascular muscle, main-
tains continuously a certain degree of contraction, upon which
the efficiency of the heart as a pumping organ is largely de-
pendent. This tone may, however, be increased or decreased
by the action of various external agents. Thus the passage of
dilute solutions of various drugs — e. g., alkalies, digitalis —
19

290 TEXT-BOOK OF PHYSIOLOGY.

through the cavities of the excised heart will so increase the tone,
or the contractile power, that complete relaxation is prevented,
until finally the heart comes to a standstill in the condition of
systole. The passage of dilute solutions of lactic acid, mus-
carine, etc., through the heart has the opposite effect— a gradual
diminution in contractile power, the heart finally coming to a
standstill in diastole. In the first instance the tonicity is said to
be increased; in the second instance, decreased.
The Response of the Heart to the Action of a Stimulus. —
The heart in many animals may be brought to a standstill by ligation
of the tissues between the sinus venosus and the auricles — the first
Stannius hgature. Under such circumstances the heart may be made
to contract by stimulating it with the induced electric current. With
each passage of the current the muscle contracts. Contrary to what is
observed in other muscles, the heart-muscle, if it contracts at all, at
once reaches its maximal value. Increase or decrease in the strength
of the stimulus has no effect on the extent or force of the contraction.
If a series of successive stimuli be thrown into a muscle, the effect
will vary in accordance with their time
intervals. Should this be less than about
three seconds, there will be a gradual
increase in the height for some half-

I dozen contractions, a result to which the

Fig 127— The Extra Con- term "staircase" contractions has been
TRACTION AND THE CoM- glvcu. If a sccoud stlmulus is thrown
PENSATORY PAUSE. The j^to thc musclc durfng the period of

break in the horizontal , . i > , • • i

line indicates the moment relaxation, a second contraction IS de-
the electric current passes veloped, which superposes itself on the
through the heart. f^^^^^ ^^^ ^^ie height of the contraction is

not any greater than the height of the
first (Fig. 127). There is here no summation of effects. With the
relaxation of the heart after the second contraction, a considerable
pause in the heart's action is noticed, to which the term "compensa-
tory" is given. During this pause the muscle accumulates a new
supply of contractile material sufficient for the next contraction. If
the stimulus be thrown into the heart during the period of contraction,
it will have no effect. For this reason the heart is said to be refrac-
tory to the second stimulus during the entire contraction period.
The explanation at hand is that the irritabihty is very much lowered
from the decomposition of energy-holding compounds. In the case
of the skeletal muscle the refractory period is confined to the latent
period. Since there is no summation of the contractions of the heart-
muscle, tetanization of the muscle can not be produced.

Though many of the experiments relating to the properties of the
heart-muscle have been made on the hearts of frogs, turtles, and

THE CIRCULATION OF THE BLOOD. 291

allied animals, there is every reason for believing that the results so
obtained hold true, with minor exceptions, for the heart of the
mammal.

THE RELATION OF THE NERVE SYSTEM TO THE HEART.

In all classes of vertebrates the heart not only contains locaHzed
collections of nerve-cells, but is also connected with the central nerve
system by two or three sets of nerve-fibers.

In the frog heart a group of nerve-cells is found in the sinus at its
junction with the auricle, known as the crescent or ganghon of Remak;
a second group is found at the base of the ventricle on its anterior
aspect, and known as the ganglion of Bidder; a third group is found
in the auricular septum, known as the septal ganglion, or v. Bezold's
or Ludwig's. The majority of the cells are situated on the surface of
the heart just beneath the pericardium. From the cell-body line
non-medullated libers pass into the substance of the heart, to be
histologically and physiologically related with the muscle-fiber.
These nerve-cells were formerly regarded as the sources of the
stimuU for the heart's activities. They are regarded by Gaskill
as trophic in function, and exerting a favorable influence on the nutri-
tion of the heart-muscle.

In the dog heart the nerve-cells are not arranged in such definite
groups, but are distributed in the terminations of the ven« cavae,
pulmonary veins, the walls of the auricles, and in the neighborhood
of the base of the ventricles.

The nerves which connect the heart with the central nerve
system are two: viz., the vagus or pneumogastric, and the sympa-
thetic.

The Vagus. — Histologic investigation has shown that the vagus
nerve-trunk contains medullated fibers of large and small size. Ex-
periment has shown that the large fibers are afferent, the small fibers
efferent in function. The small eft'erent fibers are the peripherally
coursing axons of nerve-cells situated in the gray matter beneath the
floor of the fourth ventricle at the tip of the calamus scriptorius. The
exact course of these fibers is not definitely known. According to
some investigators, they leave the medulla by way of the spinal
accessory nerve and enter the trunk of the vagus through the internal
or anastomotic branch; according to recent investigations made by
Schaternikofl" and Friedenthal, they leave the medulla along the path
by which the afferent fibers enter and never become associated with
the spinal accessor}' nerve at its origin.

Below the origin of the inferior or recurrent lar}'ngeal nerves,
branches containing the efferent fibers are given off, which pass to the
heart. The terminal branches of the fibers are not distributed

292

TEXT-BOOK OF PHYSIOLOGY.

Vagus

Sympathetic Neuron

directly to the heart-muscle, but to the nerve-cells, around the body
of which they end in basket-like formations. The fibers in the vagus
are pre-ganghonic ; those of the nerve-cells post-ganghonic. (See
Fig. 128.)

The Sympathetic. — Histologic investigation has shown that the
sympathetic nerves which pass to the heart are non-meduUated.
Experiment has shown that they are also efferent in function. The
fibers are peripherally coursing axons of nerve-cells situated in the
ganghon stellatum. After reaching the heart they may terminate
directly in the muscle-cell or indirectly through the intervention of
the heart nerve-cells. The former method is the more probable.
The nerve-cells in the ganglion stellatum are in relation with small
meduUated nerve-fibers which emerge from the cord in the anterior
roots of the second and third thoracic nerves, pass through the white
rami communicantes, and thence to the ganglion stellatum, where

their end branches arborize around the
nerve- cells. The nucleus of origin of
these medullated fibers is probably in
the medulla oblongata. The fibers
emerging from the cord are pre-
ganglionic, those emerging from the
ganglion, post-ganglionic.

In the frog these two sets of nerve-
fibers, instead of passing to the heart
along separate paths, as in man and
mammals, generally pass along the
same path and in the same sheath.
The sympathetic fibers proper, the
post-ganghonic fibers, arise from
nerve-cells in the third sympathetic
ganghon. From this origin they
ascend, passing successively through the second sympathetic gan-
ghon, the annulus of Vieussens, the first sympathetic ganglion, to
the ganghon on the trunk of the vagus, at which point they enter
the sheath of this nerve. For this reason the common trunk which
descends to the heart is generally spoken of as the vago- sympathetic
nerve. The pre-ganghonic fibers emerge from the cord in the ante-
rior roots of the third spinal nerve, pass through the rami communi-
cantes to the third sympathetic ganghon, around the cells of which
the nerve-fibers arborize.

Physiologic Action of the Vagus. — The information now pos-
sessed regarding the influence which the central nerve system
exerts upon the heart has been derived largely from experiments
made on the nerves of the frog, toad, and turtle. To demonstrate

Fig.

Mtiscle
Cell

128. — Diagram showing
THE Relation of the Vagus
TO THE Heart Muscle-cell.

THE CIRCULATION OF THE BLOOD.

293

the respective actions of the two sets of fibers they must be stimu-
lated or divided before their union at the vagus ganglion.

Stimulation of the intra-cranial roots of the vagus with very weak
induced currents is followed by a gradual diminution in the rate or
rhythm and a diminution in the force of the heart-beat. If the in-
duced currents are moderate in strength, the heart will at once come
to a standstill in diastole. Since stimulation of the nerve, which in
all probability exaggerates its normal function, is followed by a period

-oixKimrifwfmm-mmummiimummmirHiimmimimMm

Fig. 129. — Tracing showing the Diminution in the Rate of the Heart-beat
FOLLOWING Weak Tetanization of the Vagus Trunk.

of rest or inactivity, the vagus is said to have a retarding or an inhibi-
tory influence on the automatic pulsations of the heart.

After cessation of the stimulation, the heart resumes its activity.
At first the beat usually is slow and feeble, but with each succeeding
beat both rate and force increase, until they attain or exceed that
observed prior to the stimulation. The duration of the inhibitory
effect varies with the duration of the stimulation. Thus during and
after a stimulation of thirty-eight seconds the heart of the toad re-
mained at rest for 292 seconds (Gaskell). Stimulation of the sym-

VWmuMl.'mmMimmmmiiiNiuiiiimmymiim

Fig. 130. — Tracing showing Complete Inhibition following String Tetani-
zation OF THE Vagus Trunk.

pathetic fibers prior to their union with the vagus is followed by an
increase in the rate or an augmentation in the force of the heart, or
both at the same time. With the cessation of the stimulus the heart
returns to its normal condition. From the foregoing facts the vagus
is said to be the inhibitor, the sympathetic, the accelerator or aug-
mentor nerve of the heart, according as it increases the rate or force.
Stimulation of the trunk of the vagus in the frog or the toad with
weak tetanizing induced electric currents is followed merely by a

294

TEXT-BOOK OF PHYSIOLOGY.

Fig. 131. — Tracing showing Diminished
Amplitude and Slowing of the Pul-
sations OF THE Auricle and Ventri-
cle WITHOUT Complete Stoppage
during Irritation of the Vagus. —
{From Brunton, after Gaskell.)

diminution in the rate of the beat (Fig. 129), Stimulation with

strong tetanizing currents is followed by complete inhibition, and

for a short time the heart re-
mains quiescent; but notwith-
standing the continued stimu-
lation, the heart commences
again to beat (Fig. 130).
Though at first the beat is
feeble, it soon regains and far
exceeds its former rate and
force. This may be attributed
to a fatigue of the terminals
of the inhibitory fibers or to
an overpowering action of the
augmentor fibers arising after
a rather long latent period.
The foregoing facts are also

illustrated in Figs. 131 and 132, as published by Gaskell. In these

experiments the heart was suspended and clamped in the auriculo-

ventricular groove, thus permitting both auricle and ventricle to be

attached to recording levers.
In addition to the changes

in the rate and force of the

heart caused by stimulation

of the inhibitor and the

augmentor nerves, it is stated

by Gaskell that there is also

during inhibition a decrease

in the conductivity of the

heart at both the sinu-auric-

ular and auriculo- ventricular

junctions, and an increase

in the conductivity during

acceleration. The decrease

in conductivity may be so

pronounced that only every

second or third contraction

of the auricle will be followed

by a contraction of the ventri-
cle. In other instances both

auricles and ventricles remain

at rest while the sinus main-
tains its usual rate.

The increase in conductivity is shown by first artificially blocking

the contraction wave at the auriculo-ventricular junction with the

Fig. 132. — Tracing showing the Actions
OF THE Vagus on the Heart. Aur.,
Auricular; Vent., ventricular tracing.
The part between perpendicular lines
indicates period of vagus stimulation.
C8 indicates that the secondary coil
was 8 cm. from the primary. The part
of tracing to the left shows the regular
contractions of moderate height before
stimulation. During stimulation, and
for some time after, the beats of auricle
and ventricle are arrested. After they
commence again they are single at first,
but soon acquire a much greater ampli-
tude than before the application of the
stimulus. — {From Brunton, after Gas-
kell.)

THE CIRCULATION OF THE BLOOD.

295

clamp, until only every second or third auricular contraction is con-
ducted to the ventricle, and then stimulating the sympathetic. At
once the auricular contraction forces the block, and passes to the
ventricle, calHng forth a normal contraction. In the mammal the
same effects follow stimulation of the vagus and the sympathetic as
in the frog. If the thorax of a dog is opened and artificial respira-
tion maintained, the heart will continue to beat in a practically
normal manner for a long time. Stimulation of the vagus with
induced currents 06 moderate strength will be followed by a com-
plete standstill of the heart in diastole, during which the walls are
relaxed and the heart-cavities filled with blood. If the currents are
of feeble strength, the heart will come to rest gradually through a
gradual diminution in the rate and force of the contraction.
Stimulation of the sympathetic may be followed by only a slight
increase in the rate, especially if the heart action is normally

£.rcJ"JV:Aocy

Fig. 133. — Increase in the Force of the Ventricular Contraction (Curve of
Pressure in Right Ventricle) from Stimulation of the Sympathetic
Fibers. There is Little or no Change in Frequency. — {Franck.)

very rapid. There is, however, an augmentation of the force and
an increase in conductivity (Fig. 133).

The Cardio-inhibitor Center. — In the dog, and probably in
many other mammals also, the cardio-inhibitory center, in the
medulla, exerts a more or less constant inhibitory or restraining in-
fluence on the heart's activity. This is indicated by the fact that the
rate of the heart-beat is very much increased by simultaneous divi-
sion of both vagi. For this and other reasons it is beheved that this
center is in a state of tonic activity, discharging nerve impulses which
exert a regulative influence on the cardiac mechanism in accordance
with its needs, and especially in reference to the variable resistances
offered to the flow of blood which the heart must overcome. The
question has been raised as to whether the tonic activity of the center
is maintained by causes within itself, the result of an interaction of
cell substance and the surrounding lymph, or by nerve impulses

296 T^XT-BOOK OF PHYSIOLOGY.

reflected to it through afferent or sensory nerves. The latter suppo-
sition is supported by the results of experimentation, though both
factors are undoubtedly of importance.

Stimulation of the sensory nerves in almost any region of the body
is followed by a slowing of the heart's action. Thus stimulation of
the posterior roots of the spinal nerves, the trunks of the cranial
sensory nerves, the splanchnic nerves, the pulmonary branches of the
vagus, etc., give rise to a more or less pronounced inhibition. As a
rule, stimulation of the peripheral terminations of these nerves is
more effective than stimulation of their trunks, hence an explanation
is at hand for the cardiac inhibition which results from sudden dis-
tention of the stomach, intestines, or lungs.

The Cardio-accelerator Center. — The exact location of this
center is not as yet determined. It is probably in the medulla ob-
longata. The experiments of Hunt would indicate that this center is
also in a condition of tonic activity, increasing both the rate and force
of the heart's action; that it antagonizes the action of the inhibitory
center and is in time antagonized by it; that the normal rate of the
heart from moment to moment is the resultant of the action of these
two opposing forces. These experiments also support the view that
the acceleration of the heart observed during stimulation of certain
afferent nerves is not due to a reflex stimulation of the accelerator
center, but to an inhibition of the cardio-inhibitor center. It must
therefore be assumed that the afferent nerves contain two sets of
nerve-fibers, one of which inhibits, the other excites, the cardio-
inhibitor center.

The Depressor Nerve. — The vagus trunk also contains afferent
fibers stimulation of which not only brings about a reflex inhibition
of the heart, but also a dilatation of the peripheral arteries and a fall
of blood-pressure through an influence exerted on the vaso-motor
centers. To this nerve the term depressor has been given. A con-
sideration of the physiologic action of this nerve will be found in the
section devoted to the nerve mechanisms concerned in the mainte-
nance of the blood-pressure.

THE VASCULAR APPARATUS: ITS STRUCTURE AND FUNCTIONS.

The systemic vascular apparatus consists of a closed system of
vessels extending from the left ventricle to the right auricle, and
includes the arteries, capillaries, and veins. Though serving as a
whole to transmit blood from the one side of the heart to the other,
each one of these three divisions has separate but related functions,
which are dependent partly on differences in structure and physio-
logic properties, and partly on their relation to the heart and its
physiologic activities.

THE CIRCULATION OF THE BLOOD.

297

THE ARTERIAL CIRCULATION.

Structure and Properties of the Arteries. — The arteries ser\e
to transmit the blood ejected from the heart to the capillaries; that
this may be accomplished they divide and subdivide and ultimately
penetrate each and ever\^ area of the body. Their repeated division
is attended by a diminution in size, a decrease in the thickness and a
change in the structure of their walls.

A tj-pical artery consists of three coats: an internal, the tunica
intwia; a middle, the tunica media;
an external, the tunica adventitia.

The internal coat consists of a
structureless elastic basement mem-
brane, on the inner surface of which
rests a layer of elongated spindle-
shaped epithelial cells. The middle
coat consists of several layers of cir-
cularly disposed, non-striated muscle-
fibers, between which are networks
of elastic fibers. The external coat
consists of bundles of connective tis-
sue of the white fibrous and yellow
elastic varieties. Between the exter-
nal and middle coats there is an ad-
ditional elastic membrane. In the
small arteries there is but a single
layer of muscle-fibers. In the large
arteries the elastic tissue is ver\'
abundant, exceeding largely in
amount the muscle-tissue. It is also
more closely and compactly arranged.
The external coat is well developed
in the large arteries (Figs. 135 and
136).

In virtue of the presence in their
walls of both elastic and contractile
elements, the arteries possess the two properties of elasticity and con-
tractility.

The elasticity is especially well developed in the large arteries,
which are capable, therefore, of both distention and elongation, and,
when the distending force is withdrawn, of returning to their previous
condition. The elasticity permits of a wide variation in the amount
of blood the arterial system can hold between its minimum and
maximum distention. Thus the capacity of the aorta and carotid
arten,' of the rabbit can be increased four times and six times respec-

FiG. 134

Coats of a Small
Artery, a. Endothelium, b.
Internal elastic lamina, c. Cir-
cular muscular fibers of the
middle coat. d. The outer
coat. — (Landois and Stirling.)

29S

TEXT-BOOK OF PHYSIOLOGY.

tively by raising the intra-arterial pressure from o to 200 mm, of
mercury.

The contractility permits of a variation in the amount of blood
passing into a given area in a unit of time. Normally each artery
has a certain average caliber due to a given contraction of the mus-
cular coat. Beyond this average condition the artery can pass in
one direction or the other by either a relaxation or increased con-
traction of the muscular coat. During the functional activity of
any organ or tissue there is need for an increase in the amount of
blood beyond that supphed during inactivity or rest. This is ac-
complished by a relaxation of the muscle-fibers, an increase in diam-
eter, and an increase in the outflow of blood. With the cessation of

activity the muscle-
fibers contract, the
diameter diminishes,
and the outflow of
blood is reduced in
amount. An increased
contraction of the
muscle-fibers beyond
the average dimin-
ishes the outflow of
blood, and if suffi-
ciently great may give
rise to anemia and
pallor. The contrac-
tile elements at the
periphery of the arte-
rial system, in the so-
called arteriole region, regulate the supply of blood to the tissues in
accordance with their functional needs.

Structure of the Capillaries. — The capiflaries are small vessels
that connect the arteries with the veins. Though different in struc-
ture from a small artery or vein, there is no sharp boundary between
them, as their structures pass imperceptibly one into the other. A
true capillary, however, is of uniform size in any given tissue and does
not undergo any noticeable decrease in size from repeated branchings.
The diameter varies in different tissues from 0.0045 ^"^^- ^o 0-0075
mm., just sufficiently large to permit the easy passage of a single
red corpuscle. The length varies from 0.5 mm. to i mm. The
wall of the capillary (Fig. 136) is composed of a single layer of nu-
cleated endothelial cells with serrated edges united by a cement
material. Though extremely short, the capillaries divide and sub-
divide a number of times, forming meshes or networks, the closeness
and general arrangements of which vary in different localities.

^M^

Fig. 135. — Transverse Section of Part of the
Wall of the Posterior Tibial Artery (Man).
— (Schdfer.) a. EndotheKum lining the vessel,
appearing thicker than natural from the contrac-
tion of the outer coats, b. The elastic layer of
the intima. c. Middle coat composed of muscle-
fibers and elastic tissue, d. Outer coat consisting
chieflyof white fibrous tissue. — {From Yeo's ^^Phys-
iology. ")

THE CIRCULATION OF THE BLOOD.

299

Fig. 136. — Capillaries. The Outlines of the
Nucleated Endothelial Cells with the
Cement Blackened by the Action of Sil-
ver Nitrate. — {Landois and Stirling.)

The capillaries serve as a medium for the exchange of material

between the blood and tissues. It is in this region of the vascular

apparatus that the blood

fulfils its more impor-
tant functions. It is

here that the nutritive

material passes through

the walls of the capilla-
ries into the tissue spaces

and so into direct contact

with the tissue-cells; that

the waste products, the

outcome of tissue meta-

bohsm, partly pass

through the walls of the

capillaries into the

blood. The capillaries

fultil their functions by

reason of the fact that

they have not only small

diameters and thin walls,

but because they pervade

and penetrate the tissues

into their inmost recesses.

Structure of the Veins. — The veins serve to collect the blood

from the capillary areas and return it to the right side of the heart.

As they emerge from the capillary areas the veins, which in these

regions are termed venules, are quite small. By their convergence
and union the veins gradually increase in size in
passing from the periphery toward the heart.
Their walls at the same time correspondingly in-
crease in thickness. The veins from the lower ex-
tremities, the trunk, and abdominal organs finally
terminate in the inferior vena cava. The veins
from the head and upper extremities terminate in
the superior vena cava. Both venae cavae empty
into the right auricle.

A typical vein consists of the same three coats as
the artery: viz., the tunica intima, the tunica media,
and the tunica adventitia. The media, however,
does not possess as much of either the elastic or
muscle tissues as the artery, but a larger amount of
the fibrous tissue. Hence they readily collapse

when empty. In virtue of their structure the veins also possess both

elasticity and contractility, though in a far less degree than the arteries.

r

Fig. 137. — Valves
OF a Vein.
V. Semilunar
value, i. Free
edge of the
valve. — {Da-
vidson.')

300

TEXT-BOOK OF PHYSIOLOGY.

These properties come into play and are of value in furthering the
movement of the blood toward the heart, especially after a temporary
obstruction.

Veins are distinguished by the presence of valves throughout their
course. These are arranged in pairs and formed by a reduplication
of the internal coat, strengthened by fibrous tissue. They are
always directed toward the heart and in close relation to the walls
of the veins, so long as the blood is flowing forward (Fig. 137). An
obstruction to the flow causes the valves to turn backward until they
meet in the middle line, when they act as a barrier to regurgitation.
Under these circumstances the elastic tissue permits the veins to
distend and accommodate the blood. With the removal of the
obstruction the recoil of the elastic tissue, and perhaps the contrac-
tion of the muscle-tissue, forces the blood quickly onward.

The Stream-bed. — The stream-bed, the path along which the
blood flows, varies widely in its total sectional area in different parts
of its course, being greatest in the capillaries, least in the aorta and

Capillaries.

Arteries.

Veins.

Fig. 138. — Scheme of the Circulatory Apparatus.

venae cavae. In passing from the base of the aorta toward the capil-
laries the sectional area of individual arteries, in consequence of
repeated branching, diminishes, though their total sectional area
increases and in direct proportion to their distance from the heart.
In the capillary system the sectional area of an individual capillary at-
tains its minimal value, though the total sectional area attains its maxi-
mal value. Comparing one with the other, it has been estimated that
the total sectional area of the aortic bed is to the total sectional area
of the capillary bed as i is to 600 or 800. In passing from the capil-
lary into the venous system the sectional area of individual veins in-
creases, though the total sectional area decreases and in direct pro-
portion to their distance from the capillaries.

The stream-bed in the aorta is relatively narrow, but widens
gradually as it approaches the capillaries, where it attains its maxi-
mum width; it again narrows gradually as it passes into the veins,
until in the venae cavae it becomes almost as narrow as in the aorta. As
the combined sectional areas of the xense. cavae are greater than the sec-

THE CIRCULATION OF THE BLOOD. 301

tional area of the aorta, the stream-bed of the former never becomes
as narrow as that of the latter. These facts will become apparent
if the vascular apparatus is conceived of as a system of symmetri-
cally branching vessels and all vessels of the same diameter sym-
metrically disposed one to the other (Fig. 138). The gradual increase
in the width of the stream-bed which results from this repeated
branching, as well as its relative width in the arteries, capillaries,
and veins, is graphically shown in Fig. 139.

The Movement of the Blood. — The immediate cause of the
movement of the blood from the beginning of the aorta through the
arteries, the capillaries, and the veins to the right side of the heart, is

Fig. 139. — Diagram Intended to Give an Idea of the Aggregate Sectional
Area of the Different Parts of the Vascular System. A. Aorta. C.
Capillaries. V. Veins. The transverse measurement of the shaded part may be
taken as the width of the various kinds of vessels, supposing them fused together.
— (Yeo.)

a difference of pressure between these two points. The fact that the
blood flows from the aorta to the venae cavae indicates that there is a
higher pressure in the former than in the latter. The same holds true
for the pulmonary artery and veins. So long as this is the case, the
blood must flow from the point of high to the point of low pressure.
The Blood-pressure. — To this pressure the term blood-pressure
is given, and may be defined as the pressure exerted radially or
laterally by the moving blood-stream against the sides of the vessels.
That there is such a pressure within the arteries, capillaries, and veins,
ditferent in amount in each of these three divisions of the vascular
apparatus, is evident from the results which follow division of an artery

302 TEXT-BOOK OF PHYSIOLOGY.

or a vein of corresponding size. When an artery is divided, the
blood spurts from the opening for a considerable distance and with
a certain velocity. When a vein is divided, the blood as a rule merely
wells out of the opening with but slight momentum. These results
indicate that the blood in the arteries stands under a pressure con-
siderably higher than that of the atmosphere, and that in the veins
it stands under a pressure perhaps but slightly above that of the
atmosphere. Especially true is this of the larger veins.

The same facts may be demonstrated in another and more striking
way. A dog or cat is anesthetized and securely fastened in an appro-
priate holder. The carotid artery on the right side and the jugular
vein on the left side are freely exposed and clamped. Into the artery
there is inserted on the distal side of the clamp and in the direction of
the heart a cannula to which is connected a tall glass tube, 200 cm.
high and of about 4 mm. internal diameter. Into the vein there is
passed on the proximal side of the clamp and in the direction of the
capillaries a second cannula, to which is connected a similar tube,
though of less height. If the two clamps are removed at the same
time, the blood will mount in both tubes simultaneously. In the arterial
tube the blood will ascend by leaps corresponding to the heart-beats
until a certain height is reached, when the column becomes stationary,
being kept in equilibrium by the blood-pressure within the vessel
and the atmospheric pressure without. Though stationary in a
general sense, the blood-column oscillates, rising and falKng with
each contraction and relaxation of the heart. Not infrequently larger
excursions of the column are seen which correspond in a general way
to the respiratory movement. This experiment was originally per-
formed on the horse, by the Rev. Stephen Hales (1732).

In the venous tube the blood also rises to a certain height, after
which it remains quite stationary, as the effect of the cardiac con-
traction is not propagated under normal conditions beyond the
arterial system. The height to which it rises is but slight as com-
pared with that in the arterial tube. The pressure in both vessels is
thus recorded in milHmeters of blood. The absolute pressure on
any given unit of vessel surface — e. g., 1 square mm. — is obtained
by multiplying the height of the column, expressed in millimeters,
by the unit of surface, and then determining the weight of this mass
of blood. Thus if the height of the column of blood in the carotid
artery tube is 1800 mm., then the pressure on i sq. mm. is 1800 mm
of blood. The weight of 1800 c.mm. of blood is equal to 0.338 grams.

For accurate and long-continued observation the blood-pressure,
especially in the arteries, is more conveniently studied by means of
a U-shaped tube (a manometer) partially filled with mercury. One
limb of the manometer is connected by means of a tube and a cannula
with an artery. For the purpose of retarding coagulation of the blood

THE CIRCULATION OF THE BLOOD.

303

and for preventing the escape of a large volume of blood from the
vessels, the system is filled with a solution of carbonate of soda of
sp. gr. 1060 and under a pressure approximately equal to that in the
vessel of the animal as determined in previous experiments. When
communication is established between the vessel and the cannula, the

B.P TRACING

Fig. 140. — Diagram to show the Relation of the Mercurial Manometer to
THE Artery, on One Hand, and to the Recording Cylinder, on the Other
Hand, when Arranged for Recording Blood-pressure.

mercurial column adjusts itself to the pressure in the artery. It at
once begins to exhibit the same cardiac and respiratory oscillations and
undulations as did the column of blood in the previous experiment.

The height of the mercurial column kept in equiHbrium by the
pressure of the blood within and the pressure of air without the vessel

Fig. 141. — Blood-pressure Tracing.

is that between the lower level of the mercury in the proximal and
the higher level in the distal limb of the manometer, both of which
can be read off on a scale placed between the two limbs.

The height of the mercury as well as its oscillations in the distal
limb may be recorded by placing on the top of the mercury a light

304 TEXT-BOOK OF PHYSIOLOGY.

float, the upper end of which carries a writing point. When the
latter is placed in contact with the moving blackened surface of a
recording cyHnder or kymograph, the height and the oscillations are
recorded in the form of a tracing similar to that shown in Figs. 140
and 141, in which the larger curves represent the respiratory, the
smaller curves the cardiac oscillations. The height of the mercurial
column kept in equilibrium at any particular moment is determined
by measuring the distance between a base-hne or abscissa, which
represents the position of the mercury at atmospheric pressure, and
any given point on the trace above, and multiplying it by 2, for the
reason that the mercury sinks in the proximal hmb as high at it rises
in the distal limb of the manometer.

The blood-pressure as revealed by the tracing may be resolved
into two components: viz., (i) the pressure in the arteries during the
period of the cardiac diastole, which is termed the arterial pres-
sure; and (2) that additional pressure occurring at the time of the
cardiac systole, which is termed the cardiac pressure. The arte-
rial pressure is represented by the distance between the base-hne
and the points of the curve corresponding to the diastolic rest; the
cardiac pressure, by the increase of distance between these points
and the apices of the smaller oscillations. The relation of these two
components varies in different animals and in the same animal at
different times. If the arterial pressure is low, the cardiac increase
may be considerable; if the former is high, the latter may be slight.
The relation, however, of these components is not so accurately shown
by the mercurial manometer, owing to the inertia of the mercury, as
by one of the various forms of quickly responsive spring manometers
used in determining the rapid variations of intra-cardiac pressure.
These instruments show a much larger rise of pressure during the
systole, often amounting to as much as one-third or one-fourth of the
arterial pressure.

In a series of experiments it will be found that the arterial pres-
sure, though rising and falhng a certain number of milhmeters, yet
retains a fairly constant general average, the result of an adjustment
between the number of heart-beats per minute and the amount of the
resistance offered to the escape of blood into the capillaries and veins.
In a tracing in which the respiratory undulations are absent, the
arterial pressure, plus one-half of the cardiac increase, represents the
mean arterial pressure. If the respiratory undulations are present,
as is generally the case, the mean pressure may be represented by a
line drawn horizontally across the tracing midway between the apex
and trough of the undulation.

Estimates of the Blood-pressure. — By means of the kymo-
graphic methods previously mentioned the pressure in the larger
arteries has been determined for all classes of animals. In the carotid

THE CIRCULATION OF THE BLOOD.

305

artery of the dog it ranges from 140 to 160 mm.; in the horse, from
160 to 170 mm.; in the rabbit, from 90 to 100 mm. In two obser-
vations made on human beings during amputation of the hmb the
pressure was found in the brachial artery of one patient to range from
no to 120 mm., and in the anterior tibial of the other patient from
'no to 160 mm.

The Estimation of the Blood-pressure in Man.— The fore-
going method of obtaining the blood-pressure is not of general
application to human beings for obvious reasons, hence special
instruments have been devised by means of which the pressure may
be determined at least approximately without any surgical procedure.
Such instruments are termed sphygmomanometers. One of the best
is that of Mosso,
represented in Fig.
142. It consists es-
sentially of rubber
capsules, contained
within metallic
tubes and into
which two fingers
of each hand are
inserted. This sys-
tem is connected,
on the one hand,
with a pressure
apparatus, and, on
the other, with a
manometer pro-
vided with a scale.
A float and writing-
pen record the
movements of the

mercurial column on a moving blackened surface. In using this
apparatus the pressure is raised to the point at which the mercurial
column exhibits the greatest oscillations.

This sphygmomanometer, as well as the interpretation of the
results obtained with it, are based on the theory that the greatest
oscillations of the arterial walls, and hence the greatest oscillations
of the mercurial column, take place when the external pressure is
just equal to the mean arterial pressure, the latter being the mean
between the maximum pressure during the systole and the minimum
pressure during the diastole of the heart. It is only necessary, there-
fore, to take the mean of the readings corresponding to the excursions
of the mercurial column and determine from them the mean arterial
pressure.

Fig. 142. — The Sphygmomanometer of Mosso.

3o6

TEXT-BOOK OF PHYSIOLOGY.

It has been experimentally demonstrated, however, by Howell
and Brush that this interpretation is not correct, but that the greatest
oscillation takes place when the external pressure justs equals the
pressure in the artery at the end of the cardiac diastole. These ex-
perimenters found when the carotid artery of one side was connected
with a minimum valve and the carotid artery of the opposite side'
was surrounded by a plethysmograph in connection with a manometer,
that the diastolic pressure indicated by the valve just equaled the
lowest point of the greatest oscillation indicated by the manometer

Fig. 143. — Stanton's Sphygmomanometer.

Hence it is to be inferred that the greatest oscillations record the
diastolic pressure.

An excellent sphygmomanometer, especially adapted for clinical
use, is that devised by Stanton (Fig. 143 *).

In this apparatus the systolic pressure is determined by noting
the* point at which the pulse reappears after obliteration, while the
diastolic pressure is estimated by recording the point at which the

* The following description of this apparatus is abstracted from the Univ. of
Pa. Medical Bulletin, Feb., 1903.

THE CIRCULATION OF THE BLOOD. 307

greatest oscillations occur in the mcrcur)' column of the manometer.
The pressure is applied to the arm by the rubber armlet h, which is
3^ inches wide. This is the widest armlet that can be adjusted to
the average-sized arm and presents distinct advantages over the
narrow armlet hitherto employed. This armlet is prevented from
expanding outward by a cuff, f, of double thick canvas with inserted
strips of tin, which is held in place by two straps which completely
encircle the cuff. On the rigidity of this depends to a large extent
the transmission of pulsation. The rubber armlet is connected by
glass with a stiff-walled rubber tube, G, which in turn connects with
the manometer. The manometer is perhaps the most important part
of the apparatus. It is constructed entirely of. metal except for the
glass tube containing the mercury column. The chamber c com-
municates by means of a metal tube with the glass column d, which
is connected by a screw-thread at 3, the caliber of c being approx-
imately 100 times that of d. The cap of the chamber, which screws
on, is provided with a metal T which is connected at 2 with the
rubber armlet and at i with the bulb, used as an air-pump. At a
is a stop-cock shutting the rubber bulb completely from the rest
of the apparatus, while at b is a screw-valve which allows the air
to escape from the closed system. When desired, the manometer
can be made portable (without removing the mercury) by screwing
the caps i and 2 into either end of the T at i and 2. The manometer
is then tilted away from the glass column d until all the mercury
has run into the chamber, the glass is then unscrewed and cap 3
screwed in. Before removing cap 3 the manometer must always be
tilted, else the mercury will be lost.

The rubber bulb is similar to those found on atomizers.

In using this apparatus the pressure is raised by the air-bulb
forcing air into the closed system — distending the rubber armlet
and with the same degree of force displacing the mercury in c,
driving it up the glass column d. When the pulse is no longer felt,
the bulb still being compressed, the arm of valve A is turned
until it is at right angles w^ith the thumb and finger. The valve b
is now slowly unscrewed until the mercury column begins to fall.
With the eye on the scale the point at which the pulse reappears is
mentally noted as the systolic pressure. Often considerably before
the reappearance of the pulse to palpation, a pulsation is seen in
the mercur\' column. As the column slowly falls this increases up
to its greatest oscillation and then diminishes. The lowest point
of the greatest pulsation is noted as the diastolic pressure.

From experimental data and from theoretic reasoning it is certain
that the pressure in the carotid and femoral arteries is less than in
the aorta and greater than in the small peripheral arteries. In other
words, there is a fall of pressure from the beginning of the aorta to

3o8 TEXT-BOOK OF PHYSIOLOGY.

the arteriole region. The fall in pressure, however, is not great in
the larger vessels of the arterial system. It is only in the smallest
arteries, before their passage into the capillaries, that an abrupt fall
in pressure takes place.

The Capillary Pressure. — The small size of the capillaries pre-
cludes an investigation of their pressure by manometric methods.
It may be stated, however, to be approximately equal to the pressure
required to obliterate their lumen and to whiten the skin. The
apparatus of v. Kries is based on this theory. A small glass plate,
from 2.5 to 5 sq. mm., is fastened to the under surface of a support
of suitable size carrying a small scale pan. The glass plate is placed
on the skin near the root of a finger-nail and the scale pan gradually
weighted until the vessels are obliterated, as shown by the blanching
of the skin. From results obtained with this apparatus v. Kries
estimated the pressure in the capillaries of the hand at 37 mm. Hg,
and in the ear at 20 mm.

The Venous Pressure. — In passing from the capillaries to the
heart the pressure continues to fall. The increasing size of the
veins permits again of manometric observations in different regions.
In the crural vein the pressure has been found to be equal to 14 mm.
Hg, and in the brachial vein 9 mm. In the jugular and subclavian
and other vessels near the heart it is zero or even negative; that is, less
than atmospheric pressure to the extent of from i to 10 mm. mercury.

The amount and relation of the pressures in the three divisions of
the systemic vascular apparatus are approximately shown in Fig.
144.

Causes of the Blood-pressure. — In correspondence with the
laws of the flow of fluids through both rigid and elastic tubes, the
flow of blood through the blood-vessels under the driving-power of
the heart encounters friction. This is to be sought for not between
the blood and the inner surface of the vessel, but rather in the cohesion
of the particles of blood. This it is which offers resistance to the
onward movement of the blood and which must be overcome if the
circulation is to be maintained. Close to the inner surface of the
vessel there is a layer of blood which is motionless, known as the
still layer, caused by an adhesion between the blood and the vessel.
Between this layer and the axis of the stream there is an infinite num-
ber of layers. The cohesion between these layers gradually dimin-
ishes in passing from the periphery to the center of the stream. The
larger the stream, the less is the cohesion, and the reverse. In the
large arteries the still layer is small in amount as compared with the
total volume of blood passing through them; hence the axial cohesion
is readily overcome and the friction is but slight. In the smallest
arteries and capillaries the ratio changes and the friction rapidly
increases and to a considerable extent. In the veins the ratio again

THE CIRCULATION OF THE BLOOD. 309

changes, approximating that in the arteries. As the veins pass from
the periphery toward the heart and their individual sectional areas
increase there is again a diminution of the friction.

As a consequence of the friction throughout the entire vascular
apparatus the blood experiences a resistance to its onward move-
ment which, working backward, causes the blood to exert a lateral
or radial pressure against the walls of the vessels. The high pres-
sure in the aorta is the result of the total resistance of the vascular
system, and the pressure at any point of the system represents the
resistance yet to be overcome. The larger part of the pressure in
the arterial system, however, is due to the resistance offered by the

Fig. 144. — Diagram showing the Relative Height of the Blood-pressure in
THE Different Regions of the Vessels. H. Heart. A. Arteries. C. Capil-
laries. V. Large veins. 0, 0, being the zero line (= atmospheric pressure), the
pressure is indicated by the height of the cur\-e. The numbers on the left give
the pressure (approximately) in miUimeters of mercury, h. Pressure in heart.
a. Arteriole region showing sudden fall of pressure, c. The fall of pressure in
the capillaries, v. The negative pressure in the large veins. — {Yeo.)

smallest arteries and capillaries, and when peripheral resistance is
alluded to as a factor in the production or in the variation of blood-
pressure, the resistance of these vessels is mainly understood.

The primary factor in the production of the pressure is the pump-
ing action of the heart. Should there be any cessation in its activity,
the elastic walls of the arteries would recoil and force the blood into the
veins. There would be coincidently a fall to a pressure equal to
that of the atmosphere. Even under normal circumstances this
condition is approximated during the diastole. The recoil of the
arterial wall bv which the forward movement of the blood is main-

3IO TEXT-BOOK OF PHYSIOLOGY.

tained is attended by a fall in pressure. But before this reaches any
considerable extent, the heart again contracts and forces its contained
volume of blood into the arteries.

That this may be accomplished it is essential that the cardiac
energy be sufficient not only to drive a portion of the blood through
the capillaries into the veins, but to oppose the recoihng arteries, and
to distend them to their previous extent, so that the incoming volume
of blood may be accommodated. This at once reestablishes the
pressure at its former level. The alternate rise and fall of the pres-
sure is represented by the oscillations of the mercurial column or by
the small elevations and depressions on the kymographic tracing.

During the contraction of the heart the kinetic energy is trans-
formed into potential energy, represented by the tense distended walls
of the arteries. With the relaxation of the heart and the closure of
the semilunar valves the potential energy of the arteries is again trans-
formed into kinetic energy, represented by the moving blood. The
artery thus continues the work of the. heart during its period of in-
acti\dty. The rapidity with which the cardiac contractions succeed
each other prevents the pressure from sinking below a certain average
level.

The uniform level of the arterial pressure depends on the fact that
though more blood enters the arteries during the systole than escapes
into the capillaries and veins, as shown by the rise of the mercurial
column in the manometer, this is compensated for by a continued
escape during the diastole as shown by the fall of the mercurial col-
umn. So long as the inflow of blood is equaled by the outflow, there
is a balancing of opposing forces and the pressure is maintained at a
uniform level.

Changes in Blood-pressure. — It is evident from the preceding
statements that the arterial blood-pressure as a whole may be increased
by:

1. An increase in the rate or force of the heart's contraction.

2. An increase in the peripheral resistance.

3. An increase in the general volume of the arterial blood.
And that it may be decreased by :

1. A decrease in the rate and force of the heart's contraction.

2. A decrease in the peripheral resistance.

3. A decrease in the general volume of blood.

If when the arterial pressure is in a condition of equiHbrium the
heart ejects into the arteries in a given period of time an increased
quantity of blood as a result of an increased rate of contraction, there
will be an accumulation of blood temporarily in the arteries (the
peripheral resistance remaining the same), for the pressure is only
sufficient to force into the capillaries a given volume.

The same result could be brought about by an increase in the

THE CIRCULATION OF THE BLOOD.

311

force or power of ihc contraction, the fre([uency remaining the same.
An increase in the volume of blood ejected at each contraction will
necessarily lead to an accumulation. With the accumulation there
goes an increased distention of the artery and a corresponding increase
of pressure. In a short time, therefore, the increased pressure will
force out of the arteries at a
higher rate of speed this ex-
cess of blood until the outtlow
again equals the inflow. This
restores the equihbrium but
establishes the mean pressure
afa higher level.

If the peripheral resistance
is increased by a contraction
of the muscular walls of the
arterioles, the frequency and
force of the heart remaining
the same, there will also be
an accumulation of blood in
the arteries until their in-
creased distention and consequent rise of pressure become sufficient
to increase the rapidity of outflow until it counterbalances the inflow.

The converse of these statements also holds true. If when the
general arterial pressure is in a condition of equilibrium the heart
ejects into the arteries in a given period of time a decreased quantity
of blood, either as a result of a decrease in the rate or power or both.

Fig. 145. — Fall of Blood-pressure from
Arrest of the Heart's Action due
TO Stimulation of the Vagus begun
at a AND Stopped at b. — {Landois and
Stirling.)

Fig. 146. — Fall of Blood-pressure from Diminution of the Peripheral Resist-
ance, THE Result of a Dilatation of the Arterioles, brought about by
Stimulation of the Central End of the Depressor Nerve. Stimulation
begun at a, and stopped at b. — (Landois and Stirling.)

there will soon be a diminution of the arterial distention and a con-
sequent fall in pressure (Fig. 146). This continues until the outflow
no longer exceeds the inflow. Equilibrium will again be established,
but the pressure will be at a lower level.

If the peripheral resistance is diminished by a dilatation of the

312 TEXT-BOOK OF PHYSIOLOGY.

arterioles, the heart's contractions remaining tlie same, the existing
pressure soon diminishes. The outflow of blood at once lessens in
rapidity and so continues until it counterbalances the inflow. The
equilibrium is again restored, but the pressure is at a lower level.

Variations in Capillary Pressure. — The pressure in the capil-
laries, though for the most part possessing a permanent value, is
subject to variations in accordance with variations in the pressure in
either the arterial or venous systems or both. The marked difference
in the pressure in the large arteries and the capillaries is partly due to
the resistance offered by the narrow arterioles. If the latter dilate
in any given area, the capillary pressure increases because of the
propagation into them of the arterial pressure. The reverse condition
would decrease the pressure. On the other hand, any interference
with the outflow from any given area, due to venous compression,
would likewise increase the pressure ; any factor which would, on the
contrary, favor the outflow would decrease the pressure. Indepen-
dent of any change in the arteriole resistance, it is evident that a rise
in arterial pressure alone would increase the capillary pressure. If
both arterial and venous pressures rise, the capillary pressure increases ;
if both fall, it decreases.

Variations in Venous Pressure. — Independent of any change
in the venous pressure in a given area from local or temporarily
acting causes, — e. g., aspiration of the thorax or heart, muscle con-
tractions, change of position, etc., — the general venous pressure will
be increased by a decrease in the value of those factors which produce
the difference of pressure between the arteries and veins. An in-
crease in the value of these factors would necessarily decrease the
pressure.

THE VELOCITY OF THE BLOOD.

From the number of heart-beats per minute, 72, and the amount
of blood discharged from the left ventricle at each beat, 180 c.c, it is
evident that the blood must be flowing through the vascular appa-
ratus with a certain velocity, for during the minute the entire
volume of blood, 5769 grams, must have passed twice through the
heart. Direct observation of the escape of blood from the central
end of a divided artery, and from the peripheral end of a divided
vein, as well as of the flow through the capillaries as seen with the
microscope, shows that the velocity of the flow varies in different
parts of the vascular apparatus. In the arteries, moreover, the flow
is not quite uniform, but experiences alternate acceleration and
retardation with each heart-beat. In the capillaries and veins the
flow is continuous and uniform, as the conditions of the arterial walls
are such as to completely overcome the intermittency.

THE CIRCULATION OF THE BLOOD. 313

If the systemic vascular apparatus be conceived of as a system
of tubes which have s}'mmetrically divided and subdivided, and have
again united and reunited in a corresponding manner, it is clear that
the total sectional area will steadily increase from the beginning to
the middle of the system, and then as steadily decrease from the middle
to the end of the system. In such a system the same volume of blood
must pass through any given section in a unit of time if the balance
of the circulation is to be maintained. As the velocity of a fluid is
inversely as the sectional area of the tubes through which it flows, it
follows that the initial mean velocity of the blood in the aorta will
steadily decrease as it flows into the steadily enlarging blood-path
until it reaches a minimal value in the middle of the capillary system;
and that it will again steadily increase as it flows into the narrowing
blood-path until it reaches the heart. The initial mean velocity of
the blood in the aorta vdU. not be attained in the venae cavge, for the
reason that the total sectional area of the latter is somewhat greater
than that of the former. The same facts hold true for the pulmonic
vascular system.

The Velocity in the Aorta. — From the well-known fact that the
velocity with wliich a fluid is flowing through a tube may be deter-
mined by dinding its sectional area into the quantity discharged
in a unit of time, attempts have been made to determine the mean
velocity of the blood at the beginning of the aorta. If it be assumed
that the volume discharged at each contraction is 180 c.c, as stated
by Vierordt, and the number of heart-beats per minute at 72, the
total volume discharged per minute would be 12,960 c.c, or 215 c.c.
per second. The sectional area of the aorta is 6.15 sq. cm. On the
principle above stated, these two factors would show a velocity of
350 mm. per second. An objection to this estimate is that the
amount of blood discharged — i. e., the contraction volume — is much
larger than recent investigations warrant. Difl'erent obser\-ers have
estimated that in man the contraction volume is considerably less,
probably not more than 80 c.c. If this is true, the mean velocity in
the aorta would be less than in the carotids.

The Velocity in the Arteries. — The mean velocity of the blood
in the larger and more superficially hing arteries has been determined
by Volkmann with the hemodromometer, by Lud^^•ig and Dogiel
^^•ith the stromuhr, and by other investigators vrixh. different forms of
apparatus.

Since neither the blood nor any particle placed in it can be seen
through the walls of the arter\-, it occurred to Volkmann to inter-
calate along the course of a vessel a U-shaped glass tube about one
meter in length with a lumen the diameter of that of the selected
vessel, into and through which the blood could be made to flow.
The mechanic construction of the apparatus is such (Fig. 147) that

314

TEXT-BOOK OF PHYSIOLOGY.

the blood can be made to flow directly into the distal portion of the
artery across the base or indirectly by way of the glass tube. Pre-
vious to the intercalation of the tube it is filled with serum or normal
sahne solution. With the turning
of the cocks at B the blood enters
the glass tube and drives the serum
ahead of it into the arterial system.
From the difference in time between
the moment the blood enters and
the moment it leaves the tube and
from the length of the tube the
velocity is determined.

Fig. 147. — Volkmann's Hemodromometer.
C, C. Arterial cannulas.

Fig. 14S. — LuDwiG and Dogiel's
Rheometer. X, Y. Axis of
rotation. A, B. Glass bulbs.
h, k. Cannulas inserted in the
divided artery, e, e^, rotates
on g, f. c, d. Tubes.

The stromuhr or rheometer of Ludwig (Fig. 148) is constructed
on the same principle, but instead of the glass tube having the same

THE CIRCULATION OF THE BLOOD.

315

diameter it is considerably enlarged on its two sides. The bulbs are
fastened to a metallic disk which rotates around an axis in the metallic
base which carries the tubes to be inserted into the arteries. With
this device it is possible to place either bulb in connection with the
proximal end of the artery. Previous to the experiment the proximal
bulb is filled with oil, the distal bulb with serum or normal sahne.
On removing the clips on the artery the blood flows into the proximal
bulb and drives the oil into the distal bulb. As soon as the former is
filled with blood the bulbs are reversed and the same relative condi-
tions are attained. This is repeated a number of times. Knowing
the capacity of the bulbs, and the number of times they are filled in
a given period, the total quantity of blood discharged is obtained.
This divided by the sec-
tional area of the artery
gives the velocity. The fol-
lowing values have thus
been obtained: For the
carotid of the dog, 205 to
357 mm. per second; for
the carotid of the horse,
306 mm. ; for the metatar-
sal artery of the horse, 56
mm. (Volkmann). For the
carotid of rabbits, 94 to 226
mm.; for the carotid of
the dog, 349 to 733 mm.
(Dogiel).

The variations in the
velocity of the blood in the
arteries during the different
phases of the cardiac cycle
have been determined by
Chauveau and Lortet with
the hemodromograph (Fig.
149). This consists of a

metallic tube carrying a graduated disk. At one point the tube is per-
forated but covered with a rubber band through which passes an index.
When the tube is inserted into the divided ends of an artery, the cur-
rent of blood strikes the short arm of the index and gives to the outer
long arm a movement in the opposite direction. The extent of the ex-
cursion indicates the velocity. The apparatus is first graduated with
currents of water of known velocity. With this instrument Chauveau
found that in the horse the velocity during the systole was 520 mm.
per second, at the beginning of the diastole 220 mm. per second, and
during the pause 150 mm. per second.

Fig

149. — The Hemodromograph of Chau-
veau AND Lortet. A, B. Tube inserted
in artery. C. Lateral tube connected with
a manometer. b. Index moving in a
caoutchouc membrane, a. G. Handle.

3i6

TEXT-BOOK OF PHYSIOLOGY.

The Velocity in the Capillaries. — The rate of flow in the capil-
lary vessels can not be experimentally determined. It has been esti-
mated by Vierordt at 0.5 mm. per second in his own retinal capillaries ;
by Weber at 0.8 mm. In frogs the velocity can be fairly well deter-
mined by observing the time required for a corpuscle to pass over one
or more divisions of an ocular micrometer. Weber calculated in this
way that the velocity is 0.5 mm. per second.

As the velocity varies inversely with the sectional area, it becomes
possible to approximately determine the relation of the sectional area
of the capillary system to that of the aorta from the above-mentioned
velocities. If it be assumed that the velocity in the aorta averages
300 mm. and in the capillaries 0.5 mm. per second, then the sectional
area of the capillaries is to that of the aorta as 600 to i.

The Velocity in the Veins. — In the venous system the velocity
increases in proportion as the sectional area decreases. In the jugu-

Arteries.

Fig. 150.

Capillaries.
-, Blood-pressure. , Velocity.

Veins,
-o — o — o, Sectional area.

lar vein Volkmann found the velocity 225 mm. per second, which
was about one-half that in the aorta of the same animal. The reason
for the slow rate of movement in the jugular vein is to be found in the
fact that the sectional area of the combined vense cavae is about twice
that of the aorta; hence the relation of the sectional area of the cap-
illary system to the sectional area of the venae cavae is about 300 to i .
The blood-pressure, the velocity of the blood, the sectional area
of the vascular apparatus, and their relation one to the other are
shown in Fig. 150.

THE PULSE.

It has been stated (see Blood-pressure) that with each contraction
of the left ventricle a definite volume of blood is discharged into the
aorta which at the moment is already full of blood; that this incoming

THE CIRCULATION OF THE BLOOD. 317

volume is accommodated by the forward movement of the blood as
a whole and by the sudden distention of that portion of the aorta
nearest the heart, both effects being due to the energy of the heart's
contraction. The distention of this first segment of the aorta is
almost immediately followed by a recoil of its elastic walls which,
through pressure on the blood, causes the next-lying segment to
expand; this in turn recoils and causes a third segment to expand,
and so on until the expansion has traveled not only over the aorta,
but over all its branches as well, as far as their final terminations.

This expansion movement which thus passes from the beginning
to the end of the arterial system in the form of a wave is known as the
pulse-wave or pulse. Coincident with the expansion and recoil of the
arterial system there is a shght alternate increase and decrease of
the general blood-pressure, as shown by the small curves on a blood-
pressure tracing.

The pulse-wave which thus spreads itself over the entire arterial
system with each systole of the heart can be perceived in certain
locaHties by the eye, by the sense of touch, and investigated with
various forms of apparatus or instrumental means. The pulse-
wave, or at least the elevation of the soft tissues overlying it, can be
seen in the radial artery, where it passes across the wrist-joint, in the
carotid artery, in the temporal artery, in the arteries of the retina under
certain conditions, with the ophthalmoscope. If the ends of the fingers
are firmly placed over the radial artery, not only the increase and de-
crease of pressure, but also many of the peculiarities of pulse-wave, may
be perceived. Without much difficulty it may be perceived that the
expansion takes place quickly, the recoil relatively slowly; that the
waves succeed one another with a certain frequency, corresponding
to the heart-beat; that the pulsations are rhythmic in character, etc.
Inasmuch as the individuality of the pulse-wave varies at dift'ercnt
periods of Hfe and under different physiologic and pathologic condi-
tions, various terms more or less expressive have been suggested for
its varying pecuHarities. Thus the pulse is said to be frequent or
infrequent according as it exceeds or falls short of a certain average
number — 72 per minute; quick or slow, according to the suddenness
with which the expansion takes place or strikes the fingers; hard or
soft, tense or easily compressible, according to the resistance which
the vessel offers to its compression by the fingers; large, full, or small,
according to the volume of blood ejected into the aorta, or, in other
words, the degree of fullness of the arterial system.

Frequency of the Pulse. — As the pulse or the arterial expansion
is the direct result of the heart's action, its frequency must, under
physiologic conditions, coincide with that of the heart. All condi-
tions which modify the rate of the heart will modify at the same time
the rate of the pulse. (See page 275).

3i8 TEXT-BOOK OF PHYSIOLOGY.

The Velocity of Propagation of the Pulse-wave.— The propa-
gation of the pulse- wave from its origin at the root of the aorta to any-
given point of the arterial system occupies an appreciable period of
time. The difference in time between the systole and the appearance
of the pulse- wave at the dorsal artery of the foot can be appreciated
by the sense of touch. The absolute time occupied by the wave in
reaching this point was determined by Czermak to be 0.193 second.
The rate at which the wave is propagated over the vessels of the lower
extremity has been estimated by the same observer at 11. 16 meters
per second, and for the upper extremities at but 6.7 meters per second.
Other experimenters have obtained for the lower extremities some-
what different results, varying from 6.5 to 11 meters per second.
Weber's original estimate was from 7.92 to 9.24 meters per second.
The slower rate of movement in the vessels of the upper extremities
has been attributed to a greater distensibility of their walls, a condi-
tion unfavorable to rapid propagation. For this reason a low arterial
tension will occasion a delay in the appearance of the pulse- wave in
any portion of the body ; a high arterial tension will of course have the
opposite effect. The difference in the speed of the pulse-wave and
the blood-current shows that they are not identical and must not be
confounded with each other.

The Sphygmograph. — The alternate expansion and recoil of an
SLVttry caused by the temporary increase and decrease of pressure
following each heart-beat can be graphically recorded on a traveling
surface by means of a special apparatus, the sphygmograph or pulse-
writer. The tracing obtained in the form of a curve is termed the
pulse-curv'e or the sphygmogram. Different forms of this apparatus
have been devised by Marey, Dudgeon, v. Frey, and many others.
The instrument of v. Frey is shown in Fig. 151. This consists first of
a metal framework by which the apparatus is fastened to the arm and
support given to the lever, recording surface, etc. The essential part
is the spring carrying a button which is placed over the artery, usually
the radial, before it crosses the wrist- joint. A vertical rod transmits
the movement of the spring to the recording lever; the movements
of the latter are recorded on a small cyhnder inchned shghtly so that
the upstroke may be vertical. A smah electro-magnet serves to
record the time. An average tracing taken from the radial artery is
shown in Fig. 152. This, however, is not a tracing of the pulse- wave,
but rather a record of the changes in pressure, their succession and
time relations, which follow each beat of the heart. The artery
usually selected for obtaining a sphygmogram is the radial. This
artery Hes quite superficially, covered only by connective tissue and
skin and supported by the flat surface of the radial bone, conditions
most favorable to technical investigation.

The sphygmogram or pulse-curve may be divided into two portions :

THE CIRCULATION OF THE BLOOD.

319

viz., a line of ascent from a to b, and a line of descent from b to d (Fig.
152). In normal tracings the former is almost vertical and caused by
the sudden expansion of the artery immediately following the ventric-
ular contraction; the latter is in general oblique, due to the recoil of
the arterial walls, occupies a longer period of time, and is marked

Fig. 151. — Von Frey's Sphygmograph. G. S. Metal framework. P. Button
attached to spring. F. Vertical rod. U. Clock-work which turns the recording
cylinder. VI. Time marker.

by several elevations and depressions, both of which indicate that the
restoration to equihbrium is neither immediate nor uncomplicated.
One of these elevations is quite constant and known as the dicrotic
wave, c; the depression or notch just preceding it is known as the
dicrotic notch. Pre- and post-dicrotic waves are not infrequently
present. The summit is generally
sharp and pointed.

The vertical direction of the line of
ascent is taken as an indication that
the arterial walls expand readily, that
the blood is discharged quickly, and
that the ventricular action is not im-
peded. An oblique direction of the
line of ascent is an indication that the
reverse conditions obtain. The height

varies inversely as the arterial pressure, other things being equal;
being high with a low pressure, and low with a high pressure.

The dicrotic wave shows that a second expansion wave is devel-
oped which interrupts temporarily the recoil of the arterial walls.

Fig. 152. — The Pulse Curve or
Sphygmogram.

320

TEXT-BOOK OF PHYSIOLOGY.

The origin of this second expansion has been the subject of much
investigation, and at present it may be said that the question is not
fully decided. It is asserted by some investigators that it is central
in origin, beginning at the base of the aorta and passing to the pe-
riphery; by others, that it is peripheral in origin, beginning near the
capillary region and reflected to the heart. The former view is the
one more generally accepted. According to it, the expansion is the
result of the sudden closure of the aortic valves, a backward surge of
the blood-column against them. The sudden arrest of the blood
and its accumulations again expands the aorta.

The dicrotic notch is therefore taken as the moment at which the
ventricular systole ceases and the aortic valves close. From this fact
it is evident that immediately after the first expansion the pressure
begins to fall, even though the ventricular systole continues, owing
to the discharge of blood from the arterial into the capillary and

Fig. 153. — Mosso's Plethysmograph. G. Glass vessel for holding a limb. F.
Flask for varying the water-pressure in G. T. Recording apparatus. — {Landois
and Stirling.)

venous systems. The height of the dicrotic wave or the depth of
the dicrotic notch is favored by low arterial tension and highly elastic
arteries. Both features are diminished by the reverse conditions.
The apex is sometimes rounded and even fiat, indicative of a great
diminution in arterial elasticity. The sphygmogram not infrequently
varies considerably from the normal type in different pathologic
conditions of the circulatory apparatus. A consideration of these
variations does not fall within the scope of this work.

The Volume Pulse. — If an individual artery expands with each
systole and recoils with each diastole of the heart, the same is true of
all arteries, and as a result the volume of any organ or part of the body
must undergo similar changes. To such alternate changes in volume
the term volume pulse is given. The extent to which an organ will
increase in volume will depend to some extent on its elasticity. The
reason for the increase in volume is the resistance offered to the flow

THE CIRCULATION OF THE BLOOD. 321

of blood into and through the capillaries; the decrease in volume to
the overcoming of the resistance through the arterial recoil.

The variations in volume may be recorded by enclosing the organ
in a rigid glass or metal vessel, which at one point is in com-
munication with a recording apparatus, e. g., a tambour with a
lever or mercurial manometer with float and pen. The space be-
tween the organ and vessel is filled with normal saline, air, or oil.
Such an apparatus is known as a plethysmograph. A well-known
form of plethysmograph is that of ]Mosso (Fig. 153). Many forms
of this apparatus have been devised in accordance with the character
of the organ— spleen, kidney, etc. — to be investigated, though the
principle underlying them is essentially the same. In addition to
changes in volume due to the heart's action, most organs undergo
additional changes in volume from respiratory and vaso-motor causes;

THE CAPILLARY CIRCULATION.

In certain regions of the body of many animals it is possible, on
account of the dehcacy and transparency of the tissues, to observe
not only the flow of blood through the smaller arteries, capillaries,
and veins, but many of the phenomena connected with it, to which
reference has already been made. The structures usually selected
for the observation of these phenomena are the interdigital mem-
branes, the tongue, the lung, the bladder, and the mesentery of the
frog. Though any one of these structures will afford an admirable
view of the blood-flow, the mesentery for many reasons is the most
satisfactory. For a comparison of the phenomena observed in the
cold-blooded animals with those in the warm-blooded animals the
omentum of the guinea-pig may be employed. If the frog is the sub -
ject of experiment, it should be slightly curarized and the brain de-
stroyed by pithing. The animal is then placed on a small board
capable of adjustment to the stage of the microscope. The abdomen
is then opened along the side and a loop of intestine withdrawn and
placed around a cork ring which surrounds an opening in the side
of the frog board. The loop of the intestine should be so placed
that it will lie between the observer and the body of the frog. The
mesenten,' thus exposed must be kept moist with normal saline
solution.

When examined with low powers of the microscope, arteries, veins,
and capillaries will be found occupying the field of vision. Their
general arrangement, their size and connections, can be readily deter-
mined. After a few prehminary adjustments a region will be found
in which the blood is flo^Ning in opposite directions. The vessel
apparently carrying blood aivay from the observer is an arter\'; the
vessel apparently carrying blood toward the observer is a vein; the

322

TEXT-BOOK OF PHYSIOLOGY.

smallest vessels are capillaries. The blood in the artery is of a
brighter color than the blood in the vein; the blood in the capillaries
is almost colorless. The arterial blood-stream not infrequently
shows remittancy, an alternate acceleration and retardation, corre-
sponding to each heart-beat ; the capillary and venous streams are
uniform and continuous. The relative velocities in the three sets
of vessels are indicated by the movement of the red corpuscles. In
the arteries they pass before the eye so rapidly that they can not be
distinguished; in the capillaries they pass so slowly that both form

and structure may be deter-
mined; in the veins, though
again moving rapidly, they
can often be distinguished.

The relative positions of
the red and white corpuscles
in the blood-stream are also
apparent; the former occupy
the central, the latter the per-
ipheral portion, at the same
time adhering to the sides of
the vessel. Between the axial
portion of the stream occu-
pied by the red corpuscles and
the wall of the vessel there is
a clear still layer of plasma,
the result of an adhesion of
the plasma to the wall. It is
this feature which gives rise to
the friction between successive
layers of the blood-stream, the
resistance to the blood-flow,
and the development of blood-
pressure. The relative breadth
of the still layer and amount of friction are greater in small than in
large vessels.

The volume of blood passing into any given capillary area is
determined by the degree of contraction of the arterioles. Thus on
the application of warm sahne solution, which relaxes the arterioles,
there is a large increase in the inflow of blo.od ; vessels previously in-
visible suddenly come into view as the blood with its corpuscles passes
into them. On the apphcation of cold water, which contracts the
arterioles and diminishes the inflow, many of the smaller vessels
entirely disappear from view. The alternate contraction and re-
laxation of the arterioles will therefore determine the quantity of
blood flowing into and through the capillary system.

Fig. 154. — The Vessels of the Frog's
Web. — a. Trunk of vein, and {b, b) its
tributaries passing across the capillary
network. The dark spots are pigment
cells. — (Yeo's "Physiology.")

THE CIRCULATION OF THE BLOOD.

323

Functions of Capillary Vessels. — The structure of the capil-
lary vessel is such as to permit the blood to come into intimate re-
lation with the tissues; consisting of only a single layer of endothelial
cells, a free exchange between blood and tissues at once takes place.
The nutritive materials of the blood pass through the capillary wall
into the tissue spaces; the waste products, the result of tissue metabo-
lism, pass through the capillar}- wall and into the blood, and by it are
carried to the ehminating organs. As a result of these exchanges
the relative composition of the blood is changed. It now contains
a smaller quantity of nutritive material and a larger quantity of
waste materials; containing less oxygen, it changes in color from red
to bluish-red.

Though the length of the capillar}' is not more than 0.5 mm. and
the time occupied by the blood in passing through it not more than
0.8 second, yet the conditions are such that an exchange of materials
sufficient for nutritive purposes takes place. It is for this reason that
the rest of the circulator}- apparatus exists. Collectively its different
parts cooperate to give to the blood in the capillaries the volume,
the velocity, and the pressure requisite for nutritive purposes.

Migration of the White Corpuscles. — A phenomenon fre-
quently observed in the
capillar}- vessels of the
mesentery or of the blad-
der of the frog is the pas-
sage of the white corpuscles
through the walls into the
surrounding lymph-spaces.
To this process the term
migration or diapedesis is
given. After the tissues
have been exposed to the
air for some time or sub-
jected to an irritant, the
vessels dilate and become
distended with blood. In
a short time the blood-
stream slows, and finally
comes to rest. The condi-
tion of stasis is then estab-
lished. During the development of this condition the white corpus-
cles accumulate in large numbers along the inner surface of the
vessels and soon begin to pass through the vessel-walls. This they
do by the protrusion of a portion of their substance w-hich is inserted
into and through the vessel-wall. This once accomphshed, the re-
mainder of the cell in due time follows until it has entirely passed

Fig. 155. — Small Vessel of a Frog's Mesen-
tery SHOWING Diapedesis. w, w. Vas-
cular walls, a, a. Poiseuille's space, r, r.
Red corpuscles. /, /. Colorless corpuscles
adhering to the wall, and c, c, in various
stages of extrusion. /, /. Extruded cor-
puscles.— {Landois and Slirling.)

324 TEXT-BOOK OF PHYSIOLOGY.

out into the tissue-space. The opening in the cell-wall now closes.
The successive steps in this process are shown in Fig. 155. As this
migration occurs mainly after the circulation has ceased or when the
tissues present the phenomena of approaching inflammation, it is
difficult to state in how far it is strictly a physiologic process.

THE VENOUS CIRCULATION.

The blood, having passed through the capillary vessels, is gathered
up by the veins and conveyed to the right side of the heart. As the
veins converge and unite to form larger and larger trunks the sec-
tional area gradually diminishes, and hence the velocity of the blood-
flow increases, though it never attains the velocity, even in the venae
cavae, that it had in the aorta, for the reason that the sectional area of
the venae cavffi is considerably larger than that of the aorta. The
pressure also is very low in the larger veins because the friction still
to be overcome is relatively very slight.

The capacity of the venous system is considerably greater than
that of the arterial system, as there are usually two and even three
veins accompanying each artery. This, taken in connection with its
greater distensibihty, makes of the venous system a reservoir in which
blood can be stored. On this reservoir the arterial system can call
for that amount of blood necessary for the maintenance of its normal
volume and pressure, and into it any excess can be discharged.
The relative amounts contained in the two systems are regulated by
the nervous system. The movement of the blood through the veins
is accompHshed by the cooperation of several forces, reference to
which will be made in a following paragraph.

THE PULMONIC VASCULAR APPARATUS.

The pulmonic vascular apparatus consists of a closed system
of vessels extending from the right ventricle to the left auricle, and
includes the pulmonary artery, capillaries, and pulmonary veins. In
its anatomic structure and physiologic properties it closely resembles,
if it is not identical with, the systemic apparatus.

The stream-bed widens from the beginning of the pulmonary
artery to the middle of the capillary system; it again narrows from
this point to the terminations of the pulmonary veins.

The movement of the blood from the beginning to the end of the
system is due to a difference of pressure between these two points,
the result of the friction between the blood and the vascular walls.
From the difference in the extent of the pulmonic and systemic
systems it is evident that, other things being equal, the friction is less,
and therefore also the pressure is less in the former than in the latter.

THE CIRCULATION OF THE BLOOD. 325

This view is supported by the difference in the thickness of the walls of
the right and left sides of the heart. The pressure in the pulmonary
artery of the dog was shown by Bentner to be about one-third that
in the aorta; by Bradford and Dean to be one-fifth. The velocity
of the blood-stream in each of the three divisions of the system can
not well be determined. The time occupied by a particle of blood
in passing from the right to the left ventricle has been estimated at
one-fourth the time required to pass from the left to the right ven-
tricle. Assuming the latter to be thirty seconds, the former would be
seven and one-half seconds.

The capillary vessels are spread out in a very elaborate manner
just beneath the inner surface of the pulmonary air-cells, and form
by their close relation to it, a mechanism for the excretion of carbon
dioxid and the absorption of oxygen. The extent of the capillary
surface is very great. It has been estimated at 200 square meters.
The amount of blood flowing through this system hourly and exposed
to the respiratory surface is about 800 liters. The reason for the
existence of the pulmonary circulation is the renewal of the oxygen
volume in the blood and the elimination of the carbon dioxid; for
the accomplishment of both objects ample provision is here made.
The flow of blood through the cardio-pulmonary vessels is subject
to variation during both inspiration and expiration in consequence
of their relation to the respiratory apparatus. The mechanism by
which these variations are produced will be considered in the chapter
devoted to Respiration.

FORCES CONCERNED IN THE CIRCULATION OF THE BLOOD.

The Contraction of the Heart. — The primary forces which keep
the blood flowing from the beginning of the aorta to the right
side of the heart and from the beginning of the pulmonary artery
to the left side are the contractions of the left and right ventricles
respectively. This is evident from the fact that each ventricle
at each contraction not only overcomes the pressure in the aorta
and pulmonary artery, the sum of all resistances, but imparts a
given velocity to the blood. Since the pressure continuously
falls from the beginning to the end of each system, it follows that
the blood must flow from the point of high to the point of low
pressure. During the interval of the heart's activity the walls of
the arteries, to which the heart's energy was largely transferred,
now take up and continue the work of the heart, and by recoiling
drive the blood forward and into the venous system. Though
the heart's energy is probably sufficient to drive the blood into
the opposite side of the heart, it is supplemented by other
forces — e. ?. .•

326 TEXT-BOOK OF PHYSIOLOGY.

2. Muscle Contraction. — As a result of the relation which the veins

bear to the muscles in all parts of the body it is clear that with
each contraction and relaxation of the muscles there will be exerted
an intermittent pressure on the veins. With each contraction
the blood on the proximal side will at once be driven forward
with increased velocity, while that on the distal side will be re-
tarded, will accumulate and distend the veins, owing to the
closure of the valves ; with the relaxation of the muscle the elastic
and contractile tissues in the walls of the veins will come into
play and force the blood forward.

3. Thoracic Aspiration. — The inspiratory movement aids the flow

of blood through the venae cavas and their tributaries. With
each inspiration the pressure within the thorax but outside the
lungs undergoes a diminution more or less pronounced in ac-
cordance with the extent of the movement. As a result, the
blood in the large veins, now subjected to a pressure greater than
that in the thorax, flows more rapidly toward the heart. With
each expiration the reverse obtains.

4. Action of the Valves.- — It is quite probable that gravity opposes

to some extent the flow of blood through the veins below the level
of the heart. This opposition to the upward flow is largely pre-
vented by the valves, for each retardation is immediately checked
by their closure and support given to the column of blood.
The influence of gravity is shown when the relation of the arm to
the heart is changed. Thus, if the arm be allowed to hang pas-
sively by the side of the body, the veins, especially on the back of
the hand, will become distended with blood. If now the arm be
raised, the blood will flow rapidly toward the heart, as shown by
the rapid emptying of the veins.
Work Done by the Heart.— The work which the left ventricle

performs at each contraction when it discharges its contained volume

of blood into the aorta is:

1. To overcome the total resistance of the systemic vascular appa-

ratus expressed in terms of aortic pressure ; and —

2. To impart velocity to the blood.

The pressure in the aorta is not absolutely determined, though
for many reasons it may be assumed to be about 250 mm. Hg,
or its equivalent, a column of blood 3.21 meters in height. As the
heart discharges 188 grams, the work done may be calculated by
multiplying the weight by the height : viz., 0.188 X 3.2 = 0.6016 kilo-
grammeter.

The velocity of the blood in the aorta has been approximately
estimated at 0.5 meter per second. The work done in imparting this
velocity to 188 grams is estimated by squaring the velocity and dividing
by the accelerating force of gravity (^ ^^^J and multiplying the

THE CIRCULATION OF THE BLOOD. 327

quotient by 0.188. The quotient of the first two values represents
the distance a body would have to fall to acquire this velocity:
viz., 0.0127 meter. The work done is therefore 0.188 X 0.0127, or
0.0023 kilogrammctcr.

The entire work of the left ventricle is the sum of these two
amounts, or 0.604 kilogrammeter. Assuming that the heart beats 72
times per minute, the work done daily would be 0.604 X 72 +
60 X 24, or 62.622 kilogrammeters. The right ventricle approxi-
mately performs about one-third of this amount of work in over-
coming the resistance offered by the pulmonary system and in
imparting velocity to its contained volume of blood. The work of
the entire heart would therefore be for the twenty-four hours about
83.496 kilogrammeters.

THE NERVE MECHANISM OF THE VASCULAR APPARATUS.

The middle coat of the arteries, and especially of those in the
peripheral region of the arterial system, consists of a well-defined
layer of non-striated muscle-fibers arranged in a circular direction or
at right angles to the long axis of the vessel. In the physiologic con-
dition these fibers are in a state of continuous contraction, more or
less pronounced, and give to the arteries a certain average caliber
which permits a definite volume of blood to flow through them in a
given unit of time.

The cause of this tonic contraction is not definitely known. It
has been attributed to the action of local nerve-gangha, to the pres-
sure of blood from within, to the influence of organic substances in the
blood, the products of gland activity: e. g., adrenalin or epinephrin.

This tonic contraction of the vascular muscle is subject to increase
or decrease in accordance with the action of various agents. In-
creased contraction will result in a decrease of the caliber and a
reduction in the outflow of blood. Decrease of the contraction or
relaxation will result in an increase both of the caliber and outflow
of blood. The small arteries thus determine the volume of blood
passing to any given area or organ in accordance with its functional
activities.

The Vaso-motor Nerves. — The activities of the vascular muscle
are regulated by the central nerve system through the intermedia-
tion of nerve-fibers, termed vaso-motor nerves. Of these there are
two kinds, one which increases or augments the contraction, the
vaso-constrictors or vaso-augmentors ; another which decreases or
inhibits the contraction, the vaso-dilatators or vaso-inhihitors.

The vaso-motor nerves of both classes, unlike the ordinary motor
nerves, do not pass directly to the muscle-fiber, but indirectly by way
of the ganglia of the sympathetic nervous system. In these ganglia

328 TEXT-BOOK OF PHYSIOLOGY.

the vaso-motor nerves, which come from the central nervous system,
terminate, breaking up into tufts, which arborize around the nerve-
cells. From the cells new nerve-fibers arise which then pass without
interruption to their final destination.

The nerve-fibers which emerge from the central nerve system
are extremely fine in caliber and medullated; those which emerge
from the sympathetic ganglia are equally fine, but non-medullated.
The former are termed pre- ganglionic, the latter post- ganglionic
fibers. The ganglion in which the pre-ganglionic fibers end is not
necessarily found in the pre-vertebral or lateral chain; it may be
found in the collateral or even in the peripheral group.

The vaso-constrictor nerves take their origin from nerve-cells
located in the anterior horns and lateral gray matter of the spinal
cord. They emerge from the cord in company with the fibers which
compose the anterior roots of the spinal nerves from the second
thoracic to the second or third lumbar nerves inclusive. A short
distance from the cord they leave the anterior roots as the white rami
communicantes and enter the pre-vertebral or lateral sympathetic
ganglia. From the results of many observations and experiments
it is probable that the great majority of the vaso-constrictor nerves
terminate in these ganglia; that is to say, it is here that the pre-
ganglionic fibers arborize around the contained nerve- cells. From
the nerve-cells new fibers arise, the post-ganglionic, which pass to the
blood-vessels of the head, to the upper and lower extremities, and to
the thoracic and abdominal viscera. The vaso-constrictors for the
head emerge from the spinal cord in the first four thoracic nerves,
thence successively into and through the ganglion stellatum (the first
thoracic), the annulus of Vieussens, the inferior cervical ganglion,
the sympathetic cord to the superior cervical ganglion, around the
cells of which they arborize. From this ganglion the new fibers
follow the carotid artery and its branches to their terminations.

The vaso-constrictors for the fore-limbs emerge from the cord in
the roots of the fourth to the tenth thoracic nerves inclusive. Through
the white rami they pass into the sympathetic chain, after which they
take an upward direction and terminate around the cells of the gan-
ghon stellatum. From this ganglion the new fibers enter, by way of
the gray rami communicantes, the trunks of the cervical nerves which
unite to form the brachial plexus and by this route pass to the blood-
vessels.

The vaso-constrictors for the hind-limbs emerge from the cord
in the roots of the eleventh dorsal to the second or third lumbar nerves
inclusive. They then pass through the white rami to the lower
lumbar and upper sacral ganglia. Thence by way of the gray
rami they pass into the nerve-trunks which unite to form the sacral
nerves and by this route pass to the blood-vessels.

THE CIRCULATION OF THE BLOOD. 329

The vaso-constrictors for the viscera of the abdominal cavity pass
by way of the splanchnic nerves directly into the collateral ganglia,
the semilunar, the superior mesenteric, the inferior mesenteric, and
the sacral. From these ganglia an elaborate network of non-medul-
lated libers passes to the blood-vessels of the stomach, intestines, and
other viscera. The great splanchnic nerve is one of the most im-
portant vaso-constrictor trunks of the body, on account of the large
vascular area it controls.

The existence, course, distribution, and functions of the vaso-
constrictor nerves have been determined by a variety of methods,
physiologic and anatomic. Stimulation of the nerve-trunks under
appropriate conditions gives rise to a contraction, division to a dilata-
tion of the blood-vessels. The physiologic continuity of the pre-
ganglionic fibers with the nerve-cells of the sympathetic ganglia
has been shown by the intra-vascular injection or the local apphca-
tion of nicotin. This agent, as shown by Langley, has a selective
action on the arborizations of the pre-ganglionic fibers, and when
given in sufficient doses suspends their conductivity; hence stimu-
lation of the pre-ganglionic fibers is without efifect, though stimulation
of the post-ganglionic fibers is followed by the usual contraction.

The following will serve as illustrations of the functions of vaso-
constrictor nerves. Division of the great splanchnic is followed by
a marked dilatation of the blood-vessels of the intestinal tract; stimu-
lation of the peripheral end by their contraction. Division of the
cervical cord of the sympathetic is followed by dilatation of the blood-
vessels of the side of the head; stimulation of the peripheral end by
their contraction.

The vaso-dilatator nerves have their origin for the most part in
nerve-cells situated in the region of the spinal cord included between
the origins of the second dorsal to the second lumbar nerves inclusive,
though they are not confined to this region. Some vaso-dilatator
fibers have their origin in the medulla oblongata, others in the sacral
region of the spinal cord.

The general course of the dilatator fibers for the intestinal tract
is the same as that of the vaso-constrictors, though instead of becom-
ing related to the nerve-cells in the pre-vertebral ganglia, they pass
by way of the splanchnics to the collateral ganglia, the semilunar,
the superior and inferior mesenteric, and perhaps to peripheral
ganglia in or near the blood-vessels themselves.

The vaso-dilatators for the limbs are found in the common nerve-
trunks associated with the usual motor and sensory fibers, though the
exact route by which they pass from the spinal cord to the peripheral
nerves has not in all cases been determined. Their cell stations have
not been definitely located. The vaso-dilatator nerves for the blood-
vessels of the submaxillary gland arise in the medulla, pass outward

33© TEXT-BOOK OF PHYSIOLOGY.

in the trunk of the facial nerve, and reach the gland by way of the
chorda tympani branch. Their cell station is in the gangHon near
the hilum of the gland. The vaso-dilatator nerves for the blood-
vessels of the corpora cavernosa of the penis, the nervi erigentes,
have their origin in the sacral region of the spinal cord; and emerge
in the roots of the second and third sacral nerves. Their cell station
is in the ganglion near the organ.

The existence, course, distribution, and functions of the vaso-
dilatator fibers have been determined by the same methods employed
in the investigation of the vaso-constrictors. Thus division and
stimulation of the peripheral end of the chorda tympani nerve are
at once followed by an active dilatation of the blood-vessels of the
submaxillary gland. The inflow of blood is so great that the gland
becomes bright red in color. Its tissues being unable to appropriate
all the oxygen, the blood emerges in the veins almost arterial in char-
acter. Stimulation of the peripheral ends of the divided nervi
erigentes is followed by similar effects in the blood-vessels of the
corpora cavernosa. Slow stimulation, once per second, of the periph-
eral end of a divided sciatic nerve is followed by dilatation of the
blood-vessels of the leg.

From these and many other facts of a similar character it is highly
probable that the blood-vessels of each organ are under the control
of two antagonistic classes of nerve-fibers, one augmenting the
degree of their contraction, the vaso-constrictors, the other diminish-
ing it through inhibition, the vaso-inhibitors. Through the coopera-
tive antagonism of these two classes of nerves the caliber of the blood-
vessels is accurately adapted to the needs of each organ for blood,
both during rest and during activity. It is also to the alternate
activity of these nerves that the variations occurring from time to
time in the volume of organs are to be attributed.

The vaso-constrictors and the vaso-dilatators differ somewhat in
their physiologic properties, as shown by the results of experiment.
Thus, when a mixed nerve, i. e., one containing both classes of fibers,
— e. g., the sciatic, — is stimulated with frequently repeated induced
currents, the constrictor effect is the more pronounced, the dilatator
effect being wanting or prevented; when stimulated with slowly
repeated induced currents, the dilatator effect is the more pronounced.
These different effects are strikingly shown in Fig. 156, A and B.

In the experiment of which these tracings are the result the leg
of a cat was enclosed in a plethysmograph and the variations in volume
due to dilatation or contraction of the vessels, following stimulation
of the sciatic nerve, were recorded by means of a tambour and lever
on a slowly revolving cylinder. In A the fall of the curve indicates
a diminution of volume, from contraction of blood-vessels following
a rate of stimulation of the sciatic nerve of 16 per second for fifteen

THE CIRCULATION OF THE BLOOD.

33^

seconds. In B the rise of the curve indicates an increase in volume
from dilatation of the vessels following a rate of stimulation of i per
second for fifteen seconds (Bowditch and Warren). With different
rates of stimulation somewhat different results are obtained.

After division of a mixed nerve the vaso-constrictors degenerate
and lose their influence over the blood-vessel in from four to five
days, the vaso-dilatators in from seven to ten days, as shown by the
response to electrical stimulation.

When a nerve is cooled, the vaso-constrictors lose their irritabihty
before the vaso-dilatators.

Vaso-motor Centers. — The nerve-cells throughout the spinal
cord from which the vaso-motor nerves take their origin may be
regarded as nerve-centers which through their related nerve-fibers
exert from time to time either a constrictor or a dilatator influence

A B

Fig. 156.- — Plethysmograms of the Hind-leg of the Cat following Stimulation
OF THE Sciatic Nerve. In A the rate of stimulation was sixteen per second, in
B one per second for fifteen seconds.

over the blood-vessels. Though both the vaso-constrictor and vaso-
dilatator centers are in a state of continuous activity, the former
decidedly preponderates, as show'n by the maintenance of a tonic
contraction of the blood-vessels. The activity of both centers may
be increased or decreased, augmented or inhibited, by nerve impulses
reflected to them from the periphery through afferent nerves or
through nerve-fibers descending the cord from higher levels of the
nervous system. Experiment has shown that when a definite region
of the medulla oblongata is punctured or in anywise destroyed there
is an immediate dilatation of the blood-vessels throughout the body
and a fall of blood-pressure below one-half or one-third of the normal
value. This region has a width of one and a half millimeters and
extends longitudinally for a distance of four or five miUimeters,

332 TEXT-BOOK OF PHYSIOLOGY.

terminating at a point four millimeters above the tip of the calamus
scriptorius.

A transection of the medulla above the upper limit of this area is
without effect on the blood-pressure. A similar section below it,
however, is at once followed by vascular dilatation, a loss of vascular
tone, and a general fall of blood-pressure. Subsequent stimulation
of the peripheral end of the divided medulla, the animal being curar-
ized and artificial respiration maintained, will give rise to a marked
contraction of the blood-vessels and a rise of blood-pressure up to
and far beyond the normal value.

If the experimental lesion is limited to the area mentioned in the
foregoing paragraph, the vascular dilatation passes away after a
time, the blood-vessels regain their normal tone, and the pressure
again rises. These facts indicate that the area is to be regarded as
the general vaso-motor {constrictor) center which maintains the tonus
of the blood-vessels through its dominating influence over the vaso-
motor centers in the cord, the latter acting in a subsidiary manner to
the former. The nerve-fibers which transmit the regulative nerve
impulses from the general to the subsidiary centers are found in the
lateral columns of the cord. There is no evidence for the existence
of a general vaso-dilatator center in the medulla. Since the blood-
vessels maintain a more or less con^ant tone, it is assumed that the
vaso-motor centers are in a state of continuous activity. In how far,
however, this activity is the result of chemic changes between the
cells and the surrounding lymph and blood, or the result of con-
stantly arriving nerve impulses reflected from the periphery or from
higher regions of the nervous system, is not readily determinable.
Both factors are probably involved.

Direct Stimulation of the Vaso-motor Centers. — The general
vaso-motor (constrictor) center at least is markedly influenced by
the quantity and quality of blood and lymph circulating around and
through it. If the blood-supply to the medulla and associated
structures be diminished by compression of the carotid arteries, the
activity of the center is at once increased, as shown by increased vas-
cular contraction and a rise of pressure. Restoration of the blood-
supply is followed by a return of the center to its normal degree of
activity. Increased blood-supply, as in cerebral hyperemia, is at-
tended by a fall in blood-pressure indicating a decrease in the activity
of the center. A diminution in the percentage of oxygen or an in-
crease in the percentage of COj in the blood will increase the activity
of the center. In asphyxia especially the center is extremely excit-
able, as shown by rise of the arterial tension. The subsidiary centers
in the spinal cord are influenced by corresponding conditions.

Reflex Stimulation of the Vaso-motor Centers. — The results
of experiment make it certain that the degree of vascular contraction

THE CIRCULATION OF THE BLOOD. 333

maintained by the cooperative antagonism of the vaso-motor centers
can be increased or (decreased by nerve impulses reflected to the cord
and medulla from the periphery or from the brain. The effect may
be general, or local and confmed to the area from which the im-
pulses arise. The following experiments may be cited as illustrations :

Stimulation of the central end of a divided posterior root of a
spinal nerve gives rise to increased vascular contraction, as shown
by the rise of blood-pressure. The same holds true for any sensory
nerve. Stimulation of the central end of the divided sciatic will give
rise to opposite results, according to the strength of the stimulus,
weak stimuli producing dilatation, strong stimuli producing contrac-
tion of the vessels. Stimulation of the central end of the divided
vagus gives rise to dilatation of the vessels of the lips, cheeks, and nasal
and palatal mucous membranes. Stimulation of the auricular nerve
in the rabbit will, according to the strength of the currents, give rise
to either contraction or dilatation. Stimulation of the tongue is
followed by dilatation of the vessels of the submaxillary gland.

In explanation of these different results it has been assumed that
in the afferent nerves there are two classes of fibers, one which in-
creases, the other decreases the activity of the vaso-constrictor centers.
The first is termed pressor, the second depressor. Inasmuch as the
vascular dilatation is often greater than the dilatation which follows
division of the vaso-motor fibers themselves, it has been assumed
by some that the general vascular tonus, as well as its variations from
time to time, is the resultant of the simultaneous activity and varia-
tions in activity of both vaso-constrictor and vaso-dilatator centers ;
that in the afferent nerves there are fibers which when stimulated
augment, for example, the vaso-constrictor center and inhibit the
vaso-dilatator centers, or the reverse. The result, either contraction
or dilatation, which follows stimulation of their peripheral termina-
tions will depend on the character of the physiologic stimulus.

In a similar manner the vaso-motor centers are influenced by
emotional states, fear causing a contraction, shame a dilatation, of
the vessels of the face and neck. It is probable that these effects are
due to the transmission of nerve impulses from the cortex to the vaso-
motor centers in the medulla.

The Depressor Nerve. — In the rabbit there is a small nerve
formed by the union of a branch from the trunk of the vagus with a
branch from the superior laryngeal. The peripheral distribution of
this nerve is over the wall of the ventricle. The same nerve is found
in many other animals. In some, as the dog, it is bound up in the
vago-sympathetic. In man it is also present, though shortly after
its origin it enters the trunk of the vagus. Division of this nerve is
without effect either on the heart or the vessels. Stimulation of the
peripheral end has neither an accelerating nor an inhibiting action

334 TEXT-BOOK OF PHYSIOLOGY.

on the heart. Stimulation of the central end is followed by a fall in
blood-pressure, frequently to a level below one-half the normal value ;
at the same time there is a diminution, brought about reflexly, in the
rate of the heart-beat. The fall is pressure, however, is not due to
this cause, for it occurs equally well after division of all the cardiac
nerves. For this reason the nerve was termed the depressor nerve.
On exposure of the abdominal cavity, it is observed during
stimulation of the depressor that there is a notable dilatation of the
intestinal vessels. From this fact it was assumed that the action of
the depressor nerve was to lower the general pressure through reflex
dilatation of these vessels. It has been shown by Porter and Beyer
that if the splanchnics are divided and the peripheral end stimulated
. so as to maintain the tonus of the intestinal vessels, and hence the
general pressure, stimulation of the depressor nerve will nevertheless
be followed by a fall of the blood-pressure almost as great as when
the splanchnics are intact. From this it is evident that the depressor
nerve is related to centers which influence the vascular apparatus in its
entirety. The function of the depressor is not definitely known. It
has been supposed that through it the heart can protect itself from
injurious results of an excessive rise of arterial pressure.

CHAPTER XIII.
RESPIRATION.

Respiration is a process by which oxygen is introduced into, and
carbon dioxid removed from, the body. The assimilation of the
former and the evolution of the latter take place in the tissues as a
part of the general process of nutrition. Without a constant supply
of oxygen and an equally constant removal of the carbon dioxid,
those chemic changes v^hich underlie and condition all life phenom-
ena could not be maintained.

The general process of respiration may be considered under the
following headings, viz. :

1. The structure and general arrangement of the respiratory ap-

paratus.

2. The mechanic movements of the thorax by which an interchange

of atmospheric and intra-pulmonary air is accomplished.

3. The chemistry of respiration, the changes in composition ex-

perienced by the air, blood, and tissues.

4. The nerve mechanism by which the respiratory movements are

maintained.

THE RESPIRATORY APPARATUS.

The respiratory apparatus consists essentially of:

1. The lungs and the air-passages leading into them: viz., the nasal

chambers, mouth, pharynx, larynx, and trachea.

2. The thorax and its associated structures.

The nasal chambers are the natural entrances for the inspired
air. Their compHcated structure shghtly retards the movement of
the air, in consequence of which its temperature and moisture are
adjusted to the physiologic conditions of the lower respiratory pas-
sages. The mouth, though frequently serving as an entrance for air,
is not primarily a respiratory passage. Both the nasal chambers
and the mouth communicate posteriorly with the pharynx, in which
the respiratory and the deglutitory passages cross each other, the
former leading directly into the larynx.

The larynx is a comphcated mechanism serving the widely
different though related functions of respiration and phonation. It
consists of a framework of cartilages, articulating one with another,
united by ligaments and moved by muscles; it is covered externally
with fibrous tissue and lined with mucous membrane. The superior

335

336

TEXT-BOOK OF PHYSIOLOGY.

opening of the larynx, the glottis, is triangular in shape, the base
being directed upward and forward, the apex downward and back-
ward. The inchnation of the glottic opening is almost vertical.

The cavity of the larynx is partially subdivided by the inter-
position of the vocal bands into a superior and an inferior portion.

Fig. 157. — Trachea and Branchial Tubes, i, 2. Larynx. 3, 3. Trachea. 4.
Bifurcation of trachea. 5. Right bronchus. 6. Left bronchus. 7. Bronchial
division to upper lobe of right lung. 8. Division to middle lobe. 9. Division
to lower lobe. 10. Division to upper lobe of left lung. 11. Division to lower
lobe. 12, 12, 12, 12. Ultimate ramifications of bronchi. 13, 13, 13, 13.
Lungs, represented in contour. 14, 14. Summit of lungs. 15, 15. Base of
lungs. — (Sappey.)

The opening, bounded by the vocal bands, is also triangular in shape,
though in this case the base is directed backward, the apex forward.
(See chapter on Voice and Speech.)

The introduction of the vocal bands narrows at this level the air-
passage and to some extent interferes with the free entrance of air.

RESPIRATION.

337

According to the investigations of Semon, the area of the air-passage
above and below the phonatory apparatus is about 200 sq. mm.;
while the area bounded by the vocal apparatus is but 155 sq. mm.
during quiet respiration.

The trachea is a tube, some 12 centimeters in length, from one-
half to three-fourths of a centimeter in breadth, extending from the
lower border of the larynx to a point opposite the fifth dorsal verte-
bra. It consists of an external fibrous and an internal mucous
membrane, between which is a series of superposed C-shaped arches
or rings of elastic cartilage, some 18 or 20 in number. Between the
fibrous and mucous coats posteriorly, and occupying the space be-
tween and attached to the free ends of the cartilages, there is a layer
of transversely arranged non-striated muscle-fibers, known as the
tracheal muscle. The contraction of this muscle would approximate
the ends of the arches and so di-
minish the caliber of the tube. ^-^^s^r^ "''-^.
The surface of the mucous mem-
brane is covered by a layer of
stratified columnar cihated epi-
thehum (Fig. 158). In the sub-
mucous tissue there are a number
of glands the ducts of which open
on the free surface.

Opposite the fifth dorsal ver-
tebra the trachea divides into a
right and a left bronchus. Each
bronchus again subdivides into
two or three branches, which
penetrate the corresponding lung.
Within the substance of the lung
the bronchi divide and subdivide,

gi\'ing origin to a large number of smaller branches, the bronchial
tubes, which penetrate the lung in all directions. With this repeated
subdivision the tubes become narrower, their walls thinner, their
structure simpler. In passing from the larger to the smaller tubes
the cartilaginous arches become shorter and thinner, and finally
are represented by small angular and irregularly disposed plates. In
the smallest tubes the cartilage entirely disappears; coincidently
there appears a layer of non-striated muscle-fibers between the
mucous and submucous tissues, which completely surrounds the
tube and is especially well developed in those tubes devoid of carti-
laginous rings. The fibrous and mucous coats at the same time
diminish in thickness.

When the bronchial tube has been reduced to the diameter o^
about one millimeter, it is known as a bronchiole or a terminal bron-

FiG. 158. — Transverse Section of
THE Trachea of a Kitten. —
{Stirling.)

338

TEXT-BOOK OF PHYSIOLOGY.

chus.

From the sides of the terminal bronchus and from its final

termination there is

Bronchiole

given
short

Infundibulum

Air-cell .

Fig. 159. — Scheme of a Bronchiole Terminat-
ing IN Alveolar Passages, those Leading

INTO INFUNDIBULA BESET WITH AlR-CELLS. —

{Landois and Stirling.)

elaborate capillary network of blood-vessels,
as far as the alveolar passages is lined by
ciliated epithelium. The air-sacs are lined
by fiat epithehal plates of irregular shape,
termed the respiratory epithelium (Fig. 161).
The alveoli are united one to another by
fibro-elastic tissue.

The lungs in the physiologic condition
occupy the greater part of the cavity of the
thorax. They are separated from each
other by the contents of the mediastinal
space: viz., the heart, the large blood-vessels,
the esophagus, etc. Each lung is somewhat
pyramidal in shape with the apex directed
upward. The outer surface is convex and
corresponds to the general conformation of
the thorax. The inner surface is concave
and accommodates the contents of the medi-
astinal space. At about the middle of the
inner surface there enter the lung, the bron-
chi, and blood-vessels. The under surface
of the lung is concave and rests on the diaphragm.

off a series of
branches which
soon expand to form
lobules or alveoh (Fig.
159). The cavity of
the alveolus is termed
the infundibulum. From
the inner surface of the
alveolus and of the pas-
sageway leading into it,
there project thin parti-
tions which subdivide
the outer portion of the
general cavity or infundi-
bulum into small spaces
or sacs, the so-called
air- sacs (Fig. 160). The
wall of the alveolus is
extremely thin and con-
sists of fibro-elastic tis-
sue, supporting a very
The bronchial system

Fig. 160. — Single Lobule
OF Human Lung. a.
Alveolar passage, h.
Cavity of lobule or in-
fundibulum. c. Pul-
monary sacs. — {Dal-
ton.)

The posterior

RESPIRATION.

339

Fig. i6i. ^Section of Silvered Lung of Kitten,
INCLUDING Portions of Infundibulum and
Air-sac. a. Small polyhedral epithelial cells
covering the wall of the infundibulum. b. Fibro-
elastic framework, c. Large flattened epithelial
plates lining air-sac, among which lie small groups
of small cells {d). — -{Piersol.)

border is convex; the anterior border i.s thin. The lung thus consists

of bronchial tubes, pulmonary lobules or alveoh, blood-vessels,

lymphatics, and nerves

embedded in a stroma

of fibrous and elastic

tissue.

In consequence of
the presence of the
elastic tissue, the
lungs are distensible
and elastic. After re-
moval from the body
the elastic tissue at
once recoils, forcing
out a portion of the
contained air. The
condition of the lung
is now one of collapse.
Under pressure, how-
ever, the lung can be
readily distended or
inflated. These prop-
erties endure for a

long period after death, if not indefinitely, if the lungs are properly
preserved. The capacity of the lungs can be made to vary within

rather wide limits in virtue of the
presence of the elastic tissue.

The pulmonary blood-ves-
sels.— The pulmonary artery
which conducts the venous blood
from the heart to the lungs di-
vides beneath the arch of the
aorta into a right and a left
branch. Each branch with its
subdivisions enters the lung at
the hilum in company with the
larger divisions of the bronchi.
Within the lung the arteries di-
vide and subdivide in a manner
corresponding to that of the
bronchial tubes, which they fol-
low to their ultimate termina-
tions. As the pulmonar}- lobules
are approached, a small arterial branch plunges into the wall of
the lobule J (Fig. 162), in which it forms an elaborate capillary

Fig. 162. — The Relation of the Pul-
monary Artery, PA, and the Pul-
monary Vein, PV, to the Lobules,
A A. B. The Bronchiole.

340

TEXT-BOOK OF PHYSIOLOGY.

network which surrounds and embraces the air-sacs on all sides.
As this network is to subserve the respiratory exchange of gases
it hes nearer the inner than the outer surface of the lobule and
in close relation to the respiratory epithelium. The air and blood
are thus brought into intimate relationship, being separated only
by the respiratory epithelium and the waU of the capillary vessel.
The blood emerging from the capillary vessels is conducted by a
corresponding converging system of vessels, the pulmonary veins, out

Fig. 163. — BRO^■CHI and Lungs, Posterior View, i, i. Summit of lungs. 2, 2. Base
of lungs. 3. Trachea. 4. Right bronchus. 5. Division to upper lobe of lung.
6. Division to lower lobe. 7. Left bronchus. 8. Division to upper lobe. 9.
Di%'ision to lower lobe. 10. Left branch of pulmonar}' artery. 11. Right branch.
12. Left auricle of heart. 13. Left superior pulmonary vein. 14. Left inferior
pulmonary vein. 15. Right superior pulmonary vein. 16. Right inferior pul-
monary vein. 17. Inferior vena cava. 18. Left ventricle of heart, 10. Right
ventricle. — (Sappey.)

of the lungs and into the left auricle of the heart. The main func-
tion of the pulmonar}' apparatus and the pulmonary division of
the circulatory apparatus is to afford a ready means for the exhala-
tion of the carbon dioxid and the absorption of oxygen. In conse-
quence of this exchange of gases the blood changes in color from dark
bluish-red to scarlet red. The relations of the heart and its vessels
to the lungs and bronchial tubes are shown in Fig. 163.

The Thorax. — The thorax, in which the respiratory organs and

RESPIRATION.

541

their associated structures are lodged, is conic in shape, though some-
what compressed from before backward. Its apex is directed up-
ward, its base downward. The thoracic framework is formed
posteriorly by the thoracic vertebrae and the posterior extremities
of the ribs, laterally by the ribs, and anteriorly by the costal car-
tilages and the sternum. The superior opening, through which
pass the trachea, esophagus, and blood-vessels, is oval in outline
and measures from side to side about 12.5 cm., and from before
backward about 6.25 cm. The inferior opening is of large size, but
irregular in its boundaries from
the upward inchnation of the ribs
and the downward projection of
the sternum.

The ribs which form a large
part of the thoracic walls consti-
tute a series of bony arches at-
tached posteriorly to the vertebrae
and anteriorly to the sternum
through the intermediation of
their cartilages. The last two
form an exception. The ribs are
somewhat twisted upon them-
selves and pursue an oblique
direction from above downward
and forward. As a result the
anterior extremity lies at a lower
level than the posterior. The
costal cartilages are directed up-
ward and forward, with the ex-
ception of the upper three, which
are almost horizontal. The gen-
eral arrangement and appearance
of the thorax are shown in Fig.
164.

The costo-vertebral and costo-
sternal articulations are diar-

throdial in character and permit of an alternate elevation and depres-
sion of the ribs both anteriorly and posteriorly. The resultant of
all the movements permitted by these joints is an elevation of the
ribs and an advance of the sternum, and a consequent increase in the
transverse and antero-posterior diameters. Between and over the
ribs lie muscles, which are in turn covered by fascia and skin.

The diaphragm, which closes the inferior opening of the thorax
and completely separates its cavity from that of the abdomen, is a
musculo-membranous sheet. It consists of two muscles which arise

Fig. 164. — Thorax, Anterior View.
I. Manubrium sterni. 2. Gladio-
lus. 3. Ensiform cartilage of
xiphoid appendix. 4. Circumference
of apex of thorax. 5. Circum-
ference of base. 6. First rib. 7.
Second rib. 8, 8. Third, fourth,
fifth, sixth, and seventh ribs. 9.
Eighth, ninth, and tenth ribs. 10.
Eleventh and twelfth ribs. 11, 11.
Costal cartilages.

342

TEXT-BOOK OF PHYSIOLOGY.

from the bodies of the first three or four lumbar vertebrae and neigh-
boring fascia, from the border of the six lower ribs, and from the
ensiform cartilage (Fig. 165). From this extensive origin the muscle-
fibers pass centrally to be inserted into a common tendon. As the
direction of the fibers is from below upward and inward, the dia-
phragm is somewhat dome-shaped. Its inferior border is for a short

distance in con-
tact with the
sides of the
thorax. As a
result of the
complete closure
of both the su-
perior and infe-
rior openings of
the thorax, its
ca^dty is abso-
lutely air-tight.

The pleurae.
— Each lung is
surrounded by a
closed invagin-
ated serous sac,
the pleura, of
which the inner
portion is re-
flected over and
is closely adher-
ent to the sur-
face of the entire
lung as far as its
root ; the outer
portion is re-
flected over the inner wall of the thorax, the superior surface of the
diaphragm, and the viscera of the mediastinum. Under normal
conditions these two layers of the pleura, the visceral and parietal,
are in contact, or at most separated only by a thin capillary layer of
lymph. The presence of this fluid prevents friction as the two
surfaces play against each other in consequence of the movements
of the lungs.

Fig.

165. — Diaphragm, Inferior Aspect, i. Anterior and
middle leaflet of central tendon. 2. Right leaflet. 3.
Left leaflet. 4. Right cms. 5. Left cms. 6, 6. In-
tervals for phrenic nerves. 7. Muscular fibers, from
which the ligamenta arcuata originate. 8. Muscular fi-
bers that arise from the inner surface of the six lovs^er ribs.
9. Fibers that arise from ensiform cartilage. 10. Open-
ing for inferior vena cava. 11. Opening for esophagus.
12. Aortic opening. 13, 13. Upper portion of trans-
versalis abdominis, turned upvi^ard and outward. 14.
Anterior leaflet of transversahs aponeurosis. 15, 15.
Quadratus lumbomm. 16, 16. Psoas magnus. 17.
Third lumbar vertebra.

THE MECHANIC MOVEMENTS OF THE THORAX.

The blood receives oxygen from, and yields carbon dioxid to, the
alveoh of the lungs, as it flows through the pulmonary capillaries.

RESPIRATION. 343

That this exchange of gases may continue, it is of primary impor-
tance that the air within the alveoli be removed as rapidly as it is
vitiated. This is accomplished by an alternate increase and decrease
in the capacity of the thorax, accompanied by corresponding changes
in the capacity of the lungs. During the former there is an inflow
of atmospheric air (inspiration), during the latter an outflow of intra-
pulmonary air (expiration). The continuous recurrence of these
two movements brings about that degree of pulmonary ventilation
necessary to the normal exchange of gases between the blood and the
air. The two movements together constitute a respiratory act or
cycle.

In the course of the respiratory cycles the thorax presents alter-
nately a short period of rest — viz., between the end of an expiration
and the beginning of an inspiration — and a relatively long period
of activity, including both inspiration and expiration. The former
may be regarded as the static, the latter as the dynamic condition of
the thorax. In the static condition the thorax and its contained and
associated organs sustain a definite relation one to another; in the
dynamic conditions these relations undergo a change the extent
of which is proportional to the extent of the movements.*

Static Relations. — Intra-pulmonary Pressure. — In the static
condition of the thorax the lungs, by virtue of their distensibility,
completely fill all parts of the thoracic cavity not occupied by the
heart and great blood-vessels. This condition is maintained by the
pressure of the air within the lungs, the intra- pulmonary pressure, which
with the respiratory passages open, is that of the atmosphere, 760
mm. Hg. This relation persists so long as the thoracic cavity remains
air-tight. If the skin and muscles covering an intercostal space be re-
moved the lung can be seen in close contact with the parietal layer of
the pleura gliding by with each inspiration and expiration. If, how-
ever, an opening be now made in the pleura sufficient to admit air, the
lung immediately collapses and a pleural cavity is established (pneu-
mothorax). The pressure of air within and without the lung counter-
balancing, at the moment the opening is made, the elastic tissue at
once recoils and forces a large part of the air out of the lung. This
is a proof that in the normal condition, the lungs, distended by at-
mospheric pressure from wdthin, are in a state of elastic tension and
ever endeavoring to pull the visceral layer of the pleura away from

* It is a matter of dispute as to whether or not there is an absolute cessation of
movement of the thoracic walls at the end of expiration. A graphic record of the
movement shows that if there is no absolute cessation, the movement is so slight that,
for the purposes here intended, a pause may be admitted. With this admission it
is, however, recognized that the forces, both elastic and muscular, which are always
acting on the thoracic walls, though in opposite directions, have not ceased to act,
but have become so nearly equal that for a brief period they are practically in a con-
dition of equilibrium, during which the thoracic walls are stationary.

344 TEXT-BOOK OF PHYSIOLOGY.

the parietal layer. That they do not succeed in doing so is due to the
fact that the atmospheric pressure from without is prevented from
acting on the lung by the firm unyielding walls of the thorax.

Intra-thoracic Pressure. — As a result of the elastic tension of
the lungs a fractional part of the intra-pulmonary pressure, 760 mm.
Hg, is counterbalanced or opposed, so that the heart and great vessels
and other intra-thoracic viscera are subjected to a pressure somewhat
less than that of the atmosphere; the amount of this pressure will be
that of the atmosphere less that exerted by the elastic tissue of the
lung in the opposite direction, expressed in terms of milhmeters of
mercury. In the thorax, but outside the lungs, there then prevails
a pressure, intra-thoracic pressure, negative to the pressure inside the
lungs. The amount of this intra-thoracic pressure can be approxi-
mately determined in several ways. Thus, if shortly after death a
mercurial manometer be inserted air-tight into the trachea of a human
being and the thorax opened, the lungs will recoil and compress their
contained air. The mercurial manometer will at once show an
excess of pressure in the trachea of about 6 mm. This was taken
by Bonders as a measure of the force w^ith which the lungs endeavor
to recoil. The intra-thoracic pressure would be, therefore, atmos-
pheric pressure, 760 mm,, less 6 mm., or 754 mm. Hg. Another
method is to insert a rubber catheter through a small opening in an
intercostal space into the thoracic cavity. The air which enters
through the open extremities of the catheter and leads to a collapse
of the lungs may be subsequently aspirated, when the lung returns to
its normal position. The catheter is then placed in connection with
a water manometer. On estabhshing a communication between
them, by the turning of a stopcock, the water will rise in the proximal
and fall in the distal Hmb of the manometer, indicating a pressure
in the thorax negative to that in the lung. The difference in the
level of the water in the two limbs of the manometer, expressed
in milhmeters of mercury, would also represent the force with which
the elastic tissue strives to recoil, the extent to which it opposes
the atmospheric pressure. This subtracted from the atmospheric
pressure would give the intra-thoracic pressure. In the hving dog
this latter is less than the former, to the extent of from 3-5 to 5.5 mm.
For the same reason the superior surface of the diaphragm also ex-
periences a pressure less than that of the atmosphere. Omng to the
soft and yielding character of the abdominal w^alls the atmospheric
pressure is transmitted through the abdominal organs to the inferior
surface of the diaphragm. The pressure being greater from below
than above, the diaphragm is forced upward until it assumes the dome-
like appearance it usually presents. (These relations are shown in
Fig. 166.)

The cause of the negativity of the intra-thoracic pressure is con-

RESPIRATION.

345

nected with the change in the relation of the lungs to the thorax
attending the first inspiration. Previous to birth the walls of the
alveoh and bronchioles are collapsed and in apposition. The larger
bronchial tubes in all probability contain fluid. The lungs therefore
are devoid of air (atelectatic), and, having a specific gravity greater
than water, readily sink when placed in this fluid. The capacity
of the thorax does not exceed the volume of the lungs. With the first
inspiration, however, the thoracic walls take a new position. The
air at once rushes into the lungs and distends them. But as the
capacity of the thorax even at the end of the expiration is now greater

Fig. 1 66. — Section of Thorax with the Lungs, Heart, and Principal Vessels.
5. Catheter introduced into the pleural space and connected with a manometer. — •
{After Morat and Doyen.)

than the volume which the lungs could assume without consider-
able distention, there at once arises the elastic recoil in the opposite
direction, the condition which gives rise to the negativity of the
pressure in the thoracic cavity. It is also probable that as the child
develops, the thorax grows more rapidly than the lungs, giving
rise to a condition which would increase and accentuate the elastic
tension and thus increase the negativity of the intra-thoracic pressure.
Dynamic Relations. — In the dynamic conditions as previously
stated these relations change. The intra- pulmonary pressure varies
during both inspiration and expiration. With the enlargement

346

TEXT-BOOK OF PHYSIOLOGY.

Insp

Intra-pulmonary pressure.

Exp.

of the thorax through muscle activity, there goes a corresponding in-
crease in the size and capacity of the lungs in consequence of the
expansion and pressure of the air in the pulmonary alveoh. With
the expansion of the air its pressure falls; but though it is now less
than atmospheric, it is yet much greater than the opposing force
of the lung tissue. As a result of the fall of intra-pulmonary pres-
sure there is a rapid inflow of air, which continues until atmos-
pheric pressure is restored ; that is, at the end of the inspiration.
With the diminution of the thorax, through the recoil of the elastic
tissue of the thoracic and abdominal walls, there goes a correspond-
ing decrease of lung capacity, in consequence of the recoil of
the elastic tissue of the lungs. As a result, the air in the lungs
becomes compressed, its pressure rises above that of the atmosphere,
and a rapid outflow of air takes place, which continues until atmos-
pheric pressure is
again restored ; that
is, at the end of the
expiration.

The cause for the
fall of intra-pulmon-
ary pressure during
inspiration and the
rise during expiration
is to be found in the
resistance offered by
the air-passages to
the movement of the
air, throughout their
entire extent, and es-
pecially at the level of
the vocal bands. The greater the resistance, from whatever cause,
physiologic or pathologic, the greater the variations of the pressure.

In quiet inspiration the fall of pressure, as indicated by a man-
ometer inserted into one nostril, seldom amounts to more than 1.5 mm. ;
the rise in expiration, 2.5 to 3 mm. In forcible inspiratory and ex-
piratory efforts these limits may be largely exceeded. Thus it was
found by Bonders that with one nostril closed and a mercurial man-
ometer inserted into the other the pressure by voluntary efforts could
be made to fall 57 mm. during inspiration and to rise 87 mm. during
expiration. The changes in intra-pulmonary pressure are graphically
represented in the upper half of Fig. 167.

The intra-thoracic pressure also varies during both inspiration
and expiration. As the intra-pulmonary pressure falls, the recoil of
the elastic tissue increases, with the result of diminishing the intra-
thoracic pressure, though not in a steadily progressive manner. The

760 mm

C 760 mm

Intra-thoracic pressure.

Fig. 167. — Representing the Changes, i, in the
Intra-pulmonary, and, 2, in the Intra-tho-
racic Pressures during Inspiration and Ex-
piration

RESPIRATION. 347

fall of intra- thoracic pressure at the end of a quiet inspiration amounts
to about 9 mm. Hg. In forcible inspiratory cffortSi this fall in intra-
thoracic pressure may amount to 30 or 40 mm. of Hg. As the intra-
pulmonary pressure rises above the atmospheric pressure during
expiration, the recoil of the elastic tissue is again opposed, with the
result of increasing the intra-thoracic pressure, though not in a
steadily progressive manner. The changes in intra-thoracic pressure
are graphically represented in the lower half of Fig. 167.

Respiratory Movements. — The ventilation of the lungs is
accomphshed by an alternate expansion and contraction of the
thorax, accompanied by corresponding changes in the lungs, the two
movements being known as inspiration and expiration. In both
movements the lungs play an entirely passive part, their movements
being determined by the thoracic walls, with which they are in close
contact.

1. Inspiration is an active process, the result of muscle activity,

in consequence of which atmospheric air flows into the lungs.

2. Expiration is a passive process, the result mainly of the recoil of

the elastic tissue of the walls of the thorax and abdomen and of
the elastic tissue of the lungs, in consequence of which the intra-
pulmonary air flows out of the lungs.
In inspiration the thorax is enlarged in all its diameters: viz., verti-
cal, antero-posterior, and transverse. In expiration these diameters
are again decreased as the thorax returns to its previous condition.

Inspiratory Muscles. — The muscles which from their origin,
direction, and insertion contribute to the enlargement or expansion of
the thorax are quite numerous, though the extent to which they are
caUed into activity depends on the necessity for either tranquil or
energetic inspirations. The gradations between a minimum and a
maximum inspiration are very slight, and it is difficult to state at
what particular instant any given muscle begins to act. It is custom-
ary, however, to divide the muscles into two groups: (i) Those active
in the average or ordinary inspirations, and (2) those active in maxi-
mum or extraordinary inspirations. Among the muscles active in
average inspirations may be mentioned the diaphragm, the scaleni,
the levatores costarum, the serratus posticus superior, the intercostales
externi, and the intercartilaginei. Among the muscles active in
forced inspirations may be mentioned, in addition to the foregoing,
the sferno-cleido-mastoidei, the trapezei, and the pectorales minores
and majores.

The Diaphragm. — The vertical diameter is increased by the
contraction and descent of the diaphragm, and more especially of its
lateral muscular portions. At the end of an expiration the diaphragm
is relaxed, and the lower portion closely appHed to the walls of the
thorax. At the beginning of an inspiration the muscle-fibers contract,

348

TEXT-BOOK OF PHYSIOLOGY.

shorten, and approximate a straight Hne, whereby not only is the
convexity of the diaphragm diminished, but that portion in contact
with the thorax is drawn away, thus making a large free space into
which the lateral and posterior portions of the lungs at once descend.
The attachment of the central tendon of the diaphragm to the peri-
cardium prevents any marked descent of this portion except in forci-
ble inspiratory efforts (Fig. i68). The vertical diameters are thus
enlarged, though unequally in different regions of the thorax.

As the diaphragm descends it displaces the abdominal viscera,
forcing them downward and outward against the abdominal walls,
which advance and become more convex. In forcible inspiration
the diaphragm, acting from the central tendon as the more fixed

point, would draw the lower portion of the
thorax inward were this not prevented by
the outward pressure of the displaced
viscera.

The antero- posterior and transverse di-
ameters are increased by the elevation and
outward rotation of the ribs and an advance
of the sternum, both movements made pos-
sible by the construction and arrangement
of the costo-vertebral and costo-chondral
and chondro - sternal articulations. The
former articulations are two in number, the
first being formed by the beveled head of
the rib and the bodies of the vertebrae, the
second by the tubercle of the rib and the
transverse process. The construction of
these articulations is such as to permit at
the first a slight elevation and depression,
and at the second a ghding of the tuber-
cle on the transverse process. The axis
around which the rib rotates practically coincides with the axis of
the rib neck, which in the upper part of the thorax is almost hori-
zontal, in the lower part somewhat sagittal in direction. Hence
when the ribs are elevated the upper part of the thorax increases in its
antero-posterior, the lower part in its transverse diameters. At the
same time, the lower portion of the sternum is pushed forward and
upward by the elevation of the costo-chondral articulation and the
widening of its angle. With the elevation of the ribs there goes an
eversion or outward rotation which gives an additional increase to
the transverse diameters. This elevation and outward rotation of
the ribs is the resultant of the cooperation of the muscles previously
mentioned with the exception of the diaphragm.

The scaleni muscles, anticus, medius, and posticus, arise from the

Fig. i68. — Diagram show-
ing Interval be-
tween THE Position
. OF THE Diaphragm
IN Expiration {e, e)
and Inspiration {i, i) .
The Increase in
Capacity is shown
BY THE White
Areas. — {Yeo.)

RESPIRATION.

349

transverse processes of the cervical vertebnc, and after pursuing a
downward and forward direction are inserted into the sternal end of
the first and second ribs. The action of the first two, at least, is to
elevate the first rib and thus establish a fixed point from which the
intercostal muscles can act. The posticus has doubtless a similar
action on the second rib.

The levatores costarum are twelve in number on cither side. They
arise from the tips of the transverse processes of the last cervical and
the thoracic vertebrae with the exception of the last. From the point
of origin the fibers pass downward and outward in a diverging manner
to be inserted into the ribs between the tubercle and the angle. Their
action, as their name imphes, is to elevate the posterior portion of
the ribs (Fig. 169).

The serralus posticus superior,
a quadrilateral sheet of muscle-
fibers, arises mainly from the spines
of the last cervical and first and
second thoracic vertebrae. The an-
terior extremity is serrated and
attached to the outer surfaces of
the second, third, fourth, and fifth
ribs beyond the angle. The action
of the muscle is the elevation of the
ribs to which it is attached.

The intercostales externi, eleven
'in number on each side, occupy the
spaces between the ribs to which
they are attached from the tubercle
to the anterior extremity (Fig. 169).
Their fibers, which are arranged in
parallel bundles, are directed from
above downward and from behind
forward. The point of attachment,

therefore, of any given bundle of fibers to the rib above hes nearer
the vertebral column, nearer the fulcrum, than the point of attach-
ment below.

The action of the external intercostal muscles has been a subject
of much discussion. Some investigators have maintained that they
are elevators of the ribs, and therefore inspiratory; others that they are
depressors of the ribs, and therefore expiratory in function. At the
present time the general consensus of opinion is that the former view
is the one most in accordance with the facts. The situation of the
muscles and the shortness of their fibers render it extremely diffi-
cult to obtain myographic tracings of their action. This is supposed,
however, to be disclosed by the play of the apparatus suggested

Fig. 169. — View from behind of
Four Dorsal Vertebra and
Three Attached Ribs, show-
ing the Attachment of the
Elevator Muscles of the Ribs
and the Intercostals. I.
Long and short elevators. 2.
External intercostal. 3. Internal
intercostal. — {Allen Thomson.)

35°

TEXT-BOOK OF PHYSIOLOGY.

originally by Bernouilli, which consists, as shown in Fig. 171, of a
vertical support carrying two freely movable parallel bars united at
their outer extremities by a short vertical strip, representing respec-
tively the vertebral column, two adjoining ribs, and a piece of the

sternum. The paral-

?3*^'a^

lei bars are joined to
each other by a short
elastic band having
the direction of and
representing the ex-
ternal intercostal mus-
cles. If the bars are
depressed, the elastic
band is elongated and
made tense. On re-
leasing the bars the
band at once recoils
and elevates them.
Although the elastic
force is the same in
both directions, the
bars are yet elevated
for the reason that
in accordance with
the parallelogram of
forces the component'
acting upward on the
long arm of the lever
preponderates over
the component acting
downward on the
short arm of the
lever. The action of
the band is supposed
to disclose and illus-
trate the action of the
Fig. 170. — Showing the Situation, the Points of muscle.

The intercartilagi-
nei, those portions of
the intercostales in-
terni which occupy
the space between the costal cartilages from the sternum to their outer
extremity, bear the same relation to the cartilages in reference to the
sternum that the external intercostals bear to the ribs in reference to
the vertebral column; that is, the point of attachment to the cartilage

170. — Showing the Situation, the Points of
Attachment, and Direction of the Inter-
costal Muscles, i. The intercostales externi.
2. The intercostales interni. 3. The intercarti-
laginei. — (Deaver.)

RESPIRATION.

351

above, lies nearer the sternum, nearer the fulcrum, than the point of
attachment below. Hence the same action is attributed to them as
to the external intercostals : viz., that they elevate the cartilages and
the anterior extremities of the ribs.

Expiratory Forces and Muscles. — Expiration, as previously
stated, is a passive process brought about by the recoil ofj the elastic
tissues of the thoracic and abdominal walls, and of the lungs, all of
which are stretched and made tense during inspiration. With the
cessation of the inspiratory effort the elastic forces, assisted by the
weight of the ribs, sternum, and soft tissues, return the thorax to its
former condition. It is somewhat uncertain if a normal expiratory
movement necessitates active muscle contraction. But after the
elastic forces have ceased to act and the normal expiratory movement
has been brought to a close, the thorax can be, to a considerable

Fig. 171. — Diagram illustrating the Action of A, the External Intercostal,
AND B, THE Internal Intercostal Muscles. V, V. Vertical support. R, R'.
Parallel bars. S. Vertical strip representing respectively the vertebral column,
two ribs, and sternum.

extent, still further diminished in all its diameters by the contraction,
through volitional effort, of abdominal and thoracic muscles. To
this decrease in the capacity of the thorax, as a result of which a much
larger volume of air is expelled from the lungs than during passive
expiration, the term forced expiration has been given. With the
cessation of muscle activity the elastic forces of the now-compressed
thoracic walls, aided by the return of upward displaced abdominal
organs, at once restore the thoracic walls to the position they had
attained at the end of passive expiration. The muscles active in
forced expiration are the abdominales, the inter -co stales interni, the
triangularis sterni, the serratus posticus inferior, and the quadratus
lumhorum.

The externus abdominis arises by a series of muscle slips from the
outer surface of the lower eight ribs. After pursuing an oblique

352 TEXT-BOOK OF PHYSIOLOGY.

direction downward and forward, the slips blend to form a single
muscle, which is inserted mainly into the outer lip of the anterior
half of the crest of the ilium and into the central abdominal tendon
or aponeurosis.

The internus abdominis arises mainly from the anterior two-thirds
of the inner crest of the ilium and the lumbar fascia. Its fibers pass
upward and forward to be inserted into the cartilages of the last three
ribs and into the central abdominal tendon.

The rectus abdominis arises from the crest of the pubes and is
inserted above into the cartilages of the fifth, sixth, and seventh ribs,
and occasionally into the ensiform cartilage.

The transversalis arises from the cartilages of the last six ribs,
the lumbar fascia, and the anterior half of the crest of the ilium.
After passing transversely across the abdomen, the fibers are inserted
mainly into the linea alba.

The conjoint action of these muscles is to diminish the convexity
of the abdominal walls and to exert a pressure on the abdominal
organs. These, taking the line of least resistance, are forced upward
against the inferior surface of the diaphragm, which in consequence
becomes more strongly curved and ascends higher into the thorax.
The vertical diameter of the thorax is thus diminished. Acting from
the pelvis as a fixed point, these muscles will also draw downward
and inward the lower end of the sternum and the lower ribs and
diminish the antero-posterior and transverse diameters.

The triangularis sterni arises from the side of the posterior surface
of the lower third of the sternum and is inserted by fleshy slips into
the cartilages from the second to the sixth ribs. From their anatomic
relations it is asserted that these muscles assist in the depression of
the anterior extremities of the ribs during forced expiration.

The intercostales interni, eleven in number, occupy the spaces
between and are attached to the ribs from the tubercle to the anterior
extremity of the cartilages. Their fibers, which are also arranged
in parallel bundles, are directed from above downward and back-
ward (Fig. 170).

The action of the internal intercostals is less clearly understood
than that of the externals, and for the same reasons. If, however,
Bernouilli's model discloses the action of the latter, it equally well
discloses the action of the former. Thus, if the parallel bars be joined
by an elastic band having the direction of and representing the inter-
nal intercostals, and then forcibly elevated, the band is elongated and
made tense. On releasing the bars, the elastic band at once recoils
and depresses them. Here, again, though the elastic force is the same
in both directions, the bars are depressed, for the reason that the
component acting downward on the long arm of the lever pre-
ponderates over that acting upward on the short arm of the lever.

RESPIRATION.

353

The action of tlic band is supposed to disclose and illustrate the
action of the muscle.

The serratns posticus injerior arises from the spines of the last
two thoracic and first two lumbar vertebne. The fibers pass upward
to be inserted into the lower border of the last four or five ribs beyond
the angle. Their action is to depress the ribs and assist in expira-
tion.

The quadralus Jumhorum has a similar action on the last rib.

Movements of the Lungs. — As the thorax is enlarging in all its
diameters during inspiration, through muscle activity, the lungs are
correspondingly enlarging in all their diameters, by virtue of their
distensibility, through the pressure of the air within them. The
lungs must therefore move downward, outward, and forward. That
this is the case is made evident both by an examination of the lungs
through an intercostal space after removal of the skin and intercostal
muscles and by the methods of percussion. The inferior border of
each lung descends from the lower border of the sixth to the eleventh
rib, inserting itself into the space developed between the thorax and
diaphragm as the latter contracts and is drawn away from the former.
In consequence of the lateral expansion the anterior border of each
lung advances toward the middle fine until the heart is almost cov-
ered. With the beginning and continuance of expiration the lungs
exhibit a reverse movement which continues until they reach their
original position. At all times, however, the movements of the lungs
are entirely passive and determined by the movements of the thorax.

Respiratory Movements of the Upper Air-passages. — The
resistance to the entrance of air into and through the respiratory
tract is much diminished by respiratory movements of the nares and
larynx which are associated and occur synchronously with the move-
ment of the thorax.

The nares at each inspiration are dilated by the outward move-
ment of their ala? or wings, the result of muscle activity. At each
expiration they are diminished by the return of their cartilages through
the play of elastic forces. The larynx, as shown by observation
with the laryngoscope, exhibits corresponding movements of the vocal
membranes. Their introduction at this level naturally narrows the
tract, and would interfere with both the entrance and the exit of air
were they not kept widely asunder during the time they are not re-
c^uired for purposes of phonation. This is accompHshed by the
tonic contraction of the posterior crico-arytenoid muscles, which are
entirely respiratory in function.

It is not infrequently stated that these membranes exhibit consider-
able oscillations, outward and inward, corresponding to the periods
of inspiration and expiration. The statements of the majority of
laryngologists do not favor this view. During tranquil breathing

354 TEXT-BOOK OF PHYSIOLOGY.

the membranes are widely separated and almost stationary, seldom
moving in either direction more than a few millimeters. In labored
respirations these movements are naturally increased in extent. The
reflex movements of the membranes occasioned by the unskilful use
of the laryngoscope, especially with nervous patients, are not to be re-
garded as strictly physiologic. The respiratory space in quiet breath-
ing is an isoceles triangle, with a length of 20 mm. and a width at the
base of 15.5 mm.

Respiratory Types. — Observation of the respiratory movements
in the two sexes shows that while the enlargement of the thoracic
cavity is accompHshed both by the descent of the diaphragm (as
shown by the protrusion of the abdomen) and the elevation of the
thoracic walls, the former movement preponderates in the male, the
latter in the female, giving rise to what has been termed in the one
case the diaphragmatic or abdominal and in the other the thoracic or
costal type of respiration. The cause of this greater mobility and
activity of the thorax in the female has been a subject of much discus-
sion. It has been attributed, on the one hand, to the necessity for a
physiologic adjustment between respiration and child-bearing, and
therefore a specific sex peculiarity; on the other hand, it has been
attributed to persistent constriction of the waist, in consequence of
which the full play of the diaphragm is prevented and the burden of
inspiration is thrown on the thoracic muscles. It has been assumed
that if inspiration were confined in women to the diaphragm, there
would arise in the latter stages of gestation such an increase in intra-
abdominal pressure that not only would respiratory exchanges be
interfered with, but fetal life might be unfavorably influenced, if not
endangered. Modern investigations have not confirmed this assump-
tion, but, on the contrary, have corroborated the view that the pre-
ponderance of thoracic movement is due to the influences of dress
restrictions, for with their removal the so-called costal type of breath-
ing entirely disappears. While gestation may lead to a greater
activity of the thorax, this is but temporary, for with its termination
there is a return to the diaphragmatic type of breathing.

Number of Respirations per Minute. — The number of respira-
tions which occur in a unit of time varies with a variety of conditions,
the most important of which is age. The results of the observa-
tions of Quetelet on this point, which are generally accepted, are as
follows :

Age. Respirations per Minute. Age. Respirations per Minute.

o- I year, 44 20-25 years, 18.7

5 years, 26 25-30 " 16.0

15-20 " 20 30-50 " 18.0

From these observations it may be assumed that the average number
of respirations in the adult is eighteen per minute, though varying

RESPIRATION.

355

from momenl to moment from sixteen to twenty. During sleep,
however, the respiratory movements often diminish in number as
much as 30 per cent., at the same time diminishing in depth.

Rhythm. — Each respiratory act takes place normally in a regular
methodic manner, each event occurring in a definite sequence and
occupying the same
relative period of
time. This rhythm,
however, is not infre-
quently temporarily
disturbed by emo-
tions, voHtional acts,
muscle activity, pho-
nation changes in the Fig. 172. — Pneumograph. — {Fitz.)

composition of the

blood, etc. ; with the removal of these disturbing factors, the respiratory
mechanism soon returns to its normal condition.

A graphic representation of the excursions of the thoracic walls,
rhythmic or otherwise, is obtained by fastening to the thorax an
apparatus, a stethometer or a pneumograph, which by means of a tam-
bour takes up and transmits the movement to a second tambour
provided with a recording lever. A simple form of pneumograph,
suggested by Fitz (Fig. 172), consists of a coil of wire two and a
half centimeters in diameter and about 40 centimeters in length,
enclosed by thin rubber tubing, one end of which is closed, the
other placed in communication with either a tambour and lever
or with a piston recorder. By means of an inelastic cord or chain
the apparatus is securely fastened to the chest. With each inspira-
tion the spring is elongated, the air within the system is rarefied,

and as a result the lever falls;
with each expiration the reverse
conditions obtain and the lever
rises. If the lever be applied to
the recording surface of a moving
cylinder, a curve of the thoracic
movement, a pneuniaiogram, is
obtained (Fig. 173), from which it
is apparent that inspiration takes
place more abruptly and occupies
a shorter period of time than expiration; that expiration immediately
follows inspiration, but that there is a slight pause between the end
of the expiration and the beginning of the inspiration. The time
relations of the two movements can be obtained by a magnet-signal
actuated by an electric current interrupted once a second. The ratio
of inspiration to expiration has been represented as 5 to 6, or 6 to 8.

INSP.

Fig.

I73--

-A Pneumatogram. — {After

Marey.)

35^

TEXT-BOOK OF PHYSIOLOGY.

Volumes of Air Breathed. — The volumes of air which enter
and leave the lungs with each inspiration and expiration naturally
vary with the extent of the movement, though four at least may be
determined: (i) that of an ordinary inspiration; (2) that of an ordi-
nary expiration; (3) that of a forced inspiration; (4) that of a forced
expiration.

The apparatus employed for the determination of these different
volumes is the spirometer, a modification of the gasometer. The

form introduced by Jonathan Hutchinson
(Fig. 1 74) consists of two metallic cyhn-
ders, one (a) containing water, the other
(b) containing air, the latter being inserted
into the former. The air cylinder is bal-
anced by weights so accurately that it re-
mains stationary in any position. A tube,
penetrating the base of the water cylinder,
is continued upward through and above
the level of the water. The air-space
above is thus placed in free communica-
tion with the external air. A stopcock at
the outer end of this tube prevents the
escape of the air when this is not desirable.
To the free end of the tube a rubber tube
provided with a suitable mouthpiece is at-
tached, through which air can be breathed
into or out of the air-cylinder. With each
inspiration the air-cylinder descends; with
each expiration it ascends. A scale, on
one of the side supports, graduated in
cubic inches or centimeters, indicates the
volume of air inspired or expired.

With this apparatus Hutchinson, from
a long series of observations, defined and determined the above-
mentioned four volumes as follows :

1. The tidal volume, that which flows into and out of the lungs with

each inspiration and expiration, which varies from 20 to 30
cubic inches (312 to 468 c.c).

2. The complemental volume, that which flows into the lungs, in addi-

tion to the tidal volume, as a result of a forcible inspiration, and
which amounts to about no cubic inches (1748 c.c).

3. The reserve volume, that which flows out of the lungs, in addition

to the tidal volume, as a result of a forcible expiration, and which
amounts to about 100 cubic inches (1562 c.c).

After the expulsion of the reserve volume there yet remains
in the lungs an unknown volume of air which serves the mechanic

Fig.

174. — Spirometer.-
{Hutchinson.)

RESPIRATION. 357

function of distending the air-cells and alveolar passages, thus
maintaining the conditions essential to the free movement of
blood through the capillaries and to the exchanges of gases be-
tween the blood and alveolar air. As this air can not be dis-
placed by voHtional etTort, but resides permanently in the alveoli
and bronchial tubes though constantly undergoing renewal, it
was termed —
4. The residual volume, the amount of which is ditBcult of deter-
mination, but has been estimated by different observers at 914
c.c, 1562 c.c, iqSo c.c.
The Vital Capacity of the Lungs. — From foregoing statements
it is clear that the thorax and lungs are capable of a maximum degree
of expansion, at which moment the lungs contain their maximum
volume of air. This volume, whatever it may be, represents the
entire capacity of the lungs in the physiologic condition, and includes
the tidal, the complemental, the reserve, and the residual volumes.
Mr. Hutchinson, however, defined the vital or respiratory capacity
of the lungs as the amount of
air which can be expelled by ^
the most forcible expiration ""~''^"~-»^..^„__^^_^

after the most forcible inspi- "^ -^.^^^^ /

ration, and which therefore / ^""~~~'~~"~'^--^./''^

excludes the residual volume. ^ j- _^

The vital capacity was sup- ■ Hr^^

posed to be an indication of | ' ^

an indi\'iduars respiratorv

power, not only in physiologic ^^^- i/o-PNEUMATocR.^H.-CGaJ.)

but also in pathologic condi-
tions. Though averaging about 230 cubic inches (3593 c.c.) for an
individual 5 feet 7 inches in height, the vital capacity varies with a
number of conditions, the most important of which is stature. It
is found that between 5 and 6 feet the capacity increases 8 inches
(125 c.c.) for each inch increase in height.

The volume changes of the thorax indicated by the volumes of
air entering and leaving the lungs can be not only determined but
graphically represented by means of an apparatus similar in principle
to the spirometer, devised by Gad and known as the pnaimato graph or
aeroplethysmograph (Fig. 175). This consists of a quadrangular box
with double walls, the space between which is filled with water. The
center of the box is an air chamber. A thin- walled mica box sinks
into the water. Posteriorly it is attached to and rotates around an
axis, which permits of an elevation or depression of the anterior portion.
It is also carefully counterpoised. A Hght lever attached to the mica
box records its movements. The interior of the box communicates
bv a tube with a large reservoir into which the individual breathes,

358

TEXT-BOOK OF PHYSIOLOGY.

-w

EO C.IN
TIDALVOL.

the object being to prevent a too rapid vitiation of the air. In-
spiration causes the lever to descend, expiration to ascend. Previous
graduation of the apparatus is necessary to determine the volumes

breathed. A graphic record of
the volume changes is shown in
Fig. 176.

Respiratory Sounds. — On
applying the ear over the trachea
and bronchi there is heard dur-
ing both inspiration and expira-
tion a well-defined sound, loud,
harsh, and blowing in character,
which from its situation is known
as the bronchial sound. It is es-
pecially well heard between the
scapulae above the fourth dorsal
vertebra. This sound is pro-
duced in the larynx, for with its
separation from the trachea the
sound disappears. The cause
of the sound is to be found in
the narrowing of the air-passage
at the level of the vocal membranes, though the mechanism of its
production is uncertain. On applying the ear to almost any portion
of the chest-wall, but especially to the infrascapular area, there is
heard with each inspiration a delicate, sighing, rusthng sound, which
from its supposed seat of origin, the air-vesicles or -cells, is known
as the vesicular sound. This sound is supposed to be due to the
sudden expansion of the air-cells during inspiration and to the fric-
tion of the air in the alveolar passages.

Fig. 176. — Representing the Volume
Changes of the Thorax and
Lungs (Diagrammatic).

THE CHEMISTRY OF RESPIRATION.

The general nutritive process as it takes place in the tissues in-
volves the assimilation of oxygen and the evolution of carbon dioxid.
The former is the first, the latter the last, of a series of chemic changes
the continuance of which is essential to the maintenance of all hfe
phenomena. A constant supply of oxygen and an equally constant
removal of carbon dioxid are necessary conditions for tissue activity.
The respirator}^ movements constitute the means by which the oxygen
of the air is brought into, and the carbon dioxid expelled from, the
lungs into the surrounding air. The blood is the medium by which
the oxygen is transported from the lungs to the tissues and the carbon
dioxid from the tissues to the lungs.

The exchanges between blood and tissues constitute internal

RESPIRATION. 359

respiration, in contradistinction to the thoracic movements by which
the air is brought into relation with the blood, and which constitute
external respiration. The transfer of the oxygen by the blood from
the interior of the lungs to the tissues, and of the carbon dioxid from
the tissues to the interior of the lungs, is the outcome of a series of
chemic changes which are related to the exchange of gases between
the air in the lungs and the blood, on the one hand, and between
the blood and tissues, on the other.

In consequence of the many and complex chemic changes which
attend these gaseous exchanges, there arise changes in composition of:

1. The air breathed.

2. The blood, both arterial and venous.

3. The: tissue elements and the lymph by which they are surrounded.
The investigation of the nature of these changes, the mechanism

of their production, and their quantitative relations constitutes the
subject-matter of the chemistry of respiration.

CHANGES IN THE COMPOSITION OF THE AIR.

Experience teaches that the air during its sojourn in the lungs
undergoes such a change in composition that it is rendered unfit for
further breathing. Chemic analysis has shown that this change
involves a loss of oxygen, a gain in carbon dioxid, watery vapor
and organic matter. For the correct understanding of the phenom-
ena of respiration it is essential, that not only the character but the
extent of these changes be known. This necessitates an analysis of
both the inspired and expired airs, from a comparison of which certain
deductions can be made.

The results which have been obtained are represented in the
following table:

Inspired Air. Expired Air.

f Oxygen, 20.80. f Oxygen, 16.02.

100 j Carbon dioxid, traces. 100 | Carbon dioxid, 4-38.

vols. ^ Nitrogen, 79.20. vols. -| Nitrogen, 79.60.

1_ Watery vapor, variable. | Water}^ vapor, saturated.

i Organic matter.

These analyses indicate that under ordinary conditions the air
loses oxygen to the extent of 4.78 per cent, and gains carbon dioxid
to the extent of 4.38 per cent. ; that it gains in nitrogen to the extent
of 0.4 per cent, and in watery vapor from its initial amount to the
point of saturation, as well as in organic matter. It is to these changes
in their totahty that those disturbances of physiologic activity are
to be attributed which arise when expired air is re-breathed for any
length of time without having undergone renovation.

Special forms of apparatus have been devised for the collection
and analvsis of gases. Their construction as well as the methods

36o TEXT-BOOK OF PHYSIOLOGY.

of analysis involved are complicated and need not be described in
this connection. The presence of the carbon dioxid, however, may
be readily shown by breathing through a glass tube into a vessel con-
taining barium or calcium hydrate. The turbidity which immediately
follows is due to the formation of barium or calcium carbonate, which
can be due only to the presence of carbon dioxid. That this turbidity
is not due to the carbon dioxid normally present in the air is shown by
the fact that the solution remains clear until the passage of the atmos-
pheric air has been maintained for some time. From the percentage
loss of oxygen and gain in carbon dioxid, the total oxygen absorbed and
carbon dioxid exhaled may be approximately calculated. Thus, if
the volume of air breathed daily be accepted at either 10,800 or 12,-
240 hters, and the percentage loss of oxygen be 4.78, the total oxygen
absorbed may be obtained by the rule of simple proportion, e. g.:

100 : 4.78 :: 10,800 : x — 516 liters
Or

100 : 4.78 :: 12,240 : x = 585 liters.

By the same method the total carbon dioxid exhaled is found to be
either 473 or 526 liters; volumes in both instances which agree very
well with volumes obtained by other methods.

From the fact that when one volume of oxygen combines with
carbon it gives rise to but one volume of carbon dioxid, it is evident
that of the oxygen absorbed the greater portion by far is utilized in
the oxidation of the carbon, while the smaller portion is utilized in
the oxidation of other substances, but especially hydrogen, as shown
by the increase in water eliminated beyond that consumed. These
amounts, however, are not fixed but variable, and depend on the
quality and quantity of the foods, exercise, etc. The ratio of the
volume of the carbon dioxid exhaled to the volume of oxygen absorbed
is known as the respiratory quotient, and is usually represented by

CO

the symbol -q-. Thus in the foregoing analysis the respiratory
quotient is 0.916.

The gain in nitrogen is a variable factor, ranging from zero to
0.9 per cent. This gain is probably of accidental occurrence, due to
absorption from the large intestine, in which decomposition of
nitrogen-holding compounds is taking place. It is generally believed
that free nitrogen plays no part in any phenomenon of combination
or decomposition within the body.

The gain in watery vapor will depend on the amount previously
present in the air. This is conditioned by the temperature. With
a rise in temperature the percentage of water increases; with a fall,
it decreases. By breathing into a vessel containing pumice stone
saturated with sulphuric acid, the vapor may be collected. The
difference observed between the weight before and after breathing

RESPIRATION. 361

is an indication of the amount by weight of water exhaled during the
time of breathing. It has been calculated that the amount of water
exhaled daily approximates 500 grams. Though invisible at ordinary
temperatures, it becomes visible at low temperature as soon as it
emerges from the respiratory tract. The loss of heat is followed by
a condensation of the vapor, which appears at once as a cloudy pre-
cipitate.

The gain in organic matter is also variable. The amount present
is not sufficient to permit of a thorough chemic analysis, but there are
reasons for beheving that it belongs to the proteid group of bodies.
If it accumulates in the air, especially at high temperatures, it readily
undergoes decomposition, with the production of offensive odors.
Traces of free ammonia have also been found in the expired air.
In addition to these chemic changes, the air experiences physical
changes; e. g., a rise in temperature and an increase in volume. The
rise in temperature can be shown by breathing through a suitable
mouthpiece into a glass tube containing a thermometer. By this
means it has been show^n that inspired air at 20° C. rises in tem-
perature to 37° C; at 6.3° to 29.8° C. The increase in the tem-
perature will depend upon that of the air inspired and the time it
remains in the lungs. If retained a sufficient length of time it will
always become that of the body. As a result of the heat absorption
the expired air increases in volume about one-ninth over that of the
inspired air. When corrected for temperature and pressure and
freed from aqueous vapor, the volume of the expired air is less than
that of the inspired air by about one-two hundred and fiftieth.

The Composition of the Alveolar Air. — The foregoing state-
ment of the composition of the expired air, derived in part from the
upper air-passages, trachea, and bronchi, does not necessarily repre-
sent the composition of the alveolar air. It is very probable that the
percentage of carbon dioxid is greater, the percentage of oxygen less,
in the latter than in the former. This is made evident by collecting
in several portions the expired air as it escapes from the respiratory
tract and subjecting it to analysis. The last portion always contains
a larger amount of carbon dioxid and a smaller amount of oxygen
than the first portion. The determination of the composition of the
alveolar air is extremely difficult. It has been estimated to contain
from 5 to 6 per cent, of carbon dioxid and from 14 to 18 per cent, of
oxygen.

Pulmonary Ventilation. — It is owing largely to this inequahty
of volumes and consequently of the " partial pressures" of these two
gases in the trachea and alveoh that the degree of ventilation necessary
to exchange of gases between lungs and air is maintained. Though
the respiratory movements doubtless create currents in the air-passages
which carry, on the one hand, a portion of the inspired air directly

362 TEXT-BOOK OF PHYSIOLOGY.

into the alveoli, and, on the other hand, carry a portion of the alveolar
air directly out of the body, other portions find their way into and out
of the alveoli in accordance with the laws of diffusion. If the tension
of the oxygen in the trachea is 158 mm. Hg and in the alveoli 114 mm.
Hg, diffusion downward will take place. Equilibrium, however,
is never estabhshed, as the oxygen is continually disappearing by
passing into the blood. On the contrary, if the carbon dioxid tension
in the alveoli is 38 to 40 mm. Hg, and in the trachea 0.3 mm. Hg,
diffusion will take place upward. Equilibrium will never be estab-
lished, however, as the carbon dioxid is constantly coming out of
the blood. Pulmonary ventilation may also be aided by those
alternate changes in volume of the heart, great vessels, and lungs
occurring as the result of the heart-beat and producing the so-called
cardio-pneumatic movements.

CHANGES IN THE COMPOSITION OF THE^ BLOOD.

The blood which flows into the lungs through the pulmonary
artery is dark bluish- red, that which flows from the lungs into the
pulmonary veins is scarlet red, in color. The blood is changed, while
flowing through the lung capillaries, from the venous to the arterial
condition. As the air in the lungs gains carbon dioxid and loses
oxygen, it is fair to assume that what the air gains the blood loses,
and what the air loses the blood gains. In other words, the blood,
while passing through the lungs, is changed from venous to arterial
by the loss of carbon dioxid and the gain of oxygen. The change
in color of venous blood from dark bluish to scarlet red is strikingly
shown by shaking it in a test-tube with oxygen or atmospheric air.

The blood which flows into the tissues through the arteries is red,
that which flows from the tissues into the veins is bluish, in color.
The blood while flowing through the tissue capillaries is changed
from the arterial to the venous condition. Since arterial blood when
deprived of oxygen becomes bluish-red, the indication is that the
change in color is associated with, if not entirely due to, the escape
of oxygen into the tissues. The constant ehmination of carbon
dioxid from the blood into the lungs indicates that the carbon
dioxid is as constantly passing from the tissues through the capillary
walls into the blood.

These considerations are confirmed by the results of analyses
which have been made of both venous and arterial blood. The
presence of gas in the blood is demonstrated by subjecting it under
appropriate conditions to the vacuum of the mercurial air-pump,
into which it at once escapes. From 100 volumes, an average of 60
volumes of gas at standard pressure, 760 mm. Hg and temperature
0° C, can thus be obtained.

Gases of the Blood. — An analysis of the volumes of gas removed

RESPIRATION. 363

from both venous and arterial blood shows that each consists of
oxygen, carbon dioxid, and nitrogen, though in different amounts.
An average composition of the gases extracted from dog's blood
obtained from the right ventricle and carotid artery is given in the
following table:

Venous blood f 9''\^''\.--- 9-^1 ^°!^- Arterial blood f ?''T\.— - ^° ''?}'■
, i Carbon dioxid, 41; 1 -{ Carbon dioxid, 40

100 vols. T,,., ^-^ ,, 100 vols. 1 T.T, ' ^ ,,

t. Nitrogen, i- 2 (.Nitrogen, 1-2

The changes produced in the blood by respiration, both external
and internal, become apparent from a comparison of these analyses.
The venous blood while passing through the lungs gains from eight
to eleven volumes per cent, of oxygen and loses five volumes per
cent, of carbon dioxid. The arterial blood while passing through
the tissues loses oxygen and gains carbon dioxid in corrcsi)onding
amounts. The volume of nitrogen is not appreciably changed.

The Relation of the Gases in the Blood, — The mechanism
by which the gases become associated with the blood at the moment
of their entrance into it, and again become dissociated just prior to
their exit from it, as well as their relation while in transit, will be more
readily understood after reference to a few elementary facts relative
to the absorption of gases in general and the conditions of temperature
and pressure by which it is influenced.

It is well known that liquids will take up, absorb, or dissolve
unequal volumes of different gases in accordance with their solu-
bihties and with variations in temperature and pressure. Water,
for example, will absorb oxygen, carbon dioxid, and nitrogen as well
as other gases in amounts varying with the foregoing conditions.
The amount of any gas absorbed by one volume of a liquid at a tem-
perature of 0° C. and a pressure of 760 mm. Hg is known as the co-
efficient of absorption. The coefficient of absorption of i volume
of distilled water for oxygen is 0.0489 volume; of carbon dioxid,
1.797 volumes; of nitrogen, 0.023 volume. With a rise in tem-
perature, however, the absorptive power of water for each one of
these gases diminishes. On the contrary, as the pressure rises the
quantity of the gas absorbed increases, and as it falls, decreases.
In all gaseous determinations, therefore, it is always necessary, for
purposes of comparison, to reduce the obtained volumes to standard
temperature (0° C.) and pressure (760 mm. Hg).

If water be exposed to atmospheric air consisting of oxygen,
carbon dioxid, and nitrogen in the ordinary proportions, at any
given temperature and pressure, the water will absorb unequal
volumes of each of the three gases. The pressure under which
each gas is absorbed is a part only, however, of the total atmos-
pheric pressure at the time. The pressure exerted by any one of

364 TEXT-BOOK OF PHYSIOLOGY.

these three gases is known as its partial pressure, and depends on the
percentage volume of the gas present. If atmospheric air contains
at standard pressure and temperature 79.15 volumes per cent, of
nitrogen, its partial pressure will be '-'^^f of 760, or 601.54 mm. Hg;
if the air contains 0.04 volume per cent, of carbon dioxid and 20.85
volumes per cent, of ox}'gen, the partial pressure of each will be 0.30
mm. Hg and 158.46 mm. Hg respectively. The absorption of each
gas is independent of all the rest, and is the same for nitrogen, for
example, as if it alone were present at a pressure of 601.54 mm. Hg.

Again, if water holding in solution a certain volume of a gas —
carbon dioxid, for example — be exposed to an atmosphere containing
but 0.04 volume per cent, of carbon dioxid, and having therefore a
pressure of but 0.3 mm. Hg, the gas will at once begin to leave the
water, and continue to do so until the pressure of the carbon dioxid
in the atmosphere balances the tension of the gas in the water, at which
moment the escape of the gas ceases. The tension of a gas in a liquid
is equal to that pressure in miUimeters of mercur}^ of the same gas in
the atmosphere which is required to keep it in solution. Pressure
and tension are therefore in this case convertible terms. What is
true for the carbon dioxid is true for any other gas that may be in
solution. It will be recalled that the blood yields up its gases when
subjected to the vacuum of the mercurial pump; that is, to a diminu-
tion or complete removal of the atmospheric pressure. From this
it might be inferred that the gases are merely held in solution by
pressure, and at once escape the moment they are exposed to a
space in which there is a very sHght or a total absence of pressure.
It is therefore necessar}^ to test this supposed condition of the gases
in the blood by subjecting the latter to gradually diminishing pres-
sures, with a view of determining in how far the evolution of the gases
follows the law of partial pressures. For convenience the conditions
of each gas will be considered separately.

Oxygen. — If blood is subjected to a succession of pressures pro-
gressively less than the standard, it is found that though oxygen is
evolved, its evolution is not in accordance with the law of partial
pressures ; that is, in proportion to the diminution of pressure. Within
wide limits — e. g., from 760 to 238 mm. atmospheric pressure, to
which correspond oxygen pressures of 160 and 50 mm. respec-
tively— there is but a shght increase in the amount of oxygen evolved ;
and it is not until the pressure of the oxygen falls to about 40 to 30
mm. that it begins to be Uberated in large amounts From this on,
the oxygen continues to be Hberated with decreasing pressures, until
the zero point is reached, when all gaseous discharge ceases. Co-
incidently the blood changes in color from a bright red to a deep bluish -
red. It is evident from the results of this procedure that the con-
dition of the oxygen in the blood is but to a shght extent one of

RESPIRATION. 365

physical absorption. The indications are that it partakes of the
nature of a chemic combination.

If the red corpuscles be removed from the blood and the plasma
alone be treated in the manner above described, it will be found that the
oxygen Hberated now follows the law of partial pressure. The amount
so liberated, however, is small — about one per cent, of the total oxygen
of the blood. The agent therefore which holds the o.xygen in com-
bination is the red corpuscle, and more especially the hemoglobin,
which constitutes about 94 per cent, of its volume. This is proved by
the fact that a solution of gas-free hemoglobin of a strength equivalent
to that of the blood (14 per cent.), exposed to gradually increasing
pressures from zero up to 30 or 40 mm. oxygen pressure, will absorb
large quantities of oxygen; beyond this point the amount absorbed
is again small in comparison. At 70 mm. pressure the hemoglobin
is almost saturated. Coincidently with this absorption the hemo-
globin changes in color from dark blue to bright red; changes from
hemoglobin to oxyhemoglobin. The reverse method, that of subjecting
oxyhemoglobin to gradually diminishing pressures, yields opposite
results. As one gram of hemoglobin combines with 1.59 c.c. of
oxygen, and as the percentage of hemoglobin is 13.50 to 14, it is
e\'ident that there is sufficient hemoglobin to combine with practically
all the oxygen usually present in the blood.

The relation of the oxygen in the blood is therefore partly physi-
cal, partly chemical. One per cent, is physically absorbed by or
dissolved in the plasma ; the remainder is chemically combined with
the hemoglobin.

The association or combination of oxygen is favored by a pressure
of at least from 30 to 50 mm. Hg and upward; the dissociation, by
diminution of pressure. In the conversion of hemoglobin into oxy-
hemoglobin two antagonistic forces are at work, heat and chemic
affinity. The former endeavors to prevent, the latter to favor,
the union. Chemic affinity increases with the influence of mass, that is,
in proportion to the number of atoms in a unit of volume, with the
density and with the partial pressure of the oxygen. Diminution of
pressure reduces the mass influence and permits the heat to bring
about dissociation (Bunge). The following table by Hiifner shows
the relative proportion of hemoglobin and oxyhemoglobin in blood
containing 14 per cent, hemoglobin and exposed to air at gradually
diminishing pressures:

Atmospheric Pressure

Parti.al Pressc:

rf of

Hemoglobin

OxyHEMOGLOBIN

IN- MM. Hg.

OXY

GEN IN- MM.

Hg.

Percent.age.

Perce.nt.*ge.

760

159-3

1-49

98.^1

5248

no

2.14

97.S6

357-8

75

3-II

96.89

238-5

50

4.60

95-40

119 3

25

8.79

91.21

47-7

10

19.36

80.64

23.8

5

32-51

67.49

0.0

0.0

100.00

O.OD

366 TEXT-BOOK OF PHYSIOLOGY.

Carbon Dioxid. — The blood yields up its contained carbon
dioxid to the vacuum of the gas-pump as completely as it does its
oxygen. The same is not the case, however, if the red corpuscles are
first removed and the experiment made with either plasma or serum.
Even at zero pressure the fluid contains carbon dioxid, as shown by
its liberation on the addition of some weak acid, as tartaric or phos-
phoric, an indication that it exists in a state of firm combination.
The same result follows the addition of the red blood-corpuscles,
which act in a manner similar to the acids just mentioned. This
property of the corpuscles has been attributed to hemoglobin, and
especially when in the state of oxyhemoglobin. It is for this reason
that blood yields all its carbon dioxid to the vacuum of the gas-pump.

The limit of pressure at which the plasma ceases to physically
absorb carbon dioxid and begins to chemically combine it is not very
clearly defined. It has been estimated that of the entire amount,
38 to 45 volumes, only about 2.5 volumes are so absorbed, the re-
mainder being in a condition of both loose and stable combination.

An analysis of the serum, and presumably of the plasma, shows
the presence of sodium salts, with which the carbon dioxid could
enter into combination, \riz. : sodium carbonate and dibasic sodium
phosphate. The sodium is thus partly divided between carbonic acid
and phosphoric acid. The amount of the sodium which falls to
carbon dioxid will depend on the mass influence of the latter; that
is, its partial pressure.

At its origin in the tissues the carbon dioxid acquires a consider-
able tension, and its mass influence is correspondingly large. On
entering the blood it combines with sodium carbonate, with the
formation of sodium bicarbonate, as shown in the following equation :

Na2C03 + CO2 + H2O = 2NaHC03.

At the same time, having a greater mass influence than tlie phos-
phoric acid, it will withdraw from the dibasic sodium phosphate
one-half of its sodium, with the formation of sodium bicarbonate and
monobasic sodium phosphate, as shoAvn in the following equation:

NajHPOi + CO2 + H2O = NaHCOj + NaHjPO^.

With the diffusion of the carbon dioxid from the blood into the
alveoli its tension in the venous blood falls, its mass influence dimin-
ishes, while that of the phosphoric acid relatively increases. As a
result, the sodium is withdrawn from the sodium bicarbonate, an
additional liberation of carbon dioxid takes place and dibasic sodium
phosphate is re-formed. The association or combination of the
carbon dioxid with the basic salts depends on its partial pressure; its
dissociation in the lungs, on a diminution of pressure.

RESPIRATION. 367

Nitrogen. — This gas exists in both arterial and venous blood
in a state of solution. There is no evidence that it enters into com-
bination witli any other element.

Tension of the Gases in the Blood.— It will be recalled that a
liquid holding in solution one or more gases will on exposure to an
atmosphere composed of the same gases either give up or absorb
volumes var}'ing in amount and in accordance with their partial
pressures until equilibrium is established. If the pressure of any one
gas in the atmosphere is greater than in the liquid, it is absorbed;
if the pressure is less, it is discharged. Knowing the pressure of the
gases in percentages of an atmosphere, at the beginning and the end
of an experiment, the original tension or pressure of the gases in the
liquid can be easily calculated. On this principle various forms of
apparatus known as aerotonometers have been devised by which the
tension of the gases in the blood can be determined.

These appliances consist essentially of a glass tube containing
oxygen and carbon dioxid in known amounts and tensions. The
blood from an animal is then allowed to flow directly from an artery
or vein into the tube. As it flows down its sides in a thin layer it
presents a large surface to the action of the contained gases. In the
aerotonometer of Fredericq the blood made non-coagulable by the
injection of peptone is returned from the opposite extremity of the
tube to the animal. This enables the experiment to be continued
for an hour or more. A knowledge of the tensions of the blood gases
is of interest, as it affords a clue to the mechanism by which the
interchange takes place between the lungs and the blood, on the one
hand, and the blood and tissues, on the other. The results, however,
of different observers are not sufficiently in accord to permit of posiiivc
deductions.

In the well-known and generally accepted experiments of Strass-
burger, the tension of the oxygen in the arterial blood of the dog
was found to be 29.64 mm. Hg, or 3.9 per cent, of an atmosphere, and
in the venous blood 22.04 mm. Hg, or 2.9 per cent. The tension
of the carbon dioxid in the venous blood was found to be 41.04 mm.
Hg, or 5.4 per cent, of an atmosphere, and in the arterial blood 21.8
mm. Hg, or 2.8 per cent. In the experiments of Fredericq the oxygen
tension in the arterial blood was found to be 106 mm. Hg, or 14 pQr
cent, of an atmosphere.

CHANGES IN THE COMPOSITION OF THE TISSUES AND LYMPH.

From previous statements the inferences can be drawn that the
oxygen leaves the blood as the latter flows through the capillaries;
that it passes through the capillary wall into the surrounding lymph
and so to the tissue-cells; that it oxidizes food materials in the tissue-

368 TEXT-BOOK OF PHYSIOLOGY.

cells whereby the potential energy of the former is liberated as kinetic
energy; that the carbon dioxid so evolved passes into the lymph
and through the wall of the capillary into the blood.

While this is doubtless the case, the presence of free oxygen in the
tissues can not be demonstrated by the usual methods of gas analysis.
Only in the saliva and in the blood of the placental umbilical vein can
it be shown that oxygen has directly passed through the capillary wall.
For this reason it has been claimed by a few investigators that oxygen
does not leave the blood, but that the field of its activity as an oxidizing
agent is limited to the blood-current, where it meets with and oxidizes
easily reducible substances entering from the tissues. On this view
the potential energy of the food would be liberated by mere decom-
position or cleavage in consequence of cell activity.

Nevertheless many facts from the fields of comparative physi-
ology and physiologic chemistry combine to support the view that
oxygen is absolutely necessary to the maintenance of the fife of all
tissue-cells. Though they will continue to manifest their character-
istic activititss — e. g., contraction on the part of a muscle, secretion by a
gland, the conduction of a nerve impulse by the nerve, etc.— for a
variable length of time after oxygen is prevented from gaining access
to them, nevertheless they will in due time die.

The necessity for oxygen on the part of the tissues and the avidity
with which they absorb it, is shown by their power of reducing pig-
ments such as alizarine blue. If this pigment be injected into the
blood-vessels of an animal and the animal killed in about ten minutes,
it will be found that while the blood exhibits a deep blue color the
tissues present their usual colors. But after exposure to the air or to
free oxygen the latter also acquire the characteristic blue color. The
explanation offered for this fact is that the tissues in their need for
oxygen absolutely extract it from the pigment, reducing it to a color-
less compound, which, however, on exposure recombines with oxygen
and regains the original color.

Though free oxygen can not be shown to be present in the tissues,
there are many reasons for believing that it is continually passing into
them by way of the lymph-stream. Its rapid disappearance would
indicate that it is immediately utilized for the production of carbon
dioxid (which is improbable on other grounds), or that the tissues
possess a capacity for oxygen storage, of placing it in reserve under
some combination or other, by which it can be securely retained
until required for oxidation purposes. This is rendered probable
from the fact that the carbon dioxid evolved at any given moment is
not necessarily dependent on the oxygen just absorbed, for if oxygen
be withheld from a nutritive fluid which is being artificially circulated
through a recently isolated organ, carbon dioxid will continue to be
discharged for some time. A muscle, or even a living animal, — e. g.,

RESPIRATION. 369

a frog, — placed in an atmosphere of pure nitrogen will remain
active and evolve CO, for even several hours.

Naturally the absorption of oxygen and the discharge of carbon
dioxid and the changes of composition which are incident to nutri-
tion will be most marked in those tissues characterized by the
greatest degree of physiologic activity. Muscle-tissue exhibits these
changes to a greater degree than bone. Tissues with inter-
mediate degrees of activity should exhibit corresponding degrees
of respiratory change. Experiment confirms this view. Thus, loo
grams each of muscle, spleen, and broken bone from a recently
living animal exposed to the air for tw^enty-four hours absorbed
respectively 50.8 c.c, 27.3 c.c, and 17.2 c.c. of oxygen, while each
discharged during the same period 56.8 c.c, 15.4 c.c, and 8.1 c.c. of
carbon dioxid respectively. In another series of experiments by a
different observer 100 grams of muscle absorbed in three hours
23 c.c. of oxygen, and 100 grams of bone 5 c.c. of oxygen. Both
tissues discharged carbon dioxid in amounts proportional to the
oxygen absorbed. The same respiratory changes may be more
satisfactorily demonstrated by passing blood through the tissues of
isolated organs and the tissues of recently living animals. The
analysis of the blood before and after perfusion shows a loss of oxygen
and a gain in carbon dioxid.

Tension of the Gases in the Tissues. — As the presence of free
oxygen can not be demonstrated, its tension there must be regarded
as nil. The tension of the carbon dioxid is quite high, though
difficult of exact determination. It has been estimated at from
45 to 68 mm. Hg, or from 6 to 9 per cent, of an atmosphere.

The variations of tension or pressure of these two gases in the
lungs, in different parts of the vascular apparatus, and in the tissues,
and their relations to each other, are shown in Fig. 177, expressed
in mm. Hg and percentages of an atmosphere.

The Mechanism of the Gaseous Exchange. — In these pres-
sure differences sufficient cause is found for the exchange of the
gases. The oxygen pressure in the alveoli being in excess of that in
the blood, the gas passes through the thin alveolo-capillary wall into
the plasma. As the pressure in the plasma rises, the oxygen combines
with the hemoglobin, until the latter is almost saturated. On passing
into the systemic capillaries the blood enters a region in which the
oxygen tension of the surrounding tissues is nil. At once a dis-
sociation of the oxyhemoglobin and oxygen takes place, after which
the latter passes through the capillary wall into the plasma and so to
the tissue-cells, in which it is stored and utilized. The sojourn of
the blood in the capillaries being of short duration, the oxyhemo-
globin can part with but a portion of its oxygen, sufficient, how^ever, to
satisfy the needs of the tissues.
24

;70

TEXT-BOOK OF PHYSIOLOGY.

The carbon dioxid pressure in the tissues being in excess of that
in the blood, it passes through the capillary wall into the blood, where
it exists in the free and combined states. On passing into the pul-
monic capillaries the blood enters a region in which the carbon
dioxid in the alveoh is less than in the blood. At once a diffusion and
dissociation of the carbon dioxid takes place through the alveolo-
capillary wall until equilibrium is established. This, however, is of
very short duration, for the carbon dioxid so ehminated is rapidly
removed from the lungs by the respiratory movements.

While diffusion, in response to physical and chemic conditions,

thus plays a large
part in, and is suf-
ficient to account
for, the exchanges
of gases, it is pos-
sible that the alve-
olar or respiratory
epithelium may
also play an essen-
tial role. It is be-

ATMOSPHERIC AIR.

O— 156 MM HGjOR 20. 8S P.C
CO. 0.3MMHG OR O.O'^ P.C
PHER

O-TE.NSI0N

22.04- MM HGOR

CO TENSION
Z
■4-1. 04 MM HG OR
5.4 P.C.

AUVEOLUS

VENOUS
BLOOD

ARTERIAL
BLOOD

O -TENSION
O. OO MM H G
CO - TENSI ON
'i-5 - 68 M M

O — TENSION

CO —TENSION
21.28 MM HO OR
2.8 P.C.

lieved by some in-
vestigators that it
is active in both
the absorption of
oxygen and the
excretion of carbon
dioxid. This view
has been suggested
as a means of in-
terpreting the re-
sults of the experi-
ments of more re-
cent investigators,
made with a view
of determining the
tension of the
blood gases. It
was found by Bohr that the tension of the oxygen in arterial blood
was often as high as loi to 144 mm. Hg, and in many instances
higher than the tension of the oxygen in the trachea, while the
carbon dioxid tension in the trachea was higher than in the blood.
Haldane and Smith by a different method found an oxygen tension in
the arterial blood of 200 mm. Hg. If these results should prove to
be correct, though they are at present subject to considerable criticism
and not generally accepted, some other force than diffusion would

Fig. 177. — Diagram showing the Relative Tension
OF Oxygen and Carbon Dioxid in the Lungs,
in the Blood, and in the Tissues.

RESPIRATION. 371

have to be found to explain the facts. It would then remain to deter-
mine in how far the alveolar epithelium could be regarded as an
active agent in both absorption and excretion in opposition to
pressure.

THE TOTAL RESPIRATORY EXCHANGE.

The total quantities of, oxygen absorbed and carbon dioxid dis-
charged by a human being in twenty-four hours arc measures of the
intensity of the respiratory process, and an indication of the extent and
character of the chemic changes attending all life phenomena. Their
determination and their relation to each other are matters of interest
and importance. The quantities which have been obtained by differ-
ent observers are the outcome of calculations based on certain groups
of data and of experiments made with special forms of apparatus.

Thus from the total air breathed daily, estimated from the amounts
obtained during a longer or shorter period, of experiments with spiro-
metric apparatus, and from the percentage loss of oxygen and gain of
carbon dioxid shown by an analysis of the respired air, it can be cal-
culated at least approximately what the total amounts of oxygen ab-
sorbed and carbon dioxid exhaled must be. If it be assumed that
the minimum daily volume of air breathed is 10,800 liters and the
maximum volume 12,240 liters, and the percentage loss of oxygen is
4.78, then the total volume of oxygen absorbed is 516 liters (735.17
grams) or 585 liters (836.42 grams). By the same method the total
carbon dioxid exhaled daily is found to be either 473 liters (931.8 grams)
or 526 liters (1036 grams). The direct experiments which have been
made with specially devised forms of apparatus, both on human beings
and animals, have yielded similar results. With those forms which
are adapted for both human beings and animals — Scharling's, Petten-
kofer and Voit's — it is only possible, however, to determine the amount
of carbon dioxid and water, and from these to calculate the amount
of oxygen absorbed. This is done by deducting the loss in weight
by the man or animal during the experiment from the combined
weights of the carbon dioxid and water discharged. The difference
represents the oxygen absorbed.

The Pettenkofer-Voit apparatus (Fig. 178) consists essentially
of a chamber large enough to admit a man and capable of being
made air-tight with the exception of an inlet for air for breathing
purposes. The respired air is drawn through a tube and measured
by a large meter turned by a water or gas motor. By means of a side
tube a fractional quantity of the main column of air is diverted to an
absorption apparatus by a small pump. This air first passes into
a vessel containing H,SO^, by which the water is collected; then
into long tubes containing barium hydroxid, by which the carbon
dioxid is absorbed; thence into a small meter, by which its amount is

3/2

TEXT-BOOK OF PHYSIOLOGY

RESPIRATION.

373

registered. From the amount of water and carbon dioxid thus ob-
tained the amounts of both in the total air breathed are calculated.
The water and carbon dioxid previously present in the air are simulta-
neously determined by a corresponding absorption apparatus and de-
ducted from the amounts obtained from the respired air. As the
apparatus is traversed constantly by a column of air of normal
composition and the waste products removed as rapidly as discharged,

Fig. 179. — Regnault's and Reiset's Respiration Apparatus. A. Bell-jar for the
reception of the animal, surrounded by a compartment, B, containing water.
N, N, N. Reservoirs of oxygen communicating, on the one hand, with the animal
chamber, and, on the other hand, with pressure bottles, P, by which the ox^-gen
is driven into the animal chamber. G, G. Aspiratory bulbs containing sodium
hydro.xid in solution for the absorption of the carbon dioxid. The bulbs are
given an alternate up-and-down movement by a falling weight or electric motor.

the experiment can be continued for periods varying from six to
twenty-four hours without detriment to the subject of the experiment.
With those forms adapted only for animals — Regnault's and
Reiset's, or Jolyet and Regnard's — it is possible to determine simul-
taneously the absorption of oxygen and the discharge of carbon
dioxid. As the apparatus employed is completely closed, the carbon

374 TEXT-BOOK OF PHYSIOLOGY.

dioxid must be removed as soon as discharged and the oxygen re-
newed as soon as absorbed. The former is accomphshed by the as-
piratory action of moving bulbs containing an alkali, the latter by a
steadily acting pressure on a reservoir of oxygen. This apparatus
(Fig. 179) consists essentially of a bell-jar in which the animal is
placed. This is brought into connection by tubes, on the one
hand, with the oxygen reservoir, and, on the other hand, with the
aspiratory bulbs, kept in motion by some form of motor. The
construction of each of these forms of apparatus is so complex, the
conduct of an experiment and the final determination of the results
so complicated, that a detailed description would be out of place in
a work of this character.*

Among the results obtained by these and other methods a few are
given in the following table:

Oxygen Absorbed.

Observer.

Carbon Dioxid Discharged.

746 grams.

Vierordt.

876 grams.

700 "

Pettenkofer and Voit.

800

663 "

Speck.

770 "

The amounts of oxygen absorbed in Pettenkofer and Voit's experi-
ments varied from 594 to 1072 grams; of carbon dioxid exhaled, from
686 to 1285 grams.

In all these results it is evident on examination that the volume
of oxygen absorbed is always greater than the volume of carbon
dioxid exhaled, or, what amounts to the same thing, the weight of the
oxygen absorbed is always greater than the weight of the oxygen
entering into the formation of the carbon dioxid exhaled. The reason
for this difference between the amounts of oxygen in the inspired air
and in the COj exhaled is found in the fact that on a mixed diet — one
containing fat — a portion of the oxygen is utilized in the oxidation
of the hydrogen of the fat with the formation of water. Under such
a diet the respiratory quotient is always less than unity, usually
0.907. On a purely carbohydrate diet — one in which there is no
surplus hydrogen — all the oxygen will combine with carbon and be
returned as carbon dioxid, and hence the respiratory quotient will
be unity. The respiratory quotient therefore indicates the extent to
which the oxygen absorbed is utilized in oxidizing carbon, on the one
hand, and hydrogen, on the other.

Since the total oxygen absorbed and carbon dioxid discharged
will vary considerably with the size of the animal, it is customary,
for purposes of comparison, to reduce all total results to the unit of
body- weight (one kilogram) and to the unit of time (one hour).

* Both forms of apparatus are in use in the Physiological Laboratory of the Jeffer-
son Medical College and are fully described by Prof. H. C. Chapman in his text-
book on Physiology, to which the reader is directed for further information.

RESPIRATION. 375

Respiratory Activity. — The activity or the intensity of the
respiratory process may be measured either by the oxygen absorbed
or the carbon dioxid discharged. But as the carbon dioxid is more
easily estimated than the oxygen, it is usually taken as the index of
the activity, though there are reasons for believing that it would be
more accurately indicated or represented by the oxygen.

Whatever factor may be accepted as the measure, it is certain that
the respiratory activity varies in different tissues in accordance with
their functional activities, being least in bones and greatest in muscles.
This is shown by the relative amounts of oxygen absorbed and carbon
dioxid discharged by equal amounts of each of these and other tissues
in twenty-four hours, as shown in the following table:

QUANTITY OF O AND COj ABSORBED AND EXHALED DURING
TWENTY-FOUR HOURS, IN CUBIC CENTIMETERS.

By 100 Grams of:

Muscle,

Brain,

Kidneys,

Spleen,

Testicles,

Pounded bones,

C'xygcn Absorbed.

Carbonic Acid Exhaled

50.8 C.C.

56.8 C.C.

45-8 "

42.8 "

37-0 "

15.6 "

273 "

15-4 "

18.3 "

275 "

17.2 "

8.1 "

The total respiratory change therefore of the body as a whole is the
resultant of the respiratory changes of its individual organs and
tissues, and is conditioned by all influences which retard or hasten
their activity. Among these influences the more important are the
following :

Muscle Activity. — As the muscles constitute a large part of the
body, about 40 per cent., and as muscle-tissue absorbs and discharges
relatively large quantities of oxygen and carbon dioxid, it is readily
apparent that an increase in their activity would be followed or
attended by an increase in the respirator}' exchange. In passing
from a condition of body repose to one of marked activity there ought
to be an increase in the amount of oxygen absorbed and CO2 dis-
charged. Pettenkofer and Voit found that a man in repose who
absorbed daily 807.8 grams of oxygen and discharged 930 grams
COj absorbed during work ioot3 grams of oxygen and discharged
1 137 grams of CO,. Edward Smith, who estimated only the CO,,
found that a man in repose who discharged carbon dioxid at the rate
of 161. 6 C.C. per minute increased the amount while walking at the
rate of two and three miles an hour to 569 c.c. and 851 c.c. respec-
tively. Similar results have been obtained by other investigators.

Digestive Activity. — The activity of the alimentary canal,
involving contraction of its muscle coat through its entire length
as well as secretion of its related glands called forth by the inges-
tion of food, materially influences the absorption of ox)'gen and

376 TEXT-BOOK OF PHYSIOLOGY.

discharge of carbon dioxid, independent of the increase due to the
oxidation of food materials after absorption. It was found that in a
fasting man a dose of sodium sulphate increased the absorption of
oxygen as much as 17 per cent, and the discharge of CO2 24 per cent.
(Lowy). It is difficult to determine how much of the increase after
a meal is therefore due to food oxidation and how much to functional
activity of the canal itself. The consumption of nitrogenized
meals, however, has a greater effect than non-nitrogenized meals.

Temperature. — A rise in temperature of the surrounding air
has as an effect a diminution in the amounts of oxygen consumed and
carbon dioxid discharged. A fall in temperature has the opposite
effect. Thus a cat at a temperature of — 3.2° C. consumed during a
period of six hours 21.39 grams of oxygen and discharged 22 grams
of carbon dioxid, while at a temperature of 29.6° C. the correspond-
ing amounts for the same period of time were for oxygen 13.9 grams
and for carbon dioxid 13.12 grams. Lavoisier and Sequin, having
reference only to the oxygen, found that a man at a temperature of
15° C. consumed 38.31 grams of oxygen, while at a temperature of
32.8° C. the corresponding amount was but 35 grams. Similar
results have been obtained by other observers with different animals.
The explanation of these facts is to be found in the increased activity
of all physiologic mechanisms coincident with a fall, and in the
decreased activity, coincident with a rise in temperature. The lower
temperatures act as a stimulus to the peripheral terminations of the
nerve system, bringing about refiexly increased activity of the body
at large. The muscles especially are not only reflexly but vohtionally
excited to greater activity. This leads naturally to an increase in
the consumption of oxygen and in the production of carbon dioxid
and in the evolution of heat.

In cold-blooded animals the respiratory exchange is influenced in
a manner the reverse of that observed in warm-blooded animals.
With a rise of external temperature and a corresponding rise of
body-temperature the discharge of carbon dioxid steadily increases.
Thus a frog in an atmosphere at 0° C. with a body-temperature of
1° C. discharged per kilogram per hour 4.31 c.c. of carbon dioxid;
in an atmosphere of 35° C. with a body-temperature of 34° C. there
was discharged 325 c.c. per kilo per hour. Intermediate tempera-
tures were attended by corresponding increases in the amounts of
CO2 discharged. The reason for this difference in the two classes
of animals is probably to be found in the want, in the cold-blooded
animals, of a self-adjusting heat-regulating mechanism.

Age. — In early youth, as a result partly of the more pronounced
activity of the nutritive energies and partly of a cutaneous surface
relatively greater, as compared with the mass of the body, than in
adult life, the absorption of oxygen and the discharge of carbon

RESPIRATION. 377

dioxid arc greater both absolutely and relatively. Thus, in a boy of
nine and a half years with a weight of 22 kilograms it was found that
in twenty-four hours there was a discharge of carbon dioxid amounting
to 488 grams, or 0.92 gram per kilo per hour, and in man with a
weight of 65.5 kilograms there was a discharge of 804.72 grams, or 0.51
gram per kilo per hour.

MODIFICATION OF RESPIRATORY RHYTHM.

The character of the respiratory movements is materially modified
by a change in the quantitative and qualitative composition of the
air and blood as well as by changes of a pathologic nature of the re-
spiratory apparatus itself.

Eupnea. — So long as the air retains its normal composition and
the respiratory mechanism its structural integrity, so long do the
respiratory movements exhibit a normal rhythm and frequency.
To the condition of easy tranquil breathing the term eupnea is given.
In this condition the percentages of oxygen and carbon dioxid in the
blood are such as to favor at least the rhythmic discharge of nerve
impulses to the respiratory muscles, of sufficient energy and frequency
for the maintenance of normal respiration.

Hyperpnea. — The normal rate of the respiratory movements is
increased by a rise in body-temperature, by active exercise, and by
emotional states. Whatever the cause, the increase in rate and prob-
ably in depth is termed hyperpnea.

Febrile states characterized by a rise in the temperature of the
blood increase considerably the respiratory activity. This is due in
all probability to a warming of the respiratory center, in consequence
of which its excitabihty is heightened; for surrounding the carotid
arteries with warm tubes and heating the blood on its way to the
medulla has the same effect. It is also possible, however, that the
high temperature of febrile conditions may interfere with the absorb-
ing power of hemoglobin, and thus by diminishing the quantity of
oxygen absorbed lead to more frequent respirations. To the hy-
perpnea induced by heat the term thermo- polypnea is frequently
given.

Muscle activity, especially if it is violent and indulged in by
those unaccustomed to exercise, is generally followed by increased
rate and depth of breathing, and not infrequendy it is attended with
such extreme difficulty that the condition approximates that of
dyspnea. This condition is attributed to the production and dis-
charge into the blood of unknown waste products which act as
irritants to the respiratory center and thus increase its activity.
As they apparently can not be isolated and their chemic nature deter-
mined, it is presumable that they are speedily oxidized or reduced
in the blood. Experiment has shown that the increase of carbon

378 TEXT-BOOK OF PHYSIOLOGY.

dioxid does not account for the increased rate of breathing. Emo-
tional states temporarily increase respiratory activity. With their
disappearance the normal condition returns.

Apnea. — If the respiratory movements be voluntarily increased
in frequency and depth for a short time it will be found on cessation
that for a variable length of time the respiratory mechanism remains
in a condition of complete rest or inaction. To this complete cessation
of activity the term apnea is given. The same phenomenon is
witnessed in animals when the lungs are rapidly inflated with air by
means of bellows. At one time this was attributed to an excess of
oxygen in the blood (the result of the forced ventilation of the lungs),
complete saturation of the plasma and hemoglobin, in consequence of
which the respiratory center remained inactive. This has been dis-
proved, however, by modern chemic analyses of the blood. The
condition is now attributed:

1. To increased ventilation of the lungs and an increased percentage

of oxygen in the alveoH, as a result of which the normal percentage
of oxygen in the blood can be maintained for a longer period than
usual.

2. To a stimulation of the peripheral terminations of the pneumo-

gastric nerve whereby the discharge of nerve impulses from the
respiratory center is temporarily inhibited. Division of the
pneumogastric nen^e prevents the development of the apneic
condition.

Dyspnea. — Excessive and laborious respiratory movements
constitute a condition known as dyspnea. Movements of this char-
acter indicate that the blood is deficient in oxygen or overcharged
with carbon dioxid. In either case the excitabihty of the respiratory
center is abnormally heightened. These conditions of the blood
may be caused: (i) By all those pathologic conditions of the respiratory
apparatus which limit the free entrance of oxygen into and the free
exit of carbon dioxid from the blood; (2) by those alterations in the
composition of the air and subsequently in the blood which arise when
the individual is confined in a space of moderate size with imperfect
ventilation. The want of oxygen in the blood gives rise to more
forcible inspirations; the presence of CO, in excess, to more forcible
expirations — showing that the former condition affects the inspiratory
portion of the respiratory center, the latter condition the expiratory
portion. A deficiency in the amount or quality of the hemoglobin
is usually attended with dyspnea.

Asphyxia.^ — If the state of the blood observed in dyspnea be ex-
aggerated,— that is, if the decrease in the percentage of oxygen and
the increase in the percentage of carbon dioxid become more
marked, — the respiratory movements become more laborious. A
continuance of this changed composition of the blood eventuates

RESPIRATION. 379

in death. Before this occurs the individual exhibits a succession
of phenomena, to the totahty of which the term asphyxia is given.

Asphyxia may be caused: (i) By a sudden interference with the
entrance of oxygen into and the exit of carbon dioxid from the blood,
as in drowning, occlusion of the trachea from any cause, double
pneumothorax, etc. (2) By confinement in a small space the air
of which speedily undergoes a loss of oxygen and an accumulation of
carbon dioxid. In the first instance death may occur in a few minutes ;
in the second instance it may be postponed several hours or more,
the time varying with the size of the space.

The succession of phenomena presented by an individual in the
asphyxiated condition is as follows : Increased rate and depth of the
respiratory movements, passing rapidly from hyperpnea to dyspnea,
with an active contraction of all the muscles concerned in respira-
tion, ordinary and extraordinary; a blue cyanosed condition of the
face from the rapid accumulation of carbon dioxid and disappearance
of the oxygen of the blood; a diminution in the depth of inspiration
and an increase in the force and extent of expiration, followed by
general convulsions; collapse, characterized by unconsciousness, loss
of the reflexes, relaxation of the muscles, a weak action of the heart,
a disappearance of the pulse and death. As shown by observation
of the circulatory apparatus in artificially induced asphyxia, there is
primarily an increase in the activity of the heart, soon followed by
retardation; a rise of blood-pressure in the early stages and a fall to
zero after collapse has set in. The retardation and final cessation of
the heart, as well as the rise of the blood-pressure, are to be attributed
to stimulation of the cardio-inhibitory and vasomotor centers from
the accumulation of the carbon dioxid. With the exhaustion of the
nerve-centers, there is a general relaxation of the muscles and a fall
of the pressure.

THE NERVE MECHANISM OF RESPIRATION.

The nerve mechanism by which the respiratory muscles are ex-
cited to action is extremely complex and involves the action of both
afferent and efferent nerves and their related nerve-centers in the cen-
tral nerve system. For the free introduction of air into the lungs it is
essential that the nasal and laryngeal passages and the cavity of the
thorax be simultaneously enlarged. The muscles by which these
results are accomplished have already been mentioned and described.
Their simultaneous and coordinate contraction implies the coordinate
activity of motor nerves and their centers; thus, the nasal and laryn-
geal muscles (the dilator naris and the posterior crico-arytenoid)
involve the activity of the facial and inferior laryngeal nerves re-
spectively, the centers of origin of which lie in the gray matter beneath

38o TEXT-BOOK OF PHYSIOLOGY.

the floor of the fourth ventricle; the diaphragm and intercostal
muscles involve respectively the activity of the phrenic and inter-
costal nerves, the centers of origin of which He in the anterior horn
of the gray matter of the spinal cord at a level, for the phrenic, of the
fourth, fifth, and sixth cer^dcal nerves, and for the intercostals at the
level of the upper thoracic nerves. Division of any one of these nerves
is followed by paralysis of its related muscle.

The coordinate contraction of the inspirator}" muscles implies
a practically simultaneous discharge of nerve impulses from each of
the foregoing ner\'e- centers, accurately graduated in intensity in
accordance with inspiratory needs. This has been supposed to
necessitate the existence in the central nerve system of a single
group of nerve-cells from which ner^x impulses are rhythmically
discharged and conducted to the pre^dously mentioned nerve-centers
in the medulla oblongata and spinal cord, by which they are in
turn excited to activity. To this group of cells the term "inspiratory
center" has been given. For the free exit of air from the lungs it is
not only essential that the air-passages be open, but that the air in
the lungs be compressed until its pressure rises above that of the
atmosphere. This is accomplished by the recoil of the elastic tissue
of the lungs and thorax, the return of the displaced abdominal organs
aided by atmospheric pressure, and the contraction of the expiratory
muscles. In how far muscle action is necessar}^ for expirator}^ pur-
poses vdll depend on the resistance offered to the outflow of air and
on the degree of efficiency of the elastic forces. The simultaneous and
coordinate activity of the expiratory muscles also involves the action
of motor nerves and nerve-centers. The simultaneous and coordinate
discharge of ner^^e impulses, also graduated in intensity for expirator}'-
needs, apparently imphes the existence in the central nerv^e system
of a single center from which nen'e impulses are rhythmically dis-
charged which excite and coordinate the lower nerve-centers. To
this group of cells the term "expiratory center" has been given.
The two centers taken together constitute the so-called "respiratory
center,"

The existence, however, of a definite group of cells which initiates
the respirator}^ movements has not as }^et been demonstrated. Never-
theless there is in the dorsal portion of the medulla oblongata, at the
level of the sensor}^ end-nucleus of the vagus nerv^e, a region the sudden
destruction of which on one side is followed by a cessation of respira-
tory movements on the corresponding side, though they continue on
the opposite side, a fact which indicates that the area, though acting
as a unit, is bilateral. The bilateral character of the area is also
showm by the continuance of the respirator}- movements on both sides
after longitudinal division of the medulla. Destruction of the entire
region is followed by a complete cessation of respiratory activity and

RESPIRATION. 381

death of the animal. For this reason the term "noeud vital" was
applied to it. In this area the respiratory center was located. It has,
however, been shown by Gad that if this area be gradually destroyed
by cauterization the respiratory movements do not cease, but con-
tinue until the cauterization has reached a point far forward in
the formatio reticularis, in which the respiratory center was assumed
to lie.

Though its existence has not been anatomically determined
beyond question, it is permissible to speak of the central mechanism
as a "center" located in the medulla oblongata.

The activity of the respiratory center has long been described as
automatic or autochthonic (Gad) in character, expressive of the idea
that the rhythmic discharge of nerve impulses is conditioned by the
composition of the blood or lymph by which it is surrounded. Thus
so long as the blood retains its normal composition the respiratory
movements are normal. If, however, the blood becomes richer in
oxygen and poorer in carbon dioxid, the rate of discharge of nerve
impulses and the inspiratory movements diminish until the condition
of apnea results. If, on the contrary, the blood becomes poorer in
oxygen and richer in carbon dioxid, the reverse condition obtains:
viz., an increased rate of discharge of nerve impulses, increased fre-
quency of respiration, hyperpnea, and dyspnea. This view is ap-
parently supported by the fact that after division of the fifth and
vagus nerves the respiratory movements continue, though changed
in character, becoming less frequent and deeper. Whether they
would continue after division of all afferent nerves it is impossible
to state, since from the nature of the case such an experiment would
be most difficult to perform.

The first inspiration after birth is supposed to be due to the direct
stimulation of the respiratory center by the increase in the carbon
dioxid present in the blood, though it may be aided by the cooling
of the skin due to vaporization of the amniotic fluid.

Whether the respiratory center is automatic in character or not,
it may be influenced directly by nerve impulses descending from the
brain in consequence of volitional acts or emotional states, and in-
directly by nerve impulses reflected to it from the general periphery
through various afferent nerves, in consequence of agencies acting
on their peripheral filaments: e. g., cold applied to the skin, irritating
gases to the nasal and bronchial mucous membrane, distention and
collapse of the pulmonary alveoli.

Of all afferent nerves, the vagus appears to be the most influential in
maintaining the rhythmic discharge of nerve impulses from the respi-
ratory center. Thus, if while the animal is breathing regularly and
quietly both vagi are cut, the respiratory movements become much
slower, falling perhaps to one-third their original number per minute.

382 TEXT-BOOK OF PHYSIOLOGY.

If the central end of the divided vagus be stimulated with weak
faradic currents, the respiratory movements are increased in fre-
quency and their depth diminished until the normal rate is restored.
With the cessation of the stimulation the former condition at once
returns. This would indicate that in the physiologic state afferent
impulses are ascending the vagus fibers .which influence the rate of
discharge from the respiratory center. If, however, the stimulation
is increased in strength, the inspiratory movement gradually so ex-
ceeds the expiratory that the muscles pass into the tetanic state and
the chest-walls come to rest in the condition of forced inspiration.
The vagus evidently contains fibers which augment the activity of the
inspiratory center and inhibit the activity of the expiratory center.
If, on the other hand, the central end of the divided superior laryngeal
nerve be stimulated with faradic currents, the opposite effect is pro-
duced: viz., an excess of the expiratory over the inspiratory move-
ment until the chest-walls come to rest in the condition of forced
expiration. The superior laryngeal nerve evidently contains fibers
wtdch augment the activity of the expiratory center and inhibit the
activity of the inspiratory center.

The same result not infrequently follows stimulation of the divided
vagus and always after the administration of large doses of chloral.
The vagus contains two classes of fibers, one of which augments the
activity of the inspiratory while inhibiting the activity of the ex-
piratory; the other inhibiting the inspiratory while augmenting the
expiratory. The stimulus adequate to the excitation of the nerve-
fibers in the physiologic condition was formerly believed to be the
chemic action of carbon dioxid; it is now believed to be a mechanic
action, the result of the alternate distention and collapse of the walls
of the pulmonary alveoli. Thus, it has been shown by Head that
if the lungs are actively inflated there will be produced an inhibition
of the inspiratory and an augmentation of the expiratory movement
until the chest comes to rest, a result similar in all respects to that
produced by stimulation of the superior laryngeal nerve. On the
other hand, if the lungs are collapsed by the artificial withdrawal
of air, there will be produced an augmentation of the inspiratory
and an inhibition of the expiratory movements until the chest comes
to rest in extreme inspiration, a result similar in all respects to that
produced by powerful stimulation of the central end of the divided
vagus. These facts indicate that the respiratory mechanism is reflex
and self-regulating in character, and the stimulus, the alternate
collapse and distention of the pulmonary alveoli ; collapse augmenting
the inspiratory and inhibiting the expiratory, distention, inhibiting
the inspiratory and augmenting the expiratory center.

RESPIRATION. 383

THE EFFECT OF THE RESPIRATORY MOVEMENTS ON THE FLOW OF

BLOOD THROUGH THE INTRA-THORACIC VESSELS AND

ON THE ARTERIAL PRESSURE.

1 . On the Intra-thoracic Vessels. — The forces which cause the
air to How into and out of the kings will at the same time and in the
same way cause the blood of the systemic vessels to How into, through,
and out of the intra-thoracic vessels. From the tendency of the pul-
monary elastic tissue to recoil, the blood-vessels in the thorax at the
end of an expiration sustain a positive pressure, about six millimeters
of mercury less, than that in the lungs, or, in other words, a pressure
negative to that of the atmosphere by six millimeters. As a result
the blood in the systemic vessels standing under atmospheric pressure
will flow steadily toward the intra-thoracic veins, the venae cavai,
and the right side of the heart; i. e., from a point of high to a point of
low pressure. Since during inspiration, with the increasing tendency
to pulmonary recoil, the positive pressure on the veins and heart may
diminish by thirty millimeters of mercury, the blood will flow in
increased volume from the systemic to the intra-thoracic vessels.
The right heart, being more generally filled with blood, will discharge
a larger volume with each contraction into the pulmonary artery.

Coincident with these effects a similar effect is produced in the
arterioles and capillaries of the pulmonary alveoli. Situated between
the two elastic layers of the alveolar wall, embedded in a meshwork
of connective tissue, the pressure to which they are subjected at the
end of an expiration will also be a few millimeters less than that of
the intra-pulmonary air; and at the end of an inspiration it will be
considerably less. With the inspiration there will occur a dilatation
of the vessels, a larger flow of blood through them and into the pul-
monary veins. The left heart, being in consequence more generously
filled with blood, will discharge a larger volume into the aorta at each
contraction. During expiration the flow of blood through the intra-
thoracic vessels will be diminished for the reverse reasons.

2. On the Arterial Pressure. — An examination of a tracing of
the arterial pressure will show that it is characterized by small un-
dulations due to the cardiac beat and large undulations due to the
respiratory movements, inspiration being accompanied by a rise,
expiration by a fall of pressure. These results are readily accounted
for by the difference in the volume of blood discharged by the left
heart into the aorta during the time of the two movements. If a
tracing of the respiratory movements and of the blood-pressure be
taken simultaneously, it will be found that the rise of pressure does not
exactly correspond with inspiration, nor the fall of pressure with
expiration; for a certain period after the beginning of an inspiration
the pressure continues to fall, and for a certain period after the
beginning of an expiration the pressure continues to rise. During

384 TEXT-BOOK OF PHYSIOLOGY.

the remainder of the period, however, inspiration is attended by
a rise, expiration by a fall of pressure. The explanation of these
results hes in the fact that at the beginning of the inspiration, when
the vessels dilate, the blood-flow momentarily slows; the left heart
continuing to discharge small volumes into the aorta, the pressure
continues to fall. So soon as the left heart begins to be better filled, the
pressure at once begins to rise. At the end of an expiration the flow
of blood into the left heart continues and the pressure rises, but with
the return of the intra-thoracic pressure the vessels diminish in caliber,
the volume of blood transmitted by them becomes less, the output
of the left heart dechnes, and the pressure falls.

CHAPTER XIV.
ANIMAL HEAT.

The chemic changes which take place in the tissues and organs
of the Kving body and which underlie all manifestations of hfe are
attended by the evolution of heat. In consequence of this each
animal acquires a certain body-temperature.

In man, as well as in other mammals and in birds, the chemic
changes are extremely active and the evolution of heat very great.
Through some special heat-regulating mechanism, by which heat-
production and heat-dissipation are kept in equihbrium, these animals
have acquired and maintain within limits a constant temperature
which is independent of and generally above that of the surrounding
atmosphere. As the temperature of these animals is high and per-
ceptible to the sense of touch, they were originally designated "warm-
blooded" animals. As this temperature is constant notwithstanding
the great variations in external temperature during the summer and
winter seasons, they are more appropriately termed constant-tem-
peratured or homoiothermous animals. The intensity of the body-
temperature determined by the insertion of a thermometer in the
rectum varies in different classes of mammals from 37.2° C. to 40° C.
The causes of this variation are doubtless connected with pecuharities
of organization. In birds the rectal temperature is usually higher,
varying from 40.9° C. in the pigeon to 44° C. in the titmouse and
the swift.

In reptiles, amphibians, and fish chemic changes, as a rule, are
not very active and heat-production relatively shght. As they are
devoid of a sufficiently active heat-regulating mechanism, the tem-
perature of the body is largely dependent on that of the medium in
which they hve, though it is always one or more degrees above it. In
winter the body-temperature of frogs, for example, may dechne as
low as 8.9° C, the temperature of the surrounding medium being
6.7° C. When subjected to temperatures below zero, the temperature
of the body may fall below the freezing-point also, when the lymph
and jfluids of the body become ice. Though apparently dead, the
gradual elevation of the temperature restores their vitaUty. In
summer-time, on the contrar}', the body-temperature may attain to
38° C. Similar variations have been observed in other animals. As
the temperature of these animals is low and perceptibly below that of
our own bodies, thev were originallv termed "cold-blooded" animals;
^5 ' Z^S

386 TEXT-BOOK OF PHYSIOLOGY.

as their temperature is inconstant, varying with the temperature of
the surrounding medium, tliey are more appropriately termed "varia-
ble temperatured" or poikilo-tJiermous animals.

THE TEMPERATURE OF THE HUMAN BODY.

The determination of the temperature of the human body under
the changing conditions of life is a matter of the greatest physiologic
and chnical interest. The temperature of the superficial portions of
the body may be obtained by the introduction of a thermometer into
the mouth, the rectum, the vagina, or the axilla. As a result of many
observations it has been found that the temperature of the rectum is,
on the average, 37.2° C; that of the mouth, 36.8" C; that of the
axilla, 36.9° C. Owing to radiation and conduction the surface tem-
perature is lowTr than that of either the mouth or rectum, and varies
to a sHght extent in different regio"ns of the body: e. g., at a room-
temperature of 20° C. the skin of the pectoral region has a tem-
perature of 34-7°; that of the cheek, 34.4°; that of the calf, 33.6°;
that of the tip of the ear, only 28.8°, etc.

In the interior of the body, especially in organs in which oxidation
takes place rapidly, and which at the same time are protected by
their anatomic surroundings from rapid radiation, the temp'erature
is higher than that observed in the rectum. From an investigation
of the temperature of the blood as it emerges from the liver, the
muscles, the brain, alimentary canal etc., it is evident that these
organs have a higher temperature than the rectum.

As the chemic changes underlying physiologic activity vary in
intensity and extent in different regions of the body, there would be
marked variations in their temperature were it not that the blood,
having a large capacity for heat-absorption, distributes the heat
almost uniformly to all portions of the body, so that at a short distance
beneath the surface the temperature does not vary but within a few
degrees.

In the dog the temperature of the blood in the aorta and in its
principal branches is approximately 38.3° C. In passing through
the systemic capillaries the temperature falls from radiation and con-
duction to surface temperature, to again rise as the venous blood
approaches the deeper regions of the body. In the neighborhood
of the renal veins and in the superior vena cava the temperature is
again that of the aorta. In the portal vein the temperature rises to
40.2° C. ; in the hepatic vein, to 40.6° C. In the right ventricle, owing
to the admixture of blood from different localities having different
t'::mpcratures, the temperature falls to 38.2° to 40.4°. In passing
through the pulmonary capillaries the temperature of the blood again
falls, so that in the left ventricle it will register from 38° C. to 40.2° C.

ANIMAL HEAT. 387

There is thus usually a ditlerencc between the two sides of the heart
of about 0.2° C.

Variations in the Mean Temperature. — The mean tempera-
ture of the human body for twenty-four hours, which for the mouth
and rectum may be accepted at 36.7° C. and 37.2° C. respectively, is
subject to variations from a variety of circumstances, such as age,
periods of the day, food, exercise, etc.

Age. — At birth the temperature of the infant is shghtly higher
than that of the mother, registering in the rectum about 37.5° C. In
a few hours it rapidly dechnes to about 36.5°, to be followed in the
course of twenty-four hours by a rise to the normal or shghtly beyond.
During childhood the temperature gradually approximates that of
the adult. In old age the temperature rises, as a rule, and attains a
maximum at eighty years of 37.4° C.

Periods 0} the Day. — The observations of Jiirgensen show that
there is a diurnal variation in the mean temperature of from 0.5° C.
to 1.5° C, the maximum occurring late in the afternoon, from 5 to 7
o'clock, the minimum early in the morning, from 4 to 7 o'clock. This
diurnal variation in the mean temperature is related to corresponding
variations in many other physiologic processes, and its causes are to
be found in the ordinary habits of hfe as regards the time of meals,
periods of exercise, sleep, etc.

Food and Drink. — The ingestion of a hearty meal increases the
temperature but slightly — not more than 0.5° C. Insufficiency of
food lowers the temperature; total withdrawal of food, as in starva-
tion, is followed by a steady though slight dechne, until just preceding
the death of the animal, when it falls abruptly to from 6° to 8° C.
Cold drinks lower, hot drinks raise the temperature. Food and
drinks, however, only temporarily change the mean temperature,
and after a short period equihbrium is restored through the activity
of the heat-regulating mechanism. Alcoholic drinks lower the tem-
perature about 0.5° C. In large toxic doses in persons unaccustomed
to their use the temperature may be lowered several degrees. This
is attributed not to a diminution in heat-production, but rather to
an increase in heat-dissipation (Reichert) from increased action of
the heart, dilatation of the blood-vessels of the skin, and increased
activity of the sweat-glands.

Exercise. — The temperature may be raised by active muscular
exercise from 1° to 1.5° C. as a result of increased activity in
chemic changes in the muscles themselves. A rise beyond this point
is prevented by the increased activity of the circulatory apparatus,
the removal of the heat to the surface, and its rapid radiation.

External Temperature. — The external temperature influences but
slightly the mean temperature of the human body. In the tropic
as well as in the arctic regions, notwithstanding the change in the

388 TEXT-BOOK OF PHYSIOLOGY.

temperature of the air, that of the body remains almost constant.
The same is true for the seasonal variations in the temperature of
the temperate regions.

THE SOURCE AND TOTAL QUANTITY OF HEAT PRODUCED.

The Source of Heat. — The immediate source of the body-heat
is to be found in the chemic changes which take place in all the tissues
and organs of the body. Each contraction of a muscle, each act of
secretion, each exhibition of nerve-force, is accompanied by the
evolution of heat. The chemic changes are for the most part of the
nature of oxidations, the union of oxygen with the elements, carbon
and hydrogen, of the food principles either before or after they have
become constituents of the tissues. The ultimate source of the body-
heat is the latent or potential energy in the food principles, which was
absorbed from the sun's energy and stored up during the growth of
the vegetable world. In the metaboHsm of the animal body the food
principles are again reduced through oxidation, directly or indirectly,
to relatively simple bodies, such as urea, carbon dioxid, and water,
with a hberation of a large portion of their contained energy which
manifests itself as heat and mechanic motion.

The Total Quantity.- — The total quantity of heat hberated in
the body daily may be approximately determined in at least two ways :
(i) By determining experimentally the heat values of different food
principles by direct oxidation; (2) by collecting and measuring with
a suitable apparatus, a calorimeter, the heat evolved by the oxidation
of the food within, and dissipated from, the body daily.

I. Direct Oxidation. — The amount of heat which any given food
principle will yield can be determined by burning a definite amount —
e. g., I gram — to carbon dioxid and water and ascertaining the extent
to which the heat thus hberated will raise the temperature of a given
amount of water: e. g., 1 kilogram. The amount of heat may be
expressed in gram or kilogram degrees or calories; a gram calorie
or kilogram calorie being the amount of heat required to raise the
temperature of a gram or a kilogram (1000 grams) of water 1° C.
The apparatus employed for this purpose is termed a calorimeter,
which consists essentially of a closed chamber, in which the oxidation
takes place, surrounded by a water-jacket. The rise in temperature
of the water indicates the amount of heat produced.

The results obtained by investigators employing different calor-
imeters and different food principles of the same class vary, though
within narrow hmits: e. g., 1 gram casein yields 5.867 kilogram
calories; i gram of lean beef, 5.656; i gram of fat, 9.353, 9.423, 9.686
calories; i gram of starch or sugar, 4.1 16, 4.182, 4.479, etc., calories.
These results are, however, physical values, and indicate the quan-

ANIMAL HEAT. 389

tity of heat such quantities of foods give rise to when completely
oxidized to carbonic acid and water. In the human body the carbo-
hydrates and the fats, with the exception of the small portion which
escapes digestion, are reduced to carbon dioxid and water, and hence
practically liberate as much heat as they do when oxidized outside
the body. The proteids, however, are only reduced to the stage of
urea. As this compound is capable of further reduction in the calor-
imeter to carbon dioxid and water, with the liberation of heat, the
quantity of heat it contains must therefore be deducted from the
physical heat value of the proteid. According to Rubner, i gram
of urea will yield 2.523 kilogram calories. As about one-third of a
gram of urea results from the oxidation of i gram of proteid, the
amount of heat to be deducted from the heat value of the proteid is
■^ of 2.523, or 0.841 calorie. It has also been shown by the same in-
vestigator that some of the ingested proteid is found in the feces, the
heat value of which must also be determined and deducted. This
having been done, the physiologic heat value becomes 4.124 calories.
The following estimates give approximately the number of kilo-
gram calories which should be liberated within the body when the
proteid is burned to the stage of urea, and the fat and carbohydrate
to the stage of carbon dioxid and water:

I gram of proteid . 4-124 calories

I " fat 9.353

I " carbohydrate 4. 116 "

The total number of kilogram calories yielded by the various diet
scales can be readily determined by multiplying the quantities of the
food principles consumed by the foregoing factors. The diet scale
of Vierordt, for example, yields the following:

120 grams of proteid 494.88 calories

90 " fat 841.77 "

330 " starch 1358.28 "

Total, 2694.93 "

The total calories obtained from other diet scales would be as follows :
Ranke's, 2335; Voit's, 3387; Moleschott's, 2984; Atwater's, 3331;
Hultgren's, 3436. These numbers indicate theoretically the total
heat-production in the body daily.

2. Calorimetric Measurements. — By this method the heat dissi-
pated from the body of an animal is directly collected and measured,
and the amount so obtained is taken as a measure of the heat evolved
by the oxidation of the food. A calorimeter is therefore an apparatus
for the direct estimation of the quantity of heat dissipated from the
body in a given time. The substance employed for collecting and
measuring: the heat is either water or air. The calorimeters in

390

TEXT-BOOK OF PHYSIOLOGY.

general use consist essentially of two metallic boxes placed one within
the other, though separated by a space sufficiently large to hold a
definite amount of water (Fig. i8o). The animal is placed in the
inner box, which is also provided with tubes for the entrance of fresh
and the exit of expired air. The heat radiated is absorbed by the
water and its temperature raised. To prevent loss by radiation and to
render it independent of changes in the surrounding temperature the
calorimeter is surrounded by a poorly conducting material, such as
wool. The temperature of the animal is taken at the beginning and
the end of the experiment. If the temperature of the animal remains
the same at the end of the experiment, then the heat absorbed by the

water represents the
amount produced by the
animal. If, on the con-
trary, the temperature of
the animal rises or falls,
the number of calories
so retained or lost must
be added to or sub-
tracted from the amount
absorbed by the calor-
imeter. In the determi-
nation of the absolute
amount of heat retained
or lost by the animal
above or below the initial
temperature, as well as
that absorbed by the
materials of the appara-
tus in these various in-
stances, the water equiv-
alent of the tissues of the
animal and the materials
of the calorimeter must
be obtained, and then added to or subtracted from, as the case may
be, the amount of water in the calorimeter, and the amount thus ob-
tained multiplied by its rise in temperature. In properly conducted
experiments in which the sources of error are reduced to a minimum
there is a very close correspondence between the total physiologic heat
value of the food and the amount collected by the calorimeter. Thus,
in an experiment detailed by Rubner a dog was given during twelve
days 228.06 grams of proteid and 340.4 grams of fat the physical heat
value of which was estimated at 4429 calories. The urine and feces
during this period were collected and their heat value determined,
which amounted to 305 calories. The heat which theoretically

Fig. 180. — Water Calorimeter of Dulong. D
and D'. Tubes for the entrance and exit of
air. T and T'. Thermometers for ascertain-
ing the temperature of the water. S. A
mechanic contrivance for stirring the water for
the purpose of distributing the absorbed heat
uniformly. To prevent the escape of heat
with the expired air, the tube D' is wound
many times in the water-space beneath the
animal cage.

ANIMAL HEAT. 391

should have been produced was 4124 calories. During the experi-
ment the calorimeter actually absorbed 3958 calories, a difference
between the theoretic and experimental results of 156 calories.

Calorimetric experiments on man corresponding to those made
by Rubner on dogs have not been successful, owing purely to tech-
nical difficulties. Various attempts have been made, however, to
determine the daily heat-dissipation. Liebermeister immersed a
man in a bath with a temperature lower than that of the man's body.
From the rise in temperature of the water it was calculated that the
man produced daily 3525 calories. Leyden placed the leg alone of
a man in a calorimeter. In one hour 6 calories were absorbed.
Assuming that the total superficial area of the body was fifteen times
that of the leg, he calculated, taking into consideration various
sources of error, that the entire body would produce daily 2376 cal-
ories. Ott, employing a water calorimeter, found that the body of a
man produced 103 calories during an afternoon, or at the rate of
2472 calories daily. These and similar experiments, while not free
from many objections, furnish results which indicate that the heat
dissipated from the body approximates the physiologic heat values
of the foods.

HEAT-DISSIPATION AND REGULATION OF THE TEMPERATURE.

Heat-dissipation. — From the preceding statements it is evident
that the body is continually evolving heat in amounts daily far in
excess of that necessary for the maintenance of the body-temperature.
Should this heat be retained, the temperature of the body would be
raised at the end of twenty-four hours an additional 18° or 20° C, —
a temperature far in excess of that compatible with the maintenance
of physiologic processes. That the body may be kept at the mean
temperature of 37.8° C. it is essential that the heat evolved be dissi-
pated as fast as produced. This is accomplished in several ways:
(i) In warming the food and drink to the temperature of the body.
(2) In warming the inspired air to the same temperature. (3) In
the evaporation of water from the lungs. (4) In evaporating water
from the skin, (5) In radiation and conduction from the skin.
The quantities of heat lost to the body by these different processes
it is difficult for obvious reasons to accurately determine, and the
estimates usually given must be regarded only as approximative.

Assuming 2500 calories to be an average amount of heat liberated
during a day of repose, the losses, in the ways stated above, may be
given as follows :

I. In Warming Food and Drink. — The average temperature of food
and drink is about 12° C; the amount of both together is about
3 kilograms; the specific heat of food about 0.8. The absorption

392 TEXT-BOOK OF PHYSIOLOGY.

of body-heat therefore amounts to 3 X 0.8 X 25° C. = 60 calories
= 2.8 per cent. With the removal of the end-products of the
foods and drink from the body an equal amount of heat is carried
out.

2. In Warming the Inspired Air. — The average temperature of the

air is 12° C; the amount of inspired air, about 15 kilograms;
the specific heat of air, 0.26. The absorption of body-heat by
the air therefore amounts to 15 X 0.26 X 25° = 97.5 = 3.8
per cent. The expired air removes from the body a corre-
sponding volume.

3. In the Evaporation of Water from the Lungs. — The quantity of

water evaporated from the lungs may be estimated at 400 grams ;
as each gram requires for its evaporation 0.582 calorie, the
quantity of heat lost by this channel would be 400 X 0.582 =
232.8° C. = 9.4 per cent.

4. In the Evaporation of Water from the Skin. — The quantity of

water evaporated from the skin may be estimated at 660 grams,
causing a loss of heat by this channel of 660 X 0.582 = 384.1°
C. = 15.3 per cent.

5. In Radiation and Conduction from the Skin. — The amount of

heat lost by this process can be indirectly determined only by
subtracting the total amount lost by the above-mentioned
channels from the total amount produced. Thus, 2500 — 774-4
= 1725.6 = 69 per cent, would represent the average amount lost
by radiation and conduction.

Regulation of the Mean Temperature. — In order that the
mean temperature of the body may remain practically constant, the
heat produced must be exactly balanced by the heat dissipated. Should
there be any want of correspondence between the two processes, there
would arise either an increase or a decrease in the mean temperature.
As both heat-production and heat-dissipation are variable factors,
dependent on a variety of internal and external conditions, their
adjustment is accompHshed by a complex self-regulating mechanism
involving muscular, vascular, and secretory elements, co5rdinated by
the nerve system. Heat-production varies in intensity and amount,
in accordance with a number of conditions, but principally with
variations in physiologic activity, the quantity and quality of the
food, and changes in the external temperature. All physiologic and
especially muscle activity is attended by chemic changes and the
evolution of heat. The greater the activity, the larger is the volume
of heat. Foods have different physiologic heat values. If the food
consumed contains much potential energy and the quantity con-
sumed be larger than the average daily requirements, there will be
an increase in heat-production. A lowering of the external .tem-
perature, as in the winter season, leads to increased heat-production

ANIMAL HEAT. 393

through stimulation of the nerve-centers. When all these conditions,
increased muscular activity, increased amount of food of high poten-
tial energy, and a low external temperature coexist, heat-production
attains its maximum, amounting to as much as 4726 calories daily
(Hultgren).

Heat-dissipation varies in rapidity in accordance with variations
of a number of factors, but principally with variations in the external
temperature and the activity of the perspiratory apparatus. The
heat is dissipated mainly by the skin, 69 per cent., in consequence of
radiation and conduction and by the evaporation of the sweat. The
loss by this channel as well as from the lungs is dependent for the
most part on a difference of temperature of the surrounding air and
of the body. If the surrounding temperature is high, there is an
increase in the activity of both the circulatory and respiratory mechan-
isms, brought about by the central nervous system. In addition to
an increased action of the heart, the blood-vessels of the skin dilate
and deliver to the surface a larger volume of blood in a given time,
thus increasing the conditions favorable to radiation. The sweat-
glands at the same time are stimulated to increased activity, and
in consequence of the additional volumes of blood brought to the skin
a larger amount of sweat is secreted, which speedily undergoes evap-
oration. As each gram of water for its evaporation requires 0.582 of
a calorie, it is evident that increased secretion of sweat favors heat-
dissipation. The nerve-centers influencing the activity of the sweat-
glands may be stimulated not only refiexly, but directly by an excess
of heat in the blood. If, however, the atmosphere itself possesses a
high percentage of moisture, evaporation from the body is much
diminished and the value of sweating as a means of lowering the
body-temperature is much impaired. Evaporation is hastened by
air in motion. Hastened respiratory movements and the dilatation
of blood-vessels of the respiratory surface also increase the evaporation
of water from the lungs and thus occasion a greater loss of heat.

If the external temperature falls there is a decrease in the physio-
logic activity of the skin from a contraction of the blood-vessels, a
diminution of the blood-supply, and a cessation in the secretion of
sweat. The blood, being prevented from coming to the surface, is
retained in the deeper portion of the body, and in consequence the
conditions for radiation are diminished. These variations in the
cutaneous circulation in response to variations in the external tem-
perature are brought about by the vasomotor nerve mechanism; and
as they take place with extreme promptness heat-dissipation and heat-
production are quickly adjusted and the mean temperature main-
tained.

Radiation from the skin is modified to some extent by clothing.
An excess of clothing diminishes, a diminution of clothing increases

394 TEXT-BOOK OF PHYSIOLOGY.

radiation. The quality of clothing is also an important factor.
Wool is a poor conductor of heat but a good absorber and retainer of
moisture, and hence is adapted for cold weather. Linen and cotton
possess the opposite qualities, and hence are adapted for warm
weather. Radiation from the skin is somewhat interfered with by
subcutaneous fat, the extent of the interference being dependent on its
amount.

The foregoing estimates as to the amounts of heat produced have
reference only to the body in repose. When the body passes into a
state of muscle activity, there is at once a notable increase in heat-
production in consequence of the increase in the activity of the chemic
changes which underlie body activity, as shown by the increase in the
consumption of oxygen and the production of carbon dioxid. Not
all of the potential energy set free, however, appears as heat; for
if the muscles are engaged in doing work a part of the energy which
would othen^dse manifest itself as heat is converted into mechanic
motion. From the work done during a period of eight hours it has
been estimated that about 500 calories are so transformed or utilized.
Hirn calculated from an average of five experiments that a man
weighing 67 kilos in repose produced 154.4 calories per hour and
absorbed 30.7 grams of oxy^gen per hour; but when engaged in active
muscle movements produced 271.2 calories and absorbed 119.84
grams of oxygen per hour. The increase in heat-production per hour
during acti\dty was thus almost doubled, though the sum total pro-
duced daily in which there was a working period of eight or ten hours
was only about one-third more than during a day of repose. During
sleep there is a greatly diminished heat-production, not more than
40 calories per hour being produced. The preceding data may be
tabulated as follows (Martin) :

Day of Rest. Day of Work.

Heat units'Ccalor- ~l Rest 16 hrs. Sleep 8 hrs. Rest 8 hrs. Work 8 hrs. Sleep 8 hrs.
ies) produced- _ / 2470.4 320 1235-2 2169.6 320

2790.4 3724-8

CHAPTER XV.

SECRETION.

Secretion. — As the blood flows through the capillaries of the
body certain of its nutritive principles are separated by the activity
of the epithelial cells of the capillary wall, aided by the physical
processes of filtration and diffusion. To this process the term
secretion may be applied. This separated or secreted material may
be utilized in several ways:

1. For the repair of the tissues, for growth, for the hberation of

energ}-.

2. For the elaboration or production by specialized organs of a

variety of complex fluids of widely different application. The
fluids thus formed are utilized for the most part to meet some
special need of the body. All such fluids are termed secretions.
The organs concerned in the elaboration of the various secretions
are covered or Hned by epithehum to the activity of which the
secretion is to be referred. To all these organs the term gland may
be applied. As these fluids are poured out on the surface of the
body, they have been termed external secretions: e. g., mucus, sahva,
gastric juice, milk, sebaceous matter, etc. Within recent years it has
been demonstrated that the epithehum of glands and particularly
of those which do not possess a duct, such as the thyroid, thymus,
adrenals, hypophysis, etc., also produces certain specific constituents
which are reabsorbed into the blood, and which in some unknown
but yet favorable way influence the general nutrition. To such prod-
ucts of these glands the term internal secretions has been given.

The blood, in addition to its nutritive constituents, contains a
number of principles, derived from the tissues, which are to be
regarded as waste products, the outcome of the metabohc activity
of the tissues and of no further use to the body. If retained, they
would seriously if not fatally interfere with the normal physiologic
activities of the dift'erent tissues. They are therefore removed by
specialized organs after their separation from the blood-stream. The
waste products in solution thus removed are not capable of being
utihzed for any special purpose, and are therefore termed excre-
tions: e. g., urine, perspiration, etc. Excretion, however, is per-
formed by the activities of epithelial cells aided by the physical
forces of diffusion and filtration; and though a distinction is made

395

396 TEXT-BOOK OF PHYSIOLOGY.

between the two classes of fluids, no sharp line can be drawn between
the cell processes which take place in secretory and excretory organs.
All secretory organs may be divided into —

1. Epithehal.

2. Reticular and vascular, the latter term indicating merely their re-

lation to blood-vessels.

The Epithelial Secretory Apparatixs. — The apparatus essential
to the production of a secretion is a delicate homogeneous mem-
brane, on one side of which and in close contact is a layer of capillary
blood-vessels, lymphatics, and nerves; on the other side, a layer of
epithelial cells, the physiologic function of which varies in different
situations.

The epithelial organs may consist of a single layer of cells or a
group of cells, and may be subdivided into —

1. Secreting membranes.

2. Secreting glands.

The secreting membranes are the mucous membranes lining
the gastro-intestinal, the pulmonary, and the genito-urinary tracts,
and the serous membranes lining closed cavities, such as the pleural,
pericardial, peritoneal, and synovial membranes.

The mucous membranes are soft and velvety in character and
are composed of a condensed connective tissue forming a basement
membrane beneath which is a layer of blood-vessels and muscle-fibers,
and on which is a layer of epithelium, the histologic as well as physio-
logic characters of which vary in different situations. The mucus
secreted by the various epithelial forms will very naturally possess a
somewhat different composition, according to the locality in which it
is formed. In a general way it may be said that mucus is a pale,
semitransparent, alkaline fluid, containing leukocytes and epithelial
cells. It is composed chemically of water, mineral salts, and an
albuminoid body, mucin, to the presence of which it owes its vis-
cidity. Much of the mucus is secreted by the goblet cells on the
surface of the mucous membranes. The principal varieties of mucus
are the nasal, bronchial, vaginal, urinary, gastro-intestinal.

The serous membranes are composed of thin membrane formed
by a condensation of connective tissue and covered by a single layer
of large, flat, nucleated cells with irregular margins. These mem-
branes enclose what are practically large lymph sacs or spaces, and
the fluid they contain resembles lymph in all respects and is prac-
tically identical with it. It serves to diminish friction when the
viscera they enclose move over one another. The most important
of the serous membranes are the pleural, pericardial, and peritoneal.

The synovial membranes in and around joints resemble serous
membranes. The cells covering them, however, secrete a clear
colorless fluid resembling lymph, but differing from it in containing

SECRETION. 397

a mucin-like substance, a nucleo-albumin, which imparts to it con-
siderable viscidity. This synovial fluid serves to diminish friction
between the opposing surfaces of the bones as they ghde over one
another during movement.

Other secretions, such as the aqueous and vitreous humors of the
eye, the fluid of the internal ear, the cerebrospinal fluid, etc., will be
considered in connection with the organs with which they are asso-
ciated, as have been the digestive secretions.

The secreting glands are formed of the same histologic elements
as the secreting membranes. They are formed by an involution of
the mucous membrane or skin the epithelium of which is variously
modified structurally and functionally in the various situations in
which they are formed. Like the membranes themselves, the glands
are invested by capiUary blood-vessels and supphed with lymphatics
and nerves, of which the latter are in direct connection with the blood-
vessels and epithehal cells. The interior of each gland is in com-
munication with the free surface by one or more passageways known
as ducts.

These glands may be classified according as the involution is
cyhndrical or dilated as — ■

1. Tubular. The tubular glands may be simple — e. g., sweat-
glands, intestinal glands, fundus glands of the stomach ; or compound
— e. g., kidney, testicle, salivary, and lachrymal glands.

2. Alveolar. The alveolar glands may also be simple — e. g.,
the sebaceous glands, the ovarian follicles, meibomian glands; or
compound, as the mammary glands and salivary glands.

For the production of a secretion it is necessary that the plasma
of the blood, the common material, be delivered to the lymph-spaces
with which the epithelial cells are in close relation. The processes
involved in the passage of the plasma across the capillary wall have
already been considered in connection wath the production of lymph.
They include the physical processes, diffusion, filtration, and osmosis,
combined with a secretory activity of the cells of the capillary wall.
The question as to which of these processes is the more active is yet
a subject of investigation.

As the chemic composition and the chemic features of the organic
constituents of all secretions have been demonstrated to be the out-
come of metabolic processes going on within the epithelial cells, it
must be assumed at least that these differences are correlated with
differences in the histologic features and molecular structure of the
epithehum. The discharge of the secretion is, as a rule, intermittent ;
that is, there are periods of activity on the part of the gland fol-
lowed by periods of inactivity or rest. In rest more especially the
epithehal cells, after the assimilation of lymph, accumulate within
themselves such characteristic products as globules of mucin, gran-

398 TEXT-BOOK OF PHYSIOLOGY.

ules which apparently are the antecedents of the digestive enzymes,
granules of glycogen, globules of fat, sugar, and proteid, as in the
case of the mammary gland. In how far all these compounds are
the result of secretory activity or of a cell degeneration and disinte-
gration it is impossible to state in the hght of present knowledge.
During the period of gland rest the blood-supply to the gland is
merely sufficient for nutritive purposes. When the occasion arises
for gland activity, the blood-vessels, under the influence of the
vasomotor nerves, dilate and deliver to the gland an amount of blood
far beyond that required for nutritive purposes. As a result the gland
becomes red and vascular and the blood emerging by the veins fre-
quently retains its customary arterial color. The increased blood-supply
favors a rapid transudation of water and salts into the lymph-spaces
where they are speedily absorbed and transmitted by the epithelial
cells into the interior of the gland lumen. Coincident with the passage
of water through the cell, the organic constituents are extruded from
the end of the cell bordering the lumen to become dissolved, or in the
case of fat to be suspended, in the water. The secretion thus formed
accumulates, and with the rise of pressure which inevitably follows
it at once passes into the ducts to be discharged on the surface of the
mucous membrane or skin, as the case may be.

Influence of the Nerve System. — The activity of every gland
is controlled by nerve-centers situated in the central nerve system.
These centers may be excited to activity either by impressions made
on the peripheral terminations or by emotional states, or, possibly, by
changes in the composition of the blood itself. As a rule, all normal
secretion is a reflex act involving the usual mechanism: viz., a sentient
surface (skin, mucous membrane, or sense-organ), an afferent nerve, an
emissive cell from which emerges an efferent nerve to be distributed
to a responsive organ, the gland epithelium.

For the production of the secretion by the epithehal cell it
is beheved by some experimenters that two physiologically dis-
tinct, efferent nerve-fibers are involved — one stimulating the pro-
duction of the organic constituents {trophic nerves), the other stimu-
lating the secretion of water and inorganic salts {secretory nerves).
The evidence for the influence of the nerve system on secretion and
the mode of connection of the nerve-fibers with the gland-cells have
been alluded to and will again be in subsequent chapters.

The reticular and vascular glands, though not possessing any
common histologic features, are grouped together merely for con-
venience, and will be considered in a separate chapter in connection
with the problems of internal secretion.

SECRETION.

399

MAMMARY GLANDS.

The mammary glands, which secrete the milk, arc two more or
less hemispheric organs situated in the human female on the anterior
surface of the thorax. Though rudimentary in childhood, they
gradually increase in size as puberty approaches. The gland pre-
sents at its convexity a small conical eminence termed the mammilla
or nipple, surrounded by a circular area of pigmented skin, the
areola. The gland proper is covered by a layer of adipose tissue
anteriorly and is attached posteriorly to the pectoral muscles by a
network of fibrous tissue.

mammary glands become larger,
lirmer, and more lobulated; the
areola darkens and the blood-
vessels, especially the veins, be-
come more prominent. At the
period of lactation the gland is
the seat of active histologic and
physiologic changes correlated
with the production of milk.
At the close of lactation these

Durincr utero-srestation the

K-^.

■^T'

Fig. i8i. — Mammary Gland, i.
Lactiferous ducts. 2. Lobuli of
the^mammary gland.

Fig. 182. — Acini of the Mammary
Gland of a Sheep during Lacta-
tion, a. Membrana propria, h.
Secretory epithelium.

acti\dties cease, the glands diminish in size, undergo involution, and
gradually return to their former non-secreting condition.

Structure of the Mammary Gland. — Each mammary gland
consists of an aggregation of some 15 or 20 irregular pyramidal lobes,
each of which is surrounded by a framework of fibrous tissue. This
tissue affords support for blood-vessels, lymphatics, and nerves.
Each lobe is provided with a single excretory duct, the lactiferous
duct, which as it approaches the areola expands into a fusiform
ampulla or reservoir. At the base of the nipple the ampulte contract
to form some 16 or 18 narrow ducts, which, ascending the nipple,
open by constricted orifices 0.5 mm. in diameter on its apex (Fig. 181).

400 TEXT-BOOK OF PHYSIOLOGY.

On tracing the lactiferous duct into a lobe, it is found to divide
and subdivide into a number of branches, which pass into smaller
masses — the lobules. The lobule in turn is composed of a large
number of tubular acini or alveoli, the final terminations of the lobu-
lar ducts. Each acinus consists of a basement membrane lined by a
single layer of low cuboidal epithehal cells (Fig. 182). Externally
the acinus is surrounded by blood-vessels, nerves, and lymphatics.

MILK.

Milk as obtained during active lactation is an opaque bluish-
white fluid, almost inodorous, with a sweet taste, an alkaline reaction,
and a specific gravity of from 1.025 ^^ 1.040. Examined micro-
scopically, it is seen to consist of a clear fluid, the milk plasma, hold-
ing in suspension an enormous number of small, highly refractive
oil-globules, which measure on the average about tq-^ot c>f an inch
in diameter. It has been asserted by some observers that each globule
is surrounded by a thin proteid envelope which enables it to maintain
the discrete form. This, however, is at present disbeheved.

The quantity of milk secreted daily by the human female averages
about 1200 c.c.

Chemic analysis has shown that the milk of all the mammalia
consists of all the different classes of nutritive principles, though in
different proportions, which are necessary to the growth and devel-
opment of the body. The only exception appears to be an insuffi-
cient amount of iron for the formation of the coloring-matter of the
blood, the hemoglobin.

Caseinogen is the chief proteid constituent of milk. Associated
with it, however, are two other proteids, lactalbumin and lactoglob-
uhn, both of which are present in but small quantity. When milk
is treated with acetic acid, sodium chlorid, or magnesium sulphate
to saturation, the caseinogen is precipitated as such, and after the re-
moval of the fat with which it is entangled may be collected by ap-
propriate chemic methods. On the addition of rennet prepared from
the mucous membrane of the calf's stomach, which contains the
enzyme rennin or pexin, the caseinogen undergoes cleavage into
an insoluble proteid, casein or tyrein, and a small quantity of a new
soluble proteid. To this process the term coagulation has been given.
The presence of calcium phosphate appears to be essential to this
process, inasmuch as it does not take place if the milk be completely
decalcified by the addition of potassium oxalate. After coagulation,
the more or less solid mass of milk separates into a liquid portion,
the serum, and a soHd portion, the coagulum. The former, generally
termed whey, consists of water, salts, lactalbumin, sugar; the latter,
the curd, consists of the casein and entangled fat. Boihng the milk

SECRETION.

401

retards and even prevents the coagulation by rennet, owing to the
precipitation of the calcium phosphate. When milk is taken into the
stomach, it is probable that the rennin coagulates the caseinogen in a
manner similar to, if not identical with, this process, which appears
to be essential to the normal digestion of the milk.

The fat of milk is more or less solid at ordinary temperatures.
It is a compound of olein, palmitin, and stearin with small quantities
of butyrin and caproin and fatty acids. The melting-point of butter
varies between 31° and 34° C. When milk is allowed to stand for
some time, the fat-globules rise to the surface and form a thick layer
known as cream. Churning the milk or cream causes the fat-globules
to run together and form a coherent mass termed butter.

Lactose is the particular form of sugar characteristic of milk.
It belongs to the saccharose group and has the following composition :
Cj2H220jj + H20. Though incapable of undergoing fermentation
by the action of the yeast plant, it is readily reduced by the Bacillus
acidi lactici to lactic acid and carbon dioxid, 'the former of which
imparts to milk an acid reaction and a sour taste. With the accumu-
lation of the lactic acid the caseinogen is precipitated as a more or less
consistent mass.

The inorganic salts of milk are chiefly potassium, sodium,
calcium, and magnesium phosphates and chlorids. Iron is also
present in small amount. The following table of Bunge gives the
quantitative amounts of these constituents in both human and cow's
milk:

In iooo Parts.

Potas-
sium.

Sodium.

Calcium.

Magne-
sium.

Iron

OXID.

Phos-
phoric
Acid.

Chlorin.

Human milk,

Cow's milk,

0.78
1.76

0.25
I. II

0-33
1-59

0.06
0.21

0.0036
0.003

0.47
1.97

0.43
1.69

Mechanism of Milk Secretion. — ^During the time of lactation
the mammary gland exhibits periods of secretory activity which
alternate with periods of repose. Coincidently with these periods
certain histologic changes take place in the secreting epithelium.
At the close of a period of active secretion and after the discharge of
the milk each acinus presents the following features: The epithelial
cells are short, cubical, nucleated, and border a relatively wide
lumen, in which is found a variable quantity of milk. After the gland
has rested for some time active metabolism again begins. The
cells grow and elongate; the nucleus divides into two or three new
nuclei; constriction takes place and the inner portion is detached
and discharged into the lumen of the acinus. During the time these
changes are taking place oil-globules make their appearance in the cell
26

402

TEXT-BOOK OF PHYSIOLOGY.

protoplasm, some of which are discharged separately into the lumen,
while others remain for a time associated with the detached portion of
the cell (Fig. 183J. From these histologic changes it is inferred that
the caseinogen and fat are products of the metabolism of the cell
protoplasm and not derived directly through the lymph from the blood.
The lactose apparently has a similar origin, as appears from the fact
that it is not found either in the blood or any other tissue, and that it
is formed independently of carbohydrate food. The water, and
especially the inorganic salts, are the result of secretor}^ activity rather
than of diffusion and filtratior . This is rendered probable from the
fact that the proportions of the inorganic salts of milk are more closely
allied to those of the tissues of the new-born child than to blood.
With the passage of the water and salts into the lumen of the acinus

the proteids undergo disintegration and
solution and the liquid assumes the
characteristics of milk.

The discharge of milk is occasioned
by the suction efforts on the part of the
child, aided by atmospheric pressure and
the contractions of the non-striated mus-
cle-fibers of the lactiferous ducts.

Influence of the Nerve System.
■ — Judging from analogy, it is probable
that the secretion of milk is regulated
by influences emanating from the nerve
system, though the exact nerve-channels
for the transmission of such influences
have not been determined experimentally.
\"arious attempts have been made to
isolate and study these nerves, but the
results are inconclusive. It is well known
that emotional states on the part of the mother modify the quantity
as well as quahty of milk, indicating a connection between the gland-
cells and the central nervous system. Nerve terminals have been
discovered in and around the epithelial cells — a fact which supports
this view.

Colostrum. — Within a day or tAvo after parturition the alveoli
become filled with a fluid which in some respects resembles milk
and which has been termed colostrum. This is a watery fluid con-
taining disintegrated epithelial cells, fat-globules, as well as colos-
trum corpuscles, which are probably emigrated leukocytes. Colos-
trum is distinguished from milk in being richer in sugar and inorganic
salts. It is said to possess constituents which act as a laxative to
the young child.

Fig

183. — Section of the
Mammary Gland of a
Cat in the Early
Stages of Lactation.
A. Ca\dty of alveoli filled
with granules and globules
of fat. I, 2, 3. Epithe-
lium in various stages of
milk -formation. — ( Yeo.)

SECRETION.

403

THE LIVER.

The liver is a large gland situated in the upper and right side
of the abdominal cavity, where it is held in position largely by hga-
ments formed by reduplications of the peritoneal investment. In
the adult it weighs, freed of blood, from 1300 to 1700 grams. The
liver is connected with the duodenal portion of the intestine by the
hepatic duct. It receives blood both from the hepatic artery and from
the portal vein, and in this respect differs from all other glands in
the body. The epithelial structures of the liver are inclosed by a
firm fibrous membrane, known as Glisson's capsule. At the trans-
verse fissure it invests and follows the blood-vessels, which there
enter, in all their ramifications through the gland.

Structure of the Liver. — The liver is composed of an enor-
mous number of
small masses, rounded,
ovoid, or polygonal
in shape, called lo-
bules, measuring
about one milhmeter
in diameter and sepa-
rated from one an-
other by a narrow
space in which are
to be found blood-
vessels, lymphatics,
hepatic ducts, sup-
ported by connective
tissue. In the pig this
space and its con-
tained elements is
quite distinct, sharply
marking out the
border of the lobule (Fig. 184). This is not so apparent in man.
Each lobule is made up of irregular or polygonal shaped cells measur-
ing about 30 to 40 micromilhmeters in diameter. These cells are
arranged in a radial manner from the center to the circumference of
the lobule (Fig. 185). Each cell possesses one and at times two nuclei.
There is no evidence for the existence of a distinct cell-wall. The
cell protoplasm frequently contains globules of fat, granules of a
proteid nature, granules of glycogen, pigment material, etc. The
appearance presented by the cell will vary considerably, according to
the time it is observed. Thus there may be a complete absence of
these constituents, when the cell may present a series of vacuoles
separated by bands of protoplasm. The cells are the secreting

Fig. 184. — Section of Liver of Pig, showing very
DiAGRAMMATiCALLY THE LoBXJLES. a. Interlobu-
lar connective tissue, b, c. Branches of portal vein
and of hepatic artery, d. Bile-ducts. e. Intra-
lobular vein. — (Piersol.)

404

TEXT-BOOK OF PHYSIOLOGY.

Trabeculae of
hepatic cells.

Central vein.

Structures of the liver, and hence are in close relation with capillary
blood-vessels, lymphatic spaces, nerves, and irregular channels or
passageways. The latter running between the epithehal cells may
be compared to the lumen of other secreting glands.

Blood-vessels and Their Distribution. — The blood-vessels
which are in relation with the liver are :

1. The portal vein.

2. The hepatic artery.

3. The hepatic vein.

The portal vein and the hepatic artery enter the liver at the trans-
verse fissure. After penetrating its substance they divide and sub-
divide into smaller and smaller
branches, which ultimately oc-
cupy the space between the
lobules, completely surrounding
and limiting them. From their
situation they are termed inter-
lobular veins and arteries.

The interlobular veins give off
small capillary vessels which
penetrate the lobule at all points
of its surface. These capillaries,
though frequently anastomosing,
form a radial- meshwork which
converges toward the center of
the lobule. In the meshes of
this plexus are found, arranged
in a corresponding radial man-
ner, the liver cells. The inter-
lobular arteries are distributed to
the walls of the portal vein, "to
the connective tissue, and finally
terminate in the portal vein capil-
laries. The intralobular capil-
laries thus receive and transmit
blood which is an admixture of both arterial and venous blood. In
the center of each lobule there is a large vein, formed by the union of
the intralobular capillaries, known as the intralobular vein, which
collects all the blood of the lobule and transmits it through the lobule
to an underlying or sublobular vein (Fig. 186). These latter vessels,
uniting and reuniting, ultimately form the hepatic vein, which empties
the blood into the inferior vena cava.

Bile Capillaries and Hepatic Ducts. — The bile capillaries are
narrow channels which penetrate the lobule in all directions and are
generally found running along the sides of the cells. These channels,

Interlobular vein.

Hepatic duct.

Fig. iSs.^Scheme of a Hepatic Lob-
ule, REPRESENTED IN TRANSVERSE

Section below and, by Partial
Leveling, in Longitudinal Sec-
tion above. In the left half the
blood-vessels are drawn; in the right
half only the cords of hepatic cells.
X 20. — (Stdhr.)

SECRETION. 405

which are devoid of walls, receive from the cells some of the products
of their secretory activity, and hence are comparable to the lumen of
the alveoli of other secreting glands. At the periphery of the lobules
the bile capillaries communicate with larger channels which are the
beginnings of the hepatic or bile-ducts lying in the interlobular
spaces. The interlobular bile-ducts possess a distinct wall lined by
flattened epitheHum. There is, however, no distinct hne of demarca-
tion between the cells of the interlobular ducts and the secreting
cells of the liver proper, as the two blend insensibly, the one into
the other. As the hepatic ducts increase in size they gradually
acquire the structure characteristic of the main hepatic duct: viz., a
mucous, a muscle, and a fibrous coat.

Fig. 186. — Transverse Section of a Single Hepatic Lobule, i. Intralobular
vein, cut across. 2, 2, 2, 2. Afferent branches of the intralobular vein. 3, 3,
3> 3' 3> 3) 3> 3> 3- Interlobular branches of the portal vein, with its capiUary
branches, forming the lobular ple.xus, extending to the radicles of the intralobular
vein. — {Sappey.)

Nerves. — Experimental investigations have demonstrated that
the hver is supphed with nerves derived from the central nerve
system. The route of these nerves is probably by way of the splanch-
nics and the vagi. Many of the nerves which enter the hver are
vasomotor in function; as to whether others are secretoiy in character
is yet a subject of investigation. It has been asserted that nerve
terminals have been demonstrated running between the cells and
even penetrating their substance. This fact would indicate that the
metabohc processes of the liver are under the control of the central
nerve system.

Functions of the Liver. — The anatomic and histologic pecu-

4o6 TEXT-BOOK OF PHYSIOLOGY.

liarities of the liver would indicate that it has a variety of relations to
the general processes of the body. Experimental investigation has
brought some of these relations to light. Though its physiologic
actions are not yet wholly understood, it may be said that it —

1. Secretes bile.

2. Produces and stores glycogen.

3. Assists in the formation of urea.

Secretion of Bile. — The physical properties and chemic com-
position of the bile have already been considered (page 203).
The characteristic salts of the bile, sodium glycocholate and tauro-
cholate, do not pre-exist in the blood, and therefore must be formed
by the liver cells out of materials derived from the blood of the
intralobular capillaries. The antecedents of the bile salts, glycocoll
and taurin, are crystalhzable nitrogenized compounds, and known
chemically as amido-acetic and amido-ethylsulphonic acids. Their
chemic composition indicates that they are derivatives of the proteids
or the albuminoids, though the intermediate stages in their produc-
tion are unknown. The origin of the cholalic acid with which they
are combined is equally obscure. The bile salts as they are found
in the bile are produced in the liver cells by metabolic activity.

The primary coloring-matter of the bile, bilirubin, has been shown
to be a derivative of hematin, a product of the disintegration of hemo-
globin. It is supposed that the hver cells bring about this change
by combining water with hematin, with the abstraction of iron. The
product thus formed is bihrubin, which is excreted, while the iron is
for the most part retained.

Cholesterin is a waste product derived largely from the nerve-
tissue. It is brought to the Hver and simply excreted by the cells.
The remaining constituents of the bile, water and inorganic salts, are
secreted here as in all other glands.

When once formed, the liver cells discharge these various com-
pounds into the channels by which they are surrounded; they then
pass into the open mouths of the bile-ducts at the periphery of the
lobules. Under the increasing pressure which arises from the secre-
tion and accumulation of bile, this fluid flows from the smaller into the
larger bile-ducts, and finally is emptied either directly into the in-
testine or into the gall-bladder, where it is stored until required for
digestive purposes. The secretion of bile, as observed by means of
a bihary fistula, is continuous and not intermittent, though the rate
of flow is subject to considerable variation.

The hver cells, as far as the secretion of bile is concerned, appear
to be independent of the nerve system. Their activity, however,
is stimulated by the increased blood-supply which arises during
digestion in consequence of the dilatation of the intestinal vessels,
since it is at this period that the rate of discharge is the greatest.

SECRETION. 407

The same results have been shown by experiment. Thus, division
of the splanchnic nerves is followed by an increased discharge of
bile, apparently due to the dilatation of the portal vessels; stimula-
tion of their peripheral ends is followed by a decreased discharge of
bile in consequence of the contraction of the portal vessels. The
bile salts appear to be the most efficient stimulants to the activity of
the liver cells, for their administration and absorption is followed by
an increase not only in the amount of water and inorganic salts, but
of the solid constituents as well.

The flow of bile from the bile capillaries to the main hepatic
duct, though primarily dependent on differences of pressure, is aided
by the contraction of the muscular walls of the bile-ducts and the
inspiratory movements of the diaphragm. Any obstacle to the dis-
charge of bile leads to its accumulation, a rise of pressure beyond
that of the capillary blood-vessels, and a reabsorption by the lymph-
atics of the bile constituents. After their discharge into the blood
from the thoracic duct these constituents are deposited in various
tissues, gi^'ing rise to the phenomena of jaundice.

The Production of Glycogen. — In 1857 Bernard discovered the
fact that the liver normally during life produces a sugar-forming
substance, analogous in its chemic composition to starch, to which he
gave the name glycogen. This substance can be obtained by the
following method: Small pieces of the hver of an animal recently
killed, preferably after a meal rich in carbohydrates, are placed in
acidulated boihng water for a few minutes; then rubbed up in a
mortar with sand, again boiled, after w^hich the proteids are removed
by filtration. The filtrate thus obtained is opalescent and resembles
a solution of starch. The glycogen may be precipitated from this
solution with alcohol as a white amorphous powder, soluble in
water. Chemic analysis shows that it consists of CgH^^Oj, or a
multiple of it.

When either the original solution obtained by boiling or a solution
of this amorphous powder is treated with iodin, it strikes a port- wine
color. When digested with saliva, pancreatic juice, or boiled with
dilute acids, the solution becomes clear, and testing with FehHng's
solution reveals the presence of sugar.

If the Hver be allowed to remain in the body of an animal for a
period of twenty-four hours before the decoction is made as above
described, it will be found that the solution contains only a small
amount of glycogen but a relatively large amount of sugar. The
inference drawn is that after death the glycogen is transformed by
some agent, possibly a ferment, into sugar (dextrose).

The presence of glycogen in the liver cells can be shown micro-
scopically in the form of discrete hyaline and refractive granules.
As they are soluble in w\ater thev can be readilv dissolved out from

4o8 TEXT-BOOK OF PHYSIOLOGY.

the cells, leaving small vacuoles separated from one another by
strands of cell substance. The amount of glycogen in a well-fed
animal varies from 1.5 to 4 per cent, of the total weight. The pro-
duction of glycogen is dependent very largely on the consumption of
carbohydrates, the greater the amount of sugar and starch in the
food, the greater being the production of glycogen. On a pure
proteid diet it is still, produced, though in small amounts.

Glycogen is present also in muscles, in the placenta, in the tissues
of the embryo — wherever, indeed, active tissue changes and growth
are taking place.

The facts connected with the formation of glycogen, as well as its
disposition as at present generally accepted, may be stated as follows :
The dextrose into which the carbohydrates are converted by the
action of the digestive fluids is absorbed into the blood of the portal
vein and carried direct into the liver, where by the action of the cells
it is abstracted, dehydrated, and temporarily deposited under the
form of the non- diffusible body glycogen. At a subsequent period and
in proportion to the needs of the system the liver cells, through the
agency of a ferment, transform the glycogen into dextrose, return it to
the circulation, by which it is transported to the systemic capillaries,
where it disappears. The blood of the hepatic vein therefore contains
more sugar than the blood of any other part of the body, and the
blood of the arteries more than the blood of the other veins. Should
there be a failure on the part of the liver cells to abstract the sugar,
it would pass through the liver into the general circulation, from which
it would be eliminated by the kidneys. The final fate of the sugar
is uncertain. It is, however, probable that after its delivery to the
muscles, for example, it may be directly oxidized, or stored as
glycogen, or possibly utilized in the formation of living material.
Ultimately, however, through oxidation it yields heat, and contributes
to the production of muscle energy.

In opposition to this view. Dr. Pavy, after years of accurate ex-
perimentation, states that the blood on the cardiac side of the Hver
never under normal circumstances contains a larger percentage of
sugar than is to be found in any part of the circulation, except in the
portal vein. He states that glycogen is never reconverted into sugar,
and denies that the liver produces sugar, to be discharged into the
blood; that the function of the liver is merely to arrest the passage of
sugar, and so to shield the general circulation from an excess ; that the
sugar which arises in the liver after death is a postmortem product
and not an illustration of what takes place during life. Dr. Vsivj,
having apparently demonstrated the glucoside constitution of proteid
material in general, accounts for the presence of glycogen in muscles
and other tissues on the assumption that during the cleavage of the
proteid molecule the carbohydrate element is set free and temporarily

SECRETION. 409

stored as glycogen. He thus accounts for the production of sugar
in the body, even in the absence of all sugar and starch from the food.
Pavy beUeves that the glycogen produced in the liver is utilized in the
formation of fat and the synthesis of complex proteids necessar}- to
the construction of the tissues.

Influence of the Nerve System. — The nerve system influ-
ences in some way the glycogenic function of the liver. It was
discovered by Bernard that puncture of the floor of the fourth ven-
tricle at a point between the acoustic and vagus nerves, near the middle
line is followed within an hour or two by the appearance of sugar in
the urine, which lasted for twenty-four or thirty-six hours. To this
area, in close relation to the vasomotor center, he gave the name
"diabetic area." The quantity of sugar excreted in the urine will
depend on the amount of sugar previously present in the liver.
Through some agency the stored-up glycogen is rapidly converted
into sugar discharged into the blood and eliminated by the kidneys.
There is no positive evidence that the puncture destroys the vaso-
motor center for the blood-vessels of the liver, or that there is any
change in the relation of the blood-vessels to the liver-cells. Never-
theless powerful stimulation of the sciatic nerve, or the central end of
the vagus which impairs or depresses the vasomotor center, will give
rise to a similar production and elimination of sugar. The pathway
for the passage of these influences beyond the first thoracic ganglion
is unknown, but that it is not by way of the splanchnics or the vagi
is evident from the fact that division of either of these nerves is not
followed by the appearance of sugar in the urine.

Diabetes. — Diabetes is a chronic disease characterized by the
appearance of sugar in the urine in variable amounts. This patho-
logic condition has usually been associated with derangements of the
glycogenic function of the liver, though doubtless derangements of
other organic functions will produce the same condition. At the
present time it is believed that the excretion of sugar by the kidneys
depends on two causes: (i) An ineffectual abstraction and storage
of sugar due to some impairment in the activity of the liver cells; (2)
a rapid cleavage of the proteid constituents of the tissues, in conse-
quence of some profound alteration in the nutritive process, whereby
their glucose radicals are liberated in unusual amounts. The physi-
ologic mechanism by which the normal metabolism of the carbohy-
drates is regulated is unknown. That it is complex in character is
shown by the phenomena which follow not only puncture of the
medulla, but also removal of the pancreas and the administration of
various poisons.

Removal of the pancreas from the body of a dog or other ani-
mal is at once followed by a rise in the percentage of sugar in the
blood and its elimination bv the kidnevs. In a short time acetone.

4IO TEXT-BOOK OF PHYSIOLOGY.

aceto-acetic and oxybutyric acids make their appearance, attended
by the usual symptoms characteristic of glycosuria in man. The
quantity of sugar excreted and the gravity of the attendant symptoms
may be much diminished by allowing a portion of the gland to remain
in situ, even though its capacity for the production of pancreatic
juice is entirely abolished. Transplantation of the pancreas to the
subcutaneous tissue or to the abdominal cavity v^ill practically pre-
vent the glycosuria. The explanations v^hich have been offered as
to the manner in which the pancreatic tissue prevents and its absence
gives rise to the excretion of sugar are purely hypothetical. It has
been claimed by some investigators that the pancreas secretes a
specific material, which enters the blood and promotes oxidation of
the sugar. In the absence of this material the sugar accumulates,
and is finally eliminated by the kidneys. Since the discovery of the
islands of Langerhans it has been suggested by some investigators that
the production of the material which regulates carbohydrate metabo-
lism should be attributed to them rather than to the pancreas as a
whole. The sugar excreted doubtless in part comes from the glycogen
of the liver, as this disappears in a short time. But as sugar con-
tinues to be excreted, even though all carbohydrates be withdrawn
from the food, the conclusion is justifiable that it arises in conse-
quence of increased proteid metabolism. This supposition is
strengthened by the fact that the quantity of urea excreted rises and
falls with the quantity of sugar excreted.

Phloridzin, a glucoside obtained from the leaves of the cherry and
plum tree, gives rise to the appearance of sugar in the urine, in
amounts beyond that which might come from the glucose normally
present in the blood or from the glycogen of the liver. As there is a
concomitant increase in the amount of urea excreted, the supposition
is that phloridzin increases proteid metabolism.

Curara, in doses sufficient to paralyze the muscles, also gives rise
to the appearance of sugar in the urine. This is not due, however,
to an increased production on the part of the liver, but rather to a
want of consumption on the part of the muscles, due to their inac-
tivity. The accumulation of the sugar in the blood which takes place
for this reason leads very promptly to its removal by the kidneys.

The Formation of Urea. — It is now generally beheved that the
liver is the most active of all the organs which may be engaged in the
production of urea. This behef is based on numerous physiologic
and pathologic data. The compounds out of which the hepatic cells
construct urea have been for chemic reasons asserted to be the
ammonium salts, e. g., the carbonate, lactate, carbamate, which are
constantly present in the blood. These salts, which result from
proteid metabolism, are absorbed from the tissues, carried to the
liver, and there synthesized to urea. This supposition is supported

SECRETION. 411

by an experiment as follows: The liver of an animal recently living
is removed from the body and its vessels perfused continuously with
blood (the urea content of which is known) containing the ammonium
salts. An analysis of this blood shows, after a time, a diminution
of these salts, and a large increase in the amount of the urea. The
leucin and tyrosin which result from the prolonged action of pan-
creatic juice on hemi-peptone are also capable of being converted to
urea by the hepatic cells, and in all probability are so disposed of.
Destructive diseases of the liver — e. g., acute yellow atrophy, sup-
puration, cirrhosis — largely diminish the production of urea, but in-
crease the quantities of the ammonium salts in the urine. The same
is true when the Hver cells are destroyed during acute phosphorus-
poisoning.

VASCULAR OR DUCTLESS GLANDS.
INTERNAL SECRETIONS.

The metaboKsm of the body generally, as well as that of individual
organs, has been shown to be related not only to the physiologic ac-
tivity of such organs as the liver and pancreas, but also to the activity
of the so-called vascular or ductless glands. The influence of the
pancreas in regulating the production of glycogen by the liver, and
the influence of the hver in the maintenance of the general metabo-
lism through the production of glycogen and the formation of urea,
are now established facts. That the vascular or ductless glands to
an equal extent, though perhaps in a different way, assist in the main-
tenance of physiologic processes, appears certain from the results
of animal experimentation. The explanation given for the influence
of these glands is that they produce specific substances, which are
poured into the blood or lymph and carried direct to the tissues, to
the activities of which they appear to be essential; for without these
substances the nutrition of the tissues dechnes and in a short time
a fatal termination ensues.

Inasmuch as these partly unknown substances are formed by cell
acti\'ity and are poured into the interstices of the tissues, they have
been termed "internal secretions." Though the term internal secre-
tions is apphcable to all substances which arise in consequence of
tissue metabbhsm, and which, after being poured into the blood,
influence in varying degrees and ways physiologic processes, yet the
term in this connection will be applied only to the secretions of the
thyroid gland, hypophysis cerebri, and adrenal bodies.

Thyroid Gland. — The thyroid gland or body consists of two lobes
situated on the lateral aspect of the upper part of the trachea. Each
lobe is pyriform in shape, the base being directed downward and on a
level with the fifth or sixth tracheal ring. The lobe is about 50 mm.
in length, 20 mm. in breadth, and 25 mm. in thickness. As a rule.

412

TEXT-BOOK OF PHYSIOLOGY.

the lobes are united by a narrow band or isthmus of the same tissue.
The gland is reddish in color, and abundantly supplied with blood-
vessels and lymphatics.

Microscopic examination shows that the thyroid consists of an
enormous number of closed sacs or vesicles, variable in size, the
largest not measuring more than o.i mm. in diameter. Each sac is
composed of a thin homogeneous membrane hned by cuboid epithe-
lium. The interior of the sac in adult hfe contains a transparent,
viscid fluid containing albumin and termed "colloid" substance.
Externally, the sacs are surrounded by a plexus of capillary blood-
vessels and lymphatics. The individual sacs are united and sup-
ported by connective tissue, v/hich forms, in addition, a covering

for the entire gland.
^4pf7^ Function of the Thy-

roid.— The knowledge at
present possessed as to the
function of the thyroid
gland, especially in mam-
mals, is the outcome of a
study of the effects which
follow its arrested develop-
ment in the child, its de-
generation in the adult,
and its extirpation in the
human being as well as in
animals. The results, how-
ever, which follow its ex-
tirpation are not always
uniform in all animals,
though suf&cient reasons
for the lack of uniformity
can not always be assigned.
Cretinism, a condition characterized by a want of physical and
mental development, is associated with, if not directly dependent on,
a congenital absence of the thyroid or its arrested development dur-
ing the early years of childhood.

Myxedema, a condition of the skin in which there is a hyperplasia
of the connective tissue, of an embryonic type, rich in mucin, is gener-
ally regarded as one of the effects of degenerative processes in the
thyroid. Partly in consequence of this change in the skin the face
becomes broader, swollen, and flattened, giving rise to a loss of ex-
pression. At the same time the mind becomes dull, clouded, even
approximating the idiotic type. This supposed infiltration of the
skin with mucin was termed myxedema by Ord, who at the same
time associated it with a change in the structure of the thyroid as a
result of which it became functionally useless.

Fig. 187. — View of Thyroid Body. i. Thy-
roid isthmus. 2. Median portion of crico-
thyroid membrane. 3. Crico-thyroid
muscle. 4. Lateral lobe of thyroid body. —
(After Morris.)

SECRETION.

413

Extirpation of the thyroid, for relief from symptoms due to grave
pathologic changes, has been followed in human beings by symptoms
similar to those of myxedema. To this condition the terms operative
myxedema and cachexia strumipriva have been applied.

After the publication of the history of the myxedema which fol-
lowed surgical removal of the thyroid, Schiff, in 1887, repeated his
earher experiments on dogs, and found again that removal of the
th}'roid was speedily followed by tremors, convulsions, and death.
Similar experiments were made by Horsley on monkeys, with results
which resembled those characteristic of myxedema. Among the
symptoms which
developed within a
few days after the
removal of the gland
may be mentioned
loss of appetite ; fib-
rillar contractions
of muscles; tremors
and spasms; mu-
cinoid degeneration
of the skin, giving
rise to puffiness of
the eyelids and face
and to a swollen
condition of the
abdomen ; hebetude
of mind, frequently
terminating in
idiocy ; fall of blood-
pressure; dyspnea;
albuminuria; atro-
phy of the tissues,
followed by death
of the animal in the
course of from five to eight weeks. The complexus of symptoms
observed in monkeys was divided by Horsley into three stages: viz.,
the neurotic, the mucinoid, and the atrophic.

It is evident that the presence of the thyroid is essential to
the normal activity of the tissues generally. As to the manner
in which it exerts its favorable influence, there is some difference
of opinion. The view that the gland removes from the blood cer-
tain toxic bodies, rendering them innocuous and thus preserving
the body from a species of auto-intoxication, is gradually yielding to
the more probable view that the epithehum is engaged in the secre-
tion of a specific material, which finds its way into the blood or lymph

Fig

188. — A Lobule from a Thin Section of the
Thyroid Gland of an Adult Man. i. Colloid
substance. 2. Epithelium. 3. Tangential section
of a tubule, the epithelium viewed from the surface.
4. Tubule in transverse section. 5. Connective tissue.
—{Siohr.)

414 TEXT-BOOK OF PHYSIOLOGY.

and in some unknown way influences favorably tissue metabolism.
This view of the function of the thyroid is supported by the fact that
successful grafting of a portion of the thyroid beneath the skin or in
the abdominal cavity will prevent the usual symptoms which follow
thyroidectomy. The same result is obtained by the intravenous
injection of thyroid juice or by the administration of the raw gland.
It was shown by Murray that myxedematous patients could be bene-
fited, and even cured, by feeding them with fresh thyroids or with
the dry extract.

The chemic features of the material secreted and obtained from
the structures of the thyroid indicate that it is a complex proteid con-
taining iodin, which, under the influence of various reagents, under-
goes cleavage, giving rise to a non-proteid residue, which carries with
it the iodin and phosphorus. The amount of iodin in the thyroid
varies from 0.33 to i milhgram for each gram of tissue. To this
compound the term thyroiodin has been given. The administration
of this compound produces effects similar to those which follow the
therapeutic administration of the fresh thyroid itself: viz., a diminu-
tion of all myxedematous symptoms. In normal states of the body,
thyroiodin influences very actively the general metabolism. It gives
rise to a decomposition of fats and proteids and to a decline in body-
weight. In large doses it may produce toxic symptoms: e. g., in-
creased cardiac action, vertigo, and glycosuria.

The Pituitary Body. — This is a small body lodged in the
sella turcica of the sphenoid bone. It consists of an anterior lobe,
somewhat red in color, and a posterior lobe, yellowish-gray in color.
The former is much the larger and partly embraces the latter. The
anterior lobe is developed from an invagination of the epiblast of the
mouth cavity, and consists of distinct gland tissue. The posterior
lobe is an outgrowth from the brain, and is connected with the
infundibulum by a short stalk. It has been suggested that the term
infundibular body be reserved for the posterior lobe, and the term
hypophysis cerebri for the anterior lobe. This distinction appears
to be desirable, inasmuch as in their origin and structure they are
separate and distinct bodies.

Removal of the hypophysis cerebri, or the pituitary body, is always
followed by a fatal result, preceded by symptoms not unlike those
which follow removal of the thyroid: viz., anorexia, tremors, spasms,
etc. Degeneration of the pituitary body has been found in connection
with a hypertrophic condition of the bones of the face and extremities,
to which the term acromegalia has been given.

Intravenous injection of an extract of the pituitary increases
the force of the heart-beat without any change in its frequency, and
causes a rise of blood-pressure from a stimulation of the arterioles
(Schafer and Ohver). The material secreted by the pituitary has

SECRETION.

415

not been isolated, hence its chemic features are unknown. After its
formation it probably passes through a system of ducts into the
cerebrospinal lluid, after which it influences the metabolism of the
nerve and osseous tissues as well as the force of the heart muscle.

An extract of the anterior lobe itself exerts no appreciable effect
on the blood-pressure or on the rate of the heart-beat, nor does it in-
fluence the circulatory and respiratory organs. An extract of the
infundibular body intravenously injected, how-
ever, gives rise to increased blood-pressure and
to a slowing of the heart-beat (Howell).

Adrenal Bodies, or Suprarenal Capsules. —
These are two flattened bodies, somewhat cres-
centic or triangular in shape, situated each upon
the upper extremity of the corresponding kidney,
and held in place by connective tissue. They
measure about 40 mm. in height, 30 mm. in
breadth, and from 6 to 8 mm. in thickness. The
weight of each is about 4 gm.

Function of the Adrenal Bodies. — It was
observed by Addison that a profound disturbance
of the nutrition, characterized by a bronze-like
discoloration of the skin and of the mucous
membranes of the mouth, extreme muscular
weakness, and profound anemia, was associated
with, if not dependent on, pathologic conditions
of the suprarenal glands. In the progress of the
disease the asthenia gradually increases, the heart
becomes weak, the pulse small, soft, and feeble,
indicating a general loss of tone of the muscular
and vascular apparatus. Death ensues from
paralysis of the respiratory muscles. The essen-
tial nature of the lesion which gives rise to these
symptoms has not been determined.

Removal of these bodies from various animals
is invariably and in a short time followed by
death, preceded by some of the symptoms char-
acteristic of Addison's disease. Their develop-
ment, however, is more acute. From the fact that animals so
promptly die after extirpation of these bodies, and the further fact
that the blood of such animals is toxic to the subjects of recent
extirpation, but not to normal animals, the conclusion was drawn
that the function of the adrenal bodies is to remove from the blood
some toxic product of muscle metabohsm. Its accumulation after
extirpation gives rise to death through auto-intoxication.

On the supposition that the adrenals might secrete and pour into

Fig. 189. — Sagittal
Section of the
Pituitary Body
AND Infundi-

BULUM with

Adjoining
Part of Third
Ventricle. a.
Anterior lobe.
a'. A projection
from it toward
the front of the
infundibulum.
b. Posterior lobe
connected by a
stalk with the
infundibulum, i.
I.e. Lamina cin-
erea. 0. Right
optic nerve, ch.
Section of optic
chiasm, r.o. Re-
cess of ventricle
above the chias-
ma. cm. Corpus
mammillare. —
{Schwalhe, from
Qua in.)

4i6 TEXT-BOOK OF PHYSIOLOGY.

the blood a specific material which favorably influences general
metabolism, Schafer and Oliver injected hypodermically glycerin
and water extracts, and observed at once an increased activity of the
heart-beats and of the respiratory movements. The effects, however,
were only transitory. When these extracts are injected into the veins
directly, there follows in a short time a cessation of the auricular
contraction of the heart, though the ventricular contraction continues
with an independent rhythm. If the vagi are cut previous to the
injection or if the inhibition is removed by atropin, the rapidity and
vigor of both auricles and ventricles are increased. Whether the
inhibitory influence is removed or not, there is a marked increase in
the blood-pressure, though it is greater in the former instance. This
is attributed to a direct stimulation and contraction of the muscle-
fibers of the arterioles themselves, and not to vasomotor influences,
as it occurs also after division of the cord and destruction of the bulb.
The contraction of the arterioles is quite general, as shown by
plethysmographic studies of the limbs, spleen, kidney, etc. Applied
locally to the mucous membranes, adrenal extract produces contrac-
tion of the blood-vessels and pallor. The skeletal muscles are affected
by the extract very much as they are by veratrin. The duration
of a single contraction is very much prolonged, especially in the
phase of relaxation or of decreasing energy.

It is evident from these experiments that the adrenal bodies are
engaged in elaborating and pouring into the blood a specific material
which stimulates to increased activity the muscle-fibers of the heart
and arteries, and thus assists in maintaining the normal blood-pres-
sure as well as the tonicity of the skeletal muscles. An alkaloidal
substance was isolated by Abel from extracts of this gland, to which
the term epinephrin was given. A crystallizable substance was iso-
lated first by Takamine and later by Aldrich, to which the
term adrenalin was given. Both substances are apparently equally
efficacious in causing contraction of the blood-vessels and in raising
the blood pressure. The question as to which of these two
substances represents the active principle of the gland is as yet a
subject of discussion.

The Spleen. — The spleen is a soft bluish-red organ, oval in
shape, from twelve to fifteen centimeters long by eight broad and
four thick. It is situated in the left hypochondrium between the
stomach and the diaphragm. In this situation it is held in position
by a fold of the peritoneum which passes from the upper border
to the diaphragm.

Structure. — A section of the spleen shows that it consists of
connective tissue, blood-vessels, lymph corpuscles, and lymphoid
tissue. The surface of the spleen is covered by a capsule composed
of dense fibrous tissue, from the inner surface of which septa or

SECRETION.

417

trabeculae pass inward toward the center of the organ. In their
course they give off a series of processes which unite freely, forming
a spongy connective-tissue framework. The capsule and the main
trabeculae in some animals contain numerous non-striated muscle-
fibers. In man they are relatively few in number. The blood-
vessels which enter the spleen are supported by the connective-
tissue septa. As they pass toward the center of the organ they
divide very rapidly and soon diminish in size. In their course small
branches are given off, which penetrate the intertrabecular tissue
and become encased with spheric or cyHndric masses of adenoid
tissue known as Malpighian corpuscles. These corpuscles are
composed largely of leukocytes. In some animals the leukocytes,
instead of being arranged
in masses, are distributed
along the walls of the
artery as a continuous layer.
Within the corpuscles the
arteries pass into capil-
laries, whether the artery
passes directly to the splenic
pulp or indirectly by way of
the corpuscles, its ultimate
branches terminate in capil-
laries which open into the
spaces of the splenic pulp.
From these spaces a net-
work of venules gathers the
blood and transmits it to
the veins. It is a disputed
question as to whether the
spaces are hned by epithe-
lium, thus forming a con-
tinuous blood channel, or whether they are wanting in this histologic
element.

The Splenic Pulp. — The spaces of the connective-tissue frame-
work are filled with a dark red semifluid mass known as the splenic
pulp. When microscopically examined, the pulp presents a fine
loose network of adenoid tissue, large numbers of leukocytes or
lymph corpuscles, red corpuscles in various stages of disintegra-
tion, and pigment granules. Chemic analysis reveals the presence
of a number of nitrogen-holding bodies, e. g., leucin, tyrosin, xanthin,
uric acid; organic acids, e. g., acetic, lactic, succinic acids; pigments
containing iron, and inorganic salts.

The Functions of the Spleen. — Notwithstanding all the ex-
periments which have been made to determine the functions of the
27

Fig. 190. — Malpighian Corpuscle or a Cat's
Spleen Injected, a. Arter>'. b. Meshes
of the pulp injected, c. The artery of the
corpuscle ramifying in the lymphatic tis-
sue composing it.

4i8

TEXT-BOOK OF PHYSIOLOGY.

spleen, it can not be said that any very definite results have been
obtained. The fact that the spleen can be removed from the body
of an animal without appreciably interfering with the normal metabo-
lism would indicate that its function is not very important. The
chief changes observed after such a procedure are an enlargement
of the lymphatic glands and an increase in the activity of the red
rrrarrow of the bones. The presence of large numbers of leukocytes
in the splenic pulp and in the blood of the splenic vein suggested
the idea that the spleen is engaged in the production of leukocytes,
and to this extent contributes to the formation of blood. The
presence of disintegrated red blood-corpuscles has suggested the
view that the spleen exerts a destructive action on functionally
useless red corpuscles. These and other theories as to splenic func-
tions have been offered
by different observers,
but all are lacking posi-
tive confirmation.

Volume Variations
of the Spleen. — It was
shown some years since
by Roy, with the aid of
the plethysmograph, that
the spleen undergoes
rhythmic variations in
volume from moment to
moment. In the cat and
in the dog the diminu-
tion in the volume (the
systole) and the increase
in volume (the diastole)
together occupied about
one minute.
This fact was determined by withdrawing the spleen through
an opening in the abdominal wall and enclosing it in a box with
rigid walls, the interior of which was connected with a piston record-
ing apparatus. The system being filled with oil, each variation
in volume was attended by a to-and-fro displacement and a cor-
responding movement of the recording lever. The special form
of plethysmograph used for this purpose is known as the oncometer
or bulk measurer, and the recording apparatus as the oncograph
(Fig. 191 and Fig. 196).

The cause of these variations in volume Roy attributed to a
rhythmic contractility of the non-striated muscle-fibers in the capsule
and trabecuLT, and not to changes in the arterial blood-pressure,
as the curve of the pressure taken simultaneously remained prac-

FiG. 191. — Spleen Oncometer Laid Open.

SECRETION. 419

tically uniform. The effect of the rhythmic contractions of the
splenic muscle tissue is to force the blood through the organ, a
condition necessitated perhaps by the pressure relations within,
though what function is thereby fulfilled is not apparent.

It was subsequently shown by Schaf er and Moore that the splenic
volume is extremely responsive to all fluctuations of the arterial
blood-pressure; that though the spleen may passively expand and
recoil in response to the rise and fall of the blood-pressure, never-
theless the reverse conditions may obtain: viz., that the splenic
volume may diminish as the pressure rises, if the splenic arterioles
contract simultaneously with the contraction of the arterioles gener-
ally. On the contrary, the splenic volume may increase coincident
with a dilatation of the splenic and systemic arterioles. In addition
to the rhythmic variations, the spleen steadily increases in volume
for a period of five hours after digestion, and then gradually returns
to its former condition.

Influence of the Nerve System. — The nerves which supply the
vascular and visceral muscles in the spleen are derived directly
from the semilunar ganglion (post-ganghonic fibers) and pass to it
in company with the splenic artery. The nerve-cells from which
they arise are in physiologic relation with nerve-fibers (pre-ganglionic
fibers) which emerge from the spinal cord in the anterior roots of
the third thoracic to the first lumbar nerves inclusive, though they
are found most abundantly in the sixth, seventh, and eighth thoracic
nerves. Their center of origin is in the medulla oblongata.

Stimulation of the nerves in any part of their dourse gives rise
to a diminution in splenic volume; division of the nerves is followed
by an increase in the volume. In asphyxia the spleen is small and
contracted, a condition attributed to a stimulation of the centers
in the medulla by the venosity of the blood.

The musculature of the spleen may also be excited to contraction
by reflex influences, as shown by the fact that stimulation of the
central end of a sensory nerve is attended by a diminution of volume.

Inasmuch as the excised spleen will continue to exhibit variations
in volume when perfused with blood, it would appear that it possess
some mechanism independent to some extent of the nerve system.

CHAPTER XVI.

EXCRETION.

As stated in the preceding chapter, the term excretion is Hmited to
the process by which the end-products of tissue metaboHsm are re-
moved from the body, the nature of the process, however, differing
in no essential particulars from that underlying the process of secre-
tion. The histologic structures involved and the forces at work
being of the same general character, it is impossible to draw any
sharp line of distinction between them. As a general fact it may
be stated that in their composition all the characteristic ingredients
of the excretions are incapable either of entering into the formation
of tissue or of undergoing oxidation for the purpose of heat-production.
As the retention of these end-products in the body would exert a
deleterious influence on normal metabolism, their prompt removal
becomes essential to the maintenance of physiologic activity. The
principal excretions of the body — urine, perspiration, and bile — are
complex fluids in which, with the exception of those given off in the
lungs, are to bejound in varying proportions the chief end-products
of metabolism.

THE URINE.

Normal urine has a pale yellow or amber color, an aromatic
odor, an acid reaction, and a specific gravity of 1.020. As a rule, it
is perfectly transparent, though its transparency may be diminished
from the presence of mucus, calcium and magnesium phosphates, and
mixed urates.

The color, which varies within physiologic limits from a pale
yellow to a reddish-brown, is due to the presence of the coloring-
matters urobilin, urochrome, and uroerythrin, all of which are de-
rivatives from the bile pigments absorbed from the liver or the
alimentary canal.

The reaction of the urine is acid, owing to the presence of the acid
phosphates of sodium and calcium. The degree of acidity, however,
varies at different periods of the day. Urine passed in the morning
is strongly acid, while that passed during and after digestion, espe-
cially if the food be largely vegetable in character and rich in alkaline
salts, is either neutral or alkaline in reaction. The diminished acidity
after meals is attributed to the formation of hydrochloric acid by the

420

EXCRETION. 421

gastric glands and the consequent liberation of bases which are ex-
creted in the urine. The phosphoric acid which enters into com-
bination with sodium and potassium bases is a product of tissue
metaboHsm.

The specific gravity is about 1.020, though it varies from 1.015
to 1.025. It will diminish, other things being equal, with increased
consumption of water and diminished activity of the skin; it will be
increased of course by the opposite conditions.

The quantity of urine excreted in twenty-four hours varies from
1200 to 1700 c.c. Amounts both above and below these are fre-
quently passed from a variety of causes.

The odor of the urine is characteristic and due to the presence of
aromatic compounds.

COMPOSITION OF URINE.

Water, 1500.00 c.c.

Total solids, 72.00 grams.

Urea, 33.18 "

Uric acid, (urates), 0.55 "

Hippuric acid, hippurates, 0.40 "

Kreatinin, xanthin, hypoxantliin, guanin, ammo- ) „

nium salts, pigment, etc. J

Inorganic salts : sodium and potassium sulphates, "]

phosphates, and chlorids; magnesium and cal- |

cium phosphates, j- 27.00 "

Organic salts: lactates, acetates, formates in small I

amounts, J

Sugar, a trace

Gases, nitrogen, and carbonic acid.

The estimation of total urinary solids in any given sample of
urine'is frequently a matter of clinical interest. This may approxi-
mately be attained by multiplying the last two figures of the specific
g^a^"ity by the coefficient of Haeser or Christison, 2.33. The result
expresses the total solids in looo parts: e.g., urine with a specific
gra\'ityof 1.020 would contain 20X2.33, or 46.60 grams of soHd
matter per 1000 c.c. If the amount passed in twenty-four hours be
1500 c.c, the total solids would amount to 69.9 grams.

The Water of the Urine. — The amount of urinar}- water and its
ratio to the sohd constituents will vary with the amount consumed
and the activity of the skin and lungs. In summer the foods, liquid
and sohd, remaining the same, the quantity of water in the urine is
diminished in consequence of increased activity of skin and lungs
and the ratio of water to sohds decreased. In winter the reverse
conditions obtain. The food remaining the same, the consumption
of large quantities of water hastens at least the removal of end-
products from the tissues and thus increases the urinar}^ solids.

Urea is the most abundant of the organic constituents of the
urine and is present to the extent of from 2 to 3 per cent. It is a

422 TEXT-BOOK OF PHYSIOLOGY.

colorless neutral substance, crystallizing under varying conditions
in long silky needles or in rhombic prisms. It is soluble in water
and alcohol. It is composed of CON2H4. When subjected to pro-
longed boiling, it combines with water, giving rise to ammonium
carbonate. The presence of Micrococcus urea in urine will also
convert the urea, by combining it with two molecules of water, into
ammonium carbonate, C0N2H4-|-2H20=(NHJ2C03.

The average amount of urea excreted daily varies from 30 to 34
grams. As urea is now known to be the principal end-product of
proteid metabolism within the body, it is evident that the quar^tity
produced and eliminated in the twenty-four hours will depend on the
quantity of proteid food consumed and on the extent to which the
proteid constituents of the tissues are metabolized. In the condition of
nutritive equilibrium, when the proteid ingested is 100 grams and the
urea egested 31.5 grams, it is difficult to state the percentage of urea
which is derived from the metabolism of the proteid food (circulating
proteid) and that derived from the metabolism of the proteids of the
tissues (organ proteid). In this condition, however, it is found that
if the proteid consumed is varied within limits above or below the
standard amount of 100 grams, the quantity of urea excreted rises and
falls in practically the same ratio, indicating apparently that the
production of urea is directly dependent on the proteid supply. On
the contrary, it has been observed in human beings in the fasting
condition that for a period of ten days there is a daily excretion of
about 21 grams of urea, equivalent to about 70 grams of proteid.
Again, contrary to former views, the metabolism of proteid and the
production of urea are practically independent of muscular work.
Even after severe labor extending over a period of some hours there
is no noticeable increase in the urea eliminated.

Seat of Urea Formation. — It is quite certain in the hght of
present knowledge that urea is partly formed in the liver by the action
of the cells out of cleavage products of proteid metabolism. The par-
ticular compounds out of which the cells synthetize urea are the
ammonium salts, especially the carbamate and carbonate. The
experimental reasons for this view have already been stated on page
410.

Uric acid is one of the constant ingredients of the urine. It is a
crystalhne nitrogen-holding body closely resembling urea, its formula
being CjH^N^O,. The total quantity excreted daily varies from 0.2
to I gram. It is doubtful if uric acid exists in a free state in the
urine, the indications being that it is combined with sodium and
potassium in the form of a quadriurate. The urates are frequently
deposited when in excess from the urine as a brick-red sediment,
the color being due to their combination with the coloring-matter
uroerythrin. When pure, uric acid crystalhzes in the rhombic form^

EXCRETION. 423

though it assumes a variety of forms. Uric acid was long regarded
as a product of general proteid metabolism and for chemic reasons
an antecedent of urea. This view has been abandoned. At present
it is believed that it is a cleavage product of nuclcin, a constituent
of all cell nuclei. In the metabolism of nuclcin a proteid and nucleic
acid are formed, from the latter of which uric acid is derived. Nu-
cleic acid when decomposed yields a series of bases, such as xanthin,
hypoxanthin, adenin, guanin, etc., known collectively as the alloxur
bases, including uric acid, a name which indicates their relation,
on the one hand, to alloxan and on the other to urea. Though there
is a close relationship between uric acid and the alloxur bases, it has
been impossible to experimentally derive one from the other. When
hypoxanthin, however, is given internally it is oxidized and converted
into uric acid. It is extremely probable, therefore, that uric acid is
an oxidation product of one or more of the alloxur bases.

Xanthin, hypoxanthin, guanin, etc., are also found in urine
in small but variable amounts. They are nitrogenized compounds
derived mainly from the metabohsm of the nuclein bodies.

Kreatinin is a crystalline nitrogenous compound closely resem-
bling kreatin, one of the constituents of muscular tissue. The amount
excreted daily is about i gram. Though kreatinin may arise in conse-
quence of proteid metabolism, it is probable that it is largely derived
from a transformation of the kreatin contained in the meat consumed
as food.

Hippuric acid in combination with sodium and potassium is
very generally present in urine, though in small amounts. It is more
abundant in the urine of the herbivora than the carnivora. In man
the amount excreted daily is about 0.7 gram, though the amount may
be raised by a diet of asparagus, plums, cranberries, etc., and by the
administration of benzoic and cinnamic acids. There is evidence that
hippuric acid is formed in the kidney from benzoic acid, its pre-
cursors, or related bodies. Various compounds of this class are found
in vegetable foods, a fact which may account for the increase in the
excretion of uric acid on a vegetable diet.

Leucin, tyrosin, phenol, cystin, indoxyl, skatoxyl, are found
in small amounts even under normal conditions. They arise from
putrefactive change in the intestine.

Inorganic Salts. — Sodium and potassium phosphates, known
as the alkaline phosphates, are found in both blood and urine.
The total quantity excreted daily is about 4 grams. Calcium
and magnesium phosphates, known as the earthy phosphates, are
present to the extent of i gram. Though insoluble in water, they
are held in solution in the urine by its acid constituents. If the
urine be rendered alkaline, they are at once precipitated. Sodium
and potassium sulphates are also present to the extent of about

424 TEXT-BOOK OF PHYSIOLOGY.

2 grams. The phosphoric and sulphuric acids which are combined
with these bases enter the body for the most part in the foods, though
there is evidence that they also arise by oxidation in consequence of
the metaboHsm of proteids which contain phosphorus and sulphur.
Sodium chlorid is the most abundant of the inorganic salts. It is
derived mainly from the food. The amount excreted is about 15
grams in twenty- four hours.

THE KIDNEYS.

The kidneys are the organs engaged in the excretion of the
urinary constituents from the blood. They resemble a bean in shape,
are from 10 to 12 centimeters in length, 2 in breadth, and weigh from
144 to 170 grams. They are situated in the lumbar region, one on
each side of the vertebral column behind the peritoneum, and extend
from the eleventh rib to the crest of the iHum. The anterior surface
is convex, the posterior surface concave. The latter presents a deep
notch — the hilum. The kidney is surrounded by a thin smooth
membrane composed of white fibrous and yellow elastic tissue;
though it is attached to the surface of the kidney by minute processes
of connective tissue, it can very readily be torn away. The sub-
stance of the kidney is dense but friable.

Upon making a longitudinal section of the kidney it will be ob-
served that the hilum extends into the interior of the organ and
expands to form a cavity known as the sinus, in which are found the
blood-vessels, nerves, and duct (Fig. 192). This cavity is mainly
occupied by the upper part of the renal duct, the ureter, the interior
of which is termed the pelvis. The ureter divides into several por-
tions which terminate in small caps or calyces which receive the
apices of the pyramids. The parenchyma of the kidney consists of
two portions: viz. —

1. An internal or medullary portion, consisting of a series of pyramids

or cones, some twelve or fifteen in number, which present a dis-
tinctly striated appearance.

2. An external or cortical portion, half an inch in thickness and dis-

tinctly friable in character.
The Histology of the Kidney. — The kidney is composed of a
connective-tissue framework supporting secreting tubules, blood-
vessels, lymphatics, and nerves, all of which are directly connected
with the removal of the urinary constituents from the blood. The
kidney is structurally a compound tubular gland. If the apex of
each pyramid be examined with a lens, it will present a number of
small orifices which may be regarded as the beginnings of the urinifer-
ous tubules. From this point the tubules pass outward in a straight
but somewhat diverging manner toward the cortex, giving off at

EXCRETION.

425

acute angles a number of branches (Fig. 193). From the apex to the
base of the pyramids they are known as the tubules of Bellini. In
the cortical portion of the kidney the tubule becomes enlarged and
twisted, and, after pursuing an extremely convoluted course, turns
backward into the
medullary portion for
some distance, form-
ing the ascending limb
of Henle's loop; it
then turns upon itself,
forming the descend-
ing Hmb of the loop, re-
enters the cortex, again
expands and becomes
convoluted, and finally
terminates in an ovoid
enlargement known as
Miiller's or Bowman's
capsule, in which is
contained a small tuft
of blood-vessels — the
glomerulus. Each
tubule consists of a
basement membrane
hned throughout its
entire extent by epi-
thelial cells. The epi-
thehum as well as the
tubule vary in shape
and size in different
parts of its course. In
the capsule the epi-
thelium is flattened,
lining not only the
inner surface of the
capsule but reflected
over the blood-vessels
well. This

Fig.

as

IS

known as the glomer-

192. — Longitudinal Section through the
Kidney, the Pelvis of the Kidney, and a
Number of Renal Calyces. A. Branch of the
renal artery. U. Ureter. C. Renal calyx. i.
Cortex, i'. ]Meduliary rays. i". Labyrinth, or
cortex proper. 2. Medulla. 2'. Papillary por-
tion of medulla, or medulla proper. 2". Border
layer of the medulla. 3, 3. Transverse section
through the axes of the tubules of the border layer.
4. Fat of the renal sinus. 5, 5. Arterial branches.
*. Transversely coursing medulla rays. — {Tyson,
after Henle.)

ular epithehum. In
the convoluted por-
tions of the tubules the epithehum is cuboidal, granular, and some-
what striated; in Henle's loop it is more or less flattened.

The Blood-vessels of the Kidney. — The renal artery enters the
kidney at the hilum behind the ureter; it soon di\'ides into several

426

TEXT-BOOK OF PHYSIOLOGY.

large branches which penetrate the substance of the kidney between
the pyramids and pass outward into the cortex. At the base of 'the

Lobule.

Lobule.

Renal corpuscle

Thin
division of the
loop of Henle.

Collecting
tubule.

Tunica albuginea.

Arciform artery.

,. Arciform vein.

— Interlobar artery.
_- Interlobar vein.

Papillary duct.

Fig. 193. — Scheme of the Course of the Uriniferous Tubules and the Renal

Vessels.

EXCRETION.

427

pyramids branches of the arteries form an anastomosing plexus.
From this plexus vessels are given off, some of which follow the straight
tubules. toward the apex of the pyramids, vasa recta, while others
enter the cortex and pass to its surface (Fig. 193). In the course of
the latter small branches are given off, each of which soon divides and
subdivides to form a ball of capillary vessels known as the glomer-
ulus. These capillaries, however, do not anastomose, but soon re-
unite to form an efferent vessel the caHber of which is less than that
of the afferent artery. In consequence of this, there is a greater re-
sistance to the outflow of blood than to the inflow, and therefore a
higher blood-pressure in the glomerulus than in capillaries generally.
The relation of the glomer-
ulus to the tubule is im-
portant from a physiologic
point of view. As stated
above, the glomerulus is
received into and sur-
rounded by the terminal
expansion or capsule of
the tubule. This capsule,
formed by an indentation
of the terminal portion of
the tubule, consists of two
walls, an outer one consist-
ing of an extremely thin
basement membrane,
covered by flattened epi-
thehal cells, and an inner
one consisting apparently
only of flattened epithelium
which is reflected over and
closely invests the glomer-
ular blood - vessels (Fig.
194). The blood is thus separated from the interior of the capsule
by the epitheHal wall of the capillar}^ and the epithehum of the re-
flected wall of the capsule. During the periods of secretory activity
the blood-vessels of the glomerulus are filled with blood to such an
extent that the sac cavity is almost obHterated. After its exit from
the capsule the efferent vessel of the glomerulus soon again divides
and subdivides to form an elaborate capillar}- plexus which surrounds
and closely invests the convoluted tubules. From this plexus as
weU as from the plexus which surrounds the straight tubules veins
arise which pass toward and empty into veins at the base of the pyra-
mids. The renal vein formed by the union of these latter veins
emerges from the kidney at the hilum and finally empties into the
vena cava inferior.

Fig 194. — Scheme of the Renal or Mal-
pighi.a:n' Corpuscle, i. Interlobular ar-
tery. 2. Afferent vessel. 3. Efferent vessel.
4. Outer wall. 5. Inner wall. 6. Glom-
erulus. 7. Neck of tubule. — (Stokr.)

428 TEXT-BOOK OF PHYSIOLOGY.

The nerves of the kidney are derived from the renal plexus, and
follow the course of the blood-vessels to their termination.

The Renal Duct. — The excretory duct of the kidney, the ureter,
is a musculo-membranous tube about 5 mm. in diameter when dis-
tended, 30 cm. in length, and extends from the hilum to the base of
the bladder. The upper extremity is expanded and within the renal
sinus becomes irregularly branched, giving rise to a number of short
tubes, called calyces, each of which embraces the apex of a Malpighian
pyramid. The interior of the expanded portion of the ureter is
known as the pelvis. The wall of the ureter consists of a mucous
membrane, a muscle coat, and an external fibrous investment.

MECHANISM OF URINE SECRETION.

The secretion of urine is a complex process and susceptible of
several interpretations. It was originally inferred by Bowman that,
as the kidney presents anatomically an apparatus for filtration, the
capsule with its enclosed glomerulus, and an apparatus for secretion,
the epithelium of the urinary tubules, the ehmination of the urinary
constituents from the blood is accomplished by the two processes of
filtration and secretion ; that the water and highly diffusible inorganic
salts simply pass by diffusion, under pressure, through the walls of
the glomerular capillaries, while the organic constituents are removed
by the epithelium lining the tubules.

Influenced largely by the facts of blood-pressure Ludwig advanced
the view that the factors concerned in the secretion of urine were
purely physical; that in consequence of the high pressure in the
vessels of the glomeruli, due to the resistance offered by the smaller
efferent vessel, all the urinary constituents were filtered off in a
state of extreme dilution. In order to account for the higher per-
centage of the organic constituents in the urine, it was assumed that
as the dilute urine passed through the tubules the water was partly
reabsorbed, passing by diffusion into the lymph and blood until the
urine acquired its normal characteristics. In support of this view,
a large number of facts relating to the influence of an increase and a
decrease of pressure in the blood-vessels of the glomeruli, the velocity
of the blood-stream, etc., in determining the rate of urinary flow
were adduced, all of which apparently indicated that the former
stood to the latter in the relation of cause and effect, and that the
formation of urine was accomplished entirely by physical forces.

The progress of physiologic investigation, however, has thrown
some doubt on the validity of this physical interpretation, and has
rather served to support the view of Bowman that the organic con-
stituents at least are removed from the blood by a process of selection
on the part of the epithelium of the convoluted part of the urinary

EXCRETION. 429

tubules; in other words, that the secretion of urine is physiologic
rather than physical. Heidenhain has brought forward a series of
facts which support this view. As evidence that the cells possess a
selective power, he presents the following experiment : The spinal cord
of an animal is divided in the neck for the purpose of lowering the
blood-pressure in the kidney below the pressure at which the urine is
secreted; a solution of indigo-carmine is injected into the blood-
vessels; after the lapse of ten minutes the animal is killed, the blood-
vessels washed out with alcohol for the purpose of precipitating the
indigo-carmine in situ. Section of the kidney shows a uniform blue
stain of the cortex alone. Microscopic examination reveals the fact
that the blue stain is due to the deposition of the pigment in the lumen
and in the lumen border of the cells of the convoluted tubules and
the ascending limb of Hcnle's loop; while the epithelium of Bow-
man's capsule as well as the glomerular epithelium present no evi-
dence of pigmentation.

Nussbaum attempted to estabhsh the secretory power of the epi-
thelium in another way. In the frog the kidney receives blood from
two sources: the glomeruli receive their blood from the renal artery,
the tubules from the capillaries formed by the anastomosis of branches
of the efferent vessel of the glomerulus and the branches of the renal
portal vein. Nussbaum believed that by ligating the renal artery
all glomerular activity could be abolished and the part played by the
epithehum could be estabhshed. After so doing the flow of urine was
at once checked; the injection of urea at once reestabhshed it. This
fact was taken as a proof that the tubular epithelium not only ex-
creted urea, but water and perhaps other constituents as well. It
was also found that sugar, peptones, carmine, etc., which are always
eliminated from the blood under normal conditions, are not removed
after Hgation of the renal artery. It was concluded from these ex-
periments that the secreting structures of the kidney consist of two
distinct systems, the glomerular and the tubular; the former secreting
water, salts, sugar, peptone, etc.; the latter urea, uric acid, etc.
These and similar facts indicate that the renal epithehum possesses
a secretory rather than an absorptive function. Heidenhain and
those who agree with him assert that even the water and inorganic
salts which pass through the glomerular epithelium do so in conse-
quence of cell selection and cell activity; that the entire process is one of
secretion, though conditioned by blood-pressure, blood velocity, etc.

Influence of Blood-pressure. — Whether the ehmination of the
urinar}^ constituents is entirely secretor}^ (physiologic) in character
or not there can be no doubt that the whole process is largely deter-
mined by the pressure and velocity of the blood in the glomerular
capillaries, or, to state it more accurately, on the difl"erence of pres-
sure between the blood in the capillaries and the urine in the capsules.

43°

TEXT-BOOK OF PHYSIOLOGY.

As a rule, this latter pressure is at a minimum. If the urine should
accumulate in the ureter and tubules either from ligation or mechan-
ical obstruction until its pressure approximates that of the blood, the
secretion would be diminished if not abolished. It is difficult to
determine the average pressure or velocity of the blood in the
glomerular capillaries, though they both must be greater than in
capillaries in other parts of the body, from the fact that the
efferent vessel is narrower than the afferent, and therefore offers

great resistance to -the outflow
of blood, a condition most favor-
able to the production of a
high pressure in the glomerulus.
The pressure of the blood in
the glomeruli may be raised and
the velocity increased :

1. By an increase in blood-pres-
sure generally.

2. By an increase in the pressure
of the renal artery alone.

The first condition may be
brought about by an increase in
either the force or frequency of
the heart's action or by a con-
traction of the arterioles of vas-
cular areas in any or all parts of
the body, excepting, of course,
the renal vascular area. The
second condition is brought about
by a dilatation of the renal artery
alone and possibly by a contrac-
tion of the efferent vessels of the
glomeruli.

The pressure of the blood in
the glomeruli may be diminished
and the velocity decreased —

1. By a decrease in the blood-pressure generally.

2. By a decrease in the pressure of the renal artery alone.

The first condition is brought about by a decrease in either the
force or frequency of the heart's action or by a dilatation of the arteri-
oles of large vascular areas in any or all parts of the body. The
second condition is brought about by contraction of the renal artery
alone and possibly by a dilatation of the efferent vessels of the glom-
eruli. The effect of the contraction and relaxation of either the
afferent or efferent vessels on the pressure within the glomerulus
is shown in figure 195.

Fig. 195. — To Illustrate the Effect
OF Active Changes in the Vasa
Afferentia and Efferentia on
the Pressure in the Glomerular
Capillaries. A. Renal arteries.
G. Glomerular capillaries. C.

Tubular capillaries. V. Vein. The
short thick hnes represent the vasa
afferentia and efferentia. The con-
tinuous heavy Une represents the
mean average pressure. If the vas
afferens dilates and the vas efferens
contracts separately or conjointly,
the pressure will rise, as indicated by
the upper dotted line. If the vas
afferens contracts and the vas
efferens dilates separately or con-
jointly, the pressure will fall, as in-
dicated by the lower dotted Une. —
{After Moral and Starling.)

EXCRETION.

431

Coincident with the rise and fall of pressure in the glomerular
capillaries there is a rise and fall in the rate of urinary flow. Thus
it has been found that an increase in the aortic pressure from 127 to
142 mm. of mercur}', by ligation of the carotid, femoral, and vertebral
arteries, increased the rate of urinary flow from 8.7 grams in thirty
minutes to 21.2 grams. On the contrary, a decrease in aortic pres-
sure below 40 mm. of mercury caused by division of the spinal cord
is followed by a total abolition of the urinary flow. These facts
serve to indicate the dependence of the secretion on blood-pressure.

That there is an increase in the volume of the blood flowing
through the kidney during its functional activity is apparent from
inspection. It is enlarged, swollen, and red in color. The blood in
the renal vein is bright red in color and contains more oxygen and
less carbon dioxid than venous blood generally. During the intervals

Fig. 196. — Oncometer. K. Kidney; the thick line is the metallic capsule, h.

Hinge. I. Tube for filling apparatus. T. Tube to connect with T,. a, v, u.

Artery, vein, ureter. — {Stirling, after Roy.)
Fig. 197. — Oncograph. C. Chamber filled with oil, communicating by T, with
T. p. Piston. /. Writing-lever. — {Stirling, after Roy.)

of activity the kidney diminishes in size, is pale in color and the
blood of the renal vein dark and venous in character. These varia-
tions in the volume of the kidney have also been experimentally deter-
mined and registered by means of the oncometer and oncograph
devised by Roy (Figs. 196 and 197)-

The oncometer consists of a metaUic box (Fig. 196) composed
of halves which open and close by means of a hinge. It is con-
nected with a recording apparatus, the oncograph (Fig. 197), through
the tube T. The kidney, withdrawn from the body, is placed
within the oncometer. Through an opening in the side pass the
arter}-, vein, and ureter. Between the kidney and the wall of
the capsule there is placed a thin membrane. Oil is then poured
through the side tube I until the space between the capsule and

432 TEXT-BOOK OF PHYSIOLOGY.

the kidney, as well as the tube leading to the chamber of the onco-
graph, are completely filled. When the tube I is closed, the condi-
tions are such that all variations in the volume of the kidney are
taken up and reproduced by the recording lever attached to the
piston of the oncograph. A curve of the variations in the volume
of the kidney is shown in figure 198, taken simultaneously with the
curve of the blood-pressure. An examination of this curve shows
that the volume-changes coincide with changes in the blood-pressure,
exhibiting not only the respiratory but also the cardiac undulations.
Influence of the Nervous System. — The influence of the
nervous system in regulating the blood-supply to the kidney is evi-
dent from the results of experimentation. If the nerves which
accompany the renal artery into the kidney are divided, the artery
at once dilates, the kidney enlarges, and a copious flow of urine
takes place. If the peripheral ends of these nerves be stimulated
with the induced electric current, the artery contracts, the kidney

B.P.

K

..BLOOD PRESSURE CURVE
KIDNEY CURVE

V

A ,

' ' /4 M I N

Fig. 198. — B. P. Blood-pressure curve. K. Curve of the volume of the kidney. T.
Time curve; intervals indicate a quarter of a minute. A. Abscissa. — {Stirling,
after Roy.)

diminishes in size, and the flow of urine ceases. In addition to
these vaso-constrictor nerves, there is evidence that the kidney also
receives vaso-dilator nerves which emerge from the spinal cord and
are found in the anterior roots of the eleventh, twelfth, and thirteenth
dorsal nerves, in the dog. Direct and reflex stimulation of these
nerves gives rise to a dilatation of the artery, a swelling of the
kidney, and an increase in secretion, independent of any variation
in general blood-pressure.

The route of the vaso-constrictor nerves is, in the dog at least,
through the splanchnics. Section of these nerves is followed by a
dilatation of the renal vessels and an increase in the flow of urine.
Stimulation of the peripheral ends is followed by a constriction of
the vessels and a cessation of the flow of urine.

The vasomotor center for the blood-vessels of the kidney is in all
probabihty situated in the medulla oblongata in close proximity to
the general vasomotor centers, though subordinate centers are doubt-

EXCRETION.

433

less present in the spinal cord. It was found by Bernard that punc-
ture of the medulla was occasionally followed by a profuse secretion
of urine without the presence of sugar. The route of the vaso-motor
impulses which influence the renal blood-supply is down the cord
through the splanchnics and through the renal plexus.

Influence of Variations in the Composition of the Blood. —
As it is the function of the kidneys to excrete water and various end-
products from the blood and thus maintain a general average com-
position, it is highly probable that as soon as they accumulate be-
yond a certain percentage they themselves act as stimulants to renal
activity, either by acting directly on the renal epithehum or by in-
creasing the glomerular pressure. There is evidence at least that
urea acts in the former manner. An excess of water in the blood
from copious drinking or from a sudden checking of the skin from a
fall of temperature will act in the latter way. The introduction into
the blood of inorganic salts, such as potassium nitrate, sodium
acetate, etc., will in a short time lead to increased activity of the
kidneys, as shown by an increase in the quantity of urine excreted.
The manner in which these agents and other members of their class,
the so-called sahne diuretics, increase renal activity is yet a subject
of discussion. On the one hand, it is stated that they promote an
absorption of water from the tissues to such an extent that a condition
of hydremic plethora is produced, which in itself increases not only
the general blood-pressure but the local renal pressure as well, and
that it is this factor which is the cause of the increased flow of urine.
On the other hand, it is asserted that though the salts increase
the local pressure and the volume of the kidney, they nevertheless
act specifically on the renal epithelium, and therefore may be re-
garded as secreto-motor agents. An increase in the percentage of
sugar or urea in the blood has a similar influence on the kidney.

MICTURITION.

Movement of the Urine. — The urine, as soon as it is poured
into the uriniferous tubules, flows through the tubules into the pelvis,
through the ureter into the bladder. The immediate cause of this
movement is undoubtedly a difference of pressure between the
terminal portions of the tubules and the terminal portion of the
ureter, aided by the peristaltic contraction of the muscle wall of
the ureter.

The bladder is a reservoir for the temporary reception of the urine
prior to its expulsion from the body. When distended it is ovoid in
shape and is capable of holding from 600 to 800 cu. cm. The bladder
is composed of four coats: viz., serous, muscle, areolar, and mu-
cous. The muscle coat consists of an external longitudinal and an
internal circular and obhque sets of fibers of the non-striated variety
28

434 TEXT-BOOK OF PHYSIOLOGY.

which collectively encircle the entire organ. As these fibers by their
contraction expel the urine from the bladder, they are known col-
lectively as the detrusor tirincE muscle. At the exit of the bladder
the circular fibers are somewhat increased in number, giving rise to
the appearance of a distinct muscle which has been termed the
sphincter vesica muscle. The urethra just beyond the bladder is
provided with a distinct circular muscle composed of striated fibers,
the sphincter urethrce muscle. When the urine passes into the blad-
der it is retained there and prevented from escaping by the contrac-
tion of this latter muscle. Under normal conditions the urine ac-
cumulates before its presence gives rise to a characteristic sensation
and the desire for urination.

Nerve Mechanism of Urination. — The muscle mechanisms
which retain as well as expel the urine are under the control of the
nerve system. The sphincter urethrae muscle, by which the orifice
of the bladder is closed, is kept in a state of tonic contraction by nerve
impulses coming from the spinal cord through the anterior roots of
the third and fourth sacral nerves. The detrusor urinae muscle is
excited to contraction by impulses coming hkewise through the sacral
nerves from the cord. The centers of origin for these two sets of
motor nerves are located in the cord in the neighborhood of the fifth
lum.bar vertebra. The expulsion of the urine is largely a reflex act,
though under the control of the will. When the desire to urinate is
experienced, nerve impulses are coming through sensory nerves from
the mucous membrane of the bladder which are reflected to the centers
governing the sphincter urethras and detrusor urinje muscles and to
the brain. The effect of the reflected impulses is to inhibit the
sphincter center and to stimulate the detrusor center. If the act of
urination is to be permitted, volitional impulses descend through
the spinal cord which have the eft'ect of still further inhibiting the
sphincter center and stimulating the detrusor center, the result being
a relaxation of the sphincter muscle and a contraction of the detrusor
muscle and the expulsion of the urine. If the act of urination is to be
suppressed, volitional impulses inhibit the detrusor center and stimu-
late the sphincter.

PERSPIRATION; SEBUM.

The perspiration or sweat, the chief secretion of the skin, is a
clear colorless fluid, shghtly acid in reaction and saline to the taste.
Its specific gravity varies from 1.003 to 1.006. Unless collected from
the soles of the feet and the palms of the hand, it is apt to be mixed
with epithelial cells and sebum. The total quantity of perspiration
secreted daily has been variously estimated at from 700 to 1000 grams;
the exact amount, however, is difficult of determination, for the reason

EXCRETION. 435

that the rate of secretion \aries readily with variations in tempera-
ture, food, drink, season of the year, etc.

Chemic analysis of the sweat shows that it contains but from 0.5
to 2.5 per cent, of sohd constituents, the variation in the percentage
depending on the quantity of water secreted. The sohds consist
of traces of urea, neutral fats, lactic and sudoric acids in combination
with alkaline bases, and inorganic salts (Fovel). Other observers,
however, have not been able to detect the presence of either lactic
or sudoric acid. Urea is a constant ingredient, though its percentage
is extremely small, possibly not more than o.i per cent. The amount,
however, may be very much increased in uremic conditions, the
result of acute or chronic disease of the kidneys. The inorganic
constituents consist mainly of sodium chlorid and alkahne and
earthy phosphates. Carbonic acid is also present in the free state
as well as in combination with alkaline bases.

The ver\' small quantity of the solid constituents in the sweat,
taken in connection with the fact that it is excreted most abundantly
when the external temperature is high, indicates that it is not so im-
portant as an excrementitious fluid as it is as a means for the regula-
tion of the temperature of the body.

The sweat is a product of the secretory activity of specialized
glands, the sweat-glands, embedded in the skin, to the histologic
structures of which they bear a special relation.

THE SKIN.

The skin is a complexly organized structure investing the entire
external surface of the body. Its total area varies from 16 to 20 feet
in man and from 12 to 16 feet in woman. It varies in thickness in
different localities of the body from ^ to yito ^^ ^^ inch. The skin
consists of two principal layers: viz., a deep layer, the derma or
corium, and a superficial layer, the epidermis.

The derma or corium may be subdivided into a reticulated and a
papillary layer. The reticulated layer consists of white fibrous and
yellow elastic tissue, non-striated muscle fibers, w'oven together in
every direction and forming an areolar network, in the meshes of
which are deposited masses of fat and a structureless amorphous
matter; the papillar\^ layer consists mainly of club-shaped elevations
or projections of the amorphous matter constituting the papillae.
The reticulated layer serves to connect the skin with the underlying
structures and to afford support for the blood-vessels, nerves, and
lymphatics which are distributed to the papillae (Fig. 199).

The epidermis is an extra-vascular structure consisting entirely
of epithelial cells. It may also be subdivided into two layers —
the Malpighian or pigmentary layer, and the corneous or horny layer.
The former is closely applied to the papillar\^ layer of the true skin

436

TEXT-BOOK OF PHYSIOLOGY

and is composed of large nucleated cells, the lowest layer of which, the
"prickle cells," contains the pigment granules which give to the skin
its varying hues in different individuals and in different races of men;
the corneous layer is composed of flattened cells which from their
exposure to the atmosphere, etc., are hard and homy in texture.

The Sweat-glands. — These glands are tubular in shape, the inner
extremity of each being coiled upon itself a number of times, forming

a little ball situated
in the derma or
the subcutaneous
connective tissue.
From this coil the
duct passes up in a
straight direction to
the epidermis,
where it makes a
few spiral turns,
after which it opens
obliquely on the
surface. The gland
consists of a base-
ment membrane
lined with epithelial
cells. It is sup-
plied abundantly
with blood-vessels
and nerves. The
sweat - glands are
extremely numer-
ous all over the
cutaneous surface,
though they are
more thickly dis-
posed in some situ-
ations than others.
They probably
average 2500 to the
square inch; the total number has been estimated at from 2,000,000
to 2,500,000.

Influence of the Nerve System on the Production of
Sweat. — The secretion of sweat, though a product of the activity
of epithelial cells and dependent on a variety of conditions, is reg-
ulated to a large extent by the nerve system. Here as in other
secreting glands the fluid is derived from materials in the lymph-
spaces, furnished by the blood. Generally the two conditions, in-

^s;^.-

Fig.

199. — Section Perpendiculaexy Through the
Healthy Skin. a. Epidermis, or scarfskin. h.
Rete mucosum, or rete malpighii. c. Papillary
layer, d. Derma, corium, or true skin. e. Pan-
niculus adiposus, or fatty tissue. /, g, h. Sweat-
gland and duct, i, k. Hair, with its follicle and
papilla. I. Sebaceous gland.

EXCRETION. 437

creased blood-flow and increased glandular action, coexist. At
times, however, a profuse clammy perspiration is secreted with dimin-
ished blood-flow. Two sets of nerves are evidently concerned in this
process: viz., vaso-motor nerves, which regulate the blood-supply, and
secretory nerves, which stimulate the gland-cells to activity.

The nerve-centers which control the sweat-glands are situated in
the spinal cord, though the number of such centers and their exact
location for the dift'erent regions of the body have not yet been
satisfactorily determined. In a general way it may be stated that the
centers for the head and face He in the upper cervical portion of the
cord; for the upper extremities, in the lower cervical portion; for the
lower extremities, in the lower dorsal and upper lumbar portion.
The secretory nerves which emerge from these centers reach the glands
of the face and head through the cervical sympathetic; of the arms
and legs, through the brachial plexus and the sciatic nerves. It is
probable that there is also a general dominating sweat center located
in the medulla oblongata.

That the sweat-glands are stimulated to activity by nerve impulses
is shown by the fact that stimulation of the peripheral end of the
divided cervical sympathetic, of the brachial plexus, or of the sciatic
nerve is followed in a few seconds by a profuse secretion. Though
under physiologic conditions there is a simultaneous dilatation of the
blood-vessels and an increased supply of blood, this is merely a
condition and not a cause of the secretion; for the secretion can be
excited and the flow maintained for a period of from ten to fifteen
minutes after ligation of the blood-vessels of the limb or even after
its amputation, when the corresponding nerve is stimulated.

The sweat-glands may be excited to activity by their related nerve-
centers, either by central, reflex, or peripheral influences. Among
the first may be mentioned mental emotions, venosity of the blood,
increased temperature of the blood, hot drinks, violent muscular
exercise, etc. Among the second may be mentioned powerful
stimulation of various afferent or sensory nerves, heightened external
temperature, etc. Among the last may be mentioned various
drugs. Pilocarpin injected into the blood causes a profuse secretion
even when the nerves have been divided. Its action is supposed to
be exerted on the terminal branches of the nerves and possibly on
the cells themselves. As in the case of the salivary glands atropin
suspends the activity of the terminal branches of the secretory'
nerves.

Hairs. — Hairs are found in almost all portions of the body, and
can be divided into —

1. Long, soft hairs, on the head.

2. Short, stiff hairs, along the edges of the eyelids and nostrils.

3. Soft, downy hairs on the general cutaneous surface.

438

TEXT-BOOK OF PHYSIOLOGY.

They consist of a root and a shajt.

and about -^^-^ of an inch in diameter

The shaft is oval in shape
it consists of fibrous tissue,
covered externally by a layer of imbricated cells, and internally by
cells containing granular and pigment material.

The root of the hair is embedded in the hair-follicle, formed by
a tubular depression of the skin, extending nearly through to the
subcutaneous tissue; its walls are formed by the layers of the corium,
covered by epidermic cells. At the bottom of the follicle there is a
papillary projection of amorphous matter, corresponding to a papilla
of the true skin, containing blood-vessels and nerves, upon which
the hair-root rests. The investments of the hair-roots are formed of
epithelial cells, constituting the internal and external root-sheaths.

The lower portion of the hair
follicle is connected with the upper
surface of the derma by bundles of
non-striated muscle-fibers which are
termed arrectores pilorum muscles.
Their inclination and insertion are
such that their contraction is fol-
lowed by erection of the hair follicle
and hair shaft. These muscles are
excited to action by nerves termed
pilo-motor nerves.

THE SEBUM.

The sebum or sebaceous

matter is a peculiar oily material
produced by specialized glands in
the skin. It consists of water, epi-
thelium, proteids, fat, cholesterin,
and inorganic salts.

The sebaceous glands are
simple and compound racemose
glands opening by a common excretory duct on the surface of the
epidermis or into the shaft of a hair-folhcle (Fig. 200). These
glands are extremely numerous and found in all portions of the
body, with the exception of the palms of the hands and soles
of the feet, and most abundantly in the face. They are formed
by a dehcate structureless membrane lined by polyhedral epithe-
hum.

The sebum is not produced by an act of true secretion, but is
formed by a proliferation and degeneration of the gland epithehum.
When first poured on the surface, the sebum is oily and semi-hquid
in character, but soon hardens and acquires a cheese-hke consistence.

Fig. 200. — Large Sebaceous Gland.
I. Hair in its follicle. 2, 3, 4, 5.
Lobules of the gland. 6. Excre-
tory duct traversed by the hair.
— (Sappey.)

EXCRETION.

439

It serves to lubricate the hair and skin and prevent them from be-
coming dry and harsh.

The surface of the fetus is generally covered with a thick layer of
sebaceous matter, the vernix caseosa, which possibly keeps the skin
in a normal condition by protecting it from the effects of the long-
continued action of the amniotic fluid in which the fetus is suspended.

CHx\PTER XVII.

THE CENTRAL ORGANS OF THE NERVE SYSTEM AND
THEIR NERVES.

The central organs of the nerve system are the encephalon
and the spinal cord lodged within the cavity of the cranium and the
cavity of the spinal or vertebral column respectively. The general
shape of these two portions of the nerve system corresponds with
that of the cavities in which they are contained. The encephalon is
broad and ovoid, the spinal cord narrow and elongated.

The encephalon is subdivided by deep fissures into four distinct,
though closely related portions: viz., (i) the cerebrum, the large
ovoid mass, occupying the entire upper part of the cranial cavity;
(2) the cerebellum, the wedge-shaped portion placed beneath the
posterior part of the cerebrum and lodged within the cerebellar foss£e
of the cranium; (3) the isthmus of the encephalon, the more or less
pyramidal-shaped portion connecting the cerebrum and cerebellum
with each other and both with (4) the meduha oblongata. (Fig.
201.)

The spinal cord is narrow and cyhndric in shape. It occupies
the spinal canal as far as the second or third lumbar vertebra. The
central nerve system is bilaterally symmetric, consisting of distinct
halves united in the median hne. The cerebrum is subdivided by a
deep fissure, running antero-posteriorly, into two ovoid masses termed
cerebral hemispheres; the cerebellum is also partially subdivided into
hemispheres ; the isthmus likewise presents in the median line a partial
division into halves; the medulla oblongata and spinal cord are
subdivided by an anterior or ventral and a posterior or dorsal fissure
into halves, a right and a left.

From the inferior surface of the encephalon and from either side
of the median line twelve nerve-trunks emerge, which as they pass
through foramina in the walls of the cranium are termed cranial
nerves. From each side of the spinal cord thirty-one nerve-trunks
emerge, which as they pass through foramina in the walls of the
spinal column are termed spinal nerves. As both cranial and spinal
nerves are ultimately distributed to the structures of the body, — i. e.,
the general periphery, — they collectively constitute the peripheral
organs of the nerve system.

The organs of the central nerve system are supported and pro-

440

THE ENCEPHALO-SPINAL MEMBRANES.

441

tected by three membranes named, in their order from without in
ward, the dura mater, the arachnoid, and
the pia mater.

The dura mater is -a tough membrane
composed of fibrous tissue. It consists of
two layers, the outer of which lines the
cranial cavity and forms an internal peri-
osteum; the inner layer is closely attached
to the outer except at certain regions where
it separates and forms supporting structures,
such as the falx cerebri, falx cerebelli,
tentorium cerebelli, etc.; at the margin of
the foramen magnum the outer layer be-
comes continuous with the periosteal tissue,
while the inner layer invests the cord down
to its ultimate termination. (Fig, 202.)

The arachnoid is a delicate serous
membrane. The external surface is smooth
and well defined and separated from the
dura by a narrow space, the subdural space.
The inner surface sends inward fine con-
nective-tissue processes which interlace in
every direction, constituting the subarach-
noid tissue. This tissue is abundant in the
cranium, much less so in the spinal canal.
The spaces between the connective tissue,
taken collectively, constitute the general sub-
arachnoid space. Around the spinal cord
this space is well defined, and at the base of
the encephalon expands to form large cavi-
ties known as the cisterna magna, cisterna
pontis, etc.

The pia mater is a delicate membrane
composed of areolar tissue. It closely
invests the encephalon and spinal cord,
dipping into the various fissures. It is
exceedingly vascular and sends small blood-
vessels for some distance into the brain and
spinal cord.

The Encephalo-spinal Fluid. — The
general subarachnoid space, as well as cer-
tain cavities within the encephalon, contain
a clear transparent fluid, termed the en-
cephalo-spinal. This fluid has an alkaline reaction and a specific
gravity of 1.007 or i-oo8. It is composed of water, proteids (pro-

FlG

201. — The Central
Organs of the Nerve
System, f.t.o. Fron-
tal, temporal, and oc-
cipital lobes of the
cerebrum, c. Cerebel-
lum, p . Pons. mo.
Medulla oblongata.
VIS., ms. The upper
and lower limits of the
spinal cord. The re-
maining letters indicate
the region and number
of the spinal nerves. —
{Quain, after Bourgery.)

442

TEXT-BOOK OF PHYSIOLOGY.

teoses and serum-globulin), and a compound pyrocatechin, capable
of reducing copper salts, though not exhibiting any other of the
properties of sugar. In many respects this fluid resembles lymph.
The subarachnoid space and the general encephalic cavities, termed
ventricles, communicate with one another by an opening in the pia
mater (the foramen of Magendie) as it passes over the lower part
of the fourth ventricle.

The Functions of the Central Nerve System. — The functions
of the central nerve system are twofold: (i) It coordinates the

organs and tissues of the body in such
a manner that when a stimulus is
applied to one structure it gives rise to
activity in another. (2) It serves to
bring the individual' into conscious
relationship with the external world.

The coordination of the organs and
tissues is accomplished mainly by the
intermediation of the spinal cord and
the medulla oblongata. The reflex
activities connected with digestion,
the circulation of the blood, with res-
piration, excretion, etc., are illustra-
tions of the coordinating capabilities
of the nerve-centers located in these
portions of the central nerve system.

Consciousness of the existence of
the external world and of the relation
existing between it and the individual
is associated with the physiologic activ-
ities of the encephalon, and more
particularly of the cerebral hemi-
spheres. This portion of the nerve
system is the chief, though perhaps not
the sole, organ of the mind, and its
main functions are for the most part
mental. The function of a part at least
of the peripheral nerve system is to
afford a means of communication
between the central nerve system and the remaining structures of
the body. The nerve-trunks constituting this part may be divided
into two groups, as follows:

I. The first group comprises nerves in connection with the special
sense-organs, e. g., eye, ear, nose, tongue, skin, as well as nerves
in connection with the general or organic sense-organs, e. g., mu-
cous membranes, viscera, etc., which transmit nerve impulses

Fig. 202. — The Membranes of
THE Spinal Cord. i. Dura
mater. 2. Arachnoid. 3.
Posterior root of spinal nerve.
4. Anterior root of spinal
nerve. 5. Ligamentum den-
tatum. 6. Linea splendens. —
{Morn's, ajter Ellis.)

THE SPINAL CORD. 443

to certain localized areas in the cerebral cortex, where they are

translated into conscious sensations. These sensations, both

special and general, by their grouping and combinations are the

primary elements of intelligence.

2. The second group comprises those nerves which terminate in the

muscle apparatus and which transmit nerve impulses, by way of

the medulla and spinal cord, from localized areas in the cerebral

cortex to the muscles of the face, trunk and extremities, which are

in consequence excited to activity. The muscle movements thus

become physical expressions of mental states, and if directed in a

definite manner to the overcoming of the resistances offered by

the external world become capable of modifying it in accordance

with the mental states.

The first group of nerves, the afferent, especially those connected

with the special sense-organs, are excited to activity by impressions

made on their peripheral terminations by agencies in the external

world, and thus become a means of communication between the

physical and the mental worlds.

The second group of nerves, the efferent, are excited to activity
by those molecular disturbances in their related nerve-cells which
accompany volitional efforts, and thus they become a means of com-
munication between the mental and the physical worlds.

The central nerve system is thus composed of a number of
separate though closely related parts, to each of which a separate
function has been assigned. In the study of the structure and func-
tion of these separate parts it will be found convenient, and con-
ducive to clearness, to consider them in the order of their complexity,
beginning with the spinal cord and ending with the cerebrum.

THE SPINAL CORD.

The spinal cord is the narrow elongated portion of the central
nerve system contained within the spinal canal. It is cylindric in
shape though presenting an enlargement in both the lower cervical
and lower lumbar regions corresponding to the origins of the nerves
distributed to the upper and lower extremities. The cord varies
in length from 40 to 45 cm., measures 12 mm. in diameter, weighs
42 grams, and extends from the atlas to the second lumbar vertebra,
beyond which it is continued as a narrow thread, the filuin terminale.
(Fig. 203.) It is divided by the anterior and posterior longitudinal
fissure into halves, and is therefore bilaterally symmetric. A trans-
verse section of the cord shows that it is composed of both white and
gray matter, the former covering the surface, the latter occupying
the center.

444

TEXT-BOOK OF PHYSIOLOGY.

Structure of the Gray Matter. — The gray matter is arranged
in the form of two crescents, united in the median hne by a trans-
verse band or commissure forming a figure resembhng the letter H.
Though varying in shape in different regions of the cord, the gray
matter in ah situations presents on either side an anterior or ventral

Superior or Cervical Segment
of Spinal Cord.

Middle or Dorsal Portion
of Cord.

Inferior Portion of Cord and
Cauda Equina.

Fig. 203. — Superior, Middle, and Inferior Portions of Spinal Cord. —
I. Floor of fourth ventricle. 2. Superior cerebellar peduncle. 3. Middle cerebellar
peduncle. 4. Inferior cerebellar peduncle. 5. Enlargement at upper extremity
of postero-median column. 6. Glosso-pharyngeal nerve. 7. Vagus. 8. Spinal
accessory. 9, 9, 9, q. Ligamentum denticulatum. 10, 10, 10, 10. Posterior roots
of spinal nerves. 11, 11, 11, 11. Postero-lateral fissure. 12, 12, 12, 12. Ganglia
of posterior roots. 13, 13. Anterior roots. 14. Division of united roots into
anterior and posterior nerves. 15. Terminal extremity of cord. 16, 16. Filum
terminale. 17, 17. Cauda equina. I, VIII. Cervical nerves. I, XII. Dorsal
nerves. I, V. Lumbar nerves. I, V. Sacral nerves. — (Sappey.)

and'a"posterior or dorsal horn. Between the two horns there is a
portion termed the intermediate gray substance. The commissure
presents in its center a narrow canal which extends throughout the
entire length of the cord. This canal is hned by cyhndric epithelium
and surrounded by gelatinous material. (Fig. 204.)

THE SPINAL CORD.

445

5-iA A

The anterior horn is short and broad and entirely surrounded
by white matter. The posterior horn is narrow and elongated and

extends quite up to the surface of the
cord, where it is capped by gelatinous
matter, the substantia gelatinosa. In
the lower cervical and thoracic regions
a portion of the intermediate gray
substance projects outward and forms
the so-called lateral horn. The gray
matter fundamentally consists of a
framework of fine neuroglia supporting
blood-vessels, lymphatics, medullated
and non-medullatecl nerves, and groups
of nerve-cells.

The Nerve-cells. — The nerve-cells
of the cord are very numerous and
present a variety of shapes and sizes in
different regions. They are usually ar-
ranged in groups which extend for some
distance up and down the cord, forming
columns more or less continuous.

In the anterior horn two well-
marked groups are found, one situated
at the anterior and inner angle, known
as the antero-median group, the other
situated at the posterior and lateral
angle and known as the postero-lateral
group. In the lower cervical and upper
thoracic regions, in the region of the
lateral horn, another group of cells
is found, known as the intermediate
group. In the central portion of the
horn there is also a central group.

The cells of the anterior horns are
of large size, nucleated and multipolar.
They are the modified descendants
of pear-shaped cells, the neuroblasts,
which migrated from the medullary
tube (see page iii). In the course of
their migration they developed den-
drites which form an intricate felt-
work throughout the anterior horn.
One of the processes, the axon,
approached the surface of the cord, penetrated it, grew outward,
became covered with myelin and neurilemma, and developed into

D

Fig. 204. — Sections Through
Different Regions of the
Spinal Cord. A. At the
level of the sixth cervical
nerve. B. At the mid-dorsal
region. C. At the center of
the lumbar enlargement. D.
At the upper part of the
conus medullaris. i. Poste-
rior roots. 2. Anterior roots.
3. Posterior fissure. 4. Ante-
rior fissure. 5. Central canal.
— 'Morris' "Anatomy,'" after
Schwalbe.)

446

TEXT-BOOK OF PHYSIOLOGY.

an anterior root-fiber. These nerve-cells, with their dendrites,
axons, and terminal branches, form efferent neurons of the first
order. The intimate histologic and physiologic relationship existing
between the nerve-cell and the axon is revealed by the degenerative
changes which arise in the latter when separated from the former.
The cell apparently determines the nutrition of the axon and may
be regarded as trophic in function. Some of the cells of the ante-
rior horn send their axons into the white matter of the same side,

Fig. 205. — Diagram Illustrating the Chief Cellular Elements of the Spinal
Cord, and the Probable Relations between the Cells and the Fibers
AND the Principal Tracts; the Left Half of the Figure Exhibits the
Communications OF the Several Varieties OF Nerve-cells. A, P. Ventral
or anterior and dorsal or posterior horns. PR. Posterior root bundles. DP.
Direct pyramidal tract. CP. Crossed pyramidal tract. DC. Direct cerebellar
tract. GB. Gowers's tract, a. Motor cells passing directly into fibers of ventral
roots, b. Various cells of the antero-lateral column. Some give off collateral
branches of remarkable size. c. Commissural (heteromeral) cells, d. Cells to
dorsal column (tautomeral) . e. Golgi cells of dorsal horn. The right half of the
diagram shows the communications established by means of the collateral fibers.
— {Piersol, after Lenhossek.)

after which they divide into two branches, one passing up, the other
down, the cord, to re-enter the gray matter at different levels. They
are probably associative in function. Other cells send their axons
into that portion of the white matter on the same and opposite sides
known as Gowers's antero-lateral tract. (Fig. 205.)

In the posterior horn nerve-cells are also present, though they
are not so numerous as in the anterior horn. At the base of the horn

THE SPINAL CORD. 447

and on its inner side there is a well-marked group of cells which ex-
tends from the seventh or eighth cervical nerves downward to the
second or third lumbar nerves, being most prominent in the thoracic
region. This column is known as Clarke's vesicular column. From
the nerve-cells constituting this column axons pass obliquely outward
into that portion of the white matter known as the direct cerebellar
tract.

Classification of Nerve-cells. — The cells of the gray matter
may be divided into two main groups: viz., efferent and afferent.

The efferent cells, independently of their trophic influence, are
also motor in function, inasmuch as the excitation arising in them
is transmitted outwardly through their axons to muscles, blood-
vessels, glands and viscera, imparting to them motion, either molar or
molecular. As the efferent fibers in the ventral roots of the spinal
nerves are classified (see page 113) in accordance with their physio-
logic action into motor, vaso-motor, secretor, inhibitor and accelerator
nerves, so the nerve-cells of which the nerves are integral parts may
be classified physiologically as motor, vaso-motor, secretor, inhibitor,
and accelerator.- Collections or groups of such cells are termed
"centers."

The afferent cells are largely sentient or receptive in function,
inasmuch as the excitations brought to the spinal cord by the afferent
nerves in the dorsal roots from the general periphery are received
by them and transmitted through their axons toward the cortex of the
cerebrum, where they are translated into conscious sensations. As
the nerve-fibers in the dorsal roots of the spinal nerves are classified,
in accordance with the sensations to which they give rise, as sensor,
thermal, tactile, etc., so these nerve-cells may be similarly classified
according as they transmit their excitations to those specialized areas
in the cerebral cortex in which these different sensations arise.

Structure of the White Matter. — A transverse section of the
cord shows that the white matter completely covers the gray matter
except where the posterior horns reach the surface. Anteriorly the
white matter of each lateral half is connected by a narrow strip or
bridge of white matter, the anterior commissure. Microscopic
examination shows that the white matter is composed of vertically
disposed medullated nerve-fibers which are devoid of a neurilemma.
These fibers are supported partly by a framework of connective
tissue, and partly by neuroglia. The white matter of each side of
the cord is anatomically divided into an anterior, a lateral, and a
posterior column by the anterior and posterior roots of the spinal
nerves.

Classification of the Nerve-fibers. — From a study of the
embryologic development of the while matter and of the degenerative
changes which follow its pathologic and experimental destruction, it

448

TEXT-BOOK OF PHYSIOLOGY.

has been differentiated into a number of specialized tracts which
have different origins, destinations, and functions. They may be
divided, however, into efferent, afferent, and associative fibers. (Fig.
206.)

I. The anterior column, comprising that portion between the
anterior longitudinal fissure and the anterior roots, has been sub-
divided into:

(a) The direct pyramidal tract, or column of Tiirck. This tract
borders the longitudinal fissure and extends from the upper extremity
of the cord as far down as the mid-thoracic region. From above
downward this tract diminishes in size, for the reason that its fibers

Column of Lissauer.

Fig. 206. — Transection of the Cervical Spinal Cord Showing Its Chief Sub-
divisions.— {From Mills' '^ Diseases oj the Nervous System.")

or their collaterals cross at successive levels to the opposite side of the
cord by way of the anterior commissure to enter the gray matter of
the anterior horn. The cells of these axons are located in the cortex of
the cerebral hemisphere of the same side. The terminal filamients of
these fibers or axons are in physiologic relation with the dendrites of
the cornual cells. When divided in any part of their course, these
fibers undergo descending degeneration. They are therefore efferent
neurons and of the second order.

(&) The anterior root zone. This tract lies external to the pyram-
idal tract, surrounds the anterior horn of the gray matter and ex-
tends throughout the length of the cord. It is composed of short com-

THE SPINAL CORD. 449

missural fibers which come from nerve-cells in the gray matter from
the same and opposite sides of the cord. After entering the white
matter they divide into two branches, pursue opposite directions,
then re-enter the gray matter at higher and lower levels and come
into relation with other nerve-cells.

(c) The antero-lateral tract of Marchi and Lowenthal. This
tract is situated at the inner and anterior angle of the anterior column.
After removal of the one-half of the cerebellum it degenerates down-
ward.

2. The lateral column, comprising that portion between the
ventral and dorsal roots, has been divided into :

{a) The antcro-latcral tract of Gowers. This tract is somewhat
crescentic in shape and situated on the lateral aspect of the cord
external to the anterior root zone. It extends throughout the entire
length of the cord. When divided it undergoes ascending degenera-
tion, which would indicate that the axons originate in nerve-cells
in the gray matter. This tract is therefore afferent in function.

ip) The lateral limiting tract. This tract, which is quite narrow,
lies close to the external border of the gray matter. It is composed
of fibers which do not degenerate to any considerable extent and are
in all probability associative fibers which come from nerve-cells in
the gray matter to re-enter at lower and higher levels.

(c) The crossed pyramidal tract. This tract occupies the posterior
portion of the lateral column, though its exact position varies some-
what in dift'erent regions of the cord. In the cervical and thoracic
regions it is covered by a layer of fibers. In the lumbar region,
however, it comes to the surface. From above downward this tract
gradually diminishes in size, for the reason that its fibers and their
collaterals enter the gray matter at successive levels. The terminal
branches of these fibers are in close physiologic relation with the
dendrites of the cornual cells. The cells of these axons are located
in the cortex of the cerebral hemispheres of the opposite side. When
divided in any part of their course, they undergo descending de-
generation. They are therefore efferent neurons and of the second
order.

(d) The direct cerebellar tract, or column of Flechsig. This tract
is situated on the surface of the lateral column external to the crossed
pyramidal tract. It slightly increases in size from below upward.
It is composed of fibers the cells of which are found on the inner
side and base of the posterior horn (Clark's vesicular column). From
this origin the fibers pass obliquely outward to the surface and then
directly upward to terminate, as its name impUes, in the cerebellum.
Decussation of these fibers takes place in the superior vermiform lobe
of the cerebellum. When divided this tract degenerates upward. It
is therefore in all probability an afferent tract and of the second order.

29

450 TEXT-BOOK OF PHYSIOLOGY.

3. The posterior column, comprising that portion between the
dorsal roots and the posterior longitudinal fissure, has been sub-
divided into :

{a) The postero-external tract of Burdach. This tract lies just
within the posterior horns. A portion of this tract is composed
of ground fibers which, though vertically disposed, have but a short
course. They take their origin in cells in the gray matter, and after
entering this tract divide into ascending and descending branches,
which with their collaterals re-enter the gray matter at different
levels. Another portion of this tract is made up of nerve-fiber& de-
rived from the dorsal roots of the spinal nerves, which cross this
column toward the median line in an oblique or horizontal direction.
The fibers of the upper portion of this tract terminate around the
nucleus cuneatus at the medulla oblongata. When divided, these
fibers degenerate for but a short distance. The ground fibers are
probably associative in function.

(h) The postero-median internal tract, or column of GoU. This
tract is separated from the former by a septum of connective tissue
which is most marked above the eleventh thoracic segment. The
fibers which compose this tract are long and derived for the most
part from the dorsal roots of the spinal nerves of the same side. This
is shown by the fact that division of these roots central to the ganglion
is followed by ascending degeneration of the column of Goll as far
as the nucleus gracihs in the medulla. Fibers derived from cells
in the gray matter are also contained in this column. This tract is
afferent in function.

(c) The septo-marginal tract. This is an oval-shaped tract
situated along the margin of the posterior longitudinal fissure.

(d) The cornu-commissural tract. This is formed along the
border of the anterior portion of the posterior column as far forward
as the posterior commissure. Both of these tracts are best developed
in the lumbo-sacral region. They arise from nerve-cells in the gray
matter. They undergo descending degeneration when divided, but
not after division of the dorsal roots.

(e) Lissauer's tract. This tract embraces the tip of the posterior
horn and is composed principally of fibers from the dorsal roots of the
spinal nerves. After entering the tract the fibers divide into ascend-
ing and descending branches, which finally terminate around cells
in the posterior horn.

(/) The comma tract. This is a narrow tract of fibers situated
in the anterior portion of the column of Burdach. When divided,
its fibers degenerate downward.

The Relation of the Spinal Nerves to the Spinal Cord. — The
spinal nerves present near the spinal cord two divisions which from
their connection with the anterior or ventral and the posterior or

THE SPINAL CORD. 451

dorsal surfaces are known as the ventral and dorsal roots. The ventral
roots are the axons of various groups of cells in the anterior horns.
From their origin these axons pass almost horizontally forward
through the anterior column in three distinct bundles. After emerging
from the cord they curve downward and backward to join the poste-
rior root. The dorsal roots are the central axons of nerve-cells in the
spinal ganglia. After entering the cord they divide into two main
groups, a lateral and a mesial. A portion of the lateral group enters
the posterior horn directly through the caput cornu; the other portion
turns upward and runs through Lissauer's tract and ultimately enters
the posterior horn. The mesial group passes into the postero-
external column (Burdach), where the fibers divide into descending
and ascending branches. The former constitute the comma tract,
the terminal branches of which surround cells in the gray matter;
the latter (ascending) cross the column obliquely and enter the
postero-internal column (GoU), in which they pass upward to ter-
minate around the cells of the nucleus gracilis of the same side. As
these root fibers pass up and down the cord, collateral branches are
given off which enter the gray matter at successive levels and, come
into physiologic relation with the cells of Clark's vesicular column
on the same and opposite sides and with the cells of the anterior horn.

Experimentally, it has been determined that the anterior or ven-
tral roots contain all the efferent fibers, the posterior or dorsal roots
all the afferent fibers. The proofs in support of this view are as
follows :

Stimulation of the ventral roots produces :

1. Convulsive movements of muscles.

2. The discharge of a secretion from glands.

3. Changes in the caliber of blood-vessels.

4. Inhibition of the rhythmic activity of certain organs.

Division of these roots is followed by :

1. Loss of muscle movement (paralysis of motion).

2. Cessation of normal secretion.

3. Cessation of active vascular changes.

Stimulation of the dorsal roots causes :

1. Reflex activities.

2. Conscious sensations.

3. Inhibition of the rhythmic activity of certain organs.

Division of these roots is followed by:

1. Loss of reflex activities, and

2. Loss of sensation in all parts to which they are distributed.

The ventral roots are, therefore, efferent in function, transmitting
nerve impulses from the nerve centers to the periphery. The
dorsal roots are afferent in function, transmitting nerve impulses from
the general periphery to the nerve centers.

452 TEXT-BOOK OF PHYSIOLOGY.

FUNCTIONS OF THE SPINAL CORD.

Physiologic investigation has demonstrated that the spinal cord,
in virtue of the presence of nerve-cells and nerve-fibers, may be re-
garded as composed of:

1. Independent nerve-centers, each of which has a special function;

and —

2. Conducting paths by which these centers are brought into relation

with one another and with the cerebrum and its subordinate

or underlying parts.
The cord, moreover, may be considered as consisting physiologically
of a series of segments placed one above the other, the number of
segments corresponding to the number of spinal nerves. In other
words, a spinal segment comprises that portion of the cord to which
is attached a pair of spinal nerves. The nerve-cells in each segment
are in histologic and physiologic relation with definite areas of the
body, embracing muscles, blood-vessels, glands, skin, etc.

The Spinal Cord as an Independent Center. — The efferent
cells of the spinal segments are the immediate sources of the nerve
energy which excites activity in muscles, blood-vessels, glands. The
discharge of their energy may be caused:

1. By variations in the composition of the blood or lymph by which

they are surrounded. The activity of the cell thus occasioned
is termed automatic or autochthonic (Gad).

2. By the arrival of nerve energy coming through afferent nerves

from the general sentient periphery, skin, mucous membrane, etc.

3. By the arrival of nerve energy descending the spinal cord from

the cerebrum or subordinate structures. The peripheral activity
in the former instance is said to be reflex or peripheral in origin ;
in the latter instance, direct or cerebral in origin. In this latter
instance, also, the muscle movements are due to vohtional, the
vascular variations and glandular discharges to emotional,
forms of cerebral activity.
Each segment of the spinal cord may be regarded, therefore,
because of its contained nerve-cells:

1. As a center for automatic activity.

2. As a center for the reception of excitations arising either at the

periphery or in the cerebrum, and for their subsequent trans-
mission through efferent nerves to various peripheral organs.
Automatism. — The growth, the nutrition and multipHcation of
the cells of various tissues, and their continuous and rhythmic activity,
have been attributed to an automatic action of the spinal nerve-
cells. By this expression is meant a discharge of energy from the
cells occasioned by a change in their environment, i. e., in the chemic
composition of the blood or lymph by which they are surrounded,
and independent of any excitation coming through afferent nerves.

THE SPINAL CORD. 453

If the cell activity is continuous, though variable in degree from time
to time, it gives rise to what is termed tonus, e. g., trophic tonus,
vascular, muscle tonus, etc. If the cell activity is intermittent,
it imparts to muscles a certain rhythmic activity, e. g., the respiratory
movements.

As no effect arises without a sufficient cause, the term automatic
has been objected to and the term autochthonic has been suggested
(Gad), expressive of the idea that the energy originates in the nerve-
cell as a result of a reaction between the cell and its ever-changing
environment. A center so acting could not be regarded as primarily
a center for reflex action, however much it might be influenced or
conditioned secondarily by afferent impulses. Though automatic
activity of the spinal cord centers is advocated by some physiologists,
the fact must be recognized that with increasing knowledge of reflex
activities some of the phenomena hitherto regarded as automatic
have been found to be reflex in origin. Whether this will eventually
be found true for all forms of so-called automatic or autochthonic
activity remains to be seen.

Trophic Tonus. — The normal metabolism of muscle, gland, and
connective tissue which underlies the assimilation of food, the storing
of energy, and the production of new compounds, is dependent, in the
higher animals at least, on the connection of these tissues with the
central nerve system; for if the efferent nerves be divided, not only
will they undergo degeneration in their peripheral portions, but the
muscles, glands, and connective tissues to which they are distributed
will also undergo similar changes. This is to be attributed not
merely to inactivity, but rather to a loss of nerve influence, inasmuch
as inactivity leads merely to atrophy and not to degeneration. It
would appear from facts of this character that the normal metabolism
is dependent for its continuance on nerve influences. There is no
evidence, however, as to the existence of special trophic nerves,
separate from those which impart to glands and muscles their cus-
tomary activities. The trophic centers and the motor centers are
identical, though the two modes of their activity are separate and
distinct.

Vascular Tonus. — The state of moderate contraction of the
arterioles throughout the body, in consequence of which the average
arterial pressure is maintained, is attributed to constant activity of
the vaso-motor centers, this activity being conditioned by variations
in the composition of blood, either an increase in the quantity of
carbon dioxid or a decrease in the quantity of oxygen. The vaso-
motor centers are regarded as primarily automatic, though capable
of being influenced secondarily by reflected excitations from the
periphery or direct excitations from the cerebrum.

Muscle Tonus. — It is well known that if a muscle be divided in

454

TEXT-BOOK OF PHYSIOLOGY,

the living animal the two portions will contract and separate them-
selves to a certain distance. This indicates that the muscle when in
a state of rest is in a slight degree of contraction. This condition of
the muscle, to which the term muscle tonus is given, was formerly
attributed to an automatic and continuous discharge of energy from
the nerve-cells. Brondgeest, however, showed that this tonus is
entirely reflex in origin and immediately disappears on di\'ision of
the posterior roots of the spinal nerves, which would not be the case
if the cells in the cord were acting automatically. The afferent
nerves in this reflex arise in the muscle or its tendons, and the stim-
ulus is the slight degree of extension to which the muscle is subjected
in \drtue of its attachments and the ever- varying position of the limbs
and trunk.

The tonic contraction of the visceral muscles, — e. g., the pyloric,
the vesical, the anal sphincters, — though regarded as automatic by
some, is probably reflex in origin, dependent on the arrival of

Fig. 207. — ^Diagram of a Simple Reflex Arc. i. Sentient surface. 2. Afferent
nerve. 3. Emissive or motor cell. 4. Efferent nerve. 5. Muscle. — {After Moral
and Dayon.)

afferent impulses from the periphery. It is probable that future
investigation will disclose the existence and pathway of these afferent
fibers.

Reflex Actions. — It has already been stated that the nerve-cells
in the spinal cord are capable of receiving and transforming afferent
nerve impulses into efferent nerve impulses, which are transmitted
outward to muscles, exciting contraction; to glands, provoking secre-
tion; to blood-vessels, changing their caliber; and to organs, inhibit-
ing or accelerating their activity. All such actions taking place
through the spinal cord and medulla oblongata independently of
sensation or volition are termed reflex actions. The mechanism in-
volved in ever}^ reflex action consists of at least the following struc-
tures (Fig. 207) :

1. A sentient surface; e. g., skin, mucous membrane, sense
organ, etc.

2. An afferent fiber and cell.

THE SPINAL CORD.

455

3. An emissive cell, from which arises —

4. An efferent nerve, distributed to a responsive organ, as —

5. Muscle, gland, blood-vessel, etc.

In this connection the reflex contractions of skeletal muscles only
will be considered.

If a stimulus of sufficient intensity be applied to the sentient
surface, there will be developed in the terminals of the afferent
nerve a series of nerve impulses which will be transmitted by the
afferent nerve to, and received by, the dendrites of the emissive cell
in the anterior horn of the gray matter. With the reception of
these impulses there will be a dis-
turbance in the equilibrium of the
molecules of the cell, a liberation of
energy and a transmission of nerve
impulses outward through the efferent
nerve to the muscle.

A reflex mechanism or arc of this
simplicity would subserve but a simple
movement. The majority of the
reflexes, however, are extremely com-
plex and involve the cooperation and
coordination of a number of centers at
different levels of the spinal cord and
medulla, on the same and opposite
sides, and of muscles situated at dis-
tances more or less remote from one
another. The transference of nerve
impulses coming from a localized area
of a sentient surface, to emissive cells
situated at different levels is accom-
plished by the intermediation of a third
neuron situated in the gray matter
which is in connection, on the one
hand, with the central terminals of
the afferent nerve, and, on the other

hand, with the dendrites of the emissive or motor cells (Fig. 208).
A histologic and physiologic mechanism of this character readily
explains how a localized stimulation can give rise to reflex actions
extremely complex in character.

The reflex contractions of skeletal muscles are best studied after
division of the central nerve system at the upper limit of the spinal
cord. After this procedure the spinal centers can act independently
of, and uninfluenced by either sensation or volitional efforts on the
part of the animal. Though it is possible to provoke reflex contrac-
tions under such circumstances in warm-blooded animals, they are,

Fig. 208. — Diagram Showing
THE Relation of the Third
Neuron a, to the Afferent
Neuron b, and to the Ef-
ferent Neurons c, c, c. —
{After Kdlliker.)

456 TEXT-BOOK OF PHYSIOLOGY.

as a rule, incomplete and of short duration, owing to disturbances
of the circulation and respiration and the consequent loss of tissue
irritability. In frogs and in cold-blooded animals generally, the
spinal cord retains its irritabihty for a long period of time after re-
moval of the brain, and therefore is well adapted for the study of
reflex actions.

The division of the spinal cord can be readily effected by inserting
a spear-shaped knife between the occipital bone and the atlas. The
skin, occipito-atlantal membrane, and medulla can be divided with
one plunge of the knife. The brain can then be destroyed by the
insertion of a fine wire into the brain cavity. A frog so prepared,
and placed on the table and allowed to remain at rest for a few
moments until the shock of the operation passes away, will draw the
Hmbs close to the body and assume a position not unhke that of a
normal frog. If then the posterior hmbs be extended, they will
immediately be drawn close to the side of the trunk in the usual
flexed position. If the toes are pinched with forceps, the foot will
execute a series of movements as if it were trying to free itself from
the source of irritation.

If the frog be suspended, the hmbs, through the force of gravity,
will be gradually extended and hang down freely. In this, as in the
sitting position, the animal will remain perfectly quiet and will not
exhibit spontaneous movements. Any stimulus apphed to the skin,
however, provided it is of sufficient intensity, will be followed by a
more or less pronounced movement. Mechanic, chemic and electric
stimuli applied to any part of the skin will call forth the characteristic
reflex movements. Chemic stimuH such as weak solutions of
sulphuric or acetic acid placed on the toes will be followed by feeble
flexion of the corresponding leg, to be succeeded in a short time by
extension. Stronger solutions will produce more extensive and
vigorous movements, the foot at the same time being rubbed against
the thigh, apparently for the purpose of freeing it from the irritant.
Similar phenomena follow the application of the acid to the fingers
or the trunk. As a rule, the extent and complexity of the movement
is within limits proportional to the strength of the stimulus. By
limiting the sphere of action of the stimulus to definite but different
areas of the skin a great variety of movements, more or less complex
and coordinated and apparently purposive and defensive in character,
can be produced. The coordinated and purposive character of the
movements exhibited by a brainless frog led Pfliiger to the assump-
tion that the spinal cord in this as well as in other cold-blooded ani-
mals is possessed of sensorial functions, is endowed with rudimentary
consciousness. This view, however, is not generally accepted, the
movement being attributed to specialized mechanisms in the cord,
partially inherited, which permit of one and the same movement with

THE SPINAL CORD. 457

mechanic regularity and precision, so long as the conditions of the
experiment remain the same.

In warm-blooded animals similar results may be obtained for a
short time after division of the cord, especially if artificial respiration
is maintained and the circulation of the blood continued. The cord
will then retain its irritability for some time. If the conditions of
experimentation were favorable, it is highly probable that the human
spinal cord would execute similar movements. Thus it was observ'ed
by Robin in a man who had been decapitated that reflex muscle con-
tractions could be ehcited by stimulating the skin after the lapse of an
hour after execution. "While the right arm was lying extended by
the side, with the hand about 25 centimeters distant from the upper
part of the thigh, I scratched with the point of a scalpel the skin of the
chest at the areola of the nipple, for a space of 10 or 11 centimeters
in extent, without making any pressure on the subjacent muscles.
We immediately saw a rapid and successive contraction of the great
pectoral muscle, the biceps, probably the brachialis anticus, and
lastly the muscles covering the internal condyle. The result was a
movement by which the whole arm was made to approach the trunk,
with rotation inward and half- flexion of the forearm upon the arm;
a true defensive movement, which brought the hand toward the
chest as far as the pit of the stomach. Neither the thumb, which
was partially bent toward the palm of the hand, nor the fingers,
which were half bent over the thumb, presented any movements.
The arm being replaced in its former position, we saw it again
execute a similar movement on scratching the skin, in the same manner
as before, a little below the clavicle. This experiment succeeded
four times, but each time the movement was less extensive; and at
last scratching the skin over the chest produced only contractions in
the great pectoral muscle which hardly stirred the limb" (Dalton).

Laws of Reflex Action (Pfliiger).

1. Law 0} Unilaterality . — If a feeble irritation be applied to one or

more sensory nerves, movement takes place usually on one side
only, and that the same side as the irritation.

2. Law of Symmetry. — If the irritation becomes sufficiently intense,

motor reaction is manifested, in addition, in corresponding
muscles of the opposite side of the body.

3. Law of Intensity. — Reflex movements are usually more intense

on the side of irritation; at times the movements of the opposite
side equal them in intensity; but they are usually less pronounced.

4. Law of Radiation. — If the excitation still continues to increase, it

is propagated upward, and motor reaction takes place through
centrifugal nerves coming from segments of the cord higher up.

5. Law of Generalization. — When the irritation becomes very intense,

it is propagated in the medulla oblongata; motor reaction then

458 TEXT-BOOK OF PHYSIOLOGY.

becomes general, and it is propagated up and down the cord, so
that all the muscles of the body are thrown into action, the
medulla oblongata acting as a focus whence radiate all reflex
movements.
Special Reflex Movements. — Among the reflexes connected
with the more superficial portions of the body there are some which
are so frequently either exaggerated or diminished in pathologic
conditions of the spinal cord that their study affords valuable indi-
cations as to the seat and character of the lesions. They may be
divided into :

1 . The skin or superficial, and

2. The tendon or deep reflexes.

The skin reflexes are induced by stimulation of the skin and
mucous membranes — e. g., pricking, pinching, scratching, etc. The
following are the principal skin reflexes :

1 . Plantar reflex, consisting of contraction of the muscles of the foot,

induced by stimulation of the sole of the foot; it involves the
integrity of the reflex arc through the lower end of the cord.

2. Gluteal reflex, consisting of contraction of the glutei muscles

when the skin over the buttock is stimulated; it takes place
through the segments giving origin to the fourth and fifth lumbar
nerves.

3. Cremasteric reflex, consisting of a contraction of the cremaster

muscle and a retraction of the testicle toward the abdominal
ring when the skin on the inner side of the thigh is stimulated;
it depends upon the integrity of the segments giving origin to
the first and second lumbar nerves.

4. Abdominal reflex, consisting of a contraction of the abdominal

muscles when the skin upon the side of the abdomen is gently
scratched; its production requires the integrity of the spinal
segments from the eighth to the twelfth.

5. Epigastric reflex, consisting of a shght muscular contraction in

the neighborhood of the epigastrium when the skin between the
fourth and sixth ribs is stimulated; it requires the integrity of
the cord between the fourth and seventh dorsal nerves.

6. The scapular reflex consists of a contraction of the scapular muscles

when the skin between the scapulae is stimulated; it depends
upon the integrity of the cord between the fifth cervical and third
dorsal nerves.
The skin or superficial reflexes, though variable, are generally
present in health. They are increased or exaggerated when the gray
matter of the cord is abnormally excited, as in tetanus, strychnin-
poisoning, and disease of the lateral columns.

The so-called '^tendon reflexes''^ also are of much value in the
diagnosis of lesions of the cord. They are elicited by a sharp tap on

THE SPINAL CORD. 459

a given tendon. Though spoken of as reflexes, they are not such in
reahty, but rather contractions of the muscles whose irritability has
been increased in consequence of extension. To this condition of
the muscle Gowers has applied the term myotatic irritability. It has
already been stated that the slight contraction of the muscle which
gives rise to muscle tonus is a true reflex, the afferent impulses for
the same arising in the muscle itself in consequence of extension and
compression of the muscle spindles. If the muscle is extended sud-
denly, as by a short tap on the tendon, reflex contraction at once
ensues.

The following are the principal forms of the tendon reflexes :

1. Patellar reflex or knee-jerk, consisting of a contraction of the ex-

tensor muscles of the thigh when the ligamentum patellae is
struck between the patella and tibia. This reflex is best ob-
served when the legs are freely hanging over the edge of a table.
The patella reflex is generally present in health, being absent
in only 2 per cent.; it is greatly exaggerated in lateral sclerosis,
in descending degeneration of the cord; it is absent in locomotor
ataxia and in atrophic lesions of the anterior gray cornua.

2. Ankle- jerk or Reflex. — If the extensor muscles of the leg be placed

upon the stretch and the tendo Achillis be sharply struck, a
quick extension of the foot will take place.

3. Ankle Clonus. — This consists of a series of rhythmic reflex con-

tractions of the gastrocnemius muscle, varying in frequency from
six to ten per second. To elicit this reflex, pressure is made upon
the sole so as to suddenly and energetically flex the foot at the
ankle, thus putting the tendo Achilhs upon the stretch. The
rhythmic movements thus produced continue so long as the
tension is maintained. Ankle clonus is never present in health,
but is very marked in lateral sclerosis of the cord.
The toe reflex, peroneal reflex, and wrist reflex are also present in
sclerosis of the lateral columns and in the late rigidity of hemiplegia.
Reflex Irritability. — The general irritability or quickness of
response of the mechanism involved in reflex action can be approxi-
mately determined by observation of the length of time that elapses
between the application of a minimal stimulus and the appearance of
the muscle response. The method of Tiirck is sufficiently accurate
for general purposes. This consists in suspending a frog, after
removal of the brain, and immersing the foot in a 0.2 per cent, solu-
tion of sulphuric acid. The time is determined by means of a metro-
nome beating one hundred times a minute. Stimulation of the skin
can also be effected by the induced electric current, as suggested by
Gaskell. A single shock is, however, ineffective. When the shocks
follow each other with sufficient rapidity, they give rise to a summa-
tion of effects in the nerve-centers which will soon be followed by a

46o TEXT-BOOK OF PHYSIOLOGY.

muscle response. It is highly probable that the chemic stimulation
gives rise to a similar summation of effects.

The period of time thus obtained is distributed over the entire
mechanism. The true reflex time, however, — i. e., the time occupied
in the passage of the nerve impulses across the spinal mechanism, —
is shorter and is obtained by subtracting from the whole period
the time occupied by the passage of the impulses through the afferent
and efferent nerves as well as the latent period of muscle contraction.
This corrected period, the true reflex time, has been found to be
twelve times longer than the time occupied by the passage of the
nerve impulse through the nerves, including the latent period of the
muscle.

The reflex irritability is increased by:

1. Separation of the Brain from the Cord. — This is at once followed

by an increase in reflex irritability, and is taken as evidence that
the brain normally exerts an inhibitory influence over the reflex
centers of the cord. The same increase is observed upon hemi-
section of the cord, though the increase is limited to the same
side.

2. The Administration of Strychnin. — Even in small doses this alka-

loid increases the irritabihty to such an extent that a minimal
stimulus is sufficient to call forth spasmodic contractions of all
the skeletal muscles. Under its influence the usual coordinated
reflexes disappear and are succeeded by incoordinated reflexes.
The explanation of this fact is believed to be a diminution in the
resistance offered by the cord to the passage of the afferent im-
pulses rather than to a direct stimulation of the efferent cells.
So much is this resistance decreased that the nerve impulses,
instead of being confined to their accustomed paths, are radiated
in all directions. Absolute repose of the animal and the exclu-
sion of all external stimuH greatly diminish the tendency to
the occurrence of spasms.

3. Degeneration of the Pyramidal Tracts. — In primary lateral scle-

rosis, a pathologic condition characterized primarily by a degen-
eration of the terminal filaments of the pyramidal tract fibers,
the reflex activity of the cord becomes exalted. As the disease
progresses the irritability increases to such an extent that violent
spasmodic contractions of the arms and legs arise when the skin
or tendons are mechanically stimulated. The explanation
offered is practically the same as in division of the cord: viz.,
withdrawal of the inhibitory and controlHng influence of the
brain.
The reflex excitability may be decreased by:
I. Stimulation of Certain Regions of the Brain. — It was discovered
by Setchenow that when the frog brain is divided just anterior

THE SPINAL CORD. 461

to the optic lobes and the reflex time subsequently determined
according to the method of Tiirck, that the time can be
considerably lengthened by stimulation of the optic lobes.
This is readily accompUshed by placing small crystals of sodium
chlorid on the optic lobes. It was concluded from this fact that
these lobes contain centers which exert an inhibitory influence over
centers in the spinal cord through descending nerve-fibers.
This conclusion is strengthened by the fact that division of the
brain just behind the optic lobes causes a temporary inhibition
of the reflexes in consequence of a mechanical irritation of these
fibers. It is quite probable that the vohtional inhibition of
certain reflexes is accomplished through the intermediation of
this center localized by Setchenow.

2. Stimulation of Sensor Nerves. — If during the application of a

stimulus sufficient to call forth a characteristic reaction in a
definite period of time, a sensor nerve in a distant region of the
body be simultaneously stimulated, it will be found that the reflex
time will be lengthened or the reaction completely inhibited.
The explanation of this phenomenon is not apparent.

3. Lesions of the spinal cord; e. g., atrophy of the multipolar cells

of the anterior horns of the gray matter; degeneration of the
terminals of the posterior fibers.

4. The toxic actioti of various drugs, — e. g., chloroform, chloral, —

which are believed to exert their depressing action on the nerve-
cells themselves.
The Spinal Cord as a Conductor. — The white matter of the
spinal cord consists of nerve-fibers the specific function of which is:

1. To conduct nen^e impulses from one segment of the cord to another.

2. To conduct nerve impulses from the encephalon to the spinal

cord segments.

3. To conduct nerve impulses coming to the cord through afferent

nerves, directly or indirectly to various areas of the encephalon.

Intersegmental or Associative Conduction. — The spinal cord
consists of a series of physiologic segments each of which has specific
functions and is associated through its related spinal nerve with a
definite segment of the body. For the harmonious cooperation and
coordination of all the spinal segments it is essential that they should
be united by commissural or associative fibers. This is, in fact,
accomphshed by the axons of the intrinsic cells of the gray matter,
which constitute such a large part of the anterior and posterior root
zones. In consequence of this association, the cord becomes capable
of complex coordinated and purposive reflex actions.

Encephalo-spinal or Motor Conduction. — At birth the child is
capable of performing all the functions of organic life, such as sucking,
swallowing, breathing, etc. It is, however, deficient in psychic

462 TEXT-BOOK OF PHYSIOLOGY.

activity and in volitional control of its muscles. Its movements are
therefore largely, if not entirely, reflex in character.

Embryologic and histologic examination of the spinal cord and
medulla show that so far as their mechanisms for independent phys-
iologic activities are concerned both are fully developed. Similar
investigations of the cerebral hemispheres and of the nerve-fibers
which bring their nerve-cells into relation with the spinal segments
show that the cells of the cortex are not only immature, but that their
descending axons are incompletely invested with myelin. With the
growth of the child, psychic life unfolds and volitional control of-mus-
cles is acquired. Coincidently the cells of the cerebral cortex grow
and develop and the fibers become covered with myelin.

The nerve-fibers which have their origin in the cells of the cerebral
cortex, and which terminate in tufts around the cells in the anterior
horns of the gray matter of the spinal segments, are to be regarded as
long commissural tracts uniting and associating these two portions
of the central nerve system.

Experimental investigations and observations of pathologic lesions
accord with the view that physiologically these fibers are efferent
pathways for the transmission of motor or volitional impulses from
the cortex to the spinal segments. The nerve-cells in which the
motor impulses originate are located for the most part, as will be fully
stated later, in the central portion of the cortex of the cerebral hemi-
spheres in the neighborhood of the central or Rolandic fissure. The
axons of these cells from each hemisphere descend through the
corona radiata to and through the internal capsule, along the inferior
surface of the crura cerebri, behind the pons to the medulla, of which
they constitute the anterior pyramids. (Fig. 209.) At this point the
pyramidal tract* of each side divides into two portions, viz.:
T. A large portion, containing from 80 to 90 per cent, of the fibers,
which decussates at the lower border of the medulla and passes
downward in the posterior part of the lateral column of the
opposite side, constituting the crossed pyramidal tract; as it
descends it gradually diminishes in size as its fibers or their
collaterals enter the gray matter of each successive segment.
2. A small portion, containing from 20 to 10 per cent, of the fibers,
which does not decussate at the medulla but passes downward
on the inner side of the anterior column of the same side, con-
stituting the direct pyramidal tract or column of Turck. This

* From the fact that the region included between the origin of these fibers and
the internal capsule presents somewhat the form of a pyramid with four sides,
Charcot designated it the pyramidal region and the fibers composing it the pyram-
idal tract. The base of the pyramid includes the cortex of the convolutions
around the Rolandic fissure. The summit of the pyramid is truncated and covers
the pyramidal region of the internal capsule.

THE SPINAL CORD.

46:

tract can be traced down, as a rule, only as far as the mid-dorsal
region. As it descends it becomes smaller as its fibers cross the
anterior commissure to enter the gray matter of the opposite

Fig. 209. — Diagram of the Pyramidal Tract or Motor Path. III. Common
oculo-motor nerve. IV. Pathetic nerve. V. Motor division of, the trigeminal nerve.
VI. The abducens nerve. VII. Facial nerve. IX. and X. Motor divisions
of the glosso-phar}'ngeal and pneumogastric nerves. XI. Spinal accessor}^ nerve.
XII. Hypoglossal nerve. — {Van Gehuchten.)

side. Thus all the fibers of the pyramidal tract from each
cerebral hemisphere eventually are brought into relation with
the cells of the gray matter of the opposite side of the cord.

464 TEXT-BOOK OF PHYSIOLOGY.

That the pyramidal tracts are the conductors of volitional
impulses throughout the length of the cord to its various seg-
ments has been made evident by the results of section, electric stimu-
lation, and disease. Division of the anterior and lateral columns
of one side of the cord in any part of its extent is invariably followed
by a loss of motion or paralysis of the muscles below the section,
while electric stimulation of the peripheral end of the isolated crossed
pyramidal tract is followed by marked characteristic movements of
the muscles. Similar results follow di\dsion of the pyramidal tract
in any part of its course from the cerebral cortex downward. Electric
stimulation of the cortical cells which give origin to the p3Tamidal
tract is also foUowed by contraction of the muscles of the opposite
side, while their destruction is attended by paralysis of the same
muscles. As the nutrition of the fibers is governed by the cells, it
follows that when the axon is separated from its cell it degenerates.
It has been found that a lesion of the p3Tamidal tract in any part of
its course is followed by descending degeneration, which is taken in
evidence that it conducts nerve impulses from above dowmward.
Thus experimental investigation and pathologic observation are in
accord in the view that physiologically these nerve-fibers are the
pathways for the transmission of motor or voKtional impulses from
the encephalon to the spinal cord.

Spino-encephalic or Sensor Conduction. — The nene impulses
that arise in consequence of impressions made on the terminals of
the nerves in the cutaneous and mucous surfaces, in the \'iscera and
in the muscles, are transmitted through the dorsal roots of the spinal
ner^'es to the cord. WTien transmitted through the cord to the cere-
bralhemispheres directly or indirectly, they are received by specialized
ner\T-cells in the cortex and translated into conscious sensations.
The sensations thus arising may be divided into special and general
sensations. Of the former may be mentioned pain, touch, tem-
perature; of the latter may be mentioned hunger, thirst, fatigue,
well-being, etc.

The pathways through the spinal cord that conduct these afferent
impulses to the brain are ill defined and imperfectly known, and only
for a few sensations can it be said that their pathways have been
determined. The reason for this obscurity hes partly in the diffi-
culties of experimentation, partly in the difficulties of interpretation.
Clinical observations are for special reasons more or less untrust-
worthy.

Section of one lateral half of the cord, or a lesion involving the
one lateral half, as a rule abolishes all forms of cutaneous sensibihty
on the opposite side below the injur}\ This would seem to prove that
the nerv^e impulses cross the median line of the cord immediately or
very shortly after entering. At the same time, muscle sensibihty is

THE SPINAL CORD.

46s

abolished on the corresponding side below the injur)-. This would
seem to prove that the fibers of the posterior roots which enter and
cross the column of Burdach and ascend in the column of Goll are
derived mainly from the muscles. It is, however, believed by some
investigators that those
fibers which subserve the
sense of touch do not
decussate at once, but
ascend in the column of
Goll as far as the medulla
oblongata, where they,
in common with the
fibers coming from the
muscles, arborize around
the nerve-cells in the
gracile and cuneate nu-
clei. The afferent path
is then continued by
new nerve-fibers which
emerge from these ceUs,
and which, after crossing
the median plane and de-
cussating with the fibers
coming from the oppo-
site side, join the afferent
path from the spinal cord.
These fibers are known
as the internal arcuate
fibers and assist in the
formation of the lemnis-
cus or fillet. (Fig. 210.)
The sensor pathway de-
cussates in part at differ-
ent levels of the spinal
cord and in part at the
level of the gracile and
cuneate nuclei. The
former is often termed
the lower, the latter the
upper sensor decussation.
The pathways for the
impulses that give rise to the different sensation have been variously
located by different obser\-ers, e. g., in the gray matter, in the Hmiting
layer, and in the antero-lateral tract of Gowers ; the pathway for the
impulses that give rise to temperature sensations has been located
30

Fig. 210. — Diagr.a:u of the Sensor Pathways in
THE Spinal Cord AroMEXTED above by
Fibers of the Sensor CR.^^^.\L Nerves and
Nerves of Special Sense. V. The trifacial
Ner\'e. VHI. The vestibular branch of the
acoustic nene. IX. The glosso-phar\-ngeal
nene. X. The pneumogastric nene. — {Van
Gehuchteu.)

466 TEXT-BOOK OF PHYSIOLOGY.

in the gray matter; the pathway for tactile impressions has been
located in the posterior columns, though this is not beyond dispute.
The pathway for pain sensations has been located in Gowers' tract.
The relation of the motor and sensor pathways to each other in
the spinal cord and brain are shown in Plate II. The afferent fibers
which decussate at various levels through the spinal cord are not
represented.

Diagram Indicating the Course of the Motor and Sensory Fibers of the
Spinal Cord and Medulla. — {Gordinier.)

a, a. Motor cells of the cerebral cortex, b, b. Arborizations of the fibers of the sensory-
tract in the cerebral cortex, c. Nucleus of the column of Burdach, showing ter-
minal arborizations of the long sensory fibers of the cord. d. Nucleus of the
column of GoU, showing terminal arborizations of the long sensory fibers of the
cord. e. Section of the medulla, showing sensory decussation. /. Section of
medulla, showing motor or pyramidal decussation, g, g. Motorial end plates.
h. Section through the cervical region of the cord, showing termination in the
anterior horn of the motor fibers of the direct pyramidal tract after they have
crossed in the anterior commissure; also fiber of crossed pyramidal tract ending
about anterior horn cell of same side. i,i. Posterior spinal gangHa. j, k. Sensory
fibers of short course. /. Sensory fibers of long course, terminating in medulla.
m, m, m. Sensory end organs, n. Section through lumbar cord.

Plate II.

CHAPTER XVIII.

THE MEDULLA OBLONGATA; THE ISTHMUS OF THE
ENCEPHALON; THE BASAL GANGLIA.

THE MEDULLA OBLONGATA.

The medulla oblongata is that portion of the central nerve
system immediately superior to and continuous with the spinal cord.
It has the shape of a truncated cone, the base of which is directed
upward, the truncated apex downward. It is 38 mm. in length,
18 mm. in breadth, and 12 mm. in thickness. By the continuation
upward of the anterior and posterior median fissures, the medulla is
divided into symmetric halves (Figs. 211 and 212). Like the cord,
of which it is a continuation, it is composed of white matter externally
and gray matter internally.

Structure of the Gray Matter. — The gray matter of the medulla
is continuous with that of the cord, though owing to the shifting of
position of the different tracts of the white matter it is arranged
with much less regularity. The appearance which the gray matter
presents on transverse section varies also at different levels.

At the level of the first cervical nerve the posterior horns are
narrow, elongated, and directed outward. The lateral horns are well
developed and present a collection of cells near their bases which
can be traced forward and backward for some distance. At the
level of the decussation of the pyramidal tracts the head of the
anterior horn becomes completely detached from the rest of the
gray matter and is pushed backward toward the posterior horn; the
bases of the anterior horns become spread out to form a layer of
gray matter near the dorsal aspect of the medulla. Transverse sec-
tions of the medulla at all levels show a more or less extensive network
of 'nerve-fibers known as the reticular formation. In its meshes are
found collections of nerve-cells of varying size. Toward the dorsal
aspect of the medulla special groups of cells are found from which
axons arise to become the fibers of various efferent cranial nerves, e. g.,
the hypoglossal, the efferent fibers of the vagus, and glosso-pharyngeal.

Structure of the White Matter. — The white matter is com-
posed of nerve-fibers supported by connective tissue and neurogha.
It is subdivided on either side by grooves into three main columns:
viz., an anterior column or pyramid, a lateral column, and a posterior
column.

467

468 TEXT-BOOK OF PHYSIOLOGY.

The anterior column or pyramid is composed partly of 'fibers
continuous with those of the anterior column of the spinal cord (the
direct pyramidal tract), and partly of fibers continuous with those of
the lateral column of the cord of the opposite side (the crossed pyram-
idal tract), which decussate at the anterior portion of the medulla.
The united fibers can be traced upward to the pons, where they
disappear from view.

The lateral column is composed of fibers continuous with those
of the lateral column of the cord. As the fibers pass upward, how-
ever, they diverge in several directions. The fibers of the crossed
pyramidal tract cross the median line, as previously stated, to enter
into the formation of the anterior column; the fibers of the direct
cerebellar tract gradually curve backward, and in so doing unite with
other fibers to form the restiform body, after which they enter the
cerebellum by way of the inferior peduncle. Situated between the
anterior pyramid and the restiform body is a small oval mass, the
oHvary body, composed of both white and gray matter.

The posterior column is composed largely of fibers continuous with
those of the posterior column of the cord. The subdivision of this
column into a postero-external (Burdach) and a postero-internal
(Goll) is more marked in the medulla than in the cord. The former
is here known as the funiculus cuneatus, the latter as the funiculus
gracilis. These two strands of fibers are apparently continued into
the restiform body. Owing to the divergence of the restiform bodies
a V-shaped space is formed, the floor of which is covered with epithe-
lium resting on the ependyma. At the upper extremity of the
funiculus cuneatus and funiculus gracilis, two collections of gray
matter are found, known respectively as the nucleus cuneatus and
nucleus gracilis. Around the cells of these nuclei many of the fibers
of the posterior column end in brush-hke expansions.

The Fillet or Lemniscus. — From the ventral surface of the cu-
neate and gracile nuclei axons emerge which pass forward and
upward through the gray matter and decussate with corresponding
fibers coming from the opposite nuclei. They then assume a position
just posterior to the pyramids and between the olivary bodies. These
fibers thus form a new distinct tract, termed the fillet or lemniscus.
As this tract ascends toward the brain it receives additional axons from
the sensory end-nuclei of all the afferent cranial nerves of the opposite
side with the exception of the auditory. From the end-nuclei of the
auditory nerve new axons ascend as a distinct tract situated near
the lateral aspect of the pons. From their position these two separate
tracts have been termed the mesial and lateral fillets respectively.

Before proceeding to a consideration of the functions of the
medulla oblongata it will be found conducive to clearness to sketch
the saHent anatomic features of the parts anterior to it and their
relations one to another.

MEDULLA OBLONGATA.

469

Fig. 211. — Anterior or Ventral
View of the Medulla Ob-
longata AND Isthmus, i. In-
fundibulum. 2. Tuber ciner-
eum. 3. Corpora albicantia. 4.
Cerebral peduncle. 5. Tuber
annulare. 6. Origin of the mid-
dle peduncle of the cerebellum.
7. Anterior pyramids of the
medulla oblongata. 8. Decussa-
tion of the anterior pyramids. 9.
Olivary bodies. 10. Restiform
bodies. 11. Arciform fibers. 12.
Upper extremity of the spinal
cord. 13. Ligamentum denticu-
latum. 14, 14. Dura mater of
the cord. 15. Optic tracts. 16.
Chiasm of the optic nerves. 17.
Motor ocuU communis. 18.
Patheticus. 19. Fifth nerve. 20.
Motor oculi externus. 21. Facial
nerve. 22. Auditory nerve. 23.
Nerve of Wrisberg. 24. Glosso-
pharyngeal nerve. 25. Pneumo-
gastric. 26, 26. Spinal accessory.
27. Sublingual nerve. 28, 29, 30.
Cervical nerv'es. — (Sappey.)

Fig. 212. — Posterior or Dorsal View of

the MEDULL.A. OBLONGATA, ISTHMUS,

AND Basal Ganglia. i. Corpora
quadrigemina. 2. Corpus quadrige-
minum anterior (pregeminum). 3. Cor-
pus quadrigeminum posterior (post-
geminum). 4. Tract of fibers (bra-
chium) passing to the corpus genicula-
tum externum. 5. Tract of fibers
(brachium) passing to 6, the corpus
geniculatum internum. 7. Posterior
commissure. 8. Pineal gland. 9. Su-
perior cerebellar peduncle. 10, 11, 12.
The valve of Vieussens. 13. The pa-
thetic nerve. 14. Lateral groove of the
isthmus. 15. Triangular bundle of the
isthmus. 16. Superior cerebellar pedun-
cle. 17. Middle cerebellar peduncle.
18. Inferior cerebellar peduncle. 19.
.\ntero-inferior wall of the fourth ven-
tricle. 20. Acoustic nerve. 21. Spinal
cord. 22. The postero-median column.
23. The posterior pyramids. — (Sappey.)

470 TEXT-BOOK OF PHYSIOLOGY

THE ISTHMUS OF THE ENCEPHALON.

The isthmus of the encephalon comprises that portion of the
central nerve system connecting the cerebrum above, the cerebellum
behind, and the medulla below. Its ventral surface presents below
an enlargement, convex from side to side, the pons Varolii. On
each side the fibers of which the pons consists converge to form a
compact bundle, the middle peduncle, which enters the correspond-
ing half of the cerebellum. Above the pons, this surface presents
two large columns of white matter which, diverging somewhat
from below upward, enter the base of the cerebrum and are known
as the crura cerebri. Embracing the crura above are two large
bands of white matter, the optic tracts (Fig. 211).

The dorsal surface presents below two diverging columns of white
matter, the inferior peduncles; above, two converging columns, the
superior peduncles of the cerebellum (Fig. 212). At the extreme
upper part of this surface there are four small grayish eminences,
the corpora quadrigemina. From the disposition of the white matter
on the dorsal surface of the isthmus and medulla, there is formed a
lozenge-shaped space, the fourth ventricle. This space is merely an
expansion of the central cavity of the cord, the result of the changed
relations of the white and gray matter in this region of the central
nerve system. Above, this ventricle communicates by a narrow canal,
the aqueduct of Sylvius, with the third ventricle. The floor of the
fourth ventricle is covered with a layer of epithehum resting on the
ependyma continuous with that lining the central canal of the cord.
Beneath this is a layer of gray matter.

The pons Varolii comprises in a general way that portion of the
central nerve system situated between the medulla oblongata and
the crura cerebri. The ventral surface is convex from side to side;
the lateral surface, owing to the convergence of the fibers of which
it is composed, is contracted to form the middle peduncle of the
cerebellum; the posterior surface is flat and forms the upper half of
the floor of the fourth ventricle. The pons consists of white fibers
and gray matter supported by connective tissue and neuroglia. Trans-
verse sections of the pons show that it is divided into an anterior or'
ventral, and a posterior or dorsal portion, the latter being usually
termed the tegmentum.

The ventral portion consists for the most part of white fibers, ar-
ranged longitudinally and transversely (Fig. 213). The longitudinal
fibers are largely continuations of the pyramidal tracts, or the fibers
composing the anterior pyramid of the medulla. In the lower part of
the pons these fibers are compactly arranged, but at higher levels they
are separated into a number of bundles by the interlacing of the trans-
verse fibers. The transverse fibers are divided into a superficial and

ISTHMUS OF ENCEPHALON.

471

a deep set. Among these fibers are groups of nerve-cells which
collectively are knov^n as the nucleus pontis. Some of the transverse
fibers, especially the superficial ones, are commissural in character —
i. e., they connect corresponding parts of the gray matter of the lateral
halves of the cerebellum ; others coming from the gray matter of the
cerebellum cross the median line and terminate around the cells of
the nucleus pontis; others again are connected with the gray cells of
the same side. Through the intermediation of the nucleus pontis
and certain of the longitudinal fibers of the pons, the cerebellum is
brought into relation with the cerebrum.

The dorsal or tegmental portion consists of: (i) The fillet; (2) the
formatio reticularis; (3) the posterior longitudinal bundle; (4); the
substantia ferruginosa; (5) groups of nerve- cells from which arise
various cranial nerves — e. g., the fifth, sixth, seventh, and eighth.

The iillet or lemniscus in this region
is divided into a mesial and a lateral
portion. The fibers of the mesial por-
tion are partly the axons of the nerve-
cells of the gracile and cuneate nuclei
of the opposite side of the medulla,
and partly of the axons of the sensor
nerve-cells of the afferent cranial nerves
with the exception of the auditory.
The fibers of the lateral portion are
mainly the axons of the cells in the
floor of the fourth ventricle around
which the auditory nerve-fibers end.
They are therefore a continuation of
the auditory tract.

The I or m alio reticularis is a con-
tinuation of that of the medulla.

The posterior longitudinal bundle
is triangular in shape and situated behind the formatio reticularis
and close to the median fine. The fibers composing it are largely
derived from the ground fibers of the antero-lateral column of the
spinal cord.

The superior olive is a cyhndric mass of gray matter situated in
the pons in the anterior part of the formatio reticularis. It consists
of nerve-cells the axons of which pass dorso-laterally, decussate in
the median line, and form the lateral fillet of the opposite side. Some
few axons go to the lateral fillet of the same side.

The substantia ferruginosa is composed mainly of pigmented
cells.

The groups of nerve-cells lying just beneath the floor of the
fourth ventricle give origin to axons of the motor portion of the fifth.

Fig. 213. — Transection of the
Pons through its Middle
Portion, Showing the
Relation of the Nerve
Tracts of Which it is
Composed. D. 1. f. Dorsal
longitudinal fasciculus. L.c.
and c. Locus ceruleus. L.f.
Lateral fillet.

472

TEXT-BOOK OF PHYSIOLOGY.

the sixth, the seventh cranial nerves. Some of the groups are the
sensor end-nuclei of the fifth and eighth cranial nerves.

The crura cerebri comprise that portion of the central nerve sys-
tem situated between the pons below and the cerebrum above. They
are composed of strands of nerve-fibers which are divided, as shown
on cross-section, into a ventral and a dorsal portion by a crescentic
shaped layer of gray matter, the substantia nigra (Fig. 214). Of the
fibers which compose the ventral portion of each crus, the crusta
or pes, the larger part is continuous below, through the longitudinal
fibers of the pons, with the pyramid of the medulla and the pyramidal
tract; above they assist in the formation of the internal capsule.

On the inner and on the outer
.oQ_^ side of each crusta there is a

bundle of fibers derived from
the frontal, and from the
temporal and occipital por-
tions of the cerebrum respec-
tively. These fibers are con-
nected directly with the nuclei
pontis and indirectly with
the cerebellum of the same
and opposite sides. The
fibers which compose the
dorsal portion, the tegmentum,
are continuous with those
which pass upward from the
medulla and pons, e. g., the
fillet, both mesial and lateral,
the formatio reticularis, the
posterior longitudinal bundle,
and, in addition, the fibers of
the superior peduncles of the
cerebellum. Above, the fibers terminate largely in collections of gray
matter at the base of the cerebrum.

The aqueduct of Sylvius is a short narrow canal which connects
the cavity of the fourth with the cavity of the third ventricle. It is
lined by the ependyma and surrounded by a layer of gray matter
continuous with that forming the floor of the fourth ventricle. In
that portion of the gray matter lying beneath or ventral to the aqueduct
there are groups of nerve-cells which give origin to axons which unite
to form the third and fourth cranial nerves.

Fig. 214. — Scheme of Transverse Sec-
tion OF the Cerebral Peduncles.
CQ. Corpora quadrigemina. Aq. Aque-
duct, p. Lb. Posterior longitudinal bun-
dle. F. Fillet or lemniscus. RN. Red
nucleus. SN. Substantia nigra. III.
Third nerve. Py. Pyramidal tracts.
FC. Fronto-cerebellar; and TOC, tem-
poro-occipital fibers of the crusta. CC.
Caudate-cerebellar fibers in upper part
of crusta. — (After Wernicke and Gowers.)

CORPORA QUADRIGEMINA. 473

«

THE CORPORA QUADRIGEMINA.

The corpora quadrigemina are four small grayish eminences
situated beneath the posterior border of the corpus callosum and be-
hind the third ventricle. They rest upon the lamina quadrigemina,
which forms the roof of the aqueduct of Sylvius. The anterior pair
are termed the nates, or the pregeinina, the posterior pair the testes,
or the postgemina.

From the external surface of each body there pass outward
bundles of fibers termed hrachia. The fibers which compose the
brachium of the pregeminum pass outward and enter a small col-
lection of gray matter, the corpus geniculatum externum, and the optic
tract. The fibers which compose the brachium of the postgeminum
are divided into two bundles, one of which enters a second small
collection of gray matter, the corpus geniculatum internum, while the
other passes forward beneath this body to enter the internal capsule,
beyond which it passes to the cortex of the temporal region of the
cerebrum (Fig. 212).

Though these bodies are closely associated anatomically, they
differ in origin, in their relations and in their functions.

Microscopic examination of sections of the quadrigeminal bodies
shows that they are composed of nerve-cells and nerve-fibers, both of
which are so intricately arranged that it is difficult to trace their
relation one to another and to adjoining structures. Some of the
cells of the pregeminum give oft' axons which course outward and
forward, enter the internal capsule, and pass through the optic
radiation to the cortex of the occipital region of the cerebrum. Many
fibers of the optic tract, axons of the cells of the retina, end in
brush-like expansions around these same cells. There is thus formed
a connected pathway between the retina and the occipital cortex.

The cells of the occipital cortex, however, send axon fibers in the
reverse direction through the optic radiation to terminate around the
cells of the pregeminum, while axons of pregeminal cells pass for-
ward to the retina and to the cells of origin of the third nerve.

The cells of the postgeminum give origin to axons which pass
upward, forward, and outward, enter the internal capsule, and pass
by way of the auditory tract to the cortex of the temporo-sphenoidal
region of the cerebrum. Many of the fibers of the lateral fillet, a
portion of the auditory tract, terminate in brush-Hke expansions
around these same cells. There is thus estabhshed a connected
pathway between the cochlea and the temporo-sphenoidal cortex.
The cells of the temporal cortex, however, send axons in the re-
verse direction by way of the auditory tract to the cells of the
postgeminum. There is thus established a double communication
between the occipital and temporal region of the cerebral cortex,
and the pregeminal and postgeminal bodies respectively.

474

TEXT-BOOK OF PHYSIOLOGY.

THE BASAL GANGLIA. THE CORPORA STRIATA AND OPTIC

THALAMI.

The basal ganglia surmount the crura cerebri, but are only
made visible by removal of the cerebrum (Fig. 215).

Fig. 2^15. — Dissection of Brain, from above, Exposing the Lateral Fourth
AND Fifth Ventricles with the Surrounding Parts. §. — a. Anterior part,
or genu of corpus callosum. h. Corpus striatum, b'. The corpus striatum of
left side, dissected so as to expose its gray substance, c. Points by a line to the
taenia semicircularis. d. Optic thalamus, e. Anterior pillars of fornix divided;
below they are seen descending in front of the third ventricle, and between them
is seen part of the anterior commissure; in front of the letter e is seen the sht-Hke
fifth ventricle, between the two laminae of the septum lucidum. /. Soft or middle
commissure; g is placed in the posterior part of the third ventricle; immediately
behind the latter are the posterior commissure (just visible) and the pineal
gland, the two crura of which extend forward along the inner and upper margins
of the optic thalami. h and i. The corpora quadrigemina. k. Superior cms
of cerebellum. Close to k is the valve of Vieussens, which has been divided so
as to expose the fourth ventricle. /. Hippocampus major and corpus fimbria-
tum, or taenia hippocampi, in. Hippocampus minor, n. Eminentia collateraHs.
o. Fourth ventricle, p. Posterior surface of medulla oblongata, r. Section
of cerebellum, i. Upper part of left hemisphere of cerebellum exposed by the
removal of part of the posterior cerebral lobe. — {Hirschjeld and LeveilU.)

The corpora striata are two large ovoid collections of gray and
white matter situated at the base of the cerebrum. The larger portion
of each body is embedded in the cerebral white matter, while the

BASAL GANGLIA.

475

smaller portion projects into the anterior part of the lateral ventricle.
A transection of the corpus striatum shows that it is divided by a
band of white matter into two portions, viz.:

1. The caudate nucleus, the intra- ventricular portion, convex in

shape with its base directed forward, its apex or tail directed
backward and downward.

2. The lenticular nucleus, the extra- ventricular portion, somewhat

biconvex in shape and embedded largely in the white matter.

Each lenticular nucleus is sub-
divided by two lamina of white

matter into three portions. The two

inner, from their pale yellow color,

form the globus pallidus; the outer,

somewhat darker in color, is the

putamen.
The Internal Capsule. — The band
of white matter separating the caudate
from the lenticular nucleus has been
termed the internal capsule from the
manner in which it embraces the inner
surface of the lenticular nucleus. It
consists of nerve-fibers which associate
histologically and physiologically all por-
tions of the cerebral cortex with the optic
thalamus, pons, medulla, spinal cord, and
cerebellum. The relation of the capsule
to the nuclei through which it passes is
readily shown on cross-section (Fig. 216).
The appearance w^hich it presents, how-
ever, varies considerably at different levels.
At a given level it may be said to con-
sist of two segments or Hmbs, an anterior,
situated between the caudate nucleus and
the anterior extremity of the lenticular
nucleus, and a posterior, situated between
the optic thalamus and the posterior
extremity of the lenticular nucleus. The

two segments unite at an obtuse angle, termed the knee, which is
directed toward the median Hne.

The optic thalami are two oblong masses of gray matter situated
upon the crura cerebri and behind the corpora striata. The anterior
and posterior extremities of each thalamus present enlargements
known respectively as the anterior tubercle and the posterior tubercle
or pulvinar. The mesial surface of the thalamus forms the lateral
waU of the third ventricle and is covered by epithehum resting on a
thin layer of ependyma.

Fig.

216. — Horizontal Sec-
tion OF THE Internal
Capsule showing its
Relations to the Cau-
date Nucleus, Optic
Thalamus, and the
Lenticular Nucleus, i.
Caudate nucleus. 2. An-
terior segment of the in-
ternal capsule. 3. Exter-
nal capsule. 4. Lenticu-
lar nucleus. 5. Claus-
trum. 6. Posterior seg-
ment 0} hiternal capsule.
7. Optic thalamus. —
{Modified from Landois.)

476 TEXT-BOOK OF PHYSIOLOGY.

A transection of the thalamus shows that it is not only covered
externally but penetrated by white matter, which subdivides its con-
tained gray cells into four more or less distinct masses termed nuclei,
viz., an anterior, a lateral, occupying the external part of the thalamus,
a vejitral, close to the entire ventral surface, and a posterior, situated
beneath the pulvinar. Beneath and somewhat internal to each
optic thalamus there is a region, the subthalamic, consisting of an
intricate network of nerve-fibers and several nuclei of gray matter,
e. g., the red or tegmental nucleus, the subthalamic nucleus, or Luys'
body, and the substantia nigra.

Though the thalamus has extensive connections with many por-
tions of the central nerve system, the most important are with the
cortex, the tegmentum, and the optic tracts.

From the cells of these various nuclei axons emerge which pass into
the internal capsule, and through the corona radiata to all portions
of the cortex. Those axons which come from the pulvinar and pass
to the occipital lobe constitute a part of the optic radiation; those
from the lateral and ventral nuclei ultimately reach the parietal lobe ;
those from the anterior nucleus pass to the hippocampal and unci-
nate convolutions. In a similar manner all portions of the cortex are
brought into relation with the thalamus, axons from the cortical cells
passing downward to terminate in tufts around the thalamic nuclei.

The tegmentum is intimately related to the thalamus, though the
exact distribution of various strands of fibers is a subject of much
discussion. Most of the fibers of the mesial fillet end in tufts around
the cells of the ventral and lateral nuclei; other fibers pass directly
to the cortex.

The optic tract sends fibers directly into the pulvinar, around the
cells of which they terminate in brush-Kke expansions.

SUMMARY OF THE STRUCTURE OF THE MEDULLA, ISTHMUS,
AND BASAL GANGLIA.

Structure of the Central Gray Matter. — Though the general
arrangement of the central gray matter has been incidentally alluded
to in the foregoing presentation of the anatomic features of the
medulla and isthmus, it will be convenient to summarize its arrange-
ment and structure at this point.

The gray matter of the cord, of the dorsal aspect of the medulla
and pons, of the region surrounding the aqueduct of Sylvius, and of the
fining of the third ventricle, constitute practically a continuous system,
though presenting modifications in various parts of its extent. In
the transition region of the spinal cord and medulla the gray matter
of the former becomes much changed in shape owing to the shifting
of position of the various tracts of white matter, until in the medulla

MEDULLA AND BASAL GANGLIA. 477

and pons it is spread out in the form of a thin layer near their dorsal
surfaces, where, together with the ependyma, it forms the floor of
the fourth ventricle.

In the region of the aqueduct of Sylvius the gray matter again
converges and ultimately surrounds the canal, to again expand at its
anterior extremity, to form the lining of the third ventricle.

The Nerve-cells. — The nerve-cells in these different regions do
not differ morphologically from those in the gray matter of the spinal
cord. The corpus, or body of the cell, presents a number of den-
drites as well as the sharply defined axon. As a rule, the cells are
arranged in groups, or clusters, or nests, partially surrounded and
enclosed by supporting tissue, and situated beneath the floor of the
fourth ventricle and the floor of the aqueduct of Sylvius. From some
of the cell groups axons pass ventrally through the white matter to
emerge on the ventral and lateral surfaces of the medulla, pons, and
crura, where they are known as efl'erent or motor cranial nerves.
From other groups of cells, axons cross the median line, and after
joining the mesial fillet ascend toward the cerebrum. Around these
latter cells the terminal filaments of the afferent or sensor cranial
nerves arborize. The collection of cells formed in the central gray
matter may be divided into two groups— efferent and afferent.

The efferent cells, like those of the cord independent of a trophic
influence, are motor in function, inasmuch as the excitation arising
in them is transmitted outward through their related axons to mus-
cles, glands, or blood-vessels, imparting to them motion, either
molar or molecular.

The afferent cells are largely sentient or receptive in function,
inasmuch as the excitations brought to them by the aft'erent cranial
nerves from skin and mucous membranes and from sense-organs,
such as the tongue and ear, are received by them and transmitted
through their ascending axons to the cortex of the cerebrum, where
they are translated into conscious sensations.

Structure of the White Matter. — The white matter is com-
posed of medullated nerve-fibers, and though arranged in a very
complex manner may be divided into longitudinal and transverse
fibers.

The longitudinal fibers which compose the main portion of the
isthmus may be subdivided into (i) a ventral or pedal portion and (2)
a dorsal or tegmental portion. The fibers constituting the ventral
or pedal portion may for convenience be said to extend from the
cerebral cortex to the pons, medulla, and spinal cord. They may be
divided into three distinct tracts: e. g., the pyramidal tract, the
fronto-cerebellar tract, and the occipito-temporo-cerebellar tract
(Fig. 217).

The pyramidal tract descends from the cortex of the cerebrum

478

TEXT-BOOK OF PHYSIOLOGY.

■ bordering the fissure of Rolando, passes through the posterior one-
third of the anterior segment and the anterior two-thirds of the
posterior segment of the internal capsule, the middle two-fifths
of the crusta, behind the transverse fibers of the pons, to become
the anterior pyramids of the medulla, beyond which it divides into the
direct and crossed pyramidal tracts of the cord. In its course some
of the fibers and their collaterals arborize around efferent cells from
the anterior extremity of the aqueduct of Sylvius to the termination
of the spinal cord.

Fig

217. — Diagrammatic Arrangement of the Projection Tracts Connecting
THE Cerebral Cortex with the Lower Nerve-centers. A. Fronto-
cerebellar tract. B. The pyramidal or motor tract. C. Sensory tract. D.
Visual tract from optic thalamus (O.T.) to the occipital lobe. E. Central audi-
tory tract. F. Superior cerebellar peduncle. G. Middle cerebellar peduncle.
H. Inferior cerebellar peduncle. C.N. Caudate nucleus. C.Q. Corpora quad-
rigemina. Vt. Fourth ventricle. The numerals refer to cranial nerves. J.
Eighth nerve nucleus. — (After Starr.)

The fronto-cerebellar tract descends from the cortex of the frontal
portion of the anterior lobe, passes through the anterior portion of the
anterior segment of the internal capsule, the inner fifth of the crusta
to the pons, where its fibers terminate or arborize around the nucleus
pontis of the same and opposite sides.

The occipito-temporo-cerebellar tract descends from the occipital
and temporal lobes, passes to the inner side of the lenticular nucleus,

MEDULLA OBLONGATA AND ISTHMUS. 479

and continues downward on the outer side of the crusta, occupying
about one-jfifth of its bulk, to the pons, where its fibers also arborize
around the nucleus pontis of the same and opposite sides. By
means of fibers in the middle peduncle these descending fibers are
brought into relation with the cerebellum.

The fibers constituting the dorsal or tegmental portion of the
longitudinal system may be said for convenience to extend from the
posterior portion of the medulla and pons to the optic thalamus
and cerebrum. They may be subdivided into several tracts : viz., the
fillet, the posterior longitudinal bundle, Gowers' tract, etc.

The fillet or lemniscus, consisting of fibers having their origin
partly from the cells of the cuneate and gracile nuclei and partly from
the cells of the sensor end-nuclei of various sensor cranial ner^'es,
occupies a region in the ventral and mesial portion of the tegmentum
throughout its entire extent. Superiorly this mesial fillet divides
into two portions, one of which passes to the thalamus and pregem-
inum (anterior corpus quadrigeminum), the other to the cortex of-
the parietal and hmbic lobes. The fibers coming from the sensor
end-nucleus of the auditory nerve (the lateral fillet) lie on the lateral
aspect of the pons and crus. Superiorly they terminate in the post-
geminum (the posterior corpus quadrigeminum).

The posterior longitudinal bundle, an upward extension of the
fibers composing a portion of the ground bundle of the spinal cord,
is located on either side of the median line just beneath the floor
of the fourth ventricle and the aqueduct of Sylvius. As it passes
upward collateral branches are given off, some of which arborize
around the cell nuclei of the third, fourth, and sixth cranial nerves
of the same side, while others cross the median line and arborize
around the corresponding cell nuclei of the opposite side. Superi-
orly some of the fibers become related to cells in the thalamus and
subthalamic region. This bundle of fibers appears to be mainly
commissural in character.

Gowers' tract, the antero-lateral tract of the spinal cord, occupies
a position in the lateral region of the formatio reticularis both in the
medulla and pons. Continuing upward, it enters the mesial fillet,
and in company with it passes through the posterior division of the
internal capsule and finally terminates around cells in the cortex of
the parietal lobe.

The transverse fibers of the isthmus are found in the pons. The
fibers of the ventral as well as those of the more dorsal regions have
their origin in nerve-cells in the cortex of the cerebellum. From
their origin they pass through the cerebellar white matter, and through
the middle peduncle as far as the median line, where they decussate
with fibers coming from the opposite side. Beyond this point they
pass to the cerebellar cortex. From their anatomic relations it is prob-

48o TEXT-BOOK OF PHYSIOLOGY.

able that these transverse fibers are commissural in character, bring-
ing into relation opposite but corresponding regions of the cerebellar
cortex. In addition to the commissural fibers other transverse fibers
associate the cerebellar cortex with the gray matter in the pons on
both the same and opposite sides. In this way the cerebellum is
brought into relation with longitudinal fibers coming from and going
to the cerebrum.

FUNCTIONS OF THE MEDULLA OBLONGATA, ISTHMUS, AND
BASAL GANGLIA.

Microscopic examination of the white and gray matter of these
various parts of the central nerve system shows that they are com-
posed of nerve-cells and nerve-fibers which morphologically do not
differ in essential respects from those found in the spinal cord, though
their arrangement is far more complicated and involved. The func-
tions of these closely related structures are in consequence equally
complex and involved and but imperfectly known.

In a general way it may be said that by virtue of the presence
of nerve-cells and definite tracts of nerve-fibers these structures col-
lectively may be regarded as consisting :

1 . Of centers for reflex actions ; and —

2. Of conducting paths by which the various parts are brought into

relation one with another and with the spinal cord, the cerebel-
lum, and the cerebrum.

The Medulla Oblongata and Pons.^ — I'he gray matter situated
in these structures — i. e., just beneath the floor of the fourth ventricle
— contains nerve-cells arranged in more or less well-defined groups
which may be divided into efferent and afferent.

The efferent cells are the immediate sources of energy which
is transmitted through efferent axons to various peripheral organs —
muscles, glands, and blood-vessels. Their activity may be excited
by the same influences which excite the efferent cells of the spinal
cord: e. g., variations in the composition of the blood or lymph; the
arrival of nerve energy coming through afferent pathways in the
spinal cord and through afferent cranial nerves; the arrival of nerve
energy coming through efferent pathways from the cerebrum. The
peripheral activity resulting from their excitation may therefore be
automatic or autochthonic, peripheral (reflex) or cerebral (voHtional)
in origin.

The afferent cells are sentient or receptive in function, inasmuch
as they receive nerve energies coming through lower afferent pathways
and transmit them through their related axons to the cortex of the
cerebrum, where they are translated into conscious sensations.

The efferent cells give origin to nerve-fibers which pass ventrally
and become the efferent or motor cranial nerves.

FUNCTIONS OF THE MEDULLA OBLONGATA. 481

The afferent cells give origin to fibers which pass to the cerebral
cortex. Around both groups of cells, the afferent or sensor cranial
nerves terminate in tuft-like expansions. In a subsequent section the
origin, course, and distribution of the various cranial nerves will be
considered. But as the function of the nerve is but to transmit
energy from the cell of which it constitutes a part, the function
ascribed to it may without impropriety be transferred to the cell
itself.

Since it is by means of nerve-cells and their associated fibers that
many important functions of organic fife are initiated and maintained,
it would naturally be expected from its extensive nerve connections
that this region of the nerve system plays an extensive role in this
respect. As the accomphshment of these functions requires the
cooperation and coordination of a number of separate but related
structures, it is evident that there must exist in the medulla and pons
a number of coordinating mechanisms consisting of nerve-cells and
nerve-fibers which are associated in various ways for the accomplish-
ment of definite functions. To such a coordinating mechanism the
term "center" has been given: e. g., respiratory, cardiac, deglutitory,
etc.*

As centers for reflex activities. Experimentation has shown
that the medulla and pons contain a number of such centers, the
more important of which are as follows :

1. A cardiac center, which exerts (i) an accelerator influence over the

heart's pulsations through nerve-fibers emerging from the spinal
cord in the roots of the first and second dorsal nerves and reach-
ing the heart through the sympathetic nerve; (2) an inhibitor
or retarding influence on the action of the heart through efferent
fibers in the trunk of the pneumogastric nerve. (See page 295.)

2. A vasO' motor center, which regulates the caliber of the blood-

vessels throughout the body in accordance with the needs of the
organs and tissues for blood, through nerve-fibers passing by
way of the spinal nerves to the walls of the blood-vessels. (See
•page 327.)

3. A respiratory center, which coordinates the muscles concerned in

the production of the respiratory movements. (See page

4. A mastication center, which excites to activity and coordinates the

muscles of mastication. (See page 157.)

5. A deglutition center, which excites and coordinates the muscles

* By the term center as here employed is meant a collection of nerve-cells and
nerve-fibers occupying an area of greater or less extent, though its exact anatomic
limits may not be accurately defined. That an area may merit the term center, it
is necessary that its stimulation should increase, its destruction should abolish or
impair, functional activity.
31

482 TEXT-BOOK OF PHYSIOLOGY.

concerned in the transference of the food from the mouth to
the stomach. (See page 175.)
6. An articidation center, which coordinates the muscles necessary to
the production of articulate speech.

In addition, the gray matter contains centers which influence the
secretion of sahva, provoke vomiting, coordinate the muscles of the
face concerned in expression, and control the secretion of the per-
spiration.

As conducting pathways. The anterior pyramids of the medulla
and their continuations through the more ventral portions of the
pons, being portions of the general pyramidal tract, serve to conduct
vohtional efferent nerve impulses from higher portions of the brain
to the spinal cord. Division of either of these pathways is at once
followed by a loss of volitional control of the muscles below the
section.

The dorsal or tegmental portion, containing the fillet and Gowers'
tract, serv^es to transmit afferent nerve impulses from the spinal
cord to higher portions of the brain. Transverse division of one-half
of the dorsal portion of the pons is followed by complete anesthesia
of the opposite half of the body without any impairment of motion.

The restiform bodies constitute a pathway between the spinal cord
and the cerebellum. The transverse fibers of the pons associate
opposite but corresponding portions of the cerebellar hemispheres.

The Crura Cerebri. — The crura cerebri consist ventrally of fibers
which are largely derived from the pyramidal tracts and are con-
tinuous with the longitudinal fibers of the ventral portion of the pons
and medulla; and dorsally of fibers continuous with those coming
through the lower portions of the tegmentum. Hence they are con-
ductors of motor impulses in the former and of sensor impulses
in the latter region. It is not definitely known as to whether reflex
actions take place through the gray matter, the locus niger, or not.

The gray matter beneath the aqueduct of Sylvius contains nerve-
cell groups which are centers for reflex actions in connection with
ocular movements: e. g., closure of the lids, contraction of the sphinc-
ter pupillae, convergence of the eyes, etc.

The Corpora Quadrigemina. — From the anatomic relation of
the anterior quadrigemina! body (the pregeminum) to the optic tract,
on the one hand, and to the optic radiation, on the other, the in-
ference can be drawn that it is in some way essential to the per-
formance of the visual process. Experimental investigations and
pathologic changes support the inference.

Irritation of the pregeminum in monkeys on one side is followed
by dilatation of the pupils first on the opposite side and then almost
immediately on the same side. The eyes at the same time are also
widely opened and the eyeballs turned upward and to the opposite

FUNCTIONS OF THE BASAL GANGLIA.

483

side. If the irritation be continued, motor reactions are exhibited
in various parts of the body. Destruction of the pregeminum in both
monkeys and rabbits is followed by bhndncss, dilatation and immo-
bihty of the pupils, with marked disturbance of equilibrium and
locomotion (Ferricr).

From the anatomic relation of the posterior quadrigeminal body
(the postgeminum) to the lateral fillet, the basal tract for hearing,
the inference may be drawn that it is in some way connected with the
auditory process.

Stimulation of the postgeminum gives rise to cries and various
forms of vocalization.
Pathologic states of this
body are also attended by
impairment of hearing
and disorders of the
equilibrium.

From the foregoing
facts it is probable that
the corpora quadrigem-
ina are associated with
station and locomotion.
Ferrier assumes that in
these bodies "sensory
impressions, retinal and
others, are coordinated
with adaptive motor re-
actions such as are in-
volved in equilibration
and locomotion."

The Corpora Striata.
— The relation of these
bodies to the pyramidal
motor tract would indi-
cate that they are in
some way connected with
motor activities. Their
function, however, is ob-
scure. While stimulation of one corpus produces convulsion of the
muscles of the opposite side of the body, and destruction gives rise
to paralysis of the corresponding muscles, it is difficult, owing to the
intimate association of the white and the gray matter, to state to
which the phenomena are to be attributed. The evidence at hand
points to the conclusion that if a lesion is hmited to the gray matter
the paralysis which might result would be but temporary and of short
duration. The pathologic evidence is of a similar character. Gowers

Fig.

218. — Horizontal Section of the Internal
Capsule Showing the Position and Rela-
tion OF the Motor Tracts for the Eye,
Head (Hd.), Tongue (Tg.), Mouth (Mth.),
Shoulder (Shi.), Elbow (Elb.), Digits of
H.AND (Dig.), Abdomen (Abd.), Hip, Knee
(Kn.), Digits of Foot (Dig.). S. Sensor
tract. O. T. Optic tract. A. T. Auditory
tract. I. Caudate nucleus. 2. Anterior seg-
ment of internal capsule. 3. External capsule.
4. Island of Reil. 5. Lenticular nucleus. 6.
Claustrum. 7. Posterior segment of internal
capsule. — {Modified from Landois.)

484

TEXT-BOOK OF PHYSIOLOGY.

is of the opinion, that if the lesion is small and at a sufficient distance
from the white fibers of the capsule, there may even be no -initial
hemiplegia; neither motor nor sensory paralysis will arise if the lesion
is confined to the gray matter.

It is stated by some experimenters that localized injuries, both
experimental and pathologic, are followed by a persistent rise of
temperature, varying from i° to 2.6° C.

The Optic Thalami. — From the anatomic relation of the optic
thalami to the general and special sense nerve-tracts, on the one
hand, and to the cerebral cortex, on the other hand, it is assumed

that they are connected
vdth the production of
sensations both general
and special, and act as
intermediates between
the peripheral sense-
organs and the cortex.

The results of ex-
perimental stimulation
and destruction of the
thalami are extremely
contradictory and fail to
throw much light on
their functions. Ferrier
states that destruction
of the posterior part of
one thalamus produced
bhndness in the opposite
eye and impairment of
the sense of touch and
pain in the opposite side
of the body. In a pa-
tient under the care of
Hughhngs- Jackson there
was bhndness in the
right half of each eye,
loss of hearing in the left
ear, impairment of taste on the left side of the tongue, and a diminu-
tion of the sense of touch on the left side of the body. Postmortem
examination showed a patch of softening in the posterior part of the
right thalamus, the remainder of the organ being normal.

It is probable that in the thalamus visual, tactile, and labyrinthine
impressions are received, coordinated, and reflected outward, with
the result of producing various adaptive motor reactions connected
with station and equilibrium. It is also beheved by some investigators

Fig. 219. — Vertical Section Theoitgh the
Right Cerebral Hemisphere in Front of
THE Gray Commissure, i. Caudate nucleus.
2. Corpus callosum. 3. Pillars of the fornix.
4. Internal capsule. 5. Optic thalamus. 6.
Gray commissure. 7. External capsule. 8.
Claustrum.

FUNCTIONS OF THE INTERNAL CAPSULE. 485

to act as an intermediate between emotional states and their expres-
sion in the muscles of the face, this power being lost in certain patho-
logic conditions. The power of regulating the temperature of the
body has also been assigned to the thalamus, as destruction of its
anterior extremity is usually followed by a rise in temperature.

The Internal Capsule. — The internal capsule has been shown by
the results both of experiment and of pathologic processes to be, first,
a pathway for the transmission of nerve impulses from the cerebral
cortex to the pons, medulla, and spinal cord, which give rise to
contraction of the muscles of the opposite side of the body; and,
second, a pathway for the transmission of nerve impulses coming
from skin, mucous membrane, muscles, and special sense-organs to
the cortex, where they give rise to sensations general and special.
It is therefore the common motor and sensor pathway. For the
reason that it transmits both motor and sensor impulses, and for
the further reason that it is frequently the seat of pathologic lesions
which are followed by either a loss of motion or sensation or both,
the internal capsule is one of the most important parts of the central
nerve system. As shown in Fig. 218, it consists of two segments or
Hmbs united at an obtuse angle, the knee or elbow, which is directed
toward the median line. The motor tract is confined to the posterior
one-third of the anterior segment and the anterior two-thirds of the
posterior segment. The sensor tract is confined to the posterior
one-third of the posterior segment, the extreme end of which also
contains the optic and auditory tracts.

The region of the anterior segment in front of the motor tract
contains the fibers of the fronto-cerebellar tract, the function of
which is unknown.

The motor region contains fibers which descend from the cerebral
cortex to nerve-centers situated in the gray matter beneath the
aqueduct of Sylvius, in the gray matter beneath the floor of the
fourth ventricle, and in the anterior horns of the gray matter of the
spinal cord, and which in turn are connected by the cranial and
spinal nerves with the muscles of the eye, head, face, trunk, and
hmbs. The positions occupied by these different tracts are shown in
Fig. 218.

The relation of the internal capsule to the caudate nucleus and
the optic thalamus internally, and to the lenticular nucleus exter-
nally, is also shown in a vertical section of the cerebrum made in
front of the gray commissure (Fig. 219). From the fact that the
internal capsule contains efferent or motor tracts, and afferent or
sensor tracts, it is evident that a destructive lesion of the motor tract
would be follow^ed by a loss of motion; and of the sensor tract, by
a loss of sensation on the opposite side of the body.

CHAPTER XIX.
THE CEREBRUM.

The cerebrum is the largest portion of the encephalon, constitut-
ing about 85 per cent, of its total weight. In shape it is ovate, convex
on its outer surface, narrow in front and broad behind. It is divided
by a deep longitudinal cleft or fissure into halves, known as the
cerebral hemispheres. The hemispheres are completely separated
anteriorly and posteriorly by this fissure, but in their middle portions
are united by a broad white band, the corpus callosum. Each
hemisphere or hemi-cerebrum is convex on its outer aspect, and
corresponds in a general way with the cavity of the skull; the inner
or mesial surface is fiat and forms the lateral boundary of the longi-
tudinal fissure.

The surface of each hemi-cerebrum presents a series of alternate
indentations and elevations, known respectively as fissures or sulci,
and convolutions or gyres. A knowledge of the situation and extent
of the principal fissures and convolutions, as well as of their relation
one to another, is essential to a clear understanding of many phys-
iologic processes, clinical phenomena, and surgical procedures.
The general arrangement of the primary fissures and convolutions
is represented in Figs. 220 and 221.

Fissures. —

1. The fissure of Sylvius, one of the most important of the primary

fissures, is found on the side of the cerebrum. It begins at the
base and extends upward, outward, and backward to a point
corresponding to the eminence of the parietal bone, where it
usually terminates. Anteriorly a short branch is given off
which passes upward and forward into the frontal lobe. The
Sylvian fissure is the first to appear in the development
of the fetal brain, becoming visible at the third month. In the
adult it is deep and well marked and divides the hemi-cerebrum
into a frontal and a temporo-sphenoidal lobe.

2. The fissure 0} Rolando, or central fissure, equally important, is

found on the superior and lateral aspects of the cerebrum. It
runs from a point on the convexity of the hemisphere near the
median line transversely outward and downward toward the
fissure of Sylvius, but as a rule does not pass into it. It divides
the frontal from the parietal lobe. The inclination of the

CEREBRUM.

487

central fissure is such as to form with the longitudinal fissure
an angle of about 67 degrees.
The intra- parietal fissure arises a short distance behind the central
fissure. It then runs upward, backward, and downward to
terminate near the posterior extremity of the hemisphere. It
divides the parietal lobe into a superior and an inferior portion.

Fig. 220. — Diagram Showing Fissures and Convolutions of the Left Side of
THE Human Brain. F. Frontal. P. Parietal. O. Occipital. T. Temporo-
sphenoidal lobe. S. Fissure of Sylvius. S'. Horizontal. S". Ascending ramus
of S. c. Suculs centralis, or fissure of Rolando. A. Ascending frontal, and B.
Ascending parietal, convolution. Fj. Superior, Fj. Middle, and Fo. Inferior
frontal convolutions, fj. Superior, fj. Inferior, frontal fissures, fg. Sulcus prse-
centralis. P. Superior parietal lobule. P3. Inferior parietal lobule, consisting of
P2. Supramarginal gyrus, and Pj'. Angular gyrus, ip. Sulcus interparietalis.
cm. Termination of callosomarginal fissure. Oi- First, Oj. Second, O3. Third,
occipital convolutions, po. Parieto-occipital fissure, o. Transverse occipital
fissure. O3. Inferior longitudinal occipital fissure. Ti. First, T2. Second, T3.
Temporo-sphenoidal, convolutions, /j. First, /2- Second, temporo-sphenoidal
fissures. — {Landois' " Physiology.'")

4, The parieto-occipital -fissure, situated on the mesial surface of the
hemisphere, divides the latter into a parietal and an occipital
lobe. It begins as a deep notch on the surface of the hemisphere,
and is then continued downward and forward until it enters the
calcarine fissure.

8 TEXT-BOOK OF PHYSIOLOGY.

The calcarine fissure begins on the posterior extremity of the
mesial surface of the occipital lobe. From this point it passes
downward and forward to unite with the parieto-occipital
fissure.

The calloso-marginal fissure is a deep cleft on the mesial surface
of the hemisphere. It begins below the anterior extremity of the
corpus callosum and in a general way follows the course of this
structure as far as its posterior extremity, where it turns upward
to terminate at the margin of the hemisphere just posterior to
the fissure of Rolando. ^

Fig. 221. — Diagram Showing Fissures and Convolutions on Mesial Aspect
OF the Right Hemisphere. Median aspect of the right hemisphere. CC.
Corpus callosum divided longitudinally. Gf. Gyrus fornicatus. H. Gyrus hip-
pocampi, h. Sulcus hippocampi. U. Uncinate gyrus, cm. Calloso-marginal
fissure. F. First frontal convolution, c. Terminal portion of fissure of Rolando.
A. Ascending frontal, B. Ascending parietal, convolution and paracentral lobule.
P/. Precuneus or quadrate lobule. Oz. Cuneus. Po. Parieto-occipital fissure.
Oj. Transverse occipital fissure, oc. Calcarine fissure, oc'. Superior, oc". Inferior,
ramus of the same. D. Gyrus descendens. T4. Gyrus occipitotemporaHs lateralis
(lobulus fusiformis). T5. Gyrus occipitotemporalis mediahs (lobulus Hnguahs).

Secondary fissures of more or less importance are present in the
different lobes, subdividing the surface into convolutions: e. g., in the
frontal lobe are found the pre-ceniral, the superior and middle frontal
fissures; in the temporo-sphenoidal lobe the superior and inferior
or the first and second temporo-sphenoidal fissures; in the occipital
lobe, the transverse and inferior longitudinal fissures.

Convolutions. — The convolutions or gyres are the portions of
the cerebral surface comprised between the fissures. The arrange-

CEREBRUM. 489

ment of the surface is such that only the more superficial portions are
visible. The depth of the convolution, the portion bordering the
fissure, is concealed from view. Each lobe presents a series of such
convolutions, which differ considerably in their relative physiologic
importance.

The Frontal Lobe. — The frontal lobe presents on its convex
surface four convolutions: viz., the anterior or pre-central convolution,
and the superior, middle, and inferior frontal convolutions.

1. The anterior or pre-central convolution is situated just in front of

the Rolandic or central fissure, with which it corresponds in
direction. It is continuous above with the superior frontal and
below with the inferior frontal convolution.

2. The superior frontal convolution is bounded internally by the

longitudinal fissure and externally by the superior frontal fissure.
From the upper end of the pre-central convolution, with which
it is continuous, it runs forward and downward to the anterior
extremity of the frontal lobe, where it turns backward and rests
on the orbital plate of the frontal bone.

3. The middle frontal convolution is situated on the side of the lobe,

between the superior frontal fissure above and the middle frontal
fissure below. Its general direction is downward and forward.

4. The inferior frontal convolution winds around the ascending

branch of the fissure of Sylvius in the anterior and inferior por-
tion of the cerebrum. It is continuous posteriorly with the
lower end of the pre-central convolution.
The Parietal Lobe. — The parietal lobe presents three well-
marked convolutions: viz., the posterior or post-central convolution,
and the superior and inferior parietal.

1. The posterior or post-central convolution is situated just behind-

the Rolandic or central fissure, \\'ith which it corresponds in
direction. Above, it is continuous with the superior parietal
convolution; below, with the inferior parietal and the pre-central
convolutions.

2. The superior parietal convolution is bounded internally by the

longitudinal fissure and externally by the intra-parietal fissure.
From the upper end of the post-central convolution, with which
it is connected, it runs downward and backward as far as the
parieto-occipital fissure.

3. The inferior parietal convolution is connected anteriorly with the

post-central convolution. Passing backward, it winds around
the superior extremity of the fissure of Sylvius, in which situa-
tion it is kno\\Ti as the supra-marginal convolution. Beyond
this point it divides into two portions, one of which runs forward
into the temporal lobe above the first temporal fissure, while
the other runs downward and backward, following the intra-

490 TEXT-BOOK OF PHYSIOLOGY.

parietal fissure to its termination. At this point it makes a sharp
bend and runs forward into the temporal lobe just beneath the
first temporal fissure. In the neighborhood of the bend it is
generally known as the angular convolution or gyrus.
The Temporo-sphenoidal Lobe. — The temporo-sphenoidal
lobe presents on its external surface three well-marked convolutions :
viz., the superior, the middle, and the inferior temporal, separated by
the first and second temporal fissures. These three convolutions are
in a general way parallel with each other, and pursue a direction
from before backward and upward. Anteriorly, they are fused to-
gether, but posteriorly their connections are somewhat different.
The superior temporal is continuous behind and above with the
supra-marginal convolution, and behind and below with the angular
convolution or gyre. The middle temporal blends with the preceding
and with the middle occipital. The inferior temporal is continuous
with the inferior occipital.

The Occipital Lobe. — The occipital lobe is triangular in shape
and forms the posterior apex of the hemisphere. Its base on the
external surface is formed by an imaginary line drawn from the
parieto-occipital fissure to the pre-occipital notch on the inferior and
lateral border. The external surface presents three convolutions —
the superior, middle, and inferior occipital.

The inner or mesial surface of the hemisphere, formed in part
by the frontal, the parietal, the occipital, and the temporal lobes, pre-
sents several convolutions of much physiologic interest, viz. :

1. The gyrus fornicatus, situated between the calloso-marginal

fissure and the corpus callosum. From its origin anteriorly
at the base of the brain this convolution passes backward,
gradually increasing in width as it approaches the posterior
extremity of the corpus callosum. At this point it again narrows
and descends between the calcarine and hippocampal fissures
to blend with the hippocampal convolution.

2. The gyrus hippocampus, formed by the union of the posterior

extremity of the gyrus fornicatus and the median occipito-tem-
poral convolution (the hngual lobule), is situated just below
the dentate or hippocampal fissure. Anteriorly it becomes
enlarged, and just behind the apex of the temporal lobe turns
backward and inward to form a hook-shaped eminence, the
uncinate gyrus or uncus.

The limbic lobe is the name given to an area of the brain
which includes, among other structures, the gyrus fornicatus, the
gyrus hippocampus, and the uncus. As forming a part of this
general lobe may be mentioned the dentate fascia, the striae and
peduncle of the corpus callosum, the septum lucidum, the
fornix, and the infracallosal gyrus.

CEREBRUM. 491

3. The temporo-occipilal gyrus is bounded by the collateral fissure

above, and its inferior border extends from the occipital lobe to
the anterior pole of the temporal lobe.

4. The quadrate lobule, a square-shaped convolution, is situated

between the posterior termination of the calloso-marginal fis-
sure and the parieto-occipital fissure. It blends with the gyrus
fornicatus, on the one hand, and with the parietal lobule on the
other.

5. The citneus, a triangular or w^edge-shaped convolution or lobule,

is situated on the mesial surface of the occipital lobe between the

parieto-occipital and calcarine fissures.

The Insula or Island of Reil. — This anatomic structure con-
sists of a triangular shaped cluster of six small convolutions situated
at the bifurcation of the Sylvian fissure and concealed from view
by the convolutions bordering it, spoken of collectively as the oper-
culum. These convolutions are connected with the frontal, the
parietal, and the temporal lobes.

Structure of the Gray Matter or the Cortex.^The gray matter,
the cortex of the cerebrum, varies from two to four millimeters in
thickness. When examined with a lens of low power, it presents a
laminated appearance, due to differences in color and arrangement
of its constituent elements. With higher magnification the cortex
is seen to consist of neuroglia cells, nerve-cells with specialized
dendrites and axons, medullated and non-medullated nerve-fibers,
blood-vessels, connective tissue, etc., — all of which are arranged and
interblended in a most intricate manner. Notwithstanding the com-
plexity of its structure, modern histologic methods have enabled
Cajal to divide it into four fairly distinct layers or zones, from without
inward, as follows (Fig. 222):

1. The Molecular Layer. — The most superficial portion of this layer

consists mainly of neuroglia or glia cells, the processes of which
interlace in all directions, forming a distinct sheath just beneath
the pia. The deeper portions of this layer contain a specialized
type of nerve-cell (Cajal cells), of which there are several varie-
ties. These cells give off nerve-fibers which pursue a horizontal
direction for a variable distance, but in their course give off
collateral branches which ascend to the outer surface of the
layer. Among these structures are to be found, also, dendritic
processes of cells situated in the subjacent layer. The terminal
filaments of medullated nerve-fibers coming from nerve-cells in
lower regions of the encephalo-spinal axis are also present, but
for the most part they pursue a tangential direction.

2. The Layer oj Small Pyramidal Cells. — This layer consists mainly

of nerve-cells, the majority of which are pyramidal in shape
and of small size. Other cells, however, are present, which

492

TEXT-BOOK OF PHYSIOLOGY.

present a variety of shapes, for which reason the layer was at
one time termed the ambiguous layer. The apical process of the
pyramidal cells is broad at the base, but narrows rapidly as it
passes upward. It .frequently divides into several branches,

each of which develops club-
shaped processes or gemmules,
which give to it a feathery appear-
ance. Dendrites are also given
off from the sides and base of
the cell-body. From the base
a single axon descends which ulti-
mately becomes the axis-cylinder
of a medullated nerve.
The Layer of Large Pyramidal
Cells. — The nerve-cells of this
layer, as the name implies, are
also pyramidal in shape, but of
large size. Each cell presents the
same features as the cells of the
preceding layer, with the exception
that the apical process is larger,
better developed, and branches
more freely. All the dendrites
are extensively provided with
gemmules. The axon is well
developed, sharply defined, and
smooth. After giving off collateral
branches, the axon descends into
the cerebrum and becomes a
medullated nerve-fiber.
The Layer of Polymorphous Cells. —
In this layer the nerve-cells pre-
sent a variety of forms: e. g.,
spindle, polygonal, pyramidal, etc.
The spindle form is the most
common. From either end of the
spindle a large dendrite emerges
which soon branches and becomes
gemmulated. The axon is well
defined and it soon descends into
the white matter.
The Number of Cortical Cells. — Attempts have been made by
various histologists to estimate the total number of functional nerve-
cells in the cerebral cortex of man. Though the estimates are widely
different, the lowest presents numbers which are beyond compre-

FiG. 222. — Section of the Cere-
bral Cortex (Motor Area)
OF Child, Stained by
GoLGi's Silver Method.

A. Layer of neuroglia cells.

B. Layer of small pyramidal
ganglion cells. C. Layer of
large pyramidal cells. D.
Layer of irregular smaller
cells. — {Piersol.)

CEREBRUM. 493

hension. Thus, Meynert's estimate is 612 millions; Donaldson's
1200 millions; while Thompson's is 9200 millions.

Structure of the White Matter. — The white matter of the
cerebrum consists of mcdullated nerve-fibers which, though in-
tricately arranged, may be divided into three systems: viz., the
commissural, the association, and the projection.

1. The commissural system. The fibers w'hich compose this system

unite corresponding areas of the cortex of each hemisphere.
The fibers from the frontal, parietal, and occipital lobes cross
in the median line and form a band of transversely arranged
fibers, the corpus callosum. The fibers which unite the corre-
sponding areas of the temporo-sphenoid lobes cross in the
anterior commissure. All the commissural fibers are the axons
of nerve-cells in the cortex, the terminals of which are to be found
in the cortex of the opposite side.

2. The association system. The fibers which compose this system

unite neighboring as well as distant parts of the same hemi-
sphere, and may therefore be divided into long and short fibers.
They associate the inexcitable or association areas with the
excitable or projection areas.

3. The projection system. The fibers composing this system unite

certain areas of the cortex of the cerebrum with the basal
ganglia, the pons, medulla oblongata, and spinal cord. They
may be divided into: (i) afferent fibers which have their origin
in the lower nerve-centers at different levels and thence pass to
the cortex; and (2) efferent fibers which have their origin in the
cortex and thence pass to the lower nerve-centers, terminating
at different levels. The former are also termed the cortico-
afjerent or cortico- petal ; the latter, cortico-ejjerent or cortico-fugal.
The afferent fibers, the so-called sensor tract, which transmit
nerve impulses coming from the general periphery and the sense-
organs, pass through the tegmentum as the mesial and lateral fillets,
and thence to the cortex directly by way of the internal capsule, or
indirectly through the intermediation of the thalamic and subthalamic
nuclei. The distribution of these fibers to the various areas of the
cortex will be found in following paragraphs.

The efferent fibers of the so-called motor tract which transmit
motor or volitional nerve impulses from the cortex to the pons,
medulla, and spinal cord, emerge from the layer of pyramidal cells
of the gray matter of the anterior or the pre-central convolution,
the paracentral lobule and immediately adjacent areas. From this
origin the axons descend through the white matter of the corona
radiata, converging toward the internal capsule, into and through
which they pass, occupying the anterior two-thirds of the posterior
limb or segment. Beyond the capsule they continue to descend.

494 TEXT-BOOK OF PHYSIOLOGY.

occupying the middle three-fifths of the pes or crusta of the crus
cerebri, the ventral portion of the pons, and eventually the anterior
pyramid of the medulla oblongata. At this point the tract divides
into two portions, viz. :

1. A large portion, containing from ninety-one to ninety-seven per

cent, of the fibers, which decussates at the lower border of the
medulla and passes down the lateral column of the cord, con-
stituting the crossed pyramidal trad.

2. A small portion, containing from three to nine per cent, of the

fibers, which does not decussate at the medulla, but passes
down the inner side of the anterior column of the same side,
constituting the direct pyramidal tract or column of Tiirck.
After passing through the internal capsule, and as it descends
through the crus, pons, and medulla, the cortico-efferent tract gives
off a number of fibers which cross the median line and arborize around
the nerve-cells in the gray matter beneath the aqueduct of Sylvius
(the nuclei of origin of the third and fourth cranial nerves), and
around the nerve-cells in the gray matter beneath the floor of the
fourth ventricle (the nuclei of origin of the remainder of the motor
cranial nerves). The remaining fibers go to form the crossed and
direct pyramidal tracts and arborize around the cells in the anterior
horn of the gray matter of the opposite side of the cord at successive
levels. By this means the cortex is brought into anatomic and phys-
iologic relation with the general musculature of the body through the
various cranial and spinal motor nerves. (See Fig. 209, page 463.)
The fronto-cerebellar and the occipito-temporo-cerehellar tracts
are also efferent tracts and parts of the projection system. The
fronto-cerebellar, originating in the nerve-cells of the cortex of the
frontal lobe, passes down to and through the internal capsule, occupy-
ing the anterior one-third of the anterior segment. It then descends
along the inner side of the crus cerebri to the pons, where its fibers
arborize around the cells of the nucleus pontis. Through the inter-
mediation of these cells this tract is brought into relation with the
cerebellum of the same but chiefly of the opposite side. The occipito-
temporal tract, originating in the cells of the cortex of both the
occipital and temporal lobes, passes downward and inward toward
the lenticular nucleus, beneath which it passes to enter the outer
one-fifth of the crusta. It then enters the pons, and through the
nucleus pontis also comes into relation with the cerebellum of both
sides.

THE FUNCTIONS OF THE CEREBRUM.

The functions of the cerebrum comprehend, in man at least,
all that pertains to sensation, cognition, feehng, and volition. All
subjective experiences, which in their totality constitute mind, are

CEREBRUM. 495

dependent on and associated with the anatomic integrity and the
physiologic activity of the cerebrum and its related sense-organs, the
eye, ear, nose, tongue, etc.

From an examination of the anatomic development of the brain
in ditTerent classes of animals, in different men and races of men,
and from a study of the pathologic lesions and the results of ex-
perimental lesions of the brain, evidence has been obtained which
reveals in a striking manner the intimate connection of the cerebrum
and all phases of mental activity.

1. Com parative anatomic investigations show that there is a general

connection between the size of the brain, its texture, the depth
and number of convolutions, and the exhibition of mental power.
Throughout the entire animal series an increase in intelligence
goes hand in hand with an increase in the development of the
brain. In man there is an enormous increase in size over that
of the highest animals, the anthropoid apes. The most culti-
vated races of men have the greatest cranial capacity, that of the
educated European or American being approximately 92.1 cubic
inches (1835 c.c); while that of the Australian is but 81.7 cubic
inches (1628 c.c). Men distinguished for great mental power
usually have large and well developed brains; e.g., that of
Cuvier weighed 64.4 ounces (1830 grams); that of Abercrombie,
63 ounces (1786 grams). A large intelhgence, however, is not
incompatible with a much smaller brain weight; thus, the
brain of Helmholtz weighed but 50.8 ounces (1440 grams);
that of Leidy, 49.9 ounces (1415 grams); that of Liebig, 47.7
ounces (1352 grams). The average arithmetic brain weight of
96 distinguished men was found to be 51.9 ounces (1473
grams) (Spitzka).

2. Pathologic lesions and mechanic injuries which disorganize the

cerebrum are at once followed by a disturbance or an entire
suspension of mental activity. Concussion of the brain or
sudden compression from a hemorrhage destroys consciousness.
Physical and chemic alterations of the gray matter of the cere-
brum have been shown to coexist with insanity, loss of memory,
of articulate speech, etc. Congenital defects of organization are
accompanied by a deficiency in mental capacity and the higher
instincts. Under such circumstances no great advance in brain
development is possible and the intelhgence remains at a low
level. In congenital idiocy the brain is small, imperfectly
developed, and wanting in proper chemic composition.

3. Experimental lesions of the brain in lower animals are attended

by results similar to those observed in disease or after injury
in man. Removal of the cerebrum in the pigeon completely
abolishes intelligence and destroys the capabiHty of performing

496 TEXT-BOOK OF PHYSIOLOGY.

volitional movements. The pigeon remains in a state of
profound stupor, though retaining the capability of executing
reflex or instinctive movements. It can temporarily be aroused
by loud noises, light placed before the eyes, pinching of the
toes, etc., but it soon relapses into a condition of quietude.
Coincident with the destruction of the cerebrum there occurs
a loss of memory, reason, and judgment, and the animal fails
to associate the impressions with any previous train of ideas.
The higher the animal in the scale of development, the more
striking is the loss of mentality after removal of the cerebrum.
4. Experimental interference with the blood-supply to the cerebrum
is followed by a diminished or complete cessation of its activities.
There is perhaps no organ of the body that is so directly depend-
ent upon its blood-supply for the continuance of its activities
as the cerebrum. The supply of blood is furnished by four large
blood-vessels : viz., the two carotid and the two vertebral arteries.
These vessels, after entering the cavity of the skull, give off
branches which unite to form the "circle of Wilhs." From this
circle, large branches are given off which enter the cerebrum
and distribute blood to all its parts. After passing through the
capillaries the blood, greatly altered in chemic composition, is
returned by large veins. The large volume of blood that is
present in the brain and the marked changes in composition
that it undergoes while passing through the brain indicate a
very active and complex metabolism in this organ. By means
of the anatomic arrangement of the blood-vessels at the base
of the brain, the blood-supply is equalized. It also explains
why, when one, or even two, of the four large vessels are oc-
cluded by pathologic deposits or surgical procedures, brain
activity continues, though perhaps diminished in degree. Occlu-
sion of all four vessels, however, is at once followed by a complete
abolition of all forms of cerebral activity. An experiment per-
formed by Brown-Sequard illustrates the dependence of cerebral
activity on the blood-supply. A dog was beheaded at the
junction of the neck and chest. After a period of ten minutes
all evidences of life had entirely ceased. Four tubes connected
with a reservoir of warm defibrinated blood were then connected
with the four arteries of the head. By means of a pumping
apparatus imitating the action of the heart the blood was driven
into and through the brain. After a few minutes cerebral
activity returned, as shown by contraction of the muscles of
the face and eyes. The character of the contractions were such
as to convey the idea that they were directed by the will. These
vital manifestations continued for a period of fifteen minutes,
when on the cessation of the artificial circulation they disap-

THE CEREBRUM. 497

peared, and the head exhibited once again the usual phenomena
observed in dying: viz., contraction and then dilatation of the
pupils and convulsive movements of the muscles of the face.
Localization of Functions in the Cerebrum. — By the term

localization of functions is meant the assignment of dciinite phys-
iologic functions to deiinite anatomic areas of the cerebral cortex.
From experiments made on the brains of animals, by the observa-
tion and association of chnical symptoms with pathologic lesions of
the central nerve system, and from observation of the developmental
stages of the embryonic brain, it has been established in recent years:

1. That the general and special sense-organs of the body are as-

sociated through afferent nerve-tracts with definite though per-
haps not sharply dehmited areas of the cerebral cortex; and —

2. That certain areas of the cortex are associated through efferent

nerve-tracts with special groups of skeletal or voluntary muscles.

Experimental excitation of a cortical area associated with a sense-
organ is undoubtedly attended by the production of a sensation at
least similar to that produced by peripheral excitation of the sense-
organ itself; destruction of the area is followed by an abolition of all
the sensations associated with the sense-organ. For these reasons
such areas are termed sensor.

Excitation of a cortical area associated with a group of skeletal
muscles is attended by their contraction; destruction of the area is
followed by their relaxation or paralysis. For these reasons such areas
are termed motor.

Since the sense-organs are remote from the brain and the impres-
sions made upon them by the objective world can be utiHzed by the
mind, only after they have been reproduced in the cortical areas, it
may be said that each sense-organ has its special area in the cortex
by which it is represented, or, in other w^ords, each sense-organ has
a cortical area of representation.

Since the muscles are remote from the brain and since they
contract in response to the discharge of nerve impulses from the
cells of the cortical motor areas, it may be said that the activities
of the motor areas are represented by the contractions of the muscles ;
in other words, that the cortical motor areas have areas of representa-
tion in the general skeletal musculature. It is usually stated, how-
ever, in the reverse way: viz., that the muscle movements have areas
of representation in the cortex.

The cortex of the cerebrum may therefore be compared to a
mosaic made up, partially at least, of sensor and motor areas which
respectively represent sense-organs and motor organs, and which
bear a definite anatomic and physiologic relation one to the other.
Their cooperation is essential to the normal performance of all forms
of cerebral activity.
32

498 TEXT-BOOK OF PHYSIOLOGY.

A knowledge of the situation of these areas, the order of their
development, the effects that arise from their stimulation or follow
their destruction, are matters of the highest importance in the study
of cerebral activity and indispensable to the physician in the localiza-
tion of lesions which manifest themselves in perversions or abolition
of sensations and in convulsive seizures or paralyses.

The Sensor Areas. — The sensor areas which should theoret-
ically be present in the cortex are primarily those which receive
and translate into conscious sensations nerve impulses, developed by
changes going on in the body itself; and secondarily those which
receive and translate into conscious sensations the nerve impulses
developed in the special sense-organs by the impact of the external
or objective world. In the former areas, are received the nerve im-
pulses that come from the skin, mucous membranes, muscles, viscera,
etc., and give rise to cutaneous, muscle, and visceral sensations. In
the latter are received the nerve impulses that come from the sense-
organs and give rise to tactile, gustatory, olfactory, auditory, and
visual sensations. A number of such sense areas may be predicated :
e. g., areas of cutaneous and muscle sensibility, of gustatory, olfactory,
auditory, and visual sensibility.

The Motor Areas. — The motor areas which should theoretically
be present in the cortex are those which in consequence of the dis-
charge of nerve impulses excite contraction of special groups of
muscles and which, from their coordinate and purposive character,
are conventionally termed volitional. Five such general motor areas
may be predicated: e. g., one for the muscles of the head and eyes,
one for the muscles of the face and associated organs, and areas for
the muscles of the arm, leg, and trunk. They are usually designated
as head and eye, face, arm, leg, and trunk motor areas.

The existence and anatomic location of these areas in the cortex
of animals have been determined by the employment of two methods
of experimentation: viz., stimulation and destruction or extirpation;
the first by means of the rapidly repeated induced electric currents,
the second by the electric cautery and the knife. If the stimulation
or excitation of any given area is followed by contraction and its
destruction by paralysis of muscles, it is assumed that the area is
motor in function — is a center of motion. If the stimulation of a
given area is attended by phenomena which indicate that the
animal is experiencing sensation, and its destruction by a loss of
this capabihty or the loss of a special sense, it is assumed that the
area is sensor in function — is an area of special sense. The animals
generally employed for experiments of this character are dogs and
monkeys, though other animals have frequently been employed by
different investigators. Of all animals, the monkey is the most fre-
quently selected, as the configuration of the brain in its general out-

THE CEREBRUM.

499

lines more closely resembles that of man than does the brain of any
other animal. The results therefore which are obtained, there is
every reason to believe, are the results, in their general outlines, that
would follow stimulation of the human brain if this were possible
under the same condi-
tions. Indeed, the clinical
symptoms which arise
during the development
of pathologic processes,
and the phenomena
which occur during sur-
gical procedures for the
removal of growths and
pathologic cortical areas,
justify the conclusion
that the chart of the
motor and sensor areas
of the monkey brain may
be transferred to the
human brain without
introducing any serious
errors.

The Motor Areas of
the Monkey Brain. —
From experiments made
on the brains of monkeys
Ferrier mapped out a
number of areas stimu-
lation of which gives
rise to muscle contrac-
tions on the opposite
side of the body which
are so purposive and co-
ordinate in character that
they may be regarded
as identical with those
produced volitionally.
Destruction of these
areas is followed by
paralysis. The results of Ferrier's earlier work are represented in
Fig. 223, the descriptive text to which renders them intelhgible. In
a general way it may be said that the upper third of the anterior and
posterior central convolutions presides over the movements of the leg
of the opposite side of the body; the middle third over the move-
ments of the arm; the inferior third over the movements of the

Fig. 223. — Left Hemisphere of Monkey, Show-
ing Details of Motor Areas Indicated by
THE Movements Following Stimulation
of: I. Superior parietal lobule; exciting ad-
vance of the hind limb. 2. Top of ascending
frontal and parietal convolutions; flexion and
outward rotation of thigh; flexion of toes. 3.
On ascending frontal convolution near semilu-
nar sulcus; movements of hind limb, tail and
extremity of trunk. 4. On adjacent margins of
ascending frontal and parietal convolution;
adduction and extension of arm, pronation of
hand. 5. Top of ascending frontal near supe-
rior frontal convolution; forward extension of
arm. a, b, c, d. On ascending parietal; move-
ments of various muscles of the forearm. 6.
Ascending frontal convolution; flexion of
forearm and supination of hand which is
brought toward mouth. 7. Retraction and
elevation of corner of mouth. 8. Elevation of
nose and lip. 9 and 10. Opening mouth and
motions of tongue. 11. Retraction of angle
of mouth. 12. ^Middle and superior frontal
convolutions; movements of head and eyehds.
13 and 13'. Anterior and posterior limbs of
angular gyrus; movements of eyeballs. 14.
Superior temporo-sphenoidal convolution, ear

pricked and head moved,
lip and nostril. — {Ferrier.)

Movement of

500

TEXT-BOOK OF PHYSIOLOGY.

face and tongue. Collectively these areas are known as the motor
area or motor zone; and as it is ranged along the Rolandic fissure, it
is sometimes termed the Rolandic area.

The experiments of Horsley and Schafer added additional facts
and enabled them to construct a new diagrammatic representation of
the motor area and more accurately define the special areas upon
the lateral and mesial aspects of the brain of the monkey. The
boundaries of the general and special areas, as determined by these
observers, will be readily apparent from an examination of Fig. 224.
Their experiments have enabled them also to subdivide the general
into special areas as follows :

Fig. 224. — Diagram of the Motor and Sensor Areas on the Lateral Sur-
face OF the Monkey Brain. — {After Horsley and Schafer.)

I.

2.

The head area or area for visual direction into areas excitation of
which causes "opening of the eyes, dilatation of the pupils and
turning the head to the opposite side with conjugate deviation
of the eyes to that side."

The leg area may be subdivided into {a) an area both on the
lateral and mesial surfaces which presides over the movements of
the hip and thigh ; {h) an area in the posterior part which presides
over the movements of the legs and toes; (c) an area in the
paracentral lobule for the movements of the hallux or great toe.

The trunk area, situated largely on the mesial surface, may be
subdivided into an anterior and a posterior area, which respec-
tively preside over the movements of the spinal column as arch-
ing and rotation, and the movements of the pelvis and tail.

THE CEREBRUM.

SOI

The arm area may be subdivided as follows: (a) an area supe-
riorly which controls the movements of the shoulder; (b) an area
posteriorly and below this, which controls the movements of the
elbow; (c) an area anteriorly and below the preceding, govern-
ing the movements of the WTist and fingers ; (d) an area- pos-
teriorly and below governing the movements of the thumb.

The face area may be divided into an upper part, comprising
about one-third, and a lower part, comprising the remaining
two-thirds. In the upper part are areas governing the move-
ments of the opposite angle of the mouth and of the lower face.
In the lower part anteriorly there is an area governing the move-

FlG.

25. — Diagram of the Motor and Sensor Areas ox the Mesial Sur-
face OF the Monkey Braxn. — {After Horsley and Schdjer.)

ments of the vocal membranes or bands (the laryngeal area);
posteriorly areas governing the opening and closing of the
mouth, the protrusion and retraction of the tongue.
The Sensor Areas of the Monkey Brain.— From experiments
made on the brains of monkeys, Ferrier, Schafer, Horsley, and many
others have mapped out, though not with the same degree of definite-
ness and certainty, the sensor areas, stimulation of which gives rise to
sensation, destruction to loss of sensation. A diagrammatic repre-
sentation of these areas is shown in Fig. 224 and Fig. 225.

The tactile area or area of tactile perception has not been accu-
rately or definitely located. Ferrier assigned it to the hippocampal
region. Schafer and Horsley assigned it to the hmbic lobe, and
especially to that portion known as the gyrus fornicatus, as destruction

502 TEXT-BOOK OF PHYSIOLOGY.

of this convolution was followed by hemianesthesia of the opposite
side of the body which was more or less marked and persistent.
These observers conclude that the hmbic lobe "is largely if not
exclusively concerned in the appreciation of sensation, painful and
tactile." Other experimenters question this conclusion and locate
the area near to, if not within, the Rolandic area. The difference of
opinion regarding the location and probable limitation of the area
of tactile sensibility renders necessary additional and more conclusive
experiments.

The olfactory and gustatory areas or areas of olfactory and gusta-
tory perception have been located in the uncinate gyrus and the
adjacent region, though their exact limits have not been determined
?jy the experiments thus far performed.

The auditory area or area of auditory perception was located by
Ferrier in the upper two-thirds of the superior temporo-sphenoidal
convolution. Bilateral cauterization of this region gave rise to com-
plete deafness, which endured to the time of the animal's death,
more than a year later. Unilateral destruction of this region gave
rise to deafness in the opposite ear only. The results of experiments
made subsequently by other observers would indicate that the audi-
tory area is somewhat more extended than that designated by Ferrier,
as apparently animals recovered their hearing, to some extent at
least, after complete recovery from the operation. The limit or
extension of the area is, however, uncertain.

The visual area or area of visual perception has been located in
the occipital lobe, though in this, as in the previous instances, its
exact limits have not been positively determined. Experimenters
also are not in accord as to the relative functions of its different parts.
Ferrier located this area in the occipital lobe and that adjacent por-
tion of the parietal lobe on the outer surface known as the angular
gyrus. He found that extirpation of the angular gyrus alone was
followed by a temporary blindness of the opposite eye, which was,
however, not hemiopic in character.* He also found that destruction

* In a consideration of this subject certain facts connected with visual perception,
both in physiologic and pathologic conditions, must be kept in mind. Thus,
visual sensation may arise from stimulation of either the central portion, the macula,
or the peripheral portion of the retina or both. In the first instance the vision is
termed central or macular; in the second instance, peripheral or retinal. Macular
vision is clear, sharp, and distinct; retinal vision progressively indistinct from the
center toward the peripher}'. Division of one optic tract is followed, in consequence
of the partial decussation of the optic ner\'e-fibers at the chiasma, by a loss of function
in the outer two-thirds of the retina of the same side, both in the central (macular)
as well as in its peripheral portions, and the inner one-third of the retina of the oppo-
site side. To this condition the term hemiopia has been appHed. As a result of this
want of functional activity of these retinal portions on the side of the lesion, rays
of light emanating from objects situated in the opposite side of the field of vision will
not be perceived when both eyes are directed to the fixation point. To this "blind-

THE CEREBRUM. 503

of the occipital lobe together with the angular gyrus gave rise to a
more or less enduring hemianopsia, in addition to the transient
blindness of the opi)osite eye. From these and similar facts he con-
cluded that the angular gyrus is the area of representation for the
macular or central region of the retina, and the occipital lobe for
the corresponding halves of the peripheral portions of the retina.

It was, however, found by Munk, Schafer, and others that the
angular gyrus was not concerned in any way with vision; that extir-
pation of the occipital lobe alone, especially if the hne of division
be carried a little further forward on the mesial and inferior sur-
faces, was followed by homonymous hemiopia (loss of retinal func-
tion on the same side), and therefore homonymous hemianopsia.
Additional experiments lead to the conclusion that the area for
macular vision is near the anterior extremity of the calcarine fissure,
while the area for peripheral vision is in the posterior portion of the
mesial surface and for a variable distance on the outer surface.
Moreover, there is reason to believe that the area for macular vision
is in relation with homonymous halves of the two maculae luteae.
The supposed error, the assignment of macular vision to the angular
gyrus, has been attributed to destruction of the fibers of the optic
radiation, which in their course to the occipital lobe pass close to
this gyrus.

Electric stimulation of the sensor areas is attended by certain
motor reactions which vary in accordance wnth the area stimulated.
Thus, when the electrodes are applied to different portions of the
occipital lobe the eyeballs are conjugately turned upw^ard, downward,
or laterally and to the opposite side ; when placed on the upper por-
tion of the superior temporal convolution, the ear is pricked up or
retracted, the head is turned to the opposite side and the pupils
are dilated; when placed on the hippocampal convolution, there is
movement of torsion of the nostril and lips of the same side.

Ferrier assumed that these movements were the result of the
origination of subjective sensations and not an evidence that the
area in question is a motor area, in the sense that this term is apphed
to the areas of the Rolandic region, especially as their destruction
is not followed by paralysis of any of the corresponding muscles.
This interpretation is supported by the experiments of Schafer,
which showed that the contraction of the eye-muscles which followed
stimulation of the occipital lobe took place between 0.2 and 0.3

ness" in the opposite half of the field of vision the name hemianopsia is given. In
the lesion under consideration (division of one optic tract) the hemianopsia is bilateral,
and as it affects the corresponding portions associated in normal vision it is of the
homonymous variety. Division of the right optic tract is followed by left lateral homon-
ymous hemianopsia, indicative of the fact that objects in the field of vision to the
left of the binocular fixation point are invisible.

504 TEXT-BOOK OF PHYSIOLOGY.

second later than when the frontal lobe was stimulated ; and that as
the motor reaction takes place after extirpation of the frontal region,
the route of the efferent impulse cannot be to and through the
frontal lobe, but probably through some lower center. The same
facts hold true for the reactions of the ear-muscles following stimu-
lation of the temporal lobe.

The view that the cortex of the cerebrum can be divided into
separate and independent though physiologically related motor and
sensor areas has been questioned in recent years, and a somewhat
different interpretation given to the facts. It is believed by many
physiologists and neurologists that the so-called motor and sensor
areas are so closely related that it is almost impossible to distinguish
one from the other either anatomically or physiologically. Thus the
Rolandic region is believed to be both motor and sensor in function,
the former, however, being more predominant in the pre-central,
the latter in the post-central, convolution. As these two functions
are so intimately blended and their anatomic substrata so difficult
of separation, it is thought the term sensori-motor should be em-
ployed as more descriptive and more in accordance with the facts
to the entire Rolandic region.

This view has been strengthened by the results of the embryo-
logic investigations of Flechsig, which show that different nerve-tracts
become medullated or receive their myelin investment at successively
later periods and that the tracts which first become myelinated and
are hence first functionally active, belong to the afferent system.
Among the first to undergo myelinization are three tracts numbered
by Flechsig i, 2, and 3, which arise largely from the median nucleus
of the thalamus and the medial lemniscus and pass to the anterior
and posterior convolutions, to the para-central lobule and foot of
the superior frontal convolution, and to the foot of the third frontal
convolution respectively. It is these fibers which convey nerve im-
pulses to the cortex and furnish information regarding changes taking
place in the body itself and thus lead to the performance of muscle
movements. This area is therefore primarily a sensor area, an area
for body-feelings, cutaneous, tactile, muscle, and visceral, and second-
arily a motor area. The afferent fibers to this region become mye-
hnated during the ninth month of intra-uterine life, the efferent fibers
from it become myelinated during the third month of extra-uterine
hfe.

By the same method of reasoning the gustatory, olfactory, audi-
tory, and visual sense areas are to be regarded as sensori-motor in
character, for embryologic investigations show that subsequently
to the myelinization of the afferent tracts' connecting the sense-organs
with the cortex, efferent nerve-tracts arise from or near to the
same centers and undergo myelinization. In other words, these

THE CEREBRUM. 505

areas are primarily sensor and secondarily motor, and therefore
should be termed scnsori-motor. In Flechsig's own terminology
each cortico-petal or afferent tract is accompanied by a cortico-fugal
or efferent tract.

In this view sensations, or the mental processes the outcome of
sensations, are the immediate cause of the movements of the mus-
cles connected with both the sense-organs and skeletal structures.
Though this interpretation — viz., the coincidence of sensor and
motor areas — appears more in accordance with the facts than the
earher view, it must be admitted that there are many facts both of
a physiologic and pathologic character which it is difficult to har-
monize with it.

The Motor Area of the Chimpanzee Brain. — In a series of
experiments made by Sherrington and Griinbaum on the brain of the
chimpanzee it was discovered that the so-called motor area was not
so widely distributed as in the monkeys generally, but was confined
almost exclusively to the convolution just in front of the lissure of
Rolando, as it was impossible to obtain any movement on direct
stimulation of the convolution just behind it. All points on the
surface of the pre-central convolution, including the portion forming
the wall of the Rolandic fissure itself, were found to be excitable
and productive of movement when stimulated. The sequence of
representation from below upward is similar to that observed in the
monkey. One peculiarity, however, was the location of the area
for conjugate deviation of the eyeballs to the opposite side. This
is situated far forward in the middle and inferior frontal convolutions,
and separated from the areas in the pre-central convolution by a
region apparently inexcitable. These facts are of great interest and
value in the assignment of the motor areas in the cortex of the human
brain, as in its development and configuration the chimpanzee brain
more closely resembles the human brain than does the monkey's.

The Localization of Motor and Sensor Areas in the Human
Brain. — The observation of clinical symptoms and their interpreta-
tion by postmortem findings, the phenomena observed during surgical
procedures, and the results of embryologic investigations, point to the
conclusion that corresponding areas both for movements and sensa-
tions exist in the cerebral cortex of the human brain, though it is
probable that their locations do not in all respects coincide with
those characteristic of the monkey or even the ape brain. In the fol-
lowing diagrams (Figs. 226 and 227), the motor and sensor areas
are at least provisionally located, in accordance with recent obser-
vations. They are represented as limited or bounded by a serrated
fine to indicate, as suggested by jNIills, that they are not sharply
defined, but that they interfuse or interdigitate with surrounding
resfions.

5o6

TEXT-BOOK OF PHYSIOLOGY.

The Motor Area. — The general motor area is represented as
occupying the pre-central convolution, the base of the first convolu-
tion, both on its lateral and mesial aspects, and the paracentral lobule.
The exclusion of the post-central convolution from the motor area
is in accordance with the embryologic researches of Flechsig, which
indicate that the efferent fibers which compose the pyramidal tract
come from the region anterior to the central fissure, and with the
experiments of Sherrington and Griinbaum on the brain of the chim-
panzee, which demonstrate that the post-central convolution is
absolutely inexcitable to electric stimulation. It is quite probable
that with the growth of the brain in size and complexity, the motor

CONCRLTE CONCEPT

Fig. 226. — The Areas and Centers of the Lateral Aspect of the
Human Hemi-cerebrum. — (C. K. Mills.)

area has come to occupy a position somewhat farther forward in the
human brain than in the monkey brain.

This general area is also capable of subdivision into areas of
variable size, in which the movements of the face and associated
structures, the head and eyes, the arm, trunk, and leg, are represented.
The sequence of their representation from below upward is similar
to that observed in the monkey and chimpanzee. A localized irritative
lesion of any one of these areas gives rise to convulsive movements of
the muscles of the opposite side of the body, similar in character to
those resulting from electric stimulation of the corresponding areas of
the monkey and ape brains. Destruction of these areas from the

THE CEREBRUM.

507

growth of tumors, softening, etc., is followed by paralysis of the
muscles. Electric stimulation of the human brain for the purpose of
localizing obscure irritative lesions prior to surgical procedures on
the brain gives rise to the same convulsive movements.

The Sensor Areas. — The sensor areas occupy regions corre-
sponding in a general way with those of the monkey brain.

The cutaneous and muscle sense areas have been assigned to the
post-central, a portion of the superior and inferior parietal convolu-
tions on the lateral aspect, and to portions of the frontal convolution
and of the gyrus fornicatus on the mesial aspect. It is also probable
that the tactile (cutaneous) area may be assigned, though in less

Fig. 227. — The Areas and Centers of the Mesial Aspect of the
Human Hemi-cerebrum. — (C. K. Mills.)

degree, to the pre-central convolution, the general motor area. This
is in accordance with the embryologic investigations of Flechsig, who
concludes that the entire Rolandic region is to be regarded as sensor
as well as motor in function, and names it the area of body feelings,
or the somesthetic area.

The chnical and postmortem evidence as to the extent of the
area of tactile sensibility and its coincidence with the motor area is
somewhat contradictor^', and in some respects apparently in opposi-
tion to the view of Flechsig. Thus, Dr. C. K. Mills, whose skill in
interpreting the phenomena of disease is well known, states in this con-
nection in his work on nervous diseases that " innumerable cases have
been reported of lesions of the motor cortex without the slightest

So8 TEXT-BOOK OF PHYSIOLOGY.

impairment of sensibility." In several cases of excision of the human
cortex in the Rolandic region by surgical operations careful studies
of the patients failed to show any impairment of sensation. Other
competent observers, however, have reported a number of cases in
which anesthesia more or less pronounced and persistent has accom-
panied lesions of the motor area. The explanation of these contra-
dictory observations is not apparent.

The olfactory area has been assigned to the uncinate convolution,
the anterior part of the gyrus fornicatus, and the posterior part of the
base of the frontal lobe. Lesions in this region are frequently
accompanied by subjective olfactory sensations.

The gustatory area has been assigned to the fourth temporal
convolution.

The auditory area has been assigned to the posterior portion of
the superior temporal convolution and to the retro-insular convolu-
tions, the island of Reil. Unilateral destruction of this region is
followed by only a partial loss of hearing in the opposite ear (owing
to the partial decussation of the cochlear nerve), which, however,
may be recovered from after a time, owing probably to a compensatory
activity of the insular convolutions. Bilateral disease of this region
is followed by complete deafness. Within this area there is a smaller
region, disease of which is accompanied by word-deafness only, the
patient being unable to distinguish the tone intervals between words
and syllables and therefore hearing only confused noises. Object
hearing was also a separate area of representation.

The visual area has been assigned to a triangular shaped area on
the mesial surface of the occipital lobe, which includes the gray matter
above and below the calcarine fissure (the cuneus and upper part of
the lingual lobe), and to the gray matter of the first occipital convo-
lution on the lateral aspect of the occipital lobe. Focal lesions of this
area on one side are followed by lateral homonymous hemianopsia,
which, however, does not involve, as a rule, the fovea or macula.
It is, therefore, the area of homonymous half-retinal representation.
The location of the area for macular or central vision is uncertain.
Henschen locates it in the anterior part of the area near the ex-
tremity of the calcarine fissure, and asserts that in each area both
maculae are represented. From experiments made on monkeys
Schafer locates it in the same region. Beyond the limits of this
visual area and on the lateral aspect of the parietal lobe there is a
region (the supra-marginal convolution and angular gyrus) in which
impressions of words and letters seen have their representation.
Destruction of this area by diseases is followed by word- and per-
haps letter-blindness, the patient being unable to recognize words
and letters seen because of failure to revive the memory images of
words and letters. The areas for visual sensations and optic memory

THE CEREBRUM. 509

pictures are therefore separate, a fact which has led to a division of
the visual area into a lower and a higher area.

It was stated in a previous paragraph that electric stimulation of
the sensor areas of the monkey brain is attended by certain motor
reactions which vary with the area stimulated. Corresponding areas
are believed to be present in the human brain and that their stimula-
tion would be followed by similar motor reactions. Their location is
shown in Figs. 226 and 227, and named visual, auditory, olfactory,
and gustatory motor.

The stereognostic area or area 0} slereognostic perception, by which
objects are recognized through their form independent of vision and
by the sense of touch alone, has been located in the superior parietal
convolution and the precuneus (Mills). The existence of such an
area is rendered probable by the fact that cases have been recorded
in which there was a loss of this power (astereognosis) unaccompanied
by either sensor or motor disturbances. Postmortem investigations
showed that in these cases there was a destruction of the superior
parietal convolution.

Equilibratory, intonation, and orientation areas have been pre-
viously located in the sphenotemporal lobe.

Language. — The succession of motor acts by which ideas are
expressed, is known as language, which may be divided into (i)
articulate or spoken, and (2) written.

The expression of ideas both by words and signs depends primarily
on the power of reviving the images or memories of words and letters
heard and seen; and secondarily on the power of reviving the images
or memories of the muscle movements which were previously em-
ployed in an effort to imitate or reproduce the words (speech) or
the verbal signs (writing).

Chnico-pathologic investigations have shown that words and
letters heard and seen have areas of representation in the cortex, the
former in the general auditory area, the latter in the supra-marginal
convolution and angular gyrus (Fig. 226). Destruction of these
areas is followed by word-deafness and word-blindness respectively.
The same methods of investigation have shown that the muscle
movements employed to reproduce the words and the verbal signs
also have areas of representation in the cortex; the former in the
third frontal convolution (Fig. 227), and probably in the adjacent
region, the island of Reil, on the left side in the great majority of
people ; the latter in front of the arm region of the general motor area.
Destruction of these areas is followed in the first instance by a loss
of the power of executing the movements of the muscles employed
in speech, and in the second instance, of those employed in writing.

These different areas are connected with one another by associa-
tion fibers, and, taken collectively, constitute the language zone.
Their situation and relations are shown in Fig. 228. In this figure

5IO

TEXT-BOOK OF PHYSIOLOGY.

the dotted lines coming from the ear (a) and the eye (v) represent
the auditory and visual tracts through which nerve impulses pass
to the auditory (A) and the visual centers (V) respectively. Similar
Hnes coming from the muscles involved in speech and writing might

also be represented to indicate
the paths of the nerve impulses
to the motor speech (M) and
the motor writing center (E).
The continuous lines on the
surface of the cortex represent
nerve-fibers which associate
the auditory and visual centers
with the speech and writing
centers and with higher
psychic centers (0 0) as well.
The dotted Hnes coming from
the speech and writing centers
represent the tracts through
which nerve impulses pass to
the muscle of the . larynx,
tongue, mouth, and Hps, and
to the muscles of the hand.
The anatomic and physiologic
association of the various areas
is essential to the registration
of the impressions made on
the ear and eye and for the
expression of the ideas evolved
from them by words (speech)
and signs (writing). Their
collective action is essential
to the acquisition of language.
Destruction of any part of
this cerebral mechanism is
attended by an impairment
or a total loss either in the
power of obtaining auditory
images of words heard and
visual images of words seen,
or in the power of expressing
ideas by speech and writing.
To this pathologic condition the term aphasia has been given.

Aphasia. — It was discovered by Bouillaud that a destructive
lesion of the third frontal convolution on the left side was accom-
panied by a partial or complete loss of the facuUy of articulate speech,

Fig. 228. — Diagram Showing the
Relation of the Centers of
Language and their Principal
Associations. A. Auditory center.
V. Visual center. M. Motor speech
center. E. Motor writing center.
O O. Intellectual center. — (After
Grasset.)

THE CEREBRUM. 511

the power to express ideas with words. To this condition the term
aphasia was given. Though of hmited application etymologically,
the word is now employed in a wider sense to signify "jjartial or com-
plete loss of the power of expression or comprehension of the con-
ventional signs of language, " words either spoken or written, due to
lesions of different portions of the cortex, and especially on the left
side.

Aphasias arc of many degrees and kinds, though they may be in-
cluded in the two general divisions, motor and sensor.

Motor aphasia may be either ataxic or agraphic. In ataxic
aphasia the patient is unable to express or communicate his thoughts
by spoken words, owing to an inability to execute those movements
of the mouth, tongue, etc., necessary for speech without there being
any paralysis of these muscles. The lesion is usually in the third
frontal convolution and most frequently associated with right
hemiplegia. In agraphic aphasia the patient is unable to com-
municate his ideas by writing through an inability to execute the
necessary movements, though retaining his mental processes. In
this form of aphasia the lesion is in the writing area. These two forms
of motor aphasia are not infrequently associated.

Sensor aphasia or amnesia may be either visual or auditory. In
visual aphasia or amnesia the patient is unable to recognize a letter
or word, printed or written (though capable of seeing other objects),
a condition known as letter- or word-blindness. It is usually associated
with lesions in the neighborhood of the supra-marginal convolution.
In auditory aphasia or amnesia the patient cannot understand
articulate or vocal speech, though capable of hearing and understand-
ing other sounds, through an inabiHty to distinguish tone intervals
of words and letters — a condition known as word-deafness. It is
associated with lesions of the auditory area.

Paraphasia is an inability to recall the proper words to associate
with ideas and necessary to their expression.

Concept aphasia is the inability to recall the names of objects.
It is associated with lesions of the cortex of the mid-temporal or
third temporal convolution (Mills). This area is known as the
concept or naming area.

Bilateral Representation. — Though highly speciaHzed move-
ments, such as those performed by the arms and hands, legs and feet,
have their areas of representation on one side of the cerebrum only,
and that, opposite to the side of the movement, less highly specialized
movements, such as the masticatory, phonatory, respiratory, and
various trunkal movements, which require for their performance
the cooperation of muscles on both sides of the body, have their
areas of representation on both sides of the cerebrum; the area of
either side excitingr to action the muscles on both sides of the bodv.

512

TEXT-BOOK OF PHYSIOLOGY.

In the case of specialized movements the representation' is unilat-
eral; in the case of the more general movements the representation is
bilateral.

Motor and tactile area.

Parietal association area.

Visu: ]
area .

Occipito-temporal
association area.

Auditory area.
Motor and tactile area.

Parietal association area

(Precuneus)

Visual area
(cuneus).

^Hr^-

Occipito-temporal
association area.

Olfactory lobe.
Olfactory tract,

^ Olfactory area.

Gyrus hippocampus.

Fig. 229. — Diagrams to show the Position and the Relation of the
Association and Projection Areas. The Projection Areas are
Dotted. — {After FlecJisig.)

Association Centers.^ — The sensor and motor areas to which
specific functions have been assigned do not constitute more than
one-third of the total cerebral cortex. There yet remain large

THE CEREBRUM. 513

regions to which it has not been possible to assign specific functions
based on physiologic experiments. Three or four such regions
separated by the sensor and motor centers are to be recognized on
the lateral and mesial aspects of the hemisphere. In Fig. 229
the location, extent, and names of these regions are represented.
The fibers which are found in these regions belong almost exclusively
to the association system, and become meduUated at a later period
than do the fibers of the projection system; moreover, from the method
of their medulHzation it would appear that many of these fibers grow
out directly from the sensor centers into these regions and become
related to the nerve-cells of their convolutions, while others grow
out from adjacent as well as distant convolutions. From histologic
and pathologic evidence these regions were termed by Flechsig
association centers or areas, implying the idea that through the in-
tervention of their cell mechanisms the sense areas are indirectly
associated anatomically and physiologically, and together constitute
a mechanism by which sensations are associated and elaborated into
concrete forms of knowledge or related to definite forms of move-
ment.

It has been assumed by Flechsig that the frontal association center,
from its connections with the sensor and motor areas of the Rolandic
region, the oLfactor}', and perhaps other regions, is engaged in as-
sociating and registering body sensations and volitional acts, and
that the knowledge thus gained has reference largely to the personal-
ity of the individual; that the parieto-occipital association area, from
its relation to the visual, auditory, and tactile sense areas, is engaged
in associating and registering visual, auditory, and tactile sensations,
and that the knowledge thus gained has reference mainly to the
external world. These assumptions in a general way are supported
by the phenomena of disease. In certain lesions of the frontal lobe
the S}Tnptoms indicate a loss or change of ideas regarding personahty
rather than of the objective world, while the reverse is true in disease
of the parieto-occipital lobe.

ii

CHAPTER XX.
THE CEREBELLUM.

The cerebellum is situated in the inferior fossae of the occipital
bone, beneath the posterior lobes of the cerebrum, from which it
is separated by the tentorium cerebelli, a semilunar fold of the
dura mater. It is partially divided into hemispheres by a longi-
tudinal fissure, more apparent on the inferior surface, though united
by a central lobe, the vermiform process. Each hemisphere is con-
nected with the cerebrum, the pons, medulla and spinal cord by three
bundles of ner^^e-fibers known respectively as the superior, middle,
and inferior peduncles. The surface of the cerebellum presents a
series of lobes and fissures of which the former have received more
or less fanciful names. A section of the cerebellum shows that it is
composed of gray matter externally and white matter internally.
The general appearance presented on section is shown in Fig. 230.

Structure of the Gray Matter. — The gray matter consists
mainly of nerve-cells of varying size and shape, which are arranged in
two layers: viz., an outer or molecular and an inner or granular.

The molecular layer consists of stellate and multipolar cells of
small size, from which dendrites and axons pass horizontally and
vertically. The granular layer consists, as its name implies, of
granular shaped cells and large stellate cells. These cells are
characterized by the possession of dendrites and axons, the course
and relation of which have not been clearly determined.

The inner border of the molecular layer presents a series of large
cells originally described by Purkinje and known by his name. From
the outer end of the cell-body one or more dendrites emerge which
soon divide and subdivide into a number of branches which pass
toward the cerebellar surface. The general arrangement of these
dendrites gives to the entire cell a tree-like appearance (Fig. 231).
From the inner end of the cell an axon emerges which passes centrally
into the white matter.

Structure of the White Matter. — The white matter consists of
nerve-fibers which are arranged in association and projection systems.

The Association System. — The fibers which compose this system
are of variable lengths and unite adjacent as well as distant regions
of the cerebellar cortex. They doubtless associate them both anatom-
ically and physiologically.

514

THE CEREBELLUM.

515

The Projection System. — The fibers composing this system con-
nect the cerebellar cortex with certain structures in the cerebrum,
pons, medulla, and spinal cord. They may be divided into efferent
and afferent systems.

The efferent fibers have their origin in the cells of Purkinje and
the dentate nucleus. Some of these fibers emerge from the cere-
bellum in the superior
peduncles through
which they pass to-
ward and beneath the
corpora cjuadrigemina
to terminate around
the cells of the red
nucleus. As they ap-
proach this nucleus
some of the fibers
cross the median line
and decussate with
those coming from the
opposite side, while
others pursue a
straight direction,
terminating on the
same side. Through
the intervention of
fibers which arise from
the red nucleus and
ascend to the cerebral
cortex, the cortex is
thus connected with
both sides of the
cerebellum, though
chiefly with the oppo-
site side.

Efferent fibers also
leave the cerebellum by
the middle peduncle
and pass directly to

the nucleus pontis, around the cells of which their terminals arborize.
Efferent fibers also descend the inferior peduncles and constitute the
tract known as the Lowenthal and Marchi tract, situated in the
antero-lateral region of the spinal cord in its upper part.

The afferent fibers come from a variety of sources. Those found
in the superior peduncles come from the red nucleus; those in the
middle peduncles from the nucleus pontis of the opposite side, having

Fig. 230. — -View of Cerebellum in Sectiom,
AND OF Fourth Ventricle, with the
Neighboring Parts. — {From Sappey.)
I. Median groove fourth ventricle, ending
below in the calamus scriptorius, with the
longitudinal eminences formed by the fas-
ciculi 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
peduncle of the cerebellum, formed by the
restiform body. 4. Posterior pyramid ;
above this is the calamus scriptorius. 5, 5.
Superior peduncle of cerebellum, or pro-
cessvis e cerebello ad testes. 6, 6. Fillet to
the side of the crura cerebri. 7, 7. Lateral
grooves of the crura cerebri. 8. Corpora
quadrigemina. — {After Hirschfeld and L:-
veille. )

5i6

TEXT-BOOK OF PHYSIOLOGY.

crossed or decussated at the raphe near the anterior surface of the
pons ; those contained in the inferior peduncles are the most abundant
and important, and are represented by (i) the direct cerebellar tract,
which terminates in the superior vermis after decussation; (2) the
anterior and posterior arcuate fibers, the former coming from the
gracile and cuneate nuclei of the opposite side, the latter from the
same side, which also pass to the superior vermis; (3) the acustico-
cerebellar tract, composed of fibers the axons of the sensory end
nuclei (Deiters) of the vestibular portion of the auditory nerve. It

is probable that all these fibers de-
cussate prior to their final termina-
tion.

The cerebellum through this
system of efferent and afferent fibers
is brought into relation with many
different regions of the cerebrum,
pons, medulla, and spinal cord.
Each half of the cerebellum is con-
nected with the foregoing structures
of the same side, but more especially
of the opposite side.

THE FUNCTIONS
LUM.

OF THE CEREBEL-

FiG. 231. — Section of Cere-
bellar Cortex. A. Outer
or molectilar layer. B.
Inner or granular layer.
C. White matter, a. Cell
of Purkinje. b. Small cells
of inner layer, c. Dendrites
of these cells, d. A similar
cell lying in the white
matter.

From the observations of the
results of experimental lesions, from
analysis of clinico-pathologic facts,
and from its comparative anatomic
development in different animals, the
deduction has been drawn that the
cerebellum coordinates and har-
monizes the action of those muscles
the activities of which are necessary
to the maintenance of body equilibrium both during station and
progression.

By equilibrium of the body is understood a condition which may
be maintained for a variable length of time without displacement, and
is possible only so long as a line passing through the center of gravity
falls within the base of support. The support offered by the earth
to the feet neutralizes and counteracts the force of gravity. In station,
when the body is in the erect or military position, the arms by the
side, the center of gravity hes between the sacrum and the last lumbar
vertebra, and the line of gravity falls between the feet and within
the base of support. The entire skeleton for the time being is ren-
dered fixed and rigid at all its joints by the combined action of the

THE CEREBELLUM. 517

muscles connected with it. That this position may be maintained all
the different groups of antagonistic but cooperative muscles must be
accurately coordinated in their actions. Any failure in this respect is at
once attended by a disturbance of the equilibrium and displacement.

In progression, walking, running, dancing, etc., the body is trans-
lated from point to point by the alternate action of the legs. Whether
the direction of the translation be hnear or curvihnear, as the legs
change their position from moment to moment, the center of gravity
also changes, and at once the ec^uilibrium is menaced. If it is to be
maintained and displacement prevented there must be a prompt
readjustment in the relation of all parts of the body so that the hne
of gravity falls again within the base of support. The more com-
plicated the movements of progression, or the narrower the base of
support, the greater is the danger to the equihbrium, and hence the
necessity for rapid and compensatory changes in coordinated muscle
activity. All movements of this character, in man at least, are pri-
marily volitional and require for their performance the constant exercise
of the attention. With frequent repetition they gradually come to
be performed independently of consciousness and fall into the cate-
gory of secondary or acquired reflexes.

Though coordinating power is exhibited by the spinal cord,
medulla, and basal ganglia, it is only in the cerebellum that this
power attains its highest development and differentiation. To it
is assigned the power of selecting and grouping muscles, not in any
restricted part, but in all parts of the body, and coordinating their
actions in such a manner as to preserve the equihbrium.

The Results of Experimental Lesions. — If the cerebellum in
its totahty, coordinates and harmonizes the action of the muscles
on the opposite sides of the body, any derangement of its structure or
its connections with the cord, medulla, pons, or basal gangha should
at once be followed by incoordination of muscles and a want of har-
mony in their action. Experimental lesions of the cerebellum are
attended by such results. The phenomena observed are many and
complex. They differ in extent and character in different animals
and in accordance with the extent and location of the lesion, though
the note of incoordination runs through them all.

Removal of one lateral half of the cerebellum in the dog is followed
by an inability to maintain the equihbrium necessary to the erect
position. On attempting to stand, the animal at once falls toward
the side of the lesion, the muscles of which at the same time contract
and give to the body a distinctly curved condition (Fig. 232). The
anterior Hmbs are extended to the opposite side. On making efforts
to regain the standing position, the animal may roll over around the
long axis of its body. Conjugate deviation of the eyes is frequently
observed as well as nystagmus.

5i8

TEXT-BOOK OF PHYSIOLOGY.

After a few days the symptoms partially subside and the animal
acquires the power of sitting on the abdomen when the anterior
Hmbs are widely extended (Fig. 233). As the days go by the improve-
ment continues, and the animal recovers the power of walking, though
each step is attended with tremor and oscillations of the body. Any

Fig. 232. — Attitude Assumed After Destruction of the Left Half
OF THE Cerebellum. — {Morat and Doyen, after Thomas.)

change in the center of gravity such as results when one leg is Hfted
may result in a fall toward the side of the lesion, owing to an
inability to promptly bring about the necessary compensatory
muscle actions. With time the animal continues to improve in its
power of adjustment, though it never completely recovers it. Move-
ments of progression are apt
to be characterized by stiffness
and accompanied by tremor
suggestive of volitional efforts.
Total removal of the cere-
bellum is followed by a differ-
ent train of symptoms. The
extensor muscles apparently
preponderate in their action,
for the limbs are extended
and abducted, the head and
neck are retracted, and opis-
thotonos is established. In
time these effects also partially
subside, though all attempts
at walking are permanently
accompanied by tremor and oscillations. The characteristic effect
which follows section of the peduncles is again incoordination,
manifesting itself in deviation of the head, eyes, inabihty to walk,
tremor on exertion, etc. The effects vary, however, according to the
peduncle divided. Section of the middle peduncle gives rise to the
most pronounced effects. The head and the anterior part of the
body are at once drawn toward the pelvis on the side of the section.

Fig. 233. — Attitude in Repose after
THE Complete Removal of the
Cerebellum but during the
Period of Restoration of Func-
tion.— {Moral and Doyen, afUr
Thomas.)

THE CEREBELLUM.

519

A voluntary effort on the part of the animal causes it to lose all
control of its muscles and the body is rotated in the direction of its
longitudinal axis from 40 to 60 times a minute before it comes to rest.
According as the lesion is made from behind or before, the rotation
is from or to the side of the section. In time these symptoms
subside, though the animal never completely recovers.

The partial recovery of the power of coordination, observed after
removal of a portion or the whole of the cerebellum, indicates that
the centers in the cord, medulla, pons, and cerebrum endowed with
corresponding though less developed power, develop compensatory
activity and acquire to some extent the capabilities of the cerebellum
itself (Fig. 234).

Clinico- pathologic facts partly corroborate the results of phys-
iologic investigations. In various forms of uncomplicated cere-
bellar disease, vertigo, tremor on making voluntary efforts, difficulty
in maintaining the erect
position, unsteadiness in
walking, opisthotonos,
pleurothotonos, are
among the symptoms
generally observed.

Comparative anatomic
investigations reveal a
remarkable correspond-
ence between the de-
velopment of the cerebel-
lum and the complexity
of the movements ex-
hibited by animals. In

those animals whose movements are complex and require for their
performance the cooperation of many groups of muscles the cere-
bellum attains a much greater development in reference to the rest
of the brain than in animals whose movements are relatively simple
in character. This relative increase in the development of the
cerebellum is found in many animals, such as the kangaroo, the
shark, the swallow, and the predaceous birds generally.

The Coordinating Mechanism. — Though it is not known how
the cerebellum selects and coordinates groups of muscles for the per-
formance of any complex movement, it is known that its activity is
largely reflex in origin and excited by impulses reflected to it from
peripheral organs. In this as in other forms of reflex activity the
mechanism involves (i) afferent nerves, e. g., cutaneous, muscle, optic,
and vestibular, and their related end-organs, tactile corpuscles,
muscle spindles, retina, and semicircular canals, all indirectly con-
nected with (2) the cerebellar centers; (3) efferent nerves indirectly

Fig. 234. — Progression AFTER Destruction
OF THE Vermis. — -{Moral and Doyen,
after Tlwinas.)

520 TEXT-BOOK OF PHYSIOLOGY.

connected with (4) the general musculature of the body. Both station
and progression are directly dependent on the development and. trans-
mission of afferent impulses from the previously mentioned periph-
eral sense-organs to the cerebellum. Tactile, muscle, visual, and
labyrinthine impressions and sensations not only cooperate in the
development and organization of the motor adjustments necessary
to the maintenance of the equilibrium and locomotive coordination,
but even after their organization they are necessary to the excitation
of cerebellar activity. The manner in which they lead to the develop-
ment of this capability on the part of the cerebellum is conjectural.
Their ever-present influence is shown by the effects which follow their
removal, as the following facts indicate.

The prevention of the development of tactile impulses by freezing
or anesthetizing the soles of the feet, and the blocking of normally de-
veloped impulses through destruction of afferent pathways in diseases
of the spinal cord lead at once to marked impairment in the coordinat-
ing power. The removal of the skin from the hind legs of the frog,
previously deprived of its cerebrum, destroys its coordinating power,
which it would otherwise possess in a high degree.

The blocking in consequence of destructive lesions of the
spinal cord, of the impulses, which come from the muscles, tendons,
etc., and which inform us of the activity and the degree of activity
of our muscles, the location of the limbs, the amount of effort necessary
to produce a given movement, etc., also gives rise to much incoor-
dination. A blocking of both tactile and muscle impulses frequently
exists in degeneration or sclerosis of the posterior columns of the
spinal cord. The coordinating power is so much impaired in this
disease that the patient is unable to maintain, without strained effort,
the erect position and especially if the directive power of the eyes be
removed by closure of the lids. Walking becomes extremely difficult;
the gait is irregular and jerky, and equilibrium is maintained only
'by keeping the eyes fixed on the ground in front and by artificially
increasing the basis of support by the use of canes.

An interference with the development of the customary visual
impressions which in a measure maintain the sense of relation of the
individual to surrounding objects also gives rise to equihbratory dis-
turbances. A rapid change in the relation of the individual to sur-
rounding objects or the reverse; a change in the direction of one
optic axis from the use of a prism or from paralysis of an eye muscle ;
the destruction of an eye; — these and similar conditions frequently
give rise to such marked disturbances of the equihbratory power that
displacement is difficult to prevent.

An interference with the development of the so-called labyrin-
thine impressions by destruction of the semicircular canals gives rise
to the most remarkable disturbances in this respect. Section of one

THE CEREBELLUM. 521

horizontal canal* in the pigeon is followed by oscillations of the
head in a horizontal plane around a vertical axis. Bilateral section
so increases these oscillations that the pigeon is unable to maintain
equihbrium and forced to fall and turn continuously around the
vertical axis. Bilateral section of the posterior vertical canals gives rise
to oscillations around a horizontal axis which frequently become so
exaggerated as to eventuate in the turning of backward somersaults,
head over heels. Similar phenomena follow division of the superior
vertical canals.

Bilateral destruction of both sets of canals is attended by extra-
ordinary disturbances in the equihbrium. From the moment of the
operation the animal, the pigeon, loses all control of its motor mechan-
isms. It can neither maintain a "fixed attitude nor execute orderly
movements of progression ; its activity, continuous and uncontrollable,
is characterized by spinning around a vertical axis, turning somer-
saults, dashing itself against surrounchng objects until hfe is endan-
gered. If the animal be protected from injury, these disturbances
gradually subside, and in the course of a few months the equihbratory
power is so far regained that standing and walking at least become
possible. In this condition, however, the coordinating power is
directly dependent on visual impulses, for with the closure of the
eyes all the previous motor disturbances at once recur. These and
similar facts indicate that the semicircular canals are the peripheral
sense-organs from which come the nerve impulses most essential to
the excitation of the cerebellar coordinative centers in their control of
equilibrium and of progression.

The cerebellum may therefore be regarded as the essential, most
highly differentiated portion of the coordinating mechanism con-
cerned in the maintenance of equilibrium, during both station and
progression. The manner in which the cerebellum accomplishes
this result is unknown, though it is certain, from the foregoing facts,
that its special mode of activity is dependent on the excitatory action
of nerve impulses reflected from a variety of peripheral sense-organs.

* The physiologic anatomy of the semicircular canals is described in the chapter
devoted to the ear, to which the reader is referred.

CHAPTER XXI.
THE CRANIAL NERVES.

The nerve-trunks which serve as channels of communication
between the encephalon and the structures of the head, the face,
and in part the organs of the thorax and abdomen, pass through
foramina in the walls of the cranium, and for this reason are termed
cranial nerves.

According to the classification now generally adopted, there are
twelve cranial nerves on either side of the median line, which, enu-
merated from before backward, are as follows (Fig. 235):

First or Olfactory. Seventh or Facial.

Second or Optic. Eighth or Auditory.

Third or Oculo-motor. Ninth or Glosso-pharyngeal.

Fourth or Patheticus. Tenth or Pneumogastric or Vagus.

Fifth or Trigeminal. Eleventh or Spinal Accessory.

Sixth or Abducens. Twelfth or Hypoglossal.

The cranial nerves may be classified physiologically in accordance
with their functional manifestations into three groups, viz. :

1. Nerves of Special Sense: e.g., Olfactory, Optic, Auditory, Gustatory (Glosso-

pharyngeal) .

2. Nerves of General Sensibility: e.g., Large root of the Trigeminal, Glosso-

pharyngeal, and Pneumogastric.

3. Nerves of Motion: e.g., Oculo-motor, Patheticus, the small root of the Trigeminal,

Facial, Spinal Accessory, and Hypoglossal.

Though this classification in the main holds true, it must be borne
in mind that modern investigations have demonstrated that the glosso-
pharyngeal and pneumogastric nerves contain even at their junction
with the medulla oblongata a number of efferent or motor fibers,
and to this extent are mixed nerves.

The Origins of the Cranial Nerves. — In accordance with
modern views as to the origins of nerves in general, it may be stated
that—

The nerves 0} special sense have their origin respectively in the
neuro-epithehal cells in the mucous membrane of the olfactory region
of the nose, in the ganghon cells of the retina, in the cells of the spiral
ganghon of the cochlea and the ganglion of Scarpa, and in the cells
of the petrous and jugular gangha. From the cells of these gangha
dendrites pass peripherally to become associated with specialized
end-organs, while axons pass centrally in well-defined bundles to

522

THE CRANIAL NERVES.

523

become related by means of their end-tufts with primary basal
ganglia.

The nerves of general sensibility have their origin in the ganglia
on their trunks, and in this respect resemble the spinal nerves. From
the ganghon cell there emerges a short axon process which soon
divides into a central and a peripheral branch. The former passes
toward and into the gray matter located beneath the floor of the
fourth ventricle, where its end-
tufts arborize about nerve-cells.
The latter (the peripheral branch)
passes toward the general periph-
ery to be distributed to skin and
mucous membranes (Fig. 236).

The nerves of motion have
their origin in the nerve-cells in
the gray matter beneath the
aqueduct of Sylvius and beneath
the floor of the fourth ventricle
(Fig. 237). The axons emerging
from these cells course per-
ipherally to be distributed to
skeletal muscles. In some of the
motor nerves, and in some
sensory nerves as well, there are
to be found efferent fibers of
smaller size which have a similar
origin and which become related
through the intervention of
sympathetic gangha (peripheral
neurons) with visceral muscles
and glands. These nerves have
been termed autonomic nerves.

The Cerebral Connections
of the Cranial Nerves. — Each
of these three groups of cranial
nerves has special connections
with the cerebral cortex.

The nerves of special sense for the most part terminate in primary
basal ganglia, around the cells of w^hich their central end-tufts ar-
borize. From these cells axons arise which pass upward and directly
or indirectly come into physiologic relation with sensor nerve-cells
in the cerebral cortex.

The nerves of general sensibility terminate in the gray matter
beneath the floor of the fourth ventricle, around the nerve-cells of
which their end-tufts arborize. These groups of nerve-cells are

Fig. 235. — Superficial Origin of the
Cranial Nerves from the Base
OF THE Encephalon. I. Olfactory.
2. Optic. 3. Motor oculi. 4.
Patheticus. 5. Trigeminal. 6. Abdu-
cens. 7. Facial. 7'. Nerve of
Wrisberg. 8. Auditory. 9. Glosso-
pharyngeal. 10. Pneumogastric.
II. Spinal accessor}'. 12. Hypo-
glossal.

524

TEXT-BOOK OF PHYSIOLOGY.

known as sensor end-nuclei. Though once regarded as the centers
of origin of the sensor nerves, they are now regarded as the centers
of origin of axons which pass upward to the cortex of the cerebrum,
where they also come into physiologic relation with sensor nerve-
cells.

Fig. 236. — Ganglia of Origin of the
Sensor Cranial Nerves, i. Tri-
geminal (ganglion of Gasser). 2.
Nerve of Wrisberg. 3. Auditory
(ganglion of Scarpa). 4. Glosso-
pharyngeal (ganglion of Andersch).
5. Pneumogastric (ganglion plexi-
formis). — {After Moral and Doyon.)

Fig. 237. — Nuclei of Origin of the
Motor Cranial Nerves. i.
Motor ocuU. 2. Patheticus. 3.
Motor root of the trigeminal. 4.
Abducens. 5. Facial. 6. Mixed
nucleus for efferent fibers of the
glosso-pharyngeal vagus and spinal
accessory. 7. Hypoglossus. 8.
Spinal accessory. 9. Spinal

nerves. — (After Morat and Doyon.)

The axons in both of these classes of nerves thus originate in the
cells of the central nerve system and continue upward to the cere-
brum, the primary afferent path.

The motor nerves which have their origin in the cells of the gray
matter beneath the aqueduct of Sylvius and beneath the floor of the
fourth ventricle are in physiologic relation with nerve-cells in the

THE CRANIAL NERVES.

525

motor region of the cortex through descending axons contained in the
pyramidal tract. The end-tufts of these axons arborize around the
nerve-cells. The efferent path beginning in the cerebral cortex is
thus continued by the motor nerves to the general periphery.

The three groups of nerves, those of special sense, of general
sensibility, and the motor nerves, are neurons of the first order; the
nerve-cells and fibers which constitute the cerebral connections are
neurons of the second order. It is possible that the sensor cells
in the cerebral cortex are neurons of a third order.

FIRST PAIR. THE OLFACTORY.

The first cranial nerve, the olfactory, is situated in the upper
third of the nasal fossa, in the regio olfactoria. It consists of from
20 to 30 branches, the fibers of which are non-medullated.

Origin. — The olfactory nerve is composed of centrally coursing
axons w^hich have their
origin in the central ends
of bipolar, rod-shaped, or
spindle-shaped nerve-cells
interspersed among the epi-
thehal cells covering the
mucous membrane in the
regio olfactoria; the per-
ipheral ends of these cells
give off a number of den-
drites which are spread out
to form a delicate feltwork
over the surface of the
mucous membrane. From
their origin the axons
gradually converge to form
bundles which ascend to
the cribriform plate of the
ethmoid bone, through the
foramina of which they pass
to become related by their
end-tufts with structures in
the gray matter of the
olfactory bulb (Fig. 238).

Cortical Connections.
— The olfactory bulb and

olfactory tract, formerly called the olfactory nerve, are portions of
the cerebrum (the olfactory lobe) which arise embryologically by a
protrusion of the walls of the cerebral cavity. The bulb is oval-shaped

Fig. 238.— The Relation of the Olfactory
Nerves to the Olfactory Tract, i.
Olfactory nerve-cell. 2. Axon process. 3.
Epithelial cells. 4. Glomerulus. 5. Mitral
cells. 6. Centrally coursing axons of the
olfactory tract.

526

TEXT-BOOK OF PHYSIOLOGY.

and consists of both gray and white matter. It rests on the cribriform
plate of the ethmoid bone and is embraced by the olfactory nerves.
As seen on sagittal section, there is just beneath the surface a layer
of large pyramidal and spindle-shaped cells (termed also mitral cells),
each provided with an apical and two lateral dendrites. The apical
dendrite passes toward the surface and ends in a brush- or basket-like
expansion which interlaces with the end-tufts of the olfactory nerves,

forming what are
known as the olfac-
tory glomerules. The
lateral dendrites end
free.

The axons of the
pyramidal cells pass
toward the center of
the bulb and bend at
right angles, after
which they pursue a
horizontal direction
toward and into the
olfactory tract. This
tract is about five
centimeters in length,
prismatic in shape on
cross-section and di-
visible into a ventral
and a dorsal portion.
It emerges from the
posterior extremity of
the bulb, passes back-
ward to the posterior
part of the anterior
lobe, where it divides
into three roots: viz.,
a lateral or external,
a mesial or internal, a
middle or dorsal. The

■p.olf.

Fig. 239. — Olfactory Lobe of the Human Brain. —
5m. Olfactory bulb. T. Tract. Tr.o. Trigone. R.
Rostrum of corpus callosum. p. Peduncle of cor-
pus callosum, passing into G.s., gyrus subcallosus
(diagonal tract, Broca). Br. Broca's area. F.p.
Fissura prima. F.s. Fissura serotina. C.a. Posi-
tion of anterior commissure. L.t. Lamina ter-
minalis. Ch. Optic chiasma. T.o. Optic tract.
p.olf. Posterior olfactory lobule (or anterior per-
forated space), m.r. Mesial root. l.r. Lateral
root of tract. — (His.) — {After Quain.)

fibers of the lateral and mesial roots are derived almost exclusively
from the ventral portion of the tract, the fibers of which come from the
mitral cells in the bulb. The lateral root-fibers pass outward into the
fossa of Sylvius and come into relation with nerve-cells in the inferior
extremity of the gyrus hippocampus and the gyrus uncinatus. The
mesial fibers pass inward and come into relation with nerve-cells
in the pre-callosal part at least of the gyrus fornicatus. The fibers
thus far considered are undoubtedly true olfactory fibers, pursuing

THE CRANIAL NERVES. 527

a centripetal direction, carrying nerve impulses from the olfactory cells
to the cerebrum (Fig. 239).

Histologic and embryologic methods of research have shown that
some of the libers in the olfactory tract are centrifugal in direction.
They originate in the olfactory cortical areas, pass toward the
periphery as far as the anterior commissure, where they cross to
become the dorsal root, enter the olfactory tract, and finally terminate
in the bulb. This tract serves to connect the cortex with the bulb of
the opposite side, and carries impulses from the cortex to the bulb.
The two opposite cerebral olfactory areas are also united by com-
missural fibers which decussate at the anterior commissure.

Functions. — The olfactory nerves, including the olfactory tract,
are channels of communication between the olfactory region in the
nose and the cerebral cortex. The stimulus to its excitation is the
impact and chemic action of gaseous or volatile organic matter
on the dendrites of the olfactory cells. The energy set free develops
nerve impulses which, traveling through the entire olfactory tract
to the cortex, evoke the sensation of odor. The sensitiveness of the
olfactory end-organ to the action of many substances is remarkable,
responding, for example, to the y. Tiri.TT to ^^ ^ gram of oil of roses and
to the 2".T'Glr.¥o""o o^ ^ gram of mercaptan.

Division or destruction of the olfactory path at any point is fol-
lowed by an abolition of the sense of smell on the corresponding side.
Destructive lesions of the hippocampal and uncinate gyri are fol-
lowed bv similar results.

SECOND PAIR. THE OPTIC.

The second cranial nerve, the optic, consists of centrally coursing
axons of neurons, which connect the essential part of the organ of
vision, the retina, with sensory end-nuclei or gangha situated at the
base of the cerebrum.

Origin. — The axons which constitute the optic nerve have
their origin in the ganglionic cells in the anterior part of the retina.
Through their dendrites these cells are brought into relation pos-
teriorly with successive layers of cells which collectively constitute the
retina. Though the retina is said to consist of ten or eleven layers,
it may be reduced practically to three, viz. (Fig. 240) :

1. The layer of visual cells.

2. The layer of bipolar cells.

3. The layer of ganglionic cells.

The visual cells present peripherally modified dendrites, known
as the rods and cones; centrally they give off an axon which after
a short course terminates in an end-tuft. The bipolar cells also
possess dendrites and an axon; the former interlace with the end-

528

TEXT-BOOK OF PHYSIOLOGY.

tufts of the visual cell axon, the latter with the dendrites of the gang-
lion cell. The retina may be regarded therefore as the peripheral
end-organ in which the optic nerve originates. From their origin the
axons turn backward, at the same time converging to form a distinct
bundle which passes through the chorioid coat and sclera. After
emerging from the eyeball the nerve-bundle (the optic nerve) passes
backward as far as the sella turcica, traversing in its course the or-
bit cavity and the optic foramen. At the sella turcica there is a
union and partial decussation in man and other mammals of the
two nerves, forming the optic chiasm.

Decussation of the Optic Nerves. — The
results of various methods of research would seem
to indicate that the fibers from the nasal third of
the retina of the left eye cross in the chiasm to
unite with the fibers from the temporal two-thirds
of the retina of the right eye. In a similar
manner the fibers from the nasal third of the
retina of the right eye cross in the chiasm and
unite with the fibers from the temporal two-thirds
of the retina of the left eye. Posterior to the
chiasm the crossed and uncrossed fibers form
the so-called optic tracts, which after winding
around the crura cerebri enter the optic basal
gangha. Transection of the optic nerve shows
that it is composed of an enormous number of
non-medullated nerve-fibers, estimated by Salzer
at from 450,000 to 800,000, enclosed in a sheath
of the dura mater. In the central portion of the
nerve there is seen a distinct bundle of fibers,
triangular in shape, that come from the region of
the macula lutea. At the chiasm this bundle of
fibers undergoes a partial decussation similar to
that of the fibers coming from the more peripheral
portions of the retina. In the left optic tract,
therefore, fibers from four different regions are to
be found: viz., the two-thirds of the temporal side of the left retina,
the temporal half of the left macula, the nasal third of the right
retina, and the nasal half of the right macula. Corresponding fibers
are to be found in the right optic tract. As the optic tract passes
around the crus cerebri it divides into a lateral or outer, and a mesial
or inner bundle, which then terminate in the optic basal ganglia.
The fibers of the lateral bundle are traceable into the external
geniculate body (the pre-geniculum), the pulvinar of the optic
thalamus, and the anterior quadrigeminal body (the pregeminum).
These are in all probabihty the true visual fibers. The fibers of

Fig. 240. — Retinal
Cells, s', z' .
Visual cells with
their peripheral
terminations. J.
Rods. z. Cones.
h. Bipolar cells.
g. Ganglion cells
from which arise
the axons of the
optic nerve.

THE CRANIAL NERVES.

529

VISUAL riELD

VISUAL HELD

the mesial bundle are traceable into the internal geniculate body
(the post-geniculum) and the posterior quadrigeminal body (the post-
geminumj.

Cortical Connections. — After entering the basal gangHa the
visual libers terminate in end-tufts which arborize around nerve-
cells. From these cells new axons arise which ascend through the
posterior part of the" internal
capsule, at the same time curv-
ing backward to form the optic
radiation of Gratiolet, and
terminate tinally around nerve-
cells in the gray matter of the
cuneus and in the gray matter
bordering the calcarine fissure,
both situated on the mesial
aspect of the occipital lobe.

Cenirijiigal Fibers 0} the
Optic Nerve. — All the fibers
previously alluded to have been
afi"erent or centripetal in direc-
tion ; but the optic nerve also con-
tains efferent or centrifugal fibers
which come from nerve- cells in
the basal gangUa and ramify
around special cells, the amac-
rine cells, in the retina. Their
function is unkno^^Tl. It has
been suggested that they regulate
the vascular supply to the retina.
Centrifugally coursing fibers also
connect the \dsual areas of the
cortex with the basal ganglia.

Functions. — The optic nerve
apparatus in its entirety con-
nects the visual cells of the retina
with the cells of the cerebral cor-
tex. The excitation of this ap-
paratus evokes the sensation of fight and its different quafities — colors.

The specific physiologic stimulus of the \'isual retinal cells is the
impact of the undulations of the ether. The energy set free excites
in the optic nerve, nerve impulses which are transmitted first to the
optic ganglia and then to the cerebral cortex, where they evoke the
sensations of light and color.

Iris Reflex. — The optic nerve also assists in the automatic reg-
ulation of the size of the pupil. Some of its fibers form the afferent

34

Fig. 241. — Diagram Illustrating Left
Homonymous Lateral Hemianopsia
FROM A Lesion of the Right Optic
Tr,a.ct or the Right Cuneus. The
Shaded Lines in the Visual Fields
Indicate the D.ajikened Area.

53°

TEXT-BOOK OF PHYSIOLOGY.

part of the reflex nerve mechanism by which the circular fi.bers of the
iris (the sphincter pupillae) are excited to contraction. These fibers
arborize around nerve-cells in the anterior quadrigeminal body, from
which axons descend in the posterior longitudinal bundle. In their
course they give off collateral branches to the nuclei of origin of the
oculo-motor nerve, from which nerve-fibers pass to the iris.

Light falling on the retina generates nerve impulses which, when
conducted through the afferent and efferent pathways just mentioned,
stimulate the circular fibers to contraction. The extent of the con-
traction will depend on the in-
tensity of the fight. In the
absence of all light the muscle
completely relaxes.

Hemiopia and Hemian-
opsia.— Division of the optic
nerve between the eyeball
and the optic chiasm is fol-
lowed by complete blindness
in the eye of the corresponding
side. Owing to the partial
decussation of the fibers in the
chiasm, division of an optic
tract is followed by a loss of
sight in the outer two-thirds of
the eye of the same side and in
the inner third of the eye of the
opposite side. To this loss of
visual power in the retina the
term hemiopia is given. In
consequence of this loss of vis-
ual power in the retina there is
a corresponding obscuration or total obhteration of nearly one-half of
the visual field, to which the term hemianopsia is given. If, for
example, the right optic tract is divided there will be hemiopia in the
outer two-thirds of the right eye and the inner third of the left eye, with
lejt lateral hemianopsia, and as the portions of the retina which are
affected are associated in vision the loss of the visual fields is spoken
of as homonymous hemianopsia (Fig. 241). A destructive lesion of
the cerebral visual area, the cuneus and the adjacent gray matter on
the right side, is also followed by left lateral hemianopsia*

Fig. 242. — Diagram to Show the Exist-
ence OF Hemianopsia.

* It should be borne in mind that in both instances the retina itself is unaffected.
The impact of light generates, as usual, nerve impulses which proceed as far back-
ward as the point of division or destruction. In consequence those portions of the
cerebral cortex stimulation of which evokes the sensation of light remain unaffected
and the individual does not become aware through sensation, of the presence of a
luminous body in the left side of the visual field.

THE CRANIAL NERVES. 531

The existence of an homonymous hemianopsia becomes evident
when the individual is directed to focus the vision on an object placed
directly in front and with its center in the median plane of the body,
when if the lesion be on the right side, the left half of the object will
be invisible. The reason for this will be apparent on reference to
Fig. 242. All the light rays emanating from the left half of the
object fall on the retina on the side of the injury, and hence there
will be no sensation. If, however, the object be moved to the right
without change in the position of the head, the entire object will be
visible, as all the rays fall on the normal side. If, on the contrar}-, the
object be moved to the left, it will be invisible for the opposite reason.

Hemianopsia may be the result of either destruction of the optic
tract or of the cortical visual area. The seat of lesion in any given
case is indicated by a peculiarity of the iris reflex pointed out by
Wernicke, which will be referred to in connection with the considera-
tion of the oculo-motor nerve.

THIRD PAIR. THE OCULO-MOTOR.

The third cranial nerve, the oculo-motor, consists of some
15,000 peripherally coursing nerve-fibers which serve to bring the
nerve-cells from which they arise into relation with a large portion of
the general musculature of the eye.

Origin. — The axons composing the third nerve arise from a series
of seven or eight groups of nerve-cells, located in the gray matter
beneath the floor of the aqueduct of Sylvius. From each of these
groups or nuclei, bundles of axons emerge, which after a short course
unite to form the common trunk. The large majority of the fibers in
the nerve come directly from the nuclei of the same side; the re-
mainder come from a group of cells on the opposite side of the
median line. There is thus a partial decussation of its tibers (Fig.

243)-

The different groups of cells, the nuclei of origin, are arranged

in a serial manner. The anatomic arrangement of these nuclei
would indicate that each nucleus is related to an individual
member of the eye-group of muscles. CHnical observation and the
investigation of the results of pathologic processes have not only
shown that this is the case, but have succeeded in locating the
position of the nucleus for any given muscle. Though there is some
difference of opinion in regard to the exact location of one or two of
the nuclei, the tabulation subjoined is approximately correct.

Enumerating them from before backward, the nuclei occur in
the following order :

1. The sphincter pupillae.

2. The tensor chorioideae (the accommodation nucleus).

532

TEXT-BOOK OF PHYSIOLOGY.

The convergence nucleus, a common nucleus for the conjoint
action of the two internal recti muscles.

4. The superior rectus.

5. The inferior rectus.

6. The levator palpebrae.

7. The inferior oblique.
Cortical Connections. — The

oculo-motor nuclei are in histologic
and physiologic relation with the
motor area of the cerebrum. Nerve-
cells in the cortex give off axons
which, entering the pyramidal tract,
descend through the internal capsule,
and the crus cerebri, from which they
cross to the opposite side. The end-
tufts arborize around the nuclei of
the oculo-motor nerve with the ex-
ception of the nucleus for the iris
sphincter.

Distribution. — After their origin
the axons converge to form a com-
mon trunk, which emerges from the
base of the encephalon, on the inner
side of the crus cerebri, in front of
the pons Varolii. The nerve then
passes forward through the sphenoid
fissure into the orbit cavity, where
it divides into a superior and an
inferior branch. The former is dis-
tributed to the superior rectus and
the levator palpehrce muscles; the
latter is distributed to the internal
and inferior recti and inferior oblique
muscles (Fig. 244).

From the inferior branch a short
bundle of fibers passes to the ciliary
or ophthalmic ganglion, where they
terminate, arborizing around the
ganglion cells. These fibers are
smaller in size than those constitut-
ing the bulk of the nerve and belong to the system known as
the autonomic. These cells give origin to new axons, the ciliary
nerves, which enter the eyeball, pass forward between the sclera and
chorioid coat, and terminate in the ciliary muscle and iris. The
ciliary nerves are not portions of the third nerve proper, but periph-

FiG. 243. — Diagrammatic View of
THE Situation and Relation
OF THE Nuclei of Origin of
THE Oculo-motor and Path-
eticus (Trochlearis) Nerves.
The oculo-motor nuclei consist
of an anterior nucleus, the
Edinger-Westphal nucleus {a
and h), and a posterior nucleus;
the posterior nucleus has a dor-
sal, a ventral, and a mesial
portion; the decussation of
fibers from the dorsal portion
of the posterior nucleus is also
shown. The decussation of
the fibers of the fourth nerve is
also represented. — (Edinger.)

THE CRANIAL NERVES.

533

eral sympathetic neurons. As the cihary ganghon receives filaments
from the cavernous plexus of the sympathetic and filaments which
become a part of the trigeminal nerve, it is probable that the ciliary
nerves contain not only motor, but vaso-motor and sensor fibers.

Properties. — Stimulation of the nerve near its exit from the en-
cephalon is followed by contraction of the muscles to which it is dis-
tributed with the following results, viz. :

1. Diminution in the size of the pupil.

2. Accommodation of the eye for near vision.

3. Elevation of the upper eyehd.

4. Internal deviation and rotation upward and inward of the anterior

pole of the eye, combined with a small amount of torsion toward

the mesial line, due to

preponderating action

of the internal rectus

and inferior oblique

muscles.
Division of the nerve
experimentally or compres-
sion from a pathologic
lesion is followed by a
relaxation of the muscles,
with the following effects,
viz. :

1. Dilatation of the pupil,

the iris responding
neither to light nor to
efforts of accommoda-
tion.

2. Loss of the accommoda-

tive power.

3. Falling of the upper eye-

hd (ptosis).

4. External deviation and rotation downward and outward of the

anterior pole of the eyeball combined with a small amount of
torsion toward the mesial hne due to the unopposed action of
external rectus and the superior obhque muscles.

5. Double vision or diplopia. The image of the eye of the paralyzed

side is projected to the opposite side of the true image and to
the upper part of the visual field. Owing to the slight mesial
torsion the false image is inclined away from the true image.

6. Immobility and slight protrusion of the eyeball.

Function. — The function of the third nerve is to transmit nerve
impulses from the nuclei of origin to all the muscles of the eye except
the external rectus and superior oblique and excite them to activity.

Fig. 2

OF THE

2. Third
Inferior

44. — Intra-orbital Portion
Third Nerve, i. Optic nerve.
nerve. 3. Superior branch. 4
branch. 5. Abducens. 6. Triitacial. 7.
Ophthalmic branch divided. 8. Nasal
branch. 9. Ciliary ganglion. 10. Motor
branch to this ganghon from the inferior
branch of the third nerve. 11. Sensory-
fibers. 12. Sympathetic fibers. 13. Ciliary
nerves. — (Sappey.)

534

TEXT-BOOK OF PHYSIOLOGY.

The majority of the ocular movements, the power of accommoda-
tion, the variations in the size of the pupil in accordance with varia-
tions in the intensity of the hght, the power of convergence of the
visual axes, are all excited by the transmission of nerve impulses by
the constituent fibers of the nerve from their related nuclei. This
is made evident by the effects w^hich follow stimulation and division
of the nerve or lesions of the nuclei themselves.

The central nuclei can be excited to activity (i) by nerve impulses
descending the motor tract, from the cerebral cortex, (2) by nerve
impulses coming through various afferent nerves. This holds true
more especially for the sphincter pupillse nucleus.

The Iris Reflex or the Pupillary Reflex. — These are terms
applied to the variations in the size of the pupil that follow vari-

Casserian Ganglion

Ciliaru ^ ^ Nucleus of 3''— Nerue

Nerues Ciliartj GangliL

Sympathetic.
Postganglionic
fibers

Superior
Cervical
Ganglion Vv.

1— TkoracicNeroe

Preganglionic

fibers

fromSpin al Cord

Fig. 245. — Diagram Showing the Structures Involved in the Iris Reflex.

ations in the intensity of the light. In the absence of light the
pupil widely dilates, due largely to the relaxation of the sphincter
pMpillcB muscle and partly to a contraction of the radiating fibers of
the iris which collectively constitute the dilatator pupilla muscle.
With the entrance of light into the eye, the pupil narrows in con-
sequence of the contraction of the sphincter pupillcB caused by a
stimulation of the peripheral end of the optic nerve, the degree
of contraction depending within limits on the intensity of the light.

The action is a reflex one and the mechanism involved includes
the retina, the optic nerve, the anterior quadrigeminal body, the third
nerve, the ciliary nerves (the peripheral sympathetic neurons), and
the sphincter pupillse muscle. ( Fig. 245.) In this mechanism the
optic nerve is the afferent path, the motor oculi the efferent path,
and the anterior quadrigeminal body the intermediate center. These

THE CRANIAL NERVES. 535

facts are demonstrated by the entire loss of the reflex which fol-
lows division or destruction of any part of this arc. The anterior
Cjuadrigeminal body appears to be in relation through its axons and
their collateral branches with the sphincter pupilla nucleus of both
sides, inasmuch as stimulation of one retina is followed by narrow-
ing of the pupils of both eyes. To this simultaneous contraction of
the pupils the term ** consensual" has been given. Contraction of
both pupils also occurs as an associated movement in the conver-
gence of the eyes during accommodation. The dilatation of the
pupil is, however, not due exclusively to the relaxation of the
sphincter pupillae muscle, but partly to the contraction of the dila-
tator pupills muscle, which is kept normally in a state of tonic
contraction by impulses emanating from a nerve-center in the
medulla oblongata.

The axons which arise in this center pass down the cord, emerge
through the first thoracic nerve, and then ascend to the superior
cervical ganglion (see Fig. 245), in which their terminal branches
arborize around its nerve-cells. From these cells new axons of the
sympathetic system arise which pass successively to the ophthalmic
division of the fifth nerve, the nasal nerve, the long ciliar}- nerve and
the iris.

Experimental research renders it highly probable that the dilatator
center is in a state of continuous activity and the dilatator muscle in
a state of tonic contraction. Whatever the normal stimulus may be,
the center is increased in activity by dyspneic blood, by severe muscle
exercise, by emotional excitement, and by stimulation of various
sensory nerves. That the afferent pathway just alluded to transmits
the impulses to the iris is show^n by the fact that division in any part
of the course is followed by narrowing, stimulation by active dilata-
tion of the pupil.

The variations in the size of the pupil, though largely a reflex
act under the control of the oculo-motor nerve, are nevertheless
partly due to the active cooperation of the dilatator nerves and their
related muscle. The size of the pupil necessary from moment to
moment for the admission of just that amount of light essential to
the formation and perception of a distinct image is the result of two
nicely adjusted and delicately balanced forces.

Wernicke's Pupillary Reaction. — It was stated on page 531
that a modification of the pupillary reaction is observed in some
cases of hemianopsia which indicates approximately the seat of lesion.
This reaction is present only when the lesion is along the course of
the optic tract. In these cases, if a fine ray of light is projected into
the eye in such a manner that it falls entirely on the non- responsive
side of the retina, there will be an absence of a pupillary response,
owing to the break in the reflex arc. If, however, the light be

536

TEXT-BOOK OF PHYSIOLOGY.

thrown on the sensitive side of the retina the usual response, a .con-
traction of the sphincter and a narrowing of the pupil, is at once
observed.

FOURTH PAIR. THE PATHETICUS.

The fourth cranial nerve, the patheticus, consists of peripherally
coursing axons which serve to bring the cells from which they arise
into relation with the superior obhque muscle.

Origin. — The axons of this nerve arise from a group of cells
located beneath the aqueduct of Sylvius just posterior to the last

nucleus of the third nerve.
After emerging from the nu-
cleus the nerve-fibers pass down-
ward for a short distance, then
curve dorsally around the aque-
duct of Sylvius, and enter the
valve of Vieussens, where they
completely decussate with the
nerve-fibers of the opposite side.
Cortical Connections. —
The nucleus of the pathetic nerve
is in histologic and physiologic
connection with the motor area
of the cerebral cortex. Nerve
cells in this region give off axons
which enter the pyramidal tract
and descend through the inter-
nal capsule and the crus cerebri,
after which they cross to the
opposite side. Their end-tufts
arborize around the cells of the
nuclei already described.

Distribution. — After its
decussation the nerve-trunk
emerges just below the posterior
quadrigeminal body, crosses the
superior cerebellar peduncle, and winds around the crus cerebri to the
anterior border of the pons Varolii. It then enters the orbit cavity
through the sphenoid fissure and finally terminates in the superior
oblique muscle. In its course the nerve receives filaments from the
cavernous plexus of the sympathetic and the ophthalmic division of
the trigeminal.

Properties. — Stimulation of the nerve-trunk is followed by spas-
modic contraction of the superior oblique muscle, the anterior pole
of the eyeball being turned downward and outward, combined with
slight torsion away from the middle hne.

Fig. 246. — Distribution of the Patheti-
cus. I. Olfactory nerve. II. Optic
nerves. III. Motor oculi communis.
IV. Patheticus, by the side of the
ophthalmic branch of the fifth, and
passing to the superior obUque muscle.
VI. Motor oculi externus. i. Gang-
lion of Gasser. 2, 3, 4, 5, 6, 7, 8, 9, 10.
Ophthalmic division of the fifth
nerve, with its branches. — {Hirsch-
feld.)

THE CRANIAL NERVES.

537

Division of the nerve is followed by a relaxation or paralysis of
the muscle. In consequence of the now unopposed action of the
inferior oblique muscle, the anterior pole of the eyeball is turned
upward and inward with slight torsion toward the middle hne. The
diplopia consequent upon this paralysis is homonymous, the images
appearing one above the other. The image of the paralyzed eye is
below that of the normal eye and its upper end inclined toward that
of the normal eye.

Function. — The function of this nerve is to transmit nerve im-
pulses to the superior obhque muscle and to excite it to contraction.

FIFTH PAIR. THE TRIGEMINAL.

The fifth cranial nerve, the trigeminal, consists of both afferent and
efferent axons which for the most part are separate and distinct.
The afferent axons constitute by far the major portion, the efferent
fibers the minor

portion, of the ,•"•.

nerve.

Origin of the
Afferent Axons.
— The aft'erent
axons serve to
bring into relation
the skin, mucous
membranes of the
head and face,
and other sentient
structures, with
certain sensor
end-nuclei in the
pons, medulla ob-
longata, and ad-
joining structures.
They have their
origin in the mon-
axonic cells in the
ganglion of Gas-
ser, which rests
on the apex of the petrous portion of the temporal bone. The cells
of this ganglion give origin to a short process which soon divides into
two branches, one of which passes centrally, the other peripherally
(Fig. 247). The centrally directed branches collectively form the
so-called large or sensor root; the peripherally directed branches
collectively constitute the three main divisions of the nerve: viz., the

Fig. 247. — Scheme of Origin and Constitution of the
Trigeminal Nerve, i. Centrally coursing fibers. 2,3,
4. Peripherally coursing fibers of the cells of the ganglion
of Gasser. R, N. Nuclei of origin of the efferent fibers.
6. Motor root. Central terminations of the large root.

538

TEXT-BOOK OF PHYSIOLOGY.

ophthalmic, the superior maxillary, and the inferior maxillar}^
Branches of the carotid plexus of the sympathetic enter the nerve
in the neighborhood of the ganglion of Gasser and accompany its
branches.

Distribution. — i. The Central Branches. — The axons of the
large root pass backward into the pons Varolii on its lateral aspect.
After entering the pons each axon divides into two branches, one
of which passes upward a short distance, the other passes down-
ward, descending as far as the second cervical segment. Both
branches give off a number of collaterals, each of which terminates
in fine end-tufts around nerve-cells in the substantia gelatinosa.

2. The Peripheral Branches.
— -The peripheral axons emerge
from the peripheral end of the
ganglion of Gasser in three dis-
tinct and separate branches,
each of which is distributed to a
different region of the face and
head.

I . The ophthalmic branch passes
forward and subdivides
into three large branches,
the frontal, the lachrymal,
and the nasal. The ulti-
mate termination of the
branches of these nerves
is as follows: viz., the con-
junctiva and skin of the
upper eyelid, the cornea,
the skin of the forehead
and the nose, the lachrymal
gland and caruncle, and
the mucous membrane of
the nose (Fig. 248).

2. The superior maxillary branch passes forward through the fora-

men rotundum, crosses the spheno-maxillary fossa, enters the
infra-orbital canal, and emerges at the infra-orbital foramen. In
its course it gives off a number of branches which are distributed
as follows: viz., to the integument and conjunctiva of the lower
lid, the nose, cheek, and upper lip, the palate, the teeth of the
upper jaw, and the alveolar processes (Fig. 249).

3. The inferior maxillary branch passes through the foramen ovale^

after which it subdivides into three branches — the auriculo-tem-
poral, the lingual, and the inferior dental. The ultimate
branches are distributed as follows: viz., the external auditory

Fig. 248. — Ophthalmic Branch of the
Fifth, i. Ganglion of Gasser. 2.
Ophthalmic division of the fifth. 3.
Lachrymal branch. 4. Frontal branch.
5. External frontal. 6. Internal frontal.
7. Supra-trochlear
9. External nasal.
— {Hirschfeld . )

8. Nasal branch.
EG. Internal nasal.

THE CRANIAL NERVES.

539

meatus, the side of the head, the mucous membrane of the
mouth, the anterior portion of the tongue, the arches of the
palate, the teeth and alveolar process of the lower jaw and the
integument of the lower part of the face (Fig. 250).
Cortical Connections. — The nerve-cells around which the end-
tufts of the centrally coursing axons ramify collectively constitute
the "sensor end-nuclei" of the trigeminal nerve. From these cells
new axons arise which cross the median line, enter the fillet or
lemniscus, and ascend directly to the sensor area of the cerebral
cortex.

Properties. — Irritative pathologic lesions, e. g., pressure by
tumors, aneurysms, neuritis, degenerative changes in the ganglion

Fig. 249. — I. Superior maxillary nerve. 2, 3, 4, 5. Dental nerves. 6. Spheno-
palatine ganglion. 7. Vidian nerve. 8. Large superficial petrosal. 9. Carotid
branch of large petrosal. 10. Oculo-motor. 11. Superior cervical ganghon. 12.
Carotid branches of this ganglion. 13. Facial. 14. Glosso-pharyngeal. 15.
Jacobson's nerve, and 16, 17, 18, 19, branches to the sympathetic, fenestra
rotunda, Eustachian tube. 20. Deep external petrosal. 21. Deep internal
petrosal.

cells, or lesions which in any way gradually impair the physical of
chemic integrity of the nerve-fibers, give rise to a variety of painful
sensations referable to the seat of the lesion or to one or more regions
in the peripheral distribution of the nerve. Many of the various
forms of trigeminal neuralgia are caused by lesions of this character.
Exposure of the dental nerves from caries of the teeth, the presence
of minute foreign bodies in the conjunctiva, operative procedures in
the nasal chambers, all testify to the extreme sensibility of the nerve.
Division of the large root within the cranium is followed at once by
complete abolition of all sensibility in the head and face to which
its branches are distributed. The skin and mucous membranes, the
eye, nose, or teeth may be experimentally injured without any evi-

540 TEXT-BOOK OF PHYSIOLOGY.

dences of pain on the part of the animal. Various reflexes, e. g.,
those of mastication, insalivation, deglutition, the afferent paths of
which are formed in part by the fifth nerve, are often seriously im-
paired. At the same time the lacrimal secretion diminishes and the
pupil contracts. The same results are observed in human beings
in whom the nerve has been divided for relief from neuralgia. Anes-
thesia or a loss of sensibility may also be caused by pathologic lesions
of the nerve-trunks or of the sensor end-nuclei.

Division of the large root at or near the ganglion of Gasser has
not infrequently been followed by an alteration in the nutrition of
the eye and nose. In the course of twenty-four hours the eye becomes
vascular and inflamed; the cornea becomes opaque; ulceration sets
in which may lead to complete destruction of the eyeball. The
mucous membrane of the nose becomes swollen, vascular, and liable
to hemorrhage on the slightest irritation. The degenerative changes
may lead to a complete loss of the sense of smell. These results were
formerly attributed to a loss of trophic influence which it was believed
the nerve exercised over these structures. Modern experimentation
and various surgical procedures have demonstrated that the nutritive
disorders are septic in origin, made possible by the anesthetic condi-
tion and by the changed vascular supply from division of the vaso-
motor fibers which join the nerve at or near the ganglion.

Origin of the Efferent or Motor Axons. — The efferent or
peripherally coursing axons serve to bring the nerve-cells from which
they arise into relation with the muscles of mastication. They arise
from nerve-cells located in the gray matter beneath the upper half
of the floor of the fourth ventricle. These cells constitute the motor
or masticatory nucleus. A group of cells known as the superior or
accessory nucleus, situated posterior to the corpora quadrigemina,
give origin to axons which descend and join the axons from the chief
motor nucleus (Fig. 247).

Distribution. — From their origin the fibers pass forward through
the pons and emerge on its lateral aspect, forming the so-called small
root of the fifth nerve. This then passes forward beneath the ganglion
of Gasser, leaves the cavity of the skull through the foramen ovale,
and joins the inferior maxillary division already described. Its
axons are ultimately distributed to the muscles of mastication: viz.,
the masseter, the temporal, the external and internal pterj^goids, the
mylohyoid, and the anterior portion of the digastric. A few axons
are also distributed to the tensor tympani muscle (Fig. 250).

Cortical Connections. — The nuclei of origin of the small root
are in histologic and physiologic relation with the lower third of the
motor area of the cerebral cortex. Nerve-cells in this region give
off axons which enter the pyramidal tract, descend through the in-
ternal capsule and the crus cerebri, after which they cross to the

THE CRANIAL NERVES.

541

opposite side. Their end-tufts arborize around the cells of nuclei in
the medulla oblongata.

Properties. — Stimulation of the small root gives rise to convulsive
movements of the muscles of mastication. Division of the nerve is
followed by a paralysis of these muscles. Contraction or paralysis of

Fig. 250. — Inferior Maxillary Branch of the Trigeminal Nerve, i. Branch
to the masseter muscle. 2. Filament of this branch to the temporal muscle. 3.
Buccal branch. 4. Branches anastomosing with the facial nerve. 5. Filament
from the buccal branch to the temporal muscle. 6. Branches to the external
pterygoid muscle. 7. Middle deep temporal branch. 8. Auriculo-temporal
nerve. 9. Temporal branches. 10. Auricular branches. 11. Anastomosis with
the facial ner\'e. 12. Lingual branch. 13. Branch of the small root to the
mylo-hyoid muscle. 14. Inferior dental nerv-e, with its branches (15, 15). 16.
Mental branch. 17. Anastomosis of this branch with the facial nerve. — {Hirsch-
jeld.)

the tensor tympani muscle would also be observed under the same
conditions.

Functions. — The fifth nerve, by virtue of its transmitting nerve
impulses from the periphery to the cerebral corte.x, where they evoke
sensation, endows all the parts to which it is distributed with sensi-
bihty; it also endows the muscles of mastication with motility.

542

TEXT-BOOK OF PHYSIOLOGY.

Throusfh the relation of its central end-tufts with the motor nuclei in
the medulla and pons, it assists in the reflex acts of mastication and
insalivation.

SIXTH PAIR. THE ABDUCENS.

The sixth cranial nerve, the abducens, consists of peripherally
coursing axons which serve to bring the nerve-cells from which they
arise into relation with the external rectus muscle.

Origin. — The axons arise from a group of cells located in the
gray matter beneath the upper half of the floor of the fourth ventricle.

It is quite probable that a few
fibers in each nerve-trunk come
from the nucleus on the opposite
side of the middle line.

Distribution. — The nerve-
fibers pass forward from their
origin through the gray and
white matter and emerge through
the groove between the medulla
oblongata and the pons Varolii
just external to the anterior
pyramid. The nerve then passes
through the sphenoid fissure into
the orbit cavity, where it is
distributed to the external rectus
muscle (Fig. 251). In its course
the nerve receives filaments from
the carotid plexus of the S3'm-
pathetic.

Cortical Connections. —
The nucleus of the sixth nerve
is in histologic and physiologic
connection \vdth the motor area
of the cerebral cortex. From
are given off which enter the
the internal capsule and crus

Fig

251. — Distribution of the Motor

OCULI EXTERNUS OR AbDUCENS. I.

Trunk of the motor oculi communis,
vnXh its branches (2, 3, 4, 5, 6, 7). 8.
Motor oculi externus, passing to
the external rectus muscle. 9. Fila-
ments of the motor oculi externus
anastomosing with the sympathetic.
10. CiUary nerves. — {Hirschfeld.)

nerve-cells in this region axons
pyramidal tract, descend through
cerebri, after which they cross to the opposite side, where their
end-tufts arborize around the cells of the nucleus already described.
Properties. — Stimulation of the nerve is followed by spasmodic
contraction of the external rectus muscle and external deviation of
the eyeball. Division of the nerve is followed by paralysis or relaxa-
tion of the muscle. As a result of the unopposed action of the
internal rectus the anterior pole of the eyeball is turned toward the
middle Hne (internal strabismus). In consequence of this deviation
there is homonymous diplopia. The images are on the same level

THE CRANIAL NERVES. 543

and parallel. The image of the paralyzed eye lies external to that
of the normal eye.

Function. — The function of this nerve is to transmit nerve im-
pulses to the external rectus muscle and excite it to contraction.

SEVENTH PAIR. THE FACIAL.

The seventh cranial nerve, the facial, consists of peripherally
coursing nerve-fibers, which serve to bring the nerve-cells from
which they arise into relation with most of the superficial muscles of
the head and face.

The muscles supplied by this nerve, as stated by the general
anatomists, are as follows: The occipito-frontalis, corrugator super-
cilii, orbicularis palpebrarum, levator labii superioris, alaeque nasi,
zygomatici, the pyramidalis nasi, the compressor nasi, the depressor
alae nasi, levator anguli oris, buccinator, orbicularis oris, depressor
anguli oris, depressor labii inferioris, the levator menti, the posterior
belly of the digastric, the stylo-hyoid, and the platysma myoides.

Origin. — The ncrve-tibers or axons composing the seventh nerve
arise for the most part from a nucleus of large multipolar nerve-cells
situated about five millimeters beneath the upper half of the floor
of the fourth ventricle toward the middle line.

From this nucleus, which is about four millimeters long, axons
emerge which at first pass inward and backward as far as the epen-
dyma of the ventricle ; they then turn on themselves, forming an arch
that encloses the nucleus of the sixth nerve; they then course down-
ward and outward, emerging from the pons at its lower border between
the olivary and restiform bodies. As the axons approach the floor
of the ventricle collateral branches are given off which, crossing the
median line, arborize around the nerve-cells of the opposite facial
nucleus.

Clinical observations and histologic investigations also render it
probable that the fibers distributed to the occipito-frontalis, the cor-
rugator supercilii, and the upper half of the orbicularis palpebrarum,
are derived from the oculo-motor nucleus, and, descending the
posterior longitudinal bundle, enter the trunk of the facial as it
turns to pass forward through the pons. It is also probable, for
similar reasons, that the fibers distributed to the orbicularis oris are
derived from the hypoglossal nucleus.

Cortical Connections. — The nucleus of the facial nerve is in
histologic and physiologic connection with the facial region of the
general motor area of the cerebral cortex. From the cells of this
region axons descend through the pyramidal tract, the internal cap-
sule, and the crus cerebri, beyond which they cross to the opposite
side and arborize around the cells of the nucleus already described.

544

TEXT-BOOK OF PHYSIOLOGY.

Distribution. — From its superficial origin tlie trunk of tlie nerve
passes into the internal auditory meatus beside the auditory nerve.
After passing forward and outward for a short distance through the
bone above and between the cochlea and vestibule, the nerve makes

Fig. 252. — Superficial Branches of the Facial and the Fifth. — i. Trunk of the
facial. 2. Posterior auricular nerve. 3. Branch which it receives from the
cervical plexus. 4. Occipital branch. 5, 6. Branches to the muscles of the ear.
7. Digastric branches. 8. Branch to the stylo-hyoid muscle. 9. Superior ter-
minal branch. 10. Temporal branches. 11. Frontal branches. 12. Branches
to the orbicularis palpebrarum. 13. Nasal or suborbital branches. 14. Buccal
branches. 15. Inferior terminal branch. 16. Mental branches. 17. Cervical
branches. 18. Superficial temporal nerve (branch of the fifth). 19, 20. Frontal
nerves (branches of the fifth). 21, 22, 23, 24, 25, 26, 27. Branches of the fifth.
28, 29, 30, 31, 32. Branches of the cervical nerves. — {Hirschjeld.)

a sharp bend, forming the genu facialis, turns backward and enters
the aqueduct of Fallopius, the general course of which it follows as
far as the stylo-mastoid foramen. After emerging from this foramen
the nerve passes downward and forward as far as the parotid gland,.

THE CRANIAL NERVES.

545

within which it terminates by dividing into two main branches, the
temporo-facial and the cervico-facial, the uhimatc branches of which
are distributed as previously stated to the superficial muscles of the
head and face (Fig. 252).

The Pars Intermedia or Nerve of Wrisberg. — The facial nerve
at the genu facialis, the point where it turns backward to enter the
aqueduct of Fallopius, presents a shght enlargement, grayish in color,
and in which nerve-cells are contained. This enlargement is known
as the geniculate ganglion. The cells of this ganglion, originally
bipolar, present single axons which soon divide into centrally and
peripherally coursing branches. The former collectively constitute
the pars intermedia or nerve of Wrisberg, which, entering and passing
through the pons, termi-
nates around the sensor
end-nucleus of the glosso-
pharyngeal nerve ; the latter,
the peripherally directed
branches, enter the sheath
of the facial and accompany
it as far as a point about
five millimeters above the
stylo-mastoid foramen.

From its mode of origin
the nerve of Wrisberg can
not be regarded as an
integral part of the facial
nerve proper, but is to be
regarded as an independent
sensor nerve. As to the
true function and relation
of this nerve there is much
conflict of opinion.

Branches of the Fa-
cial.— In the aqueduct of

Fallopius the facial gives off the following branches: the greater
and lesser petrosals, the stapedius, and the chorda tympani (Fig.

253)-

1 . The greater petrosal nerve is given off near the geniculate ganglion.

It then passes forward into the spheno-maxillary fossa and ter-
minates in the spheno-palatine ganglion by an arborization of
its fibers around the ganglion cells.

2. The lesser petrosal nerve is given off at a point somewhat external

to the preceding. It leaves the skull by a small foramen and
terminates in the otic ganghon by an arborization of its fibers
around the ganglion cells.
35

Fig. 253. — Chorda Tympani Nerve, i, 2, 3,
4. Facial nerve passing through the aquae-
ductus Fallopii. 5. Ganglioform enlarge-
ment. 6. Great petrosal nerve. 7. Spheno-
palatine ganghon. 8. Small petrosal nerve.
9. Chorda tympani. 10, 11, 12, 13. Various
branches of the facial. 14, 14, 15. Glosso-
pharyngeal nerve. — {Hirschjeld.)

546 TEXT-BOOK OF PHYSIOLOGY.

3. The stapedius branch leaves the aqueduct of Fallopius somewhat

further down by a small foramen, enters the pyramid of the
middle ear, and is finally distributed to the stapedius muscle.

4. The chorda tympani is given off from the facial at a point about

five millimeters above the stylo-mastoid foramen. It then passes

upward and forward and enters the tympanum through the iter

chordae posterius, crosses the tympanic membrane between the

malleus and incus, leaves the tympanum by the iter chordge

anterius or canal of Huguier, and finally joins the lingual branch

of the fifth. Some of its fibers can be traced to the dorsum of

the tongue, others to the submaxillary and sublingual gangha,

where they terminate in tufts around the ganglion cells.

Properties. — Electric stimulation of the trunk of the nerve after

its emergence from the stylo-mastoid foramen produces convulsive

movements in all the muscles to which its branches are distributed.

The same results follow stimulation of the intracranial portion of the

nerve in an animal recently killed.

Irritative pathologic lesions — e. g., tumors, aneurysms, etc. —
situated along the course of the nerve or at its nuclear origin, fre-
quently give rise to spasmodic movements of the facial muscles which
may be tonic or clonic in character.

Division of the facial nerve after its emergence from the stylo-
mastoid foramen is followed by a complete relaxation or paralysis
of the superficial facial muscles. The same result follows compres-
sion of the nerve-trunk in any part of its intracranial course.

The phenomena presented by an individual suffering from division
or compression of the facial nerve, and which collectively constitute
facial paralysis, are as follows: a relaxed and immobile condition of
the side of the face corresponding to the lesion ; separation of the eye-
lids from paralysis of the orbicularis palpebrarum and the unopposed
contraction of the levator palpebrae muscles; abolition of the act of
winking; drooping of the angle of the mouth; an escape of saliva
from the mouth; contraction of the muscle and distortion of the
opposite side of the face; on attempting to laugh or talk the dis-
tortion of the face is increased; during mastication the food accu-
mulates between the teeth and cheek, from paralysis of the buccina-
tor; articulation is impaired from paralysis of the orbicularis oris
muscle, the labial sounds especially being imperfectly produced.

Properties of the Branches Given off in the Aqueduct of
Fallopius. — The great petrosal nerve is in all probability composed
of efferent fibers (vaso-dilatator and secretor) which leave the pons
by way of the nerve of Wrisberg, or pars intermedia, to be distributed
around the cells of the spheno-palatine ganglion; for stimulation
either of this nerve or of the ganglion is followed by the same results :
viz., dilatation of the blood-vessels of, and secretion from, the mucous

THE CRANIAL NERVES. 547

membrane of the nose, soft palate, upper part of the pharynx, roof
of mouth, gums, and upper hp.

The small petrosal nerve is also composed of efferent fibers;
shortly after leaving the facial it is joined by a small nerve, derived
from Jacobson's branch of the glosso-phar^'ngeal, which is also effer-
ent in function; for stimulation of Jacobson's nerve as well as stimu-
lation of the otic ganglion is followed by the same result: viz., dilata-
tion of the blood-vessels of, and secretion from, the mucous membrane
of the cheek, lower lip, and gums, and of the parotid and the orbit
glands.

The stapedius nerve, distributed directly to the stapedius muscle,
is motor in function.

The Chorda Tympani. — Stimulation of the chorda tympani nerve
in the tympanic cavity produces dilatation of the blood-vessels of,
and an increased production and discharge of saliva from, the sub-
maxillary and sublingual glands.

Division of this nerve is followed by a contraction of the blood-
vessels and a diminution of the secretion. From these results it is
certain that the chorda tympani contains both vaso-dilatator and secre-
tor fibers. Nicotin applied to the submaxillary and sublingual gang-
lia abolishes the effects of stimulation of the chorda tympani. It
does not prevent the same effects when the ganglia themselves are
stimulated. It is clear, therefore, that the vaso-dilatator and secretor
fibers arborize around the cells of the ganglia and are not distributed
directly to the gland structures. It is highly probable that the efferent
fibers in the chorda tympani emerge from the pons by way of the
pars intermedia.

Division of the chorda in the tympanum is also followed by a loss
of taste in the anterior two-thirds of the tongue. For this and other
reasons the chorda tympani has long been regarded as the nerve of
taste for this region. The specific physiologic stimulus to the chorda
tympani nerve is organic matter in solution acting on the peripheral
terminations of the nerve in the mucous membrane of the tongue.
The exact pathway for these afferent or gustatory fibers beyond the
geniculate ganglion has long been a subject of much discussion.
According to some observers these fibers enter the great petrosal
nerve, pass forward as far as the spheno-palatine ganglion, then into
the superior maxillary division of the trigeminal, and so to the brain.
According to others, these fibers pass into the pars intermedia, into
the pons, where they terminate around the sensor end-nucleus of
the glosso-pharyngeal. The evidence for and against either of these
two views is most conflicting and insufficient to justify positive state-
ments one way or the other. To the writer the weight of evidence
seems to favor the view that the gustatory fibers have their origin in
the geniculate ganglion ; that they pass centrally through the pars in-

548

TEXT-BOOK OF PHYSIOLOGY.

termedia; that they are similar in function to the glosso-pharyngeal ;
and that they are indeed but aberrant branches of this nerve.

EIGHTH PAIR. THE AUDITORY.

The eighth cranial nerve, the auditory, consists of the centrally
coursing axons of neurons which connect the essential organ of

hearing with sensor end-nuclei
,.- lo in the pons Varolii. This nerve

,--'' consists of two portions: viz., a

cochlear or auditory and a ves-
tibular or equilibratory.

Origin. — The axons compris-
ing the cochlear portion have
their origin in the bipolar nerve-
cells of the spiral ganglion located
in the spiral canal near the base
of the osseous lamina spiralis
(Fig. 254). From this origin
they pass centrally into the cen-
tral canal of the modiolus, at the
base of which they emerge in
well-defined bundles and enter
the internal auditory meatus.
Dendritic processes from these
cells pass peripherally to termi-
nate on the ciliated epithelial cells
of the organ of Corti.

The axons comprising the
vestibular portion have their
origin in the bipolar nerve-cells
of the ganglion of Scarpa located
in the internal auditory meatus.
From this origin they pass cen-
trally in connection with the
cochlear portion. Dendritic pro-
cesses from these cells pass per-
ipherally into the internal ear,
where they terminate on epithe-
lial cells situated on the inner
surface of the utricle and saccule
and in the ampullas of the semicircular canals.

The common trunk of the auditory nerve, consisting of both
cochlear and vestibular divisions after emerging from the internal
auditory meatus, passes backward, inward, and downward as far

Fig. 254. — Origin and Termination
OF THE Auditory Nerve. i.
Cochlea. 2. Spiral ganglion (Corti).
3. Cochlear nerve. 4. Ventral
acoustic nucleus. 5. Lateral acoustic
nucleus. 6. Semicircular canals. 7.
Ganglion of Scarpa. 8. Vestibular
nerve. 9. Dorso-external nucleus
(Deiters). 10. Dorso-internal nu-
cleus.— {After Moral and Doyon.)

THE CRANIAL NERVES. 549

as the lateral aspect of the pons where the two divisions again
separate.

The cochlear nerve, the external root, passes to the outer side
of the restiform body and enters the ventral acoustic nucleus and the
lateral acoustic nucleus, around the cells of which its end-tufts
arborize. The vestibular nerve, the internal root, passes on the
inner side of the restiform body to the dorsal portion of the pons,
where, after bifurcating, the end-tufts of the axons arborize around
the dorso-internal or chief auditory nucleus and the dorso-external
or Deiters' nucleus. Some of the fibers of the vestibular branch
descend through the pons and medulla as far as the cuneate nucleus.

Cortical Connections. — The cochlear nerve is ultimately con-
nected with the cerebral acoustic area, in the temporal lobe of the
opposite side through the intermediation of the auditory tract. This
tract is complex and involved. In a general way it may be said to
consist in part of fibers which come direct from the cochlear branch.
After passing through the ventral nucleus and the trapezoid body
they cross the median line, enter the lemniscus or fillet, and finally
terminate in the pre- and post-geminal bodies. In their course they
give off collateral branches to these various nuclei through which
they pass. Other fibers taking their origin from cells in these various
nuclei proceed to the cortex where they terminate.

Properties. — Stimulation of the cochlear nerve is unattended by
either motor or sensor phenomena. Division of the nerve is fol-
lowed by a loss of the sense of hearing. Irritative pathologic lesions
give rise to sensations of sound of var}^'ing character and intensity.
Degeneration of the nerve or destruction by tumors, etc., will also
be followed by a loss of the sense of hearing.

Experimental lesions of the semicircular canals involving a
destruction of the physiologic relations of the vestibular nerve are
followed by a loss of the coordinating and equihbratory power.
Disordered movements, such as rotation to the right or left, somer-
saults backward and forward, follow destruction of these canals.
Pathologic lesions in the peripheral distribution of the nerve are
attended in man by disturbances of equiHbrium; e. g., vertigo, a sense
of swaying, pitching, and staggering.

Functions. — The function of the cochlear nerve is to convey
nerve impulses from its origin to the pons, from which they are
transmitted by the auditory tract to the acoustic area in the cerebral
cortex. The specific physiologic stimulus to the development of
these impulses is the impact of atmospheric undulations on the t\Tn-
panic membrane, received and transmitted by the chain of bones
to the structures of the internal ear, — the organ of Corti, — with which
the peripheral terminations of the nerve are connected. The function
of the vestibular nerve is the transmission of nerve impulses to the

S50 TEXT-BOOK OF PHYSIOLOGY.

pons, whence they are transmitted to the cortex of both the cerebrum
and cerebellum and to other centers. The specific physiologic stim-
ulus is supposed to be a variation in pressure in the ampullae of the
semicircular canals caused by movements of the endolymph induced by
changes in the position of the head and body. The impulses carried
by the vestibular nerve give rise reflexly to certain adaptive and pro-
tective movements by which the equilibrium of the body in both,
dynamic and static conditions is maintained.

NINTH NERVE. THE GLOSSO-PHARYNGEAL.

The ninth cranial nerve, the glosso-pharyngeal, consists, as shown
by both histologic and experimental methods of research, of both
afferent and efferent nerA^e-fibers, of which the former, however, are
by far the more abundant. Near its exit from the cavity of the
skull the nerve presents two ganglionic enlargements known "as the
petrosal and jugular ganglia.

Origin of the Afferent Fibers. — The afferent fibers serve to
bring certain end-nuclei in the medulla oblongata into anatomic and
physiologic relation with portions of the mucous membrane of the
tongue, pharynx, and middle ear. The afferent fibers are axons of
the monaxonic cells of the petrosal and jugular ganglia. The single
axon from each of these cells soon divides into two branches, one
of which passes centrally, the other peripherally. The centrally
directed branches collectively form the so-called roots, four or five
in number, which enter the medulla between the olivary and resti-
form bodies. The peripherally directed branches collectively form
the two main divisions, from the distribution of which, to the tongue
and pharvmx, the nerve takes its name.

Distribution. — The axons of the centrally directed branches
after entering the medulla pass toward its dorsal aspect, where they
bifurcate, give off collateral branches, and terminate in fine end-
tufts in the immediate neighborhood of tw^o groups of nerve-cells,.
the sensor end-nuclei. The axons of the peripherally directed
branches, after emerging from the base of the skull through the
jugular foramen, pass forward and inward under cover of the stylo-
pharyngeal muscle; winding around this muscle they divide into
terminal branches which are distributed to the mucous membrane of
the posterior one-third of the tongue, pharynx, soft palate, uvula,
and tonsils fFig. 257).

Origin of the Efferent Fibers, — The efferent fibers serve to
bring the nerve-cells from w^hich they arise into connection with a
portion of the musculature of the fauces and pharynx. These nerve-
cells are located in the lateral portion of the jormatio reticularis at
some distance below the floor of the fourth ventricle. They consti-

THE CRANIAL NERVES. 551

lute the upper portion of a collection of cells known as the nucleus
cuiihii^uns.

Distribution. — From this origin the efferent fibers pass dorsally
to near the sensor end-nuclei, then turn outward and forward and
finally emerge from the medulla in intimate association with the
afferent fibers. They are ultimately distributed to the stylo-pharyn-
geal and to the middle constrictor muscles of the pharynx. In addi-
tion to the foregoing efferent fibers the glosso-pharyngeal nerve
contains at its emergence from the medulla both vaso-motor and
secretor fibers.

Jacohsori's Nerve. — This is a small branch which leaves the
glosso-pharyngeal at the petrous ganglion. After passing through a
small canal in the base of the skull it enters the tympanic cavity,
within which it gives off branches to the great and lesser petrosal
nerves, to the mucous membrane of the foramen ovale, the foramen
rotundum, and to the Eustachian tube.

Cortical Connections. — The motor nucleus is doubtless con-
nected with the general motor area of the cortex through fibers de-
scending in the pyramidal tract. The exact location of the cortical
area for the pharynx is not wtII determined, but is most likely to be
found in the lower part of the general motor area near the termination
of the Rolandic fissure. The cortical connections of the afferent
tract are unknown.

Properties. — Electric stimulation of the glosso-pharyngeal trunk
calls forth avidence of pain and contraction of the stylo-pharyngeal
and middle constrictor muscles. Division of the nerve abolishes
sensibility in the mucous membrane to which it is distributed, impairs
the sense of taste in the posterior third of the tongue, and gives rise
to paralysis of the above-mentioned muscles.

Stimulation of Jacobson's nerve is followed by dilatation of the
blood-vessels of, and secretion from, the mucous membrane of the
lower Hp, cheek, and gums, and from the parotid gland. Division
of the nerve is followed by the opposite results. The course of the
fibers which give rise to these results is by way of the lesser petrosal
to the otic ganglion, around the cells of which the fibers arborize.
From the cells of this ganglion non-medullated fibers pass to the
blood-vessels and gland cells.

Functions. — The afferent fibers of the glosso-pharyngeal trans-
mit nerve impulses from the parts to which they are distributed to
the cerebral cortex, where they evoke sensations of pain and sensations
of taste; they also assist in all probability in the performance of
certain reflexes connected with deglutition. The efferent fibers trans-
mit impulses to muscles, exciting them to activity, and to the otic
ganglion, which in turn dilates blood-vessels and excites secretion.

552 TEXT-BOOK OF PHYSIOLOGY.

TENTH NERVE. THE PNEUMOGASTRIC OR VAGUS. -

The tenth cranial nerve, the pneumogastric or vagus, consists,
as shown by histologic methods of research, of both afferent and
efferent fibers, independent of those derived in its course from adjoin-
ing motor or efferent nerves. Near the exit of the nerve from the
cavity of the cranium it presents two ganglionic enlargements known
respectively as the ganglion of the root (the jugular) and the ganglion
of the trunk (the plexiform).

Origin of the Afferent Fibers. — The afferent fibers take their
origin in the monaxonic cells of the ganglia on the root and trunk.
The single axon from each of these cells soon divides into two
branches, one of which passes centrally, the other peripherally. The
centrally directed branches collectively form the so-called roots, ten
to fifteen in number, which enter the medulla between the restiform
body and the lateral column. The peripherally directed branches
collectively form a portion of the common trunk of the nerve.

Distribution. — The axons of the centrally directed branches
after entering the medulla pass toward its dorsal aspect, where they
bifurcate, give off collaterals, and terminate in fine end-tufts in the
immediate neighborhood of two groups of nerve- cells, the sensor
end-nuclei.

The axons of the peripherally directed branches unite to form a
portion of the common trunk, which, as it descends the neck and
enters the thorax and abdomen, gives off a number of branches which
are ultimately distributed to the mucous membrane of the esophagus,
larynx, lungs, stomach, and intestine, and also to the heart. The
afferent fibers thus serve to bring into anatomic and physiologic
relation the mucous membrane of these organs with certain sensor
end-nuclei in the medulla oblongata.

Origin of the Efferent Fibers. — The efferent fibers take their
origin from nerve-cells located in the lateral portion of the formatio
reticularis at some distance below the floor of the fourth ventricle.
These cells constitute the lower portion of the nucleus ambiguus.

Distribution. — From their origin the efferent axons pass dor-
sally to near the sensory end-nuclei, then turn outward and forward,
and finally emerge from the medulla in close association with the
afferent branches. They are ultimately distributed to the levator
palati, azygos uvulae, and tensor palati muscles; to the superior and
inferior constrictor muscles of the pharynx, and to the muscles of
the esophagus; to the muscle-fibers of the stomach and perhaps the
intestines; and to the non-striated muscle-fibers of the bronchial
tubes. Among the efferent fibers are some which are distributed to
the gastric glands and to the pancreas.

The efferent fibers thus serve to brins: the nerve-cells from which

THE CRANIAL NERVES. 553

they arise into anatomic and physiologic connection with a portion of
the musculature of the alimentary canal and its diverticulum, the
lung.

Communicating Branches. — At or near the ganglia of the vagus
it receives communicating branches from the eleventh nerve, the
spinal accessory, the facial, the hypoglossal, and the anterior branches
of the two upper cervical nerves. Owing to this manifold origin of
the efferent tibcrs in the trunk and peripheral branches of the vagus,
it is, in some instances, diificult, if not impossible, to determine to
which of these nerves a given muscle contraction is to be referred.

Vagal Branches. — As the vagus passes down the neck it gives
off the following main branches (Fig. 255) :

1. The pharyngeal nerves which, after entering into the formation of

the pharyngeal plexus, are distributed to the mucous membrane
and to the muscles of the pharynx; e. g., superior and inferior
constrictors, the tensor palati, levator palati, and the azygos

2. The superior laryngeal nerve which, entering the larynx through

the thyro-hyoid membrane, is distributed to the mucous mem-
brane lining the interior of the larynx and to the crico-thyroid
muscle. From the superior laryngeal and the main trunk small
branches are given off which unite to form a single nerve, the
so-called depressor nerve. It is distributed to the heart-muscle.
Though this anatomic arrangement is not found in man, there
are many reasons for believing that analogous libers are present
in the vagus trunk of man and other animals.

3. The injerior laryngeal nerve which is distributed ultimately to all

the muscles of the larynx except the crico-thyroid and to the
inferior constrictor of the pharynx.

4. The cardiac nerves which, after entering into the formation of the

cardiac plexus, are distributed to the heart.

5. The pulmonary nerves distributed to the mucous membrane of the

bronchial tubes and their ultimate terminations, the lobules and
air-cells, as well as to their non-striated muscle-fibers.

6. The gastric and intestinal nerves, distributed to the mucous mem-

brane and muscular walls of the stomach and intestines. Other
fibers in all probabiHty pass to the Hver, spleen, kidney, and
suprarenal bodies.

Properties of the Pneumogastric or Vagus Nerve and its
Various Branches. — Faradization of the vagus nerve close to the
medulla oblongata gives rise to sensations of pain and to contraction
of the musculature of a portion of the alimentary tract: viz., the
palate, pharynx, esophagus, stomach, and possibly of the intestine
and of the pulmonary apparatus. Division of the nerve is followed
by a loss of sensibility in the mucous membrane of the alimentary

554

TEXT-BOOK OF PHYSIOLOGY.

tract and of the pulmonary apparatus, together with a loss of motility
of the structures above mentioned.

^iG. 255— Distribution of the Pneumogastric. — i. Trunk of the left pneumo-
gastric. 2. Ganglion of the trunk. 3. Anastomosis with the spinal accessory.
4. Anastomosis with the subhngual. 5. Pharyngeal branch (the auricular branch
is not shown in the figure). 6. Superior laryngeal branch. 7. External larj^ngeal
nerve. 8. Laryngeal plexus, q, 9. Inferior laryngeal branch. 10. Cersdcal car-
diac branch. II. Thoracic cardiac branch. 12, 13. Pulmonary branches. 14. Lin-
gual branch of the fifth. 15. Lower portion of the subhngual. 16. Glosso-pharj'n-
geal. 17. Spinal accessory'. 18,19,20. Spinal nerves. 21. Phrenic nerve. 22,23.
Spinal nerves. 24, 25, 26, 27, 28, 29, 30. Sympathetic gangha. — {Hirschjeld.)

Stimulation of the trunk of the nerve in different parts of its
course produces a variety of results dependent to some extent on the
presence of anastomosing branches from adjoining nerves.

THE CRANIAL NERVES. 555

The Pharyngeal Nerves. — Faradization of the pharyngeal nerves
consisting of both afferent and efferent fibers, gives rise to sensations
of pain, contraction of the pharyngeal muscles, and perhaps to vomit-
ing. Division of these nerves is followed by a loss of sensibility in
the parts to which they are distributed and by paralysis of the muscles
with a consequent impairment of deglutition.

The Superior Laryngeal Nerve. — Faradization of the superior
laryngeal nerve gives rise to sensations of pain, and to contraction of
the crico-thyroid muscle. Through reflected impulses it causes con-
traction of the muscles of deglutition, and of the muscles concerned
in the act of coughing; inhibition of the inspiratory movement and
arrest of respiration in the condition of expirator}' standstill, with
perhaps a tetanic contraction of the expiratory muscles; and con-
traction of the laryngeal muscles with closure of the glottis. Periph-
eral stimulation of this nerve — e. g., the contact of foreign particles —
gives rise to a similar series of phenomena. Division of these nerves
is followed by a loss of sensibility in the laryngeal mucous membrane,
paralysis of the crico-thyroid muscle with a consequent lowering of
the pitch, and a diminution in the clearness of the voice. In conse-
quence of the loss of the sensibility there is an inability to perceive
the entrance of foreign bodies into the lar}'nx.

The Depressor Nerve. — Stimulation of the peripheral end of the
depressor nerve is without effect; stimulation of the central end re-
tards and even arrests the heart's pulsations and lowers the general
blood-pressure. These two effects, though associated, are neverthe-
less independent of each other. If the vagus nerves be divided on
both sides between the origin of the depressor and the origin of the
cardiac nerves, and the former stimulated, there will be a fall of
pressure without retardation of the heart. The effect on the heart
is attributed to a stimulation of the cardio-inhibitory mechanism in
the medulla oblongata.

The fall of general blood-pressure was formerly attributed to a
sudden dilatation of the splanchnic blood-vessels alone, in conse-
quence of a depression of that portion of the general vaso-motor center
which maintains through the splanchnic nerves a tonic contraction of
their walls. It has been satisfactorily demonstrated that this is not
the sole cause; for after division of the splanchnic nerves, stimulation
of the depressor causes a still further fall of from 30 to 40 per cent,
in the general pressure (Porter and Beyer). Evidently, not anyone,
but all portions of the vaso-motor center are subject to the effects of
depressor stimulation.

The Inferior Laryngeal Nerves. — Faradization of the inferior
laryngeal nerves produces effects which vary in accordance with the
strength of the stimulus, with different animals, and with the same
animal at different periods of life. In the adult dog and in man, the

556 TEXT-BOOK OF PHYSIOLOGY.

glottis is kept widely open for respiratory purposes by the tonic con-
traction of the abductor muscles (the crico-arytenoids) ; for phonatory
purposes the glottis is closed and the vocal membranes approximated
by the contraction of the adductor muscles. It has been shown that
these opposed groups of muscles have independent nerve-supplies;
that two sets of fibers in the common trunk can be separated and
stimulated independently of each other. Feeble stimulation of the
common trunk produces a still further abduction of the vocal cords.
With an increase in the strength of the stimulus, however, the reverse
obtains: namely, adduction which increases until the glottis is com-
pletely closed. Division of the nerves is followed by paralysis of both
the phonatory and respiratory muscles, the abductors and adductors,
with the result of seriously impairing both phonation and respiration
and not infrequently causing death. The fibers of the inferior laryn-
geal nerve are derived from the eleventh nerve, the spinal accessory.

The Cardiac Nerves. — Faradization of the trunk of the vagus or
of the peripheral end of the divided nerve gives rise to a diminution
in the frequency and force of the heart's contractions; and if the stim-
ulation be sufficiently powerful, completely arrests it in the phase of
diastole. To these results the term inhibition is applied. Division
of the vagi or of the cardiac branches is followed by an increase in
the number of the contractions from loss of inhibitor influences.
The inhibitor fibers of the vagus are generally believed to be derived
from the spinal accessory, though this has been questioned. Accord-
ing to the recent investigations of Schaternikoff and Friedenthal,
they come direct in the vagus, from a nucleus near the vagal motor
nucleus in the medulla, the spinal accessory sending no branches to
the heart. In the frog and other batrachia the vagus contains also
accelerator or augmentor fibers derived from the sympathetic ; hence
stimulation, especially if feeble, may increase the heart's action or
may only retard, but not arrest, the heart.

The Pulmonary Nerves. — ^The pulmonary nerves, given off from
the trunk after its entrance into the thorax, do not lend themselves
readily to experimentation. Division of both vagi in the neck above
the point of exit of the pulmonary branches is followed by a decrease
in the frequency of the respiratory acts, with an increase in their depth.
At the same time there is a loss of sensibility of the mucous membrane
of the trachea and lungs and a paralysis of non-striated muscle-fibers.
Stimulation of the central end of the vagus increases the frequency,
but decreases the amplitude, of the respiratory movements. If the
stimulation be increased in intensity the respiratory movements in-
crease in frequency until the inspiratory muscles pass into the con-
dition of tetanus.

Feeble stimulation of the vagus not infrequently inhibits the
inspiratory movement and increases the expiratory until there is a

THE CRANIAL NERVES. 557

complete cessation of movement in the condition of expiratory stand-
still. The effect thus produced is similar to, if not identical with,
that produced by stimulation of the superior laryngeal nerve. This
would seem to indicate the presence in the vagus trunk of two sets
of afferent fibers coming from the lungs through the pulmonary
branches, one of which inhibits inspiration, the other expiration.

Faradization of the trunks of the pulmonary branches or stimula-
tion of their peripheral terminations in the mucous membrane of
the bronchial tubes or alveoli by the inhalation of chemic vapors
causes arrest of respiratory movements, a fall of blood-pressure, and
a reflex inhibition of the heart (Brodie).

Gastric Nerves. — Stimulation of the peripheral end of a divided
vagus nerve causes a distinct contraction of the right half of the
stomach and secretion from the gastric glands. Division of the nerve
abolishes the sensibility of the mucous membrane of the stomach,
impairs motihty, and interferes with the secretion of the gastric juice.

Similar experimentation on the trunk of the vagus has shown that
the nerve excites contraction of the upper part of the small intestine
and of the gall-bladder, the secretion of the pancreas, the renal cir-
culation, the secretion of urine, etc.

Functions. — The afferent fibers transmit nerve impulses from the
area of their distribution to the medulla and thence through cortical
connections to the sensor cerebral areas, where they evoke sensations.

The efferent fibers transmit impulses outward which excite con-
traction of the muscles of the esophagus, the stomach, the small intes-
tine, and the gall-bladder, and the muscles of the bronchial tubes
excite secretion from the glands of the stomach, pancreas, and
kidney and exert an inhibitor influence on the activity of the
heart. The efferent fibers belong to the autonomic system of nerves
and are not connected with the ganglia of the vagus, but with local
peripheral ganglia.

ELEVENTH PAIR. THE SPINAL ACCESSORY.

The eleventh cranial nerve, the spinal accessory, consists of
peripherally coursing fibers which bring the nerve-cells from which
they arise into relation with separate but functionally related muscles.
It consists of two portions, the medullary or bulbar and the spinal.

Origin. — The axons comprising the medullary portion arise from
a group of nerve-cells in the lower part of the nucleus ambiguus.
From this origin the axons pass forward and outward to emerge from
the medulla just below and in series with the roots of the vagus nerve.

The axons comprising the spinal portion have their origin' in
nerve-cells in the lateral margin of the anterior horn of the gray
matter in the cervical portion of the cord as far down as the fifth

558

TEXT-BOOK OF PHYSIOLOGY.

cervical vertebra.

Fig. 256. — Spinal Accessory Nerve.
I. Trunk of the facial nerve. 2, 2.
■ Glosso - pharyngeal nerve. 3, 3.
Pneumogastric. 4, 4, 4. Trunk of
the spinal accessory. 5. Sublingual
nerve. 6. Superior cervical gang-
Kon. 7, 7. Anastomosis of the first
two cervical nerves. 8. Carotid
branch of the sympathetic. 9,10,11,
12, 13. Branches of the glosso-
pharyngeal. 14, 15. Branches of the
facial. 16. Otic ganglion. 17.
Auricular branch of the pneumogas-
tric. 18. Anastomosing branch from
the spinal accessory to the pneumo-
gastric. 19. Anastomosis of the first
pair of cervical nerves with the sub-
lingual. 20. Anastomosis of the spi-
nal accessory with the second pair of
cervical nerves. 21. Pharyngeal
plexus. 22. Superior laryngeal
nerve. 23. External laryngeal
. nerve. 24. Middle cervical gang-
lion . — {Hirschfeld . )

rise to muscle contraction

From this origin the fibers pass to the surface of
the cord to emerge between the
ventral and dorsal roots in from
six to eight filaments, after which
they unite from below upward
to form a distinct nerve. This
enters the cranial cavity through
the foramen magnum, where it
joins with the medullary portion
to form the common trunk,
which then passes forward to
emerge from the cranium
through the jugular foramen.

Distribution. — After emerg-
ing from the cranial cavity the
nerve soon separates into two
branches :

1. An internal or anastomotic
branch, consisting chiefly
of filaments coming from
the medulla oblongata. It
soon enters the trunk of
the vagus, from which
fibers pass to the muscles of
the pharynx, to the muscles
of the larynx through the
inferior laryngeal nerve,
and to the heart accord-
ing to most authorities.

2. An external branch, consist-
ing chiefly of the accessory
fibers from the spinal cord.
It is distributed to the
sterno-cleido-mastoid and
trapezius muscles.

Cortical Connections. — The
nucleus of origin of the medul-
lary branch at least is in relation
with nerve-cells in the lower
third of the general cerebral
motor area, the axons of which
descend in the pyramidal tract.
Properties. — Faradization of
the nerve near its origin gives
Destruction of the medullary root is

THE CRANIAL NERVES. 559

followed by impairment of deglutition and a loss of the power of
producing vocal sounds on account of paralysis of the constrictor
muscles of the larynx. According to some authorities, there is also an
acceleration of the heart's action from a loss of inhibitor influences.

Stimulation of the external branch gives rise to contraction of
the sterno-cleido-mastoid and trapezius muscles, though division of
the branch does not give rise to complete paralysis, as they are sup-
plied with motor fibers also from the cervical nerves. In consequence
of division of the external branch animals experience extreme short-
ness of breath during exercise, from a want of coordination of the
muscles of the fore-limbs and the muscles of respiration.

Functions. — The spinal accessory nerve transmits nerve impulses
outward which influence the movements of deglutition, and the
vocal movements of the larynx, which inhibit the action of the heart
and which control respiratory movements associated with sustained
or prolonged muscle efforts.

TWELFTH PAIR. THE HYPOGLOSSAL.

The twelfth cranial nerve, the hypoglossal, consists of peripher-
ally coursing nerve-fibers which serve to connect the nerve-cells
from which they arise with the musculature of the tongue.

Origin. — The axons composing the hypoglossal nerve arise from
a collection of nerve-cells situated beneath the floor of the fourth
ventricle. This nucleus is elongated and extends from the medullary
striae downward as far as the lower border of the olivary body. It is
located ventro-laterally to the spinal canal. After leaving the cells
of the nucleus the axons pass forward and outward toward the surface
of the medulla, from which they emerge in ten or twelve small bundles
or filaments in the groove between the olivary body and the anterior
pyramid. Beyond this point they unite to form a common trunk.

Distribution. — The common trunk thus formed passes out of
the cranial cavity through the anterior condyloid foramen. In its
course it receives filaments from the first and second cervical nerves,
the sympathetic and vagus. It is finally distributed to the intrinsic
muscles of the tongue and to the genio-hyo-glossus, hyo-glossus, and
stylo-hyoid muscles. Branches derived from the cervical plexus
pass to muscles which elevate and depress the hyoid bone.

Cortical Connections. — The hypoglossal nerve nuclei are con-
nected with nerve-cells in the lower third of the general motor area
around the inferior termination of the fissure of Rolando by axons
which descend in the pyramidal tract.

Properties. — Faradization of the nerve gives rise to convulsive
movements of the muscles to which it is distributed. Division of the
nerve is followed by a loss of motion and an interference with deglu-

56o

TEXT-BOOK OF PHYSIOLOGY.

tition, mastication, and articulation, especially in the pronunciation
of the consonantal sounds. In hemiplegia, complicated with paraly-
sis of the tongue from injury to the hypoglossal tract, the opposite
side of the tongue is involved in the paralysis. On protrusion of
the tongue the tip is deviated to the paralyzed side, due to the
unopposed action of the muscle of the opposite side.

Fig. 257. — Distribution of the Hypoglossal Nerve. — i. Root of the fifth nerve.
2. GangHon of Gasser. 3, 4, 5, 6, 7, 9, 10, 12. Branches and anastomoses of the
fifth nerve. 11. Submaxillary ganghon. 13. Anterior belly of the digastric
muscle. 14. Section of the mylo-hyoid muscle. 15. Glosso-pharyxgeal Nerve.
16. Ganghon of Andersch. 17, 18. Branches of the glosso-phar^mgeal ner^^e.
19, 19. Pneumogastric. 20, 21. Gangha of the pneumogastric. 22, 22. Superior
laryngeal branch of the pneumogastric. 23. Spinal accessory ner\'e. 24. Sublin-
gual nerve. 25. Descendens noni. 26. Th}TO-hyoid branch. 27. Terminal
branches. 28. Two branches, one to the genio-hyo-glossus and the other to the
genio-hyoid muscle. — {Sappey.)

Function. — The hypoglossal nerve transmits nerve impulses
from its center of origin to the intrinsic and extrinsic muscles of the
tongue, endowing them with motihty. The coordinate activity of
these muscles favorably assists mastication, articulation, and deg-
lutition.

CHAPTER XXII.
THE SYMPATHETIC NERVE SYSTEM.

The sympathetic nerve system consists of a number of ganglia
united one to another by intervening cords of nerve-fibers. These
gangha may for convenience of description be divided into three
groups: viz., the vertebral or lateral, the pre-vertebral or collateral,
and the peripheral or terminal.

The vertebral ganglia are arranged in the form of chains, one on
each side of the vertebral column. The number of ganglia in the
chain varies in animals of different and in animals of the same
species. In man the number varies from 20 to 22. Each chain may
be divided into a cervical, a thoracic, a lumbar, a sacral, and a
coccygeal portion. The cervical portion is usually described as con-
sisting of three ganglia — a superior, a middle, and an inferior. This
statement is open to question, however, as the middle one is fre-
quently absent and the inferior one is regarded by some anatomists
as belonging to the pre-vertebral series. The thoracic portion con-
sists of ten or eleven gangha, the lumbar and sacral portions of four
each and the coccygeal portion of one, the so-called ganghon impar.

The pre-vertehral gangha are also united in the form of a chain
situated in the abdominal cavity. The gangha constituting this
chain are known as the semilunar, the renal, the superior and inferior
mesenteric, and hypogastric.

The peripheral ganglia are in more or less close relation with the
tissues and organs in different parts of the body. As members of
this group may be mentioned the cihary or ophthalmic, the spheno-
palatine, the otic, the submaxillary and the subhngual gangha; the
gangha in walls of the heart, the respiratory organs, the intestines,
bladder, etc.

The general arrangement of the sympathetic gangha, their inter-
connecting cords and branches, is shown in Figs. 258 and 259.

Structure of the Ganglia. — Each ganglion consists of a capsule
or stroma of connective tissue in which are contained large numbers
of nerve-cells, nerve-fibers medullated and non-medullated, and
blood-vessels. The nerve-cells give origin to two or more dendrites,
which, perforating a nucleated capsule by which each cell is sur-
rounded, branch and rebranch and interlace to form a pericapsular
plexus. Each cell gives origin also to an axon, which as it leaves
36 561

562

TEXT-BOOK OF PHYSIOLOGY

Fig. 258. — Cervical and Thoracic Portion of the Sympathetic. — i, i, i. Right
pneumogastric. 2. Glosso-phar}'ngeal. 3. Spinal accessory. 4. Divided trunk
of the sublingual. 5, 5, 5. Chain of ganglia of the sympathetic. 6. Superior
cervical ganglion. 7. Branches from this ganglion to the carotid. 8. Nerve of
Jacobson. 9. Two filaments from the facial, one to the spheno-palatine and the
other to the otic ganglion. 10. ISIotor oculi externus. 11. Ophthalmic gangUon,

THE SYMPATHETIC NERVE SYSTEM. 563

the cell becomes invested with a sheath continuous with the capsule
surrounding the cell-body. It is, however, wanting in a medullary
sheath, and hence the nerve presents a gray color. Such a structure,
in its entirety, is known as a sympathetic neuron.

Structure of the Interconnecting Cords. — The interconnecting
cords are composed of non-medullated and meduUated nerve-fibers.
The former are the axons of cells found in the ganglia more centrally
located; the latter, as will be stated later, are derived from the spinal
nerves, from the fibers of which, however, they differ in character,
being much smaller and finer. The fibers of the interconnecting
cords, as a rule, transmit nerve impulses from the more centrally to
the more peripherally located ganglia, and are therefore termed
rami ejjerenles. In the vertebral chain some of the cords transmit
nerve impulses upward, others downward, others again forward, to
the pre- vertebral and peripheral ganglia.

Among the rami eft'erentes, interconnecting cords, there are some
which possess special interest for the physiologist, viz. :

1. The cervical, which connects the thoracic ganglia with the superior

cervical ganglion. It is composed mainly of medullated nerve-
fibers which are derived originally from the spinal nerves.

2. The great splanchnic nerve, formed by the union of branches from

the fifth to the tenth thoracic ganglia. It connects these ganglia
with the semilunar ganglion.

3. The small splanchnic nerve, formed by the union of branches from

the ninth and tenth thoracic ganglia. It connects these ganglia

with the solar and renal plexuses.

Distribution of the Sympathetic Fibers. — It has been demon-
strated by histologic and physiologic methods of investigation that
the sympathetic non-medullated fibers which have their origin in

receiving a motor filament from the motor oculi communis and a sensory filament
from the nasal branch of the fifth. 12. Spheno-palatine ganglion. 13. Otic gang-
lion. 14. Lingual branch of the fifth nerve. 15. Submaxillary ganglion. 16,
17. Superior laryngeal nerve. 18. External laryngeal nerve. 19, 20. Recurrent
laryngeal nerve. 21, 22, 23. .\nterior branches of the upper four cervical nerves,
sending filaments to the superior cervical sympathetic ganglion. 24. Anterior
branches of the fifth and sixth cervical nerve, sending filaments to the middle
cervical ganglion. 25, 26. .interior branches of the seventh and eighth cervical
and the first dorsal nerves, sending filaments to the inferior cervical ganghon.
27. Middle cervical ganglion. 28. Cord connecting the two gangha. 29. In-
ferior cervical ganglion. 30, 31. Filaments connecting this with the middle
ganglion. 32. Superior cardiac nerve. ^^. Middle cardiac nerve. 34. Inferior
cardiac nerve. 35,35. Cardiac plexus. 36. Ganglion of the cardiac plexus. 37.
Nerve following the right coronary artery. 38, 38. Intercostal nerves, ^\'ith their
two filaments of communication with the thoracic ganglia. 39, 40, 41. Great
splanchnic nerve. 42. Lesser splanchnic nerve. 43, 43. Solar plexus. 44. Left
pneumogastric. 45. Right pneumogastric. 46. Lower end of the phrenic nerve.
47. Section of the right bronchus. 48. Arch of the aorta. 49. Right auricle.
50. Right ventricle. 51,52. Pulmonary artery. 53. Right half of the stomach.
54. Section of the diaphragm. — {Sappey.)

S64

TEXT-BOOK OF PHYSIOLOGY.

Fig. 259. — Lumbar and Sacral Portions of the Sympathetic. — i. Section of the
diaphragm. 2. Lower end of the esophagus. 3. Left half of the stomach. 4.
Small intestine. 5. Sigmoid ilexure of the colon. 6. Rectum. 7. Bladder. _ 8.
Prostate. 9. Lower end of the left pneumogastric. 10. Lower end of the right
pneumogastric. 11. Solar plexus. 12. Lower end of the great splanchnic nerve.
13. Lower end of the lesser splanchnic nerve. 14, 14. Last two thoracic ganglia.
15, 15. The four lumbar gangha. 16, 16, 17, 17. Branches from the lumbar
ganglia. 18. Superior mesenteric plexus. 19, 21, 22, 23. Aortic lumbar plexus.
20. Inferior mesenteric plexus. 24, 24. Sacral portion of the sympathetic. 25,
25, 26, 26, 27, 27. Hypogastric plexus. 28, 29, 30. Tenth, eleventh, and twelfth
dorsal nerves. 31, 32, ^^, 34, 35, 36, 37, 38, 39. Lumbar and sacral nerves. — (Sappey.}

THE SYMPATHETIC NERVE SYSTEM. 565

the cells of the sympathetic ganglia, vertebral, pre-vertebral, and
peripheral, are distributed ultimately and directly to but two struc-
tures: viz., non-striated muscle and secretory epithelium. Moreover,
there is no evidence to warrant the assumption that these structures
(with the exception of the heart) ever receive nerve impulses directly
from the spinal or cranial nerves. All nerve impulses which influence
their activities, either in the way of excitation or inhibition, emanate
directly though not originally from the sympathetic ganglion cells.
Since non-striated muscles are found in the walls of blood-vessels,
in the walls of hollow viscera, and around hair-follicles, and since
secretory epithelium is found in all glands, there is every reason to
beheve that the gangha in some way are associated with vaso-motor
and vaso-inhibitor, viscero-motor and viscero-inhibitor, pilo-motor
and secretor phenomena.

The Anatomic Relations of the Sympathetic and Cerebro-
spinal Systems. — The sympathetic ganglia are connected with the
spinal nerves by two branches, one white, the other gray in color,
and known respectively as the white and gray rami com?nunicantes.
These two rami differ somewhat in their topographic distribution.
The white rami are found passing only from those spinal nerves
included between the first thoracic and second or third lumbar and
their corresponding ganglia. The gray rami, on the contrary, are
found passing from the gangha to each of the spinal nerves. In the
cervical region, where the ganglia do not correspond in number with
the cervical nerves, each ganghon gives off two or more gray rami.
In man the superior cervical ganglion sends gray rami to the first
four cervical nerves; the middle and inferior ganglia apparently
send gray rami to the fifth and sixth, the seventh and eighth nerves
respectively.

The white rami are composed of fine meduUated nerve-fibers
which arise from nerve-cells situated in the lateral portion of the
gray matter in the thoracic and lumbar regions of the spinal cord.
From this origin they pass forward into the ventral roots of the
spinal nerves, in which they are contained until the spinal nerve
formed by the union of the ventral and dorsal roots divides into its
anterior and posterior divisions. At this point the fine meduUated
nerve-fibers leave the common trunk and pass forward into the cor-
responding vertebral ganglion, around the cell-bodies of which some
of the fibers at once arborize. Other fibers, however, pass through
this ganghon and ascend or descend the cord for a variable distance,
and arborize around the cells of more or less distant gangha; others
again pass forward into the pre-vertebral and even the peripheral
ganglia before they finally terminate. The nerve-cells in the spinal
cord are thus brought into relation with the gangha of all three
chains, though for each cell there is but one ganghon terminal.

566 TEXT-BOOK OF PHYSIOLOGY.

one cell station, between the spinal cord and the tissues. Though
innervated by the spinal cord, these structures receive their nerve
impulses, as previously stated, not directly but indirectly through
the ganglion cells. The medullated nerve-fibers coming from the
spinal cord are known as pre-ganglionic fibers; the non-medullated
fibers, passing from the ganglia, as post- ganglionic fibers.

The gray rami are composed of non-medullated nerve-fibers,
axons of the cells in the vertebral or lateral ganglia. After their
emergence from the ganglia they take a backward direction and
enter the spinal nerve-trunks, in company with which they pass to
the periphery, to be finally distributed to structures in the skin: viz.,
non-striated muscles of blood-vessels, non-striated muscles of the
hair-follicles and epithelium of glands. They may therefore be
regarded as having vaso-motor, pilo-motor, and secretor functions.

Afferent Sympathetic Fibers. — ^With the foregoing groups of
efferent fibers, the sympathetic nerves, in the thoracic and lumbar
regions more especially, contain a number of afferent fibers which
when stimulated give rise to sensations of pain or to reflex phe-
nomena. The routes by which these afferent fibers reach the spinal
cord lead, on the one hand, into and through . the gray rami to the
ganglia on the posterior roots, where they have their cells of origin;
and, on the other hand, into and through the white rami. The
number of afferent fibers in any trunk in comparison with the effer-
ent is quite small.

FUNCTIONS OF THE SYMPATHETIC SYSTEM.

The view according to which the sympathetic system is to be
regarded as an independent apparatus endowed with functions of its
own and in nowise directly dependent for its activities on the spinal
cord, is at the present time discarded. Peripheral structures cease
to exhibit their characteristic functions after division of the spinal
nerves in connection with their related ganglia. This does not
exclude the possibility of the sympathetic cell-body, in virtue of the
interchanges between it and the blood and lymph by which it is
surrounded, maintaining its own nutrition and exerting a favor-
able influence over the nutrition of the peripheral tissues to which
its efferent branches are distributed.

The nerve-tissue in its entirety may be regarded as a single
system which may be functionally divided into a nerve system of
animal and a nerve system of vegetative hfe, according as the nerve
energies originating in and emanating from the central nervous
system are transmitted directly to the skeletal muscles or indirectly,
through the intervention of a sympathetic neuron, to visceral muscles
and glands. In the former system but one neuron, the spino-periph-

THE SYMPATHETIC NERVE SYSTEM. 567

eric, connects the spinal cord proper Avilh the muscle; in the latter
system there are two, the spino-ganglionic and the ganglio-pcripheric.

From the distribution of the post-ganglionic fibers it may be in-
ferred that the activities of the vascular and visceral muscles, either
in the way of augmentation or inhibition, the activities of the muscles
of the hair-follicles, and of the epithelium of glands, are called forth
by the ganglia in consequence of the arrival of nerve impulses coming
from the spinal cord through the pre-gangHonic fibers. Experimental
observations show this to be true. The extent to which these different
modes of activity manifest themselves in one or more regions of the
body will depend to some extent on the portion of the sympathetic
system subjected to experimental procedures.

The Functions of the Cervical Portion. — If the sympathetic
cord central to the superior cervical ganglion be stimulated with the
induced electric current, among the resulting phenomena there will be
observed dilatation of the pupil, retraction of the nictitating mem-
brane in animals possessing it, contraction of the blood-vessels of
the skin and mucous membrane in different parts of the head and
face, contraction of the blood-vessels of the salivary glands, increase
of secretion from the submaxillary gland, the perspiratory and
mucous glands, erection of hairs in different locaHties of the head and
neck, and in the dog dilatation of the blood-vessels of the lips, gums,
and hard palate. If the cervical cord be divided, opposite effects
will be observed: viz., contraction of the pupil, dilatation and passive
congestion of the blood-vessels, a rise in temperature, and a loss of
the power of erecting hairs. Stimulation of the peripheral end causes
a disappearance of the latter and a reappearance of the former
phenomena. These facts indicate that the cervical portion is efferent
in function. The fibers composing it are medullated nerve-fibers
derived from the thoracic or dorsal nerves from the first to the seventh.
From the several sources the fibers pass via the white rami into the
vertebral chain, and thence without interruption to the superior
cervical ganghon, in and around the cells of which their end-tufts
arborize in their characteristic manner.

That the superior cervical ganglion is the cell station between the
spinal cord and the peripheral organs is shown by the fact discovered
and applied by Langlcy that the intravenous injection of nicotin or
the local application of it to the ganglion itself, impairs the conductivity
of the terminals of pre-ganglionic fibers, after which their stimulation
has no effect on the ganglion cells, though the latter retain their
activity, as shown on direct stimulation. Of the nerve-centers in the
spinal cord which through pre-ganglionic fibers influence peripheral
structures, some appear to be in a state of constant activity: e. g.,
the vaso-constrictor centers and the pupillo-dilatator centers. In how
far this action is automatic or autochthonic, or reflex, is uncertain.

568 TEXT-BOOK OF PHYSIOLOGY.

The Functions of the Thoracic Portion. — The phenomena
which follow sumulation of this portion of the sympathetic system
resemble in a general way those observed in the head when the cervical
portion is stimulated. The situation of the resulting phenomena
will vary in accordance with the part the subject of the experiment.
For an understanding of the results of experiment the origin and
distribution of the following nerve-branches must be kept in view :
(a) The cardiac nerves which have their origin in the first thoracic
ganglion. From this point they pass by way of the annulus of
Vieussens to the inferior cervical ganglion (from which they
probably receive additional fibers) and thence to the heart.
Stimulation of these nerves gives rise to an increased frequency
and an augmentation in the force of the heart-beat. The pre-
ganglionic fibers by which these cells are excited to activity
emerge from the cord by the first and second thoracic nerves.
{h) The splanchnic nerves the roots of which emerge from the fourth
to the tenth or eleventh thoracic ganglia. The fibers composing
these nerves are for the most part pre-ganglionic and derived
from the corresponding spinal nerves. The cell stations of the
splanchnic fibers are in the semilunar, superior mesenteric, and
renal ganglia. From these ganglia non-medullated post-gang-
lionic fibers pass peripherally to the walls of the intestines, the
blood-vessels of the intestines, liver, kidneys, spleen, etc.
Stimulation of the great splanchnic produces inhibition of the
intestinal movements, a marked primary contraction of the
intestinal blood-vessels and other viscera, followed by dilatation,
coincidently with which there is a primary rise succeeded by a
fall of blood-pressure throughout the body. Division of the
nerve is followed by dilatation of the intestinal vessels and a fall
of blood-pressure. Stimulation of the central end of the divided
nerve excites the activity of the general vaso-motor center, as
shown by the rise of the general blood-pressure. Stimulation of
the smaller splanchnics gives rise to a slight primary contraction
of the blood-vessels, soon followed by a marked dilatation. These
facts indicate that the splanchnic nerves contain visceral nerves
which inhibit intestinal movements, vaso-motor fibers both aug-
mentor and inhibitor. The presence of secretory nerves for
the intestinal glands is disputed,
(c) The cutaneous nerves for the trunk leave the lateral ganglia by
the gray rami, enter the thoracic spinal nerves, and pass in com-
pany with them to their terminations, to be ultimately distrib-
uted to the walls of the blood-vessels, the arrectores pilorum
muscles, and the sweat-glands. The pre-ganglionic fibers come
from the spinal nerves by the white rami. Their functions are
vaso-motor, pilo-motor, and secretor. The cutaneous nerves

THE SYMPATHETIC XER\'E SYSTEM. 569

for the fore-Ii))ibs have their origin from cells in the stellate gang-
lion (first dorsal). After a short upward course they enter
the trunks of the nerves composing the brachial plexus. The
pre-ganglionic fibers come from the white rami of the fourth to the
ninth thoracic nerves. After entering the lateral chain they take
an upward direction and arborize around the cells of the stellate
ganglion. The cutaneous nerves for the hind-limhs are derived
from the lower lumbar and the upper sacral ganglia. They also
enter the spinal nerves by the gray rami and pass to the blood-
vessels and glands of the skin. The pre-ganglionic fibers come
from the twelfth thoracic to the third lumbar nerves. In both
the brachial and sciatic nerves vaso-motor fibers (constrictors
and dilatators) and secretor nerves are present, as shown by
experimental methods (see page 331).
The Functions of the Lumbo-sacral Portion. — From the
ganglia of the lumbar and sacral regions gray rami enter the lumbar
and sacral nerves and accompany them to their distribution. In
the lumbar region the vertebral chain contains a number of pre-
ganglionic fibers which have descended from the thoracic region as
well as fibers which have come into the chain by the white rami from
the lumbar nerves themselves. ]Many of these fibers pass to the
inferior mesenteric ganglion, in wliich they find their cell station.
Fibers from the sacral cord pass into the h}^ogastric plexus. The
course and distribution of the individual nerves is complicated and
involved. In a general way it may be said that these two regions of
the lateral chain send viscero-motor and viscero-inhibitor, vaso-con-
strictor and dilator nerves to the pelvic viscera and to the external
organs of generation. Their function therefore is to regulate the
activities of the viscera as well as the blood-supply in accordance
vnth. functional needs.

The Functions of the Cephalic Ganglia. — The ganglia situated
in the head are usually described in connection with and as con-
stituent parts of the cranial nerve system. They, however, bear the
same relation to the cranial nerves that the ganglia of the trunk
bear to the spinal nerves. They consist of ganglion cells jrom which
post-ganglionic fibers pass to glands, blood-vessels, and non-striated
muscles, and to which pre-ganglionic fibers pass from the cranial
nerv^es. Motor and sensor nerves pass through one or more ganglia,
though they have no anatomic connection with them. In their
structure, distribution, and functions they closely resemble the col-
lateral ganglia of the abdominal s}Tnpathetic :

I. The ciliary or ophthalmic ganglion is situated in the orbital cavity
posterior to the eyeball. It is small in size, gray in color, and
consists of a connective-tissue stroma containing nerve-cells.
From these cells post-ganglionic fibers emerge which, after a

570 TEXT-BOOK OF PHYSIOLOGY.

short course forward, penetrate the eyeball and terminate in the
circular fibers of the iris and the ciliary muscle. Pre-ganglionic
fibers of small size, and similar in their anatomic features to
the fibers of the white rami of the spinal nerves, leave the motor
oculi by a short root from the inferior division and arborize
around the ganglionic cells. Stimulation of the pre-ganglionic
fibers gives rise to contraction of the circular fibers of the
iris, with a diminution in the size of the pupil, and contraction
of the ciliary muscle with accommodation of the eye for near
vision. Division of these fibers is followed by the opposite
results. Post-ganglionic fibers from the superior cervical gang-
lion which come through the cavernous plexus pass through the
cihary ganglion to the blood-vessels of the iris and retina which
are vaso-constrictor in function. Sensor fibers from the per-
ipheral division of the fifth nerve pass to the cornea and endow it
with sensibility.

2. The spheno- palatine ganglion is situated in the spheno-maxillary

fossa. Its nerve-cells send non-medullated post-ganghonic fibers
to the blood-vessels and glands of the mucous membrane of the
nasal and oral regions. Stimulation of the ganghon gives rise
to dilatation of the blood-vessels and increase of secretion in this
entire region. The pre-ganglionic fibers are derived from the
seventh or facial nerve by way of the great petrosal. Sensor
fibers from the superior maxillary division of the fifth nerve pass
through the ganglion to the same regions.

3. The otic ganglion is situated just below the foramen ovale and

internal to the third division of the fifth nerve. The post-gang-
lionic fibers pass to the parotid gland by way of the auriculo-
temporal division of the fifth nerve, and to the blood-vessels of the
lower lip, cheek, and gums. The pre-ganghonic fibers are de-
rived from the efferent fibers in the glosso-pharyngeal or ninth
nerve, by way of Jacobsen's nerve and the small petrosal. Stimu-
lation of these nerves in any part of their course gives rise to
vascular dilatation and increase of secretion in the region of
their distribution. Motor fibers from the small or motor root
of the fifth nerve pass through this ganglion to the tensor tym-
pani muscle.

4. The submaxillary and sublingual ganglia are situated close to the

corresponding glands. Their post-ganglionic fibers pass to the
blood-vessels and gland-cells. The pre-ganglionic fibers are
derived from the seventh or facial nerve through the chorda
tympani branch. Stimulation of the chorda or of the gangha
themselves gives rise to marked dilatation of the blood-vessels
and an increased flow of saliva. It therefore contains vaso-
dilatator and secretor fibers for these glands. Vaso-constrictor

THE SYMPATHETIC NERVE SYSTE^E 571

and a few sccretor nerves, it will be recalled, come to these

glands from the superior cervical ganglion.
Peripheral Ganglia. — Among the peripheral ganglia may be
mentioned those in the heart and those in the intestinal walls. The
pre-ganglionic fibers are contained in the trunk of the vagus nerve.
Stimulation of the peripheral end of the divided vagus gives rise to
inhibition of the heart, contraction of the walls of the stomach and
intestines, secretion from the gastric and perhaps the pancreatic
gland.

CHAPTER XXIII.
PHONATION; ARTICULATE SPEECH.

Phonation, the emission of vocal sounds, is accomplished by the
vibration of two elastic membranes which cross the lumen of the
larynx antero-posteriorly and which are thrown into vibration by a
blast of air from the lungs.

Articulate speech is a modification of the voice produced by the
teeth and the muscles of the lips and tongue and employed for the
expression of ideas.

The larynx, the organ of the voice, is situated in the forepart of
the neck, occupying the space between the hyoid bone and the upper
extremity of the trachea. In this situation it communicates with the
cavity of the pharynx above and the cavity of the trachea below.
From its anatomic relations and its internal structure — the interpola-
tion of the elastic membranes — the larynx subserves the two widely
different yet related functions, respiration and phonation.

THE ANATOMY OF THE LARYNX.

The larynx consists primarily of a series of cartilages united one
with another in such a manner as to form a more or less rigid frame-
work, yet possessing at its different joints, a certain amount of
motion; and, secondarily, of muscles and nerves which conjointly
impart to the cartilages the degree of movement necessary to the
performance of the laryngeal functions. It is covered externally
by fibrous tissue and lined throughout by mucous membrane con-
tinuous with that lining the pharynx and trachea.

The larynx presents a superior or pharyngeal and an inferior or
tracheal opening. The pharyngeal opening is triangular in shape,
the base being directed forward, the apex backward. The plane of
this opening in the living subject is almost vertical. The tracheal
opening is circular in shape and corresponds in size with the upper
ring of the trachea. Viewed from above, the general cavity of the
lar}'nx is seen to be partially subdivided by two membranous bands —
the vocal hands or cords — which run from before backward in a hori-
zontal plane. The space between the bands, the glottis, varies in
size and shape from moment to moment in accordance with respira-
tory and phonatory necessities. The average width of the glottis, at

572

PHONATION; ARTICULATE SPEFXH.

573

its widest part, during quiet respiration is about 13.5 mm. in men

and 1 1.5 mm. in women (Semon).
the vocal membranes are at once
approximated, and to such an
extent that the glottic opening is
reduced to a mere sht. It is then
spoken of as the rima glolHdis, or
chink of the glottis.

The space above the vocal bands,
the supra-glottic or supra-rimal
space, is triangular in shape and
extends from the pharyngeal open-
ing to the plane of the vocal bands.
The mucous membrane lining the
walls of this space, presents on either
side, just above the vocal bands, a
crescentic fold which runs from
before backward, and is known as
the false vocal band or cord. Be-
tween the true and false bands
there is a cavity or space prolonged
upward and outward for some
distance, forming what is known as
the ventricle of the larynx. The
space below the vocal bands, the
infra-glottic or infra-rimal space, is
narrow above and elongated from
before backward, but wide and
circular below, corresponding to the
lumen of the trachea.

The Laryngeal Cartilages,
Articulations, and Ligaments. —
The cartilages which compose the
framework of the larynx are nine
in number, three of which are
single: viz., the cricoid, the thyroid,
and the epiglottis, while six occur
in pairs: viz., the arytenoids, the
cornicula laryngis, and the cunei-
form.

The cricoid cartilage is the
foundation cartilage, and affords
support to the remaining cartilages
and the structures attached to them.

With the advent of phonation

Fig. 260. — Longitudinal^ Section
OF THE Human Larynx, Show-
ing THE Vocal Bands. i.
Ventricle of the larynx. 2. Supe-
rior vocal cord. 3. Inferior vocal
cord. 4. Arytenoid cartilage. 5.
Section of the arytenoid muscle.
6, 6. Inferior portion of the cavity
of the larynx. 7. Section of the
posterior portion of the cricoid
cartilage. 8. Section of the an-
terior portion of the cricoid car-
tilage. 9. Superior border of the
cricoid cartilage. 10. Section of
the thyroid cartilage. 11, 11.
Superior portion of the cavity of
the larynx. 12, 13. Arytenoid
gland. 14, 16. Epiglottis. 15,17.
Adipose tissue. 18. Section of
the hyoid bone. 19, 19, 20.
Trachea. — {Sappey.)

In shape it resembles a signet-

ring, the broad quadrate portion of which is directed backward,

574

TEXT-BOOK OF PHYSIOLOGY.

while the narrow ch-cular portion is directed forward. It rests upon
the upper ring of the trachea, to which it is firmly attached by
fibrous tissue. The posterior upper border of the quadrate portion
presents on either side an oval convex facet for articulation with the
arytenoid cartilage. The long axis of this facet is directed down-
ward, outward, and forward.

Fig. 261 . — Laryngeal Cartilages and
Ligaments, Anterior Surface.
I. Hyoid bone. 2, 2, 3, 3. Greater
and lesser cornua. 4. Thyroid
cartilage. 5. Thyro-hyoid mem-
brane. 6. Thyro-hyoid Hgaments.
7. Cartilaginous nodule. 8. Cri-
coid cartilage. 9. The crico-thyroid
membrane. 10. The crico-thyroid
ligaments. 11. Trachea. — (Sap-
pey.)

Fig. 262. — Laryngeal Cartilages
AND Ligaments. Posterior Sur-
face. I, I. Thyroid cartilage. 2.
Cricoid cartilage. 3, 3. Arytenoid
cartilages. 4, 4. Crico-arytenoid
articulations. 5, 5. Crico-thyroid
articulations. 6. Union of the
cricoid cartilage and of the trachea.
7. Epiglottis. 8. Ligament uniting
it to the reentering angle of the
thyroid cartilage. — {Sappey.)

The thyroid, the largest of the laryngeal cartilages, is composed
of two flat quadrilateral plates, united anteriorly, at an angle of
about 90 degrees. Each plate is directed backward and outward
and terminates in a free border, which is prolonged upward and
downward for some distance, terminating in two processes, the
superior and inferior cornua. The upper border of the thyroid is
deeply notched in front. The inferior border overlaps laterally
the cricoid.

PHONATION; ARTICULATE SPEECH. 575

The epiglottis is a leaf-shaped piece of cartilage attached to the
thyroid at the median notch. It is firmly united by membranes and
ligaments to the thyroid and arytenoid cartilages and to the base of
the tongue.

The arytenoid cartilages are two in number and symmetric in
shape. Each cartilage is a triangular pyramid, the apex of which is re-
curved, and directed backward and inward. The base presents three
angles — an anterior, an external, and an internal. The anterior angle
is long and pointed and projects forward in a horizontal plane. It
serves for the attachment of the vocal membranes and is therefore
termed the vocal process. The external angle is short, rounded, and
prominent, and serves for the attachment of muscles. The internal
angle affords a point of insertion for a ligament. The inferior surface
of the arytenoid is concave for articulation with the convex surface
of the cricoid facet. Its long axis, however, is directed from before
backward and almost at right angles to the long axis of the cricoid
facet.

The cornicula laryngis and the cuneiform cartilages are small
nodules of yellow elastic cartilage embedded in a fold of membrane
which unites the arytenoid and the epiglottis. They are fragments
of a ring of cartilage which in some animals — e. g., anteater — extends
between these two cartilages.

The crico-thyroid articulation is formed by the apposition of the
tip of the inferior cornu of the thyroid cartilage and an articular
facet on the side of the cricoid. The joint is provided with a synovial
membrane and enclosed by a capsular ligament. The movements
permitted at this joint take place around a horizontal axis and consist
of an upward and downward movement of both the thyroid and
cricoid, combined with a sliding movement of the latter upward and
backward.

The crico-arytenoid articulation is formed by the apposition of
the articulating surfaces of the cricoid and arytenoid cartilages.
This joint is provided with a synovial membrane and enclosed by
a loose capsular ligament which would permit of an extensive sliding
of the arytenoid cartilage downward and outward were it not pre-
vented by the posterior crico-arytenoid ligament, which is attached,
on the one hand, to the cricoid, and, on the other, to the inner angle
of the arytenoid. The movements permitted at this joint are: (i)
Rotation of the arytenoid around a vertical axis which lies close to
its inner surface. (2) A sliding motion inward and forward with
inward rotation of the vocal process, or a sliding motion outward and
backward with outward rotation of the vocal process. In either case
the process describes an arc of a circle. (3) A sliding movement
towards the median line in consequence of which the inner surfaces
of the arytenoids are brought almost in contact.

576 TEXT-BOOK OF PHYSIOLOGY.

The crico-thyroid membrane is composed mainly of elastic tissue.
It may be divided into a mesial and two lateral portions. The
mesial portion is well developed, triangular in shape, and unites the
contiguous borders of the cricoid and thyroid cartilages. The lateral
portion is attached below to the superior border of the cricoid. From
this attachment it passes upward and inward under cover of the
thyroid. As it ascends it elongates and becomes thinner, and is
finally attached anteriorly to the thyroid near the median line, and
posteriorly to the vocal process of the arytenoid, thus constituting
the inferior thyro-arytenoid ligament. It is covered internally by
mucous membrane and externally by the internal thyro-arytenoid
muscle. The free edge of this ligament forms the basis of the true
vocal band. A superior thyro-arytenoid ligament forms the basis
of the false vocal band.

The thyro-hyoid membrane, composed of elastic tissue, unites
the superior border of the thyroid to the hyoid bone.

The mucous membrane lining the larynx is thin and pale. As
it passes downward it is reflected over the superior thyro-arytenoid
ligament, and assists in the formation of the false vocal band; it
then passes into and lines the ventricle, after which it is reflected
inward over the superior border of the thyro-arytenoid muscle and
ligament, and assists in the formation of the true vocal band ; it
then returns upon itself and passes downward over the lateral
portion of the crico-thyroid membrane into the trachea.

The thin, free, reduplicated edge of the mucous membrane con-
stitutes the true vocal band. The surface of the mucous membrane
is covered by ciliated epithelium except in the immediate neighbor-
hood of the vocal bands.

The vocal bands are attached anteriorly to the thyroid cartilage
near the receding angle and posteriorly to the vocal processes of the
arytenoid cartilages. They vary in length in the male from 20 to 25
mm. and in the female from 15 to 20 mm.

The Muscles of the Larynx. — The muscles which have a direct
action on the cartilages of the larynx and determine the position of the
vocal bands both for respiratory and phonatory purposes, and which
regulate their tension as well, are nine in number and take their
names from their points of origin and insertion: viz., two posterior
crico-ar}'tenoids, two lateral crico-arytenoids, two thyro-arytenoids,
one arytenoid, and two crico-thyroids (Figs. 263 and 264).

The posterior crico-arytenoid muscle lies on the posterior surface
of the quadrate plate of the cricoid cartilage, on either side of the
median line, from which it takes its origin. The fibers of the
muscle pass upward and outward and in their course converge to
be inserted into the external angle of the arytenoid cartilage. The
superior and more horizontally directed fibers rotate the arytenoid

PRONATION; ARTICULATE SPEECH.

577

around its vertical axis; the inferior and obliquely directed fibers
draw the cartilage downward and inward. As a result of the action
of the muscle in its entirety, the vocal process is turned upward and
outward, and as the vocal band is carried with it the glottis is widened,
a condition necessary to the free entrance of air into the lungs (Fig.

Fig. 263. — Posterior View of the
Muscles of the Larynx. i.
Posterior crico-arytenoid muscle.
2, 3, 4. Different fasciculi of the
arytenoid muscle. 5. Aryteno-
epiglottidean muscle. — (Sappey.)

265). Since the contraction of the
crico-arytenoid has this result, it is
generally spoken of as the abductor or
respiratory muscle.

The lateral crico-arytenoid muscle
arises from the side of the cricoid
cartilage. From this point its fibers
are directed upward and backward to

Fig. 264. — Lateral View of the
Muscles of the Larynx, i.
Body of the hyoid bone. 2. Verti-
cal section of the thyroid cartilage.
3. Horizontal section of the thyroid
cartilage turned downward to show
the deep attachment of the crico-
thyroid muscle. 4. Facet of articu-
lation of the small cornu of the
thyroid cartilage with the cricoid
cartilage. 5. Facet on the cricoid
cartilage. 6. Superior attachment of
the crico-thyroid muscle. 7. Pos-
terior crico-arytenoid muscle. 8,
ID. Arytenoid muscle. 9. Thyro-
arytenoid muscle. II. Aryteno-
epiglottidean muscle. 12. Middle
thyro-hyoid ligament. 13. Lateral
thyro-hyoid ligament. — (Sappey.)

be inserted into the external process
of the arytenoid. Its action is to draw the arytenoid cartilage for-
ward and inward, thus approximating and relaxing the vocal band.

The thyro-arytenoid muscle arises from the inferior two-thirds
of the inner surface of the thyroid cartilage just external to the
median line. From this origin the fibers pass backward and outward,
37

578

TEXT-BOOK OF PHYSIOLOGY.

to be inserted into the anterior surface and external angle of the
arytenoid cartilage. The inner portion of the muscle lies close to
and supports, if it does not constitute a part of, the vocal band.
The action of the thyro-arytenoid muscle in conjunction with the
lateral crico-arytenoid is to rotate the arytenoid cartilage around
the vertical axis and to draw the vocal process forward and inward,
thus carrying the vocal cord toward the median line. When the
muscles of the two sides simultaneously contract, the vocal bands
are closely approximated and the space between them, the rima
vocalis, reduced to a mere slit, one of the conditions essential to
phonation (Fig. 266).

The arytenoid muscle consists (i) of transversely arranged fibers
which arise from and are inserted into the outer surface of the oppo-

^ap

Fig. 265. — Glottis Widely Opened
FROM Simultaneous Contraction
OF Both Crico-arytenoid Mus-
cles, b. Epiglottis. rs. False
vocal band. ri. True vocal band.
ar. Arytenoid cartilages, a. Space
between the arytenoids, c. Cunei-
form cartilages, ir. Interarytenoid
fold. rap. Aryepiglottic fold. cr.
Cartilage rings. — {Mandl.)

Fig. 266. — Position of the Vocal
Bands Due to the Simultaneous
Contraction of Both Lateral
Crico-arytenoid Muscles and
Both Thyro-arytenoid Muscles.
b. Epiglottis, rs. False vocal band.
ri. True vocal band. or. Space be-
tween the arytenoid cartilages, the
glottis respiratoria. ar. Arytenoid
cartilages, c. Cuneiform cartilages.
rap. Aryepiglottic fold. ir. Interary-
tenoid fold. — (Mandl.)

site arytenoid cartilages, and (2) of obliquely directed fibers which
arise from the outer angle of one arytenoid to be inserted into the
apex of the other. In their course they decussate in the median
line. The action of this muscle is to approximate the arytenoid
cartilages and thus obliterate that portion of the glottis between the
vocal processes, the rima respiratoria, and so direct the expiratory
blast of air toward and through the rima vocalis.

The collective actions of the three foregoing muscles is to close or
constrict the glottis, and for this reason they are spoken of as the
adductor or phonaiory muscles.

The crico-thyroid muscle arises from the side and front of the
cricoid cartilage and is inserted above into the lower border of the
thyroid cartilage. The action of this muscle is to draw up the an-
terior part of the cricoid cartilage toward the thyroid, which remains

PHONATION; ARTICULATE SPEECH. 579

stationary, and to swing the quadrate plate of the cricoid and the
arytenoid cartilages downward and backward. This movement
has the result of tensing the vocal bands. The cricoid is at the same
time drawn backward by the action of the more longitudinally dis-
posed fibers.

Nerves of the Larynx. — The nerves which innervate the muscles
of the larynx and endow the mucous membrane with sensibiHty are
derived from the vagus trunk. The superior laryngeal is for the
most part sensor and distributed to the mucous membrane, though
it contains motor fibers for the crico-thyroid muscle. The inferior
laryngeal is purely motor and is distributed to all the muscles with
the exception of the crico-thyroid.

THE MECHANISM OF PHONATION.

Phonation, the production of vocal sounds in the larynx, is the
result of the vibration of the vocal bands caused by an expiratory
blast of air from the lungs. That a sound may arise it is essential
that the glottis be approximately closed and the vocal bands be made
more or less tense.

The closure of the glottis — the approximation of the vocal pro-
cesses and the vocal bands — is accomplished, it will be recalled, by
the contraction of the lateral crico-arytenoid, the arytenoid, and the
thyro-arytenoid muscles. The increase in tension is accomplished
by the contraction of the crico-thyroid and the thyro-arytenoid
muscles, the former by the backward displacement of the cricoid and
arytenoid cartilages, the latter by converting the natural concave
edge of the vocal band to a straight line. The lengthening and
tensing of the vocal bands by the crico-thyroid muscle is regarded
by some investigators as a coarse means, the approximation of
the free edges by the thyro-arytenoid, as a finer means, of adjust-
ment for the production of shght changes in the pitch of sounds.
The extent to which the glottis is closed and the membranes tensed
will depend, however, on the pitch of the sound to be emitted. The
appearance presented by the glottis just previous to the emission
of a note of medium pitch, as determined by laryngologic examina-
tion, is shown in Fig. 267. When the foregoing conditions in
the glottis are realized, the air stored or collected in the lungs is
forced by the contraction of the expiratory muscles, through the
narrow space between the bands. As a result of the resistance
offered by this narrow outlet and the force of the expiratory
muscles the air within the lungs and trachea is subjected to pressure,
and as soon as the pressure attains a certain level the vocal bands
are thrown into vibrations, which in turn impart to the column of air
in the upper air-passages a corresponding series of vibrations by

;8o

TEXT-BOOK OF PHYSIOLOGY.

which the laryngeal vibrations are reinforced. The degree of -pres-
sure to which the air in the lungs and trachea is subjected was
determined by Latour to vary from i6o mm. of water for sounds of
moderate, to 940 mm. of water for sounds of highest intensity. With
the escape of the air or the separation of the vocal bands the \dbra-
tion ceases and the sound dies away.

The Characteristics of Vocal Sounds. — In common with the
sounds produced by all other music instruments, all vocal sounds
are characterized by intensity, pitch and quality, tone or color.

The intensity or loudness of a sound depends on the extent or
ampKtude of the up-and-down vibration or the extent of the excur-
sion of the vocal band on either side of the position of equihbrium
or rest ; and this in turn depends on the force with which the blast of
air strikes the band. The more forceful the blast of air, the larger,
other things being equal, will be the primary vibrations of the bands,

Fig. 267. — Position of the Vocal
Bands Previous to the Eihssion
of a Sound, b. Epiglottis, rs. False
vocal band. ri. True vocal band.
ar. Arjlenoid cartilages.

Fig. 268. — Position of the Vocal
Bands in the Production of
Notes of Low Pitch. I. Epiglottis.
or. Glottis, ns. False vocal cord.
ni. True vocal cord. ar. Arytenoid
cartilages. — {Mandl.)

and hence the secondary \dbrations of the air in the upper air-
passages.

The pitch of the voice depends on the number of vibrations in
a unit of time, a second. This will be conditioned by the length of
the bands in vibration or the length and width of the aperture through
which the air passes and the degree of tension to which the bands are
subjected. In the emission of sounds of highest pitch the tension of
the vocal bands and the narrowing of the glottis attain their maxi-
mum. In the emission of sounds of lowest pitch the reverse conditions
obtain. In passing from the lowest to the highest pitched sounds in
the range of the voice peculiar to any one individual, there is a pro-
gressive increase in both the tension of the vocal bands and the
narrowing of the glottic aperture. In the production of low-pitched
notes of men, those due to vibrations lying between 80 and 240 per
second, the tension is regulated by the crico-thyroid muscle; the

PHONATIOX; ARTICULATE SPEECH.

58T

Fig.

aperture of the glottis during this time being elliptic in shape and
relatively wide (Fig. 268). In the production of notes due to
vibrations lying between 240 and 512 vibrations per second, the
anterior libers of the crico-thyroid muscle relax and the thyro-ar}'-
tenoid muscle comes into play; by its action the vocal bands are
more closely approximated and the vocal aperture reduced to a
linear sht. In the high-pitched notes emitted by soprano singers the
vocal bands are so closely apphed to each other that only a ver\-
small portion in front, bounding a small oval aperture, is capable
of vibrating (Fig. 269). The difference in the pitch of the voice
in men and women is due largely to the
greater size and development of the vocal
bands in the former than in the latter. _' :;t^- . ,^;-j/

The quality of the voice, the timbre or
color, depends on the form combined with
the intensity and pitch of the vibration.
As with sounds produced by music in-
struments, the primary or fundamental
vibration of the vocal band is compH-
cated by the superposition of secondary
or partial vibrations (overtones). The
form of the vibration will therefore be
a resultant of the blending of a number
of different vibrations. The quahty of
the sound produced in the larynx is,
however, modified by the resonance of
the mouth and nasal cavities; certain of
the overtones being reinforced bv changes
in the shape of the mouth cavity more
especially, thus giving to the voice a
somewhat different quahty.

The Varieties of Voice. — The
region of the music scale, comprising all
vibrations between 32 and 2048 per

second, with which laryngeal sounds are in accord will vary in the two
sexes and in different individuals of the same sex. It is customary
to classify voices, especially those of singers, into bass, baritone, tenor,
contralto, mezzo-soprano, and soprano, in accordance with the regions
of the music scale with which they correspond. Thus the succession
of notes characteristic of the bass voice vary in pitch from F, fa', to
C, dOg, or from 87 to 256 vibrations per second; those of the baritone
from A, la, to F', fa^, or from 106 to 341 vibrations per second;
those of the tenor from C, do.,, to a', lag, or from 128 to 435 \-ibrations
per second; those of the contralto from e, mi,, to C", do^, or from 160
to 512 vibrations per second; those of the mezzo-soprano from g, solj,

269. — Glottis Seen
witd the l.\ryngo-

SCOPE DTJRIXG THE EmIS-

siox OF High-pitched
Sounds, i, 2. Base of
the tongue. 3, 4. Epiglot-
tis. 5, 6. Phan'n.x. 7.
Ar}-tenoid cartilages. 8.
Opening between the true
vocal cords. 9. Aiyteno-
epiglottidean folds. 10.
Cartilage of Santorini. 11.
Cuneiform cartilage. 12.
Superior vocal cords. 13.
Inferior vocal cords. — (Le
Bon.)

582 TEXT-BOOK OF PHYSIOLOGY.

to e", mi^, or from 192 to 640 vibrations per second; those of the
soprano from b, si2, to g", sol^,^or 768 vibrations per second. ' The
range of the voice is thus seen to embrace from one and three- cjuarters
to two octaves. Some few individual singers have far exceeded this
range, but they are exceptional.

Speech is the expression of ideas by means of articulate sounds.
These sounds may be divided into vowel and consonant sounds.

The vowel sounds, a, e, i, 0, u, are laryngeal sounds modified by
the superposition and reinforcement of certain overtones developed
in the mouth and pharynx by changes in their shapes. The number
of vibrations underlying the production of each vowel sound is a
matter of dispute. According to Konig, the sound of a is the result
of 940 vibrations; of e, 1880 vibrations; of i, 3760 vibrations; of o,
470 vibrations; of ou, 235 vibrations.

Consonant sounds are produced by the more or less complete in-
terruption of the vowel sounds during their passage through the organs
of speech. These may be divided into:

1. Labials, p, b, m.

2. Labio-dentals, /, v.

3. Linguo-dentals, s, z.

4. Anterior linguo-palatals, t, d, I, n.

5. Posterior linguo-palatals, k, g, h, y, r.

The names of these different groups of consonants indicate the
region of the mouth in which they are produced and the means by
which the air blast is interrupted.

THE NERVE MECHANISM OF THE LARYNX.

The nerve mechanism by which the musculature of the larynx
is excited to action and coordinated so as to subserve both res-
piration and phonation involves the fibers contained in the superior
and inferior laryngeal nerves (both branches of the vagus) and their
related nerve-centers in the central nerve system.

For respiratory purposes it is essential that the lumen of the
glottis shall be sufficiently large to permit the entrance and exit of air
without hindrance. Laryngoscopic examination of the larynx in the
human being shows that during quiet respiration the vocal bands are
widely separated and almost stationary, moving but shghtly during
either inspiration or expiration. At this time, according to the in-
vestigations of Semon, the area of the glottis is approximately
160 sq. mm., somewhat less than the area of either the supraglottic
or infraglottic regions, which is about 200 sq. mm. This condition
of the glottis is maintained by the steady continuous contraction
of the posterior crico-arytenoid muscles, the abductors of the vocal
bands.

PRONATION; ARTICULATE SPEECH. 583

For phonatory purposes it is essential that the respiratory function
be temporarily suspended and the vocal bands closely approx-
imated. This is accomplished by the contraction of the remaining
muscles of the larynx, with the exception of the crico-thyroid,
which are collectively known as the adductors oj the vocal hands.
During phonation the adductor muscles overcome the activity of the
abductors. With the cessation of phonation the abductors immedi-
ately restore the vocal bands to their former respiratory position.

The activities of these two antagonistic groups of muscles are under
the control of the central nerve system. The only pathway for
the excitatory nerve impulses is through the fibers of the inferior or
recurrent laryngeal nerve. The relation of these nerve-fibers both
centrally and peripherally, as well as their physiologic action, has been
the subject of much experimentation. The resuhs have not always
been in accord, owing to the choice of animal, the use of anes-
thetics, strength of stimulus, etc.

As the outcome of many investigations it is believed that each
muscle group is innervated by its own bundle of nerve-fibers, both
of which are contained in the inferior laryngeal, though coming
from two separate centers in the medulla oblongata. Russell suc-
ceeded in separating the fibers for the abductors from the fibers
for the adductors in the inferior laryngeal, and in tracing them
to their terminations. So completely was this done that it became
possible to produce at will, through stimulation, either abduction or
adduction, without contraction of the muscle of opposite function.

The laryngeal respiratory center was located by Semon and
Horsley, in the cat, in the upper part of the floor of the fourth ven-
tricle. Stimulation of this area during etherization was followed by
abduction of the vocal bands. The efferent fibers of this center are
believed by some investigators to leave the central nerve system in
the spinal accessory nerve, by others in the lower roots of the vagus.

From the continuous activity of the abductor muscle, and the
stationary position of the vocal bands, it is probable that the medul-
lary center is in a state of continuous activity or tonus, the result
probably of reflex influences.

A cortical representation for laryngeal respiratory movements
has been determined by Semon and Horsley in different classes of
animals. In the cat especially, stimulation of the border of the
olfactory sulcus gives rise to complete abduction- of the vocal bands
on both sides. The representation is therefore bilateral.

The phonatory center was located by the same investigators in
the medulla near the ala cinerea and the upper border of the calamus
scriptorius. Stimulation of this area was invariably followed by
bilateral adduction of the vocal bands and closure of the glottis.

A cortical representation for phonatory movements also was

584 TEXT-BOOK OF PHYSIOLOGY.

located in the lower portion of the precentral convolution, near the
anterior border. Stimulation of this area gives rise to marked ad-
duction of both vocal bands, indicating that the representation is
also bilateral.

Faradic stimulation of the inferior laryngeal nerve during slight
ether anesthetization gives rise to closure of the glottis; the same
stimulation, however, during deeper anesthetization gives rise to
opening or dilatation of the glottis, a fact indicating that either
the adductor muscles or their nerve terminals are depressed by the
action of the ether before the muscles and nerves of opposite function.
The superior lar}^ngeal nerves contain motor fibers for the crico-
thyroid muscles. Stimulation of the nerve gives rise to contraction
of the muscle and increased tension of the vocal bands. It is beheved
that these fibers are derived originally from the efferent fibers of the
glosso-pharyngeal nerve. The remaining fibers of the superior
laryngeal endow the upper portion of the larynx with extreme sen-
sibility which to a certain extent protects the air-passages against the
entrance of foreign bodies. Irritation of the terminal filaments of
this nerve by particles of food, solid or Hquid, gives rise to marked
reflex spasm of the adductor muscles and closure of the glottis, fol-
lowed by a strong expiration blast of air from the lungs by which the
offending particles are removed. Division of this nerve on both
sides is followed by a paralysis of the crico-thyroid muscles, a lower-
ing of the tension of the vocal bands, and a loss of sensibility of the
laryngeal mucous membrane.

CHAPTER XXIV.
THE SPECIAL SENSES.

It is one of the functions of the nerve system to bring the
individual into conscious relation with the external world. This
is accomplished through the intermediation of afferent nerves, con-
nected peripherally, with highly specialized terminal organs and
centrally, with speciahzed areas in the cerebral cortex.

Excitation of the terminal organs by material changes in the
environment develops nerve impulses which, transmitted to the
cortical areas, evoke sensations. These sensations, differing in
character from those vague ill-defined sensations — e. g., fatigue,
well-being, discomfort, etc. — caused by material changes occurring
within the body, are termed special sensations — e. g., touch; pres-
sure ; pain ; temperature; taste; smell; light and its varying quah-
ties, intensity, hue, and tint ; sound and its varying qualities, intensity,
pitch, and timbre.

The terminal organs which receive the impress of the external
world are the skin, tongue, nose, eye, and ear, and collectiA-ely con-
stitute the special sense-organs. The physiologic mechanisms which
underlie and develop these special sensations are known respectively
as the tactile, gustatory, olfactory, optic, and auditory. Each
mechanism responds to but a single form of stimulus and to no
other. Thus, the stimulus for the skin is mechanic pressure;
for the tongue, soluble organic and inorganic matter; for the nose,
volatile or gaseous matter; for the eye, ether vibrations; for the
ear, atmospheric undulations. These stimuli alone are adequate
to the physiologic excitation of the different mechanisms.

The factors involved in the production of the sensations include
(i) a special physical stimulus; (2) a specialized terminal organ;
(3) an afferent nerve; and (4) a specialized receptive sensor cell.

Though the resulting sensations in each instance differ widely in
their characteristics, it is difficult to present a satisfactory explanation
for these differences. If it be assumed that the nerve impulses which
ascend the different nerves of special sense are ahke in quality, then
it must be admitted that the character of the sensation is the ex-
pression of a specialization and organization of the cortical area.
If, on the other hand, speciahzation of the cortex is denied, then
there must be admitted a specialization of the peripheral organ — with

585

586 TEXT-BOOK OF PHYSIOLOGY.

a resulting difference in quality or rapidity of the nerve impulses
which would impress or excite the non-specialized cortex in 'such a
way as to call forth the characteristic sensation. It is possible, how-
ever, that neither supposition is wholly correct, and that the char-
acter of the sensation depends on the construction and adaptation
of the entire sense apparatus to the character of the stimulus.

Whatever the conditions for their origin and whatever their
characteristics, sensations in themselves do not constitute knowledge;
they are but elementary states of consciousness, raw materials out
of which the mind elaborates conceptions and forms judgments as
to the character of any given object in comparison with former
experiences.

THE SENSE OF TOUCH.

The physiologic mechanism involved in the sense of touch in-
cludes the skin and the mucous membrane lining the mouth, the
afferent nerves, their cortical connections, and nerve-cells in the
cortex of the parietal lobe and the gyrus fornicatus (Figs. 226, 227).

Peripheral excitation of this mechanism develops nerve impulses
which, transmitted to the cortex, evoke sensations of touch and
temperature. To the skin, therefore, is ascribed a touch sense
and a temperature sense. Of the touch sensations two kinds may
be distinguished: viz., pressure sensations and place sensations.
With the contact of an external body there arises the perception
not only of the pressure, but also the perception of the place or
locality of the contact. In accordance with this, it is customary to
attribute to the skin a pressure sense and a location sense.

The specific physiologic stimuli to -the terminal organs in the skin
and oral mucous membrane are mechanic pressure and thermic
vibrations.

The Skin. — The skin, which constitutes the basis for the sense
of touch, covers and closely invests the entire body. It varies in
thickness and delicacy in different regions, though its structure is
everywhere essentially the same. As the physiologic anatomy of the
skin has elsewhere been detailed (page 435), it is only necessary to
state here that it is divided into a deep and a superficial layer. The
former, known as the derma, consists of an inner layer of rather
loose connective tissue and an outer layer of condensed connective
tissue. The latter, known as the epidermis, consists of an inner
layer of pigment cells and a thick outer layer of epithelial cells.
The derma is characterized by the presence of elevations (papillae)
which are everywhere extremely abundant. Throughout the derma
ramify blood-vessels and nerves.

The Peripheral or Terminal Organs. — Between the contact
surface and the afferent nerves specialized structures are found

THE SENSE OF TOUCH.

5S7

which serve as intermediates between the stimulus, on the one hand,
and the afferent nerves, on the other hand. By virtue of their struc-
ture they are far more irritable than the nerve-fibers and hence
respond more quickly to the physiologic stimulus than the nerve-
fiber itself. To these specialized organs, found not only in the
skin but in other sense-organs as well, the term peripheral or terminal
organ is given. It is these structures that are primarily excited to
activity by the physiologic stimulus, and that in turn arouse the
nerve to activity. Peripheral organs are to be regarded as special
modes of termination of afferent nerves and adapted for the impress
of a specific stimulus. The peripheral organs of afferent nerves
found in the skin and oral mucous membrane present a variety of
forms, some of which are as follows:

1. Free Endings. — These are pointed or club-shaped processes, the

ultimate terminations of af-
erent nerve-fibrils, found in
and among epidermic cells.

2. Tactile Cells. — These are oval

nucleated bodies found in
the deeper layers of the
epidermis. They rest upon
or are embraced by a cres-
centic shaped body, the
tactile meniscus, which in
turn is directly connected
with the nerve-fibril and
probably a modification of it
(Fig. 270).

3. The Corpuscles of Meissner

and Wagner. — In the papillae

of the derma, especially in the palm of the hand and in the
finger-tips, are found eUiptical bodies consisting of a connective-
tissue capsule containing a number of tactile discs with which the
nerve-fibrils are connected. If the aft'erent nerve is traced to
the capsule, it is found to lose both its neurilemma and medulla,
after which the naked fibril penetrates the capsule, breaks up
into a number of branches, and after pursuing a more or less
spiral course becomes connected with the tactile discs (Fig. 271).

4. Hair Wreaths. — Just below the openings of the sebaceous gland

the hair follicles are surrounded by naked axis-cylinder fibrils
in the form of a wreath, which in all probability terminate in
the cells of the external root-sheath. These, too, are to be
regarded as part of the touch apparatus.

5. Corpuscles of Voter or Pacini. — These are oval-shaped structures

found along the nerves distributed to the palms of the hands and

Fig. 270. — Tactile Cells from Snout
OF Pig. a. Tactile cell. m. Tactile
disc. n. Nerve-fiber. — {Stirling.)

588

TEXT-BOOK OF PHYSIOLOGY.

.1

the soles of the feet, on the nerves distributed to the external
genital organs, to joints and other structures. They consist of
a thick capsule of lamellated connective tissue in the interior
of which is a bulb resembling granular protoplasm. The axis-
cylinder of the nerve-fiber enters the capsule and becomes con-
nected with the bulb (Fig. 272).
Other forms of peripheral organs are found in special regions of
the skin as well as in different animals.

Touch Sense. — The area, stimulation
of which evokes sensations of touch, is
coextensive with the skin and that limited
portion of the mucous membrane lining
the mouth. Careful stimulation of the
skin by means of a fine stiff bristle has
revealed the fact, however, that the touch
area is not continuous, but discrete, pre-
senting itself under the form of small areas
or spots, separated by relatively large areas
insensitive to the same agent. Stimulation
of these spots always calls forth a sensation
of touch. For this reason they are known
as "touch spots." The number of such
spots in any given area of skin varies
considerably. Thus, in the skin of the calf
fifteen such spots have been counted in a
square centimeter. In the palm of the
hand, from forty to fifty have been counted
in an area of the same extent. They are
also especially abundant in the immediate
neighborhood of the hair follicles.

The peripheral end-organ associated
with the touch spots in the neighborhood
of a hair follicle is in all probability the
wreath of nerve-fibrils surrounding the
follicle. In regions devoid of hairs the
end-organ is the Meissner corpuscle, for
in the palmar surface of the last phalanx
of the index-finger, where the touch sense is quite acute, about 20
corpuscles are present in each square millimeter of surface. The
specific stimulus necessary to evoke the sensation of touch is a
deformation of the skin; and the greater this is within physiologic
limits, the more pronounced is the sensation.

Pressure Sense. — The contact of an external body is attended
by a certain amount of pressure, which, however, must attain a
certain degree before the sensation can be evoked. This is known

Fig. 271. — Touch Corpus-
cle OF Meissner and
Wagner, b. Papilla of
cutis, d. Nerve-fiber of
touch-corpuscle. e, /.
Nerve-fiber in touch-
corpuscle, g. Cells of
Malpighian layer. —

{From Stirling.)

THE SENSE OF TOUCH.

589

as the threshold value, or the degree of liminal intensity. Since
the sensations are the result of pressure, they are termed pressure
sensations, and their intensity may be expressed in terms of pressure.

The sensitivity of the skin as determined by the pressure sense
varies in different regions of the body and in accordance with the
size of the area pressed. Thus, the liminal intensity of a stimulus
for an area of nine square millimeters for the skin of the forehead is
0.002 gram; for the flexor aspect of the forearm, 0.003 gram; and
for the hips, thigh, and abdomen, 0.005 gram; for the palmar surface
of the finger, 0.019 gram; for the heel, i gram. The delicacy of the
sense of touch is measured by the slight
increase or decrease in the intensity of the
stimulus that will produce an appreciable
change in the intensity of the sensation.
Not all changes in the stimulus, however,
are attended by a change in the sensation.
It has been determined that the latter will
change only when the former changes in a
definite ratio, which for the volar surface of
the third phalanx of the index-finger is as 29
is to 30. Thus, other things being equal,
a sensation caused by a given weight will
only change with moderate stimulation when
one-thirtieth of the weight is either added
or subtracted. The ratio of change, how-
ever, varies in different regions of the body :
thus, for the back of the hand the ratio
varies from one-tenth to one-twentieth; for
the tongue, one-thirtieth to one-fortieth.
The difference of stimulus necessary to
evoke a sensation is known as the threshold
difference. It seems to be a law not only
for the skin, but for other senses as well,
that a change in the intensity of a sensation,

to an appreciable extent, will occur only when the objective stimulus
changes in a definite ratio. This ratio, however, will vary not only
in different regions of the skin, in different individuals, but with the
sense-organ investigated.

Place Sense. — The sensation evoked by stimulation of the skin
is always, under normal conditions, referred to the place stimulated.
This holds true not only for two or more points near or widely sepa-
rated on the same side, but also for corresponding points on
opposite sides of the body, even when the stimuli have the same
intensity and are simultaneously apphed. The cause for this localiz-
ing power is to be found in a difference in the quality of the sensation

Fig. 272. — Pacinian

Corpuscles, c. Cap-
sules, d. Endothelial
lining separating the
latter, n. Nerve. /.
Funicular sheath of
nerve. m. Central
mass. n'. Terminal
fiber; and a. Where
it splits up into finer
fibrils.

590

TEXT-BOOK OF PHYSIOLOGY

related in some way to the part stimulated. Each cutaneous area
is supposed to give to the tactile sensation a quality or local sign
by virtue of which the mind is enabled to localize the point of contact.

Each cutaneous area which has a local sign of its own is known
as a sensory circle, for the reason that the mind does not refer the
sensation to a point, but to an area more or less circular in outline.
The skin may therefore be regarded as composed of myriads of
such circles varying in size in different regions of the body.

The delicacy of the localizing power in any part of the skin is
determined by testing the power which the part possesses, of
distinguishing the sensations produced by the contact of the
points of a pair of compasses placed close together. The distance
to which the points must be separated in order to evoke two separate
recognizable sensations is a measure of the diameter of the sensory
circle. Within this circle the two sensations become fused into one
sensation. The discriminative sensibility of different regions as
determined by compass points is shown in the following table; the
numbers represent the distances at which two sensations are recog-
nized :

MM.

Tip of tongue, i.i

Palmar surface of third phalanx of index-linger, 2.2

Red surface of lips, 4-5

Palmar surface of first phalanx of finger, 5.5

Tip of nose, 6.8

Palm of hand, 8.9

Lower part of forehead, 22.6

Dorsum of hand, 31.6

Dorsum of foot, 40-6

Middle of the back, 67.7

The discriminative sensibihty of any portion of the body is a
function of its mobihty. This is shown by the fact that it increases
rapidly from the shoulders to the fingers and from the hips to the
toes.

The Temperature Sense. — The sensations of heat and cold
which are experienced from time to time are caused by changes in
the temperature of the skin produced in a variety of ways. As
these sensations are specifically different from those of touch, as
well as different from each other, it is highly probable that for each
sensation there are special nerve-endings distributed throughout the
skin. Investigations have shown that all over the skin there are
innumerable spots of varying size which if stimulated evoke
sensations of heat or cold. Such points are termed heat and
cold spots. Each responds to but one kind of stimulus. A warm
object applied to a heat spot will evoke a sensation of warmth.
It will have no effect on the cold spot. The reverse is also true.
Between the cold and heat spots there are areas that are neutral,

THE SENSE OF TOUCH.

591

insensitive lo either heat or cold. The cold spots are more numerous
than the heat spots in almost all regions of the body.

The sensitivity of the skin to temperature changes is very acute,
as shown by the fact that even 0.05° C. is readily appreciable. This
holds true, however, only when the temperature of the object lies
between 27° and 33° C. This capabihty varies in different regions
of the skin, and depends on the number of heat and cold spots
present, the thickness of the epidermis, the thermal conductivity
of the object touching it, and the extent to which it is habitually
exposed or protected.

The physiologic stimulus to the thermic end-organs is the passage

Fig. 27,^. — Cold and Hot Spots from the Anterior Surface of the Forearm.
a. Cold spots, b. Hot spots. The dark parts are the most sensitive, the hatched
the medium, the dotted the feebly, and the vacant spaces the non-sensitive.

of heat through the skin from the interior of the body to the sur-
rounding air. If the radiation is continuous and uniform, the end-
organs soon adapt themselves to the temperature of the surrounding
air and the sensation of heat, under physiologic conditions, is not
evoked. If there is a sudden rise in the external temperature caused
by natural or artificial means, which diminishes the radiation, the
temperature of the skin will at once rise, the end-organs will be
stimulated, and a sensation of warmth developed. If, on the other
hand, there is a sudden fall in temperature and an increased radia-
tion, the temperature of the skin will fall, the end-organs will be
stimulated, and a sensation of cold developed. Experiment also
teaches that the intensity of a warm or cold sensation will depend

592 TEXT-BOOK OF PHYSIOLOGY.

on the existing temperature of the skin, and not upon the absolute
temperature of the object. Thus, water at 20° C. will evoke a
sensation of heat or cold according as the skin has previously been
cooled below or warmed above this temperature.

The Muscle Sense. — ^As a result of the activities of the muscula-
ture of the body or even of its individual parts, there arises in con-
sciousness a series of sensations, which are termed muscle sensations.
These sensations give rise to the perception —

1. Of the direction and duration of both passive (due to external

causes) and active movements (due to internal, volitional efforts)
which take place without hindrance;

2. Of the resistance offered to movements by external bodies; and —

3. Of the posture of the body or of its individual parts.

As to the seat of the physiologic processes which precede and
underlie the development of the sensations two views, at least, may
be advanced, viz. :

1. That the processes are central in origin and partake of the nature

of a discharge of nerve impulses from the nerve-cells through
the motor nerves to the muscles, the entire process being accom-
panied by sensation. This is known as the innervation theory.

2. That the processes are peripheral in origin, initiated by stimulation

of specialized end-organs in the muscles and tendons which are
connected through the intermediation of afferent nerves with
nerve- cells in the cerebral cortex.
The physiologic mechanism subserving the muscle sense, accord-
ing to the second theory, now held by many physiologists, thus in-
volves peripheral end-organs, afferent nerves, their cortical connec-
tions and nerve- cells in the cerebral cortex at or near the junction
of the superior and inferior parietal convolutions.

The End-organs. — These are small fusiform structures found in
and among the muscle bundles of all the muscles of the body with
the exception of the diaphragm and eye muscles. In the muscles of
the arm and in the small muscles of the hand they are especially
abundant. From their shape they are known as muscle spindles.
They vary in length from 2 to 12 mm. and in breadth from 0.15
to 0.4 mm. Each spindle (Fig. 274) consists of a connective-tissue
capsule containing from two to ten longitudinally arranged striated
muscle fibers of fine diameter. In the middle or equatorial region
of these intra-jusal fibers there is frequently found a quantity of
non-striated protoplasmic matter. The spindle is supplied with both
sensor and motor nerves. The sensor fiber loses its external invest-
ments as it approaches the capsule. The naked axis-cylinder then
penetrates the capsule, and after dividing several times terminates in
a ribbon-like or spiral manner around the intra-fusal muscle fiber.
This ending was described by and is known as Ruffini's "annulo-

THE SENSE OF TOUCH.

593

spiral ribbon." The motor nerve also penetrates the capsule and
terminates in the polar extremities of the intra-fusal fiber. Sensor
end-organs supposed to be connected with the muscle sense are also
found in the tendons of muscles.

Afferent Nerves. — That muscles are abundantly supplied with
afferent nerves has been proved by different methods of investigation.
With histologic methods Sherrington has traced afferent fibers from
the muscle spindles directly into the spinal nerve gangha. The con-
tractions of muscles from electric stimulation as well as the con-
tractions known as muscle cramp, due to unknown agents, give rise
to sensations of pain, a fact which indicates the presence in muscles
of afferent or sensor nerves.

Cortical Area. — Pathologic findings have shown that an im-
pairment or a loss of the muscle sense is associated with de-
structive lesions of perhaps the superior and inferior parietal

Fig. 274. — A Neuro-muscle Spindle of a Cat. (Rttffini.) c. Capsule, pr. e.
Primary ending. 5. e. Secondary ending, pi. e. Plate ending. (All these are
probably sensor in function.) — {Starling's "Physiology.")

convolutions (Fig. 226). In a case reported by Starr the removal
of a small tumor in the pia mater situated over the junction
of the superior and inferior parietal lobules was followed by a
loss of the muscle sense and marked ataxia in the right hand
for a period of six weeks, after which recovery took place. These
symptoms were attributed to injury of the cortex from unavoidable
surgical procedures.

The muscle sensations, as stated in foregoing paragraphs, form
the basis of the perception not only of the direction and the duration
of a body movement and the resistance experienced, but also of the
position and the tension of the muscle groups. The latter fact
more especially makes it possible for the mind to direct the muscles
and to graduate the energy necessary to the accomplishment of a
definite purpose.

Active Touch. — x^ctive touch or the application of the fingers
to the surfaces of external objects implies the cooperation of the
skin and the muscles. The sensations which are evoked are combina-
38

594

TEXT-BOOK OF PHYSIOLOGY.

tions of contact and muscle sensations. The union of these sensa-
tions forms the basis of the perception of hardness, softness, smooth-
ness, and roughness of bodies.

THE SENSE OF TASTE.

The physiologic mechanism involved in the sense of taste includes
the tongue, the gustatory nerves (the'chorda tympani and the glosso-
phar}'ngeal), their cortical connections and nerve-cells in the gray
matter of the fourth temporal convolutions. The peripheral
excitation of this apparatus gives rise to nerve impulses which
transmitted to the brain evoke the sensations of taste. The
specific physiologic stimulus is matter, organic and inorganic, in a
state of solution.

The Tongue. — The tongue consists of both intrinsic and extrinsic
muscles, in virtue of which it is susceptible
of both a change in shape and position.
The movements of the tongue, though not
essential to taste, are made use of in the
finer discrimination of tastes.

The tongue is covered over by mucous
membrane continuous with that lining the
oral cavity. The dorsum of the tongue
presents a series of papillae richly supplied
with blood-vessels and nerves. Of these
there are three varieties, the filiform, the
fungiform, and the circumvallate (Fig. 275).

1. The filiform papilla, the most numerous,
cover the anterior two-thirds of the
tongue; they are conical or filiform in
shape and covered with horny epithe-
lium which is often prolonged into
filamentous tufts.

2. The fungiform papilla, found chiefly at
the tip and sides of the tongue, are
less numerous but larger than the pre-
ceding and of a deep red color.

The circumvallate papillcE, from eight to ten in number, are

situated at the base of the tongue arranged in the form of the

letter V. They consist of a central projection surrounded by

a wall or circumvallation from which they take their name.

The Peripheral End-organs. The Taste-buds. — Embedded

in the epithelium covering the mucous membrane not only of the

tongue but of the palate and posterior surface of the epiglottis are

small ovoid bodies which from their relation to the gustatory nerves

Fig. 275. — The Tongue.
I . Papillae circumval-
latse. 2. Papillae fungi-
formes.

3

THE SENSE OF TASTE.

595

are regarded as their peripheral end-organs and known as taste-buds
or taste-beakers. Each bud is ovoid in shape (Fig. 276). Its base
rests on the tunica propria; its apex comes up to the epithehum, where
it presents a narrow funnel-shaped opening, the taste-pore. The wall
of the bud is composed of elongated curved epithehum. The
interior contains narrow spindle-shaped neuro-epithelial cells pro-
vided at their outer extremity with stiff hair-like
filaments which project into the taste-pore.

The neuro-epithelial cells are in physiologic
relation with the nerves of taste. The terminal
branches, after entering the bud at its base,
develop fine tufts which come into contact with
the cells. That the taste-buds are connected with
the nerves of taste is rendered probable from the
fact of their degeneration after division of the
nerves.

The Taste Area. — The taste area, though
confined for the most part to the tongue, extends
itself in different individuals to the mucous mem-
brane of the hard palate, to the anterior sur-
face of the soft palate, to the uvula, the anterior
and posterior half arches, the tonsils, the posterior
wall of the phan^nx, and the epiglottis.

The Taste Sensations. — The sensations
which arise in consequence of impressions made
by different substances on the peripheral appara-
tus of this area are in so many instances com-
binations of taste, touch, temperature, and smell
that they are extremely difficult of classification.
Nevertheless four primary tastes can be recog-
nized: viz., bitter, sweet, acid or sour, salt or saline.
Though the contact of any bitter, sweet, acid,
or salt substance with any part of the tongue
will, if the substance be present in sufficient
quantity or concentration, develop a corresponding
sensation, some regions of the tongue are more sensitive and respon-
sive than others. Thus, the posterior portion is more sensitive to
bitter substances than the anterior; the reverse is true for sweet
substances and perhaps for acids and salines.

The intensity of the resulting sensation in any given instance
will depend on the degree of concentration of the substance, while
its massiveness will depend on the area afi'ected.

Fig. 276. — Taste-
bud FROM ClR-
cumvallate
Papilla of a
Child. The
oval structure is
limited to the
epithelium {e)
lining the fur-
row, encroach-
ing slightly
upon the adja-
cent connective
tissue (/) ; o,
taste-pore
through which
the taste - cells
communicate
with the mucous
surface. — {After
Pier sol.)

596 TEXT-BOOK OF PHYSIOLOGY.

THE SENSE OF SMELL.

The physiologic mechanism involved in the sense of smell in-
cludes the nasal foss£e, the olfactory nerves, the olfactory tracts, and
nerve-cells in those areas of the cortex known as the uncinate con-
volution and anterior part of the gyrus fornicatus. Peripheral stimu-
lation of this mechanism develops nerve impulses which, transmitted
to the cortex, evoke the sensations of odor. The specific physiologic
stimulus is matter in the gaseous or volatile state.

The Nasal Fossae. — The nasal fossae are irregularly shaped
cavities separated by a vertical septum formed by the perpendicular
plate of the ethmoid bone, the vomer, and the triangular cartilage.
The outer wall presents three recesses separated by the projection
inward of the turbinated bones. Each fossa opens anteriorly and
posteriorly by the anterior and posterior nares, the latter com-
municating with the pharynx. Both fossae are lined throughout by
mucous membrane. The upper part of the fossa is known as the
olfactory, the lower portion as the respiratory region. In the former^
the mucous membrane over the septum and superior turbinated
bone is somewhat thicker than elsewhere and covered with a neuro-
epithelium which constitutes —

The Peripheral End-organ. — This consists of a basement
membrane supporting two kinds of cells, the olfactory and the
sustentacular. The olfactory cells are bipolar nerve-cells, the center
of which contains a large spheric nucleus. The peripheral pole
is cyHndric or conic in shape and provided at its extremity with
several hair-like processes. The central pole becomes the axon
process and passes directly to the olfactory bulb.

The sustentacular cells are epithelial in character and, as their
name impHes, support or sustain the olfactory cells.

For the appreciation of odorous particles the air must be drawn
through the nasal fossae with a certain degree of velocity. If the
particles are widely diffused in the air, they must be drawn not only
more quickly but more forcibly into contact with the olfactory
hairs, as in the act of sniffing, the result of short energetic inspira-
tions. To many substances the olfactory apparatus is extremely
sensitive. Thus, it has been shown that a particle of mercaptan.
the actual weight of which was calculated to be igpkooo ^^ ^ milli-
gram gave rise to a distinct sensation.

The Olfactory Sensations. — The sensations which arise in
consequence of the excitation of the olfactory apparatus are very
numerous and their classification is extremely difficult. For this^
reason it is customary to divide them into two groups: viz., agreeable
and disagreeable, in accordance with the feelings they excite in the
individual. As the olfactory sensations give rise to feelings rather

THE SENSE OF SMELL. 597

than ideas, this sense plays in man a subordinate part in the acquisi-
tion of knowledge. In lower animals this sense is employed for the
purpose of discovering and securing food, for detecting enemies and
friends, and for sexual purposes. In land animals the entire olfac-
tory apparatus is well developed and the sense keen; in some aquatic
animals, as the dolphin, whale, and seal, the apparatus is poorly
developed and the sense dull.

CHAPTER XXV.
THE SENSE OF SIGHT.

The physiologic mechanism involved in the sense of sight in-
cludes the eyeball, the optic nerve, the optic tracts, their cortical
connections, and nerve-cells in the cuneus and adjacent gray matter.
Peripheral stimulation of this mechanism develops nerve impulses
which transmitted to the cortex evoke (i) the sensation of light and
its different qualities — colors; (2) the perception of light and color
under the form of pictures of external objects; and (3) in connection
with the ocular muscles, the production of muscle sensations by
which the size, distance, and direction of objects may be judged.

The specific physiologic stimulus to the terminal end-organ,
the retina, is the impact of ether vibrations. In general, it may
be said that, at least for the same color, the intensity of the objective
vibration determines the intensity of the sensation.

THE PHYSIOLOGIC ANATOMY OF THE EYEBALL.

The eyeball is situated at the fore part of the orbit cavity, and
in such a position as to permit of an extensive range of vision. It
is loosely held in position by a fibrous membrane, the capsule of
Tenon, which is attached, on the one hand, to the eyeball itself,
and, on the other, to the walls of the orbit cavity. Thus suspended,
the eyeball is susceptible of being moved in any direction by the
contraction of the muscles attached to it.

The ball is spheroid in shape, measuring about 24 millimeters
in its antero-posterior diameter and a little less in its transverse
and vertical diameters. When viewed in profile, it is seen to con-
sist of the segments of two spheres, of which the posterior is the
larger, occupying five-sixths, and the anterior is the smaller, occupy-
ing one-sixth of the ball. It is composed of several concentrically
arranged membranes enclosing various refracting media essential to
vision.

The membranes, enumerating them from without inward, are
as follows: the sclera and cornea, the chorioid and iris, and the
retina. The refracting media are the aqueous humor, the crystal-
line lens, and the vitreous humor.

The Sclera and Cornea. — The sclera is the thick opaque mem-
brane covering the posterior five-sixths of the ball. It is composed

598

THE SENSE OF SIGHT. 599

of layers of connective tissue which are arranged transversely and
longitudinally. It is pierced posteriorly by the optic nerve about
3 or 4 millimeters internal to the optic axis. By virtue of its firmness
and density the sclera gives form to the eyeball, protects delicate
structures enclosed by it, and serves for the attachment of the muscles
by which the ball is moved. The cornea is the transparent mem-
brane forming the anterior one-sixth of the ball. It is nearly circular
in shape, measuring in its horizontal meridian 12 mm., in its vertical
meridian 11 mm. The curvature is therefore sharper in the latter
than in the former. The radius of curvature of the anterior surface
at that central portion ordinarily used in vision is 7.829 mm.; that
of the posterior surface about 6 mm.

The substance of the cornea is made up of thin layers of deHcate
transparent fibrils of connective tissue continuous with those found
in the sclera. Lymph-spaces are present throughout the cornea, in
which are to be found lymph-corpuscles. The anterior surface of
the cornea is covered with several layers of nucleated epitheHum
supported by a structureless membrane, the anterior elastic lamina.
The posterior surface also is covered by a layer of epitheHum sup-
ported by a similar membrane, the membrane of Descemet, which
at its periphery becomes continuous with the iris. At the junction
of the cornea and sclera there is a circular groove, known as the
canal of Schlemm.

The Chorioid, Iris, Ciliary Muscle, and Ciliary Processes.—
The chorioid is the dark brown membrane which extends forward
nearly to the cornea, where it terminates in a series of folds, the
cihary processes. Posteriorly, it is pierced by the optic nerve. It
is composed largely of blood-vessels, arteries, capillaries, and veins,
supported by connective tissue. Externally it is loosely connected
to the sclera; internally it is hned by a layer of hexagonal cells con-
taining black pigment which, though usually described as a part of
the chorioid, is now known to belong, embr}'ologically and physio-
logically, to the retina. Lying within the outer layer of arteries and
veins there is a thick layer of small arterioles and capillaries, known
as the chorio-capillaris. The chorioid with its contained blood-vessels
bears an important relation to the nutrition and function of the eye.
It provides a free supply of lymph and presents a uniform temperature
to the retina in contact with it (Fig. 277).

The iris is the circular, variously colored membrane in the anterior
part of the eye just behind the cornea. It presents a httle to the
nasal side of the center a circular opening, the pupil. The outer or
circumferential border is united by connective tissue to the cornea,
sclera, and ciliary muscle; the inner border forms the boundary of
the pupil. The iris consists of a framework of connective tissue sup-
porting blood-vessels, muscle-fibers, and pigmented connective-tissue

6oo

TEXT-BOOK OF PHYSIOLOGY.

cells. The anterior surface is covered by a layer of cells continuous
with those covering the posterior surface of the cornea. The pos-
terior surface is formed by a thin structureless membrane supporting
a layer of pigment cells continuous with those lining the chorioid.
The color which the iris presents in different individuals depends on
the relative amount of pigment in the connective-tissue corpuscles.
In blue eyes the pigment is wanting. In gray, brown, and black
eyes the pigment is present in progressively increasing amounts. The

blood - vessels are

.™~.2 i\ r. 13 1

13 If, i-

FiG, 277. — Chorioid Coat of the Eye. — i. Optic
nerve. 2, 2, 2, 2, 3, 3, 3, 4. Sclerotic coat divided
and turned back to show the chorioid. 5, 5, $, 5.
The cornea, divided into four portions and turned
back. 6, 6. Canal of Schlemm. 7. External
surface of the chorioid, traversed by the ciliary-
nerves and one of the long ciliary arteries. 8.
Central vessel into which open the vasa vorticosa.
9, 9, 10, 10. Chorioid zone. 11, 11. Ciliary
nerves. 12. Long ciliary artery. 13, 13, 13, 13.
Anterior ciliary arteries. 14. Iris. 15, 15. Vas-
cular circle of the iris. 16. Pupil. — (Sappey.)

connected with
those of the chori-
oid coat.

The muscle-
fibers are of the
non-striated variety
and arranged in
two sets, one cir-
cularly, the other
radially, disposed.

The circular
fibers are found
close to the pupil
near the posterior
surface of the iris.
Contraction of this
band of fibers di-
minishes, relaxation
increases, the size
of the pupil. This
muscle is known
as the sphincter

pupillcE or sphincter
iridis.

The radial
fibers form a more
or less continuous
layer in the posterior part of the iris, extending from the margin
of the pupil, where they blend with the circular fibers, to the outer
border. Contraction of the fibers enlarges the size of the pupil.
The muscle is known as the dilatator pupillcE.

The nerves exciting the circular fibers to action are the ciliary
nerves, axons of nerve-cells located in the ciliary or ophthalmic gan-
glion. Stimulation of these fibers gives rise to contraction of the
sphincter and diminution in the size of the pupil. The nerves excit-
ing the dilatator fibers are axons of nerve-cells located in the superior

THE SENSE OF SIGHT.

60 1

cervical ganglion. They reach the iris by way of the cervical sympa-
thetic, the ophthalmic division of the fifth, and the long cihary nerve.
Stimulation of these nerves is followed by dilatation of the pupil.
Both the ciliary and superior cervical gangha are in relation with
pre-ganglionic fibers coming from the central nerve system. (See

page 535-)

The ciliary muscle is a gray circular band about two millimeters
in width, consisting of non-striated muscle-fibers. The majority of
these fibers pursue a radial or meridional direction. Taking their
origin from the junction of the sclera, cornea, and iris, they pass
backward to be inserted into the chorioid coat opposite the cihary
processes. The inner portion of the muscle is interrupted by bundles
of fibers which pursue a circular direction. They collectively con-
stitute the annular or ring muscle of Miiller. The ciliary muscle in

Fig. 278. — Section through the Ciliary Region of the Human Eye. a. Radi-
ating bundles of the ciliary muscle, b. Deeper bundles, c. Circular network.
d. Annular muscle of Miiller. e. Tendon of ciliary muscle. /. Muscle-fiibers
on posterior side of the iris. g. Muscles on the ciliary border of the same. h.
Ligamentum pectinatum. — {After Iwaiioff.)

common with the circular fibers of the iris receives its nerve-supply
direct from the nerve-cells in the ciliary ganglion. Contraction of
the ciliary muscle tenses the chorioid coat, and for this reason it is
frequently termed the tensor chorioidea.

The Retina. — The retina is the internal coat of the eye, extending
forward almost to the ciliary processes, where it terminates in an
indented border, known as the ora serrata. In the living condition
it is clear, transparent, and pink in color. After death it becomes
opaque. The retina is abundantly supplied with blood-vessels, de-
rived from the arteria centralis retince, a branch of the ophthalmic,
which pierces the optic nerve near the sclera, runs forward in its
center, to the retina, in which its terminal branches are distributed.
The veins arising from the capillary plexus leave the retina by the
same route.

6o2

TEXT-BOOK OF PHYSIOLOGY.

In the posterior portion of the retina, at a point corresponding
with the axis of vision, there is a small oval area about 2 nim. in
its transverse and about 0.8 mm. in its vertical diameter. From the

fact that it becomes

I. Pigment-layer (not shown). yclloW after death, it is

known as the macula
lutea. This area pre-
sents in its center a
depression with slop-
ing, sides, known as
the jovea centralis.
About 3.5 mm. to the
nasal side of the
macula is the point of
entrance of the optic
nerve.

The retina is re-
markably complex in
structure, presenting
an appearance when
viewed microscopic-
ally, something like
that represented in
Fig. 279, indicating
that it is composed of
different cellular ele-
Tliese have been named, from behind

m^>

Fig. 279. — Vertical Section of
— {Schdper.y

2. Layer of rods and cones.

3. External limiting membrane.

4. Outer nuclear layer

5. Outer molecular layer.

6. Inner nuclear layer.

7. Inner molecular layer.

8. Layer of ganglion cells.

9. Layer of nerve-fibers.

Human Retina.

ments arranged in layers,
forward, as follows :

1. The layer of pigment cells.

2. The layer of rods and cones, or Jacobson's layer.

3. The external limiting membrane.

4. The outer nuclear or granular layer.

5. The outer molecular or reticular layer.

6. The inner nuclear or granular layer.

7. The inner molecular or reticular layer.

8. The layer of ganglion cells.

9. The layer of nerve-fibers.

Modern histologic methods of research have made it possible to
reduce the retina, exclusive of the pigment cells, to three successive
layers of nerve-cells, supported by a highly developed neurogha,,
forming what has been termed the fibers of Miiller. These nerve-
cells are as follows :

1. The visual cells.

2. The bipolar cells.

3. The ganglion cells.

THE SENSE OF SIGHT.

603

The relation of these nerve-cells one to another and to the supporting
neuroglia tissue and the manner in which they unite to form the
above-mentioned layers are schematically shown in Fig. 280.

The pigment layer is composed of hexagonal cells. Though
formerly described as forming a part (the inner layer) of the chorioid,
these cells belong embr}'Ologically to the retina. From their retinal
surface delicate pigmented processes extend into and between the
rods and cones. On expo-
sure to light these processes
elongate and push themselves
between the rods. In the
dark they retract and with-
draw into the cell-body.

The visual cells which
form the layer of rods and
cones are of two varieties, the
rod-shaped and the cone-
shaped.

The rod-shaped visual cells
consist of a straight elongated
cylinder extending through the
entire thickness of Jacobson's
membrane and a fine fiber
containing a nucleus, which,
after piercing the external
limiting membrane, passes
into the outer molecular layer,
where it terminates in a spheric
enlargement. The outer por-
tion of the rod is clear and
homogeneous, though contain-
ing a pigment known as visual
purple or rhodopsin ; the inner
portion of the rod is slightly
granular.

The cone - shaped visual
cells also consist of two por-
tions, a conic portion situated in Jacobson's membrane between the
rods, and a fine fiber, containing a nucleus, which, after piercing the
external limiting membrane, passes into the outer molecular layer,
where it terminates in a fine tuft. • The inner portion of the cone is
thicker than the rod and rests on the hmiting membrane; the outer
portion tapers to a fine point and is knoAvn as the cone-style. The
cones, as a rule, are shorter than the rods. The proportion of rods
to cones varies in different parts of the retina, though there are on

Fig

2S0. — Cross-section of the Retina
FROM A Mammal. A. Layer of rods
and cones. B. Visual cells (outer gran-
ules). C. Outer molecular layer. E.
Bipolar cells (inner granules). F. In-
ner molecular layer. G. Ganglion cells.
H. Layer of nerve-fibers, a. Rods. b.
Cones, e. Bipolar rod. f. Bipolar
cone. r. Lower ramification of a bi-
polar rod. f. Lower ramification of a
bipolar cone, g, h, i, j, k. Ganglion
cells in various stages, branching from
F. X, z. Bipolar contact of rods and
cones, t. Miiller's supporting fibers.
S. Centrifugal nerve-fibers. — {After Ra-
mon y Cajal.)

6o4 TEXT-BOOK OF PHYSIOLOGY.

the average about fourteen rods to one cone. In the macula the rods
are almost entirely absent, cones alone being present.

The layer of visual cells together with the neuroglia constitute the
first three layers of the retina proper. The external limiting mem-
brane is formed by the blending of the ends of neuroglia cells.

The bipolar cells consist of a central portion, found in the inner
nuclear layer, from which are given off two processes which pass in
opposite directions, one toward the visual cells, the other toward the
ganglion cells. The former terminate in tufts which arborize around
the tufts and spheric enlargements of the visual cells, and assist in
the formation of the outer molecular layer; the latter terminate in
similar tufts in the inner molecular layer.

The ganglion cells are arranged in a single layer, as a rule. They
are large and nucleated. From the inner side of each cell there is
given off a single axon which passes toward the center of the retina
(forming the nerve-fiber layer), where it enters and assists in forming
the optic nerve. From the outer side of the ganglion cell dendrites
pass into and assist in forming the inner molecular layer. These den-
drites come into physiologic relation with those of the inner pro-
cesses of the bipolar cells.

Horizontally disposed nerve-cells are also present in the outer
molecular layer in relation with the visual cells. Spongioblasts or
amacrine cells are also present at the border of and in the inner molec-
ular layer.

From the relation of the ganglion cells, from which the optic ner\T-
fibers take their origin, to the visual cells and the bipolar cells, the
latter may be regarded as the terminal visual organ, the intermediate
between the ether vibrations and the ganglion cell. The visual cells
are directed toward the chorioid, away from the entering light,
dipping into the pigment cells. They, with the pigment layer, are
the elements by which the ether vibrations are transformed into ner\-e
energy.

In the fovea most of the retinal elements are wanting or are
reduced in thickness. The cones alone are present. The cone-fibers
with their nuclei are directed obliquely upward and outward along
the slope -of the fovea, to end in tufts which come into physiologic
relation with the dendrites of the ganglion cells which at the top of
the fovea are generally increased in number (Fig. 281).

It is estimated that the optic nerve contains about 500,000 nerve-
fibers, and that for each fiber there are about 7 cones, 100 rods, and
7 pigment cells. In accordance with this estimate there would be
about 3,500,000 cones, 50,000,000 rods, and 3,500,000 pigment cells.
The distance between the centers of two adjacent cones in the fovea
is 4 micromillimeters.

THE SENSE OF SIGHT.

605

The vitreous humor is the largest of the refracting media and
occupies by far the largest portion of the interior of the eyeball. From
its position it gives support to the retina. Anteriorly it presents a
concavity, in which the crystalline lens is lodged. The vitreous humor
consists of water (97 per cent.), organic matter and salts, enclosed in a
transparent membrane, the tunica hyaloidea. The mass of the vitre-
ous humor is penetrated by a species of connective tissue.

The aqueous humor is small in amount in comparison with the
vitreous and is found in the space between the cornea and the lens
(the anterior and posterior chambers). It is a clear, watery, alkaline

Fig. 281. — Horizontal Section through the Macula and Fovea of a Man
Sixty Years Old. The section is not through the exact center of the fovea,
for there are only cone visual cells and no remnants of the confluence of the inner
granule and ganglion cell layers are present, i. Cones. 2. External limiting
membrane. 3. Outer nuclear layer. 4. Henle's fiber layer. 5. Outer molec-
ular or reticular layer. 6. Inner nuclear layer. 7. Inner molecular or reticular
layer. 8. Layer of ganglion cells. 9. Nerve-fiber layer. — {After Schaper,
Siohr's "Histology")

fluid derived from or secreted by the capillary blood-vessels of the
ciliary body. From this origin it passes through the pupil into the
anterior chamber. It serves to keep the cornea tense and smooth.
The ocular tension partly depends on the presence of this fluid in
the eyeball. There is every reason for believing that there is a
constant stream of fluid from the blood-vessels into the eye and
from the eye through the spaces of Fontana at the base of the iris
into the canal of Schlemm, and so into the blood. Any interference
with the exit of this fluid rapidly increases the ocular tension.

The lens is the transparent biconvex body situated just behind
the iris, in the concavity of the vitreous. The thickness of the lens

6o6

TEXT-BOOK OF PHYSIOLOGY.

is 3.6 mm., the diameter about 9 mm. It consists of a transparent
capsule containing elongated hexagonal fibers which, having their
origin near the anterior central portion of the lens, pass out toward
the margin, where they bend around to terminate in a triradiate
figure on the opposite side. Chemically the lens consists of water,
a globulin body (crystallin), and salts.

The Suspensory Ligament. — The lens is held in position by the
suspensory ligament, formed in part by the hyaloid membrane and
in part by fibers derived from the ciliary processes. The former be-
comes attached to the posterior surface, the latter to the anterior

Fig. 282. — Horizontal Section of the Eyeball. — i. Sclera. 2. Cornea. 3.

Chorioid. 4. Iris. 5. Ciliary muscle. 6. Retina. 7. Lens. 8. Suspensory

ligament. 9. Canal of Schlemm. 10. Canal of Petit. 11. Optic nerve. —
{Deaver.)

surface of the lens near the equator. The space between the two
layers of the ligament is the canal of Petit. The anterior surface of
the ligament presents a series of plications conforming to correspond-
ing plications on the surface of the ciliary processes.

The relations of all the parts entering into the structure of
the eye are shown in Fig. 282.

THE SENSE OF SIGHT. 607

THE PHYSIOLOGY OF VISION

The Retinal Image. — The general function of the eye is the
formation of images of external objects on the free ends of the per-
cipient elements of the retina, the rods and cones. The existence of
an image on the retina can be readily seen in the excised eye of an
albino rabbit, when placed between a lighted candle and the eye of
an observer. Its presence in the human eye can be demonstrated
with the ophthalmoscope. It is this image, composed of focal points
of luminous rays, which stimulates the rods and cones, which is
the basis of our sight-perceptions, and out of which the mind con-
structs space-relations of external objects. In only two essential
respects does the image on the retina differ from the object, aside
from the fact that the object has usually three, the image only two,
dimensions — viz., in size and relative arrangement of its parts. What-
ever the distance, the image is generally smaller than the object; it
is also reversed, the upper part of the object becoming the lower
part of the image, and the right side of the object the left of the
image.

The Dioptric Apparatus. — The formation of an image is made
possible by the introduction of a complex refracting apparatus con-
sisting of the cornea, aqueous humor, lens, and vitreous humor.
Without these agencies the ether vibrations would give rise only to
a sensation of diffused luminosity. Rays of Hght emanating from
any one point — that is, homocentric rays — arriving at the eye must
traverse successively the different refracting media. In their passage
from one to the other, they undergo at the surfaces changes in direc-
tion before they are finally converged to a focal point. In order to
mathematically follow the rays in all their deviations through the
media, to determine their focal points and to construct an image, a
knowledge of the form of the refracting surfaces, the refractive indices
of the different media, and the distances of the surfaces from one
another must be known.

The following constants are now accepted : The radius of curvature
of that portion of each refracting surface used for distinct vision is
for the cornea 7.829 mm., for the anterior and posterior surfaces of
the lens 10 and 6 mm., respectively. The indices of refraction of the
different media are as follows: cornea and aqueous humor, 1.3365;
lens, 1. 4371; vitreous body, 1.3365. The distance from the vertex of
the cornea to the lens is 3.6 mm.; the thickness of the lens, 3.6 mm.;
the distance from the posterior surface of the lens to the retina, 15 mm.
As the two surfaces of the cornea are practically parallel, and as
the index of refraction of the aqueous humor is the same as that of
the cornea, they may be regarded as but one medium. The refracting
surfaces mav therefore be reduced to the anterior surface of the

6o8 TEXT-BOOK OF PHYSIOLOGY.

cornea, the anterior surface of the lens, and the posterior surface of
the lens.*

Parallel rays of light entering the eye pass from air, with an index
of refraction of 1.00025, into the cornea, with an index of refraction
of 1.3365. In passing from the rarer into the denser medium they
undergo refraction in accordance with the laws of optics and are
rendered somewhat convergent. The extent of this first refraction
and convergence is sufficiently great to bring parallel rays, if con-
tinued, to a focus about 10 mm. behind the retina. This would be
the condition in aphakia whether the lens is congenitally absent or
has been removed by surgical procedures. Perfect vision, however,
requires that the convergence of the light must be great enough to
bring the focal point, the image, on the retina. This is accomphshed
by the introduction of an additional refracting body, the lens. On
entering the lens the rays are for the same reason — i. e., the passage
from a rarer into a denser medium — again refracted and converged,

and if continued would
come to a focus about 6.5
mm. behind the retina. On
passing from the lens into
the vitreous — i. e., from a
denser into a rarer medium
— the rays are once more
converged and to an extent
sufficient to focalize them
Fig. 283.— Refraction of Homocentric Rays on the retina (Fig. 283).

AND THE Formation of an Image. While it is thus possible

to geometrically follow the
rays through these media by means of the above-mentioned factors,
the procedure is attended with many difficulties. Moreover, as the
relations all change when rays enter the eye from objects situated
progressively nearer the eye, a separate calculation is necessitated for
each distance for the determination of the size of the image.

A method by which these difficulties are much reduced was sug-
gested by Gauss and developed by Listing. It was demonstrated by
Gauss that in every complicated system of refracting media separated
by centered spheric surfaces there may be assumed certain ideal
or cardinal points, to which the system may be reduced, and which,
if their relative position and properties be known, permit of the de-

* Strictly speaking, the posterior surface of the cornea is not parallel to the
anterior surface, and the index of refraction of the cornea is a trifle greater than that
of the aqueous humor, viz., 1.377. But as the increase in the corneal refraction due
to a higher index is almost exactly counteracted by a decrease in refraction, due to
the higher curvature of the posterior corneal surface, the usual assumptions furnish
quite accurate results.

THE SENSE OF SIGHT. 609

termination, either by calculation or geometrical construction, of the
path of the refracted ray, and the position and size of the image in
the last medium, of the object in the first.

Every dioptric system can be replaced, as Gauss showed, by a
single system composed of six cardinal points and six planes per-
pendicular to the common axis — e. g., two focal points, two principal
points, two nodal points, two focal planes, two principal planes, and
two nodal planes.

Properties of the Cardinal Points. — The first focal point, F^,in
Fig. 284, has the property that every ray which before refraction passes
through it, after refraction is parallel to the axis.

The second focal point, F^, has the property that every ray which
before refraction is parallel to the axis, passes after refraction
through it.

The second principal point, H^, is the image of the first, H^; that
is, rays in the first medium which go through the first principal point
pass after the last refraction through the second. Planes at right

F, ■^'

'4^ 1^ ^^ ^

Fig. 284. — Diagram showing the Position and Relation of the Cardinal

Points.

angles to the axis at these points are principal planes. The second
principal plane is the image of the first. Every point in the first
principal plane has its image after refraction at a corresponding point
in the second principal plane at the same distance from the axis and
on the same side.

The second nodal point, N^_, is the image of the first, N ^: a ray
which in the first medium is directed to the first nodal point passes
after refraction through the second nodal point, and the directions of
the rays before and after refraction are parallel to each other. In
Fig. 284 let A B represent the axis. The distance of the first focal
point, -Fj, from the first principal plane, H^, is the anterior focal
distance. The distance of the posterior focal point, F^, from the
second principal plane, iJ,, is the posterior focal distance. The dis-
tance of the first nodal point, A^j, from the first focal point is equal
to the second focal distance. The distance of the second nodal
point, N^, from the posterior focal point is equal to the anterior focal
distance. It is evident, therefore, that the distance of the correspond-
ing principal and nodal points from each other is equal to the dift'er-
39

6io

TEXT-BOOK OF PHYSIOLOGY.

ences between the two focal distances. Also the distance of the two
principal points from each other is equal to the distance of the two
nodal points from each other. Finally, the focal distances are pro-
portional to the refractive indices of the first and last media. Planes
passing through the focal points vertically to the axis are known as
focal planes.

A

Fig.

285. — Diagram to Find the Image in Last Medium of a Luminous Point
IN THE First.

From these properties of the cardinal points the position of an
image in the last medium of a luminous point in the first may be
determined, and the course of a refracted ray in the last medium be
constructed if its direction in the first be given according to the fol-
lowing rules :

I. To find the image in the last medium of a luminous point in the
first: Let A (Fig. 285) be this given point. Draw A B parallel to
the axis until it meets the second principal plane in B; then B F^
will be this ray after refraction. Draw a second ray from A to

^/ ^,

Fig. 286. — Diagram to Find the Refracted Ray in the Last Medium of a
Given Ray in the First Medium.

the first nodal point; then draw another ray, D E, from the
second nodal point parallel to A C. This will be the refracted
ray in the last medium. Where the two refracted rays, BF^ and
D E, intersect, the image of A will he A^.*
2. To find the refracted ray in the last medium of a given ray in the
first medium : Let A B (Fig. 286) be the given ray. Continue this

* If the point A is infinitely far from the eye, all the rays striking the eye will be
parallel to each other. The nodal ray must therefore be drawn, and the point
where this nodal ray meets the second focal plane will be the image of A = A■^,
where all rays parallel to the nodal ray will meet.

THE SENSE OF SIGHT.

6ii

ray until It meets the first principal plane in C. Draw C D

parallel to the axis. Now assume any point, such as E, in the

given ray, and find its image £^ by the Rule i. Then D E^

becomes the course of the refracted ray.

The Schematic Eye. — Accepting the system of cardinal points,

Listing, Bonders, and v. Helmholtz have constructed "schematic"

eyes to be substituted for the refracting system of the natural eye.

For this purpose it is necessary to make use of the various esti-
mates of the indices of refraction of the different media, of the radii
of curvatures of the different refracting surfaces, and of the distances

Tig. 287. — Diagram showing the Positiox of the Cardinal Points in the
"Schematic Eye." The continuous lines in the upper half of the figure show
their position in the passive emmetropic eye. The dotted lines indicate the
change in their position in an eye accommodated for the object A at the distance
a from the cornea, or 152 mm. The lower half of the figure shows the formation
of a distinct image on the retina of an eye accommodated for the object .4 at the
distance a from the cornea.

separating them, to deduce an average eye as a basis for calculation.
The most widely accepted attempt is that of v. Helmholtz. The data
he assumed are as follows : The refractive index of air = i ; of the
cornea and aqueous humor, 1.3365; of the lens, 1.4371; of the
vitreous humor, 1.3365; the radius of curvature of the cornea, 7.829
mm.; of the anterior surface of the lens, 10 mm.; of the posterior
surface, 6 mm.; the distance from the apex of the cornea to the ante-
rior surface of the lens, 3.6 mm.; thickness of lens, 3.6 mm. From
the above-mentioned data v. Helmholtz calculated the position of
the cardinal points for the eye as follows (see Fig. 287): The first

6i2 TEXT-BOOK OF PHYSIOLOGY.

focal point is situated 13-745 mm. before the anterior surface of the
cornea; the posterior focal point is situated 15.619 mm. behind the
posterior surface of the lens; the first principal point, 1.753 mm.
behind the cornea; the second principal point, 2.106 mm. behind the
cornea; the first and second nodal points, 6.968 and 7.321 mm.
behind the apex of the cornea, respectively. The anterior focal
distance of this schematic eye, the distance between F^ and H^,
therefore amounts to 15.498 mm., and the posterior focal distance,
H^ to F^, to 20.713 mm.

When the eye, however, is accommodated for near vision, the
relations of the cardinal points are changed and will be as follows,
if the point accommodated for, lies 152 mm. from the cornea:
Anterior focal distance, 13.990 mm.; posterior focal distance, 18.689
mm. ; distance from cornea of the first and second principal points,
1.858 and 2.257 mm. respectively; distance of the posterior focus,
20.955 mm. from cornea. Given this schematic eye in the accom-
modated state, ■ the course of the rays and the determination of the

position of an image in the last medium
of a luminous point in the first can
easily be determined by the rules already
given.

The Reduced Eye. — As suggested by
Listing, this schematic eye may be yet
further simplified or reduced to a single
Fig. 288.— The Reduced Eye. refracting surface bounded anteriorly by

air and posteriorly only by aqueous or
vitreous humor. Without introducing any noticeable error in the
determination of the size of the retinal image, the anterior principal
and the anterior nodal points may be disregarded, owing to the minute-
ness of the distances (0.39 mm.) separating the two systems of points-
There is thus obtained one principal point and one nodal point,
which latter becomes the center of curvature of the single refracting
surface. The dimensions of this "reduced" eye are as follows (see
Fig. 288): From the anterior surface of the cornea, corresponding to
the principal plane, to the nodal point, 5.215 mm.; the anterior focal
distance, 15.498 mm.; the posterior focal distance, 20.713 mm.; the
index of refraction is 1.3365. There is thus substituted for the
natural eye a single refracting surface with a radius of curvature of
5.215 mm. In such an eye luminous rays emanating from the ante-
rior focal point are parallel to the axis after refraction in the interior
of the eye. Also rays parallel to the axis before refraction unite at
the posterior focal point.

By means of this reduced eye the construction of the refracted ray,,
the various calculations as to the size of the image, the size of diffusion:
circles, etc., are greatly facihtated: e. g.,

THE SENSE OF SIGHT. 613

In Fig. 289 let A B represent an object. From A homocentric rays
fall on the single refracting surface. One of the rays, the nodal
ray, falling on the surface perpendicularly, passes unrefracted through
the single nodal point, iV, to the posterior focal plane. The remain-
ing rays, partially represented in the figure, faUing on this surface
under varying degrees of incidence, undergo corresponding degrees of
refraction, by which they
form a converging cone
of rays which unite at a
point situated on the
nodal ray. These two
points, A, <z, are known
as conjugate foci. The

same holds true for ho-

, . , Fig. 280. — -The Formation of an Image in the

mocentric rays emanat- ^ reduced Eye.

ing from B or any other

point of the object.

The Size of the Retinal Image. — The size of the retinal image,

/, may now be easily calculated, when the size of the object, O, and

its distance, D, from the refracting surface with radius of curvature

R, are known, by the following formula :

0:I = D + R:F2 — R.

For, as the triangles A N B and a N b a.Te equal, we have

AB:ab=fN:Ng, or ah== — ^ /^"^ ^.

Independent of the foregoing method, the size of the retinal
image may be calculated if it is remembered that, the eye, hke any
optic system, has a point of such a quahty that a ray of hght which
before entering the eye was directed toward it, after refraction con-
tinues as if it came from this point. In other words, there is in the
eye a point which allows a ray of Hght to pass unrefracted. This
point, termed the nodal point of the eye, determines the size of the
image ; for if a line be drawn from both the upper and lower ends of
an object through this nodal point, it is clear that the images of the
respective points must lie on these two rays where they intersect the
retina. The distance of this nodal point from the retina is 15.498
mm. It is clear, therefore, that the size of the object is to the size
of the image, as the distance of the object from the nodal point is
to the distance of the nodal point from the retina.

The Visual Angle. — The angle included between the hues coming
from the opposite extremities of an object and crossing at the
nodal point is termed the visual angle. The size of this angle in-
creases with the nearness and decreases with the remoteness of an
object. The retinal image correspondingly increases or decreases
in size. The acuteness of vision depends on the power of. the emme-
tropic eye to distinguish the smallest retinal image or the smallest

6i4

TEXT-BOOK OF PHYSIOLOGY.

distance between two points on the retina. It lias been experiment-
ally determined that the retina can not distinguish two points unless
their images are separated by a distance of 0.004 mm. corresponding
to a visual angle of 60 seconds. If the distance is less than this the
two sensations fuse into one. The reason assigned for this is, that
the distance between the centers of two adjoining cones in the

D=6 D=18 D-60

Fig. 290. — Visual Angle of 5 Minutes. — {After Hansell and Sweet.)

macula is 0.004 n^in- With a visual angle of 60 seconds the two
foci fall on separate cones; with a smaller visual angle the two
foci fall on and excite but a single cone, and hence there arises
the sensation of but a single point.

In ophthalmic practice it is customary in testing the acuteness
of vision to employ test type of a certain size for specified distances.

Fig. 291. — The Refraction of Parallel and Divergent Rays in the Emme-
tropic Eye in the Passive and in the Active or Accommodated Con-
dition.

Though the entire letter is embraced in an angle of 5 minutes,
the strokes are included within an angle of 60 seconds or one minute
(Fig. 290).

Accommodation. — In a normal or emmetropic eye, homocentnc
parallel rays of hght (Fig. 291, a, h) after passing through the optic
media are converged and brought to a focus on the retina, /. Rays,

THE SENSE OF SIGHT. 615

however, which come from a luminous point .situated near the eye,
P, and are therefore divergent, passing through the optic media at
the same time, are intercepted by the retina before they are focused,
and give rise to the formation of dijjusion-circles and indistinctness
of vision. The reverse is also true. When the eye is adjusted for
the refraction and focusing of divergent rays (Fig. 291, P) parallel
rays will be brought to a focus before reaching the retina, and,
again diverging, will form diffusion-circles. It is evident, there-
fore, that it is impossible to simultaneously focus both parallel
and divergent rays, and to see distinctly at the same time, two
objects which are situated at different distances. The eye must be
alternately adjusted first to one object and then to another. The
capabihty which the eye possesses of adjusting itself to vision at
different distances is termed accommodation.

The following table of Listing shows the size of the diffusion-
circles formed of objects situated at different distances when the
accommodative power is suspended :

Distance of Luminous Point.

65 m.

25

12 "
6

3
1.500 "

0.750 "

0-37S "
0.1S8 "

O.OQ4 "

0.0S8 "

The normal eye when adjusted for distant vision is in a passive
condition, and hence vision of distant objects is unattended with
fatigue. In the act of adjustment, however, for near vision the
eye passes into an active state, the result of a muscle effort, the
energy of which is proportional to the nearness of the object toward
which the eye is directed.

From the foregoing table it is evident that between infinity and
65 meters, the diffusion-circles are so sHght that no perceptible
accommodative eft'ort is required to eliminate them. From 65 meters
to 6 meters the diff'usion-circles gradually become larger, though they
are yet so faint as to require for their correction an accommodative
effort which is scarcely measurable. From 6 meters up to 6 centi-
meters, however, a progressive increase in accommodative powTr
is demanded for distinct vision.

Mechanism of Accommodation. — Inasmuch as neither the
corneal curvature nor the shape of the eyeball undergoes any change

Distance of the Focal

Point behind the Posterior

Surface of the Retina.

Diameter of the Diffusion-circle.

0.0 mm.

0.0 mm.

0.005 "

O.OOII "

0.012 "

0.0027 "

0.025 "

0.0056 "

0.050 "

O.OII2 "

0.100 "

0.0222 "

0.20 "
0.40 "
0.80

0.0443 "

0.0825 "
O.I6I6 "

1.60 "

0.3122 "

3.20
342 "

0.5768 "

0.6484 "

6i6 TEXT-BOOK OF PHYSIOLOGY.

during accommodation, the necessary change, wliatever it may be,
is to be sought for in the lens. As to the character of the changes
in this body, two views are held, based largely on the fact and its
interpretation, that images of a luminous point reflected from the
anterior surface of the cornea, the anterior and posterior surfaces
of the lens, change their relative positions during accommodation.

Thus, if in a darkened room a lighted candle be placed in front

of and to the side of an individual whose eye is directed to a distant

object, an observer placed in the same relative position as the

candle will observe three images in the eye, one at the surface of the

cornea, two at the pupillary margin (Fig. 292). Of the two latter,

one is quite large and situated apparently in front of the third, which

is faint, small, and inverted. The middle image

^tBt^^ is reflected from the convex surface of the lens,

^^^^^^^ the last from the concave surface. These images

^VS^B of reflection are known as catoptric images. If

^^^Jfl^V now the individual be directed to fix the gaze on a

^^^^^^ near object, the second image changes its position,

i^^^i advances toward the corneal image and at the

a h c same time becomes smaller, a change which, in

Fig. 292.— Catop- accordance with the laws of optics, could only be

TRIG Images in (^^g ^q ^-^ increase in the convexity of the anterior

Upright image surface of the Icns. A slight displacement of the

of reflection, third image sometimes observed indicates a pos-

from the cornea. ^{\j[q increase in the convexity of the posterior

0. Upright image r ^ j sr

from the ante- SUrface Icns.

rior surface of According to Helmholtz, during accommoda-

verteT^ image' ^^°^ ^^^ entire anterior surface of the lens becomes
from the poste- more convex, while at the same time it slightly
nor surface of advances, possibly as much as 0.4 mm. in extreme
(Helmholtz.) efforts. This change is represented in Fig. 293.

According to Tscherning, the increase in convexity
of the anterior surface is confined to the central portion, the re-
mainder of the surface becoming somewhat flattened. There is,
moreover, no evidence that there is any advance of the surface or
any increase in the thickness of the lens. A series of new and
ingenious experiments lend support to Tscherning's view. The
radius of curvature in either case approximates 6 mm. in extreme
effort of accommodation. The increase in convexity naturally in-
creases the refracting power.

Whichever view is accepted, the nearer the object, — that is, the
greater the degree of divergence of the light rays, — the more pro-
nounced must be the increase in convexity in order that they may be
sufficiently converged and focahzed on the retinal surface. Changes in
the convexity of the lens, either of increase or decrease, are attended

THE SENSE OF SIGHT.

617

by changes in the distinctness of images. Coincident with the
lens change, the pupillary margin advances and the pupil itself
becomes smaller. By this means an indistinctness of the image is
prevented by cutting off the rays which would give rise, owing to
the angle at which they fall on the surface, to ditTusion circles, from
spheric aberration.

The Function of the Ciliary Muscle. — Though it is generally
admitted that the increase in the convexity of the lens is caused by
the contraction of the cihary muscle, the exact manner in which this
is accomplished is not clearly understood. According to Helmholtz,
when the eye is in repose and directed to a distant object the lens is
somewhat flattened from a traction exerted by the suspensory liga-
ment. When the eye is directed to a near object, the ciliary muscle
contracts, thereby relaxing the ligament, as a result of which the lens,
by virtue of an inherent elasticity, bulges forward and becomes more
convex. In consequence of this latter fact the refracting power is

- Zpi/^^Ioim.

Oirne^t proper
Mesre^ne^ 'Jfem^rojte

SpuicterJH£U^

~^ScZe

CUutru

Fig. 293.

-The Left Half Represents the Eye in a State of Rest.
Right Half in State of Accommodation.

The

proportionally increased. In extreme efforts of accommodation it is
beheved by some observers that the circularly arranged fibers, the
so-called annular muscle, contract and exert a pressure on the periph-
ery of the lens and thus aid other mechanisms in relaxing the ligament
and in increasing the convexity. This view appears to be supported
by the fact that in hypermetropia, where a constant effort is re-
quired to obtain a distinct image of even distant objects, the annular
muscle becomes very much hypertrophied, thus reinforcing the
meridional fibers. In myopia, on the contrary, where the accommo-
dative effort is at a minimum, the entire muscle possesses less than
its average size and development.

According to Tscherning, a different explanation of the action of
the ciliary muscle must be given. Thus, when it contracts, the antero-
internal angle, that portion in close relation with the suspensory
ligament, recedes and exerts on the ligament a pressure which in
turn exerts a traction on the peripheral portions of the anterior
surface of the lens, which produces the deformation observed.

6i8 TEXT-BOOK OF PHYSIOLOGY.

the same time the postero-external portion of the muscle exerts
traction on the chorioid, thus sustaining the vitreous and indirectly
the lens.

The reason for the flattening of the periphery of the lens from
zonular compression and the sharpening of the central convexity is
to be found in the fact that the convexity of the more solid central
portion, the nucleus, is greater than that of the lens itself. Hence it
is easily understood why a zonular traction would give rise to periph-
eral flattening.

There is, however, one point which seems difficult to harmonize
with Tscherning's view; that is, the fact that during accommodation
the lens appears to be shghtly tremulous, thus showing relaxation,
and not increased tension, of the suspensory ligament.

Range of Accommodation. — It has been stated that rays of
light coming from a luminous point situated at any distance beyond
65 meters are so nearly parallel that no accommodative effort is re-
quired for their focalization. So long as the luminous point remains
between infinity and 65 meters, the eye, directed toward it, remains
completely relaxed. The point at which the object can be distinctly
seen without accommodation is termed the far point or the punctum
remotum. This for the normal eye is at a distance of 65 meters or
beyond.* If the luminous point gradually approaches the eye from
a point 65 meters distant, the accommodative power comes into
play and gradually increases until it attains its maximum, which it
does when the object arrives at a point 20 cm. from the eye. Within
this latter distance, distinct vision in the adult is difficult. That
point or distance within which a particular eye can not form distinct
images of objects is called its near point or punctum proximum.
The distance between the punctum remotum and the punctum proxi-
mum is termed the range of accommodation.

Force of Accommodation. — The increase in curvature of the
lens necessary to focalize rays when the eye is directed from the far
to the near point necessitates the expenditure of energy on the part
of the ciliary muscle. The energy expended may be measured by a
lens the refracting power of which is such as to enable it to produce
the same result — that is, to give the diverging rays coming from the
near point a parallel direction. A lens, therefore, which has for a
near point a focal distance of 20 cm. would be a measure of the
force expended, for such a lens placed in front of the natural lens,
when in a state of repose, would, with the assistance of the latter,
bring diverging rays coming from the near point to a focus on
the retina. A lens of this character is said to have a refract-

* In practical ophthalmic work a point six meters distant is taken as the far point
for the reason that the rays at this distance are practically parallel.

THE SENSE OF SIGHT. 619

ing power of 5 dioptrics. This measure of the energy expended in
accommodation holds true only for emmetropic eyes and at about
forty years of age.

Since lenses of the same curvature made from different materials
have different refracting powers, it becomes necessary to have, for
purposes of comparison, some unit of measurement. The unit now
accepted is the refracting power of a glass lens which is sufficient
to focalize parallel rays at a distance of 100 cm. or i meter. This
amount of refracting power is termed a dioptry. Lenses which
would focalize parallel rays at a distance of 50, 20, or 10 cm. are
said to have a refractive power of 2, 5, or 10 dioptrics, respectively,
obtained by dividing into 100 cm. the focal distance. The refracting
power of a biconcave lens is determined by prolonging backward in
the direction the parallel rays have come, the rays which have been
rendered divergent by the lens.

The refracting media of the human eye in repose have collectively
a refracting power of about 52 dioptrics, the reciprocal of its focal
length. The refracting power of the corneal surface alone is equiva-
lent to 32 dioptrics. From the position occupied by the lens it would
require jor parallel rays a refracting power of 14 dioptrics. But
owing to its position in a medium denser than air and to the con-
verging direction of the rays which enter it, it has been calculated
that its refracting power is about 20 dioptrics.

The capabihty of the lens to increase its refraction during accom-
modative efforts beyond the 20 dioptrics varies considerably at
different periods of hfe. At ten years the increase is 14 dioptrics,
as the near point is 7 cm.; at thirty years the increase is but 7 diop-
trics, as the near point is 14 cm.; at sixty the increase is but i dioptry,
and the near point 100 cm.; at seventy it is zero. From youth to old
age, the elasticity of the lens steadily dechncs, and the range of accom-
modation diminishes from the recession of the near point.

Convergence of the Eyes during Accommodation. — In binocu-
lar vision the eyes are turned inward and the optic axis of each — a
line passing through the center of the cornea and the center of the
eye — turned toward the median line during accommodation. So
long as the eyes are directed toward the far point, 65 meters or beyond,
the optic axes are parallel. When the eyes are directed to any point
within 65 meters the optic axes are converged, the convergence in-
creasing steadily as the near point is approached. In this way the
fovea of each eye is directed to the same point and single vision made
possible. Were this not the case, double vision would result.

Functions of the Iris. — For purposes of distinct vision it is essen-
tial that the quantity of light entering the interior of the eye shall
be so adjusted that the formation and subsequent perception of the
image shall be sharp and distinct. This is accomplished by the iris,

620 TEXT-BOOK OF PHYSIOLOGY.

the circular fibers of which ahernately contract and relax with in-
creasing and decreasing intensities of the light. The size of the pupil,
therefore, through which the light passes, will vary from moment
to moment and in accordance with variation in the light intensity.
The quantity of light necessary to distinct vision is thus regulated.

In the total absence of light the sphincter pupillse muscle is
relaxed and the pupil widely enlarged. With the appearance of light
and an increase in its intensity the muscle again contracts and the
pupil progressively narrows. With a given intensity in the light, the
sphincter contraction is greater when the light falls directly into the
fovea. Contraction of this muscle also occurs as an associated move-
ment in the convergence of the eyes during accommodation and in
consensus with the other eye.

In addition to this function of the iris, it constitutes, by virtue of
the sphincter muscle contraction, an important corrective apparatus.
Being non-transparent, it serves as a diaphragm intercepting those
rays which would otherwise pass through the peripheral portions of
the lens and by spheric aberration give rise to indistinctness of the
image. The movements of the iris by which the size of the pupil is
determined are caused by the contractions and relaxations of the
sphincter pupilla and dilatator pupillce muscles. The contraction of
the sphincter is entirely reflex and involves those structures necessary
to the performance of any reflex act, viz. : a sentient surface, the
retina; an afferent nerve, the optic; a central emissive center situated
in the gray matter beneath the aqueduct of Sylvius; and an efferent
nerve, the motor oculi. The stimulus requisite to the excitation of
this mechanism is the impact of light waves or ether vibrations on
the rods and cones. According to the intensity of these vibrations
will be the resulting contraction of the muscle. The contraction of
the dilatator pupillse muscle is determined by the activity of a con-
tinuously active nerve-center in the medulla oblongata which trans-
mits its nerve impulses through the spinal cord, along the first and
second dorsal nerves to the superior cervical ganglion, and thence to
the iris by way of the fifth nerve. (See Fig. 245, page 534.) These
two muscles appear to bear an antagonistic relation to each other, for
section of the motor oculi is followed by relaxation of the sphincter
muscle and dilatation of the pupil. Stimulation of the sympathetic
is followed by a more pronounced dilatation. The size of the pupil
is the outcome of a balancing of these two forces.

OPTIC DEFECTS.

Presbyopia. — This is a condition of the eye characterized by a
defective or diminished accommodative power. As age advances the
lens loses its elasticity and the power to increase its refraction, and

THE SENSE OF SIGHT.

621

vision at the normal near point becomes impossible. The latter,
therefore, advances toward the far point, or recedes from the indi-
vidual. The range of accommodation is also diminished. At forty
years the near point is about 22 cm.; at forty-five years it has receded
to 28 cm. This would indicate that the lens in these five years has
lost I dioptry of refracting power; at fifty years the near point
recedes to 43 cm., and at sixty to 200 cm., indicating a loss in refract-
ing power on the part of the lens of 2 and 4 dioptrics respectively.
Convex lenses placed before the eyes having a refracting power of
I, 2, and 4 dioptrics would in the three instances return the near point
to its normal position. At the age of seventy the lens is incapable
of any increase during an accommodative effort. A lens of 4.5 diop-
trics would therefore be required for near vision.

Myopia. — This is a condition of the eye characterized by an
increase in the antero-posterior diameter or a hypernormal refracting
power of the lens. The former is the usual condition. Parallel rays
of light brought to a focus in front of the retina again diverge, giving

Fig. 294. — Myopia. Parallel rays
focus at F, cross and form diffu-
sion-circles; divergent rays from
A focus on the retina. — {Hansell
and Sweet.)

Fig. 295. — Correction of Myopia
BY A Concave Lens. — {Hansell
and Sweet.)

rise to diffusion-circles and indistinctness of the image. Divergent
rays alone are capable of being focalized on the retina in its new
position. The punctum remotum is always at a definite distance,
but approaches the eye as the myopia increases. The near point
is usually much nearer the eye than 20 cm. For this reason the
condition is termed near sight.

The increase in the length of the antero-posterior diameter may
range from a fraction of a milhmeter up to 10 mm. With an increase
of 0.16 mm. the far point is but 200 cm. distant; and with an increase
of 2>-^ rrivci. it is but 10 cm. distant. Inasmuch as only divergent
rays can be focaHzed by the myopic eye normal vision can be restored
by the use of a biconcave lens with a diverging power in the first
instance of 0.5 dioptry and the second of 10 dioptrics.

Hypermetropia. — This is a condition of the eye characterized by
decrease of the normal antero-posterior diameter or by a subnormal
refracting power of the lens. The former is the usual condition.
Parallel rays of light do not, therefore, come to a focus when the

622

TEXT-BOOK OF PHYSIOLOGY.

accommodation is suspended. Falling on the retina previous to
focalization, they give rise to diffusion-circles and indistinctness of the
image. As no object can be seen distinctly no matter how remote,
there is no positive far point. The near point is abnormally distant —
sometimes as far as 200 cm. For this reason the condition is termed
jar sight. A hypermetropic eye without accommodative effort can
focahze only converging rays on the retina. If rays of Hght were to
come from the retina of such an eye, they would, on emerging, take

!r^...::;;;:;; ="- iff

Fig. 296. — The Hypermetropic Eye. Parallel rays {A, B) can be focused only at a
point behind the eye, as at /; rays of light coming from the retina take, on
emerging from the eye, a divergent direction, C, D. K. The negative punctum
remotum.

a divergent direction, as shown in Fig. 206, dotted hne C and D.
If these same rays were to be prolonged backward, they would meet
at the point K, which is the punctum remotum; and as it is behind
the eye, it is termed negative. Since rays coming from the retina
take a divergent direction on emerging from the eye, it is evident
that only converging rays can be focahzed by a passive hyperme-

FiG. 297. — Hypermetropia. Par-
allel Rays Focused behind
THE Retina. — {Hansell and
Sweet.)

Fig. 298. — Correction of Hyper-
metropia BY a Convex Lens.
{Hansell and Sweet.)

tropic eye. As there are no convergent rays in nature, it is necessary
for distinct vision that all rays, parallel and divergent, shall be given
a convergent direction before entering the eye. This is done by
placing before the eye convex lenses the converging power of which
is proportional to the degree of hypermetropia (Figs. 297, 298).

Astigmatism. — This is a condition of the eye characterized by
an inequality of curvature of its refracting surfaces in consequence of
which not all of a homocentric bundle of rays are brought to the

THE SENSE OF SIGHT.

623

same focus. The inequality may be cither in the cornea or lens, or
both, though usually in the cornea.

In the normal cornea the radius of curvature in the vertical
meridian is a trifle shorter, 7.6 mm., than that of the horizontal, 7.8
mm., and hence its focal distance is slightly shorter. The difference,
however, in the focal distances is so shght that the error in the forma-
tion of the image is scarcely noticeable. A transection of a cone of
light coming from the cornea is practically a circle. If, however, the
vertical curvature exceeds the normal to any marked extent, the rays
passing through this meridian will be more sharply refracted and
brought to a focus much sooner than the rays passing through the
horizontal meridian. The result will be that the cone of light will
be no longer circular, but more or less elliptic. The variations of the
shape of this cone are shown in Fig. 299, which represents the
appearances presented on cross-section both before and after focaliza-
tion of each set of rays. Though the vertical meridian has usually

Fig. 299. — Refraction by an Astigmatic Surface. — {Hansell and Sweet.)

the sharper curvature, it not infrequently happens that the reverse
is true. For the reason that the rays from one point do not all
come to the same focus or point, the condition is termed astig-
matism.

Spheric Aberration.— On account of the difference in curvature
of successive portions of the surface of the lens, there is an unequal
refraction of the rays which pass through those portions between the
center and the periphery. This would give rise to many focal points
and hence an indistinctness of the image. That this condition is
present to but a slight extent in the normal eye is due to the presence
of the iris, which intercepts those rays which would otherwise pass
through the marginal portions of the lens.

Chromatic Aberration. — When a beam of white light is made
to pass through a prism, it is decomposed into the primary colors
owing to a difference in the refrangibility of the rays. In passing
through the refracting media of the eye the different rays composing
white hght also undergo unequal refraction and those rays which

624 TEXT-BOOK OF PHYSIOLOGY.

give rise to one color are brought to a focus at a point somewhat
different from those which give rise to other colors. If the eye is
accommodated for one set of rays, it is not for another, and the result
is a fringe of colors around the image. This defect in the normal
eye is so slight that the mind fails to take cognizance of it. That the
eye is incapable of simultaneously focalizing rays of widely different
refrangibihty, as those which give rise to the blue and red colors,
is shown by the following experiment: The eye being directed to a
luminous point, a plate of cobalt-glass is placed between the Hght and
the observer close to the e3^e. This substance has the property of
intercepting all rays but the red and the blue and hence these alone
will be seen. The center of the image produced will be red and clearly
defined, the periphery blue and ill defined. The reason for this is
clear. The eye more readily accommodates itself for the red rays,
and hence their focal point is distinct. The blue rays, having a
higher degree of refrangibihty, come to a focus, cross and diverge,
and give rise to diffusion-circles. If a biconcave glass be placed before
the cobalt, the blue rays can be focalized on the retina, while the red
will fall on the retina without focalization. The image will now be
blue and distinct in the center, the periphery red and ill defined.
With the removal of the minus glass the reverse condition again
obtains.

Imperfect Centering. — From a purely physical point of view,
the eye is not a perfect optic instrument. In addition to the defects
noticed in the foregoing paragraphs, there is yet another, viz.: an
imperfect centering of the refracting surfaces. In first-class optic
instruments the lenses are centered — that is, their exact centers are
situated on the same axis. In viewing an object through such a
system the visual Hne corresponds with the axis of the lens system.
This is not the case with the refracting system of the eye. A hne
passing through the center of the cornea and the center of the eye,
the optic axis (O A in Fig. 300), does not pass exactly through the
center of the lens and does not fall into the point for most distinct
vision, the fovea. This has led to the recognition of other lines the
relations of which must be kept in mind in all optic discussions, viz. :

1. The visual axis or visual line {V L), the line connecting the point

viewed, the nodal point and the fovea centrahs.

2. The line of fixation or line of regard (V C), the line connecting the

point viewed with the center of rotation, the latter being situated
6 mm. behind the nodal point of the eye and 9 mm. before the
retina. The relations of these lines and certain angles connected
with them are shown in Fig. 300. The angle included between
the line D D (the major axis of the corneal ellipse) and the visual
line is the angle alpha, amounting on the average to 5°. The
angle included between the optic axis and the hne of fixation or

THE SENSE OF SIGHT.

625

regard is the angle gamma, while the angle between the optic
axis and the line of vision is the angle beta. In emmetropia the
angle alpha is about 5°. In hypermetropia it is greater, amount-
ing to 7° or 8°, giving to the eye an appearance of divergence.
In myopia it is much smaller — 2° — or in extreme cases may be
abolished, the line of vision corresponding with the optic axis
or even passing beyond it. The angle gamma is of value in de-
termining the relative power and action of the extra-ocular
muscles.
Functions of the Retina. — Of all the layers of the retina, the
rods and cones appear to be the most essential to vision. It is only
this layer that is capable of-receiving the hght stimulus and of trans-
forming it into some specific form of energy, which in turn arouses

JempofaZ Si^^e

/^rtsal SuZe.

Fig. 300. — Diagram showing the Corneal Axis D D, the Optic Axis O A, the
Visual Axis V L, and the Line of Fixation V C; also the Three Angles,

in the libers of the optic nerve the characteristic nerve impulses.
A ray of light entering the eye passes entirely through the various
layers of the retina, and is arrested only upon reaching the pigmentary
epithelium in which the rods and cones are embedded. As to the
manner in which the objective stimuli — light and color, so called —
are transformed into nerve impulses, but little is known. It is prob-
able that the ether vibrations are transformed into heat, which
excites the rods and cones. These, acting as highly specialized end
organs of the optic nerve, start the impulses on their way to the brain,
where the seeing process takes place. As to the relative function of
the rods and cones, it has been suggested, from the study of the facts
of comparative anatomy, that the rods are impressed only by differ-
ences in the intensity of light, while the cones, in addition, are im-
pressed by qualitative differences in color. The nerve-fibers them-
40

626 TEXT-BOOK OF PHYSIOLOGY.

selves are insensible to the impact of the ether vibrations, and' require
for their excitation some intermediate form of energy. That this is
the case was shown by Donders, who reflected a beam of light on
the optic nerve at its entrance without the individual experiencing any
sensation of light. This region, occupied only by the optic-nerve
fibers and devoid of any special retinal elements, is therefore an
insensitive or hlind spot. The diameter of this spot is about 1.5 mm.,
and occupies in the field of vision a space of about 6°. It is situated
about 3.5 mm. to the nasal side of the visual axis. Its existence can
be demonstrated by the famihar experiment of Mariotte, which con-
sists in placing before the eye two objects having the relation to
each other as in Fig. 301. With the left eye closed and the right eye
directed to the cross, both objects may be visible. But by moving
the figure away from or toward the eye, there will be found a distance,
about 30 cm., when the circle will be invisible. This occurs when
the image falls on the optic nerve at its entrance. The experiment of
Purkinje as described in the following paragraph demonstrates also

Fig. 301. — Diagram for Observing the Situation of the Blind Spot. —

{Helmholtz.)

the fact that the sensitive portion of the retina is to be found only in
the layer of rods and cones.

It is well known that the blood-vessels of the retina are situated
in its innermost layers a short distance behind the optic-nerve fibers.
Owing to this anatomic arrangement, a portion of the light coming
through the pupil will be intercepted by the vessels and a shadow
projected on the layer of rods and cones. Ordinarily, these shadows
are not perceived, for the reason that the shaded parts are more
sensitive, so that the small amount of light passing through the vessels
produces as strong an impression on this part as does the full amount
of hght on the unshaded parts of the retina, and perhaps because the
mind has learned to disregard them. But if Hght be made to enter
the eye obliquely, the position of the shadows will be changed, when at
once they become apparent. This can be shown in the following way :
If in a darkened room a lighted candle be held several inches to
the side and to the front of the eye, and then moved up and down,
there will be perceived, apparently in the field of vision, an arbores-
cent figure corresponding to the retinal blood-vessels. This is due

THE SENSE OF SIGHT. 627

to the falling of the shadows on unusiial portions of the layer of rods
and cones.

Excitahility oj the Retina. — The retina is not equally excitable in
all parts of its extent. The maximum degree of sensibility is found
in the macula lutea, and especially in its central portion, the fovea.
In this region the layers of the retina almost entirely disappear, the
layer of rods and cones alone remaining, and in the fovea only the
latter are present. That this area is the point of most distinct vision
is shown by the observation that when the eye is directed to any given
point of light, its image always falls in the fovea. Any pathologic
change in the fovea is attended by marked indistinctness of vision.
The sensibility of the retina gradually but irregularly diminishes from
the macula toward the periphery. This diminution in sensibility
holds true for monochromatic as well as white light.

As stated above, the nature of the molecular processes which take
place in the retinal tissue, caused on one hand by the light vibrations,
and on the other hand developing nerve impulses, is entirely un-
known. The discovery of the visual purple in the outer segment of
the rods gave promise of some explanation of the process, especially
when it was shown to undergo changes when exposed to the action
of hght. But as the pigment is wanting in the cones, and especially
in the fovea, it cannot be considered essential to distinct vision,
although that it plays some important role in the visual process is
highly probable. It was observed by Van Genderen Stort, that
when an animal is kept in darkness some time before death, the
cones are long and filiform; but if the animal has been exposed to
light, they are short and swollen. It was discovered by Ball that
if an animal is kept in darkness an hour or two before death the
pigment is massed at the ends of the rods and cones, but after ex-
posure to Hght it becomes displaced and extends over and between
the rods almost to the external limiting membrane. These condi-
tions are represented in Fig. 302.

The Eye a Living Camera. — In its construction, in the arrange-
ment of its various parts, and in their mode of action the eye may be
compared to a camera obscura. Though the comparison may not be
absolutely exact, yet in a general way it is true that there are many
striking points of similarity between them ; e. g., the sclera and chorioid
may be compared to the walls of the camera ; the combined refracting
media to the single lens, the action of which results in the focusing
of the light rays ; the retina to the sensitive plate receiving the image
formed at the focal point ; the iris to the diaphragm for the regulation
of the amount of light to be admitted, and for the partial exclusion
of those marginal rays which give rise to spheric aberration; the ciliary
muscle to the adjusting screw, by means of which the image is brought
to a focus on the sensitive plate, notwithstanding the varying distances

628

TEXT-BOOK OF PHYSIOLOGY.

of the object from the lens. The presence of the visual purple in the
rods of the retina capable of being altered by light makes the com-
parison still more striking.

Kiihne even succeeded in obtaining a fixed image or an optogram
of an external object in a manner similar to that by which an image
is fixed on the sensitive plate of a camera. An animal is kept in
the dark for about ten minutes in order to permit the retinal pigment
to be completely regenerated. The animal, with the eyes covered^
is then brought into a room with a single window. After the head
is steadily directed to the window, the eye is exposed for several
minutes. The eyes are again covered, the animal killed, and the
eyes removed by the light of a sodium flame. The retina is then

Fig. 302. — Section of the Retina of a Frog. A. In darkness. B. In light. —
{After Van Genderen Start, from Tscherning's "Physiologic Optics.")

placed in a 4 per cent, solution of alum. In a short time the image
of the window, the optogram, will be fixed (Fig. 303). That portion
of the retina corresponding to the image is quite bleached in appear-
ance from the action of the light on the pigment. During life the
regeneration of the visual purple must take place with extreme
rapidity. It is believed to be derived from a pigment secreted by
the layer of pigment cells.

Binocular Vision. — Though two images are formed, one on each
retina, when the eyes are directed to a given object, there results but
one sensation. If the direction of either visual axis be changed by
pressure on the eyeball, there arise two sensations, and the object
appears to be doubled. The reason assigned for this, in the first

THE SENSE OF SIGHT

629

Fig. 303. — Retina of
A Rabbit. Opto-
gram OF A Win-
dow Four Meters
Distant, a. Yellow
spot, b, b. White
streak of nerve-
fibers. — (Kuhne.)

instance, is that the two images fall into the foveae, two corresponding
points; while in the second instance they fall on non-corresponding
points. It would appear, therefore, that for the purpose of seeing
an object singly when the eyes are directed toward it, the rays eman-
ating from it must fall on corresponding parts of the retina. As all
portions of the retina are sensitive to light, though in varying degrees,
it is not essential that the images always fall in the fovea;. The parts
of the retinae which correspond physiologically
are shown in Fig. 304. In this figure the
retinal area is divided into quadrants by
vertical and horizontal lines of separation, as
they are termed. If one retina is placed in
front of or over the other, it will be found that
the quadrants bearing similar letters cover
each other. So long as the rays of Hght,
entering the eye, fall on corresponding areas
the sensation of but one object arises. If,
however, they fall on non-corresponding areas,
two sensations arise, due to the stimulating
action of two images. Normal binocular
vision enlarges very considerably the area of
the visual field, permits of a better estimation of the size and dis-
tance of objects, enables the mind to form more readily a perception
of depth, increases the intensity of sensations and makes sensation
more uniform by offsetting retinal rivalry.

The Horopter. — When the eyes are in the so-called secondary
position, — that is, in a position in which the visual axes are con-
verged and directed to a point in front of and in the middle plane of

the body, — it will be found
on examination that rays of
light from a number of other
objects enter the eye, pass
through the nodal point, and
fall on corresponding parts of
the two retinas and give rise
to but single images. All
such points lie, for the hori-
zontal line of separation, on
a line termed the horopter. The form of this line is that of a circle
which passes through the fixation point and the two nodal points.
Any object on the horopter will give rise to but a single image.
This is shown in Fig. 305, in which the objects I, II, III project
their rays into both eyes which fall on corresponding areas.

In addition to the horopter for the horizontal line of separation,
there is also an horopter for the vertical line of separation. At a

Fig. 304.-

-Corresponding Areas of the
Retina.

630

TEXT-BOOK OF PHYSIOLOGY.

distance of two meters the vertical horopter is a plane. Within this
distance it is concave to the face ; beyond this distance it is convex.

An object which lies either in front of or behind the fixation point
will project its rays on parts of the retinae which do not correspond,
and hence give rise to double images. This is evident from examina-
tion of Fig. 306. While the eyes are directed to figure 2, of which
there is but a single image, the objects B and A give rise to double
images, for reasons already given. If the eyes are now directed to
B, double images will be formed of 2 and A.

At all times, therefore, double images are formed on the retinae
the existence of which is scarcely noticed unless the attention is

B

Fig. 305. — Horopter for the
Secondary Position, with
Convergence of the Vis-
ual Axes. — {Landois.)

Fig. 306. — Scheme of Identical and Non-
identical Points of the Retina. —
{Landois.)

directed to them. This is due to the fact that many of the images
fall on the peripheral, less sensitive parts of the retinae. At the
same time, from a want of accommodation and the formation of
diffusion-circles, they are indistinct. For these reasons they are
readily neglected.

In the primary position of the eyes — that is, a position in which
the visual axes are parallel — the horopter is a plane in infinity. In
the tertiary position the horopter is a curve of complex form.

Movements of the Eyeball .^ — The almost spheric eyeball Hes
in the correspondingly shaped cavity of the orbit, like a ball placed
in a socket, and is capable of being moved to a considerable extent

THE SENSE OF SIGHT

631

bv the six muscles which are attached to it. These muscles are
the superior and inferior recti, the external and internal recti, and
the superior and inferior oblic[ui (Fig. 307). The jour recti muscles
arise from the apex of the orbit cavity, from which point they pass
forward to be inserted into the sclera about 7 to 8 mm. from the
corneal border. The superior oblique muscle having a similar origin
passes forward to the upper and inner angle of the orbit cavity, at
which point its tendon passes through a cartilaginous pulley, after
which it is reflected backward to be inserted into the superior sur-
face of the sclera about 16 mm. behind the corneal border. The
inferior oblique muscle arises from the inner and inferior angle of the
orbit cavity. It then passes outward, upward, and backward,
to be inserted into
the upper, posterior
and temporal portion
of the sclera about 4
or 5 mm. from the
optic nerve entrance.

The movements of
each eye are referred
to three fixed lines
or axes, which
have their origin at
the point of rota-
tion of the eyeball,
this point lying about
1.7 mm. behind the
center of the globe.
If the eye looks
straight forward in the
horizontal plane (the
head being erect), the
line joining the center

of rotation with the object looked at is the visual line or visual axis.
Around this antero-posterior axis the eye may be regarded as perform-
ing its circular rotation or torsion. At right angles to this line, and
joining the center of rotation of both eyes, is the horizontal or
transverse axis, around which the movements of elevation (up to
34 degrees) and depression (down to 57 degrees) take place. At
right angles to both of these lines there is the vertical axis, around
which the movements of adduction (toward the nose up to 45 degrees)
and abduction (toward the temple up to 42 degrees) occur. The six
muscles may be divided into three pairs, each of which has a common
axis around which it tends to move the eyeball. But only the common
axis of the internal and external recti coincides with one of three axes

Fig. 307. — Muscles
Ligament of Zinn.
ternal rectus divided,
rectus. :;. Superior

OF

THE Eye. Tendon or
I. Tendon of Zinn. 2. Ex-
3. Internal rectus. 4. Inferior
rectus. 6. Superior oblique.

7. Pulley for superior oblique. 8. Inferior oblique.
9. Levator palpebrae superioris. 10,10. Its anterior
expansion. 11. Optic nerve. — {Sappey.)

632 TEXT-BOOK OF PHYSIOLOGY.

before mentioned — namely, with the vertical axis — thus moving the
ball only inwardly or outwardly— respectively. The other two pairs,
however, have their own axes of action, and their movements of the
ball must be therefore analyzed with regard to all the three axes,
each of these four muscles producing rotation, elevation, and depres-
sion, and abduction or adduction. The superior and inferior recti
muscles, forming one pair, move the eye around a horizontal axis
which intersects the median plane of the body in front of the eyes at
an angle of 63 degrees, and the superior and inferior oblique muscles
forming the third pair rotate the globe around a horizontal axis which
cuts the median plane of the body behind the eyes at an angle of
39 degrees. Thus it is that each muscle moves the eye as follows, the
movement for practical purposes being referred to the cornea: The
rectus externus draws the cornea simply to the temporal side, the
rectus internus simply to the nose; the superior rectus displaces the
cornea upward, shghtly inward, and turns the upper part toward the
nose (medial torsion) ; the inferior rectus moves the cornea downward,
slightly inward, and twists the upper part away from the nose (lateral
torsion) ; the superior oblique displaces the cornea downward, slightly
outward, and produces medial torsion; while the inferior oblique
moves the cornea upward, slightly outward, and produces lateral tor-
sion. These facts show that for certain movements of the eye at
least three muscles are necessary (see following table) :

Inward, Rectus internus.

Outward, Rectus externus.

jr. J f Rectus superior.

Upward, -; ^,,. '. . .

^ t Obliquus interior.

T, J f Rectus inferior.

Downward, < /-.i_i-

(, Obliquus superior.

Inward and f Rectus internus.

upward, < Rectus superior.

Inward and f Rectus internus.

downward, < Rectus inferior.

i Obliquus superior.
Outward and ( Rectus externus.

upward, \ Rectus superior.

( Obliquus inferior.
Outward and ( Rectus externus.
downward, < Rectus inferior.

( Obliquus inferior. | I Obliquus superior.

If both eyes have their line of vision in the horizontal plane parallel
with each other and with the median plane of the body, they are
said to be in the primary position. All other positions are called
secondary. Both eyes always move simultaneously, which is called
the associated movement of the eyes. There are three forms of asso-
ciated movements: (i) movement of both eyes in the same direction;
(2) movements of convergence by which the visual lines are con-
verged on a point in the middle line of the body; (3) movements of
divergence, by which the eyes are brought back from convergence to
parallelism, or even to divergence, as in certain stereoscopic exercises.
A combination of (i) and (2) or of (i) and (3) takes place for certain
positions of the object looked at.

Color-perception. — A beam of sunlight passed through a glass
prism is decomposed into a series of colors — red, orange, yellow,

THE SENSE OF SIGHT.

633

green, blue, and violet — the so-called spectral colors, so well exem-
plified in the rainbow. The spectral colors are termed simple
tions of the ether, from about 400 millions of millions per second for
Objectively, the spectral colors consist of very rapid transverse vibra-
colors, because they can not be any further decomposed by a prism,
red to about 760 millions of miUions for violet, but subjectively they
are sensations caused by the impact of the ether-waves on the per-
cipient layer of the retina.

It is possible to mix or blend these spectral color-sensations in
the eye by stimulating the same area of the retina by different spectral
colors, either at the same time or in rapid succession. The following
table shows the results of such experiments as performed by v. Helm-
holtz (Dk. = dark; Wh. = whitish):

Violet.

Red.

Orange.

YeUow.

Gr.-yellow.

Green.

Bluish-green.

Cyan-blue.

! Purple.
, Dk.-rose.

I Wh.-rose

Indigo.

Dk.-rose.
Wh.-rose.
White.
Wh.-green.

Cyan-blue.

Wh.-rose.
White.
Wh.-green.
Wh.-green.

WTiite. '' Wh.-green. Wh.-greei

WTiite-blue. Water-blue. Bl.-green

Water-blue.' Water-blue

Indigo. I

Bluish-
green.

Green.

White. Wh.-yellow.

Wh .-yellow. , Yellow.

Wh.-yeUow. Gr.-yellow.

Green.

Greenish

Yellow.

Gold-yeUow Orange.
Yellow.

These are the mixed colors. But it is to be observed that only two
new color-sensations can be produced, white and purple, the remain-
ing mixed colors already finding their equivalent in the spectrum.
White and purple, therefore, are color-sensations which have no
objective equivalent in a simple number of ether-vibrations Hke the
spectral colors.

Two spectral colors which by their mixture produce the sensation
of white are called complementary colors. Such are red and green-
blue, golden yellow and blue, green and violet. The mixture of all
the spectral colors produces white again. This is the result of adding
two or more color-sensations. Different results are obtained, however,
by adding color pigments. Yellow and blue, for example, produce
in the eye white, but on the painter's palette green. The colors of
nature are usually mixtures of simple colors, as can be shown by
spectroscopic analysis or by a synthesis of spectral colors.

In all color-sensations we must distinguish three primary quahties :
(i) hue; (2) purity or tint; (3) brightness or luminosity. The first
quahty gives the main name to the color — e. g., red or blue — this de-
pending on the spectral color or the mixture of two spectral colors
with which it can be matched. The second quahty, the tint, depends
on the admixture of white with the ground color; and the third quahty,
brightness, depends on the objective intensity of the light and the
subjective sensitiveness of the retina. Color-perception thus far refers

634 TEXT-BOOK OF PHYSIOLOGY.

only to the most sensitive part of the retina. At the more peripheral
parts of the retina the colors are seen somewhat differently, as is
shown by the following table giving the limits up to which the colors
are recognized :

White. Blue. Red. Green.

Externally qo° 8o° 65° 50°

Internally 60° 55° 50° 40°

Superiorly 45° 40° 35° 30°

Inferiorly 70° 60° 45° 35°

Theories of Color-perception. — The theory of v. HelmhoUz,
originated by Thomas Young (1807), assumes in its latest form the
existence in the human retina of three different kinds of end-organs,
each of which is loaded with its own photo-chemical substance
capable of being decomposed by a certain color, and thus exciting
the fiber of the optic nerve.

In the first group these end-organs are loaded with a red-sensitive
substance, which is affected mainly by the red part of the spectrum;
the second group has its end-organs provided vdth a green-sensitive
substance, which is mainly excited by the green color; while the third
group is provided with a blue-sensitive substance, this latter being
mainly affected and decomposed by the blue-violet portion of the
spectrum. All these three different end-organs are present in every
part of the most sensitive area of the retina, and are connected by
separate nerve-fibers with special parts of the brain, in the cells of
which each calls up its separate sensation of red or green or blue.

Out of these three primary color-sensations all other color-sensa-
tions arise. If a light mainly excites the red- or green- or blue-sensi-
tive substance of a retinal area, we term it red, green, or blue, re-
spectively. But if two of these photo-chemical substances are stimu-
lated simultaneously, quite different sensations arise. Thus simul-
taneous stimulation of the red and green substances gives rise to the
sensation of yellow, that of red and blue to the sensation of purple,
and that of blue and green to the sensation of blue-green. Simul-
taneous stimulation of all three substances of a certain area produces
the sensation of white. iVccording to this theory, complementary
colors are all those which together excite all the three substances.
Color-blindness is explained by this theory, on the assumption that
two of the photo-chemical substances have become similar or equal
in composition to each other.

The theory 0} Hering, brought forward in 1874, has the under-
lying assumption that the process of restitution in a nerve-element
is capable of exciting a sensation. This theory asserts that there are
three visual substances in the retina — a white-black, a red-green, and
a yellow-blue visual substance. A destructive process in the white-
black substance, such as is induced not only by white light, but alsa

THE SENSE OF SIGHT.

^0 3

by any other simple or mixed color, produces the sensation of white,
while the process of restitution or assimilation in this substance pro-
duces the sensation of black. Similarly, red Ught produces dis-
assimilation or decomposition in the red-green substance, and this,
again, the sensation of red. Green light, however, favors the process
of restitution or assimilation in the red-green substances, and thus
gives rise to the sensation of green. In the same way the sensation
of yellow has its cause in the decomposition of yellow-blue substance
induced by yellow hght, while the sensation of blue is produced
by an assimilative process in the same substance. Simultaneous
processes of disassimilation and assimilation in the same visual sub-
stance antagonize each other, and consequently produce no color-sen-

FiG. 308. — The Lacrimal .\nd Meibomian Glands, and Adjacent Organs of
THE Eye. I, I. Inner wall of orbit. 2, 2. Inner portion of orbicularis palpe-
brarum. 3, 3. Attachment to circumference of base of orbit. 4. Orifice for
transmission of nasal artery. 5. Muscle of Horner (tensor tarsi). 6, 6. Mei-
bomian glands. 7, 7. Orbital portion of lacrimal gland. 8, 9, 10. Palpebral
portion. 11, 11. Mouths of excretory ducts. 12, 13. Lacrimal puncta. — {Sappey.)

sation by means of this substance, but only the sensation of white, by
reason of decomposition, by both colors, in the white-black substance.
Thus, yellow and blue, impinging on the same retinal area, have no
effect on the yellow-blue substance, because they are antagonistic in
their action on this substance, but only produce the sensation of white,
as both yellow and blue decompose the white- black material. Color-
blifidness is explained by the assumption of the absence of either the
red-green or the yellow-blue visual substance in the retina.

Accessory Structures. — The eyeball is protected anteriorly by
the eyehds and their associated structures, the Meibomian glands,
the lacrimal glands, and tears.

636 TEXT-BOOK OF PHYSIOLOGY.

The eyelids consist of a central framework of connective tissue
supporting muscle tissue (the orbicularis palpebrarum muscle) and
glands, and covered externally by skin and internally by a modified
skin, the conjunctiva. The free border of each lid is strengthened
by a semilunar plate of dense fibrous tissue, the tarsus. The cuta-
neous edge of the lid is bordered with short stift' hairs. At the inner
extremity each eyelid presents a small opening, the punctum lacri-
malis, the beginning of the lacrimal duct. The two ducts after
uniting open into the nasal duct.

The Meibomian glands are modified sebaceous glands imbedded
in the posterior portion of the lids (Fig. 308). Their ducts open on
the free border of the lid. These glands secrete an oleaginous ma-
terial resembhng sebaceous matter which accumulates along the
margin of the lid and prevents the tears from flowing down the
cheek.

The lacrimal gland is situated at the upper and outer part of the
orbit cavity. It consists of a series of compound tubules lined by
epithehum. The secretion (the tears) is conducted from the gland
to the outer part of the conjunctiva by seven or eight ducts. The
lacrimal secretion consists of water and inorganic salts. It is dis-
tributed over the corneal surface during the act of winking, thus
keeping it moist and free from foreign particles. It eventually passes
into the lacrimal ducts and then into the nose. The lacrimal glands
receive secretory fibers by way of the fifth nerve and the cervical
sympathetic. The secretion can be excited reflexly from stimulation
of sensor nerves as well as bv emotional states.

CHAPTER XXVI.
THE SENSE OF HEARING.

The physiologic mechanism involved in the sense of hearing in-
cludes the ear, the auditory nerve, its cortical connections, and nerve-
cells in the cortex of the temporal lobe.

Peripheral excitation of this mechanism develops nerve impulses
which, transmitted to the cortex, evoke the sensation of sound and
its var}'ing qualities — intensity, pitch, and timbre.

The specific physiologic stimulus to the terminal organ, the organ
of Corti, is the impact of atmospheric undulations of varying energy
and rapidity.

THE PHYSIOLOGIC ANATOMY OF THE EAR.

The ear, the organ of hearing, is lodged within the petrous portion
of the temporal bone. It may, for convenience of description, be
divided into three portions: viz., the external, the middle, and the
internal portions (Fig. 309).

The external ear consists of the pinna or auricle and the external
auditory canal. The pinna is composed of a thin layer of cartilage
which presents a series of elevations and depressions. It is attached
by fibrous tissue to the outer edge of the auditory canal and covered
by a layer of skin continuous with that covering adjacent structures.
The general shape of the pinna is concave. Its anterior surface pre-
sents, a httle below the center, a deep depression — the concha.

The external guditory canal extends from the concha inward for
a distance of from 25 to 30 mm. It is directed at first upward, for-
ward, inward, and then downward to its termination. It is composed
partly of bone and partly of cartilage and lined by a reflection of
the skin covering the pinna. - At the external portion of the canal
the skin contains a number of tubular glands, the ceruminoiis glands,
which resemble in their conformation the perspiratory glands. They
secrete cerumen or ear-wax.

The middle ear, or tympanum, is an irregularly shaped cavity
hollowed out of the temporal bone and situated between the external
auditor}' canal and the internal ear. It is narrow from side to side,
though wider above than below. It is relatively long in its antero-
posterior and vertical diameters. The upper portion is kno'v\Ti as the
attic. The middle ear is in communication posteriorlv with the

6^.7

638

TEXT-BOOK OF PHYSIOLOGY.

mastoid cells, anteriorly with the pharynx through the Eustachian
tube.

The Eustachian Tube. — The passageway between the tympanic
cavity and the naso-pharynx is known from its discoverer as the
Eustachian tube. It is composed internally of bone, externally of
cartilage, and is lined by mucous membrane covered with ciliated
epithelium. Near the middle of its course the tube is contracted,
though expanded at either extremity (Fig. 312). It measures about
40 mm. in length. Its general direction from the pharyngeal orifice
is outward, backward, and upward at an angle of about 45 degrees.

Fig. 309. — The Ear. — i. Pinna, or auricle. 2. Concha. 3. External auditory canal.
4. Membrana tympani. 5. Incus. 6. Malleus. 7. Manubrium mallei. 8. Tensor
tympani. 9. Tympanic cavity. 10. Eustachian tube. 1 1 . Superior semicircular
canal. 12. Posterior semicircular canal. 13. External semicircular canal. 14.
Cochlea. 15. Internal auditory canal. 16. Facial nerve. 17. Large petrosal nerve.
18. Vestibular branch of auditory nerve. 19. Cochlear branch.- — (Sappey.)

The middle ear cavity is separated from the external ear by
a membrane — the membrana tympani — and from the internal ear by
an osseo-membranous partition which forms a common wall for both
cavities. The interior of the cavity is crossed from side to side by a
chain of bones and lined by a mucous membrane continuous with
that lining the pharynx.

The membrana tympani is a thin, translucent, nearly circular
membrane, measuring about 10 mm. in diameter, placed at the inner
termination of the external auditory canal. It is inclosed in a ring
of bone which in the fetal condition can be easily removed, but in

THE SENSE OF HEARING.

639

the adult condition can not be removed, owing to its consolidation
with the surrounding bone. This membrane consists primarily of
a layer of fibrous tissue which is covered externally by a thin layer
of skin continuous with that lining the auditor}' canal, and internally
by a thin mucous membrane. The tympanic membrane is placed
obliquely at the bottom of the auditory canal, inclining from above
and behind downward and forward at an angle of about forty-five
degrees. The external surface of this membrane presents a funnel-
shaped depression, the sides of which are shghtly convex.

The Ear-hones. — Running across the tympanic cavity and form-
ing an irregular line of
joined levers is a chain
of bones, which articu-
late one with another at
their extremities. These
bones are known as
the malleus, incus, and
stapes. The form and
arrangement of these
bones are shown in
Figs. 310, 311.

The malleus, or ham-
mer bone, consists of a
head, neck, and handle,
of which the latter is
attached to the inner
surface of the membrana
tympani. The incus or
anvil bone presents a
concave articular sur-
face which receives the
head of the malleus.
The stapes, or stirrup-
bone, articulates exter-

FiG. 310. — Tympanic Membrane and the Audi-
tory Ossicles (Left) seen from within,
i. e., FROM THE Tympanic Cavity. M. Manu-
brium or handle of the malleus. T. Inser-
tion of the tensor tympani. h. Head. IF.
Long process of the malleus, a. Incus, with
the short {K) and the long (/) process. 5.
Plate of the stapes. Ax, Ax, is the common
axis of rotation of the auditory ossicles. 5'.
The pinion-wheel arrangement between the
malleus and incus. — {Landois.)

nally with the long pro-
cess of the incus, and internally, by its oval base, with the edges of
an oval opening, the foramen ovale. The entire chain is partially
supported by a ligament attached to the short process of the incus
and to the walls of the tympanic cavity.

The Tensor Tympani Muscle. — This is a delicate muscle,
about 15 mm. in length, situated in a narrow groove just above the
Eustachian tube (Fig. 312). It arises from the cartilaginous portion
of the Eustachian tube and the adjacent portion of the sphenoid bone.
From this origin it passes nearly horizontally backward to the tym-
panic cavity; just opposite to the foramen ovale, its tendon bends at

640

TEXT-BOOK OF PHYSIOLOGY.

Fig. 311. — Audi-
tory Ossicles.
— I. Head of
malleus. 2. Pro-
cessus brevis. 3.
Processus graci-
lis. 4. Manubri-
um. 5. Long pro-
cess of incus. 6.
Articulation be-
tween incus and
stapes. 7. Stapes.
— (Sappey.)

a right angle over the processus cochleariformis and then passes
outward across the tympanic cavity to be inserted into the handle
of the malleus near the neck.

The stapedius muscle emerges from the cavity
of a pyramid of bone which projects from the
posterior wall of the tympanum. Its tendon
passes forward to be inserted into the neck of
the stapes bone near its point of articulation with
the incus.

The internal ear, or labyrinth, is located
within the petrous portion of the temporal bone.
It consists of an osseous and a membranous por-
tion, the latter contained within the former.

The osseous labyrinth is subdivided into
vestibule, semicircular canals, and cochlea.

The vestibule is a small, triangular-shaped
cavity between the semicircular canals and the
cochlea. It is separated from the cavity of the
middle ear by an osseous partition which pre-
sents near its center an oval opening, the foramen
ovale. In the living condition this opening is
closed by the base of the stapes bone, which is
held in position by an annular ligament. The inner wall presents
a number of openings for the passage of nerve-fibers (Fig. 313).

The semicircular canals are three in number, a superior vertical,
an inferior vertical, and a horizontal,
each of which opens by two orifices into
the cavity of the vestibule, with the ex-
ception of the two vertical, which unite
at one extremity and then open by a
single orifice. Each canal near its vesti-
bular orifice is enlarged to almost twice
the size of the rest of the canal, forming
what is known as the ampulla.

The cochlea, the anterior portion of
the labyrinth, is a gradually tapering
canal, about 35 mm. in length, wound
spirally two and a half times around a
central bony axis, the m,odiolus. The
cavity of the cochlea is partially subdi-
vided into two cavities by a thin spiral
plate of bone which projects from the inner wall, known as the
lamina osseous spiralis. In the natural condition this partition is
completed by a connective-tissue membrane, so that the two passages
are completely separated from each other. The upper passage or

Fig. 312. — M, The Tensor
Tympani Muscle — the
Eustachian Tube (Left).
— {Landois.)

THE SENSE OF HEARING.

Fig. 313. — Bony Cochlea, i.

Ampulla of superior semi-
circular canal. 2. Horizontal
canal. 3. Junction of supe-
rior and posterior semicircu-
lar canals. 4. The posterior
semicircular canal. 5. Fora-
men rotundum. 6. Foramen
ovale. 7. Cochlea.

scala is in free communication with the vestibule, and is known as
the scala vestihuli; the lower passage or scala in the dead condition
communicates with the tympanum by means of a round opening,
the foramen rotundum, and is therefore known as the scala tympani.
In the living condition this opening is completely closed by a mem-
brane, a second membrana tympani.
Both the scalae vestibuli and tympani
communicate at the apex of the
cochlea by a small opening, the heli-
cotrema. The modiolus, the central
bony axis, is perforated from base to
apex by a canal for the passage of the
auditory nerve-fibers; lateral canals,
diverging from the central canal, pass
through the osseous lamina spirahs
and transmit fibers of the auditory
nerve. The interior of the bony laby-
rinth is lined by periosteum covered by
epithelium and in communication with
lymph-spaces at the base of the skull by
means of the aqueduct of the vestibule.
The membranous labyrinth,
lying within the osseous labyrinth, corresponds with it in form, though
it is smaller in size. It may be subdivided into vestibule, semi-
circular canals, and cochlea (Fig. 314).

The vestibular portion consists of two small sacs, the utricle and
the saccule, which communicate with each other by means of the

two branches of a duct passing through
the aqueduct of the vestibule — the ductus
endolymphaiicus .

The semicircular canals communicate
with the utricle in the same manner as
the bony canals communicate with the
vestibule. The saccule communicates
with the membranous cochlea by a short
canal, the canalis reuniens. The walls of
the utricle, saccule, and semicircular
canals are composed of connective tissue
lined by epithehum. At the points of
entrance of the auditory nerve, the
maculce acusticce, in all three structures, the epithelium undergoes a
marked change in appearance and structure. It becomes columnar
in shape and provided with stiff hair-like processes or threads,
which project into the cavity. In the saccule and utricle the hair-
like processes are covered by a layer of small crystals of calcium
41

Fig. ,314. — I. Utricle. 2. Sac-
cule. 3. Vestibular end of
cochlea. 4. Canalis reuniens.

5. Membranous cochlea.

6. Membranous semicir-
cular canal. — {Patterns
^^ Anatomy.'")

642

TEXT-BOOK OF PHYSIOLOGY.

Fig

carbonate held together by a gelatinous material. The crystals are
known as otoliths.

The fibers of the vestibular nerve, arising from the cells of the

ganglion of Scarpa in the internal
auditory meatus, send their peri-
pherally directed branches through the
foramina in the inner wall of the vesti-
bule, through the walls of the utricle
and semicircular canals near the am-
pulla. As the fibers approach the
maculae acusticae they subdivide into
delicate fibrillae, which ultimately
become histologically and physiologi-
cally related to the neuro-epithelium.
From the relation of the nerve-fibers
to the epithelium, the latter must be
regarded as the highly specialized
terminal organ of the vestibular portion
of the auditory nerve.

The cochlea is a closed mem-
branous tube situated between the
osseous lamina spiralis and the outer
bony wall. A transection of the entire
cochlea shows the relation of the os-
seous and membranous portions (Fig.
316). The cochlear tube is triangular in shape. The base is attached
to the bony wall, the apex to the edge of osseous lamina spiralis.
One side of the tube forms
in part the membrane of
Reissner, the other side forms
in part the basilar membrane.
The sides of the cochlea to-
ward the scala vestibuli and
scala tympani are covered
with epithelium. The tri-
angular cavity of the cochlear
tube is known as the scala
media. The inner surface
of the cochlear tube is lined
by epithelium, which be-
comes extraordinarily modi-
fied and speciahzed along the
surface of the basilar membrane, to constitute what is known as —
The Organ of Corti. — In Fig. 316 this organ is represented as
it appears on cross-section of the cochlea. It consists primarily of

315. — Section of Wall of
Utricle of the Internal
Ear, through macular region,
from rabbit, showing otoUths
(0), embedded -within granu-
lar substance (g). h. Cili-
ated cells with processes (p),
extending between sustentacu-
lar elements (s). m. Base-
ment membrane, n. Nerve-
fibers within fibrous tissue (/)
passing toward hair-cells and
becoming non-medullated at
basement-membrane. — {After
Piersol.)

Fig.

316. — A Transverse Section
Turn of the Cochlea.

THE SENSE OF HEARING. 643

an arch composed of two modified epithelial cells known as the rods
or pillars of Corti, which rest below on the basilar membrane, but
meet and interlock above; it consists secondarily of a series of colum-
nar epithelial cells provided with hair-like processes which rest upon
and are supported by the rods both on the inner and outer aspects
of the arch. The space beneath the arch is known as the tunnel.
The inner hair cells are not nearly so numerous as the outer hair
cells. The epithelial cells external to the outer and inner hair cells
are supporting or sustentacular in character.

The organ of Corti extends the entire length of the cochlea. The
number of rods which, standing side by side, form the inner limb
of the arch is estimated at 5600; the number which form the outer
limb is estimated at 3850. The outer rods are broader than the
inner and at some places articulate with two or three inner rods.
The upper edges of the rods are flattened, elongated, and project
outward, forming a reticulated membrane through the meshes of
which the hair-like processes of the cells project.

From the connective-tissue thickening on the upper surface of
the osseous lamina spiralis there extends outward over the organ of
Corti a thin membrane, the membrana tectoria. The common cavity
between the walls of the osseous and membranous labyrinth in the
vestibule, the semicircular canals, in the scala vestibuli and scala
tympani of the cochlea, is filled with a clear fluid — the perilymph; the
common cavity within the w^alls of the entire membranous labyrinth
is also filled with a similar fluid — the endolymph. The hair-like pro-
cesses of the epithehal cells covering the maculee acusticas and the
rods of Corti are consequently bathed by endolymph. Both fluids
are in relation with the subarachnoid lymph-spaces at the base of the
brain, the perilymph through the aqueduct of the vestibule, the endo-
lymph through the endolymphatic duct.

The fibers of the cochlear nerve, arising from the ganglion cells
of the spiral ganglion situated in the osseous lamina spirahs near
the modiolus, send their peripheral branches to the saccule and to
the organ of Corti. As they approach this structure they lose their
medullary sheath and become naked axis-cyhnders. The fibers then
divide into two parts, of which one passes to the inner hair cells; the
other passes between the inner rods and crosses the tunnel between
the outer rods to the outer hair cells. The exact method of termina-
tion of these fibers in the hair cells is unknown, but doubtless it is
both histologic and physiologic.

From the relation of the nerve-fibers to the organ of Corti the
latter must be regarded as the highly specialized terminal organ of
the cochlear division of the auditory nerve.

644 TEXT-BOOK OF PHYSIOLOGY.

THE PHYSIOLOGY OF AUDITION.

The general function of the ear is the reception and transmission
of atmospheric vibrations from the concha to the percipient elements
— the hair cells — of the organ of Corti. The vibratory excitation of
these end-organs thus caused, is the basis of auditory perceptions.
The atmospheric vibrations are collected by the pinna and concha,
conveyed by the auditory canal to the tympanic membrane, trans-
mitted by the chain of bones to the labyrinth to pass successively
through the perilymph, the membranous walls, the endolymph, to
the hair cells. The nerve impulses generated by these vibrations are
then transmitted by the cochlear nerve to the auditory centers of the
cerebrum, where the sensations of sound are evoked. In order to
appreciate the function of the individual structures concerned in this,
general function there must be kept in mind a few of the character-
istics of atmospheric vibrations.

Atmospheric Vibrations.— The vibrations of the atmosphere
which are the objective causes of the sensations of sound are com-
municated to it by the vibrations of elastic bodies such as tuning-
forks, rods, strings, membranes, etc. These produce in the air a
to-and-fro movement of its particles, resulting in a succession of
alternate condensations and rarefactions which are propagated in
all directions. The impact of a rhythmic succession of such con-
densations on the ear gives rise to musical sounds ; the impact of an
arrhythmic or irregular succession gives rise to noises.

. If a writing point attached to a tuning-fork in vibration be placed
in contact with a traveling recording surface, each vibration will be
recorded in the form of a wave. For this reason atmospheric vibra-
tions are generally spoken of as sound-waves. A line drawn hori-
zontally through such a curve indicates the position of rest of the
fork; the extent of the curve on each side of this line indicates the
excursion of the fork or the amplitude of its movement.

The sounds which physiologically result from the impact and
transmission of the effects of sound-waves, possess intensity, pitch, and
quality or tone.

The intensity or loudness of a sound depends on the amplitude
of the vibration which causes it. The greater the amphtude or
swing of the vibrating body, the greater is the energy with which it
strikes the ear.

The pitch of a sound depends on the number of vibrations which
strike the ear in a unit of time — a second. The greater the number,,
the higher the pitch. Thus while the pitch of the sound caused by
the note C, on the first leger line below, of the music scale, corre-
sponds to 256 vibrations, the pitch of the sound caused by the note C
an octave above, corresponds to 512 vibrations. The lowest rate of

THE SENSE OF HEARING. 645

vibration which can produce a distinct sound varies in different
individuals from 14 to 18; the highest rate varies from 35,000 to
40,000 per second. Between these two extremes hes the range of
audibiHty, which embraces about 11 octaves. Vibrations less than
14 per second can not be perceived as a continuous sound; vibrations
beyond 40,000 also fail to be so perceived. In the ascent of the
music scale from the lowest to the highest regions there is a gradual
increase in the vibration frequency.

The quality of a sound depends on the jorm of the vibration. It
is this feature which gives rise to those dififerenccs in sensations which
permit one to distinguish one instrument from another when both
are emitting the same note. The form of the sound-wave in any
given instance is the resultant of a combination of a fundamental
vibration and certain secondary vibrations of subdivisions of the
vibrating body. These secondary vibrations give rise to what is
known as overtones. By their union with and modification of the
fundamental vibration there is produced a special form of vibration
which gives rise not to a simple but a composite sensation. It is
for this reason that the same note of the piano, the violin, and the
human voice varies in quality.

The Function of the Pinna and External Auditory Canal. —
In those animals possessing movable ears the pinna plays an im-
portant part in the collection of sound-waves. In man it is doubtful
if it plays a part at all necessary for hearing. Nevertheless an indi-
vidual with defective hearing may have the perception of sound
increased by placing the pinna at an angle of 90 degrees to the side
of the head or by placing the hand behind it. The external auditory
canal transmits the sonorous vibrations to the tympanic membrane.
From the obliquity of this canal it has been supposed that the vibra-
tions, after passing the concha, undergo a series of reflections on their
way to the tympanic membrane, which, owing to its inclination, would
be struck by them in a much more effective manner.

The Function of the Tympanic Membrane. — The function of
the tympanic membrane is the reception of the atmospheric vibrations
which are transmitted to it. This it does by vibrating in unison with
them. The vibrations which the membrane exhibits correspond in
ampUtude, in frequency, and in form to those of the atmosphere.
That this membrane actually reproduces all vibrations within the
range of audibility has been experimentally demonstrated. The
membrane not being fixed, as far as its tension is concerned, does
not possess a fixed fundamental note, like a stationary fixed mem-
brane, and is therefore just as well adapted for the reception of one
set of vibrations as another. This is made possible by variations in
its tension in accordance with the pitch or frequency of the atmos-
pheric vibrations. In the absence of vibration the membrane is in

646 TEXT-BOOK OF PHYSIOLOGY.

a condition of relaxation; with the advent of sound-waves possessing
a gradual increase of pitch, as in the ascent of the music scale, the
tension of the membrane increases until its maximum is reached at
the upper limit of the range of audibility. By this change in tension
certain tones become perceptible and distinct, while others become
imperceptible and indistinct.

The Function of the Tensor Tympani Muscle. — The function
of this muscle is, as its name indicates, to change and to fix the
tension of the tympanic membrane, so that it can most readily vibrate
in unison with vibrations of varying degrees of rapidity. The tendon
of this muscle playing around the processus cochleariformis is attached
almost at a right angle to the handle of the malleus. Hence as the
muscle contracts it exerts its traction from the process and draws the
handle of the malleus inward, thus increasing the convexity of the
tympanic membrane and at the same time its tension. With the
relaxation of the muscle the handle of the malleus passes outward,
and the convexity and tension diminish.

In the ascent of the music scale, each note corresponding to an
increase in vibration frequency, requires for its perception an increase
in tension and an increase in the force of the contraction of the tensor
muscle. In the descent of the music scale the reverse conditions
obtain. The contraction of the muscle is of the nature of a
single twitch, and of just sufficient force and duration to tense the
membrane for a given rate of vibration.

The contraction of the muscle is excited reflexly. The afferent
path is through fibers of the trigeminal nerve distributed to the tym-
panic membrane ; the efferent path is through fibers in the small root
of the trigeminal. The stimulus is sudden pressure on the tympanic
membrane. The more frequently and forcibly the stimulus is applied,
the greater is the muscle response. The tensor tympani muscle may
therefore be regarded as an accommodative apparatus by which the
tympanic membrane is adjusted for the reception of vibrations of
varying degrees of frequency.

The Function of the Chain of Bones. — The function of the
chain of bones is to transmit the effects of the atmospheric vibrations
to the fluid of the labyrinth. The manner in which this is accom-
plished becomes evident from the relation which the bones of this
chain bear to one another and to the tympanic membrane on the
one hand and to the fluid of the labyrinth on the other.

When pressure is made on the outer surface of the tympanic mem-
brane it is at once pushed inward, carrying with it the handle of
the malleus, the head at the same time rotating outward around an
axis corresponding to its ligamentous attachments. As the handle
moves inward a small ledge of bone just below the malleo-incudal
joint locks with, and hence pushes inward, the long process of the

THE SENSE OF HEARING. 647

incus. Since this process is united at almost a right angle to the
stapes bone, the latter is forced toward and into the foramen ovale,
thus producing a pressure on the perilymph. With the cessation of
the pressure the elastic forces of the membrane and of the ligaments
return the handle of the malleus to its former position; by the un-
locking of the malleo-incudal joint the entire chain also returns to
its former position without exerting undue traction on the basal
attachment of the stapes.

As the long process of the incus is shorter than the handle of the
malleus, and as the movement between them takes place around an
axis from before backward, it follows that the excursion of the incus
and stapes will be less than that of the malleus, while the force will
be greater. Hence as the vibrations are transferred from the tym-
panic membrane of large area to the base of the stapes of small area
(20 to 1.5), they lose in amplitude but increase in force. Their pres-
sure on the perilymph is therefore thirty times greater than on the
membrana t}Tiipani. In addition to its function as a transmitter of
vibrations, the chain of bones serves as a point of attachment for
muscles which regulate the tension of the tympanic membrane and
the pressure on the labyrinth.

The Function of the Stapedius Muscle. — The function of the
stapedius muscle is a subject of much discussion. According to
Henle, its function is to so adjust the stapes bone that it will be
prevented from exerting an undue pressure on the perilymph during
the inward excursions of the incus process. According to Toynbee,
its function is to press the posterior part of the stapes inward, make
it a fixed point, and place the anterior part in such a position that
it will vibrate freely and accurately.

The Function of the Eustachian Tube. — In order that the tym-
panic membrane may vibrate freely it is essential that the air pressure
on both sides shall be equal at all times. This is made possible by
the Eustachian tube. Were it not for this passageway, with each
inward swing of the membrane the air in the tympanic cavity would
be condensed and its pressure raised, in consequence of which the
movement of the membrane would be retarded; with each outward
swing, the air would be rarified and its pressure lowered below that
of the atmosphere, and in consequence the movement outward would
be retarded; the maximum response, therefore, of the membrane to
a given vibration could not be attained and the resulting sound
would be muffled and indistinct. But as with each vibration of the
membrane the air can pass into and out of the tympanum through
this tube, inequalities of pressure are prevented and a free vibration
permitted.

The impairment in the acuteness of hearing which is caused by
either a rise or fall of pressure in the middle ear can be shown —

648 TEXT-BOOK OF PHYSIOLOGY.

1. By closing the mouth and nose and then forcing air from the

lungs through the Eustachian tube into the tympanum, thus in-
creasing the pressure.

2. By closing the mouth and nose and then making an effort of

deglutition. As this act is attended by an opening of the phar-
yngeal end of the Eustachian tube, the air in the tympanum is
partly withdrawn and the pressure lowered. In each instance
hearing is impaired. After either experiment the normal con-
dition is restored by swallowing with the nasal passages open.
The Functions of the Internal Ear. — From the anatomic
arrangement of the structures of the internal ear it is evident that if
the vibrations of the stapes bone are to reach the peripheral organs —
the hair cells — of both the vestibular and cochlear nerves, they must
traverse successively the perilymph, the membranous walls, and the
endolymph. As the perilymph is incompressible, the inward move-
ment of the stapes would be prevented were it not for the elastic
character of the membrane closing the foramen rotundum. The
pressure wave occasioned by each inward movement of the stapes
is transmitted through the scala vestibuli, the helicotrema, the scala
tympani, to this membrane, which by virtue of its elasticity is pressed
into the tympanic cavity. With the outward movement of the stapes,
equilibrium is at once restored.

The Functions of the Cochlea. — The cochlea is the portion
of the internal ear which is concerned in the perception of tones.
The arrangement of the histologic elements of the organ of Corti
indicates that they in some way respond to the vibrations of varying
frequency and form, and through the development of nerve im-
pulses, evoke the sensations of pitch and quahty. The manner in
which this is accomplished is largely a matter of speculation. While
many theories have been offered in explanation of the power to
distinguish the pitch and the quahty or timbre of a tone, most physiol-
ogists prefer that of Helmholtz, who regarded the transverse fibers
of the basilar membrane as the elements immediately concerned,
and compared them, both in their arrangement and power of sympa-
thetic vibration, with the strings of a piano. He said: "If we could
so connect every string of a piano with a nerve-fiber that the nerve-
fiber would be excited as often as the string vibrated, then, as is
actually the case in the ear, every musical note which affected the
instrument would excite a series of sensations exactly corresponding
to the pendulum-like vibrations into which the original movements
of the air can be resolved; and thus the existence of each individual
overtone would be exactly perceived, as is actually the case with
the ear. The perception of tones of different pitch would, under
these circumstances, depend upon different nerve-fibers, and hence
would occur quite independently of each other. Microscopic in-

THE SENSE OF HEARING. 649

vestigation shows that there are somewhat similar structures in
the ear. The free ends of all the nerve-fibers are connected with
small elastic particles which we must assume are set into sympathetic
vibration by sound-waves." (Stirling.)

The mechanism might be regarded, therefore, somewhat as
follows: The sound-waves received by the membrana tympani and
transmitted by the chain of bones to the fenestra ovalis produce
variable pressures in the fluids of the internal ear; these pressures
vary in intensity, in number, and in quahty, and correspond with
the intensity, pitch, and quahty of the tones. If, therefore, a com-
pound wave of pressure be communicated by the base of the stapes,
it will be resolved into its constituents by the different transverse
fibers of the basilar membrane, each picking out its pecuhar portion of
the wave and thus stimulating corresponding nerve filaments. Thus
different nerve impulses are transmitted to the brain, where they are
fused in such a manner as to give rise to a sensation of a particular
quahty, but still so imperfectly fused that each constituent, by a
strong effort of attention, may be still recognized. The transverse
fibers of the basilar membrane vary in length from 0.04125 mm. at
the base of the cochlea to 0.495 ^^- ^^ the apex, and, according to
Retzius, are about 24,000 in number. As the human ear usually
cannot distinguish more than 11,064 tones, it is evident that there
is a sufficient anatomic basis for this theory.

The functions of the semicircular canals have already been
stated in connection with the chapter relating to the functions of the
cerebellum.

CHAPTER XXVII.
REPRODUCTION.

Reproduction is the process by which a new individual is initiated
and developed and the species to which it belongs is preserved.
Reproduction is the result of the union and subsequent development
of germ- and sperm-cells. These cells are produced and their union
accomplished by the cooperation of the reproductive organs charac-
teristic of the two sexes.

Embryology is a department of anatomic science which has for
its object the investigation of the successive stages that the new
being passes through during its gradual development prior to birth.

THE REPRODUCTIVE ORGANS OF THE FEMALE.

The reproductive organs of the female comprise the ovaries,
Fallopian tubes, uterus, and vagina (Fig. 317).

The Ovaries. — The ovaries are two small, flattened bodies,
measuring about 40 mm. in length and 20 in breadth. They are
situated in the cavity of the pelvis, one on either side, and embedded
in a fold of the peritoneum, known as the broad ligament. A section
of the ovary shows that it consists externally of a thin, firm, connective-
tissue membrane and internally of a fine connective-tissue stroma,
supporting blood-vessels, non-striated muscle-fibers and nerves, and
containing in its meshes a very large number of spheric sacs named
after their discoverer, de Graaf, the Graafian sacs or follicles. These
follicles are very numerous and are present in all portions of the
ovary, though they are most abundant toward its peripheral portions.
It is estimated that the human ovary contains from 20,000 to 40,000
follicles. The follicles vary considerably in size ; while many are visible
to the unaided eye, others require for their detection high powers
of the microscope. Although the follicles are present in the ovary
at the time of birth, it is not until the period of puberty that they
assume functional activity.

From this time on to the catamenial period there is a constant
growth and development of these follicles. Each follicle consists of
an external investment of fibrous tissue and blood-vessels, and an
internal investment of cells, the membrana granulosa. At the lower
portion of this membrane there is an accumulation of cells, the pro-

650

REPRODUCTION.

651

ligerous disc (Fig. 318). The cavity of the follicle contains a slightly
yellowish, alkaline, albuminous fluid, a transudate in all probability
from the blood-vessels. The Graafian follicle is of especial interest,
for it is in this structure, and more especially in the proligerous
disc, that the true germ-cell or ovum is developed.

The ovum is a spheric body measuring about 0.3 mm. in diameter.
It consists of a mass of living, protoplasmic material, cytoplasm, a
nucleus or germinal vesicle, and a nucleolus or germinal spot. The
cytoplasm presents toward its central portion a quantity of granular
material, partly fatty in character, the deutoplasm or vitellus. The
peripheral portion of the cytoplasm is surrounded by a delicate
radially striated border, the zona pellucida or radiata (Fig. 319).

Fig. 317. — Uterus, Fallopian Tubes and Ovaries; Posterior View, i, i.
Ovaries. 2> 2. Fallopian tubes. 3, 3. Fimbriated extremity of the left Fallopian
tube seen from its concavity. 4. Opening of the left tube. 5. Fimbriated
extremity of the right tube, posterior view. 6, 6. Fimbriae which attach the
e.xtremity of each tube to the ovary. 7, 7. Ligaments of the ovar}^ 8, 8, 9, 9.
Broad ligament. 10. Uterus. 11. Cervix uteri. 12. Os externum. 13, 13.
Vagina.

The nucleus consists of a nuclear membrane enclosing contents.
The latter consist of an amorphous material in which is embedded
a network, some of the threads of which have a strong affinity for
certain staining materials, and hence are known as chromatin, while
others stain less deeply and are known as achromatin.

The Fallopian Tubes. — The Fallopian tubes are about 12 centi-
meters in length and extend from the upper angles of the uterus
to the ovaries. Each tube is somewhat trumpet-shaped, the narrow
portion being close to the uterus, the wide portion close to the ovary.
The outer extremity of the tube is expanded and subdivided, and
presents a series of processes termed fimbriae, one of which is attached

652

TEXT-BOOK OF PHYSIOLOGY.

to the ovary. The tube consists of three coats — an external or
serous; a middle or muscular, the fibers of which are arranged
longitudinally and transversely; and an internal or mucous. The
surface of the mucous coat is covered with a layer of ciliated epithelial
cells, the motion of which is toward the uterus.

The Uterus. — The uterus is pyriform in shape and divided into
a body and neck. It measures, before the first pregnancy, about

7 cm. in length, 5 cm.
5 ^ in breadth and 2^
cm. in thickness. A
frontal section of the
uterus shows a central
cavity which in the
body is triangular in
shape, in the neck
oval or fusiform (Fig.
320). At the upper
angles of the uterus
the cavity is contin-
uous with the cavity of
each Fallopian tube.
At the junction of the
body and the neck,
the cavity presents a
constriction, the inter-
nal OS. The constric-
tion at the end of the
neck is known as the
external os. The
walls of the uterus
are extremely thick
and composed of non-
striated muscle-fibers
arranged in a very
complicated manner.
The interior of the
uterus is lined by
mucous membrane
covered with cylindric
ciliated epithehal cells, the motion of which is toward the external
OS. Tubular glands are found in large numbers in the mucous
membrane lining the cavity, while racemose glands are found in
the mucous membrane fining the neck. Owing to the flattening of
the uterus from before backward the walls are almost in contact
and the cavity almost obliterated.

The Vagina. — The vagina is a musculo-membranous canal, from

Fig. 318. — Section of Cortex of Cat's Ovary,
Exhibiting Large Graafian Follicles. — a.
Peripheral zone of condensed stroma, b. Groups
of immature follicles, c. Theca of follicle, d.
Membrana granulosa, e. Discus proligerus. /.
Zona pellucida. g. Vitellus. h. Germinal vesi-
cle, i. Germinal spot. k. Cavity of liquor fol-
liculi. — (After Piersol.)

REPRODUCTION.

653

12 to 18 cm. in length, situated between the rectum and bladder.
It extends from the surface of the body to the brim of the pelvis,
and embraces at its upper extremity the neck of the uterus.

Ovulation. — After the establishment of puberty a Graafian folUcle
develops and ripens or matures periodically, usually every twenty-
eight days. During the time of maturation the follicle increases in
size, from an augmentation of its fluid contents, and approaches the
surface of the ovary, where it forms a projection varying from 6
to 12 mm. in size. When maturation is complete the vesicle rup-

^ A'-
'•'It.

%

^-^K

'^

J^

Fig. 319. — 0^■^^I of a Cow. — i. Zona pe!-
lucida. 2. Cytoplasm, vitellus. 3. Nu-
cleus, germinal vesicle. 4. Nucleolus,
germinal spot. 5. Corona radiata. The
radial striation of the zona pellucida
can not be seen. — (Stohr.)

Fig. 320. — Frontal Section
OF THE Uterus, i. Cav-
ity of the body. 2, 3.
Lateral walls. 4, 4. Cor-
nua. 5. Os internum. 6.
Ca^^ty of the cervix. 7.
Arbor vitae of the cervix.
8. Os externum. 9. ^'a-
gina..—(Sappey.)

tures, and the ovum and Hquid contents are discharged. The ovum,
by a mechanism not fully understood, is received by the fimbriated
extremity of the Fallopian tube and enters its cavity. The ovum is
then transferred through the tube by the peristaltic contraction of
its muscle-fibers and by the action of the ciha of its lining epithelium.
The time occupied in the transference of the ovum from the ovary
to the interior of the uterus has been estimated to be from four to
ten days.

Either at the time, or very shortly after, its discharge from the
folhcle, the ovum, and more especially the nucleus, undergoes a series
of histologic changes which eventuates in an extrusion of a portion

654 TEXT-BOOK OF PHYSIOLOGY.

of the chromatin material. The extruded portions are known as the
polar bodies. The non-extruded portion of the chromatin material
is known as the female pronucleus. The succession of changes which
the nucleus undergoes is termed maturation. As the nucleus is
regarded as the part of the ovum which transmits parental character-
istics it is assumed that the extrusion of a portion of the nuclear
material is a means by which an excess of inherited substance is
prevented.

Menstruation. — Menstruation is a periodic discharge of blood
and mucus from the surface of the mucous membrane of the uterus,
and occurs about every twenty-eight days. The duration of the
menstrual period extends over four or five days and the amount of
blood discharged varies from i8o c.c. to 200 c.c. Menstruation is
usually an accompaniment of ovulation, though the latter process may
take place independently of the former. It is characterized by both
local and systemic changes. The local changes are most marked
in the uterus, the mucous membrane of which increases in thickness
from a proliferation of the connective tissue and a hyperemic condi-
tion of the blood-vessels. Subsequently to these changes the epithe-
lial surface, as well as the more superficial portions of the connective
tissue, undergo degeneration and exfoliation, after which the finer
blood-vessels rupture and permit of an escape of blood into the
uterine cavity. At the end of the menstrual period regenerative
changes set in which continue until the normal condition of the
mucous membrane is reestablished.

The Corpus Luteum. — With the rupture of the Graafian follicle
there is an effusion of blood into the follicular cavity which soon
coagulates, loses its color and assumes the characteristics of fibrin.
The walls of the follicle, which have become thickened from the
deposition of a reddish-yellow glutinous substance, now become con-
voluted and undergo a still further hypertrophy, until they encroach
upon and almost obliterate the follicular cavity. In a few weeks the
mass loses its red color and becomes decidedly yellow, when it is
known as the corpus luteum. With the continuance of reparative
changes this body gradually disappears until at the end of two months
nothing remains but a small cicatrix on the surface of the ovary.
Such are the changes in the follicle if the ovum has not been im-
pregnated.

The corpus luteum, after impregnation has taken place, undergoes
a much slower development, becomes larger, and continues during
the entire period of gestation. The difference between the corpus
luteum of the unimpregnated and pregnant condition is expressed in
the following table by Dalton :

REPRODUCTION.

655

Corpus Luteum of Menstruation. Corpus Luteum of Pregn.vncy.

At the end of

weeks.
One month.

Two months.
Four months.
Six months.
Nine months.

three Three-quarters of an inch in diameter
convoluted wall pale.
I Smaller; convoluted
wall bright yellow ; clot
' still reddish.

Reduced to the condition
of an insisrnificant cicatrix.

central clot reddish ;

Larger ; convoluted wall bright
vellow ; clot still reddish.

Absent or unnoticeable.

Absent.

Absent.

Seven-eighths of an inch in
diameter ; convoluted wall bright
yellow ; clot perfectly decolorized.

Seven-eighths of an inch in
diameter ; clot pale and fibrinous;
convoluted wall dull yellow.

Still as large as at the end of
second month ; clot fibrinous ;
convoluted wall paler.

Half an inch in diameter ; cen-
tral clot converted into a radiating
cicatrix ; external wall tolerably
thick and convoluted, but without
anv bright vellow color.

THE REPRODUCTIVE ORGANS OF THE MALE.

The reproductive organs of the male comprise the testicles, vasa
deferentia, vesiculce seminales, and penis.

The Testicles. — The testicles are oblong glands, about 40 mm. in
length, 30 mm. in breadth and 20 mm. in
thickness, and contained within the cavity
of the scrotum. A section of the testicle
(Fig. 321) reveals the presence externally
of a dense fibrous membrane, the
tunica albuginea, and internally a con-
nective - tissue framework consisting
mainly of septa, which enter the organ
on its posterior aspect at the mediastinum
testis, passing inward in a diverging
manner. The spaces between the septa
are occupied by the true gland substance,
the seminiferous tubules.

The seminiferous tubules are very
numerous, the estimate as to their
number varving from 800 to

1000.
When unraveled thev measure from 30

mm. in

to 40 cm. in length and
diameter. At their peripheral extrem-
ities the tubules are very much con-
voluted, but as they pass toward the
mediastinum testis, the convolutions
disappear, and after uniting with one another terminate in from
twenty to thirty straight tubes, the vasa recta, which pass through

Fig. 321. — Diagram of a Ver-
tical Section throltqh a
Testicle, i . Mediastinum
testis. 2, 2. Trabeculae.
3. One of the lobules. 4, 4.
Vasa recta. 5. Globus ma-
jor of the epididymus. 6.
Globus minor. 7. \'as def-
erens.— {Holden.)

656

TEXT-BOOK OF PHYSIOLOGY.

the mediastinum and form the rete testis. At the upper part of
the mediastinum the tubules unite to form from nine to thirty small
ducts, the vasa efferentia, which soon become very much convoluted.
After a short course they unite to form a single tortuous tube, about
7 meters in length and 0.4 mm. in diameter, which descends behind
the testicle to its lower border. This tube is known as the epididy-
mis. The seminal tubule consists of a basement membrane lined
by granular nucleated epithelium.

The vas deferens, the excretory duct of the testicle, is about 60 cm.
in length and from 2 to 3 mm. in diameter, and extends upward

from the epididymis to the
inguinal canal, through which
it passes into the abdominal
cavity and then to the under
surface of the base of the
bladder, where it unites with the
duct of the vesicula seminalis to
form the ejaculatory duct.

The vesiculae seminales
are two lobulated pyriform
bodies, about 40 mm. in length,
situated on the under surface
of the bladder. Each vesicula
seminalis consists of an external
fibrous coat, a middle, muscular
coat, and an external mucous
coat. The mucous coat con-
tains a number of small tubu-
lar albumin-producing glands
which secrete a characteristic
fluid.

The ejaculatory duct, formed
by the union of the vas deferens
and the duct of the vesicula semi-
nalis, opens into the prostatic
portion of the urethra (Fig. 322).
The prostate gland is a musculo-glandular mass situated at the
posterior extremity of the urethra. It contains a large number of
tubules, more or less branched and convoluted, and lined by columnar
epithelium. They secrete a fluid which is poured into the urethra
at the time of the ejaculation of semen.

The penis consists of three parts : the corpus spongiosum below,
through which passes the urethra, and the two corpora cavernosa,
one on either side and above. The corpus spongiosum terminates
anteriorly in a conic-shaped structure, the glans penis; the corpora

Fig. 322. — Vas Deferens, Vesicula
Seminales, and Ejaculatory
Ducts. — a. Vas deferens, h. Semi-
nal vesicle, c. Ejaculatory duct. d.
Termination of the ejaculatory duct.
e. Opening of the prostatic utricle.
/, g. Veru montanum. h, I. Pros-
tate.— (Liegeois.)

REPRODUCTION. 657

cavernosa consist externally of a fibrous investment and internally
of erectile tissue. These bodies are abundantly supplied with blood,
which after entering their substance by the arteries, passes into sinuses
or reservoirs, from which it is carried away by veins. These vessels
pass to the dorsum of the penis and unite to form a large vein by
which the blood is returned to the general circulation. By virtue
of the erectile tissue in the corpora cavernosa the penis becomes
erect and rigid when the blood supply is increased. This takes place
in response to peripheral stimulation or emotional states, or both
combined. When these conditions are estabhshed nerve-impulses
pass outward through nerves, the nervi erigenteSy which have their
origin in the lumbar region of the spinal cord, and bring about an
active dilatation of the arteries and a relaxation of the non-striated
muscle-fibers in the corpora cavernosa. With these events there is a
rapid influx of blood and a distention and an erection of the organ.
This condition is furthered and maintained by a partial compression
of the dorsal vein by the fibrous capsule.

Semen. — The semen is a complex fluid composed of the secretions
of the testicles, the vesiculae seminales, the prostatic tubules, and
urethral glands. It is grayish-white in color, mucilaginous in con-
sistence, characteristic in odor, and somewhat heavier than water.
In response to appropriate stimulation the muscle-fibers in the walls
of the vasa deferentia, vesiculas seminales, and prostatic tubules
contract and discharge their contents into the urethra, from which
they are forcibly ejected by the rhythmic contraction of the ejaculatory
muscles, the ischio and bulbo caver no si. The amount of semen dis-
charged at each ejaculation varies from i to 5 c.c.

Spermatozoa. — The spermatozoa are peculiar morphologic ele-
ments which arise within the seminiferous tubules as a result of
complex histologic changes in the lining epithelium. An adult sper-
matozoon consists of a conoid slightly flattened head, from the pos-
terior part of which there projects a short straight rod, provided with
a long filamentous tail or cihum and an end-piece (Fig. 323). The
head contains a nucleus of chromatin material. The total length of
a spermatozoon varies from 50 to 80 micromillimeters. The char-
acteristic physiologic feature of spermatozoa is incessant locomotion
when in a suitable medium. So long as they are confined to
the vas deferens they are quiescent, but wdth their advent into the
vesicula seminalis and dissemination in its contained fluid, they be-
come extremely active and move around with considerable rapidity.
The power of locomotion depends on the possession of the tail,
which, by lashing the surrounding fluid now in this and now in that
direction, propels the head from place to place. The vitality of
spermatozoa is such as to enable them to retain their physiologic
activities in the uterus for more than eight days.
42

658

TEXT-BOOK OF PHYSIOLOGY.

The development of spermatozoa from testicular cells as observed
in lower animals indicates that each cell gives rise to four embryonic
forms — spermatids — which subsequently develop into adult sperma-
tozoa. In this process the primary nuclear chromatin undergoes a
division, so that each spermatozoon receives but a fractional amount.
The changes by which this condition is brought about are comparable
to the changes exhibited by the ovum, and have for their result a
reduction in the quantity of hereditary substance
to be transmitted.

Fecundation. — Fecundation is the union of
the spermatozoon (the sperm-cell) with the ovum
(the germ-cell) and takes place in the great
majority of instances in the Fallopian tube.
After the introduction of the spermatozoa into
the vagina during the act of copulation, they
soon begin to pass upward, into and through,
the uterine cavity and out into the Fallopian tube,
where they accumulate in large numbers and
retain their vitality for some days. The migration
is effected by the propelling power of the
filamentous tail.

From observations made on the behavior of
the spermatozoa toward the ovum in lower
animals, and on the manner by which their
union is effected, the inference may be drawn
that a similar procedure takes place in mammals.
In lower animals the spermatozoa on approaching
an ovum take on increased activity, swimming
around it in all directions and apparently seeking
a point of entrance. In fish and molluscs the
zona pellucida presents a distinct opening, the
micropyle, through which the spermatozoon
passes. Inasmuch as the mammalian ovum is
devoid of such an opening, the mechanism of
entrance of the spermatozoon is not clearly
understood. Notwithstanding their enormous numbers it is gener-
ally believed that but a single spermatozoon effects an entrance
into the ovum. With the accomplishment of this, however, the
spermatozoon loses its vitality, after which the body and tail dis-
appear. The head, which in this instance also is the transmitter of
the inherited material, advances to meet and unite with the nucleus
of the ovum. A series of histologic changes now arise, which
eventuate in the production of a new cell, a parent cell, possessing
all the features of cell structure and the physiologic activities and

Fig. 323. — Human
Spermatozoon.

1 . Front view,

2, side view, of
the head. k.
Head. m. mid-
dle piece. /.
Tail. e. Termi-

• nal filament. —
{After Retzius.)

REPRODUCTION.

659

characteristics of both ancestral cells. From this parent cell the
new being develops through successive division, multiplication, and
differentiation of cells.

The Fixation of the Ovum.— If the ovum is to develop into a
new being it is essential that it be retained within the cavity of the
uterus. This is accompHshed by the development of speciaHzed
structures on the surface of the uterine mucosa and on the surface
of the ovum. With the fertihzation of the ovum, the mucous mem-
brane of the uterus takes on an increased growth ; it becomes hyper-
trophied and vascular, and develops small elevations known as villi.
Inasmuch as this membrane is detached and discharged at the birth
of the fetus, it is known as the decidua vera. With the fertilization

Fig. 324. — Impregnated Uterus, with
Folds of Decidua Growing up
Around the Egg. The narrow
opening, where the folds approach
each other, is seen over the most
prominent portion of the egg. —
{Dalton.)

Fig. 325. — Impregnated Uterus;
showing the connection between the
villosities of the chorion and the
decidual membranes. — {Dalton.)

of the ovum, the zona pellucida or radiata also develops villosities,
and as it passes from the Fallopian tube into the uterus the villi
interdigitate, and its further progress is retarded. (Figs. 324 and
325.) In a short time a portion of the decidua vera grows up
on all sides and encloses the ovum. Its retention is thus secured.
That portion of the decidua which grows around the ovum
is termed the decidua reflexa; while the portion to which the
ovum attaches itself is termed the decidua seroiina, and is of interest
for the reason that it becomes the seat of development of the placenta,
the organ by which the fetus is nourished. As development advances
the decidua reflexa also increases in size and extent, and about the
end of the fourth month comes into contact with the decidua vera,
with which it ultimately fuses.

66o

TEXT-BOOK OF PHYSIOLOGY.

DEVELOPMENT OF FETAL ACCESSORY STRUCTURES.

Segmentation of the Ovum. — Shortly after the formation of the
parent cell, segmentation of the nucleus and cytoplasm takes place
in accordance with karyokinetic methods. The two new cells thus
formed undergo a similar division into four, the four into eight, the
eight into sixteen, and so on until the space within the zona pellucida
is completely filled with a large number of small cells, each possessing
the characteristic cell structures. The peripheral cells then arrange
themselves in the form of a membrane, and as they are, at the same
time, subjected to mutual pressure they assume a polyhedral shape,
and give to the membrane a mosaic appearance (Fig. 326). The

central cells then
undergo liquefac-
tion. At some
point on the inner
surface of the
membrane, cells ac-
cumulate which by
their division and
multiplication form
a second mem-
brane. The two
together are known
as the external and
internal blasto-
dermic membranes.
Germinal Area.
— At about this
period there is an
accumulation o f
cells at a certain
spot in the sub-
stance of the blastodermic membranes which marks the position of
the future embryo. This spot, at first circular, soon becomes
elongated. A slight indentation now develops into what is known as
the primitive trace. Around this area there is a clear space, the
area pellucida, which is in turn surrounded by a darker region, the
area opaca. The primitive trace soon disappears and the area
pellucida becomes guitar-shaped. A second groove, the medullary
groove, is now formed, which develops from before backward and
becomes the neural medullary canal.

Blastodermic Membranes. — The embryo, at this period, con-
sists of three layers — viz., the external and the internal blastodermic
membranes and a middle membrane formed by a genesis of cells

Fig. 326. — PiaiiiTiVE Trace of the Embryo, a. Primi-
tive trace, h. Area pellucida. ' c. Area opaca. d.
Blastodermic cells, e. Villi beginning to appear on
the surface of the zona pellucida. — (Lugois.)

REPRODUCTION.

66i

.,- «<s

—VP

from their internal surfaces. These layers are known from without
inward as the epiblast, mesoblast, and hypoblast.

The epiblast gives rise to the central nerve system, the epidermis
and its appendages, and the primitive kidneys.

The mesoblast gives rise to the dermis, muscles, bones, nerves,
blood-vessels, sympathetic nerve system, connective tissue, the
urinary and reproductive apparatus, and the walls of the alimentary
canal.

The hypoblast gives rise to the epithelial lining of the alimentary
canal and its glandular appendages,
the liver and pancreas, and the epithe-
lium of the respiratory tract.

Dorsal Laminae. — As develop-
ment advances, the true medullary
groove deepens, and there arise two
longitudinal elevations of the epiblast
— the dorsal lamince, one on either side
of the groove, — which grow up, arch
over, and unite so as to form a closed
tube, the primitive central nerve
system.

The Chorda Dorsalis. — Just be-
neath the neural canal there arises a
group of mesoblastic cells which ar-
range themselves in the form of a
cylindric rod, which marks out the
position of the future bony axis of the
body. This rod is known as the
chorda dorsalis or notochord.

Primitive Vertebrae. — On either
side of the neural canal the cells of
the mesoblast undergo a longitudinal
thickening, which develops and extends
around the neural canal and the
chorda dorsalis, and forms the arches

and bodies of the vertebrae. They become divided transversely
into segments.

The mesoblast now separates into two layers: the external, joining
with the epiblast, forms the somato pleura; the internal, joining with
the hypoblast, forms the splanchno pleura; the space between them
constitutes the pleiiro- peritoneal cavity (Fig. 327).

Visceral Laminae. — The walls of the pleuro-peritoneal cavity
are formed by a downward prolongation of the somatopleura (the
visceral lamiiKE), which, as they extend around in front, pinch off
a portion of the yolk-sac (formed by the splanchnopleura), which

Fig. 327. — Diagram Represent-
ing THE Relation of Prim-
ary Structures in a Devel-
oping Chicken; Vertical
Transverse Section. The
medullary groove and chorda
dorsalis are seen in section;
the ahmentary canal pinched
off from the yolk-sac is com-
pletely closed, a. Amnion.
a, c. Amniotic cavity filled
v^dth amniotic fluid, pp.
Space between amnion and
chorion continuous with the
pleuro-peritoneal cavity in-
side the body. vt. Vitelhne
membrane, or zona pellucida.
ys. Yolk-sac, or umbihcal
vesicle. — {Foster and Balfour.)

662

TEXT-BOOK OF PHYSIOLOGY.

becomes the primitive alimentary canal; the lower portion, remaining
outside of the body cavity, forms the umbilical vesicle.

The Fetal or Embryonic Membranes. — ^With the appearance
of the visceral laminae two membranes develop in succession, both
of which play an important part in the subsequent life of the embryo.
These are known as the amnion and the allantois.

The amnion is formed by folds of the epiblast and the external
layer of the mesoblast rising up in front, behind, and at the sides.
These folds gradually extend over the back of the embryo to a certain
point where they meet, coalesce, and enclose a cavity known as the
amniotic cavity. The membranous partition between the folds is
absorbed, after which the outer layer recedes and becomes blended
with the primitive enveloping membrane of the ovum and thus

Fig. 328. — Diagram of Fecundated
Egg. a. Umbilical vesicle. h.
Amniotic cavity. c. Allantois. —
(Dalton.)

Fig. 329. — Fecundated Egg with
Allantois nearly Complete, a.
Inner layer of amniotic fold. b.
Outer layer of ditto, c. Point where
the amniotic folds come in contact.
The allantois is seen penetrating
betv^reen the outer and inner layers
of the amniotic folds. — {Dalton.)

assists in the formation of the chorion — the external covering of the
embryo.

The cavity enclosed by the amnion is at first quite small, but
soon enlarges from the accumulation of a clear, transparent fluid, the
amniotic fluid. It gradually increases in amount up to the latter
period of gestation, when its volume reaches about one liter. This
fluid is derived mainly from the blood, as it contains albumin, sugar,
fatty matter, and inorganic salts. Traces of urea indicate that some
of its constituents are derived from the embryo itself.

The allantois is primarily a pouch or diverticulum which develops
from the posterior portion of the alimentary canal. As it develops
it enlarges, and in its growth inserts itself between the two layers
of the amnion, coming into contact more especially with the external
layer. It finally completely surrounds the embryo, after which its
edges become fused together (Figs. 328 and 329),

REPRODUCTION.

663

The allantois is of especial interest and importance, as it is the
means by which the blood of the embryo is brought into relation
with the blood of the mother. As it develops, two arteries, the
hypogastrics, one from each internal iliac, pass out of the abdominal
cavity within the walls of the allantois, and follow it in its course
around the embryo. The ultimate branches of these arteries pene-
trate the villous processes which develop on the surface of the chorion
and which take part in the formation of the placenta. A single
large vein emerges from the placenta and returns the blood to the
embryo. In its course it winds around the arteries in a spiral
manner a number of times. These vessels — the umbihcal arteries
and vein — are enclosed by the walls of the allantois and amnion,
and together constitute the umbilical cord which at the end of gesta-
tion is about 60 cm. in length.

The Chorion.— The cho-
rion, the external investment
of the embryo, is formed by
the fusion of the primitive egg
membrane — the zona pellu-
cida — the external layer of the
amnion, and the allantois.
Very early in development its
external surface becomes
covered with homogeneous,
granular, club-shaped proces-
ses, which by continued bud-
ding and growth, give to the
membrane a shaggy appear-
ance. At about the end of
the second month these pro-
cesses begin to atrophy and
disappear from the surface of the chorion, with the exception of that
portion which is in contact with the decidua serotina. At this point
the processes or villi continue to grow and develop, and insert them-
selves more deeply into the mucous membrane. Corresponding
processes from the mucous membrane insert themselves between
the villi of the chorion, which by their growth and fusion secure,
among other things, the retention of the embryo.

The Nutrition of the Embryo. — Coincidently with the develop-
ment of the amnion, allantois, and chorion, there arises within the
body of the embryo the early forms of many, if not all, of the future
viscera. The nutritive material required for their growth is partly
contained within the umbilical vesicle lying without the body cavity.
That this material may be utilized, blood-vessels emerge from the
body and ramify within the walls of the vesicle. The capillaries to

Fig. 330. — Human Embryo and its En-
velopes AT THE End of the Third
Month.

664

TEXT-BOOK OF PHYSIOLOGY.

which these vessels give rise come into close relation with and absorb
the food material, after which it is carried by veins to the heart,
by which it is distributed to all parts of the embryo. These vessels
are collectively known as the omphalo-mesenteric arteries and veins.
This primitive or vitelline circulation is of short duration in mam-
mals, as the nutritive material in the vesicle is small in amount and
is soon exhausted. In birds, however, it is of primary importance.
The main supply of nutritive material, however, is derived from
the mother by means of a highly developed and specialized organ —
The Placenta. — Of all the embryonic structures the placenta
is the most important. It is formed by the end of the third month,

after which it gradually
increases in size up to the
end of the eighth month,
by which time it is fully
developed. It then mea-
sures from 1 8 to 24 cm.
in diameter and weighs
from 400 to 600 grams.
It is most frequently situ-
ated at the upper and
back part of the uterine
cavity. Though exceed-
ingly complex in structure
it consists essentially of
two portions, a fetal and a
maternal.

The fetal portion con-
sists primarily of those villi
on the chorion in relation
with the decidua serotina.
These structures gradu-
ally increase in size and
number, and receive the
ultimate branches of the umbilical arteries. The maternal portion
consists primarily of the decidua serotina. As gestation advances the
chorionic villi rapidly increase in size and number, and receive the
branches of the umbilical arteries. At the same time the decidua
serotina becomes hypertrophied and vascular. With the continued
growth and development of these two structures they gradually fuse
together and finally become inseparable. In accordance with the
needs of the embryo, the decidua serotina and its contained blood-
vessels undergo certain histologic changes which result in the forma-
tion of large cavities, sinuses, or lakes, into which the blood of the
uterine vessels is emptied. Coincidently the vilH of the chorion grow

Fig. 331. — Human Embryo, with Amnion and
Allantois, in the Third Week. There
are as yet no limbs; the embryo and its
appendages are surrounded by the tufted
chorion. — (Haeckel.)

REPRODUCTION.

665

and give off numerous branches, which project themselves in all direc-
tions into the blood of uterine sinuses (Figs. 332, S33)- As the
placenta develops, the structures separating the blood of the mother
from that of the child gradually become modified until they are repre-
sented by a thin cellular or homogeneous membrane. The conditions
now are such as to permit of a free exchange of material between the
mother and child. Whether by osmosis or by an act of secretion, the
nutritive materials of the maternal blood pass through the intervening
membrane into the fetal blood on the one hand, while waste products

Fig. 332. — Diagram showixg the Relations of the Fetal Membranes. Am.
Amnion. Ch. Chorion. M. Muscle wall of uterus. R. Decidua reflexa. 5.
Serotina. T''. Decidua vera. Y. Yolk stalk.— {McMur rich.)

pass in the reverse direction into the maternal blood on the other
hand. Inasmuch as oxygen is absorbed and carbon dioxid exhaled
by the same structures, the placenta is to be regarded as both a
digestive and a respiratory organ. So long as these exchanges are
permitted to take place in a normal manner the nutrition of the
embryo is secured.

The Fetal Circulation. — The composition of the blood as well
as the course it pursues through the heart and vascular apparatus
presents peculiarities which have arisen in consequence of the neces-
sity of obtaining nutritive material through the placenta and the

666

TEXT-BOOK OF PHYSIOLOGY.

almost impervious condition of the pulmonary capillaries. On re-
turning from the placenta, the blood in the umbilical vein is relatively
rich in nutritive material and scarlet red in color from the presence
of oxygen. As it passes into the abdominal cavity a portion of the
blood is directed by the ductus venosus into the vena cava, while
another portion is emptied into the branches of the portal vein, by
which it is distributed to the liver and from which it emerges by
the hepatic veins and poured into the vena cava. The blood in the
vena cava is thus a mixture of venous blood from the lower extremi-
ties and liver, and oxygenated blood from the placenta. After its
discharge into the right auricle the blood is directed by a fold of

Chorion

Choriomc villi.

Inter\'illous spaces.
Floating villus.

Compact
layer

Cavernous)
layer. |

Musculans.

■\ttached villi.

Fig. 333. — Diagram of Human Placenta at the Close of Pregnancy.-

{Schdper.)

the lining membrane, the Eustachian valve, through an opening in
the interauricular septum, the foramen ovale, into the left auricle.
It then flows through the auriculo-ventricular opening into the left
ventricle, thence into the aorta, and by its branches is distributed
to all parts of the body.

The blood from the head and upper extremities is emptied by
the superior vena cava into the right auricle, but as it passes in
front of the Eustachian valve, it flows directly into the right ventricle
and then into the pulmonary artery. On account of the unexpanded
condition of the lungs and the almost impervious condition of the
pulmonary capillaries, but a small portion of the blood passes
through them, while the larger portion by far passes into the aorta

DL^GRAM OF FCET.AL CIRCULATION.

W.Preyer del.

REPRODUCTION. 667

directly through a duct, the ductus arteriosus, which enters at a point
below the origin of the left carotid and subclavian arteries. A com-
parison of the blood distributed to the head and upper extremities, with
that distributed to the lower extremities, will show a larger percentage
of nutritive material and oxygen in the former than in the latter,
a fact which has been offered as an explanation of the more rapid
growth of the upper half of the body. As the blood passes through
the aorta, a portion is directed from the main current by the hypogas-
tric and umbilical arteries to the placenta, where it loses carbon
dioxid and gains oxygen, and changes in color from a bluish red to a
scarlet red.

Parturition. — -At the end of gestation — approximately 280 days
from the time of conception — a scries of changes occur in the uterine
structures which lead to an expulsion of the child, the placenta, and
decidua vera. To this process in its entirety the term parturition
is given. At this time, from causes not clearly defined, the uterine
walls begin to exhibit throughout their extent a series of slight con-
tractions which are somewhat peristaltic in character; these con-
tractions, which gradually increase in frequency and vigor, bring
about a dilatation of the internal os and a descent of the membranes
into the cervical canal. The pressure exerted by these membranes
during the time of the contraction materially assists in the relaxation
of the circular fibers and a dilatation of the external os. When the
dilatation has so far advanced that the diameter of the external os
attains a measure of 7 or 8 cm., the tension of the membranes becomes
sufficiently great to lead to their rupture and to a partial escape of
the amniotic fluid. With this event, the presenting part of the
child, usually the head, descends into the cervical canal. After a
short period of rest the uterine contractions return and rapidly
increase in vigor and duration. As a result of the pressure thus
exerted from all sides on the body of the child, the head gradually
descends into the vagina and finally emerges through the vulva to
be followed in a short time by the expulsion of the trunk and limbs,
and a discharge of the remaining amniotic fluid. With the expulsion
of the child the uterine contractions cease for a period of ten or
fifteen minutes, when they again recur, with the result of detaching
the placenta and expelling it into the vagina. It is then removed
by the co-operative action of the abdominal and perineal muscles.
The hemorrhage which would naturally occur with the detachment of
the placenta and the laceration of the maternal vessels is prevented
by the firm continuous contraction of the uterine walls, by which
the vessels are compressed and permanently closed.

The Establishment of Inspiration and the Adult Circulation.
— After the birth of the child and the detachment of the placenta,
there speedily occurs a decrease in the quantity of ox\-gen and an

668 TEXT-BOOK OF PHYSIOLOGY.

increase in tlie quantity of carbon dioxid in the blood, a condition
which causes a discharge of nerve energy from the inspiratory center,
a contraction of the inspiratory muscles, an expansion of the thorax,
and an inflow of air into the lungs.

In the later months of intrauterine life the vascular apparatus
undergoes certain anatomic changes which favor the transition from
the placental to the adult circulation. Thus the ductus venosus con-
tracts, and shunts a larger volume of blood into and through the
liver; the Eustachian valve diminishes in size and at the time of
birth has almost disappeared; a membranous fold grows upward
and backward from the edge of the foramen ovale on the left side;
the ductus arteriosus also contracts. With the first inspiration and
the expansion of the lungs, the blood which enters the pulmonary
artery passes through the pulmonary capillaries in large volume and
is returned by the pulmonary veins to the left auricle. The en-
trance of the blood into this cavity presses the membranous fold
against the margins of the foramen ovale and thus prevents the
further flow of blood from the right auricle. The blood entering the
right auricle by the inferior vena cava now flows into the right ven-
tricle, which is favored by the small size of the Eustachian valve.
The foramen ovale is permanently closed at the end of a week or
ten days; the ductus arteriosus at the end of four days. The um-
bilical vein and ductus venosus, at the end of four or five days,
have also become almost impervious from the contraction of their
walls. The hypogastric arteries remain open and carry blood to
the walls of the bladder.

Lactation. — -As pregnancy advances the mammary glands in-
crease in size, partly from a deposition of fat and connective tissue
and partly from a multiplication of the secreting acini. The lining
epithelial cells at the same time increase in size, and toward the
end of pregnancy begin to exhibit functional activity. At the time
of birth, or within a day or so after birth, the acini are filled with
a fluid which in its qualitative composition resembles milk and is
known as colostrum. It is distinguished from milk more especially
in the fact that it contains in large quantity a proteid which coagulates
on boiling, and certain inorganic salts which have a laxative effect
on the new-born child. Normal lactation and the phenomena which
accompany it are fully established by the end of the second or third
day.

The composition of milk and the mechanism of its production
have been stated in the chapter on Secretion, page 401.

Physiologic Activities of the Embryo. — During intrauterine
life the evolution of structure is accompanied by an evolution of
function. The relatively simple and uniform metabolism of the
undifferentiated blastodermic membranes gradually increases in

REPRODUCTION. 669

complexity and variety, as the individual tissues and organs make
their appearance and assume even a slight degree of functional
activity. As to the periods at which different organs begin to func-
tionate, but little is positively known.

The primitive heart, in all probability, begins to pulsate very
early, as in an embryo from fifteen to eighteen days old and measuring
but 2.2 mm. in length, Coste found the amnion, the allantois, the
omphalo-mesenteric vessels, and the two primitive aortae developed.
In the earlier weeks, all products of metabolism are doubtless elimi-
nated by the placental structures; but as metaboUsm increases in
complexity the liver and kidney assume excretory activity. Thus,
at the end of the third month the intestine contains a dark, greenish,
viscid material — meconium — composed of bile pigments, bile salts,
and desquamated epithelium ; the amniotic fluid, as well as the fluid
within the bladder, contains urea at the end of the sixth month,
indicating the estabhshment of both hepatic and renal activity. Con-
tractions of the skeletal muscles of the limbs begin about the fifth
month, from which it may be inferred that the mechanism for muscle
activity, viz., muscles, efferent nerves, and spinal centers, has
become anatomically developed and associated, and capable of
coordinate activity. These contractions are, in all probabihty, auto-
matic or autochthonic in character due to stimuli arising within the
spinal centers. The remaining organs remain more or less inactive.

After birth, with the first inspiration and the introduction of food
into the ahmentary canal, the physiologic mechanisms which sub-
serve general metaboHsm begin to functionate and in the course
of a week are fully established. At this time the cardiac pulsation
averages about 135 a minute; the respiratory movements vary from
30 to 35 a minute, and are diaphragmatic in type; the urine, which
was at first scanty, is now abundant and proportional to the food
consumed; the digestive glands are elaborating their respective
enzymes, digestion proceeding as in the adult. The hepatic secre-
tion is active and the lower bowel is emptied of its contents; the
coordinate activities of the nerve-, muscle-, and gland-mechanisms
are entirely reflex in character. Psychic activities are in abeyance by
reason of the incomplete development of the cerebral mechanisms.

APPENDIX.

PHYSIOLOGIC APPARATUS.

The study of the physical and physiologic properties of muscles and
nerves necessitates the employment of some stimulus which, when applied
to either tissue, will call forth a contraction of the muscle, or the develop-
ment of a nerve impulse in the nerve. The most convenient stimulus
is electricity, for the reason that, with appropriate apparatus, its intensity
and duration can be graduated with the utmost nicety. JNIoreover, it
does not destroy the tissues, as do many chemic, physical, and mechanic
stimuli.

It is therefore necessary that the student should have a practical acquaint-
ance with those appUances by means of which elec-
tricity is generated, applied and controlled.

The electric cell is an apparatus composed of
different elements, which, by virtue of chemic actions
taking place among them, generate and conduct elec-
tricity. In its simplest form an electric cell consists of
two metals — zinc and copper, or carbon, or platinum,
etc., immersed in an exciting fluid, usually dilute sul-
phuric acid (Fig. 334).

The zinc element is the one acted on chemically by
the sulphuric acid, and at the expense of which the
electricity is maintained. It is kno\Mi as the generating
element. The copper is the collecting and conducting
element.

With the immersion of these elements in a solution
of H2SO4 a chemic action at once takes place between
the zinc and the acid, with the formation of zinc sulphate and the libera
tion of hydrogen, as expressed in the following formula:

Fig. 334. — An
Electric Cell.

Zn

H,SO, = ZnSO^ + Hj.

The zinc sulphate passes into the solution, while the hydrogen accumulates
on the surface of the copper element.

As all chemic action is accompanied by the development of electricity,
it can be showTi by appropriate means that this is the case at the surface
of the zinc. Such a combination is the means of establishing a difference
of potential between t'uv points; the point of highest potential being the
surface of the zinc or the positive element, the point of lowest potential

671

672

TEXT-BOOK OF PHYSIOLOGY.

being the copper or the negative element. So long as the elements remain
miconnected there is no movement of electricity, no current.

If the ends of the elements projecting beyond the fluid are connected
by a copper wire, a pathway or circuit is estabHshed, and a movement of
the electricity takes place. As electricity flows from the point of high to
the point of low potential, it follows that inside the cell the current flows
from the zinc to the copper, and outside the cell from the copper to the
zinc. Such a current is termed a continuous, a galvanic or a voltaic cur-
rent. Inasmuch as there is a progressive fall in potential between the
highest and lowest points, it follows that any two points in the circuit will
exhibit a similar difference of potential. For this reason the projecting
end of the copper element is at a higher potential than the projecting end
of the zinc element. The end of the copper is, therefore, termed the posi-
tive, -j- pole or anode, the end of the zinc the negative, — pole or kathode.
Electric Units. — Owing to the difference of the electric potential in
the cell, the electricity leaves the cell imder a certain degree of pressure,
termed the "electro-motive force." As it passes through the circuit it
meets with resistance, the amount of which will depend on the nature of

the circuit material, its
length, and the area of its
cross-section. In accord-
ance with the resistance
will depend the quantity of
electricity that a given elec-
tro-motive force will press
through in a unit of time.
The strength of the current
will therefore not depend
entirely on the electro-
motive force, but, rather,
on the ratio between the
electro-motive force and
the resistance.
For the measurement of electric quantities, a system of units has been
devised. The imit of electro-motive force is the volt; the unit of resistance
is the ohm, i. e., the resistance offered by a column of mercury 106.3 *^J^-
long and i sq. mm. in section at 0° C; the unit of quantity is the coulomb;
the tmit of time is one second. One A^olt is the electro-motive force which,
when steadily applied, will press through a resistance of one ohm, one
coulomb of electricity in one second of time yielding a current strength
of one ampere.

This relation may be expressed in the following formula. Ohm's law:

T +

FlG.

335. — Two Simple Electric Cells Joined
IN Series. C. Copper. Z. Zinc.

C (current strength)

Electro-motive force (E. M. F.) . Volt
_ -_ ^^ ^ or Ampere =

Resistance (R)

Ohm

In practical work it is often necessary to increase the strength of the
current. This is done by uniting two or more cells in series, i. e., uniting
the copper of one cell to the zinc of a second, and so on (Fig. 335). If the
resistance remains the same the total voltage is that of one cell multi-
plied by the number of cells united.

PHYSIOLOGIC APPARATUS.

673

The cell as above described cannot maintain a current of constant
strength for any length of time, for the following reasons:

1. The sulphuric acid solution, in consequence of its chemic action,
soon becomes nothing more than a saturated solution of zinc sulphate,
after which its chemic activity ceases. The current, therefore, soon
diminishes in strength.

2. The accumulation of hydrogen bubbles on the surface of the copper
hinders the passage of the electricity. In a short time they develop a
current in the opposite direction, which also tends to weaken the original
current. This action is termed polarization of the elements.

Cells of this character are not suited for physiologic work, in which
constancy in the strength of the current is absolutely necessary. To
overcome these disadvantages, cells have been devised which are less
violent in action, which prevent polarization, and which maintain a cur-
rent of constant strength for
a long period of time. One
of the most generally used for
physiologic purposes is —

The Daniell cell. This
consists of a porous cup con-
taining a saturated solution of
CuSO^, copper sulphate, in
which is immersed a copper
plate or rod. This combina-
tion is placed in a glass vessel
containing a solution of H2SO4
(1:15). In this solution is
immersed a roll of sheet zinc
(Fig. 336). Each of the plates
is provided with a binding
screw. When the cell is in
action the sulphuric acid at-
tacks the zinc, forming zinc
sulphate, and liberates hydro-
gen ; the cup being porous, the hydrogen passes into the copper sulphate
solution, wdiere it combines with the sulphuric acid radicle, and liberates
metalUc copper. Polarization of the copper is thus prevented. The
metalhc copper is deposited on the copper plate, which is thus kept
bright. The copper sulphate solution is kept at the point of saturation
by packing around the copper cylinder a quantity of the crystals of the
salt. The sulphuric acid passes back into the porous cup, to take the
place of that used. This cell is remarkably constant for these reasons,
and well adapted for physiologic as well as other purposes where a current
of uniform strength is necessary.

The projecting ends of the copper and zinc plates are termed respec-
tively the positive pole or anode, and the negative pole or kathode. The
electro-motive force of a Daniell cell is practically i volt; but when the
two poles are connected by a wire of i ohm resistance, the current strength
will be less than i ampere, possibly only 0.7, owing to the resistance offered

43

Fig. 336. — Daniell Cell.

674

TEXT-BOOK OF PHYSIOLOGY.

to the flow of electricity by the fluids between the zinc and the copper.
In all measurements, the internal resistance of the cell must be taken into
consideration.

The Dry Cell. — The commercial dry cell is a convenient source of
electricity for general laboratory work. It consists of a cup of zinc, the
inner surface of which is covered over with a thick layer of a paste of plaster
of Paris, saturated with ammonium chlorid. In the center of the cup
there is a rod of carbon. Surrounding this rod and occupying the space
between it and the plaster of Paris paste, is a mixture of manganese dioxid
and charcoal. The upper surface of the cell is sealed to prevent evapora-
tion. The electricity is generated at the surface of the zinc cup by the

chemic action of the chlorin which
arises from the dissociation of the am-
monium chlorid. When the plates
are united by a conjunctive wire the
current within the cell flows from the
zinc (the positive element) to the
carbon (the negative element), and
without the cell from the carbon (the
positive pole) to the zinc (the negative
pole) .

Leads. — By means of insulated
wires attached to the poles of a cell,
the electricity may be conducted from
the cell and used for exciting or
stimulating purpose. As the wires
thus become practically prolongations
of the plates their ends become the
corresponding poles. In experimental
work the ends of the wires are provided
with special devices, termed —

Non-polarizable electrodes.
The necessity for the employment of
such electrodes arises from the fact
that when the ends of the wires from
a cell are placed in direct contact with
the tissues chemic changes are pro-
duced in a short time, which lead to their polarization. As a result, a
current opposite in direction to that of the cell is developed, which tends
to weaken or neutralize it. This polarization current vitiates the result
of many experiments made with highly irritable tissue such as nerve tissue.
Whether for stimulating purposes or for the purpose of detecting the exist-
ence of electric currents in living tissues, it is essential that the electrodes
used shall be non-polarizable. The earliest electrodes of this character
were made by du Bois-Reymond and were based on the fact discovered
by Regnault that a strip of chemically pure zinc or amalgamated zinc
(Matteucci) immersed in a saturated solution of zinc sulphate would not
polarize. One form made by du Bois-Reymond is shown in Fig. 337. It

Fig. 337. — Non-polarizable Elec-
trodes. I. Du Bois-Reymond's.
2. Von Fleischl's. 3. d'Arson-
val's.

PHYSIOLOGIC APPARATUS.

67 s

consists of a flattened glass tube attached to a universal joint and supported
bv an insulated brass stand. The lower end of the tube is closed with
kaolin or China clay made into a paste with a 0.6 per cent, solution of
sodium chlorid. It can be molded into any desired shape. The interior
of the tube is partially filled with a saturated solution of sulphate of zinc
in which is immersed the strip of amalgamated zinc. To the upper end
of the zinc the conducting wire is attached.

The V. Fleischl brush electrode is similar to the preceding except that
the end of the tube is closed by the brush of a camel's-hair pencil.

The d'Arsonval electrode consists of a glass tube containing a silver
rod coated with fused silver chlorid. The interior of the tube is filled
with normal salt solution 0.6 per cent, and
the end closed with a thread or plug of
asbestos which is made to project beyond
the tube for a short distance.

Any one of the these three electrodes is
suitable for physiologic experimentation, as
their free ends neither corrode the tissues nor
develop electric currents.

Keys. — ^luscle and nerve tissues are con-
ductors of electricity. When, therefore, the
terminals (the non-polarizable electrodes) of
the wires of a cell are placed in contact with
either a muscle or a nerve a circuit is made
through which a current of electricity flows;
when one or both are removed, the circuit is
broken and the current ceases. In practical
work it is often necessary to keep the elec-
trodes in contact with the tissues for a varia-
ble length of time. The circuit, however,
may be alternately made and broken at will
by interposing along the return wire a
mechanic contrivance known as a key, of
which there are many forms.

The du Bois Reymond Friction Key. —
This consists of a plate of vulcanite attached
to a screw clamp by which it can be fastened
to the edge of a table (Fig. 338). The
surface of the vulcanite plate carries two

rectangular blocks of brass, each of which has two holes drilled through
it, for the insertion of wires, which are held in position by small screws. A
movable bridge of brass, provided with an ebonite handle, serves to make
connection between the blocks. There are two ways of interposing this
key in the circuit.

1. As a Simple Key. — For this purpose one of the wires, usually the nega-

tive, is carried from the cell to one block and then continued from
the second block. When the bridge is down, the circuit is made and
the current passes; when it is up, the circuit is broken.

2. As a Short-circuiting Key. — When used for this purpose, the wires of

Fig. 338. — Du Bois-Rey-
MOND Friction Key.

676

TEXT-BOOK OF PHYSIOLOGY.

the cell are carried to the inner holes of each block and then contmued
from the outer holes to the tissues or to some form of apparatus
which it is desired to actuate. When the key is closed, i. e., when
the bridge is down, the current on reaching the key, will divide, one
portion passing across the bridge and so back to the cell, the other
portion passing to the tissue or apparatus. The amount of the cur-
rent which is returned to the cell through the short circuit will be
proportional to the resistance of the longer circuit. As the latter is
usually great in comparison with the former, practically all the current
is short-circuited. When the bridge is lowered, therefore, the current
is short-circuited; when it is raised, the current flows into the longer
circuit through the tissue or apparatus.
The Mercury Key. — In this form the connection is established by
means of mercury. It consists of a circular block in the center of which
there is a cup containing mercury (Fig. 339). At opposite points there
are binding posts, one of which is provided with a rigid fixed copper rod

passing into the mercury; the
other is provided with a mova-
ble bent rod which may be
made to dip into or be with-
drawn from the mercury by
the ebonite handle.

The effect of a constant or
galvanic current on a muscle
or nerve will depend to some
extent on its strength. This
may be accurately regulated
by means of an apparatus
known as —

The Rheocord. With this
apparatus an electric current
may be divided, one portion continuing through a conductor back to the
battery, the other portion being sent off through the nerve. The strengths
of these two currents are inversely proportional to the resistances of their
circuits. A simple form of rheocord (Fig. 340) consists of a long wire
arranged for convenience in parallel lines on a small wooden base and
connected at its two ends with binding posts A and B. The resistance
of this wire, 1.6 ohms, can be increased by the introduction of small re-
sistance coils, between D and B, varying from 5 to 20 ohms.

The two binding posts A and B are connected with the positive and
negative poles of an electric cell respectively. A simple key is placed in
the circuit.

From A, a wire passes to one of the electrodes on which the muscle or
nen^e rests. A second wire passes from the second electrode to a clamp
S, by way of the binding post C, which can be fastened to the long wire
at any given point. The current, on reaching A, will divide into two
branches, one of which will pass along the wire A, B, and thence back to
the cell; the other will pass through the nerve and back to S and thence-

Fig. 339. — A Mercury Key.

PHYSIOLOGIC APPARATUS.

677

also to the cell. The amount of current passing through the nerve circuit
will be inversely ]:)roi)ortional to the resistance of the nerve and directly
proportional to the difference of potential between A and S. If S is close
to A, the difference of potential is sUght. If S is removed from A toward
B, the difference of potential is increased and the current sent through
the nerve circuit is increased.

Li many experiments it is necessary to reverse the direction of the cur-
rent, in other experiments to deflect it, without changing the position of
the electrodes. Both these results may be accomplished by the use of —

Pohl's commutator. This is a round block of wood with six cups,
each of which is in connection with a binding post (Fig. 341). In each of
the two cups marked i and
2, -|- and — , is inserted one
end of a copper wire bent at
right angles. The other ends
of the wires are supported and
insulated by a hard-rubber
handle. To the top of each
wire is soldered a semicircular
copper wire. This arrange-
ment permits of a rocking
movement, whereby the oppo-
site ends of the semicircular
wires can be made to dip into
cups 3 and 4, and into cups
5 and 6 alternately. Two
wires crossed in the middle of
the block serve to connect-
opposite pairs of cups. When
in use, the cups are filled with
clean mercury. The method
of using the commutator is as
follows :

I . As a Current Reverser. — The
positive and negative poles

of the electric cell are connected by wires with binding posts i and 2
respectively. A key is interposed in the circuit. Wires are then carried
from binding posts 3 and 4 to the electrodes in connection with the
muscle or nerve. The rocker of the commutator is so turned that the
ends of the semicircular wires dip into cups 3 and 4. The direction of
the current will be on the closure of the circuit from i to 3, then from
3 along a wire to and through the tissue and back to 4, and thence
to the cell. If the position of the rocker be now reversed so that the
opposite ends of the semicircular wires dip into cups 5 and 6, the
direction of the current through the tissue will be reversed. The
positive current, after entering binding post i, will flow to 5; then
along one of the cross wires to 4; then along a wire to and through
the tissue and back to 3, along the opposite cross wire to 6, thence to 2,
and so back to the cell.

Fig 340. — Rheocord.

678

TEXT-BOOK OF PHYSIOLOGY.

2. As a Current Deflector. — When it is desirable to deflect the current to

two pairs of electrodes differently situated, wires are carried from

binding posts 3 and 4 to one pair, and from 5 and 6 to the other pair.

The cross wires are then removed. According to the position of the

rocker the current will be deflected to one or the other.

The Inductorium. — This is an apparatus designed for the purpose

of obtaining single or rapidly succeeding electric currents by induction.

Its construction is based on facts discovered by Faraday, some of which

are the following:

If two circuits, a primary and a secondary, are placed parallel to each
other, the former connected with a galvanic cell, the latter with a galvan-
ometer, it is found that, at the moment the primary circuit is made, and
at the moment it is broken, a current is induced in the secondary circuit,
as shown by a momentary deflection of the galvanometer needle. During
the continuous flow of the current through the primary circuit there is no

Fig. 341. — Pohl's Commutator. A. Arranged as a current reverser; B, as a cur-
rent deflector.

evidence of a current in the secondary circuit. The induced current is
but of momentary duration. The current flowing through the primary
circuit is termed the inducing, the current flowing through the secondary
circuit the induced current.

The induced current is opposite in direction to that of the inducing
current when the circuit is made or closed; it is in the same direction,
however, when the circuit is broken or opened.

If the circuits are arranged in the form of coils, it is found that, other
things being equal, the strength of the induced currents will be proportional
to the number of turns in the coils.

If the coils are placed at varying distances from each other, the strength
of the induced current varies, increasing as the coils are approximated,
decreasing as they are separated.

Apj)roximation or separation of the coils while the current is flowing
through the primary circuit develops an induced cvirrent, which disappears,

PHYSIOLOGIC APPARATUS.

679

however, the moment the movement of the coil ceases. A sudden increase
or decrease in the strength of the inducing current also develops an induced
current.

When the coils are approximated or the primary current increased in
strength, the induced current is opposite in direction to that of the inducing
current; with the reverse conditions, the induced current has the same
direction.

The induced currents have been termed, in honor of their discoverer,
Faradic currents.

The du Bois-Reymond inductorium, based on the foregoing^ facts,
consists essentially of two coils of insulated copper wire, termed primary
and secondary (Fig. 342).

The primary
coil, R', consists S

of thick copper
wire wound
around a wooden
spool attached to
a vertical support.
The beginning of
this coil is at the
binding post S",
its termination
either at binding
post P" or S'".
In the course of
this primary wire
or circuit, there
are placed two
vertical bars of
soft iron, B', con-
nected at their
bases to form a
horseshoe magnet,

around the ends of which the wire is coiled. The object of this device
will be explained later.

Inside the primary coil there is placed a bundle of soft iron wires,
which, as soon as the circuit is made, become magnetized, with the effect
of increasing the action of the inducing current.

The secondary coil, R", consists of a much greater number of turns
of a finer copper wire, the ratio being about 40 to i, also wound around a
spool, having a tunnel sufficiently large to enable it to slide over the pri-
mary. By these means the strength of the induced current is increased.
As a result of the construction of the inductorium, the low electro-motive
force of the cell is transformed into the high electro-motive force charac-
teristic of the induced current. As the number of turns of wire in the
secondary coil is to the number in the primary, so are the electro-motive
forces in the secondary coil to those in the primary coil.

The secondary coil slides along a track, B, which permits it to be

Fig. 342. — Inductorium of du Bois-Reymond. R', Pri-
mary, R", secondary spiral. B. Board on which R"

moves. I. Scale. -| . Wires from battery. P', P".

Pillars. H. Neef's hammer. B'. Electro-magnet. S'.
Binding screw touching the steel spring (H). S" and
S'". Binding screws to which to attach wires where Neef's
hammer is not required.

68o TEXT-BOOK OF PHYSIOLOGY.

moved toward or away from the primary. The distance between the two
coils can be measured and the strength of the induced current again re-
produced, other things being equal, by means of a centimeter-millimeter
scale pasted on the edge of B.

The ends of the wire of the secondary coil are fastened to two binding
posts to which conducting wires provided with hand electrodes can be
attached.

The inductorium may be used for obtaining either a siiagle current or
a series of rapidly repeated induced currents.

The Single Induced Current. — On accomit of its high electro-motive
force, its penetrative power, and short duration, the single induced current
is a most convenient and suitable form of stimulus for many purposes.
In order to obtain such a current, the positive wire of the cell is carried to
bindmg post S", and the negative wire either to S"' or V". A key is placed
m the primary circuit. The course of the current will then be on the
closure of the circuit from the cell to S", thence around R' to S'", and so
back to the cell; or if the negative wire is connected with P", the course
of the current on leaving R' will be through the coils surroimding the two
vertical bars B', thence to V", and so back to the cell. If the secondary
coil be placed close to the primary and the wires of the secondary brought
into contact with a muscle, it will be found that with both the make and
the break of the primary circuit a current is induced in the secondary, as
shown by a short quick pulsation of the muscle; but during the time of
closure of the circuit, the induced current is wanting, as shown by the
quiescent condition of the muscle. It will be apparent, however, from
the energy of the contraction that the break induced current is a more
efficient stimulus than the make induced current. That this is the case
is made evident by removing the secondary to the end of the slideway and
then gradually bringing it toward the primary half a centimeter at a time,
making and breaking the circuit after each movement until a pulsation of
the muscle occurs. It will be foimd to occur first on the break of the
circuit. As the secondary approaches the primary a position will be
reached when a pulsation occurs on the make as well as on the break of
the circuit, though it will be less pronoimced.

The explanation offered for this difference in the strength of the two induced
currents is as follows: With the make of the circuit and the passage of the batter}-
current through the primary coil there is induced in the neighboring and parallel
turns of the ware an extra current opposite in direction to the primary current. This
extra or self-induced current antagonizes and prevents the current from attaining
its maximum development as quickly as it otherwise would, and therefore its efficiency
as an inducer of a current in the secondary is diminished. On the break of the circuit
the primar}' current disappears quickly, and as there is nothing to retard its disappear-
ance its efficiency as an inducer of a current in the secondary coil is not diminished.
It is not infrequently stated that the disappearance of the primary current induces in
the neighboring coils a break extra current corresponding in direction which assists
in the development of the induced current. This is not the case, however, as no
break extra current is developed in the inductorium as ordinarily used when actuated
by a battery current of moderate strength.

As it is not so much the intensity of the current as it is rapid variations in intensity
that produce effects, it is readily apparent why the induced current developed at
the break of the primary is more effective as a stimulus than the induced current
developed at the make of the primary circuit. The quantity of the electricity is,
however, the same in both cases.

PHYSIOLOGIC APPARATUS. 68i

If the secondary be pushed furtlier along the slideway until it
largely covers the primary coil, a position will be reached when the make
induced current equals in its efficiency as a stimulus the break induced
current; and if the secondary be yet further advanced, a position is
reached when the make induced current becomes more powerful and
efficient than the break induced current, as shown by the greater contrac-
tion of the muscle. This result is explained by the fact that the make
extra current is now able of itself to induce a current in the secondary
coil, on account of its proximity, which, added to that induced by the
battery current, produces a current, greater than 'that induced on the
break of the circuit.*

Rapidly Repeated Induced Currents. — As the single induced current
is of extremely short duration, it is inefficient as a stimulus in the conduct
of many experiments. It is necessary, therefore, to develop it with a fre-
quency that is sufficient to give rise to a summation of effects. The dura-
tion of the stimulation may be thus considerably prolonged. This is
accomplished by introducing in the primary circuit close to the primary
coil an automatic interrupter, usually Neef's modification of Wagner's
hammer (Fig. 342). This consists of a vertical post, P', to the top of
which is fastened a metallic spring carrying at its opposite end a steel or
iron hammer, H, which hangs over, but does not touch, the two vertical
bars of soft iron around which the wire of the primary coil is wound.
About the middle of the spring on its upper surface there is a small
plate of platinum which is in contact with an adjustable, platinum-tipped
screw, S', carried by a plate of brass in connection with binding post S".

For the purpose of interrupting the primary circuit frequently in a
unit of time, and thus developing induced currents in quick succession, the
apparatus is arranged in the following way: The positive and negative
poles of the electric cell are connected by wires with bmding posts P' and
P", a key being interposed in the circuit. If the screw S' is in contact
with the spring, the current on the closure of the circuit will enter P', pass
along the spring to S', thence into and through the primary coil R', to the
coils surrounding the vertical bars B', then to P", and so back to the cell.

As the current passes around the vertical bars, they are magnetized.
The magnetization draws down the hammer, and, in so doing, breaks
the circuit at the tip of the screw, S'. The vertical bars are at once
demagnetized, and the hammer is restored to its original position by the
elasticity of the spring. The circuit is thus re-estabhshed, the current
flows through the coils, the bars are again magnetized, the hammer is
drawn down, to be followed by a second break of the circuit.

The number of times the circuit is thus made and broken per second will
vary with the length of the sprmg.

As each interruption of the primary circuit develops an induced current,
it follows that the latter must succeed each other with a frequency corre-
sponding with the frequency of the former. If while the primary circuit
is thus being interrupted the wires of the secondary coil be placed m con-

*"On certain peculiarities of the inductorium," Prof. Colin C. Stewart, "Univ.
Pa. Medical Bulletin," Feb., 1904.

682

TEXT-BOOK OF PHYSIOLOGY.

tact with a muscle, the induced current will give rise to contractions which
will succeed each other so rapidly that they fuse together, producing a
spasm or tetanus of the muscle. For this reason these currents are fre-
quently spoken of as tetanizing currents, and the procedure as tetanization
or Faradization. These currents also increase in strength as the secondary
approaches the primary.

Helmholtz's Modification of the Inductorium. — With a view of equalizing
the strengths of the induced currents, Helniholtz suggested a device the adoption of
which accompHshes this to a certain extent. It consists (Fig. 342) in connecting with a
wire binding posts P' and S", and in providing binding post P" with an adjustable screw
which can be raised until the spring comes in contact with it, when the hammer is

drawn down by the electromagnet B'. This
latter arrangement is practically a short-
circuiting key by which a portion of the cur-
rent is returned to the cell without ever enter-
ing the primary coil. The same arrange-
ment, though differently lettered, is shown in
Fig. 343. By the use of the entire device
the changes in the primary coil are made
not by making and breaking the primary
current, but by alternately long- and short-
circuiting the current. "When the short-
circuiting key is opened, the full volume of
the primary current flows through the pri-
mary coil. When the short-circuiting key
is closed, most of the current fails to enter
the coil, taking the easier path through
the key. Some of the current, however,
always flows through the coil and is never
diverted. The cycle of changes in the
electric condition of the primary coil is-
thus altered for two reasons:

"First, we no longer have an alternation
between a full primary current and none
at all — rather an alternation between a full
primary current and a weaker one. The
difference in the phases is thus lessened,
the extent of the change on making and
breaking is lessened, and correspondingly
the efficiency of the make and break cur-
rents induced in the secondary coil is
slightly decreased.
"Second, on making the primary current, as in the ordinary coil, the sudden
appearance of the primary current is antagonized by the opposing make extra current^
with the result that the make induced current is still further reduced; while on break-
ing the current the break extra current can now flow through the primary coil across
the short-circuiting key. This current, trailing behind the disappearing primary
current in the same direction, produces the same effect as if the primary current itself
were to disappear slowly. As a result the disappearance of the primary current loses,
its former efficiency as an inducer of secondary currents, and the break induction
current is reduced to about the efficiency of the make.

"This so-called 'equalizing' of the make and break induced currents is never
perfect, if for no other reason, because the make extra current must take the long
circuit through the battery, while the break extra current has an easier path through
the short-circuiting key, and is thus greater than the make extra current." (C. C
Stewart.)

Fig,

343. — Helmholtz's Modifica-

TION or NeEF'S H.A.MMER. As

long as c is not in contact with d,
^ h remains magnetic; thus c is
attracted to d and a secondary
circuit, a, b, c, d, e, is formed; c
then springs back again, and
thus the process goes on. A new
wire is introduced to connect a
with /. K. Battery.

PHYSIOLOGIC APPARATUS.

683

THE GRAPHIC METHOD.

The term graphic is applied to a method by which curves or tracings
are obtained which represent the extent, duration, and time relations of
the movements accompanying physiologic processes. If these movements
can be translated in one direction, they may be recorded in different ways:

1. By attaching the moving structure — e. g., heart, muscle, etc. — to a

delicate lever the free extremity of which is provided with a writing
point.

2. By transmitting the movement through a column of air enclosed in a

rubber tube the two ends of which are attached to a metallic capsule,
covered by a
rubber mem-
brane, termed
a drum or tam-
bour. When
the membrane
of the first tam-
bour is pressed
or driven in-
ward, the air is
forced through
the rubber tube
into the second
tambour and its
membrane is
pushed out-
ward. As soon

as the primary pressure is removed, the membranes return to their
former condition. If the membrane of the first tambour is dra\Mi
outward, the air in the system is rarefied and the membrane of the
second tambour is pressed inward. For the purpose of register-
ing the movement
transmitted by the
column of air, the
second tambour is
provided with a
light lever support-
ed by a vertical
bearing resting on
a small metallic
disk. The mem-
brane of the first
tambour is frequently provided with a button, which is placed over
the mov-ing structure. The inward movement of the membrane of
the first tambour produces an outward movement of the membrane of
the second tambour, indicated, though magnified, by the rise of the
free end of the lever. The reverse movement of the membrane is
attended by a fall of the lever. The first tambour is termed the
receiving, the second the recording tambour (Figs. 344, 345).

Fig. 344. — A Receiving Tambour.

Fig. 345. — A Recording Tambour. — {Marey.)

6S4

TEXT-BOOK OF PHYSIOLOGY.

3. By enclosing an organ — e. g., kidney, spleen, arm, fii:iger, etc' — in a
rigid glass or metal vessel which, at one point is in commimication
with a recording apparatus — e. g., (i) a piston provided with a lever
(page 431) ; or (2) a tambour and lever (page 320) ; or (3) a mercurial
manometer carrying a float and pen (page 305). The space between
the part investigated and the vessel is filled with fluid. The varia-
tions in volume of the organ cause a displacement of the fluid and

give rise to a to-and-fro
movement which is taken
up and reproduced by the
recording apparatus.
The writing point may be
(i) some form of pen carry-
ing ink which records the
movement on a white paper
surface, or (2) a piece of
metal, glass, or paper which
records the movement on
smoked paper or glass.

The Recording Sur-
face.— The surface which
receives and records the
movements of a pen or lever
is usually that of a cylinder
which is covered with glazed
paper and coated with a thin
layer of soot, obtained by
passing the cylinder through
the flame of a gas burner.
The axis of the cylinder is
supported by a metal frame-
work. If the writing point of
the lever be placed against
the cylinder and a movement
be imparted to it, a portion
of the soot is rubbed off, leav-
ing a white line behind. If
the cylinder be stationary, the
rise and fall of the lever are
recorded as a vertical line. Such a record shows only the extent of
a movement. If the cylinder is traveling, however, at a imiform rate, the
rise and fall of the lever are recorded in the form of a curve the width
of the two arms of which will depend partly on the rapidity of the move-
ment of the lever and partly on the rate of movement of the cyhnder.
The cylinder movement is initiated and maintained by clock-work or by
the transmission of power by belting to a system of pulleys in connection
with its axis. As the tracing is wave-like in form, the cylmder is frequently
spoken of as a kymograph or wave recorder (Fig. 346).

From the record thus obtained it is possible to determine not only the

Fig. 346. — Kymograph. (Boruttau's, Pet-
zold, Leipzig.)

PHYSIOLOGIC APPARATUS.

685

Fig. 347. — SiGXAL Magnet.

extent but also the duration, the form, and the rate of recurrence of any
given movement.

The Extent of a Movement. — As the lever not only takes up and repro-
duces a movement, but at the same time magnifies it, it is essential that
the degree of magnification be known, in order to determine the actual
extent of the movement. The magnification of the lever is readily deter-
mined by dividing the distance between the axis of the lever and its writing
point by the distance between the axis and the point of attachment of the
structure, and tlien dividing the height of the tracing by this quotient.
The final quotient
represents the extent
of the movement.

The Time Rela-
tions of a Movement. " fXt^Ifltlr^^^
—When recorded in ('^JIIilH^aWi^
the form of a curve,
the duration of the
entire movement, or

of any one portion of it, can be determined by means of a time marking
or chronographic apparatus, consisting of (i) a small signal magnet
provided with a movable armature, to which is attached a writing style;
(2) an automatic interrupter; and (3) an electric cell.

The Signal Magnet. — The magnet (Fig. 347) is actuated by the electric
current made and broken at regular and known intervals by an auto-
matically-acting interrupter
placed in the circuit. With
each make and break of the
circuit the armature and style
move alternately do^vnward
and upward. The excursion
of the style can be readily
recorded on a traveling sur-
face. The character and num-
ber of the interruptions per
second will determme the
character of the tracing. If
they occur in a rhythmic
manner, the tracing will be
sinusoidal or wave-like in
form. If the time of interruption is of short duration as compared with
the time of closure of the circuit, the tracing will be a horizontal line
with short vertical elevations at regular intervals.

The Automatic Interrupter. — The circuit may be interrupted by
virbating reeds, tuning-forks, metronomes, etc. A well-kno\Mi form of vibrat-
ing reed is shoAMi in Fig. 348. This consists of a metallic frame carrying a
coil of wire in the center of which there is a core of soft iron. To the
vertical part of the frame there is fastened the reed, the distal end of which
is bent to dip into an adjustable mercury cup. When in circuit the current
enters the coil, then flows into and through the frame and the reed to the

-Page's Vibratixg Reed.
ert's modification.)

(Reich-

686

TEXT-BOOK OF PHYSIOLOGY,

mercury, and thence back to the cell. On the closure of the circuit and the
magnetization of the iron core the reed is \vithdra^vn from the mercury, the
circuit broken, and the core demagnetized. The elasticity of the spring
returns it to the mercury, when the circuit is again restored. The reed
may be so constructed that it will be raised and lowered 50, 100, or 200
times a second. The armature of the signal magnet undergoes a corre-
sponding number of elevations and depressions. If the reed vibrates
100 times in a second, the distance from crest to crest of the wave tracmg
will represent yuq of a second. Interrupters of various kinds have been
devised which make and break the circuit from i to 250 times a second.

Moist Chamber. — In many experiments, it is necessary to keep the
nerve or muscle preparation in a uniformly moist atmosphere. To secure

Fig. 349. — Moist Chamber.

this, a moist chamber is employed. This consists of a hard-rubber plat-
form, supported by a piece of brass, which slides up and do^vn a vertical
rod, and which can be clamped at any height. By means of a short lever
the vertical rod can be turned, carrying the platform from side to side.
The rod is secured to a firm iron base.

Six double binding posts for the attachment of wires pass through the
platform. Near the side of the upper surface of the platform there rises a
vertical rod, carrying a clamp for holding the femur of a nerve-muscle
preparation, as well as a horizontal rod for supporting three pairs of non-
polarizable electrodes. A groove around the outer edge of the platform
receives a glass shade, which covers the whole. The air of the chamber
is kept moist by placing in it pieces of blotting-paper saturated with water.

PHYSIOLOGIC APPARATUS. 687

From the under surface of the platform there descends a rod, which,
by means of a doul)le bindmg screw, supports a horizontal rod, modified
at one end to carry the delicate axis of a light stiff recording lever. The
end of this lever is pointed, to enable it to write on a smoked glass or paper.
Beneath the a.xis is a strip of brass, carrying a screw, which gives support
to the lever until the instant the contraction of the muscle iDegins. This
screw, the after-loading screw, also enables the lever to be placed in a
horizontal position. The portion of the lever near the axis is provided
with a double hook, the lower portion of which serves for the attach-
ment of the weight by which the muscle is counterpoised.

In some experiments, as in the registration of a muscle contraction
under varying conditions, it is necessary to give the lever mass by attaching
weights directly beneath the muscle. This, however, introduces certain
errors in the movements of the lever, which somewhat deform what w^ould
otherwise be the normal curve. If the weight be attached, not opposite
to the muscle attachment, but close to the axis of the lever, the undesirable
acceleration of the lever movement, during both contraction and relaxa-
tion, is largely prevented. The lever may be a straw, a strip of celluloid
or aluminium. It should be as light as possible. The writing point may
be made of stiff paper, a piece of tinsel, glass or aluminium. It should
have sufi&cient elasticity to keep it in contact with the cylinder during the
excursion of the lever. The writing point should be placed as nearly
parallel as possible to the surface of the cylinder.

Normal Saline Solution. — To prevent drying and a loss of irrita-
bility the tissue under investigation should be kept moist with the normal
salme solution (NaCl 0.6 per cent.). This solution very largely prevents
either absorption or extraction of water from the tissues and thus retards
chemic changes in their composition.

Ringer's solution, largely used for the same purpose, is made by
saturating 0.65 per cent. NaCl solution with calcium phosphate and then
adding 2 c.c. of a i per cent, solution of potassium chloric! to each 100 c.c.

The Galvanometer and Capillary Electrometer. — In the detection
and investigation of the electric currents of muscles, nerves, and other
tissues, the physiologist is limited to the galvanometer and capillary elec-
trometer. The principle of the galvanometer is based on the fact that an
electric current tiowing through a wire parallel in direction with a magnetic
needle will tend to set the needle at right angles to the direction of the
current. The essential requisite of any galvanometer used for physiologic
purposes is that it will respond quickly to the influence of extremely weak
currents. This is realized by the use of small light needles, the adoption
of the astatic system, or some similar device by which the directive influ-
ence of the earth's magnetism is eliminated, and the multiplication of
the number of turns of the wire in the coils which surround the needle.

The tangent galvanometer, or boiissole, as constructed by Wiedemann, is
tlie form most frequently employed in physiologic investigations (Fig. 350).
It consists primarily of a thick copper cylinder, through which a tunnel has
been bored. Within this tunnel is suspended a magnetized ring, just
large enough to swing clear of the sides of the chamber. The object of

688

TEXT-BOOK OF PHYSIOLOGY.

making the magnet ring-shaped is to increase its strength in proportion to
its size, and to get rid of the central inactive part. Connected with and
passing upward from the magnetized ring through the copper cylinder is
an aluminium rod, surmounted by a circular plane mirror. Above the
mirror rises a glass tube, which carries on top, on an ebonite support, a
little windlass, capable of being centered by three small screws. On the
wmdlass is wo\md a single filament of silk, which passes do-\^aa the tube
and is attached to the mirror. The magnet can, by this contrivance, be
raised or lowered and centered in the copper chamber. Deflections of
the mirror from currents of air are prevented by inclosing it with a brass
cover provided with a glass window. The coils are placed on each side
of the copper chamber, and supported by a rod, on which they shde. By
this arrangement they can be approximated until they meet and completely

conceal the cylin-
der. By varying
the position of the
coils the influence
of the current
upon the needle
can be increased
or diminished.
An advantage
which this galvan-
ometer possesses
is the damping of
the oscillation of
the needle, so that
it quickly comes to
rest after deflec-
tion. This is ac-
complished by the
development of
induction currents
in the copper cyl-
inder, the direc-
tion of which is
opposite to that of the movement of the needle. The instrument,
therefore, is aperiodic — that is to say, when the needle is influenced
by a current it moves comparatively slowly imtil the maximum deflec-
tion is reached, when it comes to rest without oscillations. When the
circuit is broken the needle swings slowly back to zero, and again comes
to rest without oscillations.

Inasmuch as the needle is not astatic, it is rendered so by the use of an
accessory magnet — the so-called Hauy's bar. This magnet, supported
by a rod directed perpendicular to the coils, is placed in the magnetic
meridian, horizontal to the needle, with its north pole pointing north. By
sHding the magnet toward the needle the directive influence of the earth's
magnetism is gradually diminished, and when it is reduced to a minimum
the needle acquires its highest degree of instabiHty. By means of a pulley

Fig. 350. — Wiedemann's Boussole.

PHYSIOLOGIC APPARATUS.

689

an angular movement can be imparted to the end of the accessory magnet
in the direction of the magnetic meridian, which serves to keep the needle
on the zero of the scale. The deflections of the needle are observed by
means of an astronomic telescope, above which is placed a scale divided
into centimeters and millimeters, and distant from the galvanometer about
six or eight feet. As the numbers on the scale are reversed, they will be
seen in the mirror in their natural position, and with the deflection of the
needle the numbers will appear as if dra-\ATi across the mirror. The extent
of the deflection is readily determined when the needle comes to rest.

The reflecting galvanometer of Sir William Thompson is also used for
the same purposes.

The Capillary Electrometer. — Notwithstanding the extreme sensi-
tiveness of the modem galvanometer, it has been found desirable, in the
investigation of many
physiologic processes, to
possess some means
which will respond even
more promptly to slight
variations in electromo-
tive force. This has
been realized in the con-
struction by Lippmann
of the capillary electro-
meter. The principle
of this apparatus rests
upon the fact that the
capillary constant or the
surface-tension of mer-
cury undergoes a change
upon the passage of an
electric current, in con-
sequence of a polariza-
tion by hydrogen taking
place at its surface. If
a capillary glass tube be
filled with mercur}- and
its lower end inserted
into a solution of sul-
phuric acid, and the

former connected with the positive and the latter with the negative
electrode, it will be observed, upon the passage of the current, that a
deiinite movement of the mercury takes place, in the direction of the nega-
tive electrode, in consequence of the diminution of its capillary constant or
the tension of its surface in contact with the acid. As a reverse movement
follows a cessation of the current, a series of oscillations will follow a rapid
making and breaking of the current. If the direction of the current is
reversed, the capillary constant is increased and the mercur\' ascends the
tube toward the negative pole. From facts such as these Lippmann con-
structed the capillary electrometer, a convenient modification of which.

Fig. 351. — Von Frey's Capillary Electrometer.

44

690

TEXT-BOOK OF PHYSIOLOGY.

devised by M. v. Frey, is shown in Fig. 351. This consists of a glass
tube, A , forty millimeters m length, three millimeters m diameter, the lower
end of which is dra\Mi out to a fine capillar}- point. The tube is filled with
mercury and its capillary pomt immersed in a 10 per cent, solution of
sulphuric acid. The vessel containing the acid
is filled to the extent of several milUmeters with
mercury also. The mercun' in the tube is put
in connection with a platinum wire (a), and the
acid in the vessel with a second wire (b). When
a constant current passes into the apparatus in
the direction from b to a the mercury is pushed
up the tube, and, upon the breaking of the cur-
rent, it may or may not return to the zero-point.
For the purpose of measuring in milhmeters of
mercury the pressure necessan,- to compensate this
change m the capillar}' constant produced by the
electro-motive force of polarization, the apparatus
is provided with a pressure-vessel, H, and a
manometer, B. This electrometer can be applied
to any microscope having a reversible stage. The
oscillations of the mercur}^ can then be observed
with the microscope provided with an ocular
micrometer (Fig. 352). The special advantage of
the electrometer is, that it will respond instantl}^ to
any variation in the electro-motive force, and indi-
cate a difference of potential, according to Lipp-
mann's observation, as sHght as the y^-o-g-g- of a
Daniell. These rapid oscillations can be recorded
by photographic methods.

In usmg either the galvanometer or the elec-
trometer for detecting the existence of electric
currents or differences of potential in Hving tissues, it is absolutely
essential that non-polarizable electrodes be employed in connection with it

i/^

Fig. 352. — Capillary
Electroiieter. R.
Mercur\- in tube ;
capillary tube. s.
Sulphuric acid. q.
Hg. B. Obser^-er.
M. Microscope

DISSECTION OF THE HIND-LEG OF THE FROG.

Much of our knowledge of the physiologic properties of muscles and
nerves has been derived from the study of the muscles and nerves of the
cold-blooded animals, especially of the frog, for the reason that in these
animals the tissues retain their vitality under appropriate conditions for a
considerable period of time after death or removal from the body. The
muscles generallv employed for experimental purposes are the gastroc-
nemius, the sartorius, the semi-membranosus, the gracilis, and the hyo-
glossus. The nerve generally employed is the sciatic. Both muscle and
nerve may be studied independently of each other, or they may be studied
together, as when in their usual physiologic relation. For this latter pur-
pose the gastrocnemius muscle and sciatic nerve are employed, constituting
the so-called "nerve-muscle preparation."

For these, and many other reasons, the student should familiarize
himself with the general anatomy of the frog, and especially with the
anatomy of the posterior extremities.

PHYSIOLOGIC APPARATUS.

691

Preparation of the Frog. — Destroy the frog by plunging a pin through
the skin and st)lt tissues covering the space between the occipital bone and
the first vertebra until the point is stopped by the vertebra. Turn the
pin toward the head and push it into the brain cavity; move it from
side to side and destroy the brain. Pass the pin into the spinal canal
and destroy the spinal cord. With a stout pair of scissors cut off the body
behind the fore-hmbs. Remove the viscera and the abdominal walls.
Draw the hind-legs out of the skin. Place the legs on a glass plate, back
uppermost, and moisten them freely with normal saline solution.

ec

Fig. 353.^Leg Muscles of the Frog. Fig. 354. — Leg Muscles of the

Ventral Surface. — (Ecker.)

Frog. Dorsal Sltiface. —
(Ecker.)

Observe on the outer side of the dorsal surface of the thigh the following
muscles (Figs. 353, 354). The triceps femoris (tr), made up of the rectus
anticus (ra), the vastus extemus (ve), and the vastus intemus (vi), not
seen from behind; on the inner side, the semi-membranosus (sm) and the
rectus intemus minor or graciUs (ri"). Between these two groups, note
the biceps femoris (b). Above the thigh observe the gluteus (gl), the ileo-
coccyg-eus (ci), and the pyriformis (p).

In the leg observe the gastrocnemius (g) with its tendon (the tendo
Achillis), the tibialis anticus (ta), and the peroneus (pe).

Turn the frog on its back and note the muscles on the ventral surface
of the thigh, the rectus intemus major (ri'), and minor (ri"), the adductor
magnus (ad"), the sartorius (s), the adductor longus (ad'), and the vastus

692 TEXT-BOOK OF PHYSIOLOGY.

intemus (vi). In the leg, iii addition to those akeady seen from behind,
note the tibiahs posticus (tp) and the extensor cruris (ec).

Note in the abdominal ca^•ity the three large spmal nerves, the seventh,
eighth, and ninth.

Dissection of the Sciatic Nerve. — The sciatic nerve is composed of
the seventh, eighth, and ninth spinal nerves. After its emergence from
the pelvic cavity, it passes down the thigh between the semi-membranosus
and the biceps muscles, in company with the femoral blood-vessels. Below
the knee it divides into the tibialis and peroneus nerves ; the former sending
branches into the gastrocnemius. In its course, the sciatic sends branches
to the muscles of the entire leg.

Carefully separate the biceps and semi-membranosus by tearing the
connective tissue uniting them.. The sciatic nerve and femoral blood-
vessels come into view, with a bent glass rod gently separate the nerve
from its surroundings from the knee to the thigh. Begin at the knee. In
order to expose the nerve at the pelvis, it wall be necessary to divide the
p}Tiformis and the ileo-coccygeus muscles. Care must here be exercised,
so as not to injure the nerve which lies immediately beneath. Lift up
the uro-style with the forceps and separate it from the last vertebra.
With the scissors cut off the vertebral column above the seventh vertebra.
Place the legs on the dorsal surface and then divide the seventh, eighth,
and ninth vertebrae lengthwise. With the forceps lift up one lateral half
of the vertebra; and free the nerve as far as the knee by dividing con-
nective tissue and nerve branches. Be careful not to injure the nerve
with scissors or forceps.

The Nerve-muscle Preparation. — Divide the tendo Achillis just
below its fibro-cartilaginous thickening at the heel, and detach the
gastrocnemius up to the knee. Cut through the tibio-fibular bone just
below the knee-joint. Cut the femur transversely near its middle and
remove the muscles from the low^er end, carefully avoiding injury to the
nen^e. The completed preparation consists of the gastrocnemius muscle,
the sciatic nerv-e, with half of the seventh, eighth, and ninth vertebra
and the lower half of the femur. Place the preparation on a clean glass
plate and moisten with normal saline solution, 0.6 per cent.

INDEX.

A.

Abducens nerve, 542
Aberration, chromatic, 623

spheric, 623
Absorption, 213

by epithelium of villi, 224

of foods, 225

of lymph, 622

spectra of blood, 248
Accommodation of the eye, 614

convergence of eyes during, 619

force of, 618

mechanism of, 615

range, 618
Action currents of muscles, 92
of nerves, 121

reflex, 131

of medulla oblongata, 481
of spinal cord, 453
Adrenal bodies, 415
Agraphia, 511
Albuminoids, 34
Alcohol, effects of, 140
Alimentary canal, 152

principles, 136
Allantois, 662
Amnion, 662
Amylopsin, 200
Amy loses, 25
Animal body, structure of, 19

heat, 385
Ankle clonus, 459

jerk, 459
Aphasia, 510

ataxic, 511

amnesic, 511
Apnea, 3 78
Arterial circulation, 297

pressure, 302
Arteries, structure and properties of,
Articulate speech, 572
Asphyxia, 379

Association centers of cerebrum, 512
Astigmatism, 622
Auditory area, 508

nerve, 548

297

B.

Basal gangUa, 474
Bile, 203

Bile, composition of, 205
mode of secretion, 206
physiologic action, 207
pigments, 206
salts, 205
Blastodermic membranes, 660
Blind spot, 626
Blood, 229

changes in, during respiration, 362
circulation of, 263
coagulation of, 231

chemistry of, 259

extravascular, 260

intravascular, 261
constituents of, 229.
corpuscles, 236, 254, 257
defibrinated, 233
general composition of, 259
physical properties of, 230
pressure, 301

causes of, 308

changes of, 310

methods of estimation, 302, 305
quantity of, 258
velocity of, in arteries, 313

of, in capillaries, 316

of, in veins, 316
Burdach, column of, 450

C.

Calorimeter, 390
Capillary blood-vessels, 298
functions of, 323

circulation, 321

electrometer, 689
Capsule, internal, 475

functions of, 485
Carbohydrates, 25
Carbon monoxid hemoglobin, 252
Cardiac cycle, 274
Cardio-accelerator center, 296
Cardio-inhibitor center, 295
Cardio-pulmonary vessels, 267
Caseinogen, 400
Caudate nucleus, 475
Cells, structure of, 41

manifestations of Hfe by, 43
Central organs of the nerve system, 440
Cerebellum, 514

693

694

INDEX.

Cerebellvim, functions of, 516

results of experimental lesions, 517

Cerebrum, 486

convolutions of, 488

fissures of,- 486

functions of, 494

localization of function in, 505

motor area of the chimpanzee brain,

505
motor area of the human brain, 506
motor area of the monkey's brain,

49S
sensor areas of the human brain, 507
sensor areas of the monkey's brain,

499
structure of the gray matter, 491
structure of the white matter, 493
Chemic composition of the body, 24
Chimpanzee brain, motor area of, 505
Cholesterin, 205

Chorda tympanum nerve, 546, 547
Chorion, 663
Chyle, 226

Ciliary movement, 100
muscle, 601

functions of, 617
Circulation of blood, 263

forces concerned, 325
Cochlea, 640

functions of, 648
Colostrum, 402
Commutator, 677
Connective tissues, 49
Corpora quadrigemina, 473
fimctions of, 482
striata, 474

functions of, 482
Cranial ners^es, 522
Crura cerebri, 472

functions of, 482
Crystalline lens, 605

D.

Daily ration of U. S. soldier, 150
Decidual membrane, 659
Defecation, 211

nerv'e mechanism of, 212
Deglutition, 169

nerve mechanism of, 175
Demarcation current, 91
Depressor nerve, 296, 324, 555
Dextroses, 26
Diabetes, 409
Diaphragm, 341
Dietaries, 150
Digestion, 131

Dilatator pupilla? muscle, 600
Direct cerebellar tract, 449

pyramidal tract, 446

Ductless glands, 411
Ductus arteriosus, 667

venosus, 666
Dyspnea, 378

E.

Electrodes, non-polarizable, 674
Electrotonic alterations in excitability of
nerves, 122

current, 122
Electrotonus, 122
Encephalon, 440
Encephalo-spinal fluid, 441
Endocardium, 267
Enterokinose, 202
Epididymis, 656
Epinephrin, 416

Epithelial tissues, functions of, 47
Equilibration, mechanism of, 519
Erythrocytes, 236
Eupnea, 377
Eustachian tube, 638
Excretion, 420

Expiratory forces and muscles, 351
Expired air, composition of, 359
Eye, cardinal points of, 609

dioptric apparatus of, 607

lids of, 636

muscles of, 632

physiologic anatomy of, 598

reduced, 612

schematic, 611

Facial nerve, 543

paralysis of, 546
Fallopian tube, 651
Fat, 29

absorption of, 226

digestion of, 201

emulsilication of, 31

saponification of, 30
Feces, 211
Fecundation, 658
Fehling's solution, 27
Female organs of generation, 650
Fetal circulation, 665

membranes, 662

structures, 660
Fibrin, 34
Fibrinogen, 235
Fillet, 468

Follicle, Graafian, 650
Food, 133

animal, 146

cereal, 147

disposition of, 137

heat value of, 141

INDEX.

69s

Food, percentage composition of, 145

principles, 136

quantities required daily, 134

vegetable, 148
Fovea, 602, 604
Funiculus cuneatus, 468

gracilis, 468

G.

Gall-bladder, 203

Galvanic current, effect of, on nerv-es, i:

Galvanometer, 687

Ganglia, cephalic, 569, 570

Gaseous exchange in lungs, 369

in tissues, 370
Gases of blood, relation of, 363

tension of, 366
Gastric digestion, 176
glands, 178
juice, 181

mode of secretion, 184

physiologic action of, 186
Glossophar\-ngeal nerve, 550
Glycogen, 26, 407

Glycogenic function of the liver, 407
Gmeiin's test for bile pigments, 206
Goll, columns of, 450
Gowers' antero-lateral tract, 449
Graafian follicle, 650
Graphic method, 683
Green vegetables, 149

Hairs, 437

Hearing, sense of, 637

Heart, 263

action of sympathetic ner\-e on, 295
of vagus ner\"e on, 292

blood supply, 283

beat, causation, 285
frequency of, 282

course of blood through, 268

cycle of, 274

inhibition of, 293

intraventricular pressure of, 279

mechanics of, 273

muscle-fibers of, 271

negative pressure on, 282

nerve system of, 291

orifices and valves, 269, 276

physiologic anatomy of, 263

sounds, 282

synchronism of the two sides, 278

work done by, 326
Heart -muscle, properties of, 288
Heat dissipation, 391

income, 389

relation to work, 394

rigor, 79

Helmholtz's theory of color perception,

634
Hemianopsia, 530
Hemoglobin, 244

absorption spectra, 248

compounds of, 251
Hemoglobinometer, Gowers', 247
Hemometer, v. Fleischl's, 248
Hering's theory of color perception, 634
Horopter, 628
Hypermetropia, 621
Hyperpnea, 377
Hypoglossal nerve, 559
Hypophysis cerebri, 414

Incus, 639

Induced currents, 680, 681
Inductorium, 678
Insalivation, 158

nerve mechanism of, 165
Inspiration, 347

movements of thorax, 347

muscles, 347
Insula^ 491

Intercostal muscle, 347
Internal capsule, 475

functions of, 485

secretion, 411
Intestinal digestion, 193

juice, 195

physiologic action of, 202

movements, 208
Intracardiac pressure, 278
Intrapulmonary pressure, 343
Intrathoracic pressure, 344
Intravascular coagulation, 261
Iris, 599

functions of, 619

nerv-e mechanism of, 534, 620
Iron of the body, 39, 139
IrritabiHty of muscles, 70

of nerves, 115
Island of Langerhans, 197

of Reil, 491
Isthmus of encephalon, 470
functions of, 480

Jacobsen's nerve, 551
Joints, 58

classification of, 59

K.

Kidney, 424

histology of, 424
Knee-jerk, 459
Kymograph, 684

696

INDEX.

L.

Labyrinth of ear, 640
Lacrimal glands, 636
Lactation, 401
Lacteals, 227
Language, 509
Large intestine, 209
'Larynx, 572

ner\'e mechanism of, 582

structure of, 575
Lateral columns of the spinal cord, 449
Law of contraction, 126
Lemniscus, 468
Lens, crystalline, 605
Lenticular nucleus, 475
Leukocytes, 256

classification of, 256
Levers, 94
Limbic lobe, 490
Liver, 203, 403

formation of urea in, 410

functions of, 405

production of glycogen, 407

secretion of bile, 406
Localization of functions in cerebrum,

497
Lungs, structure of the, 338
Lymph, 219

composition of, 219

functions of, 221

movement of, 227

production of, 220

properties of, 219
Lymph-glands, 216
LjTnph-vessels, 214
Lymphocytes, 219, 256

M.

Macula lutea, 602
Malleus, 639
Mammary gland, 399
Mastication, 153

muscles of, 155

nerve mechanism of, 156
Meats, composition of, 146
Medulla oblongata, 467

reflex activities of, 481
Meibomian glands, 636
Membrana tympani, 638
Menstruation, 654
MetaboKsm on proteid diet, 145

on fat and carbohydrate diet, 145
Methemoglobin, 252
Micturition, 433

nerve mechanism of, 434
Migration of leukocytes, 323
Milk, 400

composition of, 146, 400

mechanism of secretion, 401

Moist chamber, 686
Mosso's plethysmograph, 320
Motor area of chimpanzee brain, 505
of human brain, 506
of monkey brain, 499
ocuh nerve, 531
Mouth digestion, 153
Movements of the eyeball, 630
of the intestines, 208
of the stomach, 190
Muscle action currents, 92
contraction, 75

chemic phenomena of, 86
electric phenomena of, 89
graphic record of, 76
modif3dng influences of, 78
physical phenomena of, 73
rigor mortis, 87
tetanus, 84

thermic phenomena of, 88
electric currents from, 89
electric currents, negative variation

of, 91
energy, source of, 87
fatigue, 80

groups, special action of, 94
sense, 592
sound, 87
spindle, 592
stimuH, 71
tissue, 63

chemic composition of, 67
histolog}' of, 64, 97
physical properties of, 68
physiologic properties of, 69
Myopia, 621
Myosinogen, 33, 67
Myxedema, 412

Nerve, abducens, 542

auditory, 548

facial, 543

glossopharyngeal, 550

hypoglossal, 559

impulse, 117

irritabiHty, 115

motor ocuU, 531

olf actor}', 525

optic, 527

patheticus, 536

pneumogastric, 552

spinal accessory, 557

stimuli, 115

tissue, histology of, 103

trigeminal, 537
Nerve-muscle preparation, iii
Nerves, classification of, 113

development of, in

INDEX.

697

Nerves, electric currents of, 119

electric currents of, negative varia-
tion of, 120
effects of galvanic current on, 122
peripheral endings of, 109
physiologic properties of, 115
pilo-motor, 438

polar stimulation of, 126, 127
relation of, to central nerve system,
loS

Neuron, 103

Nicotin, actions of, 168, 567

Nucleus caudatus, 475
cuneatus, 468
gracilis, 468
lenticularis, 475

Nutrition of the embryo, 663

O.

Oculo-motor ner\'e, 531
Ohm's law, 672
Olein, 30

Olfactory nerve, 525
Oncograph, 431
Oncometer, 431
Operculum, 491
Ophthalmic ganglion, 569
Optic constants, 607

thalamus, 474

functions of, 484
Optogram, 628
Organ of Corti, 642
Osazones, 29
Ossicles of ear, 639, 644
Otic ganglion, 570
Ovary, 650
Ovulation, 653
Ovum, 651
Oxygen in blood, 364

in tissues, 368

quantity absorbed daily, 374
Oxyhemoglobin, 251

P.

Pacinian corpuscle, 589
Palmitin, 30
Pancreas, 196
Pancreatic juice, 198

physiologic action of, 200
Partial pressure of gases, 363
Parturition, 667
Pathetic nerve, 536
Pepsin, 182
Peptones, 188
Perspiration, 454
Petrosal nerves, 546
Pettenkofer-Voit respiration apparatus,
372

Pexin, 182

Phagocytosis. 257
Phloridzin diabetes, 410
Phonation, 572

mechanism of, 582
Pilo-motor nerves, 438
Pituitary body, 414
Placenta, 664

Plasma of blood, composition of, 233
Pleura, 342
Pneumatograph, 357
Pneumogastric nerve, 552
Pneumograph, 355
Pons varolii, 470

functions of, 481
Portal vein, 224
Presbyopia, 620
Proteids, 31

color tests for, 36
Protoplasm, properties of, 44
Ptyalin, 165
Pulmonary vascular apparatus, 329

ventilation, 301
Pulse, 316

frequency, 317

wave, velocity of, 318
Punctum proximum, 618

vemotum, 618
Pyramidal tracts of spinal cord, 449

R.

Reaction of degeneration, 131
Red corpuscles, 236

chemic composition of, 244

function of, 242

life history of, 243

number of, 238

of vertebrated animals, 241
Reduced hemoglobin, 250, 251
Reflex action, 131, 453

laws of, 458
Refractory period of the heart, 290
Regnault's and Reisset's respiration ap-
paratus, 373
Relation of gases in the blood, 363
Rennin, 182
Reproduction, 650
Reserve air, 356
Residual air, 357
Respiration, 335

changes in composition of air during,

359
changes in composition of blood, 362
changes in tissues, 367
chemistry of, 358
complemental air, 356
frequency of, 354

mechanism of gaseous exchange, 379
nerve mechanism of, 379

698

INDEX.

Respiration, total respiratory exchange,

371
volumes of air breathed, 356
Respiratory apparatus, 335
movements, 347

effects of, on arterial pressure,

383
effects of, on the flow of blood
through the thoracic vessel, 383
pressures, 343, 344
quotient, 360
rhythm, 355
sounds, 35S
types, 354
Retina, 601
Retinal image, 607

size of, 613
Rigor mortis, 87
Rima glottidis, 573
respiratoria, 578
vocahs, 578
Routes of the absorbed food, 27

S.

Saccharose, 28
Saliva, 161

physiologic action of, 163
Salivary glands, 158

histologic changes in during

secretion, 162
nerve mechanism of, 168
Sebaceous glands, 438
Secretin, 199
Secretion, 394

internal, 411
Semen, 657

Semicircular canals, 529
Sensor areas of human brain, 507

of monkey brain, 501
Setchenow's center, 460
Sight, sense of, 598
Skeleton, physiology of, 58
Skin, 435

nerve endings in, 587
Smell, sense of, 596
Spectroscope, 249
Speech, 572
Spermatozoa, 657
Spheno-palatine ganghon, 570
Sphygmograph, 319
Sphygmomanometer, 305
Spinal accessory nerve, 557
cord, 443

encephalo-spinal conduction,

462
functions of, 452

as a conductor, 452
as an independent center,
461

Spinal cord, nerve fibers of, 447

nerve fibers of, classification of,

447
reflex actions of, 453
reflex irritability of, 459
relation of spinal nerves to, 450
spino-encephalic conduction,

463
structure of gray matter, 444
structure of white matter, 447
tracts of, 448
Spirometer, 356
Splanchnic nerves, 568
Spleen, 416
Stapes, 639

Starch, digestion of. 164
Starvation, 142
Stearin, 30

Stereognostic area, 509
Stomach, movements of, 190
nerve mechanism of, 193
Suprarenal capsules, 415
Sweat-glands, 436
Sympathetic nerve system, 561

cephahc ganglia of, 569
functions of the cervical

portion, 567
functions of the lumbo-
sacral portions, 569
functions of the thoracic
portion, 568

Taste buds, 595
nerve of, 594
sense of, 594

Tears, 636

Teeth, 153

Tegmentum, 472

Temperature of body, 386
sense, 590

Tension of gases in blood, 367

Tensor tympani muscle, 639

functions of, 646

Testicles, 655

Tetanus, 84

Thoracic duct, 218

Thorax, 340

dynamic relations of, 345
mechanic movements of, 342
static relation of, 343

Thyroid gland, 411

functions of, 412

Tidal air, 356

Tongue, 594

Total carbon-dioxid exhaled, 374
oxygen absorbed, 374
respiratory exchange, 371

Touch, sense of, 5S6

INDEX.

699

Trachea, 337

Tracts of spinal cord, 449

Trigeminal nerve, 537

Trypsin, 200

Tvirck, column of, 448

Tympanum, 637

U.

Umbilical cord, 663

Upper air-passages, respiratory move-
ments of, 353
Urea, 410

seat of formation, 422
Uric acid, 422
Urine, 421

composition of, 421
mechanism of secretion, 428

influence of blood composi-
tion, 435
influence of ner\^e system,

432
relation of blood-pressure
to, 429
Uterus, 652

Vagus nerve, 552

influence on heart, 292
Valves of heart, 276
Vasa deferentia, 656
Vascular apparatus, 296

nerve mechanism of, 327

glands, 411
Vaso-motor center, 331

nerves, 327
Veins, 299

Velocity of blood, 312, 316
Vertebral column, 61
Vesiculas seminales, 656
Villi, 222

Visceral muscle, 97

Vision, 598

accommodation, 614
astigmatism, 622
binocular, 628
color perception, 634
functions of retina, 625
hypermctropia, 621
myopia, 621
presbyopia, 620

Visual angle, 613

Vital capacity of lungs, 357

Vocal bands, 576
sounds, 580

Voice and speech, 582

Volume of pulse, 320

W.

Walking, 97

Water, amount of, in the body, 37
Watery vapor in breath, 360
Wernicke's pupillary reaction, 531,
White blood-corpuscles, 254
function of, 257
migration of, 323
origin of, 257
Wrisberg, nerve of, 545

535

Yellow spot, 602

Zona pellucida, 660

Zymogen, 165

pepsinogen, 182
ptyalogen, 165
trypsinogen, 202

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Coblentz. Manual of Pharmacy.

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The Newer Remedies.

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Climatology and Health Resorts, Including Mineral Springs.
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Rest — Mental Therapeutics — Suggestion. Ready.

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MEDICAL AND SCIENTIFIC PUBLICATIONS. 11

Cohen. Physiologic Therapeutics. — Continued.

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Coplin. Manual of Pathology. Third Edition. 330 Illustrations.

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Practical Hygiene.

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Darier. Ocular Therapeutics.

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Davis. Dietotherapy. Food in Health and Disease.
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Davis. The Principles and Practice of Bandaging.

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Davisson. Mammalian Anatomy.

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Domville. Manual for Nurses

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Donders. Refraction. Portrait of Author.

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Da Costa. Clinical Hematology. Colored Plates.

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Deaver. Surgical Anatomy. 499 Full-page Plates. Now Ready.

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Professor of Applied Anatomy, L^^niversity of Pennsylvania, etc. With 499
very handsome Full-page Illustrations engraved from original drawings made by
special artists from dissections prepared for the purpose in the dissecting-rooms of the
University of Pennsylvania. Three large volumes. Royal square octavo. Sold by
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Half Morocco or Sheep, $24.00 ; Half Russia, $27.00

See next page for Reviews.

MEDICAL AND SCIENTIFIC PUBLICATIONS. 13

Deaver's Surgical Anatomy

THREE VOLUMES— NOW READY

Synopsis of Contents.

Volume I. — Upper Extremity — Back of Neck, Shoulder, and Trunk — Cranium

— Scalp — Face.
Volume II. — Neck — Mouth, Pharynx, Larynx, Nose — Orbit — Eyeball — Organ

of Hearing — Brain — Female Perineum — Male Perineum.
Volume III. — Abdominal Wall — Abdominal Cavity — Pelvic Cavity — Chest —

Lower Extremity.

The illustrations, which at the first glance appear as the prominent feature of
the book — but which in reality do not overshadow the text — consist of a series of
pictures absolutely unique and fresh. They will bear comparison from an artistic point
of view with any other work, while from a practical point of view there is no other
volume or series of volumes to which they can be compared. When originally an-
nounced, the book was to contain two hundred illustrations. As the work of prepara-
tion progressed, this number gradually increased to nearly five hundred full-page
plates, many of which contain more than one figure. With the exception of
a few minor pictures made from preparations in the possession of the author, they have
all been drawn by special artists from dissections made for the purpose in the dissecting-
roorr.s of the University of Pennsylvania. Their accuracy cannot be questioned, as
each drawing has been submitted to the most careful scrutiny.

From The Medical Record, New York.

*' The reader is not only taken by easy and natural stages from the more superficial to the
deeper regions, but the various important regional landmarks are also indicated by schematic
tracing upon the limbs. Tlius the courses of arteries, veins, and nerves are indicated in a way that
makes the lesson strikingly impressive and easily learned. No expense, evidently, has been
spared in the preparation of the work, judging from the number of full-page plates it contains, not
counting the smaller drawings. Most of these have been 'drawn bv special artists from dissections
made for the purpose in the dissecting-rooms of the University of Pennsylvania.' In summing up
the general excellences of this remarkable work, we can accord our unqualified praise for the
accurate, exhaustive, and systematic manner in which the author has carried out his plan, and we
can commend it as a model of its kind, which must be possessed to be appreciated."

From The Philadelphia Medical Journal.

" Many members of the profession to whom Dr. Deaver is well known either personally or by
reputation as a surgeon, writer, teacher, and practical anatomist, have awaited the appearance of
his Surgical Anatomy with the expectation of finding in it a guide in this difficult branch of medi-
cine of much more than ordinary practical value, and their expectations "will not be disappointed."

From The Journal of the American Medical Association.

" In order to show its thoroughness, it is only necessary to mention that no less than twelre
full-page plates are reproduced in order to accurately portray the surgical anatomy of the hand,
and it is doubtful whether any better description exists in any w^orfc in the English language.**

From The New Orleans Medical and Surgical Journal.

" While the needs of the undergraduate have been fully kept in view, it has been the aim of
the author to provide a work which would be sufficient for reference for use in actual practice. We
believe the book fulfils both requirements. The arrangement is systematic and the discussion o£
surgical relations thorouarh."

Lar^e Descriptive Circular will be sent upon application

14 P. BLAKISTON'S SON &- CO: S

Deaver. Appendicitis. Third Edition.

Its History, Anatomy, Etiology, Pathology, Symptoms, Diagnosis, Prognosis, Treat-
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Third Edition, Revised and Rewritten. Preparing.

Dercum. Rest — Mental Tlierapeutics — Suggestion.

See Cohen, Physiologic Therapeutics, page 10.

Douglas. Surgical Diseases of the Abdomen.

With Special Reference to Diagnosis. By Richard Douglas, m.d., late Professor
of Gynecology and Abdominal Surgery, Medical Department Vanderbilt University ;
Ex-President of the Southern Surgical and Gynecological Association, etc. Illustrated
by 20 Full-page Plates. Large Octavo. 883 pages. Just Ready.

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Diihrssen. A Manual of Gynecological Practice.

By Dr. A. Duhrssen, Privat-Docent in Gynecology in the University of Berlin.
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Dulles. What to Do First In Accidents and Poisoning.

By C. W. Dulles, m.d.. Surgeon to the Rush Hospital ; formerly Assistant Surgeon
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Edgar. The Practice of Obstetrics.

By J. Clifton Edgar, m.d., Professor of Obstetrics and Clinical Midwifery, Medical
Department of Cornell University, New York City ; Attending Obstetrician to the New
York Maternity Hospital, etc. With 1221 Illustrations, largely from Original Sources
and many of which are printed in Colors. Just Ready. Cloth, $6.00 ; Leather, $7.00

Emery. A Handbook of Bacteriological Diagnosis.

By W. d'Este Emery, m.d., b.Sc. Lond., Lecturer in Pathology and Bacteriology in
the University of Birmingham. With two colored plates and 32 other illustrations.

Cloth, $1.50

Fagge. Practice of Medicine.
A Text-Book of Medicine by the late C. Hilton Fagge, m.d. Fourth Edition,
Revised and Edited by P. H. Pye-Smith, m.d.. Consulting Physician to Guy's
Hospital, London, etc. Two Vols. Svo. Vol. I, Cloth, $6.00 ; Vol. II, Cloth, $6.00

Fenwick. Cancer of Stomach.
By Samuel Fenwick, m.d., m.r.c.p.. Physician to the London Hospital, etc., and
W. Soltan Fenwick, m.d., b.s. Cloth, 1:3.00

Fick. Diseases of the Eye and Ophthalmoscopy.

By Dr. Eugen Fick, University of Zurich. Authorized Translation by A. B. Hale,
M.D., Consulting Ophthalmic Surgeon Charity Hospital, Chicago ; late Vol. Assistant
Imperial Eye CUnic, University of Kiel. Glossary and 158 Illustrations, many of
which are in Colors. 8vo. Cloth, $4.50 ; Sheep, $5.50

Fillebrown. A Text-Book of Operative Dentistry.

Written by invitation of the National Association of Dental Faculties. By Thomas
Fillebrown, m.d., d.m.d.. Professor of Operative Dentistry in the Dental School of
Harvard University. Illustrated. 8vo. Cloth, |2. 25

Fowler's Dictionary of Practical Medicine.

By Various Writers. An Encyclopedia of Medicine. Edited by James Kingston
Fowler, m.d., f.r.c.p., Senior Assistant Physician to the Middlesex Hospital,
London. Svo. Cloth, $3.00 ; Half Morocco, ^4.00

MEDICAL AND SCIENTIFIC PUBLICATIONS. 15

Frenkel. Tabetic Ataxia.

Its Treatment by Systematic Exercise. By Dr. H. S. Frknkel. Authorized Trans-
lation by L. Freyherger, m.d., m.u.c. p. 132 Illustrations. Octavo. Cloth, $3.00

Fullerton. Obstetric Nursing.

By Anna M. Fullerton, m.d.. Demonstrator of Obstetrics in the Woman's Medical
College ; Obstetrician and Gynecologist to the Woman's Hospital, Philadelphia, etc.
41 Illustrations. Fifth Edition, Revised and Enlarged. i2mo. Cloth, $1.00

Surgical Nursing.

Comprising the Regular Course of Lectures upon Abdominal Surgery, Gyne-
cology, and General Surgical Conditions delivered at the Training School of the
Woman's Hospital, Philadelphia. Third Edition. 69 lUus. i2mo. Cloth, $1.00

Gardner. The Brewer, Distiller, and Wine Manufacturer.

A Handbook for all interested in the Manufacture and Trade of Alcohol and its
Compounds. Edited by John Gardner, F.c.s. Illustrated. Cloth, $1.50

Goodall and Washbourn. A Manual of Infectious Diseases.

By Edward W. Goodall, m.d. (London), Medical Superintendent Eastern (Fever)
Hospital, London ; and J. W. Washbourn, f.r.c.p.. Physician to the London Fever
Hospital. Illustrated with Charts, Diagrams, and Full-page Plates. Cloth, $3.00

Gould. The Illustrated Dictionary of Medicine, Biology, and
Allied Sciences. Fifth Edition.

Being an Exhaustive Lexicon of Medicine and those Sciences Collateral to it :
Biology (Zoology and Botany), Chemistry, Dentistry, Pharmacology, Microscopy,
etc. By George M. Gould, a.m., m.d.. Editor of Americati Medicine ; President,
1893-94, American Academy of Medicine, etc. With many Useful Tables and numer-
ous Fine Illustrations. Large Square Octavo. 1633 pages. Fifth Edition.

Full Sheep or Half Dark-Green Leather, $10.00
With Thumb Index, $11.00 ; Half Russia, Thumb Index, $12.00

" Few persons read dictionaries as Theophile Gautier did — for pleasure ; if, however, all
dictionaries were as readable as the one under consideration, his taste for this kind of literature
would be less singular. . . . The book is excellently printed, and the illustrations are admir-
ably executed." — The British Medical Journal, London.

The Student's Medical Dictionary. Eleventh Ed. Illustrated.

Enlarged. Including those Words and Phrases generally used in Medicine,
with their proper Pronunciations and Definitions, based on Recent Medical
Literature. With Tables of the BaciUi, Micrococci, Leukomains, Ptomains,
etc., of the Arteries, Muscles, Nerves, Ganglia, and Plexuses; Mineral Springs
of the U. S., etc., and a new Table of Eponymic Terms and Tests. Rewritten,
Enlarged, and Improved. With many Illustrations. Small octavo. 840 pages.

Half Morocco, $2.50; Thumb Index, $3.00
Full Flexible Leather, Burnished Edges, Round Corners, Thumb Index, $3.50

The Illustrations in this book, of which there are about 300, are extremely practical.
Those of the Bones, Muscles, Nerves, etc., when taken together with the anatomical
tables which they illustrate, will be found particularly useful for reference and for
memorizing. There are 41 cuts of the Bones, 34 of the Muscles, 21 of Nerves, 18 of
the Joints, 3 of the Heart, 10 of Ligaments, 12 of Pelvis, a plate of the Skeleton, a
plate of the Veins, a plate of the Arteries, etc., 31 cuts of Bandages, 20 of Urinary
Sediments, 10 of Postures, 6 of Motor Points, 6 of Surgical Knots, 8 of Hernia, 21 of
Sutures, 2 of Tongue, 4 of Brain, and many others.

Altogether the student will find "Gould's Student's Dictionary" a most valuable
book, not only as a dictionary but also as an atlas illustrative of many subiects which
need pictures to thoroughly explain their details.

16 P. BLAKISTON'S SOA &- CO.'S

Gould. The Pocket Pronouncing Medical Lexicon. Fourth Edition.
(30,000 Medical Words Pronounced and Defined.)

A Student's Pronouncing Medical Lexicon. Containing all the Words, their Defini-
tions and Pronunciations, that the Student generally comes in contact with ; also
elaborate Tables of the Arteries, Muscles, Nerves, Bacilli, etc., etc.; a Dose List in
both English and Metric Systems, a new table of Clinical Eponymic Terms, etc.,
arranged in a most convenient form for reference and memorizing. Thin 64mo.
(6 X 334' inches.) 838 pages. T/ie System of Pronunciation used in this book is very
simple. Full Limp Leather, Gilt Edges, $1.00 ; With Thumb Index, $1.25

" This ' Dictionary ' is admirably suited to the uses of the lecture-room, or for the purposes of
a medical defining vocabulary — many of the words not yet being found in any other dictionary,
large or small, while all of the words are those of the living medical literature of the day." — The
Virginia Medical Monthly.

*^* 145,000 copies of Gould's Dictionaries have been sold.
Sample pages and descriptive circulars of Gould's Dictionaries free upon application.

Biographic Clinics.

The Origin of the Ill-Health of DeOuincy, Carlyle, Darwin, Huxley, and Brown-
ing. i2mo. fust Ready. Cloth, $1.00

Borderland Studies.

Miscellaneous Addresses and Essays Pertaining to Medicine and the Medical
Profession, and their Relations to General Science. 350 pages. i2mo. Cloth, $2.00

Gould and Pyle. Cyclopedia of Practical Medicine and Surgery.
72 Special Contributors. Illustrated. One Volume.

A Concise Reference Handbook, Alphabetically Arranged, of Medicine, Surgery,
Obstetrics, Materia Medica, Therapeutics, and the various specialties, with Particular
Reference to Diagnosis and Treatment. Compiled under the Editorial Supervision
of Drs. George M. Gould and W. L. Pyle. Illustrated. Large Square Octavo.
Uniform with Gould' s ' ' Illustrated Dictionary. ' ' Full Sheep or Half Dark-Green
Leather, $10.00; With Thumb Index, $11.00; Half Russia, Thumb Index, $12.00

*^* The great success of Dr. Gould' s ' ' Illustrated Dictionary of Medicine ' ' sug-
gested the preparation of this companion volume, which should be to the physician the
same trustworthy handbook in the broad field of general information that the Dictionary
is in the more special one of the explanation of words and the statement of facts. The
aim has been to provide in a one-volume book all the material usually contained in the
large systems and much which they do not contain. Instead of long, discursive papers
on special subjects there are short, concise, pithy articles alphabetically arranged, giv-
ing the latest methods of diagnosis, treatment, and operating — a working book in which
the editors and their collaborators have condensed all that is essential from a vast
amount of literature and personal experience.

The seventy-two special contributors have been selected from all parts of the
country in accordance with their fitness for treating special subjects about which they
may be considered expert authorities. They are all men of prominence, teachers,
investigators, and writers of experience, who give to the book a character unequaled by
any other work of the kind.

" The book is a companion volume to Gould's 'Illustrated Dictionary of Medicine,' which
every physician should possess. With these two books in his library, every busy physician will save
a vast amount of time in having at hand an instant reference cyclopedia covering every subject in
surgery and medicine." — Chicago AleJical Recorder.

Pocket Cyclopedia of Medicine and Surgery.

Based upon Gould and Pyle's Cyclopedia ot Practical Medicine and Surgery.
Uniform with Gould's Pocket Dictionary.

Full Limp Leather, Gilt Edges, $1.00 ; With Thumb Index, $1.25

See next page for List of Contributors.

MEDICAL AXD SCTENTIFIC PUBLICATIONS.

17

Gould and Pyle^s Cyclopedia of Medicine
LIST OF CONTRIBUTORS

Samuel W. Abbott, A.M., M.D., Boston.

James M. Anders, M.D., LL.D., Phila.

Joseph D. Bryant, M.D., New York.

James B. Bullitt, M.D., Louisville.

Charles H. Burnett, A.M., M.D., Phila.

J. Abbott Cantrell, M.D., Philadelphia.

Archibald Church, M.D., Chicago.

L. Pierce Clark, M.D., Sonyea, N. Y.

Solomon Solis-Cohen, M.D., Philadelphia.

Nathan S. Davis, Jr., M.D., Chicago.

Theodore Diller, M.D., Pittsburg.

Augustus A. Eshner, M.D., Philadelphia.

J. T. Eskridge, M.D., Denver, Col.

J. McFadden Gaston, A. B., M.D., Atlanta,
Ga.

J. McFadden Gaston, Jr., A.M., M.D., At-
lanta, Ga.

Virgil P. Gibney, M.D., New York.

George M. Gould, A.M., M.D., Phila.

W. A. Hardaway, A.M., M.D., St. Louis.

John C. Hemmeter, M.B., M.D., Baltimore.

Barton Cooke Hirst, M.D., Philadelphia.

Bayard Holmes, M.D., Chicago.

Orville Horwitz, B.S., M.D., Philadelphia.

Daniel E. Hughes, M.D., Philadelphia.

James Nevins Hyde, A.M., M.D., Chicago.

E. Fletcher Ingals, A.M., M.D., Chicago.

Abraham Jacobi, M.D., New York.

William W. Johnston, M.D., Washington,
D. C.

Wyatt Johnston, M.D., Montreal.

Allen A. Jones, M.D., Buffalo.

William W. Keen, M.D., LL.D., Phila.

Howard S. Kinne, M.D., Philadelphia.

Ernest Laplace, M.D., Philadelphia.

Benjamin Lee, M.D., Philadelphia.

Charles L. Leonard, M.D., Philadelphia.

James Hendrie Lloyd, A.M., M.D., Phila.

J. W. MacDonald, M.D. (Edin.), F.R.C.S.
Ed., Minneapolis.

L. S. McMurtry, M.D., Louisville.

G. Hudson Makuen, Philadelphia.

Matthew D. Mann, M.D., Buffalo.

Henry O. Marcy, A.M., M.D., LL.D.,

Boston.
Rudolph Matas, M.D., New Orleans.
Joseph M. Mathews, M.D., Louisville.
John K. Mitchell, M.D., Philadelphia.
Harold N. Moyer, M.D., Chicago.
John H. Musser, M.D., Philadelphia.
A. G. Nicholls, M.D., Montreal.

A. H. Ohmann-Dusmesnil, M.D., St.
Louis.

William Osier, M.D., Baltimore.

Samuel O. L. Potter, A.M., M.D., M.R.

C.P. (London), San Francisco.
Walter L. Pyle, A.M., M.D., Philadelphia.

B. Alexander Randall, A.M., M.D., Phila.
Joseph RansohofF, M.D., F.R.C.S. (Eng.),

Cincinnati.
Jay F. Schamberg, A.M., M.D., Phila.
Nicholas Senn, M.D., LL.D., Chicago.
Richard Slee, M.D., Swiftwater, Pa.
S. E. Solly, M.D., M.R.C.S., Colorado

Springs, Col.
Edmond Souchon, M.D., New Orleans.
Ward F. Sprenkel, M.D., Philadelphia.
Charles G. Stockton, M.D., Buffalo.
John Madison Taylor, A.M., M.D., Phila.
William S. Thayer, M.D., Baltimore.
James Thorington, A.M., M.D., Phila.
Martin B. Tinker, M.D., Philadelphia.
James Tyson, M.D., Philadelphia.
J. Hilton Waterman, M.D., New York.
H. A. West, M.D., Galveston, Texas.
J. William White, M.D., PH.D., Phila.
Reynold W. Wilcox, M.A., M.D., LL.D.,

New York.
George Wilkins, M.D., Montreal.
DeForest Willard, M.D., Philadelphia.
Alfred C. Wood, M.D., Philadelphia.
Horatio C. Wood, M.D., LL.D., Phila.
Albert Woldert, Ph.G., M.D., Phila.
James K. Young, M.D., Philadelphia.

'• It is difficult to describe the volume before us, and one must imagine all that is clinical
at the present day as being briefly and yet sufficiently set forth under an alphabetical
arrangement, with frequent illustrations, with many formula and diagnostic distinctions, and
with perfect homogeneity ; then he will have a fair picture of the work. We feel sure, however,
that many of our readers will make the better acquaintance of the book by becoming its possessors,
and we commend it to them without hesitation. We have yet to find wherein it is erroneous or
disappointing, and we regard it as of unlimited value to the average medical man." — The
New York Medical Journal.

*^* Sample pages and description upon application.

18 P. BLAKISTON'S SON 6- CO: S

Gould and Pyle. Compend of Diseases of the Eye.

Including Refraction Treatment and Operations, with a Section on Local Therapeutics.
With Formulae, Glossary, and several Tables. By Drs. George M. Gould and
W. L. Pyle. Second Edition. 109 Illustrations, several of which are Colored.
No. 8 f Qiiiz- Compend f Series. Cloth, 80.; Interleaved for Notes, $1.00

Gordinier. The Gross and Minute Anatomy of the Central Nervous
System. 261 Illustrations.
By H. C. Gordinier, a.m., m.d., Professor of Physiology and of the Anatomy of
the Nervous System in the Albany Medical College ; Member American Neurological
Association. With 48 Full-page Plates and 213 other Illustrations, a number of
which are printed in Colors and many of which are original. Large 8vo.

Cloth, $6.00 ; Sheep, $7.00

Gorgas' Dental Medicine.

A Manual of Dental Materia Medica and Therapeutics. By Ferdinand J. S. Gorgas,
M.D., D.D.S., Professor of the Principles of Dental Science, Oral Surgery, and Dental
Mechanism in the Dental Department of the University of Maryland. Seventh
Edition, Revised and Enlarged, with many Formulas. 8vo.

Cloth, I4.00 ; Sheep, I5.00 ; Half Russia, IS6.00

Questions and Answers.

Embracing the Curriculum of the Dental Student. Divided into three parts.
By Ferdinand J. S. Gorgas, a.m., m.d., d.d.s.. Author of " Dental Medicine,"
Editor of ' ' Harris' Principles and Practice of Dentistry ' ' and ' ' Harris' Dictionary
of Medical Terminology and Dental Surgery," Professor of the Principles of
Dental Science, Oral Surgery, etc., in the University of Maryland, Dental
Department, Baltimore. Octavo. Cloth, I6.00

Gray. A Treatise of Physics.

By Andrew Gray, ll.d., f.r.s.. Professor of Natural Philosophy in the University
of Glasgow. In Three Volumes.

Vol. I. Dynamics and Properties of Matter. 350 Illustrations. Octavo,
688 pages. Cloth, I4.50

GreefF. The Microscopic Examination of the Eye.

By Professor R. Greeff. Surgeon to the Ophthalmic Department of the Royal Charity
Hospital, Berlin. Translated from the Second German Edition by Hugh Walker,
M.A., M.D., Assistant Surgeon and Pathologist to the Ophthalmic Department of the
Glasgow Royal Infirmary. i2mo. Cloth, ^(51.25

Greene. The Medical Examination for Life Insurance

and its Associated Clinical Methods. With Chapters on the Insurance of Sub-
standard Risks and Accident Insurance. By Charles Lyman Greene, m.d., of St.
Paul, Clinical Professor of Medicine and Physical Diagnosis in the University of Min-
nesota. With 99 Illustrations, many of which are original, several being printed
in Colors. Second Edition, Revised. Octavo. In Press.

Griffith's Graphic Clinical Chart.

Designed by J. P. Crozer Griffith, m.d.. Instructor in Chnical Medicine in the
University of Pennsylvania. Sample copies free. Put up in loose packages of 50, .50
Price to Hospitals: 500 copies, $4.00; 1000 copies, $7.50.

Groff. Materia Medica for Nurses.

With Questions for Self-examination. By John E. Groff, Apothecary in the Rhode
Island Hospital, Providence ; Professor of Materia Medica, Botany, and Pharma-
cognosy in the Rhode Island College of Pharmacy. Second Edition, Revised and
Improved. i2mo. Just Ready. Cloth, $1.25

MEDICAL AND SCIENTIFIC PUBLICATIONS. 19

Greenish. Microscopical Examination of Foods and Drugs.

Being a systematically arranged Course of Practical Instruction in the Methods
adopted in the Analysis of Foods and Drugs by means of the Microscope, including
a description of the structure of the more important. Designed for the use of Analysts,
Pharmacists, and Students training for those Professions. By Henry G. Greenish,
F.i.c, F.L.S., Professor of Pharmaceutics to the Pharmaceutical Society of Great
Britain. With 1 68 Illustrations. Octavo. Just Ready. Cloth, $3.50

Groves and Thorp. Chemical Technology.

A New and Complete Work. The Application of Chemistry to the Arts and Manu-
factures. Edited by Charles E. Groves, f.r.s., and Wm. Thorp, b.sc, f.i.c,
assisted by many experts. With numerous Illustrations. Each vohwie sold separately.
Vol. I. Fuel and Its Applications. 607 Illustrations and 4 Plates. Octavo.

Cloth, $5.00; ]i Mor., $6.50

Vol. II. Lighting. Candles, Oils, Lamps, etc. By W. Y. Dent, L. Field,

BovERTON Redwood, and D. A. Louis. Illustrated.

Octavo. Cloth, $4.00; yi Mor., I5.50

Vol. III. Gas Lighting. By Charles Hunt, Manager of the Birmingham

Gasworks. Illustrated. Octavo.

Cloth, $3.50; yi Mor., $4.50
Vol. IV. Electric Lighting and Photometry. By Arthur G. Cooke, m.a..
Head of the Physics and Electric Engineering Department
at the Battersea (London) Polytechnic ; and W. J. Dibdin,
F.I.C, F.cs., late Chemist and Superintending Gas Ex-
aminer, London County Council. With 10 Plates and 181
other Illustrations. Octavo. Cloth, $3.50 ; >^ Mor., $4.50

Gowers. Manual of Diseases of the Nervous System.
A Complete Text-Book. By Sir William R. Gowers, m.d., f.r.s.. Physician to
National Hospital for the Paralyzed and Epileptic, etc. Revised and Enlarged.
With many new Illustrations. Two volumes. Octavo.

Vol. I. Diseases of the Nerves and Spinal Cord.

Third Edition. Cloth, $4.00 ; Sheep, $5.00 ; Half Russia, $6.00

Vol. II. Brain and Cranial Nerves; General and Functional

Diseases.

Second Edition. Cloth, $4.00; Sheep, $5.00; Half Russia, J6.00

*:* This book has been translated into German, Italian, and Spanish. It is pub-
lished in London, Milan, Bonn, Barcelona, and Philadelphia.

Syphilis and the Nervous System.

Being a Revised Reprint of the Lettsomian Lectures for 1890, delivered before
the Medical Society of London. i2mo. Cloth, |i.oo

Epilepsy and Other Chronic Convulsive Diseases.

Their Causes, Symptoms, and Treatment Second Edition. Cloth, $3.00

Hadley. General Medical and Surgical Nursing.

A Manual for Nurses. By Dr. W. G. Hadley, Physician to, and Lecturer on
Medicine to the Nurses at, the London Hospital. With an Appendix on Sick-Room
Cookery. i2mo. 326 pages. Cloth, ^1.25

Haig. Causation of Disease by Uric Acid. Sixth Edition.

A Contribution to the Pathology of' High Arterial Tension, Headache, Epilepsy,
Mental Depression, Gout, Rheumatism, Diabetes, Bright' s Disease, Anaemia, etc.
By Alexander Haig, m.a., m.d. (Oxon.), f.r.c.p., Physician to Metropolitan Hos-
pital, London. 75 Illustrations. Sixth Edition, Enlarged by 100 pages. 8vo.
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Diet and Food.

Considered in Relation to Strength and Power of Endurance, Training and
Athletics. Fourth Edition, Revised. 7 Illustrations. Cloth, |i.oo

20 P. BLAKISTON'S SON &- CO.' S

Hall. Diseases of the Nose and Throat.

By F. DE Havilland Hall, m.d., f.r.c.p. (Lond.), Physician to the Westminster
Hospital ; President of the Laryngological Society of London ; Joint Lecturer on the
Principles and Practice of Medicine at the Westminster Hospital ; and Herbert
TiLLEY, M.D., B.s. (Lond.), F.R.c.s. (Eng.), Surgeon to the Throat Hospital, Golden
Square ; Lecturer on Diseases of the Nose and Throat, London Post-Graduate College
and Polyclinic. Second Edition, Revised, with 2 Plates and 80 Illustrations. Cloth,$2.75

Hamilton. Lectures on Tumors

from a CHnical Standpoint. By John B. Hamilton, m.d., ll.d., late Professor of
Surgery in Rush Medical College, Chicago ; Surgeon Presbyterian Hospital, etc.
Third Edition, Revised. With New Illustrations. i2mo. Cloth, $1.25

Hansell and Sweet. Diseases of the Eye.

A Treatise on the Principles and Practice of Ophthalmic Medicine and Surgery. By
Howard F. Hansell, a.m., m.d., Clinical Professor of Ophthalmology, Jefferson
Medical College ; Professor of Diseases of the Eye, Philadelphia Polyclinic and
College for Graduates in Medicine ; Ophthalmic Surgeon, Philadelphia Hospital, etc.,
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College ; Assistant Attending Surgeon and Chief of Eye Clinic, Jefferson Medical
College Hospital ; Associate in Ophthalmology, Philadelphia Polyclinic ; Ophthalmic
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Hansell and Reber. Muscular Anomalies or the Eye.

By Howard F. Hansell, a.m., m.d., Clinical Professor of Ophthalmology, Jefferson
Medical College ; Professor of Diseases of the Eye, Philadelphia Polyclinic, etc. ; and
Wendell Reber, m.d.. Instructor in Ophthalmology, Philadelphia- Polyclinic, etc.
With I Plate and 28 other Illustrations. i2mo. Cloth, $1.50

Hansell and Bell. Clinical Ophthalmology.

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of Normal Fundus and 120 Illustrations. i2mo. Cloth, $1.50

Hare. Mediastinal Disease.

The Pathology, Clinical History, and Diagnosis of Affections of the Mediastinum
other than those of the Heart and Aorta. By H. A. Hare, m.d., Professor of
Mat. Med. and Therap. in Jefferson Med. College. 8vo. Illustrated. Cloth, $2.00

Harlan. Eyesight
and How to Care for It. By George C. Harlan, m.d.. Professor of Diseases of
the Eye, Philadelphia Polyclinic. Illustrated. Cloth, .40

Harris' Principles and Practice of Dentistry.

Including Anatomy, Physiology, Pathology, Therapeutics, Dental Surgery, and
Mechanism. By Chapin A. Harris, m.d., d.d.s., late President of the Baltimore
Dental College ; Author of ' ' Dictionary of Medical Terminology and Dental Sur-
gery." Thirteenth Edition, Revised and Edited by Ferdinand J. S. Gorgas,
a.m., m.d., D.D.S., Author of "Dental Medicine;" Professor of the Principles of
Dental Science, Oral Surgery, and Dental Mechanism in the University of Maryland.
1250 Illustrations. 1 180 pages. 8vo. Cloth, |6.oo ; Leather, $7.00

Dictionary of Dentistry.

Including Definitions of such Words and Phrases of the Collateral Sciences as
Pertain to the Art and Practice of Dentistry. Sixth Edition, Rewritten, Re-
vised, and Enlarged. By Ferdinand J. S. Gorgas, m.d., d.d.s.. Author of
" Dental Medicine ;" Editor of Harris' "Principles and Practice of Dentistry ;"
Professor of Principles of Dental Science, Oral Surgery, and Prosthetic Dentistry
in the University of Maryland. Octavo. Cloth, $5.00; Leather, $6.00

MEDICAL AND SCIENTIFIC PUBLICATIONS. 21

Hartridge. Refraction.

The Refraction of the Eye. A Manual for Students. By Gustavus Hartridge,
F.R.C.S., Senior Surgeon Royal Westminster Ophthalmic Hospital ; Ophthalmic
Surgeon to St. Bartholomew's Hospital, etc. 105 Illustrations and Sheet of Test
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On the Ophthalmoscope.

A Manual for Physicians and Students. Fourth Edition, Revised. With Colored
Plates and 68 Wood-cuts. i2mo. Cloth, $1.50

Hartshorne. Our Homes.

Their Situation, Construction, Drainage, etc. By Henry Hartshorne, m.d. Illus-
trated. Cloth, .40

Hatfield. Diseases of Children.

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i2mo. Just Ready. Cloth, .80 ; Interleaved for the Addition of Notes, $1.00

" Dr. Hatfield seems to have most thoroughly appreciated the needs of students, and most
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teachings, and while brief and concise, is surprisingly complete." — Annals of Gynecology and
Pediatry.

Heath. Minor Surgery and Bandaging.

By Christopher Heath, f.r.c.s.. Holme Professor of Clinical Surgery in Univer-
sity College, London. Twelfth Edition, Revised and Enlarged by Bilton Pollard,
F.R.C.S., Surgeon University College Hospital, London. With 195 Illustrations,
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Practical Anatomy.

A Manual of Dissections. Ninth edition, Edited by H. Ernest Lane, f.r.c.s.
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Clinical Lectures on Surgical Subjects. Second series. Cloth, $2.00
Hedley. Therapeutic Electricity and Practical Muscle Testing.

By W. S. Hedley, m.d., m.r.c.s., in charge of the Electrotherapeutic Department
of the London Hospital. 99 Illustrations. Octavo. Cloth, $2.50

Heller. Essentials of Materia Medica, Pharmacy, and Prescription
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By Edwin A. Heller, m.d., Quiz-Master in Materia Medica and Pharmacy at the
Medical Institute, University of Pennsylvania. i2mo. Cloth, $1.50

Henderson. Notes on The Eye.

For L-ndergraduate Students. By Frank Laramore Henderson, m.d., Professor
of Ophthalmology in the Barnes Medical College, St. Louis, etc. With Colored
Plates and 100 other Illustrations. Third Edition, Enlarged. Just Ready.

Cloth, $1.50
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By Fred'k p. Henry, m.d. Half Cloth, .50

Heusler. The Terpenes.

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Ostrom. Massage and the Original Swedish Movements.

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MEDICAL AND SCIENTIFIC PUBLICATIONS. 31

The Physician's Visiting List.

Published Annually. Fifty-Third Year (1904) of its Publication.

Hereafter all styles will contain the interleaf or special memoranda page, except
the Monthly Edition, and the sizes for 75 and 100 Patients will come in two volumes
only.

REGULAR EDITION.

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i- = 5

f Jan. to June

( July to Dec.

For 25 Patients

\\

'eekly.

50

' '

50

" 2 vols,

75
100

" 2 vols.
" 2 vols,

[ Jan. to lune ) ,, ,, ,

I July to Dec. j ^'^

\ Jan. to June | ,, ,, ,, ,, ,,

[July to Dec. | ^--5

Perpetual Edition,

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Potter. A Handbook of Materia Medica, Pharmacy, and Thera-
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32 P. BLAKISTON'S SON &- CO: S

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MEDICAL AND SCIENTIFIC PUBLICATIONS. 33

Richardson's Mechanical Dentistry.

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Richter's Inorganic Chemistry.

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34 P. BLAKISTON'S SON &- CO.' S

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MEDICAL AND SCIENTIFIC PUBLICATIONS. 35

Starling. Elements of Human Physiology.

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Stohr. Text-Book of Histology, Including the Microscopical
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Symonds. Manual of Chemistry

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Taft. Index of Dental Periodical Literature.
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MEDICAL AND SCIENTIFIC PUBLICATIONS. 37

Tanner's Memoranda of Poisons

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Taylor and Wells. Diseases of Children. Illustrated.

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38 P. BLAKISTON'S SON &^ CO.'S

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Tissier. Pneumatotherapv and Inhalation Methods.

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BLAKISTON'S ?QUIZ=COMPENDS?

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No. 6. MATERIA MEDIC A, THERAPEUTICS, AND PRESCRIPTION

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43

SECOND EDITION REVISED

PRACTICAL GYNECOLOGY

A Modern Comprehensive Text-Book
By E. E, MONTGOMERY, M.D.

Professor of Gynecology, Jefferson Medical College; Gynecologist to the Jefferson Medical

College and St, Joseph's Hospitals; Consulting Gynecologist to

the Philadelphia Lying-in Charit)'

WITH FIVE HUNDRED AND SEVENTY
ILLUSTRATIONS

Nearly all of which hare been Drawn and Engraved Specially for this
"Work, for the most part from Original Sources

OCTAVO. CLOTH, $5.00; LEATHER, $6.00

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before us is the work of one individual, and the personality of that individual is evident
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in conciseness of statements, in arrangement of subjects, and in the systematic order
and completeness in which each is considered. . . . The author is neither too
radical nor too conservative in his consideration of the conditions that may need radical
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to-day — a practical work for practical workers."

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44

NOW READY

DISEASES OF THE

SKIN

Their Description, Pathology, Diagnosis, and Treatment, with
Special Reference to the Skin Eruptions of Children.

By H. RADCLIFFE CROCKER, M.D.

7hysicia.n to the Department of Skin Diseases, University College Hospital, London

MESSRS. P. Blakiston's Son & Co. take pleasure in announcing the
publication of the new third revised edition of Diseases of the Skin, by
Dr. H. Radcliffe Crocker. This announcement, coming at a time when
recent progress in dermatology makes an authoritative work upon the subject a
positive necessity, is considered of special importance by the publishers, and it is
believed the same view will be taken by the profession. Crocker on the Skin is
a book built entirely upon superior merit. It has been acknowledged by the
American medical press as "the best text-book in the English language." The
new third edition maintains this high standard of excellence.

It is a safe, accurate, eminently practical and strictly modern treatise, well
and clearly written by a man of large experience and most excellent judgment.
Though completely scientific, it is written in such a happy manner that the tyro
may follow the writer almost as readily as the expert on diseases of the skin. It
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while to the student it will serve as a valuable guide when he enters upon the
more arduous task of practice.

The etiology, symptomatology, pathology and minute anatomy, constitutional
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and bacteriological researches, in their bearing upon dermatology, are carefully
noted; and particular attention is paid to eruptions as they occur in childhood.
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morbid conditions of the different structures affected in diseases of the skin, are
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Many valuable additions to the text are noted in the new third edition of
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numerous changes made where recent progress in dermatology and a more exact
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bears the impress of honesty, thoroughness, and large personal experience.

Third Edition, Thoroughly Revised, with New Illustrations. Octavo ; 140c oages.
Cloth, $5.00 ; Leather, $6.00.

45

Carpenter on THE MICROSCOPE

AND ITS REVELATIONS

EIGHTH ETtlTIOJ^

Edited by W. H. Dallin^cr, D.Sc, D.C.L, F.R.S.

With 23 Plates and nearly 900 Engravings

OCTAVO. 1181 PAGES. CLOTH, $8.00; HALF MOROCCO, $9.00

*^* Eigfht of the chapters have been entirely rewritten and the text
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of E. M. Nelson, ex-President of The Royal Microscopical Society;
Arthur Bolles Lee, author of **The Microtomist^s Vade Mecum^^; Dr. E.
Crookshank, the well-known Bacteriologist; Prof* T. Bonney, F,R.S»;
"W. J. Pope, F;LC., F.C.S., etc.. Chemist to the Goldsmith^s Technical
Institute ; Prof. A. "W. Bennett, Lecturer on Botany at St. Thomas' Hos-
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King's College, London.

*:j;*A thorough and complete revision of the entire text has
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been included and it has been very materially increased in size.

"CARPENTER" is the only complete and exhaustive nr\odern work on

the Science of Microscopy

46

Diseases of tke Digestive Tract

Their Special Pathology^ Diagnosis^ and Treatment* With
Sections on Anatomy and Physiology » Analysis of Stomach
and Intestinal Contents^ Secretions^ Fecesy Urine» Bacteria,
Parasites, etc.. Surgery » Dietetics, Diseases of the Rectum, etc.

AN EXHAUSTIVE SYSTEMATIC TREATISE

By JOHN C. HEMMETER., M.D.

Professor in the Medical Department of the University of Maryland 5 Consultant to the University Hospital and

Director of the Clinical Laboratory, etc. 5 formerly Clinical Professor of Medicine

at the Baltimore Medical College, etc.

DISEASES OF THE STOMACH. Third Edition.

With 15 Plates and 41 other Illustrations, some of which
are printed in Colors. Octavo. 894 pages.

Cloth, $6.00 ; Sheep, $7.00

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With 19 Plates and iio other Illustrations, some of which
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*:4;* These books form a complete treatise on Diseases of the Digestive Tract.
The subject is covered thoroughly and systematically by an author of well-known
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living, diet, and climate.

" We wish to express unqualified approval of the tendency which is shown to emphasize the
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EDGAR'S Obstetrics

A NEW TEXT-BOOK

By J. CLIFTON EDGAR, M,D.

Professor of Obstetrics and Clinical Midwifery in the Cornell University Medical College, New York City, and
Attending Obstetrician to the New York Maternity Hospital.

Octavo^ J 1 00 Pa§fes; J 22 1 Illustrations^ many of which are in Colors.

Handsome Cloth, $6.00 ; Full Leather, $7.00.

EDGAR'S OBSTETRICS excels all other works on the
subject in completeness, in uniformity and consistency
in arrangement, thoroughness in handling details, and
in the number and usefulness of its illustrations.

The author's fifteen ^^ears' experience in hospital and
private practice and as a teacher, his cosmopolitan knowledge
of literature and methods, and an excellent judgment based
upon all of these fit him especially to prepare what must be
a standard work for both students and physicians.

The author's effort has been to cover his subject thor-
oughly ; to arrange his material systematically ; to avoid un-
necessary words, yet to be plain and distinct in all explanations ;
to present each section with a careful outline of the subject
dealt with therein ; to be uniform and consistent in amount of
space devoted to subjects ; to consider . relative values and
proportion in both text and illustrations ; to illustrate the book
in the best manner ; to create a book which should not only
equal but would surpass all others. Nothing of importance
remains unsaid.

48

QP34 B^2

Brubaker

Text-book of liumnn physiology